Patent Description:
The following technology is known as technology of controlling prevention of drying of an ink adhering to a nozzle of an ink jet head and condensation of a jetting surface in an ink jet printing device. For example, <CIT> discloses a liquid droplet jetting device comprising a jet head that jets liquid droplets of a jetting liquid from a nozzle disposed on a jetting surface, a jetting liquid tank that stores the jetting liquid, a circulation unit that circulates the jetting liquid between the jetting liquid tank and the jet head, a temperature adjustment unit that adjusts a temperature of the jetting liquid, a controller that sets the temperature of the jetting liquid adjusted by the temperature adjustment unit to a first temperature, a moisturizing cap that stores a cap liquid and covers the jetting surface to form a moisturizing space between the moisturizing cap and the jetting surface, a storage unit that stores a first relationship between the temperature of the jetting liquid and a temperature of the cap liquid for allowing humidity of the moisturizing space to be humidity at which drying of the nozzle and the condensation of the jetting surface are prevented, a temperature measurement unit that measures the temperature of the cap liquid, and a determination unit that determines whether or not the measured temperature of the cap liquid and the first temperature of the jetting liquid satisfy the first relationship, in which, in a case in which the determination unit determines that the first relationship is not satisfied, the controller sets the temperature of the jetting liquid to a second temperature at which the first relationship is satisfied in the measured temperature of the cap liquid.

On the other hand, <CIT> discloses a printing device comprising an ink jet head that jets an ink, a wiping member that wipes the inkjet head, an ink storage unit that stores the ink supplied to the ink jet head, an ink circulation flow passage that includes a circulation sending flow passage through which the ink supplied from the ink storage unit to the ink jet head flows, and a circulation return flow passage through which the ink returning from the ink jet head to the ink storage unit flows, a circulation unit that circulates the ink in the ink circulation flow passage, and a first pressurization unit that pressurizes an inside of the ink storage unit to a first pressure higher than a pressure in the ink storage unit during a printing operation of jetting the ink to a printing medium by the inkjet head in a case of wiping in which the wiping member wipes the ink jet head, in which an operation of the circulation unit is stopped in a case of the wiping.

<CIT> describes a recording head cleaning device including a cleaning liquid holding unit, a cleaning liquid applying portion that applies a cleaning liquid to a cleaning liquid holding surface and a cleaning unit that cleans a nozzle surface of a recording head, in which a nozzle for jetting ink is disposed. A back pressure control unit sets a back pressure of the nozzle in a case of cleaning the nozzle surface to -<NUM> pascals to -<NUM> pascals.

<CIT> discloses a recording head cleaning device wherein the pressure inside the head and of the interior of the cap are controlled.

In a case in which an ink jet printing device is stopped, the ink circulation in an ink jet head is stopped. In a case in which the ink circulation is stopped, an ink adhering to the vicinity of an ink outlet (hereinafter referred to as outlet) of the inkjet head tends to dry, in a period in which the ink circulation is stopped (hereinafter, referred to as ink circulation stop period), an ink jetting surface (hereinafter, referred to as jetting surface) of the inkjet head is covered with a cap to suppress drying of the ink adhering to the vicinity of the outlet.

However, by moisturizing the jetting surface of the ink jet head with the cap for a long time, ink dripping from the outlet occurs. Ink dripping occurs due to the ink in the vicinity of the outlet absorbing moisture in the air and the meniscus of the ink formed in the vicinity of the outlet swelling to the outside of the ink jet head, or the ink in the vicinity of the outlet binding to water droplets adhering to the jetting surface of the ink jet head due to the condensation. Even in a case in which ink dripping on the jetting surface of the inkjet head is wiped by WetWeb built in the printing device in a case in which the printing device is operated, the ink cannot be completely absorbed, so that there is a problem, such as a jetting failure due to the ink left on the jetting surface or head modules adhering due to the ink being pushed into a gap between the head modules.

On the other hand, it is possible to suppress ink dripping by setting a back pressure of the inkjet head to a negative pressure during the ink circulation stop period. However, it is difficult to maintain a fixed back pressure of the ink jet head during the ink circulation stop period. That is, in a state in which the ink circulation is stopped, the back pressure of the ink jet head shifts to a positive pressure side with time. Therefore, as the ink circulation stop period is longer, a risk of the occurrence of ink dripping is higher. Therefore, in anticipation of the shift of the back pressure of the ink jet head to the positive pressure side with time and the condensation on the jetting surface of the inkjet head, it is also conceivable to set a set value of the back pressure at the start of the ink circulation stop period to the negative pressure having a sufficiently large absolute value. However, in a case in which a negative pressure level of the back pressure is excessively increased, the meniscus of the ink formed in the vicinity of the outlet of the inkjet head becomes a shape that is largely recessed inward the inkjet head, so that the ink in the vicinity of the outlet tends to dry. In addition, another problem arises in which the air bubbles easily enter from the outlet.

The invention is made in view of such circumstances, and is to provide a printing device and a back pressure control method in which ink dripping can be suppressed while suppressing drying of an ink and entering of air bubbles in an ink jet head during an ink circulation stop period. This technical object is achieved by the inventive printing device and back pressure control method as defined by the appended independent claims <NUM> and <NUM>.

An aspect of the invention relates to a printing device comprising an inkjet head that jets an ink from a jetting surface, an ink circulation flow passage through which the ink circulates, a moisturizing unit that moisturizes the jetting surface in an ink circulation stop period in which circulation of the ink in the ink circulation flow passage is stopped, a reception unit that receives a set input value of the ink circulation stop period, and a controller that controls a back pressure of the ink jet head at a start of the ink circulation stop period in accordance with the set input value of the ink circulation stop period received by the reception unit.

According to the inventive aspect, the controller controls a negative pressure level of the back pressure of the ink jet head at the start of the ink circulation stop period to be higher as the ink circulation stop period is longer. In addition, the controller may control the back pressure of the inkjet head at the start of the ink circulation stop period by using a table in which the ink circulation stop period and a set value of the back pressure of the ink jet head are associated with each other.

In addition, the controller may control the back pressure of the inkjet head at the start of the ink circulation stop period by using an expression representing a relationship between the ink circulation stop period and a set value of the back pressure of the inkjet head. In this case, in a case in which the ink circulation stop period is defined as X [h] and the set value of the back pressure of the inkjet head at the start of the ink circulation stop period is defined as Y [Pa], the expression may be Y = -<NUM> × X - <NUM> ± <NUM>.

The controller may control a negative pressure level of the back pressure of the ink jet head not to exceed a preset limit value.

The jetting surface of the ink jet head may be inclined with respect to a horizontal direction. The inkjet head may include a plurality of head modules, and the plurality of head modules may be arranged such that adjacent head modules have a gap therebetween. The printing device according to the disclosed technology may further comprise a wiping section that wipes the jetting surface by a wiping member.

The invention relates to a back pressure control method of an ink jet head of a printing device including the ink jet head that jets an ink from a jetting surface, an ink circulation flow passage through which the ink circulates, and a moisturizing unit that moisturizes the jetting surface in an ink circulation stop period in which circulation of the ink in the ink circulation flow passage is stopped, the method comprising receiving a set input value of the ink circulation stop period, an controlling a back pressure of the inkjet head at a start of the ink circulation stop period in accordance with the received set input value of the ink circulation stop period.

The invention provides the printing device and the back pressure control method in which ink dripping can be suppressed while suppressing drying of the ink and entering of air bubbles in the ink jet head during the ink circulation stop period.

In the following, an example of embodiments of the invention will be described with reference to the drawings. It should be noted that the same or equivalent components and portions in the respective drawings are represented by the same reference numerals, and the overlapping description will be omitted.

As a printing device according to an embodiment of the disclosed technology, an example applied to a printing device that jets liquid droplets of an ink to record an image on a recording medium. The term recording medium used in recording the image is a general term of various terms, such as paper, recording paper, printing paper, a printing medium, a printed medium, an image formation medium, an image-formed medium, an image reception medium, and a jetted medium. A material, a shape, and the like of the recording medium are not particularly limited, and various sheet bodies can be used, such as seal paper, a resin sheet, a film, cloth, and a non-woven fabric, regardless of the material or the shape thereof. The recording medium is not limited to a single-sheet medium, the recording medium may be a continuous medium, such as continuous paper, continuous-form paper, and a film for flexible packaging. The continuous medium may be stored in a roll shape.

<FIG> is a side view of a schematic configuration of an image recording unit of the printing device that records the image on single-sheet paper through a single-pass method according to the embodiment of the disclosed technology. As shown in <FIG>, an image recording unit <NUM> transports single-sheet paper <NUM> by an image recording drum <NUM>. In addition, the image recording unit <NUM> jets ink droplets of cyan (C), magenta (M), yellow (Y), and black (K) during a transport process by the image recording drum <NUM> from ink jet heads 16C, <NUM>, 16Y, and <NUM> arranged around the image recording drum <NUM>, respectively, to record a color image on a surface of the single-sheet paper <NUM>.

The image recording drum <NUM> has a rotation shaft <NUM>, and both end portions of the rotation shaft <NUM> are rotatably provided by being pivotally supported by a pair of bearings <NUM> (see <FIG>). The pair of bearings <NUM> is provided in a body frame <NUM> of the printing device, both end portions of the rotation shaft <NUM> are pivotally supported by the pair of bearings <NUM> to be parallel to a horizontal installation surface, and the image recording drum <NUM> is horizontally attached.

