Abstract:
Enhanced printing solutions are enabled by providing ultraviolet curing conditions without requiring complete evacuation of atmospheric oxygen. Increased ink coverage and adjusted surface appearance are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of the U.S. Utility patent application Ser. No. 12/423,700 filed on Apr. 14, 2009, which is incorporated herein by this reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
       [0002]    The invention relates to the field of inkjet printing. More specifically, the invention relates to techniques for more efficient curing of ultraviolet curable ink deposited in a printing environment. 
       Description of the Related Art 
       [0003]    Ultraviolet curing of liquid chemical formulations has been an established practice for many years. In ultraviolet curing, a liquid chemical formulation comprising photoinitiators, monomers and oligomers, and possibly pigments and other additives is exposed to ultraviolet light, thereby converting the liquid chemical formulation into a solid state. 
         [0004]    Ultraviolet-curable inks are oftentimes used advantageously in the field of ultraviolet inkjet printing. In these applications, ultraviolet-curable ink is jetted from a print head onto a substrate to form a portion of an image. Typically the print head scans back and forth across a width of the substrate, while the substrate steps forward for progressive scan passes. Thus a relatively small print head is used to build a very large image. 
         [0005]    In some cases of ultraviolet inkjet printing, an ultraviolet light source is mounted on either side of a print head to cure the ink. Using this configuration, ultraviolet-curable ink can be jetted and cured in the same print head pass. Other times, the ink is jetted in one pass and cured in a subsequent print head pass. 
         [0006]    In some cases of ultraviolet inkjet printing, the width of the print head is at least equal to that of the substrate and the entire image is formed with a single pass of the substrate underneath the print head. In these cases, the ultraviolet light source is typically in a fixed location, with the substrate moving under the print head first and subsequently under the ultraviolet light source. 
         [0007]    As explained above, curing ink involves directing photons, typically with wavelengths in the ultraviolet spectrum, onto an ink deposit. The photons interact with photoinitiators present within the ink, creating free radicals. The created free radicals initiate and propagate polymerization (cure) of the monomers and oligomers within the ink. This chain reaction results in the ink curing to a polymer solid. However, the presence of oxygen at the ink surface inhibits such a chain reaction from occurring within the ink. This is often referred to as oxygen inhibition. 
         [0008]    In normal ultraviolet curing in an air environment, a high amount of ultraviolet energy and/or a high concentration of photoinitiator are needed to achieve a full cure, compared to the ultraviolet power and photoinitiator concentration required in an oxygen free curing environment. Indeed, both higher ultraviolet energy and higher photoinitiator concentration deleteriously affect the final film properties, and increase ink and printer costs. 
         [0009]    Common solutions for providing less reactive curing include completely supplanting atmospheric oxygen with a less reactive gas such as nitrogen in the cure zone. For example, U.S. Pat. No. 6,126,095 to Matheson et al., entitled “Ultraviolet Curing Apparatus Using an Inert Atmosphere Chamber” teaches a curing apparatus comprising a curing chamber for accommodating a controlled atmosphere. The curing chamber includes inlets and nozzle assemblies for supplying less reactive gas into the chamber and maintaining a less reactive atmosphere therein. 
         [0010]    Likewise, U.S. Pat. No. 7,431,897 to Hahne et al., entitled “Apparatus Replacing Atmospheric Oxygen with an Inert Gas from a Laminar Air Boundary Layer and Application of Said Apparatus” (hereinafter referred to as “Hahne”) teaches completely replacing atmospheric oxygen with a less reactive gas. 
         [0011]    These prior art references disclose specialized and expensive approaches to providing reduced oxygen curing conditions, but fall short of achieving feasibility for common inkjet printing systems, because it remains difficult and expensive to supply the printing environments with enough inerting gas to effectively rid the curing region of oxygen. It would be desirable to address this shortcoming. 
         [0012]    Additionally, ultraviolet ink has a significant cost associated with it. Therefore, thicker films of ultraviolet-curable ink increase the cost of the finished image. It is oftentimes desirable to lay down as thin a film of ink as possible without compromising color strength. In typical ultraviolet inkjet printing applications, there is a small time delay before a jetted droplet of ink is exposed to the ultraviolet light source. In that time delay, sometimes known as “time to lamp,” the drop generally tends to spread out and wet the media. This phenomenon is known as “dot gain.” Longer time to lamp results in higher dot gain and thinner final ink layer thickness. However, longer times to lamp also tend to increase the size of the print head or printer, and decrease the overall print speed. It would be desirable to address this problem as well. 
