JP2023086468A - Drying device, image formation device, and drying method - Google Patents

Abstract

To provide a drying device, an image formation device, and a drying method which can prevent deterioration in drying capability to ink when a flow rate is low.SOLUTION: A drying device includes: a gas supply part for supplying a predetermined flow rate of gas to a ventilation flue provided on the downstream side of an inkjet head in a conveyance direction of a recording medium; and a control part for performing such control as to change a cross-sectional area of the ventilation flue in a gas supply direction. A drying method supplies a predetermined flow rate of gas to a ventilation flue provided on the downstream side of an inkjet head in a conveyance direction of a recording medium, and changes a cross-sectional area of the ventilation flue in a gas supply direction.SELECTED DRAWING: Figure 1

Description

The present invention relates to a drying device, an image forming device and a drying method.

2. Description of the Related Art There is known an inkjet image forming apparatus that ejects liquid such as ink onto a recording medium such as paper to form an image on the recording medium. Some of such image forming apparatuses have a drying device that dries ink on a recording medium on which an image is formed.

For example, Japanese Patent Application Laid-Open No. 2002-100000 describes a ventilation passage extending in a direction intersecting a conveying path of a recording medium, and heating the outside air introduced into the ventilation passage to blow dry air onto the surface of the recording medium conveyed on the conveying path. A drying apparatus is disclosed having a heated air blowing means. In the drying apparatus disclosed in Patent Document 1, the outside air is introduced into the ventilation path by the blower, and the blowing amount of the blower is controlled according to the amount of ink ejected onto the recording medium.

JP 2013-154620 A

By the way, in the drying device disclosed in Patent Document 1, in order to reliably dry the ink, the amount of air blown by the blower is controlled according to the amount of ink ejected onto the recording medium. In this kind of control, if the blowing volume of the blower is reduced, the wind speed (flow velocity) becomes slower, and the time for the wind to pass through the surface of the recording medium (the time for the wind to take in the vapor that evaporates from the ink) becomes longer. , the amount of vapor taken into the air increases as the ink dries. As a result, the amount of steam in the air increases, and if the amount of steam exceeds the saturated amount, the air can no longer take in the steam, so there is a problem that the drying ability for drying the ink is lowered.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a drying apparatus, an image forming apparatus, and a drying method capable of preventing a decrease in ink drying performance when the flow velocity is slow.

The drying device according to the present invention is
a gas supply unit that supplies a predetermined flow rate of gas to a ventilation path provided downstream of the inkjet head in the conveying direction of the recording medium;
a control unit that performs control to change the cross-sectional area of the ventilation passage in the gas supply direction;
Prepare.

An image forming apparatus according to the present invention includes:
an inkjet head that forms an image on a recording medium;
a drying device as described above;
Prepare.

The drying method according to the present invention is
supplying a predetermined flow rate of gas to a ventilation path provided downstream of the inkjet head in the conveying direction of the recording medium;
A cross-sectional area of the ventilation passage in the gas supply direction is changed.

According to the present invention, it is possible to prevent a decrease in ink drying performance when the flow velocity is slow.

1 is a diagram showing a schematic configuration of main parts of an image forming apparatus provided with a drying device according to an embodiment of the present invention; FIG. 2 is a block diagram showing main parts of a control system of the image forming apparatus shown in FIG. 1; FIG. FIG. 2 is a sectional view taken along the line II of the image forming apparatus shown in FIG. 1; FIG. 2 is a diagram showing a case where the cross-sectional area of a ventilation passage is increased in the drying apparatus shown in FIG. 1; FIG. 2 is a diagram showing a case where the cross-sectional area of a ventilation passage is reduced in the drying apparatus shown in FIG. 1; FIG. 5 is a diagram for explaining changes in water content with respect to different flow velocities when the thickness of the recording medium is thin; FIG. 5 is a diagram for explaining changes in water content with respect to different flow velocities when the thickness of the recording medium is large; FIG. 5 is a diagram for explaining changes in water content with respect to different flow velocities when the amount of ink adhered is small. FIG. 10 is a diagram for explaining changes in water content with respect to different flow velocities when the amount of adhered ink is large; 4 is a table showing setting examples of flow velocities with respect to the amount of ink adhered and the basis weight of a recording medium; FIG. 2 is a diagram for explaining changes in the amount of steam with respect to different flow rates in the drying apparatus shown in FIG. 1; It is a figure which shows schematic structure of the modification (modification 1) of the drying apparatus shown in FIG. FIG. 10 is a cross-sectional view illustrating a modification (modification 2) of the drying device illustrated in FIG. 9 ; FIG. 10 is a diagram showing a schematic configuration of a modified example (modified example 3) of the drying apparatus shown in FIG. 9, and is a diagram showing a case where the cross-sectional area of the ventilation passage on the upstream side in the transport direction is reduced. FIG. 10 is a diagram showing a schematic configuration of a modified example (modified example 3) of the drying device shown in FIG. 9, and is a diagram showing a case where the cross-sectional area of the ventilation passage on the upstream side in the transport direction is increased. FIG. 10 is a diagram showing a schematic configuration of a modified example (modified example 3) of the drying apparatus shown in FIG. 9, and is a diagram showing a case where the cross-sectional area of the ventilation passage on the downstream side in the transport direction is reduced. FIG. 10 is a diagram showing a schematic configuration of a modified example (modified example 3) of the drying apparatus shown in FIG. 9, and is a diagram showing a case where the cross-sectional area of the ventilation passage on the downstream side in the conveying direction is increased.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of main parts of an inkjet printer 100 including a drying section 40 according to this embodiment. FIG. 2 is a block diagram showing main parts of the control system of the inkjet printer 100. As shown in FIG. In this embodiment, the inkjet printer 100 corresponds to the image forming apparatus of the invention, and the drying section 40 corresponds to the drying apparatus of the invention.