A motor (not shown) is connected to the rotation shaft <NUM> via a rotation transmission mechanism (not shown). The image recording drum <NUM> is driven by the motor (not shown) to be rotated.

The image recording drum <NUM> has a gripper <NUM> that grips a leading end portion of the single-sheet paper <NUM>. The gripper <NUM> is provided in two places on an outer circumferential surface of the image recording drum <NUM>, respectively. The leading end portion of the single-sheet paper <NUM> is gripped by the gripper <NUM>, and is transported along the outer circumferential surface of the image recording drum <NUM>.

The image recording drum <NUM> includes a suction holding mechanism (not shown), such as using electrostatic suction and vacuum suction. A rear surface of the single-sheet paper <NUM> of which a leading end portion is gripped by the gripper <NUM> and wound on the outer circumferential surface of the image recording drum <NUM> is sucked by the suction holding mechanism (not shown) and held on the outer circumferential surface of the image recording drum <NUM>.

It should be noted that the single-sheet paper <NUM> before image recording is transported from a transporting drum <NUM> to the image recording drum <NUM>. The transporting drum <NUM> is disposed to be juxtaposed with the image recording drum <NUM>, and transports the single-sheet paper <NUM> to the image recording drum <NUM> in accordance with a timing.

In addition, the single-sheet paper <NUM> after image recording is transported from the image recording drum <NUM> to a transporting drum <NUM>. The transporting drum <NUM> is disposed to be juxtaposed with the image recording drum <NUM>, and receives the single-sheet paper <NUM> from the image recording drum <NUM> in accordance with a timing.

The four inkjet heads 16C, <NUM>, 16Y, and <NUM> are line heads corresponding to a length of the single-sheet paper <NUM> in an X direction. The X direction is a direction along an axial direction of the rotation shaft <NUM>.

The ink jet heads 16C, <NUM>, 16Y, and <NUM> are attached to a head support frame <NUM>, and are disposed radially at fixed intervals on a concentric circle about the rotation shaft <NUM> of the image recording drum <NUM> and to be bilaterally symmetrical to each other with the image recording drum <NUM> interposed therebetween. That is, with respect to a vertical line segment passing through the center of the image recording drum <NUM>, the inkjet head 16C of cyan and the inkjet head <NUM> of black are disposed to be bilaterally symmetrical to each other and the inkjet head <NUM> of magenta and the ink jet head 16Y of yellow are disposed to be bilaterally symmetrical to each other.

The ink jet heads 16C, <NUM>, 16Y, and <NUM> have jetting surfaces 30C, <NUM>, 30Y, and <NUM>, each of which has an outlet <NUM> (see <FIG>) disposed in a bottom portion. The inkjet heads 16C, <NUM>, 16Y, and <NUM> are disposed to be orthogonal to a Y direction, which is a transport direction of the single-sheet paper <NUM>, and are disposed such that the jetting surfaces 30C, <NUM>, 30Y, and <NUM> face the outer circumferential surface of the image recording drum <NUM>. The inkjet heads 16C, <NUM>, 16Y, and <NUM> are disposed such that an interval between the outer circumferential surface of the image recording drum <NUM> and each of the jetting surfaces 30C, <NUM>, 30Y, and <NUM> is the same distance. The jetting surfaces 30C, <NUM>, 30Y, and <NUM> are disposed to face the outer circumferential surface of the image recording drum <NUM>, and are inclined with respect to a horizontal direction.

The inkjet heads 16C, <NUM>, 16Y, and <NUM> jet the ink droplets vertically toward the outer circumferential surface of the image recording drum <NUM> from the outlets <NUM> disposed in the jetting surfaces 30C, <NUM>, 30Y, and <NUM>.

<FIG> is a front view showing a schematic configuration of the image recording unit of the printing device. The head support frame <NUM> to which the inkjet heads 16C, <NUM>, 16Y, and <NUM> are attached is composed of a pair of side plates <NUM> and 42R provided to be orthogonal to the rotation shaft <NUM> of the image recording drum <NUM> and a connection frame <NUM> that connects upper end portions of the pair of side plates <NUM> and 42R to each other.

The pair of side plates <NUM> and 42R has a plate shape and is disposed to face each other with the image recording drum <NUM> interposed therebetween. On an inside of the pair of side plates <NUM> and 42R, attachment portions for attaching the ink jet heads 16C, <NUM>, 16Y, and <NUM> are provided. It should be noted that, for convenience, <FIG> shows only the attachment portion 46Y. In the following, in a case in which the distinction is not necessary or the general term is used, the attachment portions corresponding to the ink jet heads 16C, <NUM>, 16Y, and <NUM> are referred to as the attachment portion <NUM>.

The attachment portions <NUM> are disposed radially at fixed intervals on the concentric circle about the rotation shaft <NUM> of the image recording drum <NUM>. The inkjet heads 16C, <NUM>, 16Y, and <NUM> are attached to the head support frame <NUM> by fixing attached portions provided in both ends to the attachment portion <NUM>, respectively. It should be noted that, for convenience, <FIG> shows only the attached portion 48Y.

The head support frame <NUM> is guided by a guide rail (not shown), and is provided to be slidably movable along the axial direction of the rotation shaft <NUM> of the image recording drum <NUM>. The head support frame <NUM> is driven by a linear drive mechanism (not shown) (for example, feed screw mechanism and the like) to move at a predetermined movement speed between an "image recording position" shown by a solid line in <FIG> and a "maintenance position" shown by a broken line in <FIG>.

In a case in which the head support frame <NUM> is positioned at the image recording position, the ink jet heads 16C, <NUM>, 16Y, and <NUM> are disposed around the image recording drum <NUM>, and are in a state in which the image can be recorded.

The maintenance position is set to a position at which the inkjet heads 16C, <NUM>, 16Y, and <NUM> are retracted from the image recording drum <NUM>. A moisturizing unit <NUM> that moisturizes the inkjet heads 16C, <NUM>, 16Y, and <NUM> is provided at the maintenance position.

The moisturizing unit <NUM> comprises caps that cover the jetting surfaces 30C, <NUM>, 30Y, and <NUM> of <NUM> of the inkjet heads 16C, <NUM>, 16Y, and <NUM>, respectively. It should be noted that, for convenience, <FIG> shows only the cap 52Y. In the following, in a case in which the distinction is not necessary or the general term is used, the caps corresponding to the ink jet heads 16C, <NUM>, 16Y, and <NUM> are referred to as the cap <NUM>. A moisturizing liquid is stored in the cap <NUM>. In a case in which the printing device is stopped, the jetting surfaces 30C, <NUM>, 30Y, and <NUM> are covered with the cap <NUM> in which the moisturizing liquid is stored. As a result, it is possible to prevent non-jetting caused by drying of the outlets <NUM>.

It should be noted that the cap <NUM> comprises a pressurization mechanism and a suction mechanism (not shown), and can pressurize and suck the nozzles communicating the outlets <NUM>. In addition, the cap <NUM> comprises a cleaning liquid supply mechanism (not shown), and can supply a cleaning liquid to the inside.

A waste liquid tray <NUM> is disposed at a position below the cap <NUM>. The cleaning liquid supplied to the cap <NUM> is wasted to the waste liquid tray <NUM>, and is collected in a waste liquid tank <NUM> via a waste liquid collection pipe <NUM>.

A jetting surface cleaning device <NUM> that cleans the jetting surfaces 30C, <NUM>, 30Y, and <NUM> of the inkjet heads 16C, <NUM>, 16Y, and <NUM> is provided between the image recording position and the maintenance position. By moving the ink jet heads 16C, <NUM>, 16Y, and <NUM> between the maintenance position and the image recording position, the jetting surfaces 30C, <NUM>, 30Y, and <NUM> are cleaned by the jetting surface cleaning device <NUM>.

The inkjet heads 16C, <NUM>, 16Y, and <NUM> have the common configuration. In the following, in a case in which the distinction is not necessary or the general term is used, the ink jet heads 16C, <NUM>, 16Y, and <NUM> are referred to as the ink jet head <NUM>.

<FIG> is a perspective view of the inkjet head <NUM>. The ink jet head <NUM> is configured by connecting n head modules <NUM> (i = <NUM>, <NUM>,. n) to each other in the X direction. Here, an example is shown in which <NUM> (n = <NUM>) head modules <NUM> are arranged. A frame <NUM> functions as a frame for fixing the n head modules <NUM>. The head modules <NUM> are arranged such that adjacent head modules have a gap therebetween, and each of which is fixed to the frame <NUM> with the jetting surface <NUM> facing in a common direction. A structure of each of the head modules <NUM> is common.

A flexible substrate <NUM> is connected to each of the head modules <NUM>. A drive signal, a jetting control signal, and the like are supplied to each of the head modules <NUM> via the flexible substrates <NUM>.

<FIG> is an enlarged view of the ink jet head <NUM> as viewed from the jetting surface <NUM> side. As shown in <FIG>, a length of the ink jet head <NUM> in a direction orthogonal to the X direction, which is a Y direction along the jetting surface <NUM>, is Dh. The ink jet head <NUM> supports each of the head modules <NUM> from both sides in the Y direction by a head module holding member <NUM>. In addition, the inkjet head <NUM> supports a head module row consisting of the n head modules <NUM> from both sides in the X direction by a head protective member <NUM>.

