Gas impingement unit

Abstract

A gas impingement unit comprising a gas supply source (10) and an array (24) of nozzles (20) connected to the gas supply source (10) and arranged to support a sheet-like or web-like medium (16) and move them in a transport direction (A) over a support transport surface (14) directed towards the array of nozzles (20), wherein the nozzles (20) are uniformly distributed above a portion of the support transport surface (14), and the array (24) is an array of alternately arranged nozzles (20) and vents (22), and the vents (22) are arranged to allow the gas blown out from the nozzles (20) to escape in a direction perpendicular to the support transport surface (14).

Description

Technical Field

[0001] The present invention relates to a gas impingement unit comprising a gas supply source and an array of nozzles connected to the gas supply source, the array of nozzles being directed onto a supporting conveying surface arranged to support sheet-like or web-like media and move the same in a conveying direction through the array of nozzles, wherein the nozzles are uniformly distributed above a portion of the supporting conveying surface.

Background Art

[0002] In inkjet printing, gas impingement units, more specifically hot air impingement units, are frequently used to dry or cure printed media sheets. The array of nozzles extends across the full width of the media conveying path and extends over a specific distance in the conveying direction, as a result of which a flow of high-temperature air can be directed to each point on the wet surface of the media for sufficient time to cure or dry the ink as the media moves under the nozzle array. The hot air blown onto the surface of the media transfers a certain amount of heat to the media, absorbs and carries away water vapor (in the case of aqueous inks) evaporated from the surface of the media. The air then flows out in a direction parallel to the supporting conveying surface towards the ends of the nozzle array.

[0003] In known gas impingement units, the nozzle array takes the form of a box supplied with high-temperature air, the bottom of which is perforated by a regular pattern of holes forming the nozzles. An example of this type of gas impingement unit is described in US Patent Application Publication No. 2018142413.

[0004] European Patent Application Publication No. 3932680 discloses an inkjet printer in which one or more air knives each comprising a row of nozzles are arranged above a conveying section for a media sheet, whereby the nozzles are directed towards the ends of the sheet to prevent the sheet from curling.

Prior Art Documents

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 142413 [Patent Document 2] European Patent Application Publication No. 3932680 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a gas impingement unit that can more efficiently dry or cure a medium.

[0007] Another object of the present invention is to provide a gas impingement unit that can provide more reliable media transport under the gas impingement unit, for example, by reducing the risk of media clogging. [Means for solving the problem]

[0008] To achieve these objectives, the gas impingement unit according to the present invention is characterized in that the array is an array of alternately arranged nozzles and vents, the vents being arranged such that the gas blown out from the nozzles escapes in a direction perpendicular to the support conveying surface.

[0009] Thanks to the alternating nozzles and vents, air impacting the media surface can be easily removed from the media surface near the nozzle from which the gas is blown, thus eliminating the need for the gas to travel a greater distance towards the edges of the array parallel to the support transport surface. As a result, the gas flow rate per unit surface area of ​​the media can be significantly increased without generating high-speed gas flows (cross-flows) that tend to flow over the media surface and displace or lift the media on the support transport surface. This is particularly advantageous in cut-sheet printers where high-speed gas flows significantly increase the risk of the edges of the media sheet, especially the leading and trailing edges, being lifted from the support transport surface, or causing the sheet to cockle.

[0010] Another advantage is that the momentum of the gas, which collides with the medium and is then deflected into the vent, helps to firmly hold the medium on the support and conveying surface, thereby generating a force that contributes to safe medium transport. Combined with the absence of high-speed gas flow (cross-flow), it is even possible to transport the medium without the need for vacuum suction to hold it on the medium conveyor (e.g., a belt).

[0011] Furthermore, uniformly distributed vents improve the energy efficiency of the gas impingement unit because they significantly reduce the flow resistance that the gas flowing out from the surface of the medium must overcome by the gas supply source.

[0012] As a result of these beneficial effects, the flow rate of gas or hot air per surface of the medium, and therefore the intensity of the curing or drying effect, can be significantly increased without resulting in higher energy losses or impairing the transport of the medium.

[0013] Any more specific features of the present invention are shown in the dependent claims.