As shown in FIG. 1, the inkjet printer 100 includes a transport section 10, a carriage section 20 having an inkjet head (hereinafter simply referred to as head) 21, a heating section 30, a drying section 40, and the like. The inkjet printer 100 also includes an operation display section 70, an input/output interface 80, a control section 90, and the like, as shown in FIG.

Although not shown, the inkjet printer 100 also includes a supply unit that supplies the medium M, which is a recording medium, to the transport unit 10 and a collection unit that collects the medium M ejected from the transport unit 10 .

In the inkjet printer 100, the types of media M include, for example, paper (coated paper, non-coated paper, etc.), fabric, plastic film, and various other media on which the ink ejected from the head 21 can be fixed. can be used. Further, the medium M may be in the form of a sheet cut into a predetermined size, or may be in the form of a long sheet unwound from a roll.

A supply unit (not shown) is arranged on the upstream side of the transport unit 10 in the transport direction T of the medium M. As shown in FIG. The supply unit is configured to store media M inside and supply the stored media M to the transport unit 10 . For example, if the media M are sheet-shaped, the supply unit is configured to stack and store a plurality of media M and supply the stored media M to the transport unit 10 one by one. . Further, if the medium M is long, the supply unit stores the medium M in a rolled state, unwinds the stored medium M, and supplies the medium M to the transport unit 10 . It is configured.

A collecting section (not shown) is arranged downstream of the conveying section 10 in the conveying direction T. As shown in FIG. The collection unit is configured to collect the media M discharged from the transport unit 10 and store the media M inside. For example, if the media M are sheet-shaped, the collecting unit is configured to collect the media M discharged from the conveying unit 10 one by one, and stack and store a plurality of media M inside. ing. Further, if the medium M is elongated, the collecting section is configured to collect the medium M ejected from the conveying section 10 so as to wind it up and store the medium M inside.

The transport unit 10 has a transport belt 11, a driving roller 12, a driven roller 13, and the like. The transport belt 11 is an endless belt, stretched in a loop shape between a drive roller 12 and a driven roller 13, and rotates in the transport direction T as the drive roller 12 is rotationally driven. The medium M supplied from the supply unit is placed on the transport surface 111 of the transport belt 11 . Then, the medium M is conveyed so as to sequentially pass under the carriage section 20 and the drying section 40 by the rotation of the conveying belt 11 described above.

The driving roller 12 and the driven roller 13 may have a heater inside so as to heat the conveying belt 11 together with the heating unit 30 described later.

Further, the conveying belt 11 may be configured to have a large number of suction holes (not shown) over the entire surface. In this case, for example, a suction device (not shown) is provided in the heating unit 30, which will be described later. The suction device applies a negative pressure to the lower side of the conveying surface 111 of the conveying belt 11, and the medium M is conveyed while being sucked by the suction holes. make it With such a configuration, the medium M comes into close contact with the heated conveying belt 11, and the heat can be efficiently transferred to the medium M to heat it.

Further, here, as an example, the medium M is conveyed using one conveying belt 11, but the medium M is conveyed using separate conveying belts in the carriage section 20 and the drying section 40. good too.

Further, here, as an example, the transport unit 10 that transports the medium M with the transport belt 11 is illustrated, but the transport unit 10 is not limited to the transport belt 11, and may be configured to transport the medium M with a drum or a roller. good.

The carriage unit 20 has a head 21 that ejects ink onto the medium M being transported to form an image (print). Although the detailed illustration of the internal configuration of the carriage section 20 is omitted, the carriage section 20 includes not only the head 21 but also a drive substrate for driving the head 21, an ink flow path for supplying ink to the head 21, and other components that are used by the head 21. A large number of devices and members necessary for image formation are arranged.

The head 21 of the carriage unit 20 may be configured to be a single-pass (one-pass) system in which image formation is performed by one scan, or to be a scan (multi-pass) system in which image formation is performed by multiple scans. may be configured as follows. Further, the head 21 for the number of ink colors may be arranged in one carriage portion 20, or a different carriage portion 20 may be provided for each ink color.

The head 21 has a plurality of nozzles (not shown) on a surface (nozzle surface) facing the conveying surface 111 of the conveying belt 11 . The head 21 forms an image on the surface of the medium M by ejecting ink from each nozzle. The nozzle surface of the head 21 is arranged so that the distance (gap) to the surface of the medium M is within a specified range, thereby forming an image with desired quality.

The heating unit 30 is configured to heat the conveying belt 11 . Specifically, the heating unit 30 is disposed on the downstream side of the carriage unit 20 in the conveying direction T, facing the lower surface of the conveying surface 111 of the conveying belt 11, and the portion of the conveying belt facing the heating unit 30. 11 is configured to heat. By heating the portion facing the heating unit 30, the medium M on which the image is formed with the ink is heated, and the ink is heated to promote the drying of the ink. As the heating source of the heating unit 30, for example, an infrared heater or the like with good responsiveness during control is used.