<FIG> is a plan view showing an example of the jetting surface <NUM> of the head module <NUM>. The head module <NUM> has a parallel quadrilateral shape in a plan view, which has end surfaces on a long side along a V direction having an inclination of an angle γ with respect to the X direction and end surfaces on a short side along a W direction having an inclination of an angle α with respect to the Y direction. The outlets <NUM> are two-dimensionally arranged on the jetting surface <NUM>. The outlet <NUM> has a circular shape in an XY-plan view in the example shown in <FIG>, but may have a quadrangular shape or a polygonal shape.

An arrangement LN of the outlets <NUM> projected in the X direction is equivalent to an array in which the outlets <NUM> are arranged at equal intervals in the X direction at a density that achieves a desired recording resolution. A nozzle density of the head module <NUM> in the X direction is, for example, <NUM> dots per inch (dpi).

By connecting the n head modules <NUM> in the X direction (see <FIG>), in the inkjet head <NUM>, the outlets <NUM> are disposed over the entire length of the single-sheet paper <NUM> in the X direction. That is, the ink jet head <NUM> is a full-line type bar head capable of printing at a recording resolution of <NUM> dpi in one time of transporting of the single-sheet paper <NUM>.

The full-line type bar head applied to the single-pass method is not limited to a case in which the entire surface of the single-sheet paper <NUM> is set as a printing range, and the outlets need only be disposed in a range necessary for printing in a case in which a part of the single-sheet paper <NUM> is set as a printing region, such as a case in which a margin portion is provided around the single-sheet paper <NUM>.

The number of outlets <NUM> provided in the head module <NUM>, the density of the outlets <NUM>, and the arrangement form of the outlets <NUM> are not particularly limited. The present embodiment is particularly effective for the inkjet head having a resolution of <NUM> dpi or more.

The head module <NUM> comprises a plurality of ink chamber units <NUM> (see <FIG>) comprising a jetting energy generation element (for example, piezoelectric element or heat generation element), which generates jetting energy necessary for ink jetting, corresponding to each of the outlets <NUM>. The head module <NUM> jets the ink on demand in accordance with the drive signal and the jetting control signal which are supplied via the flexible substrate <NUM>.

<FIG> is a cross-sectional view showing an example of an internal structure of the ink chamber unit <NUM> provided in the head module <NUM>. The ink chamber unit <NUM> includes a nozzle plate <NUM> in which the outlet <NUM> is formed, and a flow passage plate <NUM> in which flow passages, such as a nozzle <NUM> communicating with the outlet <NUM>, a pressure chamber <NUM>, a supply port <NUM>, and a common flow passage <NUM> are formed.

The flow passage plate <NUM> is a flow passage forming member that configures a side wall portion of the outlet <NUM> and the pressure chamber <NUM> and forms the supply port <NUM> which is a narrowed portion (most constricted portion) of an individual supply passage through which the ink is introduced from the common flow passage <NUM> to the pressure chamber <NUM>. The flow passage plate <NUM> may be composed of one substrate, or may have a structure obtained by laminating a plurality of substrates. The nozzle plate <NUM> and the flow passage plate <NUM> can be processed into a required shape using a semiconductor manufacturing technology with silicon as a material.

The pressure chamber <NUM> of each of the plurality of ink chamber units <NUM> is connected to the common flow passage <NUM> via each of the supply ports <NUM>. In addition, the common flow passage <NUM> communicates with an ink supply port <NUM> and an ink collection port <NUM> (see <FIG>), which are provided in the inkjet head <NUM>, and the ink circulates by an ink circulation system <NUM> (see <FIG>).

A piezoelectric element <NUM> is provided for each pressure chamber <NUM> on a surface of a vibration plate <NUM> configuring a part of a surface (top surface in <FIG>) of the pressure chamber <NUM>. An individual electrode <NUM> for individually applying a voltage to a rolling element <NUM> for each pressure chamber <NUM> is provided on the surface of a piezoelectric element <NUM>. The vibration plate <NUM> is made of silicon with a conductive layer that functions as a common electrode <NUM> commonly used for the piezoelectric element <NUM> for each pressure chamber <NUM>. It should be noted that, an aspect can be adopted in which the vibration plate <NUM> is made of a non-conductive material, such as a resin, and in this case, a common electrode layer made of a conductive material, such as a metal, is formed on the surface of the vibration plate <NUM>. In addition, the vibration plate that serves as the common electrode may be made of a metal (conductive material), such as stainless steel.

As a drive voltage is applied to the individual electrode <NUM>, the piezoelectric element <NUM> deforms and the volume of the pressure chamber <NUM> is changed, and the ink is jetted from the outlet <NUM> due to a pressure change associated with the volume change. After ink jetting, the pressure chamber <NUM> is again filled with a new ink from the common flow passage <NUM> through the supply port <NUM>.

As the drive voltage to be applied to the individual electrode <NUM> is selected, the head module <NUM> can jet any ink droplet among three types of ink droplets, including a small droplet with a relatively small ink amount from each of the outlets <NUM>, a medium droplet with an ink amount relatively larger than the small droplet, and a large droplet with an ink amount relatively larger than the medium droplet. As described above, the head module <NUM> can form a plurality of ink dots having different diameters on the single-sheet paper <NUM>.

As shown in <FIG>, the jetting surface cleaning device <NUM> is composed of a cleaning liquid applying section <NUM> that cleans the jetting surfaces 30C, <NUM>, 30Y, and <NUM> of the ink jet heads 16C, <NUM>, 16Y, and <NUM> by applying the cleaning liquid and a wiping section <NUM> that wipes the jetting surfaces 30C, <NUM>, 30Y, and <NUM> to which the cleaning liquid is applied. The jetting surface cleaning device <NUM> is disposed on a movement path of the head support frame <NUM>.

The jetting surface cleaning device <NUM> cleans the jetting surfaces 30C, <NUM>, 30Y, and <NUM> by moving the inkjet heads 16C, <NUM>, 16Y, and <NUM> from the maintenance position to the image recording position, or from the image recording position to the maintenance position (example of relative movement).

The wiping section <NUM> is disposed on the image recording position side with respect to the cleaning liquid applying section <NUM> in the example shown in <FIG>, but may be disposed on the maintenance position side with respect to the cleaning liquid applying section <NUM>.

<FIG> is a side view of the cleaning liquid applying section <NUM> as viewed from the maintenance position side. The cleaning liquid applying section <NUM> is provided on an inside of the waste liquid tray <NUM> provided in the moisturizing unit <NUM> (see <FIG>). The cleaning liquid applying section <NUM> comprises cleaning liquid applying units 70C, <NUM>, 70Y, and <NUM> which are provided to correspond to the inkjet heads 16C, <NUM>, 16Y, and <NUM> respectively, and a body <NUM> on which the cleaning liquid applying units 70C, <NUM>, 70Y, and <NUM> are mounted.

The body <NUM> is horizontally provided and is freely raised and lowered by a raising and lowering device (not shown). The body <NUM> includes cleaning liquid applying unit attachment portions 72C, <NUM>, 72Y, and <NUM> on an upper surface portion. The cleaning liquid applying units 70C, <NUM>, 70Y, and <NUM> are fixed to the cleaning liquid applying unit attachment portions 72C, <NUM>, 72Y, and <NUM> provided in the body <NUM> by a bolt and the like, and are disposed on the movement paths of the corresponding ink jet heads 16C, <NUM>, 16Y, and <NUM>.

The basic configurations of the cleaning liquid applying units 70C, <NUM>, 70Y, and <NUM> are common. In the following, in a case in which the distinction is not necessary or the general term is used, the cleaning liquid applying units 70C, <NUM>, 70Y, and <NUM> are referred to as the cleaning liquid applying unit <NUM>. <FIG> and <FIG> are a front view and a side view of the cleaning liquid applying unit <NUM>, respectively. As shown in <FIG> and <FIG>, the cleaning liquid applying unit <NUM> comprises a cleaning liquid applying head <NUM> that applies the cleaning liquid to the jetting surface <NUM> and a cleaning liquid collection dish <NUM> that collects the cleaning liquid that falls from the jetting surface <NUM>.

The cleaning liquid collection dish <NUM> has a rectangular box shape with an open upper portion. The cleaning liquid applying head <NUM> is vertically erected inside the cleaning liquid collection dish <NUM>.

The cleaning liquid applying head <NUM> has a square block shape, and comprises a cleaning liquid holding surface 74A inclined with respect to a horizontal surface on the upper portion. The cleaning liquid holding surface 74A has the same inclined angle as the jetting surface <NUM> of the inkjet head <NUM>, which is a cleaning target. That is, the cleaning liquid holding surface 74A is parallel to the jetting surface <NUM> of the inkjet head <NUM>, which is the cleaning target.

The cleaning liquid applying head <NUM> cleans the jetting surface <NUM> facing the cleaning liquid holding surface 74A with the cleaning liquid held by the cleaning liquid holding surface 74A. The cleaning liquid holding surface 74Ahas a rectangular shape of which a length in the X direction is W and a length in the direction orthogonal to the X direction, which is a direction along the cleaning liquid holding surface 74A, is Dm, which is larger than Dh. That is, a relationship of Dm > Dh is satisfied.

It should be noted that, in a case of cleaning the jetting surface <NUM>, the entire jetting surface <NUM> faces the cleaning liquid holding surface 74A. In addition, an interval (distance) between the jetting surface <NUM> and the cleaning liquid holding surface 74A in a case in which the jetting surface <NUM> and the cleaning liquid holding surface 74A face each other is H.

