Patent Publication Number: US-9421756-B1

Title: Roller contact adjustment for flexographic printing system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned, co-pending U.S. patent application Ser. No. 14/146,867 (now U.S. Publication No. 2015/0191006), entitled “Inking system for flexographic printing,” by J. Shifley; to commonly-assigned U.S. patent application Ser. No. 14/162,807 (now U.S. Pat. No. 9,233,531), entitled “Flexographic printing system with solvent replenishment,” by J. Shifley et al.; to commonly-assigned, co-pending U.S. patent application Ser. No. 14/296,513 (now U.S. Publication No. 2015/0352835), entitled “Solvent replenishment using density sensor for flexographic printer,” by S. Haseler et al.; to commonly-assigned, co-pending U.S. patent application Ser. No. 14/524,247, entitled “Flexographic ink recirculation with anti-air-entrainment features,” by Shifley et al.; and to commonly-assigned, co-pending U.S. patent application Ser. No. 14/694,172, entitled “Flexographic printing system with pivoting ink pan,” by Smith et al, each of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention pertains to the field of flexographic printing, and more particularly to adjustable ink pans for controllably providing ink to an anilox roller. 
     BACKGROUND OF THE INVENTION 
     Flexography is a method of printing or pattern formation that is commonly used for high-volume printing runs. It is typically employed for printing on a variety of soft or easily deformed materials including, but not limited to, paper, paperboard stock, corrugated board, polymeric films, fabrics, metal foils, glass, glass-coated materials, flexible glass materials and laminates of multiple materials. Coarse surfaces and stretchable polymeric films are also economically printed using flexography. 
     Flexographic printing members are sometimes known as flexographic printing plates, relief printing members, relief-containing printing plates, printing sleeves, or printing cylinders, and are provided with raised relief images onto which ink is applied for application to a printable material. While the raised relief images are inked, the recessed relief “floor” should remain free of ink. 
     Although flexographic printing has conventionally been used in the past for printing of images, more recent uses of flexographic printing have included functional printing of devices, such as touch screen sensor films, antennas, and other devices to be used in electronics or other industries. Such devices typically include electrically conductive patterns. 
     Touch screens are visual displays with areas that may be configured to detect both the presence and location of a touch by, for example, a finger, a hand or a stylus. Touch screens may be found in televisions, computers, computer peripherals, mobile computing devices, automobiles, appliances and game consoles, as well as in other industrial, commercial and household applications. A capacitive touch screen includes a substantially transparent substrate which is provided with electrically conductive patterns that do not excessively impair the transparency—either because the conductors are made of a material, such as indium tin oxide, that is substantially transparent, or because the conductors are sufficiently narrow that the transparency is provided by the comparatively large open areas not containing conductors. As the human body is also an electrical conductor, touching the surface of the screen results in a distortion of the screen&#39;s electrostatic field, measurable as a change in capacitance. 
     Projected capacitive touch technology is a variant of capacitive touch technology. Projected capacitive touch screens are made up of a matrix of rows and columns of conductive material that form a grid. Voltage applied to this grid creates a uniform electrostatic field, which can be measured. When a conductive object, such as a finger, comes into contact, it distorts the local electrostatic field at that point. This is measurable as a change in capacitance. The capacitance can be changed and measured at every intersection point on the grid. Therefore, this system is able to accurately track touches. Projected capacitive touch screens can use either mutual capacitive sensors or self capacitive sensors. In mutual capacitive sensors, there is a capacitor at every intersection of each row and each column. A 16×14 array, for example, would have 224 independent capacitors. A voltage is applied to the rows or columns. Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field which reduces the mutual capacitance. The capacitance change at every individual point on the grid can be measured to accurately determine the touch location by measuring the voltage in the other axis. Mutual capacitance allows multi-touch operation where multiple fingers, palms or styli can be accurately tracked at the same time. 
     WO 2013/063188 by Petcavich et al. discloses a method of manufacturing a capacitive touch sensor using a roll-to-roll process to print a conductor pattern on a flexible transparent dielectric substrate. A first conductor pattern is printed on a first side of the dielectric substrate using a first flexographic printing plate and is then cured. A second conductor pattern is printed on a second side of the dielectric substrate using a second flexographic printing plate and is then cured. In some embodiments the ink used to print the patterns includes a catalyst that acts as seed layer during subsequent electroless plating. The electrolessly plated material (e.g., copper) provides the low resistivity in the narrow lines of the grid needed for excellent performance of the capacitive touch sensor. Petcavich et al. indicate that the line width of the flexographically printed material can be 1 to 50 microns. 
     To improve the optical quality and reliability of the touch screen, it has been found to be preferable that the width of the grid lines be approximately 2 to 10 microns, and even more preferably to be 4 to 8 microns. Printing such narrow lines stretches the limits of flexographic printing technology, especially when relatively high viscosity printing inks are used. In particular, it has been found to be difficult to achieve a desired tolerance of plus or minus one micron in line width tolerance. 
     The ink used to print the patterns used for electroless plating typically includes one or more UV curable monomers or polymers in which a catalyst is dispersed, and an amount of solvent to provide good flexographic printing characteristics. The ink is typically transferred to the flexographic printing members using anilox rollers. In some configurations, ink is transferred from an ink pan to the anilox rollers using fountain rollers mounted in the ink pan. Any variation of the contact pressure between the fountain rollers and the anilox rollers can result in inconsistent or unreliable transfer of ink, which can impact the ability of the flexographic printing system to deliver the required tolerances in the features of the printed images. There remains a need for ink pan configurations and adjustment methods which enable the extent of contact between a fountain roller and an anilox roller in a flexographic printing system to be adjusted in an accurate and consistent manner. 
     SUMMARY OF THE INVENTION 
     The present invention represents a method for adjusting an extent of contact between a fountain roller mounted within a pivotable ink pan and an anilox roller in a flexographic printing system, the pivotable ink pan being adapted to pivot around a pivot axis disposed proximate to a first end of the pivotable ink pan, comprising: 
     positioning the pivotable ink pan to provide a predetermined gap between the anilox roller and the fountain roller; 
     adjusting a position of the pivotable ink pan by adjusting a height of a distal portion of the pivotable ink pan by a predetermined amount that is known to close the predetermined gap between the anilox roller and the fountain roller to a desired extent; and 
     locking the position of the pivotable ink pan such that the distal portion of the pivotable ink pan is maintained at the adjusted height. 
     This invention has the advantage that the extent of contact between the anilox roller and the fountain roller can be controlled in an accurate and repeatable fashion. This will provide improved performance for the flexographic printing system. This is particularly important when the printing system is being used for applications such as printing grids of fine lines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a flexographic printing system for roll-to-roll printing on both sides of a substrate; 
         FIG. 2  is a prior art flexographic printing apparatus using a fountain roller for ink delivery; 
         FIG. 3  is a prior art flexographic printing apparatus using a reservoir chamber for ink delivery; 
         FIG. 4  is a schematic side view of an inking system using a pivotable ink pan with a fountain roller in contact with the anilox roller for a first roller rotation direction; 
         FIG. 5  is a schematic side view of an inking system using a pivotable ink pan with a fountain roller in contact with the anilox roller for a second roller rotation direction; 
         FIG. 6  is a top perspective of an ink pan for ink recirculation that can be used with embodiments of the invention; 
         FIG. 7  is similar to  FIG. 6 , but with the fountain roller removed; 
         FIG. 8  is a schematic of an ink recirculation and solvent replenishment system that can be used with embodiments of the invention; 
         FIG. 9  is a schematic side view of a pivotable ink pan according to an exemplary embodiment; 
         FIG. 10  is a schematic side view showing an alternate arrangement for mounting a pivotable ink pan; 
         FIG. 11  is a flowchart illustrating a method for adjusting the pivotable ink pan of  FIG. 9  to control the extent of contact between the fountain roller and the anilox roller; 
         FIG. 12  is a high-level system diagram for an apparatus having a touch screen with a touch sensor that can be printed using embodiments of the invention; 
         FIG. 13  is a side view of the touch sensor of  FIG. 12 ; 
         FIG. 14  is a top view of a conductive pattern printed on a first side of the touch sensor of  FIG. 13 ; and 
         FIG. 15  is a top view of a conductive pattern printed on a second side of the touch sensor of  FIG. 13 . 
