BACKGROUND

[1] Printers can be used to generate predefined structures by depositing a printing fluid, such as an ink, on a substrate. The geometry of the structure can be defined by a relative movement between a printhead ejecting the printing fluid and a substrate holder.

[2] To print on the substrate, pigment or dye based inks can be directly deposited onto the substrate, or can be deposited onto an intermediate transfer medium to be transferred to the substrate in a following process. While paper-based substrates may show good adherence to printing fluids after deposition, other substrates may be post-processed to provide durable prints.

BRIEF DESCRIPTION OF THE DRAWINGS

[31 The following detailed description will best be understood with reference to the drawings, wherein:

[4] Fig. 1 illustrates a printer for printing on a substrate according to an example.

[5] Fig. 2 illustrates a printer for printing on a substrate in a roll-to-roll process according to an example.

[6] Fig. 3 illustrates a printer for printing on a substrate in a roll-to-roll process according to another example.

[7] Fig. 4 illustrates an output stage of a printer for handling a substrate according to an example.

[8] Fig. 5 illustrates a flow diagram of a method for printing on a substrate according to an example.

DETAILED DESCRIPTION

[9] Fig. 1 illustrates a printer 10 comprising a printhead 12 for printing on a substrate S. The substrate S is supplied via a substrate input stage 14 at an upstream position towards a substrate output stage 16 at a downstream position via transfer rollers 18 defining a media path to guide the substrate S through the printer 10. The printhead 12 deposits a printing fluid on the substrate S, and the substrate S is guided via transfer rollers 18 downstream of the printhead 12 past a drying unit 20. The drying unit 20 supplies heat to the substrate S to increase the temperature of the substrate S to dry the printing fluid deposited onto the substrate S. Additional transfer rollers 18 downstream of the drying unit 20 transfer the substrate S towards the output stage 16 downstream of the printhead 12.

[10] The substrate S may be any substrate S on which a printing fluid can be applied. In the following, the functionality of printers, systems or methods according to examples will be described with respect to a substrate S made of a textile, such as a fabric textile including polyester fibres or a polyester-coated textile, or a textile including other synthetic fibres, such as polyamide fibres, or natural cellulose fibers, like cotton, silk, or wool, and the substrate S may be pretreated to increase adherence of a printing fluid to the substrate S or to reduce bleed or coalescence of the printing fluid; however, any substrate S may be used. For example, the substrate S may be or comprise paper-based material, such as cardboard, leather, polymers, fiberboard, combinations thereof, etc.

[11] The printing fluid may be any appropriate material suitable to print an image onto the substrate S, such as ink. In the following, the functionality of printers 10 and associated systems will be described mostly with respect to dye sublimation inks as the printing fluid. The dye sublimation ink may be water-based or solvent-based, and may be activated to diffuse and sublimate into the substrate S, such as to fix a printed image of the deposited printing fluid. However, the associated concepts may also be applied to other printing methods wherein the substrate S may be post-processed to fix the printing fluid, e.g. in an external post-processing unit, such as direct dispersion printing. The printing fluid may be jetted directly onto the substrate S, such as by jetting the printing fluid onto the substrate S with the printhead 12. The printed image and/or a composite or perceived image may be a digitized color distribution, text, lines, shapes, letters, numerals, signs, symbols or a combination of these in an arbitrary color, alignment or shape.

[12] When a printer 10 is employed to generate an image on a textile substrate S, dye sublimation inks can be employed to create durable images with good color saturation by diffusing the dye sublimation inks into the substrate S following a deposition process. For example, the dye sublimation ink may be deposited onto the substrate S directly with the printhead 12 and a sublimation process may be initiated in a prost-processing unit by heating the substrate S above a sublimation temperature of the dye sublimation ink.

[131 The sublimation process of the dye sublimation ink may be initiated in an external post-processing unit (not shown) outside of the printer 10 to avoid a generation of ink vapors within the printer 10. For example, the substrate S may be transferred from the printer 10 to a calender, and may be heated above the sublimation temperature within the calender to initiate the sublimation process and diffuse dyes of the dye sublimation ink into the substrate

S.

