EP4592087A1

EP4592087A1 - Inkjet printer

Info

Publication number: EP4592087A1
Application number: EP25153154.7A
Authority: EP
Inventors: Toshihiro Bansyo
Original assignee: Riso Kagaku Corp
Current assignee: Riso Kagaku Corp
Priority date: 2024-01-29
Filing date: 2025-01-21
Publication date: 2025-07-30
Also published as: JP2025116409A

Abstract

An inkjet printer includes an inkjet head including nozzles arranged in a nozzle array and configured to eject ink. While moving relative to a print medium, the inkjet head is configured to perform printing on a printing surface of the print medium by ejecting ink from the nozzles for every line of an image along a direction orthogonal to a direction of the relative movement, the printing surface being non-horizontal and parallel to the direction of the relative movement. The nozzle array is inclined such that positions of the nozzles are lower toward an upstream side in the direction of the relative movement of the print medium as viewed from the inkjet head.

Description

BACKGROUND

1. TECHNICAL FIELD

The present invention relates to an inkjet printer.

2. RELATED ART

Japanese Unexamined Patent Application Publication No. 2023-86350 discloses an inkjet printer configured to perform printing on a vertical printing surface of a print medium by ejecting ink in a horizontal direction.
Japanese Unexamined Patent Application Publication No. 2004-167802 discloses a technique for improving print resolution of an inkjet printer by narrowing a nozzle pitch with an inkjet head obliquely inclined relative to a direction orthogonal to a direction of conveyance of a print medium.