     
    
    
     It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present invention. It is to be understood that elements not specifically shown, labeled, or described can take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements. It is to be understood that elements and components can be referred to in singular or plural form, as appropriate, without limiting the scope of the invention. 
     The invention is inclusive of combinations of the embodiments described herein. References to “a particular embodiment” and the like refer to features that are present in at least one embodiment of the invention. Separate references to “an embodiment” or “particular embodiments” or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. It should be noted that, unless otherwise explicitly noted or required by context, the word “or” is used in this disclosure in a non-exclusive sense. 
     The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention. 
     As described herein, the example embodiments of the present invention provide an inking system for use in a flexographic printing system, particularly for printing functional devices incorporated into touch screens. However, many other applications are emerging for printing of functional devices that can be incorporated into other electronic, communications, industrial, household, packaging and product identification systems (such as RFID) in addition to touch screens. Furthermore, flexographic printing is conventionally used for printing of images and it is contemplated that the inking systems described herein can also be advantageous for such printing applications. 
       FIG. 1  is a schematic side view of a flexographic printing system  100  that can be used in embodiments of the invention for roll-to-roll printing on both sides of a substrate  150 . Substrate  150  is fed as a web from supply roll  102  to take-up roll  104  through flexographic printing system  100 . Substrate  150  has a first side  151  and a second side  152 . 
     The flexographic printing system  100  includes two print modules  120  and  140  that are configured to print on the first side  151  of substrate  150 , as well as two print modules  110  and  130  that are configured to print on the second side  152  of substrate  150 . The web of substrate  150  travels overall in roll-to-roll direction  105  (left-to-right in the example of  FIG. 1 ). However, various rollers  106  and  107  are used to locally change the direction of the web of substrate as needed for adjusting web tension, providing a buffer, and reversing a side for printing. In particular, note that in print module  120  roller  107  serves to reverse the local direction of the web of substrate  150  so that it is moving substantially in a right-to-left direction. 
     Each of the print modules  110 ,  120 ,  130 ,  140  includes some similar components including a respective plate cylinder  111 ,  121 ,  131 ,  141 , on which is mounted a respective flexographic printing plate  112 ,  122 ,  132 ,  142 , respectively. Each flexographic printing plate  112 ,  122 ,  132 ,  142  has raised features  113  defining an image pattern to be printed on the substrate  150 . Each print module  110 ,  120 ,  130 ,  140  also includes a respective impression cylinder  114 ,  124 ,  134 ,  144  that is configured to force a side of the substrate  150  into contact with the corresponding flexographic printing plate  112 ,  122 ,  132 ,  142 . 
     More will be said below about rotation directions of the different components of the print modules  110 ,  120 ,  130 ,  140 , but for now it is sufficient to note that the impression cylinders  124  and  144  of print modules  120  and  140  (for printing on first side  151  of substrate  150 ) rotate counter-clockwise in the view shown in  FIG. 1 , while the impression cylinders  114  and  134  of print modules  110  and  130  (for printing on second side  152  of substrate  150 ) rotate clockwise in this view. 
     Each print module  110 ,  120 ,  130 ,  140  also includes a respective anilox roller  115 ,  125 ,  135 ,  145  for providing ink to the corresponding flexographic printing plate  112 ,  122 ,  132 ,  142 . As is well known in the printing industry, an anilox roller is a hard cylinder, usually constructed of a steel or aluminum core, having an outer surface containing millions of very fine dimples, known as cells. How the ink is controllably transferred and distributed onto the anilox roller is described below. In some embodiments, some or all of the print modules  110 ,  120 ,  130 ,  140  also include respective UV curing stations  116 ,  126 ,  136 ,  146  for curing the printed ink on substrate  150 . 
     U.S. Pat. No. 7,487,724 to Evans et al. discloses inking systems for an anilox roller in a flexographic printing apparatus.  FIG. 2  is a copy of Evans&#39;  FIG. 1  showing a flexographic printing apparatus using a fountain roller device  20  for delivering printing liquid (also called ink herein) to an anilox roller  18 .  FIG. 3  is a copy of Evans&#39;  FIG. 2  showing a reservoir chamber system  30  for delivering printing liquid to the anilox roller  18 . The flexographic apparatuses shown in  FIGS. 2 and 3  each comprises a rotatably driven impression cylinder  10  adapted to peripherally carry and transport a printable substrate  12 , such as paper or a similar web-like material. A plate cylinder  14  is rotatably disposed adjacent the impression cylinder in axially parallel coextensive relation. The circumferential periphery of the plate cylinder  14  carries one or more flexible printing plates  16  formed with an image surface (not shown), for example in a relief image form, for peripherally contacting the circumferential surface of the impression cylinder  10  and the substrate  12  thereon. The anilox roller  18  is similarly disposed adjacent the plate cylinder  14  in axially parallel coextensive relation and in peripheral surface contact therewith. 
     The anilox roller  18  has its circumferential surface engraved with a multitude of recessed cells, which may be of various geometric configurations, adapted collectively to retain a quantity of printing liquid in a continuous film-like form over the circumferential surface of the anilox roller  18  for metered transfer of the liquid to the image surface on the printing plate  16  of the plate cylinder  14 . 
     The flexographic printing apparatuses of  FIGS. 2 and 3  differ principally in construction and operation in the form of delivery device provided for applying printing liquid to the anilox roller  18 . In the  FIG. 2  apparatus, the delivery device is in the form of a so-called fountain roller device  20 , wherein a cylindrical fountain roller  22  is disposed in axially parallel coextensive relation with the anilox roller  18  in peripheral surface contact therewith, with a downward facing lower portion of the fountain roller  22  being partially submerged in a pan  24  containing a quantity of printing liquid. The fountain roller  22  rotates and constantly keeps the engraved cell structure of the circumferential surface of the anilox roller  18  filled with the printing liquid, thereby forming a thin film of the liquid as determined by the size, number, volume and configuration of the cells. A doctor blade  26  is preferably positioned in angled surface contact with the anilox roller  18  downstream of the location of its contact with the fountain roller  22 , as viewed in the direction of rotation of the anilox roller  18 , to progressively wipe excess printing liquid from the surface of the anilox roller  18 , which drains back into the pan  24 . 
     In contrast, the flexographic printing apparatus shown in  FIG. 3  does not utilize a fountain roller, but instead uses a reservoir chamber  32  positioned directly adjacent the anilox roller  18 , with forwardly and rearwardly inclined blades  34 ,  46  disposed in axially extending wiping contact with the surface of the anilox roller  18  at a circumferential spacing from each other. Blade  34  is upstream of the contact of the printing liquid from reservoir chamber  32  with anilox roller  18 , and serves as a containment blade. Blade  46  is downstream of the contact of the printing liquid from reservoir chamber  32  with anilox roller  18 , and serves as a doctor blade to wipe excess printing liquid from the surface of the anilox roller  18 . Printing liquid is continuously delivered into the reservoir chamber  32  at ink entry  39  and is exhausted from the reservoir chamber  32  at ink exit  38  so as to maintain a slightly positive fluid pressure within the reservoir chamber  32 . In this manner, the reservoir chamber system  30  serves to constantly wet the peripheral surface of the anilox roller  18 . 
     U.S. Patent Application Publication 2012/0186470 to Marco et al. entitled “Printing device and method using energy-curable inks for a flexographic printer,” discloses a flexographic printer adapted for printing an energy-curable printing ink containing components including resin, pigment and a non-reactive evaporable component such as water or another solvent. A reservoir chamber, such as reservoir chamber  32  mentioned above with reference to  FIG. 3 , having an ink supply line and an ink return line is used to apply ink to the anilox roller. A reading device, such as a viscometer, is used to characterize a ratio of the non-reactive evaporable component of the printing ink in the ink supply line to the reservoir chamber  32 . A suitable amount of the non-reactive evaporable component is added to the ink based on the viscometer reading. 
     As disclosed in commonly-assigned, co-pending U.S. patent application Ser. No. 14/146,867 to Shifley, entitled “Inking system for flexographic printing,” filed Jan. 3, 2014, which is incorporated herein by reference, it has been found that for printing of narrow lines with somewhat viscous inks, line quality is generally better when using an ink pan and a fountain roller to provide ink to the anilox roller than when using a reservoir chamber to deliver ink directly to the anilox roller. It is believed that the fountain roller is more effective in forcing viscous inks into the cells on the surface of the anilox roller than is mere contact of ink at an ink delivery portion of a reservoir chamber. 
