Abstract:
A machine can deposit a film on a roll that will be used as a rotogravure printing medium. The machine has a carriage for rotatably holding the roll. Also included is a rotary driver for rotating the roll, and a linear driver for moving the carriage downstream along a processing path in order to move the roll axially. The machine also has a coating head with an orifice that is in communication with a source of composition for dispensing the composition onto the roll helically as a merging series of adjacent, self-leveling strip or bead portions. The carriage can be moved to one or more curing stations where the composition film will be (a) initially cured with a UV energy source at a primary energy flux density, and (b) secondarily cured with a UV energy source at a secondary energy flux density that is greater than the primary energy flux density.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a machine and method for making a rotogravure printing medium and more particularly, to applying a plastic printing medium to a printing roll or other workpiece, which is employed in rotogravure printing.  
           [0003]    2. Description of Related Art  
           [0004]    Rotogravure printing is a generally conventional method of printing on a sheet, web, or other substrate. The substrate may be a coated, uncoated, or metallized paper; glassine; plastic films and sheets made from vinyl, cellulose, acetate, polyester and polyethylene; plastic shrink films; paperboard; aluminum foil; fabrics; and similar materials. Rotogravure printing is capable of reproducing both subtle shades of color and black and white, and is particularly well suited for printing great numbers of copies precisely and rapidly. Typical end products for the printed substrates include labels, cartons, paper and plastic cups, trading stamps, wrapping paper, and sheet vinyl flooring.  
           [0005]    Rotogravure printing is the only commercial printing process which can control both ink thickness and the area of ink coverage. This is achieved by etching or engraving recessed microscopic wells, frequently referred to as “cells,” of varying depth and area in a printing medium or image carrier surface. In controlling the size and depth of the cells, the amount of ink available for placement on the substrate is controlled to generate an image composed of an arrangement of large and small dots. Other types of printing, such as flexographic printing, are generally similar to rotogravure printing, but are specifically different, e.g., as to thickness of the printing medium and the character and formation of ink-transferring surfaces.  
           [0006]    In typical rotogravure printing, the printing medium or image carrier is a copper film electro-deposited from a chemical bath on a specially prepared steel roll or cylinder. U.S. Pat. Nos. 5,694,852 and 6,136,375 and pending U.S. patent application Ser. No. 09/678,470 (filed Oct. 3, 2000), which are incorporated herein by reference, describe coating a surface by any method including helically depositing a beads or strip of curable plastic material onto a printing roll or cylinder. This coating, upon application, preferably has a thickness of from about 0.003″ to about 0.015″, preferably from about 0.0032″ to about 0.0040″. Where the printing substrate is to be used for other types of printing, such as flexographic printing, thickness up to about 0.040″ or more. This method is capable of effecting the deposit of a uniform, continuous and engraveable or etchable film onto a printing roll or cylinder.  
           [0007]    While satisfactory as far as they go, the above patents do not disclose apparatus and method that would be tailored for efficient manufacturing, by taking into account production line workflow, and efficient setup techniques.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the illustrative embodiments demonstrating features and advantages of the present invention, there is provided a machine for depositing a film on a roll that can be used as a rotogravure printing medium. The machine has a carriage for rotatably holding the roll. Also included is a rotary driver for rotating the roll, and a linear driver for moving the carriage downstream along a processing path in order to move said roll. The machine also has a coating head having an orifice in communication with a source of composition for dispensing the composition onto the roll as a merging series of adjacent, self-leveling strip or bead portions.  
           [0009]    In accordance with another aspect of the invention a machine is provided for depositing a film on a member that can be used as a rotogravure printing medium. The machine has a carriage for holding the member, and a coating head for dispensing a composition onto the member. Also included is a curing means for (a) initially curing the composition film with an energy source at a primary energy flux density, and (b) secondarily curing the composition film with an energy source at a secondary energy flux density that is greater than the primary energy flux density. The carriage being translatable from the coating head toward the curing means.  
           [0010]    In accordance with yet another aspect of the invention a method is provided for making a rotogravure printing medium which includes a member with a film coating that is selectively alterable to produce ink-retaining cells. The method includes the step of depositing on the surface of the member a composition film of irreversibly curable plastic composition which is engraveable after curing to produce ink-retaining cells. Another step is initially curing the composition film with an energy source at a primary energy flux density. The method also includes the step of secondarily curing the composition film with an energy source at a secondary energy flux density that is greater than the primary energy flux density.  
           [0011]    In accordance with still yet another aspect of the invention a method employs a coating head for dispensing a composition on a roll in order to make a rotogravure printing medium which includes a film coating that is selectively alterable to produce ink-retaining cells. The method includes the step of positioning the roll at the coating head in order to dispense the composition onto the roll with the coating head. Another step is rotating the roll about its axis while translating the roll axially past the coating head. The method also includes the step of helically dispensing the composition onto the roll as a merging series of adjacent, self-leveling strip or bead portions. The adjacent strip or bead portions can merge and self-level at and after deposition to produce a uniform, continuous coating of the plastic composition.  
