Abstract
A method of coating threads using a printhead having rows of nozzles extending along a length of the printhead. The method includes the steps of: feeding the thread along a length of the printhead; and ejecting ink from the rows of nozzles towards the thread. Thread-coating modules and thread-coating systems make use of the method described.
Claims
1. A thread-coating system for coating one or more threads, said system comprising a plurality of thread-coating modules arranged in series, each thread-coating module coating the threads with a different colored ink in a predetermined amount to provide a contone coating, each thread-coating module comprising: an elongate coating chamber having enclosed sidewalls, a thread entrance at one end and a thread exit at an opposite end thereof; and one or more printheads positioned at the sidewalls for ejecting ink droplets into the coating chamber, the sidewalls have one or more openings aligned with every printhead, wherein an exhaust opening is positioned opposite every printhead, the exhaust opening receiving ink droplets ejected into the coating chamber.
2. The thread-coating system of claim 1, wherein a longitudinal axis of each printhead is angled relative to a longitudinal axis of its respective coating chamber.
3. The thread-coating system of claim 1 further comprising at least one of: a thread gatherer upstream of a first thread-coating module, the thread gatherer being configured for gathering a plurality of threads into a thread group for feeding through a first coating chamber; a thread expander downstream of a second thread-coating module for expanding the thread group; a thread vibrator; and a thread rotator.
4. The thread-coating system of claim 1, further comprising an ink recycling system for recycling ink received in every exhaust opening of a respective thread-coating module into an ink reservoir supplying ink to every printhead, said ink recycling system comprising a return line interconnecting the exhaust opening and the ink reservoir.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
(2) FIG. 1 is a schematic side view of a thread-coating system;
(3) FIG. 2 is a schematic perspective of a thread-coating module according to a first embodiment;
(4) FIG. 3 is a schematic end view the thread-coating module according to the first embodiment showing airflow jets;
(5) FIG. 4 is a schematic end view a thread-coating module according to a second embodiment having acoustic levitation devices;
(6) FIG. 5 is a schematic side view of a thread-coating system having multiple thread-coating modules arranged in series;
(7) FIG. 6 is a schematic side view of a thread-coating system with pre- and post-processing of threads;
(8) FIG. 7 is a top perspective of a thread-coating module according to a third embodiment;
(9) FIG. 8 is a bottom perspective of the thread-coating module shown in FIG. 7;
(10) FIG. 9 is a longitudinal sectional perspective of the thread-coating module shown in FIG. 7; and
(11) FIG. 10 is a schematic view of an ink delivery system for a plurality of monochrome thread-coating modules.
DETAILED DESCRIPTION OF THE INVENTION
(12) In the following description of various embodiments of the present invention, like features are given like reference numerals, where appropriate.
(13) Referring to FIG. 1, there is shown schematically a system according to a first embodiment for coating ink onto a thread 10 using a pagewide printhead 1 having longitudinal rows of inkjet nozzles. The printhead 1 typically has a length of at least 200 mm and may be part of a print module, as described in U.S. Pat. No. 10,144,232, the contents of which are incorporated herein by reference. Maintenance systems for such print modules are also described in U.S. Pat. No. 10,144,232.
(14) Still referring to FIG. 1, the thread 10 is fed in a direction indicated by arrow T along a long axis of the printhead 1 whilst being rotated using a thread rotator 3. Typically, print media are fed transversely past pagewide inkjet printheads across the rows of nozzles; however, pagewide printheads have hitherto not been used for coating ink onto threads longitudinally in the manner shown in FIG. 1. Memjet® printheads are suitable for use as the printhead 1 and contain a plurality of butting printhead chips defining multiple rows of nozzles extending along the length of the printhead, thereby providing excellent ink coverage of the thread 10. Rotation of the thread 10 during its traverse along the length of the printhead 1 may be used to ensure that each part of the thread is colored by ink jetted from the printhead. Alternatively or additionally, the thread 10 may be vibrated whilst being fed along the printhead 1.