SUMMARY

In the above-mentioned inkjet printer configured to perform printing on the vertical printing surface, the ink landed on the printing surface moves in a downward direction due to a gravitational force before being fixed to the printing surface. The movement of the ink in the downward direction may cause ink dot coalescence in which ink dots coalesce together. The coalesced ink dots are even more prone to be affected by the gravitational force. This may result in the occurrence of ink dripping in which the ink drips on the printing surface and therefore deteriorate print quality.
In the case where the inkjet printer to perform printing on the vertical printing surface, in particular, is configured to improve the print resolution with the inkjet head obliquely inclined relative to the vertical direction, which is orthogonal to the direction of conveyance of the print medium, a distance between the dots is reduced and the aforementioned ink dot coalescence is prone to occur.
Not only on the vertical printing surface, but also on a non-horizontal printing surface, the ink dots may move due to the gravitational force and cause ink dot coalescence and resultant deterioration in print quality.
An object of the present invention is to provide an inkjet printer capable of reducing ink dot coalescence while improving print resolution in printing on a non-horizontal surface.
An inkjet printer in accordance with the present invention includes an inkjet head including nozzles arranged in a nozzle array and configured to eject ink. While moving relative to a print medium, the inkjet head is configured to perform printing on a printing surface of the print medium by ejecting ink from the nozzles for every line of an image along a direction orthogonal to a direction of the relative movement, the printing surface being non-horizontal and parallel to the direction of the relative movement. The nozzle array is inclined such that positions of the nozzles are lower toward an upstream side in the direction of the relative movement of the print medium as viewed from the inkjet head.
According to the above-described configuration, it is possible to reduce ink dot coalescence while improving print resolution in printing on a non-horizontal surface.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a block diagram illustrating a configuration of an inkjet printer according to an embodiment of the present invention.
Fig. 2 is a schematic configuration diagram of a conveyor and head bars of the inkjet printer illustrated in Fig. 1.
Fig. 3 is a schematic configuration diagram of inkjet heads in one of the head bars of the inkjet printer illustrated in Fig. 1.
Fig. 4 is a diagram for explaining a behavior of ink which is ejected from the inkjet heads in the inkjet printer illustrated in Fig. 1 and is landed on a printing surface.
Fig. 5 is a diagram for explaining a behavior of ink which is ejected from an inkjet head of a comparative example and is landed on a printing surface.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing.
Description will be hereinbelow provided for embodiments of the present invention by referring to the drawings. It should be noted that the same or similar parts and components throughout the drawings will be denoted by the same or similar reference signs, and that descriptions for such parts and components will be omitted or simplified. In addition, it should be noted that the drawings are schematic and therefore different from the actual ones.
Fig. 1 is a block diagram illustrating a configuration of an inkjet printer 1 according to an embodiment of the present invention. Fig. 2 is a schematic configuration diagram of a conveyor 2 and head bars 3 of the inkjet printer 1 illustrated in Fig. 1. Fig. 3 is a schematic configuration diagram of inkjet heads 21 in one of the head bars 3. In the following description, a direction orthogonal to a sheet surface of Fig. 2 will be referred to as a front-rear direction, and a front side of the sheet surface will be referred to as a front side. Meanwhile, upward, downward, rightward, and leftward arrows in Fig. 2 will be referred to as up-down and right-left directions. The up-down direction is a vertical direction. The right-left direction and the front-rear direction are directions orthogonal to each other, orthogonal to the up-down direction, and parallel to a horizontal direction. In Figs. 2 to 5, the rightward direction, the leftward direction, the upward direction, the downward direction, the frontward direction, the rearward direction, and a conveyance direction are denoted by RT, LT, UP, DN, FT, RR, and TD, respectively.
As illustrated in Fig. 1, the inkjet printer 1 includes the conveyor 2, four head bars 3, and a controller 4.
The conveyor 2 conveys a print medium 11. The conveyance direction of the print medium 11 by the conveyor 2 is a direction from right to left which is parallel to the horizontal direction. The print medium 11 is a cardboard box, for example. The print medium 11 has a printing surface 11a to be printed by the head bars 3. In the present embodiment, the printing surface 11a is a vertical surface that is orthogonal to the front-rear direction.
The head bars 3 perform printing by ejecting ink to the printing surface 11a of the print medium 11. The four head bars 3 eject inks of different colors (black, cyan, magenta, and yellow, for example). The four head bars 3 are arranged side by side in the conveyance direction of the print medium 11 (the right-left direction). In the front-rear direction, the head bars 3 are arranged in front of a region where the print medium 11 is conveyed. The four head bars 3 have the same configuration except that they eject the inks of the different colors.