           [0012]    By employing apparatus and methods of the foregoing type an improved production version machine can be used to efficiently produce a thin polymeric coating preferably on a cylindrical roll that can be processed and utilized, after engraving, as a rotogravure image carrier. The improvements provide the following benefits: Preferably, a continuous process can be achieved that allows for loading and unloading of finished rolls, while the machine is kept in operation. One can accommodate rolls of variable length and variable diameters. The preferred machine and method allows a coating head with an elliptical orifice to remain stationary while the roll or part moves past it. The preferred coating head can provide a continuous flow of a polymer liquid. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The above brief description as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a side elevational view of a machine implementing a method in accordance with principles of the present invention;  
         [0015]    [0015]FIG. 2 is a plan view of the machine of FIG. 1;  
         [0016]    [0016]FIG. 3 is a side elevational view of a portion of the machine of FIG. 1;  
         [0017]    [0017]FIG. 4 is a plan view of the machine portion of FIG. 3;  
         [0018]    [0018]FIG. 5 is a sectional view taken along line A-A of FIG. 1;  
         [0019]    [0019]FIG. 6 is a diagram showing components of the machine of FIG. 1 together with this schematic diagram of controllers for regulating the operational speed of various machine components;  
         [0020]    [0020]FIG. 7 is an elevational view of the coating head of FIG. 1, showing a displaced position of the head in phantom;  
         [0021]    [0021]FIG. 8 is a diagram of a portion of the coating head of FIG. 7 showing its pitching motion;  
         [0022]    [0022]FIG. 9 is a front view of the coating head of FIG. 7;  
         [0023]    [0023]FIG. 10 is an exploded view of the coating head of FIG. 9; and  
         [0024]    [0024]FIG. 11 is an axial, sectional view of a modified version of the coating head of FIG. 7.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    The machine is generally arranged as shown in FIGS. 1 and 2, which are respectively, a side elevation and plan view of the entire machine. The machine base  1  is supported from the floor at table level and consists of a heavy weldment consisting of two square tie-bars with end-plates. The length of the machine can be varied, however, about 12 feet is considered satisfactory.  
         [0026]    The roll  2 , is supported on a carriage  3 , the design of which will be described hereinafter. The carriage assembly  3  containing the roll  2  is placed on the machine at the left-hand end (this view) and is caused to move to the right (downstream) and also caused to rotate in precise relationship to the rightward linear movement. The means to drive the roller in rotation, and also linearly in precise relationship will be described hereinafter.  
         [0027]    As the roll  2  moves to the right from the left-hand side, it first enters a cleaning station  4 , which consists of a source of ionized air (e.g., Chapman Static Eliminator model I-VSE 5000) followed by a vacuum cleaner nozzle  5  located at the top of the rotating roll. The ionized air flow causes any loose dust or dirt to be loosened from the roll surface by eliminating a static charge and the vacuum removes the loosened particles.  
         [0028]    The roll  3 , as it is vacuum cleaned, is also subjected to a heating system  6 , consisting of a bar  6  with electric heaters, which is closely spaced to the surface of the roll  2  as it rotates to heat it by radiant and convective means. The heater bar  6  may have a V-shaped valley facing roll  2  to provide for more intimate heat transfer. Heater bar  6  is supported on adjustment struts  6 A that allow adjustment of the spacing between roll  2  and bar  6 . Struts  6 A accommodate variations in the size of roll  2 .  
         [0029]    Heater  6  is sufficiently long to straddle coating head  8  and extend upstream (to the left) enough to heat the roll  2  to a temperature of a desired level, preferably in the range 100°-150° F. prior to reaching the coating head  8  (head described in further detail hereinafter). Also heater bar  6  has a length extending downstream (to the right) beyond coating head  8  to maintain this temperature for a period following the application of the coating by head  8 .  
         [0030]    Since the polymeric coating material is in the viscosity range of approximately 800 to 5,000 cP, the heat applied to the roller helps the material to “level out” on the roll surface immediately following its application. The level of heat can be thermostatically controlled via an optical or infrared sensor  7  that reads the roll surface temperature immediately prior to application of the coating. (Temperature control can be effected by, for example, an REX-D type controller from RKC Instrument Inc.) The properties of a suitable polymeric material is described in U.S. Pat. Nos. 5,694,852 and 6,136,375 and pending U.S. patent application Ser. No. 09/678,470 (filed Oct. 3, 2000) and as further refined hereinafter. Also coating head  8  has an elliptically shaped orifice similar to that described in that Patent.  
