GB2046635A - Magnetic Brush Developer - Google Patents

Abstract

Magnetic brush developer employs a scraper blade 6 or roller 6' (Fig. 5) to remove residual toner from the toner support sleeve 2 or bolt 9 (Fig. 4A) prior to application of fresh tones thereto from hopper 5. The blade 6 includes apertures 7 so that scraped-off toner passes therethrough and is re-applied to the support. <IMAGE>

Description

SPECIFICATION Developing Device Background of the Invention Field of the Invention This invention generally relates to a developing device, more particularly, it relates to a developing device in which a uniform thin layer of one-component developer is formed on developer holding means and thin layer is opposed to a latent image bearing member to develop the same.

Description of the Prior Art For the developing devices using onecomponent developer, various methods are known or have been proposed.

Among these, the jumping developing method is known as a unique method. This method comprises applying developer as a thin layer onto developer holding means, thereafter opposing an electrostatic latent image surface to the surface of the thin layer of developer with a small gap interposed therebetween, and then causing the developer to jump from the developer holding means to the electrostatic latent image surface by the electrostatic attraction thereof to thereby effect development (see U.S. Patents Nos.

2,839,400 and 3,232,190). According to this method, the developer is not only not attracted to the non-image bearing portion having no latent image potential but also does not contact the non-image bearing portion and therefore, good development free of fog can be accomplished.

Further, where use is made of one-component developer using no carrier particle, there are also obtained good effects that the mixture ratio of the developer does not fluctuate and that there is no deterioration of carrier particles.

Also, the applicant has proposed, as developing methods, different from this jumping developing method, entirely novel developing methods as disclosed in British Patent Appln. Nos.

7835338 Serial Nos. 2006054,2006055, 2028176 and 2030478; 7835339; 7925725 and 7925724.

The former two developing methods comprise disposing one-component magnetic developer, developer holding means (nonmagnetic) and magnetic fied generating means in the named order, forming a uniform thin layer of developer on the developer holding means by the magnetic force of the magnetic field generating means, and opposing the surface of the thin layer of developer to the electrostatic latent image forming surface with a minute gap interposed therebetween so that the former surface does not contact the latter surface. The developer opposed to the image bearing portion is extended by the electrostatic attraction thereof to thereby effect development.

These methods can also obtain developed images free of fog because development is affected without the developer contacting the non-image bearing portion.

The latter two methods comprise disposing one-component magnetic developer, developer holding means (non-magnetic) and magnetic field generating means in the named order, forming a uniform thin layer of developer on the developer holding means by the magnetic force of the magnetic field generating means, and opposing the surface of the thin layer of developer to the electrostatic latent image forming surface with a minute gap interposed therebetween so that the former surface does not contact the latter surface.

As a developing bias voltage, an AC bias voltage is applied to the same and further, the gap between the electrostatic latent image surface and the developer holding means is varied with time to thereby effect development. By these latter methods, in the initial stage of the development, the developer is caused to arrive e at the non-image bearing portion of the electrostatic latent image as well to thereby effect the development of the half-tone portion and the developer is caused to arrive only at the image bearing portion with time to thereby effect the development of such portion. By this, there is obtained the effect of development which is excellent in half-tone reproducibility as compared with the former methods and moreover is free of fog.

According to such developing methods in which development is effected with the thin layer of one-component developer disposed in opposed relationship with the latent image surface, there are obtained very excellent effects in respect of developing performance, image reproducibility, life of developer, etc, as compared with the conventional methods. However, even these developing methods may in some cases encounter the following problems when actually put into practice.

(1) By the developing action, the history of development is left on the layer of developer on the developer holding means to cause a ghost image to be developed during the next cycle of development.

In the aforementioned developing methods, the developer layer formed on the developer holding means is a very thin layer. Therefore, once this developer layer is used for development, a great difference in thickness of the developer layer is created between the portion thereof corresponding to the image bearing portion and the portion thereof corresponding to the nonimage bearing portion. Such thickness history of the developer layer is intactly left even if fresh developer is supplied after the developer layer has been used for development, to greatly affect the next cycle of development and cause a disadvantage that the so-called ghost which is a negative pattern of the previously developed image is created in the next cycle of development.

This is considered to be attributable to the inability to sufficiently replenish the surface of the developer holding means from which the developer has been brought away with fresh developer in the developer supplying step thereafter (or to some difference in characteristic (especially, toribo) between the developer remaining on the surface of the developer holding means and the developer newly supplied thereto).

