Digital printing process and apparatus of a substrate in the form of continuous sheet

Abstract

A substrate in the form of a continuous sheet is fed towards a belt conveyor and is lied out on the conveyor itself. By means of the belt conveyor, the substrate is moved along a feed direction, while a printing unit operating above the belt conveyor realizes a print pattern on the substrate. The printed substrate is withdrawn by a traction unit operating downstream of the belt conveyor. In a section of its longitudinal extension between the belt conveyor and the traction unit, the substrate is subjected to a braking action to retain the substrate in contrast to traction actions induced on the same by the traction unit. A drying group operates on the substrate in the area affected by the braking action, with a combined action of radiation and ventilation.

Claims

1. A digital printing process of a substrate formed as a continuous sheet, comprising the steps of: feeding to a belt conveyor a substrate formed as a continuous sheet; laying the substrate on the belt conveyor; via the belt conveyor, translating the substrate along a feed direction; forming a printed substrate by realizing a print pattern on the substrate by a printing unit operating above the belt conveyor; withdrawing the printed substrate by a traction unit operating downstream of the belt conveyor; subjecting the printed substrate to a braking action between the belt conveyor and the traction unit to retain the printed substrate in contrast to traction actions induced by the traction unit, wherein the braking action is carried out by a suction carried out at through openings formed in a slide plate that is skimmed by the printed substrate.

2. The process according to claim 1, subjecting the printed substrate to a drying action that is implemented along a longitudinal section of the printed substrate interposed between the belt conveyor and the traction unit.

3. The process according to claim 2, performing the drying action with a light radiation produced by radiant elements supported at a spaced position from the printed substrate, and with a ventilation flow directed against the printed substrate.

4. The process according to claim 3, further comprising cooling the radiant elements with the ventilation flow, before directing the ventilation flow against the printed substrate.

5. A digital printing apparatus of a substrate formed as continuous sheet, comprising: a feeding unit for feeding a substrate formed as a continuous sheet; a transport group comprising a belt conveyor configured to receive the substrate from the feeding unit and to translate the substrate along a feed direction; a printing unit operating above the belt conveyor to produce a print pattern on the substrate to form a printed substrate; a traction unit operating downstream of the transport group to withdraw the printed substrate; a braking unit operably interposed between the belt conveyor and the traction unit, to retain the printed substrate so as to counteract traction actions induced on the printed substrate by the traction unit; wherein the braking unit comprises: a slide plate configured to be slidably skimmed by the printed substrate and having a plurality of through openings; a suction chamber delimited by the slide plate; a suction unit configured to create a vacuum inside the suction chamber.

6. The apparatus according to claim 5, wherein the plurality of through openings are formed as slots extending along the feed direction.

7. The apparatus according to claim 5, and further comprising a drying group integrated with the braking unit, drying group configured for drying the printed substrate.

8. The apparatus according to claim 7, wherein the drying group comprises at least one heater suspended at a spaced position from the slide plate.

9. The apparatus according to claim 8, wherein the at least one heater comprises a panel, with opposite sides of the panel engaging with respective extensions, which extend from columns which support the slide plate.

10. The apparatus according to claim 9, wherein the at least one heater comprises radiant elements operatively carried by the panel.

11. The apparatus according to claim 7, wherein the drying group comprises ventilation devices configured to provide a ventilation flow towards the slide plate.

12. The apparatus according to claim 11, wherein the drying group includes at least one heater, the at least one heater comprising radiant elements, wherein the ventilation flow skims the radiant elements before reaching the slide plate.

13. The apparatus according to claim 11, wherein the drying group includes at least one heater, wherein the at least one heater comprises a panel, with opposite sides of the panel engaging with respective extensions, which extend from columns which support the slide plate, wherein the ventilation devices include a ventilation path extending internally towards the panel and exiting in a direction of the slide plate, through one or more vent openings in a lower surface of the panel.

14. A digital printing process of a substrate formed as a continuous sheet, comprising the steps of: feeding to a belt conveyor a substrate formed as a continuous sheet; laying the substrate on the belt conveyor; via the belt conveyor, translating the substrate along a feed direction; forming a printed substrate by realizing a print pattern on the substrate by a printing unit operating above the belt conveyor; withdrawing the printed substrate by a traction unit operating downstream of the belt conveyor; subjecting the printed substrate to a braking action between the belt conveyor and the traction unit to retain the printed substrate in contrast to traction actions induced by the traction unit; subjecting the printed substrate to a drying action that is implemented along a longitudinal section of the printed substrate interposed between the belt conveyor and the traction unit; performing the drying action with a light radiation produced by radiant elements supported at a spaced position from the printed substrate, and with a ventilation flow directed against the printed substrate; cooling the radiant elements with the ventilation flow, before directing the ventilation flow against the printed substrate.

