Abstract:
A method for printing an image on a substrate, the method including the steps of providing a plurality of rollers for moving a substrate on which the image is printed; depositing a plurality of different colored inks on a print side of the substrate which form the image; depositing clear liquid on the non-print side of the substrate in a predetermined pattern for permitting the substrate to have uniform substrate growth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned, co-pending U.S. patent application Ser. No. ______ (Kodak Docket K001708US01) filed concurrently herewith, entitled “METHOD FOR PREVENTING FLUTES ON A PRINT SIDE” by David J. Cornell, et al., the disclosure of which is incorporated herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to preventing flutes in digital printing and, more particularly, to depositing a plurality of clear liquid patterns on the substrate for preventing flutes. 
       BACKGROUND OF THE INVENTION 
       [0003]    In a digitally controlled inkjet printing system, a receiver media (also referred to as a print medium) is conveyed past a series of components. The receiver media can be a cut sheet of receiver media or a continuous web of receiver media. A web or cut sheet transport system physically moves the receiver media through the printing system. As the receiver media moves through the printing system, liquid (e.g., ink) is applied to the receiver media by one or more printheads through a process commonly referred to as jetting of the liquid. The jetting of liquid onto the receiver media introduces significant moisture content to the receiver media, particularly when the system is used to print multiple colors on a receiver media. Due to the added moisture content, an absorbent receiver media expands and contracts in a non-isotropic manner, often with significant hysteresis. The continual change of dimensional characteristics of the receiver media can adversely affect image quality. Although drying is used to remove moisture from the receiver media, drying can also cause changes in the dimensional characteristics of the receiver media that can also adversely affect image quality. 
         [0004]      FIG. 1  illustrates a type of distortion of a receiver media  3  that can occur during an inkjet printing process. As the receiver media  3  absorbs the water-based   inks applied to it, the receiver media  3  tends to expand. The receiver media  3  is advanced through the system in an in-track direction  4 . The perpendicular direction, within the plane of the un-deformed receiver media  3 , is commonly referred to as the cross-track direction  7 . Typically, as the receiver media  3  expands in the cross-track direction  7 , contact between the receiver media  3  and the contact surface  8  of the rollers  2  (or other web guiding components) in the inkjet printing system can produce sufficient friction such that the receiver media  3  is not free to slide in the cross-track direction  7 . This can result in localized buckling of the receiver media  3  away from the rollers  2  to create lengthwise flutes  5 , also called ripples or wrinkles, in the receiver media  3 . Wrinkling of the receiver media  3  during the printing process can lead to permanent creases in the receiver media  3  which adversely affects image quality. 
         [0005]    U.S. Pat. No. 8,079,694 to Daly et al., entitled “Clear Fluid Patterning on Paper Media,” discloses depositing clear toner surrounding the entirety of the image or images, and the clear toner covers all or, in one case, most of the page on which the image is printed. “The pattern of clear fluid is defined by a maximum width that is generally equal to the maximum width of the image to be formed,” (Abstract) and the clear fluid must “contact” the image it surrounds. 
         [0006]    While U.S. Pat. No. 8,079,694 is satisfactory, it includes drawbacks. 
         [0007]    First, the present invention overcomes the limited teachings of U.S. Pat. No. 8,079,694, in which the maximum width of a pattern must be equal to the image to be formed. Second, this method is costly since clear fluid is deposited in large quantities on the page of interest. Costly is obviously a driver in deciding whether a method is suitable for commercial use. Therefore, a need exists for a means to prevent the formation of receiver media wrinkles as a receiver media contacts web-guiding structures in a digital printing system which is cost effective in the use of clear fluid and overcomes technical limitations of the prior art. 
         [0008]    As will be described below, the present invention solves the shortcomings of U.S. Pat. No. 8,079,694. 
       SUMMARY OF THE INVENTION 
       [0009]    A method for printing an image on a substrate, the method comprising the steps of providing a plurality of rollers for moving a substrate on which the image is printed; depositing a plurality of different colored inks on a print side of the substrate which form the image; depositing clear liquid on the non-print side of the substrate in a predetermined pattern for permitting the substrate to have uniform substrate growth. 
