Patent Description:
The present invention relates to an inkjet printer equipped with a pair of inkjet heads.

Printing performed by ejecting ink having high viscosity in the inkjet printer is performed by heating the ink in a flow path for supplying the ink to the inkjet head to lower the viscosity and improve the fluidity, thereby supplying the ink to the inkjet head.

<CIT> describes a technique of an inkjet print head package including an ink supplying unit including a preheating plate, a print head chip or the like including an auxiliary heater, and an ink hose connecting an ink supplying device and the print head chip or the like.

Conventionally, an ink supplying device that supplies ink to a print head chip has been known (see e.g., <CIT>). The ink supplying device includes a preheating plate and a preheating heater, where the preheating plate and the preheating heater heat ink to be supplied to the print head chip. The ink heated by the ink supplying device is supplied to the print head chip. The print head chip ejects the ink supplied through an ink supply port through a plurality of nozzles.

<CIT> discloses an inkjet printer that is equipped with a first ink heating means which heats the ink in an ink supply system of the upstream side in a feeding direction of the ink of the ink supply system, a second ink heating means which heats the ink in the ink supply system of the downstream side in the feeding direction of the ink of the ink supply system, and a control means which controls driving of the first ink heating means and the second ink heating means. The control means drives only the second ink heating means for a period while recording is carried out by ejecting the ink from ejection openings of a recording head, and drives both of the first ink heating means and the second ink heating means for a period while the maintenance is carried out.

<CIT> discloses an inkjet printhead assembly including an inkjet printhead chip having an ink inflow hole, a frame having an ink supply hole, and an ink supply apparatus having a preheater and an ink supply outlet, wherein the frame is disposed between the inkjet printhead chip and the ink supply apparatus, the inkjet printhead chip is attached to the frame, and the ink supply hole is disposed between the ink supply outlet and the ink inflow hole, so as to channel ink between the ink supply apparatus and the inkjet printhead chip.

<CIT> discloses a flow channel member comprising a flow channel plate provided with a liquid flow channel adapted to communicate a supply source of liquid and a head chip with each other, wherein the flow channel plate is disposed in a state in which a thickness direction of the flow channel plate crosses a gravitational direction. The liquid flow channel includes a filtration flow channel through which the liquid flows along the thickness direction of the flow channel plate, and in which a filter adapted to filtrate the liquid is disposed, an upstream flow channel which is communicated with an upstream end of the filtration flow channel, and through which the liquid flows along a surface direction of the flow channel plate, and a downstream flow channel disposed on a downstream side of the filtration flow channel, and a reservoir wall part is formed in a part located on a downstream side of the filter on an inner surface of the filtration flow channel, the reservoir wall part separating between the filtration flow channel and the downstream flow channel, and having a communication flow channel adapted to communicate the filtration flow channel and the downstream flow channel with each other in upper end parts in the gravitational direction.

<CIT> discloses an injection molding apparatus including a manifold having a manifold channel for receiving a melt stream of moldable material and delivering the melt stream to a mold cavity through a nozzle channel of a nozzle and a mold gate. A heater is coupled to the manifold. The heater includes a heater plate that is formed by an extrusion process and at least one channel for receiving a heating element.

<CIT> discloses a liquid jetting device including a plurality of nozzles from which a liquid can be ejected, a plurality of pressure chambers, each being in fluid communication with an associated nozzle in the plurality of nozzles, actuators associated with each pressure chamber and configured to cause a pressure change in an associated pressure chamber in the plurality of pressure chambers, a heat-conductive chassis to which the plurality of nozzles, the plurality of pressure chambers, and the actuators are mounted, an integrated circuit held inside the chassis and configured to drive the actuators to eject liquid from the plurality of nozzles, a circuit board electrically connected to the integrated circuit and configured supply an electrical signal to integrated circuit, and a heat-conductive support to which the circuit board is mounted, the heat-conductive support held by the heat-conductive chassis to contact the integrated circuit and an inner surface of the heat-conductive chassis.

Since the ink is not heated at the protrusion connecting the ink supplying device and the print head chip or the like, the viscosity of the ink increases, and the fluidity may not be maintained in some cases.

The present invention has been made in view of such a problem.

An inkjet head such as a general print head chip moves in a main scanning direction with respect to a recording medium, and a plurality of nozzles are in a nozzle row arranged side by side in a sub scanning direction orthogonal to the main scanning direction. In some inkjet heads, an ink supply port is provided on one side in the sub scanning direction with respect to the nozzle row. Furthermore, in order to lengthen the nozzle row in the sub scanning direction, two nozzle rows may be arranged in the sub scanning direction using two inkjet heads. In this case, the two ink supply ports provided in the two inkjet heads are respectively generally arranged on one side in the sub scanning direction with respect to the nozzle row.

Here, in the nozzle row, the nozzle on one side in the sub scanning direction, which is a side closer to the ink supply port, may not have the temperature of the ink immediately after the start of ejection of ink stable, as compared with the nozzle on the other side in the sub scanning direction, which is a side farther from the ink supply port. This is because the temperature distribution of the ink becomes non-uniform when the ink in the head is warmed by the ink warming heater provided in the inkjet head. Therefore, the nozzle on the side closer to the ink supply port has a larger variation in the ejection speed of the ink than the nozzle on the side farther from the ink supply port immediately after the start of ejection of the ink. Therefore, the nozzle on the side closer to the ink supply port has a larger variation in the ejection speed of the ink than the nozzle on the side farther from the ink supply port immediately after the start of ejection of the ink.

Of the two nozzle rows arranged in the sub scanning direction, in one nozzle row, the nozzle on the other nozzle row side is a nozzle on the side closer to the ink supply port, and in the other nozzle row, the nozzle on the one nozzle row side is a nozzle on the side farther from the ink supply port. This is because the two ink supply ports provided in the two inkjet heads are arranged on the same side in the sub scanning direction with respect to each nozzle row. Therefore, since the two nozzle rows are combined such that the nozzle on the side closer to the ink supply port and the nozzle on the side farther from the ink supply port are continuous or overlap in the sub scanning direction, the nozzle having a large variation in the ink ejection speed and the nozzle having a small variation in the ink ejection speed are combined. As a result, stripes due to shading, that is, banding is likely to occur, and there is a possibility that image quality may degrade.

The present invention thus provides an inkjet printer capable of improving image quality.

An inkjet printer for solving the above problem includes the features of claim <NUM>.

A warming block is provided preferably on an upstream side of each of the inkjet heads in the flow direction of the ink and warms the ink supplied to the ink supply port.

According to this configuration, since the ink to be supplied to the inkjet head can be warmed, non-uniformity of the temperature of the ink in the head can be suppressed.

When performing printing operation on the recording medium at the same time, the pair of inkjet heads preferably have the other end portions proximate to each other so that the respective nozzle rows of the pair of inkjet heads are regarded as a continuous nozzle row.

According to this configuration, printing can be performed on the recording medium by a long nozzle row in which a pair of nozzle rows is continuous using a pair of inkjet heads.

