Image forming apparatus

An image forming apparatus includes an image forming portion including an image bearing member, a developing device, and an intermediary transfer belt; a feeding device including a feeding belt; an ultraviolet irradiation portion; a cover; a first shielding plate extending in a direction perpendicular to the feeding direction on a feeding surface of the feeding belt from an inner surface of the cover downwardly with respect to the vertical direction and configured to shield the intermediary transfer belt from the ultraviolet radiation toward the intermediary transfer belt; and a second shielding plate provided on the cover and extending downwardly with respect to the vertical direction along an outer surface of the intermediary transfer belt. The second shielding plate is configured to shield the intermediary transfer belt from the ultraviolet radiation toward the intermediary transfer belt.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus including a fixing device for fixing a liquid developer on a recording material by irradiation with ultraviolet radiation (UV light).

In a printing machine or a coating device in which a drying device for drying a liquid, such as ink or varnish, supplied to a sheet-like member is provided, conventionally, in printing units each including a printing cylinder, a rubber cylinder and an impression cylinder, a toner surface of a print (printed matter) immediately after being subjected to printing between the impression cylinder and the rubber cylinder is dried by an ultraviolet (UV) lamp provided at a position opposing the impression cylinder (example A), or a drying unit including a feeding cylinder and a UV lamp provided at a position opposing the feeding cylinder is provided separately from the printing unit for a plurality of colors, a print surface of a print subjected to printing between an impression cylinder and a rubber cylinder of each of the printing units for the plurality of colors is dried by the drying unit at a position downstream of the printing units with respect to a paper (sheet) feeding direction immediately after the paper passed through the printing unit (example B).

In the case of the example A, there is a problem that the ultraviolet radiation emitted from the UV lamp onto the print surface for drying the print surface is reflected and cures the ink, the varnish or the like which is curable on the printing cylinder and the rubber cylinder. In the case of the example B, although the problem of the example A can be solved, there are problems that the print surface is damaged by contact of the print surface with the plurality of feeding cylinders before drying or the ink or the varnish is peeled off of the print and is deposited on the feeding cylinders and then a subsequent print surface is contaminated with the ink or the varnish and that the printing units and the drying unit are spaced from each other and thus a full length of a device (apparatus) becomes long.

In view of the above problems, Japanese Laid-Open Patent Application 2008-275300 has proposed a constitution in which not only the problems of the example B are solved by providing a drying portion including a UV lamp immediately behind a printing portion of each of the printing units, but also the problem of the example A is solved by shielding the print surface from the ultraviolet radiation emitted from the UV lamp.

Specifically, each of the printing units includes a feeding cylinder including a means which receives and holds the print immediately after being subjected to printing by the printing portion, and includes a UV lamp for drying the print surface inside the feeding cylinder at a position opposing the print surface of the print held by a print holding portion of the feeding cylinder. Reflected light, by the print, of the ultraviolet radiation emitted from an inside of the feeding cylinder is shielded by a shielding plate covering an upper surface and a side surface of the UV lamp, so that leakage of the reflected light toward the printing cylinder and the rubber cylinder which are provided on the feeding cylinder side is prevented.

In a liquid development electrophotographic apparatus using a liquid developer as a developer, in the case where toner images formed on a plurality of photosensitive members provided for respective colors are transferred onto an intermediary transfer belt and thereafter are transferred from the intermediary transfer belt onto a print and then a print surface of the print is cured by irradiation with ultraviolet radiation by an ultraviolet (UV) irradiation device, when the print is fed by nipping a print surface by feeding rollers in a period from after image transfer from the intermediary transfer belt onto the print until the toner images are cured (fixed) by the UV irradiation device, there is a liability that the images on the print surface are damaged or a print surface of a subsequent print is contaminated with a part of the images peeled off of the print surface toward the feeding roller on the print surface side. Accordingly, it is desired that the print is placed on and fed by a belt while attracting a back-surface side of the print surface to a belt surface by air and then the toner images on the print surface (toner image surface) of the print are cured by passing the print under the ultraviolet radiation by the UV irradiation device.

