ELECTROSTATIC RECORDER

Abstract: An electrostatic recorder includes electrostatic latent image recording means for forming an electrostatic latent image on a recording medium conveyed at a predetermined speed, toner feed means for feeding a toner to a surface of the recording medium on which an electrostatic image is formed, and toner recovery means for recovering an excess of toner stuck to the recording medium. The toner recovery means can execute the recovery of an excess of toner not only by suction but also by scraping from the recording medium prior to this suction and means for eliminating the mixing of foreign matters into the feed side in conjunction with the recovered toner are provided.

Description: TECHNICAL FIELD The present invention relates to an electrostatic recorder, so arranged to develop an electrostatic latent image formed on a recording medium such as paper, film or cloth by using electrostatic recording heads, and in particular to an electrostatic recorder providing with a system for feeding a liquid toner to develop an electrostatic latent image and recovering an excess of liquid toner. BACKGROUND ART EP0578243A published on 12th January 1992 describes a wet toner electrostatic recording apparatus in which excess toner is removed by the recording medium with air and vacuum. EP026654A published on 8th April 1981 and PAJ06194964A published on 15th July 1994 describe wet toner electrographic printing apparatuses comprising a toner reservoir from which toner is drawn from the bottom and returned to the top. EP0226213A published on 24th June 1987 describes a wet type colour electrographic copying machine comprising a scraper roller and a blade for removing excess toner from recording medium. FIG. 8 shows a general color electrostatic recorder of the single path scheme. With this apparatus, a recording medium 10 wound in a roll is conveyed through four primary color recording sections 104a to 104d, for example, related to black, cyan, magenta and yellow, at a predetermined speed with the aid of a feed roller 102. When the recording medium passes through individual primary-color recording sections, images of the respective color components for a recording image are recorded and developed, so that a color image is finally obtained only by one-time passage. On a recording medium conveyed to the first primary color recording section 104a, first, an electrostatic latent image for an image of corresponding color component is formed by using the electrostatic recording head 106a. Next, by a counterclockwise rotating toner roller 108a, a liquid toner of corresponding color is lifted while sticking to a spiral groove (not shown) formed on the surface of the toner roll and applied to a record face of the recording medium 10. The liquid toner includes toner particles charged at the reverse polarity to that of the electrostatic latent image made to be dispersed in a suitable organic solvent. Accordingly, the toner particles sticking to the formed region of the electrostatic latent image are combined with the electrostatic latent image on the recording medium and thus the image is developed. Then, in a suction device 109a, an unnecessary liquid toner sticking to the underside surface of the recording medium is removed. The suction device 109a includes a groove of U-shaped section and an outer vacuum pump connected through a tube to the bottom of the groove, sucks an excess of liquid toner sticking to the recording medium by making the interior of the groove to a negative pressure with the vacuum pump and sends it to a liquid toner recycling device. Then, by blast from the underside of the recording medium with a blower 110a, the recording medium wet with the solvent of a liquid toner is dried and the procedure proceeds to the recording in the next primary-color recording section. And, at the stage after the passage of all primary-color recording sections, a color image is obtained. The system of an electrostatic recorder in which such operations of formation of electrostatic latent images by removal of unnecessary liquid toner are carried out in a single path from the primary-color recording sections 104a to 104d is referred to as a single path scheme. Meanwhile, with the single path scheme, the primary-color recording sections are continuously placed and when the recording medium passes through one primary-color recording section, recording in the next primary-color recording section is performed immediately. Accordingly, if removal of an excess of liquid toner stuck in the preceding recording and its solvent is insufficient, the relevant toner is mixed with the color toner for the preceding stage or the next color toner blots into the preceding-stage solvent in the recording at the next stage, thereby deteriorating the image quality. For this reason, for a sufficient removal and drying of an excess of liquid toner, it is required to slow down the conveyance of the recording medium in a certain degree. Since a large quantity of liquid toner is applied to the recording medium by using a toner roller, the interior of the groove in the suction section is filled with liquid toner and liquid toner jams between the recording medium and the top of the groove with which it makes sliding contact, thereby leaving no room for air to be sucked in. Consequently, an excessive suction force of a vacuum pump accompanies a fear of the recording medium itself to be sucked into the interior of the groove and the suction force is forced to be restricted to some extent. Thus, to remove a liquid toner or its solvent completely, the conveying speed of a recording medium had to be suppressed below a certain rate, which hindered an improvement in recording speed. In addition, with such an electrostatic recorder as mentioned above, an electrostatic latent image is formed by allowing a discharge to occur between the electrodes corresponding to individual pixels of the electrostatic recording head with a backrest pressed from above the recording medium and the record face kept in sliding contact with the head surface under a suitable pressure. On the surface of the recording medium, plenty of minute spacer for forming a suitable discharge gap between the record face and the electrostatic recording head is stuck. To the recording medium having passed by the electrostatic recording head, a liquid toner including toner particles dispersed in a predetermined solvent is applied with the aid of a toner roller. The liquid toner includes plenty of charged minute toner particles at the reverse polarity to that of electrostatic latent image dispersed in a predetermined solvent. When the liquid toner is applied to the recording medium, these particles are attracted to the electrostatic latent image formed on the recording medium by an electrostatic force and combined with the surface layer of the recording medium, so that the electrostatic latent image is developed. A toner roller applies a liquid toner over the whole record face of the recording medium to feed a sufficient