Wet type electrophotographic printer comprising a carrier liquid removing unit

To remove a surplus carrier liquid after development on the surface of a photoconductor drum to obtain homogeneous printed images without being affected by an error in rotational accuracy of such as a carrier liquid removing roller, there is provided a wet type electrophotographic printer in which the carrier liquid removing roller 14 of a carrier liquid removing unit 8 is caused to come in rotational contact with the photoconductor drum 1 to remove a carrier liquid from the liquid toner image, thereby making a toner image for transfer onto a recording medium 7, the wet type electrophotographic printer being so configured that the carrier liquid removing roller in rotational contact with the photoconductor drum is urged against the latter under an urging force made adjustable; and a scraping blade 23 is brought into contact with the carrier liquid removing roller while being urged against the latter under an urging force made adjustable.

TECHNICAL FIELD

The present invention relates to a wet type electrophotographic printer and in particular to a wet type electrophotographic printer provided with a carrier liquid removing unit for removing an excessive amount of carrier liquid from the surface of a photoconductor drum on which an electrostatic latent image is developed with a liquid toner comprising the carrier liquid and toner particles.

BACKGROUND ART

The carrier liquid removing unit in the wet type electrographic printer is disposed downstream of a developing unit in the rotary direction of the photoconductor drum. With its carrier liquid removing roller placed with a given spacing from or in pressure contact with the peripheral surface of the photoconductor drum, the carrier liquid removing roller is rotated so that its peripheral surface moves in an identical direction in which the peripheral surface of the photoconductor drum moves, to remove an excessive carrier liquid of the liquid toner supplied onto the photoconductor drum surface in the developing unit, thereby making proper the toner density of the liquid toner supplied onto the photoconductor drum surface.

The axial distance between the carrier liquid removing roller and the photoconductor drum must be kept constant at a given distance to keep proper the gapping space or nip pressure between the carrier liquid removing roller surface and the photoconductor drum surface.

The carrier liquid removing roller so far used in a carrier liquid removing unit of this sort is provided at its opposite axial ends with auxiliary rollers coaxially which are rotated in contact with the peripheral surface of the photoconductor drum while being spring biased to set positioning of the carrier liquid removing roller relative to the photoconductor drum (see JP H01-43307 B).

In the conventional carrier liquid removing unit mentioned above, for the convenience of maintaining the proximity at a fixed distance of the carrier liquid removing roller from the photoconductor drum, there exist problems that their respective contacting surfaces which need to be of a certain hardness wear as they contact and with the progress of such wear the accuracy of the proximity at the fixed distance may deteriorate, that its manufacturing cost increases due to the need for its high-precision components and an increase of the necessary parts and that the influences of deterioration in rotational accuracy and surface state of the carrier liquid removing roller sides cannot be eliminated. Besides, problems likewise arise if there is an imperfect manufacturing accuracy such as a runout of the rollers themselves.

Made to resolve these problems, the present invention has as of its objects to provide a wet type electrophotographic printer whereby an excessive carrier liquid subsequent to development on the surface of a photoconductive drum can be removed to obtain homogeneous images, without being affected by an error in rotational accuracy caused in assembling such as carrier liquid removing roller and so forth in the manufacture and/or by their changes with time.

SUMMARY OF THE INVENTION

In order to achieve the object mentioned above, there is provided in accordance with the present invention in a first aspect thereof a wet type electrophotographic printer in which an electrostatic latent image formed on a photoconductor drum is developed into a liquid toner image by a developing unit using a liquid toner and then a carrier liquid removing roller of a carrier liquid removing unit is caused to come in rotational contact with the photoconductor drum to remove a carrier liquid from the liquid toner image, thereby making a toner image for transfer onto a recording medium, wherein the wet type electrophotographic printer is so configured that the carrier liquid removing roller in rotational contact with the photoconductor drum is urged against the latter under an urging force made adjustable; and a scraping blade is brought into contact with the carrier liquid removing roller while being urged against the latter under an urging force made adjustable.