(2) A thin layer of developer is formed on the surface of the developer holding means in a long time during which the developing action is carried out, to reduce the developing performance.

During the developing action, the developer always repeats contact with and separation from the surface of the developer holding means, so that the surface of the developer holding means is contaminated by the developer and a film layer of developer is liable to form thereon. This film layer consists of resin component of low molecular weight contained in the developer, or a control agent for providing the toribo, or a layer of very minute powder which does not contribute to the development. In any case, if these components cover the surface of the developer holding means, the amount of charge of the developer becomes deficient particularly in the case of the developing methods utilizing the charge created by the friction between the developer and the developer holding means, thus reducing the developing density and or aggravating the image reproducibility.

(3) In a long time during which the developing action is carried out, aggregation of the developer is created or the adhesive force between the developer and the surface of the developer holding means is enhanced to make difficult the formation of a layer having a uniform thickness and cause irregularity of development.

There is no problem when the developer applied onto the developer holding means contributes to development and separates from the surface of the developer holding means within a short time, but if developer which does not contribute to development because of its low developing density is left on the surface of the developer holding means for a long time, the aggregation force of the developer is enhanced or the adhesive force between the developer and the surface of the developer holding means is enhanced to form a partially thick layer of developer which may create irregularity of the developed image.

A developing device having a member for removing toner greater in thickness than at least the toner layer brought away to the electrostatic latent image provided within a toner supply hopper in order to remove the history of development and prevent the creation of the socalled ghost image is disclosed, for example, in U.S. Patent No.4,100,884.

However, the device disclosed in this U.S.

patent is not of the type in which all the developer on the surface of the developer holding means is once removed as far as possible and then fresh developer is supplied to the developer holding means to effect development and therefore, it still suffers from the problems as mentioned under items (2) and (3), especially the problem (2).

Summary of the Invention It is an object of the present invention to provide a developing device which alleviates the above-noted problems and which is good in image reproducibility and fidelity of reproductipn and permits a long service life of developer.

It is another object of the present invention to alleviate the disadvantage peculiar to the prior art that in a long time during which the developing action is carried out, a thin layer of developer is formed on the surface of the developer holding means to reduce the developing performance.

A developing device according to the present invention operates to remove the developer on developer holding means by an electrical cleaning method (for magnetic developer) or a mechanical cleaning method during the time from after the termination of the development until the supply of developer is terminated, in a developing method which comprises disposing endless developer holding means with a minute gap with respect to a latent image bearing member, supplying developer to said developer holding means, controlling the thickness of the layer of developer supplied, and opposing the controlled layer of developer to the latent image bearing member to effect development.

Other objects and features of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings.

Brief Description of the Drawings Figures 1A and 1B are graphs illustrating the particle number distribution for the particle diameter of developer particles and the weight distribution for the particle diameter, respectively.

Figure 2A is a cross-sectional view illustrating the construction of an embodiment of the developing device according to the present invention.

Figure 2B is a partial cross-sectional view of a modification thereof.

Figure 2C is a front view of a developer removing plate.

Figures 3A and 4A are cross-sectional views showing further embodiments of the present invention.

Figures 3B and 4B are partial cross-sectional views of modifications thereof.

Figure 5 is a cross-sectional view illustrating the construction of still another embodiment of the developing device according to the present; invention.

Figure 6A is a cross-sectional view showing still a further embodiment of the present invention.

Figure 6B is a perspective view showing another embodiment of the developer removing means.

Description of the Preferred Embodiments Before specific embodiments of the present invention are described, the problem mentioned under item (2) above, namely, the contamination of the surface of the developer holding means by developer, will be further discussed to make clear the objects, operation and effect of the present invention.

As already described, in a long time during which the developing action is carried out, a time layer of developer may be formed on the surface 'of the developer holding means to reduce the developing performance.

During developing action, the developer always repeats contact with and separation from the surface of the developer holding means and therefore, the surface of the developer holding means is contaminated by the developer and a film layer of developer is liable to form on that surface. This film layer consists of resin component of low molecular weight contained in the developer, or a control agent for providing toribo, or a layer of very fine powder which does not contribute to development. More particularly, the following chemicals are generally often used as said control agent: Spyron Blue GNH (produced by Hodogaya Kagaku Co., Ltd., C.l. Solvent Blue 67), Zabbon Fast Black B (produced by BASF, C.l.

12195), Oil Blue No. 1 5 (produced by Yamamoto Kagaku Co., Ltd., C.l. 74350, C.l. Solvent Blue 25), Microlex Blue (produced by Baiel Co., C.l.