amount of toner, but a part of the fed toner is actually submitted to the development of the electrostatic latent image. An excess of applied toner dropped off from the surface of the recording medium or sucked with a suction device to be returned to a toner tank is admitted to the recycling. At this time, because the recording medium comes into sliding with many machine elements such as electrostatic recording head and toner roller, some amount of spacer peels off every time of sliding contact and is mixed into the liquid toner to be recovered. In this way, a liquid toner recycled at many times deteriorates in quality by the mixing of other-color toner and spacer. Accordingly, the liquid toner having experienced fixed use cycles is replaced with a new liquid toner as a whole tank. The period of time from the mounting of a new tank to the need for replacement is substantially proportional to the length of a used recording medium if the type of recorded images is general. On the side of a maker, the amount of recording medium used till the replacement of a liquid toner becomes necessary is determined in advance for the convenience of replacement of a liquid-toner tank. Meanwhile, the demand for a continuous recording of color images in a much longer recording medium by using an electrostatic recorder other than conventional ones has recently become stronger. However, since the amount of images that can be recorded without replacement of a liquid toner tank is restricted in a conventional electrostatic recorder, there was a problem that the apparatus is compelled to be stopped halfway during the recording for the replacement of a toner tank in a continuous recording of color images on a long recording medium, the operation is interrupted and the efficiency lowers. Furthermore, if the above electrostatic recorder is described concretely, the principle of electrostatic recording in an electrostatic recorder of the single path scheme is described below as shown in FIG. 9. The recording medium 10 is conveyed in the arrow direction indicated. On the underside of the recording medium 10, there is provided a recording section 80 comprising electrostatic recording heads 82a to 82d comprising many electrodes arranged along the width direction of the recording medium 10, the respective liquid toner feed sections 83a to 83d disposed on the directly downstream side of the individual electrostatic recording heads and further the respective suction sections 84a to 84d disposed on the downstream sides thereof for the primary colors of black, cyan, magenta and yellow. When the recording medium 10 passes the recording section 80 while making sliding contact with the top of the electrostatic recording heads 82a to 82d, electrostatic latent images are formed with the electrostatic recording heads 82a to 82d, a liquid toner is applied from the liquid toner feed sections 83a to 83d to the recording medium 10 on directly downstream sides thereof, a liquid toner is stuck to the formed portions of electrostatic latent images on the recording medium 10 and an excess of liquid toner is sucked in with the suction devices 84a to 84d on the directly downstream sides thereof. By repeating this procedure for the primary colors of black, cyan, magenta and yellow, a color image is printed on the recording medium 10. As shown in FIG. 10, the electrostatic recorder so arranged as mentioned above also comprises a conventional piping system for feeding a liquid toner to a liquid toner feed section and for recovering an excess of liquid toner by using a suction device. Incidentally, the piping system shown here is a piping system only for one color out of the aforesaid four primary colors of black, cyan, magenta and yellow (here, chosen at black). Four systems of such piping are provided in the electrostatic recorder mentioned above. From the toner bottle 91 filled with a liquid toner, a liquid toner is sucked by means of a pump 92 and the liquid toner delivered from this pump is fed through a Y-shaped junction 93 to a liquid toner feed section 83a on one hand and applied to the recording medium 10. Alternatively, the other liquid toner passing through the joint 93 is exhausted through an aspirator 94. The exhausted liquid toner is returned to the toner bottle 91 again. When the liquid toner passes the aspirator 94, a negative pressure is generated inside a suction device 84a and the route leading thereto, and the liquid toner 95 applied in excess on the recording medium 10 is sucked in the suction device 84a. The liquid toner recovered in this manner is exhausted together with the liquid toner delivered from the pump 92 and passing through the aspirator 94. Midway in the piping leading from the suction device 84a to the aspirator 94, a vacuum switch 96 is provided. The level of a negative pressure is monitored with the vacuum switch 96 and, when the suction device 84a cannot exhibit its function sufficiently, for example, due to the presence of folds or creases, the conveyance of the recording medium 10 is stopped to prevent an excess of liquid toner 95 from being delivered without sucked in the suction device 84a while kept stuck to the recording medium 10. With the piping system so arranged as mentioned above, a much greater amount, e.g., double or more, of liquid toner needs to flow through the aspirator 94 than the amount required for the printing itself because the liquid toner have to be let to flow through the aspirator 94. For this reason, a large size of pump 92 becomes necessary, so that the installation space of a pump increases and the price becomes also high. In addition, there is a limit for the installation of a large-sized pump 92 or a large-capacity aspirator 94. Thus, only the presence of slight folds or creases would make it impossible to suck an excess of liquid toner on the recording medium 10 and it takes time till the suction becomes possible again, so that there is a problem that a stained image is printed on the recording medium 10 in the end. DISCLOSURE OF THE INVENTION The present invention is made with the above problems of the background art in mind, and it is an object of the present invention to provide an electrostatic recorder having a liquid toner feed system enabling plenty of images to be recorded at the one-time replacement of a liquid toner tank. To attain the above object, present invention provides the electrostatic recorders according to claims 1 and 7. Further embodiments of the present invention are covered by the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of the section for the recording of an image for one color in a color electrostatic recorder of the single path scheme according to the present invention. FIG. 2 is a schematic illustration of liquid toner feed means not only for feeding a liquid toner for development but also for recovering an excess of liquid toner after the development in an electrostatic recorder according to the present invention. FIG. 3 is a perspective view of the main body of an electrostatic recorder and