         [0031]    In the present case the orifice, is mounted on a stationary structure, with adjustments in two directions to bring it in proximity to the surface of roll  2 , as will be further described later. A polymer coating in liquid form is pumped through the orifice by a system to be described hereinafter, and is applied to the rotating surface of the roll  2  which generates a helical pattern noted as bead or strip  9  (pitch angle exaggerated). The flow of the material can be interrupted and re-started at the beginning and end of each roll by stopping the pump (pump shown hereinafter).  
         [0032]    As the plastic composition is being applied to the roll  2 , drum  12  is rotated at a rate of from about 30 rpm to about 90 rpm, preferably at about 45 rpm. Preferably, the drum  12  has a surface velocity of from about 5.0 inches per second to about 35.0 inches per second, more preferably from about 7.5 inches per second to about 16.0 inches per second.  
         [0033]    As the roll  2  continues to turn and translate in a downstream (left-to-right) direction, after a short distance the roll  2  enters a primary curing station  10 , which consists of a variable-level UV lamp. This lamp is generally of a wattage level between 10 and 200W, which causes the coating to partially “set” or cure. The reason for the low-level, primary energy flux density is to cause the material to solidify gradually so as not to craze the surface or produce an “orange peel” appearance, which is a common phenomenon when curing thick coatings. A higher intensity UV lamp would immediately harden the surface of the curable material to form a shell above a fluid layer. Thereafter, the underlying fluid layer would rapidly cure and collapse at non-uniform rates to cause dimpling or crazing that produces the orange-peel effect. The length of UV lamp  10  is sufficiently long to maintain the low-level UV cure such that the polymer coating is exposed to the lamp for a period of 20 to 80 minutes as roll  2  processes downstream.  
         [0034]    Following the primary UV cure station  10  the roll  2  then moves to a secondary UV cure station  11 . In this station the linear drive from left to right may be disengaged and only the rotative drive is applied to the roll. The entire carriage remains stationary. The secondary UV cure station  11  consists of a high intensity UV curing lamp of approximately 200 to 600 watts per inch. This lamp is energized for a period of approximately 2 to 5 minutes and at a rotational speed of approximately ½ to 1 revolution per second which imparts enough secondary UV energy flux density to the coating to produce cross-linking of the polymer molecules.  
         [0035]    Since the secondary UV cure station performs its function while the roll  2  is in a rotational pattern, this process could also be done off-line in a separate fixture that provides the rotational speed to the roll while the lamp is energized.  
         [0036]    Finally, the process also involves a final post-cure operation, which consists of heating the entire roll coating in a furnace at approximately 300° to 400° F. for a period of 1 to 3 hours. This allows for the final cross-linking to produce a very hard durable surface.  
         [0037]    In summary, this new apparatus is efficient in continuous production as it allows for multiple functions to be performed simultaneously, i.e. roll preparation and mounting on the carriage of a new roll, de-ionizing and vacuum cleaning, preheating, coating application, primary cure and final cure, all simultaneously without interruption to the flow of the machine. While continuous production line processing is preferred, in some embodiments the process may be broken up into discrete stages, where a roll is carried on a cart to conduct a successive stage. Such separation may be desirable for the secondary cure stage where high intensity UV may inadvertently and prematurely reach a roll before the coating or primary curing stage is completed. (The primary curing station and the subsequent secondary stage will nevertheless still operate together as a curing means.) The process will preferably be conducted in a clean room environment with clear plastic drapes surrounding a region of positive pressure.  
         [0038]    Design Details  
         [0039]    [0039]FIGS. 3, 4 and  5  show respectively a side elevation, plan view and end view of the carriage and drive assembly. Referring to these figures a rotary driver is shown therein as a precision machined drum  12  running the length of the machine and driven by an electric motor  14  and timing belt drive  13 . Drum  12  is machined accurately on its journals and has a smooth surface on the outside diameter. The carriage  3  is partially supported on the drum  12  and is also driven in a rotational manner from the drum  12  by a series of bearers  15  and  16 . Note that there are a set of bearers  15  and  16  located at each end of the roll  2 . The bearers convey the rotative motion to a roll  2  as follows:  
         [0040]    Each bearer  15  and  16  comprises a steel bearer wheel with a smooth OD. A bearer  16  is mounted to each end of the roll and is located by shaft  17 . A pair of bearers  15  are separately mounted at each end of the carriage frames  23  and  23 ′ and are free turning on ball bearings and are held in contact with bearer  16  because of the weight of the roll  2  and shaft assembly (shaft  17  and associated structure). The precise positioning of the roll  2  and shaft structure  17  while it is driven is described hereinafter.  