       FIG. 4  shows a close-up side view of an ink pan  160  with a fountain roller  161  for use in flexographic printing systems for providing ink to anilox roller  175 . In this embodiment, the configuration and rotation directions of impression cylinder  174 , plate cylinder  171  and anilox roller  175  are similar to the corresponding impression cylinder  114 , plate cylinder  111  and anilox roller  115  in print module  110  of  FIG. 1 . 
     Ink pan  160  includes a front wall  162  located nearer to impression cylinder  174 , a rear wall  163  located opposite front wall  162  and further away from impression cylinder  174 , and a floor  164  extending between the front wall  162  and the rear wall  163 . The ink pan  160  also includes two side walls (not shown in  FIG. 4 ) that extend between the front wall  162  and the rear wall  163  on opposite sides of the ink pan  160  and intersect the floor  164 . It should be noted that there may or may not be distinct boundaries between the front wall  162 , the rear wall  163 , the floor  164  and the side walls. In some embodiments, some or all of the boundaries between these surfaces can be joined using rounded boundaries that smoothly transition from one surface to the adjoining surface. 
     Fountain roller  161  is partially immersed in an ink  165  contained in ink pan  160 . Within the context of the present invention, the ink  165  can be any type of marking material, visible or invisible, to be deposited by the flexographic printing system  100  ( FIG. 1 ) on the substrate  150 . Fountain roller  161  is rotatably mounted on ink pan  160 . Ink pan  160  is pivotable about pivot axis  166 , preferably located near the front wall  162 . 
     A lip  167  extends from rear wall  163 . When an upward force F is applied to lip  167  as in  FIG. 4 , ink pan  160  pivots upward about pivot axis  166  until fountain roller  161  contacts anilox roller  175  at contact point  181 . In the upwardly pivoted ink pan  160  the floor  164  tilts downward from rear wall  163  toward the front wall  162  so that fountain roller  161  is located near a lowest portion  168  of floor  164 . If upward force F is removed from lip  167 , ink pan  160  pivots downward under the influence of gravity so that fountain roller  161  is no longer in contact with anilox roller  175 . 
     As described with reference to  FIG. 1 , a flexographic printing plate  172  (also sometimes called a flexographic master) is mounted on plate cylinder  171 . In  FIG. 4 , flexographic printing plate  172  is a flexible plate that is wrapped almost entirely around plate cylinder  171 . Anilox roller  175  contacts raised features  173  on the flexographic printing plate  172  at contact point  183 . As plate cylinder  171  rotates counter-clockwise (in the view shown in  FIG. 4 ), both the anilox roller  175  and the impression cylinder  174  rotate clockwise, while the fountain roller  161  rotates counter-clockwise. Ink  165  that is transferred from the fountain roller  161  to the anilox roller  175  is transferred to the raised features  173  of the flexographic printing plate  172  and from there to second side  152  of substrate  150  that is pressed against flexographic printing plate  172  by impression cylinder  174  at contact point  184 . 
     In order to remove excess amounts of ink  165  from the patterned surface of anilox roller  175  a doctor blade  180 , which is mounted to the frame (not shown) of the printing system, contacts anilox roller  175  at contact point  182 . Contact point  182  is downstream of contact point  181  and is upstream of contact point  183 . For the configuration shown in  FIG. 4 , in order to position doctor blade  180  to contact the anilox roller  175  downstream of contact point  181  where the fountain roller  161  contacts the anilox roller  175 , as well as upstream of contact point  183  where the anilox roller  175  contacts the raised features  173  on the flexographic printing plate  172 , doctor blade  180  is mounted on the printer system frame on a side of the anilox roller  175  that is opposite to the impression cylinder  174 . 
     After printing of ink on the substrate, it is cured using UV curing station  176 . In some embodiments, an imaging system  177  can be used to monitor line quality of the pattern printed on the substrate. 
     The configuration of the pivotable ink pan  160  with the doctor blade  180  located on the side of the anilox roller  175  that is opposite to the impression cylinder  174 , as shown in  FIG. 4 , is compatible for the rotation directions of the rollers that are as shown in print modules  110  and  130  of  FIG. 1  for printing on second side  152  of substrate  150 . In such configurations (with reference to  FIG. 4 ), the side of anilox roller  175  that moves upward toward plate cylinder  171  after receiving ink  165  from fountain roller  161  is the side that is located farther away from the front wall  162  of ink pan  160 , and also farther away from impression cylinder  174 . Comparing  FIG. 1  with  FIG. 4  it can be appreciated that for print modules  120  and  140 , where the rotation directions of the impression cylinders  124  and  144  are opposite the rotation directions of the impression cylinders  114  and  134  in print modules  110  and  130 , the side of the corresponding anilox rollers  125  and  145  that would move upward from the ink pans  160  (not shown in  FIG. 1 ) toward the plate cylinders  121  and  141  would be the side that is next to the front wall  162  of ink pan  160 . In some flexographic printing systems, spatial constraints due to the proximity of the impression cylinder  174  to the near side of the anilox roller  175  limit where a doctor blade could be positioned on that side of the anilox roller  175 . (By contrast, the more spread-out prior art configuration shown in  FIG. 2  does not have such spatial constraints, so that the doctor blade  26  can be located on that side of anilox roller  18 .) 
     A close-up schematic side view of an inking system for flexographic printing using viscous inks for print modules having tight spatial constraints around the anilox roller when printing on a side of the substrate requiring that the side of the anilox roller that faces the impression cylinder moves upward is shown in  FIG. 5 . The configuration shown in  FIG. 5  can be used, for example, for print modules  120  and  140  in  FIG. 1  where the web of substrate  150  reverses direction for printing on first side  151 , such that a direction of rotation of impression cylinder  274  causes a surface of the impression cylinder  274  to move in a downward direction on a side of the impression cylinder  274  facing front wall  202  of ink pan  200 . In the configuration of  FIG. 5 , pivotable ink pan  200  with fountain roller  201  positioned in proximity to lowest floor portion  208  of floor  204  of ink pan  200  is used to transfer ink  205  to anilox roller  275  at contact point  281 . Ink  205  is transferred to raised features  273  of flexographic printing plate  272  on plate cylinder  271  at contact point  283  and is subsequently printed onto first side  151  of substrate  150 , being pressed into contact by impression cylinder  274  at contact point  284 . As in  FIG. 4 , a force F can be applied to lip  207  on rear wall  203  of the ink pan  200  to pivot the ink pan  200  around the pivot axis  206 , bringing the fountain roller  201  into contact with the anilox roller  275 . UV curing station  276  is optionally provided for curing the printed ink on first side  151  of substrate  150 . Imaging system  277  is provided for monitoring the line quality of the lines printed on the substrate  150 . 
     As disclosed in commonly-assigned, co-pending U.S. patent application Ser. No. 14/146,867, fitting doctor blade  220  within the tight spatial constraints downstream of contact point  281  and upstream of contact point  283  (where anilox roller  275  transfers ink  205  to raised features  273  of flexographic printing plate  272 ) can be addressed by mounting the doctor blade  220  to the ink pan  200  on the side of the anilox roller  275  that is nearest to the impression cylinder  274 . In particular, doctor blade  220  can be mounted within ink pan  200  using a blade holder  210  positioned near the front wall  202  of the ink pan  200  such that the doctor blade  220  contacts the anilox roller  275  at contact point  282 . 
     It has recently been found that it is difficult to maintain tight tolerances (plus or minus one micron for example) on line width of narrow lines as the ink increases in viscosity due to evaporation of solvent in the ink. Although ink recirculation and solvent replenishment for a reservoir chamber have previously been disclosed in U.S. Patent Application Publication No. 2012/0186470 as described above, ink replenishment in an ink pan for a flexographic printing system is typically done by pouring additional ink into the ink tank. The newly added ink does not always mix well with the residual ink that is still in the ink pan. Such incomplete mixing can result in ink viscosity variation within the ink pan, giving rise to excessive variation in line width and quality of the printed narrow lines. 
     Commonly-assigned, co-pending U.S. patent application Ser. No. 14/162,807 to Shifley et al., entitled “Flexographic printing system with solvent replenishment”, filed Jan. 24, 2014, which is incorporated herein by reference, discloses a solvent replenishment system for inks in a flexographic printing system. Although that system works well, in some cases it has been found that more precise control of the timing and rate of solvent replenishment is desirable. 