an external reservoir comprising a plurality of bottles integrated into a single unit. FIG. 4 is a front view of the internal structure of a gear pump for the feed and recovery of a liquid toner in an electrostatic recorder according to the present invention. FIG. 5 is a bottom view of the gear pump of FIG. 4. FIG. 6 is an illustration of one gear in the gear pump of FIG. 4. FIG. 7 is a schematic perspective and partly cutaway view illustrating the replacement operation of an electrostatic recording head in an electrostatic recorder according to the present invention. FIG. 8 is a schematic sectional view of a conventional electrostatic recorder. FIG. 9 is a schematic perspective view for illustrating the principle of electrostatic recording in an electrostatic recorder. FIG. 10 is a piping diagram showing one example of piping system for feeding a liquid toner and recovering an excess of liquid toner in an electrostatic recorder. BEST MODE FOR CARRYING OUT OF THE INVENTION Hereinafter, one embodiment of the present invention as claimed in claims 2-6 will be described referring to the drawings. FIG. 1 is a sectional view showing the outline of a section for conducting an image recording for one color in a color electrostatic recorder of the single path scheme. With an actual color electrostatic recorder of the single path scheme, for example, four of image recording sections similar to that of FIG. 1 are provided for individual colors. In FIG. 1, a recording medium 10 on which an image is formed is conveyed in the direction of the arrow a 1 of FIG. 1 (subscanning direction) while a back tension applied. The electrostatic recording head 11 serves to form an electrostatic latent image on the recording medium 10 sliding thereon and is driven in accordance with an image signal fed from a predetermined signal processing circuit. A press roller 12, pad roller for a backrest, presses the recording medium 10 to the side of the electrostatic recording head 11 and brings the recording medium into sliding contact with the electrode part of the electrostatic recording head 11 under a suitable pressure. On the record face (underside of FIG. 1) of the recording medium 10, spacer comprising silica particles on the order of 5 to 30 µm in diameter is dispersed at a suitable density. By this spacer, a discharge gap is produced between the electrostatic recording head and the dielectric layer of the recording medium, the recording medium is charged by a discharge between the recording medium and the recording head, and an electrostatic latent image is formed. The recording medium 10 passing through the electrostatic recording head 11 is sent to a development section 20. In the development section 20, press rollers 26, 27, 28 for bringing the recording medium 10 into sliding contact with a toner roller 21, a scraper 22 and guide bars 24, 25 of the suction section 23 are provided on the upside of the recording medium 10. The scraper 22, the guide bars 24, 25 and a support member for the guide bars are all made of stainless steel rod-shaped members which are detachably fixed to a case member 29 containing the toner roller 21 with the aid of a fixing member (not shown). These parts with which the recording medium is always in sliding contact and requires a high frequency of a replacement, but the above arrangement enables only the necessary parts to be replaced while the case member left as it is after the fixing member detached when replacement is required. Accordingly, in contrast to a conventional recorder in which these part and the case are arranged in a one-piece unit, the replacement operation of parts becomes easy and simple, and the operator's burden is reduced. With color electrostatic recorder of the single path scheme, such electrostatic recording heads and development sections are provided in series, for example, as four stages and finally a color image is obtained by conducting a recording for the respective primary colors at individual stages. A toner feed tray 30 situated below the toner roller 21 is filled with a liquid toner 31 comprising toner particles diffused into a predetermined solvent to the level slightly beyond the lower end of the toner roller 21. This liquid toner is sent from the toner bottle mentioned later through a predetermined route to the toner feed tray 30 by a gear pump 150. Toner particles in the liquid toner are charged in the opposite polarity to that of an electrostatic latent image. When the toner roller 21 is rotated counterclockwise, the liquid toner 31 is lifted along the groove on the surface of the toner roller 21 and applied to the under face of the recording medium 10 at the portion contacting the recording medium 10 in the toner roller 21. Toner particles in the liquid toner, sticking to the portion in which the electrostatic latent image is formed, are drawn to the electrostatic latent image formed on the recording medium by the electrostatic force and combined with the surface layer of the recording medium in a formed proportion of the electrostatic latent image and the electrostatic latent image is developed. If another-color image is recorded with the solvent of the liquid toner remaining on the recording medium 10 after one-color image is recorded, the color image quality deteriorates. For this reason, the toner remaining on the recording medium is removed after the development and further the solvent is dried with the aid of a blower device installed downstream the development section. With this embodiment, to remove the greater part of unnecessary liquid toner prior to drying with the blower device, the scraper 22 and suction section 23 are provided at the following step of the toner roller 21. The scraper 22 is made of a stainless steel rod-shaped member a little longer than the width of the recording medium 10 and the section is a circle of about 5mm diameter. The shaft of a scraper 22 is fixed at the case member 29 so as to cross the progressing direction of the recording medium at a right angle. The scraper 22 scrapes off the greater part of unnecessary liquid toner remaining on the recording medium by the sliding of the recording medium 10 thereon. The scraped off liquid toner drops off along the inner wall of the case member as indicated with the arrow a 2 . On the other hand, the suction section 23 is made to a negative pressure in the space between the guide bars 24 and 25 below the recording medium 10 with the aid of a pump (not shown) connected through the suction path 33 to suck the liquid toner remaining on the recording medium. The scraper 22 was made of a stainless steel rod-shaped member because of taking it into consideration that the corner parts that might damage the recording medium coming into sliding contact therewith are eliminated, the linearity of the portion making contact with the recording medium can be easily provided in manufacturing and a sufficient wear resistance is observed. Thus, if these conditions are satisfied, any others than a stainless steel rod-shaped member may be