         [0041]    Also mounted to shaft  17  is a sheave type wheel  22  coaxially located adjacent to bearer  15  on each end of the shaft  17 . This sheave  22  contains a ball bearing so it does not have to rotate with shaft  17 . When loading the shaft assembly  17 ′ (shorthand notation for shaft  17 , roll  2 , bearers  16 , and sheaves  22 ) vertically downward into slots provided in the carriage frames  23  and  23 ′, sheave  22  engages gibs  21  and  21 ′ located on each side of the slot for each end of the assembly.  
         [0042]    Gibs  21  and  21 ′ are pairs of plates with tapered vertical edges facing each other and designed to slide into the annular groove on the periphery of sheave  22 . (Hereinafter gib  21  shall be deemed to refer to gib  21 ′ as well, unless the context indicates otherwise.) The function of the gibs  21  and sheave  22  is to provide precise horizontal positioning of roll  2  and shaft  17  without confining it in the vertical direction (when viewing FIG. 5).  
         [0043]    The vertical positioning of the roll  2  and shaft assembly  17 ′ is determined by the contact of the bearers  16  against bearers  15 , which is rotatably mounted to the carriage side-frames  23  and  23 ′ as best viewed in FIG. 5 (Frames  23  and  23 ′ are also referred to herein as end supports).  
         [0044]    Finally, contact between end-bearers  15  and drum  12  is caused by the weight of the roll  2  and shaft assembly  17 ′ on bearer  15  so that, in turn, the entire mass is then pressed against drum  12 , which ultimately determines the vertical positioning of shaft  17 .  
         [0045]    The horizontal positioning of the carriage assembly  3  is determined as follows: Referring to FIG. 5, the front (right side in this view) of each carriage frame  23  (and frame  23 ′) is supported on a beam  18  and linear ball bushing structure  19  (e.g., Thompson type bearing). This determines the horizontal and vertical location of one side of the carriage frame  23  while allowing slight rotational motion of the entire carriage structure  3  about beam  18 . The final rotational positioning of the carriage  3  is determined by the contact of bearers  15  against drum  12 , wherein the structure is being forced generally downward against the drum  12  due to the weight of the combined parts, housed in carriage  3 . This weight being sufficient to provide frictional traction between drum  12 , bearer  15  through bearer  16 , necessary to drive roll  2  and shaft  17  in a positive counter-clockwise direction when viewing FIG. 5.  
         [0046]    Note that carriage frames  23  and  23 ′ located on each end of the shaft structure  17 ′ (as well as the ball bushings  19  mounted on each carriage frame) are independent of each other. The only connection between frames  23  and  23 ′ being the contact of sheave  22  against gibs  21  on each end of shaft  17 . Thus, when carriage frames  23  and  23 ′ are caused to translate in a horizontal direction as viewed in FIG. 1, generally from left to right along the axis of drum  12 , the spacing of carriage frames are maintained by sheaves  22  and gibs  21 .  
         [0047]    Frames  23  and  23 ′ are separately attached to independent platform frames  46  and  46 ′, respectively (FIGS. 1 and 2). Platform  46  has depending from it a pair of linear bearings  19  and  19 A that are spaced to reinforce frame  23  from any tendency to rotate about a horizontal axis that is perpendicular to lead screw  24 .  
         [0048]    The linear movement of carriage  3  from left to right (downstream) is conveyed by means of a linear driver, shown as a lead screw  24 , which is precisely rotated from a drive system connected to drum  12 . The linear driver produces carriage motion in a downstream direction along a processing path P. This linear driver is powered through gear  42  (FIG. 2) mounted on the end of drum  12  for driving a gear reducer  25 , the output of which travels through a set of change gears  44  to provide variance to the rotational speed of the lead screw with respect to drum  12 .  
         [0049]    In some embodiments reducer  25  may be a transmission having a discretely or continuously variable transmission ratio. Alternatively, gears in train  44  may be replaced to effectively produce a variable transmission ratio. In many embodiments a variable transmission ratio will be unnecessary if the size of roll  2  does not vary dramatically, in which case variations in roll size can be accounted for by varying the rate of deposition of composition by coating head  8 , in a manner to be described presently.  
         [0050]    Referring to FIGS. 3 and 5 on the trailing one of the carriage frames  23  is located a split nut  26  device, which can be manually engaged and disengaged from the lead screw  24 . This split nut device  26  is similar to that described in U.S. Pat. No. 6,136,375. When split nut  26  is disengaged, carriage assembly  3  is no longer driven by lead screw  24 .  
         [0051]    In the beginning stages of preparing a roll  2  for coating as described above, a new roll  2  is mounted onto shaft  17  along with the bearers  16  and sheave  22  assemblies on each side of the roll  2 . The entire assembly is then dropped into carriage frames  23  and  23 ′. The carriage frames  23  and  23 ′ are laterally positioned relative to each other by virtue of their engagement of sheaves  22  and gibs  21  on each end. The entire assembly is mounted on the left-hand side of the machine (FIG. 1) and slid to the right so ball-bushing  19  can engage rod  18 , which runs the entire length of the machine.  