Preferably, a control unit is further provided that controls a printing operation of the inkjet head; where the control unit causes each of the inkjet heads to perform printing on the print medium by a multi-pass method of performing a plurality of main scans for a plurality of print passes with respect to each position of the recording medium, and causes each of the inkjet heads to eject ink droplets to a pixel designated by mask data using mask data, the mask data being data designating a pixel to which ink droplets are to be ejected in each of the plurality of print passes performed on each position of the recording medium; and in the mask data, a nozzle usage frequency on the other end portion side proximate to each other of the nozzle rows of the pair of inkjet heads becomes high, and a nozzle usage frequency on the one end portion side of the nozzle row becomes low.

According to the configuration, the nozzle having a high nozzle usage frequency can be the nozzle having a small variation in the ink ejection speed. Therefore, the usage frequency of the nozzle having high ink ejection stability can be increased, and on the other hand, the usage frequency of the nozzle having low ink ejection stability can be reduced, so that the ink can be stably ejected onto the recording medium.

Furthermore, preferably, the pair of inkjet heads have the same structure, and are arranged point-symmetrically with a phase differed by <NUM> degrees about a symmetry point in a plane where the inkjet heads and the recording medium relatively move.

According to this configuration, since the pair of inkjet heads can be made to have the same structure by arranging the pair of inkjet heads point-symmetrically, an increase in device cost can be suppressed.

The ink preferably is an ultraviolet-curable ink that cures by ultraviolet light.

According to this configuration, even when the ink is the ultraviolet-curable ink, the image quality of the target object can be improved.

According to the inkjet printer of the present invention, as the protrusion is overheated through the heat transfer portion, an increase in ink viscosity at the protrusion is suppressed. Thus, the fluidity of the ink can be maintained.

Hereinafter, an example of the present invention will be described with reference to the drawings. Note that the present invention is not limited only to the present examples.

Hereinafter, an inkjet printer according to the present example will be described with reference to <FIG> and <FIG>. <FIG> is a perspective view of an inkjet printer according to the present example. <FIG> is a schematic front view for explaining a configuration of the main part of the inkjet printer shown in <FIG>.

The inkjet printer <NUM> (hereinafter referred to as a "printer <NUM>") ejects UV (UV, Ultra Violet) ink from an inkjet head <NUM> (hereinafter referred to as "head <NUM>") onto a print medium <NUM> to perform printing. As illustrated in <FIG>, the printer <NUM> includes a head unit <NUM>, a platen <NUM>, a carriage <NUM>, an ink storage unit <NUM>, a storage unit connecting unit <NUM>, a hose <NUM>, and a carriage driving unit <NUM>.

In the following description, a feeding direction of the print medium <NUM> is an X direction, a moving direction of the head <NUM> is a Y direction, and a direction orthogonal to the X direction and the Y direction is a Z direction. In the X direction, a front direction of the printer <NUM> in <FIG> is an X+ direction, and a back direction of the printer <NUM> is an X- direction. In the Y direction, a left side direction of the printer <NUM> in <FIG> is a Y+ direction, and a right side direction of the printer <NUM> is a Y- direction. Furthermore, in the Z direction, a direction opposite to a vertical direction of the printer <NUM> in <FIG> is a Z+ direction, and a vertical direction of the printer <NUM> is a Z- direction. Moreover, a plane constituted by the X direction and the Y direction is referred to as an XY plane. A direction along the XY plane is referred to as a horizontal direction.

As shown in <FIG>, the ink storage unit <NUM> has an outflow port downwardly attached with respect to the storage unit connecting unit <NUM>. The ink in the ink storage unit <NUM> flows through the hose <NUM> attached to the storage unit connecting unit <NUM> and is fed to a pressure control unit <NUM> mounted on the carriage <NUM>. Here, the height of the ink storage unit <NUM> attached to the storage unit connecting unit <NUM> is a higher position than the pressure control unit <NUM>. The ink storage unit <NUM> and the storage unit connecting unit <NUM> may be mounted on the carriage <NUM>.

The ink storage unit <NUM> is made of a flexible material. The ink storage unit <NUM> is airtightly attached to the storage unit connecting unit <NUM>. The ink storage unit <NUM> is configured to keep the pressure of the internal air constant when the remaining amount of ink is decreased.

The ink supplied from the storage unit connecting unit <NUM> including the ink storage unit <NUM> contains UV ink. The viscosity of the UV ink has high temperature dependency, and has high viscosity at normal temperature, but the viscosity lowers by heating. That is, the fluidity of the UV ink can be improved by heating. Here, the UV ink is an ink having a property of being cured when irradiated with UV.

The UV ink contains a pigment that is a colorant, a monomer that is a material polymerized to form a film, a photopolymerization initiator that absorbs UV light to start a polymerization reaction of the monomer, and an adjuster that adjusts the ink after printing, and has ultraviolet curability. When the UV ink is irradiated with ultraviolet light, a photopolymerization initiator reacts to start a polymerization reaction of a monomer, and the UV ink is cured.

The hose <NUM> has one end connected to the storage unit connecting unit <NUM> and the other end connected to the pressure control unit <NUM> of the head unit <NUM>. The hose <NUM> bends and follows in the horizontal direction as the carriage <NUM> moves in the Y+ direction or the Y- direction.

The head unit <NUM> ejects ink onto the platen <NUM>, described later. As illustrated in <FIG>, the head unit <NUM> includes the pressure control unit <NUM>, an ink warming block <NUM>, a conducting portion <NUM>, a head <NUM>, and a protrusion <NUM>. The head unit <NUM> is mounted on the carriage <NUM> described later.

The pressure control unit <NUM> causes the ink supplied from the ink storage unit <NUM> to guide to the ink warming block <NUM>. The pressure control unit <NUM> includes a control flow path <NUM> for guiding ink, a buffer <NUM>, and a suck back <NUM>. The pressure control unit <NUM> is disposed below the ink storage unit <NUM>. Here, the ink is guided from the ink storage unit <NUM> to the pressure control unit <NUM> by the water head difference h between the height of the liquid level of the ink in the ink storage unit <NUM> and the height of the ink at the inlet of the pressure control unit <NUM> illustrated in <FIG>.

When guiding the ink, if the flow rate of the ink supplied from the ink storage unit <NUM> is larger than the amount of ink ejected from the head <NUM>, the pressure control unit <NUM> increases the volume of the buffer <NUM> to hold the surplus ink in the buffer. If the flow rate of the ink supplied from the ink storage unit <NUM> is smaller than the amount of ink ejected from the head <NUM>, the pressure control unit <NUM> decreases the volume of the buffer <NUM> to additionally supply the ink held in the buffer. This allows a sudden increase and decrease in the amount of ink ejected from the head <NUM>. Furthermore, when the ejection of ink from the head <NUM> is not performed, the pressure control unit <NUM> performs an operation of slightly pulling back the ink between the pressure control unit <NUM> and the head <NUM> by increasing the volume of the buffer <NUM> by the suck back <NUM>.