Further, in the case where air attraction belt feeding is carried out, when a print low in flexibility is passed through a feeding path having upwardly convex curvature or downwardly convex bending, there arise problems such as improper feeding due to improper attraction of the print and contact of the print surface with a member, provided on a side above a feeding portion, due to raising of a trailing end of the print, and therefore, it is desirable that the air attraction belt feeding is carried out along a straight feeding path.

In this case, on a side above the feeding path, there is a need that a member provided on the side above the feeding path is disposed with a distance such that the print does not contact the member even when for example, at an end portion of the print, flexure such as a curl or the like which cannot be completely attracted by air suction exists on the print. That is, on the feeding path, there is a space extending from the intermediary transfer belt to the UV irradiation device (i.e., there is a space in which there is a possibility that reflected light from the print surface irradiated with the ultraviolet radiation emitted from the UV irradiation device).

Particularly, in the case where the device is intended to be made compact by shortening a distance from an image transfer position, from the intermediary transfer belt onto the print, to the UV irradiation device, the ultraviolet radiation reflected by the surface of the print reaches an excessive developer remaining on the intermediary transfer belt and the developer is cured in a deposited state on the intermediary transfer belt, so that there are liabilities that improper cleaning occurs in a cleaning operation for the excessive developer remaining on the intermediary transfer belt and that the intermediary transfer belt is broken.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide an image forming apparatus in which even in a constitution having a gap (spacing) through which a recording material on a belt for feeding the recording material passes, ultraviolet radiation emitted from an ultraviolet irradiation device does not readily reach an intermediary transfer belt by reflection thereof by the belt.

According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image forming portion including an image bearing member, a developing device configured to form a toner image on an image bearing member with a liquid developer including toner, and an intermediary transfer belt onto which the toner image is transferred from the image bearing member; a feeding device including a feeding belt configured to feed a recording material on which the toner image is transferred from the intermediary transfer belt, while carrying the recording material on a surface thereof; an ultraviolet irradiation portion arranged with the intermediary transfer belt in a horizontal direction while opposing the feeding belt and configured to irradiate the toner image, with ultraviolet radiation, formed on the recording material carried on the feeding belt; a cover provided below the image bearing member with respect to a vertical direction and configured to cover at least a feeding surface of the feeding belt between the ultraviolet irradiation portion and the intermediary transfer belt with respect to a feeding direction on a side where the cover opposes the ultraviolet irradiation portion; a first shielding plate extending in a direction perpendicular to the feeding direction on the feeding surface from an inner surface of the cover downwardly with respect to the vertical direction and configured to shield the intermediary transfer belt from the ultraviolet radiation toward the intermediary transfer belt; and a second shielding plate provided on the cover while facing the intermediary transfer belt and extending downwardly with respect to the vertical direction along an outer surface of the intermediary transfer belt, wherein the second shielding plate is configured to shield the intermediary transfer belt from the ultraviolet radiation toward the intermediary transfer belt.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

FIG. 1is a schematic view of an image forming apparatus according to Embodiment 1 of the present invention.

The image forming apparatus shown inFIG. 1is a digital printer10of an electrophotographic type in which a toner image is formed on a sheet. The digital printer10operates on the basis of an image forming signal, and in the printer10, toner images formed by an image forming portion12are transferred onto sheets S successively fed from sheet cassettes11aand11band then are fixed, so that images are obtained.

In the image forming portion12, a photosensitive drum13, a charger14, a laser exposure device15, a developing device16and a drum cleaner19are provided, and the toner image depending on the image forming signal is formed on the photosensitive drum13. The toner image is obtained by developing an electrostatic latent image, formed by exposure to laser light E, with a liquid developer D in which powdery toner is dispersed in a thermosetting (heat-curable) liquid carrier.

