Image formation device

Image formation device having: an image formation drum (50) for rotationally conveying a recording medium while holding the recording medium; a supply means (22) for supplying the recording medium (P) to the drum; a recording head (71) for forming an image on the recording medium on the drum; and a conveyance mechanism (80) for receiving the recording medium from the drum at a reception position (m2) on the downstream side in a conveyance direction from the recording head and distributing the recording medium to a paper discharge path or an inversion path. The conveyance mechanism returns the recording medium to the drum at a return position (m9) on the downstream side in the conveyance direction from the reception position (m2) after the front and back surfaces thereof are inverted, and a drum heating means (94) for heating the surface drum is provided between the reception position and the return position.

RELATED APPLICATIONS

This is a U.S. National stage of International application No. PCT/JP2013/062643 filed on Apr. 30, 2013.

This patent application claims the priority of Japanese application no. 2012-104619 filed May 1, 2012, the disclosure content of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an image formation device that performs image formation on both sides of a recording medium.

BACKGROUND ART

Image formation using ink, such as inkjet recording, enables formation of high-definition images with a relatively simple configuration, and the range of its use is increasing.

Among such inkjet recording devices, an inkjet recording device is known that includes an image formation drum to convey a recording medium while the recording medium is lying along the outer periphery of the image formation drum, a supply part to supply a recording medium at a predetermined supply position on the image formation drum, heads to eject ultraviolet curable ink to a recording medium, which is being conveyed on the image formation drum, to perform image formation, a UV irradiating unit to irradiate with UV rays a recording medium on which image formation has been performed, and an output unit to receive a recording medium at a predetermined output position of the image formation drum and to output the recording medium to the outside of the device (See Patent Literature 1).

In recent years, such an image formation device that ejects ink for image formation while conveying a recording medium lying along the outer periphery of the image formation drum is required to have a function of image formation on both sides of recording media.

In order to perform image formation on both sides of recording media, a medium inversion mechanism may be provided. The medium inversion mechanism pulls a recording medium away from the image formation drum to turn over the recording medium after image formation has been performed on the front side of the recording medium, and then returns the turned-over recording medium to the image formation drum. Image formation is then performed on the back side of the turned-over recording medium. Image formation on both sides of the recording medium is thus achieved.

PRIOR ART LITERATURES

Patent Literatures

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-196347

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

In image formation using ink, such as inkjet recording involving ejection of liquid, proper temperature management of ink is required in many cases. In order to manage the temperature of ink before being ejected, it is only necessary to heat ink at the heads and maintain a proper temperature; whereas in order to ensure a proper temperature of ink drops that have been ejected on a recording medium, it is necessary to heat a recording medium or an image formation drum to maintain the proper temperature.

In the case of an image formation device that conveys a recording medium on the image formation drum, a proper temperature can be maintained more easily by heating the surface of the image formation drum than by heating a recording medium itself, which has only a small thickness and a small heat capacity. Accordingly, it is effective to heat the surface of the image formation drum when the surface of the image formation drum is not covered with a recording medium.

In the case of an image formation device that performs image formation on only the front side, the region from the output part to the supply part of the outer periphery of the image formation drum is not used to convey a recording medium. Thus a heater may be disposed over this region to heat the surface of the image formation drum.

In the case of an image formation device that performs image formation on both sides of a recording medium, on the other hand, a medium inversion mechanism to turn over a recording medium is expected to be disposed over the region from the output part to the supply part of the outer periphery of the image formation drum. In the case of an image formation device that performs image formation on both sides of a recording medium, therefore, there is a problem of the difficulty in placing a heater to heat the image formation drum.

An example case of using ultraviolet curable ink is shown above with reference to the prior art, but heating the surface of the image formation drum is required not only for such ultraviolet curable ink but also for any type of liquid ink in order to achieve a proper ink viscosity and to achieve drying and fixing after the image formation.

An object of the present invention is to allow temperature management by heating the surface of an image formation drum while performing image formation on both sides of a recording medium through inkjet recording.

Means for Solving Problems

The present invention is an image form device to eject ink to perform recording on a recording medium, the image form device including: an image formation drum which rotates in a predetermined direction to convey the recording medium held on an outer periphery of the image formation drum; a recording medium supplying unit which supplies the recording medium to the image formation drum at a predetermined supply position; a recording head including a plurality of nozzles to individually eject the ink onto the recording medium which has been supplied to the image formation drum, the nozzles being arranged in a direction perpendicular to a conveyance direction of the recording medium; and a conveying mechanism which receives the recording medium, onto which the ink has been ejected, from the image formation drum at a reception position downstream of the recording head in the conveyance direction, and conveys the recording medium selectively either to a paper output path for outputting the recording medium or to an inversion path for turning over the recording medium, wherein the conveying mechanism returns the turned-over recording medium to the image formation drum at a return position downstream of the reception position in the conveyance direction and upstream of the supply position in the conveyance direction; and a drum heater which heats a surface of the image formation drum is provided between the reception position and the return position.

Further, the ink may have a property of curing when irradiated with energy rays; and an energy-ray irradiator may be provided which irradiates the recording medium on the image formation drum with the energy rays at a position downstream of the recording head in the conveyance direction and and upstream of the reception position in the conveyance direction.

Further, an ink heater may be provided which heats the ink to be supplied to the recording head before the ink is ejected.

Further, the ink may have a property of changing phase depending on a temperature of the ink.

Further, the drum heater may heat the image formation drum by non-contact heating or may heat the image formation drum by contact heating.

Further, a medium heater may be provided which heats a recording surface of the recording medium at a position downstream of the supply position in the conveyance direction and and upstream of the recording head in the conveyance direction.

Effects of the Invention

At the time of image formation, the present invention heats an image formation drum with a drum heater, supplies a recording medium at a supply position on the image formation drum, and performs image formation on the front side of the recording medium with a recording head. A conveying mechanism receives the recording medium from the image formation drum at a reception position, turns over the recording medium in an inversion path, and returns the recording medium to the image formation drum at a return position. Image formation is then performed on the back side of the recording medium. After the conveying mechanism receives the recording medium from the image formation drum at the reception position, the recording medium is sent to a paper output path to be output. The image formation on both sides of the recording medium is thus completed.

With such a configuration, a recording medium does not exist in the region from the reception position to the return position, at which the conveying mechanism receives and returns the recording medium, respectively, on the outer periphery of the image formation drum at any time. The drum heater heats the image formation drum using this region. The image formation device for both-side image formation having such a configuration achieves efficient heating of the image formation drum with no recording medium between the drum heater and the drum.

The ink having the property of curing when irradiated with energy rays is often subject to effects of temperature. If the ink having such a curing property is used, the drum heater that enables a proper temperature of the image formation drum achieves excellent image formation with stable quality.

An ink heater to heat the ink to be supplied to a recording head enables a proper temperature of ink before being ejected and thereby enables the ink to be ejected at a proper viscosity. This configuration enables image formation with more stable quality and enhances the reliability of the recording head.

If the ink has the property of changing phase depending on its temperature, a proper temperature of the image formation drum leads to proper change in phase, enabling excellent image formation with more stable quality.

A medium heater to heat the recording surface of a recording medium eliminates the influence on the ejected ink by the temperature of the recording medium before being supplied, enabling excellent image formation with more stable quality.

EMBODIMENT TO CARRY OUT THE INVENTION

Outline of Image Formation Device

An image formation device1, which is an embodiment of the present invention, will now be described in detail with reference to the drawings. The embodiment is an example of the present invention, and the invention is not limited to the embodiment.

FIG. 1is a diagram showing the main configuration of the image formation device1, which is an embodiment of the present invention.

The image formation device1includes a paper feeding unit10, an image formation unit20, a paper output unit30, and a control unit40(seeFIG. 5). The image formation device1conveys recording media P stored in the paper feeding unit10to the image formation unit20, forms images on one side or both sides of the recording media P in the image formation unit20, and outputs the recording media P, on which images have been formed, to the paper output unit30, under the control of the control unit40.

The paper feeding unit10includes a paper feeding tray11to store recording media P, and a conveying unit12to convey recording media P from the paper feeding tray11to the image formation unit20.