[0014] In one embodiment, the nozzles may be arranged in parallel rows, and the vents may be formed by gaps or slots separating the rows of nozzles. In this way, gas from a gas source can be efficiently supplied to the nozzles via supply lines extending along the rows, and yet the vents are located very close to each nozzle.

[0015] In particular, with cut-sheet printers, it can be advantageous for the rows of nozzles and vents to extend parallel to the direction in which the media sheet is transported. This reduces the risk of paper jams, which could otherwise be caused by the leading edge of the sheet getting caught in one of the gaps or slots that make up the vents.

[0016] The rows of nozzles may be formed in a comb-like structure of parallel distribution lines, connected to a common supply line that extends laterally when the distribution line extends in the direction of medium transport. The supply line may be positioned sufficiently high above the support transport surface so as not to obstruct the gas exiting through the vents.

[0017] In one embodiment, the vent may be connected to one or more suction devices by which gas is actively recovered from the medium surface. A particularly energy-efficient gas circulation system can be formed by directly recirculating the gas recovered from the vent to a gas supply source.

[0018] Here, an example of an embodiment will be described in conjunction with the drawings. [Brief explanation of the drawing]

[0019] [Figure 1] This is a bottom view of the gas impingement unit according to the present invention. [Figure 2] Figure 1 is a schematic side view of the gas impingement unit. [Figure 3] This is a schematic front view of the gas impingement unit. [[Mode for Carrying Out the Invention]]

[0020] As shown in Figure 1, a gas supply source 10 is connected to a laterally extending supply line 12 on a supporting conveying surface 14 arranged to support medium sheets 16 (Figure 2) and advance the same in the conveying direction indicated by arrow A. Although the supporting conveying surface 14 is only shown in imaginary lines in Figure 1, it may be constituted by a circulating conveyor belt, preferably a perforated belt running over a suction box, whereby the medium sheets can be safely held in place on the conveyor by vacuum suction. The supply line 12 extends in the conveying direction A and is connected to a plurality of parallel distribution lines 18 each having a plurality of nozzles 20 arranged at equal intervals along the distribution line 18. The distribution lines 18 are separated from each other by gaps that form ventilation openings 22 through which gas ejected from the nozzles 20 and colliding with the medium sheets can easily escape in the direction perpendicular to the supporting conveying surface 14, so that the gas does not need to travel a large distance parallel to the supporting conveying surface 14. The nozzles 20 of the various distribution lines 18 and the ventilation openings 22 between these distribution lines together constitute an alternately arranged array 24 of nozzles and ventilation openings covering a rectangular surface area above the supporting conveying surface 14.

[0021] The gas supply source 10 may be constituted, for example, by a blower connected to an air heater H, whereby high-temperature air is transferred at a constant pressure into the supply line 12 and further into the distribution lines 18. The array 24 is arranged above a portion of the supporting conveying surface 14 downstream of an inkjet print engine where an image is printed on a medium sheet conveyed in the conveying direction A. Then, when the medium sheet, on which the image has just been printed and thus still has a moist surface, reaches the array 24, the ink (e.g., water-based ink) is cured and dried by the high-temperature air blown out from the nozzles 20 and impinging on the surface of the medium sheet. Since the nozzles 20 formed on the various distribution lines 18 are uniformly distributed over the area of the array 24, the curing treatment can be uniformly applied to the entire surface of the medium sheet. In the example shown, the nozzles 20 formed on two adjacent distribution lines 18 are offset relative to each other so as to obtain a particularly uniform distribution of the nozzles.

[0022] As can be seen in Figure 2, the supply line 12 has a substantially circular cross-section over its entire length, and has a connector 26 connected to the gas supply source 10 at one end (the upper end in Figure 1). In the example shown, the connector 26 has a rectangular cross-section and is integrated with a rectangular duct 32 extending along the upper portion of the supply line 12, which opens into the lower portion of the supply line that has a circular cross-section and from which the distribution lines 18 branch (Figure 3).

