Image formation device

An image formation device may include a recording head which has a plurality of nozzles inlet; a flow channel member which is connected to the inlet and forms a flow channel for supplying the discharge liquid to the recording head; and a heating section which heats the flow channel member. The flow channel member may include a first flow channel section one end of which is inserted into the inlet; and a second flow channel section that is a cylindrical member inside of which the first flow channel section passes through and that externally covers a connection part between the one end of the first flow channel section and the inlet. The second flow channel section may be connected with the first flow channel section and the inlet via an elastic member, and the one end of the first flow channel section and the inlet may be connected.

This is the U.S. national stage of application No. PCT/JP2014/057683, filed on Mar. 20, 2014. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §368(b) is claimed from Japanese Application No. 2013-072048, filed Mar. 29, 2013, the disclosure of which is also incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image formation device which includes a mechanism for performing heating control of a discharge liquid.

BACKGROUND ART

There are image formation devices each of which discharges a discharge liquid by providing a heater to a recording head and heating the discharge liquid in the recording head to a predetermined temperature by electric conduction to the heater so that the discharge liquid has a viscosity which can be discharged.

Though various discharge liquids can be used in such image formation devices, in recent years, the requirement for recording and forming images has been increased even on a recording medium such as a plastic sheet which does not absorb a discharge liquid well. Thus, instead of general dye discharge liquid and pigment discharge liquid, an ink such as a gel ink, hot-melt dry ink and wax ink is used, the ink being in a gel form or solid at an ordinary temperature and changing in phase to a liquid form with a lower viscosity by heating (hereinafter, such discharge liquid is described as a phase transition ink).

Since such discharge liquid becomes mostly gelled or solid at a normal temperature, when landing on the recording medium, the viscosity rapidly increases, and thus, it is possible to prevent the image deterioration due to combined adjacent drops of discharge liquid. Accordingly, there is a merit in that recording can be performed with high image quality without generating color mixture even on the above-mentioned recording medium which does not absorb the discharge liquid well.

In an image formation device, the discharge liquid is generally supplied to the recording head via the outside of the recording head, for example, through a supplying flow channel from a discharge liquid tank storing the discharge liquid separately. Thus, it is necessary to not only maintain the stability of viscosity when discharging the liquid but also maintain a predetermined viscosity on a supplying path from the discharge liquid tank to the recording head in order to supply the discharge liquid stably. Especially, this is remarkably necessary for the above-mentioned phase transition ink which sensitively changes in viscosity due to the temperature.

In such circumstances, there are known techniques to heat the supplying path itself as a configuration for heating the ink supplied from outside of the recording head main body (patent documents 1 and 2).

In the patent document 1, in order to efficiently heat the ink supplied to the recording head, a heater is embedded in a base body forming a flow channel for supplying the ink to the recording head, the ink being supplied from outside the recording head, and the heater heats the discharge liquid flowing through the flow channel.

In the patent document 2, in order to evenly heat the ink flowing through the supplying path, the flow channel connecting the recording head and the discharge liquid tank is wounded around the heater, and the discharge liquid flowing through the flow channel is heated.

PRIOR ART DOCUMENTS

Patent Documents

Patent Document 1: Japanese Patent Application Laid Open Publication No. 2009-83470Patent Document 2: Japanese Patent Application Laid Open Publication No. 2009-233900

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In recent years, image recording has been speeded up, and accordingly, the discharge amount of discharge liquid per unit time has been also increased. Accordingly, in order to discharge a discharge liquid with a stable discharge viscosity by a recording head in an image recording device which is suitable for such speeded image recording, a heating structure which can rapidly and evenly discharge the discharge liquid with a stable viscosity from the recording head is desired, and thus it is necessary to study the heating structure in consideration of even the connection part between the recording head main body and the heated supplying path.

When studying such heating structure, it is also necessary to consider the connection between the recording head and the supplying path which does not disturb the high positioning accuracy of recording head itself as much as possible since there are image formation devices requiring highly accurate positioning of recording head to the device main body due to the recording head not performing scanning in addition to due to the increase in the number of recording heads, the image formation devices being an image formation device which is superior in speeding up, for example, a full line image formation device in which a plurality of recording heads are disposed along the width direction over the entire width of the recording medium so as to be fixed for respective colors.

However, in a case of above conventional techniques, though the ink can be warmed by heating the ink flow channel and a sub tank, the connection part between the recording head and the supply channel is not heated, and thus, the ink viscosity is increased at the connection part and ink supply to the head becomes unstable. As a result, adjustment such as raising the heating temperature is required. In addition, providing a heater at the connection part between the recording head and the supply channel could not be a heating structure considering maintaining the positioning of head itself to the device main body since heater wiring needs to be provided near the recording head, the wiring disturbs the work of replacing the recording head, and thus, head positioning is disturbed when replacing the head.

An object of the present invention is to provide an image formation device including a supply mechanism of a discharge liquid which can provide the discharge liquid with a stable discharge viscosity even at the connection part between the recording head main body and the supply flow channel connected thereto and does not disturb the high positioning accuracy of recording head to the image formation device main body.

Means for Solving the Problem

In order to achieve the above object, a first aspect of the present invention is an image formation device, including: a recording head which has a plurality of nozzles for discharging a discharge liquid onto a conveyed recording medium, the discharge liquid being supplied to an inside of the recording head through an inlet; a flow channel member which is connected to the inlet and forms a flow channel for supplying the discharge liquid to the recording head; and a heating section which heats the flow channel member, wherein the flow channel member includes: a first flow channel section one end of which is inserted into the inlet; and a second flow channel section that is a cylindrical member inside of which the first flow channel section passes through and that externally covers a connection part between the one end of the first flow channel section and the inlet, and the second flow channel section is connected with each of the first flow channel section and the inlet via an elastic member, and the one end of the first flow channel section and the inlet are connected to each other.

A second aspect is the image formation device according to the first aspect, wherein the first flow channel section is a member having a thermal conductivity of 100 W/(m·K) or more.