Description

(1) Further characteristics and advantages will appear more clearly from the detailed description of a preferred, but not exclusive, embodiment of a process and apparatus for the digital printing of a substrate in the form of a continuous sheet according to the present invention. This description is provided herein below with reference to the attached drawings, which are provided solely for the purpose of providing approximate and thus non-limiting examples, and in which:

(2) FIG. 1 is a schematic side view of a digital printing apparatus according to the present invention;

(3) FIG. 2 is a perspective, partially interrupted view of a braking unit and a traction unit arranged in the digital printing apparatus of FIG. 1;

(4) FIG. 3 shows the braking unit sectioned according to a substantially median vertical plane.

(5) With reference to the mentioned figures, the reference number 1 comprehensively indicates a digital apparatus for printing a substrate in the form of a continuous sheet according to the present invention.

(6) The apparatus 1 is adapted to perform a digital printing process on a substrate 3, for example of paper or textile material, fed in the form of a continuous sheet having a width that can indicatively range between 1600 and 3200 mm and over.

(7) The apparatus 1 comprises a feed unit 2 configured to feed the substrate 3 towards a transport group 4. The feed unit 2 can, for example, comprise a feeding support (not shown) arranged to rotatably support the substrate 3, arranged in the form of a feed roller 3a, and possibly one or more idler and/or stretching rollers 6, to suitably accompany the substrate 3 which is gradually unwound from the feed roller 3a towards the transport group 4.

(8) The transport group 4 comprises at least one belt conveyor 7, suitably motorized, that receives the substrate 3 coming from the feed unit 2 at an input end 4a. The belt conveyor 7, suitably motorized, translates the substrate 3 along a predetermined feed direction F, toward an outlet end 4b of the transport group 4.

(9) A printing unit 8 operates above the belt conveyor 7, and is configured to realize a print pattern on the substrate 3 laying on the belt conveyor 7. The printing unit 8 usually comprises one or more print heads 9 carried by a carriage 10 alternately movable along a direction which is transverse to the feed direction F of the substrate 3.

(10) The belt conveyor 7 is typically operated according to a step-by-step movement, so as to impose to the substrate 3 a sequence of translation steps alternated with stopping steps, corresponding to the alternate translation of the carriage 10 of the printing unit 8. When the substrate 3 is in the stopped step, the carriage 10 carries out a translational motion outward in order to allow the delivery of ink from the print heads 9. When the substrate 3 is in the movement step, the carriage 10 can perform a return translation to return the print heads 9 to the section from which they started.

(11) To facilitate the correct timing between the movement of the substrate 3 and the movement of the printing unit 8, it is preferably envisaged that the transport group 4 is operatively associated with suitable anchoring devices 11 which assist in the correct adhesion of the substrate 3 itself to the belt conveyor 7. In the example shown, the anchoring devices 11 comprise at least one suction plane 11a, 11b arranged to exert a suction action through a plurality of through holes (not shown) distributed on the belt conveyor 7. More in particular, a first suction plane 11a and a second suction plane 11b can be provided, respectively operating upstream of the printing unit 8 and below the same, for example as described in document WO2017/060875. In addition or alternatively, the anchoring action can be achieved in other ways, for example by means of adhesive substances spread on the surface of the belt conveyor 7 and/or by electrostatic systems.

(12) The apparatus 1 further comprises at least one traction unit 12, operating downstream of the transport group 4 for withdrawing the printed substrate 3 coming from the belt conveyor 7. The traction unit 12 can for example comprise a winding group 13 configured to collect the substrate 3 by winding it in the form of a collection roll or reel 3b, after passing around one or more idler rollers 13a. To determine the translation of the substrate 3 toward the collection reel 3b, the same collection reel 3b and optionally at least one of the idler rollers 13a can be motorized.

(13) Preferably, the traction unit 12 further comprises at least one dancing roller 14 configured to operate on the substrate 3 upstream of the collection reel 3b. Preferably, the dancing roller 14 is rotatably carried by a pair of arms 15 oscillatably bound with respect to a supporting base 16, with freedom of rotation around a preferably horizontal axis of oscillation, parallel to the substrate 3. Loading devices 17 comprising, for example, one or more counterweights, springs or other thrust elements not shown, operating on the arms 15 and/or directly on the dancing roller 14 to push the latter against the substrate 3 with a predetermined force. The substrate 3 is therefore subjected to a traction action, preferably constant, correlated to the intensity of the force exerted by the dancing roller 14, which can be adjusted by acting on said loading devices 17.

(14) Between the belt conveyor 7 and the traction unit 12 a braking unit 18 is operably interposed, configured to retain the substrate 3 so as to counteract the traction action induced on the same by the traction unit 12.

(15) Preferably, the braking unit 18 comprises a slide plate 19 configured to be skimmed by the substrate 3, along the path that the substrate 3 itself travels by translating from the transport group 4 towards the traction unit 12.

(16) The slide plate 19, preferably positioned below the substrate 3, can be for example a metal plate having a plurality of through openings, suitably distributed at least in the area skimmed by the substrate 3, or near this area.

(17) The slide plate 19 delimits from above at least one suction chamber 20 subjected to the action of at least one suction unit 21.

