Abstract:
Individually controllable ultraviolet (UV) light-emitting diodes (LEDs) are used to cure ink and generate different effects. The UV LEDs only expose specified areas to generate the different effect and can create multiple effects on the same substrate by exposing different areas to varying amounts of time or by performing a curing stage and post-dosage curing stages. The different effects include generating a glossy surface, a matte surface, and sharper images.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates generally to the field of selective ink curing. More specifically, this invention relates to creating different curing effects on the same print through the use of ultraviolet light-emitting diodes. 
     2. Description of the Related Art 
     Digital inkjet printers are used to generate different effects on substrates, such as a glossy surface or highlighting. One way to generate these effects is by using different substrates, such as paper coated with a glossy substance. These substrates, however, cause the entire substrate to show the effect and are more expensive than traditional substrates.  FIG. 1A  (prior art) is an example of using a matte substrate  100  as a background for printing an object  105 . Because the matte substrate  100  applies to the entire background, it cannot be used to highlight specific areas of the substrate, such as text. 
     As a result of the problems associated with substrates, using a curable inkjet ink to produce the effect is more cost effective and preferable because the effect can be isolated to specific locations. These effects can be produced during ink curing or after the ink has hardened. The ink is typically cured by exposing ink that contains a photoinitiator to ultraviolet (UV) light. 
     Curable inkjet inks are particularly popular for grand or super-wide format printing systems, which are adapted for billboards, museum displays, billboards, sails, etc. because UV cured inks remain durable on a variety of substrate media. 
     Printers typically perform UV curing with various light sources, for example, mercury vapor lamps or metal halide bulbs. The problem with these types of various light sources, however, is that they require several minutes after activation to stabilize, they produce excessive heat during curing, ozone is a byproduct of their use, and the light sources have a limited shelf-life. 
     Another technique for UV curing involves the use of light emitting diodes (LED) that emit UV radiation. UV LEDs are ready to perform curing as soon as they are activated, they require less energy than UV bulbs, and they produce less heat because the LED can be designed to emit a narrow range of wavelengths. U.S. Pat. No. 6,786,589 discloses an ink jet printer in which multiple UV light sources use LEDs to harden the ink drops. U.S. Publication Number 2004/0166249 discloses the use of UV-LED chip arrays to cure inks, where each row in an array can emit a different wavelength of light, but each LED in a row is activated at the same time. In US2006/0119686, each printhead ejector corresponds to one UV-LED and each ink droplet is exposed to the UV-LED exactly once. 
       FIG. 1B  (prior art) illustrates the results of using the UV-LEDs, as taught in these references, to create a matte surface next to an object. Because the UV LEDs are always activated together, the matte is created in all places where a UV curing ink is deposited. Thus, in this example the matte  110  and the object  105  create a matte surface because both inks contain photoinitiators and the entire surface is exposed to the UV-LEDs. 
     Printers are configured to generate different curing effects using UV ink on a single print by adjusting the UV lamp output to vary the ink curing and surface characteristics. For example, reducing the initial dosage of UV output generates a glossy effect. Increasing the dosage creates a more matte surface. The area can be manipulated by curing once to set the ink and followed with post-dosages to generate different effects. 
     SUMMARY OF THE INVENTION 
     Individually controllable UV LEDs are used to cure inks on demand to generate different patterns. In one embodiment, the inks are cured once to set the ink. In another embodiment, post-dosage curing of the inks generates a different effect. 
     The array of print head nozzles lay down ink in a specified pattern. A lamp module contains UV LEDs that cure the ink. In one embodiment, the one printing assembly contains both the print head nozzles and LEDs. In another embodiment, one printing assembly dispenses the ink and another printing assembly cures the ink. 
     In one embodiment, the LEDs are configured in a binary mode, i.e. either on or off. In another embodiment, the LEDs are configured on a grayscale and, therefore, cure at different levels of intensity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a prior art example of a matte surface for printing an object; 
         FIG. 1B  is a prior art example of using UV LEDs to generate a matte effect; 
         FIG. 2  shows a diagram of the configuration of the printing system according to one embodiment of the invention; 
         FIG. 3  shows a diagram of the UV LEDs used within the printing system according to one embodiment of the invention; 
         FIG. 4  shows an example of different effects produced using the UV LEDs according to one embodiment of the invention; 
         FIG. 5  shows an example of a software application that includes a user interface for allowing a user to specify different effects according to one embodiment of the invention; and 
         FIG. 6  is a flow diagram showing the steps for generating different effects using UV LEDs according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention comprises a printing assembly and method for generating different printing effects by manipulating the UV curable ink with individually controllable UV LEDs. In one embodiment, the ink is exposed to the UV LEDs once to set the ink. In another embodiment, the ink is exposed to the UV LEDs after the ink has set to generate post-dosage effects. 
