Printing apparatus, printing system and printing method

The printing medium M after color printing is performed on the front surface M1 (recording surface) by the color printing unit 32 can be conveyed while the front surface M1 and the back surface M2 of the printing medium M are inverted twice by the only rollers 471 to 478 (rotary bodies) in contact with the back surface M2 (non-recording surface) of the printing medium M (inverting conveying part 47). In this way, without providing air turn bars, a time to convey the printing medium M from the color printing unit 32 to the white printing unit 33 can be secured while the printing medium M is firmly supported by the rollers 471 to 478 in contact with the back surface M2 of the printing medium M.

CROSS REFERENCE TO RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2020-050487 filed on Mar. 23, 2020 including specification, drawings and claims is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a technique for printing by discharging a white ink to a printing medium after discharging color ink(s) to the printing medium.

2. Description of the Related Art

A printing apparatus which prints using color inks and a white ink is described in WO2017/138436. In this printing apparatus, four ink-jet heads which respectively discharges the color inks of black, cyan, magenta and yellow and an ink-jet head which discharges the white ink are arranged in a conveying direction of a printing medium. Printing is performed by discharging the white ink to the printing medium after discharging the color inks to the printing medium.

SUMMARY OF THE INVENTION

If a time from the discharge of the colors to the discharge of the white ink is short, the drying of the color inks has not progressed, wherefore the color inks and the white ink may be mixed in some cases. That can be dealt with by securing a time from the discharge of the color inks to the discharge of the white ink by disposing a vertically folded path, for example, by moving the printing medium upward after moving the printing medium downward. However, in such a configuration, the printing medium needs to be folded on a recording surface (surface adhered with the inks) side of the printing medium to move the printing medium upward. At this time, the printing medium needs to be folded, for example, by air turn bars provided on the recording surface side to suppress a disturbance of an image on the recording surface.

However, the air turn bars support the printing medium with a clearance between the air turn bars and the printing medium. Thus, it has been difficult to stably convey the printing medium due to the meandering of the printing medium, the convex deformation of the printing medium to form creases, and the like.

This invention was developed in view of the above problem and aims to stably convey a printing medium while securing a time from the discharge of color ink(s) to the printing medium to the discharge of a white ink.

A printing apparatus according to the invention, prints an image on a recording surface of a printing medium by discharging an ink while conveying the printing medium in the form of an elongated belt having the recording surface and a non-recording surface opposite to the recording surface, and comprises: a conveyor which conveys the printing medium; a color printing unit which discharges a color ink from above to the recording surface of the printing medium being conveyed; and a white printing unit which discharges a white ink from above to the recording surface of the printing medium being conveyed, wherein: the conveyor includes: a first conveying part which conveys the printing medium toward one side along the recording surface with the recording surface of the printing medium facing up below the color printing unit; an inverting conveying part which vertically inverts the recording surface and the non-recording surface of the printing medium by conveying the printing medium conveyed from the first conveying unit downward and further conveying the printing medium with changing a moving direction of the printing medium to another side opposite to the one side, vertically inverts again by conveying the printing medium from the one side to another side, subsequently conveying the printing medium upward and further changing a moving direction of the printing medium to the one side, and conveys the printing medium from another side to the one side, a second conveying part which conveys the printing medium conveyed from the inverting conveying part toward the one side along the recording surface with the recording surface of the printing medium facing up below the white printing unit, and the inverting conveying part includes a plurality of rotary bodies configured to rotate while being in contact with only the non-recording surface of the printing medium and having the non-recording surface wound thereon.

A printing method according to the invention, prints an image on a recording surface of a printing medium by discharging an ink while conveying the printing medium in the form of an elongated belt having the recording surface and a non-recording surface opposite to the recording surface, comprises: a conveying step of conveying the printing medium; a color printing step of discharging a color ink from above to the recording surface of the printing medium being conveyed; a white printing step of discharging a white ink from above to the recording surface of the printing medium being conveyed, wherein: the conveying step includes: a first conveying step of conveying the printing medium toward one side along the recording surface with the recording surface of the printing medium facing up in performing the color printing step; an inverting conveying step of vertically inverts the recording surface and the non-recording surface of the printing medium by conveying the printing medium downward after the first conveying step and further conveying the printing medium with changing a moving direction of the printing medium to another side opposite to the one side, vertically inverts again by conveying the printing medium from the one side to another side, subsequently conveying the printing medium upward and further changing a moving direction of the printing medium to the one side, and conveys the printing medium from another side to the one side, and; a second conveying step of conveying the printing medium toward the one side along the recording surface with the recording surface of the printing medium facing up in performing the white printing step after the inverting conveying step, and the inverting conveying step is performed using a plurality of rotary bodies configured to rotate while being in contact with only the non-recording surface of the printing medium and having the non-recording surface wound thereon.

In the invention (printing apparatus, printing method) thus configured, the printing medium after color printing is performed on the recording surface of the printing medium in the color printing unit can be conveyed while the recording surface and the non-recording surface of the printing medium are inverted twice by the only rotary bodies in contact with the non-recording surface of the printing medium (inverting conveying part, inverting conveying step). In this way, without providing air turn bars, a time to convey the printing medium from the color printing unit to the white printing unit can be secured while the printing medium is firmly supported by the rotary bodies in contact with the non-recording surface of the printing medium. In this way, the printing medium can be stably conveyed while a time from the discharge of the color ink to the printing medium to the discharge of the white ink is secured.

A printing system according to the invention, comprises: the printing apparatus according to any one of claims1to7; and a drying apparatus which dries a printing medium having a color ink and a white ink adhered thereto by the printing apparatus. Accordingly, the printing medium can be stably conveyed while the time from the discharge of the color ink to the printing medium to the discharge of the white ink is secured.

As described above, according to the invention, it is possible to stably convey a printing medium while securing a time from the discharge of color ink(s) to the printing medium to the discharge of a white ink.

As described above, according to the invention, the formation of wrinkles in an ink discharge range can be suppressed in printing an image by discharging ink to a printing medium while conveying the printing medium in a conveying direction.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

FIG. 1is a front view schematically showing an example of a printing system according to the invention. InFIG. 1and subsequent figures, a horizontal direction X and a vertical direction Z are shown as appropriate. As shown inFIG. 1, the printing system1has a configuration with a coating apparatus2, a printing apparatus3and a drying apparatus5arrayed in this order in the horizontal direction X (array direction). In this printing system1, the printing apparatus3prints an image by an ink-jet method on a printing medium M having a coating liquid applied thereto by the coating apparatus2and the drying apparatus5dries the printing medium M having the image printed thereon while the printing medium M in the form of an elongated belt is conveyed in a roll-to-roll manner from an unwinding roll11to a winding roll12. Note that a material of the printing medium M is a film made of OPP (oriented polypropylene), PET (polyethylene terephthalate) or the like. However, the material of the printing medium M is not limited to the film and may be paper or the like. Such a printing medium M is flexible. Further, out of both surfaces of the printing medium M, the surface on which images are to be printed is referred to as a front surface M1and the surface opposite to the front surface M1is referred to as a back surface M2as appropriate.