The liquid developer D is formed in a mixer31by mixing and dispersing toner T in a liquid carrier C with a predetermined ratio and is supplied to the developing device16. The liquid carrier C and the toner T are stored in a carrier tank32and a toner tank33, respectively, and are supplied to the mixer31depending on a mixing state of the liquid carrier C and the toner T in the mixer31.

The liquid developer D supplied from the mixer31to the developing device16is coated on a developing roller18by a coating roller17in a supplying section16aof the developing device16and is used for developing the electrostatic latent image. The liquid carrier C and the toner T which remain on the developing roller18after the development are collected in a collecting section16bof the developing device16.

A toner image formed on the photosensitive drum13is transferred onto an intermediary transfer belt20and is fed to a nip formed by the intermediary transfer belt21and a transfer roller21. The toner T and the liquid carrier C which remain on the photosensitive drum13after the transfer of the toner image onto the intermediary transfer belt20is collected by the drum cleaner19.

Sheet feeding portions22aand22bfeed sheets S, stacked on the sheet cassettes11aand11b, respectively, to a registration feeding portion23. The registration feeding portion23feeds the sheet to the nip between the intermediary transfer belt20and the transfer roller21in synchronism with timing of the toner image transferred on the intermediary transfer belt20.

At the nip between the intermediary transfer belt20and the transfer roller21, the toner image is transferred onto the sheet S passing through the nip, and the sheet S on which the toner image is transferred is fed to a fixing device (UV irradiation device)25by a feeding belt of a feeding portion24.

The fixing device (UV irradiation device)25fixes the toner image transferred on the sheet S (i.e., cures the toner image on the sheet S) by ultraviolet radiation, and the sheet S on which the toner image is fixed is discharged to an outside of the image forming apparatus, so that an image forming step is completed.

The intermediary transfer belt20and the transfer roller21are provided with an intermediary transfer belt cleaner26and a transfer roller cleaner27, respectively, for collecting the remaining toner and the remaining liquid carrier C.

The liquid developer D including the toner T and the liquid carrier C which remain on the developing roller18after the development and which are collected in the collecting section16bof the developing device16, and the liquid developer D including the toner and the liquid carrier C which are collected by the drum cleaner19, the intermediary transfer belt cleaner26and the transfer roller cleaner27are separated into a reusable carrier and other components by a separation and extraction device34and the reusable carrier is used again.

Further, when the carrier and the toner are separated by the separation and extraction device34, a deteriorated carrier, the deteriorated toner and impurities which are separated as a waste liquid, and then the waste liquid is collected in a waste liquid collecting container35.

FIG. 2shows a schematic view of a liquid feeding path of a liquid feeding system for feeding the developer, the waste liquid and the like.

Transferring pipes from a carrier tank (container)32and a toner tank (container)33to the mixer31are provided with solenoid (-controlled) valves41and42, respectively, and the solenoid valves41and42adjust supply amounts of the liquid carrier C and the toner to the mixer31, respectively. From the mixer31, the liquid developer D necessary for the development is supplied to the developing device16by using a pump44.

The developer collected in the collecting section16bof the developing device16is fed to the separation and extraction device34by the pump43, and the liquid developer D, including the remaining liquid carrier C and the toner T, collected by each of the drum cleaner19, the intermediary transfer belt cleaner26and the transfer roller cleaner27is also fed to the separation and extraction device34by associated one of pumps48,49and50.

In this embodiment, the liquid developer D is fed using the pumps, but in the case where the liquid developer D can be moved by self-weight fall (free fall), a feeding system using self-weight without providing the pump may also be employed.

The reusable carrier is fed from the separation and extraction device34to the carrier tank32by a solenoid valve45. The waste liquid separated by the separation and extraction device34is appropriately fed to the waste liquid collecting container35by the self-weight fall through a solenoid valve47provided in the transporting pipe.

