Patent Publication Number: US-6698879-B1

Title: Printing textile using an inkjet printer

Description:
The invention relates to a method and apparatus for printing air-permeable textile material. 
     Such a method and such an apparatus are known from European patent application 0 633 345. Also, European patent applications 0 633 346 and 0 633 347 describe such apparatuses. 
     In comparison with the more conventional transfer system, in which first printing is effected on a paper carrier in reverse using an ink jet printer and then the pattern applied is transferred to textile by sublimation, such known methods and apparatuses have the advantage that the intermediate step of printing on paper and attendant losses of time, paper and printing ink are prevented. 
     A drawback of using these known methods and apparatuses is, however, that relatively much ink does not sufficiently adhere to the textile, as a result of which it separates during use and when washing the textile. In general, it is necessary for this reason to wash such products before use so as to prevent staining. 
     Another drawback of using these known methods and apparatuses is that the print sharpness is affected by the spreading of the ink as soon as it has been applied to the textile material. 
     It is an object of the invention, when printing textile directly by means of an ink jet printer, to ensure a better take-up of the ink in the textile, on the one hand, and, on the other hand, to limit the spreading of ink. 
     This object is achieved by carrying out a method according to the present invention which preferably includes incrementally bringing successive areas of a textile material to be printed into an area covered by at least one ink jet print head, selectively applying ink to the textile material by means of the ink jet print head according to predetermined picture information, and subjecting the applied ink to a treatment for at least fixing the ink. Preferably, the textile material is kept tensioned in the area covered by the ink jet print head over a free space on the side of the textile material remote from the ink jet print head. In order to be able to carry out the printing of textile in this manner, the invention further provides for an apparatus to carry out the above-described method. Preferably, the apparatus includes at least one ink jet print head reciprocable to cover a particular print area, a print head control for controlling the movement and ink delivery by the aforementioned ink jet print head, a guide table for guiding textile material to be printed in the area covered by the print head, and a conveying structure for incrementally bringing successive parts of the textile material to be printed into the area covered by the ink jet print head. 
     By effecting each printing on a part of the textile material behind which a free space is situated, and which is thus not in contact with a surface located behind it, discharged ink is less impeded to rapidly penetrate far into the textile material. Furthermore, it is not inconvenient if a part of the ink penetrates through the textile material completely because the absence of contact with a subjacent surface in the area covered by the print head or print heads prevents smearing of penetrated ink. This ensures a rapid deep penetration of the ink transversely to the plane in which the textile extends and a limitation of the spreading parallel to the plane in which the textile extends. 
    
    
     Further objects, structural aspects and structural details of the invention will be described and explained below by means of an exemplary embodiment, with reference to the drawings in which: 
     FIG. 1 is a slightly schematized, cut-away side view of an apparatus according to an exemplary embodiment of the invention, and 
     FIG. 2 is a further schematized, cut-away rear view of the apparatus of FIG.  1 . 
    
    
     The printer shown in the drawings has an assembly  1  of four print heads, mutually staggered in a textile conveying direction (arrow  2 ) and in a print head moving direction (arrow  3 ), for printing with ink in the colors yellow, magenta and cyan and with black ink. The print head assembly  1  is reciprocable along a rail  4  for covering a particular print area  5 . 
     To control movement and ink delivery by the print head assembly  1 , the apparatus comprises a print head control as schematically indicated in FIG. 2 by a block  6 . 
     Opposite the print head assembly, a guide table  7  is situated for guiding textile material  8  to be printed (only shown in FIG. 1) in the area  5  covered by the print heads. 
     To stepwise bring successive parts of the textile material  8  to be printed into the area covered by the print heads  1 , the apparatus has a conveying structure. Upstream of the guide table  7 , this conveying structure comprises a holder  9  for carrying a roll  10  of textile to be printed, a driving unit  11  for driving rotation of the holder  9  and the roll  10 , a web tensioner in the form of a ballast roller  12 , a loop detector  13 , a deflecting roller  14  and a conveying roller  15 . 
     The loop detector  13  is coupled via a line  16  with the driving unit  11  for activating the driving unit  11  in reaction to the rise of the loop of the textile material passing around the ballast roller  12  above a scanning plane  17  of the detector  13 . When the detector observes that the loop around the ballast roller  12  is above the plane  17 , the driving unit  11  is activated to unroll the roll  10  over a particular distance. If required, a second detector can be used at a distance below the detector  11  to always unroll the same amount of textile material, irrespective of the instantaneous thickness of the roll  10 . 