A third aspect is the image formation device according to first or second aspect, wherein the second flow channel section is a member having a thermal conductivity less than 100 W/(m·K).

A fourth aspect is the image formation device according to any one of first to third aspects, wherein the flow channel member includes a third flow channel section which is connected to the other end of the first flow channel section, and the first flow channel section and the third flow channel section are connected to each other so as to be attachable and detachable.

A fifth aspect is the image formation device according to the fourth aspect, wherein the heating section heats the third flow channel section.

A sixth aspect is the image formation device according to any one of first to fifth aspects, further including: a plurality of recording heads; and a holding member which holds the plurality of recording heads, wherein the plurality of recording heads is arranged along a direction orthogonal to a conveyance direction of the recording medium so that the nozzles are across an entire width of the direction orthogonal to the conveyance direction of the recording medium.

A seventh aspect is the image formation device according to sixth aspect, wherein the holding member has an opening in which a part of the recording head including a discharge surface to discharge the discharge liquid is insertable, and the recording head includes a recording head fixing section which includes an abutting surface to abut on the holding member, the abutting surface being formed on a side closer to the discharge surface than the inlet and being parallel to the discharge surface, the recording head is held by exposing the discharge surface through the opening and making the abutting surface abut on the holding member, and the one end of the first flow channel section is inserted through the inlet to the abutting surface.

An eighth aspect is the image formation device according to the seventh aspect, wherein the inlet is formed in a shape protruding from the recording head fixing section toward an opposite side of the discharge surface.

A ninth aspect is the image formation device according to any one of first to eighth aspects, wherein the discharge liquid changes in phase between a gel form or a solid form and a liquid form according to a temperature.

A tenth aspect is the image formation device according to ninth aspect, wherein a gelation temperature of the discharge liquid is equal to or more than 40° C. and less than 90° C.

An eleventh aspect is an image formation device, including: a first recording head including a first inlet through which a discharge liquid is supplied, a first outlet from which the discharge liquid flows out, and a plurality of nozzles which discharges the discharge liquid onto a conveyed recording medium, the discharge liquid being supplied to an inside of the first recording head through the first inlet; a second recording head including a second inlet which is connected to the first outlet of the first recording head, a second outlet from which the discharge liquid flows out, and a plurality of nozzles which discharges the discharge liquid onto the conveyed recording medium, the discharge liquid flowing out from the first outlet and being supplied to an inside of the second recording head through the second inlet; a first flow channel member which is connected to the first inlet and forms a flow channel to supply the discharge liquid to the first recording head; a second flow channel member which is connected to the second inlet and forms a flow channel to supply the discharge liquid to the second recording head, the discharge liquid flowing out from the first outlet of the first recording head; and a heating section which heats the first and second flow channel members, wherein each of the first and second flow channel members includes: a first flow channel section one end of which is inserted into the first or second inlet; and a second flow channel section that is a cylindrical member inside of which the first flow channel section passes through and that externally covers a connection part between the one end of the first flow channel section and the first or second inlet, and the second flow channel section is connected with each of the first flow channel section and the first or second inlet via an elastic member, and the one end of the first flow channel section and the first or second inlet are connected to each other.

A twelfth aspect is the image formation device according to the eleventh aspect, wherein the first flow channel section of each of the first flow channel member and the second flow channel member is a member having a thermal conductivity of 100 W/(m·K) or more.

A thirteenth aspect is the image formation device according to eleventh or twelfth aspect, wherein the second flow channel section of each of the first flow channel member and the second flow channel member is a member having a thermal conductivity less than 100 W/(m·K).

A fourteenth aspect is the image formation device according to any one of eleventh to thirteenth aspects, wherein the first flow channel member and the second flow channel member includes a third flow channel section which is connected to the other end of the first flow channel section, and the first flow channel section and the third flow channel section are connected to each other so as to be attachable and detachable.

A fifteenth aspect is the image formation device according to the fourteenth aspect, wherein the heating section heats the third flow channel section.

A sixteenth aspect is the image formation device according to any one of eleventh to fifteenth aspects, further including a holding member which holds the first recording head and the second recording head, wherein the first recording head and the second recording head are arranged along a direction orthogonal to a conveyance direction of the recording medium so that the nozzles are across an entire width of the direction orthogonal to the conveyance direction of the recording medium.

A seventeenth aspect is the image formation device according to the sixteenth aspect, wherein the holding member has an opening in which apart of the first recording head or the second recording head including a discharge surface to discharge the discharge liquid is insertable, and each of the first recording head and the second recording head includes a recording head fixing section which includes an abutting surface to abut on the holding member, the abutting surface being formed on aside closer to the discharge surface than the first inlet or the second inlet and being parallel to the discharge surface, each of the first recording head and the second recording head is held by exposing the discharge surface through the opening and making the abutting surface abut on the holding member, and the one end of the first flow channel section is inserted through the first inlet or the second inlet to the abutting surface.

An eighteenth aspect is the image formation device according to the seventeenth aspect, wherein each of the first inlet and the second inlet is formed in a shape protruding from the recording head fixing section toward an opposite side of the discharge surface.

A nineteenth aspect is the image formation device according to anyone of eleventh to eighteenth aspects, wherein the discharge liquid changes in phase between a gel form or a solid form and a liquid form according to a temperature.

A twentieth aspect is the image formation device according to the nineteenth aspect, wherein a gelation temperature of the discharge liquid is equal to or more than 40° C. and less than 90° C.

Effects of the Invention

According to the image formation device of the present invention, it is possible to supply a discharge liquid with a stable viscosity to the recording head without disturbing the positioning of the recording head.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The best modes to carry out the present invention are described below with reference to the drawings. Although various limitations which are technically preferable to carry out the present invention are added in the embodiments below, the scope of the invention is not limited to the embodiments below and the examples shown in the drawings.