Solvent Blue 97), Barifast Blue 2606 (produced by Orient Kagaku Co., Ltd., oil colour), Oil Blue BOS (produced by Orient Kagaku Co., Ltd., oil colour, C.l. 74350), Cassette Yellow G (produced by Nippon Kagaku Co., Ltd., C.l. 11855, C.1.

Solvent Yellow 77), Eisenspyronred BEH (produced by Hodogaya Kagaku Co., Ltd., C.l.

Solvent Red 83), Celitonred SF 7874 (produced by BASF, dispersed dyes), and Cassette Yellow 963 (produced by Nippon Kagaku Co., Ltd., dispersed dyes). Also, the main component of said fine powder which does not contribute to development but adheres to the surface of the developer holding means and forms a thin layer thereon is the resin component contained in the developer and more particularly, it includes the following:: styrene and monopolymers of substitution products thereof such as polystyrene, poly-p-chlorostyrene and polyvinyl toluene, styrene copolymers such as styrene-p chlorostyrene copolymer, styrene-vinyl toluene copolymer, styrene-vinyl naphthalene copolymer, styrene-acrylic acid methyl copolymer, styrene acrylic acid ethyl copolymer, styrene-acrylic acid butyl copolymer, styrene-acrylic acid octyl 'copolymer, styrene-metaacrylic acid methyl copolymer, styrene-meta-acrylic acid ethyl copolymer, styrene-meta-acrylic acid butyl copolymer, styrene-d-chlorometa-acrylic acid methyl copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer and styrene-acrylonitrile-indene copolymer, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, silicone resin, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, rosin, denatured rosin, terpene resin, phenol resin, fatty hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin and paraffin wax. Further, the material which adheres to the surface of the developer holding means may sometimes be the extraneously added fine particles of the so-called one-component developer which consists of toner particles and hydrophobic silica having a particle diameter smaller than that of said toner particles and extraneously added to said toner particles and which does not contain carrier particles greater in particle diameter than the toner particles.

The fine particles containing much resin which do not contribute to development but adhere to the surface of the developer holding means to form a time layer can be produced as by mixing resin with magnetic powder, charge control agent, carbon, etc., melting the mixture in a roll mill, cooling the same, roughly powdering the same by the use of a hammer mill, and then finely powdering the same into developer by the use of an ultrasonic jet powdering machine. The particle diameter distribution of the developer particles produced by the fine powdering contains considerably many fine particles. Therefore, rough particles are removed therefrom by the use of a classifier and these fine particles are also removed. However, fine particles having a low content of magnetic powder cannot yet be removed completely.An example of the particle diameter distribution of the developer particles after the classification is shown in Figures 1 A and 1 B. Figure 1A shows the particle number distribution for the particle diameter, and Figure 1 B shows the weight distribution for the particle diameter. As shown in these Figures, considerably many fine particles which are light in weight (low in magnetic powder content) are still present even after the classification. These fine particles low in magnetic powder content or free of magnetic powder (they consist of only resin when observed through a microscope), once they electrostatically strongly adhere to the developer holding means, are not moved even by magnetic force because the magnetic force received by these particles is weak, so that a thin layer of these fine particles is formed on the surface of the developer holding means. When the surface of the developer holding means is thus covered with such fine particles, the frictional charge between the surface of the developer holding means and the developer is so affected that the developer cannot be friction-charged to a normal value and the amount of charge of the developer becomes deficient and in addition, where the application of the developer onto the developer holding means depends on the electrostatic force between the developer holding means and the developer, it becomes difficult for the developer to be applied onto the develoer holding means and this leads to occurrence of the problem that the developing density is reduced or the image reproducibility is aggravated The present invention solves such a problem and embodiments thereof will hereinafter be described.

Figures 2A and B show an embodiment of the present invention and a modification thereof, respectively. Designated by 1 in Figure 2 is an electrostatic latent image bearing member such as a photo-sensitive medium or an insulative medium on which an electrostatic latent image has been formed. It is movable in the direction of arrow a. Reference numeral 2 designates a nonmagnetic developing sleeve (formed of, for example, stainless metal or brass) disposed with a minute gap with respect to the electrostatic latent image bearing member. The sleeve 2 is rotatable in the direction of arrow b. This minute gap is set to a gap greater than the thickness of the thin developer layer formed on the developing sleeve.