Further, a cleaning liquid jetting port <NUM> from which the cleaning liquid is jetted is disposed at a position facing the head module holding member <NUM> in a case in which the jetting surface <NUM> and the cleaning liquid holding surface 74A face each other, which is in the vicinity of the upper portion of the cleaning liquid holding surface 74A in an inclination direction. The cleaning liquid jetted from the cleaning liquid jetting port <NUM> flows and falls from the inclined cleaning liquid holding surface 74A. As a result, a layer (film) of the cleaning liquid is formed on the cleaning liquid holding surface 74A. By bringing the jetting surface <NUM> of the ink jet head <NUM> into contact with the layer of the cleaning liquid formed on the cleaning liquid holding surface 74A, the cleaning liquid is applied to the jetting surface <NUM>, and the jetting surface <NUM> is cleaned by the applied cleaning liquid.

The cleaning liquid applying head <NUM> includes a supply flow passage <NUM> that communicates with the cleaning liquid jetting port <NUM>. The supply flow passage <NUM> communicates with a communication flow passage 76A provided in the cleaning liquid collection dish <NUM>. The communication flow passage 76A communicates with a cleaning liquid supply port 76B provided in the cleaning liquid collection dish <NUM>. As the cleaning liquid is supplied to the cleaning liquid supply port 76B, the cleaning liquid applying head <NUM> jets the cleaning liquid from the cleaning liquid jetting port <NUM>.

The cleaning liquid is supplied from a cleaning liquid tank (not shown) to the cleaning liquid supply port 76B. A pipe (not shown) connected to the cleaning liquid tank is connected to the cleaning liquid supply port 76B. A cleaning liquid supply pump (not shown) and a valve (not shown) are provided in the pipe. In a case in which a valve is opened and the cleaning liquid supply pump is driven, the cleaning liquid is supplied from the cleaning liquid tank to the cleaning liquid applying head <NUM>.

In addition, a bottom portion of the cleaning liquid collection dish <NUM> is inclined with respect to the horizontal surface, and has a collection hole <NUM> in a lower end portion in the inclination direction. The collection hole <NUM> communicates with a cleaning liquid outlet 76D via a collection flow passage 76C. The cleaning liquid outlet 76D is connected to the waste liquid tank <NUM> (see <FIG>) via a pipe (not shown). The cleaning liquid jetted from the cleaning liquid jetting port <NUM> of the cleaning liquid applying head <NUM> flows and falls from the cleaning liquid holding surface 74A to be collected in the cleaning liquid collection dish <NUM>, and is collected in the waste liquid tank <NUM> via the pipe (not shown).

Here, the cleaning liquid is supplied to the cleaning liquid holding surface 74A by jetting the cleaning liquid from the cleaning liquid jetting port <NUM> disposed in the cleaning liquid holding surface 74A, but a method of supplying the cleaning liquid is not limited to this. For example, the cleaning liquid may be supplied by adding the cleaning liquid dropwise in the vicinity of the upper portion of the cleaning liquid holding surface 74A in the inclination direction from the cleaning liquid nozzle which is separately provided.

For example, a cleaning liquid containing diethylene monobutyl ether as a main component is used as the cleaning liquid. By applying this type of the cleaning liquid to the jetting surface <NUM>, it is possible to dissolve and easily remove an ink-derived adhered matter adhering to the jetting surface <NUM>.

<FIG> is a side view of the wiping section <NUM> as viewed from the maintenance position side. As shown in <FIG>, the wiping section <NUM> comprises wiping units 300C, <NUM>, 300Y, and <NUM> which are provided to correspond to the inkjet heads 16C, <NUM>, 16Y, and <NUM>, and a body frame <NUM> on which the wiping units 300C, <NUM>, 300Y, and <NUM> are set.

The body frame <NUM> has a box shape in which an upper end portion is open. The body frame <NUM> is horizontally provided and is freely raised and lowered by the raising and lowering device (not shown). Wiping unit mounting portions 304C, <NUM>, 304Y, and <NUM> on which the wiping units 300C, <NUM>, 300Y, and <NUM> are mounted are provided inside the body frame <NUM>.

The wiping unit mounting portions 304C, <NUM>, 304Y, and <NUM> are spaces which can accommodate the wiping units 300C, <NUM>, 300Y, and <NUM>, and the upper portions thereof are open. By being inserted vertically downward from upper opening portions of the wiping unit mounting portions 304C, <NUM>, 304Y, and <NUM>, the wiping units 300C, <NUM>, 300Y, and <NUM> are set on the wiping unit mounting portions 304C, <NUM>, 304Y, and <NUM>.

It should be noted that the wiping unit mounting portions 304C, <NUM>, 304Y, and <NUM> comprise a lock mechanism (not shown), and the mounted wiping units 300C, <NUM>, 300Y, and <NUM> are locked by the lock mechanism. In a case in which the wiping units 300C, <NUM>, 300Y, and <NUM> are inserted into the wiping unit mounting portions 304C, <NUM>, 304Y, and <NUM>, the lock mechanism is operated automatically.

The basic configurations of the wiping units 300C, <NUM>, 300Y, and <NUM> are common. In the following, in a case in which the distinction is not necessary or the general term is used, the wiping units 300C, <NUM>, 300Y, and <NUM> are referred to as the wiping unit <NUM>.

<FIG> is a plan view of the wiping unit <NUM>, and <FIG> is a front partial cross-sectional view of the wiping unit <NUM>. As shown in <FIG> and <FIG>, the wiping unit <NUM> wipes the jetting surface <NUM> by winding a strip-shaped wiping web <NUM> (example of a wiping member) around a pressing roller <NUM> installed in an inclined manner, and pressing and abutting the wiping web <NUM> wound around the pressing roller <NUM> with the jetting surface <NUM> (see <FIG>) of the ink jet head <NUM>. In the present embodiment, the wiping unit <NUM> wipes the jetting surface <NUM> by the wiping web <NUM> which is in a dry state in which the cleaning liquid is not allowed to be infiltrated.

The wiping unit <NUM> comprises a case <NUM>, a feeding shaft <NUM> that feeds the wiping web <NUM>, a rolling shaft <NUM> that rolls the wiping web <NUM>, a front stage guide <NUM> that guides the wiping web <NUM> fed from the feeding shaft <NUM> to be wound around the pressing roller <NUM>, a rear stage guide <NUM> that guides the wiping web <NUM> wound around the pressing roller <NUM> to be rolled by the rolling shaft <NUM>, and a grid roller (drive roller) <NUM> that transports the wiping web <NUM>.

The feeding shaft <NUM> has a cylindrical shape. The feeding shaft <NUM> is fixed (cantilever-supported) to a pivot-support unit of which a base end portion is provided in a case body <NUM>, and is horizontally provided inside the case body <NUM>. On the feeding shaft <NUM>, a feeding core <NUM> is attachably and detachably mounted. It should be noted that a length of the feeding shaft <NUM> is slightly shorter than a length of the feeding core <NUM>. Therefore, in a case in which the feeding core <NUM> is mounted, the feeding shaft <NUM> retracts to an inner circumferential portion of the feeding core <NUM>.

The feeding core <NUM> has a cylindrical shape. The strip-shaped wiping web <NUM> is wound around the feeding core <NUM> in a roll shape.

The feeding core <NUM> is mounted on the feeding shaft <NUM> by inserting the feeding shaft <NUM> into the inner circumferential portion to be fitted to the feeding shaft <NUM>. The feeding core <NUM> mounted on the feeding shaft <NUM> is rotated around the feeding shaft <NUM> and is rotatably supported.

It should be noted that the wiping web <NUM> is composed of, for example, a sheet consisting of knitting or weaving made of ultrafine fibers, such as polyethylene terephthalate (PET), polyethylene (PE), and nylon (NY). The wiping web <NUM> has a width corresponding to a width of the inkjet head <NUM>, which is a wiping target.

The rolling shaft <NUM> is horizontally provided at a position below the feeding shaft <NUM>. That is, the rolling shaft <NUM> and the feeding shaft <NUM> are disposed to be vertically juxtaposed.

A rolling core <NUM> which rolls the wiping web <NUM> fed from the feeding core <NUM> is mounted on the rolling shaft <NUM>.

A configuration of the rolling core <NUM> is almost the same as a configuration of the feeding core <NUM>. That is, the rolling core <NUM> has a cylindrical shape. A distal end of the wiping web <NUM> wound around the feeding core <NUM> is fixed to the rolling core <NUM>.

The rolling core <NUM> is mounted on the rolling shaft <NUM> by fitting the rolling shaft <NUM> to an inner circumferential portion.

A base end portion of main shaft of the rolling shaft <NUM> is provided to protrude to an outside of the case body <NUM>, and a rolling shaft gear <NUM> is attached to the protruding base end portion. The rolling shaft <NUM> (main shaft) is rotated as the rolling shaft gear <NUM> is rotationally driven by a motor (not shown).

The pressing roller <NUM> is disposed above the feeding shaft <NUM> (in the present example, the pressing roller <NUM>, the feeding shaft <NUM>, and the rolling shaft <NUM> are disposed on the same line), and is disposed to be inclined at a predetermined angle with respect to the horizontal surface. That is, since the pressing roller <NUM> causes the wiping web <NUM> to be pressed and abutted to the jetting surface <NUM> of the ink jet head <NUM>, the pressing roller is disposed to be inclined in accordance with an inclination with respect to the horizontal surface of the jetting surface <NUM> of the inkjet head <NUM>, which is the wiping target, and the pressing roller <NUM> and the jetting surface <NUM> are disposed to be parallel to each other.