employed as the scraper. With a conventional recorder equipped with no scraper, it is required to remove the liquid toner only in the suction section, but since the recording medium is conveyed to the suction section with an excess of liquid toner stuck thereto, the space formed with a spacer between the recording medium and the guide bars is filled with the liquid toner. For this reason, it was required to restrict the suction force in some degree so that the recording medium itself comes to be sucked, to slow down the conveyance of the recording medium in consideration for this restriction and to remove the liquid toner. Furthermore, it became necessary to dry the remaining solvent by means of a blower device at the next stage. This makes a hindrance in promoting the recording speed. In contrast to this, with this embodiment, since the greater part of liquid toner is scraped off in advance by the scraper 22 provided in front of the suction section 23, the amount of liquid toner to be sucked in the suction section 23 greatly decreases. In advance, since the greater part of liquid toner is scraped off by the scraper 22, a sufficient gap is produced by a spacer between the recording medium 10 and the guide bars 24, 25 and air is sucked through this gap, so that the suction force of the suction section 23 can be made stronger than conventional. Concretely speaking, though the pressure of water head 600 mm H 2 O was a conventional limit, the limit of suction pressure could be elevated to water head 1500 mm H 2 O in this embodiment. From these, the time taken for the removal of liquid toner is greatly shortened. In addition, since drying of a solvent is accelerated by the air sucked in through the gap between the recording medium 10 and the guide bars 24, 25, the drying time in the blower device at the next stage is also shortened. In consequence, the conveyance of a recording medium can be further speeded up. And, since the solvent remaining in the recording medium is almost completely dried by the sucked air, the deterioration of image quality due to the mixing with the toner at this stage can be prevented. Furthermore, even if a floating of the recording medium 10 occurs due to a small degree of folding, breaking or creasing, the recording medium 10 can be firmly brought into close contact with the guide bars 24, 25 by intensifying the suction force of the suction section 23. Thus, in contrast to a conventional recorder in which it was required to stop the recorder every time when a slight fold or the like occurred, the operating efficiency is promoted. Next, referring to FIG. 7, the replacement operation according to claim 16 of an electrostatic recording head (11) will be described. On the electrostatic recording head (11), electrostatic recording electrodes and auxiliary electrodes are embedded, for example, at a density of 400 dpi over a length nearly equal to the width of the recording medium in the main scanning direction into an dielectric material such as epoxy resin and formed. In addition, under the electrostatic recording head (11), numbers of integrated circuits for driving the electrodes and other circuit parts are packaged. Accordingly, in a large-sized electrostatic recorder for a 36 inch wide or wider recording medium, the weight of the electrostatic recording head (11) amounts even to several tens of kg. When replacing an electrostatic recording head in a conventional recorder, the lower end of the head had to be lifted to the upper end of the side wall of the main body to demount the head from inside the recorder after opening or removing the top cover. For this reason, replacement operation of an electrostatic recording head was difficult to conduct for oneself and required the cooperation of two persons or more in principle. In contrast to this, with this embodiment of electrostatic recorder, cutaway portions 251 equal in number to the electrostatic recording heads 11 are provided in the side wall 250 on one side of the main body as shown in FIG. 7. Incidentally, for simplicity, only one of the electrostatic recording heads (11) is shown in FIG. 7. Each cutaway portion 251 is provided directly above the exactly lateral side of such a portion as to install the corresponding electrostatic recording head (11). Accordingly, when replacing an electrostatic recording head 11, first, one side (side with the cutaway 251) of the electrostatic recording head 11 to be replaced is lifted and put onto the corresponding cutaway portion 251. At this time, on the other side of the electrostatic recording head (11), a roller provided at the bottom gets on a rail (not shown) provided at the corresponding position of the bottom of the electrostatic recording head (11) and the recording head becomes simply movable. By drawing out the lifted side toward outside the main body of the recorder from this state as shown in FIG. 7, the electrostatic recording head (11) can be taken out outside the electrostatic recorder. The lifting weight of one side of the electrostatic recording head (11) becomes about a half of the weight of the electrostatic recording head (11). Besides this, the vertical distance along which to be lifted is significantly shorter than the height of the electrostatic recording head (11). Consequently, the labor required for the replacement operation reduces and it becomes sufficiently possible even for a single operator to replace the electrostatic recording head 11. As described above, according to the present invention, since the greater part of an unnecessary liquid toner is scraped off by toner removal means before the recording medium reaches the suction means, the interior of the suction means is not filled with a liquid toner and by making a negative pressure through the suction, air is sucked from the contact portion of the recording medium and suction means to the interior. In this way, since the recording medium itself is not sucked and the suction force of the suction means can be elevated to a considerable extent, drying of the recording medium is greatly accelerated, thereby making it possible to provide an electrostatic recorder that can maintain a high image quality even if the conveyance of the recording medium is speeded up. Hereinafter, another embodiment of the present invention according to claims 1 and 7 will be described referring to Fig. 2. This system comprises a large-volume external bottle 40 provided outside an electrostatic recorder and an internal bottle 50 provided inside the recorder. The cap part 56 is fixed detachably at the top of the internal bottle 50 by fit in the opening. A feed pipe 52, a first toner feed pipe according to the present invention, and a recovery pipe 54, a first toner recovery pipe are linked with the cap part 56, serving to mutually separate the routes of these two pipes. In the internal bottle 50, another small-sized bottle 60 is further provided. This bottle 60 serves as an intra-reservoir reservoir according to the present invention. The bottle 60 is provided with a pipe 62 