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 arranged to support a sheet-like or web-like medium and to move them in a transport direction through the array of nozzles, the nozzles being uniformly distributed above a portion of the support transport surface.

Background Art

[0002] In inkjet printing, a gas impingement unit, more specifically a hot air impingement unit, is frequently used to dry or cure the printed media sheet. The array of nozzles extends across the entire width of the media transport path and extends for a specific distance in the transport direction, such that the flow of hot air can be directed at 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 and absorbs and carries away the water vapor (in the case of aqueous ink) evaporating from the surface of the media. The air then flows out towards the ends of the nozzle array in a direction parallel to the support transport surface.

[0003] In known gas impingement units, the nozzle array takes the form of a box with a perforated bottom by a regular pattern of holes through which hot air is supplied. An example of this type of gas impingement unit is described in US Patent Application Publication No. 2018 / 142413.

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

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a gas impingement unit capable of more efficiently drying or curing a medium.

[0007] Another object of the present invention is to provide a gas impingement unit capable of providing more reliable media conveyance under the gas impingement unit, for example, reducing the risk of media clogging.

Means for Solving the Problems

[0008] To achieve these objects, the gas impingement unit according to the present invention is characterized in that the array is an array of alternately arranged nozzles and vents, and the vents are arranged so that the gas blown out from the nozzles can escape in a direction perpendicular to the support conveyance surface.

[0009] Thanks to the vents arranged alternately with the nozzles, the air that impinges on the media surface can be easily removed from the media surface near the nozzle from which the gas is ejected. Therefore, the gas does not need to move a greater distance parallel to the support transport surface towards the end of the array. As a result, the gas flow rate per unit surface area of the media can be significantly increased without generating a high-speed gas flow (cross-flow) that tends to flow over the media surface and shift or lift the media on the support transport surface. This is particularly advantageous in the case of a cut-sheet printer where a high-speed gas flow significantly increases the risk that the ends of the media sheet, especially the leading and trailing edges, will be lifted from the support transport surface, or that the sheet will cockle.

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

[0011] Furthermore, the uniformly distributed vents improve the energy efficiency of the gas impingement unit because the flow resistance that the gas flowing out from the media surface is subject to and that must be overcome by the gas supply source is significantly reduced.

[0012] As a result of these advantageous effects, the gas or hot air flow rate per unit surface area of the media, and thus the intensity of the curing or drying effect, can be significantly increased without causing higher energy losses or impairing the transport of the media.

[0013] Any more specific features of the present invention are set forth 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 that separate the rows of nozzles. In this way, the gas from the gas source can be efficiently supplied to the nozzles via a supply line that extends along the rows, and yet there will be vents in the immediate vicinity of each nozzle.

[0015] Particularly in the case of a cut-sheet printer, it may be advantageous for the rows of nozzles and vents to extend parallel to the transport direction of the media sheet. This reduces the risk of paper jams, which could otherwise be caused by the leading edge of the sheet catching on one of the gaps or slots that form the vents.

[0016] The rows of nozzles may be formed in a comb-like structure of parallel distribution lines that are connected to a common supply line that extends laterally when the distribution line extends in the transport direction of the media. The supply line may be positioned at a sufficient height above the support transport surface so as not to be an obstacle to the gas exiting through the vents.

[0017] In one embodiment, the vents may be connected to one or more suction devices by which gas is actively recovered from the media surface. In particular, a highly energy-efficient gas circulation system can be formed by recycling the gas recovered from the vents directly back to the gas source.

[0018] Here, examples of the embodiments will be described in conjunction with the drawings.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0020] As shown in FIG. 1, the gas supply source 10 is connected to a supply line 12 extending in the lateral direction on a support conveyance surface 14 arranged to support the media sheets 16 (FIG. 2) and advance them in the conveyance direction indicated by arrow A. The support conveyance surface 14, although only shown in phantom lines in FIG. 1, may be constituted by a circulating conveyor belt, preferably a perforated belt running on a suction box, whereby the media sheets can be safely held in place on the conveyor by vacuum suction. The supply line 12 extends in the conveyance direction A and is connected to a number of parallel distribution lines 18 each having a number of nozzles 20 arranged at equal intervals along the distribution lines 18. The distribution lines 18 are separated from each other by gaps that form ventilation openings 22 through which the gas ejected from the nozzles 20 and impinging on the media sheets can easily escape in a direction perpendicular to the support conveyance surface 14, so that the gas does not have to move a large distance parallel to the support conveyance surface 14. The nozzles 20 of the various distribution lines 18 and the ventilation openings 22 between these distribution lines together constitute an array 24 of alternately arranged nozzles and ventilation openings covering a rectangular surface area on the support conveyance surface 14.

