Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-11-21
2004-06-29
Meier, Stephen D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C345S101000
Reexamination Certificate
active
06755518
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to printing onto rigid substrates, and to the printing onto textured, contoured or other three-dimensional substrates. The invention is particularly related to the printing onto such substrates as those having textile fabric surfaces or molded objects, rigid panels such as office partitions, automobile interior panels and other contoured objects, and to such printing using ink jet printing techniques.
BACKGROUND OF THE INVENTION
Applying ink to a substrate by ink jet printing requires a proper spacing between the ink jet nozzles and the surface of the substrate to which the printing is applied. Normally, this spacing must be set to within one or two millimeters to maintain effective printing by an ink jet process. If the distance from the nozzles to the surface being printed is too great, deviations from ideal parallel paths of the drops from different nozzles become magnified. Further, the longer the flight path of the drops from the printhead to the substrate, the more dependent the accuracy of the printing becomes on the relative speed between the printhead and the substrate. This dependency limits the rate of change in printhead-to-substrate velocity, including changes in direction. Also, the velocity of the drops moving from the printhead nozzles to the substrate declines with the distance traveled from the nozzles, and the paths of such drops become more greatly affected by air currents and other factors with increased nozzle to substrate distance. Additionally, droplet shape changes the farther the drop moves from the nozzle, which changes the effects of the drop on the substrate. Accordingly, variations in the distance from the printhead to the substrate can cause irregular effects on the printed image.
In addition to problems in jetting ink onto contoured surfaces, the curing of UV inks requires delivery of sufficient curing energy to the ink, which is often difficult to achieve where the surface is contoured.
Further, some substrates deform, even temporarily, when heated. Deformation caused by heat may be such that, for example, the material returns to its undeformed state when it cools. Nonetheless, even temporary deformation can adversely affect the print quality if it exists when ink is being jetted onto the substrate. Where spot curing of UV inks is employed, which is performed by exposing ink to UV immediately upon its contacting the substrate, UV that is accompanied by heat producing radiation can deform substrates such as foamboard while the ink jets are making single or multiple passes over the deformed print area.
For these reasons, ink jet printing has not been successful on contoured materials and other three-dimensional substrates, particularly when printing with UV curable inks.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide for the ink jet printing onto substrates that tend to deform when heated. A particular objective of the present invention is to maintain desired printhead-to-substrate spacing when jetting ink onto rigid substrates, particularly with UV curable inks.
According to the principles of the present invention, printed images are applied to rigid substrates with printing elements that may be moveable relative to the plane of the substrate being printed. In certain embodiments, the invention provides a wide-substrate ink jet printing apparatus with printheads that move toward and away from the plane of a substrate to maintain a fixed distance between the nozzles of the printhead and the surface onto which the ink is being jetted. The variable distance over the plane of the substrate allows a controlled and uniform distance across which the ink is jetted.
According to the invention, the printing element may include an ink jet printhead set having a plurality of heads, typically four, each for dispensing one of a set of colors onto the substrate to form a multi-colored image. To maintain the constant distance or to otherwise control the distance, one or more sensors may be provided to measure the distance from the printhead or from the printhead carriage track to the point on the substrate on which ink is to be projected. Such sensors generate reference signals that are fed to a controller that controls a servo motor on the printhead carriage. The printhead may be moveably mounted to the carriage, for example, on a ball screw mechanism, and be moveable toward and away from the plane of the substrate by operation of the servo motor. Each printhead of the set may include four different color printheads that are separately moveable relative to a common printhead carriage, and are each connected to one of a set of four servo motors by which its position relative to the plane of the substrate is capable of control relative to the positions of the other printheads. The printheads of the set may be arranged side-by-side in the transverse direction on the carriage so that one head follows the other across the width of the substrate as the carriage scans transversely across the substrate.
Each printhead has, in the preferred embodiment, a plurality of ink jet nozzles thereon for dispensing a given color of ink in a corresponding plurality of dots, for example, 128 in number, that extend in a line transverse to the carriage, which is in a longitudinal direction perpendicular to the scan direction of the carriage. Two laser or optical sensors are provided on the carriage, one on each side of the heads, so that a distance measurement of the surface to the substrate can be taken ahead of the printheads when the heads are scanning in either direction. The controller records the contour of the substrate ahead of the printheads and varies the position of each printhead, toward and away from the substrate plane, as each printhead passes over the points at which the measurements were taken, so that each of the independently moveable heads follows the contour and maintains a fixed distance from the surface being printed. While it is preferred to adjust the position of the printhead or nozzle thereof relative to the substrate which is fixed on a printing machine frame, the substrate surface can alternatively be positioned relative to a printhead that is maintained at a fixed vertical position on the frame.
According to the preferred embodiment of the invention, UV ink is printed onto material and the cure of the ink is initiated by exposure to UV light radiated from UV curing lights mounted on the printhead carriage, one on each side of the printhead set. The lights are alternatively energized, depending on the direction of motion of the carriage across the substrate, so as to expose the printed surface immediately behind the heads. By so mounting the UV curing lights on the printhead carriage, the jetted ink can “spot cure” the ink, or to cure the ink immediately upon its contacting the substrate. Such spot curing “freezes the dots” in position and prevents their spreading on or wicking into or otherwise moving on the substrate. With certain substrates, conventional or broad spectrum UV curing lights include radiation that can heat the substrate. Such radiation includes infra-red radiation and radiation of such other wavelengths that tend to heat a particular substrate.
In the case of many rigid substrates, such as foamboard and several other of the more commonly used substrates, energy radiating from the UV light curing source onto the substrate heats the substrate enough to deform it. Such deformation can deform rapidly, with the surface of the substrate rising or rippling within seconds of exposure. Usually, this deposition is temporary in that the substrate blisters or swells when heated but returns to its original condition immediately upon cooling. Where the UV exposure is carried out downstream of the printhead carriage, usually no harm results.
In the case of spot curing, the UV exposure occurs close to the point of printing. Deformation of the substrate surface that occurs due to heat in spot curing can extend to the portion of the substrate that is still to be printed, t
L&P Property Management Company
Meier Stephen D.
Tran Ly T
Wood Herron & Evans L.L.P.
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