The paper feeding tray11is a plate member on which a stack of recording media P, which have been cut into a standardized size, can be placed. The paper feeding tray11moves up and down in accordance with the number of recording media P placed on the paper feeding tray11, and is held at a position to allow the conveying unit12to convey the topmost recording medium P, with respect to the up-and-down motion direction.

The conveying unit12includes a conveying mechanism to drive a looped belt123, whose inner face is supported by a plurality of (e.g., two) rollers121and122, to convey recording media P on the belt123; and a supplying unit (not shown) to deliver the topmost recording medium P, placed over the paper feeding tray11, to the belt123. The conveying unit12conveys a recording medium P, which has been delivered by the supplying unit to the belt123, along the belt123.

[Configuration of Image Formation Unit]

The image formation unit20includes an image formation drum50to hold a recording medium P on its cylindrical outer periphery; a delivering unit22to deliver a recording medium, which has been conveyed by the conveying unit12of the paper feeding unit10, to the image formation drum50; a first heater91as a medium heater which heats a recording medium P held on the image formation drum50; head units70to eject ink onto a recording medium P held on the image formation drum50to form an image; a cleaning unit60(seeFIG. 4) which receives ink ejected from the head units70at the time of maintenance of the head units70; an irradiating unit93as an energy-ray irradiator which emits energy rays for curing ink ejected onto a recording medium P; a conveying mechanism80which receives a recording medium P, which has been irradiated by the irradiating unit93, from the image formation drum50and selects and performs either conveying the received recording medium P to the paper output unit30or turning over the received recording medium P to return it to the image formation drum50; and a second heater94as a drum heater which directly heats the outer periphery of the image formation drum50with no recording medium P between the second heater94and the drum50.

FIG. 2is a perspective view of the image formation drum50.

The image formation drum50includes nail parts51and a suction part212to hold a recording medium P on the outer periphery of the image formation drum50. A drum rotation motor53(seeFIG. 5) is provided to rotate the image formation drum50in a predetermined conveyance direction F (counterclockwise direction inFIG. 1).

The image formation drum50has three equal recording medium P holding areas, into which the outer periphery of the image formation drum50is divided. In other words, a maximum of three recording media P can be held on the image formation drum50.

The nail parts51are disposed at the boundaries of the three recording medium P holding areas, i.e., disposed at intervals of 120° about the rotation axis of the image formation drum50. Each of the three nail parts51includes a plurality of nails arranged in a row in the direction of the rotation axis (X direction) on the outer periphery of the cylindrical image formation drum50.

The position at which a nail part51allows transfer of a recording medium P from the delivering unit22to the image formation drum50by the rotation of the image formation drum50is referred to as a supply position m1, and the position at which a nail part51allows transfer of a recording medium P from the image formation drum50to the conveying mechanism80is referred to as a reception position m2. The image formation drum50is provided with a cam mechanism (not shown) to provide an opening motion for the nails of the nail parts51to be released when the nail parts51come to the supply position m1 and the reception position m2.

Specifically, the nail parts51come to the supply position m1 with their nails open. When the nail parts51leave the supply position m1, the nail parts51close their nails to catch the end of a recording medium P. The nail parts51thus receive the recording medium P from the delivering unit22and start conveying the recording medium P.

When the nail parts51come to the reception position m2, the nails of the nail parts51are opened to release a recording medium P which has been conveyed. The nails are closed when the nail parts51leave the reception position m2, and then the empty holding area moves downstream.

The reception position m2 is equivalent to “reception position downstream of the recording head in the conveyance direction”.

With reference toFIG. 2, the suction part52includes a plurality of suction holes and a suction generating part (e.g., an air pump, fan, or injector). The suction holes are disposed in the outer periphery of the image formation drum50, on which a recording medium P is to lie while an end of the recording medium P is caught by a nail part51. The suction generating part generates suction force to suck gas into the image formation drum50through the suction holes. Specifically, the suction part52allows a recording medium P to stick to the outer periphery of the image formation drum50so as to lie along the outer periphery with the suction force generated by suction through the suction holes.

The internal space of the image formation drum50is divided into three compartments corresponding to the three recording medium P holding areas, respectively. A suction circuit54(seeFIG. 5) is provided that selects the suction part52for an individual holding area to give suction force to the selected holding area. This configuration can operate the suction part52not to give suction force to a holding area that is not holding a recording medium P, preventing the reduction of suction force of the suction part52for a holding area that is not holding a recording medium P. Such reduction of suction force would occur if the internal space of the image formation drum50is not divided into compartments.

InFIG. 2, a part of the recording medium P is turned up from the outer periphery of the image formation drum50for the purpose of showing the suction holes. In reality, however, an entire recording medium P is held on the outer periphery of the image formation drum50so as to lie along the outer periphery at the time of image formation by the image formation unit20.

The delivering unit22is disposed between the conveying unit12of the paper feeding unit10and the image formation drum50. The delivering unit22includes a delivering nail part221to catch one end of a recording medium P which has been conveyed by the conveying unit12, and a cylindrical delivering drum222to receive a recording medium P caught with the delivering nail part221and to deliver the received recording medium P to the image formation drum50at the supply position m1.

The delivering drum222has one nail part223to tightly hold one end of a recording medium P with the same structure as that of the nail parts51of the image formation drum50. The delivering drum222is provided with a cam mechanism that opens and closes the multiple nails constituting the nail part223to allow the nails to receive and deliver a recording medium P.

The cam mechanism closes the nails of the nail part223to catch a recording medium when the nail part223comes to the transfer position m3 where the nail part223is close to and faces the delivering nail part221. The cam mechanism opens the nails of the nail part223to allow a recording medium to be transferred to the image formation drum50when the nail part223comes to the supply position m1 where the nail part223is close to and faces a nail part51of the image formation drum50.

A gear mechanism (not shown) allows the linkage of the delivering drum222and the image formation drum50in such a way that the rotation of the image formation drum50by one recording medium P holding area (i.e., 120°) makes a full revolution of the delivering drum222in the direction opposite to that of the image formation drum50.

The first heater91is a lamp heater, such as a non-contact halogen lamp for infrared irradiation, and includes a reflector to reflect the light from the lamp heater to be orthogonal to the outer periphery of the image formation drum50uniformly, thereby efficiently irradiating and heating the outer periphery of the image formation drum50.

The first heater91is disposed downstream of the supply position m1 in the conveyance direction and upstream of the head units70in the conveyance direction over the outer periphery of the image formation drum50. In other words, the first heater91is provided to heat a recording medium P on the outer periphery of the image formation drum50before image formation.

A temperature sensor92to detect the temperature of a recording medium P held on the image formation drum50is disposed near the first heater91and downstream of the first heater91in the conveyance direction. A contact temperature detection element, such as a thermocouple and a thermistor, may be used as the temperature sensor92, but a non-contact temperature detection element, such as a thermopile, is more preferable.

The control unit40controls the heating operation of the first heater91on the basis of the temperature detected by the temperature sensor92so that a recording medium P passing near the first heater91on the image formation drum50becomes a predetermined temperature.

FIGS. 3A and 3Bshow the internal configuration of a head unit70.FIG. 3Ais a schematic diagram of the internal configuration, seen from the side, of the head unit70; andFIG. 3Bis a schematic diagram of the internal configuration, seen from the above, of the head unit70. In connection with the term “above” used here, the side of one surface of the head unit70facing the outer periphery of the image formation drum50is “below the head unit70”. The case in which the head unit70is viewed from the side means the case in which the head unit70is viewed assuming that one lateral face along the top/bottom direction and the X direction of the head unit70is the front face.

Four head units70are arranged in the conveyance direction F in which the image formation drum50conveys a recording medium P. The head units70of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in this order from the upstream side in the conveyance direction. Since the structures of the head units70of the colors are the same, only one head unit70is described here.

The head units70are disposed with their lower surfaces at a predetermined distance from the image formation drum50along the outer periphery of the image formation drum50.

With reference toFIGS. 3 and 3B, each head unit70includes a plurality of recording heads71, an ink tank72to store ink to be supplied to the recording heads71, and an ink heater73to heat the ink before being ejected in ink paths (not shown) connecting the ink tank72and the recording heads71for temperature regulation of the ink.