         [0013]    In scanning printer applications, droplets of ink are laid down then cured. Then additional drops are jetted onto the cured drops. This method tends to create a coarse surface finish, i.e. a matte finish, which reduces the glossiness of the image. In many applications, a high gloss finish is desirable in the final appearance of the print job. However, in some applications, it may be desirable to vary the level of gloss/matte or surface appearance. Current inkjet printing does not allow for such variations in surface appearance. It would be desirable to address these issues as well. 
       SUMMARY OF THE INVENTION 
       [0014]    In view of the foregoing, the invention provides enhanced printing solutions by providing ultraviolet curing regions without requiring the introduction of less reactive gas while also increasing ink coverage and adjusting surface appearance. 
         [0015]    In some embodiments of the invention, one or more ultraviolet light source and a means for providing a reduced oxygen curing region are used to cure ink. In some embodiments of the invention, an apparatus with a reduced oxygen curing region is used in conjunction with common inkjet printing systems. 
         [0016]    In some embodiments of the invention, a reduced oxygen curing region is created by depositing ultraviolet curable ink on a substrate; depositing a barrier over the resulting ink droplets in the curing region; exposing the curing region to ultraviolet radiation; and removing the barrier from the cured ink. 
         [0017]    In some embodiments of the invention, a print carriage has one or more attached film canisters. The carriage contains print heads, which deposit ink droplets onto a substrate as they traverse the substrate. The film canisters lay down an atmospheric-barrier film onto the ink droplets as the carriage continues to traverse the substrate, thus creating a reduced oxygen curing region around the ink droplets. The carriage is also coupled to an ultraviolet light source that trails the motion of the carriage. As such, the covered ink is subsequently cured as the UV light source passes over the film-covered droplets. As the carriage continues its movement, the atmospheric-barrier film is removed; leaving only cured, and flattened ink on the substrate. 
         [0018]    In some embodiments of the invention, a barrier to atmospheric oxygen is applied to ink droplets with an associated force. According to these embodiments, this force spreads out the ink droplet, thus increasing ink coverage. In some embodiments, the force smoothes out peaks and valleys between neighboring ink droplets, thus altering the surface appearance of the printed substrate. In some embodiments wicking between the substrate and the barrier film also causes the ink drop to spread out. 
         [0019]    In some embodiments of the invention, a carriage containing print heads is coupled to one or more ultraviolet lights. The ultraviolet light is coupled to a roller that is substantially transparent to ultraviolet light. In some embodiments the roller is a substantially rigid rolling rod. The rolling rod is configured to make substantial contact with the substrate as the carriage traverses the substrate. According to these embodiments, the rolling rod trails the carriage and rolls over deposited ink laid down by the print heads, thus creating a momentarily oxygen free cure zone at the contact area beneath the roller. The ultraviolet light is directed on the ink beneath the rolling rod at this moment for curing the ink. 
         [0020]    In other embodiments, the roller is substantially flexible and spreads out over the ink as it makes contact with the substrate. According to these embodiments, the reduced oxygen curing region is larger and easier to expose to adequate ultraviolet light. In some embodiments, a film-barrier on a roller guide replaces the roller to provide an even larger contact surface area between the film and the substrate. 
         [0021]    Some embodiments of the invention involve other methods of providing a reduced oxygen curing region. According to these methods, the process begins with depositing ultraviolet curable ink on a moving ultraviolet-transparent film. The film is then rotated, causing contact to be made at a contact point between the deposited ink and a substrate. This contact point is exposed to ultraviolet radiation, thus transferring the ink to the substrate, and substantially simultaneously curing the ink. Finally, the ultraviolet-transparent film is rotated further, thus removing the film from the contact point and leaving a cured ink deposit on the substrate. 
         [0022]    In some other embodiments, a carriage assembly is disclosed that includes one or more inkjet print heads, and an atmospheric-barrier film system that surrounds an ultraviolet light source. The print heads deposit ink onto the film, which rotates around the light source as the carriage assembly traverses a substrate. When the deposited ink makes contact with the substrate the light source exposes the deposited ink with ultraviolet radiation, thus curing the ink and transferring it to the substrate. 