<Sheet Feeding Portion in Section from Toner Image Transfer from Intermediary Transfer Belt to Irradiation of Ultraviolet Radiation by UV Irradiation Device>

FIG. 3Ais a perspective view of the feeding portion24for feeding the sheet S in a section from the toner image transfer from the intermediary transfer belt20to irradiation of ultraviolet radiation by the UV irradiation device.FIG. 3Bis a perspective view of the feeding portion24in a partially enlarged form.

When the sheet S passes through a nip N between the intermediary transfer belt20and the transfer roller21, an unfixed (uncured) toner image is placed on the sheet S. At this time, for example, in the case where a toner image surface side is nipped with a roller in order to feed the sheet S, there is a liability that the toner image is damaged and a part of the toner image peeled off of the sheet S toward the feeding roller side transfers to a subsequence sheet and a toner image surface of the subsequent sheet is contaminated therewith. For that reason, the sheet S on which the toner image is transferred from the intermediary transfer belt20is fed to an endless feeding belt242in a rotational direction (arrow direction inFIG. 3A) of the feeding belt242in a state in which a back-surface opposite from the unfixed (uncured) toner image surface is attracted by air. At this time, there is no member contacting the toner image surface and therefore there is no liability that the toner image surface is damaged or contaminated with the toner image transferred to the feeding roller.

A constitution of attraction by the air will be described.

As shown inFIG. 3B, the feeding belt242for feeding the sheet S placed thereon is provided with a plurality of holes2421, and a feeding unit frame241for supporting the feeding belt242by rollers is provided with a plurality of holes2411in a surface on a side where the sheet S is to be fed. The air sucked by a suction fan attracts the sheet S to the feeding belt242through the holes2411of the feeding unit frame241and the holes2421of the feeding belt242.

In the case where attraction feeding by the air is carried out, when a constitution in which the feeding path has upwardly convex curvature or a feeding unit is divided into feeding belts with respect to a feeding direction and the divided belts for delivering the sheet S therebetween have a V-character relationship is employed, there is a liability that in the case where the sheet S having flexibility which is not high is fed, improper feeding due to incomplete attraction of the sheet S by the feeding belts and damage of the toner image surface, on the sheet S, contacting peripheral members provided above the feeding portion due to a trailing end curling phenomenon that a trailing end of the sheet S curls toward a side where the trailing end is spaced from the feeding belt. For that reason, the feeding path along which the air attraction feeding is carried out is formed straightly (as a feeding path along which the sheet S is straightly fed without bending the sheet S).

FIGS. 4A and 4Bare perspective views andFIG. 4Cis a sectional view, in which an arrangement of the UV irradiation device25relative to the feeding portion24and a positional relationship of the UV irradiation device25with the intermediary transfer belt20are shown.

The UV irradiation device25for fixing (curing) the toner image (formed with the developer having a UV curable characteristic) transferred on the sheet S is provided perpendicularly above a feeding surface of the feeding portion24, and the toner image on the surface is fixed (cured) by passing the sheet through below UV radiation (light), emitted from the UV irradiation device25toward the feeding surface side, by the feeding portion24.

The UV irradiation device25uses a UV-LED as a UV irradiation source but may also be a UV lamp.

As shown inFIGS. 4B and 4C, in order to prevent leakage of UV leakage light to an outside of a region between the UV irradiation device25and the feeding portion24, a cover251for covering a periphery of the region can be provided. In this embodiment, the cover251includes side walls which are parallel to the sheet feeding direction of the feeding portion24and which are perpendicular to the feeding surface, and includes a ceiling wall parallel to and spaced from the feeding surface with a distance (for example, 10 mm or more) in which even when an end portion of the sheet S includes a curled portion or the like which cannot be attracted by the feeding portion24during feeding of the sheet S, the toner image surface of the sheet S is prevented from contacting the ceiling wall and from being damaged and caught by the ceiling wall during feeding of the sheet S.

In this embodiment, the toner image surface of the sheet S passed through the UV radiation from the UV irradiation device25is fixed (cured), and therefore, in a subsequent feeding path after passed below the UV irradiation device25, even when the toner image surface contacts the rollers for feeding the sheet S and a guide for feeding the sheet S, there is no liability that the toner image surface is damaged, so that a feeding roller for nipping the toner image surface S is provided.