         [0052]    As described earlier, bearer  15  then becomes engaged with drum  12 , which commences the rotational operation of roll  2 . To provide for disengagement at any time of the rotative drive to the roll  2 , each carriage frame  23  (and  23 ′) is fitted with a lift wheel  38  which is mounted on eccentric shaft  39 . By rotation of lever  40  on one end of shaft  39  by approximately 180°, the gap  20  is eliminated because wheel  38  contacts auxiliary rail  41 , lifting bearer  15  out of contact with drumroll  12 . If at the same time split nut  26  is disengaged from lead screw  24 , frame  3  can be freely moved upstream and downstream, riding then on linear bearing  19  and wheel  38 .  
         [0053]    When the entire carriage assembly  3  is in the proximity of the ionizer cleaning station  4 , split nut  26  is manually engaged to lead screw  24 . The linear motion of the carriage  3  from left to right (downstream) is now commenced as roll  2  with shaft  17  are now rotated and driven linearly from left to right in precise relationship. More than one carriage assembly  3  containing a roll can be introduced to the machine at one time from the left hand end. In fact, normal operation would allow for a carriage  3 ′ and roll  2 ′ (FIG. 1) to be introduced to the left hand side of the machine to the cleaning section  4 , while another carriage unit  3  containing a roll  2  is being coated, while another carriage  3 ″ and roll unit  2 ″ is undergoing primary UV cure and yet another roll  2 ′″ and carriage assembly  3 ′″ is undergoing secondary UV cure under UV source  11  at the illustrated secondary curing station, which really exhibits the in-line continuous nature of the machine.  
         [0054]    Ultimately, Simultaneously by disengaging split-nut  26  as described above, the entire carriage can now be freely moved manually along the machine bed. Specifically, roll  2 ′″ and carriage  3 ′″ can be removed from the machine so that roll  2 ′″ can be separated from carriage  3 ′″ and subjected to final heat curing. Carriage  3 ′″ can then be recycled by placing it at the upstream end of the machine and loading on it a new roll for processing in the manner just described.  
         [0055]    Details of Elliptical Orifice and Polymeric Pumping System  
         [0056]    [0056]FIGS. 6, 10, and  11  show further details of the orifice and method to convey the polymeric liquid precisely to coat a roll. Orifice  27  is positioned in close proximity to surface of roll  2  as noted in FIG. 6.  
         [0057]    Referring to FIG. 11, orifice  27  is the opening at the distal end of a thin metal tube  48  that is much like a hypodermic needle. Tube  48  may be built in accordance with U.S. Pat. Nos. 5,694,852 and 6,136,375 and pending U.S. patent application Ser. No. 09/678,470 (filed Oct. 3, 2000). Specifically, tube  48  has a cylindrical central bore and its distal end is cut at an angle so that orifice  27  has an elliptical rim.  
         [0058]    The diameter of the bore, and the minor axis of the elliptical orifice, when viewed normally to the plane thereof, is about 0.010″ to about 0.055″, and is preferably about 0.030″. The major axis of the elliptical orifice, when viewed normally to the plane thereof, is about 4 to 8 times larger than the minor axis, that is, about 0.040″ to about 0.440″, and is preferably about 0.120″ to about 0.240″.  
         [0059]    Tube  48  is coaxially mounted in a tubular barrel  50  that is threaded into an annular plug  52 . The proximal side of plug  52  has a conical cavity  54  that is overlaid with a filter assembly  56 . While shown coaxially mounted in the simplified embodiment of FIG. 11, in other embodiments barrel  50  may be eccentrically mounted in plug  52 , leaving the floor of cavity  54  free for a center stud (e.g., a screw—not shown) to support the center of filter assembly  56 . Filter assembly  56  may employ a filter substrate juxtaposed on a reinforcing metal screen for additional support. Plug  52  is threaded into rotor  58  to capture filter assembly  56 .  
         [0060]    An integral, cylindrical journal  58 A extending behind rotor  58  is rotatably mounted in support block  60 . A control plate  62  is bolted to journal  58 A for rotating rotor  58  and thereby turning needle  48  about its axis. A fitting  64  is inserted through a hole in control plate  62  and is threaded into journal  58 A. A probe fitting  66  is threaded in turn into fitting  64  to provide fluid communication from supply tubing  68  through fittings  66  and  64  through a passage in rotor  58  leading to conical cavity  58 B.  
         [0061]    Temperature sensor  70  is installed in the back of fitting  66  and extends through fittings  66  and  64  into conical cavity  58 B in order to sense the temperature of material about to the flow out of orifice  27 . Temperature sensor  70  may operate through a temperature controller (for example, a REX-D type of controller manufactured by RKC Instrument Inc.) to regulate an electrical heater  72  installed on rotor  58 .  