[141 Prior to the transfer of the substrate S from the printer 10 to a post-processing unit, the drying unit 20 may dry the printing fluid on the substrate S to avoid redepositing of the printing fluid onto different surface portions of the substrate S, such as by inadvertent transfer of the printing fluid by a transfer roller 18 contacting the front-side of the substrate S in the printer 10, or by direct contact of the substrate S surface portions during the transfer, e.g. between the front-side and the backside of the substrate S when winding the substrate S.

[151 The drying unit 20 may comprise a heat source, such as an irradiation unit for infrared irradiation of the substrate S, a heated air blower to blow air at the substrate S, a heated contact plate to contact a surface of the substrate S or a conveying structure, or a combination thereof, to heat the substrate S at or towards a drying temperature to dry the printing fluid on the substrate S.

[16] However, when applying a large printing fluid load to obtain good color saturation on textile substrates S, a drying time to dry the printing fluid may increase correspondingly with increased printing fluid load. The drying time in a printer 10 may be given by a ratio of the media path length in the drying unit 20 and the media speed along the media path. For example, a printer 10 may feature a media speed of 100-130 m ² /h for a media width of 1.5 m, and the drying unit 20 may apply heat along a media path length of 1 m or 0.5 m, which may be insufficient to dry the substrate S when good color saturation is desired, e.g. for flags or backlit media applications.

[17] The drying time may be increased by increasing a media path length in the drying unit 20 or by reducing a media speed through the drying unit 20. However, increasing the media path length in the drying unit 20 may increase the footprint of the printer 10, while reducing the media speed may be associated with reduced throughput. On the other hand, the drying time may be decreased by increasing the drying temperature or an airflow of the drying unit 20. However, depending on the properties of the substrate S or of the printing fluid, the airflow or drying temperature may be limited to a maximum airflow or maximum drying temperature, respectively. For example, when the printing fluid comprises a dye sublimation ink, the drying temperature should be smaller than the sublimation temperature, such that a sublimation process of the printing fluid is not initiated within the printer 10.

[18] Fig. 2 illustrates an example of a printer 10 comprising a printhead 12 to print a printing fluid onto a front-side of a substrate S, wherein the substrate S is transported along a media path from an input roll 22 towards a collection drum 24 to form an output roll. Hence, the printer to may be a roll-to-roll printer and the substrate S may be transferred between the input roll 22 and the collection drum 24. In some examples, the substrate S extends continuously between the input roll 22 and the collection drum 24 in the printer 10.

[191 In some examples, the printer 10 is a direct-to-textile printer and the substrate S is a textile. The printhead 12 may directly apply a printing fluid onto the front-side of the textile substrate S to generate an image on the textile substrate S.

[20] A conveyor belt (not shown) may support the substrate S along the media path, and may hold the substrate S in a fixed relative alignment along the media path. The conveyor belt may prevent inadvertent displacement of the substrate S during a deposition process of the printing fluid by providing an adhesive force between the substrate S and the conveyor belt. For example, the conveyor belt may comprise an adhesive coating, such as a thermoplastic coating, to stick to a textile substrate S while the substrate S is transferred between the input roll 22 and the collection drum 24. Pulleys of the conveyor belt may be arranged at or close to the input roll 22 and the collection drum 24, e.g. concentrically with the input roll 22 and the collection drum 24, to guide the substrate S continuously along the media path from the input roll 22 to the collection drum 24.

[21] The media path may be defined by guiding rollers 26 contacting a backside of the substrate S or the conveyor belt to shape the media path of the substrate S.

[22] A drying unit 20 is arranged downstream of the printhead 12 and can be coupled to a heating plate 28 to heat the substrate S to a drying temperature below a sublimation temperature of the printing fluid. The drying unit 20 supplies heat towards the heating plate 28, such as by blowing hot air onto the heating plate 28, irradiating the heating plate 28 with infrared light, or driving heaters contacting the heating plate 28. The substrate S may be pulled over or past the heating plate 28 to approach the drying temperature and to dry the printing fluid. The drying unit 20 may heat the heating plate 28 to the drying temperature to heat the substrate S at the drying temperature. However, the heating plate 28 may also exceed the drying temperature, and the substrate S may be heated to the drying temperature during a time of heat exchange while the substrate S passes the drying unit 20. In other words, the heating plate 28 may define a physical drying zone over which the substrate S may be pulled while the drying unit 20 heats the substrate S passing the heating plate 28.