The coating apparatus2includes a pan21storing a liquid primer (coating liquid), a gravure roller22partially immersed in the primer stored in the pan21and a conveying unit23conveying the printing medium M. In the coating apparatus2, a coating region is provided where the gravure roller22contacts the printing medium M conveyed by the conveying unit23from below, and the conveying unit23conveys the printing medium M along the coating region with the front surface M1of the printing medium M facing down. On the other hand, the gravure roller22supplies the primer to the coating region by rotating while holding the primer on the peripheral surface thereof. In this way, the primer supplied by the gravure roller22is applied to the front surface M1of the printing medium M in the coating region. Further, in the coating region, a moving direction of the printing medium M and a rotating direction of the peripheral surface of the gravure roller22are opposite. That is, the primer is applied to the printing medium M by a reverse kiss method. Then, the conveying unit23carries out the printing medium M from the coating apparatus2to the printing apparatus3with the front surface M1of the printing medium M having the primer applied thereto facing up.

FIG. 2is a front view schematically showing the printing apparatus provided in the printing system ofFIG. 1. InFIG. 2and subsequent figures, one side X1and the other side X2of the horizontal direction X are shown as appropriate. Here, the one side X1is a side from the coating apparatus2to the printing apparatus3and from the printing apparatus3to the drying apparatus5, and the other side X2is a side opposite to the one side X1. The printing apparatus3includes a housing31, a color printing unit32arranged in the housing31, a white printing unit33arranged above the color printing unit32in the housing31, and a conveying unit4conveying the printing medium M by a plurality of rollers arranged in the housing31.

The color printing unit32includes a plurality of (six) discharge heads321arrayed in the moving direction (direction from the other side X2toward the one side X1) of the printing medium M above the printing medium M conveyed by the conveying unit4. The plurality of discharge heads321include nozzles facing the front surface M1of the printing medium M passing therebelow from above, and discharge color inks of mutually different colors from the nozzles by the ink-jet method. Here, the color inks mean inks other than a white ink and include inks of cyan, magenta, yellow, black and the like. In this way, the plurality of discharge heads321of the color printing unit32print a color image on the front surface M1of the printing medium M by discharging the color inks to the front surface M1of the printing medium M passing therebelow from above.

Further, the white printing unit33includes a single discharge head331arranged above the printing medium M conveyed by the conveying unit4. The discharge head331includes nozzles facing the front surface M1of the printing medium M passing therebelow from above, and discharges the white ink from the nozzles by the ink-jet method. In this way, the discharge head321of the white printing unit33prints a white image on the front surface M1of the printing medium M by discharging the white ink to the front surface M1of the printing medium M passing therebelow from above.

A carry-in port311is open in a side wall on the other side X2of the housing31. The printing medium M carried out from the coating apparatus2is carried into the housing31through the carry-in port311. In contrast, the conveying unit4includes a carry-in part41(fourth conveying part). The carry-in part41includes a plurality of rollers411arrayed in the horizontal direction X below the color printing unit32and conveys the printing medium M carried in from the carry-in port311from the other side X2toward the one side X1while supporting the printing medium M by the plurality of rollers411.

Further, the conveying unit4includes an ascending conveying part42(fifth conveying part) provided on the one side X1of the carry-in part41. The ascending conveying part42includes a plurality of rollers421arrayed in the vertical direction Z outside (one side X1of) the color printing unit32. This ascending conveying part42conveys the printing medium M upward while supporting the printing medium M by the plurality of rollers421after changing the moving direction of the printing medium M from a direction toward the one side X1to an upward direction by bending the printing medium M, which is conveyed from the carry-in part41, upward by the lowermost roller421, out of the plurality of rollers421.

Further, the conveying unit4includes an upper conveying part43(sixth conveying part) provided above the color printing unit32. The upper conveying part43includes a plurality of rollers431arrayed in the horizontal direction X above the color printing unit32. This upper conveying part43conveys the printing medium M toward the other side X2while supporting the printing medium M by the plurality of rollers431after changing the moving direction of the printing medium M from the upward direction to a direction toward the other side X2by bending the printing medium M, which is conveyed from the ascending conveying part42, toward the other side X2by the roller431located at the end of the one side X1, out of the plurality of rollers431.

Further, the conveying unit4includes a descending conveying part44(seventh conveying part) provided on the other side X2of the upper conveying part43. The descending conveying part44includes a plurality of rollers441arrayed in the vertical direction Z outside (other side X2of) the color printing unit32. This descending conveying part44conveys the printing medium M downward while supporting the printing medium M by the plurality of rollers441after changing the moving direction of the printing medium M from the direction toward the other side X2to a downward direction by bending the printing medium M, which is conveyed from the upper conveying part43, downward by the uppermost roller441, out of the plurality of rollers441. Out of the plurality of rollers441of this descending conveying part44, the uppermost roller441is located to be higher than the respective discharge heads321of the color printing unit32, and the lowermost roller441is located to be lower than the respective discharge heads321of the color printing unit32. That is, the descending conveying part44conveys the printing medium M from a side above the color printing unit32to a side below the color printing unit32.

Further, the conveying unit4includes a color conveying part45(first conveying part) provided below the upper conveying part43and on the one side X1of the descending conveying part44. This color conveying part45includes a plurality of rollers451arrayed in the horizontal direction X and configured to contact the back surface M2of the printing medium M, and the printing medium M conveyed from the descending conveying part44is supported below the color printing unit32by the plurality of rollers451. In this way, the plurality of rollers451of the color conveying part45convey the printing medium M from the other side X2toward the one side X1while supporting the printing medium M conveyed from the descending conveying part44from below by contacting the back surface M2of the printing medium M from below. The color printing unit32discharges the color inks from above to the front surface M1of the printing medium M conveyed along the front surface M1by the color conveying part45.

At this time, the front surface M1of the printing medium M conveyed by the color conveying part45is facing up, and the back surface M2of the printing medium M is facing down. Specifically, the printing medium M carried out from the coating apparatus2is carried in through the carry-in port311with the front surface M1thereof facing up, and conveyed from the other side X2toward the one side X1by the carry-in part41. The printing medium M having passed through the carry-in part41is conveyed from the one side X1toward the other side X2by the upper conveying part43while being vertically inverted by the ascending conveying part42and the upper conveying part43. Thus, the front surface M1of the printing medium M conveyed by the upper conveying part43is facing down. The printing medium M having passed through the upper conveying part43is conveyed from the other side X2toward the one side X1by the color conveying part45while being vertically inverted by the descending conveying part44and the color conveying part45. Thus, the front surface M1of the printing medium M conveyed by the color conveying part45is facing up.

Further, the conveying unit4includes rollers461,462configured to contact the front surface M1of the printing medium M on a side upstream of the color conveying part45in the moving direction of the printing medium M. The roller461is a drive roller driving the printing medium M, and the roller462is a driven roller including a tension sensor detecting a tension applied to the printing medium M. Such drive roller461and driven roller462constitute a tension adjuster which adjusts a tension of the printing medium M together with a driven roller472including a later-described tension sensor detecting a tension applied to the printing medium M, a drive roller471and a drive roller491. Specifically, the rollers461,471and491respectively rotate at speeds corresponding to the tensions detected by the tension sensors of the rollers462,472, whereby the entire tension of the printing medium M conveyed by the conveying unit4is adjusted to a predetermined target tension. In this way, the color inks and the white ink can be discharged to the printing medium while a proper tension is applied to the printing medium.