Within the developing sleeve 2, a magnetic roll 3 magnetized as shown is fixedly provided. By the magnetic force of this magnetic roll 3, a layer of developer T is formed on the surface of the developing sleeve. The layer of developer has its thickness controlled by a doctor blade 4 (formed of iron, for example) disposed in proximity to the surface of the developing sleeve. The spacing between the tip end of this doctor blade 4 and the developing sleeve is set to 200 ym, for example.

To make the thickness control of the developer layer more accurate and positive, a magnetic pole is disposed inside the developing sleeve at a portion thereof opposed to the tip end of the blade. The developer layer whose thickness has been controlled then reaches the developing position opposed to the electrostatic latent image bearing member 1 and effects development by any one of the aforementioned developing methods.After the termination of the development, the thickness of the developer layer has already been varied in accordance with the electrostatic latent image in such a manner that the portion thereof which has corresponded to the image bearing portion becomes thinner, the portion thereof which has corresponded to the non-image bearing portion maintains its original thickness and the portion thereof which has corresponded to the half-tone portion is changed to a thickness corresponding to the electrostatic latent image potential.

If, here, fresh developer is supplied onto the developer layer whose thickness has been varied after the development, as has conventionally been done, the developer supplied will be affected by the history of development and will not be able to form a developer layer having a uniform thickness control by the doctor blade 4, and even if a developer layer having a uniform thickness is obtained, faithful development will not be effected in the next cycle of development but the previously developed image will appear as a ghost. This is considered to be attributable not only to the difference in thickness of the developer layer before the fresh developer is supplied but also to the difference in characteristic (toribo condition, etc.) between the developer of the developer layer once used for development and the newly supplied developer.

The present invention has been improved to overcome such disadvantage and in the embodiments of Figures 2A and B, the improvements are as follows. As already described, on the surface of the developing sleeve 2 after development, not only the thickness of the developer layer has been varied but also the characteristic of the developer has been varied and therefore, design is made such that before developer is supplied by a hopper 5, the developer on the surface of the developing sleeve is once scraped off by a developing removing plate 6 disposed in contact with the surface of the developing sleeve. That is, at a position upstream of the hopper 5 with respect to the direction of movement of the developer layer on the developing sleeve 2, the developer removing plate 6 is attached so as to be in contact with the surface of the developing sleeve.The angle of attachment thereof may preferably be an angle in the counter direction with respect to the direction of movement of the developer layer so that the developer may be scraped up, as shown. This removing plate may preferably be formed of phosphor bronze having a thickness of about 130 Mm, for example. This removing plate 6 is provided on a developer scatter preventing cover 8, extending in the upstream direction from the hopper 5 (Figure 2A). Alternatively, the removing plate 6 may be provided at the end of the wall 5a of the hopper which is upstream with respect to the direction of movement of the developer layer (Figure 2B). In this latter case, the removing plate may be an extension of the hopper wall 5a, but again in this case, it may preferably be a resilient member which can uniformly contact the developing sleeve.As shown in Figure 2C, a number of apertures 7 are provided in the neighbourhood of that portion of the removing plate which is in contact with the developing sleeve. The shape of these apertures may preferably be a square having sides of 10 mm each, for example.

In the above-described construction, the developing sleeve is rotated in the direction of arrow b, whereby the developer in the hopper is moved in the direction of arrow to form a layer of developer on the surface of the developing sleeve and is uniformly applied to the thickness of about 80 um by the doctor blade 4. After the uniform application of the developer, the developer layer becomes opposed to the photosensitive medium 1 having an electrostatic latent image formed thereof, by further rotation of the developing sleeve, to thereby develop the latent image.After the termination of the development, the developer layer is scraped off from the surface of the developing sleeve by the developer removing plate 6 attached to the developer scatter preventing cover 8, or the developer removing plate 6 attached to the front wall 5a of the hopper, and the scraped-off developer passes through the apertures 7 provided in the neighbourhood of that portion of the removing plate which is in contact with the developing sleeve, and again adheres to the surface of the developing sleeve.

In this case, where the fluidity of the magnetic developer T is high, the developer passes through the apertures 7 in the developer removing plate 6, but where the fluidity of the magnetic developer T is low, it becomes difficult for the developer to stably pass through these apertures 7. It is therefore necessary to generate a magnetic field which will attract the magnetic developer near the apertures 7 so that the developer may pass through the apertures in the removing plate.

That is, if a magnetic pole N3 or a magnetic pole S3 is disposed inside the developing sleeve 2 at a portion thereof opposed to these apertures as shown in Figures 2A or 2B, the magnetic developer scraped off by the developer removing plate 6 can easily pass through the apertures 7.