In a second aspect of the present invention, a wet type electrophotographic printer as mentioned above includes a cassette frame supporting the carrier liquid removing roller and the scraping blade of the carrier liquid removing unit and supported by a supporting frame so that it can be slidably moved in a direction parallel to the shaft of the photoconductor drum, wherein the supporting frame is movable in directions in which the carrier liquid removing roller is brought into contact with and away from the photoconductor drum and the scraping blade is capable of being brought into contact with and away from the carrier liquid removing roller. Further, in a third aspect of the present invention, a wet type electrophotographic printer as mentioned above includes a set charger disposed between the developing unit and the carrier liquid removing unit so as to apply a voltage to move toner of the liquid toner image on the photoconductor drum towards a surface of the photoconductor drum.

According to the first aspect of the present invention, causing the carrier liquid removing roller of the carrier liquid removing unit to come in rotational contact with the surface of the photoconductor drum while being urged against the latter under an urging force made adjustable allows the pressure of contact between the photoconductor drum and the carrier liquid removing roller to be held always proper to obtain homogeneous printed images stably, even if there exists an error in rotational accuracy caused in assembling in manufacture of the photoconductor drum, the carrier liquid removing roll and the like or brought about by their changes with time. Also, while influences from the error in accuracy appear noticeably with an increase in printing speed, the invention enables stably printed images with enhanced printing quality and productivity even with a traveling speed of the recording medium, namely its printing speed of as high as 60 m/min.

Also, causing the scraping blade to contact the carrier liquid removing roller while being urged against the latter under the urging force made adjustable in the first aspect of the invention allows achieving stabilization of the pressure of contact between the carrier liquid removing roller and the scraping blade.

Further, according to the first aspect of the invention made up as mentioned above, consumable parts are reduced and a proper contact pressure can be maintained with parts simply configured. And, it is also possible to preserve a stabilized working state for an extended time period, to increase the productivity and to achieve large effects in economy in respect of the production cost.

Further, while the cost for maintaining the photoconductor drum, the carrier liquid removing roller and the like at precision has so far largely determined the total cost, the economical effect is also obtained that the cost for their maintenance is reduced.

According to the second aspect of the present invention, the carrier liquid removing roller and the scraping blade for contact therewith are made capable of being taken in and out together with the cassette frame. This improves their inspection-serviceability and facilitates maintaining them in a proper state.

Besides, during a standstill of the printer, the carrier liquid removing roller and the scraping blade can be held apart from the photoconductor drum and the carrier liquid removing roller, respectively, to prevent them from getting permanent deformation due to their contact at halts.

Further, according to the third aspect of the present invention, the combined use of a set charger allows preserving a printing quality that is high in density and stable.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1is an explanatory view which diagrammatically illustrates the makeup of an electrophotographic printer for carrying out the present invention. As shown, a photoconductor drum1is in rotational contact with a transfer drum2which in turn is in rotational contact with a backup roll3.

In such a wet type electrophotographic printer, the photoconductor drum1when in image formation thereon is rotated by a drive means such as a motor (not shown) at a fixed speed in a direction of the arrow. The surface of the photoconductor drum1is charged uniformly in the dark by a charging unit4and then an original light figure is irradiated and imaged thereon by an exposure unit5, whereby an electrostatic latent image is formed on the surface of the photoconductor drum1. Thereafter, the electrostatic latent image when passing through its developing region is visualized by a developing unit6with a liquid toner into a liquid toner image, forming a toner image on the surface of the photoconductor drum1.

The toner image on the surface of the photoconductor drum1is primarily transferred onto a surface of the transfer roller2in its primary transfer region under a bias voltage applied via the transfer roller2and a nip pressure between the photoconductor drum1and the transfer roller2. This primarily transferred toner image is secondarily transferred in its secondary transfer region on a recording medium7passing between the transfer drum2and the backup roller3. The transfer roller2has its peripheral surface covered with an electrically conductive and elastomeric material.