The front stage guide <NUM> is composed of a first front stage guide <NUM> and a second front stage guide <NUM>, and guides the wiping web <NUM> fed from the feeding shaft <NUM> to be wound around the pressing roller <NUM> installed in an inclined manner.

On the other hand, the rear stage guide <NUM> is composed of a first rear stage guide <NUM> and a second rear stage guide <NUM>, and guides the wiping web <NUM> wound around the pressing roller <NUM> installed in an inclined manner to be rolled by the rolling shaft <NUM> which is horizontally installed.

The front stage guide <NUM> and the rear stage guide <NUM> are symmetrically disposed with the pressing roller <NUM> interposed therebetween. That is, the first front stage guide <NUM> and the first rear stage guide <NUM> are disposed symmetrically with the pressing roller <NUM> interposed therebetween, and the second front stage guide <NUM> and the second rear stage guide <NUM> are disposed symmetrically with the pressing roller <NUM> interposed therebetween.

The first front stage guide <NUM> has a plate shape having a predetermined width, and is vertically erected on a raising and lowering stage <NUM>. The first front stage guide <NUM> has an upper edge portion 360A, which is a wound portion of the wiping web <NUM>, and has an arc shape on the surface. In addition, the upper edge portion 360A is inclined at a predetermined angle with respect to the horizontal surface. As a result, a traveling direction of the wiping web <NUM> is converted.

The first rear stage guide <NUM> has the same configuration as the first front stage guide <NUM>. That is, the first rear stage guide <NUM> has a plate shape having a predetermined width, and is vertically erected on the raising and lowering stage <NUM>. The first rear stage guide <NUM> has an upper edge portion 364A, which is a wound portion of the wiping web <NUM>, and has an arc shape. In addition, the upper edge portion 364A is inclined at a predetermined angle with respect to the horizontal surface.

The first front stage guide <NUM> and the first rear stage guide <NUM> are symmetrically disposed with the pressing roller <NUM> interposed therebetween. By being wound around the first front stage guide <NUM>, a direction of the wiping web <NUM> fed from the feeding shaft <NUM> is changed from a direction orthogonal to the feeding shaft <NUM> to a direction substantially orthogonal to the pressing roller <NUM>. In addition, by being wound around the first rear stage guide <NUM>, the direction of the wiping web <NUM> wound around the second rear stage guide <NUM> is changed to a direction orthogonal to the rolling shaft <NUM>.

The second front stage guide <NUM> is configured as a guide roller that includes flanges <NUM> and 362R in both end portions. The second front stage guide <NUM> is disposed between the first front stage guide <NUM> and the pressing roller <NUM>, and guides the wiping web <NUM> wound around the first front stage guide <NUM> to be wound around the pressing roller <NUM>. That is, the traveling direction of the wiping web <NUM> is finely adjusted such that the wiping web <NUM> of which a direction is changed to the direction substantially orthogonal to the pressing roller <NUM> by the first front stage guide <NUM> travels in the direction orthogonal to the pressing roller <NUM>. In addition, skewing of the wiping web <NUM> is prevented by the flanges <NUM> and 362R in both ends.

The second front stage guide <NUM> is provided in an inclined manner at a predetermined angle as one end thereof is cantilever-supported by a bracket 368A. As shown in <FIG>, the bracket 368A has a plate shape in which a distal end is bent, and a base end portion thereof is fixed to a rear surface upper end portion of the case body <NUM>. The bracket 368A is provided to vertically protrude upward from the upper end portion of the case body <NUM>. The second front stage guide <NUM> is supported to be movable rotationally by being cantilever-supported by a bent portion of the distal end of the bracket 368A.

The second rear stage guide <NUM> has the same configuration as the second front stage guide <NUM>. That is, the second rear stage guide <NUM> is configured as a guide roller that includes flanges <NUM> and 366R in both end portions, and is provided in an inclined manner at a predetermined angle with one end thereof is cantilever-supported by a bracket 368B. The bracket 368B has a plate shape in which a distal end is bent, and a base end portion thereof is fixed to the rear surface upper end portion of the case body <NUM>. The second rear stage guide <NUM> is supported to be movable rotationally by being cantilever-supported by a bent portion of the distal end of the bracket 368B.

The second rear stage guide <NUM> is disposed between the pressing roller <NUM> and the first rear stage guide <NUM>, and guides the wiping web <NUM> wound around the pressing roller <NUM> to be wound around the first rear stage guide <NUM>.

The second front stage guide <NUM> and the second rear stage guide <NUM> are symmetrically disposed with the pressing roller <NUM> interposed therebetween. The traveling direction is finely adjusted such that the wiping web <NUM> of which a direction is changed to the direction substantially orthogonal to the pressing roller <NUM> by the first front stage guide <NUM> is wound around the second front stage guide <NUM> to travel in the direction orthogonal to the pressing roller <NUM>. In addition, the traveling direction is finely adjusted by the second rear stage guide <NUM> such that the wiping web <NUM> wound around the pressing roller <NUM> is wound around the first rear stage guide <NUM>. By being wound around the first rear stage guide <NUM>, the direction of the wiping web <NUM> is changed to the direction orthogonal to the rolling shaft <NUM>.

As described above, by switching the traveling direction of the wiping web <NUM> step by step, the front stage guide <NUM> and the rear stage guide <NUM> guide the wiping web <NUM> to be wound around the pressing roller <NUM> without difficulty.

Therefore, the inclined angle of the second front stage guide <NUM> is an angle close to the inclined angle of the pressing roller <NUM> as compared with the inclined angle of the first front stage guide <NUM>. Similarly, the inclined angle of the second rear stage guide <NUM> is an angle close to the inclined angle of the pressing roller <NUM> as compared with the inclined angle of the first rear stage guide <NUM>.

<FIG> is a schematic configuration diagram of the ink circulation system <NUM> provided in the printing device according to the embodiment of the disclosed technology. The ink circulation system <NUM> includes a main tank <NUM>, a buffer tank <NUM>, a main pump <NUM>, a supply tank <NUM>, a collection tank <NUM>, a supply pump <NUM>, a collection pump <NUM>, pressure sensors <NUM> and <NUM>, a controller <NUM>, a reception unit <NUM>, and pipes <NUM>, <NUM>, <NUM>, and <NUM>. The ink circulation system <NUM> is a system that circulates the ink between the buffer tank <NUM> and the inkjet head <NUM>. An ink circulation flow passage through which the ink circulates is composed of the pipes <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, the supply tank <NUM>, and the collection tank <NUM>.

A color ink to be jetted by the ink jet head <NUM> is stored in the main tank <NUM>. The ink may contain at least one of a metal pigment or carbon black. The viscosity of the ink is preferably in a range of <NUM> to <NUM> pores. <NUM> pore is <NUM> pascal seconds (Pa·s). It should be noted that, in the present specification, in a case in which a numerical range is indicated by using "to", the numerical range includes numerical values of upper and lower limits indicated by "to".

The main tank <NUM> is connected to the buffer tank <NUM> via the pipe <NUM>. The main pump <NUM> is provided in the pipe <NUM>. The main pump <NUM> is operated in response to a control signal Sc supplied from the controller <NUM>, and feeds the ink stored in the main tank <NUM> to the buffer tank <NUM>.

An inside of the buffer tank <NUM> is open to the atmosphere via an atmosphere opening hole 206A provided in a top surface thereof. A predetermined amount of the ink is stored inside the buffer tank <NUM> by the ink supplied from the main tank <NUM>.

The buffer tank <NUM> communicates with the supply tank <NUM> via the pipe <NUM>. The supply tank <NUM> communicates with the ink supply port <NUM> of the ink jet head <NUM> via the pipe <NUM>.

In addition, the buffer tank <NUM> communicates with the collection tank <NUM> via the pipe <NUM>. The collection tank <NUM> communicates with the ink collection port <NUM> of the inkjet head <NUM> via the pipe <NUM>.

The supply pump <NUM> is provided in the pipe <NUM>. The supply pump <NUM> feeds the ink from the buffer tank <NUM> to the supply tank <NUM>. In addition, the collection pump <NUM> is provided in the pipe <NUM>. The collection pump <NUM> feeds the ink from the collection tank <NUM> to the buffer tank <NUM>.

An inside of the supply tank <NUM> is divided into an ink chamber 214A and a gas chamber 214B by an elastic film <NUM>. The pipe <NUM> and the pipe <NUM> communicate with the ink chamber 214A. The ink stored in the buffer tank <NUM> is supplied by the supply pump <NUM> to the ink jet head <NUM> via the pipe <NUM>, the ink chamber 214A, and the pipe <NUM>.

On the other hand, the gas chamber 214B is filled with gas. An atmosphere opening pipe <NUM> for opening the gas chamber 214B to the atmosphere communicates with the gas chamber 214B. An atmosphere opening valve <NUM> is provided in the atmosphere opening pipe <NUM>. The atmosphere opening valve <NUM> is operated in response to the control signal supplied from the controller <NUM> to open and close the atmosphere opening pipe <NUM>. With the supply tank <NUM>, sudden pressure change inside the supply flow passage including the pipe <NUM> and the pipe <NUM> is suppressed by the appropriate elastic force due to the compressibility of the air enclosed in the elastic film <NUM> and the gas chamber 214B.