coupled with the feed pipe 52, a inflow port 63 for a liquid toner and an overflow exhaust port 64. The pipe 62 is provided with a flange-shaped lid 62a which hermetically seals the upper opening of the bottle 60. The liquid toner 31 in the external bottle 40 is sucked up from near the bottom of the external bottle 40 by means of a pump 70 and delivered through pipes 42a, 42b, a second toner feed route according to the present invention, and a inflow port 63 to the bottle 60 in the internal bottle 50. The liquid toner delivered to the bottle 60 is further sucked up from near the bottom thereof, delivered through the pipe 62 and the feed pipe 52 to the toner feed tray 30 and thereafter applied to the recording medium with the toner roll. At that time, the pump 70 makes the amount of liquid toner fed to the bottle 60 greater than that of liquid toner sucked up through the feed pipe 52 from the bottle 60, thus leading the bottle 60 to an overflow state. Accordingly, there is a state that a liquid toner is always flowing out from the overflow exhaust port 64. On the other hand, an excess of liquid toner after the development processing is recovered through the recovery pipe 54 to the internal bottle 50, further returned through pipes 44a, 44b, a second recovery route, to the external bottle 40 by means of a pump 72 and recycled. At this time, in the internal bottle 50, the liquid toner recovered from the recovery pipe 54 and the liquid toner to be fed through the feed pipe 52 to the toner feed tray 30 are not mixed together on account of the structure of the cap part 56 shown in FIG. 2 and the provision of the bottle 60. In the interior of the internal bottle 50, a float sensor 58 is provided. The normal liquid surface of the internal bottle 50 is at the level indicated with "2" of this sensor and at that time, the pumps 70, 72 are both ON. When the liquid surface rises and reaches the level indicated with "1", the pump 70 becomes OFF and the pump 72 is ON to lower the liquid surface level. On the other hand, when the liquid surface falls and reaches the level indicated with "3", the pump 70 is ON and the pump 72 becomes OFF to raise the liquid surface level. By such operations, the liquid surface level of liquid toner in the internal bottle 50 is maintained nearly constant. Incidentally, Numeral 58a denotes an output signal line of the float sensor 58 for controlling the switches of individual pumps. Meanwhile, when air bubbles are mixed in the liquid toner applied to the recording medium by using the toner roller of the development section, no toner is stuck to the recording medium at these bubble portions and therefore an unevenness in the stuck amount of toner occurs at some positions of the recording medium, thus deteriorating the image quality. Since the recovered liquid toner is always returned to the external bottle 40, air bubbles are generated near the liquid surface as a result of splashes or ripples caused by accompanying impacts. Since a certain period of time is taken till the air bubbles generated once disappear, air bubbles contained in a large quantity are carried with the toner roller as they are and stuck to the recording medium when the pump 70 sucks up the liquid toner near the liquid surface. However, if the external bottle 40 is chosen at a large volume and a depth of the order of approx. 50 cm, almost all air bubbles have disappeared in the liquid toner near the bottom. Thus, by sucking up the liquid toner 31 from near the bottom of the external bottle 40, the liquid toner can be delivered to the internal bottle 40 without mixing of air bubbles generated near the liquid surface. In an excess of liquid toner recovered in the recording section of the electrostatic recorder, air bubbles are generated when the liquid toner is removed from the recording medium. In addition, when the recovered liquid toner is returned from the recovery pipe 54 at a considerable power to the internal bottle 50, the liquid surface in the internal bottle 50 is rippled and plenty of air bubbles are generated also here. However, by having a bottle 60 separated from this liquid surface in the internal bottle 50 provided and feeding the liquid toner through this bottle to the toner feed tray 30, the mixing of air bubbles can be prevented which would occur if the liquid toner fed from here through the feed pipe 52 to the toner feed tray 30 is mixed with that recovered and returned from the recovery pipe 54. Like this, since it can be effectively prevented that air bubbles are mixed into the liquid toner fed to the toner feed tray 30, the quality of printed images is improved as compared with a conventional recorder. Furthermore, by the provision of a large-volume external bottle 40, separate from the internal bottle, the increasing rate of impurities per unit time can be suppressed low. Accordingly, the period of time from the replacement of the external reservoir 40 till the liquid toner becomes so contaminated as to require the next replacement is greatly prolonged and the cycle of liquid toner replacement or condensed toner supply becomes longer. Thus, even when plenty of images are continuously printed, the frequency of stopping a recorder halfway is lowered and the operating efficiency is promoted. FIG. 3 is a perspective view showing the main body 1 of an electrostatic recorder and an external bottle unit 2 comprising a plurality of external bottles integrated into a single unit. Incidentally, in FIG. 3, for simplicity, only the external bottle for one color is shown. The external bottle unit 2 is equipped with the respective external bottles for four colors and further each external bottle 40 comprises a feed pump 70, a recovery pump 72, a pump control substrate 130 and a power supply switch 140. In the tank housing section inside the main apparatus body 1, internal bottles 50 for four colors are equally provided. In FIG. 3, small bottles 120 shown behind the internal bottles 50 are reservoirs for a condensed toner and when the concentration of a liquid toner is lowered, the corresponding condensed toner is additionally poured into the relevant internal bottle 50 by means of exclusive-use pump (not shown) according to the need. Each internal bottle 50 of the main apparatus body 1 and the corresponding external bottle 40 are mutually connected through a feed pipe 42a, a recovery pipe 44a and an output signal line of a float sensor 58a, but the respective bottles can be installed at different places apart from each other by lengthening these pipes and the signal line. As indicated with dotted lines in FIG. 3, an internal bottle 50 can be easily taken out of the main apparatus body 1. This internal bottle 50 has a bottle 60 shown in FIG. 2 and is connectable to an external bottle 40, but has the same form and size as with a conventional liquid toner reservoir, that is, a general liquid toner reservoir not containing a bottle 60 and unconnectable to an external bottle 40 or a cap part 56. Accordingly, when a user wants the additional installation of an