     Since the textile material, before reaching the conveying roller  15 , passes over the deflecting roller  14 , the textile material, in operation, abuts against the conveying roller  15  over a great part of the circumference. This has the result that at a relatively low tension on the textile web without clamping sufficient traction can be transferred to the textile web to ensure a reliable passage. To ensure a passage of the textile web without clamping, a free zone is situated, in operating, along the section of the conveying surface against which the textile material abuts. Since the textile material passes freely over the surface of the roller  15 , a uniform, accurate conveyance is ensured with a very slight deformation of the web. This is of special importance to the printing of textile because such material generally has a substantially lower diagonal stiffness than paper and the use of temporary stiffenings of the textile is attended with the drawback of the necessity of the subsequent removal of the temporary stiffening. 
     The deflecting roller  14  is suspended in swinging means  18  capable of swinging about an axis  19  from the position indicated by full lines to the position indicated in FIG. 1 by dot-dash lines. The insertion of a paper web is simply possible if the swinging means  18  is in the position indicated in FIG. 1 by dot-dash lines. After the web has been arranged over the guide table  7  and coupled to the conveying structure downstream of the guide table  7 , a loop can simply be formed by placing the ballast roller  12  between the roll  10  and the deflecting roller  14  and then unrolling the roll  10  until the ballast roller  12  has sunk to the desired level. Then the textile web can be arranged to abut against the conveying roller by swinging the swinging means  18  to the position indicated by full lines. 
     The conveying roller  15  is coupled with a driving unit  20  for stepwise passing the textile web  8 . This driving unit  20  is controlled with the print head control  6  by a central control unit  21 . The accuracy of the stepwise movements of the textile web  8  is of particular importance to the accurate connection to each other of successive strips of the pattern to be formed by the print heads  1 . 
     On the downstream side of the area  5  covered by the print heads  1 , that is to say on the side of the area  5  covered by the print heads  1  remote from the conveying roller  15 , a further tension roller is located in the form of a ballast roller  22 . The textile web  8  passes around the ballast roller  22  in a loop and from the ballast roller  22  to a take-up roller  23  where printed material can be stored until it is further treated in another machine so as to fix the ink. 
     Between the ballast roller  22  and the conveying roller  15 —and thus also in the area  5  covered by the print heads—a very constant tension is kept on the textile material  8  to be printed in a very simple manner so that relative smooth textile can also be accurately conveyed and printed. This advantage is also important when printing is effected without an open space behind the textile in the area  5  covered by the print heads  1 , as will be described below. This advantage, however, is of special importance when printing relatively open textile which is generally smoother, and thus harder to control, and is readily printable exactly in the presence of an open space behind the textile in the area  5  covered by the print heads  1 , without using temporary stiffenings. 
     Since both upstream of the area  5  covered by the printer and downstream of the area  5  covered by the printer tension rollers  12 ,  22  are situated, the textile web between these tension rollers  12 ,  22  is held in equilibrium and the conveying roller  15  needs to exert only little traction on the textile web  8  to move and stop the textile web  8 . This enables a very accurate control of the conveyance in the area covered by the print heads  1  with simple means at a minimum of deformations. 
     The traction to be exerted by the conveying surface of the conveying roller  15  on the textile web  8  is particularly limited because the ballast roller  22  downstream of the guide table  7  is slightly heavier than the ballast roller  12  on the upstream side of the guide table  7  and thus exerts a slightly greater tension force on the textile web  8 . The tension difference thereby also compensates a part of the friction between the textile web  8  and the guide table  7  so that the traction to be exerted by the conveying roller  15 , and thus any attendant slip, is further limited. 
     The take-up roller  23 , too, is driven in reaction to the length of the loop passed around the ballast roller  22 . To this end, a detector  24  is coupled via a line  25  with a driving unit  26  of the take-up roller  23 . When the loop sinks below a detection plane  27  of the detector  24 , the driving unit  26  is activated to rotate the take-up roller  23  through a particular angle in the roll-up sense. Here, too, a second detector may of course be used, in this case to stop rolling-up whenever the loop has reached a particular maximum level. Instead of the ballast rollers  12 ,  22 , which, because of their mass and the force of gravity acting thereon, maintain a tension in the textile web  8 , other types of tensioner may of course also be used, such as tension rollers operated by spring force. 