FIG. 1is a typical view of the internal configuration of an image formation device of an embodiment of the present invention. As shown inFIG. 1, an image formation device1of the present embodiment includes an image formation section2, a paper feed section3which feeds paper to the image formation section2, and an accumulation section4which accumulates a recording medium P on which image formation has been performed at the image formation section2.

The paper feed section3includes a paper feed tray31for storing recording media P, a paper feed conveyance section32for conveying a recording medium P from the paper feed tray31to the image formation section2, a supplying section33which supplies a recording medium P in the paper feed tray31to the paper feed conveyance section32. The paper feed conveyance section32includes a pair of paper feed conveyance rollers321and322, and a paper feed conveyance belt323is stretched between the paper feed conveyance rollers321and322. The paper feed conveyance belt323carries a recording medium P supplied from the paper feed tray31by the supplying section33to the image formation section2.

The accumulation section4includes a storage tray41for storing a recording medium P on which image formation has been performed, and a accumulation conveying section42for accumulation which conveys a recording medium P from the image formation section2to the storage tray41. The accumulation conveying section42includes a plurality of accumulation conveying chain sprockets421,422and423. Among the plurality of accumulation conveying chain sprockets421to423, one accumulation conveying chain sprocket421is disposed in the image formation section2, and the other accumulation conveying chain sprockets422and423are disposed in the accumulation section4. A recording medium P on which image formation has been performed at the image formation section2is conveyed, with the recording medium P held on the conveying belt424by accumulation nails425. When the recording medium P comes to the position above the storage tray41, the recording medium P is released from the accumulation nails425and put into the storage tray41.

FIG. 2is a typical view showing the internal configuration of the image formation section2. As shown inFIG. 2, in order to perform image formation on a recording medium P, the image formation section2includes an image formation drum21which holds a recording medium P on its surface, and a delivering drum22which delivers a recording medium P, which is carried from the paper feed section3, to the image formation drum21.

The delivering drum22includes a plurality of nails (not shown) to catch one end portion of a recording medium P, and an adsorption section (not shown) to make a recording medium P stick to the outer peripheral surface of the delivering drum22, so as to hold a recording medium P at the outer peripheral surface. The adsorption section makes a recording medium P to stick to the outer peripheral surface of the delivering drum22by an electrostatic adsorption or suction. A part of the outer periphery of the delivering drum22is adjacent to the image formation drum21. The delivering drum22delivers a recording medium P to the image formation drum21at this adjacent part.

FIG. 3is a schematic view showing an outline configuration of the image formation drum21.FIG. 4is a sectional view showing an outline configuration of the image formation drum21, seen from the cut plane of IV-IV inFIG. 5.FIG. 5is a sectional view showing an outline configuration of the image formation drum21, seen from the cut plane V-V inFIG. 4. As shown inFIGS. 3 to 5, the image formation drum21is provided with a main body section215in a cylindrical shape the inside of which is hollow, and a pair of supporting sections216and217which is separate from the main body section215and supports both ends of the main body section215.

Around the main body section215, a plurality of nails211to catch one end portion of a recording medium P are provided so that the main body section215holds a recording medium P on its outer peripheral surface. The nails211are contained along the axis direction in each of concave portions213formed on the outer peripheral surface of the main body section215. The tips214of the nails211can touch and get out of touch with the outer peripheral surface of the image formation drum21. A recording medium P is held on the outer peripheral surface of the image formation drum21in such a way that the tips214of the nails211and the outer peripheral surface of the image formation drum21catch the end portion of the recording medium P. Around the main body section215, a plurality of suction holes212are formed for a recording medium P to stick to the outer peripheral surface of the main body section215.

The pair of supporting sections216and217stick to the main body section215over its entire circumference. Among the pair of supporting sections216and217, one supporting section216has a communication opening241which communicates with the interior of the hollow portion219of the main body section215. A suction pump (not shown), for example, is connected to the communication opening241. The suction pump causes the hollow portion219of the image formation drum21to be at a negative pressure. When the hollow portion219is at a negative pressure, a recording medium P sticks to the outer peripheral surface of the main body section215through the suction holes212.

The plurality of suction holes212of the adsorption section are arranged in a pattern having blue noise characteristics. Therefore, even when the marks of the suction holes212are left on a recording medium P after image formation, the irregular patter makes the marks visually inconspicuous. Further, since the suction holes212are disposed only in the area outside of the image formation area of a recording medium P, the marks of the suction holes212are prevented from being left in the image formation area.

The image formation section2uses a discharge liquid (described later in detail) which changes in phase from a gel form to a liquid form in accordance with temperature. At the time of image formation, temperature regulation is performed by heating a recording medium P so as to control the smoothness and the gloss of discharge liquid dots. Therefore, it is assumed that the image formation drum21is heated, and the outer peripheral surface of the image formation drum21has a multi-layer structure where a heat-storage layer is formed on a heat-insulating layer.

As shown inFIG. 2, the image formation section2includes a plurality of discharge sections51, a UV lamp52, a drum temperature sensor91, heating rollers71and72and a cooling fan53, which are disposed around the image formation drum21.

Each of the discharge sections51is configured by including ahead section51awhich discharges a discharge liquid and a carriage51bwhich holds the head section51a(to be described in detail later).

The plurality of discharge sections51(head sections51a) are disposed along the circumferential direction of the image formation drum21so as to be aligned in the conveyance direction Y (seeFIG. 12) of recording medium P. Each of the head section51aof discharge section51is a line type recording head extending over the entire length of the image formation drum21. The image formation device1according to the present embodiment includes a total of four discharge sections51to eject discharge liquids of four colors of Black (K), Yellow (Y), Magenta (M) and Cyan (C). The number of discharge sections51may be increased or decreased according to the number of required colors.

The discharge liquids ejected from the head sections51aof the discharge sections51change in phase between a gel form or a solid form and a liquid form in accordance with temperature. The discharge liquids have a phase transition point at not less than 40° C. and less than 100° C. Among the discharge liquids ejected from the discharge sections51, a discharge liquid ejected at the upstream side in the conveyance direction Y has a higher phase transition temperature than a discharge liquid ejected at the downstream side in the conveyance direction Y.