       FIG. 6  shows a top perspective of an ink pan  200  for use with an ink recirculation system  250  (see  FIG. 8 ).  FIG. 6  does not show the configuration of the doctor blade as the ink recirculation system  250  of the invention is applicable to both the ink pan  160  of  FIG. 4  and the ink pan  200  of  FIG. 5 . (In other words, the numbering of ink pan  200  in  FIG. 6  is meant to be exemplary rather than exclusively referring to the inking system of  FIG. 5 .) First side wall  211  and its opposing second side wall  212  are shown in this perspective as extending between the front wall  202  and the rear wall  203  and intersecting the floor  204 . A width W of ink pan  200  is defined by first and second side walls  211  and  212 . 
     Some components of ink recirculation system  250  are shown in  FIG. 6 . In particular, an ink recirculation port  240  is disposed near the center of the width W of ink pan  200  near front wall  202  and near a lowest floor portion  208  of the floor  204  of the ink pan  200 . Ink recirculation port  240  is hidden behind fountain roller  201  in  FIG. 6  and extends below ink pan  200 , but the opening  215  of ink recirculation port  240  is shown covered by ink  205  in the perspective of  FIG. 7 , where the fountain roller  201  has been removed for clarity. In some embodiments (not shown) there is a plurality of ink recirculation ports in proximity to the lowest floor portion  208  of the floor  204  of the ink pan  200 . 
     Ink  205  is drawn out of the ink pan  200  through the ink recirculation port  240  as described in further detail below. Solvent replenished ink is returned to the ink pan  200  via ink distribution tube  230 . Ink distribution tube  230  can have a cylindrical geometry as shown in  FIGS. 6 and 7 , or alternatively can have other configurations. Ink distribution tube  230  includes a plurality of ink supply ports  232  at a plurality of spaced apart locations across the width W of the ink pan  200 . Ink distribution tube  230  is preferably substantially parallel (i.e., within about 20 degrees of parallel) to a rotation axis of fountain roller  201 . In a preferred embodiment, pressure P is applied to both ends of ink distribution tube  230  using pressurized lines  234 . In the example shown in  FIGS. 6 and 7 , ink supply ports  232  are disposed along a bottom of ink distribution tube  230  aimed toward floor  204 , although this is not a requirement. In some embodiments, ink supply ports  232  can be equally spaced and have equal cross-sectional areas as shown. The replenished ink flows downward toward ink  205  along replenished ink entry paths  235 . 
     It is generally a desirable feature for the ink pan  200  to be removable from the flexographic printing system  100  ( FIG. 1 ), for example to facilitate cleaning. To facilitate this, one approach that can be used is to affix brackets  262  onto the first and second side walls  211 ,  212  of the ink pan  200 . The brackets  262  are adapted to rest on pivot elements  260  mounted on a frame of the flexographic printing system  100 . The brackets  262  support at least a portion of the weight of the ink pan  200 , and together with the pivot elements  260  define the pivot axis  206  around which the ink pan  200  is adapted to pivot. In the illustrated embodiment, the bracket  262  makes contact with an outer surface of the pivot element  260  along an arc that includes an upper part of the pivot element  260 . To remove the ink pan  200 , it can be tilted around the pivot axis  206  to move the fountain roller  201  away from the anilox roller  275  ( FIG. 5 ). The ink pan  200  can then be lifted to disengage the bracket  262  from the pivot element  260  so that the ink pan  200  can be removed. 
       FIG. 8  shows a schematic of the ink recirculation system  250  according to an embodiment of the invention. Direction of ink flow is indicated by the straight arrows. The fountain roller  201  ( FIG. 6 ) is hidden in this figure in order to show opening  215  of the ink recirculation port more clearly. Furthermore, the ink distribution tube  230  ( FIG. 6 ) is not visible in the perspective of  FIG. 8 . 
     Ink  205  exits ink pan  200  via ink drain line  239  due to the pumping action of ink recirculation pump  242 , and optionally assisted by gravity. In some embodiments the ink recirculation pump  242  is a peristaltic pump. Action of ink recirculation pump  242  is controlled by control system  243 . Ink is then moved back toward ink pan  200  via ink return line  256 . Collectively, the ink drain line  239  and the ink return line  256  are referred to as ink recirculation line  241 . The ink drain line  239  is on the low pressure side of ink recirculation pump  242 , while ink return line  256  is on the high pressure side. 
     Over the course of time as ink  205  circulates through the ink recirculation system  250 , particulates can enter the ink  205 . This can include airborne particulates landing in ink pan  200 , or particles being generated in other parts of the system. In some embodiments, a filter  244  is provided in the ink recirculation line  241  in order to remove particles that otherwise could degrade the quality of the printed pattern. For printing a touch screen sensor pattern having fine lines with widths between 4 microns and 8 microns, an inline filter  244  designed to remove particles larger than 1 micron or 2 microns, for example, can be provided in ink recirculation line  241 . Typically, because of the pressure drop that occurs across filter  244 , it is preferable for it to be located in the ink return line  256  on the high pressure side of the ink recirculation pump  242 . 
     The ink recirculation system  250  is used to recirculate the ink  205  while the flexographic printing system  100  ( FIG. 1 ) is printing in order to maintain the printing properties of ink  205  to be substantially consistent. This provides reduced variability in the performance of the flexographic printing system  100 . In order to maintain the consistent printing properties of the ink  205  such that actual printed feature sizes are equal to the desired printed feature sizes within the required tolerances, it is necessary to maintain the solvent in the ink  205  at an appropriate concentration. It is therefore necessary to replenish the solvent in the ink  205  as it evaporates during operation of the flexographic printing system  100 . To replenish the solvent, solvent from a solvent replenishment chamber  245  is pumped by metering pump  246  into solvent replenishment line  257  and enters ink recirculation pump  242  together with ink  205  from ink drain line  239 . Valve  249  can be used to isolate metering pump  246  from the solvent replenishment line  257 . 
     If the viscosity of the ink  205  is much higher than the viscosity of the solvent, it is found that simply pumping solvent into the ink  205  does not mix them to a sufficiently uniform extent. For example, a typical viscosity of an ink for functional printing of devices using a flexographic printing system will typically range between 10 centipoises and 20,000 centipoises, and in a preferred embodiment will be between about 40 centipoises and 2000 centipoises. By contrast, the viscosity of the solvent is typically between 0.3 and 3 centipoises. It is therefore advantageous to incorporate a mixing device  254  in the ink recirculation system  250  to provide sufficiently uniform solvent-replenished ink. In the example shown in  FIG. 8 , mixing device  254  is provided inline with ink return line  256 . Mixing device  254  can be a dynamic mixing device or a static inline mixing device. 
     A rate of flow of solvent into solvent replenishment line  257  is controlled by control system  247  for metering pump  246 . Metering pump  246  is a piston pump or a syringe pump, for example. The rate of flow can be controlled by an amount of solvent delivered per stroke, as well as the frequency of strokes of the metering pump  246 . The preferred rate of flow is dependent on the evaporation rate of the solvent, which can depend on factors such as the volatility of the solvent, the temperature, and the surface area of exposed ink. 
     In some applications a closed loop system can be used in which properties of the ink  205  can be measured either continuously or on a sampled basis in order to control the replenishment of solvent. Commonly-assigned, co-pending U.S. patent application Ser. No. 14/296,513 to Shifley et al., entitled “Solvent replenishment using density sensor for flexographic printer”, filed Jun. 5, 2014, which is incorporated herein by reference, discloses a solvent replenishment system including a density sensor  255  to characterize the ink and provide ink property information to control system  247  for controlling the rate of solvent flow. More specifically, control system  247  controls the flow rate of solvent provided by metering pump  246  based on a measured density of the ink  205  measured by density sensor  255 . Herein when referring to a density sensor or ink density, what is meant is the volumetric mass density, typically expressed in grams per cubic centimeter (g/cc) or similar units. 
     Measuring the density of the ink to control the solvent concentration is particularly advantageous where the density of the solvent is significantly different from the remainder of the ink components without the solvent. The remainder of ink components excluding the solvent will be referred to herein as “solids.” In a first example Dowanol™ PM glycol ether (available from the Dow Chemical Company) having a density of 0.92 g/cc at 20° C. was used as the solvent, and the solids had a density of 1.39 g/cc. In a second example again Dowanol™ PM glycol ether was used as the solvent and the solids had a density of 1.79 g/cc. In both of these examples the density of the solids is significantly different from the density of the solvent, so that as the solvent level changes there is a correspondingly change in the density that is significant and measurable with a high signal-to-noise ratio. A significant difference in density herein will be considered to be a density difference of at least 10%. It is more preferable to have a density difference of at least 30%, and still more preferable to have a density difference of 50% or more, as is the case for the two examples described above. 