external bottle unit 2 later, the additional installation becomes easily possible only by replacing the general liquid toner reservoir used formerly in the apparatus with an internal bottle 50 according to this embodiment. Besides this, by a simple operation, the volume of a bottle is easily increased and an improvement for an electrostatic recorder of a longer bottle replacement cycle becomes possible. As described above, according to the present invention, by having a large-volume liquid toner reservoir separate from the main body of an electrostatic recorder provided and sucking up a liquid toner from near the bottom of a liquid toner reservoir to feed the liquid toner to a development section of the electrostatic recorder, the increasing rate of impurities per unit time can be suppressed low. Accordingly, the period of time from the replacement of the liquid toner reservoir till the liquid toner becomes so contaminated as to require the next replacement is greatly prolonged and the cycle of liquid toner replacement or condensed toner supply becomes longer. Thus, it is possible to provide a liquid toner feed system for an electrostatic recorder in which, even when plenty of images are continuously printed, the frequency of stopping a recorder halfway is lowered and the operating efficiency is promoted. Also, according to the present invention, it is possible to provide a liquid toner feed system for an electrostatic recorder in which, not only by having an internal reservoir provided inside the main body of an electrostatic recorder but also by having a large-volume liquid toner reservoir separate from the main body of the electrostatic recorder provided and making it into an overflow state as to feed a liquid toner from the external reservoir through an intra-reservoir reservoir in the internal reservoir to the development, the liquid toner fed to the development and the liquid toner recovered and returned after the development are completely separated, so that no air bubbles contained in the liquid toner after the recovery is mixed into the liquid toner to be fed to the development, and further by sucking up the liquid toner from near the bottom of the external reservoir with hardly any air bubble generated, the deterioration of print image quality originating from air bubbles is effectively prevented and a high print image quality is obtained. Next, a gear pump for the electrostatic recorder (hereinafter, referred to as "gear pump"), the principal part of still another embodiment of the present invention, as claimed in claim 14, will be described. FIG. 4 is a partly omitted front view showing the internal structure of a gear pump 150, FIG. 5 is a bottom view of a gear pump 150 and FIG. 6 is an illustration of the shape of a gear 161 (or gear 162). Incidentally, for simplicity, the teeth of the gears 162 and 163 are omitted in FIG. 4 and only about a quarter of the teeth of the gear 161 (or gear 162) are depicted. The case 151 has a size of approx. 70 mm in width and approx. 90 mm in length, and in the interior, a region surrounded with an approx. 10 mm high side walls 152a to 152d is provided, while an approx. 10 mm high upheaval 153 is formed at the center of the side wall 152c. In the space formed with the side walls 152a to 152d and the upheaval 153, gears 160 to 163 are rotatably disposed. Among these, the gear 160 is a gear for transmitting the rotational driving force of a motor to the gear 161. The gear 161 is a first gear according to the present invention, the gear 162 is a second gear according to the present invention and the gear 163 is a third gear according to the present invention. Incidentally, when the gear pump 150 is actuated, a planar cover is mounted at the top to tightly seal the interior. The gears 161 to 163 are all approx. 10 mm in thickness. The gears 161 and 162 are equal in shape and size, and teeth are provided in the inner and outer peripheries as shown in FIG. 6. These inner teeth and outer teeth are equal in number and so formed that the inner tooth flank comes to the outer tooth crest. This is because the thickness of a gear is made as constant as possible so that a change in strength with different places is minimized. The position of the gear 161 is defined by the side wall 152a and the outer teeth thereof come in sliding contact with the side wall 152a. The position of the gear 162 is defined by the side wall 152c and the upheaval 153, the outer teeth thereof come in sliding contact with the side wall 152c and the inner teeth come in sliding contact with the wall 153a of the upheaval 153. And, the position of the gear 163 is defined by the upheaval 153 and the gear 162, the teeth thereof come in sliding contact with the side wall 153b of the upheaval 153. Incidentally, the gear 160 is made of metal. On the other hand, the gears 161, 162 and 163 are obtained by molding from a raw material such as, e.g., phenol resin or polyacetal and annealed thereafter. At that time, to raise the wear resistance, silica may be mixed. The gear 160 is rotationally driven counterclockwise around the center axis 160a, for example, at a rate of 300 r.p.m. by means of a motor not shown. Teeth of the gear 160 and inner teeth of the gear 161 are engaged with each other, outer teeth of the gear 161 and outer teeth of the gear 162 are engaged with each other and further inner teeth of the gear 162 and teeth of the gear 163 are engaged with each other. Accordingly, when the gear 160 is rotationally driven counterclockwise by means of a motor, the gear 161 rotates counterclockwise, the gear 162 rotates clockwise and the gear 163 rotates clockwise. In the case 151, as shown in FIG. 4, four openings 170, 171, 172 and 173 are further provided. As shown in FIG. 5, these openings couple with corresponding insert ports 170a, 171a, 172a and 173a provided so as to protrude in the rear side direction. To individual insert ports, corresponding hoses are inserted. The opening 170 couples through the insert port 170a with a toner bottle (not shown) in which a liquid toner is stored and the opening 171 couple through the insert port 171a with the aforesaid toner feed tray 30. Since the counterclockwise rotation of the gear 161 and the clockwise rotation of the gear 162 will make the space (center right space) surrounded with the side wall 152b and the gears 161, 162 into a negative pressure, a liquid toner is sucked from the toner bottle and flows through the opening 170 into the gear pump. This liquid toner enters between outer teeth of the rotating gears 161 and 162, is carried to the space (center left space) surrounded with the opposite side wall 152d and the gears 161, 162, pressurized here and delivered from the opening 171 to the toner feed tray 30. In this manner, one pumping route leading from the opening 170 to the opening 171 is formed. Incidentally, at the route leading from the opening 171 to the toner feed tray 30, a pressure regulating valve not shown is provided. When the pressure in this route exceeds a fixed value, the pressure