DE1522739A1 - Apparatus for developing an electrostatic latent image - Google Patents

Description

Apparatus for developing an electrostatic latent image. The present invention relates to an apparatus for developing an electrostatic latent image formed on an electrostatic recording medium by either an electrophotographic method or an electrostatic printing method, and more particularly to an apparatus for developing an electrostatic latent image using a liquid developer.

When the liquid is developed, an electrostatic recording sheet is on which an electrostatic latent image by the electrophotography method or the electrostatic printing method is implemented in a liquid developer brought about by dispersing fine solid particles in an electrically insulating liquid medium is produced, whereby the solid particles on the areas of the electrostatic latent image on the recording sheet are attracted so that the electrostatic image is converted into a visible image. A developing device i in which the removal of the on the developing and recording sheet accordingly the method of remaining developer is essentially automatic an assembly with an electrographic apparatus or an electrostatic one Printing apparatus assembled.

In a recording sheet, which is developed with a conventional apparatus for the liquid development, which can Form.und the Abstufung'der darkness and blackness in a subject -to reproduced with high quality reproduced werdent_ when the elektrogitatisc-li latent] image - a form of fine lines having. As soon as the electrostatic image forms massive area forms, however, a high: # - quality of the color reproduction can only be achieved with reference to limited areas of the edge parts of the electrostatic image and the density becomes more and more inadequate in the direction of its central parts, whereby there is a fear that a so-called edge effect is caused.

In order to form a clearer visible image on the recording sheet tracing the object by reducing or eliminating the edge effect and increasing the density of the developed image, an apparatus has been developed in which developing electrode plates are arranged so as to be close to the electrostatic image supporting sheets lie and the liquid developer is fed between the platen and the sheet. In order to sufficiently improve the developed image in such an apparatus, it is necessary to arrange the recording sheet and the electrode plate as close as possible with a space therebetween. However, it is practically difficult to adjust the distance between one lead electrode plate and the other electrode plate guiding the sheet so that there is a narrow and uniform distance of, for example, about 1 mm. Further, when the electrostatic sheet passes through such a small distance, it easily contacts the electrode plate, with the result that an image formed on the sheet and not yet fixed is damaged. The image damaged in this way has undesirable thin stripe-like scratches.

An excess amount of developer resting on the electrostatic What remains is a sheet that is passed through a developer and a developed one Image has: must in particular from its image-bearing surface to achieve # one thing is clear Image to be removed. According to a previously known Device for liquid development are a pair of rollers, each with a metal and a rubber surface, which are rotatable in opposite directions, in Pressure contact with each other, namely in a position in which the recording sheet after immersion in the developer is added, and before the sheet dem is subjected to subsequent fixing, the excess developer becomes intermediate two rollers while the image-bearing surface of the sheet is in Comes up in contact with the rubber roller. Such an arrangement of the roles brings something Disadvantages with themselves, in that there are solid particles that make up the unfixed image. form, formed on the recording sheet partly on the peripheral surface the roll are transferred with the result that the density of the image after Passing the sheet through the rollers is made insufficient, and also that the particles thus transferred to the roller surface in turn to the subsequent ones Recording sheets are deposited and thus spoil the image-bearing surface. Further, when the metallic roller and the rubber roller with surface layers of considerable different elasticity can be caused under pressure contact to work, the peripheral speeds become unequal and this results in a Distortion of the unfixed image on the recording sheet.

A Aulgabe of the invention is to provide an apparatus for developing an electrostatic latent image using a liquid escaped coupler, wherein the the elehtrostatisch latent image bearing surface of an electrostatic recording sheet, and a development electrode at a very low and uniform exhaust faced an.geordnet are whereby an edge effect is sufficiently avoided and a visible image of a high quality standard is produced. Another object of the invention is to provide a developing device in which a liquid developer of constant uniform composition is continuously fed between the electrostatic latent image bearing surface of an electrostatic recording sheet and a developing electrode so as to be in the same direction and at substantially the same direction at the same speed as the trajectory of the recording sheet so that a visible image having sufficient density and clarity can be formed at an advantageous speed.

Another object of the invention is to provide a developing device in which there are a pair of rotatable members rotatable in opposite directions and in pressure contact with each other for the purpose of removing an excessive amount of a liquid developer from a developed electrostatic recording sheet, any of the foregoing rotatable member that contacts the image bearing surface of the recording sheet is a roller-having an outer peripheral surface-which consists of a layer of fibrous substance or a loose fiber belt, whereby a clear and undistorted image is delivered to the subsequent fixing device can be. These and other objects of the invention are best understood with reference to the following description in conjunction with the accompanying drawings. Figure 1 is a longitudinal sectional view of a developing apparatus incorporating features of the invention.