     Any type of density sensor  255  known in the art can be used. One type of density sensor  255  that can be used to make highly precise density measurements of a fluid is an oscillating U-tube. This type of measurement was first demonstrated by Anton Parr GmbH, and density sensors  255  of this type are commercially available from Anton Parr GmbH. In such devices, a fluid is made to pass through a U-tube that is supported by bearing points and the U-tube is excited into resonance. The resonant frequency depends on the mass of the fluid contained in the known volume of the tube between the bearing points, so that the density of the fluid at any given time is related to the resonant frequency that is measured. As the solvent concentration changes, the density changes so that the frequency changes. 
     In an exemplary embodiment, the density of an ink  205  for flexographic printing was maintained within the tight specification of ±0.001 g/cc at a target value of density near 1.3 g/cc. The corresponding solvent weight percent was controlled to within ±0.1% at a target of approximately 35%. The measurement scheme for solvent replenishment control does not require the density measurement to be highly accurate, nor to provide an accurate measurement of the ink&#39;s solvent concentration. It only requires that the density measurement be highly precise (i.e., reproducible and repeatable) in order for the control system  247  to control the flow rate of the solvent provided by the metering pump  246  such that variations in the measured density of the ink  205  as a function of time are reduced relative to a target density. 
     Also shown in the ink recirculation system  250  of  FIG. 8  is an ink recovery tank  253 . In some applications, the ink  205  can be very expensive. When it is desired to purge the ink  205  from the printing system, the ink  205  in ink pan  200 , as well as in ink recirculation line  241 , can be pumped into the ink recovery tank  253 . In an exemplary embodiment, a multi-position ink recovery valve  251  is provided downstream of the ink recirculation pump  242 . When the ink recovery valve  251  is in a first position the ink is directed to pressure manifold  233 , which allows ink to flow through the pressurized lines  234  at the ends of the ink distribution tube  230  ( FIG. 6 ). The ink is then directed from both ends through the ink distribution tube  230  and out of the ink supply ports  232  ( FIG. 6 ) into the ink pan  200 . When the ink recovery valve  251  is in a second position, the ink is diverted into the ink recovery tank  253 . Optionally, after the ink has been moved to the ink recovery tank  253 , the ink recirculation system  250  can be solvent flushed for maintaining good flow through the various lines and orifices. 
     In some embodiments, it can be advantageous to provide independent control of flow rate of solvent for some or all of the various print modules  110 ,  120 ,  130 ,  140  of the flexographic printing system  100  ( FIG. 1 ). In some instances this can be due to different types of ink and different volatility of solvent used for different print modules. In other instances the environmental conditions, such as temperature, can be different for different print modules. In still other instances, the dwell time of the ink on the flexographic printing plate can be different among different print modules, which leads to different amounts of evaporation of solvent prior to printing on substrate  150 . In particular, consider the inking system shown in  FIG. 4  that can be employed for print modules  110  and  130  ( FIG. 1 ) for printing on second side  152  of substrate  150  as discussed above. After ink is transferred from anilox roller  175  to flexographic printing plate  172  at contact point  183 , plate cylinder  171  only needs to rotate counterclockwise by about 60 degrees before the ink is printed on second side  152  of substrate  150  at contact point  184 . In contrast, for the inking system shown in  FIG. 5  that can be employed for print modules  120  and  140  ( FIG. 1 ) for printing on first side  151  of substrate  150 , after ink is transferred from anilox roller  275  to flexographic printing plate  272  at contact point  283 , plate cylinder  271  needs to rotate clockwise by about 300 degrees before the ink is printed on first side  151  of substrate  150  at contact point  284 . Thus the dwell time of the ink in a very thin layer on flexographic printing plate  272  ( FIG. 5 ) is about 5 times as long as it is on flexographic printing plate  172  ( FIG. 4 ). This can lead to a greater degree of solvent evaporation in print modules  120  and  140  after ink transfer to anilox roller  275  than in print modules  110  and  130  ( FIG. 1 ). As a result, the control systems  247  for the metering pumps  246  in print modules  120  and  140  may need to provide a higher flow rate than the control systems  247  for the metering pumps  246  in print modules  110  and  130 . 
     To save on space and cost in the flexographic printing system  100  ( FIG. 1 ), it can also be advantageous in some cases to share portions of ink recirculation system  250  among the different print modules  110 ,  120 ,  130  and  140  rather than duplicating all components in each print module. With reference also to  FIGS. 8-10 , two components that can be particularly useful to share among a plurality of print modules are the solvent replenishment chamber  245  and the ink recovery tank  253 . In some embodiments, a valve  248  can be associated with the solvent replenishment chamber  245 . In some configurations, the valve  248  can be a shut-off valve isolating solvent replenishment chamber  245 . In other configurations, the valve  248  can be a multi-position valve allowing connection of the solvent replenishment chamber  245  to ink recirculation systems  250  for a plurality of print modules  110 ,  120 ,  130  and  140 . Similarly, a valve  252  can be associated with the ink recovery tank  253 . In some configurations, the valve  252  can be a multi-position valve allowing connection of ink recovery tank  253  to ink recirculation systems  250  for a plurality of print modules  110 ,  120 ,  130  and  140 . 
     Commonly-assigned, co-pending U.S. patent application Ser. No. 14/524,247 to Shifley et al., filed Oct. 27, 2014, entitled “Flexographic ink recirculation with anti-air-entrainment features,” which is incorporated herein by reference, describes improvements to the ink recirculation system to provide reduced introduction of air into the ink recirculation lines, which can result in the formation of printing defects. The features described in this patent application can be used in accordance with embodiments of the present invention. 
     In the configuration for the ink pan  200  described in  FIGS. 6-7 , the bracket  262  supports at least a portion of the weight of the ink pan  200 . There will generally be lifting mechanism (not shown) to provide the upward force F ( FIG. 5 ) to lift the rearward end of the ink pan  200  (i.e., the end toward rear wall  203 ), thereby bringing the fountain roller  201  into contact with the anilox roller  275  ( FIG. 5 ) with a controlled amount of pressure. The lifting mechanism will also generally support at least a portion of the weight of the ink pan  200 . This ink pan configuration relies on the weight of the ink pan  200  to keep the bracket  262  in tight contact with the pivot element, thereby constraining the ink pan  200  to pivot around the pivot axis  206 . However, it has been found that the components of the ink recirculation system  250  discussed with respect to  FIGS. 6-8  can apply forces to the ink pan  200  which can cause one or both of the brackets  262  to lift away from the pivot element  260 . For example, the weight of the ink recirculation lines  241  and the ink return line  256  can provide forces and torques that can cause the ink pan  200  to shift out of its intended position. This can cause the magnitude and uniformity of the contact pressure between the fountain roller  201  and the anilox roller  275  to vary from the desired characteristics. This can affect the amount of ink transferred to the anilox roller  275 , which will in turn adversely affect the performance of the flexographic printing system  100 . 
       FIG. 9  illustrates an improved ink pan  290  according to an embodiment of the present invention. The ink pan  290  shares many similar features to the ink pan  200  of  FIGS. 5-7 , and includes front wall  202 , rear wall  203  and floor  204 . The ink pan  290  is adapted to pivot around pivot axis  206  disposed proximate to the front wall  202 . The pivot axis  206  is defined by pivot element  260 , which is mounted on an external component such as a frame of the flexographic printing system  100  ( FIG. 1 ). Fountain roller  201  is mounted within the ink pan  290  in proximity to lowest floor portion  208  between extended side walls  213  and is at least partially immersed in the ink  205  in the ink pan  290 . The fountain roller  201  is adapted to rotate to carry ink  205  to the anilox roller  275 , which in turn applies a controlled amount of ink to the raised features  273  ( FIG. 5 ) of the flexographic printing plate  272  ( FIG. 5 ) on the plate cylinder  271  ( FIG. 5 ) for printing on substrate  150  ( FIG. 5 ). 