         [0023]    In some embodiments of the invention a printing system includes a reduced oxygen curing region using an atmospheric-barrier film, and incorporating less reactive gas introduction. In some embodiments, the curing region comprises a roller system for the application of an atmospheric-barrier film to a substrate, and also a less reactive gas introduction means. In some embodiments, the roller system is disposed at an angle to the surface of the curing region, thus forming a pocket. The less reactive gas introduction means is configured to deliver less reactive gas into the pocket. As explained above, a substrate is fed through the printing region, and ultraviolet-curable ink is deposited onto the substrate. The substrate is then fed into the curing region, thereby encountering the less reactive gas. Subsequently, the substrate makes contact with the atmospheric-barrier film. The less-reactive gas and the atmospheric-barrier film work synergistically to reduce the possibility of oxygen reacting with the ink during curing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  illustrates an isometric view of a common printing system adapted for printing images on a variety of substrates; 
           [0025]      FIG. 2  illustrates an exemplary process for ultraviolet curing of deposited ink according to some embodiments of the invention; 
           [0026]      FIG. 3  illustrates a schematic representation of a printer using film barriers for providing the reduced oxygen curing region for ultraviolet curable inkjet printing applications, according to some embodiments of the invention; 
           [0027]      FIG. 4A  illustrates a front view of a portion of substrate with ink droplets deposited thereon from an inkjet print head, according to some embodiments of the invention; 
           [0028]      FIG. 4B  illustrates a front view of the portion of substrate with ink droplets and a deposited film barrier layer, according to some embodiments of the invention; 
           [0029]      FIG. 4C  illustrates a front view of a portion of a substrate with flattened and cured ink droplets, after removal of a film barrier layer, according to some embodiments of the invention; 
           [0030]      FIG. 5  is a front view of an alternative printing system using one or more rotating rods to provide a reduced oxygen curing region for inkjet printers, according to some embodiments of the invention; 
           [0031]      FIG. 6A  is a front view of a printing system that includes a reduced oxygen curing region, according to some embodiments of the invention; 
           [0032]      FIG. 6B  is a front view of an alternative printing system that includes a reduced oxygen curing region, according to some embodiments of the invention; 
           [0033]      FIG. 7A  illustrates another process for ultraviolet curing of deposited ink in an inkjet printing system, according to some embodiments of the invention; 
           [0034]      FIG. 7B  is a front view of yet another embodiment of a printer system that includes a less reactive curing region, according to some embodiments of the invention; and 
           [0035]      FIG. 8  illustrates a side view of a printing system with a reduced oxygen curing region using an atmospheric-barrier film and incorporating less reactive gas introduction, according to some other embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    Systems and methods are provided for curing ink, using one or more ultraviolet light sources and a means for providing a reduced oxygen curing region. The means for providing a reduced oxygen curing region can be adapted for use with a common printing system.  FIG. 1  is an isometric view of a common printing system  10 , adapted for printing images on a variety of substrates. The printing system  10  includes a base  12 , a transport belt  14  which moves the substrate through the printing system, a rail system  16  attached to the base  12 , and a carriage  18  coupled to the rail system  16 . The carriage  18  holds a series of inkjet print heads (not shown) and is attached to a belt  20  which wraps around a pair of pulleys (not shown) positioned on either end of the rail system  16 . A carriage motor is coupled to one of the pulleys and rotates the pulley during the printing process. As such, when the carriage motor causes the pulley to rotate, the carriage moves linearly back and forth along the rail system  16 . 
         [0037]    As the substrate moves through the system  10 , the inkjet print heads deposit ink onto the substrate. The carriage  18  moves along the rail system  16 , depositing ink on the substrate as it traverses the rail system  16 . Upon the completion of a traversal, the substrate steps ahead by movement of the transport belt  14  to position the substrate for a return traversal and subsequent ink deposit. In some embodiments, the carriage passes over the same area multiple times, laying down swaths of image pixels each time, building an image consecutively. 
         [0038]    In some other embodiments of the invention, a fixed group of print heads spans the width of the substrate and remains fixed as the substrate transport system moves a substrate beneath the print heads. 
         [0039]    In either case, when ultraviolet curable ink is used, it is desirable to cure the ink shortly after being deposited. 
       Process for Ultraviolet Curing in a Less Reactive Environment 
       [0040]      FIG. 2  illustrates an exemplary process  200  for ultraviolet curing of deposited ink in an inkjet printing system, according to some embodiments of the invention. The process begins with depositing ultraviolet-curable ink on a substrate  201 . In some embodiments of the invention, the ultraviolet-curable ink is deposited using a scanning print head configuration as disclosed in  FIG. 1 . Next, a barrier film is physically placed on the ultraviolet-curable ink deposit  202  in a curing region. Various means for placing a barrier film on the ink deposit are disclosed below. In some embodiments of the invention, the atmospheric-barrier film is substantially transparent to at least a portion of the ultraviolet spectrum of light. 
         [0041]    In some embodiments of the invention, the barrier film accomplishes supplementary goals in addition to eliminating oxygen from the curing area of the ink. For example, in some embodiments, a barrier film is applied to the deposited ultraviolet ink with pressure to cause positive dot gain (as explained in more detail below). In some embodiments wicking between the substrate and the barrier film also causes positive dot gain. In some embodiments, the barrier film affects the surface appearance of cured ink (as explained also in more detail below). 
