METHOD AND DEVICE FOR STEPWISE PRINTING OF A CONTINUOUS MATERIAL WEB

Abstract: In a method for stepwise printing of a continuous material web (4), in particular a textile web, the printing is carried out by means of one or more jet nozzles of a printing station (9). According to the invention, the material web (4) is guided, freely suspended, in an upward direction past said one or more jet nozzles at a substantially constant web tension. During the carrying out of the method, no large quantities of waste are produced, and little substrate loss occurs during starting up of the printing. Furthermore, staining on parts of the device is prevented. A device for carrying out the method is also described.

Description: Method and device for stepwise printing of a continuous material web The invention relates to a method for stepwise printing of a continuous material web, in particular a textile web, by means of one or more jet nozzles of a printing station. Such a method is known in the trade. In the case of the known method the substrate to be printed is stuck on a(n) (endless) band by means of resin. After the desired illustration and/or text has been printed on the substrate by means of the jet nozzles of the printing station, the substrate is pulled off the band. In the process, material of the substrate, ink residues and the like are left behind in the resin. The resin is washed off the band, so that the latter can be reused. On account of the fact that it contains environmentally harmful pigments, the effluent thus obtained has to be treated as chemical waste and disposed of as such. As a result of this necessary disposal, in combination with the large quantities of waste, the operating costs are high. An object of the present invention is to provide a method for stepwise printing of a material web, in particular a textile web, in the case of which effluent containing no resin and pigments is produced, so that the operating costs are relatively low. A further object of the present invention is to provide a method which is such that no staining from printing ink and the like occurs on parts of the device used for carrying out the method. Yet a further object of the invention is to provide a device for carrying out the method according to the invention which is in particular easily accessible for maintenance purposes. Yet another object of the invention is to provide a compact device, so that little waste is produced during the tentering of the material web to be printed. The printing method according to the invention is characterized in that the material web is guided, freely - suspended, in an upward direction past said one or more jet nozzles at a substantially constant web tension. In the case of the method according to the invention, the material web is guided at a certain constant web tension in an upward direction past the jet nozzles of the printing station, while the material web is not supported in that position. The web tension will depend on the type of material from which the substrate to be printed is made. The printing is carried out at a position where the material web is not supported, because otherwise soiling of counterpressure rollers and the like could occur as a result of ink droplets passing through the substrate. In the case of the method according to the invention, no supporting layer on which the material web is stuck is used, so that there is no washing operation for the supporting layer after printing, which has very advantageous consequences as regards the operational costs, in particular those of the method itself, and for the envi- ronment. According to a preferred embodiment of the method, the material web is guided vertically past the jet nozzles, which are advantageously positioned at right angles to the material web. In the case of the jet nozzles used, very many droplets - of the order of magnitude of 625,000 per second - are forced out of a jet nozzle and are guided past a charging electrode, where the droplets are electrically charged, and subsequently past deflection electrodes, so that the droplets are deflected in the desired direction. Incorrectly charged droplets, which are therefore not deflected in the desired direction, are collected by means of a "knife" which is disposed between the print head and the material web. If such a print head were set up above a horizontally moving substrate, it would be difficult to collect and discharge those incorrectly charged droplets. Printing from underneath gives the same problem and, in addition, the risk of blockage of a jet nozzle. Therefore, in the case of the invention, the material web to be printed is preferably guided substantially vertically past jet nozzles disposed- at right angles thereto. Some deviation from the vertical is, however, permissible. In addition, the distance between jet nozzles and material web to be printed is advantageously kept constant, so that variations in the thickness of the material web do not have an effect on the print quality. If the distance would become shorter, a greater sharpness in fact occurs in the vertical direction in the case of horizon- tally arranged jet nozzles past which the substrate is guided vertically. The printing according to the invention is carried out stepwise, i.e. in the course of creation of the image after each printed strip thereof, the material web will be moved a small step (for example, approximately 8 mm) further by means of suitable web conveyor means, which will be explained in greater detail below. The invention also relates to a device for stepwise printing of a continuous material web, in particular a textile web, which device comprises a web conveyor system, comprising a feed unit for feeding in the material web to be printed, and a discharge unit for discharging the printed material web, and also a printing station with one or more jet nozzles for printing the material web, and means for keeping the web tension constant, the device having defined therein a web throughput route, through which the material web is to be passed, and the web throughput route comprising a free printing section in an upward direction past the jet nozzles of the printing station. Preferred embodiments of the device according to the invention are defined in the dependent device claims. The invention will be explained in greater detail below with reference to the appended drawing, in which: Fig. 1 shows a first embodiment of a device according to the invention; Fig. 2 shows a second embodiment of a device according to the invention, and Fig. 3 shows a third embodiment of a device according to the invention. - — Fig. 1 shows an embodiment of a printing device according to the invention, indicated in its entirety by reference numeral 1. The printing device 1 comprises a web conveyor system, comprising a first feed roller 2 driven by a stepping motor (not shown) , and a second feed roller 3, also driven. The rollers 2 and 3 are made from, for example, aluminium, which has sufficient friction resistance to carry along a material web 4 , the direction of movement of which is indicated by arrows. If the friction resistance is insufficient, and the substrate consequently slips over such a roller, the roller can be provided with a suitable cladding, for example rubber. The material web 4 is unwound from a stock roll 5 for substrate which has been pretreated if desired, and is guided over a leveller 6 and subsequently spreaders 7. A leveller generally comprises a rotatable shaft having thereon spiral-shaped grooves (worms) running from the centre in opposite directions. In the