Further, the conveying unit4includes an inverting conveying part47vertically inverting the printing medium, which is conveyed from the color conveying part45toward the one side X1, twice. This inverting conveying part47includes a plurality of rollers471,472arrayed in the vertical direction Z on the one side X1of the color conveying part45and configured to contact the back surface M2of the printing medium M. Out of the plurality of rollers471,472, the upper roller471changes the moving direction of the printing medium M from the direction toward the one side X1to the downward direction by bending the printing medium M, which is conveyed from the color conveying part45, downward, and the lower roller472changes the moving direction of the printing medium M from the downward direction to the direction toward the other side X2by bending the printing medium M, which is conveyed from the roller471, toward the other side X2. In this way, the printing medium M is vertically inverted by the rollers471,472in contact with the back surface M2of the printing medium M, whereby the back surface M2of the printing medium M is facing up and the front surface M1of the printing medium M is facing down.

Further, the inverting conveying part47includes a plurality of rollers473arrayed in the horizontal direction X below the color conveying part45and on the other side X2of the roller472and configured to contact the back surface M2of the printing medium M. These rollers473convey the printing medium M conveyed from the roller472from the one side X1toward the other side X2. In this way, the printing medium M whose back surface M2is facing up is conveyed from the one side X1toward the other side X2by the plurality of rollers473in contact with the back surface M2of the printing medium M.

Furthermore, the inverting conveying part47includes a plurality of rollers474,476and477arrayed in the vertical direction Z on the other side X2of the plurality of rollers473and the descending conveying part44and configured to contact the back surface M2of the printing medium M. Out of the plurality of rollers474to477, the lowermost roller474changes the moving direction of the printing medium M from the direction toward the other side X2to the upward direction by bending the printing medium M, which is conveyed from the plurality of rollers473, upward, and the uppermost roller477changes the moving direction of the printing medium M from the upward direction to the direction toward the one side X1by bending the printing medium M, which is conveyed from the roller474via the roller476, toward the one side X1. In this way, the printing medium M is vertically inverted by the rollers474to477in contact with the back surface M2of the printing medium M, whereby the front surface M1of the printing medium M is facing up and the back surface M2of the printing medium M is facing down.

Further, the inverting conveying part47includes a roller478arranged above the upper conveying part43and on the one side X1of the roller477and configured to contact the back surface M2of the printing medium M. The roller478conveys the printing medium M conveyed from the roller477from the other side X2toward the one side X1. In this way, the printing medium M whose front surface M1is facing up is conveyed from the other side X2toward the one side X1by the roller478in contact with the back surface M2of the printing medium M.

As just described, the inverting conveying part47vertically inverts the front surface M1and the back surface M2of the printing medium M by conveying the printing medium M conveyed from the color conveying part45downward by the rollers471,472and further conveying the printing medium M with changing the moving direction of the printing medium M to the direction toward the other side X2by the roller472. Subsequently, the inverting conveying part47conveys the printing medium M from the one side X1toward the other side X2by the plurality of rollers473, and then conveys the printing medium M upward by the rollers474to477. Further, the inverting conveying part47vertically inverts the front surface M1and the back surface M2of the printing medium M again by changing the moving direction of the printing medium M to the direction toward the one side X1by the roller477, and conveys the printing medium M from the other side X2toward the one side X1by the roller478.

In this way, the inverting conveying part47vertically inverts the front surface M1and the back surface M2of the printing medium M twice by the only rollers471to478rotating while being in contact with the back surface M2of the printing medium M and having the back surface M2wound thereon. Specifically, the inverting conveying part47can vertically invert the front surface M1and the back surface M2of the printing medium M twice without providing supporting members such as rollers and air turn bars on the side of the front surface M1of the printing medium M at all.

Further, the conveying unit4includes a white conveying part48(second conveying part) provided above the upper conveying part43and on the one side X1of the roller478of the inverting conveying part47. This white conveying part48includes a roller481, and the printing medium M conveyed from the roller478of the inverting conveying part47is supported below the white printing unit33by the roller481. As just described, the roller481of the white conveying part48conveys the printing medium M from the other side X2toward the one side X1while supporting the printing medium M from below by being in contact with the back surface M2of the printing medium M conveyed from the roller478of the inverting conveying part47from below. The white printing unit33discharges the white ink from above to the front surface M1of the printing medium M conveyed along the front surface M1by the white conveying part48.

Further, the conveying unit4includes a carry-out part49(third conveying part) provided above the upper conveying part43and on the one side X1of the white conveying part48. The carry-out part49includes a plurality of rollers491arrayed in the horizontal direction X and configured to contact the back surface M2of the printing medium M. In contrast, a carry-out port312is open in a side wall on the one side X1of the housing31, and the plurality of rollers491of the carry-out part49carry out the printing medium M from the carry-out port312by conveying the printing medium M from the other side X2toward the one side X1while being in contact with the back surface M2of the printing medium M from below.

As just described, the conveying unit4includes supporting members to support the printing medium M, which is vertically inverted twice and reaches the carry-out port312after entering the color conveying part45, not on the side of the front surface M1of the printing medium M, but only on the side of the back surface M2of the printing medium M.

Further, the printing apparatus3includes a pre-dryer34arranged in the housing31. The pre-dryer34is arranged between the carry-in part41and the inverting conveying part47in the vertical direction Z. This pre-dryer34includes a plurality of nozzles341arrayed in the moving direction of the printing medium M conveyed from the one side X1toward the other side X2by the plurality of rollers473of the inverting conveying part47. Each nozzle341faces the front surface M1of the printing medium M conveyed by the plurality of rollers473from below and injects room-temperature air to the front surface M1of this printing medium M from below. That is, the front surface M1of the printing medium M, to which the color inks were discharged from the color printing unit32, is dried by the pre-dryer34. Note that this pre-dryer34is not necessarily limited to the one between the carry-in part41and the inverting conveying part47, and the arrangement position of the pre-dryer34is not limited as long as the pre-dryer34can be positioned to inject air to the front surface M1of the printing medium M conveyed by the inverting conveying part47. Specifically, this pre-dryer34can be so arranged that air can be injected to the front surface M1of the printing medium M before the white ink is discharged to the front surface M1of the printing medium M by the white printing unit33after the color inks are discharged to the front surface of the printing medium M by the color printing unit32. However, if this pre-dryer34is arranged between the carry-in part41and the inverting conveying part47, there is a merit that a space below the inverting conveying part47can be utilized as an arrangement space for the pre-dryer and the printing apparatus can be reduced in size in the horizontal direction.