The pressure sensor <NUM> detects a pressure inside the ink chamber 214A of the supply tank <NUM>, and outputs a detection signal Sd indicating the magnitude of the detected pressure. The output detection signal Sd is supplied to the controller <NUM>.

In the supply pump <NUM>, a rotation speed per unit time (hereinafter, simply referred to as "rotation speed") is controlled by the control signal Sc supplied from the controller <NUM>.

The same also applies to the configuration of the collection tank <NUM>. That is, an inside of the collection tank <NUM> is divided into an ink chamber 222A and a gas chamber 222B by an elastic film <NUM>.

The pipe <NUM> and the pipe <NUM> communicate with the ink chamber 222A. The ink inside the inkjet head <NUM> is collected by the collection pump <NUM> into the buffer tank <NUM> via the pipe <NUM>, the ink chamber 222A, and the pipe <NUM>.

The gas chamber 222B is filled with gas. An atmosphere opening pipe <NUM> for opening the gas chamber 222B to the atmosphere communicates with the gas chamber 222B. An atmosphere opening valve <NUM> is provided in the atmosphere opening pipe <NUM>. The atmosphere opening valve <NUM> opens and closes the atmosphere opening pipe <NUM> in response to the control signal supplied from the controller <NUM>. With the collection tank <NUM>, sudden change fluctuation inside the collection flow passage including the pipe <NUM> and the pipe <NUM> is suppressed by the appropriate elastic force due to the compressibility of the air enclosed in the elastic film <NUM> and the gas chamber 222B.

The pressure sensor <NUM> detects a pressure inside the ink chamber 222A of the collection tank <NUM>, and outputs a detection signal Sd indicating the magnitude of the detected pressure. The output detection signal Sd is supplied to the controller <NUM>.

A rotation speed of the collection pump <NUM> is controlled by the control signal Sd supplied from the controller <NUM>.

A valve <NUM> is provided in the pipe <NUM>, and a valve <NUM> is provided in the pipe <NUM>. Each of the valves <NUM> and <NUM> opens and closes in response to the control signal Sc supplied from the controller <NUM>. In the ink circulation system <NUM>, in a case in which the ink circulates, the valves <NUM> and <NUM> are controlled to be in an open state. On the other hand, in the ink circulation system <NUM>, in a case in which the ink circulation is stopped, the valves <NUM> and <NUM> are controlled to be in a closed state.

By driving the supply pump <NUM> and the collection pump <NUM>, a circulation flow is generated in which the ink returns to the buffer tank <NUM> via the buffer tank <NUM>, the pipes <NUM> and <NUM>, the inkjet head <NUM>, the pipe <NUM>, and the pipe <NUM>.

The reception unit <NUM> comprises operation members, such as operation buttons, a keyboard, and a touch panel, receives information input from the operation members, and outputs the received information to the controller <NUM>. In a case in which the printing device is stopped, the ink circulation in the ink circulation system <NUM> is stopped. The reception unit <NUM> receives, for example, a set input value Ain of an ink circulation stop period, which is a period in which the ink circulation is stopped in the ink circulation system <NUM>. The ink circulation stop period is a period in which the ink circulation in the ink circulation system <NUM> is stopped in a stop period of the printing device, and is, for example, a period optionally set based on an operation schedule of the printing device. An input operation of the set input value Ain of the ink circulation stop period is performed in a case in which the printing device is stopped by a user.

The controller <NUM> controls the circulation flow of the ink by controlling the supply pump <NUM>, the collection pump <NUM>, and the valves <NUM> and <NUM>. In addition, in a case in which the printing device is stopped, the controller <NUM> controls a back pressure of the ink jet head <NUM> at the start of the ink circulation stop period based on the set input value Ain of the ink circulation stop period supplied from the reception unit <NUM> and a back pressure setting table <NUM> (see <FIG>) to be described below. More specifically, by referring to the back pressure setting table <NUM>, the controller <NUM> controls the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period to a value in accordance with the set input value Ain of the ink circulation stop period. By controlling the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time, the controller <NUM> controls the back pressure of the inkjet head <NUM>. The controller <NUM> specifies the back pressure of the inkjet head <NUM> from a difference between the pressure indicated by the detection signal Sd supplied from the pressure sensor <NUM> and the pressure indicated by the detection signal Sd supplied from the pressure sensor <NUM>.

In a case in which the back pressure of the inkjet head <NUM> specified based on the detection signal Sd supplied from the pressure sensors <NUM> and <NUM> is the value in accordance with the set input value Ain of the ink circulation stop period, the controller <NUM> controls the valves <NUM> and <NUM> to be the closed state, and then stops the supply pump <NUM> and the collection pump <NUM>. By stopping the supply pump <NUM> and the collection pump <NUM>, the ink circulation is stopped. After stopping the ink circulation, a power supply of the printing device is turned off.

Here, <FIG> is a graph showing an example of a time transition of the back pressure of the ink jet head <NUM> according to a comparative example. It should be noted that, in the graph of <FIG>, the back pressure indicated on a vertical axis is a relative pressure with an atmospheric pressure as <NUM> [Pa].

In an ink circulation period in which the printing device is operated, the back pressure of the ink jet head <NUM> is set to a set value Pc. By setting the set value Pc to a negative pressure, the meniscus formed in the outlet <NUM> of the inkjet head <NUM> can be maintained to have a shape recessed inward the ink jet head <NUM>, so-called ink dripping in which ink leaks from the outlet <NUM> can be suppressed.

In a case in which the ink circulation in the ink circulation system <NUM> is stopped due to the stop of the printing device, the back pressure of the inkjet head <NUM> is set to a set value Ps which is a level further shifting to a negative side with respect to the set value Pc in the ink circulation period. Thereafter, the valves <NUM> and <NUM> are in the closed state, and the supply pump <NUM> and the collection pump <NUM> are stopped. Thereafter, the power supply of the printing device is turned off.

As shown in <FIG>, the back pressure of the inkjet head <NUM> during the ink circulation stop period shifts to a positive pressure side with the elapse of time. Ink dripping occurs from the time when the ink circulation stop period is long, the back pressure exceeds the atmospheric pressure of <NUM> Pa, and a relationship of ink gravity > surface tension is satisfied. As described above, the back pressure of the ink jet head <NUM> during the ink circulation stop period shifts to the positive pressure side with the elapse of time, so that a risk of the occurrence of ink dripping is higher as the ink circulation stop period is longer.

In addition, in a case in which the printing device is stopped, the jetting surface <NUM> of the ink jet head <NUM> is covered with the cap <NUM> storing the moisturizing liquid in order to suppress the drying of the ink in the ink jet head <NUM>. As a result, the humidity of the space formed between the jetting surface <NUM> and the cap <NUM> is maintained at about <NUM>%, for example. However, in a case in which the jetting surface of the ink jet head <NUM> is exposed to a high humidity atmosphere, the ink in the vicinity of the outlet <NUM> absorbs moisture, or the ink in the vicinity of the outlet <NUM> binds to the water droplets adhering to the jetting surface <NUM> due to condensation, so that ink dripping is promoted.

Here, <FIG> is a diagram showing a result of a timing at which ink dripping occurs in a case in which the set value of the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period, which is acquired by an experiment. In the ink circulation stop period, the jetting surface <NUM> of the inkjet head <NUM> was covered with the cap <NUM> storing the moisturizing liquid. In <FIG>, no ink dripping is indicated by A, and ink dripping is indicated by B.

In <FIG>, the numerical values shown in the columns are the set values of the back pressure (unit: Pascal (Pa)) at the start of the ink circulation stop period, and the numerical values shown in the rows are the ink circulation stop periods (unit: h). The set value of the back pressure is the relative pressure with the atmospheric pressure as <NUM> [Pa].

The set values of the back pressure at the start of the ink circulation stop period were set to <NUM> patterns of -<NUM> Pa, -<NUM> Pa, -<NUM> Pa, and -<NUM> Pa, and periods from the start of the ink circulation stop period to the elapse of <NUM> hours were investigated. The inks used in the experiment were manufactured by FUJIFILM Corporation, the part numbers were black: C-WP-QK, cyan: C-WP-QC, magenta: C-WP-QM, and yellow: C-WP-QY, and the physical property values were viscosity: <NUM> mP·s and the surface tension: <NUM> mN/m.

As shown in <FIG>, in a case in which the set value of the back pressure at the start of the ink circulation stop period was set to -<NUM> [Pa], no ink dripping occurred until <NUM> hours elapsed from the start of the ink circulation stop period. In a case in which the set value of the back pressure at the start of the ink circulation stop period was set to -<NUM> [Pa], no ink dripping occurred until <NUM> hours elapsed from the start of the ink circulation stop period. In a case in which the set value of the back pressure at the start of the ink circulation stop period was set to -<NUM> [Pa], no ink dripping occurred until <NUM> hours elapsed from the start of the ink circulation stop period. In a case in which the set value of the back pressure at the start of the ink circulation stop period was set to -<NUM> [Pa], no ink dripping occurred until <NUM> hours elapsed from the start of the ink circulation stop period.

As described above, as a negative pressure level (absolute value of the negative pressure) of the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period is higher, the period in which no ink dripping occurs is longer in the ink circulation stop period. Therefore, by setting the set value of the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period to the negative pressure having a larger absolute value as the ink circulation stop period is longer, it is considered that ink dripping can be suppressed in the ink circulation stop period.