The intensity of this magnetic pole N3 or S3 may preferably be of the order of 450 to 850 Gausses on the developing sleeve 2, and a greater intensity of the magnetic field has ensured greater stability with which the developer passes through the apertures 7. The developer scraping action of the developer removing plate 6 on the developing sleeve and the passage of the developer through the apertures in the removing plate 6 have been carried out satisfactorily without the developer accumulating on the tip end of the removing plate 6 even if the developing sleeve has been continuously rotated. Members 8, and 82 provided upstream and downstream of the hopper are developer scatter preventing covers.

By so providing the developer removing plate before developer is newlysupplied after the termination of the development, it is possible to make the surface of the developing sleeve always clean and then effect the application of developer and this leads to the ability to maintain a stable developing performance without the-fusion of the developer onto the surface of the developing sleeve.

Figures 3A and B show further embodiments of the present invention. These embodiments are generally identical in construction to the embodiments of Figures 2A and B, with the exception that a developer removing plate 6 is provided below the developing sleeve. In this case, to prevent the scraped-off developer from falling downwardly, a magnetic pole S2 is disposed inside the developing sleeve at a portion thereof opposed to the apertures provided in the removing plate. By attaching the removing plate to a developer scatter preventing cover provided upstream of the hopper5 (Figure 3A) or by attaching the removing plate to the front wall 5a of the hopper 5 (Figure 3B), the developer is prevented from dropping from the developer scatter preventing cover 8, or the hopper.The developer scatter preventing cover 8, is removably mounted to the hbpper by means of a rail. The developer scatter preventing cover 81 is particularly effective when scatter of developer takes place near the removing plate 6. It also serves as a receptacle for receiving the developer dropping from the hopper. The movement of the developer is generally the same as that in the embodiments of Figures 2A and B, but the developer removed by the removing plate passes through the apertures 7 in the removing plate and is carried while again adhering to the surface of the developing sleeve for collection into the hopper 5 and is sufficiently stirred for mixing with the developer in the hopper, whereafter a layer of developer is newly formed on the developing sleeve so that it may be used for development.

Figures 4A and B show still further embodiments of the present invention. In these embodiments, as the developer holding means, a belt 9 is used instead of a developing sleeve and magnetic developer is applied onto this belt, which is moved round. Development is effected with the belt 9, having magnetic developer applied thereto, being opposed to an electrostatic latent image bearing member 1. Designated by 2 is a sleeve having a magnet roll 3 therewithin and driving the belt 9. Denoted by loins a rotatable rdller. The belt 9 is passed over the sleeve 2 and the roller 10 and is moved round. Designated by 11 is a back side supporting member of nonmagnetic material for positioning the belt 9 in place. Denoted by 4 is a doctor blade for controlling the thickness of the magnetic developer layer on the belt 9.One of the poles of a magnet 12 is disposed adjacent to that portion of the back side of the belt 9 which is opposed to the tip end of the doctor blade, to thereby ensure the accuracy with which the thickness of the developer layer is controlled. A developer removing plate (a phosphor bronze plate) 6 having apertures at the end thereof is attached to a developer scatter preventing cover 81 disposed upstream of a hopper 5 which is a device for supplying magnetic developer T (Figure 4A), and the end of the developer removing plate is in contact with the belt 9 (Figure 4A). Or a developer removing plate (a phosphor bronze plate) 12 having apertures at the end thereof is attached to the wall 5a of a hopper 5 which is a device for supplying magnetic developer T and the end of the developer removing plate is in contact with the belt 1 5 (Figure 4B). The end of the phosphor bronze plate 6 is in contact with the belt 9 in such a manner that said end is opposed to the direction in which the developer on the belt comes back, and the other pole of the magnet 1 2 is disposed adjacent to that portion of the back side of the belt which is opposed to the apertures formed at the end of the removing plate 6. The magnet may be a permanent magnet or an electromagnet and the magnetic field reaching the apertures at the end of the removing plate 6 may be an alternating magnetic field. (This also holds true with the embodiments of Figures 2A and B and Figures 3A and B).The developer scraped off by the end of the removing plate 6 slightlyaccumulates on the portion of contact with the developer removing plate, whereafter such developer passes through the apertures provided at the end of the removing plate 6 and into the hopper 5 to assume a substantially steady state.

Common effects in the above-described embodiments are as follows: (a) Ease of replacement of the removing plate; (b) Ease of removal of undesirable admixture such as paper powder or the like; and (c) Ease with which the once removed toner is returned to the hopper through the openings formed in the removing plate.