Each of the recording heads71has a plurality of nozzles711arranged in the direction parallel to the rotation axis direction (i.e., X direction) of the image formation drum50, that is, the direction perpendicular to the conveyance direction F of a recording medium P. The recording heads71eject ink individually through the nozzles711to form an image on a recording medium P held on the image formation drum50. Specifically, the nozzles711of the recording heads71are exposed on the lower sides of the head units70. The recording heads71shown inFIG. 3Beach have a plurality of nozzles711arranged in such a way that two nozzle rows extend in the X direction.

With reference toFIG. 3B, for example, the recording heads71are arranged in pairs in such a way that the pairs of the recording heads71form a plurality of rows of the recording heads71extending in the X direction. The positional relationships of the pairs of the recording heads71in adjacent rows are such that the pairs are arranged in a staggered fashion in the direction perpendicular to the X direction (i.e., in the conveyance direction F).

The ink paths extending from the ink tank72to the recording heads71are provided with a mechanism for regulating the supply pressure which adjusts the supply pressure to be a little lower than atmospheric pressure to prevent the ink from dropping from the nozzles711of the recording heads71.

A temperature sensor to detect the temperature of the ink to be supplied is provided for the ink heater73. The control unit40controls the output of the ink heater73to achieve a proper temperature while monitoring the temperature of the ink to be supplied.

The head unit70is individually provided for each of the colors (YMCK) used for image formation, as described above. The image formation device1shown inFIG. 1has the head units70for the colors of Y, M, C, and K, respectively, in this order from upstream in the conveyance direction in which a recording medium P is conveyed by the rotation of the image formation drum50.

With reference toFIG. 4, each head unit70has an X-direction width wide enough to cover the X-direction width of a recording medium P to be held and conveyed by the image formation drum50(e.g., a width smaller than but close to the width of the image formation drum50). At the time of image formation, the positions of the head units70are fixed relative to the image formation drum50. In other words, the image formation device1is a single-pass inkjet recording device, where the number of all the nozzles711of the recording heads71arranged in the X direction on each head unit70corresponds to the width of an image to be formed on a recording medium P in the direction (i.e., X direction) perpendicular to the conveyance direction.

FIG. 4is a perspective view showing the positional relationship between the image formation drum50and the cleaning unit60, and showing the positions of a head unit70before and after being moved.

Each of the four head units70is supported in such a way as to be movable individually along the X direction in the image formation unit20. Specifically, with reference toFIG. 4, each head unit70can move between the image formation drum50and the cleaning unit60disposed to be adjacent to each other in the X direction. The head unit70moves to the position such that the lower surface of the head unit70faces the image formation drum50at the time of image formation, and moves to the position such that the lower surface of the head unit70faces the cleaning unit60at the time of various kinds of maintenance, described later, under the control of the control unit40.

The cleaning unit60includes a waste ink part (not shown) to receive and collect ink ejected from the head units70at the time of maintenance, thereby preventing the image formation unit20from being dirtied by the ink ejected from the head units70at the time of maintenance.

The irradiating unit93includes a lamp, such as a high-pressure mercury lamp. The lamp emits light to provide energy rays, such as ultraviolet rays. The irradiating unit93is disposed near the outer periphery of the image formation drum50, downstream of the head units70, and upstream of the conveying mechanism80in the conveyance direction F in which a recording medium P is conveyed by the rotation of the image formation drum50. The irradiating unit93irradiates, with energy rays, a recording medium P which is held on the image formation drum50and on which ink has been ejected. The energy rays cure the ink on the recording medium P.

The lamp to emit ultraviolet rays is not limited to a high-pressure mercury lamp but may be a mercury lamp having an operating pressure from several hundred Pa to 1 MPa, a light source to be used as a germicidal lamp, a cold-cathode tube, an ultraviolet laser source, a metal halide lamp, and a light-emitting diode, for example. A light source which can emit ultraviolet rays at high intensity and consumes less power (e.g., a light-emitting diode) is preferred. The energy rays are not limited to ultraviolet rays but may be any other energy rays that have the property of curing ink according to the type of ink. A light source is replaced in accordance with energy rays.

The conveying mechanism80includes a first conveyance drum81to receive a recording medium P from the image formation drum50, a second conveyance drum82to receive a recording medium P from the first conveyance drum81, a paper output drum83to receive a recording medium P from the second conveyance drum82, a paper output belt mechanism84to receive a recording medium P from the paper output drum83to deliver the recording medium P to the paper output unit30, an inversion drum85to receive a recording medium P from the second conveyance drum82, and an inversion arm86to pull a recording medium P away from the inversion drum85and give the recording medium P to a nail part51of the image formation drum50.

The first conveyance drum81has one nail part811to tightly hold one end of a recording medium P with the same structure as that of the nail parts51of the image formation drum50. A cam mechanism is provided that opens and closes the multiple nails constituting the nail part811to allow the nails to receive and deliver a recording medium P when the nail part811of the first conveyance drum81is at the reception position m2 and the transfer position m4. The reception position m2 is the position at which a recording medium P is transferred from the formation drum50to the first conveyance drum81. The transfer position m4 is the position at which a recording medium P is transferred from the first conveyance drum81to the second conveyance drum82.

A gear mechanism (not shown) allows the linkage of the first conveyance drum81and the image formation drum50in such a way that the rotation of the image formation drum50by one recording medium P holding area (i.e., 120°) makes a full revolution of the first conveyance drum81in the direction opposite to that of the image formation drum50.

The second conveyance drum82has one nail part821to tightly hold one end of a recording medium P with the same structure as that of the nail parts51of the image formation drum50. A cam mechanism is provided that opens and closes the multiple nails constituting the nail part821to allow the nails to receive and deliver a recording medium P when the nail part821of the second conveyance drum82is at (1) the transfer position m4 at which a recording medium P is transferred from the first conveyance drum81to the second conveyance drum82, (2) the transfer position m5 at which a recording medium P is transferred from the second conveyance drum82to the paper output drum83, and (3) the transfer position m6 at which a recording medium P is transferred from the second conveyance drum82to the inversion drum85. The cam mechanism can switch between two operation states under the control of the control unit40, as described later.

A gear mechanism (not shown) allows the linkage of the first conveyance drum81and the second conveyance drum82in such a way that a full revolution of the first conveyance drum81makes a full revolution of the first conveyance drum81in the direction opposite to that of the first conveyance drum81.

The image formation device1can select one of image formation on only the front side of a recording medium P and image formation on both of the front and back sides. When image formation on only the front side is performed in succession, a recording medium P is transferred from the second conveyance drum82to the paper output drum83each time to be output.

Specifically, when image formation on only the front side is performed, the control unit40controls an actuator to switch the operation of the cam mechanism so that the nail part821operates in the states of (1) and (2) described above. In the state of (3) described above, the nail part821operates with no recording medium P held.

When image formation on both of the front and back sides is performed in succession, the three recording medium holding areas of the image formation drum50alternately receive a recording medium P from the delivering unit22. Accordingly, the second conveyance drum82alternately receives a recording medium P from the first conveyance drum81to deliver it to the inversion drum85and receives a recording medium P from the first conveyance drum81to deliver it to the paper output drum83. Thus every other holding area of the recording medium holding areas on the image formation drum50is empty at the beginning of image formation, but the recording media P passing the inversion drum85and turned over are returned to the empty areas. Specifically, a recording medium P with its front side facing outward and a recording medium P with its back side facing outward are arranged alternately on the image formation drum50. The recording medium P on which image formation has been performed with its back side facing outward is output, whereas the recording medium P on which image formation has been performed with its front side facing outward is turned over to be returned to the image formation drum50.

Thus when image formation is performed on both sides of a recording medium P, the control unit40controls the actuator to switch the operation of the cam mechanism so that the nail part821operates (i.e., receives a recording medium P) at the transfer position m4 of (1) for every revolution; and the operation of the nail part821(i.e., release of a recording medium P) and the non-operation of the nail part821(i.e., holding of a recording medium P) at the transfer position m5 of (2) alternately occur on a revolution basis. The operation of the nail part821at the transfer position m6 of (3) (i.e., release of a recording medium P) is performed for every revolution, but a recording medium P is output once in every two revolutions at the transfer position m5. Thus a recording medium P is transferred to the inversion drum85at the transfer position m6 once in every two revolutions.