In order to suppress ink dripping, in anticipation of the shift of the back pressure of the inkjet head <NUM> to the positive pressure side with time and the condensation on the jetting surface <NUM> of the ink jet head <NUM>, it is also conceivable to set the set value of the back pressure of the ink jet head <NUM> to the negative pressure having a sufficiently large absolute value. However, in a case in which the negative pressure level of the back pressure of the ink jet head <NUM> is excessively increased, the meniscus of the ink formed in the vicinity of the outlet <NUM> becomes a shape that is more largely recessed inward the ink jet head <NUM>, so that the ink in the vicinity of the outlet <NUM> tends to dry. In addition, air bubbles may enter the ink jet head <NUM>, which may cause an ink jetting failure.

In the printing device according to the present embodiment, it has been found by the experiment that entering of air bubbles from the outlet <NUM> occurred in a case in which the back pressure was increased to exceed -<NUM> [Pa] on the negative side. That is, in a case in which the back pressure of the ink jet head <NUM> is set to the magnitude that does not exceed -<NUM> [Pa] on the negative side, it is possible to avoid entering of air bubbles. In addition, by setting the value of the back pressure of the ink jet head <NUM> to a range that does not excessively deviate from a limit value that does not cause ink dripping to the negative side, it is possible to suppress the shape, which is largely recessed inward the ink jet head <NUM>, of the meniscus of the ink formed in the vicinity of the outlet <NUM>, and it is possible to suppress drying of the ink in the vicinity of the outlet <NUM>.

Therefore, by controlling the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period as described below, the controller <NUM> suppresses ink dripping while suppressing drying of the ink and entering of air bubbles in the inkjet head <NUM>. In the following, a hardware configuration of the controller <NUM> will be described.

As shown in <FIG>, the controller <NUM> includes a central processing unit (CPU) <NUM>, a memory <NUM> as a transitory storage region, a non-volatile storage unit <NUM>, a network interface (I/F) <NUM> connected to a network, and an external I/F <NUM>.

The controller <NUM> is connected to the main pump <NUM>, the supply pump <NUM>, the collection pump <NUM>, the pressure sensors <NUM> and <NUM>, the valves <NUM> and <NUM>, and the reception unit <NUM> via the external I/F <NUM>.

The CPU <NUM>, the memory <NUM>, the storage unit <NUM>, the network I/F <NUM>, and the external I/F <NUM> are connected to a bus <NUM>. The controller <NUM> may be a personal computer or a server computer, for example.

The storage unit <NUM> is realized by a hard disk drive (HDD), a solid state drive (SSD), a flash memory, and the like. A back pressure control program <NUM> and the back pressure setting table <NUM> are stored in the storage unit <NUM>. The CPU <NUM> reads out the back pressure control program <NUM> from the storage unit <NUM>, expands the read out back pressure control program <NUM> into the memory <NUM>, and executes the expanded program.

In the following, the back pressure setting table <NUM> according to the first embodiment of the disclosed technology will be described.

<FIG> is a diagram showing an example of the back pressure setting table <NUM>. As shown in <FIG>, the back pressure setting table <NUM> records the ink circulation stop period and the set value of the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period in association with each other. It should be noted that the set value of the back pressure shown in <FIG> is the relative pressure with the atmospheric pressure as <NUM> [Pa]. The back pressure setting table <NUM> is configured such that the set value of the back pressure is a value that does not cause ink dripping from the start of the ink circulation period to the elapse of the corresponding ink circulation stop period. In addition, the back pressure setting table <NUM> is configured such that the set value of the back pressure is larger on the negative side as the ink circulation stop period is longer. In addition, the back pressure setting table <NUM> is configured such that the set value of the back pressure does not exceed the limit value that does not cause entering of air bubbles. For example, in a case in which the limit value of the back pressure that does not cause entering of air bubbles is -<NUM> [Pa], the set value of the back pressure in the back pressure setting table <NUM> is set to a value that does not exceed -<NUM> [Pa] on the negative side. In addition, the back pressure setting table <NUM> is configured such that the set value of the back pressure is a value having a certain margin with respect to the limit value that does not cause ink dripping, but is in a range that does not excessively deviate from the limit value to the negative side. As a result, it is possible to suppress the shape, which is largely recessed inward the inkjet head <NUM>, of the meniscus of the ink formed in the vicinity of the outlet <NUM>, and it is possible to suppress drying of the ink in the vicinity of the outlet <NUM>. That is, in the back pressure setting table <NUM>, a value at which ink dripping in the corresponding ink circulation stop period can be suppressed while suppressing entering of air bubbles and drying of the ink is recorded as the set value of the back pressure. The back pressure setting table <NUM> can be created, for example, based on the experimental results shown in <FIG>.

In the example shown in <FIG>, the set value of the back pressure -<NUM> [Pa] is associated with the ink circulation stop period of less than <NUM> hours. This is because, in a case in which the ink circulation stop period is less than <NUM> hours, the back pressure of the inkjet head <NUM> at the start of the ink circulation stop period is set to -<NUM> [Pa], so that ink dripping in the corresponding ink circulation stop period can be suppressed while suppressing entering of air bubbles and drying of the ink. In addition, in the example shown in <FIG>, the set value of the back pressure -<NUM> [Pa] is associated with a case in which the ink circulation stop period is <NUM> hours or more and less than <NUM> hours. This is because, in a case in which the ink circulation stop period is <NUM> hours or more and less than <NUM> hours, the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period is set to -<NUM> [Pa], so that ink dripping in the corresponding ink circulation stop period can be suppressed while suppressing entering of air bubbles and drying of the ink.

The set value of the back pressure in the back pressure setting table <NUM> is not limited to that shown in <FIG>, and need only be a value at which ink dripping in the corresponding ink circulation stop period can be suppressed while suppressing entering of air bubbles and drying of the ink. It is considered that the appropriate set value of the back pressure in the back pressure setting table <NUM> is changed in accordance with the configurations of the ink jet head <NUM> and the ink circulation system <NUM>. In addition, in the example shown in <FIG>, the case has been described in which the set value of the back pressure is defined in unit time of <NUM> hours, but the disclosed technology is not limited to this, for example, the set value of the back pressure may be defined the unit time of <NUM> hours or unit time of <NUM> hours, and does not have to be defined in a fixed unit time.

In the following, the actions of the printing device according to the first embodiment of the disclosed technology will be described. <FIG> is a flowchart showing a flow of a back pressure control process executed by the controller <NUM> executing the back pressure control program <NUM>.

In a case in which the printing device is stopped, in a case in which the reception unit <NUM> receives the set input value of the ink circulation stop period, the CPU <NUM> of the controller <NUM> reads out the back pressure control program <NUM> from the storage unit <NUM> and executes the read out back pressure control program <NUM>.

In step S1, the CPU <NUM> acquires the set input value of the ink circulation stop period received by the reception unit <NUM>. The acquired set input value of the ink circulation stop period is recorded in the memory <NUM>.

In step S2, the CPU <NUM> extracts, from the back pressure setting table <NUM> the set value of the back pressure corresponding to the set input value of the ink circulation stop period recorded in the memory <NUM>. The extracted set value of the back pressure is recorded in the memory <NUM>.

In step S3, the CPU <NUM> controls the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time in accordance with the set value of the extracted back pressure recorded in the memory <NUM>. By controlling the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time, the back pressure of the ink jet head <NUM> is set to the value extracted from the back pressure setting table <NUM>. Here, the back pressure of the inkjet head <NUM> can be adjusted by a difference between a flow rate of the ink flowing in the supply flow passage including the pipe <NUM> and the pipe <NUM> and a flow rate of the ink flowing in the collection flow passage including the pipe <NUM> and the pipe <NUM>. Therefore, it is possible to control the back pressure of the inkjet head <NUM> by controlling the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time. The controller <NUM> specifies the back pressure of the ink jet head <NUM> from the difference between the pressure indicated by the detection signal Sd supplied from the pressure sensor <NUM> and the pressure indicated by the detection signal Sd supplied from the pressure sensor <NUM>. The CPU <NUM> controls the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time such that the value of the back pressure of the inkjet head <NUM> specified based on the detection signal Sd supplied from the pressure sensors <NUM> and <NUM> matches the value extracted from the back pressure setting table <NUM>. It should be noted that the CPU <NUM> may control the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time based on the table that records a correspondence relationship between the back pressure of the ink jet head <NUM> and the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time.

In step S4, in a case in which it is determined that the value of the back pressure of the ink jet head <NUM> specified based on the detection signal Sd supplied from the pressure sensors <NUM> and <NUM> reaches the value extracted from the back pressure setting table <NUM>, the CPU <NUM> controls the valves <NUM> and <NUM> to be the closed state.

In step S5, the CPU <NUM> stops the supply pump <NUM> and the collection pump <NUM>. By stopping the supply pump <NUM> and the collection pump <NUM>, the ink circulation is stopped. After the ink circulation is stopped, the power supply of the printing device is turned off.

<FIG> is a graph showing an example of the time transition of the back pressure of the ink jet head <NUM> by a back pressure control according to the first embodiment of the disclosed technology. It should be noted that, in the graph of <FIG>, the back pressure indicated on a vertical axis is a relative pressure with an atmospheric pressure as <NUM> [Pa].