         [0042]    The process  200  continues as an ultraviolet light source is directed onto the ink deposit through the barrier film, exposing photoinitiators to ultraviolet radiation  203 , thus curing the ink. Finally, the process  200  terminates as the barrier is removed from the cured ink  204 . 
         [0043]    The process  200  disclosed above effectively removes oxygen from the curing region of a printing system as an ultraviolet-curable ink is deposited on to a substrate. Removing oxygen from the curing region allows a lower power ultraviolet light source to be used. Indeed, in some embodiments of the invention, the power of the ultraviolet light source may be reduced by approximately ninety percent using the methods disclosed herein. In some embodiments, removing atmospheric oxygen from the curing region allows less photoinitiator to be used in the ink. Ultraviolet power reduction and the reduction of the photoinitiator concentration increases efficiency and reduces cost. For example, in some embodiments of the invention, an ultraviolet light-emitting diode is used for a light source. Various means for providing an atmospheric-barrier to the curing region exist and are disclosed in more detail below. 
       Atmospheric-Barrier Film 
       [0044]      FIG. 3  illustrates a schematic representation of a printer  300  using atmospheric-barrier films for providing a reduced oxygen curing region in ultraviolet curable inkjet printing applications according to some embodiments of the invention. 
         [0045]    According to  FIG. 3 , a carriage  318  containing print heads  301 ,  302 ,  303 , and  304  is coupled to a printer  300 . The carriage  318  is coupled to the base  312  of the printer  300  via the rail system  316 . The rail system  316  includes a belt  340  for moving the carriage  318  back and forth across the base  312 . 
         [0046]    A transport belt  314  is disposed on a surface of the printer base  312  and a substrate  399  is arranged between the carriage  318  and the transport belt  314 . In operation, the transport belt  314  steps forward and/or backward, thus moving the substrate  399  in and/or out of the page. 
         [0047]    The carriage  318  is also coupled to the ultraviolet light sources  320  and  330  with arms  321 ,  322 ,  331 , and  332 . The ultraviolet light sources  320 ,  330  are enveloped by films  323  and  333 . The films  323 ,  333  are wound between film canisters  324 ,  325  and film canisters  334 ,  335 , respectively. Furthermore, a lower portion of the films  323 ,  333  are held substantially parallel with the substrate  399  by application roller guides  326 ,  327 ,  336 ,  337 . As such, the films  323 ,  333  are disposed in near or actual contact with, and substantially parallel to the plane of the substrate  399 . 
         [0048]    The films  323  and  333  are substantially transparent to at least a portion of the ultraviolet spectrum of light. In other embodiments of the invention, the films  323  and  333  are polyethylene. In some embodiments of the invention, the films  323  and  333  are polyester. It will be readily apparent to those with ordinary skill in the relevant art having the benefit of this disclosure that in other embodiments, any suitable film can be used that is substantially transparent to at least part of the ultraviolet spectrum. 
         [0049]    For the purpose of simple viewing, the film canisters  324 ,  325 ,  334 ,  335  and the application roller guides  326 ,  327 ,  336 ,  337  are shown without a means for coupling with the arms  321 ,  331  and/or the ultraviolet light sources  320 ,  330 . However, it will be clear to those with ordinary skill in the art having the benefit of this disclosure that a variety of coupling means can be used to accomplish this goal, such as arms coupling the axis of the canisters  324 ,  325 ,  334 , and  335  and guides  326 ,  327 ,  336 , and  337  to the arms  321  and  331 . 
         [0050]    In some embodiments of the invention, the carriage  318  moves back and forth across the base  312  to deposit ink onto the substrate  399 . According to these embodiments, the film canisters  324 ,  325 ,  334  and  335  contain an extra supply of film. As the carriage  318  traverses the base  312  the film canisters  324 ,  325 ,  334  and  335  either let out extra film or intake excess film such that the film shared by canisters  324  and  325  and canisters  334  and  335  is long enough to cover the entire width of the substrate  399 . The rate at which the canisters  324 ,  325 ,  334  and  335  let out and take in film is driven by the roller guides  326 ,  327 ,  336 , and  337 . This rate is synchronized with the speed of the carriage  318  traversing the substrate  399 . 
         [0051]    According to these embodiments, as the carriage  318  traverses from the left limit of the rail system  316  to the right limit of the rail system  316 , the film canisters  325  and  335  let out excess film, while the film canisters  324  and  334  intake excess film. As such, a new portion of film is continuously rolling under the trailing roller guide  327  and roller guide  337 . Likewise, as the carriage traverses from the right limit of the rail system  316  to the left limit of the rail system  316 , the film canisters  324  and  334  let out excess film, while the film canisters  325  and  335  intake excess film. As such, a new portion of film is continuously rolling under the trailing roller guide  336  and roller guide  326 . 