The paper output drum83has one nail part831to tightly hold one end of a recording medium P with the same structure as that of the nail parts51of the image formation drum50. The paper output drum83is provided with a cam mechanism embedded therein that opens and closes the multiple nails constituting the nail part831to allow the nails to receive and deliver a recording medium P when the nail part831of the paper output drum83is at the transfer positions m5 and m7. The transfer position m5 is the position at which a recording medium P is transferred from the second conveyance drum82to the paper output drum83(i.e., a position close to and facing the nail part821of the second conveyance drum82). The transfer position m7 is the position close to and facing the paper output belt mechanism84. Specifically, the cam mechanism allows the nail part831to operate at the transfer position m5 to receive a recording medium P, and allows the nail part831to operate at the transfer position m7 to release a recording medium P.

A gear mechanism (not shown) allows the linkage of the second conveyance drum82and the paper output drum83in such a way that a full revolution of the second conveyance drum82makes a full revolution of the paper output drum83in the direction opposite to that of the second conveyance drum82.

The paper output belt mechanism84is mainly constituted of two sprockets841and842, a timing belt843stretched between the sprockets841and842, and a tension roller844to give a tensile force to the timing belt843. The paper output belt mechanism84conveys recording media P from the paper output drum83to the paper output unit30.

The path of recording media P from the paper output drum83through the paper output belt mechanism84to the paper output unit30constitutes “paper output path”.

The inversion drum85has one nail part851to tightly hold one end of a recording medium P with the same structure as that of the nail parts51of the image formation drum50. A cam mechanism is provided that opens and closes the multiple nails constituting the nail part851to allow the nails to receive and deliver a recording medium P when the nail part851of the inversion drum85is at the transfer positions m6 and m8. The transfer position m6 is the position at which a recording medium P is transferred with the nail part851close to and facing the nail part821of the second conveyance drum82. The transfer position m8 is the position at which a recording medium P is transferred to the inversion arm86.

The inversion drum85, which has a diameter about twice as large as the diameter of the second conveyance drum82, is rotated by a later-described inversion motor861(seeFIG. 5), which is an independent drive source.

The inversion arm86has a nail at its tip to catch an end of a recording medium P. The tip of the inversion arm86can swing between the position at which the tip of the inversion arm86is in contact with the outer periphery of the inversion drum85and the position at which the tip of the inversion arm86is in contact with the outer periphery of the image formation drum50.

The transfer of a recording medium P from the inversion drum85to the inversion arm86is performed as follows: the nail part851of the inversion drum85conveying a recording medium P passes the position close to and facing the inversion arm86; when the nail part851comes to the transfer position m8 at which the end, not held by the nail part851, of the recording medium P (i.e., the end on the upstream side in the conveyance direction) is close to the inversion arm86, the nail of the inversion arm86catches the end of the recording medium P (i.e., the end not held by the nail part851); and at the same time, the nail part851releases the recording medium P with the cam mechanism.

The transfer of a recording medium P from the inversion arm86to the image formation drum50is performed as follows: the inversion arm86catching the end of a recording medium P swings to the return position m9, which is the position close to and facing a nail part51of the image formation drum50, and then releases the end of the recording medium P.

The inversion drum85and the inversion arm86thus constitutes “inversion path” to turn over a recording medium.

The return position m9 is equivalent to “return position downstream of the reception position in the conveyance direction and upstream of the supply position in the conveyance direction”.

Each of the first conveyance drum81, the second conveyance drum82, the paper output drum83, and the paper output belt mechanism84of the conveying mechanism80rotates in conjunction with the image formation drum50with a gear mechanism (not shown); and the inversion arm86swings in conjunction with the image formation drum50. Only the inversion drum85is rotated by the inversion motor861(seeFIG. 5) because the length of a recording medium P in the conveyance direction varies depending on the size of the recording medium P. Specifically, when the inversion arm86, which swings at the timing according to the rotation of the image formation drum50, comes to the position for receiving a recording medium P from the inversion drum85, the rotation speed needs to be controlled according to the size of the recording medium P so that the end, not held by the nail part851, of the recording medium P reaches the position close to and facing the inversion arm86. For this reason, the rotation speed of the inversion motor861is controlled independently of the rotation of the image formation drum50.

The second heater94is a lamp heater, such as a non-contact halogen lamp for infrared irradiation, and includes a reflector, having the same configuration as that of the first heater91, to efficiently irradiate and heat the outer periphery of the image formation drum50.

In the case of both-side image formation, the conveying mechanism80is required to pull a recording medium P away from the image formation drum50at the reception position m2 to turn over the recording medium P, and is required to return the recording medium P to the return position m9 of the image formation drum50, to achieve the function of turning over recording media P. Accordingly, a recording medium P does not exist on the region from the reception position m2 to the return position m9 of the image formation drum50in the conveyance direction F. In the case of image formation on only the front side, a recording medium P is pulled away from the image formation drum50at the reception position m2 to be output. In this case, too, therefore, a recording medium P does not exist on the region from the reception position m2 to the return position m9 of the image formation drum50in the conveyance direction F.

The second heater94is disposed to face the region from the reception position m2 to the return position m9 of the image formation drum50in the conveyance direction F. Thus, the second heater94can heat the outer periphery of the image formation drum50without a recording medium P between the second heater94and the image formation drum50at any time.

A temperature sensor95to detect the temperature of the outer periphery of the image formation drum50is disposed near the second heater94and downstream of the second heater94in the conveyance direction. A contact temperature detection element, such as a thermocouple and a thermistor, may be used as the temperature sensor95, but a non-contact temperature detection element, such as a thermopile, is more preferable.

The control unit40controls the heating operation of the second heater94on the basis of the temperature detected by the temperature sensor95so that the outer periphery of the image formation drum50passing near the second heater94becomes a predetermined temperature.

The paper output unit30includes a plate paper output tray31on which recording media P sent from the image formation unit20by the conveying mechanism80are placed. Recording media P on which images have been formed are held in the paper output unit30until picked up by a user.

Inks used for image formation by the image formation device1will now be described.

The ink used in the present invention is an activating beam curable ink which is cured by being irradiated with energy rays (activating beams). The ink has the property of changing phase between gel or solid and liquid depending on the temperature of the ink.

The activating beam curable ink contains a gelling agent in an amount of 1 percent by mass or more but less than 10 percent by mass, and exhibits a reversible sol-gel phase transition depending on temperature. The term “so-gel phase transition” used in the present invention refers to a phenomenon in which a liquid state at an elevated temperature is transformed into a non-fluid gel state at a cooled temperature lower than or equal to a gelation temperature, and the non-fluid gel state is reversibly transformed into a liquid state at an elevated temperature higher than or equal to the solation temperature.

The term “gelation” used in the present invention refers to a solidified, semi-solidified, or thickened state accompanied by sharp increases in viscosity and elasticity; for example, a lamella structure, a polymer network formed by non-covalent bonds or hydrogen bonds, a polymer network formed by physical aggregation, and an aggregated structure composed of substances each immobilized by interactions between fine particles or between deposited fine crystals. The term “solation” refers to a liquid state in which the interactions formed during the gelation are released. The term “solation temperature” used in the present invention refers to an elevated temperature at which a gel ink is transformed into a sol state having fluidity. The term “gelation temperature” refers to a cooled temperature at which a sol ink is transformed into a gel state having reduced fluidity.