(15) Referring to FIG. 2, there is shown schematically a thread-coating module 20 comprising an elongate coating chamber 22 in the form of a cylindrical tube and first and second pagewide printheads 1A and 1B positioned around the coating chamber for ejecting ink droplets towards a thread (not shown in FIG. 2) fed longitudinally through the coating chamber. Each printhead is aligned with a respective slot (not shown in FIG. 2), thereby enabling the printheads to fire droplets into the coating chamber 22.
(16) The first printhead 1A is upstream of the second printhead 1B in a staggered overlapping arrangement in order to maximize coating efficiency. It will of course be appreciated that additional printheads may be provided in the thread-coating module 20, both circumferentially to increase ink cloud density and/or lengthwise to increase an effective “coating zone”.
(17) A distance between the thread 10 and each printhead 1 may be fixed or varied and suitable mechanisms may be provided for adjusting the height of the printhead relative to the thread. In conventional media printing, inkjet printheads are positioned about 0.5 to 5 mm away from a media surface for optimal drop placement accuracy. By contrast, thread printing optimally employs a dispersed ink cloud and the ‘throw distance’ (that is, the distance between the thread and the printhead nozzles) is typically large compared to conventional media printing. For example, the distance between the thread and printhead nozzles may be greater than 5 mm, greater than 10 mm, greater than 20 mm, greater than 50 mm or greater than 100 mm. Accordingly, an effective ink cloud density experienced by the thread may be controlled by at least two factors: (1) a distance between the thread and the printhead; and (2) dot data supplied to the printhead. In some embodiments, the ‘throw distance’ may be varied by adjusting the position(s) of the printhead(s). Optimization of coating uniformity, coating density, coating speed etc. are factors that may determine the throw distance for any given coating job.
(18) FIG. 3 is a schematic sectional view of the thread-coating module 20 having airflow jets 24 for controlling an ink cloud inside the coating chamber 22. It may be desirable to increase the dwell time of an ink cloud inside the coating chamber 22 by inducing vortices in therein using suitably controlled airflow jets positioned around the coating chamber. Increasing the dwell time of the ink cloud advantageously maximizes ink usage. The configuration of the coating chamber 22 may also be optimized for generating controllable vortices. For example, cross-sectional chamber profiles, such as spiral, multi-lobed, elliptical, star-shaped etc. are all within the ambit of the present invention. Additionally, a suction port 26 may be used for controlling air pressure inside the coating chamber 22 as well as removing unused ink for recycling back to an ink reservoir.
(19) FIG. 4 is a schematic sectional view of a thread-coating module 30 according to a second embodiment, similar to the thread-coating module 20 shown in FIG. 3. However, in the thread-coating module 30 according to the second embodiment, a plurality of acoustic devices 28 are provided for suspending ink droplets in the coating chamber 22 using acoustic levitation. Acoustic levitation may be used as an alternative to or in addition to airflow jets for controlling the ink cloud inside the coating chamber 22 and increasing the dwell time of the ink cloud.
(20) Referring to FIG. 5, there is shown a thread-coating system 40 comprising three thread-coating modules 20 arranged in series and a thread-feed assembly for feeding the thread 10 along a direction indicated by arrows T. In order to occupy minimal space, the thread-coating modules 20 are arranged laterally and the thread 10 is fed in opposite directions through sequential modules using a series of rollers 42.
(21) Although three thread-coating modules 20 are shown in FIG. 5, it will be appreciated that any number of modules may be used in such a system. For example, multiple monochrome modules supplied with ink of the same color may be provided to increase ink coverage. Furthermore, multiple monochrome modules of different colors (e.g. CMYK) may be used to provide colored threads in any given color on demand from an available color gamut. It will be appreciated that different ink cloud densities in respective coating chambers may be used to build up a desired contone thread color in an analogous manner to contone printing using monochrome halftone images.