         [0052]    In some other embodiments of the invention, the arms  322  and  332  are configured to raise and lower. According to these embodiments, the unused film canisters and the roller guides (those not trailing the motion of the carriage) are lifted when preceding the motion of the carriage  318 , and thus do not contact the substrate  399 . 
         [0053]    As the carriage  318  traverses the substrate  399 , the print heads  301 ,  302 ,  303 ,  304  deposit ultraviolet-curable ink onto the substrate  399  as ink droplets (not shown). Shortly after the ink droplets are deposited, film  323 ,  333  is guided under the roller guide trailing the carriage (either  327  or  336 , depending on the direction of motion). The roller guide (either  327  or  336 , depending on the direction of motion) encounters and passes over an ink droplet. As the roller guide ( 327  or  336 ) passes over an ink droplet, it applies pressure to the film ( 323  or  333 ) and the ink droplet, effectively depositing the film ( 323  or  333 ) onto the droplet. Since the film ( 323  or  333 ) is continuously moving between the film canisters  324 ,  325  and  334 ,  335 , and its rate corresponds with that of the roller guide ( 327  or  336 ), it does not tend to drag or plow the ink droplet. As the films  323  and  333  are deposited on ink droplets, the droplets are isolated from atmospheric elements, such as oxygen. 
         [0054]    After the film is deposited onto the ink droplets, the carriage  318  continues in its motion. Soon after, the ultraviolet light source ( 320  or  330 ) moves over the film-covered ink droplets. The ultraviolet light source ( 320  or  330 ) shines ultraviolet radiation on the film-covered ink droplets, thus curing the ink. Due to the presence of the film, the ultraviolet light sources  320 ,  330  require less power and the ink requires less photoinitiator, as compared to techniques that do not use film in this manner. 
         [0055]    The carriage  318  continues its motion along the rail system  316  as the ink droplets are cured with the ultraviolet light source ( 320  or  330 ). The next roller guide ( 326  or  337 , depending on the direction of motion) then encounters the film-covered and cured ink droplets. As the roller guide  326 ,  337  passes over the cured droplets, the film  323  or  333  is directed up toward the film canister  324  or  335 , thus removing the film  323  or  333  from the cured ink droplet. The ink is cured to the extent that it does not stick to the film  323  or  333 . 
       Surface Feature Alteration 
       [0056]    The system disclosed by  FIG. 3  uses rollers to direct a film over ink droplets and apply pressure to the film. A direct effect of this manner of depositing film onto an ink droplet is to provide a reduced oxygen curing region. However, other advantages for the printing process are also achieved including altering the surface features of the ink. 
         [0057]    Finish on printed substrate can range from a matte finish to a high-gloss finish as desired. Matte finishes are a result of an uneven surface texture in which the ink has valleys and peaks, while high-gloss finishes have a smooth surface texture. Inkjet printing typically results in a printed substrate having a matte finish because it necessarily involves depositing a series of ink droplets, thus forming peaks and valleys. According to some embodiments of the invention, the deposition of a smooth film and pressure on ink droplets deposited by an inkjet print head flattens out the surface of the ink, thereby resulting in a more glossy finish. 
         [0058]      FIGS. 4A through 4C  illustrate how the process of applying a film to ink droplets can also provide a more high-gloss finish to the printed substrate, while also achieving the benefits of a reduced oxygen curing region.  FIG. 4A  illustrates a front view of a portion of substrate  499  with ink droplets  400  deposited thereon from an inkjet print head, according to some embodiments of the invention. The ink droplets  400  shown in  FIG. 4A  define discrete peaks  410  and valleys  411 , which would normally result in a substrate  499  having a matte finish if cured. 
         [0059]      FIG. 4B  illustrates a front view of the same portion of substrate  499  with ink droplets  400  and an applied film layer  430  according to some embodiments of the invention. The film layer  430  is applied in a fashion consistent with this disclosure, and is preferably applied with pressure to the ink droplets  400 . The application of pressure flattens and spreads the ink droplets  400 . The ink droplets  400  are subsequently cured using ultraviolet radiation. Accordingly, any peaks or valleys present in  FIG. 4B  are much less apparent. 
         [0060]      FIG. 4C  illustrates a front view of the same portion of substrate  499  with flattened and cured ink droplets  400 , after the film layer is removed. The ink droplets  400  are flattened and spread out, severely diminishing the distinctive peaks and valleys as shown in  FIG. 4A . Accordingly, the substrate  499  gains a high-gloss finish. 