case of a spreader only the ends are provided with such grooves. A nip roller 8 is disposed at the first driven roller 2. A printing station 9 with horizontal jet nozzles is situated between the rollers 2 and 3. The printing section 10 of the web throughput route to be travelled by the material web in the device 1 runs vertically, so that the material web 4 is guided in an upward direction past the printing station 9. It is pointed out that the term "web throughput route" is used to indicate the path of a material web from the inlet through the device to the outlet thereof. Distance rollers 11 are placed at both ends of the printing route 10, along which rollers the material web 4 is guided in the manner indicated, so that the distance between print head 9 and substrate 4 is always constant, even if substrates of differing thicknesses have to be printed in the device, or if one and the same substrate is not of uniform thickness. Due to the presence of the distance rollers the driven rollers 2 and 3 respectively and the printing station 9 may be disposed in a fixed position, which does not have to be changed when the material web is changed. The distance from the top distance roller IT. to _ the printing position will be selected in such a way that at a given printing and conveyor speed (of the order of magnitude of approximately 12 m per hour at a printing width of 1.7 m) there is sufficient drying time to allow the printed material web to dry before it reaches the top roller 11. At the web conveyance speed mentioned above, a centre-to-centre distance of 30 cm between the two distance rollers is sufficient. The roller 3 gives a constant web tension over the printing section 10 by means of a couple. A nip roller 12 beside the roller 3, interacting therewith, ensures further conveyance of the material web 4, for example to a take-up roll 13, onto which the printed material web is wound. An additional advantage of the arrangement of the rollers 2 and 3 above one another is that, if necessary, the bottom roller 2 is also easily accessible, for example for maintenance work. In order to feed the material web into the device, use is made of a web throughput system, consisting of a web pick-up, on which an end of the material web is fixed, and also guide means for the web take-up, for example rails, which are disposed along the web throughput route through the device. During the infeed of the material web into the device the spreaders, nip rollers and distance rollers will be held in a neutral position, while the material web is actually brought into contact with the leveller, in order to feed in the material web as evenly as possible, in order to limit material loss. During the infeed, all shafts of the various parts of the device are freely rotatable. After the infeed of the material web has been completed, all parts are activated. In the case of the device according to the invention the web throughput route is preferably kept as short as possible, in order to limit substrate loss when the device is started up. The device described above can have a web throughput route with a total length of, for example, approximately 1 metre, in which case the distance from the printing station 9 to the nip roller 12 is approximately 40 cm, which means that the substrate loss (unprmted material web) is also 40 cm. The whole device - is therefore compact. Detection means for determining the presence of a material web are advantageously disposed at strategic positions, such as at the beginning and end of the web throughput route. Said detection means are used for controlling the device, in which case, for example, the detection of the presence of the material web after it has been fed into the device releases the device for the printing itself. In order to intercept and collect paint or ink droplets passing through the substrate, a collection container (not shown) is disposed at the rear side of the substrate. Fig. 2 shows another embodiment of the device according to the invention, in which parts corresponding to parts in Fig. 1 are indicated by the same reference numeral + 20. In the case of this embodiment, no nip rollers are disposed beside the driven rollers 22 and 23, and a separate web tensioning mechanism 34 is provided between the stock roll 25 and the leveller 26. Such web tensioning mechanisms are known in the art, so that a detailed description will not be given here. An additional leveller 35 and a nip roller 36 are disposed downstream of the second roller 23. The operation of both devices is the same for the printing. A material web is guided in a vertical printing section past the jet nozzles of the printing station. The material web is not supported at that point, but is held under a constant web tension as indicated in Figs. 1 and 2. Staining from ink on parts of the device cannot occur; and there is no source of waste such as in the prior art, where large quantities of effluent have to be disposed of and, on account of the substances they contain, have to be treated as chemical waste. Moreover, the device according to the invention is compact, so that unnecessary substrate loss is limited. The printing position between the two rollers provides good accessibility to the entire device. Fig. 3 illustrates a third embodiment of the device according to the invention, in which parts identical to ~ those of Fig. 1 are indicated by the same reference numerals + 40. The material web 44 is unwound continuously from the driven roll 45 and subsequently guided to a buffer system indicated in its entirety by reference numeral 60. The buffer system 60 consists of a non-driven auxiliary roller 61, a so-called dancing roller 62 and a leveller (smoothing roller) 63 with screw thread running from the centre to each end of the roller, in order to level out the material web 44. The dancing roller 62 moves downwards during the printing of the material web 44 (i.e. during standstill of the roller 48 to be discussed below) , and moves upwards during further throughput of the material web 44. After the buffer system 60, the material web 44 is guided by way of a non-driven roller 48 and a driven roller 42, and further by way of a guide plate 64 along in front of the print head 49 in the printing section 50. The guide plate 64, which extends over the full width of the material web 44, is rigid and smooth and made of, for example, aluminium. After the printing section 50, the printed material web is guided around a driven roller 43 and a non-driven roller 52, both of which are provided with a rubber cladding layer. Finally, the material web is wound onto a driven and slipping roller 53. Compared with the device according to Fig. 1, in the case of the device according to Fig. 3, the function of the rolls 11, which determine the distance between the material web 4 and the print head 9, is taken over by the roller 43 together with the guide plate 64, which make the material web 44 hang taut as close as possible to the print head 49. From the point of view of costs, the device according to Fig. 3 is more advantageous than that according to Figs. 1 and 2. The guide plate 64, in addi- tion to the abovementioned function, serves to remove creases from, or prevent them from occurring in, the material web prior to printing thereof. The guide plate 64 has a certain curvature, with the result that a certain part of the material web rests against said plate 64. Compared with the web tensioning device ^ 34 _ according to Fig. 2, the material web 44 in Fig. 3 is held tensioned by the combinations of the rollers 42, 48 and 43, 52 respectively.

