Abstract:
A roll for distributing printing liquid in a printing press is provided. The roll includes a roll core having at least a first and a second axial zone, a first liquid feed for feeding liquid to the first axial zone, a second liquid feed for feeding the liquid to the second axial zone independent of the first axial zone and a porous shell covering the first and second axial zones. A printing press, a method for providing printing liquid through a porous shell of a printing liquid supply roll to a cylinder of a printing press, an inking apparatus and a method for providing ink to an anilox roll are also provided.

Description:
The present invention relates generally to printing presses, and more particularly to ink and dampening fluid metering devices for printing presses. 
     BACKGROUND OF THE INVENTION 
     Printing processes, such as the lithographic web offset process, commonly use an arrangement of rollers called an inker to accept ink from an ink metering device and deliver it to a printing plate. A goal of the inker is to supply the plate with a thin, uniform film of ink. An inker may contain as many as twenty rollers to achieve this goal. 
     One reason for the large number of rollers in an inker is that the ink feed from prior art ink metering devices, such as ink fountains, ductors, and metering rolls, is intermittent. Typically the ink is supplied by the ink metering device in the form of stripes or spots spaced about two or more inches apart in the circumferential direction on the first inker roll. An inker contains extra rollers to filter out these spots or stripes so that the plate receives a uniform ink film and the spots or stripes do not appear in the print. 
     To produce a high quality printed product, most ink metering devices allow the feed rate of ink into the inker to be varied laterally across the web or sheet. Typically the metering device is divided into separate lateral zones about one or two inches in width, with the ink feed in each zone being separately controllable. 
     Printing processes, such as the lithographic web offset process, commonly use an arrangement of rollers called a dampener. The goal of the dampener is to deliver a thin, uniform film of dampening fluid to a printing plate. Typical prior art dampeners are of two basic types, generally called spray dampeners and pan-roll dampeners. Spray dampeners typically have the dampening fluid sprayed onto the first dampener rollers. Pan-roll dampeners typically transfer the dampening fluid onto the first dampener rollers from a pan-roller which is partially submerged in a pan containing dampening fluid. 
     To transfer more or less dampening fluid on a localized lateral area of the lithographic printing plate, the typical pan-roll dampeners has only roller-squeeze and roller-skew for coarse adjustments. The typical spray dampener accomplishes lateral control for localized areas by varying the fluid flow rate through laterally spaced spray nozzles. The typical spray dampeners also have over-spray issues and rely on the sprayed fluid to adhere to the dampener rollers. 
     Printing processes, such as the flexographic printing process, commonly use an engraved anilox roller to deliver a quantity of ink from an ink chamber to a flexographic printing plate. The raised image sections of the flexographic printing plate then transfer a portion of the ink delivered by the anilox roll to the substrate being printed. 
     The goal of the anilox roller is to supply the flexographic printing plate a quantity of ink proportional to the volume of the engraved anilox cells. The goal of the flexographic printing plate is to selectively transfer a portion of the ink delivered by the anilox roll to the printing substrate. 
     To transfer more or less ink on a localized lateral area of the substrate being printed, typically the flexographic printing plate is replaced by another flexographic printing plate having a larger or smaller image transfer areas. 
     To transfer more or less ink laterally uniform across the substrate being printed, typically the engraved anilox roller is replaced by another engraved anilox roller having a larger or smaller engraved anilox cell volume. 
     SUMMARY OF THE INVENTION 
     A roll for distributing printing liquid in a printing press is provided. The roll includes a roll core having at least a first and a second axial zone, a first liquid feed for feeding liquid to the first axial zone, a second liquid feed for feeding the liquid to the second axial zone independent of the first axial zone and a porous shell covering the first and second axial zones. 
     A printing press is also provided. The printing press includes a plate cylinder, a printing liquid supply roll and at least one printing liquid pump. The printing liquid supply roll forms a nip with the plate cylinder and includes an interior region and a porous layer surrounding the interior region. The at least one printing liquid pump is adapted to pump printing liquid into the interior region and through the porous layer. The printing liquid supply roll is adapted to transfer the printing liquid to the plate cylinder at the nip. 