The ink warming block <NUM> heats the ink supplied from the pressure control unit <NUM>. As illustrated in <FIG>, the ink warming block <NUM> includes a warming flow path <NUM> for guiding the ink therein. The warming flow path <NUM> connects the inflow port <NUM> and the connection port <NUM>. The ink warming block <NUM> has a connection end face <NUM> continuing from the connection port <NUM>. The ink warming block <NUM> has a hole <NUM> for attaching a sealing member <NUM> to the connection end face <NUM>. The ink warming block <NUM> includes a sheet heater <NUM> on a side surface. In the ink warming block <NUM>, a fixing portion <NUM> is fastened and fixed to the carriage <NUM> with a screw.

According to <FIG>, the warming flow path <NUM> internally provided in the ink warming block <NUM> is formed by a first warming path <NUM> that lies from the inflow port <NUM> along the Z- direction, a second warming path <NUM> that continuously lies from the first warming path <NUM> along the X+ direction, and a third warming path <NUM> that continuously lies from the second warming path <NUM> along the Z- direction and reaches the connection port <NUM>. The ink warming block <NUM> having the warming flow path <NUM> is heated by the sheet heater <NUM> described later. That is, the ink flowing through the warming flow path <NUM> is heated by the warming flow path <NUM>, whereby the viscosity is lowered and the fluidity is improved.

In the following description, the warming flow path <NUM> refers to the third warming path <NUM> unless otherwise specified. The flow path diameter dimension of the warming flow path <NUM> is represented as d<NUM>. The flow path diameter dimension d<NUM> of the warming flow path <NUM> is, for example, ϕ <NUM>. The ink warming block <NUM> may have a plurality of warming flow paths <NUM>, and may be configured such that the ink is supplied from the plurality of ink storage units <NUM> to the respective warming flow paths <NUM> via the pressure control unit <NUM>.

In the present example, a description will be made for a case where the flow path cross-sectional shape of the warming flow path <NUM> is a circular shape having the flow path diameter dimension d<NUM>, and the flow path cross-sectional shape of the protruding flow path <NUM> is a circular shape having the flow path diameter dimension d<NUM>. However, the flow path cross-sectional shapes of the warming flow path <NUM> and the protruding flow path <NUM> are not limited to circular shapes. That is, when the flow path cross-sectional shapes of the warming flow path <NUM> and the protruding flow path <NUM> are other than the circular shape, the respective flow path cross-sectional shapes can be made to correspond to the circular shape having the flow path diameter dimension d<NUM> and the flow path diameter dimension d<NUM>, and can be applied to the present example. Here, the diameter dimension for a case where the flow path cross-sectional shape is made to correspond to a circular shape is calculated, for example, on the assumption that the area of the circular shape to be corresponded and the area of the flow path cross-sectional shape are equivalent.

The material of the ink warming block <NUM> is made of a material that easily transfers heat, and is, for example, an aluminum alloy. For example, after the entire shape of the ink warming block <NUM> is molded with a mold, the inflow port <NUM>, the warming flow path <NUM>, the connection port <NUM>, the hole <NUM>, the connection end face <NUM>, and the like are provided by cutting. Unnecessary holes and the like generated by cutting are appropriately sealed.

The sheet heater <NUM> heats the ink warming block <NUM>. The sheet heater <NUM> has flexibility and is mainly disposed on a side surface of the ink warming block <NUM>. Specifically, according to <FIG>, the sheet heater <NUM> is disposed to include and cover the side surface in the Y+ direction of the ink warming block <NUM> so as to lie along the second warming path <NUM> from the end face in the X- direction to the end face in the X+ direction of the ink warming block <NUM>.

The sheet heater <NUM> is, for example, configured by covering heating wires with silicon rubber from both surfaces. The sheet heater <NUM> includes a temperature sensor. The sheet heater <NUM> can adjust the temperature by adjusting the supply voltage. The temperature sensor may be provided in the ink warming block <NUM>. A power output of the sheet heater <NUM> is, for example, <NUM> W. The set temperature of the sheet heater <NUM> is, for example, <NUM>.

As illustrated in <FIG>, the sealing member <NUM> seals and connects the ink warming block <NUM> and the protrusion <NUM>. The sealing member <NUM> is, for example, a ring shaped seal ring. The seal ring (sealing member) <NUM> is attached to the hole <NUM> of the ink warming block <NUM>. The outer diameter dimension of the seal ring <NUM> corresponds to the inner diameter dimension of the hole <NUM>. The inner diameter dimension of the seal ring <NUM> corresponds to the outer diameter dimension of the protrusion <NUM>.

When the conducting portion <NUM> is fixed to the ink warming block <NUM>, the seal ring <NUM> attached to the hole <NUM> is pressed and deformed by the end face <NUM>, and the position thereof is restricted with respect to the hole <NUM>. When the head <NUM> is attached to the carriage <NUM>, the distal end of the protrusion <NUM> penetrates the inner periphery of the seal ring <NUM> and is connected to the connection port <NUM>. At this time, the protrusion <NUM> presses the surface of the inner periphery of the seal ring <NUM> with the surface of the outer periphery of the protrusion <NUM>. The seal ring <NUM> deformed by the protrusion <NUM> closes a gap between the surface of the outer periphery of the distal end portion of the protrusion <NUM> and the hole <NUM>. In this manner, the protruding flow path <NUM> is connected to the warming flow path <NUM>.

As shown in <FIG>, the ink flow path portion <NUM> includes the ink storage unit <NUM>, the storage unit connecting unit <NUM>, the hose <NUM>, the pressure control unit <NUM>, and the ink warming block <NUM>.

As illustrated in <FIG>, the protrusion <NUM> is provided to protrude from a head <NUM> described later. The protrusion <NUM> has a protruding flow path <NUM> for guiding the ink to the head <NUM> therein. As illustrated in <FIG>, the protruding flow path <NUM> is connected to the warming flow path <NUM>. The protrusion <NUM> causes ink to flow from the ink flow path portion <NUM> to the head <NUM>.

The protrusion <NUM> has a tubular shape and has an outer peripheral surface and an inner peripheral surface. The flow path formed by the inner peripheral surface of the protrusion <NUM> is the protruding flow path <NUM>. The inner diameter dimension of the inner peripheral surface of the protruding flow path <NUM> is d<NUM>. The protrusion <NUM> is made of resin, and is manufactured by, for example, injection molding. The flow path cross-sectional area of the protruding flow path <NUM> is configured to be smaller than the flow path cross-sectional area of the warming flow path <NUM>. In the present example, a case where the protruding flow path <NUM> has a circular shape having the flow path diameter dimension d<NUM> will be described, but the protruding flow path <NUM> is not limited to a circular shape.

The head <NUM> ejects the ink fed from the protrusion <NUM> onto the print medium <NUM>. As illustrated in <FIG>, the head <NUM> internally includes a built-in heater <NUM>, a nozzle <NUM>, an ink chamber <NUM>, a substrate <NUM>, a heat insulating material <NUM>, a radiator <NUM>, a fan <NUM>, and a head cover <NUM>. The head <NUM> is disposed on the bottom surface of the carriage <NUM> so as to face the platen <NUM>.