         [0061]    Likewise, it will be readily apparent to those with ordinary skill in the relevant art, having the benefit of this disclosure, that a textured film can be used in place of the smooth film as disclosed above. Using a textured film will result in a matte finish by causing or increasing the size of the peaks and valleys between deposited ink droplets. 
       Dot Gain and Ink Coverage 
       [0062]    As explained above, common inkjet printing applications involve jetting ink onto a substrate. These methods typically include a small time delay before the ink is exposed to the ultraviolet light source. In that time delay, sometimes known as “time to lamp,” ink drops generally tend to spread out and wet the media. This phenomenon is known as “dot gain.” Longer time to lamp results in higher dot gain and thinner final ink layer thickness. However, longer times to lamp will also tend to increase the size of the print head or printer, and decrease the overall print speed of the printer. 
         [0063]    According to the present invention, the pressure applied to the ink droplets encourages ink to spread out, thereby increasing the coverage of deposited ink and reducing the amount of ink needed for the creation of an image. Increasing ink coverage in square meters per liter reduces the end cost of printing. 
       Other Configurations for Providing Less Reactive Curing 
       [0064]    As disclosed above, the deposition of an atmospheric-barrier film is effective for providing a reduced oxygen curing region to cure deposited ink. Various other configurations can also provide a less reactive curing region for inkjet printing applications.  FIG. 5  is a front view of a printing system  500  using rotating rods  528 ,  529  to provide a reduced oxygen curing region for inkjet printers according to some embodiments of the invention. As illustrated in  FIG. 5 , a carriage  518  containing print heads  501 ,  502 ,  503 , and  504  is coupled to a printer  500 . The carriage  518  is coupled to the base  512  of the printer  500  via the rail system  516 . The rail system  516  includes a belt  540  for moving the carriage  518  back and forth across the base  512 . 
         [0065]    A transport belt  514  is disposed on the surface of the base  512 , and a substrate  599  is arranged between the carriage  518  and the transport belt  514 . In operation, the transport belt  514  steps forward and/or backward, as explained above, thus moving the substrate  599  in and/or out of the page. 
         [0066]    The carriage  518  is also coupled to ultraviolet light sources  520  and  530 . The ultraviolet light sources  520  and  530  are coupled to arms  531  and  532 , respectively. The arms  531  and  532  are coupled to the rotating rods  528  and  529  by a substantially axial member. 
         [0067]    In some embodiments of the invention, the carriage  518  moves back and forth across the base  512  to deposit ink onto the substrate  599 . According to these embodiments, the print heads  501 ,  502 ,  503 , and  504  deposit ink on the substrate  599  as it moves across the rail system  516 . Shortly after depositing ink, a rotating rod ( 528  or  529 , depending on the direction of the carriage) encounters the ink droplet. The rotating rod  528  or  529  passes over the ink droplet, thus applying pressure to the droplet and isolating a portion of the droplet from atmosphere. The isolation of the droplet from atmosphere creates a momentarily oxygen-free curing environment. At that time ultraviolet light is directed to the isolated droplet, thus curing the ink. 
         [0068]    In some embodiments, the vertical position of the substrate  599  is adjustable such that the amount of pressure applied to ink droplets by the rotating rods  528  and  529  can vary. According to these embodiments, the rotating rods  528  and  529  apply pressure to the ink droplet, thus affecting surface appearance and dot gain as explained above. Also, since the rotating rods  528  and  529  rotate at a rate that corresponds with that of the carriage  518 , they tend not to drag or plow the ink droplet. 
         [0069]    The rotating rods  528  and  529  are substantially transparent to at least a portion of the ultraviolet spectrum of light. In one embodiment of the invention, the rotating rods  528  and  529  are quartz, however it will be readily apparent to those with ordinary skill in the relevant art having the benefit of this disclosure that any suitable material can be used that is substantially transparent to at least part of the ultraviolet spectrum. 
         [0070]      FIG. 6A  is a front view of another printing system  600  that provides a less reactive curing area for inkjet printers according to some embodiments of the invention.  FIG. 6A  represents a modified version of the printing system  500  disclosed above. Specifically, flexible rotating cylinders  628  and  629  are used, as opposed to rotating rods. 
         [0071]    Similar to the printer system  500  of  FIG. 5 , the printer  600  includes a carriage  618  containing print heads  601 ,  602 ,  603 , and  604 . The carriage  618  is coupled to the base  612  of the printer  600  via the rail system  616 . The rail system  616  includes a belt  640  for moving the carriage  618  back and forth across the base  612 . Also, a transport belt  614  is disposed on the surface of the base  612 , and a substrate  699  is arranged between the carriage  618  and the transport belt  614 . In operation, the transport belt  614  steps forward and/or backwards, as explained above, thus moving the substrate  699  in and/or out of the page. 