Further, feeding of the sheet S by the feeding roller is higher in feeding force than feeding of the sheet S by a belt through attraction with the air, and therefore, the sheet S is fed by being slid on a feeding guide surface on a side downstream of the feeding roller for nip-feeding the sheet S.

Further, a constitution in which an opening, between the cover251and the feeding surface with respect to a perpendicular direction, which is a gap between upper and lower feeding guides at an exit of the cover251and through which the sheet S passes is narrowed is employed. Specifically, on a side downstream of the feeding roller with respect to the feeding direction, a guide is provided so that the gap between the feeding guides becomes narrow toward a downstream side with respect to the feeding direction in a beak shape (t1>t2) and an opening, of the cover251, through which the sheet S is fed is narrowed (for example, an opening width t2is 3 mm). In this embodiment, in the feeding path downstream of the UV irradiation device25, the opening is narrowed, so that leakage of the UV leakage light, emitted from the UV irradiation device25, to the outside is prevented by the cover251, the feeding rollers, unshown members for supporting the feeding rollers and the feeding guides.

On the other hand, on the feeding portion24for feeding the sheet S in a section from the toner image transfer from the intermediary transfer belt20to the irradiation with the UV radiation by the UV irradiation device25, light beams of the UV radiation (principally, light reflected by a surface of the sheet S opposing the UV irradiation device25, i.e., the toner image surface; general reflectance of white paper: 60%-90%) pass toner between the feeding portion24and the ceiling wall of the cover251.

On an upstream side of the feeding direction where reflected light beams of the UV radiation from the UV irradiation device25pass, there is a liability that a surface of the intermediary transfer belt20downstream of the nip N between the intermediary transfer belt20and the transfer roller21for transferring the toner image onto the sheet S is exposed to the reflected light beams. Particularly, in the case where in order to make an entirety of the image forming apparatus compact, the feeding portion24for feeding the sheet S in the section from the toner image transfer from the intermediary transfer belt20to the irradiation with the UV radiation from the UV irradiation device25is shortened, a liability that the intermediary transfer belt surface is exposed to the reflected light beams becomes high. On the surface of the intermediary transfer belt20downstream of the nip N, the remaining liquid developer Dl including transfer residual toner T and the liquid carrier C after the toner image transfer onto the sheet S is placed. When the remaining liquid developer D1is exposed to the reflected light beams of the UV radiation until the remaining liquid developer D1is collected by an unshown intermediary transfer belt cleaner, the remaining liquid developer D1is cured in a deposited state on the intermediary transfer belt20, so that there is a liability that breakage of the intermediary transfer belt20and improper cleaning by the intermediary transfer belt cleaner are caused to occur.

Shielding plates as a feature of the present invention will be described with reference toFIGS. 5A and 5B.

A UV irradiation source of the UV irradiation device25has directivity (directional characteristic), so that when an optical axis center is taken as 0 degrees, a radiation angle is ±0 degrees (for example, when the optical axis center is 0 degrees as an example thereof in the UV-LED, the radiation angle is ±60 degrees).