Provided also around the circumference of the photoconductor drum1are a carrier liquid removing unit8, a charge eliminator9, a photoconductor drum cleaning device10and a set charger11. The carrier liquid removing unit8is disposed downstream of the position of the developing unit6in the direction of rotation of the photoconductor drum1for removing a portion (surplusage) of a carrier liquid of the liquid toner image after development. The charge eliminator9is disposed downstream of the area where the photoconductor drum1is in rotational contact with the transfer roller2for removing a residual potential residual on the photoconductor drum1after the primary image transfer onto the transfer roller2. The photoconductor drum cleaning device10acts to remove a residual toner residual on the surface of the photoconductor drum1. And, the set charger11is disposed between the developing unit6and the carrier liquid removing unit8for applying a bias voltage to the toner of the liquid toner image on the surface of the photoconductor drum1.

Also, provided around the transfer roller2are a carrier liquid supply unit12and a transfer roller cleaning device13. The carrier liquid supply unit12and the transfer roller cleaning device13are disposed downstream of the area where the transfer roller2is in rotational contact with the backup roller3in its direction of rotation and between that area and the area where the transfer roller2is in rotational contact with the photoconductor drum1in order from its upstream side. The carrier liquid supply unit12acts to supply the carrier liquid onto the transfer roller2after the secondary image transfer, and the transfer roller cleaning device13serves to clean the surface of the transfer roller2. And, this cleaning device13is disposed spaced at a given distance from the carrier liquid supply unit12, e.g., at a distance that is equal to ¼ of the peripheral length of the transfer roller2.

An explanation is next given of the makeup of an essential part of the carrier liquid removing unit8, referring toFIGS. 2 and 3which diagrammatically illustrate the same.FIG. 2is a cross sectional view in part broken andFIG. 3is a sectional view as seen in the direction of arrow A inFIG. 2.

Reference numeral14in the Figures indicates a carrier liquid removing roller brought in rotational contact with the peripheral surface of the photoconductor drum1and driven to rotate following its rotation in the forward direction. The carrier liquid removing roller14is supported by a cassette frame16supported by a frame15so as to be slidably movable axially or parallel to an axial direction, of the photoconductor drum1and is at the same time urged by spring means against the peripheral surface of the photoconductor drum1. The supporting frame15and the cassette frame16are coupled together in a rail type mechanism (sliding mechanism) so that the cassette frame16can be slidably moved relative to the supporting frame15. Parenthetically, an auxiliary roller may be interposed in an area of their coupling of the rail type to reduce their sliding resistance.

The surface of the carrier liquid removing roller14is made of an electrically conductive rubber and has a bias voltage applied thereto which is identical in polarity to the toner of the liquid toner to repel the toner.

The cassette frame16has a pair of brackets16aand16bat opposed sides axially of the carrier liquid removing roller14. On the insides of each bracket16a,16b, a bearing lever17a,17bis rotatably supported on through a rotary fulcrum18. By these bearing levers17aand17b, the carrier liquid removing roller14is rotatably supported at its opposed ends. The rotary fulcrum18on the bearing levers17aand17bis provided at their end side which relative to the center of rotation of the carrier liquid removing roller14is remote from its rotational contacting point with the photoconductor drum1whereby rotation of the bearing levers17aand17bcentering on the rotary fulcrum18causes the peripheral surface of the carrier liquid removing roller14to be displaced in directions in which it is brought into contact with and away from the photoconductor drum1.

The bearing lever17a,17bis provided with a spring plunger19awhich has an internal coil spring acting in a direction parallel to its tangential direction and has a working end20that acts in a direction in which it becomes remote from the photoconductor drum1. And, a supporting member21with which the working end20is in contact is fastened to the bracket16a,16b. With the working end20in contact with the supporting member21, the bearing lever17a,17b, hence the carrier liquid removing roller14, is spring biased, or urged, towards the photoconductor drum1. The spring plunger19aas a male screw is screwed with the bearing lever17a,17b. By rotating the spring plunger19awith a screwdriver or the like to axially advance or retract it, it is made possible for the force of urging towards the photoconductor drum1to be adjusted at the working end20.