Figure 5 shows still a further embodiment of the present invention. Designated by 1 in Figure 5 is an electrostatic latent image bearing member such as a photosensitive medium or an insulative medium on which an electrostatic latent image has been formed. It is movable in the direction of arrow a. Reference numeral 2 designates a nonmagnetic developing sleeve (formed of, for example, stainless metal, brass, plastics, rubber or the like) disposed with a minute gap with respect to the electrostatic latent image bearing member.

The sleeve 2 is rotatable in the direction of arrow b. This minute gap is set to a gap greater than the thickness of the developer layer formed on the sleeve as the developer holding means. Within the developing sleeve 2, a magnetic roll 3 magnetized as shown is fixedly provided. By the magnetic force of this magnetic roll, a layer af developer T is formed on the surface of the developing sleeve. The layer of developer has its thickness controlled by a doctor blade 4 (formed of iron, for example) disposed in proximity to the surface of the developing sleeve. The spacing between the tip end of this doctor blade and the developing sleeve is set to 200,cm, for example.

To make the thickness control of the developer layer more accurate and positive, a magnetic pole is disposed inside the developing sleeve at a portion thereof opposed to the tip end of the blade. The developer layer whose thickness has been controlled then reaches the developing position opposed to the electrostatic latent image bearing member and effects development by any one of the aforementioned developing methods.

After the termination of the development, the thickness of the developer layer has already been varied in accordance with the electrostatic latent image in such a manner that the portion thereof which has corresponded to the image bearing portion becomes thinner, the portion thereof which has corresponded to the non-image bearing portion maintains its original thickness and the portion thereof which has corresponded to the half-tone portion is changed to a thickness corresponding to the electrostatic latent image potential.

On the surface of the developing sleeve after the termination of the development, not only the layer thickness has been varied as already described, but also the characteristic of the developer has been varied. Accordingly, in this embodiment, a developer removing roller 6' to which a voltage opposite in polarity to the developer has been applied is disposed in proximity to the surface of the developing sleeve at a position upstream of a hopper 5 so as to electrostatically attract and remove the developer on the developing sleeve after the termination of the development. The developer on the developer removing roller 6' is collected onto the surface of the developing sleeve by a collecting blade 1 3.

Designated by 8, is a cover for preventing the scattering of the developer.

By the developer removing roller 6' being thus provided at the position upstream of the hopper 5, it is possible to make the surface of the developing sleeve always clean and then apply the developer thereonto and thus, it is possible to solve all the aforementioned problems and ensure a stable developing performance to be maintained.

In this construction, the developing sleeve is rotated in the direction of arrow b, whereby the developer in the hopper is moved in the direction of arrow to form a layer of developer on the surface of the developing sleeve and is uniformly applied to the thickness of about 80 ,um by the doctor blade 4. After the uniform application of the developer, the developer layer becomes opposed to the photosensitive medium 1 having an electrostatic latent image formed thereon, by further rotation of the developing sleeve, to thereby develop the latent image. After the termination of the development, the developer layer is scraped off from the surface of the developing sleeve by the developing removing roller 6' and the scraped-off developer is collected from the removing roller 6' into the hopper by a collecting blade 13.

Figure 6A shows a further embodiment of the present invention. In Figure 6A, those members designated by reference characters similar to those in Figure 5 have similar functions. In Figure 6A, as the construction for removing the developer on the developing sleeve, a developer removing plate 14 urged against the surface of the developing sleeve is disposed within the hopper 5 so as to once remove the developer from the surface of the developing sleeve within the hopper 5. By this, the aforementioned problems are all solved as previously described.