         [0062]    A pressure sensor  74  installed atop a port of fitting  66  will send an electrical signal to display panel  76  to allow an operator to monitor the back pressure of material supplied by tubing  68 . This back pressure signal can indicate a problem due to clogging of filter  56  or high material viscosity caused by inadequate heating from heater  72 .  
         [0063]    Rotor  58  can be rotated by turning control plate  62 . To accomplish such rotation, the upper end of plate  62  is attached to a horizontally movable adjustment shuttle bar  78 , which will be described further hereinafter.  
         [0064]    Referring to FIG. 10, components previously illustrated in FIG. 11 bear the same reference numerals, with similar but modified components marked with a distinguishing prime (′). Previously mentioned needle  48  will be threaded by means of its barrel  50  into a modified plug  52 ′. Barrel  50  will be threaded into an eccentric position. Filter assembly  56  is shown cooperating with an “O” ring  56 A. Rotor  58 ′ is shown as a rectangular block having a cylindrical journal  58 A′. Fitting  64 ′ will be installed in an eccentric position in journal  58 A′. The eccentric mountings of fitting  64 ′ and barrel  50  offset each other so that needle  48  is coaxial with journal  58 A′.  
         [0065]    Journal  58 A′ is rotatably mounted in block  60 , a rectangular block with a relatively large central opening. Previously mentioned control plate  62  is attached to journal  58 A′ and its upper end is bolted to previously mentioned adjustment block  78 . Block  78  is attached to the threaded shaft of adjustment knob  80 , which is rotatably mounted in bracket  82  attached to the outside of block  60 . By rotating adjustment knob  80 , plate  62  can rotate rotor  58 ′ to cause needle  48  to rotate about its axis. This adjustment is discrete, in the sense that the needle just rotates about its axis (roll), without disturbing any of its other positional coordinates (elevation and two dimensional horizontal location).  
         [0066]    Block  60  is attached to slide plate  84 , which is slidably mounted between rails  86  on pitch plate  88 . Rotatably mounted on plate  88  is an adjustment knob  90  whose threaded shaft engages threaded bore  92  in slide plate  84 . Rotation of knob  90  slides plate  84 , causing needle  48  to move axially.  
         [0067]    Pitch plate  88  is attached at pivot point  94  to base plate  96 . Due to the weighting about pivot point  94 , tab  88 A of pitch plate  88  normally swings counter-clockwise against the inside end of stop screw  98 , which is threadably mounted in block  100  attached to base plate  96 . Adjustment of stop screw  98  can swing pitch plate  88  about pivot point  94  to change the pitch or angle of elevation of needle  48 . Pitch plate  88  can be locked into position by turning the threaded locking knob  102 , which fastens plate  88  to base plate  96  through arcuate slot  88 B.  
         [0068]    Slider  106  supports base plate  96  and slides along an adjustment path between rails  108 , which are attached to upright  104  (FIG. 1). Threaded locking knob  110  is threaded into backer block  112 , which rides behind ridges  108 A of rails  108 . Locking cross plate  114  rides over ridges  108 A and can be tightened by locking knob  110  to squeeze ridges  108 A between elements  112  and  114 , locking them onto rails  108 . Threaded height adjustment knob  116  non-threadably passes through block  112  and screws into slider  106 . Accordingly, rotation of knob  116  can lift and lower slider  106  between rails  108 .  
         [0069]    Referring to FIG. 7, coating head  8  is shown with the tip of needle  48  at the circumference of roll  2 . Needle  48  is also shown in phantom repositioned to accommodate a smaller roll  2 A. When being adjusted to accommodate different size rolls, the orifice  27  at the tip of needle  48  follows a discrete adjustment path R that is radial with respect to roll  2  and that is at an acute angle to vertical; suitably, 20° (although various other angles can be used instead). This repositioning to accommodate different size rolls is accomplished simply by adjusting the position of slider  106 , which also follows a 20° inclined path. This adjustment is discrete, in the sense that the needle just translates along a path without disturbing any of its other angular coordinates (pitch, roll, or yaw). (It will be appreciated that slider  106  is given in a simplified form without the block  112  of FIG. 10, for illustrative purposes.)  
         [0070]    It will be further appreciated that the other needle adjustments described presently need not be readjusted to compensate for a new roll size. These other adjustments establish the pitch and roll of the axis of needle  48  and the axial position of needle  48  relative to radial track R. These ordinarily remain unchanged if the needle is readjusted for roll size.  
         [0071]    Referring again to FIG. 7, the axial extension of needle  48  can be adjusted by turning knob  90  to rotate its shaft and move slide block  84  between rails  86 . This adjustment is made to place the center of elliptical orifice  27  on radial track R. The plane of the ellipse of orifice  27  is preferably kept tangential to the circumference of roll  2 . By adjusting stop screw  98  and rotating pitch plate  88 , tangency can be established by discretely adjusting the pitch of needle  48  about pivot  94 . This pitch is held by clamping plate  88  in position by tightening locking knob  102 . This pitching motion is illustrated in FIG. 8.  