The nozzle <NUM> is provided on a surface of the head <NUM> facing the platen <NUM>, and ejects ink. The nozzle <NUM> includes a plurality of arranged ejection holes (not illustrated), a piezoelectric element (not illustrated) that ejects ink from the ejection holes, a substrate <NUM> that controls the piezoelectric element, and a heat insulating material <NUM>. The heat insulating material <NUM> is disposed between the built-in heater <NUM> and the substrate <NUM>. The ejection of ink from the ejection hole of the nozzle <NUM> is controlled by the substrate <NUM> that controls the piezoelectric element. The substrate <NUM> includes a radiator <NUM> and a fan <NUM> on a surface opposite to a surface in contact with heat insulating material <NUM>. The built-in heater <NUM> is configured similarly to the sheet heater <NUM>. The set temperature of the built-in heater <NUM> is, for example, <NUM>.

The ink chamber <NUM> supplies the ink from the protrusion <NUM> to the entire surface of the nozzle <NUM>. The ink chamber <NUM> is provided between the nozzle <NUM> and the built-in heater <NUM>, and faces the surface of the nozzle <NUM>. That is, the surface of the ink chamber <NUM> in the Z+ direction is in contact with the built-in heater <NUM>, and the surface of the ink chamber <NUM> in the Z- direction is in contact with the nozzle <NUM>. In the ink chamber <NUM>, the ink warmed by the built-in heater <NUM> is supplied to the nozzle <NUM>. The ink in the head <NUM> is heated by the built-in heater <NUM> to maintain a high fluidity state.

The conducting portion <NUM> heats the protrusion <NUM>. The conducting portion <NUM> is formed integrally with the ink warming block <NUM> so as to easily transfer heat from the ink warming block <NUM>. The conducting portion <NUM> of the present example is a member separate from the ink warming block <NUM>. As illustrated in <FIG>, the conducting portion <NUM> is disposed on the connection end face <NUM> of the ink warming block <NUM>. The material of the conducting portion <NUM> is made of a material that easily conducts heat, and is, for example, an aluminum alloy. The material of the conducting portion <NUM> may be made of the same material as the ink warming block <NUM>.

As illustrated in <FIG>, the conducting portion <NUM> has a cylindrical shape, and has an outer periphery <NUM> and an inner periphery <NUM> of the conducting portion <NUM>. The diameter dimension of the inner periphery <NUM> of the conducting portion <NUM> is the dimension corresponding to the outer diameter dimension of the protrusion <NUM> to be described later. The diameter dimension of the inner periphery <NUM> of the conducting portion <NUM> is the dimension corresponding to the outer diameter dimension of the protrusion <NUM>. The conducting portion <NUM> can adjacently surround the periphery of the protrusion <NUM>.

The end face <NUM> of the conducting portion <NUM> is precisely polished. The conducting portion <NUM> has an attachment hole (not illustrated), and is fastened and fixed to the ink warming block <NUM> from the lower side (Z-direction side) of the attachment hole with a screw. The conducting portion <NUM> may have a positioning structure with respect to the ink warming block <NUM>. The conducting portion <NUM> may have, for example, an inlay structure. Thus, the conducting portion <NUM> can be easily and conveniently positioned with respect to the ink warming block <NUM>.

Furthermore, in the present example, the case where the conducting portion <NUM> is a member separate from the ink warming block <NUM> has been described, but the configuration of the conducting portion <NUM> is not limited thereto. That is, the conducting portion <NUM> may be a part of the member of the ink warming block <NUM>. In this case as well, the conducting portion <NUM>, which is a part of the member of the ink warming block <NUM>, is arranged adjacent to the protrusion <NUM>. Furthermore, in this case, the conducting portion <NUM> may be disposed so as to adjacently surround the periphery of the protrusion <NUM>.

In the present example, the case where the conducting portion <NUM> has a cylindrical shape has been described, but the shape of the conducting portion <NUM> is not limited thereto. The conducting portion <NUM> may be disposed adjacent to the protrusion <NUM>. Here, "disposed adjacent to" means that the protrusion <NUM> is disposed adjacent to the conducting portion <NUM>, and a distance between the protrusion <NUM> and the conducting portion <NUM> is close to an extent that heat can be transferred between the protrusion <NUM> and the conducting portion <NUM>, and includes a contact state. The conducting portion <NUM> may be configured by a plurality of structural bodies.

According to <FIG>, the conducting portion <NUM> is disposed adjacent to the protrusion <NUM> between the ink warming block <NUM> and the carriage <NUM>, but the position where the conducting portion <NUM> is disposed is not limited thereto. The conducting portion <NUM> may be disposed adjacent to the protrusion <NUM> between the ink warming block <NUM> and the head <NUM>. Thus, the conducting portion <NUM> can heat the protrusion <NUM> at a longer distance. In this case, the carriage <NUM> has a hole having a diameter larger than the diameter of the outer periphery <NUM> of the conducting portion <NUM> through which the conducting portion <NUM> is disposed.

The head unit <NUM> is mounted on the carriage <NUM>. The carriage <NUM> may include a plurality of head units <NUM>. The carriage <NUM> is guided by the guide rail <NUM> over the entire width in the Y direction of the print medium <NUM> by the carriage driving unit <NUM>, and moves in the Y+ direction or the Y- direction. The carriage <NUM> includes a control unit (not illustrated) for controlling the sheet heater <NUM>, the built-in heater <NUM>, and the like to be described later, and a UV irradiator (not illustrated) for curing the ejected UV ink.

The carriage driving unit <NUM> moves the carriage <NUM> in the Y+ direction or the Y- direction, as described above. The carriage driving unit <NUM> can adjust the moving speed of the carriage <NUM> and stop the carriage <NUM> with high stop position accuracy. The carriage driving unit <NUM> includes, for example, a belt and pulley mechanism (not illustrated) and a motor.

The print medium <NUM> is placed on the platen <NUM>. The platen <NUM> includes a feed roller <NUM> for feeding the print medium <NUM> in the feeding direction (X+ direction). The platen <NUM> performs a so-called intermittent operation of feeding the print medium <NUM> by a certain length in the feeding direction (X+ direction) in correspondence with the printing operation.

The print medium <NUM> is placed on the platen <NUM>, as illustrated in <FIG>. The print medium <NUM> is set in the printer <NUM> in a state of being wound in a roll form, and is drawn out in correspondence with a printing operation and placed on the platen <NUM>. The material of the print medium <NUM> is, for example, paper, fabric, resin film, or the like. The print medium <NUM> may be configured to be set in a state of a unit with respect to the printer <NUM> and supplied in correspondence with the printing operation.

Hereinafter, a mechanism in which the heat from the ink warming block <NUM> heats the ink via the conducting portion <NUM> and the protrusion <NUM> will be described. First, the heat from the ink warming block <NUM> heated by the sheet heater <NUM> is transferred to the conducting portion <NUM> through a contact portion between the connection end face <NUM> and the end face <NUM> of the conducting portion <NUM>. The heat transferred from the ink warming block <NUM> to the end face <NUM> spreads into the conducting portion <NUM> by heat conduction, whereby the temperature of the conducting portion <NUM> rises.