(22) Referring to FIG. 6, there is shown a thread-coating module 20 for coating multiple threads 10 with pre- and post-processing of the threads. Six thread spools 44 continuously feed respective threads 10 into a thread gatherer 46, which arranges the threads into a 3×2 array for coating. The six threads are then fed longitudinally through the coating chamber 22 for coating simultaneously using the first and second printheads 1A and 1B. The coated threads then exit the coating chamber 22 into a thread expander 47 before being flattened into a 6×1 array in a thread flattener 48, and dried through a heated roller assembly 49. In order to optimize coating uniformity in the coating chamber 22, the thread gatherer 46 imparts a transverse vibrational force onto the threads 10 indicated by arrow Y, while the thread expander 47 imparts a longitudinal vibrational force onto the threads indicated by arrow X.
(23) FIGS. 7 to 9 show a thread-coating module 50 according to a third embodiment. In this third embodiment the elongate coating chamber 22 is generally rectangular in cross-section having a thread entrance 52 at one end, a thread exit 54 at an opposite end and a roof defining an elongate utility slot 55 enabling control of air pressure inside the coating chamber as well as maintenance/cleaning of the coating chamber when required. The thread entrance 52 is configured to receive six threads in a linear array for coating using first and second print modules 56A and 56B, although it will be appreciated that the number of threads and print modules may be varied. Each print module is of the type described in U.S. Pat. No. 10,144,232 and each comprises a respective replaceable pagewide printhead 1. The second print module 56B is positioned downstream of the first print module 56A relative to a thread feed direction. Further, the first print module 56A is mounted to a first sidewall 58A of the coating chamber 22 while the second print module 56B is mounted to an opposite second sidewall 58B thereof, such that respective printheads 1 overlap along a longitudinal axis of the coating chamber. Each sidewall defines a slot 59 enabling respective printheads 1 to eject ink droplets into the coating chamber 22 (see FIG. 9).
(24) The first and second print modules 56A and 56B are slidably received in respective sleeves 60 fastened to the first and second sidewalls 58A and 58B, respectively, and extending outwardly therefrom. Each sleeve 60 is supported by means of a respective brace 62 extending outwardly from a support chassis 64 fastened to a lower portion of the coating chamber 22. The support chassis 64 and braces 62 provide structural rigidity to the thread-coating module 50 as well as providing a convenient means for mounting the module in a thread-coating system.
(25) The printhead 1 of each print module 56 has an associated exhaust slot 68 defined in a respective opposite sidewall of the coating chamber 22 and aligned with a respective printhead. Each exhaust slot 68 is connected to an exhaust manifold 70, which receives ink droplets ejected into the coating chamber 22 via the exhaust slot. Suction may be applied to the exhaust manifold 70 to assist with ink extraction and recycling of ink.
(26) As best seen in FIG. 9, the longitudinal axis of each printhead 1 is angled relative to a longitudinal axis of the coating chamber 22. This ensures coverage of all six threads, which may be wider than the combined width of the nozzle rows. Likewise, the aligned exhaust slots 68 and exhaust manifolds 70 are correspondingly angled.
(27) FIG. 10 shows schematically an ink delivery system 80 suitable for use with the thread-coating module 50 according to the third embodiment. An ink reservoir 82 supplies ink to both the first print module 56A and the second print module 56B via a positively pressurized supply line 84 and a negatively pressurized return line 85. To this extent, the ink delivery system 80 may be as described in U.S. Pat. No. 10,252,540, the contents of which are incorporated herein by reference. However, each exhaust manifold 70 is connected to the return line 85 via a respective exhaust line 88 having an inline filter 90. In this way, ink captured by the exhaust manifolds 70 is filtered and recycled to the ink reservoir 82 for subsequent use.
(28) From the foregoing, it will be appreciated that pagewide inkjet coating technology is continuously expanding into new markets and can potentially revolutionize traditional thread coloring processes by improving speed, versatility and efficiency, as well as lowering costs and reducing ink and water wastage.
(29) It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.