         [0010]    These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
           [0012]    While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, it is believed that the invention will be better understood from the following description when taken in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a perspective view of a prior art substrate in a digital printing system; 
           [0014]      FIG. 2A  is a simplified side view of a digital printing system of the present invention; 
           [0015]      FIG. 2B  is a simplified side view of a digital printing system of the present invention using gravure rollers in lieu of printhead for the water or clear ink; 
           [0016]      FIG. 3A  is a simplified side view of a digital printing system inclusive of a turnover mechanism; 
           [0017]      FIG. 3B  is a simplified side view of a digital printing system inclusive of a turnover mechanism using gravure rollers in lieu of printheads; 
           [0018]      FIG. 4  is a top view of a substrate having images and clear ribs of the present invention; 
           [0019]      FIG. 5  is a top view of the substrate having images and the clear ribs in another configuration; 
           [0020]      FIG. 6  is a top view of the substrate having images and the clear ribs in yet another configuration; 
           [0021]      FIG. 7  is a view of the non-print side of the substrate having images on the print side and the clear ribs on the non-print side; 
           [0022]      FIG. 8  is a view of the non-print side of the substrate having images on the print side and the clear ribs on the non-print side in yet another configuration; 
           [0023]      FIG. 9A  is a view of the non-print side of the substrate having clear fluid hexagons; and 
           [0024]      FIG. 9B  is a view of the print side having clear fluid hexagons. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    As described herein, the exemplary embodiments of the present invention provide receiver media guiding components useful for guiding the receiver media in inkjet printing systems. However, many other applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. Such liquids include inks, both water based and solvent based, that include one or more dyes or pigments. These liquids also include various substrate coatings and treatments, various medicinal materials, and functional materials useful for forming, for example, various circuitry components or structural components. As such, as described herein, the terms “liquid” and “ink” refer to any material that is ejected by the printhead or printhead components described below. Inkjet printing is commonly used for printing on paper, however, there are numerous other substrates in which inkjet is appropriate. For example, vinyl sheets, plastic sheets, textiles, paperboard and corrugated cardboard in addition to paper can comprise the substrate. Additionally, although the term inkjet is often used to describe the printing process, the term jetting is also appropriate wherever ink or other liquids is applied in a consistent, metered fashion, particularly if the desired result is a thin layer or coating. 
         [0026]    Referring to  FIG. 2A , there is shown a simplified side view of a portion of a digital printing system  100  for printing on a first side  15  of a continuous web of substrate  10  with a printing module  50  having printheads  75   a ,  20   a,    20   b,    20   c,    20   d,  dryers  40 , and a quality control sensor  45 . In this exemplary system, the first printhead  75   a  jets water or clear ink, the second printhead  20   a  jets cyan ink, the third printhead  20   b  jets magenta ink, the fourth printhead  20   c  jets yellow ink, and the fifth printhead  20   d  jets black ink. The printing module also includes a printhead  75   b  for printing on a second side  18  (non-print side), if desired, with water or clear ink. As will be described in detail herein below, the printheads  75   a  and  75   b  deposits the water or clear ink in a pattern for permitting cross-track stretching to occur in a more uniform manner. The printheads  75   a  and  75   b  may be used in combination or either may print singularly without printing by the other. 
         [0027]    Below each printhead  20   a,    20   b,    20   c,    20   d  is a media guide assembly including print line rollers  31  and  32  that guide the continuous web of substrate  10  past a first print line  21  and a second print line  22  as the substrate  10  is advanced along a media path in the in-track direction  4 . Below each dryer  40  is at least one dryer roller  41  for controlling the position of the web of substrate  10  near the dryers  40 . 
         [0028]    Substrate  10  originates from a source roll  11  of unprinted substrate  10 , and printed substrate  10  is wound onto a take-up roll  12 . Other details of the printing module  50  and the digital printing system  100  are not shown in  FIG. 2  for simplicity. For example, to the left of printing module  50 , a first zone  51  (illustrated as a dashed line region in substrate  10 ) can include a slack loop, a web tensioning system, an edge guide and other elements that are not shown. To the right of printing module  50 , a second print zone  52  (illustrated as a dashed line region in substrate  10 ) can include a turnover mechanism and a second printing module similar to printing module  50  for printing on a second side of the substrate  10 . 
         [0029]    Referring to  FIG. 2B , in another embodiment, gravure rollers  80   a  and  80   b  may be used in lieu of the printheads  75   a  and  75   b  if desired. All the other components are the same as in  FIG. 2A . 