The activating beam curable ink, which exhibits such so-gel phase transition, is transformed into a liquid state at an elevated temperature, and thus can be ejected from recording heads. Upon recording using the activating beam curable ink at an elevated temperature, ink drops on a recording medium are spontaneously cooled and rapidly solidified by a temperature difference between the ink drops and the recording medium. This can prevents poor quality of an image due to integration of adjacent dots. Unfortunately, ink drops that are readily solidified may be isolated from each other to form a rough image. The roughness may lead to inhomogeneous gloss such as extremely low gloss and unnatural glitter. Vigorous investigation by the inventors found that the control of solidifying properties of ink drops, a gelation temperature of ink, and the temperature of a recording medium within the following range can prevent poor image quality due to integration of the ink drops, and can also achieve highly natural gloss on the image. Specifically, printing or image formation with the ink which contains a gelling agent in an amount ranging of 0.1 percent by mass or more but less than 10 percent by mass and has a viscosity of 102mPa·s or higher but lower than 105mPa·s at 25° C., under the control of the difference between the gelation temperature (Tgel) of ink with the gelling agent and the surface temperature (Ts) of the recording medium within the range of 5 to 15° C. can prevent integration of the ink drops and thus simultaneously achieve high image quality and natural gloss on an image. In this case, the temperature of the recording medium is controlled within the range of 42 to 48° C.

The inventors guess that such a phenomenon involves the following processes. When an ink drop ejected onto a recording medium is solidified before an adjacent ink drop is ejected, low gloss and unnatural glitter on an image are caused; whereas, when adjacent ink drops are solidified a certain time after the ink drops are ejected and integrated with each other, extremely poor image quality is caused due to overlap of the ink drops. Vigorous investigation by the inventors found that the control of viscosity of the ejected ink drops can prevent integration of ink drops and facilitate proper leveling of adjacent ink drops, which leads to natural gloss on an image.

Using the ink containing a gelling agent in an amount of 0.1 percent by mass or more but less than 10 percent by mass and exhibiting a viscosity of 102mPa·s or higher but lower than 105mPa·s at 25° C. allows the viscosity of the ink to be controlled within the temperature range of substrate. This control can simultaneously achieve high image quality and natural gloss on an image. Such a finding is based on the following assumption: the ink having viscosity lower than 102mPa·s at 25° C. cannot sufficiently prevent the integration of ink drops, and thus causes poor image quality within the above-described temperature range. The ink having viscosity of 105mPa·s or higher at 25° C. may exhibit high viscosity after gelation and cause a noticeable increase in viscosity during a cooling process. The viscosity of such an ink is barely controlled to an extent to be properly leveled within the above-described temperature range, which may reduce the gloss of an image. Contrarily, the ink of the present invention, which is transformed into a viscous gel having proper viscosity after gelation, can effectively inhibit the solidification of the dots, and thus achieve image quality exhibiting relatively natural gloss.

The term “homogeneous gloss” in the present invention does not define an absolute gloss, e.g., a specular reflection gloss at 60 degree. It, however, refers to entirely homogeneous gloss of an image (in particular, a solid image) without partially inhomogeneous gloss of the image, e.g., unnatural glitter, undesirable decreases in gloss, and stripe inconsistencies in gloss on the image, due to microscopic differences in gloss.

Use of the activating beam curable ink described in the present invention under the control of the difference between the gelation temperature (Tgel) of the ink and the surface temperature (Ts) of the recording medium within the range of 5 to 15° C. can prevent poor image quality, and achieve high image quality exhibiting high sharpness of fine lines in characters and natural gloss. To achieve higher image quality, the temperature of the recording medium is preferably controlled within the range of 5 to 10° C.

The composition of the activating beam curable ink used in the present invention will now be described in sequence.

The term “gelation” used in the present invention refers to a solidified, semi-solidified, or thickened state accompanied by sharp increases in viscosity and elasticity; for example, a lamella structure, a polymer network formed by non-covalent bonds or hydrogen bonds, a polymer network formed by physical aggregation, and an aggregate structure composed of substances each immobilized by interactions between fine particles or between deposited fine crystals.

Typical examples of gels include a thermoreversible gel and a non-thermoreversible gel. The thermoreversible gel is transformed into a fluid solution (also referred to as “sol”) when heated, while it is reversibly transformed into gel when cooled. The non-thermoreversible gel is not reversibly transformed into a fluid solution when heated once it gelates. The gel of the present invention, which contains an oil gelling agent, is preferably a thermoreversible gel to prevent clogging of the heads.

The gelation temperature (phase transition temperature) of the activating beam curable ink of the present invention is preferably 40° C. or higher but lower than 100° C., and more preferably, 45° C. or higher but 70° C. or lower. Taking into account summer environmental conditions, an ink exhibiting a phase transition at a temperature of 40° C. or higher can be stably ejected from recording heads regardless of the environment temperature during printing or image formation. An ink exhibiting a phase transition at a temperature lower than 90° C. eliminates the need for heating of the image formation device1to an extremely high temperature, which can reduce load on the recording heads71of and the components of the ink supply system of the image formation device1.

The term “gelation temperature” used in the present invention, which refers to a temperature at which a liquid is transformed into a gel state accompanied by a rapid change in viscosity, is a synonym of a “gel transition temperature”, “gel dissolution temperature”, “phase transition temperature”, “sol-gel phase transition temperature”, and “gelation point”.

A gelation temperature of ink in the present invention is calculated from a viscosity curve and a viscoelasticity curve observed with, for example, a rheometer (e.g., a stress controlled rheometer having a cone-plate, PhysicaMCR, Anton Paar Ltd.). The viscosity curve is observed during a temperature change in a sol ink at an elevated temperature under a low shear rate, whereas the viscoelasticity curve is observed during a measurement of a temperature change dependent on dynamic viscoelasticity. One example technique to obtain a gelation temperature involves placing a small piece of iron sealed in a glass tube into a dilatometer. With the temperature varied, a temperature at which the piece of iron in the ink liquid stops free-falling is determined to be a phase transition point (J. Polym. Sci, 21, 57 (1956)). Another example technique involves placing an aluminum cylinder on an ink to be subjected to a temperature change for gelation. A temperature at which the aluminum cylinder begins free-falling is determined to be a gelation temperature (Nihon Reoroji Gakkaishi (Journal of the Society of Rheology, Japan), Vol. 17, 86(1989)). An example simple technique involves placing a specimen in a gel state on a heat plate to be heated. A temperature at which the shape of the specimen collapses is determined to be a gelation temperature. Such a gelation temperature (phase transition temperature) of an ink can be controlled depending on the type of the gelling agent, the amount of the added gelling agent, and the type of the activating beam curable monomer.

The ink applied to the present invention preferably has a viscosity of 102mPa·s or higher but lower than 105mPa·s at 25° C., and more preferably, of 103mPa·s or higher but lower than 104mPa·s. Ink having a viscosity of 102mPa·s or higher can prevent poor image quality due to the integration of dots, while ink having a viscosity of lower than 105mPa·s can be properly leveled after being ejected onto a recording medium under a controlled surface temperature of the recording medium, and thus can provide homogeneous gloss. The viscosity of the ink can be appropriately controlled depending on the type of the gelling agent, the amount of the added gelling agent, and the type of the activating beam curable monomer. The viscosity of the ink in the present invention is observed with a stress controlled rheometer including a cone-plate (PhysicaMCR, Anton Paar, Ltd.), at a shear rate of 11.7 s−1.

The gelling agent contained in the ink used in the present invention may be composed of a high-molecular compound or low-molecular compound; however, the gelling agent is preferably composed of a low-molecular compound for a good inkjet ejection.

Non-limiting specific examples of the gelling agents which can be formulated in the ink according to the present invention are listed below.

Specific examples of high-molecular compounds preferably used in the present invention include fatty acids with inulin, such as inulin stearate; dextrins of fatty acids, such as dextrin palmitate and dextrin myristate (Rheopearl, available from Chiba Flour Milling Co., Ltd.); glyceryl behenate/eicosadioate; and polyglyceryl behenate/eicosadioate (Nom Coat, available from The Nisshin Oillio Group, Ltd.).