     In a typical printing assembly, an array of print head nozzles ejects UV curable ink onto a substrate. The print head nozzles are controlled by a data file containing instructions to lay the ink down in a specified pattern. In one embodiment, the print head nozzles dispense ink using thermal inkjet cartridges. In a thermal inkjet cartridge, a current runs through heating elements, which causes the ink to form a bubble until it bursts and is sprayed on a substrate. In another embodiment, the print heads include piezoelectric inkjets. Piezoelectric inkjets comprise crystals that vibrate in response to an electric charge. The crystals apply pressure to the ink reservoir within the print head and force ink through nozzles positioned on the underside of the print head. 
     At this stage the ink is wet and can move around on the substrate, especially if a low viscosity ink is used. Thus, the ink is exposed to UV light, which sets the ink. In one embodiment, a single printing assembly performs both the printing and the setting of the ink. In another embodiment, separate assemblies are used to perform each step. 
     Printing Assembly 
       FIG. 2  is an example of a printing assembly according to one embodiment of the invention. The substrate  200  is positioned below the print head carriage  205 . The print head carriage  205  includes any number of print heads  210  that are needed to deposit ink. The print heads  210  include inkjet nozzles (not shown), which are spaced apart along the y-axis of the print heads  210 . 
     The resolution of each print head  210  is typically specified in dots per unit length. In one embodiment, the print heads  210  are native 100 dots per inch (dpi) and the carriage total generates a resolution of 540×600 dpi. In one embodiment, the print heads  210  contain only black ink. In another embodiment, the print heads  210  contain colored ink as well. The print head carriage  205  scans across the width of a substrate  200  as the substrate  200  advances beneath the print heads  210 , which eject ink droplets until the ink is properly deposited. 
     The lamp  215   220  comprise UV LEDs. In one embodiment, the UV LEDs correspond to the number of print heads. In another embodiment, there are fewer UV LEDs than print heads. Once the ink heads  210  complete the step of ink deposition, the first lamp  215  cures the ink by moving over the substrate  200  until in position, and then exposing the ink to UV light. The first lamp  215  can either cure the ink completely or, if the user wants to generate a second effect, can partly cured, i.e. set the ink. The wavelength and time of exposure depend upon the ink properties, e.g. the mixing ratio of the pigment and the sensitivity of the ink and the effect desired by a user. In one embodiment, the intensity ranges from several hundred milliJoules (mJ) to several hundred thousand mJ. 
     If the first lamp  215  is smaller than the length and width of the substrate  200 , the first lamp  215  moves to a different position and cures a new section of the substrate  200 . The printer keeps track of the locations on the substrate that are exposed to UV curing to ensure that the exposure is uniform. Because the UV LEDs are individually controllable, there is no overlap of exposure. 
     If the user wants to generate effects after the ink has been set, the second lamp  220  is positioned over the substrate and exposes the ink to UV light complete the curing. In one embodiment, the first lamp  215  and the second lamp  220  emit UV light at different wavelengths. If the second lamp  220  is not long or wide enough to expose the entire substrate all at once, the second lamp  220  module is repositioned and exposes a different surface area. A person of ordinary skill in the art will recognize that the printing assembly can use the same lamp for both the initial curing and post dosage stages. 
       FIG. 3  shows an example of a UV LED array according to one embodiment of the invention. Although this UV LED array is illustrated as being a 25 dpi LED array, a person of ordinary skill in the art will recognize that a different sized array could easily be used. As smaller UV LEDs become available, the LEDs per inch will increase. 
     In addition to curing, the UV light is used to generate an ink effect. For example, a low dosage set cure produces a glossy surface. Increasing the dosage creates a more matte surface. Because the UV LEDs are individually controllable, different effects can be generated on the same substrate.  FIG. 4  shows an example of generating multiple effects on the same substrate. A low dosage, i.e. intensity set cure is applied to an area  400  next to the logo  405  to generate a glossy effect. A high dosage set cure is then applied to the logo  405  to generate a sharp text effect. In addition, a higher dosage is applied to the background to develop a matte background. 
     In another embodiment, the UV LEDs expose very small areas within a pattern or logo to create a glossy effect. For example, curing selected parts of a logo with a low dosage set cure creates bits of gloss within the logo for an overall sparkling appearance. 