     A first bracket  262  is affixed to each side wall  213 , and is configured to rest on the pivot element  260  for supporting at least a portion of the weight of the ink pan  290 . The bracket  262  can be affixed to the side wall  213  using any method known in the art. In an exemplary configuration, the bracket  262  includes holes that are adapted to fit over alignment pins  266  formed onto the side wall  213 . Once placed into position, the bracket  262  is tack welded to the side wall  213 . In other embodiments, the bracket  262  can be affixed to the side wall using other fastening means such as screws, or can be formed as a component of the side wall  213 . 
     A second bracket  263  is configured to be affixed to each side wall  213  of the ink pan  290  in an adjustable position. The second bracket  263  is configured to constrain motion of the ink pan  290  to a pivoting motion around the pivot axis  206 . The position of the bracket  263  is adjustable such that it can slide laterally toward or away from the pivot element  260 . 
     A clamping element is used to affix the bracket  263  to the ink pan  290  at a position where a portion of the bracket  263  maintains contact with the pivot element  260  during pivoting, thereby constraining the motion of the ink pan  290  to a pivoting motion around the pivot axis  206 . In an exemplary embodiment, the clamping element is a clamping screw  264 , which passes through a slot  268  formed in the side wall  213  of the ink pan  290  and is threaded into a threaded hole in the bracket  263 . When the clamping screw  264  is tightened, the bracket  263  is tightly affixed to the side wall  213 . When the clamping screw  264  is loosened, it is adapted to slide within the slot  268  along a slot direction, thereby enabling the position of the bracket  263  to slide laterally in the slot direction  268   a.    
     In the illustrated configuration, a pin  265  extends through a second slot  269  in the side wall  213 , and through a hole in the bracket  263  where it is held in place with a retaining ring  267  (e.g., a split ring). Alternatively, the pin  265  can be permanently affixed to the bracket  263 . In the illustrated configuration, the slots  268 ,  269  are shown as being linear and with respective parallel slot directions  268   a ,  269   a , however this is not a requirement. In other configurations, the slots  268 ,  269  may be curved, or may have non-parallel slot directions  268   a ,  269   a  so that the bracket  263  pivots as it is repositioned to bring it into contact with the pivot element  260 . In the illustrated embodiment, the clamping screw  264  passes through the slot  268  which is distal to the pivot element  260  and the pin  265  passes through the slot  269  which is proximate to the pivot element  260 . In other configurations these positions can be reversed, or clamping screws  264  can be used in both positions. 
     In the illustrated configuration, the first bracket  262  has an arced lower surface having a radius of curvature that matches the radius of the pivot element  260 , so that the bracket  262  contacts the pivot element  260  along an arc that extends at least from an upper contact point  261   a  to a first side contact point  261   b  proximate to the front wall  202 . In other configurations, the lower surface of the bracket  262  can have other shapes so that it only contacts the pivot element  260  at discrete contact points (e.g., upper contact point  261   a  and first side contact point  261   b ). 
     When the second bracket  263  is positioned to constrain motion of the ink pan  290  to a pivoting motion around the pivot axis  206 , the bracket  263  makes contact with the pivot element  260  at one or more contact points. In the illustrated configuration, the bracket  263  makes contact with the pivot element  260  at a lower contact point  261   c  (opposite the upper contact point  261   a ) and a second side contact point  261   d  (distal to the front wall  202  and opposite the first side contact point  261   b ). In total, the first and second brackets  262 ,  263  together should contact the pivot element  260  at a sufficient number of contact points so that the motion of the ink pan  290  is constrained to a pivoting motion around the pivot axis  206 . Generally this will require that the total number of contact points be three or more. 
     When the clamping screw  264  is loosened and second bracket  263  is slid out of contact with the pivot element  260 , the ink pan  290  is adapted to be removable from the flexographic printing system  100 . In an exemplary embodiment, the ink pan  290  is removed by pivoting the ink pan  290  around the pivot axis  206  to lower the rear end of the ink pan (i.e., the end proximate the rear wall  203 ) to move the fountain roller  201  away from the anilox roller  275 . The ink pan  290  can then be lifted off the pivot element  260  and pulled in rearward direction to remove the ink pan  290  from the flexographic printing system  100 . This process can be reversed to reinstall the ink pan  290 . 
     A height adjustment mechanism  297  is provided for adjusting a height of a portion of the ink pan  290  that is distal to the pivot axis  206  (i.e., the rearward end proximate the rear wall  203 ). In a preferred embodiment, two height adjustment mechanisms  297  are provided, one on each side of the ink pan  290 . Only one height adjustment mechanism  297  is visible in  FIG. 9  for controlling the height of the near side (sometimes called the “operator side”) of the ink pan  290 . An analogous height adjustment mechanism  297  is not visible in this view, which would be used for controlling the height of the far side (sometimes called the “gear side”) of the ink pan  290 . 
     In an exemplary configuration, the height adjustment mechanism  297  includes a pneumatic adjustment mechanism  291  that can be used to make large adjustments in the height of the distal portion of the ink pan  290 , as well as an adjustment screw  293  that can be used to make fine adjustments. In the illustrated configuration, the pneumatic adjustment mechanism  291  includes a piston  292  extending from cylinder  298 , whose height can be adjusted using control means well known in the art. In other configurations, a hydraulic adjustment mechanism or any other type of height adjustment mechanism known in the art can be used in place of the pneumatic adjustment mechanism  291 . 
     The adjustment screw  293  threads through a threaded hole in a block  295  affixed (directly or indirectly) to the ink pan  290 . The adjustment screw  293  is adapted to push against a block  294  mounted onto the piston, thereby adjusting the height of the distal end of the ink pan  290  up or down as the adjustment screw  293  is turned clockwise or counter-clockwise. In some arrangements, the adjustment screw  293  is adapted to be turned manually using a tool such as a wrench or a screwdriver. In other arrangements, an automatic mechanism (e.g., a computer-controlled stepper motor) can be used to turn the adjustment screw  293 . The adjustment screw  293  has a predetermined thread pitch such that the height can be adjusted by a predetermined amount by turning the adjustment screw  293  a predetermined angle in a predetermined direction. A lock nut  296  is also provided which can be tightened to lock the adjustment screw  293  into position to maintain the ink pan  290  in a fixed position after the height has been adjusted to a desired operating position. In other configurations, any other type of locking mechanism known in the art can be used to lock the ink pan  290  into a fixed position. 
     A number of components of the ink recirculation system  250  ( FIG. 8 ) are also shown in  FIG. 9 . In particular, an ink drain line  239  is shown for drawing ink  205  out of the ink pan  290  through the ink recirculation port  240 . Recirculated ink  205  is returned into the ink pan  290  through ink return line  256  and ink distribution tube  230 . The components of the ink recirculation system were discussed in more detail with respect to  FIGS. 6-8 . 
     As discussed earlier, the components of the ink recirculation system  250  can apply forces and torques to the ink pan  290 . The arrangement of brackets  262 ,  263  in the configuration of  FIG. 9  provide additional constraints on the ink pan  290  relative to the ink pan  200  of  FIG. 6 . This greatly reduces any potential for the position of the ink pan  290  to move to an unintended position, thereby significantly improving the reliability and consistency of the performance of the flexographic printing system  100  ( FIG. 1 ). 
     In order to enable transferring a controllable amount of ink to the flexographic printing plate  272  ( FIG. 5 ), it is important to be able to control an extent of contact at the contact point  281  between the fountain roller  201  and the anilox roller  275 . Within the context of the present disclosure, the term “extent of contact” relates to how firmly the rollers are pressed together. It could be measured in a variety of different ways such as the contact pressure or nip width. One way to control the amount of contact is to use the height adjustment mechanism  297  to adjust the contact pressure to a predefined level. However, it has been found in some situations that the contact pressure is not always a good predictor of the extent of contact, and as a result that the amount of ink  205  transferred to the anilox roller  275  can vary, thereby affecting the performance of the flexographic printing system  100  ( FIG. 1 ). 
     In the configuration of  FIG. 9 , the brackets  262 ,  263  are affixed to the side wall  213  of the pivotable ink pan  290 , and the pivot element  260  is affixed to an external component, such as a frame of the flexographic printing system  100  ( FIG. 1 ).  FIG. 10  illustrates an alternate configuration where the mounting components are reversed. In this case, the brackets  262 ,  263  are affixed to a frame  299  of the flexographic printing system  100  and the pivot element  260  is affixed to the side wall  213  of the ink pan  290 , proximate to the front wall  202 . For clarity, other elements of the ink pan  290  are not shown in  FIG. 10 , but will be analogous to those shown in  FIG. 9 . 