[23] In some examples, the printing fluid is a dye sublimation ink which is fixed to the substrate S above the sublimation temperature, and the substrate S is not heated to the sublimation temperature prior to being wound onto the collection drum 24. For example, the drying temperature attained by the substrate S may be below 110 °C or below too °C. [24] As an example, the substrate S may be pulled over a heating plate 28 and the heating plate 28 may be heated to a temperature of ioo°C and may feature a length of 500 mm along the media path of the substrate S to transfer heat to the substrate S.

[25] However, the heat supplied from the drying unit 20 to the substrate S may not prevent a transfer of the printing fluid to a backside of the substrate S when the substrate S is wound onto the collection drum 24.

[26] A cleaning unit 30 downstream of the drying unit 20 can remove an excess of the printing fluid from the substrate S, such that a transfer of the printing fluid onto the backside of the substrate S is prevented when winding the substrate S onto a collection drum 24 to form the output roll.

[27] The media path of the substrate S in the printer 10 may be shaped such that the frontside of the substrate S is not contacted by printer components between the printhead 12 and the cleaning unit 30. For example, the transfer of the substrate S along the media path may be driven by reeling the substrate S from the input roll 22 along the media path defined by the guiding rollers 26 and the heating plate 28 onto the output roll. The guiding rollers 26 contacting a backside of the substrate S may deflect the substrate S onto a winding path between the input roll 22 and the output roll. The winding path may curve along one direction between the printhead 12 and the cleaning unit 30, such that the front-side of the substrate S may not be contacted by the printer 10 along the media path section between the printhead 12 and the cleaning unit 30 to avoid damaging non-dried printing fluid.

[28] In some examples, the cleaning unit 30 contacts the substrate with an absorbing contact surface, and an advance of the substrate S and a motion of the absorbing contact surface of the cleaning unit 30 along the media path are synchronized such that the cleaning unit 30 removes an excess of the printing fluid from the substrate S without applying a shearing friction to the substrate S to prevent damage to or relocation of non-dried printing fluid by the cleaning unit 30.

[29] The output roll wound onto the collection drum 24 may be removed and transferred to a calender to fix the printing fluid by heat processing. For example, the substrate S may be heated above the sublimation temperature of a dye sublimation ink to diffuse dye components into the substrate S and to fix the image to the substrate S.

[30] By combining the drying unit 20 with a heat application length along the media path of less than 1 m, or less than 750 mm, with the cleaning unit 30, a printer 10 with a low physical footprint may be provided to print with high color bleed-through in a roll-to roll process, while avoiding backside staining or low printing speed.

[31] The drying unit 20 may feature a heat application length along the media path of at least 300 mm, such as 500 mm, to reduce the amount of non-dried ink removed from the substrate S by the cleaning unit 30, such as to minimize damage to the printed image by the cleaning unit 30 or to minimize a servicing rate of the cleaning unit 30.

[32] The substrate S wound on the collection drum 24 may be removed from the printer 10 to perform post-processing in a modular printing system.

[331 In some examples, a printing system further comprises a sublimation unit, such as a calender, to receive the substrate S wound onto the collection drum 24 and to fix the printing fluid to the substrate S.

[34] Fig. 3 illustrates a similar example of a printer 10, wherein the cleaning unit 30 comprises a cleaning roller 32. The printer 10 deposits a printing fluid onto a front-side of the substrate S upstream of a drying unit 20. The substrate S is transported past the drying unit 20 and the cleaning roller 32 from an input roll 22 towards a collection drum 24 along a media path shaped by guiding rollers 26.

[35] The cleaning roller 32 is arranged downstream of a heating plate 28, wherein the substrate S is pulled over the heating plate 28 to be dried by the drying unit 20 after the printing fluid has been deposited onto the front-side of the substrate S. The cleaning roller 32 contacts the substrate S with an absorbent material to remove an excess of non-dried printing fluid persisting on the front-side of the substrate S after the substrate S passes the drying unit 20.