Figure 2 is a longitudinal section showing a further embodiment of the Invention illustrated.

Figure 3 is a longitudinal section illustrating yet another embodiment of the invention. Figure 5 is a longitudinal section of another variation of the squeegee roller.

Referring to Fig. 1 , a developing apparatus, a developing device 11 for performing development according to a liquid developing system by immersing an electrostatic recording sheet bearing an electrostatic latent image in a liquid developer, a device which supplies the developer 12 including a kettle 13 and an associated one Feed system 14, wherein the vessel feeds the liquid developer to said developing device and at the same time takes back the developer released therefrom, and a squeezing device 15, by means of which the excess amount of developer is scraped off the recording sheet, which is passed through the developing feeder seal 11 'has been developed. The developing device 11 consists of a tank 1.6 made of conductive material, such as metal, and a drum or cylinder 17, of which approximately half of the entire outer spherical surface is kept immersed in the liquid developer contained in the tank 16, the tank 16 is used to store the developer continuously supplied by the developer supply device and to dispense a substantially equal amount. At one of its end parts , the tank has a bearing part 19, which is delimited by a partition 20 and which is arranged below the nozzle of an outlet line 18 of the feed system 1, 4 in order to temporarily store the continuously fed developer, and at its other end it has end a Ablaßt "eil 21 for overflow and draining the developer downward. the inner bottom surface of the boiler 16 is-curved so that it follows the peripheral surface of the cylinder 17 at an equal small distance. the liquid developer from the storage vessel 13 pumped into a suction line 22 of the feed system 14 by a pump 23 and temporarily stored in the bearing part 19 of the boiler 16 , after it has come in there from the nozzle of an outlet pipe 18. As soon as the level of the wing exceeds the height of the partition 20, the developer flows through a narrow passage leading from the inner lower surface of the kettle and the outer pe peripheral surface of the cylinder is circumscribed and # returns to the container 13 from the discharge part-21, whereby a closed circuit is formed. the excessive amount of the developer remaining on the recording sheet is removed. Said squeezing device consists of a rotatable element 26, which is partially immersed in a liquid developer, which is filled in a container 25 and can be rotated in the direction of an arrow at the same circumferential speed as cylinder 17 by means of a suitable drive means, not shown, and another rotatable element 28, which under pressure contacts said rotatable element 26 under the action of a spring 27 and is rotatable at the same speed but in the opposite direction of rotation of element 26 .

The electrostatic recording sheet to which the liquid developing system is applicable can be produced. is made of a base paper or a synthetic plastic material that is thinly coated with a light-sensitive layer of a photoconductive material, as far as the method of electrophotography is concerned, or with an insulating layer of an electrically highly resistant material, as far as the electrostatic printing method is concerned. In either case, the recording sheet bears an electrostatic charge corresponding to the model to be printed, so that an electrostatic latent image is formed thereon. The recording sheet 29 bearing this electrostatic latent image is fed to the developing apparatus by a suitable transport device and inserted between the cylinder 17 and the guide roller 24 pressing against it. Before developing, the storage container 13 is filled with a known liquid developer for the development of electrostatic latent images, which is obtained by dispersing fine solid particles in a liquid medium with electrical insulation, and the liquid developer thus filled is discharged through the tank 16 The circuit above and through the container 2.5 of the squeezing device along a similar circuit, not shown. With the developing liquid flowing, the cylinder 17 and the rotatable members 26 and 28 are rotated at a predetermined rotational speed so that their peripheral speeds are the same. A suitable amount of DC voltage can preferably be applied to the vessel 16 .

The recording sheet 29 inserted between the cylinder 17 and the guide roller 25 effectively adheres to the peripheral surface of the cylinder 17 due to the pressing force of the guide roller as well as due to the adhesion force of the cylinder surface which is in the developing liquid during rotation is moistened and then advanced into the liquid developer flowing in vessel 16. The recording sheet 29 is subjected to the pressure of the developer moving at an appropriate speed as it passes through the developer in accordance with the rotation of the cylinder 17, and is held in a position adhered to the cylinder surface.

The electrostatic latent image bearing surface of the recording sheet which comes into contact with the developer in the kettle attracts fine solid particles contained in the developer according to the magnitude of the electrostatic potential and forms a visible image. This formation of the visible image is accelerated by the action of an electric field in the developer between Deng Kessel and deL. electrostatic image is generated. Since the electrostatic charge on the lower surface of the vessel 16 is induced by the electrostatic charge on the recording sheet, the electric field is intensified in a direction perpendicular to the surface of the recording sheet, whereby solid particles in the electrostatic latent image even in the case of a relatively thick electrostatic latent image Developers adhere uniformly to the entire surface of the image without adhering them concentrically to its peripheral parts, thereby sufficiently avoiding an undesirable edge effect.