Each head bar 3 includes the inkjet heads 21, a head holder 22, and an angle adjuster (adjuster) 23.
Each inkjet head 21 includes a nozzle array 26 as illustrated in Fig. 3. The nozzle array 26 is formed by linearly arranging nozzles 27 along a longitudinal direction of the inkjet head 21. The nozzles 27 are opened in a nozzle surface 21a that is a vertical surface of the inkjet head 21 opposed to the printing surface 11a of the print medium 11 being conveyed, and are configured to eject the ink in the horizontal direction to the printing surface 11a. Fig. 3 is the diagram of the inkjet heads 21 viewed from the rear side (the print medium 11 side).
The inkjet head 21 is inclined relative to the up-down direction (the vertical direction) such that the position of the inkjet head 21 becomes lower as it goes to an upstream side in the conveyance direction of the print medium 11. Accordingly, the nozzle array 26 is inclined such that the positions of the nozzles 27 become lower toward the upstream side.
The nozzle arrays 26 of the inkjet heads 21 perform printing on the printing surface 11a by ejecting the ink from the nozzles 27 in each line along the up-down direction (the vertical direction) of an image. The inclination of the nozzle arrays 26 relative to the up-down direction makes it possible to obtain a finer nozzle pitch in the up-down direction than in the case of nozzle arrays in parallel with the up-down direction and thus to improve print resolution.
The inkjet heads 21 are arranged side by side along the up-down direction in the inclined state as described above. The inkjet heads 21 are arranged such that an interval in the up-down direction between the lowermost nozzle 27 in the upper inkjet head 21 and the uppermost nozzle 27 in the lower inkjet head 21 out of every adjacent two of the inkjet heads 21 in the up-down direction is equal to the nozzle pitch in the up-down direction of the inkjet heads 21.
The head holder 22 holds all the inkjet heads 21.
The angle adjuster 23 adjusts an angle of inclination of each inkjet head 21, or in other words, an angle of inclination of each nozzle array 26 by rotating the inkjet head 21 about a pivot axis that is parallel to the front-rear direction. The angle adjuster 23 adjusts the intervals in the up-down direction between the inkjet heads 21 such that the interval in the up-down direction between the lowermost nozzle 27 in the upper inkjet head 21 and the uppermost nozzle 27 in the lower inkjet head 21 out of every adjacent two of the inkjet heads 21 in the up-down direction is equal to the nozzle pitch in the up-down direction of the inkjet heads 21.
The controller 4 controls operations of units in the inkjet printer 1. The controller 4 includes a CPU, a RAM, a ROM, a hard disk, and so forth.
Next, operations of the inkjet printer 1 will be described.
When a print job is inputted, the controller 4 obtains data on the type of the print medium 11 from setting information included in the print job. Then, the controller 4 performs control to cause the angle adjuster 23 of each head bar 3 to adjust the inclination angle of the inkjet heads 21 (the inclination angle of the nozzle arrays 26) depending on a type of the print medium 11.
Here, the ink ejected from the nozzles 27 and landed on the printing surface 11a of the print medium 11 permeates the printing surface 11a and evaporates to be fixed to the printing surface 11a as described later. In this process, before being fixed, the ink dots landed on the printing surface 11a may move in the downward direction and coalesce together due to the gravitational force. The coalesced ink dots are even more prone to be affected by the gravitational force, resulting in the occurrence of ink dripping on the printing surface 11a and deteriorating the print quality.
The above-mentioned ink movement on the printing surface 11a is more likely to occur as the print medium 11 is of a type having poorer wettability.
The likelihood of occurrence of the above-described ink movement on the printing surface 11a varies depending on ink characteristics. To be more precise, as the density of the ink is higher, the ink is more affected by the gravitational force and is therefore more likely to move. As the dynamic surface tension of the ink is higher, the ink permeates the printing surface 11a more slowly and is therefore more likely to move. As the viscosity of the ink is lower, the ink is more likely to move on the printing surface 11a.
As the inclination angle of the nozzle arrays 26 relative to the up-down direction increases, the nozzle pitch in the up-down direction becomes smaller and the ink dot coalescence is therefore more likely to occur.
To address this, in the inkjet printer 1, the inclination angle of the nozzle arrays 26 relative to the up-down direction in each head bar 3 is set for each type of the print medium 11 depending on the density, the dynamic surface tension, and the viscosity at a standard temperature of the ink used in the head bar 3. The inclination angle of the nozzle arrays 26 relative to the up-down direction is set to a smaller angle as the print medium 11 is of a type having poorer wettability.
The controller 4 causes the angle adjuster 23 in each head bar 3 to adjust the inclination angle of each inkjet head 21 (the inclination angle of each nozzle array 26) so that the inclination angle of the nozzle array 26 can be equal to the angle set depending on the type of the print medium 11 as described above.