Examples of low-molecular compounds preferably used in the present invention include oil gelling agents having low molecular weight; amid compounds, such as N-lauroyl-L-glutamic acid dibutylamide and N-2-ethylhexanoyl-L-glutamic acid dibutylamide (available from Ajinomoto Fine-Techno Co., Inc.); dibenzylidene sorbitol compounds, such as 1,3:2,4-bis-O-benzylidene-D-glucitol (Gell All D available from New Japan Chemical Co., Ltd.); petroleum-derived waxes, such as paraffin wax, micro crystalline wax, and petrolatum; plant-derived waxes, such as candelilla wax, carnauba wax, rice wax, Japan wax, jojoba oil, jojoba solid wax, and jojoba ester; animal-derived waxes, such as beewax, lanolin, and spermaceti; mineral waxes, such as montan wax and hydrogenated wax; denatured waxes such as hardened castor oil and hardened castor oil derivatives, montan wax derivatives, paraffin wax derivatives, micro crystalline wax derivatives, and polyethylene wax derivatives; higher fatty acids, such as behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid; higher alcohols such as a stearyl alcohol and behenyl alcohol; hydroxystearic acids, such as 12-hydroxystearic acid; derivatives of 12-hydroxystearic acid; fatty acid amides, such as a lauric acid amide, stearic acid amide, behenic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide, and 12-hydroxystearic acid amide (for example, Nikka Amide from Nippon Kasei Chemical Co., Ltd, ITOWAX available from Itch Oil Chemicals Co., Ltd, and FATTYAMID available from Kao Corporation); N-substituted fatty acid amides, such as N-stearyl stearic acid amide, N-oleyl palmitic acid amide; special fatty acid amides, such as N,N′-ethylenebisstearylamide N,N′-ethylenebis(12-hydroxystearic amide), and N,N′-xylylene bisstearylamide; higher amines, such as dodecylamine, tetradecylamine, and octadecylamine; fatty acid esters, such as stearyl stearate, oleyl palmitate, glycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, ethylene glycol fatty acid ester, and polyoxyethylene fatty acid ester (e.g., EMALLEX available from Nihon Emulsion Co., Ltd., Rikemal available from Riken Vitamin Co., Ltd., and Poem available from Riken Vitamin Co., Ltd.); sucrose fatty acid esters, such as sucrose stearate and sucrose palmitate (for example, Ryoto Sugar Ester available from Mitsubishi-Kagaku Foods Corporation); synthetic waxes, such as polyethylene wax and α-olefin maleic anhydride copolymer wax; polymerizable waxes (UNILIN from Baker-Petrolite Corporation); dimer acids and dimer diols (PRIPOR available from Croda International Plc); which are described in Japanese Unexamined Patent Application Publication Nos. 2005-126507, 2005-255821, and 2010-111790. These gelling agents may be used alone or in combination as appropriate.

The ink used in the present invention, which contains the gelling agent, is transformed into a gel state immediately after being ejected from a recording head71onto a recording medium. This prevents the mixing and integration of dots and thus can provide high quality image during high-speed printing or image formation. The ink dots are then cured by activating beams to be fixed on the recording medium, forming a firm image film. The amount of the gelling agent included in the ink is preferably 1 percent by mass or more but less than 10 percent by mass, and more preferably, 2 percent by mass or more but less than 7 percent by mass. The ink containing the gelling agent in an amount of 1 percent by mass or more can be subjected to sufficient gelation and thus can prevent poor image quality due to the integration of the dots. Moreover, the ink drops having an increased viscosity after gelation decrease photocurable properties due to oxygen inhibition when the ink is photo-radically cured. The ink containing the gelling agent of less than 10 percent by mass can prevent poor quality of a cured film due to non-cured component after irradiation with activating beams and can prevent poor inkjet ejection characteristics.

The ink of the present invention contains a gelling agent, coloring material, and an activating beam curable composition to be cured by activating beams.

The activating beam curable composition (hereinafter also referred to as “photopolymerizable compound”) used in the present invention will now be described.

Examples of the activating beams used in the present invention include electron beams, ultraviolet rays, α beams, γ beams, and x-rays; however, ultraviolet rays and electron beams are preferred that are less damaging the human body, easy to handle, and industrially widespread. In the present invention, ultraviolet rays are particularly preferred.

In the present invention, any photopolymerizable compound that can be cross-linked or polymerized by irradiation with activating beams may be used without limitation; and, photo-cationically or photo-radically polymerizable compounds are preferred.

Any known cationically polymerizable monomers may be used as photo-cationically polymerizable monomers; examples of the cationically polymerized monomers include epoxy compounds, vinyl ether compounds, and oxetane compounds described in Japanese Unexamined Patent Application Publication Nos. 6-9714, 2001-31892, 2001-40068, 2001-55507, 2001-310938, 2001-310937, and 2001-220526.

In the present invention, the photopolymerizable compound preferably contains at least one oxetane compound and at least one compound selected from an epoxy compound and a vinyl ether compound in order to prevent contraction of the recording medium during curing of the ink.

Preferred examples of aromatic epoxides include di- or poly-glycidyl ethers prepared by the reaction of polyhydric phenol having at least one aromatic nucleus or an alkylene oxide adduct thereof with epichlorohydrin, such as diglycidyl or polyglycidyl ethers of bisphenol A or an alkylene oxide adduct thereof, diglycidyl or polyglycidyl ethers of hydrogenated bisphenol A or an alkylene oxide adduct thereof, and novolac epoxy resin. Examples of the alkylene oxides include ethylene oxide and propylene oxide.

Preferred examples of alicyclic epoxides include a cyclohexene oxide-containing compound and a cyclopentane oxide-containing compound that are prepared by epoxidizing a compound having at least one cycloalkane ring such as a cyclohexene ring and a cyclopentene ring with a proper oxidant, such as hydrogen peroxide and a peracid.

Preferred examples of aliphatic epoxides include diglycidyl or polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof. Representative examples of the diglycidyl or polyglycidyl ethers include diglycidyl ethers of alkylene glycols, such as diglycidyl ether of ethylene glycol, diglycidyl ether of propylene glycol, and diglycidyl ether of 1,6-hexanediol; polyglycidyl ethers of polyhydric alcohols, such as diglycidyl ether or triglycidyl ether of glycerine or alkylene oxide adducts thereof; and diglycidyl ethers of polyalkylene glycols, such as diglycidyl ethers of polyethylene glycol or alkylene oxide adducts thereof, and diglycidyl ethers of polypropylene glycol or alkylene oxide adducts thereof. Examples of the alkylene oxides include ethylene oxide and propylene oxide.

Preferred epoxides among these epoxides are aromatic epoxides and alicyclic epoxides, and more preferred are alicyclic epoxides because of their rapid curability. In the present invention, the above-described epoxides may be used alone or in combination as appropriate.

Preferred vinyl ether compounds among these vinyl ether compounds are di- or tri-vinyl ether compounds, and more preferred are di-vinyl ether compounds because of their curing properties, adhesion, and surface hardness. In the present invention, the above-described vinyl ether compounds may be used alone or in combination as appropriate.

The term “oxetane compound” used in the present invention refers to a compound having one or more oxetane rings. Any known oxetane compound may be used, for example, described in Japanese Unexamined Patent Application Publication Nos. 2001-220526 and 2001-310937.

The use of an oxetane compound having five or more oxetane rings in the present invention may lead to an increase in viscosity of the ink composition. Such an ink composition is hard to handle, has a high glass transition temperature, and thus exhibits low adhesion after curing. The oxetane compound used in the present invention thus is preferably a compound having one to four oxetane rings.

Example of the oxetane compounds preferably used in the present invention include compounds represented by Formulae (1), (2), (7), (8), and (9) respectively described in paragraphs [0089], [0092], [0107], [0109], and [0166] of Japanese Unexamined Patent Application Publication No. 2005-255821.

Specific examples of the oxetane compounds include example compounds 1 to 6 described in paragraphs [0104] to [0119], and compounds described in paragraph [0121] of Japanese Unexamined Patent Application Publication No. 2005-255821.

A radically polymerizable compound will now be described.

Any known radically polymerizable monomers may be used as photo-radically polymerizable monomers. Example of the known radically polymerizable monomers include photo-curable material prepared using photo-polymerizable compounds, and cationically polymerizable photo-curable resin, which are described in Japanese Unexamined Patent Application Publication No. 7-159983, Japanese Examined Patent Application Publication No. 7-31399, and Japanese Unexamined Patent Application Publication Nos. 8-224982 and 10-863. In addition to these monomers, photo-cationically polymerizable photo-curable resin that is sensitized to light having wavelengths longer than those of visible light may also be used, the resin being described in Japanese Unexamined Patent Application Publication Nos. 6-43633 and No. 8-324137, for example.