For example, the heating unit 30 has a length in the transport direction T that is greater than or equal to the length in the transport direction T of the sheet-like medium M that can be processed by the inkjet printer 100 . Further, as shown in FIG. 3 to be described later, the heating unit 30 has a length in the width direction W of the transport belt 11 in the width direction W of the transport belt 11 (the direction of the transport belt 11 orthogonal to the transport direction T). or longer.

Corresponding to the heating section 30 arranged in this way, the ventilation passage 41 of the drying section 40 is arranged so as to cover the heating section 30 and part of the conveying belt 11 from above (see FIG. 3).

If the ink can be dried by the air blown by the drying section 40 at room temperature, the heating section 30 may be omitted. It suffices if it is arranged on the downstream side.

The drying section 40 has a ventilation path 41, a first duct 42, a second duct 43, a first blower section 421, a second blower section 431, and the like. The first blower part 421 and the second blower part 431 correspond to the gas supply part in the present invention.

The ventilation path 41 is arranged along the conveying direction T in the conveying section 10 so as to partially cover the heating section 30 and the conveying belt 11 from above. The air passage 41 has an upper surface 411, two side surfaces 412, and the like, as shown in FIG. 3, which will be described later. In the air passage 41, the portion surrounded by the upper surface 411, the two side surfaces 412, and the conveying surface 111 serves as a passage through which the supplied air flows, and the medium M conveyed through this portion is moved by the supplied air. , drying of the ink is performed.

The first duct 42 is connected to the downstream end in the conveying direction T of the air passage 41 . Also, the first air blower 421 is connected to the end of the first duct 42 opposite to the end connected to the air passage 41 . That is, the first air blowing section 421 is connected to the ventilation passage 41 via the first duct 42 . The first air blower 421 takes in air around the inkjet printer 100 , supplies the air to the first duct 42 , and supplies the air to the ventilation path 41 via the first duct 42 .

Also, the second duct 43 is connected to the upstream end in the transport direction T of the air passage 41 . In addition, the second air blower 431 is connected to the end of the second duct 43 opposite to the end connected to the air passage 41 . That is, the second air blower 431 is connected to the ventilation passage 41 via the second duct 43 . The second air blower 431 discharges the air in the second duct 43 to discharge the air in the ventilation passage 41 via the second duct 43 .

With the above configuration, the drying section 40 supplies air to the ventilation path 41, and the medium M conveyed in the ventilation path 41 is dried by the supplied air.

In this embodiment, the air around the inkjet printer 100 is supplied to the ventilation path 41 by the first blower 421 . It is good also as a structure which supplies. In this case, the inkjet printer 100 may be configured to include a device that supplies gas such as dry air or nitrogen to the first blower section 421 .

Further, here, the drying section 40 supplies air from the downstream side in the transport direction T toward the upstream side in the ventilation passage 41, but the air is supplied from the upstream side in the transport direction T toward the downstream side. may be configured to supply. In this case, the air blowing directions of the first air blowing unit 421 and the second air blowing unit 431 are adjusted so that the second air blowing unit 431 supplies air to the air passage 41 and the first air blowing unit 421 discharges air from the air passage 41. Change it.

Moreover, although the air flows through the ventilation passages 41 along the conveying direction T here, the ventilation passages 41 may be arranged so that the air flows crosswise to the conveying direction T.

Further, here, the drying section 40 is configured to have the first blower section 421 and the second blower section 431 , but may be configured to have only one of the first blower section 421 and the second blower section 431 .

The operation display section 70, the input/output interface 80, and the control section 90 will be described with reference to FIG.

The operation display unit 70 is, for example, a flat panel display such as a liquid crystal with a touch panel or an organic EL (Electro Luminescence). The operation display unit 70 displays an operation menu for the user, information regarding image data of an image to be formed, various states of the inkjet printer 100, and the like. The operation display unit 70 also has a plurality of keys and receives various input operations of the user.

The input/output interface 80 mediates transmission and reception of data between the external device 200 and the controller 90 . The input/output interface 80 is composed of, for example, various serial interfaces, various parallel interfaces, or a combination thereof.

The external device 200 is, for example, a personal computer, a facsimile device, or the like, and supplies print jobs, image data, and the like to the control section 90 via the input/output interface 80 .

The control unit 90 has a CPU (Central Processing Unit) 91, a RAM (Random Access Memory) 92, a ROM (Read Only Memory) 93, a storage unit 94, and the like.

The CPU 91 reads various control programs and setting data stored in the ROM 93, stores them in the RAM 92, and executes the programs to perform various arithmetic processing. For example, based on the image data received via the input/output interface 80 , the control unit 90 generates a drive signal for forming an image and outputs it to the head 21 .

RAM 92 provides working memory space for CPU 91 and stores temporary data. Note that the RAM 92 may include a nonvolatile memory.

The ROM 93 stores programs for various controls executed by the CPU 91, setting data, and the like. Instead of the ROM 93, a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or flash memory may be used.

The storage unit 94 stores print jobs input from the external device 200 via the input/output interface 80 and image data related to the print jobs. As the storage unit 94, for example, an HDD (Hard Disk Drive) is used, and a DRAM (Dynamic Random Access Memory) or the like may be used together.

The conveying section 10, the carriage section 20, the heating section 30, the drying section 40, the operation display section 70, the input/output interface 80, and the like are connected to the control section 90, respectively. The control unit 90 centrally controls the overall operation of the inkjet printer 100 . The conveying unit 10, the carriage unit 20, the heating unit 30, the drying unit 40, the operation display unit 70, and the input/output interface 80 are controlled by the control unit 90 to perform predetermined processing.

