Abstract:
A method for continuously electroplating metal webs by coating a masking ink thereto in a fashion resembling flexographic printing, then electroplating the uncoated areas of the web and finally removing the ink, is described. The masking ink is applied continuously from a reservoir to an “anilox” roller which synchronously and rotatingly contacts either a plate roller or an intermediate roller. Contact between the rollers transfers the masking ink from one roller to the other. The plate roller has “proud” or raised areas in which the ink is drawn and contacts a guided metal web that is coated with the ink in a pattern matching that of the plate roller. Electroplating is effected after cleaning the inked web in an aqueous acid media. Finally, the masking ink is removed in an alkali medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority based on provisional application Serial No. 60/060,737 filed Oct. 2, 1997 and is a divisional of application Ser. No. 09/165,217, filed Oct. 1, 1998 now U.S. Pat. No. 6,143,145 issued Nov. 7, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a selectively plated substrate and, more particularly, to an apparatus for continuously masking selected areas of a metal web with a non-conductive coating. The masked web is then processible in an electroplating apparatus followed by stripping the maskant to produce a web having selectively plated and unplated areas. The present invention is particularly advantageous for plating narrow, well defined metal stripes on a metal web. 
     2. Prior Art 
     It is known to selectively electroplate a metal web with plated stripes by first applying a resist to the metal surface, plating the areas devoid of resist material and then removing the resist after the plating step. Several techniques are known for accomplishing this including applying a liquid resist by silk screening, applying a dry resist by laminating the resist material to the metal web, and applying a resist by electrophoretic deposition. These techniques do not necessarily provide a plated pattern having sharp definition and close location tolerances. Further, dry photo resists are much more costly than the non-conductive ink maskant of the present invention. Electrophoretic resists, while less costly than dry resists are still more costly than the present ink maskant. Also, electrophoretic resists can not be applied at speeds comparable with the present invention. 
     Another technique that provides improved plating definition uses a photo resist applied over the entire workpiece by one of the liquid resist, dry resist or electrophoretic deposition techniques. The photo resist is then selectively exposed by interposing a mask between a source of actinic radiation and the resist coated workpiece. This causes the exposed area to be more soluble in the case of a positive photo resist, or less soluble in the case of a negative photo resist when the workpiece is subsequently immersed in a developing solution. Such an electrophoretically applied photo resist technique is described in European Patent Application 0 507 043 A2. Again, electrophoretically deposited resists are more costly than the present ink maskants, and their process speeds are slower than the present invention. 
     Still another prior art process uses mechanical masks such as moving belts to produce stripes of electrodeposited material while the belt contacted portions of the substrate are left unplated. However, this technique is inadequate for producing thin, well defined stripes because fabricating very narrow belts and locating them accurately against the web to be masked presents many difficulties. 
     SUMMARY OF THE INVENTION 
     Accordingly, there is a need for metal web substrates that are electroplated in well defined, sharp and, if required, narrow stripes. In that respect, it is important that the unplated portions of the web are free of electro deposited metal, and the plated area transitions into the unplated area at a substantially perpendicular slope to the plane of the web. The masking apparatus and method of the present invention provide such a web substrate having well defined ink stripes applied thereto with precise boundaries and very little wander. Accordingly, important aspects of the present invention are that the applied ink maskant has extremely close width tolerances, very little wander along the length of the web and is laid down free of pinholes and like defects. 
     These and other aspects of the present invention will become more apparent to those skilled in the art by reference to the following description and to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of an apparatus  10  for continuously applying a non-conductive ink maskant to selected areas of a web according to the present invention. 
     FIG. 2 is a perspective view of an adjustable guide for accurately aligning the web  12  as ink is being applied thereof. 
     FIG. 3 is a partial plan view of a web  12  having a pair of spaced apart ink stripes  14  contacted thereto according to the present invention. 
     FIG. 4 is a partial plan view of the web  12  of FIG. 3 after plating and removal of the masking ink. 
     FIG. 5 is a partial cross-sectional view of FIG.  3 . 
     FIG. 6 is a partial cross-sectional view of FIG.  4 . 
     FIG. 7 is a partial cross-sectional view of a web having a masking ink contacted thereto according to the prior art. 
     FIG. 8 is a partial cross-sectional view of the web in FIG. 7 after plating and removal of the masking ink. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As defined in this application, the terms “forward”, “rearward”, “upper”, “upwardly”, and “downwardly” refer to the orientation of FIGS. 1 to  8 , and are not intended to be limiting. 
     Turning now to the drawings, FIGS. 1 and 2 schematically illustrate an apparatus  10  for continuously masking selected area of a web  12  (FIGS. 3 and 5) with stripes  14  of a masking ink according to the present invention. The continuous masking apparatus  10  includes a platform  16  having a pair of spaced apart side walls  18  (only one side wall is shown) extending upwardly therefrom at a forward end of the platform. A larger, main wall  20  extends upwardly from the platform  16  at a rearward end thereof. The spaced apart side walls  18  and the main wall  20  support various rotating rollers and guide structures for providing selected areas of the web with a non-conductive ink maskant according to the present invention, as will be described in detail presently. 