Furthermore, the printing apparatus3includes an upper dryer35arranged in the housing31. The upper dryer35is arranged above the carry-out part49. This upper dryer35includes a plurality of nozzles351arrayed in the moving direction of the printing medium M conveyed from the other side X2toward the one side X1by the carry-out part49. Each nozzle351faces the front surface M1of the printing medium M conveyed by the carry-out part49from above and injects room-temperature air to the front surface M1of this printing medium M from above. That is, the front surface M1of the printing medium M, to which the white ink was discharged from the white printing unit33, is dried by the upper dryer35.

FIG. 3is a front view schematically showing the drying apparatus equipped in the printing system ofFIG. 1. The drying apparatus5dries the printing medium M while appropriately conveying the printing medium M in the horizontal direction X in a zigzag manner. This drying apparatus5includes a housing6(drying furnace) arranged on the one side X1of the housing31of the printing apparatus3. This housing6has a rectangular parallelepiped shape extending in the horizontal direction X, and both side walls6a,6bof the housing6in the horizontal direction X are parallel to the vertical direction Z, perpendicular to the horizontal direction X and facing each other while being spaced apart in the horizontal direction X.

A carry-in port61penetrates in the horizontal direction X through the side wall6aon the side X2of the horizontal direction X, out of the side walls6a,6b, and a carry-out port66penetrates in the horizontal direction X through the side wall6bon the side X1(side opposite to the printing apparatus3) of the horizontal direction X. The printing medium M carried out from the carry-out port312of the printing apparatus3is carried into the housing6through the carry-in port61and carried out to the outside of the housing6through the carry-out port66.

That is, the drying apparatus5includes a conveying unit51conveying the printing medium M in the housing6, and the conveying unit51conveys the printing medium M from the carry-in port61to the carry-out port66. This conveying unit51includes an upper-stage conveying part51uconveying the printing medium M from the other side X2toward the one side X1, a middle-stage conveying part51mconveying the printing medium M from the one side X1toward the other side X2, and a lower-stage conveying part51lconveying the printing medium M from the other side X2toward the one side X1. The middle-stage conveying part51mis arranged below the upper-stage conveying part51u, and the lower-stage conveying part51lis arranged below the middle-stage conveying part51m. Accordingly, the printing medium M conveyed by the upper-stage conveying part51u, the printing medium M conveyed by the middle-stage conveying part51mand the printing medium conveyed by the lower-stage conveying part51lare arranged in the vertical direction Z, in other words, overlap each other when viewed from the vertical direction Z. Specifically, the upper-stage conveying part51uconveys the printing medium M at the same height as the carry-in port61, and the printing medium M is conveyed in the horizontal direction X by the upper-stage conveying part51uwith the front surface M1facing up and the back surface M2facing down. The middle-stage conveying part51mconveys the printing medium M below the upper-stage conveying part51u, and the printing medium M is conveyed in the horizontal direction X by the middle-stage conveying part51mwith the front surface M1facing down and the back surface M2facing up. The lower-stage conveying part51lconveys the printing medium M below the middle-stage conveying part51m, and the printing medium M is conveyed in the horizontal direction X by the lower-stage conveying part51lwith the front surface M1facing up and the back surface M2facing down.

The upper-stage conveying part51uincludes a roller52at an end of the one side X1, and the middle-stage conveying part51mincludes a roller53at an end on the one side X1. The rollers52,53are vertically arranged, and fold the printing medium M from the one side X1toward the other side X2. That is, out of the rollers52,53, the roller52on an upper side folds the printing medium M downward by contacting the back surface M2of the printing medium M conveyed from the carry-in port61toward the one side X1, and the roller53on a lower side folds the printing medium M toward the other side X2by contacting the back surface M2of the printing medium M conveyed downward from the roller52. By folding the printing medium M from the one side X1toward the other side X2in this way, the front surface M1and the back surface M2of the printing medium M are vertically inverted.

Further, the middle-stage conveying part51mincludes an air turn bar54at an end on the other side X2, and the lower-stage conveying part51lincludes an air turn bar55at an end on the other side X2. The air turn bars54,55are vertically arranged, and fold the printing medium M from the other side M2toward the one side X1. That is, out of the air turn bars54,55, the air turn bar54on an upper side injects air to the front surface M1of the printing medium M conveyed from the roller53toward the other side X2. In this way, the air turn bar54folds the printing medium M downward while being spaced apart from the front surface M1of the printing medium M. Further, the air turn bar55on a lower side injects air to the front surface M1of the printing medium M conveyed downward from the air turn bar54. In this way, the air turn bar55folds the printing medium M toward the one side X1while being spaced apart from the front surface M1of the printing medium M. By folding the printing medium M from the other side X2toward the one side X1in this way, the front surface M1and the back surface M2of the printing medium M are vertically inverted.

Further, the lower-stage conveying part51lincludes a roller56at an end on the one side X1. This roller56is arranged for the carry-out port66, and conveys the printing medium M toward the carry-out port66by rotating while contacting the back surface M2of the printing medium M conveyed from the air turn bar55toward the one side X1.

Such a drying apparatus5includes six air-blow dryers7ato7f. Out of these, two air-blow dryers7a,7bare provided for the printing medium M conveyed by the upper-stage conveying part51uand arranged between the carry-in port61and the roller52. The air-blow dryers7a,7bdry the printing medium M conveyed by the upper-stage conveying part51u. Two air-blow dryers7c,7dare provided for the printing medium M conveyed by the middle-stage conveying part51mand arranged between the roller53and the air turn bar54. The air-blow dryers7c,7ddry the printing medium M conveyed by the middle-stage conveying part51m. Two air-blow dryers7e,7fare provided for the printing medium M conveyed by the lower-stage conveying part51land arranged between the air turn bar55and the carry-out port66. The air-blow dryers7e,7fdry the printing medium M conveyed by the lower-stage conveying part51l.

FIG. 4is a schematic diagram partially and enlargedly showing the air-blow dryer provided for the upper-stage conveying part, andFIG. 5is a schematic diagram partially and enlargedly showing the air-blow dryer provided for the middle-conveying part and the lower-stage conveying part. Next, the air-blow dryers7ato7fare described also with reference toFIGS. 4 and 5.

The air-blow dryer7aincludes an air blower unit71uarranged above the printing medium M conveyed by the upper-stage conveying part51u. The air blower unit71uincludes an air blower chamber72uextending in the horizontal direction X above the printing medium M. Opposite end surfaces in the horizontal direction X of the air blower chamber72uare planes perpendicular to the horizontal direction X and parallel to the vertical direction Z. A hot wind generated by heating air by a heater provided outside the printing system1is supplied to the air blower chamber72u. The lower surface of the air blower chamber72uis a nozzle arrangement plane73ufacing the front surface M1(upper surface) of the printing medium M facing up from above. This nozzle arrangement plane73uis a plane parallel to the horizontal direction X and perpendicular to the vertical direction Z. Further, the air blower unit71uincludes a plurality of nozzles76uarranged at a predetermined interval in the horizontal direction X on this nozzle arrangement plane73u. In this way, the plurality of nozzles76uare arranged between the nozzle arrangement plane73uand the front surface M1of the printing medium M and face the front surface M1of the printing medium M. The respective nozzles76ucommunicate with the air blower chamber72u, and the hot wind supplied to the air blower chamber72uis injected to the front surface M1of the printing medium M from the nozzles76uto dry the printing medium M. As just described, out of the plurality of air-blow dryers7ato7f, the air-blow dryer7afirst dries the printing medium M carried into the housing6.