A first shielding plate252is provided perpendicularly to the feeding surface in a section between a position of the toner image transfer from the intermediary transfer belt20and the UV irradiation device25. The first shielding plate252in this embodiment is formed of a UV absorber (absorbing agent) (for example, a resin material containing a benzotriazole-based UV absorber). The first shielding plate252increases in a range, in which reflected light by the sheet S expands, with a distance from the UV irradiation device25, and therefore, the first shielding plate252may desirably be provided in the neighborhood of the UV irradiation device25. On the other hand, a distance Y2from the feeding surface (toner image surface of the sheet S) to a lower end of the first shielding plate252opposing the feeding surface is required that the lower end of the first shielding plate252is spaced from the feeding surface not less than a distance such that the toner image surface of the sheet S does not contact the first shielding plate lower end (for example, the distance is not less than 10 mm). Further, the reflected light by the sheet S passes through a portion which is lowest and remotest in the case where the radiation angle from the UV radiation irradiation source is θ degrees (for example 60 degrees) when the optical axis center is taken as 0 degrees, and in order to shield with the first shielding plate the reflected light of the UV radiation (light), emitted with the radiation angle of θ degrees, by the sheet S, the following relationship is satisfied.
Y2<(X−Y1×tanθ)×tan(90−θ),
where Y1if a distance between the UV irradiation device25and the feeding surface with respect to a perpendicular direction to the feeding surface, Y2is a distance from the feeding surface to the lower end of the first shielding plate252opposing the feeding surface, and X is a distance between the first shielding plate252and the UV irradiation device25with respect to the feeding direction.

Accordingly, the distance Y2from the feeding surface to the lower end of the first shielding plate252is set so as to satisfy:
(Distance in which toner image surface of sheet does not contact first shielding plate)<Y2<(X1−Y1×tanθ)×tan(90−θ).

On the other hand, for example, in the case where the reflected light passes through under the first shielding plate252with an angle thereof with the feeding surface which is not more than an angle determined by a radiation angle of the irradiation source (for example, the reflected light passes with an angle not more than an assumed angle due to occurrence of a partial float or the like of an attitude of the sheet S relative to the feeding surface), when the reflected light passes through under the first shielding plate252in a direction toward the intermediary transfer belt20, the reflected light is blocked (shielded) by a second shielding plate253provided substantially parallel to a surface of the intermediary transfer belt20downstream of the nip N. In the case where the first shielding plate252is formed of the UV absorber, the second shielding plate253may return the reflected light toward the first shielding plate252or the UV irradiation device25(and the returned reflected light is absorbed by the first shielding plate252), and therefore, the second shielding plate253may also be formed of a material which is not the UV absorber unless the material permits transmission of the UV radiation to the intermediary transfer belt20side, and may be formed of metal (iron), for example. It is desirable that the second shielding plate253is formed of a black body (having light absorptivity and low reflectance) absorbing and reducing energy of the reflected light. For example, the second shielding plate253is formed of iron subjected to black coating (painting) or black plating (such as black nickel plating).

In this embodiment, the first shielding plate252is formed of the UV absorber, but similarly as in the second shielding plate253, may also be formed of the black body absorbing and reducing the energy of the reflected light (the light absorptivity of the black body is 90%-98% in general). In that case, the reflected light may be required to be reflected plural times by the first shielding plate252(when the light absorptivity is 90%, reflected light energy is reduced to 1/10 by once of reflection and is reduced to 1/10× 1/10= 1/100 by twice of reflection, i.e., is reduced to 1/10 to the 10th power) when the number of times of reflection is 10), and for example, the reflected light can be reflected plural times by the first shielding plate252by increasing a distance from the feeding surface to the ceiling wall of the cover251at the feeding portion24. Or, an outer wall of the UV irradiation device25is formed of the black body similarly as in the first shielding plate252, and the reflected light may also be reflected plural times between the UV irradiation device25and the first shielding plate252.

Further, in this embodiment, in order to prevent the leakage light of the reflected light, the feeding portion24is provided with the cover251, but for example, in the case where the image forming apparatus is constituted by a casing divided into a first casing including an image forming portion including the intermediary transfer belt20and a second casing including the UV irradiation device25, the leakage light may also be prevented by a frame of the second casing or an outer casing. Further, a frame surface of either one of opposing surfaces of the first casing and the second casing or an outer casing surface may also function as the first shielding plate252.

According to the constitution of this embodiment, it becomes possible to prevent the intermediary transfer belt20to be exposed to the light, reflected by the sheet S, emitted from the UV irradiation device25.

This application claims the benefit of Japanese Patent Application No. 2017-161730 filed on Aug. 25, 2017, which is hereby incorporated by reference herein in its entirety.