     In the illustrated configuration, the positions of the fixed bracket  262  and the adjustable bracket  263  are reversed relative to  FIG. 9  such that bracket  262  is below the pivot element  260  and bracket  263  is above the pivot element  260 . The pivot element  260  is configured to rest on the bracket  262  to support at least a portion of the weight of the ink pan  290 . 
     The adjustable bracket  263  is configured to be affixed to the frame  299  in an adjustable position, and is adapted to constrain the motion of the ink pan  290  to a pivoting motion around the pivot axis  206 . Clamping screw  264  passes through slot  268 , which in this configuration is formed into the frame  299 , and threads into a threaded hole in the bracket  263 . Similarly, pin  265  passes through slot  269  formed into the frame  299 , and is affixed to the bracket  263  (e.g., using a retaining ring  267 ). The position of the bracket  263  is adjustable such that it can slide laterally toward or away from the pivot element  260 . As in the configuration of  FIG. 9 , the bracket  263  can be adjusted by loosening the clamping screw  264  and sliding the clamping screw  264  and the pin  265  within respective slots  268 ,  269  having slot directions  268   a ,  269   a.    
     With the configuration of  FIG. 10 , the ink pan  290  can be removed by loosening the clamping screw  264  and sliding the bracket  263  away from the pivot element  260 . The distal end of the ink pan  290  can then be lowered using the height adjustment mechanism  297  to move the fountain roller  201  out of contact with the anilox roller  275  as was described relative to the discussion of  FIG. 9 . The ink pan  290  can then be lifted so that the pivot element  260  lifts off the bracket  262 , and the ink pan  290  can then pulled in a rearward direction to remove it from the flexographic printing system  100  (e.g., to be cleaned). 
       FIG. 11  is a flow chart illustrating a method for adjusting the pivotable ink pan  290  of  FIG. 9  to control the extent of contact between the fountain roller  201  and the anilox roller  275 . (Note that this same method could also be used to adjust other types of ink pans such as the ink pan  200  of  FIG. 6 .) 
     First a position ink pan step  400  is used to position the ink pan  290  in an initial position where the fountain roller  201  is out of contact with the anilox roller  275 . If the ink pan  290  has not already been installed into the flexographic printing system  100  ( FIG. 1 ), the position ink pan step  400  can include installing the ink pan  290  and positioning the brackets  263  to constrain the motion of the ink pan  290  to a pivoting motion around the pivot axis  206  as was described earlier. In an exemplary arrangement, the height adjustment mechanism  297  is adjusted to make a coarse adjustment in the position of the ink pan  290 . For example, this can be done by using the pneumatic adjustment mechanism  291  to extend the pistons  292  to a predetermined position. (At the predetermined position, there should still be a gap between the fountain roller  201  and the anilox roller  275 .) In an exemplary arrangement, the adjustment screws  293  are backed off and the pneumatic adjustment mechanisms  291  are set to provide a maximum pressure, thereby fully extending the pistons  292 . 
     Next, the position of the ink pan  290  is adjusted to provide a predetermined gap between the fountain roller  201  and the anilox roller  275 . In an exemplary embodiment, this is accomplished by using shims having a thickness corresponding to the predetermined gap. Note that the “corresponding to” terminology does not necessarily imply that thickness of the shim is exactly the same as the size of the predetermined gap, but rather means that there is a known relationship between the thickness of the shim and the size of predetermined gap. 
     In an insert shim(s) step  405 , an operator inserts one or more shims between the fountain roller  201  and the anilox roller  275  at contact point  281 . In a preferred embodiment, two shims are inserted, one at each end of the fountain roller  201  to provide for a consistent gap along the length of the contact point  281 . In an exemplary arrangement, the shims have a thickness of 0.0075 inches. One skilled in the art will recognize that shims of different thicknesses can also be used in accordance with the method of the present invention. 
     An adjust position of ink pan step  410  is next used to adjust the position of the ink pan  290  to grip the shim(s) between the fountain roller  201  and the anilox roller  275 . In an exemplary arrangement, this is done by turning the adjustment screw  293  to pivot the ink pan  290  about the pivot axis  206  until the shim is gripped between the fountain roller  201  and the anilox roller  275 . In a preferred embodiment where one shim is inserted at each end of the fountain roller, the adjustment screws  293  on each side of the ink pan  290  can be adjusted to grip the corresponding shim. For example, the adjustment screw  293  in the near side (i.e., “operator side”) height adjustment mechanism  297  can be turned until the shim on the near side of the ink tray is gripped, and the adjustment screw  293  in the far side (i.e., “gear side”) height adjustment mechanism  297  can be turned until the shim on the far side of the ink tray is gripped. 
     Once the height adjustment mechanisms  297  have been adjusted to grip the shim(s) between the fountain roller  201  and the anilox roller  275 , a remove shim(s) step  415  is used to remove the shim(s), pulling them out from between the fountain roller  201  and the anilox roller  275 , leaving the fountain roller  201  and the anilox roller  275  positioned with the desired predetermined gap between them. It may be desirable to tighten the lock nuts  296  while the shims are being removed to maintain the ink pan  290  in a fixed position. Once the shims have been removed, the lock nuts  296  are then loosened before the next step is performed. 
     Next, an adjust position of ink pan step  420  is used to adjust the position of the ink pan  290  by a predetermined amount to close the predetermined gap between the fountain roller  201  and the anilox roller  275  and to provide the desired extent of contact between the rollers. Preferably, the position of the ink pan  290  is adjusted by using the height adjustment mechanism  297  to adjust the height of the distal portion of the ink pan  290 , thereby pivoting the ink pan  290  about the pivot axis  206 . In an exemplary arrangement, adjustment screws  293  have a known thread pitch, and the predetermined amount of adjustment is provided by turning the adjustment screws  293  by a predetermined angle in a predetermined direction. In an exemplary configuration, the adjustment screws  293  have a  20  threads/inch thread pitch, and the adjustment screws  293  are turned one complete turn (i.e., 360°) in a counter-clockwise direction, thereby lifting the distal end of the ink tray by 0.050 inches. (The fountain roller  201  is closer to the pivot axis  206  than the adjustment screws  293 , therefore the fountain roller  201  will be lifted by a proportionally smaller amount.) In an exemplary arrangement, the adjustment screws  293  are turned manually using a wrench or a screwdriver. In other arrangements, the adjustment screws  293  can be turned using an automatic mechanism (e.g., a computer-controlled stepper motor). 
     The amount of adjustment in the height of the distal portion of the ink pan  290  that is required to provide the desired extent of contact between the fountain roller  201  and the anilox roller  275  will be coupled to the thickness of the shim(s) used in the insert shim(s) step  405 . It is generally desirable that the amount that the adjustment screws  293  are to be turned in the adjust position of ink pan step  420  be a convenient and controllable amount (e.g., one complete turn or an integer number of turns). In an exemplary embodiment, the thickness of the shim(s) is selected to provide the desired extent of contact between the fountain roller  201  and the anilox roller  275  when the adjustment screws  293  are turned by one complete turn (i.e., by 360°). The thickness of the shim(s) needed to provide the desired extent of contact can be determined using any method known in the art. In an exemplary embodiment, the appropriate thickness of the shim(s) can be determined by using empirical process where a sequence of different shim thicknesses are used and the performance of the flexographic printing system  100  is evaluated for each shim thickness. The shim thickness that produces the best performance (e.g., the cleanest line profiles or the most consistent line widths in printed images) can then be selected for use in the ink pan adjustment process. 
     After the position of the ink pan  290  has been adjusted by the predetermined amount, a lock position of ink pan step  425  is used to lock the position of the ink pan  290  such that the distal portion of the ink pan  290  is maintained at the adjusted height. In an exemplary arrangement, the position of the ink pan  290  is locked into position by tightening the lock nuts  296  on the adjustment screws  293 . In other arrangements, any locking mechanism known in the art (e.g., set screws) can be used to hold the ink pan  290  in a fixed position. 