Further, the air-blow dryer7aincludes a plurality of (as many as the nozzles76u) rollers74arranged below the printing medium M conveyed by the upper-stage conveying part51u. The plurality of rollers74are arrayed at a predetermined interval in the moving direction (horizontal direction X) of the printing medium M conveyed by the upper-stage conveying part51u, and the peripheral surface of each roller74contacts the back surface M2(lower surface) of the printing medium M conveyed by the upper-stage conveying part51ufrom below. Each roller74supports the printing medium M from below while rotating about an axis of rotation parallel to a direction (width direction of the printing medium M) perpendicular to the horizontal direction X and the vertical direction Z, following the printing medium M. Further, a fine groove is spirally provided on the roller74, so that air easily escapes from between the printing medium M and the peripheral surface of the roller74.

Incidentally, the nozzle76ufaces a range between two rollers74adjacent in the horizontal direction X from above, and the roller74faces a range between two nozzles76uadjacent in the horizontal direction X from below. That is, the nozzles76uand the rollers74are alternately arranged at an interval, which is half the predetermined interval, in the horizontal direction X, and alternately arranged one by one in the horizontal direction X in a plan view viewed from the vertical direction Z. In other words, the nozzles76uand the rollers74are arrayed in a staggered manner.

In such a configuration, as shown inFIG. 4, the printing medium M is shifted further downward than the upper ends of the rollers74by being pressed downward by the hot wind from the nozzles76uin parts facing the nozzles76u, and is supported by the rollers74in parts facing the rollers74. Accordingly, the printing medium M is conveyed in the horizontal direction X from the other side X2toward the one side X1while becoming wavy between the upper ends of the rollers74and a side below these upper ends.

Further, as shown inFIG. 4, the upper ends of the rollers74are located below the lower ends of the nozzles76u. Accordingly, there is a clearance in the vertical direction Z between the nozzles76uand the rollers74when viewed from an array direction (horizontal direction X) of the nozzles76uor the rollers74, in other words, from the moving direction of the printing medium M conveyed by the upper-stage conveying part51u. Thus, if the injection of the hot wind from the nozzles76uis stopped due to the occurrence of a certain trouble, the printing medium M is supported from below by the rollers74with the front surface M1of the printing medium M separated from the nozzles76uand the back surface M2of the printing medium M held in contact with the rollers74.

The air-blow dryer7bis arranged downstream of the air-blow dryer7ain the moving direction of the printing medium M conveyed by the upper-stage conveying part51u. Similarly to the air-blow dryer7a, this air-blow dryer7bincludes an air blower unit71uarranged above the printing medium M conveyed by the upper-stage conveying part51uand a plurality of rollers74arranged below the printing medium M. In such an air-blow dryer7b, a plurality of (as many as rollers74) of nozzles76uof the air blower unit71uinject a hot wind to the front surface M1of the printing medium M from above to dry the printing medium M while the plurality of rollers74support the back surface M2of the printing medium M from below.

The air-blow dryer7cincludes air blower units71u,71lrespectively arranged above and below the printing medium M conveyed by the middle-stage conveying part51m. The upper air blower unit71uincludes an air blower chamber72uextending in the horizontal direction X above the printing medium M. Opposite end surfaces in the horizontal direction X of the air blower chamber72uare planes perpendicular to the horizontal direction X and parallel to the vertical direction Z. The above hot wind is supplied to the air blower chamber72u. The lower surface of the air blower chamber72uis a nozzle arrangement plane73ufacing the back surface M2(upper surface) of the printing medium M facing up from above. This nozzle arrangement plane73uis a plane parallel to the horizontal direction X and perpendicular to the vertical direction Z. Further, the air blower unit71uincludes a plurality of nozzles76uarranged at a predetermined interval in the horizontal direction X on this nozzle arrangement plane73u. In this way, the plurality of nozzles76uare arranged between the nozzle arrangement plane73uand the back surface M2of the printing medium M and face the back surface M2of the printing medium M. The respective nozzles76ucommunicate with the air blower chamber72u, and the hot wind supplied to the air blower chamber72uis injected to the back surface M2of the printing medium M from the nozzles76u.

The lower air blower unit71lincludes an air blower chamber72lextending in the horizontal direction X below the printing medium M. Opposite end surfaces in the horizontal direction X of the air blower chamber72lare planes perpendicular to the horizontal direction X and parallel to the vertical direction Z. The above hot wind is supplied to the air blower chamber72l. The upper surface of the air blower chamber72lis a nozzle arrangement plane73lfacing the front surface M1(lower surface) of the printing medium M facing down from below. This nozzle arrangement plane73lis a plane parallel to the horizontal direction X and perpendicular to the vertical direction Z. Further, the air blower unit71lincludes a plurality of nozzles76larranged at a predetermined interval in the horizontal direction X on this nozzle arrangement plane73l. In this way, the plurality of nozzles76lare arranged between the nozzle arrangement plane73land the front surface M1of the printing medium M and face the front surface M1of the printing medium M. The respective nozzles76lcommunicate with the air blower chamber72l, and the hot wind supplied to the air blower chamber72lis injected to the front surface M1of the printing medium M from the nozzles76l.

As just described, the air blower units71u,71lsandwich the printing medium M. In other words, the printing medium M conveyed by the middle-stage conveying part51mpasses between the air blower units71uand71l. In this way, the air-blow dryer7cdries the printing medium M by injecting the hot wind to the printing medium M conveyed by the middle-stage conveying part51mfrom the both upper and lower air blower units71u,71l.

Incidentally, the upper nozzle76ufaces a range between two nozzles76ladjacent in the horizontal direction X from above, and the lower nozzle76lfaces a range between two upper nozzles76uadjacent in the horizontal direction X from below. That is, the upper and lower nozzles76u,76lare alternately arranged at an interval, which is half the predetermined interval, in the horizontal direction X, and alternately arranged one by one in the horizontal direction X in a plan view viewed from the vertical direction Z. In other words, the nozzles76u,76lare arrayed in a staggered manner. Such a staggered array of the nozzles76u,76lis realized by displacing the positions of the air blower chambers72u,72lfrom each other in the horizontal direction X.

In such a configuration, as shown inFIG. 5, the printing medium M is shifted further downward than a conveyance center line L by being pressed downward by the hot wind from the nozzles76uin parts facing the upper nozzles76u, and is shifted further upward than the conveyance center line L by being pressed upward by the hot wind from the nozzles76lin parts facing the lower nozzles76l. Here, the conveyance center line L is a horizontal virtual straight line equidistant from each nozzle76uand each nozzle76lin the vertical direction Z. Thus, the printing medium M is conveyed in the horizontal direction X from the one side X1toward the other side X2while becoming wavy between upper and lower sides of the conveyance center line L.