[0021] The gas supply source 10 may, for example, be constituted by a blower connected to an air heater H, whereby hot air is transferred at a constant pressure into the supply line 12 and further into the distribution line 18. The array 24 is arranged above a part of the support conveyance surface 14, downstream of an inkjet print engine on which an image is printed on a media sheet conveyed in the conveyance direction A. Then, when the media sheet having a surface that has just been printed and thus is still wet reaches the array 24, the ink (for example, aqueous ink) is cured and dried by the hot air blown out from the nozzles 20 and impinging on the surface of the media sheet. Since the nozzles 20 formed in the various distribution lines 18 are uniformly distributed over the area of the array 14, the curing process will be uniformly applied over the entire surface of the media sheet. In the example shown, the nozzles 20 formed in two adjacent distribution lines 18 are offset with respect to each other so as to obtain a particularly uniform distribution of the nozzles.

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

[0023] As can further be seen in FIG. 2, the distribution line 18 has 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 supply line tapers towards the opposite end so as to obtain a substantially uniform flow of gas through the nozzles 20. The nozzles 20 are formed in each bottom or base wall of the distribution line 18 and thus are not visible in FIG. 2. However, the jet of air emerging from the nozzles 20 is represented by arrows in FIG. 2.

[0024] As shown by the dashed line in FIG. 2, an array 24 of nozzles and vents (the gaps between the distribution lines 18) forms the bottom of a suction box 28 connected to the suction side of a gas source 10 (a blower) by a line 30 shown in FIG. 1. Thereby, the blower promotes the recovery of air from the vents 22 by sucking air from the suction box 28. The air recovered from the suction box 28 via the line 30 is recirculated to the blower (gas source 10) and mixed with the hot air from the air heater H. The ratio of the hot air to the recirculated air is adjusted such that the hot air replaces the losses caused by the outflow of air at the periphery of the array 24. Thus, since a part of the air exiting the nozzles 20 is replaced with the dry hot air from the heater H, the moisture content of the air ejected from the nozzles 20 can be controlled.

[0025] FIG. 3 shows the array 24 in a front view, as a result of which the comb-like structure of the distribution lines 18 and the vents 22 formed therebetween on one side can be seen. The flow of air exiting the nozzles 20, impinging on the media sheet 16, and then being recovered through the vents 20 is represented by the arrows. As further seen in FIG. 3, a rectangular duct 32 adjacent to the connector 26 tapers towards the opposite end of the supply line 12, so that the air is evenly 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), the array of nozzles being directed onto a support and transport surface (14) arranged to support a sheet-like or web-like medium (16) and to move them in a transport direction (A) through the array of nozzles, wherein the nozzles (20) are uniformly distributed above a part of the support and transport surface (14), the said array (24) being an array of alternately arranged nozzles (20) and vents (22), the vents (22) being arranged so as to allow the gas blown out from the nozzles (20) to escape in a direction perpendicular to the support and transport surface (14), the nozzles (20) within the array (24) being arranged in parallel rows, the vents (22) extending parallel to the rows of nozzles (20) and being arranged alternately with these rows such that each row of nozzles (22) has at least one vent (22) adjacent thereto, the rows of nozzles (20) extending in the transport direction (A).

2. The nozzles (20) of each row are formed in a distribution line (18), the array (24) comprising at least six, preferably at least twelve, distribution lines (18) extending parallel to one another, the vents (22) being formed by the gaps between the distribution lines (18), the gas impingement unit according to claim 1.

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

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

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

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

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

8. The dispensing line (18) has a triangular profile when viewed from the side and tapers towards the end remote from the supply line (12), the gas impingement unit according to claim 7. **Claim 9** A suction device (28) is provided for promoting the flow of air through the vent (22) and preferably recirculating the recovered air to the gas supply source (10), the gas impingement unit according to any one of claims 1 to 8.

Images