The phase transition temperature of a discharge liquid can be adjusted by varying the type of gelling agent to be added to the discharge liquid, the amount of added gelling agent, and the type of activating beam curable monomer. By performing such adjustments, the phase transition temperature of a discharge liquid ejected at the upstream side in the conveyance direction Y is set to be higher than that of a discharge liquid ejected at the downstream side in the conveyance direction Y, as described above. Specifically, among the plurality of discharge sections51(head sections51a), the phase transition temperature of the discharge liquid ejected from each discharge section51is adjusted such that the difference between the phase transition temperatures of the inks ejected from a pair of discharge sections51, respectively, adjacent to each other in the conveyance direction Y falls within the range of not less than 0.5° C. and not more than 10° C., and more preferably, in the range of not less than 1° C. and not more than 5° C. The details about discharge liquid are described later.

As shown inFIG. 2, a UV (ultraviolet) lamp52which emits energy rays such as ultraviolet rays, is disposed immediately downstream of the plurality of discharge sections51in the conveyance direction Y of a recording medium P. The UV lamp52extends over the entire length of the image formation drum21, and irradiates a recording medium P on the image formation drum21with energy rays.

When ultraviolet rays are used as the energy rays, the examples of a source of ultraviolet irradiation include a fluorescent tube (low-pressure mercury lamp and a sterilization lamp); a cold-cathode tube; an ultraviolet laser; low-pressure, medium-pressure and high-pressure mercury lamps having an operating pressure of from several hundred Pa to 1 MPa; a metal halide lamp; and an LED. In the light of curability, a light source which can emit UV light having a high illumination intensity of 100 mW/cm2or more, such as a high-pressure mercury lamp, a metal halide lamp, and an LED, is preferable. Above all, an LED which consumes less power is preferable, but the light source is not limited thereto.

Immediately downstream of the UV lamp52in the conveyance direction Y, the accumulation conveying chain sprocket421of the accumulation conveying section42mentioned above is disposed. A part of the outer periphery of the accumulation conveying chain sprocket421is adjacent to the image formation drum21via the conveying belt424. A recording medium P is delivered from the image formation drum21to the conveying belt424at the adjacent part. Further, immediately downstream of the accumulation conveying chain sprocket421, the cooling fan53which sends air to cool the outer peripheral surface of the image formation drum21is disposed.

Immediately downstream of the cooling fan53, the heating roller72is disposed. Further, immediately downstream the heating roller72, the drum temperature sensor91, which measures the surface temperature of the image formation drum21, is disposed. A contact-type temperature detection element, such as a thermocouple and a thermistor, may be used as the drum temperature sensor91, but a contactless temperature detection element, such as a thermopile, is more preferable.

The heating roller71(heating body) is disposed immediately downstream of the delivering drum22in the conveyance direction Y, i.e., disposed between the delivering drum22and the discharge sections51, the heating roller71heating a recording medium P held on the image formation drum21before recording is performed on the medium P by the discharge sections51. Apart of the heating roller71is in contact with the outer peripheral surface of the image formation drum21. At the time of image formation, a recording medium P is disposed between the heating roller71and the image formation drum21. At this time, the heating roller71presses a recording medium P against the outer peripheral surface of the image formation drum21so as to bring the recording medium P into close contact with the image formation drum21.

FIG. 6is a cross-sectional view showing the schematic configuration of the heating roller71. As shown inFIG. 6, the heating roller71includes a hollow pipe711composed of a metal such as aluminum; an elastic layer712, such as a silicon rubber, which covers the entire circumference of the hollow pipe711; and a heat source713, such as a halogen heater, which is built in the hollow pipe711to heat the hollow pipe711and the elastic layer712.

The elastic layer712is preferably made of material having good thermal conductivity. Further, the surface of the elastic layer712may be coated with a material (such as a PFA tube) which slide smoothly to improve durability.

The image formation device1is provided with a heating-section temperature sensor92, in addition to the heating roller71, to detect the temperature of the heating roller71. A contact-type temperature detection element, such as a thermocouple and a thermistor, may be used as the heating-section temperature sensor92, but a contactless temperature detection element, such as a thermopile, is more preferable, similarly to the drum temperature sensor91. The heating roller72(heating body), which is disposed downstream of the accumulation conveying chain sprocket421and upstream of the delivering drum22around the image formation drum21(to be more exact, which is disposed between the cooling fan53and the drum temperature sensor91), has a structure identical to that of the heating roller71.

(Specific Configuration of Discharge Section)

FIG. 7is a schematic view showing the configuration of discharge section51.

As shown inFIG. 7, the discharge section51includes the head section51aand the carriage51bholding the head section51a. The head section51aincludes a plurality of recording heads510which discharges a discharge liquid, a recording head fixing plate511on which the plurality of recording heads510are disposed, a discharge liquid tank512which stores the discharge liquid supplied to the recording heads510, and a flow channel for supplying the discharge liquid from the discharge liquid tank512to the recording heads510.

The recording head fixing plate511of the head section51ahas a length over the entire length of the image formation drum21, and the plurality of recording heads510are arranged in a plurality of lines along the direction (for example, direction orthogonal to the conveyance direction Y) crossing the conveyance direction Y of the recording medium P by the image formation drum21. This configuration is what is called a full line recording system.