The air-blow dryer7dis arranged downstream of the air-blow dryer7cin the moving direction of the printing medium M conveyed by the middle-stage conveying part51m. This air-blow dryer7dincludes air blower units71u,71lsandwiching the printing medium M conveyed by the middle-stage conveying part51min the vertical direction Z, similarly to the air-blow dryer7c. In such an air-blow dryer7d, the air blower unit71uinjects the hot wind to the back surface M2of the printing medium M from above, and the air blower unit71linjects the hot wind to the front surface M1of the printing medium M from below, whereby the printing medium M is dried.

Similarly to the air-blow dryer7c, the air-blow dryer7eincludes air blower units71u,71lsandwiching the printing medium M in the vertical direction Z. However, since the air-blow dryer7eis arranged for the printing medium M conveyed by the lower-stage conveying part51l, the air blower units71u,71lof the air-blow dryer7esandwich the printing medium M conveyed by the lower-stage conveying part51lin the vertical direction Z. In such an air-blow dryer7e, the air blower unit71uinjects the hot wind to the front surface M1of the printing medium M from above, and the air blower unit71linjects the hot wind to the back surface M2of the printing medium M from below, whereby the printing medium M is dried.

The air-blow dryer7fis arranged downstream of the air-blow dryer7ein the moving direction of the printing medium M conveyed by the lower-stage conveying part51l. This air-blow dryer7fincludes air blower units71u,71lsandwiching the printing medium M conveyed by the lower-stage conveying part51lin the vertical direction Z, similarly to the air-blow dryer7e. In such an air-blow dryer7f, the air blower unit71uinjects the hot wind to the front surface M1of the printing medium M from above, and the air blower unit71linjects the hot wind to the back surface M2of the printing medium M from below, whereby the printing medium M is dried.

Further, the drying apparatus5includes exhaust units8a,8bin the housing6, exhaust units8a,8bexhausts the air in the housing6to outside of the housing6. The exhaust unit8ais arranged at an end part on the side X2in the housing6and located between the air-blow dryers7a,7dand7eand the side wall6a. The exhaust unit8bis arranged at an end part on the X1side in the housing6and located between the air-blow dryers7b,7cand7fand the side wall6b. These exhaust units8a,8bhave a common configuration. The exhaust unit8a,8bincludes four exhaust chambers81to84arrayed in the vertical direction Z. The exhaust chamber81is arranged above the printing medium M conveyed by the upper-stage conveying part51u, the exhaust chamber82is arranged between the printing medium M conveyed by the upper-stage conveying part51uand the printing medium M conveyed by the middle-stage conveying part51m, the exhaust chamber83is arranged between the printing medium M conveyed by the middle-stage conveying part51mand the printing medium M conveyed by the lower-stage conveying part51l, and the exhaust chamber84is arranged below the printing medium M conveyed by the lower-stage conveying part51l. Each of the exhaust chambers81to84exhausts the air sucked from the inside of the housing6to the outside of the carry-in port61.

FIG. 6is a block diagram schematically showing a hot wind supply mechanism equipped in the drying apparatus. An upper-stage drying unit Du including the air-blow dryers7a,7barranged for the upper-stage conveying part51u, a middle-stage drying unit Dm including the air-blow dryers7c,7darranged for the middle-stage conveying part51m, and a lower-stage drying unit Dl including the air-blow dryers7e,7farranged for the lower-stage conveying part51lare shown inFIG. 6.

The hot wind supply mechanism9includes an upper-stage supplying unit91usupplying the hot wind to the upper-stage drying unit Du, a middle-stage supplying unit91msupplying the hot wind to the middle-stage drying unit Dm and a lower-stage supplying unit91lsupplying the hot wind to the lower-stage drying unit Dl. Since the upper-stage supplying unit91u, the middle-stage supplying unit91mand the lower-stage supplying unit91lhave a common configuration, this common configuration is described for the upper-stage supplying unit91u.

The upper-stage supplying unit91uincludes an input part91ito which the air heated by the external heater, i.e. the hot wind is input, an introduction pipe912which introduces the hot wind input from the input part911, and a branched pipe913branched from the introduction pipe912to the respective air-blow dryers7a,7b. Accordingly, the hot wind input from the input part911is supplied to the respective air-blow dryers7a,7bvia the branched pipe913after passing through the introduction pipe912, and injected from the nozzles76uof the respective air-blow dryers7a,7b. Further, a blower914which blows the hot wind from the side of the input part911to the side of the upper-stage drying unit Du is mounted in the introduction pipe912, and a wind velocity (m/s) of the hot wind to be supplied to the respective air-blow dryers7a,7bis changed by changing a rotation speed of the blower914, with the result that the wind velocity of the hot wind to be injected from the nozzles76ucan be adjusted.

Similarly, for the middle-stage drying unit Dm, the hot wind having the wind velocity thereof adjusted by a blower914is supplied to the air-blow dryers7c,7dby the middle-stage supplying unit91m, and injected from the nozzles76u,76lof the air-blow dryers7c,7d. Further, for the lower-stage drying unit Dl, the hot wind having the wind velocity thereof adjusted by a blower914is supplied to the air-blow dryers7e,7fby the lower-stage supplying unit91l, and injected from the nozzles76u,76lof the air-blow dryers7e,7f.

Further, the rotation speeds of the blowers914of the upper-stage supplying unit91u, the middle-stage supplying unit91mand the lower-stage supplying unit91lare adjusted in advance, for example, by an operator, and the wind velocity of the air injected from each nozzle76uprovided in the upper-stage drying unit Du is lower than that of the air injected from each nozzle76u,76lprovided in the middle-stage drying unit Dm and lower than that of the air injected from each nozzle76u,76lprovided in the lower-stage drying unit Dl. Incidentally, the wind velocity may be adjusted regardless of the rotation speed of the blower914. That is, a damper may be provided between the blower914and the branched pipe913and the wind velocity of the hot wind may be adjusted by changing an opening of the damper.

Further, in this example, the plurality of nozzles76uof the air-blow dryers7a,7binject the air at the same wind velocity. Accordingly, a uniform air can be injected to the front surface M1of the printing medium M conveyed by the upper-stage conveying part51ufrom the plurality of nozzles76u.

Furthermore, the plurality of nozzles76lof the air-blow dryers7c,7dinject the air at the same wind velocity. Accordingly, a uniform air can be injected to the front surface M1of the printing medium M conveyed by the middle-stage conveying part51mfrom the plurality of nozzles76l.

Similarly, the plurality of nozzles76uof the air-blow dryers7c,7dinject the air at the same wind velocity. Accordingly, a uniform air can be injected to the back surface M2of the printing medium M conveyed by the middle-stage conveying part51mfrom the plurality of nozzles76u.

Particularly, in the air-blow dryers7c,7d, the wind velocity of the air injected by the plurality of nozzles76land that of the air injected by the plurality of nozzles76uare equal. Accordingly, it can be suppressed that the printing medium M conveyed by the middle-stage conveying part51mis shifted to contact either the nozzles76lor the nozzles76u.