     A method for providing printing liquid through a porous shell of a printing liquid supply roll to a cylinder of a printing press is also provided. The method includes the steps of rotating the printing liquid supply roll; supplying the printing liquid into the inside of the printing liquid supply roll; feeding the printing liquid from the inside of the printing liquid supply roll through the porous shell; and transferring the printing liquid from the printing liquid supply roll to the cylinder. 
     An inking apparatus for a printing press is also provided. The inking apparatus includes an anilox roll and at least one ink pump. The anilox roll includes an interior region, a porous layer surrounding the interior region and an outer surface of engraved cells surrounding the porous layer. The at least one ink pump is adapted to pump ink into the interior region and through the porous coating to the outer surface of engraved cells. 
     A method for providing ink to an anilox roll is also provided. The method includes the steps of rotating the anilox roll; filling engraved cells of the anilox roll with ink from outside of the anilox roll; removing any excess ink from the anilox roll with a doctor blade; and providing additional ink to the engraved cells from the inside of the anilox roll. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described below by reference to the following drawings, in which: 
         FIG. 1  shows a schematic perspective view of a porous roll with axial zones according to an embodiment of the present invention; 
         FIG. 2  shows a schematic perspective view of a porous roll with axial zones according to another embodiment of the present invention; 
         FIG. 3   a  shows a schematic view of an axial cross-section of a porous roll according to another embodiment of the present invention; 
         FIG. 3   b  shows a schematic view of a cross section of porous roll shown in  FIG. 3   a;    
         FIG. 3   c  shows the cross section of the porous roll shown in  FIG. 3   b , according to another embodiment of the present invention; 
         FIG. 4   a  shows a schematic view of an axial cross-section of a porous roll according to another embodiment of the present invention; 
         FIG. 4   b  shows a schematic view of a cross section of the porous roll shown in  FIG. 4   a;    
         FIG. 5  shows a highly schematic side view of an inking or dampening apparatus according to an embodiment of the present invention; 
         FIG. 6  shows a schematic cross-sectional side view of a porous roll according to another embodiment of the present invention; 
         FIG. 7  shows a schematic view of an axial cross-section of an inking apparatus according to an embodiment of the present invention, including the porous roll shown in  FIG. 6  and an adjacent roller; and 
         FIG. 8  shows an inking apparatus according to an embodiment of the present invention, having an anilox roll, an ink chamber and a plate cylinder. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic perspective view of a porous roll  10  with axial zones  44 ,  46 ,  48  according to an embodiment of the present invention. Porous roll  10  includes a porous shell  12 , a roll core  14 , seals  16 ,  18 ,  20 , fittings  22 ,  24 ,  26 , a bearing  28 , and interior tubes  30 ,  32 ,  34 . For clarity,  FIG. 1  shows only one axial end of porous roll  10 , and porous shell  12  has been moved axially away from an axial edge  36  to expose roll core  14 , seals  16 ,  18 ,  20 , fittings  22 ,  24 ,  26 , and bearing  28 . Porous roll  10  may be used to distribute ink or dampening fluid in a printing press. 
     Porous shell  12  is supported by an outer race  38  of bearing  28  near edge  36  of roll core  14 . Porous shell  12  may be supported by one or more additional bearings on roll core  14 . Porous shell  12  is free to rotate around a center axis CA 1 . 
     Roll core  14  has an outer surface  40  supporting an inner race  42  of bearing  28  and seals  16 ,  18 ,  20 . Seals  16 ,  18 ,  20  form the axial boundaries of axial zones  44 ,  46 ,  48 . Axial zones  44 ,  46 ,  48  have holes  50 ,  52 ,  54 , respectively, extending from outer surface  40  to an inner radius RI of roll core  14 . Holes  50 ,  52 ,  54  contain fittings  22 ,  24 ,  26  attached to interior tubes  30 ,  32 ,  34 , respectively. Interior tubes  30 ,  32 ,  34  extend through a hole  56  at edge  36  and are coupled to liquid pumps  13 ,  15 ,  17 , respectively. Interior tubes  30 ,  32 ,  34  may act as liquid feeds to axial zones  44 ,  46 ,  48 . The liquid may be conveyed in interior tubes  30 ,  32 ,  34  or roll core  14  may be solid and liquid may be conveyed in channels machined directly into roll core  14 , for example as channels  116 ,  118 ,  120  of  FIG. 2 . 