Claims: Claims 1. Method for stepwise printing of a continuous material web (4; 24; 44), in particular a textile web, by means of one or more jet nozzles of a printing station (9; 29; 49), characterized in that the material web (4; 24; 44) is guided, freely suspended, in an upward direction past said one or more jet nozzles at a substantially constant web tension. 2. Method according to claim 1, characterized in that the material web (4; 24; 44) is guided vertically past said one or more jet nozzles. 3. Method according to claim 1 or 2 , characterized in that the distance between the material web (4; 24; 44) and said one or more jet nozzles is kept constant. 4. Printing device (1) for stepwise printing of a continuous material web (4; 24; 44), in particular a textile web, which device comprises a web conveyor system, comprising a feed unit for feeding in the material web (4; 24; 44) to be printed, and a discharge unit for discharging the printed material web, and also a printing station (9; 29; 49) with one or more jet nozzles for printing the material web (4; 24; 44), and means (3; 34; 42, 48, 43, 52) for keeping the web tension constant, the device having defined therein a web throughput route through which the material web (4; 24; 44) is to be passed, characterized in that the web throughput route comprises a free printing section (10; 50) in an upward direction past the jet nozzles of the printing station (9; 29; 49). 5. Device according to claim 4, characterized in that the free printing section (10; 50) runs vertically. 6. Device according to claim 4 or 5, characterized in that distance means are disposed before and after the printing section (10; 50), for keeping the distance between jet nozzles and the material web (4; 44) constant. 7. Device according to claim 6, characterized in that said distance means are selected from distance rollers (11) , guide plates (64) , or combinations thereof. 8. Device according to one of the preceding claims 4- ~ 7, characterized in that the feed unit comprises a driven feed roller (2; 22; 42). 9. Device according to claim 8, characterized in that the feed roller (2; 22; 42) is driven by a stepping motor. 10. Device according to one of the preceding claims 4- 9, characterized in that the discharge unit comprises a second driven discharge roller (3) with couple for setting the web tension. 11. Device according to one of the preceding claims 4- 9, characterized in that a web tensioning mechanism (34) is disposed before the infeed roller (22) . 12. Device according to one of the preceding claims 4- 9, characterized in that the means for keeping the web tension constant comprise a first pair of rollers, comprising a driven roller (42) and a free roller (48) interacting therewith, which rollers are disposed before the printing section (50) , and a second pair of rollers, comprising a driven roller (43) and a free roller (52) interacting therewith, which rollers are disposed after the printing section (50) . 13. Device according to one of the preceding claims 4- 12, characterized in that one or more spreading rollers (7; 27) and smoothing rollers (6; 26; 63) are disposed upstream of the infeed roller (2; 22; 42). 14. Device according to one of the preceding claims 4- 13, characterized in that a collection container for collecting throughgoing droplets is disposed opposite said one or more jet nozzles of the printing station (9; 29; 49). 15. Device according to one of the preceding claims 4- 14, characterized in that the device is provided with detectors for detecting the presence of a material web in the device.

Inventors: GLOUDEMANS MARINUS JOHANNES HE, GLOUDEMANS, MARINUS, JOHANNES, HENDRIKUS
Applicants: GLOUDEMANS MARINUS JOHANNES HE, STORK DIGITAL IMAGING B V, GLOUDEMANS, MARINUS, JOHANNES, HENDRIKUS, STORK DIGITAL IMAGING B.V.
Application year: 1999
Main classification: B41J15
IPC codes: B41J2, B41J3, B41J11, B41J15