Further, the wind velocity of the air injected by the nozzles76uof the air-blow dryers7e,7fand that of the air injected by the nozzles76lof the air-blow dryers7c,7dare equal. Accordingly, the drying of the printing medium M can be promoted by injecting the air at a high wind velocity to the front surface M1of the printing medium M conveyed by the middle-stage conveying part51mand the front surface M1of the printing medium M conveyed by the lower-stage conveying part51l.

Incidentally, in this specification, the hot wind is a wind of 60° C. or higher and the temperature of the hot wind is preferably 80° or higher. Further, the type of a gas injected from the nozzles76u,76lis not limited to the air as in this example.

In the embodiment described above, the printing medium M after color printing is performed on the front surface M1(recording surface) by the color printing unit32can be conveyed while the front surface M1and the back surface M2of the printing medium M are inverted twice by the only rollers471to478(rotary bodies) in contact with the back surface M2(non-recording surface) of the printing medium M (inverting conveying part47). In this way, without providing air turn bars, a time to convey the printing medium M from the color printing unit32to the white printing unit33can be secured while the printing medium M is firmly supported by the rollers471to478in contact with the back surface M2of the printing medium M. Thus, the printing medium M can be stably conveyed while the time from the discharge of the color inks to the printing medium M to the discharge of the white ink is secured.

Incidentally, a distance from the color printing unit32to the white printing unit33along the printing medium M conveyed by the conveying unit4can be equal to or more than double or triple of a length of the color printing unit32along the printing medium M, for example, as shown inFIG. 2. However, a distance relationship of these is not limited to the example here.

Further, the white printing unit33is arranged above the color printing unit32. In such a configuration, a distance from the color printing unit32to the white printing unit33can be secured, which contributes to securing a time from the discharge of the colors inks to the printing medium M to the discharge of the white ink.

Further, the carry-out part49(third conveying part) is equipped which is arranged above the color printing unit32and conveys the printing medium M conveyed from the white conveying part48(second conveying part) toward the one side X1up to the carry-out port312of the printing apparatus3with the front surface M1of the printing medium M facing up. In such a configuration, a space above the color printing unit32can be utilized as an arrangement space for the carry-out part49to convey the printing medium M to the outside of the printing apparatus3.

Further, the upper dryer35is equipped which is arranged above the carry-out part49(third conveying part) and blows the air from above to the front surface M1of the printing medium M conveyed by the carry-out part49. In such a configuration, the drying of the printing medium M completed with the discharge of the color inks and the white ink can be quickly started by the upper dryer35. Moreover, the space above the color printing unit32can be utilized as an arrangement space for the upper dryer35, and the printing apparatus3can be reduced in size in the horizontal direction X.

Further, the pre-dryer34is equipped which is arranged below the inverting conveying part47and blows the air from below to the front surface M1of the printing medium M conveyed toward the other side X2by the inverting conveying part47. In such a configuration, the drying of the printing medium M completed with the discharge of the color inks can be quickly started by the pre-dryer34. Moreover, a space below the inverting conveying part47can be utilized as an arrangement space for the pre-dryer34and the printing apparatus3can be reduced in size in the horizontal direction X.

Further, the conveying unit4includes the rollers461,462(tension adjuster) arranged upstream of the color printing unit32to adjust a tension of the printing medium M. In such a configuration, the color inks can be discharged to the printing medium M while a proper tension is given to the printing medium M.

Further, the conveying unit4conveys the printing medium M toward the color printing unit32by the carry-in part41, the ascending conveying part42, the upper conveying part43and the descending conveying part44. Specifically, the carry-in part41(fourth conveying part) conveys the printing medium M from the other side X2toward the one side X1at a position below the inverting conveying part47. The ascending conveying part42(fifth conveying part) conveys the printing medium M conveyed from the carry-in part41upward at a position outside (on the one side X1of) the inverting conveying part47. The upper conveying part43(sixth conveying part) conveys the printing medium M conveyed from the ascending conveying part42toward the other side X2at a position above the color printing unit32and below the carry-out part49. Then, the descending conveying part44(seventh conveying part) conveys the printing medium M conveyed from the upper conveying part43from a side above the color printing unit32to a side below the color printing unit32at a position outside (on the other side X2of) the color printing unit32. In such a configuration, the printing medium M carried in from the other side X2can be conveyed to the color printing unit32.

In the embodiment described above, the printing system1corresponds to an example of a “printing system” of the invention, the printing apparatus3corresponds to an example of a “printing apparatus” of the invention, the color printing unit32corresponds to an example of a “color printing unit” of the invention, the white printing unit33corresponds to an example of a “white printing unit” of the invention, the pre-dryer34corresponds to an example of a “pre-dryer” of the invention, the upper dryer35corresponds to an example of an “upper dryer” of the invention, the conveying unit4corresponds to an example of a “conveyor” of the invention, the carry-in part41corresponds to an example of a “fourth conveying part” of the invention, the carry-out port312corresponds to an example of a “carry-out port” of the invention, the ascending conveying part42corresponds to an example of a “fifth conveying part” of the invention, the upper conveying part43corresponds to an example of a “sixth conveying part” of the invention, the descending conveying part44corresponds to an example of a “seventh conveying part” of the invention, the color conveying part45corresponds to an example of a “first conveying part” of the invention, the rollers461,462,471,472and491correspond to an example of a “tension adjuster” of the invention, the inverting conveying part47corresponds to an example of an “inverting conveying part” of the invention, the rollers471to478correspond to an example of “a plurality of rotary bodies” of the invention, the white conveying part48corresponds to an example of a “second conveying part” of the invention, the carry-out part49corresponds to an example of a “third conveying part” of the invention, the drying apparatus5corresponds to an example of a “drying apparatus” of the invention, the printing medium M corresponds to an example of a “printing medium” of the invention, the front surface M1corresponds to an example of a “recording surface” of the invention, the back surface M2corresponds to an example of a “non-recording surface” of the invention, the one side X1corresponds to an example of “one side” of the invention, the other side X2corresponds to an example of “another side” of the invention, the color printing unit32performs a “color printing step” of the invention, the white printing unit33performs a “white printing step” of the invention, the conveying unit4performs a “conveying step” of the invention, the color conveying part45performs a “first conveying step” of the invention, the inverting conveying part47performs an “inverting conveying step” of the invention, and the white conveying part48performs a “second conveying step” of the invention.

Note that the invention is not limited to the above embodiment and various changes other than the aforementioned ones can be made without departing from the gist of the invention. For example, in the air-blow dryer7aor7b, the number of the nozzles76uand that of the rollers74need not be equal, and the number of the nozzles76umay be more than or less than that of the rollers74.

Alternatively, as shown inFIG. 7, some rollers74may be replaced by nozzles76l. Here,FIG. 7is a front view schematically showing a modification of the drying apparatus. A drying apparatus5ofFIG. 7differs from the drying apparatus5ofFIG. 3in that an air-blow dryer7aincludes the nozzles76lbelow the printing medium M, and the other configuration is common in these drying apparatuses5.