     During operation of porous roll  10 , liquid is pumped at controlled liquid flow rates Q 1 , Q 2 , Q 3  through respective interior tubes  30 ,  32 ,  34  and into respective axial zones  44 ,  46 ,  48 . In each axial zone  44 ,  46 ,  48 , the liquid may fill respective interior regions  58 ,  60 ,  62  between an outer radius R 2  of roll core  14 , and an inner radius R 3  of porous shell  12 . Seals  16 ,  18 ,  20  prevent liquid from flowing axially between axial zones  44 ,  46 ,  48 . Liquid flows radially from interior regions  58 ,  60 ,  62  through porous shell  12  to an outer surface  64  of porous shell  12  at an outer radius R 4 . Liquid transfers from outer surface  64  to an adjacent inker roll or dampener roll, at a region of contact, or contacting nip, formed between outer surface  64  and the adjacent roll. 
     By constructing porous roll  10  with porous shell  12 , liquid transfer from porous roll  10  to an adjacent roll is quasi-continuous. Porous roll  10  can advantageously improve the uniformity of liquid supplied to the printing plate and allows the number of rollers in an inker or dampener to be reduced. 
     Liquid delivered by porous roll  10  into an inker or dampener is pre-metered by liquid pumps  13 ,  15 ,  17  coupled to respective interior tubes  30 ,  32 ,  34 . At steady state operation, a flowrate of liquid out of outer surface  64  and to an adjacent roll in axial zones  44 ,  46 ,  48  is equal to liquid flowrates Q 1 , Q 2 , Q 3 , respectively. Porous roll  10  thus advantageously can reduce or eliminate the intermittent liquid feed. 
     While  FIG. 1  shows only three axial zones  44 ,  46 ,  48 , porous roll  10  may contain as many zones as needed for the desired print quality. As more axial zones are added, additional liquid pumps, interior tubes, seals, and fittings are added accordingly. Additional interior tubes or channels may also enter through the opposite axial end of roll core  14 . Porous shell  12  may be of composite construction, or may alternately be comprised of multiple cylindrical elements. 
     In the embodiment in  FIG. 1 , porous shell  12  is free to rotate around center axis CA 1  while roll core  14  does not rotate around center axis CA 1 . In another embodiment, shown in  FIG. 2 , a porous shell  82  and a roll core  84  are both free to rotate together around a center axis CA 2 . 
       FIG. 2  shows a schematic perspective view of a porous roll  80  with axial zones  104 ,  106 ,  108  according to another embodiment of the present invention. Porous roll  80  includes porous shell  82 , roll core  84 , seals  86 ,  88 ,  90 , a bearing  92 , a bearing hanger  94 , and a rotary union  96 . For clarity,  FIG. 2  shows only one axial end of porous roll  80 , and porous shell  82  has been moved axially away from an axial edge  98  to expose roll core  84  and seals  86 ,  88 ,  90 . 
     Roll core  84  has an outer surface  100  supporting an inner race  102  of bearing  92  and seals  86 ,  88 ,  90 . Seals  86 ,  88 ,  90  form the axial boundaries of axial zones  104 ,  106 ,  108 . An outer race  110  of bearing  92  is supported by bearing hanger  94 . 
     Porous shell  82 , roll core  84 , seals  86 ,  88 ,  90 , inner race  102  of bearing  92 , and an inner race  112  of rotary union  96  are free to rotate about a center axis CA 2 . Outer race  110  of bearing  92 , an outer race  114  of rotary union  96 , and bearing hanger  94  are not free to rotate about center axis CA 2 . 
     Roll core  84  has channels  116 ,  118 ,  120  extending in the axial direction from axial edge  98  to axial zones  104 ,  106 ,  108 . Channels  116 ,  118 ,  120  act as liquid feeds for respective axial zones  104 ,  106 ,  108  and are machined into roll core  84 . Roll core  84  also has holes  122 ,  124 ,  126  extending in the radial direction to connect outer surface  100  with respective channels  116 ,  118 ,  120 . 