Such an advantage can be obtained by setting the distance between the electrodes and the surface of the recording sheet to be a little less than 2 mm, preferably about -0.5 mm, and the developing device of this invention can accommodate this. According to the invention, these electrodes are represented by the bowl 16 which is made of conductive material for containing the liquid developer and the recording sheet can be passed through the developer while it is closely spaced from the bowl 16 on the peripheral surface of the cylinder.

According to the developing device of the invention, it is possible to move the developer in the same direction as the direction of movement of the recording sheet. It is assumed that the cross-sectional area between the recording sheet 29 and the inner lower surface of the kettle 16 is such that the flow rate of the developer is controlled by a difference in the liquid levels of the filling and filling sides for the liquid developer. With the kettle By choosing this difference in liquid heights to the desired extent, the flow rate of the developer can be substantially equal to that of the moving recording sheet. In this case, a successively advancing length of a recording sheet is always in contact with a fresh developer, so that a visible image of a constant density can be formed over the entire surface of the recording sheet. Since the relative speed between the recording sheet and the developer is essentially zero, there is no degradation in the clarity of the visible image caused, for example, by the fact that the solid particles, as soon as they adhere to the electrostatic image with respect to the Forward direction can be moved backwards due to the friction with the developer.

A variant of the developing device is shown in FIG. 2, in which parts similar to those in FIG. 1 are identified by the same reference numbers and their description is omitted. In this variant, the liquid developer in the storage container 13 is sucked into a suction line 22 by a pump 23 and passed on to three lines 31, 32 and 33 which are connected to the outlet side of the pump 23 . One end of the aforementioned three lines opens into the interior of the boiler 16 at its two side parts or its lower part, the boiler 16 having a curved bottom made of conductive material. This allows the developer to be continuously fed into the tank 16 through these lines. The vessel 16 has on its curved lower surface two drainage pipes 34 and 35 which are in contact with its interior and also an outlet port 21 at one end portion thereof. The liquid developer fed into the vessel is temporarily stored therein and then mostly through the Lines 34 and 3'5 drained and the remainder from drain opening 21, whereby a predetermined amount of developer is always present in the vessel, so that the supplied and discharged amounts of developer can be balanced.

Inside the vessel is a cylinder 17 which guides the recording sheet to be developed in the developer "while maintaining a small and uniform distance between the outer surface of the cylinder and the curved inner lower surface of the vessel. In this variant too, the recording sheet adheres 29x that carries an electrostatic latent image to be developed in a wi mamer manner on the wet surface of the cylinder 17 by the aid of the guide roller 24 and while the sheet in the developer passes into such a tightly adhering layer, the electrostatically charged areas become a visible image Further, in this variant, it is possible to greatly increase the supply amount of the developer per unit time for the purpose that the surface of the recording sheet can contact the fresh liquid developer so that a visible image of sufficient Density trained we even if the immersion time of the recording sheet in the liquid developer is shortened.

Figure 3 illustrates another variant of the developing device used in the developing apparatus of the invention. In this variant, the cylinder 17 is arranged so that one half of its entire peripheral surface is immersed in a liquid separator in the storage container 13. Therefore, the developer tank 16 and as failed shown in Figure 1 and 2. Inside the storage container-131 is disposed an electrode -11 which is opposite to that formed by the outer peripheral surface of the cylinder. Rollers 42, 13 and 44, which are rotated by suitable drive means (not shown), are provided so that they can transport the developer at a suitable speed through a narrow and uniform distance defined by electrodes 41 and 41 the cylinder surface is formed. In this variant as well, the recording sheet to be developed is in pressure contact with the wet surface of the cylinder 17 by means of a roller 24, and while it is moved through the narrow distance between the cylinder surface and the electrode, it contacts the fluid flowing through such parts Developer., The visible image thus developed is similar to the image developed with the apparatus shown in Figs. 1 and 2 in that it is free from the edge and has high quality color aberration., On the surface of the recording sheet with a small distance opposite electrode, a bias voltage is applied with the same or opposite polarity as that of the electrostatic latent image formed on the recording sheet. A visible image of normal color gradation or an image corresponding to the original is obtained by controlling the bias voltage as known when further the outer surface of the cylinder for supporting the recording pad is made of a conductive material such as metal and with a bias voltage of the opposite Polarity versus the electrostatic potential of the electrostatic latent image, the solid particles are prevented from depositing on the non-image areas or discharged areas, thereby reducing the obscurity of the resulting image.