FIG. 12is a conceptual view showing the head location in the discharge section51and the positional relationship between the heads and the recording medium P in the embodiment. As seen from the positional relationship between the recording medium P and the nozzles discharging discharge liquids of the plurality of recording heads510inside each of the discharge sections51Y,51M,51C and51K which respectively discharge yellow, magenta, cyan and black inks, the full line recording system is a recording system in which long recording heads are used, each of the recording heads having nozzles, over the entire recording width, for discharging a discharge liquid, the recording medium P is moved in the conveyance direction Y, and main scanning in the direction orthogonal to the conveyance direction Y is not performed. Compared to the scan type, this system is excellent in high speed recording since recording can be performed over the entire recording width without performing main scanning. Here, if a single recording head510is lengthened over the entire width of the recording medium P, it is difficult to form nozzle pitch or the like with high accuracy, and thus, a plurality of short recording heads510are connected to each other along the arrangement direction of nozzles discharging the discharge liquid. Each of the recording heads510has a plurality of nozzles. The recording head510discharges an ink from the plurality of nozzles to form an image on the recording medium P held on the image formation drum21. That is, the recording head510is provided to be exposed at the lower side thereof so that the plurality of nozzles face the recording medium P. In the recording head510of the embodiment, nozzles are provided in two lines along the direction orthogonal to the conveyance direction Y of the recording medium P, two recording heads510form a pair, and a plurality of pairs of the recording heads510are provided along the direction orthogonal to the conveyance direction Y of the recording medium P to make lines of recording heads510. Furthermore, the plurality of lines of recording heads510are provided so that the positional relationship between the pairs of recording heads510in adjacent lines makes a staggered arrangement in the conveyance direction Y of the recording medium P.

As shown inFIG. 12, as for recording head lines formed of recording heads510inside each of the discharge sections51Y,51M,51C and51K, two recording head lines are arranged in the conveyance direction Y for each of the discharge sections, and each recording head line is arranged so as to be shifted from each other in the nozzle line direction, which is what is called a staggered arrangement configuration.

Next, fixing structure of recording heads510to the recording head fixing plate511will be described by usingFIG. 13. For the purpose of illustration,FIG. 13is an outline view when a single short recording head510is fixed to the recording head fixing plate511; however, in the embodiment, a plurality of recording heads510are disposed on the recording head fixing plate511for each of the discharge sections51as mentioned above.

At the position to dispose each of the recording heads510, the recording head fixing plate511is provided with a frame (recording head fixing frame)54which has an opening to insert a part of the recording head510including a discharge surface55(seeFIG. 9) discharging a discharge liquid and fixes the position of the recording head510. The discharge surface55is exposed through the opening so as to face the conveyed recording medium P. A recording head fixing section56has a larger circumference than that of the recording head fixing frame54, and includes abutting surfaces56A (seeFIG. 9) of recording head fixing section56which can abut on the upper surface511B (seeFIG. 9) of the recording head fixing plate511. The abutting surfaces56A are positioned between the above-mentioned inlet of the recording head510and the discharge surface55of the recording head510, and are formed of surfaces parallel to the discharge surface55. Since the abutting surfaces56A are also formed to be parallel to the upper surface511B of the recording head fixing plate511, the recording head510is held to the recording head fixing plate511by the abutting surfaces56A and the upper surface511B abutting on each other. By the upper surface511B of the recording head fixing plate511and the abutting surfaces56A of the recording head fixing section56abutting on each other and by the pressing force being applied to the recording head510in the direction to discharge a discharge liquid, the recording head510is supported and fixed at a position appropriate for image formation by the abutting recording head fixing plate511. The method for fixing the recording head510to the recording head fixing plate511is not limited to the above-mentioned method, and the recording head510may be fixed by providing nails to the recording head510and the recording head fixing plate511and fitting the nails to each other, for example.

The carriage51bincludes a pair of arms520holding the recording head fixing plate511so as to sandwich the both ends thereof and two connecting plates521connecting the pair of arms520.

The carriage51bis connected to a rail (not shown in the drawings) which extends in the direction crossing (for example, direction orthogonal to) the conveyance direction Y of the recording medium P. The carriage51bis provided so as to be movable in the direction crossing the conveyance direction Y of the recording medium P along the rail, and the head section51aheld by the carriage51bcan be moved in the direction crossing the conveyance direction Y. That is, carriages51bsupport the respective plurality of head sections51aprovided for respective colors to be individually movable.

The discharge sections51Y,51M,51C and51K can be moved to print positions facing the image formation drum21to perform image formation and to maintenance positions to depart from the image formation drum21in the direction crossing the conveyance direction Y of the recording medium P, preferably, in the direction orthogonal to the conveyance direction Y. When perform printing, the discharge sections51are fixed at the print positions facing the image formation drum21to perform image formation.

(Specific Configuration of Flow Channel Member to Supply Discharge Liquid to Recording Head)

The discharge section51shown inFIG. 7has a configuration of circulation flow channel through which the discharge liquid of discharge liquid tank512flows in the plurality of recording heads510and returns to the discharge liquid tank512again.

FIG. 11is an outline view of the circulation flow channel. The discharge liquid flows from the discharge liquid tank512to the upstream recording head510A through the inlet510Aa in the direction X which is the flowing direction of discharge liquid. The discharge liquid flows from the outlet510Ab through a common flow channel communicating with discharge flow channels of respective nozzles and is supplied to the inlet510Ba of the downstream recording head510B. The discharge liquid returns to the separate discharge liquid tank512through the outlet510Bb of the downstream recording head510B. By such configuration, the flow channel connects the outlet510Ab of a first recording head with the inlet510Ba of a second recording head, and by the outlet510Bb of the second recording head being connected to the discharge liquid tank512, the discharge liquid can be circulated. Thus, compared to the configuration in which the discharge liquid is heated from first at each recording head, the configuration of the present invention makes it possible to efficiently make the discharge liquid have a viscosity appropriate for discharge in a short time by supplying the discharge liquid heated at one recording head510to another recording head510. Furthermore, by returning the discharge liquid which flows out from the downstream recording head510B to the discharge liquid tank512again, the discharge liquid can be reused, and it is possible to reduce the heating of discharge liquid at the discharge liquid tank512and at the supply flow channel, leading to efficient heating control. The configuration is also preferable from the viewpoint of maintenance since it is possible to eject air bubbles in the recording head outside the recording head through the outlets510Ab and510Bb by circulating the discharge liquid when the air bubbles are mixed into the recording head.