In the inkjet printer 100 having the above configuration, under the control of the control unit 90, the carriage unit 20 forms an image on the medium M conveyed to the conveying unit 10, and the ink on the medium M on which the image is formed is dried by the heating unit 30. Dry in section 40 .

By the way, in the conventional drying apparatus as disclosed in Patent Document 1, the amount of air blown by the blower is controlled according to the amount of ink ejected onto the medium M in order to dry the ink reliably. In such control, if the blowing volume of the blower is reduced, the wind velocity (flow velocity) becomes slow, and the time for the wind to pass through the surface of the medium M (the time for the wind to take in the vapor that evaporates from the ink) becomes longer. , the amount of vapor taken into the air increases as the ink dries. As a result, the amount of steam in the air increases, and if the amount of steam exceeds the saturated amount, the air can no longer take in the steam, so there is a problem that the drying ability for drying the ink is lowered.

Therefore, in the present embodiment, the drying section 40 includes a gas supply section (first blowing section 421, A second air blower 431) is provided. The drying section 40 also includes a control section 90 that performs control to change the cross-sectional area of the ventilation passage 41 in the air supply direction. The control unit 90 changes the flow velocity of the air so as to maintain the flow rate of the air flowing through the ventilation passage 41 by performing control to change the cross-sectional area of the ventilation passage 41 in the air supply direction. The air thus controlled dries the ink on the medium M ejected by the head 21 .

Control for changing the cross-sectional area of the ventilation passage 41 is provided as one function of the control unit 90, and is provided as a program executed by the control unit 90, for example. Specifically, the control unit 90 controls a cross-sectional area changing unit 440, which will be described later, to change the cross-sectional area of the air passage 41 in the air supply direction, thereby changing the flow velocity of the air flowing through the air passage 41. .

The cross-sectional area changing portion 440 will be described with reference to FIGS. 1 and 2 as well as FIGS. 3, 4A, and 4B. FIG. 3 is a cross-sectional view of the inkjet printer 100 shown in FIG. 1 taken along line II. FIG. 4A is a diagram showing a case where the cross-sectional area of the ventilation passage 41 is increased in the drying section 40 shown in FIG. FIG. 4B is a diagram showing a case where the cross-sectional area of the ventilation passage 41 is reduced in the drying section 40 shown in FIG. In addition, hereinafter, the cross-sectional area of the ventilation path 41 means the cross-sectional area of the ventilation path 41 in the air supply direction.

As shown in FIG. 3, the ventilation path 41 has an upper surface 411 (facing portion), two side surfaces 412, and the like, and is arranged to cover the heating unit 30 and part of the conveying belt 11 from above. With such a configuration, the upper surface 411 (opposing portion) faces the medium M to be transported from above. Although detailed illustration is omitted, the upper surface 411 is supported by the ventilation path 41 and the cross-sectional area changing portion 440 so as to be able to move up and down with respect to the conveying surface 111 of the conveying belt 11 .

In order to change the cross-sectional area of the ventilation passage 41, the cross-sectional area changing unit 440 is configured to change the vertical height of the upper surface 411 of the ventilation passage 41, that is, to move the upper surface 411 up and down. there is Although detailed illustration is omitted, the cross-sectional area changing unit 440 has, for example, a ball screw mechanism and a cam mechanism for moving up and down the upper surface 411, a motor that is an actuator that drives the ball screw mechanism and the cam mechanism, and the like. Under the control of the control unit 90 , the cross-sectional area changing unit 440 drives the ball screw mechanism and the cam mechanism with a motor or the like to raise and lower the upper surface 411 .

In this way, the cross-sectional area changing unit 440 moves up and down the upper surface 411 of the ventilation passage 41 to change the cross-sectional area of the ventilation passage 41 (the portion surrounded by the upper surface 411, the two side surfaces 412, and the conveying surface 111 shown in FIG. 3). cross-sectional area) can be changed.

For example, as shown in FIG. 3, when the upper surface 411 is raised from the position of the upper surface 411 indicated by the dotted line to the position of the upper surface 411 indicated by the solid line, the portion surrounded by the upper surface 411, the two side surfaces 412, and the conveying surface 111 is increased. The cross-sectional area, that is, the cross-sectional area of the air passage 41 is increased.

The flow rate (air volume) of the air supplied to the ventilation passage 41, the flow velocity (wind velocity) of the air flowing through the ventilation passage 41, and the cross-sectional area of the ventilation passage 41 have the relationship of "flow rate = flow velocity x cross-sectional area". , if the flow rate is constant, the flow velocity can be changed by changing the cross-sectional area. As shown in FIG. 3, the larger the cross-sectional area of the ventilation passage 41, the slower the flow velocity. Conversely, when the cross-sectional area of the ventilation passage 41 is reduced, the flow velocity is increased.

FIG. 4A is a diagram showing a case where the cross-sectional area of the ventilation passage 41 is increased in the drying section 40. FIG. As described above, the cross-sectional area changing unit 440 increases the cross-sectional area of the ventilation passage 41 by raising the upper surface 411 from the position indicated by the dotted line in FIG. 4A to the position indicated by the solid line. In this case, the flow velocity is slower than when the cross-sectional area of the ventilation passage 41 is small (see the dotted line in FIG. 4A).