Along with the adjustment of the inclination angle of each inkjet head 21, the controller 4 performs control to cause the angle adjuster 23 to adjust the intervals in the up-down direction between the inkjet heads 21 such that the interval in the up-down direction between the lowermost nozzle 27 in the upper inkjet head 21 and the uppermost nozzle 27 in the lower inkjet head 21 out of every adjacent two of the inkjet heads 21 in the up-down direction is equal to the nozzle pitch in the up-down direction of the inkjet heads 21.
The density, the dynamic surface tension, and the viscosity of the ink vary depending on the temperature of the ink. For this reason, each head bar 3 may be provided with an ink temperature detector (not illustrated) configured to detect the temperature of the ink, and the controller 4 may control the inclination angle of the nozzle arrays 26 in each head bar 3, which is set depending on the type of the print medium 11, based on the temperature of the ink detected with the ink temperature detector provided to the head bar 3.
The controller 4 starts execution of the print job after the adjustment of the inclination angles of the nozzle arrays 26 (the inkjet heads 21) in all the head bars 3. To be more precise, the controller 4 performs control to print an image on the printing surface 11a of the print medium 11 by ejecting the ink from the inkjet heads 21 of the head bars 3 while conveying the print medium 11 by using the conveyor 2.
In this printing, the nozzles 27 of the nozzle arrays 26 of the inkjet heads 21 eject the ink for every line along the up-down direction (the vertical direction) of an image. Since each nozzle array 26 is inclined such that the positions of the nozzles 27 become lower toward the upstream side, the ink is ejected to the same line along the up-down direction from the nozzles 27 of each nozzle array 26 sequentially in the order from lower to upper sides.
The series of operations is terminated when the printing based on the print job is completed.
Next, a behavior of the ink which is ejected from the inkjet heads 21 in the inkjet printer 1 and is landed on the printing surface 11a will be described with reference to Fig. 4.
Fig. 4 illustrates the behavior of the ink ejected from three consecutive nozzles 27 in the nozzle array 26. The three consecutive nozzles 27 will be referred to as nozzles 27A, 27B, and 27C in the order from the lower side (the upstream side).
As a result of sequentially ejecting the ink from the nozzles 27A, 27B, and 27C to the same line, ink dots 31A, 31B, and 31C are sequentially formed in the order from lower to upper sides as illustrated in Fig. 4. The ink dots 31Ato 31C are formed by the ink ejected from the respective nozzles 27A to 27C and landed on the printing surface 11a.
The ink landed on the printing surface 11a permeates the printing surface 11a and evaporates, thereby being fixed to the printing surface 11a. However, before being fixed, the ink moves in the downward direction due to the gravitational force.
For this reason, after the ink ejected from the nozzle 27A is landed, the ink of the ink dot 31A formed by the ink ejected from the nozzle 27A moves in the downward direction at the time when the ink ej ected from the nozzle 27B is landed. Likewise, after the ink ejected from the nozzle 27B is landed, the ink of the ink dot 31B formed by the ink ejected from the nozzle 27B moves in the downward direction at the time when the ink ejected from the nozzle 27C is landed.
Since the ink ejected from the nozzle 27B is landed above the ink dot 31A as illustrated in Fig. 4, the ink dot 31B formed by the ink ejected from the nozzle 27B and the ink dot 31A are less likely to coalesce. Likewise, since the ink ejected from the nozzle 27C is landed above the ink dot 31B, the ink dot 31C formed by the ink ejected from the nozzle 27C and the ink dot 31B are less likely to coalesce. In the example of Fig. 4, the ink dots 31A to 31C are fixed to the printing surface 11a without causing any ink dot coalescence.
As described above, the inkjet printer 1 is less likely to cause the ink dot coalescence and the resultant ink dripping.
Next, a behavior of ink ejected from an inkjet head of a comparative example and landed on the printing surface 11a will be described with reference to Fig. 5.
An inkjet head 41 of the comparative example illustrated in Fig. 5 includes a nozzle array 42. The nozzle array 42 is formed by linearly arranging nozzles 43 along a longitudinal direction of the inkjet head 41.
Unlike the inkjet head 21 of the present embodiment, the inkjet head 41 is inclined relative to the up-down direction (the vertical direction) such that the position of the inkjet head 41 becomes higher as it goes to the upstream side in the conveyance direction of the print medium 11. Accordingly, the nozzle array 42 is inclined such that the positions of the nozzles 43 become higher toward the upstream side.
Since the nozzle array 42 is inclined as described above, the ink is ejected to the same line along the up-down direction from the nozzles 43 in the nozzle array 42 sequentially in the order from upper to lower sides.
Fig. 5 illustrates the behavior of the ink ejected from three consecutive nozzles 43 in the nozzle array 42. The three consecutive nozzles 43 will be referred to as nozzles 43A, 43B, and 43C in the order from the upper side (the upstream side).
As a result of sequentially ejecting the ink from the nozzles 43A, 43B, and 43C to the same line, ink dots 51A, 51B, and 51C are sequentially formed in the order from upper to lower sides as illustrated in Fig. 5. The ink dots 51A to 51C are formed by the ink ejected from the respective nozzles 43A to 43C and landed on the printing surface 11a.