Radically polymerizable compounds have radically polymerizable ethylenically unsaturated bonds. Any radically polymerizable compound that has at least one radically polymerizable ethylenically unsaturated bond in a molecule may be used that has a chemical form such as a monomer, oligomer, or polymer. Such radically polymerizable compounds may be used alone or in combination in any proportion to improve target properties.

Any known (meth)acrylate monomers and/or oligomers may be used as radically polymerizable compounds for the present invention. The term “and/or” used in the present invention means that the radically polymerizable compound may be a monomer, oligomer, or combination thereof. The same is applied to the term “and/or” in the following description.

The polymerizable compound of the present invention may be combinations of various vinyl ether compounds and maleimide compounds. Non-limiting examples of the maleimide compounds include N-methylmaleimide, N-propylmaleimide, N-hexylmaleimide, N-laurylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N,N′-methylenebismaleimide, polypropylene glycol bis(3-maleimidepropyl) ether, tetraethylene glycol bis(3-maleimidepropyl) ether, bis(2-maleimide ethyl) carbonate, N,N′-(4,4′-diphenylmethane) bismaleimide, N,N′-2,4-tolylene bismaleimide, and multifunctional maleimide compounds which are ester compounds containing maleimide carboxylic acids and various polyols, the multifunctional maleimide compound being described in Japanese Unexamined Patent Application Publication No. 11-124403.

The amount of added cationic polymerizable compound or radically polymerizable compound described above is preferably within a range of 1 to 97 percent by mass, and more preferably, of 30 to 95 percent by mass.

Components, other than the components described above, of the ink of the present invention will now be described.

The ink of the present invention may contain any dye or pigment as a color material. The preferred materials are pigments with stable dispersion in the ink components and weatherability. Examples of pigments according to the invention include, but not limited to, organic and inorganic pigments represented by the following color index numbers, which can be used in accordance with the purpose.

The pigments may be dispersed, for example, with a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, or a paint shaker.

A dispersant may be added for dispersion of the pigments. The preferred dispersant is a polymer dispersant. Examples of polymer dispersants include Solsperse® series by Avecia Inc., PB series by Ajinomoto Fine-Techno Co., Inc., and the following materials.

The ink preferably contains a pigment dispersant in an amount of 0.1 to 20 percent by mass. Synergists dedicated to the respective pigments may be used as dispersion aids. The dispersant and dispersion aids are preferably added in amounts of 1 to 50 parts by mass for 100 parts by mass of pigments. A dispersion medium may be a solvent or a polymerizable compound. Preferably, the ink of the present invention, which is subjected to reaction and curing after printing or image formation, contains no solvent. Residual solvent in cured-ink images causes a decrease in solvent resistance and problems of remaining volatile organic compound (VOC). The preferred dispersion media are therefore polymerizable compounds, especially a monomer with the lowest viscosity rather than a solvent, in view of dispersion characteristics.

The pigment preferably has an average particle diameter in the range of 0.08 to 0.5 μm and a maximum diameter of 0.3 to 10 μm, more preferably 0.3 to 3 μm in view of dispersion of the pigment. These diameters are appropriately determined depending on the types of the pigment itself, dispersant, and dispersion medium, dispersion conditions, and filtration conditions. Such size control prevents nozzle clogging in the nozzles of the recording heads and leads to high storage stability, transparency, and curing sensitivity of the ink.

The ink of the present invention may optionally contain a known dye, preferably an oil-soluble dye. Non-limiting oil-soluble dyes that can be used in the present invention are listed below.

The pigments or oil-soluble dyes are preferably added in amounts of 0.1 to 20 percent by mass, more preferably 0.4 to 10 percent by mass. Addition of 0.1 percent by mass or more yields desirable image quality, and addition of 20 percent by mass or less provides appropriate ink viscosity during ejection of ink. Two or more colorants may be appropriately used for color adjustment.

The ink of the present invention preferably contains at least one photopolymerization initiator when ultraviolet rays, for example, are used as activating beams. For use of electron beams as activating beams, no photopolymerization initiator is necessary in many cases.

Photopolymerization initiators are broadly categorized into two types: an intramolecular bonding cleavage type and an intramolecular hydrogen abstraction type.

The preferred amount of a photopolymerization initiator, if used, is 0.01 to 10 percent by mass of an activating beam curable composition.

Examples of the radical polymerization initiators include triazine derivatives disclosed in documents, such as Japanese Examined Patent Application Publication Nos. S59-1281 and S61-9621, and Japanese Unexamined Patent Application Publication No. S60-60104; organic peroxides disclosed in documents, such as Japanese Unexamined Patent Application Publication Nos. S59-1504 and S61-243807; diazonium compounds disclosed in documents, such as Japanese Examined Patent Application Publication Nos. S43-23684, S44-6413, S44-6413, and S47-1604 and U.S. Pat. No. 3,567,453; organic azide compounds disclosed in documents, such as U.S. Pat. Nos. 2,848,328, 2,852,379, and 2,940,853; orthoquinonediazides disclosed in documents, such as Japanese Examined Patent Application Publication Nos. S36-22062, S37-13109, S38-18015, and S45-9610; onium compounds disclosed in documents, such as Japanese Examined Patent Application Publication No. S55-39162 and Japanese Unexamined Patent Application Publication No. S59-14023 andMacromolecules,10, P. 1307, 1977; azo compounds disclosed in Japanese Unexamined Patent Application Publication No. S59-142205; metal allene complexes disclosed in documents, such as Japanese Unexamined Patent Application Publication No. H1-54440, EP patent Nos. 109,851 and 126,712 andJ. Imag. Sci.,30, P.174, 1986; (oxo)sulfonium organoboron complexes disclosed in Japanese Patent Nos. 2711491 and 2803454; titanocenes disclosed in Japanese Unexamined Patent Publication No. S61-151197; transition metal complexes containing transition metals, such as ruthenium disclosed inCoordination Chemistry Review,84, pp. 85-277, 1988 and Japanese Unexamined Patent Application Publication No. H2-182701; 2,4,5-triarylimidazole dimer; carbon tetrabromide disclosed in Japanese Unexamined Patent Application Publication No. H3-209477; and organic halogen compounds disclosed in Japanese Unexamined Patent Application Publication No. S59-107344. The preferred amount of a polymerization initiator ranges from 0.01 to 10 parts by mass for 100 parts by mass of a compound containing a radically polymerizable ethylenically unsaturated bond.

The ink of the present invention may contain a photoacid generator serving as a photopolymerization initiator.

As photoacid generators, compounds that are used, for example, for a chemically amplified photoresist or photo cationic polymerization are used (The Japanese Research Association for Organic Electronics Materials (ed.),Organic materials for imaging, pp. 187-192, BUNSHIN, 1993). Examples of such a compound suitable for the present invention are as follows.

Specific examples of the onium compound usable in the invention are disclosed in paragraph [0132] of Japanese Unexamined Patent Publication No. 2005-255821.

Second group: sulfonated compounds generating sulfonic acid. Specific examples of such a sulfonated compound are disclosed in paragraph [0136] of Japanese Unexamined Patent Publication No. 2005-255821.

Second group: halides photogenerating hydrogen halide. Specific examples of such a halide are disclosed in paragraph [0138] of Japanese Unexamined Patent Publication No. 2005-255821.

Third group: iron-allene complexes disclosed in paragraph [0140] of Japanese Unexamined Patent Publication No. 2005-255821.

The activating beam curable ink of the present invention may also contain a variety of additives, other than those described above. Examples of such additives include surfactants, leveling agents, matting agents, polyester resins, polyurethane resins, vinyl resins, acrylic resins, gum resins, and waxes for adjusting membrane properties. Any known basic compound can be used for improvement in storage stability. Typical examples include basic alkali metal compounds, basic alkali earth metal compounds, and basic organic compounds, such as amines.

Specific examples of inks used in this embodiment are listed below.