On the other hand, FIG. 4B is a diagram showing a case where the cross-sectional area of the ventilation passage 41 in the drying section 40 is reduced. As described above, the cross-sectional area changing unit 440 reduces the cross-sectional area of the ventilation passage 41 by lowering the upper surface 411 from the position indicated by the dotted line in FIG. 4B to the position indicated by the solid line. In this case, the flow velocity is faster than when the cross-sectional area of the ventilation passage 41 is large (see the dotted line in FIG. 4B).

Note that the cross-sectional area changing unit 440 is not limited to the configuration for moving up and down the upper surface 411 of the ventilation path 41, and may have another configuration as long as the cross-sectional area of the ventilation path 41 can be changed. For example, the cross-sectional area of the ventilation passage 41 may be changed by widening or narrowing the distance between the two side surfaces 412 in the width direction.

Further, here, the cross-sectional area changing unit 440 moves up and down the upper surface 411 of the ventilation passage 41 so as to keep parallel to the conveying surface 111 of the conveying belt 11 , but for example, the cross-sectional area changing unit 440 moves up and down so as to be inclined with respect to the conveying surface 111 . Alternatively, the upper surface 411 may be raised and lowered. Thereby, in the ventilation passage 41, the flow velocity in the direction in which the air flows can be changed. For example, when it is desired to change the drying speed in the transport direction T of the medium M according to the amount of ink adhered (discharged) or the thickness of the medium M, the upper surface 411 is inclined with respect to the transport surface 111. It should be raised and lowered.

Thus, in the present embodiment, even if the flow rate of air supplied to ventilation passage 41 is constant, the flow velocity of air flowing through ventilation passage 41 can be changed by changing the cross-sectional area of ventilation passage 41 . The relationship between the flow rate and the drying rate will be explained below. Even if the flow rate is constant, the fact that the flow rate can be changed means that the drying rate (drying capacity) can be changed.

The relationship between the flow velocity and the ink drying speed will be described. Although water-based ink will be described as an example here, inks other than water-based ink, such as solvent ink, can be used in the same way.

S (g/m ² /s) is the drying speed of the ink, Di (m ² /s) is the diffusion coefficient of moisture in the ink, d (m) is the thickness of the boundary film of the ink, and C _air is the vapor concentration of the atmosphere. (g/m ³ ), and the ink surface vapor concentration is C _surface (g/m ³ ). The drying speed S can be represented by the following formula (1).

S=Di×(C _surface −C _air )/d (1)

The ink ejected onto the medium M is dried by the air flowing through the drying section 40 while being heated by the heating section 30 as described above. When the air wind is applied to the ink, the boundary film of the ink becomes thin, and the flow velocity of the air and the thickness d of the boundary film of the ink are in an inversely proportional relationship. Therefore, the faster the flow velocity, the thinner the thickness d of the ink boundary film. As the thickness d of the boundary film of the ink is reduced, the drying speed S of the ink is increased, and the drying is accelerated, as can be seen from the above formula (1). In other words, the drying speed (drying capacity) can be changed by changing the flow rate.

In this way, the drying speed can be changed by changing the flow speed. Then, the medium M may be deformed, and it is necessary to dry it properly.

FIG. 5A is a diagram illustrating changes in water content with respect to different flow velocities when the thickness of the media M is thin. When heating is performed by the heating unit 30, if the thickness of the medium M is small, the medium M is easily warmed, and the ink dries quickly. Therefore, if the flow rate is high, excessive drying may occur, so the flow rate should be slowed down to suppress drying.

On the other hand, FIG. 5B is a diagram for explaining changes in water content with respect to different flow velocities when the media M is thick. If the thickness of the medium M is large, it is difficult to warm the medium M, and drying of the ink is delayed. Therefore, if the flow rate is slow, it may become undried, so the flow rate is increased to promote drying.

In this way, there is an optimum flow rate corresponding to the thickness (basis weight) of the medium M, and the flow rate is changed according to the thickness of the medium M.

FIG. 6A is a diagram illustrating changes in water content with respect to different flow velocities when the amount of attached ink is small. If the amount of ink adhering to the medium M is small, the drying time will be short. Therefore, if the flow rate is high, excessive drying may occur, so the flow rate should be slowed down to suppress drying.

On the other hand, FIG. 6B is a diagram for explaining changes in water content with respect to different flow velocities when the amount of attached ink is large. If the amount of ink deposited is large, the drying time will be long. Therefore, if the flow rate is slow, it may become undried, so the flow rate is increased to promote drying.

In this way, there is an optimum flow velocity corresponding to the amount of ink adhered to the medium M, and the flow velocity is changed according to the amount of ink adhered.

As described above, in the drying section 40, the flow velocity is set according to the thickness of the medium M and the amount of ink adhering to the medium M. FIG. FIG. 7 is a table showing setting examples of the flow velocity with respect to the ink adhesion amount and the basis weight of the recording medium (thickness of the medium M). In FIG. 7, for example, ~60 is less than 60, 60 to 80 is greater than or equal to 60 and less than 80, and so on. Based on such a table, the control unit 90 controls the cross-sectional area changing unit 440 of the drying unit 40 so that the flow velocity corresponds to the thickness of the medium M and the amount of ink adhered to the medium M. The upper surface 411 is moved up and down.

The flow velocity set as described above is also set in consideration of the amount of steam taken into the air flowing through the ventilation passage 41 as described below. For example, in the case of water-based ink, water, which is liquid contained in the ink on the medium M, evaporates into water vapor. considered. In the case of solvent ink, the solvent (for example, organic solvent), which is a liquid contained in the ink on the medium M, evaporates into solvent vapor. The vapor content of the solvent vapor contained in the flowing air is taken into account.