         [0072]    Finally, needle  48  can be rotated about its axis using the adjustments shown in FIG. 9. Adjustment knob  80  is rotated to shift block  78  and thereby rotate control plate  62 . Since control plate  62  is bolted to rotor  58  (FIG. 11), the rotor and needle  48  will rotate about their axes.  
         [0073]    These adjustments can be used to locate orifice  27  in contact with roll  2 . Such light contact tends to avoid orifice-roll spacing problems. Specifically, attempts to produce a uniform coating with the tube  48  and its orifice  27  spaced from the roll  2  met with difficulty as non-circular rotation of the roll  2  led to varying spacings between the orifice  27  and the roll  2 . These varying spacings affected the uniformity of the cured coating. With at least a portion of the tube  48  contacting and riding on the roll  2  at all times, the orifice  27  is maintained in a fixed spatial relationship relative thereof.  
         [0074]    The adjustment of needle  48  is facilitated by overhead camera C 1  (FIG. 1) and side camera C 2  (FIG. 2). These cameras may be fitted with telephoto (or in some cases macro) lenses to provide close-up views of the orifice  27 .  
         [0075]    Referring to FIG. 6, tubular needle  48  is clamped into position on coating head  8  and so its internal passageway can be used to feed polymer material from pipe  32 . The material is pumped through this passageway and out the internal orifice  27  to form coating  31 , as the roll  2  rotates. Details of the coating material are noted below. The previously mentioned filter assembly  56  is shown located in head  8 . Also tubular electrical heater elements  72  located on head  8  are, by virtue of the aluminum construction of head  8 , able to convey heat to the polymeric material as it passes through the housing. As previously mentioned, this heater is thermostatically controlled. (Temperature control can be effected by, for example, an REX-D type controller from RKC Instrument Inc.)  
         [0076]    A precision gear-type pump  33  driven from a digital drive system includes a motor  34  with shaft encoder  34 A. A digital drive controller  118  is shown connected and responsive to the output of shaft encoder  34 A in order to send a control signal to a power modulator  120  that regulates the electrical drive and therefore the speed of motor  34 . In some cases motor  34  may be a stepper motor whose shaft position is digitally incremented by controller  118 . In other embodiments motor  34  may be a DC motor whose speed is regulated in the usual manner.  
         [0077]    Drive controller  118  is connected to previously mentioned shaft encoder  37  for sensing the precise rotational speed of motor  14 , which directly drives roll  2 . Accordingly, controller  118  responds to the angular speed of roll  2  and commands supply  120  to drive motor  34  at a speed bearing a precise ratio to the angular speed of roll  2 . The method of controlling precise speeds of two independently rotating elements using a digital drive with a shaft encoder located on each rotational element as a reference is a common method of speed control. For example such ratio control can be accomplished by an MDC type motor controller manufactured by Red Lion Controls, York, Pa. and Berkshire, England.  
         [0078]    The operating speed of the system is determined by setting first the speed of motor  14  and therefore the angular speed of roll  2 . Specifically, motor controller  122  starts motor  14  and then senses its angular speed via shaft encoder  37 . The speed is regulated by sending a speed control signal to the power modulator  124 , which drives main motor  14 . In some embodiments, controller  122  may be a relatively simple feedback system offering a knob or dial for adjusting the speed of motor  14 .  
         [0079]    Once the speed of motor  14  is established, controller  118  establishes the speed ratio between roll  2  and material pump  33 . An operator can adjust this ratio by using the display and keys on controller  118 , basing the ratio on the roll size, the desired coating thickness, material density and viscosity, etc. Also as mentioned previously, the linear speed of the carriage  3  carrying roll  2  is determined by the drive ratio of the reducer  25  and gear train  44  (FIG. 2). In some embodiments this drive train may include a transmission for adjusting this drive ratio discretely or continuously.  
         [0080]    Consequently, the drum rotates and moves linearly at a precise ratio that is proportional to the rate of composition pumped through orifice  27  by means of metering pump  33 . The plastic composition, when applied to the printing roll or cylinder, has a viscosity of from about 800 cP to about 5,000 cP, the viscosity preferably being from about 1,000 cP to about 2,000 cP. The plastic composition is applied at a pressure of from about 8 psi to about 60 psi, preferably at about 30 psi. This pressure can be measured by sensor  74  and displayed on monitor  76 .  
         [0081]    The printing roll  2  may be of a standard size, for example, it may have a diameter of about 361 mm, and be rotated at speeds of about 30 to about 90 rpm, with about 45 rpm being preferred. The tube  48  and its orifice  27  are moved along the rotating roll&#39;s surface at a rate of from about 0.008″ per revolution to about 0.048″ per revolution, with about 0.0192″ per revolution being preferred.  