     Rotary union  96  allows liquid to be pumped from a non-rotating liquid pump into channels  116 ,  118 ,  120  of roll core  84  as roll core  84  is rotating about center axis CA 2 . For illustration purposes, rotary union  96  is shown detached from roll core  84  in  FIG. 2 . One or more liquid pumps are coupled to holes  128 ,  130 ,  132  in outer race  114  of rotary union  96  and supply liquid to holes  128 ,  130 ,  132 . Holes  128 ,  130 ,  132  extend in the radial direction from an outer surface  134  of rotary union  96  to annular channels  136 ,  138 ,  140  between inner race  112  and outer race  114 . Holes  142 ,  144 ,  146  extend in the radial direction from annular channels  136 ,  138 ,  140  to a radial location of radius R 6 . Also at the radial location of radius R 6 , holes  148 ,  150 ,  152  extend in the axial direction from holes  142 ,  144 ,  146  to an axial edge  154 . By aligning holes  148 ,  150 ,  152  with channels  116 ,  118 ,  120  and attaching rotary union  96  to roll core  84 , liquid may be pumped from the one or more liquid pumps, through rotary union  96 , and out of holes  122 ,  124 ,  126  in roll core  84 . 
     During operation of porous roll  80 , liquid is pumped at controlled liquid flowrates Q 4 , Q 5 , Q 6  through holes  122 ,  124 ,  126  and into axial zones  104 ,  106 ,  108 . In each axial zone, the liquid may fill regions  156 ,  158 ,  160  between an outer radius R 7  of roll core  84 , and an inner radius R 8  of porous shell  82 . Seals  86 ,  88 ,  90  prevent liquid from flowing axially between axial zones  104 ,  106 ,  108 . Liquid flows radially from regions  156 ,  158 ,  160  through porous shell  82  to an outer surface  162  of porous shell  82  at an outer radius R 9 . Liquid transfers from outer surface  162  to an adjacent inker roll or dampener roll at a region of contact, or contacting nip, formed between outer surface  162  and the adjacent roll. 
     By constructing porous roll  80  with porous shell  82 , liquid transfer from porous roll  80  to the adjacent roll is quasi-continuous. Porous roll  80  may advantageously improve the uniformity of liquid supplied to the printing plate and may allow the number of rollers in an inker or dampener to be reduced. 
     Liquid delivered by porous roll  80  into an inker or dampener is pre-metered by the one or more liquid pumps connected to holes  128 ,  130 ,  132 . At steady state operation, a flowrate of liquid out of outer surface  162  and to the adjacent roll in axial zones  104 ,  106 ,  108  is equal to liquid flowrates Q 4 , Q 5 , Q 6 , respectively. Porous roll  80  thus advantageously can reduce or eliminate the intermittent liquid feed. 
     While  FIG. 2  shows only three axial zones  104 ,  106 ,  108 , porous roll  80  may contain as many zones as needed for the desired print quality. As more zones are added, additional liquid pumps, channels, seals, and fittings are added accordingly. Additional channels may also enter through the opposite axial end of roll core  84 . 
       FIG. 3   a  shows a schematic view of an axial cross-section of a porous roll  170  according to another embodiment of the present invention. Porous roll  170  is similar to porous roll  10  shown in  FIG. 1  and includes roll core  14  and porous shell  12 . Similar to porous roll  10  shown in  FIG. 1 , in porous roll  170 , liquid may be fed to a plurality of axial zones of porous roll  170  via interior tubes.  FIG. 3   a  shows a cross section of a single axial zone being fed liquid by an interior tube  172  to a hole  182  in roll core  14 . Interior tube  172  transports liquid from an axial direction and then radially towards hole  182 . Interior tube  172  may be similar to interior tube  32  ( FIG. 1 ), and hole  182  may be similar to hole  52  ( FIG. 1 ). In an alternative embodiment, roll core  14  may be solid and interior tube  172  may be a channel machined into roll  14 . The view in  FIG. 3   a  splits down a center of hole  182 . Porous roll  170  includes a distribution ring  801  between a liquid flow region  89  and porous shell  12 . Liquid flow region  89  is defined by an inner surface  101  of distribution ring  801  and an outer surface  100  of role core  14  and allows liquid to flow circumferentially around outer surface  100  of role core  14 . 