     The guide table is provided in the area  5  covered by the print heads  1  with a hollow space  28  open towards the print heads  1 . In use, this hollow space  28  forms a free space on the side of the textile material  8  remote from the print heads  1 . 
     In use, the textile web is conveyed stepwise over the guide table, and whenever a next part of the textile material  8  has been brought into the area  5  covered by the print heads  1 , that part of the textile material  8  is printed with a strip of the total picture to be formed. The print heads  1  selectively apply ink to the textile according to predetermined picture information. In the apparatus according to this example, each part of the textile to be printed moves in four steps through the area covered by the print heads  1 , after each of which steps one of the four print heads  1  applies its portion to the relevant part of the textile web  8 . 
     By keeping the textile material tensioned in the area covered by the print heads  1  over a free space on the side of the textile material remote from the print heads, a more rapid penetration of ink into the cloth becomes possible without the risk of smearing, and lateral spreading of ink is inhibited. In particular when printing adjacent surfaces in different colors, spreading leads to discolored edges spoiling the appearance of the print. 
     After the ink has been applied and dried, the ink is subjected to a treatment for fixing the ink. To print polymer materials, such as polyester bunting, a sublimation ink can advantageously be used, which, by sublimation, makes a final bond with the textile and obtains its final color. Other inks, too, such as those described in European patent application 0 633 345, may be used in combination with the associated fixation treatments. 
     The hollow space  28  communicates via a channel  29  with a reduced pressure source  30 . In operation, a reduced pressure with respect to the surroundings is thus maintained in the hollow space  28  by extracting air from that hollow space  28 . This ensures a substantial further improvement of the penetration speed of the ink and further inhibits spreading of the ink. Depending on the type of cloth processed, such an effective penetration of the ink into the cloth may be secured that, after fixation, it is no longer necessary to wash the cloth. In this connection it is important that cloth with so little finish or no finish at all is used so that it can be used in unwashed condition. Very good results are obtained when printing polyester bunting with an air permeability of 20-40% and preferably 30%, the ink being sublimated with a thermosol or thermofixation treatment. 
     A further advantage of the extraction of air on the side of the textile material  8  remote from the print heads  1  is that slipped ink is extracted from the textile, thereby preventing or at least limiting the formation of veils and the like on the rear side of the textile web  8 . Another advantage of the extraction of air through the area of the textile web  8  covered by the print heads  1  is that the air movement through the textile  8  is connected with little air movement along the print heads  1 , which could thus be easily clogged. 
     To generate a strong, drying air current through the area covered by the print heads  1 , the apparatus further comprises an air supply channel  31  opening into the area covered by the print heads  1 , in which air supply channel  31  a heating element  32  is located. Air extracted through the textile material  8  is thus supplemented with preheated air, which particularly inhibits spreading of the ink. 
     The heating element  32  also forms a heating element of the guide table  7  and is arranged upstream of the hollow space  28  to preheat textile material  8  passed over the guide table  7 . By preheating the textile material  8  before applying the ink, it is dried, whereby the ink can penetrate more rapidly and ink applied to the textile material dries more rapidly so that spreading is further inhibited. Furthermore, by preheating the textile, the effect is secured that at the moment of printing the properties of the textile hardly depend on ambient conditions, such as temperature and humidity, so that an improved controllability and reproducibility of the printing is ensured. 
     In the proposed printer, an efficient construction with a two-fold use of generated heat is further secured because the heating element  32  in the air supply channel  31  also forms the heating element of the guide table  7  for preheating textile material  8  passed over the guide table  7 . When preheating, heat penetrated through the textile  8  is discharged and used once more to promote the drying of ink in the area  5  covered by the print heads  1 . 
     The apparatus comprises a sealing cap  33  which forms an airtight or practically airtight seal. This ensures that extracted air is substantially supplemented via the air channel  31 . 
     The guide table  7  further comprises a heating element  34  downstream of the hollow space  28 . Furthermore, a heating element  35  is arranged above the guide table  7 . These heating elements  34 ,  35  downstream of the hollow space  28  serve to further dry applied ink so that when winding on the roll this ink does not come off on a preceding or following layer.