regulating valve operates to let air or toner off, thus lowering the internal pressure. By the function of the pressure regulating valve, the pressure in this route is always kept nearly constant. Furthermore, at the toner suction route from the opening 172 to the suction section 23, a pressure regulating valve is also provided so that a definite negative pressure is prevented from occurring. The opening 172 couples through the insert port 172a with the suction path 33 of the suction section 23 for removing the unnecessary toner not contributing to the development from the recording medium after the development and the opening 173 couples through the insert port 172a with a recycling device for liquid toner. Since the clockwise rotation of the gears 162 and 163 will make the space on the left side of the gear 163 into a negative pressure, the liquid toner is sucked in the suction section 23 and the air blown in flow into the opening 172. The liquid toner and air enter between inner teeth of the rotating gear 162 and between teeth of the rotating gear 163, carried to the space on the right side of the gear 163, pressurized here and discharged from the opening 173 to a toner recycling device not shown. In this manner, a pumping route leading from the opening 172 to the opening 173, separated from and independent of the above-mentioned pumping routes is formed. Incidentally, at the route coupling from the opening 173 with the toner recycling device, a pressure regulating valve not shown is also provided. By the function of this pressure regulating valve, the pressure in this route is always kept nearly constant. Meanwhile, it is known that, when plenty of air bubbles are mixed in the liquid toner to be fed to the toner feed tray 30, the liquid toner applied to the recording medium 10 is rippled and consequently an unevenness occurs in print images, thus deteriorating the image quality. With a gear pump according to this embodiment, however, as mentioned above, the region surrounded with the side walls 152a to 152d and the outer peripheries of the gears 161 and 162 and the region of the inner periphery of the gear 162 are completely separated, while the liquid toner feed route and the liquid toner recovery route are independent. Accordingly, the route of the liquid toner discharged from the toner bottle to the toner feed tray 30 and that of the liquid toner recovered from the suction section 23 are not joined and air of the liquid toner recovered from the suction section 23 is not mixed into the liquid toner to be delivered to the toner feed tray 30. Thus, the liquid toner applied to the recording medium is not rippled and high-quality print images are obtained. In addition, as shown in FIG. 4, the pump for delivering a liquid toner to the toner feed tray 30 and the pump for sucking the unnecessary liquid toner from the suction section 23 comprise a single gear pump and moreover, because of its simple structure, this is unlikely to get out of order and thus can be downsized. Furthermore, since such an aspirator as conventional becomes unnecessary and only one motor is needed for the drive of this gear pump, a cost-saving is also attainable. For example, with the embodiment mentioned above, the gear 160 is connected to a motor, through which the gear 161 is rotationally rotated by means of the motor, but in stead, the gear 163 provided inside the gear 162 may be rotationally rotated. As described above, according to the present invention, by having first to third gears provided, having the first gear provided outside the second gear and having the third gear provided inside the second gear among them, a first region and a second region are separated and the pumping route provided in the first region and the pumping route provided in the second region become completely independent, so that the fluids passing through these routes are never mixed with each other. Accordingly, by selecting one as the feed route of the liquid toner for development and the other as the recovery route of the unnecessary liquid toner after the development out of these two routes, the recovered liquid toner with air bubbles mixed therein and the liquid toner for development can be pumped without mutual mixing and thus it is effectively prevented that the liquid toner for development is rippled with the mixing of air to deteriorate the image quality. Besides this, if such two-path pumping operations are performed in a simple structure by means of one pump, an aspirator and such others become unnecessary and therefore it is possible to provide an electrostatic recorder in which the downsizing cf apparatus and cost cut are attained. INDUSTRIAL APPLICABILITY An electrostatic recorder according to the present invention can execute the development of electrostatic latent images formed on a recording medium by using a liquid toner. This electrostatic recorder is suitable especially for a color electrostatic recorder of the single path scheme allowing a recording medium to continuously pass a plurality of recording sections and development sections.

Claims: An electrostatic recorder comprising, electrostatic latent image recording means (11) for forming an electrostatic latent image on a recording medium (10) conveyed at a predetermined speed; toner feed means (30, 21) for feeding a liquid toner (31) to a surface of said recording medium (10) on which an electrostatic image is formed; and toner recovery means for recovering an excess toner from said recording medium (10), wherein said toner feed means comprises a toner feed route and a toner recovery route, said toner recovery route connected to said toner feed route and a toner reservoir having a capacity separated from said electrostatic recorder, and said toner recovery route is so arranged as to communicate with the top of said reservoir and moreover the tip of said toner feed route is so arranged so as to be situated near the bottom of said reservoir. The electrostatic recorder as set forth in claim 1, said toner recovery means can execute the recovery of said excess toner not only by suction but also by scraping from the recording medium prior to this suction and said toner recovery means comprises means for eliminating the mixing of foreign matters into the feed side in conjunction with said recovered toner. The electrostatic recorder as set forth in Claim 1 or 2, wherein the provision of the single-path scheme wherein a plurality of pairs of said toner feed means and said toner recovery means are arranged in series and a color image can be finally obtained by forming and developing electrostatic images of different colors in individual pairs. The electrostatic recorder as set forth in any of Claims 1 to 3, wherein said toner recovery means comprises toner removal means (22) and suction means (23), said toner removal means (22) being provided between said toner feed means and said suction means (23) for performing the recovery of said excess toner by suction and for scraping off said excess toner from the recording medium (10). The electrostatic recorder set forth in claim 4, wherein said toner removal means is configured to scrape said liquid toner while being kept in sliding contact with the record face of the recording medium conveyed, characterized in that a greater part of said excess toner is removed from said recording medium in advance before the recording medium (10) reaches said suction means (23). The electrostatic recorder as set forth in Claim 4 or 5, wherein said toner removal means comprises a bar block of nearly circular section. An electrostatic recorder comprising: electrostatic latent image recording means (11) for forming an electrostatic latent image on a recording medium (10) conveyed at a predetermined speed; development means (20) for developing the electrodevelopment means for developing the electrostatic latent image formed on said recording medium (10); toner feed means for feeding a liquid toner to a surface of said recording medium (10) in said development means (20), and toner recovery means for recovering an excess toner from said recording medium (10); wherein said toner feed means comprises, an internal reservoir (50) provided inside the main body of said electrostatic recorder, equipped with a first toner feed route (52) for feeding a liquid toner to said development means (20) and a first toner recovery route (54) for recovering the liquid toner after the development, and an external reservoir (40) provided outside the main body of said electrostatic recorder, equipped with a second toner feed route (42a, 42b) for feeding a liquid toner (31) to said internal reservoir (50) and a second toner recovery route (44a, 44b) for returning the liquid toner (31) recovered from said internal reservoir (50) wherein said second toner recovery route (44a, 44b) is so arranged as to communicate with the top of said external reservoir (40) and moreover the tip of said toner feed route is so arranged so as to be situated near the bottom of said external reservoirs (40). The electrostatic recorder as set forth in Claim 7, further comprising: an intra-reservoir reservoir (60) placed inside said internal reservoir (50) and communicating with said internal reservoir (50) through an overflow exhaust port (64), wherein said first toner feed route (52) is made to communicate with the interior of said intra-reservoir reservoir (60) and said second toner feed route is made to communicate with said intra-reservoir reservoir (60), and the liquid toner in said intra-reservoir reservoir (60) is made into an overflow state and is fed through said external reservoir (40), said second toner feed route, said intra-reservoir (60) and said first toner feed route to said development means (20) and the liquid toner (31) after use is recovered through said first toner recovery route (54), said internal reservoir and said second toner recovery route to the external reservoir (40). The electrostatic recorder as set forth in either Claim 7 or Claim 8, wherein a float sensor (58) is provided in said internal reservoir (50) and the liquid surface level of a liquid toner in said internal reservoir (50) is maintained at a nearly constant level by controlling the feed amount of a liquid toner through said second toner feeder route (42a, 42b) and the recovery amount of a liquid toner through said second toner recovery route (44a,44b). The electrostatic recorder as set forth in either Claim 7 or Claim 8, wherein said toner feed means further comprises a gear pump (150) having a first (161) and second (162) gears with their outer teeth engaged with each other and a third gear (163) inside the second gear (162) so arranged as that its outer teeth are engaged with the inner teeth of said second gear (162), said gear pump (150) comprising, a first suction path provided on one side and a first discharge path provided on the other side relative to the engaged portion of both teeth outside said first (161) and second (162) gears, and a second suction path provided on one side and a second discharge path provided on the other side relative to the engaged portion of both teeth inside said second gear (162) and outside the third gear (163), said gear pump (150) pumping out a first fluid through said first suction path and said first discharge path by a rotation of said first to third gears (161, 162, 163) in a predetermined direction and pumping out a second fluid through said second suction path and said second discharge path by the rotation of said first to third gears (161, 162, 163). The electrostatic recorder as set forth in Claim 10, wherein said gear pump (150) is actuated by a rotational drive of said first gear (161). The electrostatic recorder as set forth in Claim 10, wherein said first gear (161) has teeth provided on the inner periphery thereof, a fourth gear to engage with the teeth provided on the inner periphery of said first gear (161) is provided inside said first gear (161), and said first gear (161) is rotationally driven through said fourth gear. The electrostatic recorder as set forth in Claim 10, characterized in that said gear pump (150) is actuated by a rotational drive of said third gear (143). The electrostatic recorder as set forth in any of claims 1 to 13, wherein said electrostatic latent image recording means comprises a plurality of electrostatic recording heads. The electrostatic recorder as set forth in claim 14, further comprising head replacing means for replacing an electrostatic recording head of said electrostatic recorder; said head replacing means comprising a plurality of cutaway portions (251) provided on a side wall (250) of said main body of said electrostatic recorder, said plurality of cutaway portions (251) being equal in number to said plurality of electrostatic heads; and wherein each cutaway portion (251) is laterally aligned in one-to-one correspondence to a side portion of an electrostatic recording head such that, when replacing said electrostatic recording head, one side of said electrostatic recording head is lifted and placed into said cutaway portion (251) for removal. A method for replacing an electrostatic recording head being comprised in the electrostatic recorder of claim 15, said method comprising the steps of: laterally aligning a cutaway portion (251) of a head replacing means of said electrostatic recorder with a side portion of said electrostatic recording head; tilting said electrostatic recording head by lifting said side portion of said electrostatic recording head; placing said side portion of said electrostatic recording head into said cutaway portion (251); and removing said electrostatic recording head through said cutaway portion (251).

Inventors: AKICHIKA YOSHINORI, KAWATSU TOSHITATSU, KOMATSU FUMITO, TAKASAWA KIYOTSUGU, AKICHIKA, YOSHINORI, KAWATSU, TOSHITATSU, KOMATSU, FUMITO, TAKASAWA, KIYOTSUGU, AKICHIKA, Yoshinori Nippon Steel Corporation, TAKASAWA, Kiyotsugu Sankyoshataku 4-2, Yashiro
Applicants: NIPPON STEEL CORP, NIPPON STEEL CORPORATION
Application year: 1996
Main classification: G03G15
IPC codes: G03G15