The recording sheet thus subjected to development by the devolatilizing device as described above can be conveyed to a fixing device after an excessive amount of the developer adhered thereon is removed by a normal squeezing device. With the arrangement as described above, it is possible to obtain a clear visual image excellent in density and color gradation with the edge effect almost completely disappearing in relation to the images obtainable by the conventional developing devices known heretofore. When the removal of the excessive developer adhering to the recording sheet is carried out by passing the recording sheet through the nipping device shown in Fig. 1 , an unfixed visible image formed by passing the developer is at least not damaged. The crimping device 15 shown in Figure 1 has a pair of rotatable elements 26, and 28, the axes of which are arranged in parallel, said one rotatable element 28 being in pressure-contact with said rotatable element 26 by means of a coil spring 27. The rotatable Element 26 has a surface layer 261 which consists of porous fibrous substance and is arranged so that a part of it is immersed in a liquid developer which is located in the container-25 located below. Both rotatable elements rotate at the same peripheral speed as the cylinder of the developing device-11 by means of a suitable "(not shown) drive unit which is connected to both or to one of the rotatable elements.

The recording sheet 29, which has been developed by being passed through the liquid developer, is detached from the surface of the cylinder 17 after being immersed in the developer and, due to its rigidity, is moved upward, where it is squeezed between the rotatable members of the squeezing device 15 . The surface of the recording sheet bearing the visible image comes into pressure contact with the fibrous surface layer 261 of the rotatable member 26 by the rotatable member 28 which presses against the opposite surface of said recording sheet and is held under the influence of the spring, whereby excess developer adhering thereto is squeezed out without damaging the un-lexed visible image. Although it is not yet known exactly by which particular, D: echanische structure damage to the visible image, such as occurs when using a rotating element with a rubber-like surface layer, can be completely avoided, it is believed that this according to the invention, in which the The surface layer of the rotatable element which touches the surface of the recording sheet bearing the visible image, is composed of fibrous material, is for the following reasons. The fibrous material has almost no adhesion and microscopically the surface has a suitable unevenness. Thus, it does not contact the surface of the recording sheet as a surface of relatively large size but only at an extremely large number of points, whereby the visible image on the recording sheet is not damaged. Since solid particles are electrostatically deposited on the recording sheet , are not transferred to the rotatable element, for a similar reason there should be no fear that the density of the visible image will be lowered "and that it will be contaminated, which can happen once the transferred onto the surface of the rotatable element as it rotates Particles are reapplied to the surface of the subsequent recording sheet.

Among the fibrous materials which the above-described . Have restrictions, those shown in Figure 4 may be with the exception of masses of natural or synthetic fibers which are bound together by a suitable binder which is not soluble in the liquid developer. A rotatable in figure 4 A displayed element has, there is a surface layer, which is coated with a number of thin and short fibrous elements 52, with the surfaces layers of knitted fabric, which is put aside in the desired-'Dicke. Figure 4 B and 4 C illus - each trate a rotatable member having a surface layer of a knitted fabric layer 53 is umwickeit in suitable thickness lind with cotton ink 54, the said layer 53 covered and a rotatable element as a surface layer an oil-tight sponge layer 55 which is covered with cotton cloth 56. Each of these surface layers can be used as a fibrous endless belt which runs around a plurality of rollers instead of being fixedly connected to the rotatable element. Figure-5 shows an example of the crimping device in which the surface layer of one of the two opposing rotatable parts is a fibrous endless belt. A pair of rollers 61 and 62 are arranged to face a rotatable element 28 which is kept under pressure under the influence of a spring 27 , said rollers 61 and 62 guiding an endless belt 63 of fibrous matter. One of the rollers 62 is pivotally mounted at one end of a lever 65 which is movable about its pivot point 64 which is arranged at its central part and is constantly pulled in a direction opposite to the other rollers # 61 by the action of a coil spring 66, which is connected to the other end of said lever, a part of the total part of the roller 62 is located in a liquid developer ist.Somit in --dem-developer storage container 13 is Däs endless belt that is stretched between the rollers 62 and 61 always obtained under constant tension and successively immersed in the developer as the rollers rotate. Adjacent to the outer peripheral surface of the roller 61 is a roller 67 , said roller 67 being constantly pulled towards the roller 61 by a spring 68 , thereby removing developer from the endless belt 63 that has passed through the developer, and leads it with you. As soon as the recording sheet reaches the position between the rotatable element 28 and the endless belt 63 , its visible image-bearing surface contacts the endless belt 63 which has been braked in a suitable manner by the developer and the excess developer adhering to the surface is removed. Similarly, in this one. The unfixed visible image is not damaged and its clarity is not lost due to undesirable contamination. In the arrangement described herein, the squeezing device was described as consisting of two rotatable elements 26 and 28 . However, one of the rotatable members 23 which press the recording sheet 29 on its rear side against the fibrous layer can be omitted, and the cylinder 17 can also be used in common for this purpose. In this case, the rotatable element 26 shown in FIG. 1 or the rotatable element 61 or the endless belt 63 in FIG. 5 is gripped directly under pressure with the drum 17 and rotated therewith at the same circumferential speed. The recording sheet which has been treated with the squeezing device shown in FIG. 1 or 5 can be transported to the subsequent fixing device (not shown) and fixed there. The resulting image will have sufficient darkness and excellent color gradation at which the edge effect disappears completely. Although the invention has been described with reference to the particular embodiment shown here, it is not limited to the details and arrangement shown. The application is intended to cover all such variations or deviations that fall within the scope of the appended claims.