         [0030]    Referring to  FIG. 3A , there is shown a simplified side view of a portion of a printing system  110  for printing on both a first side  15  and a second side  16  of a continuous web of substrate  10 . Printing system  110  includes a first printing module  55 , for printing on a first side  15  of the continuous web, having four printheads  75   a,    75   b,    20   a,    20   b  and a dryer  40 ; a turnover mechanism  60 ; and a second printing module  65 , for printing colored inks on the second side of the continuous web, having four printheads  75   c,    75   d,    25   a  and  25   b  and a dryer  40 . It is instructive to note that the printheads  75   a,    75   b,    75   c  and  75   d  also deposit water or clear ink for permitting cross-track stretching to occur in a more uniform manner. The printheads  75   a  and  75   d  print on the first side  15  and the printheads  75   b  and  75   c  print on the second side  16 . In the case of printhead  75   d,  the clear ribs  130  (see  FIGS. 4-8 ) will be printed over the printed image  120  (see  FIGS. 4-8 ). 
         [0031]    A web-guiding system  30  guides the web of substrate  10  from upstream to downstream along a transport path in an in-track direction  4  past through the first printing module  55  and the second printing module  65 . The web-guiding system  30  includes rollers aligned with the print lines of the printheads  20   a,    20   b,    25   a,  and  25   b.  These rollers  2  maintain the substrate  10  at a fixed spacing from the printing modules to ensure a consistent time of flight for the print drops emitted by the printheads  20   a,    20   b,    25 ,  25   b.  The web-guiding system  30  also includes a web-guiding structure  70 , which can be a roller for example, positioned near the exit of first printing module  55  for redirecting a direction of travel of the web of substrate  10  along exit direction  9  in order to guide the web of substrate  10  toward the turnover mechanism  60 . The movement of the receiver media  3  of the guiding rollers  2  of the web guiding system  30  also maintains the cross-track position of the continuous web provided there is sufficient traction between the continuous web and the guiding rollers  2 . 
         [0032]    It is not uncommon for a web-guiding system  30  to include a web-guiding structure  70  that provides a large angular change in the direction of travel of the web of the substrate  10 . Such large angular changes may be required by geometric constraints on the overall dimensions of the web-guiding system  30  or the need to align the web of substrate  10  with a downstream portion of the web-guiding system  30 . For example, web-guiding structure  70 , which is positioned near the exit of first printing module  55 , redirects the direction of travel of the web of substrate  10  by about 90° into exit direction  9  in order to guide web of substrate  10  toward the turnover mechanism  60 . 
         [0033]    When the substrate  10  is a hygroexpansive material such as cellulose based paper, and at least portions of the substrate  10  are moistened such as by inkjet printing, the receiver media  3  can be prone to wrinkling when wrapped at high wrap angles around a roller  2 . A similar tendency to wrinkle exists at high wrap angle rollers when a very thin receiver media  3 , such as plastic films of polyethylene and poly (ethylene terephthalate), is being transported along the transport path by the web-guiding system  30 , as such substrate  10  lacks the compressive strength to flatten the ripples produced in the substrate  10  by the variations in the in-track and cross-track tension. 
         [0034]    Referring to  FIG. 3B , in another embodiment, gravure rollers  80   a ,  80   b,    80   c  and  80   d  may be used in lieu of the printheads  75   a,    75   b,    75   c  and  75   d  if desired. All the other components are the same as in  FIG. 3A . 
         [0035]    Referring to  FIG. 4 , there is shown a top view of the substrate  10  having a plurality of image  120  printed thereon. The present invention deposits a plurality of spaced apart, linear clear ribs  130  formed of the clear liquid, such as water or clear ink, and arranged in parallel, equally spaced, continuous straight lines in the in-track direction adjacent the images  120 . The maximum width of each clear rib  130  is smaller than the image to which it is adjacent. The clear ribs  130  are adjacent the image  120  which means that the clear ribs  130  may abut a plurality of portions of the image or be in close proximity, but not touching, leaving a small space  131  between the image  120  and clear rib  130 . It is understood that the clear liquid is devoid at a plurality of portions between the clear liquid ribs. The option to have spacing  131  or not is a user preference and preferably all the clear ribs  130  are either abutting the image  120  or includes the spacing  131 , although a combination of the two may be used. The clear ribs  130  permit cross-track stretching to occur in a more uniform manner regardless on the image size or location. The plurality of clear ribs  130  also breaks up the stiffness of non-printed areas to permit cross-track stretching and softens in-track transitions from the non-printed areas to heavy ink areas (images). As will be apparent, the present invention permits stretching but overcomes the cost inefficiencies of the prior art. The clear ribs  130  do not cover all or substantially all of the substrate  10  and is deposited more sparingly than the prior art so that the cost incurred as a result of depositing the clear ink is lowered. This has distinct advantages in commercialization especially considering the mass production of substrate  10  produced by digital printing systems  100 . The embodiment of  FIG. 4  is preferably done by printhead  75   a.    