Pigment dispersion elements for the following ink composition are obtained by heating and stirring a mixture of 5 parts by mass of SOLSPERSE 32000 (Lubrizol Corporation) and 80 parts by mass of HD-N (1,6-hexanediol dimethacrylate: Shin-Nakamura Chemical Co., Ltd.) in a stainless steel beaker to dissolve the mixture, cooling the mixture to room temperature, adding 15 parts by mass of Carbon Black #56 (Mitsubishi Chemical Corporation) to the mixture, putting the mixture and zirconia beads of 0.5 mm in a sealed glass vial, performing dispersion of the mixture with a paint shaker for 10 hours, and removing the zirconia beads therefrom.

FIG. 5is a block diagram showing the main control configuration of the image formation device1. As shown in the drawing, the control unit40of the image formation device1is electrically connected to the paper feeding unit10to convey a recording medium P to the image formation unit20, the drum rotation motor53to rotate the image formation drum50, the suction circuit54for air suction for the drum50, the ink heater73to heat the ink to be supplied to the heads71, the inversion motor861to allow the rotation of the inversion drum85, the first heater91to heat a recording medium P on the outer periphery of the image formation drum50before image formation, the temperature sensor92to detect the temperature of a recording medium P heated by the first heater91, the irradiating unit93to irradiate with UV rays an ink image formed on a recording medium P, the second heater94to directly heat the outer periphery of the image formation drum50with no recording medium P between the second heater94and the image formation drum50, the temperature sensor95to detect the temperature of the outer periphery of the image formation drum50heated by the second heater94, and a head drive circuit74to drive the recording heads71.

The control unit40is constituted of a ROM to store a program to control each component of the image formation device1, a CPU to execute the program, and a RAM to serve as a work area at the time of the execution of the program, for example.

Further, an image memory circuit42to store the data of image to be formed inputted from a host computer, a higher-level device, via an interface circuit41is provided in addition to the control unit40. The CPU of the control unit40performs computing on the basis of image data stored in the image memory circuit42and the program, and sends a control signal to each component on the basis of the computing results.

[Explanations of Behavior of Image Formation Device]

The behavior of the image formation device1, having the above-described configuration, at the time of image formation on both sides of a recording medium P will now be described.

The image formation drum50is rotated by the drum rotation motor53, the second heater94is turned on, and the outer periphery of the image formation drum50is heated to a target temperature on the basis of the temperature detected by the temperature sensor95.

The control unit40controls the p per feeding unit10to intermittently convey a recording medium P to every other recording medium holding area on the image formation drum50which is being rotated.

The downstream end, in the conveyance direction, of the recording medium P supplied from the delivering unit22is caught with a nail part51of the image formation drum50at the supply position m1, and the recording medium P sticks to a holding area. The recording medium P that starts to be conveyed by the image formation drum50is heated to a predetermined target temperature by the first heater91controlled on the basis of the temperature detected by the temperature sensor92.

A plurality of heads71of each head unit70are then driven to form an image based on image data.

The dots of the formed ink image are fixed through UV-ray irradiation from the irradiating unit93disposed downstream of the head units70in the conveyance direction.

When the nail part51holding the downstream end, in the conveyance direction, of the recording medium P comes to the reception position m2, the recording medium P is transferred to the first conveyance drum81. At this time, the front side, on which an image has been formed, of the recording medium P comes into close contact with the outer periphery of the first conveyance drum81, and the back side of the recording medium P is facing outward.

Further, when the nail part811holding the downstream end, in the conveyance direction, of the recording medium P comes to the transfer position m4, the recording medium P is transferred to the second conveyance drum82. At this time, the back side of the recording medium P comes into close contact with the outer periphery of the second conveyance drum82, and the front side of the recording medium P is facing outward.

When the nail part821of the second conveyance drum82passes the transfer position m5, the cam mechanism operates the nail part821so that the recording medium P goes forward without being transferred from the second conveyance drum82to the paper output drum83. Further, when the nail part821holding the upstream end, in the conveyance direction, of the recording medium P comes to the transfer position m6, the recording medium P is transferred to the inversion drum85. At this time, the front side of the recording medium P comes into close contact with the outer periphery of the inversion drum85, and the back side of the recording medium P is facing outward.

Further, when the nail part851holding the downstream end, in the conveyance direction, of the recording medium P comes to the transfer position m8, the upstream end, in the conveyance direction, of the recording medium P (i.e., the end of the recording medium P opposite to the end held by the nail part851) is close to and facing the tip of the of the inversion arm86. The nail part851then cancels the holding state, and the upstream end, in the conveyance direction, of the recording medium P is caught by the tip of the inversion arm86.

The inversion arm86then swings to the image formation drum50, and the end of the recording medium P, which is on the upstream side on the inversion drum85in the conveyance direction, is pulled to the return position m9, with the back side of the recording medium P remaining facing outward. The image formation drum50is controlled so that a nail part51of an empty recording medium holding area comes to the return position m9 at the same time as the end of the recording medium P being pulled to the return position m9. The end of the recording medium P, which was originally on the upstream side in the conveyance direction, is caught by the nail part51with the back side of the recording medium P facing outward. Thus the recording medium P is turned over, comes into close contact with the outer periphery of the image formation drum50, and passes the supply position m1. Image formation then is performed on the back side through the same process as that in the image formation on the front side.

When the image formation on the back side and UV irradiation are completed, the recording medium P is transferred from the image formation drum50to the first conveyance drum81at the reception position m2. On the first conveyance drum81, the front side of the recording medium P is facing outward.

Further, the recording medium P is transferred from the first conveyance drum81to the second conveyance drum82at the transfer position m4. On the second conveyance drum82, the back side of the recording medium P is facing outward.

The recording medium P is then transferred from the second conveyance drum82to the paper output drum83at the transfer position m5. On the paper output drum83, the front side of the recording medium P is facing outward.

The recording medium P is then transferred from the paper output drum83to the paper output belt mechanism84at the transfer position m7, and the recording medium P is output to the paper output unit30with its back side facing outward.

[Technical Effects of Image Formation Device]

As described above, the image formation device1separates a recording medium P away from the outer periphery of the image formation drum50to turn over the recording medium P while conveying the recording medium P from the reception position m2 to the return position m9 in the conveyance direction F with the conveying mechanism80. The second heater94thus heats the image formation drum50through the region from the reception position m2 to the return position m9, achieving efficient heating of the image formation drum50with no recording medium P between the second heater94and the image formation drum50.

Further, the image formation device1uses ink having the property of changing phase depending on its temperature. Around the image formation drum50, the second heater94that directly heats the outer periphery of the image formation drum50, and the first heater91that heats a recording medium P on the outer periphery of the image formation drum50are provided. The recording medium P therefore can be maintained at a proper temperature before image formation is performed, achieving excellent image formation with stable quality.

Further, each head unit70is provided with the ink heater73to heat the ink to be supplied to the recording heads71. This configuration enables a proper ink temperature before the ink ejection and thereby allows the ink to be ejected at a proper viscosity, achieving image formation with stable quality and enhancing reliability of the recording heads71.

Both of the first and second heaters91and94in the image formation unit20are non-contact heaters using infrared irradiation, but one of or both of the heaters91and94may be a contact heater.

FIG. 6is a cross-sectional view showing the schematic configuration of a heating roller91A as a contact heater. As shown inFIG. 6, the heating roller91A includes a hollow pipe911A composed of a metal such as aluminum; an elastic layer912A, such as a silicon rubber, which covers the entire circumference of the hollow pipe911A; and a heat source913A, such as a halogen heater, which is built in the hollow pipe911A to heat the hollow pipe911A and the elastic layer912A.

The elastic layer912A is preferably made of material having good thermal conductivity. Further, the surface of the elastic layer912A may be coated with a material (such as a PFA tube) which slides smoothly to improve durability.

The ink used for the image formation has properties of curing when irradiated with energy rays and changing phase depending on the ink temperature. The ink to be used, however, is not limited to such type of ink. An ink without the property of changing phase depending on its temperature, an ink without the property of curing when irradiated with energy rays, or an ink without any of these properties may be used for the image formation. In the case of using such types of inks, the temperature regulation with the heaters91,94, and73is meaningful if an ink to be used needs to be at a proper temperature for the image formation.

INDUSTRIAL APPLICABILITY

The present invention is applicable to the field of image formation devices to perform image formation on both sides of a recording medium where there is demand for image formation at a proper temperature.

REFERENCE NUMERALS