FIG. 8is an enlarged view of such recording head510. In such way, the recording head510forming a part of the above-mentioned circulation flow channel has a pair of convex inlet510aand outlet510bof discharge liquid, and the discharge liquid to which heating control was performed at the upstream recording head is supplied through the inlet of the downstream recording head to be used.

Next, the specific configuration of the flow channel member513supplying the discharge liquid to the recording head510will be described by usingFIGS. 8 and 9. In the following description, the discharge liquid is supplied by the flow channel member513to the recording head, and the side of the flow channel member513closer to the discharge liquid tank512is defined as upstream and the side closer to the recording head is defined as downstream. In the flow channel member513, first flow channel sections514and515, second flow channel section516, recording head510and elastic members518are described as a recording head unit hereinafter.

FIG. 9is an explanation view showing a cut plane of the flow channel member513supplying the discharge liquid to the recording head510.

The flow channel member513is configured by including a member connecting the first flow channel sections514and515, second flow channel section516and the third flow channel section517, and forms a flow channel through which the discharge liquid supplied from the discharge liquid tank512is supplied to the recording head510. A heating section H (for example, sheathed heater) for heating the third flow channel section517is provided on the lower surface side of the third flow channel section517, and the discharge liquid passing a flow channel R can be heated. Here, the first flow channel sections514and515are configured by including a material having a high thermal conductivity as well as the third flow channel section517. Accordingly, the heat added to the third flow channel section517by the heating section H is conducted to the first flow channel sections514and515while maintaining the high temperature, and thus, it is not necessary to heat the first flow channel sections514and515themselves by the heating section H, and there is no problem of disturbing the replacement work of recording head510due to a wiring of the heating section H provided near the recording head510, allowing the maintenance of recording head510to be performed as usual. From the viewpoint of conducting heat of the heating section H more efficiently, it is more preferable that the first flow channel sections514and515and the third flow channel section517are configured by including a member having a thermal conductivity of 100 W/(m·K) or more, for example, aluminum and carbon nanotube.

The first flow channel sections514and515can be connected to the third flow channel section517so as to be attachable and detachable by a bolt B which can fix from the upper surface side opposite to the discharge surface55, and thus, the flow channels of the first flow channel sections514and515and the flow channel of the third flow channel section517can be connected to each other.

By such configuration of connecting the flow channel sections so as to be attachable and detachable by a bolt B which can fix the flow channels from upper surface side opposite to the discharge surface55, for example, even in a case as shown inFIG. 7where a plurality of recording heads510is arranged, the recording heads510are close to each other and there is no space on a lateral side of each recording head510, the bolt B can be attached and detached from the upper side relatively having more space, and thus, it is possible to replace recording heads510easily and accurately without generating a positioning gap due to contact with a recording head510which is already positioned.

Also in a case of replacing the part located downstream of the third flow channel section517simultaneously when replacing the recording head510, since the heating section H is provided to the third flow channel section517, the heating section H does not need to be replaced, and thus, it is possible to suppress the cost when replacing the part of flow channel member513located downstream of the third flow channel section517and the recording head510.

The first flow channel sections514and515are cylindrical members, one end of the first flow channel section515is inserted into the inlet510a, and the ink supplied from the discharge liquid tank512is supplied to the inlet510aof recording head.

Since one end of the first flow channel section515is inserted into the inlet510ain such way, compared to the configuration in which the inlet510aof the recording head is inserted into the first flow channel section515, it is possible to conduct the discharge liquid heated by the heat of heating section H through the first flow channel sections514and515, and supply the discharge liquid into the inlet510aof recording head while heating the discharge liquid by making the discharge liquid contact the first flow channel sections514and515. This is preferable in an image formation device which is required to stabilize the supply of discharge liquid which transitions in phase. By the insertion configuration, it is also possible to supply the discharge liquid to a recording head flow channel519in the recording head while making the first flow channel sections514and515contact with the discharge liquid by extending the flow channel pipe as needed as described later.

The second flow channel section516is a cylindrical member covering the outside of the first flow channel section515. The first flow channel section515is inserted and connected to one opening of the second flow channel section516via the elastic member518, and the inlet510aof recording head510is inserted and connected to the other opening via the elastic member518.

In the above-mentioned second flow channel section516, it is possible to suppress the heat release from the first flow channel section515and reduce the load of heating section H. Accordingly, it is preferable to use a member having a heat retaining and insulating effect, for example, a member such as stainless having a thermal conductivity less than 100 W/(m·K).

As described above, each of the first flow channel section515and the inlet510ais connected to the second flow channel section516via the elastic member518.

That is, a gap larger than a gap between members in normal fitting exists between the outer circumferential surface of first flow channel section515and the inner circumferential surface of the second flow channel section516and between the internal circumferential surface of the second flow channel section516and the outer circumferential surface of the inlet510a, and the connection is made between the gap via the elastic member518. Thus, it is possible to absorb the load with the elastic member518even when the direction or posture is slightly shifted therebetween due to the load at the connection part between the first flow channel section515and the second flow channel section516.

Furthermore, the first flow channel section515, second flow channel section516and inlet510ahave a configuration of sealing the internal space via the elastic members518, not sealing the connection parts between the members via the elastic members518. Thus, the configuration can avoid leakage of the discharge liquid supplied through the first flow channel section515to the outside of the recording head. In addition, since there is no need for sealing with a high dimensional accuracy of one end of the first flow channel section515and the internal diameter of the inlet510a, when inserting the first flow channel section515, it is possible to reduce the risk such as positioning gap of a positioned recording head510due to the contact between one end of the first flow channel section515and the wall surface of the inlet510a.

That is, even in a case where the recording head510is fixed at an appropriate position, and the third flow channel section517and the first flow channel section514are connected, it is possible to connect the flow channel sections having a relatively high degree of freedom without disturbing the positioning of recording head510. This is especially effective when adopting a full line recording system as in the embodiment which requires high accuracy of positioning.