     Flow into distribution ring  801  may be regulated by one or more pressure relief or check valves  803 . Pressure relief valves  803  require liquid to exceed a pre-determined pressure value before the valves  803  will open. By proper selection of this value, liquid can be fully distributed axially and circumferentially in the axial zone before the one of more valves  803  open. Multiple valves  803  may be employed ( FIG. 3   b ) to adequately distribute the liquid. Liquid passing through valves  803  enters an inner channel  811  through a passage  810 . Inner channel  811  may be configured to allow liquid to flow in circumferential and axial directions with respect to a center axis of porous roll  170 . Liquid may then travel through flow distribution tubes  812 ,  813 , which may alternate about the center axis of porous roll  170  to distribute liquid to from inner channel  811  to respective surface channels  814 , which run parallel to the center axis of porous roll  170  and provide ink to porous shell  12 . Liquid may then be transferred through outer surface  64  to an adjacent roll. Distribution tubes  812 ,  813  may alternate at constant angle around roll  170 , meaning surface channels  814  are fed from alternating axial directions. The number of pressure relief valves  803  and the number of surface channels  814  need not be equal. 
       FIG. 3   b  shows a schematic view of a cross section of porous roll  170  along AA of  FIG. 3   a.  The outer wall of roll core  14  and the inner wall of liquid distribution ring  801  are attached to two sealing elements  116 ,  118  which prevent liquid from flowing between liquid flow region  89  and liquid flow regions of adjacent axial zones. Once liquid in liquid flow region  89  exceeds a pre-determined pressure value and pressure relief valve  803  has opened, liquid flows through passage  810  into inner channel  811 , distributing laterally and circumferentially. Once liquid arrives at the extreme lateral extents of inner channel  811 , liquid flows into distribution tubes  812 ,  813 . Distribution tube  813  is shown dotted because it is not part of the cross section of  FIG. 3   a ; distribution tube  813  is shown to indicate liquid can feed in either direction. Liquid then flows into surface channel  814 , from which it enters porous shell  12 . 
       FIG. 3   c  shows the cross section of porous roll  170  shown in  FIG. 3   b , according to another embodiment of the present invention. In this embodiment, distribution ring  801  may not include pressure relief valve  803  and distribution tube  812  takes a diagonal path  512  between inner channel  811  and surface channel  814 . Distribution tube  812  extends diagonally from inner channel  811  away from porous shell  12  before following a path to surface channel  814 . For the embodiment shown in  FIG. 3   b , without pressure relief valves  803 , liquid may tend to drain out of inner channel  811  under the action of centrifugal forces caused by rotation of porous roll  170 . Diagonal path  512  may prevent liquid channel  811  from flowing to porous shell  12  solely because of centrifugal forces caused by rotation because liquid has to flow radially inward, against the centrifugal forces, prior to moving from distribution tubes  812 ,  813  into surface channels  814 . In this embodiment, in order for liquid to pass into surface channels  814 , a positive pressure may need to be supplied from a liquid pump coupled to interior tube  172  ( FIG. 3   a ) to force the liquid down diagonal path  512  and out to porous shell  12 . 
       FIG. 4   a  shows a schematic view of an axial cross-section of a porous roll  180  according to another embodiment of the present invention. Porous roll  180  is similar to porous roll  10  shown in  FIG. 1  and includes roll core  14  and porous shell  12 . Interior tube  172  transports liquid from an axial direction and then radially towards hole  182  and through roll core  14  into liquid flow region  89 . In this embodiment, check valves  903 , which regulate liquid flow in a distribution ring  901 , may be arranged axially with respect to a center axis of porous roll  180 . When liquid in liquid flow region  89  exceeds a pre-determined pressure value, liquid may flow through check valves  903  and passages  910  directly into distribution tubes  912 ,  913 . Distribution tubes  912 ,  913  may alternate about the center axis of porous roll  180  to distribute liquid to respective surface channels  914 , which run parallel to the center axis of porous roll  180  and deliver liquid to porous shell  12 . Ink may then be transferred through outer surface  64  to an adjacent plate cylinder. Distribution tubes  912 ,  913  may alternate at constant angle around the roll, meaning surface channels  914  are fed from alternating axial directions. In this embodiment, one check valve  903  may be provided for each surface channel  914 . 