(18) More in particular, in the example shown, the slide plate 19 is associated with two suction chambers 20, respectively separated by a central partition 22, arranged parallel to the feed direction F of the substrate 3. The suction chambers 20 are connected laterally, on opposite sides with respect to the slide plate 19, to two suction units 21 each of which is housed within a box-like column 23 which laterally supports the slide plate 19 itself. Each suction unit 21 produces a vacuum inside the respective suction chamber 20, expelling the sucked air into the respective box-like column 23.

(19) The substrate 3 is consequently braked against the slide plate 19 due to the effect of the vacuum produced by means of through openings 24 provided in the slide plate 19. This braking action is distributed, preferably in a uniform manner, along the longitudinal section of the substrate 3 which skims the slide plate 19.

(20) Preferably, the through openings 24 are made in the form of slots extending along a feed direction F of the substrate 3 to favour longitudinal sliding. In order to avoid jamming of and/or damage to the substrate 3, each through opening 24 is preferably provided in the form of a slot with a width below 3 mm, preferably comprised between 1.5 mm and 2 mm. The length of each slot is preferably greater than 20 mm, more preferably comprised between 35 mm and 70 mm.

(21) By adequately modulating the action of the suction units 21, it is possible to adjust the intensity of the braking action induced on the substrate 3 that slides along the slide plate 19. The braking action imparted to the substrate 3 by the braking unit 18 intercepts the traction action applied to the substrate 3 by the traction unit 12, so as to prevent the same traction action from wholly propagating along the substrate 3 up to the transport group 4. Consequently, the traction unit 12 can be activated so as to produce a traction action that is also rather strong in the section downstream of the braking unit 18. This traction action is however sufficiently attenuated, or if necessary completely eliminated, in the section of the substrate 3 extending upstream of the braking unit 18.

(22) This circumstance offers the possibility of reducing the anchorage action of the substrate 3, which is required to ensure the stability of the substrate 3 on the belt conveyor 7 during processing, without risking that the substrate 3 can undergo unwanted displacements due to the traction produced by the traction unit 12. The processing of substrates which are particularly delicate and could easily be damaged by the effects of an energetic anchorage action is thus facilitated, also due to the weakening directly at the print area where the substrate 3 itself is wetted by the ink delivered by the printing unit 8. It is also possible to increase, where required, the traction action exerted by the traction unit 12 to ensure more regular and compact winding of the substrate 3 on the collection reel 3b, without the risk of compromising the integrity and stability of the substrate 3 itself along the transport group 4.

(23) It is preferably envisaged that the printed substrate 3 is subjected to a drying action performed along a longitudinal section of the substrate interposed between the belt conveyor 7 and the traction unit 12. The drying action makes it possible to dry the ink delivered onto the substrate 3 so as to prevent the transfer of the ink itself between adjacent turns created during the step of winding on the collection reel 3b. The drying process also eliminates the excess moisture from the substrate 3, so as to mitigate or eliminate the effect of structural weakening that the same could have as a result of the absorption of the ink.

(24) More in particular, the drying action can advantageously be performed in the same longitudinal section of the substrate 3 affected by the braking action.

(25) It can be advantageously envisaged that the braking unit 18 is integrated with a drying group 25 of the substrate 3. The drying group 25 preferably comprises at least one heater 26 suspended at a spaced position above the slide plate 19.

(26) In the embodiment illustrated, the heater 26 comprises a panel 27, preferably having a box-like structure, whose opposite sides are engaged in respective extensions 23a which extend from the box-like columns 23. The heater 26 can comprise one or more radiant elements 28, typically infrared radiation lamps, engaged to one or more reflective elements 29 carried by the panel 27. More in particular, the radiant elements 28 are each housed at a concavity facing the slide plate 19, defined by a respective reflecting element 29.

(27) The radiation produced by the radiant elements 28 and/or reflected towards the substrate 3 determines the drying during the translation along the slide plate 19.

(28) In addition or alternatively, the drying can be advantageously assisted by a ventilation action directed against the substrate 3.

(29) For this purpose, the drying group 25 preferably comprises ventilation devices 30 configured to provide at least one flow of air towards the slide plate 19.

(30) In the example described, these ventilation devices 30 comprise at least one, preferably two ventilation units 30a, each housed inside one of the box-like columns 23. Each ventilation unit 30a delivers a flow of air through the respective side openings 31 arranged at the top of the box-like columns 23 and/or at the respectively opposite sides of the panel 27. The side openings 31 terminate near a lower surface of the panel 27 and/or within the same, so that the flow of air is directed to skim the radiant elements 28 and/or the inner surfaces of the box-like structure of the panel 27 itself. More in particular, first flows of ventilation produced from the respective ventilation units 30a skim the radiant elements 28 in opposed directions and mutually meet below the panel 27 to deviate towards the slide plate 19. In addition or alternatively, second flows of ventilation follow a ventilation path extending inside the box-like structure of the panel 27 and flowing in the direction of the slide plate 19, through vent openings 32 obtained in a lower surface of the panel 27 itself.

(31) The flow of air produced by the ventilation units 30a skims the radiant elements 28 and/or the surfaces of the panel 27, removing heat so as to avoid overheating. At the same time, the flow of air thus heated skims the substrate 3 laying on the slide plate 19, facilitating the drying of the printing ink.