The bearing lever17a,17bis provided at its forward end with a yoke in which a stopper pin22fastened to the bracket16a,16bis freely fitted with a play. With such a play, the range of rotation of the bearing lever17a,17brelative to the bracket16a,16b, hence the range of movement of the carrier liquid removing roller14relative to the photoconductor drum1in their rotational contacting direction can be controlled.

Inside of the cassette frame16there is provided a scraping blade23come in contact with the peripheral surface of the carrier liquid removing roller14in a direction opposite to its rotary direction. The scraping blade23extends longitudinally and is supported by a bracket23amounted rotatably. And, each bracket23ais spring biased, or urged, by a spring plunger19bin a direction in which the forward end of the blade comes in contact with the carrier liquid removing roller14. The spring plunger19bhas a working end (tip) coming in contact with an eccentric cam24. Rotating the eccentric cam24displaces the working end, thus making it possible for the force of urging by the spring plunger19bto be adjusted. Parenthetically, note that alternatively the spring plunger19bcan be rotated with a screwdriver or the like to adjust the force of urging. The eccentric cam24can be rotated by a predetermined angle or more to separate the scraping blade23from the carrier liquid removing roller14.

The cassette frame16as mentioned above is supported by the supporting frame15so that it can be slidably moved in a direction parallel to the shaft of the photoconductor drum1. This makes it possible to dismount the entire cassette frame16from the supporting frame15. And, at opposed sides in its fitting direction there are disposed positioning plates25aand25bof which the positioning plate25at the backside is brought into contact with one end of the cassette frame16and the positioning plate25bat the foreside is brought into contact with its other end to enable positioning of the cassette frame16in its inserting direction.

Also, the cassette frame16is provided in its lower part with a liquid pool26formed in a shape of trough, and in the bracket16aat the backside with one coupler27in communication with the liquid pool26. On the other hand, the supporting frame15is provided with the other coupler28which establishes the communication by being pushed against the coupler27. The couplers27and28are pushed against each other to communicate with each other when the cassette frame16is in its set state, and thereby liquid in the liquid pool26is discharged from a liquid recovery duct29via the couplers27and28.

The supporting frame15has its opposed ends supported via slide guides32and33by fixed brackets31aand31bfastened to a left and a right hand side frame30aand30b, respectively, so that it can be moved in directions in which the carrier liquid removing roller14is brought into contact with and away from the photoconductor drum1. And, between the supporting frame15and the fixed bracket31a,31bthere is arranged an air cylinder34,34so that its base is supported by the fixed bracket31a,31band its piston rod is screwed into the supporting frame15whereby extending the piston rods of the air cylinders34and34synchronously advances the carrier liquid removing roller14to a point at which it comes in contact with the photoconductor1and retracting them retracts it to a position at which it is largely apart from the photoconductor drum1.

InFIGS. 2 and 3, Reference numerals35and36indicate a stopper to regulate advancing of and a stopper to regulate retracting of the supporting frame15, respectively. Their respective stopper positions are made adjustable each by varying the position with a screw. Positioning the advancing stopper35can alternatively be achieved by adjusting the stroke end of the air cylinder34,34. The adjustment of the stroke end in this case can be made by length adjustment by screwing the piston rod.

Mention is next made of an operation of the carrier liquid removing unit made up as described above.

The carrier liquid removing roller14is pressed on and brought into rotational contact with the peripheral surface of the photoconductor drum1by the spring plunger19aunder a predetermined force of urging and is driven to rotate following rotation of the photoconductor drum1in an identical peripheral direction whereby a surplus carrier liquid in the liquid toner image developed on the surface of the photoconductor drum1by the developing roller6aof the developing unit6is removed by adhering on the surface of carrier liquid removing roller14.

