Patent Grant
11161355
This disclosure relates generally to aqueous ink printing systems, and more particularly, to media transport belts that carry media through dryers in such printers.
Known aqueous ink printing systems print images on uncoated and coated substrates. Whether an image is printed directly onto a substrate or transferred from a blanket configured about an intermediate transfer member, once the image is on the substrate, the water and other solvents in the ink must be substantially removed to fix the image to the substrate and enable contact between the image and subsequent paper transport rollers without adverse impact to the image. A dryer is typically positioned after the transfer of the image from the blanket or after the image has been printed on the substrate for removal of the water and solvents. To enable relatively high speed operation of the printer, the dryer heats the substrates and ink to temperatures that typically reach well above 100° C. for effective removal of the liquids from the surfaces of the substrates.
Typical dryers include a plurality of media transport belts that carry substrates through the dryer or dryers in a printer. The belts pass over a perforated platen covering a vacuum plenum. The platen helps support the belts and the substrates on the belts. Some known belts have holes so as the belt passes over the perforated platen covering the vacuum plenum, a vacuum can exert a pull on the media substrates through the perforated platen and the holes in the belt to acquire and hold the substrates in position for drying. The substrate areas that are adjacent the holes in the belt are cooler than the substrate areas adjacent the belt material because the void in the belt does not transfer heat energy to the back side of the substrate as the belt material does. The resulting temperature differential between these two types of areas in the substrates produces the image defects shown in
As noted above, some dryers have an arrangement of a plurality of belts that pass over the perforated platen covering the vacuum plenum. Each belt is narrower than a width of the media carried by the belt in the cross-process direction so the belts are separated from one another in the cross-process direction. Thus, portions of the platen between the belts are thermally insulated from the heat produced by the heating elements by the substrates and the air adjacent these platen portions. Inter-document gaps between successive media substrates in the process direction are not covered by the substrates so these areas of the belts and platens are exposed to the heating elements. Consequently, these areas of the belts and platen absorb more heat than the areas covered by the substrates, particularly when the heating elements are infrared (IR) emitters. Additionally, the material of which the belts are made absorb heat more readily than the metal material of which the platen is made so the exposed portions of the platen do not become as hot as the exposed portions of the belts. Since the substrates are not synchronized with the rotation of the media transport belt, an inter-document gap area of the belt during one revolution of the belt is covered by a substrate during a subsequent revolution of the belt. Thus, the heat from these heated portions of the belts eventually spreads in the belts so the temperatures of the belts become higher than the temperature of the air adjacent the areas of the platen between the belts in the cross-process direction. The higher temperature of the belts produces temperature gradients between the areas of the substrates contacting the belts and the areas of the substrates passing over the air adjacent to the platen. Temperature gradients greater than 10 degrees C. between these areas can cause the water and solvents in the ink on the substrates to evaporate at different rates. The non-uniformity of the evaporation rate can cause ink to flow on the substrate surface and concentrate pigments in the ink along the temperature gradient edges. The differing pigment concentration produces non-uniform images in solid density coverage areas. The darker lines extending in the process direction 112 in
A new printer includes a dryer having belt diversion components that attenuate the temperature differentials between media transport belts and the areas of the platen between the media transport belts. The printer includes at least one printhead configured to eject drops of an ink onto substrates moving past the at least one printhead to form ink images on the substrates, and a dryer having a platen, a heater configured to direct heat toward the platen, at least one media transport belt configured to slide over the platen to move the substrates past the heater after the ink images have been formed on the substrates, and at least one belt diversion component configured to divert the at least one media belt from a straight-line path over the platen.
A new dryer for an aqueous ink printer includes belt diversion components that attenuate the temperature differentials between media transport belts and the areas of the platen between the media transport belts. The dryer includes a platen, a heater configured to direct heat toward the platen, at least one media transport belt configured to slide over the platen to move substrates past the heater after ink images have been formed on the substrates, and at least one belt diversion component configured to divert the at least one media belt from a straight-line path over the platen.
The foregoing aspects and other features of a dryer having belt diversion components that attenuate the temperature differentials between media transport belts and the areas of the platen between the media transport belts are explained in the following description, taken in connection with the accompanying drawings.
For a general understanding of the present embodiments, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements.
The pretreating unit 120 includes at least one transport belt 124, which receives the media sheets 108 from the media supply 104 and transports the media sheets 108 in a process direction 112 through the pretreating unit 120. The pretreating unit 120 includes one or more pretreating devices 128 that condition the media sheets 108 and prepare the media sheets 108 for printing in the marking unit 140. The pretreating unit 120 may include, for example, one or more of coating devices that apply a coating to the media sheets 108, a drying device that dries the media sheets 108, and a heating device that heats the media sheets 108 to a predetermined temperature. In some embodiments, the printer 100 does not include a pretreating unit 120 and media sheets 108 are fed directly from the media supply 104 to the marking unit 140. In other embodiments, the printer 100 may include more than one pretreating unit.
The marking unit 140 includes at least one marking unit transport belt 144 that receives the media sheets 108 from the pretreating unit 120 or the media supply 104 and transports the media sheets 108 through the marking unit 140. The marking unit 140 further includes at least one printhead 148 that ejects aqueous ink onto the media sheets 108 as the media sheets 108 are transported through the marking unit 140. In the illustrated embodiment, the marking unit 140 includes four printheads 140, each of which ejects one of cyan, magenta, yellow, and black ink onto the media sheets 108. The reader should appreciate, however, that other embodiments include other printhead arrangements, which may include more or fewer printheads, arrays of printheads, and the like.
With continued reference to
With further reference to
It will be appreciated that variations of the above-disclosed apparatus and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.
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