The above-mentioned elastic member518is a member which is capable of elastic deformation, and it is preferable that the elastic member518is formed of a member resistant to discharge liquid to be discharged from the recording head510. For example, a member in an O-ring shape formed of rubber such as nitrile rubber, styrene rubber, silicon rubber, and fluorine-containing rubber can be used as the elastic member518.

As mentioned above, the discharge liquid can be supplied with a stable viscosity to the recording head510without a configuration of directly heating the first flow channel sections514and515and the second flow channel section516.

The heat of discharge liquid supplied through the first flow channel section515is released to the recording head fixing plate511from the recording head fixing section56abutting on the recording head fixing plate511to which the recording head510is fixed. Accordingly, as shown inFIG. 9, it is preferable that the first flow channel section515is inserted to the position of recording head510corresponding to the recording head fixing section56. Thereby, it is possible to supply the discharge liquid into the head with more stable viscosity even when the recording head fixing plate511releases heat.

The inlet510aof recording head510in the embodiment is provided on the upper surface of the recording head fixing section56, protrudes to the side opposite to the discharge surface55of recording head510and has a step with a sharp end. Since the inlet510aprotrudes and extends toward the opposite side of the discharge surface55, that is, toward the side closer to the tank supplying the discharge liquid in such way, it is not necessary to make the first flow channel section515long. However, the shape of the inlet510ais not limited to this, and any arbitrary shape may be used as long as there is a slight gap between the outer circumferential surface of the inlet510aand the internal circumferential surface of the second flow channel section516and they can be connected via the elastic member518. Each ofFIGS. 14A and 14Bis an enlarged view of the inlet510ashowing a shape other than the inlet510aof recording head510in the embodiment. As shown inFIG. 14A, the present invention may have a configuration in which the inlet510aitself does not protrude, a concave portion is provided around the inlet510a, one end of the second flow channel section516is inserted into the concave portion via the elastic member518, and as a result, the inlet510ais connected to the second flow channel section516via the elastic member518. Also, as shown inFIG. 14B, the present invention can similarly adopt the configuration in which the inlet510areversely has a flared end.

In the embodiment, the first flow channel section is formed of two members of514and515; however, these members may be a single member one end of which is connected to the third flow channel section517and the other end of which is connected to the inlet510a, and the discharge liquid may be supplied from the discharge liquid tank512to the recording head510through the first flow channel section, and thus, the present invention is not limited to the embodiment.

In the embodiment, the respective elastic members518between the inlet510aand the second flow channel section516and between the first flow channel section515and the second flow channel section516are formed of separate O-rings; however, the elastic members518may be formed as a united elastic member518.

The heating in the present invention is not only direct heating by the heating section H but also heating by the member which receives heat conducting from the heating section H, and the heating section H can be disposed at any position as long as the flow channel member513can be heated. Alternatively, all the used recording heads510may be connected to form a single circulation path, or all the used recording heads may be divided into a plurality of groups to form a plurality of circulation paths by the groups.

(Main Control Configuration of Image Formation Device)

FIG. 10is a block diagram showing the main control configuration of image formation device1. As shown inFIG. 10, the controller10of image formation device1is electrically connected to a delivering motor62which rotates the delivering drum22, a drum rotation motor61which rotates the image formation drum21, a paper feed motor63which drives driving sections of paper feed section3, a paper output motor64which drives driving sources of the accumulation section4, a head driving circuit65which drives the discharge section51(head section51a), a drum temperature sensor91, a heating roller71, a heating-section temperature sensor92, a heating roller72, suction holes212, a UV lamp52, a cooling fan53, a heating section H, a gloss adjustment button68for an operator to set and input the degree of gloss of formed image, a recording medium thickness input section81and a recording medium type input section82.

The controller10is constituted of a ROM which stores a program to control each component of the image formation device1, a CPU which executes the program, and a RAM which is a work area at the time of the execution of the program, for example.

Further, an image memory circuit67which stores the data of image to be formed inputted from a host computer via an interface circuit66is provided in addition to the controller10. The CPU of the controller10performs computing on the basis of image data stored in the image memory circuit67and the program, and sends a control signal to each component on the basis of the computing results.

The controller10performs heat control of the heating roller71.

The recording medium thickness input section81is a section with which an operator inputs the thickness of a recording medium P on which image formation is to be performed. The recording medium type input section82is a section with which an operator inputs the type of recording medium P on which image formation is to be performed.

The controller10performs heat control according to the thickness and the type of recording medium P. Specifically, the controller10stores table data where the set temperatures T4and T5of the heating roller71are set according to the two parameters of the type and thickness of recording medium P. The controller10performs the processing of determining the set temperatures T4and T5on the basis of the input of these.

The heating roller71is provided in order to raise the temperature of a recording medium P to a desired temperature range quickly. T4and T5are determined according to the thermal conductivity of the heating roller71and a contact time between the heating roller71and a recording medium P, for example.

The table below shows an example of the table data where the set temperatures T4and T5are set according to the two parameters of the type and thickness of recording medium P. The temperatures in the table are all expressed in Celsius. T1in the table is the lower limit of the range of image-forming-drum set temperature, which is the target temperature band of the image formation drum21at the time of image formation; T2is the intermediate value of the range of image-forming-drum set temperature; and T3is the upper limit of the range of set temperature of the image formation drum21.

The discharge liquid used in the embodiment is an activating beam curable ink which is cured by being irradiated with energy rays (activating beams, for example, ultraviolet rays). 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 herein refers to a phenomenon in which a liquid state having fluidity 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 state at a cooled temperature is reversibly transformed into a liquid state having fluidity when heated to a temperature higher than or equal to the solation temperature.

The term “gelation” 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 having a fluidity in which the interactions formed during the gelation are released. The term “solation temperature” used in the present invention refers to a temperature at which a gel ink is warmed to be transformed into a sol state and have fluidity. The term “gelation temperature” refers to a temperature at which a sol ink is cooled to be transformed into a gel state and have 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 a recording head510. 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. This can prevent 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 inventor 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 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 medium is controlled within the range of 42 to 48° C.

The inventor guesses 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 inventor 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.