In this comparative example, as illustrated in Fig. 5, the ink of the ink dot 51A formed by the ink ejected from the nozzle 43A moves in the downward direction due to the gravitational force, whereas the ink ejected from the nozzle 43B is landed below the ink dot 51A. In this case, the ink dot 51B formed by the ink ejected from the nozzle 43B and the ink dot 51A are more likely to coalesce. The coalesced ink dots are even more likely to be affected by the gravitational force and cause ink dripping.
In the example of Fig. 5, the ink dots 51A and 51B coalesce and cause the ink dripping. Then, the dripped ink reaches the ink dot 51C, and the ink dots 51A to 51C are indistinguishably fixed to the printing surface 11a.
The configuration in which the nozzle array is inclined such that the positions of the nozzles become higher toward the upstream side as in this comparative example is more likely to cause the ink dot coalescence and the resultant ink dripping, and accordingly is more likely to cause deterioration in print quality.
As described above, in the inkjet printer 1, the nozzle array 26 is inclined such that the positions of the nozzles 27 become lower toward the upstream side. With this configuration, the ink is ejected to the same line along the up-down direction from the nozzles 27 of each nozzle array 26 sequentially in the order from lower to upper sides. Hence, even when the ink landed on the printing surface 11a moves in the downward direction due to the gravitational force, the ink is less likely to cause the ink dot coalescence. As a consequence, in printing on the vertical printing surface 11a, the inkjet printer 1 is capable of reducing the ink dot coalescence while improving the print resolution with the nozzle arrays 26 inclined.
In the inkjet printer 1, the controller 4 performs control to cause the angle adjuster 23 of each head bar 3 to adjust the inclination angle of each nozzle array 26 depending on the type of the print medium 11. Although the likelihood of occurrence of the ink movement varies depending on the type of the print medium 11, it is possible to further reduce the ink dot coalescence while improving the print resolution by adjusting the inclination angle of the nozzle array 26 and adjusting the nozzle pitch in the up-down direction.
Instead, the angle adjuster 23 may be omitted and the inclination angle of the nozzle array 26 may be set to a fixed angle.
The above embodiment describes the inkjet printer 1 of a line type configured to perform printing while conveying the print medium 11. However, the present invention is not limited to this and is also applicable to an inkjet printer of a serial type configured to perform printing on a print medium while moving an inkjet head. Such an inkjet printer only has to be configured such that an inkjet head provided with a nozzle array performs printing on a print medium while moving relative to the print medium and that the nozzle array is inclined such that the positions of nozzles become lower toward an upstream side in a direction in which the print medium is moved relative to the inkjet head.
The above embodiment describes the inkjet printer 1 configured to perform printing by ejecting the ink in the horizontal direction to the vertical printing surface 11a. However, the present invention is applicable to an inkjet printer configured to perform printing not only on a vertical surface but also on a non-horizontal printing surface in parallel with a direction in which a print medium is moved relative to the inkjet head.
The present application includes the following configurations, for example.
An inkjet printer includes an inkjet head including nozzles arranged in a nozzle array and configured to eject ink. While moving relative to a print medium, the inkjet head is configured to perform printing on a printing surface of the print medium by ejecting ink from the nozzles for every line of an image along a direction orthogonal to a direction of the relative movement, the printing surface being non-horizontal and parallel to the direction of the relative movement. The nozzle array is inclined such that positions of the nozzles are lower toward an upstream side in the direction of the relative movement of the print medium as viewed from the inkjet head.
The inkjet printer may further include: an adjuster configured to adjust an inclination angle of the nozzle array; and a controller configured to control the adjuster to adjust the inclination angle of the nozzle array depending on a type of the print medium.
Further, the features of all embodiments and all claims can be combined with each other as long as they do not contradict each other.

Claims

An inkjet printer (1) comprising:
an inkjet head (21) including nozzles (27) arranged in a nozzle array (26) and configured to eject ink, wherein

while moving relative to a print medium (11), the inkjet head (21) is configured to perform printing on a printing surface (11a) of the print medium (11) by ejecting ink from the nozzles (27) for every line of an image along a direction orthogonal to a direction of the relative movement, the printing surface (11a) being non-horizontal and parallel to the direction of the relative movement, and

the nozzle array (26) is inclined such that positions of the nozzles (27) are lower toward an upstream side in the direction of the relative movement of the print medium (11) as viewed from the inkjet head (21).
The inkjet printer (1) according to claim 1, further comprising:
an adjuster (23) configured to adjust an inclination angle of the nozzle array (26); and

a controller (4) configured to control the adjuster (23) to adjust the inclination angle of the nozzle array (26) depending on a type of the print medium (11).