[36] The absorbent material may be any material suitable to absorb the printing fluid or a solvent of the printing fluid, such as a porous material, e.g. a sea sponge, or a synthetic sponge made of polyester, polyurethane, polyvinyl alcohol, or vegetal cellulose. For example, the absorbing material may be a non-woven cloth, a foamed hydrophilic porous member, or the like. The absorbent material may be removable from the cleaning roller 32 to exchange the absorbent material based on a service criterion. In some examples, the absorbent material forms an outer cylinder of the cleaning roller 32 to contact the substrate S during a revolving motion of the cleaning roller 32. In some examples, the absorbent material is unrolled from the cleaning roller 32 during a revolving motion of the cleaning roller 32, such that a stained surface of the absorbent material may be removed from the cleaning roller 32. In some examples, the cleaning roller 32 holds a portion of an extended sheet of the absorbent material against the substrate S as a pulley, and the extended sheet of the absorbent material is advanced by the revolving motion of the cleaning roller 32.

[37] The cleaning roller 32 should not drive a motion of the substrate S. The cleaning roller 32 may contact the substrate S with no friction to avoid damaging the non-dried printing fluid. In this context the term “contact with no friction” may be understood as no shearing friction between the cleaning roller 32 and the substrate S acting on the non-dried ink, and may not exclude a frictional force between the substrate S and the cleaning roller 32 as such. For example, the outer perimeter of the cleaning roller 32 and the facing substrate surface may be in a frictional connection, such that the outer perimeter of the cleaning roller 32 and the substrate S move synchronously at a contact point between the substrate S and the cleaning roller 32 while the substrate S advances along the media path. In other words, an absorbing contact surface of the cleaning roller 32 may rotate in accordance with the velocity of the substrate S along the media path to remove an excess of the printing fluid from the substrate S without applying a shearing strain to non-dried printing fluid. For example, the cleaning roller 32 may be an idle roller resting on the substrate S, and the cleaning roller 32 may be pulled by a movement of the substrate S along the media path, or the cleaning unit 30 may actively drive a rotation of the cleaning roller 32 with a motor, such that the tangential speed of the outer perimeter of the cleaning roller 32 and the advance velocity of the substrate S are synchronized.

[38] In some examples, the cleaning roller 32 is the first printer component to contact the front-side of the substrate S downstream of the print-head 12. In other words, the curvature of the media path followed by the substrate S between the printer 10 and the cleaning unit 30 may be zero or may pull the substrate S away from the side contacted by the cleaning roller 32, to transport the substrate S from the printhead 12 towards the cleaning roller 32 without contacting the front-side of the substrate S with other printer components, such as guiding rollers 26.

[391 In some examples, the cleaning unit 30 comprises a plurality of cleaning rollers 32 arranged downstream of the heating unit 20 to remove an excess of the printing fluid from the substrate S without applying a shearing strain to non-dried printing fluid. The cleaning rollers 32 may be arranged in sequence along the media path and may progressively remove the excess of the printing fluid from the substrate S.

[40] A collection drum 24 can be arranged downstream of the cleaning unit 30 and coupled to the media path to wind the substrate S onto the collection drum 24. Since the printing fluid has been dried by the drying unit 20 or removed by the cleaning roller 32, a transfer of the printing fluid from the front-side of the substrate S to the backside of the substrate S may be prevented during winding.

[41] Fig. 4 illustrates an output stage 34 for a printer 10, such as the printers 10 of the previous examples. The output stage 34 comprises a media path to transport a substrate S past a drying unit 20 and a cleaning unit 30 towards a collection drum 24. The drying unit 20 is coupled to the substrate S along the media path to heat the substrate S and to dry a printing fluid on the substrate S. The cleaning unit 30 is downstream of the drying unit 20 to contact the substrate S with a cleaning roller 32 and to remove an excess of non-dried printing fluid from the substrate S. The collection drum 24 is downstream of the cleaning unit 30 and coupled to the media path to wind the substrate S onto the collection drum 24.