Printing with 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: an 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. An 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” 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 printing 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 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.

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, which contains an oil gelling agent, is preferably a thermoreversible gel to prevent clogging of the recording heads.

The gelation temperature (phase transition temperature) of the activating beam curable ink used in the present invention is preferably 40° C. or higher but lower than 100° C., and more preferably, ranges from 45 to 70° C. 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 a recording head510regardless of the environment temperature during printing. An ink exhibiting a phase transition at a temperature lower than 90° C. eliminates the need for heating of an image formation device to an extremely high temperature, which can reduce load on the recording heads510of and the components of the ink supply system of an image formation device.

The term “gelation temperature”, which refers to a temperature at which a liquid having fluidity is transformed into a gel form 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”.

In the present invention, a gelation temperature of ink 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 form 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 to be discharged 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 effectively 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 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 as the discharge liquid according to 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 because it can readily ejected from recording heads.

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

Specific examples of high-molecular compounds preferably used 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 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 Itoh 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 glycol 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 Patent Application Laid Open Publication Nos. 2005-126507, 2005-255821, and 2010-111790. These gelling agents may be used alone or in combination as appropriate.

The ink as discharge liquid of the present invention, which contains the gelling agent, is transformed into a gel form immediately after being ejected from a recording head510onto a recording medium. This prevents the mixing and integration of dots and thus can provide high quality image during high-speed printing. 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 increased viscosity after gelation are photoradically cured with a decrease in photocurable properties due to oxygen inhabitation. 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 characteristics.

The ink as discharge liquid of the present invention is characterized in that it contains a gelling agent, coloring material, and an activating beam curable composition cured by activating beams.

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

Examples of the activating beams 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; examples of the cationically polymerized monomers include epoxy compounds, vinyl ether compounds, and oxetane compounds described in Japanese Patent Application Laid Open 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” refers to a compound having one or more oxetane rings. Any known oxetane compound may be used, for example, described in Japanese Patent Application Laid Open 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 Patent Application Laid Open 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 Patent Application Laid Open 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 Patent Application Laid Open Publication No. 7-159983, Japanese Examined Patent Application Publication No. 7-31399, and Japanese Patent Application Laid Open 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 as a photo-radically polymerizable monomer, the resin being described in Japanese Patent Application Laid Open 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.

In the present invention, any known (meth)acrylate monomers and/or oligomers may be used as radically polymerizable compounds. The term “and/or” used herein 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 polymer 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 carboxylic acids and various polyols, the multifunctional maleimides compound being described in Japanese Patent Application Laid Open Publication No. 11-124403.

The amount of added cationic polymer 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 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, contains no solvent. Residual solvent in cured-ink images causes a problem of the decrease in solvent resistance and a volatile organic compound (VOC) of the residual solvent. 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 recording head510and 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 Patent Application Laid Open Publication No. S60-60104; organic peroxides disclosed in documents, such as Japanese Patent Application Laid Open 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 Patent Application Laid Open Publication No. S59-14023 andMacromolecules, 10, P. 1307, 1977; azo compounds disclosed in Japanese Patent Application Laid Open Publication No. S59-142205; metal allene complexes disclosed in documents, such as Japanese Patent Application Laid Open Publication No. H1-54440, EP patent Nos. 109,851 and 126,712 andJ. Imag. Sci.,30, P. 174, 1986; (oxo)sulfoniumorganoboron complexes disclosed in Japanese Patent Nos. 2711491 and 2803454; titanocene dichlorides disclosed in Japanese Patent Application Laid Open Publication No. S61-151197; transition metal complexes containing transition metals, such as ruthenium disclosed inCoordination Chemistry Review,84, pp. 85-277, 1988 and Japanese Patent Application Laid Open Publication No. H2-182701; 2,4,5-triarylimidazole dimer; carbon tetrabromide disclosed in Japanese Patent Application Laid Open Publication No. H3-209477; and organic halogen compounds disclosed in Japanese Patent Application Laid Open 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 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 Patent Application Laid Open 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 Patent Application Laid Open Publication No. 2005-255821.

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

Fourth group: iron-allene complexes disclosed in paragraph of Japanese Patent Application Laid Open Publication No. 2005-255821.

The activating beam curable ink according to 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 for adjusting membrane properties, polyurethane resins, vinyl resins, acrylic resins, elastomeric resins, and waxes. 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.

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.

As described above in detail, according to the present invention, by the above-mentioned recording head unit supplying a discharge liquid from the discharge liquid tank512to a recording head510, it is possible to supply the discharge liquid to the recording head510in a state where the discharge liquid is warmed so as not to raise the viscosity thereof, and to stabilize the supply of discharge liquid to the recording head510. That is, the discharge liquid can be supplied with a stable discharge viscosity to the connection part between the recording head main body and the supply flow channel connected thereto. Furthermore, since the recording head510can be disposed to the image formation device main body while maintaining the positioning accuracy, it is possible to provide an image formation device which is excellent in high image quality and speeding up.

In the embodiment, a full line recording head is used as the image formation device, and the embodiment is described by using an ink jet recording device configured by including an ink circulation flow channel which ejects a specific ink as the discharge liquid; however, the present invention is not necessarily limited to this.

That is, even in an image formation device using a general scan type recording head and an image formation device not using an ink circulation mechanism, the present invention can be similarly applied if the discharge liquid needs to be supplied with the above-mentioned stable viscosity and the positioning accuracy of recording head510is required.

The discharge liquid is also not limited to the above-mentioned activating beam curable ink. An ink and a discharge liquid other than ink which require stable management of viscosity by heating can also be used as well as other phase transition ink, for example, ink such as hot-melt ink and wax ink.

The present invention is not limited to the above-mentioned embodiment, and changes can be appropriately made within the scope of the present invention.

INDUSTRIAL APPLICABILITY

The image formation device according to the present invention is applicable in the image formation field of ejecting discharge liquid from recording heads onto a recording medium to perform image formation.

EXPLANATION OF REFERENCE NUMERALS