       FIG. 4   b  shows a schematic view of a cross section of porous roll  180  along BB of  FIG. 4   a . Outer surface  100  of roll core  14  and inner surface  201  of liquid distribution ring  901  are attached to two sealing elements  116 ,  118  which prevent liquid from flowing between liquid flow region  89  and adjacent liquid flow regions. Once liquid in liquid flow region  89  exceeds a pre-determined pressure value and axially oriented pressure relief valve  903  has opened, liquid flows through passage  910  into feeds  912 ,  913 . Distribution tube  913  is shown dotted because it is not part of the cross section of  FIG. 3   a ; distribution tube  193  is shown to indicate that check valves  903  can be arranged in different axial positions and liquid can feed in either direction. Liquid then flows into surface channel  914 , from which it enters porous shell  12 . 
       FIG. 5  shows a highly schematic side view of an inking or dampening apparatus  400  according to an embodiment of the present invention. Apparatus  400  includes a gear side section  450  and a working side section  452 . For illustrative purposes, sections  450 ,  452  are shown divided by a dotted line  510 . Each section  450 ,  452  includes a rotary union  404 , a coupling  406  and a roll section  428 . Roll sections  428  may include a plurality of axial zones  408 . Liquid is fed to axial zones  408  via interior tubes  172  and holes  182 . Roll sections  428  may include roll core  14  and porous shell  12 , which are shown in  FIGS. 1 ,  3   a ,  4   a , for example, and may include one or more components that aid in distributing liquid between roll core  14  and porous shell  12 , such as one or more components of distribution ring  801  shown in  FIGS. 3   a  to  3   c  or one or more components of distribution ring  901  shown in  FIGS. 4   a ,  4   b.    
       FIG. 6  shows a schematic cross-sectional side view of a porous roll  210  according to another embodiment of the present invention. Porous roll  210  includes a porous shell  212 , a roll core  214 , seals  216 ,  218 ,  220 , bearings  222 ,  224 , and channels  226 ,  228 . For clarity,  FIG. 1  shows only two axial zones  240 ,  242  of porous roll  210 , and porous shell  212  has been sectioned away to expose roll core  214 , seals  216 ,  218 ,  220 , and bearings  222 ,  224 . 
     Porous shell  212  is supported by the outer race of bearings  222 ,  224  at the edges of roll core  214 . Porous shell  212  may be supported by one or more additional bearings on roll core  214 . Porous shell  212  is free to rotate around a center axis CA 3 . 
     Roll core  214  has an outer surface supporting the inner race of bearings  222 ,  224  and seals  216 ,  218 ,  220 . Seals  216 ,  218 ,  220  form the axial boundaries of zones  230 ,  232 . Zone  242  has a channel  228  internal to roll core  214 , extending from outer surface of roll core  214 , under bearing  224  and under seal  220 , to the outer surface of roll core  214 , out-board of bearing  224 , delivering liquid to an interior region  232 . Similarly, zone  240  has a channel  226  internal to roll core  214 , extending from outer surface of roll core  214 , under bearing  224  and under seals  218 ,  220  to the outer surface of roll core  214 , out-board of bearing  224 , delivering liquid to an interior region  230 . Channels  226 ,  228  extend through roll core  214 , out-board of bearing  224  and are coupled to liquid feed pumps  160 ,  162 . Channels  226 ,  228  act as liquid feeds to axial zones  240 ,  242  respectively. 
     During operation of porous roll  210 , liquid is pumped at controlled flowrates Q 7 , Q 8  through channels  226 ,  228  and into regions  230 ,  232 . In each zone  240 ,  242 , the liquid may fill interior regions  230 ,  232  between an outer radius R 10  of roll core  214 , and an inner radius R 11  of porous shell  212 . Seal  218  prevents liquid from flowing axially between zones  240 ,  242 . Seals  216 ,  220  prevent ink from flowing axially outward from zones  240 ,  242 . Liquid essentially flows radially from regions  230 ,  232  through porous shell  212  to an outer surface  234  of porous shell  212  at an outer radius R 12 . Liquid transfers from outer surface  234  to an adjacent roller at a region of contact, or nip, formed between outer surface  234  and the adjacent roller. 