With the printing device according to the first embodiment of the disclosed technology, as shown in <FIG>, the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period is set to the set value Ps (negative pressure) in accordance with the set input value of the ink circulation stop period received by the reception unit <NUM> by the controller <NUM> referring to the back pressure setting table <NUM>. The controller <NUM> controls the negative pressure level of the back pressure of the ink jet head at the start of the ink circulation stop period to be higher as the ink circulation stop period is longer. Stated another way, the controller <NUM> controls the back pressure of the ink jet head at the start of the ink circulation stop period to the negative pressure having a larger absolute value as the ink circulation stop period is longer. As a result, even in a case in which the back pressure of the ink jet head <NUM> shifts to the positive pressure side with the elapse of time, the power supply of the printing device is turned on before the back pressure reaches the back pressure that causes ink dripping, and the ink circulation is restarted. By restarting the ink circulation, the back pressure of the inkjet head <NUM> is set to the set value Pc in the ink circulation period in which no ink dripping occurs. In addition, the set value Ps of the back pressure set based on the back pressure setting table <NUM> is set to a value that does not exceed the limit value that does not cause entering of air bubbles. As a result, it is possible to suppress entering of air bubbles in the ink jet head <NUM>. In addition, the set value Ps of the back pressure set based on the back pressure setting table <NUM> is set to a value that does not excessively deviate from the limit value that does not cause ink dripping to the negative side. As a result, the shape, which is largely recessed inward the ink jet head <NUM>, of the meniscus of the ink formed in the vicinity of the outlet <NUM> can be suppressed, and drying of the ink in the vicinity of the outlet <NUM> can be suppressed.

<FIG> is a diagram showing a hardware configuration of the controller <NUM> according to a second embodiment of the disclosed technology. In <FIG>, the same elements as those of the controller (see <FIG>) according to the first embodiment are designated by the same reference numerals, and the detailed description thereof will be omitted.

In the first embodiment, the storage unit <NUM> of the controller <NUM> comprises the back pressure control program <NUM> and the back pressure setting table <NUM>, but in the second embodiment, the storage unit <NUM> of the controller <NUM> comprises a back pressure control program <NUM> and a back pressure setting expression <NUM>.

The CPU <NUM> reads out the back pressure control program <NUM> from the storage unit <NUM>, expands the read out back pressure control program <NUM> into the memory <NUM>, and executes the expanded program.

In the following, the back pressure setting expression <NUM> according to the second embodiment of the disclosed technology will be described.

<FIG> is a graph showing an example of a relationship between the ink circulation stop period and the set value of the back pressure at the start of the ink circulation stop period in which no ink dripping occur. It should be noted that the graph shown in <FIG> corresponds to the experimental results shown in <FIG>.

In <FIG>, a standard value (cross plot), an upper limit value (circle plot), and a lower limit value (triangular plot) are shown for the set values of back pressure at the start of the ink circulation stop period in which no ink dripping occurs. It should be noted that, here, a value having a smaller absolute value of the back pressure is set as the upper limit value, and a value having a larger absolute value of the back pressure is set as the lower limit value. In addition, in <FIG>, a limit value (diamond plot) that does not cause ink dripping and a limit value (square plot) that does not cause entering of air bubbles are shown. The back pressure is set within a range that does not exceed these limit values. Here, in a case in which the ink circulation stop period is defined as X [h] and the set value (relative pressure) of the back pressure at the start of the ink circulation stop period that does not cause ink dripping is defined as Y [Pa], the graph shown in <FIG> shows that a set value Y of the back pressure at the start of the ink circulation stop period is determined in accordance with an ink circulation stop period X to satisfy Expression (<NUM>). Expression (<NUM>) is stored in the storage unit <NUM> of the controller <NUM> as the back pressure setting expression <NUM>. According to Expression (<NUM>), the set value Y of the back pressure of the ink jet head at the start of the ink circulation stop period is set to have negative pressure level, which is higher (to be the negative pressure having a larger absolute value) as the ink circulation stop period X is longer.

The back pressure setting expression <NUM> is not limited to Expression (<NUM>), and need only be an expression in which a value of the back pressure calculated by using the expression is a value that does not exceed the limit value that does not cause ink dripping in accordance with the ink circulation stop time, and does not exceed the limit value that does not cause entering of air bubbles in an assumed range of the ink circulation stop period.

The controller <NUM> controls the back pressure of the inkjet head <NUM> at the start of the ink circulation stop period by using the back pressure setting expression <NUM>.

In the following, the actions of the printing device according to the second embodiment of the disclosed technology will be described. <FIG> is a flowchart showing a flow of the back pressure control process executed by the controller <NUM> executing the back pressure control program <NUM>.

In step S11, the CPU <NUM> acquires the set input value of the ink circulation stop period received by the reception unit <NUM>. The acquired set input value of the ink circulation stop period is recorded in the memory <NUM>.

In step S12, the CPU <NUM> calculates the set value of the back pressure by substituting the set input value of the ink circulation stop period recorded in the memory <NUM> into the back pressure setting expression <NUM>. The calculated set value of the back pressure is recorded in the memory <NUM>.

In step S13, by controlling the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time in accordance with the calculated set value of the back pressure recorded in the memory <NUM>, the CPU <NUM> sets the back pressure of the ink jet head <NUM> to the value calculated by using the back pressure setting expression <NUM>. The controller <NUM> specifies the back pressure of the ink jet head <NUM> from the difference between the pressure indicated by the detection signal Sd supplied from the pressure sensor <NUM> and the pressure indicated by the detection signal Sd supplied from the pressure sensor <NUM>. The CPU <NUM> controls the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time such that the value of the back pressure of the inkjet head <NUM> specified based on the detection signal Sd supplied from the pressure sensors <NUM> and <NUM> matches the value calculated from the back pressure setting expression <NUM>. It should be noted that the CPU <NUM> may control the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time based on the table that records a correspondence relationship between the back pressure of the ink jet head <NUM> and the rotation speeds of the supply pump <NUM> and the collection pump <NUM> per unit time.

In step S14, in a case in which it is determined that the value of the back pressure of the ink jet head <NUM> specified based on the detection signal Sd supplied from the pressure sensors <NUM> and <NUM> reaches the value calculated from the back pressure setting expression <NUM>, the CPU <NUM> controls the valves <NUM> and <NUM> to be the closed state.

In step S15, the CPU <NUM> stops the supply pump <NUM> and the collection pump <NUM>. By stopping the supply pump <NUM> and the collection pump <NUM>, the ink circulation is stopped. After the ink circulation is stopped, the power supply of the printing device is turned off.

With the printing device according to the second embodiment of the disclosed technology, as in the first embodiment, as shown in <FIG>, the back pressure of the ink jet head <NUM> at the start of the ink circulation stop period is set to the set value Ps (negative pressure) in accordance with the set input value of the ink circulation stop period received by the reception unit <NUM> by the controller <NUM> using the back pressure setting expression <NUM>. The controller <NUM> controls the negative pressure level of the back pressure of the ink jet head at the start of the ink circulation stop period to be higher as the ink circulation stop period is longer. As a result, even in a case in which the back pressure of the ink jet head <NUM> shifts to the positive pressure side with the elapse of time, the power supply of the printing device is turned on before the back pressure reaches the back pressure that causes ink dripping, and the ink circulation is restarted. By restarting the ink circulation, the back pressure of the ink jet head <NUM> is set to the set value Pc in the ink circulation period in which no ink dripping occurs. In addition, the set value Ps of the back pressure calculated by using a back pressure setting expression <NUM> is set to a value that does not exceed the limit value that does not cause entering of air bubbles. As a result, it is possible to suppress entering of air bubbles in the inkjet head <NUM>. In addition, the set value Ps of the back pressure set based on the back pressure setting expression <NUM> is set to a value that does not excessively deviate from the limit value that does not cause ink dripping to the negative side. As a result, the shape, which is largely recessed inward the ink jet head <NUM>, of the meniscus of the ink formed in the vicinity of the outlet <NUM> can be suppressed, and drying of the ink in the vicinity of the outlet <NUM> can be suppressed. In addition, by using the back pressure setting expression <NUM>, the set value of the back pressure can be controlled more finely as compared to a case in which the back pressure setting table <NUM> is used.

Claim 1:
A printing device comprising:
an inkjet head (<NUM>, 16C, <NUM>, 16Y, <NUM>) that is configured to jet an ink from a jetting surface (<NUM>);
an ink circulation flow passage in the ink jet head (<NUM>, 16C, <NUM>, 16Y, <NUM>) through which the ink circulates;
a moisturizing unit (<NUM>) that is configured to moisturize the jetting surface (<NUM>, 30C, <NUM>, 30Y, <NUM>) with a moisturizing liquid in an ink circulation stop period in which circulation of the ink in the ink circulation flow passage is stopped;
a reception unit (<NUM>) that is configured to receive a set input value of the ink circulation stop period; and
a controller (<NUM>) that is configured to control a back pressure of the inkjet head (<NUM>, 16C, <NUM>, 16Y, <NUM>) at a start of the ink circulation stop period in accordance with the set input value of the ink circulation stop period received by the reception unit (<NUM>), the controller (<NUM>) is configured to control a negative pressure level of the back pressure of the inkjet head (<NUM>, 16C, <NUM>, 16Y, <NUM>) at the start of the ink circulation stop period to be higher as the ink circulation stop period is longer.