Since the air in the ventilation path 41 flows from the entrance to the exit of the ventilation path 41 while taking in the vapor evaporated from the ink on the medium M, the amount of vapor in the air increases from the entrance to the exit of the ventilation path 41. do. At this time, if the flow velocity of the air is slow, the time for the air to pass through the ventilation passage 41 is long, and the time for the air to take in steam is long, so the amount of steam taken into the air is also large. When the amount of vapor contained in the air increases and exceeds the saturated amount of vapor, the air cannot take in any more vapor, so the drying ability to dry the ink decreases. Therefore, the flow velocity is increased so that the amount of steam contained in the air does not exceed the saturated amount of steam.

In this way, the flow rate is changed so that the amount of steam contained in the air does not exceed the saturated amount of steam. If the amount of steam contained in the air does not exceed the saturated amount of steam at the outlet of the ventilation passage 41, the amount of steam contained in the air exceeds the saturated amount of steam at the inlet side of the outlet. no. Therefore, for example, at the outlet of the ventilation passage 41, the flow velocity is set so that the amount of steam contained in the air does not exceed the saturated amount of steam.

As described above, the flow velocity is set according to the thickness of the medium M and the amount of ink adhering to the medium M, and is set so that the amount of vapor contained in the air does not exceed the saturated vapor amount. need to In the present embodiment, as described above, by changing the cross-sectional area of the ventilation path 41, the thickness of the medium M and the amount of ink adhering to the medium M are changed, and the amount of vapor contained in the air is changed. can be set to an appropriate flow rate so that does not exceed the saturated steam amount.

Next, the relationship between the flow rate and the amount of steam will be described. FIG. 8 is a diagram for explaining changes in the amount of steam with respect to different flow rates in the drying section 40. As shown in FIG.

The flow rate of the air flowing through the ventilation passage 41 is also set so that the amount of steam contained in the air does not exceed the saturated amount of steam. As described above, if the amount of steam contained in the air does not exceed the saturated amount of steam at the outlet of the ventilation passage 41, the amount of steam contained in the air is saturated at the position on the inlet side of the outlet. Do not exceed steam volume. Therefore, for example, at the outlet of the ventilation passage 41, the flow rate is set so that the amount of steam contained in the air does not exceed the saturated amount of steam. The flow rate set in this manner is the lower limit of the flow rate required for the ventilation passage 41 .

Here, how to obtain the lower limit value of the flow rate described above will be described. The maximum amount of moisture to be dried is A (g/m ² ), the drying time is B (s), the area of the drying section 40 is C (m ² ), and the maximum amount of steam that the air can contain is D (g/m ^{3 )} . ) (see FIGS. 5A and 8), the lower limit of the flow rate E (m ³ /s) can be obtained from the following equation (2).

E=A/B×C/D (2)

The maximum moisture content A to be dried can be obtained from the amount of ink adhering to the medium M, for example. Also, the drying time B can be obtained from the length of the ventilation path 41 in the transport direction T and the transport speed of the medium M. FIG. The maximum steam content D that air can contain can be obtained from the saturated steam content and the initial steam content (for example, the steam content in the ambient air), as shown in FIG.

As described above, the lower limit of the flow rate required for the ventilation passage 41 can be obtained, and the first blower section 421 and the second blower section 431 having the blowing capacity capable of supplying such a flow rate (predetermined flow rate) are used. make it

As described above, if a predetermined flow rate can be set such that the amount of steam contained in the air does not exceed the saturated amount of steam at the outlet of the ventilation passage 41, the blowing capacity of the first blower section 421 and the second blower section 431 is need not be changed. Therefore, it is not necessary to use the first blowing unit 421 and the second blowing unit 431 with a large blowing capacity in order to increase the blowing amount, and the first blowing unit 421 and the second blowing unit 431 with the minimum required blowing capacity can be used. Therefore, the device cost is not increased.

Then, as described above, by changing the cross-sectional area of the ventilation passage 41, it is possible to set an appropriate flow velocity. Also, the ink can be properly dried without lowering the drying ability.

For example, in FIG. 4A described above, the flow velocity is decreased by increasing the cross-sectional area of the ventilation passage 41 . If this flow velocity is an appropriate flow velocity and the required minimum predetermined flow rate is supplied to the ventilation passage 41, the amount of steam contained in the air will not exceed the saturated steam amount even if the predetermined flow rate is constant. .

Similarly, in FIG. 4B described above, the flow velocity increases by reducing the cross-sectional area of the ventilation passage 41 . If this flow velocity is an appropriate flow velocity and the required minimum predetermined flow rate is supplied to the ventilation passage 41, the amount of steam contained in the air will not exceed the saturated steam amount even if the predetermined flow rate is constant. . Even if the predetermined flow rate is constant, the flow velocity can be increased by reducing the cross-sectional area of the ventilation passage 41, so that the drying speed can be increased.

In practice, if the cross-sectional area of the ventilation passage 41 is reduced, the pressure loss in the ventilation passage 41 increases and the flow rate decreases. Considering this, when the cross-sectional area through which air hardly passes is the smallest, in other words, when the flow velocity is the fastest and the drying speed is the fastest, the flow rate is set so as not to fall below the above lower limit. By setting such a flow rate, even when the cross-sectional area is increased, the flow rate does not fall below the lower limit, and the ink can be dried appropriately.