         [0072]    The carriage  618  is also coupled to the ultraviolet light sources  620  and  630 . The ultraviolet light sources  620  and  630  are coupled to arms  631  and  632 , respectively. The arms  631  and  632  are coupled to flexible rotating cylinders  628  and  629  by a substantially axial member. 
         [0073]    The carriage  618  moves back and forth across the base  612  to deposit ink onto the substrate  699 . According to these embodiments, the print heads  601 ,  602 ,  603 , and  604  deposit ink on the substrate  699  as it moves across the rail system  616 . Shortly after depositing ink, a flexible rotating cylinder ( 628  or  629 , depending on the direction of the carriage) encounters the ink droplet. The flexible rotating cylinder  628  or  629  passes over the ink droplet, thus applying pressure to the droplet and isolating a portion of the droplets from atmosphere. 
         [0074]    According to these embodiments, the surface area under the flexible rotating cylinders  628  and  629  is greater because the cylinders  628  and  629  are flattened due to their flexibility. The increased surface area increases the size of the portion of the droplets isolated from atmosphere. Therefore the reduced oxygen curing region is larger than would be available by using rigid cylinders. The isolation of the droplets from atmosphere creates a momentarily oxygen-reduced curing environment. At that time ultraviolet light is directed to the isolated droplets, thus curing the ink. 
         [0075]      FIG. 6B  is a front view of a printing system for providing a reduced oxygen curing region in inkjet applications according to some embodiments of the invention.  FIG. 6B  represents the printing system  600  from  FIG. 6A , with the addition of film-barrier rollers  650  and  651  replacing the flexible rotating cylinders. 
         [0076]    The printing system  600  also includes a carriage  618  containing print heads  601 ,  602 ,  603 , and  604 . The carriage  618  is coupled to the base  612  of the printer  600  via the rail system  616 . The rail system  616  includes a belt  640  for moving the carriage  618  back and forth across the base  612 . Also, a transport belt  614  is disposed on the surface of the base  612 , and a substrate  699  is arranged between the carriage  618  and the transport belt  614 . In operation, the transport belt  614  steps forward and/or backward, as explained above, thus moving the substrate  699  in and/or out of the page. 
         [0077]    The carriage  618  is also coupled to the ultraviolet light sources  620  and  630 . The ultraviolet light sources  620  and  630  are coupled to film-barrier rollers  650  and  651 , respectively. The film-barrier rollers  650  and  651  comprise two rotating guides having an ultraviolet transparent film strung around them. The film-barrier rollers  650  and  651  lay down a film upon ink droplets as the carriage  618  traverses the substrate  699 . The film-barrier rollers  650  and  651  provide an increased area of contact between the film and the substrate  699 . 
       Other Methods and Apparatus 
       [0078]      FIG. 7A  illustrates another process  700  for ultraviolet curing of deposited ink in an inkjet printing system, according to some embodiments of the invention. The process begins with depositing ultraviolet curable ink on a rotating UV-transparent film  798 . The film is then rotated, causing contact to be made over a contact area between the deposited ink and a substrate  797 . This contact area is exposed to ultraviolet radiation, thus transferring the ink to the substrate and substantially simultaneously curing the ink  796 . Finally, the ultraviolet-transparent film is rotated further, thus removing the film from the contact point and leaving a cured ink deposit on the substrate  795 . 
         [0079]    In some embodiments of the invention, the method described in  FIG. 7A  is carried out using the system disclosed in  FIG. 7B .  FIG. 7B  is a front view of yet another example of a printer system  700  that provides a less reactive curing region according to some embodiments of the invention. According to  FIG. 7B , the printer system  700  includes a carriage  718  coupled to the printer  700 . The carriage  718  is coupled to the base  712  of the printer  700  via the rail system  716 . The rail system  716  includes a belt  740  for moving the carriage  718  back and forth across the base  712 . Also, a transport belt  714  is disposed on the surface of the base  712 , and a substrate  799  is arranged between the carriage  718  and the transport belt  714 . In operation, the transport belt  714  steps forward and/or backwards, as explained above, thus moving the substrate  799  in and/or out of the page. 
         [0080]    The carriage  718  contains two inkjet cartridges  725  and  735 , one on either side of a barrier film assembly  730 . The barrier film assembly  730  contains an ultraviolet light source  720 . The inkjet cartridges  725  and  735  contain print heads  701 ,  702 ,  703 ,  704 ,  705 ,  706 ,  707 , and  708 . The barrier film assembly comprises the UV light source  720  surrounded by a film  750  supported by guides  751 ,  752 ,  753 , and  754 . 