The heat is transferred to the protrusion <NUM> by the conducting portion <NUM> disposed adjacent to the protrusion. The transfer of heat from the conducting portion <NUM> to the protrusion <NUM> is mainly performed by heat conduction through a contact portion between the inner periphery <NUM> of the conducting portion <NUM> and the outside of the protrusion <NUM>. When the inner periphery <NUM> of the conducting portion <NUM> and the outside of the protrusion <NUM> do not come into contact with each other, heat transfer from the conducting portion <NUM> to the protrusion <NUM> is mainly performed by heat transfer or heat radiation from the inner periphery <NUM> of the conducting portion <NUM> to the outside of the protrusion <NUM>.

In the heat transfer from the protrusion <NUM> to the ink flowing through the protruding flow path <NUM>, first, the heat transferred from the conducting portion <NUM> to the protrusion <NUM> is heat conducted in the protrusion <NUM>, so that the temperature of the protrusion <NUM> rises. Thereafter, heat is transferred from the wall surface of the protruding flow path <NUM> whose temperature has raised to the ink flowing through the protruding flow path <NUM>. The heat transfer from the wall surface of the protruding flow path <NUM> to the ink flowing through the protruding flow path <NUM> is carried out by heat conduction. In this manner, the heat of the ink warming block <NUM> is transferred to the protruding flow path <NUM> through the conducting portion <NUM> and the protrusion <NUM> to heat the ink flowing through the protruding flow path <NUM>.

Hereinafter, the relationship between the protruding flow path <NUM> and the warming flow path <NUM> will be described with reference to <FIG>. Here, the density of the ink in the flow path from the ink flow path portion <NUM> to the head <NUM> can be regarded as constant. Furthermore, the flow rate of the ink in the flow path from the ink flow path portion <NUM> to the head <NUM> is constant. Therefore, in the flow path having a small flow path cross-sectional area, the flow velocity of the flowing ink becomes faster than in the flow path having a large flow path cross-sectional area. In this case, as shown in <FIG>, when the flow velocity of the ink flow in the warming flow path <NUM> is v<NUM> and the flow velocity of the ink flow in the protruding flow path <NUM> is v<NUM>, the following equation (<NUM>) is given.

The flow path cross-sectional area will be specifically described with reference to <FIG>. As illustrated in <FIG> and <FIG>, the flow path diameter dimension d<NUM> of the protruding flow path <NUM> is smaller than the flow path diameter dimension d<NUM> of the warming flow path <NUM>. That is, the flow path cross-sectional area A<NUM> of the protruding flow path <NUM> is smaller than the flow path cross-sectional area A<NUM> of the warming flow path <NUM>. In the warming flow path <NUM>, when the flow path diameter dimension d<NUM> is ϕ <NUM>, the flow path cross-sectional area A<NUM> of the warming flow path <NUM> becomes about <NUM><NUM>. In the protruding flow path <NUM>, when the flow path diameter dimension d<NUM> is ϕ <NUM>, the flow path cross-sectional area A<NUM> becomes about <NUM><NUM>.

In this case, when the flow path cross-sectional area A<NUM> of the warming flow path <NUM> and the flow path cross-sectional area A<NUM> of the protruding flow path <NUM> are substituted into Equation (<NUM>) to obtain the flow velocity v<NUM> of the ink in the protruding flow path <NUM>, the flow velocity v<NUM> is about <NUM> times the flow velocity v<NUM> of the ink flow in the warming flow path <NUM>. In this manner, the fluidity can be increased in the protruding flow path <NUM> than in the warming flow path <NUM> by making the flow path cross-sectional area A<NUM> of the protruding flow path <NUM> smaller than the flow path cross-sectional area A<NUM> of the warming flow path <NUM>.

From another point of view, when the flow path cross-sectional area A<NUM> of the protruding flow path <NUM> is made smaller than the flow path cross-sectional area A<NUM> of the warming flow path <NUM>, the time during which the ink stays in the protruding flow path <NUM> becomes shorter than the time during which the ink stays in the warming flow path <NUM>. Therefore, the time during which the heat energy is transferred between the protrusion <NUM> and the ink flowing through the protruding flow path <NUM> is shorter than the time during which the heat energy is transferred between the warming flow path <NUM> and the ink flowing through the warming flow path <NUM>.

This case will be specifically described. When the temperature T<NUM> of the ink flowing through the protruding flow path <NUM> is higher than the temperature T<NUM> of the warming flow path <NUM> and the protruding flow path <NUM>, the heat energy of the ink flowing through the protruding flow path <NUM> is transferred to the protrusion <NUM>. In the present example, the flow path diameter dimension d<NUM> of the protruding flow path <NUM> is smaller than the flow path diameter dimension d<NUM> of the warming flow path <NUM>. Therefore, the flow velocity v<NUM> of the ink flowing through the protruding flow path <NUM> is faster than the flow velocity v<NUM> of the ink flowing through the warming flow path <NUM>. As a result, the time during which the ink stays in the protruding flow path <NUM> is shortened, and the amount of heat energy released from the ink passing through the protruding flow path <NUM> is suppressed. The increase in ink viscosity is suppressed by reducing the decrease in the ink temperature in the protruding flow path <NUM>, and the fluidity of the ink is maintained.

When the temperature T<NUM> of the ink flowing through the protruding flow path <NUM> is lower than the temperature T<NUM> of the protruding flow path <NUM>, the ink flowing through the protruding flow path <NUM> receives the heat energy from the protruding flow path <NUM>. Thus, the viscosity of the ink in the protrusion <NUM> can be lowered, and the fluidity can be improved.

In addition, when a heat transfer area in which the ink per unit volume V in the warming flow path <NUM> receives heat energy from the wall surface of the warming flow path <NUM> is R<NUM>, and a heat transfer area in which the ink per unit volume V in the protruding flow path <NUM> receives heat energy from the wall surface of the protruding flow path <NUM> is R<NUM>, Equation (<NUM>) is obtained. Here, when the height (length in the Z direction) of the ink per unit volume V in the warming flow path <NUM> is L<NUM> and the height (length in the Z direction) of the ink per unit volume V in the protruding flow path <NUM> is L<NUM>, the heat transfer area R<NUM> is πd<NUM>L<NUM> and the heat transfer area R<NUM> is πd<NUM>L<NUM>.

In other words, the heat transfer area R<NUM> in which the ink per unit volume V in the protruding flow path <NUM> receives heat energy from the wall surface of the protruding flow path <NUM> becomes larger than the heat transfer area R<NUM> in which the ink receives heat energy from the wall surface of the warming flow path <NUM>. Thus, the ink is more efficiently heated by the warming flow path <NUM> in the protruding flow path <NUM>.