Claims (1)

Claims A liquid developer apparatus for developing an electrostatic latent image, d a d URC hg e k ted b y ei ch net that an electrostatic recording sheet which carries an electrostatic latent image of fine through a Flüssigkeitsentwicklerzur liquid development including solid particles dispersed in an insulating liquid medium , an electrode is disposed in said liquid developer which faces said recording sheet with a small space therebetween and a device removes an excess amount of the liquid developer adhering thereto by squeezing from the recording sheet coming out of the liquid developer Cylinder is housed in a container for storing the liquid developer and for the positive guidance of the mentioned-'Aufze- * Liehnungsblatt that carries the electrostatic latent image, and this when it is rotated by the called A liquid developer guides and a device through which the liquid developer forcibly circulates through the said gap between said cylinder and said electrode. 2. A device, d a d g e k urch hen according Anspruch.1, zeic HNET that said device for zwangläufigen circulation of the liquid developer includes a-plurality of driven rollers of said cylinder are arranged close to the outer surface of such parts which is in the liquid developer contained in said container. 3. A liquid developer apparatus for electrostatic latent images, d a d u rch g e k ennzeichnet that a container a lower part of a conductive material for storing a liquid developer for liquid development including fine solid has in an insulating liquid medium divided particles "said lower part is curved outwardly to form part of a cylinder, a cylinder effectively transports an electrostatic recording sheet on which an electrostatic latent image has been formed and which is spaced a short distance from said curved base of said container and which as it rotates guides said recording sheet through the liquid developer, a device forcibly circulating the liquid developer through the gap between said cylinder and said curved base of said container, and a squeezing device which removes an excessive amount of the liquid developer remaining on the above recording sheet coming out of the liquid developer. 4. An apparatus according to claim 3, d a d u rc h ge k ennzeichnet that said container has a Entwicklerfüllteil and a developer discharge part that are arranged at a distance from the -diametral opposite direction of said cylinder, said filling and said drainage member lie so that they move the liquid developer through the gap between said cylinder and the curved lower part of said container from said filling part in the direction of said drainage part and one device in each case continuously delivers the liquid developer to said filling part and the Lets liquid developer continuously drain from said drainage part. 5. An apparatus according to claim 3, d a d g e k urch ennzeichnet that a supply line supplies the liquid developer said container and a discharge pipe discharges the liquid developer from the said container, said lines at a given part. of the lower part of said container are arranged and said supply line is connected to a supply device which can continuously deliver liquid developer. 6. A device according to claim 1 to d a d ur c'h g e k ennze ichnet that at least the outer surface of said cylinder is made of a conductive material. 7. A device according to claim 1 to 6, d a d urch g e k ennz c ichnet that the (- "- named squeezing device is a rotatable element which is biased against said cylinder parallel thereto and has a layer of fibrous matter as well 8. a device is partially immersed in the liquid developer. according to claim 1 to 6, -da d urch g e k ennzeichnet that the crusher called consists of a pair of rotatable members and said one rotatable member which is in contact with the image carrying surface of said recording sheet, a layer of fibrous material has and is partially-in immersed developer the liquid. 9. a device as in claim 7 or 8, d a d u rch g e k ennzeichnet that said rotatable member is in accordance with an endless belt made of fibrous substance which is stretched over a plurality of rollers. 10. a device according to claim 7 to 9, since urch d g e k ted b y c ichnet that said fibrous Substance consists of a layer of natural or synthetic fibers which are bound with a binding agent which is insoluble in relation to the liquid developer. 11. A device according to claim 7 to i ;, d a d urch g e k ennzeich net that said fibrous substance is an elastic layer, the surface of which with a. Cloth is covered.