         [0082]    The orifice area, the viscosity of the plastic composition, the pressure at which the plastic composition is applied, the cylinder rotational speed, and the rate of movement of the tube and orifice across the cylinder surface are adjusted such that when the plastic composition is applied to the printing roll or cylinder, the thickness of the plastic composition deposited upon the cylinder is from about 0.003″ to about 0.015″, preferably from about 0.0032″ to about 0.0035″, and most preferably at about 0.0040″. The plastic composition preferably is applied to the printing roll or cylinder at room temperature (about 23° C.), while the printing roll or cylinder, prior to application of the plastic composition, may be preheated to a temperature of from about 23° C. to about 40° C., preferably to about 30° C.  
         [0083]    Preferably, the plastic is dispensed at a rate of from about 0.035 cc to about 0.155 cc per revolution of cylinder  12 . To produce the preferred 0.0035″ thick composition film, tubes  48  having bores with 0.010″, 0.023″ or 0.053″ diameters (and ellipse minor axes) were used and were moved across the surface of the rotating roll  2  at respective rates of 0.008-0.010″ per revolution, 0.019-0.021″ per revolution, and 0.040″-0.048″ per revolution. These dimensions also represent the approximate center-to-center spacing of the adjacent runs or portion of the strip or bead when tubes  48  with the illustrative bore sizes are used.  
         [0084]    The polymeric material  36  is supplied from reservoir  35  (referred to herein as a source of composition), which contains a suction tube  35 A connected via tubing  35 B to the input of pump  33 . The polymeric material  36  can be periodically replaced in reservoir  35  while the system is operating through an opening in the top of the reservoir. The flow of composition  36  from reservoir  35  is boosted by a source N of compressed nitrogen gas.  
         [0085]    Generally the generation of the coating is in helical form and the build up of the coated surface is described thoroughly in U.S. Pat. Nos. 5,694,852 and 6,136,375 and pending U.S. patent application Ser. No. 09/678,470 (filed Oct. 3, 2000). Also the general mounting of needle  48  is shown in that patent with the exception of the improvement shown in FIG. 7 and elsewhere. In particular, the present coating head  8  is carried on a slide that is mounted on an angle (of approximately 20°), such that the entire assembly can be translationally adjusted so that the orifice tip  27  moves in a radial direction toward the center line of roll  2 . Similarly the perpendicular motion “in-out” can also be by a second slide assembly of similar nature.  
         [0086]    Finally pivot  94  (FIG. 8) provides for throw-off of the elliptical orifice  27 , during periods of set up. This is beneficial since the upward tilt of the orifice assembly facilitates the bleeding of air from the passages.  
         [0087]    Details of the Liquid Polymer  
         [0088]    The plastic composition has a preferred viscosity of about 2,000 CPS to 40,000 CPS, preferably from about 2,000 CPS to 5,000 CPS. Possible compounds include plastic compositions which include one or more epoxide resins (e.g., cycloaliphatic epoxides or amine-based epoxides), vinyl esters formed from an epoxy-novolac compound, bisphenol A epoxy resins modified with cresol novolac§), cycloaliphatic or amine based epoxide resins, epoxy resins which are the reaction product of epichlorohydrin and bisphenol A, and mixtures of expanding polycyclic monomers. As a result, as is known, these compositions are irreversibly cured. To these compositions there may be added, as appropriate, flexibilizers, photoinitiators, surfactants, slip agents, modifiers, dyes, additional epoxy resins, catalysts, promoters and accelerators. The compositions, once cured, are engraveable or etchable to produce printing cells or elevated printing surfaces.  
         [0089]    The preferred composition is self-leveling, UV curable, formed from a liquid Epoxy-Novolac resin compound. In an ultraviolet cured Epoxy-Novolac system, the plastic composition would include products of reactions of Phenol(s) or Cresol(s) with Formaldehyde(s) such as Orthocresol Formaldehyde, the UV system may further include flexibilizing components, a photoinitiator component, a surfactant and a dye.  
         [0090]    Optional flexibilizing components may include, but are not limited to, Polyols, Diols, Triols and Activated Polyolefins. Examples of photoinitiators which may be employed, include, but are not limited to, Triaryl or Triphenyl-Sulfonium Salts. Surfactants or surface modifiers which may be employed in the UV curable system, include, but are not limited to, Nonionic Fluoroaliphatic Polymer Ester surfactants and organomodified Polymethyl Siloxane Copolymers.  
         [0091]    Dyes or near infrared absorption dyes that may be employed in the UV curing system include, but are not limited to, antimony compounds as Sb. An example of a near infrared absorption dye is sold as ADS1060A by ADS American Dye Source.  
         [0092]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.