The air-blow dryer7aof the drying apparatus5shown inFIG. 7includes a plurality of (less than the number of nozzles76uby N) rollers74and N nozzles76larranged below the printing medium M. Note that N is an integer of 1 or greater, and “4” in this example. The plurality of rollers74are arrayed at a predetermined interval in the moving direction (horizontal direction X) of the printing medium M conveyed by the upper-stage conveyor51u, and the peripheral surface of each roller74contacts the back surface M2(lower surface) of the printing medium M conveyed by the upper-stage conveyor51ufrom below. Further, the N nozzles76lare arrayed at a predetermined interval in the horizontal direction X and inject a hot wind to the back surface M2of the printing medium M from below. In the moving direction of the printing medium M conveyed by the upper-stage conveyor51u, the plurality of these rollers74are located downstream of the N nozzles76l, and the printing medium M conveyed by the upper-stage conveyor51uis supported from below by the rollers74after the hot wind is injected from the nozzles76l.

As just described, in the example ofFIG. 7, the air-blow dryers7a,7binclude the nozzles76larranged upstream of the most upstream roller74(roller74at a right end ofFIG. 7), out of the plurality of rollers74(rotary bodies), in the moving direction of the printing medium M conveyed by the upper-stage conveyor51uon the side of the back surface M2(non-recording surface) of the printing medium M, and the nozzles76linject the hot wind to the back surface M2. In an initial stage in which the printing medium M enters the air-blow dryers7a,7bthrough the carry-in port61, a temperature distribution in the printing medium M is relatively uniform. Thus, the drying of the printing medium M can be promoted by injecting the hot wind to the back surface M2of the printing medium M from the nozzles76l.

FIG. 8is a diagram schematically showing another modification of the drying apparatus. In this modification, a drying apparatus5includes heating unit75to heat a plurality of rollers74. The heating unit75includes a heating wire751arranged inside the roller74and a power supply752supplying a current to the heating wire751. The heating wire751is provided in each of the plurality of rollers74. The heating wire751generates heat by the current supplied from the power supply752and heats the roller74. Accordingly, the printing medium M conveyed by the upper-stage conveyor51uis supported from below by the heated rollers74. In such a configuration, the drying of the printing medium M can be promoted by the heat of the rollers74.

Further, modifications different from those ofFIGS. 7 and 8can also be added. For example, the air-blow dryer7bmay have the same configuration as the air-blow dryer7e. In such a modification, the air-blow dryer7bdoes not include the rollers74and supports the printing medium M by nozzles76uand nozzles76larranged above and below the printing medium M, and only the air-blow dryer7aincludes the rollers74.

Further, in the above example, the plurality of nozzles76uof the air-blow dryers7a,7binject the air at the same wind velocity, and the plurality of nozzles76lof the air-blow dryers7c,7dinject the air at the same wind velocity. However, a setting example of the wind velocities is not limited to this. That is, the respective nozzles76uof the air-blow dryers7a,7bneed not necessarily inject the air at an equal wind velocity and the wind velocity may be different among these nozzles76u. Similarly, the wind velocity may be different among the respective nozzles76lof the air-blow dryers7c,7d. If the wind velocity is different, a maximum wind velocity, out of the wind velocities of the air injected from the respective nozzles76uof the air-blow dryers7a,7b, may be set to be lower than a minimum wind velocity, out of the wind velocities of the air injected from the respective nozzles76lof the air-blow dryers7c,7d.

Further, it is not always necessary to arrange two air-blow dryers for each of the upper-stage conveyor51u, the middle-stage conveyor51mand the lower-stage conveyor51l. Accordingly, a single air-blow dryer7amay be arranged for the upper-stage conveyor51u, a single air-blow dryer7dmay be arranged for the middle-stage conveyor51mand a single air-blow dryer7emay be arranged for the lower-stage conveyor51l.

Further, the air-blow dryers7ato7fneed not necessarily be arranged separately in the vertical direction. Accordingly, the air-blow dryers7ato7dmay be arranged at the same height and arrayed in the horizontal direction X. Alternatively, the air-blow dryers7ato7fmay be arranged at the same height and arrayed in the horizontal direction X.

Further, the upper-stage supplier91u, the middle-stage supplier91mand the lower-stage supplier91lneed not have the same configuration. Accordingly, a feedback pipe returning the air exhausted from the exhaust chambers82,83to the introduction pipe912of the middle-stage supplier91mmay be, for example, provided. Further, a similar feedback pipe may be provided in the lower-stage supplier91lto return the air exhausted from the exhaust chambers83,84.

Further, the specific configuration of the conveying unit4is not limited to the above example. Accordingly, the arrangement or number of the rollers can be changed as appropriate in the carry-in part41, the ascending conveying part42, the upper conveying part43, the descending conveying part44, the color conveying part45, the inverting conveying part47, the white conveying part48and the carry-out part49.

Further, the printing medium M needs not be carried into the housing31of the printing apparatus3through the carry-in part41. For example, the printing apparatus3may be so configured as to carry the printing medium M into the upper conveying part43from the one side X1of the housing31without providing the carry-in part41and the ascending conveying part42.

Further, it is not essential to provide the pre-dryer34and the upper dryer35in the printing apparatus3.

As described above, the printing apparatus may be configured so that the white printing unit is arranged above the color printing unit. In such a configuration, a distance from the color printing unit to the white printing unit can be secured, which contributes to securing the time from the discharge of the color ink to the printing medium to the discharge of the white ink.

The printing apparatus may further comprises a third conveying part which is arranged above the color printing unit and conveys the printing medium conveyed from the second conveying part toward the one side up to a carry-out port of the printing apparatus with the recording surface of the printing medium facing up. In such a configuration, a space above the color printing unit can be utilized for the third conveying part which conveys the printing medium toward the outside of the printing apparatus.

The printing apparatus may further comprises an upper dryer which is arranged above the third conveying part and blows a gas from above to the recording surface of the printing medium conveyed by the third conveying part. In such a configuration, the drying of the printing medium completed with the discharge of the color ink and the white ink can be quickly started by the upper dryer. Moreover, the space above the color printing unit can be utilized as an arrangement space for the upper dryer and the printing apparatus can be reduced in size in a horizontal direction.

The printing apparatus may further comprises a pre-dryer which blows a gas to the recording surface of the printing medium conveyed by the inverting conveying part. In such a configuration, the drying of the printing medium completed with the discharge of the color ink can be quickly started by the pre-dryer.

The printing apparatus may be configured so that the conveyor includes a tension adjuster to adjust a tension of the printing medium. In such a configuration, the color ink and the white ink can be discharged to the printing medium while a proper tension is given to the printing medium.

The printing apparatus may be configured so that the conveyor includes a fourth conveying part to convey the printing medium from another side toward the one side at a position below the inverting conveying part, a fifth conveying part to convey the printing medium conveyed from the fourth conveying part upward at a position outside the inverting conveying part, a sixth conveying part to convey the printing medium conveyed from the fifth conveying part toward another side at a position above the color printing unit and below the third conveying part, and a seventh conveying part to convey the printing medium conveyed from the sixth conveying part from a side above the color printing unit to a side below the color printing unit at a position outside the color printing unit. In such a configuration, the printing medium carried in from another side can be conveyed to the color printing unit.

The invention is applicable to techniques in general for drying a printing medium M adhered with aqueous ink(s) by a hot wind.