Here, since the flow path diameter dimension d<NUM> of the protruding flow path <NUM> is configured to be smaller than the flow path diameter dimension d<NUM> of the warming flow path <NUM>, the temperature T<NUM> of the protruding flow path <NUM> is higher than the temperature T<NUM> of the ink flowing through the protrusion <NUM> in the protrusion <NUM> disposed adjacent to the conducting portion <NUM> to where the heat is transferred from the ink warming block <NUM>. Therefore, the ink can be efficiently heated in the protruding flow path <NUM>.

Next, the shape of the protruding flow path <NUM> will be described. In <FIG>, the shape of the protruding flow path <NUM> is represented by the same flow path diameter dimension d<NUM> over the entire length of the protrusion <NUM>, but this is not the sole case. The flow path diameter dimension of the protrusion <NUM> merely needs to be smaller than the flow path diameter dimension d<NUM> of the warming flow path <NUM> in at least a part of the entire length of the protrusion <NUM>. As a result, the flow velocity of the ink flowing through the protruding flow path <NUM> becomes faster than the flow velocity of the ink in the warming flow path <NUM>, and hence the fluidity of the ink can be improved.

Furthermore, as shown in <FIG>, for example, the shape of the protruding flow path <NUM> of the protrusion <NUM> may include a portion having a flow path diameter dimension d<NUM> in an orifice form at a portion facing the connection end face <NUM> of the protrusion <NUM>, and the other portion may be configured to have the same flow path diameter dimension as the flow path diameter dimension d<NUM> of the warming flow path <NUM>. In addition, the protrusion <NUM> has the flow path diameter dimension d<NUM> in the surface of the protrusion <NUM> in contact with the connection end face <NUM>, and may change, for example, by uniformly expanding from the flow path diameter dimension d<NUM> to the same diameter dimension as the flow path diameter dimension d<NUM> of the warming flow path <NUM> in the entire length. Furthermore, the flow path diameter dimension of the protrusion <NUM> is d<NUM> in the surface of the protrusion <NUM> in contact with the connection end face <NUM>, and may change, for example, by expanding in a stepwise manner from the flow path diameter dimension d<NUM> to the same dimension as the flow path diameter dimension d<NUM> of the warming flow path <NUM> in the entire length.

A method for assembling the head unit <NUM> of the printer <NUM> according to the present invention will be described. The head <NUM> is assembled to the ink warming block <NUM> attached to the carriage <NUM>. That is, the sealing member <NUM> is arranged in the hole <NUM> of the ink warming block <NUM>, and the sealing member <NUM> is positioned by fixing the conducting portion <NUM> to the ink warming block <NUM>. Thereafter, the protrusion <NUM> of the head <NUM> is attached from below. The protrusion <NUM> penetrates an opening provided in the carriage <NUM> and an inner periphery of the conducting portion <NUM>, and is connected to the connection port <NUM> of the ink warming block <NUM>. Here, the seal surface at the distal end of the protrusion <NUM> is sealed by pressing the inner periphery of the sealing member <NUM>. Thereafter, the head <NUM> is fixed to the carriage <NUM>.

The sealing member <NUM> may be attached to the distal end portion of the protrusion <NUM> instead of the ink warming block <NUM>. In this case, the conducting portion <NUM> is configured separately from the ink warming block <NUM>. The sealing member <NUM> is attached to a distal end portion of the protrusion <NUM> where the conducting portion <NUM> is adjacently arranged in advance. That is, the conducting portion <NUM> is located between the sealing member <NUM> and the head <NUM> with respect to the protrusion <NUM>. Thereafter, the protrusion <NUM> including the conducting portion <NUM> and the sealing member <NUM> is attached to the ink warming block <NUM>.

An embodiment according to the present invention will be described in detail below based on the drawings. It should be noted that the present invention is not to be limited by the embodiment. Furthermore, the constituent elements in the following embodiment include those that can be easily replaced by those skilled in the art, or those that are substantially the same. Moreover, the constituent elements described below can be appropriately combined, and when there are a plurality of embodiments, it is also possible to combine the respective embodiments.

An inkjet printer <NUM> (hereinafter also simply referred to as printer <NUM>) according to the present embodiment is a device that prints an image on a medium <NUM> serving as a recording medium through an inkjet method. As the medium <NUM>, for example, an impermeable medium that uses metal, resin, and the like which is impermeable to ink, and a permeable medium that uses fabric, paper and the like which is permeable to ink can be applied, and any material can be applied as long as it is a medium <NUM> on which an image can be formed. Furthermore, as the ink, for example, an ultraviolet-curable ink (UV ink) that cures by irradiation of ultraviolet light may be used. The UV ink of the present embodiment is an ink having a high viscosity in a temperature range of normal temperature (e.g., <NUM> to <NUM>). Next, the printer <NUM> will be described with reference to <FIG>.

<FIG> is a perspective view of an inkjet printer according to the present embodiment. <FIG> is a schematic view schematically showing a configuration around an inkjet head. <FIG> is a plan view showing an inflow port side of the inkjet head. <FIG> is a plan view showing a nozzle surface side of the inkjet head. <FIG> is an explanatory view illustrating an ejection frequency of ink in a nozzle row.

As shown in <FIG> and <FIG>, the printer <NUM> includes an inkjet head <NUM> (hereinafter also simply referred to as the head <NUM>), a carriage <NUM>, a platen <NUM>, a warming block <NUM>, a pressure adjustment unit <NUM>, a carriage driving unit <NUM>, a guide rail <NUM>, an ink tank <NUM>, and a control unit <NUM>. In <FIG> and <FIG>, the X direction is a direction in which the medium <NUM> is conveyed, and is a sub scanning direction. The Y direction is a direction in which the inkjet head <NUM> is moved, and is the main scanning direction. The Z direction is a direction orthogonal to the main scanning direction and the sub scanning direction, and is, for example, a vertical direction when a plane including the main scanning direction and the sub scanning direction is a horizontal plane.

The head <NUM> is provided on the carriage <NUM>, and ejects the UV ink toward the medium <NUM>. The head <NUM> has a nozzle row 921a including a plurality of nozzles <NUM> arranged in the X direction (sub scanning direction). Furthermore, a plurality of nozzle rows 921a are provided according to the type of color to use in the head <NUM>, and for example, the nozzle rows 921a for four colors of C, M, Y, and K are arranged side by side in the Y direction. Two (a pair of) heads <NUM> are provided on the carriage <NUM>. The two nozzle rows 921a of the two heads <NUM> are formed as long nozzle rows 921a continuous in the X direction by aligning the end portions in the X direction when viewed from the Y direction (main scanning direction).

The platen <NUM> is provided to face the head <NUM> in the Z direction. The medium <NUM> is placed on the platen <NUM>. The platen <NUM> heats the medium <NUM> placed thereon and heats the ink ejected on the medium <NUM> through the medium <NUM> to promote drying of the ink.

The carriage <NUM> includes a warming block <NUM> and a pressure adjustment unit <NUM> in addition to the head <NUM>. The carriage driving unit <NUM> moves the carriage <NUM> along the guide rail <NUM>. The guide rail <NUM> is provided to extend in the Y direction, and the carriage driving unit <NUM> moves the carriage <NUM> along the Y direction. At this time, the carriage <NUM> moved by the carriage driving unit <NUM> integrally moves the head <NUM>, the warming block <NUM>, and the pressure adjustment unit <NUM>. The head <NUM>, the warming block <NUM>, and the pressure adjustment unit <NUM> are integrally configured as a head unit <NUM>.