The drying section 40 having the above configuration uses the gas supply section (the first air blowing section 421 and the second air blowing section 431) in the ventilation path 41 provided downstream of the head 21 in the transport direction T of the medium M. Air is supplied at a predetermined flow rate as described above. Then, the drying unit 40 controls the cross-sectional area changing unit 440 by the control unit 90 to change the cross-sectional area of the ventilation passage 41 in the air supply direction, thereby maintaining the flow rate of the air flowing through the ventilation passage 41. Second, change the flow velocity of the air. The air thus controlled dries the ink on the medium M ejected by the head 21 (drying method).

As described above, in the present embodiment, the drying section 40 includes a gas supply section (first A blower unit 421 and a second blower unit 431) are provided. The drying section 40 also includes a control section 90 that performs control to change the cross-sectional area of the ventilation passage 41 in the air supply direction.

According to the present embodiment configured as described above, by changing the cross-sectional area of the ventilation passage 41 , the flow velocity of the air is changed so as to maintain the flow rate of the air flowing through the ventilation passage 41 . With this, it is possible to obtain an appropriate drying rate by changing the flow rate while securing a constant drying capacity by maintaining the flow rate. Therefore, even when the flow velocity is slow, a certain level or more of the drying ability is ensured, so it is possible to prevent the deterioration of the drying ability for the ink.

Further, by changing the cross-sectional area of the air passage 41, the flow velocity can be adjusted so as to achieve an appropriate drying speed according to the basis weight of the medium M and the amount of ink adhering to the medium M. In this way, the flow speed is adjusted so that the drying speed is appropriate, so even if the first blower unit 421 and the second blower unit 431 that supply the minimum required flow rate are used, the drying capacity is lowered. The ink can be properly dried without causing the ink to dry. As a result, it is possible to prevent a decrease in drying performance without increasing the cost of the apparatus.

<Modification 1>
FIG. 9 is a diagram showing a schematic configuration of a modification of the drying section 40 shown in FIG.

In this modified example, the drying section 40 further includes a radiation section 450 . The radiation section 450 is arranged on the upper surface 411 on the upstream side in the transport direction T in the air passage 41 . The radiation unit 450 radiates radiation to the medium M on which an image is formed by ink ejected from the head 21, heats at least one of the ink on the medium M and the medium M, and dries the ink. We are trying to promote

For example, if the radiation unit 450 is a device that emits infrared rays as radiation, the radiation unit 450 emits infrared rays to the medium M, heats the medium M and/or the ink, and promotes drying of the ink. do. Further, if the radiation unit 450 is a device that emits ultraviolet rays as radiation, the radiation unit 450 emits ultraviolet rays to the medium M to heat the medium M and/or the ink (the ink is ultraviolet curable). In the case of resin, it cures the ink) to accelerate the drying of the ink.

By heating the medium M and/or the ink with the radiation section 450 in addition to the heating section 30, the medium M and/or the ink can be heated in a short time even if the thickness of the medium M changes. drying time can be shortened. Therefore, the length in the conveying direction T of the ventilation path 41 can also be shortened.

In the case of this modification, the radiation section 450 is configured to move up and down integrally with the upper surface 411 by means of the cross-sectional area changing section 440 . Alternatively, the radiation section 450 may be configured to move vertically together with the upper surface 411 by a device other than the cross-sectional area changing section 440 . With such a configuration, the flow velocity of the air flowing through the ventilation passage 41 is adjusted.

As described above, in this modification, the drying section 40 further includes the radiation section 450, so that the ink drying time can be shortened, and the length of the air passage 41 in the transport direction T can be shortened. can.

<Modification 2>
FIG. 10 is a cross-sectional view explaining a modification of the drying section 40 shown in FIG.

In this modified example, the drying section 40 further includes a reflecting section 413 . The reflecting section 413 is arranged so as to reflect the radiation emitted from the radiation section 450 toward the medium M. As shown in FIG. Specifically, the reflecting portion 413 is arranged on the inner surface of the side surface 412 of the portion of the ventilation passage 41 where the radiation portion 450 is arranged.

The reflecting portion 413 is made of a material having a high reflectance with respect to radiation. Alternatively, the reflecting portion 413 may be formed by coating the inner surface of the side surface 412 with a material having a high reflectance to radiation.

In this way, by reflecting the radiation emitted from the radiation section 450 toward the medium M by the reflection section 413, the medium M and/or the ink can be efficiently heated, and the drying time of the ink is can be shortened. Therefore, the length in the conveying direction T of the ventilation path 41 can also be shortened.

As described above, in this modification, the drying section 40 further includes the reflecting section 413, so that the ink drying time can be shortened, and the length of the air passage 41 in the transport direction T can be shortened. can.

<Modification 3>
11A to 11D are diagrams showing schematic configurations of modifications of the drying section 40 shown in FIG. FIG. 11A is a diagram showing a case where the cross-sectional area of the upstream ventilation passage 41B in the transport direction T is reduced, and FIG. 11B shows a case where the cross-sectional area of the upstream ventilation passage 41B in the transport direction T is increased. It is a diagram. FIG. 11C is a diagram showing a case where the cross-sectional area of the ventilation passage 41A on the downstream side in the transport direction T is reduced, and FIG. It is a figure which shows.

In this modified example, the drying section 40 includes a plurality of ventilation paths 41A and 41B. The air passages 41A and 41B are arranged in series along the transport direction T, the air passage 41A is arranged downstream in the conveying direction T, and the air passage 41B is arranged upstream in the conveying direction T. The radiation section 450 shown in FIG. 9 is arranged on the upper surface 411B of the ventilation path 41B.