In the embodiment of Figure 6A, when the removing plate 14 was absent, the developing reflection density was reduced from 1.2 to 0.5 after about one-hour use, but when use was made of the method of cleaning the surface of the developing sleeve by the removing plate, the developing density remained unchanged, maintaining 1.2. In this case, the ability to prevent the deterioration of the image by providing the removing plate was attributable to the ability to remove, by the removing plate, fine powder which could not be removed during the developer manufacturing step and which strongly adhered to the surface of the developing sleeve and silicon dioxide which was added to the developer for the purpose of improving the charging characteristic and fluidity of the developer and which also strongly adhered to the developing sleeve.In this case, as a great effect, it may further be said that it has been possible to entirely improve the case where a certain component of the developer adheres to the surface of the developing sleeve to ,.prevent sufficient contact between the developer and the developing sleeve and the developer cannot provide a sufficient toriboelectrical charging effect. Further, it is possible to easily position and mount the scraper having openings by urging such scraper against the surface of the sleeve within the hopper and in addition, the use of the scraper having openings ensures efficient passage and conveyance of toner.Also, a similar effect could be obtained by bringing a thin metal wire 1 5 into contact with the entire lengthwise dimension of the surface of the developing sleeve at an angle with respect to the axis of the sleeve, as shown in Figure 6B. In this case where a copper wire having a diameter of 0.2 mm was obliquely stretched on a sleeve having an outside diameter of 30 mm and a length of 350 mm (if the angle formed by the wire with the axis of the sleeve is O, Tan f) i 1/70) to clean the sleeve surface, the tension of the metal wire had to be 1 Kg or more. When the tension was substantially more than this value, the aforementioned substances liable to adhere to the sleeve surface could be removed.

As the result of such construction and operation as shown in the above-described embodiments, the history of development of the developer layer on the developer holding means is erased and therefore, no ghost is created during the next cycle of development and in addition, even if the developing action is effected for a long time, no thin layer of developer is formed on the surface of the developer holding means, so that the friction charge effect is weli maintained to ensure a good developing performance to be maintained. Further, the developer layer used for development is once removed and a fresh developer layer is newly formed and thus, no aggregation of the developer occurs.Furthermore, there is obtained a remarkable effect that the materials of the developer may be selected by paying attention only to the initial developing and fixing performances and so, the range of selection of the materials can be widened. Another great effect of the present invention is that the developer on the surface of the developer imparting means is always replaced by fresh developer and so, irregularity of the developer layer on the surface of the developer imparting means does not occur which is liable to occur when a developer having a high aggregating force is used.If the developer which has not contributed to development remains immovable on the developer imparting means for a long time, the aggregating force of the developer or the adhering force between the developer and the imparting means is increased and the thickness of the developer layer tends to increase, thus making stable image reproducibility difficult to obtain.

However, this problem can be solved by giving movement to the developer on the imparting means as in the present invention. The cleaning step for the developer imparting means of the present invention becomes necessary for the purposes of stably supplying the charge amount of the developer as described above and avoiding the aggregation of the developer, whereas the cleaning step need not always be carried out for the developer imparting means at all times, but a considerably high effect can be achieved, for example, by carrying out one cleaning step after the termination of one hundred developing steps.

If the cleaning step is adopted, the device tends to become complicated in respect of the re-use of the removed developer and for example, in the device having the removing plate disposed in the hopper, the removing plate may be intermittently brought into contact with and separated from the imparting means to thereby make the developer accumulated on the front face of the removing plate readily available for re-use.

What has been referred to as the onecomponent developing method in the foregoing description is so referred to for the mixed system of carried particles and toner particles, and the mixture of toner particles and a charge control agent, a lubricant, an abrasive or the like is within the range of one-component development. In the foregoing embodiments, the latent image bearing member has been described with respect to an electrostatic latent image, but is it also applicable to magnetic latent images. In this latter case, magnetic field generating means which will disturb the magnetic latent image must not be disposed within the magnetic sleeve opposed to the magnetic latent image. Further, in the foregoing embodiments, the magnetic roll has been described as fixed and the developing sleeve has been described as movable, but the magnetic roll may be movable and the developing sleeve may be fixed and other various relative movements are applicable. Also, the developer holding means has been described with respect to a non-magnetic developing sleeve, but it may also be in the form of a belt.

Claims (28)

Claims

1. A developing device comprising: developer holding means disposed with a minute gap with respect to a latent image bearing member; developer supply means for supplying developer to the surface of said developer holding means; control means for controlling the thickness of a developer layer on said developer holding means; and a developer removing member adapted to be in contact with the surface of said developer holding means to remove the developer on the surface of sid developer holding means and again impart the removed developer to the surface of said developer holding means at a position before the supply of developer is terminated after the controlled developer layer has been used for development.

2. The developer device according to Claim 1, characterized in that said developer removing member has developer passage openings in the neighbourhood of the portion thereof which is in contact with the surface of said developer holding means, thereby rendering the removed developer available for re-use.

3. The developing device according to Claim 1, characterized in that said developer removing member removes any developer remaining on the surface of said developer holding means prior to the supply of developer by said developer supply means.

4. The developing device according to Claim 1, characterized in that said developer removing member is attached to a wall of said developer supply means.

5. The developing device according to Claim 1, characterized in that said developer removing member is provided within said developer supply means.