The warming block <NUM> is provided on the upstream side of the head <NUM> in the flow direction of the ink. The warming block <NUM> heats and warms the UV ink supplied to the head <NUM> to lower the viscosity of the ink supplied to the head <NUM>.

Ink is supplied to the pressure adjustment unit <NUM> from the ink tank <NUM> through the ink supply line <NUM>. The ink tank <NUM> is disposed above the pressure adjustment unit <NUM>, and ink is supplied to the pressure adjustment unit <NUM> by a water head difference. The pressure adjustment unit <NUM> adjusts the pressure of the ink supplied to the warming block <NUM>. The pressure adjustment unit <NUM> is, for example, a mechanical pressure damper configured similarly to the pressurization damper disclosed in <CIT>. Specifically, the pressure adjustment unit <NUM> adjusts the pressure of the ink so that the ink chamber formed inside the head <NUM> has a negative pressure.

The control unit <NUM> is connected to the head <NUM>, the warming block <NUM>, and the carriage driving unit <NUM>. The control unit <NUM> includes, for example, an integrated circuit such as a central processing unit (CPU). The control unit <NUM> performs ink ejection control by the head <NUM>, performs ink warming control by the warming block <NUM>, and performs movement control of the head <NUM> in the main scanning direction by the carriage driving unit <NUM>.

In the inkjet printer <NUM> described above, the ink first flows out from the ink tank <NUM> to the ink supply line <NUM>, and flows into the pressure adjustment unit <NUM> through the ink supply line <NUM>. The ink whose pressure has been adjusted by the pressure adjustment unit <NUM> is supplied to the warming block <NUM>. The ink is warmed in the warming block <NUM> to lower the viscosity, and then supplied toward the head <NUM>. Then, the head <NUM> ejects the ink toward the medium <NUM> while moving in the Y direction.

Next, the periphery of the inkjet head <NUM> will be described with reference to <FIG> and <FIG>. As described above, two inkjet heads <NUM> are mounted on the carriage <NUM>, and attached to the base plate <NUM>. As shown in <FIG> and <FIG>, the two heads <NUM> are arranged side by side with a predetermined gap in the main scanning direction with respect to the base plate <NUM>. Furthermore, the two heads <NUM> are arranged at different positions in the sub scanning direction such that the two nozzle rows 921a are arranged in the sub scanning direction when viewed from the main scanning direction. The end portions of the two nozzle rows 921a arranged in the sub scanning direction overlap each other when viewed from the main scanning direction.

Each head <NUM> includes a nozzle row 921a consisting of a plurality of nozzles <NUM>, an ink supply port <NUM>, and an ink warming heater <NUM>. The ink warmed by the warming block <NUM> flows into the ink supply port <NUM>. The ink supply port <NUM> is provided on one side in the sub scanning direction with respect to the nozzle row 921a. A plurality of ink supply ports <NUM> are provided according to the type of color to use, and for example, the ink supply ports <NUM> for four colors of C, M, Y, and K are arranged side by side in the Y direction.

The ink warming heater <NUM> warms the ink inside the head <NUM>. The ink warming heater <NUM> warms the ink flowing inside the head <NUM> to lower the viscosity of the ink.

Here, since the ink supply port <NUM> is provided on one side in the sub scanning direction with respect to the nozzle row 921a, in the nozzle row 921a, one side in the sub scanning direction become a side closer to the ink supply port <NUM>, and the other side in the sub scanning direction becomes a side farther from the ink supply port <NUM>. That is, the nozzle <NUM> on the side closer to the ink supply port <NUM> has a short flow path length from the ink supply port <NUM>, and the nozzle <NUM> on the side farther from the ink supply port <NUM> has a long flow path length from the ink supply port <NUM>. In the case of such head <NUM>, since the nozzle <NUM> on the side closer to the ink supply port <NUM> has a short flow path length, the warming of ink becomes insufficient immediately after the ejection of ink, and the ejection speed of the ink varies as compared with the nozzle <NUM> on the side farther from the ink supply port <NUM>.

As shown in <FIG>, the two heads <NUM> are arranged side by side with a predetermined interval in the main scanning direction. Furthermore, the two heads <NUM> are arranged such that each of the ink supply ports <NUM> is located on the outer side in the sub scanning direction. That is, the ink supply port <NUM> of each head <NUM> are arranged so as to be located on both end sides in the sub scanning direction with respect to the two nozzle rows 921a continuous in the sub scanning direction. That is, the two heads <NUM> are arranged adjacent to each other in the sub scanning direction so that the end portions on the other side (side farther from the ink supply port <NUM>) of the nozzle row 921a are proximate to each other. That is, when two heads <NUM> perform the printing operation on the medium <NUM> at the same time, the other end portions of the two heads <NUM> are proximate to each other so that the nozzle row 921a of each of the two heads <NUM> can be regarded as a continuous nozzle row. Therefore, among the two nozzle rows 921a arranged in the sub scanning direction, one nozzle row 921a becomes the nozzle <NUM> on the side of the other nozzle row 921a, and on the side farther from the ink supply port <NUM>. Similarly, among the two nozzle rows 921a arranged in the sub scanning direction, the other nozzle row 921a becomes the nozzle <NUM> on the side of the one nozzle row 921a, and on the side farther from the ink supply port <NUM>. In the two nozzle rows 921a, the nozzles <NUM> on the side farther from the ink supply port <NUM> are aligned in the sub scanning direction, and thus the nozzles <NUM> having a small variation in the ink ejection speed are aligned.

Furthermore, as illustrated in <FIG> and <FIG>, the two heads <NUM> have the same structure, and are arranged point-symmetrically with phases differed by <NUM> degrees about the symmetry point P in a plane including the X direction and the Y direction. That is, one head <NUM> is at a position rotated by <NUM> degrees about the symmetry point P with respect to the other head <NUM> in a plane including the X direction and the Y direction. For this reason, the nozzle rows 921a for the four colors of C, M, Y, and K in the two heads <NUM> are also arranged point-symmetrically with the phase differed by <NUM> degrees about the symmetry point P.

Next, ink ejection control by the control unit <NUM> will be described with reference to <FIG>. The control unit <NUM> performs printing through a multi-pass method of performing a plurality of main scans for a plurality of print passes with respect to each position of the medium <NUM>. The main scan is an operation of ejecting ink droplets onto the medium <NUM> while moving the head <NUM> in the main scanning direction.

Specifically, the printer <NUM> performs printing through, for example, a multi-pass method in which the pass number of printing is N (N is an integer of two or more). The pass number N of printing is, for example, four or more, preferably eight or more. Furthermore, in this case, the nozzles <NUM> in the nozzle row 921a of each head <NUM> are assigned according to the respective print pass of the first pass to the Nth pass.