[0023] As can further be seen in Figure 2, the distribution lines 18 have a triangular shape when viewed from the side, with the height being maximum at the center of the supply line 12, and the cross-section of the distribution line tapers toward the opposite end so as to obtain a substantially uniform flow of gas through the nozzles 20. The nozzles 20 are formed on the bottom wall or base wall of each distribution line 18, and thus are not visible in Figure 2. However, the jets of air exiting from the nozzles 20 are represented by arrows in Figure 2.

[0024] As shown by the dashed line in Figure 2, the array 24 of nozzles and vents (gaps between distribution lines 18) forms the bottom of a suction box 28 connected to the suction side of the gas supply source 10 (blower) by line 30 shown in Figure 1. This allows the blower to draw air from the suction box 28, thereby facilitating the recovery of air from the vents 22. The air recovered from the suction box 28 via line 30 is recirculated to the blower (gas supply source 10) and mixed with hot air from the air heater H. The ratio of hot air to recirculated air is adjusted so that the hot air replaces the losses caused by air outflow at the periphery of the array 24. In this way, a portion of the air coming out of the nozzles 20 is replaced with dry hot air from the heater H, allowing control of the moisture content of the air ejected from the nozzles 20.

[0025] Figure 3 shows the array 24 in a front view, as it reveals the comb-like structure of the distribution lines 18 and the vents 22 formed between them on one side. The airflow exiting the nozzle 20, impacting the media sheet 16, and then being collected through the vents 20 is represented by arrows. As can be seen further in Figure 3, the rectangular duct 32 adjacent to the connector 26 tapers toward the opposite end of the supply line 12, so that the air is uniformly distributed across the series of distribution lines 18.

Claims

1. A gas impingement unit comprising a gas supply source (10) and an array (24) of nozzles (20) connected to the gas supply source (10), wherein the array of nozzles (20) (24) is positioned above a support transport surface (14) which is arranged to support a sheet-like or web-like medium (16) and to move them through the array of nozzles in the transport direction (A), and the array of nozzles (20) (24) is positioned opposite the support transport surface so as to sandwich the sheet-like or web-like medium (16) between the array and the support transport surface, wherein the nozzles (20) are uniformly distributed above a portion of the support transport surface (14), and the A A gas impingement unit characterized in that a ray (24) is an array of alternately arranged nozzles (20) and vents (22), the vents (22) being arranged such that gas blown out from the nozzles (20) can escape in a direction perpendicular to the support conveying surface (14), the nozzles (20) in the array (24) are arranged in parallel rows, the vents (22) extend parallel to the rows of nozzles (20) and are arranged alternately with these rows such that each row of nozzles (22) has at least one adjacent vent (22), and the rows of nozzles (20) extend in the conveying direction (A).

2. The gas impingement unit according to claim 1, wherein each row of nozzles (20) is formed on a distribution line (18), and the array (24) comprises at least six distribution lines (18) extending parallel to each other, and the vents (22) are formed by the gaps between the distribution lines (18).

3. The gas impingement unit according to claim 2, wherein each distribution line (18) forms exactly one row of nozzles (20).

4. The gas impingement unit according to claim 2, wherein each distribution line (18) forms a plurality of rows of nozzles (20).

5. The gas impingement unit according to any one of claims 2 to 4, wherein the distribution line (18) extends laterally from the supply line (12).

6. The gas impingement unit according to claim 5, wherein the supply line (12) is common to all distribution lines (18) and extends in a direction perpendicular to the distribution lines.

7. The gas impingement unit according to claim 6, wherein the distance between the position where the distribution line (18) is connected to the supply line (12) and the support conveying surface (14) is greater than the distance between the nozzle (20) and the support conveying surface (14).

8. The gas impingement unit according to claim 7, wherein the distribution line (18) has a triangular cross-section that tapers toward the end away from the supply line (12).

9. A gas impingement unit according to any one of claims 1 to 4, further comprising a suction device (28) for promoting the airflow through a vent (22) and for recirculating the recovered air to a gas supply source (10).

10. The gas impingement unit according to claim 1, wherein each row of nozzles (20) is formed on a distribution line (18), and the array (24) comprises at least 12 distribution lines (18) extending parallel to each other, and the vents (22) are formed by the gaps between the distribution lines (18).

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