6. The developing device according to Claim 1, characterized in that said developer removing member is in the form of a blade and the end edge thereof is in resilient contact with the surface of said developer holding means.

7. The developing device according to Claim 1, characterized in that said developer removing member is a roller and the surface thereof is in resilient contact with the surface of said developer holding means.

8. A developing device comprising: endless developer holding means disposed with a minute gap with respect to a latent image bearing member; developer supply means for supplying magnetic developer to the surface of said developer holding means; control means for controlling the thickness of a developer layer on said developer holding means; and a developer removing member adapted to be in contact with the surface of said developer holding means to remove the developer on the surface of said developer holding means and again impart the removed developer to the surface of said developer holding means at a position before the supply of developer is terminated after the controlled developer layer has been used for development, said developer removing member having developer passage openings in the neighbourhood of the portion thereof which is in contact with the surface of said developer holding means.

9. The developing device according to Claim 8, characterized in that said endless developer holding means has a magnet roll and a relatively movable non-magnetic sleeve enclosing said roll, and said magnet roll has at least magnetic poles at a developing position and a position opposed to said developer layer thickness controlling means

10. The developing device according to Claim 9, characterized in that said developer layer thickness controlling means is in the form of a magnetic blade.

11. The developing device according to Claim 8, characterized in that said developer supply means is a hopper containing one-component magnetic toner therein.

12. The developing device according to Claim 8, characterized in that said developer supply means has attached thereto a scatter preventing cover covering the other portion of the surface of said developer holding means than a developing opening.

1 3. The developing device according to claim 8, characterized in that said endless developer holding means is an endless belt.

14. The developing device according to Claim 8, characterized in that said developer removing member is attached in a counter direction with respect to the direction of movement of the developer layer on said developer holding means.

1 5. A developing device comprising: endless developer holding means disposed with a minute gap with respect to a latent image bearing member; developer supply means for supplying developer to the surface of said developer holding means; control means for controlling the thickness of a developer layer on said developer holding means;; a developer removing member adapted to be in contact with the surface of said developer holding means to remove the developer on the surface of said developer holding means and again impart the removed developer to the surface of said developer holding means at a position before the supply of developer is terminated after the controller developer layer has been used for development said developer removing member having developer passage openings in the neighbourhood of the portion thereof which is in contact with the surface of said developer holding means; and a magnetic field generating portion provided on that side of said developer holding means which is adjacent to said developer passage openings.

1 6. A device in which toriboelectrical charge is imparted to developer and the developer is provided to a surface to be developed to thereby effect development, said device comprising a developer holding member disposed with a minute gap with respect to a latent image bearing member, a doctor blade for controlling the thickness of a developer layer on said holding member, and a member disposed at a suitable position during the time from after development until the supply of developer for the next cycle of development is terminated, for removing the developer used for said development and remaining on said developer holding member, whereby development may be effected with developer supplied for each cycle of development.

1 7. A device in which toriboelectrical charge is imparted to developer by the friction between the developer and its carrying means and the developer is used for development, said device having: a station for supplying the developer to the developer carrying means in each cycle of development; a station for imparting the developer to a surface to be developed to thereby develop said surface; and a station disposed at a predetermined position during the time from after development until said supply of developer is terminated, for removing from said developer carrying means substantially all of the developer remaining after having passed through said developing station.

1 8. A developing device for developing a latent image on an image carrying element, in which developer is supplied at a developer loading station onto the surface of a developer carrier which moves on an endless path and in which developer still carried on the carrier after transfer of developer from the carrier to develop the latent image is removed from the surface prior to reloading with developer at the loading station.

1 9. A developing device substantially as hereinbefore described with reference to Figure 2A of the accompanying drawings.

20. A developing device substantially as hereinbefore described with reference to Figure 2B of the accompanying drawings.

21. A developing device substantially as hereinbefore described with reference to Figure 3A of the accompanying drawings.

22. A developing device substantially as hereinbefore described with reference to Figure 3B of the accompanying drawings.

23. A developing device substantially as hereinbefore described with reference to Figure 4A of the accompanying drawings.

24. A developing device substantially as hereinbefore described with reference to Figure 4B of the accompanying drawings.

25. A developing device substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

26. A developing device substantially as hereinbefore described with reference to Figure 6A of the accompanying drawings.

27. A developing device substantially as hereinbefore described with reference to Figure 6B of the accompanying drawings.

28. Printing apparatus which includes a developing device according to any preceding claim for developing a latent image formed during the performance of a printing operation by said printing apparatus.