[42] The cleaning roller 32 is pivotally mounted on a pivot mount 36 in the output stage 34 via an articulated arm 38 to rest on the substrate S transported in the media path. Absorbent material may be mounted at the outer surface of the 32 to contact the substrate S during a revolving motion of the cleaning roller 32. The articulated arm 38 may be inclined such that a normal force of the cleaning roller 32 onto the substrate S is adjusted to a target value, when the cleaning roller 32 rests on the substrate S. The normal force of the cleaning roller 32 onto the substrate S may be adjusted by the inclination angle or a weight of the cleaning roller 32, such that the absorbent material removes an excess of non-dried printing fluid from the substrate S while limiting damage to the non-dried printing fluid.

[431 The inclination of the articulated arm 38 or the weight of the cleaning roller 32 may be adjusted empirically to prevent damaging the non-dried ink on the substrate S. For example, the inclination of the articulated arm 38 or the weight of the cleaning roller 32 may be progressively increased to a point where a transfer of printing fluid from the front-side of the substrate S to the backside of the substrate S remains below a staining threshold after winding the substrate S onto the collection drum 24, to adjust the normal force of the cleaning roller 32 onto the substrate S. In other words, the inclination of the articulated arm 38 or the weight of the cleaning roller 32 may be adjusted to obtain an advantageous compromise between printing fluid absorption from the substrate S by the cleaning roller 32 and damage to the non-dried printing fluid.

[441 In some examples, the pivot point 34 to which the cleaning roller 32 is pivotally mounted is movable to dynamically adjust a normal force of the cleaning roller 32 onto the substrate S. For example, the position of the pivot point 34 may be adjusted based on a media speed of the substrate S in the output stage 34 or based on a drying temperature imposed by the drying unit 20 onto the substrate S, such as to dynamically adjust an inclination of the articulated arm 38. [45] Fig. 5 illustrates an example of a method for printing on a substrate S. The method comprises applying a printing fluid directly onto the substrate S (S10). The method further comprises drying the substrate S at a drying temperature below a sublimation temperature of the printing fluid (S12), and transporting the substrate S past a cleaning roller 32 to absorb an excess of printing fluid (S14), wherein the cleaning roller 32 is resting on the substrate S and is driven by the transporting motion of the substrate S.

[46] The method may comprise transporting the substrate S over a heated plate 28 for drying the substrate S at the drying temperature without contacting the front-side of the substrate S between applying the printing fluid and drying the substrate S.

[471 The cleaning roller 32 may comprise an absorbent material at an outer surface of the cleaning roller 32 and may be pivotally hinged to rest on the substrate S. The substrate S may pull the cleaning roller 32 to drive a revolving motion of the cleaning roller 32, such that the substrate S and the cleaning roller 32 are in contact without a shearing friction onto the substrate S.

[48] The printing fluid may be a dye sublimation ink and the substrate S may be a textile substrate S. The method may comprise limiting a drying temperature attained by the substrate S to remain below a sublimation temperature of the dye sublimation ink in the printer 10.

[491 The substrate S may be transferred from an input roll 22 towards an output roll in between applying a printing fluid directly onto the substrate S and drying the substrate S, and the method may further comprise unwinding the substrate S from a roll 22. In some examples, the method comprises unwinding the substrate S onto a conveyor belt to transfer the substrate S in a roll-to-roll printer 10. The method may further comprise winding the substrate S onto a roll at an output stage 34 of the printer 10.

[50] The method may further comprise initiating a sublimation process of the printing fluid on the substrate S. For example, a dye sublimation ink may be applied to the substrate S directly as the printing fluid, and the substrate S may be wound onto the roll to be transferred to a post-processing unit, such as a calender. In other words, the method may comprise transferring the substrate S wound onto a collection drum 24 towards the calender.

[51] The calender may apply heat to the substrate S above a sublimation temperature, such as 180 °C or 200 °C to fix the printing fluid to the substrate S. Hence, a durable print with good color saturation may be obtained for applications sensitive to backside staining, such as flags or backlit substrates S.