       FIG. 12  shows a high-level system diagram for an apparatus  300  having a touch screen  310  including a display device  320  and a touch sensor  330  that overlays at least a portion of a viewable area of display device  320 . Touch sensor  330  senses touch and conveys electrical signals (related to capacitance values for example) corresponding to the sensed touch to a controller  380 . Touch sensor  330  is an example of an article that can be printed on one or both sides by the flexographic printing system  100  including print modules that incorporate embodiments of ink recirculation system  250  and ink pans  200  described above. 
       FIG. 13  shows a schematic side view of a touch sensor  330 . Transparent substrate  340 , for example polyethylene terephthalate, has a first conductive pattern  350  printed on a first side  341 , and a second conductive pattern  360  printed on a second side  342 . The length and width of the transparent substrate  340 , which is cut from the take-up roll  104  ( FIG. 1 ), is not larger than the flexographic printing plates  112 ,  122 ,  132 ,  142  of flexographic printing system  100  ( FIG. 1 ), but it could be smaller than the flexographic printing plates  112 ,  122 ,  132 ,  142 . Optionally, the first conductive pattern  350  and the second conductive pattern  360  can be plated using a plating process for improved electrical conductivity after flexographic printing and curing of the patterns. In such cases it is understood that the printed pattern itself may not be conductive, but the printed pattern after plating is electrically conductive. 
       FIG. 14  shows an example of a conductive pattern  350  that can be printed on first side  341  ( FIG. 13 ) of substrate  340  ( FIG. 13 ) using one or more print modules such as print modules  120  and  140  of flexographic printing system ( FIG. 1 ). Conductive pattern  350  includes a grid  352  including grid columns  355  of intersecting fine lines  351  and  353  that are connected to an array of channel pads  354 . Interconnect lines  356  connect the channel pads  354  to the connector pads  358  that are connected to controller  380  ( FIG. 12 ). Conductive pattern  350  can be printed by a single print module  120  in some embodiments. However, because the optimal print conditions for fine lines  351  and  353  (e.g., having line widths on the order of 4 to 8 microns) are typically different than for printing the wider channel pads  354 , connector pads  358  and interconnect lines  356 , it can be advantageous to use one print module  120  for printing the fine lines  351  and  353  and a second print module  140  for printing the wider features. Furthermore, for clean intersections of fine lines  351  and  353 , it can be further advantageous to print and cure one set of fine lines  351  using one print module  120 , and to print and cure the second set of fine lines  353  using a second print module  140 , and to print the wider features using a third print module (not shown in  FIG. 1 ) configured similarly to print modules  120  and  140 . 
       FIG. 15  shows an example of a conductive pattern  360  that can be printed on second side  342  ( FIG. 13 ) of substrate  340  ( FIG. 13 ) using one or more print modules such as print modules  110  and  130  of flexographic printing system ( FIG. 1 ). Conductive pattern  360  includes a grid  362  including grid rows  365  of intersecting fine lines  361  and  363  that are connected to an array of channel pads  364 . Interconnect lines  366  connect the channel pads  364  to the connector pads  368  that are connected to controller  380  ( FIG. 12 ). In some embodiments, conductive pattern  360  can be printed by a single print module  110 . However, because the optimal print conditions for fine lines  361  and  363  (e.g., having line widths on the order of 4 to 8 microns) are typically different than for the wider channel pads  364 , connector pads  368  and interconnect lines  366 , it can be advantageous to use one print module  110  for printing the fine lines  361  and  363  and a second print module  130  for printing the wider features. Furthermore, for clean intersections of fine lines  361  and  363 , it can be further advantageous to print and cure one set of fine lines  361  using one print module  110 , and to print and cure the second set of fine lines  363  using a second print module  130 , and to print the wider features using a third print module (not shown in  FIG. 1 ) configured similarly to print modules  110  and  130 . 
     Alternatively in some embodiments conductive pattern  350  can be printed using one or more print modules configured like print modules  110  and  130 , and conductive pattern  360  can be printed using one or more print modules configured like print modules  120  and  140  of  FIG. 1 . 
     With reference to  FIGS. 12-15 , in operation of touch screen  310 , controller  380  can sequentially electrically drive grid columns  355  via connector pads  358  and can sequentially sense electrical signals on grid rows  365  via connector pads  368 . In other embodiments, the driving and sensing roles of the grid columns  355  and the grid rows  365  can be reversed. 
     The 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 
     
         
           10  impression cylinder 
           12  substrate 
           14  plate cylinder 
           16  printing plate 
           18  anilox roller 
           20  fountain roller device 
           22  fountain roller 
           24  pan 
           26  doctor blade 
           30  reservoir chamber system 
           32  reservoir chamber 
           34  blade 
           38  ink exit 
           39  ink entry 
           46  blade 
           100  flexographic printing system 
           102  supply roll 
           104  take-up roll 
           105  roll-to-roll direction 
           106  roller 
           107  roller 
           110  print module 
           111  plate cylinder 
           112  flexographic printing plate 
           113  raised features 
           114  impression cylinder 
           115  anilox roller 
           116  UV curing station 
           120  print module 
           121  plate cylinder 
           122  flexographic printing plate 
           124  impression cylinder 
           125  anilox roller 
           126  UV curing station 
           130  print module 
           131  plate cylinder 
           132  flexographic printing plate 
           134  impression cylinder 
           135  anilox roller 
           136  UV curing station 
           140  print module 
           141  plate cylinder 
           142  flexographic printing plate 
           144  impression cylinder 
           145  anilox roller 
           146  UV curing station 
           150  substrate 
           151  first side 
           152  second side 
           160  ink pan 
           161  fountain roller 
           162  front wall 
           163  rear wall 
           164  floor 
           165  ink 
           166  pivot axis 
           167  lip 
           168  lowest portion 
           171  plate cylinder 
           172  flexographic printing plate 
           173  raised features 
           174  impression cylinder 
           175  anilox roller 
           176  UV curing station 
           177  imaging system 
           180  doctor blade 
           181  contact point 
           182  contact point 
           183  contact point 
           184  contact point 
           200  ink pan 
           201  fountain roller 
           202  front wall 
           203  rear wall 
           204  floor 
           205  ink 
           206  pivot axis 
           207  lip 
           208  lowest floor portion 
           210  blade holder 
           211  first side wall 
           212  second side wall 
           213  side wall 
           215  opening 
           220  doctor blade 
           230  ink distribution tube 
           232  ink supply port 
           233  pressure manifold 
           234  pressurized line 
           235  replenished ink entry path 
           239  ink drain line 
           240  ink recirculation port 
           241  ink recirculation line 
           242  ink recirculation pump 
           243  control system 
           244  filter 
           245  solvent replenishment chamber 
           246  metering pump 
           247  control system 
           248  valve 
           249  valve 
           250  ink recirculation system 
           251  ink recovery valve 
           252  valve 
           253  ink recovery tank 
           254  mixing device 
           255  density sensor 
           256  ink return line 
           257  solvent replenishment line 
           260  pivot element 
           261   a  upper contact point 
           261   b  first side contact point 
           261   c  lower contact point 
           261   d  second side contact point 
           262  bracket 
           263  bracket 
           264  clamping screw 
           265  pin 
           266  alignment pin 
           267  retaining ring 
           268  slot 
           268   a  slot direction 
           269  slot 
           269   a  slot direction 
           271  plate cylinder 
           272  flexographic printing plate 
           273  raised features 
           274  impression cylinder 
           275  anilox roller 
           276  UV curing station 
           277  imaging system 
           281  contact point 
           282  contact point 
           283  contact point 
           284  contact point 
           290  ink pan 
           291  pneumatic adjustment mechanism 
           292  piston 
           293  adjustment screw 
           294  block 
           295  block 
           296  lock nut 
           297  height adjustment mechanism 
           298  cylinder 
           299  frame 
           300  apparatus 
           310  touch screen 
           320  display device 
           330  touch sensor 
           340  transparent substrate 
           341  first side 
           342  second side 
           350  conductive pattern 
           351  fine lines 
           352  grid 
           353  fine lines 
           354  channel pads 
           355  grid column 
           356  interconnect lines 
           358  connector pads 
           360  conductive pattern 
           361  fine lines 
           362  grid 
           363  fine lines 
           364  channel pads 
           365  grid row 
           366  interconnect lines 
           368  connector pads 
           380  controller 
           400  position ink pan step 
           405  insert shim(s) step 
           410  adjust position of ink pan step 
           415  remove shim(s) step 
           420  adjust position of ink pan step 
           425  lock position of ink pan step 
         F force 
         P pressure 
         W width