         [0081]    The carriage  718  moves back and forth across the base  712 . As the carriage  718  traverses the substrate  799 , the film  750  rotates around the guides  751 ,  752 ,  753 , and  754 . The print heads  701 ,  702 ,  703 ,  704 ,  705 ,  706 ,  707 , and  708  deposit droplets of ink on the film  750 . Accordingly, the droplets make contact with the substrate  799  when it rotates under the guides  753  or  754  (depending on the direction of motion). When the ink contacts the substrate  799  it is transferred to the substrate  799  and cured simultaneously or nearly simultaneously by the UV light source  720  passing nearby or directly over the transferred ink. 
         [0082]      FIG. 8  illustrates a side view of a printing system  800  with a reduced oxygen curing region accomplished by using atmospheric-barrier films, and incorporating less reactive gas introduction according to some embodiments of the invention. The printing system  800  includes a printer base  801  with a printing region  802  and a curing region  803 . A carriage  804  containing print heads is disposed above the printing region  802 . The carriage  804  traverses the printing region  802 , in and out of the page, as a substrate (not shown) is introduced to the printing system  800  as indicated by the arrow. In some embodiments, the substrate is moved through the printing system  800  with a transport belt (not shown). The carriage  804  deposits UV curable ink onto the substrate as it passes underneath the carriage  804 . In some embodiments, the carriage  804  can extend the full width of the printing system  800 . In other embodiments, the carriage  804  is configured to traverse the width of the printing area  802 . 
         [0083]    After the substrate receives ink droplets from the carriage  804 , it continues into the curing region  803 , which includes a roller system  805 ; a less-reactive gas introduction means  806 ; a less reactive gas pocket  807 ; and a UV light source  809 . 
         [0084]    The curing region  803  comprises a roller system  805  for the application of an atmospheric-barrier film  808  to a substrate, as well as less reactive gas introduction means  806 . In some embodiments, the roller system is disposed at an angle to the surface of the curing region  803 , thus forming a pocket  807 . The less reactive gas introduction means  806  is configured to deliver less reactive gas into the pocket  807 . 
         [0085]    In some embodiments of the invention, the roller system  805  extends the full width of the printing system  800 . Likewise, in some embodiments, the UV light source  809  can extend the full width of the printing system  800 . In some other embodiments, the UV light source  809  is coupled to the printing system  800 , and configured to traverse the curing area  803  in concert with the carriage  804 . 
         [0086]    In some embodiments of the invention, the printing system  800  with a reduced oxygen curing region accomplished by using atmospheric-barrier films, and incorporating less reactive gas introduction is used by choosing either the barrier film application or less reactive gas introduction in a given application. For instance, in applications demanding a matte finish, the application of barrier film will smooth out the peaks and valleys, as explained above. Therefore, according to these embodiments, a gas introduction method is desired over the barrier film application. Likewise, the barrier film application can be chosen over the gas introduction methods. 
         [0087]    In other embodiments, both the barrier film application and the gas introduction methods are used together. According to these embodiments, a substrate is fed through the printing region  802 , and UV-curable ink is deposited onto the substrate. It is then fed into the curing region  803 , thus encountering the less reactive gas. Subsequently, the substrate makes contact with the atmospheric-barrier film  808 . The less reactive gas and the atmospheric-barrier film  808  work synergistically to reduce the possibility of oxygen reacting with the ink during curing. Furthermore, the film barrier  808  applies pressure to the ink droplets, thus increasing coverage and altering surface appearance, as explained above. 
         [0088]    In some embodiments, the roller system  805  begins at an angle to the curing region  803 , thus forming the less reactive gas pocket  807 , and rotates down to contact the substrate for curing. In any event, the “downstream” roller in the roller system  805  consistently makes contact with substrate that is passing through. 
         [0089]    In some cases of UV inkjet printing, the UV light source is a low power UV source, sufficient to only partially cure the ink. This practice is known as pinning because it prevents movement of the ink droplets, but does not fully cure them. In these cases, a full cure is oftentimes performed after the image is completely printed. In some embodiments, a low power UV lamp (not shown) is additionally included upstream from the curing region  803  to “pin” the ink droplets before a full cure. 
         [0090]    The covered and less reactive gas exposed substrate is then exposed to UV radiation from the light source  809 , thus curing the ink. The substrate continues past the roller system  805  and the film barrier  808  is removed, leaving cured ink on the substrate. 
         [0091]    It will be readily apparent to those with ordinary skill in the relevant art will having the benefit of this disclosure that in other embodiments, electromagnetic radiation at other ranges of wavelengths can be used to cure ink. According to these embodiments, the barrier used is substantially transparent to those ranges of wavelengths. 
         [0092]    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.