     In one embodiment, the UV LEDs are set to a binary mode, i.e. they emit light at the same intensity and are either on or off. In another embodiment, the UV LEDs are configurable to a grayscale of intensities to create different effects. An example of a grayscale setting on UV LED is setting one UV LED to glossy and progressively increasing the intensity until the last UV LED is set to matte. As a result, a section of the substrate can be treated to display a progression from glossy to matte. 
     Ink 
     The ink contains a photoinitiator, which is activated upon exposure to UV light to set the ink. In one embodiment, the photoinitiator comprises 0-20% of the ink composition by weight depending upon the ink color. In another embodiment, the photoinitator comprises 5-15% of the ink composition by weight depending upon the color. 
     In one embodiment, the inkjet inks are colored in common shades such as cyan, magenta, yellow, or black (“CMYK”). The colored inks can also include light cyan, light magenta, light yellow, light black, red, blue, green, orange, white, gray, spot colors, etc. 
     User Interface 
       FIG. 5  shows an example of a software application that includes a user interface for allowing a user to specify different effects according to one embodiment of the invention. A person of ordinary skill in the art will recognize that this is one example of a software application for specifying different effects and that different mechanisms for specifying effects require minor modifications in the software application. 
     The user interface comprises several icons for specifying the different effects. For example, a user specifies a specific effect using the slider  500 , which progresses from glossy to matte. In one embodiment, the user can click on an object and then use the slider  500  to experiment with different gradients of glossy or matte. Alternatively, the user can click on the grayscale icon  505  to apply a grayscale to the selected object. 
     The user targets parts of the object using the arrow icon  510 , the pencil icon  515 , or the paintbrush icon  520 . The arrow icon  510  is used to select an isolated part of the object. In this example, the user used the arrow icon  510  to select the branch  525  and moved the slider  500  to apply a matte to the branch  525  as indicated by the circle  530 . 
     The pencil icon  515  allows a user to select very specific portions of the object for creating an effect. In this example, the user selects the pencil icon  515  to begin pencil mode, selects an effect from the slider  500 , and clicks on sections of the pigeon&#39;s eye  535  to apply the effect. The pencil feature can also be used to make tiny markings within, for example, a logo to create a sparkly effect if the slider  500  is set to glossy. The paintbrush icon  520  allows for broader swathes of the effect. In this example, the user could use the paintbrush icon  520  to color the entire background. 
     Once the user is satisfied with the image, the user can save the data file by selecting the save icon  540 . The software application generates instructions for correlating the sections of the image that are modified by the user with the individually controllable UV LEDs and for assigning an intensity and a time of exposure to each UV LEDs for any section of the substrate that is cured by the UV LEDs. Selecting the printer icon  545  transmits the request to print to the printer. 
     Steps for Using UV LEDs 
       FIG. 6  is a flow diagram that illustrates the steps for generating different effects using UV LEDs according to one embodiment of the invention. The printer receives  600  a data file that contains instructions from a software application to control the printer assembly to lay down ink in a specified pattern. The instructions are typically transmitted via a connection interface, e.g. parallel, universal serial bus (USB), etc. The printer stores  605  the instructions in a buffer. The buffer can be any form of computer-readable memory, e.g. random access memory (RAM). If the printer has been inactive for an extended period of time, the printer cleans  610  the print heads  210 . The printer activates  615  the paper feed stepper motor, which engages the rollers, thereby feeding the substrate  200  from the paper tray into the printer. In one embodiment, the printer is configured to use grand or super-wide substrates  200 . The substrate  200  is positioned on rollers or a conveyor assembly, e.g. a conveyor belt, which transports the substrate  200  inside the printer for printing. 
     The print head carriage  205  is positioned  620  over the substrate  200 . The print head carriage  205  scans across the width of a substrate  200  while the print heads  210  dispense  625  ink. In one embodiment, the print heads  210  are individually controllable. The print heads  210  are again positioned  520  and again dispense  625  ink until the substrate  200  is covered. In one embodiment, the print head carriage  205  passes over the same area of the substrate  200  multiple times to generate a higher resolution. 
     The first lamp  215  module is positioned  630  over the substrate  200 . The ink is cured  635  using a predefined intensity. Because the UV LEDs are individually controllable, different parts of the substrate  200  may be exposed to different intensities. The steps of positioning  630  and curing  635  are repeated until the ink is cured and the desired effects are generated. 
     The second lamp  220  is positioned  630  over the substrate  200 . The ink is subjected to a post-curing  635  dosage using a predefined intensity. These steps are repeated until the post-curing is complete. 
     As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Likewise, the particular naming and division of the members, features, attributes, and other aspects are not mandatory or significant, and the mechanisms that implement the invention or its features may have different names, divisions and/or formats. Accordingly, the disclosure of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following Claims.