Then, as a bias voltage which is identical in polarity to the toner of the liquid toner is applied to the carrier liquid removing roller14, the toner of the liquid toner is pressed on the surface of the photoconductor drum1with the result that mainly the carrier liquid comes to adhere on the roller surface of the carrier liquid removing roller14.

The force under which the carrier liquid removing roll14is urged against the photoconductor drum1is made variable by adjustment of the spring plunger19a. Thus, even if there exists a runout of the roller due to a distortion of the photoconductor drum1, changes with time of the accuracy of the carrier liquid removing roller14and its diameter, and its assembling inaccuracy, the contact pressure at a point of its contact with the photoconductor drum can be held always constant.

The carrier liquid adhering on the carrier liquid removing roller14is scraped off by the scraping blade23, stored in the liquid pool26of the cassette frame16and then discharged therefrom passing through the couplers27and28and the liquid recovery duct29.

The scraping blade23is then pressed under a biasing or urging force by the spring plunger19bon the surface of the carrier liquid removing roller14. The pressing force is then adjusted by adjusting the urging force by the spring plunger19b. If a runout of the photoconductor drum and a runout of the carrier liquid removing roller14exist, amounts of such runout may be overlapped to influence on the pressure of contact between the scraping blade23and the carrier liquid removing roller14, but such influence is absorbed by the spring plunger19bto allow the contact pressure to be held constant by the spring plunger19b. The result is the achievement of an improved carrier liquid removal (recovery) made always stable. It can also absorb individual differences in the scraping blade23as regards its torsion and the like and facilitates adjusting the blade contact pressure.

Further, the carrier liquid removing roller14is moved between a position at which it is in rotational contact with the photoconductor drum1and a position at which it is apart from the photoconductor drum1, by an extending and retracting operation by the piston rod of the air cylinder34,34. And, holding the carrier liquid removing roller14apart from the photoconductor drum1during a standstill of the printer makes it possible to prevent a permanent deformation from occurring in the carrier liquid removing roller14when it comes to a stop. Also, at the stop, the eccentric cam24supporting the spring plunger19bthat is urging the scraping blade24can be largely rotated to separate the tip of the scraping blade23from the carrier liquid removing roller14, thereby preventing a permanent deformation of the carrier liquid removing roller14due to its contact with the scraping blade23.

Further, in the state that the carrier liquid removing roller14is apart from the photoconductor drum1by retracting the piston rod of the air cylinder34, the foreside positioning plate25bcan be removed to remove the cassette frame16from the fixing frame15and thereby to take the entire cassette frame16out of the apparatus. In this state, maintenance operations for parts in the cassette frame16such as the carrier liquid removing roller14can be performed. Moreover, the communication and its interruption between the liquid pool26in the cassette frame16and the liquid recovery duct29are then made automatically by the couplers which are coupled and decoupled as the cassette frame16is inserted and removed.

In a wet type electrophotographic printer with a carrier liquid removing unit8acting as mentioned above, a liquid toner image developed and visualized with a liquid toner by a developing unit6from an electrostatic latent image formed on a photoconductor drum1has a bias voltage applied to toner by a set charger11immediately after the development to separate the toner in the visualized image from the carrier liquid, the toner in its densified state being attracted towards the photoconductor drum1.

Accordingly, in the carrier liquid removing unit8disposed downstream of the set charger11, the carrier liquid removing roller14is pressed against the liquid toner in which the toner is attracted by the set charger11towards the photoconductor drum1, to ensure that the liquid toner after the development is pressed on the photoconductor drum1in the densified state by the carrier liquid removing unit8.

While in the form of implementation of the invention described hereinbefore for a wet type electrophotographic printer, a toner image on a photoconductor drum1as illustrated is transferred via a transfer roller2onto a recording medium7, the present invention may be applied to a wet type electrophotographic printer in which a recording medium7is run along the photoconductor drum1to acquire a direct transfer therefrom.