For example, when the print pass number is N, the nozzle row 921a is divided into N regions in which the plurality of nozzles <NUM> arranged in the sub scanning direction is the same in number. Then, the respective print passes of the first pass to Nth passes are assigned to the nozzle row 921a divided into the N regions in order from the region that overlaps the medium <NUM> first in accordance with the conveyance of the medium <NUM> in the sub scan. Here, the sub scan is an operation of conveying the medium <NUM> in the sub scanning direction with respect to the head <NUM>. Then, the control unit <NUM> sets the movement amount in one sub scan to a pass width, which is the width (width in the sub scanning direction) of the arrangement of the nozzles <NUM> for one print pass. The pass width is a width in the sub scanning direction of each of the regions divided into N. The control unit <NUM> causes the head <NUM> to perform the sub scan between the main scans by the head <NUM>. As a result, every time each main scan is performed, the control unit <NUM> shifts the region of the medium <NUM> facing the head <NUM> by the pass width in the sub scanning direction. In each main scan, the nozzles <NUM> in each region in the nozzle row 921a perform printing for the corresponding print pass.

Furthermore, in the control of printing corresponding to each print pass, the control unit <NUM> selects the pixel to which the ink droplet is to be ejected. More specifically, for example, the control unit <NUM> uses mask data, which is data designating a pixel to which an ink droplet is to be ejected, in each of a plurality of print passes performed for each position of the medium <NUM>, and causes each head <NUM> to eject the ink droplet to the pixel designated by the mask data. As described above, the control unit <NUM> performs printing through the multi-pass method using the mask data. That is, the control unit <NUM> uses the mask data to control the ejection frequency of the ink ejected from the nozzle row 921a of the head <NUM> as the ejection control of the head <NUM> at the time of executing the main scan. The control unit <NUM> controls the ejection frequency of the ink to suppress the occurrence of bounding formed in the main scanning direction, and form an image having a smooth gradation. As such control of the ejection frequency of ink, Mimaki Advanced Pass System (MAPS) is known.

Here, when performing printing through the multi-pass method using the two heads <NUM>, the mask data used for each of the plurality of print passes is, for example, a pattern shown in <FIG>. The mask data shown in <FIG> is mask data of a pattern in which the nozzle usage frequency continuously changes in the sub scanning direction, in other words, a pattern in which the concentration of the ink ejected to the medium <NUM> continuously changes.

In the mask data shown in <FIG>, the nozzle usage frequency (concentration) at the center in the sub scanning direction is set higher than the nozzle usage frequencies on both sides with respect to the entire length of the two nozzle rows 921a arranged in the sub scanning direction. In other words, in the mask data shown in <FIG>, the nozzle usage frequency on the other end portion side (side farther from the ink supply port <NUM>) proximate to each other of the nozzle rows 921a of the two heads <NUM> becomes high, and the nozzle usage frequency on one end portion side (side closer to the ink supply port <NUM>) of the nozzle row 921a becomes low. The ejection frequency of the ink controlled using the mask data shown in <FIG> is a triangular pattern in which the nozzle usage frequency at the center in the sub scanning direction is set to the maximum (apex) and the nozzle usage frequency at both ends in the sub scanning direction is set to zero in the entire length of the nozzle row 921a, and the frequency decreases constantly from the center toward both sides in the sub scanning direction. The triangular pattern may have a trapezoidal shape. The pattern shape of the nozzle usage frequency may be any shape as long as the nozzle usage frequency at the center in the sub scanning direction is higher than the nozzle usage frequency on both sides in the sub scanning direction.

In the present embodiment, the ink ejection control is performed using the mask data described above, and hence the nozzle <NUM> having a high nozzle usage frequency becomes the nozzle on the side farther from the ink supply port <NUM>, and the nozzle <NUM> having a low nozzle usage frequency becomes the nozzle <NUM> on the side closer to the ink supply port <NUM>. Therefore, the nozzle <NUM> having a high nozzle usage frequency is the nozzle <NUM> having a small variation in the ink ejection speed, and the nozzle <NUM> having a low nozzle usage frequency is the nozzle <NUM> having a large variation in the ink ejection speed.

As described above, according to the present embodiment, the nozzles <NUM> on the side farther from the ink supply port <NUM> can be combined in the two nozzle rows 921a arranged in the sub scanning direction. That is, the nozzles <NUM> on the side where the variation in the ejection speed of the ink is small and the ejection stability of the ink is high may be combined so as to be continuous or overlap in the sub scanning direction. Therefore, streaks due to shading, that is, banding can be made less likely to occur, and the image quality of the medium <NUM> can be improved.

Furthermore, according to the present embodiment, since the ink to be supplied to the ink supply port <NUM> of the head <NUM> can be warmed by the warming block <NUM>, the unevenness of the ink temperature in the head <NUM> is suppressed.

According to the present embodiment, printing can be performed on the medium <NUM> by a long nozzle row in which the two nozzle rows 921a are continuous by using the two heads <NUM>.

Furthermore, according to the present embodiment, the nozzle <NUM> having a high nozzle usage frequency can be the nozzle <NUM> having a small variation in the ink ejection speed. Therefore, the usage frequency of the nozzle <NUM> having high ink ejection stability can be increased, and on the other hand, the usage frequency of the nozzle <NUM> having low ink ejection stability can be reduced, so that the ink can be stably ejected onto the medium <NUM>.

Furthermore, according to the present embodiment, since the two heads <NUM> can have the same structure by arranging the two heads <NUM> point-symmetrically, an increase in device cost can be suppressed.

In addition, according to the present embodiment, even when using the UV ink, the image quality on the medium <NUM> can be improved.

Claim 1:
An inkjet printer (<NUM>) comprising:
an inkjet head (<NUM>) configured to eject ink;
an ink warming block (<NUM>) that includes an ink flow path portion (<NUM>) and that is configured to heat the ink inside the ink flow path portion (<NUM>),
a pressure control unit (<NUM>) configured to supply ink from an ink storage unit (<NUM>) to the ink warming block (<NUM>) while adjusting the flow rate of the ink, the pressure control unit (<NUM>) being arranged above the ink warming block (<NUM>), so that the ink is guided from the ink storage unit (<NUM>) to the pressure control unit (<NUM>) by the water head difference (h) between the height of the liquid level of the ink in the ink storage unit (<NUM>) and the height of the liquid level of the ink at the inlet of the pressure control unit (<NUM>); and
a protrusion (<NUM>) that protrudes from the inkjet head (<NUM>) and is configured to guide the ink to the inkjet head (<NUM>) through a protruding flow path (<NUM>) that is formed in the protrusion (<NUM>);
wherein the ink flow path portion (<NUM>) is configured to supply the ink to the protruding flow path (<NUM>) of the protrusion (<NUM>); and
a conducting portion (<NUM>) that is formed in the ink warming block (<NUM>) itself or separately from the ink warming block (<NUM>) and through which heat from the ink warming block (<NUM>) is conducted is disposed outside of and adjacently to the protrusion (<NUM>), the conducting portion (<NUM>) being configured to heat the protrusion (<NUM>) with the conducted heat.