         [0036]    Referring to  FIG. 5 , there is shown another embodiment of the present invention. In this embodiment, the clear ribs  130  are the same as in  FIG. 4  except that the plurality of clear ribs  130  are under the images  120  and also extend away from each image  120  in a continuous manner. It is instructive to note that the clear ribs  130  are deposited before the colored inks, which means the clear ribs  130  are extended under the images  120 . The embodiment of  FIG. 5  is preferable done by the printhead  75   a  if there is spacing  131  and either printhead  75   a  or gravure roller  80   a  if there is no spacing. 
         [0037]    Referring to  FIG. 6 , the clear ribs  130  include all of the features of  FIG. 5  except that the clear ribs  130  are formed in either a dashed  130   a  or dotted pattern  130   b.  The embodiment of  FIG. 6  is preferable done by either the printhead  75   a  or the gravure roller  80   a.  The embodiment of  FIG. 6  is preferable done by the printhead  75   a  if there is spacing  131  and either printhead  75   a  or gravure roller  80   a  if there is no spacing. 
         [0038]    Referring to  FIG. 7 , the clear ribs  130  are deposited on the non-print side of the substrate  10  in a linear, equally spaced apart pattern in the in-track direction. The clear ribs  130  are a continuous line disposed both extending under the image on the non-print side and away from the images on the non-print side. This permits the substrate to have uniform substrate growth needed as a result of the properties if the deposited ink interacting with the substrate  10 . The embodiment of  FIG. 7  is preferably done by either the printhead  75   b  or the gravure roller  80   b.    
         [0039]    Referring to  FIG. 8 , there is shown the clear ribs  130  as in  FIG. 7  except that the lines are made of dashed  130   a  or dotted lines  130   b.  The embodiment of  FIG. 8  is preferable done by either the printhead  75   b  or the gravure roller  80   b.    
         [0040]    Referring to  FIG. 9A , there is shown yet another embodiment having a plurality of one or more shapes, each shape formed from clear liquid deposited on the non-print side  18  of the substrate  10  (deposited clear liquid) which deposited clear liquid has a width smaller than a width of an image to which it is adjacent. In this embodiment, the shape is a plurality of connected line segments formed in a hexagonal shape  135 . As used herein, the shape of the present invention is not limited to the hexagonal shape  135  but may be any shape including, but not limited to, polygons, circles, scattered dots, polygons or polygons and circles formed of dots. These shapes are preferably symmetrical so that uniform growth occurs in both the in-track and cross-track directions. The embodiment of  FIG. 9A  is preferable done by either the printhead  75   b  or the gravure roller  80   b.    
         [0041]    Referring to  FIG. 9B , the clear fluid hexagonal shapes  135  are deposited on the first side  15  of the substrate  10 . The embodiment of  FIG. 9B  is preferable done by either the printhead  75   a  or the gravure roller  80   a.    
         [0042]    The present invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
       PARTS LIST 
       [0043]      2  rollers 
         [0044]      3  receiver media 
         [0045]      4  in-track direction 
         [0046]      5  flutes 
         [0047]      7  cross track direction 
         [0048]      8  contact surface 
         [0049]      9  exit direction 
         [0050]      10  substrate 
         [0051]      11  source roll 
         [0052]      12  take up roll 
         [0053]      15  first side 
         [0054]      16  second side 
         [0055]      20   a - 20   d  printheads 
         [0056]      18  second side 
         [0057]      21  first print line 
         [0058]      22  second print line 
         [0059]      25   a,    25   b  printhead 
         [0060]      30  web guiding system 
         [0061]      31  print line rollers 
         [0062]      32  print line rollers 
         [0063]      40  dryers 
         [0064]      41  dryer roller 
         [0065]      45  control sensor 
         [0066]      50  printing module 
         [0067]      51  first zone 
         [0068]      52  second print zone 
         [0069]      55  first printing module 
         [0070]      60  turnover mechanism 
         [0071]      65  second printing module 
         [0072]      70  web-guiding structure 
       Parts List (con&#39;t) 
       [0073]      75   a  printhead 
         [0074]      75   b  printhead 
         [0075]      75   c  printhead 
         [0076]      75   d  printhead 
         [0077]      80   a  gravure roller 
         [0078]      80   b  gravure roller 
         [0079]      80   c  gravure roller 
         [0080]      80   d  gravure roller 
         [0081]      100  digital printing system 
         [0082]      110  printing system 
         [0083]      120  images 
         [0084]      130  clear ribs 
         [0085]      130   a  dashed pattern 
         [0086]      130   b  dotted pattern 
         [0087]      131  space 
         [0088]      135  hexagonal shape