The ventilation path 41A may have the same structure as the ventilation path 41 described with reference to FIGS. 1 to 8, so redundant description will be omitted here. The air passage 41B may also basically have the same configuration as the air passage 41 described with reference to FIG. are configured to be able to ascend and descend independently.

In this manner, the upper surfaces 411A and 411B of the air passages 41A and 41B can be raised and lowered independently of each other. Therefore, for example, the upper surfaces 411A and 411B can be raised and lowered independently according to the amount of ink adhered and the thickness of the medium M, and the flow velocities in the ventilation paths 41A and 41B can be adjusted.

For example, when the amount of attached ink is large, as shown in FIG. 11A, the upper surface 411B of the ventilation path 41B is lowered to increase the flow velocity of the ventilation path 41B, thereby promoting drying of the ink in the ventilation path 41B. make sure to

Further, when the amount of attached ink is small, as shown in FIG. 11B, the upper surface 411B of the air passage 41B is raised to slow down the flow velocity of the air passage 41B, thereby suppressing drying of the ink in the air passage 41B. make sure to

Further, when the thickness of the medium M is thick, as shown in FIG. 11C, the upper surface 411A of the ventilation path 41A is lowered to increase the flow velocity of the ventilation path 41A, thereby drying the ink in the ventilation path 41A. to promote.

Further, when the thickness of the medium M is thin, as shown in FIG. 11D, the upper surface 411A of the ventilation path 41A is raised to slow down the flow velocity of the ventilation path 41A, thereby drying the ink in the ventilation path 41A. try to suppress it.

11A to 11D are merely examples, and both the top surfaces 411A and 411B may be lowered depending on the amount of ink adhered and the thickness of the medium M, for example. , may be raised.

As described above, in this modified example, the drying section 40 includes a plurality of air passages 41A and 41B, and the upper surfaces 411A and 411B can move up and down independently of each other. Therefore, it is possible to adjust the flow velocities in the air passages 41A and 41B according to the amount of ink adhered and the thickness of the medium M, so that the ink can be dried appropriately.

All of the above-described embodiments are merely examples of specific implementations of the present invention, and the technical scope of the present invention should not be construed to be limited by these. Thus, the invention may be embodied in various forms without departing from its spirit or essential characteristics.

10 Conveying section 11 Conveying belt 12 Drive roller 13 Driven roller 20 Carriage section 21 Inkjet head 30 Heating section 40 Drying section 41, 41A, 41B Ventilation path 42 First duct 43 Second duct 70 Operation display section 80 Input/output interface 90 Control section 100 inkjet printer 111 conveying surface 200 external device 411, 411A, 411B upper surface 412 side surface 413 reflecting portion 421 first air blowing portion 431 second blowing portion 440 cross-sectional area changing portion 450 radiation portion

Claims (13)

a gas supply unit that supplies a predetermined flow rate of gas to a ventilation path provided downstream of the inkjet head in the conveying direction of the recording medium;
a control unit that performs control to change the cross-sectional area of the ventilation passage in the gas supply direction;
drying equipment. The predetermined flow rate is a flow rate of the gas that does not exceed the saturated vapor amount in the air passage, including vapor generated by vaporizing the liquid contained in the ink on the recording medium. be,
A drying apparatus according to claim 1. The controller controls the ventilation path so that the vapor amount of the vapor contained in the gas, including the vapor obtained by vaporizing the liquid contained in the ink on the recording medium, does not exceed the saturated vapor amount in the ventilation path. controlling the flow rate of the gas supplied to the channel;
A drying apparatus according to claim 1 or 2. wherein the control unit changes the flow velocity of the gas supplied to the ventilation path according to the type of the recording medium;
A drying apparatus according to any one of claims 1 to 3. wherein the control unit changes the flow velocity of the gas supplied to the ventilation path according to the basis weight of the recording medium;
A drying apparatus according to any one of claims 1 to 3. The control unit changes the flow velocity of the gas supplied to the ventilation path according to the amount of ink ejected onto the recording medium.
A drying apparatus according to any one of claims 1 to 3. The air passage has a facing portion that faces the conveyed recording medium from above,
The control unit changes the cross-sectional area of the ventilation passage by changing the vertical height of the facing portion.
A drying apparatus according to any one of claims 1 to 6. A heating unit that heats at least one of the ink on the recording medium and the recording medium in order to dry the ink on the recording medium in the air passage,
A drying apparatus according to any one of claims 1 to 7. The heating unit heats at least one of the ink on the recording medium and the recording medium with radiation.
A drying apparatus according to claim 8 . The ventilation passage has a reflecting portion that reflects the radiation,
10. Drying apparatus according to claim 9. The ventilation path comprises a plurality of ventilation paths arranged along the conveying direction of the recording medium,
The control unit changes the flow velocity of the gas supplied to the plurality of ventilation passages by changing the cross-sectional areas of the plurality of ventilation passages.
Drying apparatus according to any one of claims 1 to 10. an inkjet head that forms an image on a recording medium;
a drying apparatus according to any one of claims 1 to 11;
An image forming apparatus comprising: supplying a predetermined flow rate of gas to a ventilation path provided downstream of the inkjet head in the conveying direction of the recording medium;
changing the cross-sectional area of the ventilation passage in the gas supply direction;
drying method.

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