     By constructing porous roll  210  with porous shell  212 , liquid transfer from porous roll  210  to an adjacent roller is quasi-continuous. Porous roll  210  can advantageously improve the uniformity of liquid supplied to the printing plate and allows the number of rollers to be reduced. 
     Liquid delivered by porous roll  210  is pre-metered by the liquid feed pumps  160 ,  162  coupled to channels  226 ,  228 . At steady state operation, a flowrate of liquid out of outer surface  234  and to an adjacent roll in ink zones  240 ,  242  is equal to ink flowrates Q 7 , Q 8 , respectively. Porous roll  10  thus advantageously can reduce or eliminate intermittent ink feed. 
     While  FIG. 6  shows only two zones  240 ,  242 , porous roll  210  may contain as many zones as needed for the desired print quality. As more zones are added, additional liquid pumps, channels, and seals are added accordingly. Additional channels may also enter through the opposite axial end of roll core  214 . 
       FIG. 7  shows a schematic side view of axial cross-section of an inking apparatus  200  according to an embodiment of the present invention, having an adjacent roller  236  and porous roll  210  shown in  FIG. 6 . The axial cross-section of porous roll  210  shown in  FIG. 7  is in axial zone  240 . Adjacent roller  236  and porous shell  12  rotate about center axes CA 4  and CA 3 , respectively, at a velocity V 1 . 
     During operation of porous roll  210 , liquid is pumped through channel  226  and into region  230 . In each zone, the liquid may fill region  230  between roll core  214 , and porous shell  212 . Liquid flows radially from region  230  through porous shell  212  to an outer surface  234  of porous shell  212 . Liquid transfers from outer surface  234  to an adjacent roller at a region of contact, or nip, formed between outer surface  234  and the adjacent roller  236 . Region  230  between the roll core  214  and the porous shell  212  may contain one or more components to aid in liquid distribution such as a secondary porous material, a material with channels, a void region, check valves, or any combination thereof. These one or more components may include, for example, one or more components of distribution ring  801  shown in  FIGS. 3   a  to  3   c  or one or more components of distribution ring  901  shown in  FIGS. 4   a ,  4   b.    
       FIG. 8  shows an inking apparatus  300  according to an embodiment of the present invention, having an anilox roll  310 , an ink chamber  306  and a plate cylinder  308 . Anilox roll  310  includes a roll core  314 , an interior region  332 , a porous layer  312  and an outer surface  304  of engraved cells. The engraved cells preferably have a cell wall thickness of less than or equal to 10 microns. Anilox roll  310  and plate cylinder  308  rotate about center axes CA 5 , CA 6 , respectively, at a velocity V 2 . As outer surface  304  passes under ink chamber  306 , ink chamber  306  fills cells with ink and removes excess ink with a doctor blade. As outer surface  304  travels from ink chamber  306  to a nip  330  formed between anilox roll  310  and plate cylinder  308 , additional ink may be supplied to outer surface  304  by pumping ink supplied to interior region  332  by a channel  326  through porous layer  312 . Ink is transferred from outer surface  304  to plate cylinder  308  in nip  330 . Plate cylinder  308  may be flexographic, for example. 
     In one preferred embodiment, anilox roll  310  is similar to porous roll  210  shown in  FIGS. 6 and 7 , except that anilox roll  310  includes outer surface  304 . Thus, in this one preferred embodiment, roll core  314  is similar to roll core  214 , interior region  332  is similar to interior region  230  and porous layer  312  is similar to porous shell  212 . Anilox roll  302  may include a plurality of axial zones separated by seals and one or more ink pumps may pump ink into the axial zones. 
     Interior region  332  between the roll core  314  and the porous layer  312  may contain one or more components to aid in liquid distribution such as a secondary porous material, a material with channels, a void region, check valves, or any combination thereof. These one or more components may include, for example, one or more components of distribution ring  801  shown in  FIGS. 3   a  to  3   c  or one or more components of distribution ring  901  shown in  FIGS. 4   a ,  4   b.    
     Porous shells  12 ,  82 ,  212  and porous layer  312  may be constructed of a matrix material, for example, a sintered plastic, metal or ceramic material, or may alternatively be constructed by machining pores into an originally solid shell. 
     In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.