     The continuous masking process of the present invention begins with the web  12  initially rolled up on a spool  22  that serves as a pay-off uncoiler. The web typically has a thickness of about 0.0005 inches to about 0.040 inches. After the web  12  moves off the spool  22 , the web passes over a first alignment roller  24 , between a pair of second and third alignment rollers  26  and  28  rotating about shafts supported by the forward side walls  18  and under a fourth alignment roller  30  rotating about a shaft supported on the rearward, main wall  20 . The web  12  leaves the fourth alignment roller  30  and travels upwardly to a first guide roller  32  and then downwardly to a second guide roller  34 . The guide rollers  32  and  34  are supported by the main wall  20  and provide for coarse adjustment and tensioning of the web  12  prior to entry into a first adjustable guide  36 . The web  12  now moves through the first adjustable guide  36  aligned with a cooperating plate roller  38  and an impression roller  40  and on to a second adjustable guide  42 . 
     The plate roller  38  is provided with one or more proud areas disposed angularly about its circumference and preferably provided by a fine grinding manufacturing process and the like. The width of the proud areas and their relative location define the boundaries and the location of the masking that will occur on the web, and ultimately, the areas on the web devoid of plated material. 
     The plate roller  38  contacts an intermediate transfer roller  44  which, in turn, contacts an aluminum “anilox” or ink roller  46  that picks up ink  48  from a well  50 . The ink roller  46  has a pattern of high and low areas etched or laser engraved on its surface. A doctor roller  52  is located immediately after the ink pick-up point to remove excess ink from the high areas of the ink roller  46 . A threaded jack screw  54  provides for adjusting the pressure of the doctor roller  52  to regulate the wiping action of the doctor roller  52  against the ink roller  46 . The design of the raised pattern and the depth of the recessed areas on the ink roller  46  regulate the amount of ink that is retained on the roller  46  after contact with the doctor roller  52 . 
     The contact pressure and the angle of contact between the ink roller  46 , the intermediate roller  44  and the plate roller  38  are adjustable to ensure that the rollers are square to one another and provide an even dispersion of ink on the plate roller. In particular, a pair of plates  56  (only one shown) connect the transfer roller  44  to the ink roller  46 . Jack screws  58  connected to link arms  60  provide for independent adjustment of the intermediate roller  44  towards and away from the plate roller  38  as the plates  56  pivot on the shaft  62  supporting the ink roller  46 . A pair of jack screws  64  (only one shown) provide for adjustment of the transfer roller  44  with respect to the ink roller  46 . 
     The plate roller  38  and the ink roller  46  are synchronously driven from a common drive (not shown) having a chain  66  and the like connected between them. The intermediate transfer roller  44  is mounted on an idler shaft and rotates by being in light contact with the ink roller  46  and the plate roller  38 . The web  12  is moved through the present masking apparatus  10  by a separate drive roller  68 . 
     The ink  48  picked up from well  50  by the rotating ink roller  46  can be a solvent based, water soluble ink, or a UV curable formulation which is soluble in an aqueous alkaline media but insoluble in an aqueous acid media. In the alternative, the ink  48  is soluble in an aqueous acid media and insoluble in an aqueous alkaline media. The well  50  is maintained at a constant height by continuously operable pump  70  in communication with a supply container  72 . The well  50  is fitted with an overflow weir (not shown) adjusted to maintain the desired ink level. The overflow ink returns by gravity to the supply container  72 . 
     The structure of the first and second adjustable guides  36  and  42  is shown in FIG.  2 . The adjustable guides each include a base  74  secured to the main wall  20  by a screw  76  disposed through a slot  78  in the base. The slot  78  provides for coarse position adjustment of the guide with respect to the travel path of the web. The base  74  supports a tower  80  having a channel shape provided by spaced apart side walls  82  and  84  extending to and meeting with a back wall  86 . The back wall  86  is provided with an elongated aperture (not shown) running longitudinally along the length thereof. The tower  80  is closed by an end wall  88  having a circular aperture (not shown) through which a threaded shaft  90  extends to a blind bore (not shown) in the base  74 . A hand knob  92  is provided on the shaft  90  proximate the end wall  88 . The shaft  90  threadingly mates with the block portion  94  of a T-shaped slide  96 . The block portion  94  is captured between the side walls  82 ,  84  and supports a bar portion  98  of the T-slide  96  so that rotational movement of the knob  92  and associated threaded shaft  90  raises and lowers the T-slide  96  along the length of the tower  80 . The spaced apart legs  100  (only one shown) of a generally U-shaped member  102  are connected to the opposed ends of the bar portion  98  of the T-slide  96  by threaded members  104 . A coil spring  106  surrounds the threaded shaft  90  and biases between the base  74  and a bushing  108  mounted on the shaft. The bushing  108  contacts the block portion  94  of the T-slide  96  under the force of the spring  106 . Course positioning of the T-slide  96  is provided by rotating the shaft  90  to move the T-slide  96  along the tower  80 . Once the T-slide  96  is so positioned, it is locked by threading a screw  110  into a tightened position. 
     The bar  98  of the T-slide  96  supports an adjustable guide  112  comprising an L-shaped bar  114  secured to the T-slide by threaded members  116 . A stepped bar  118  is adjustably supported on an upper end  120  of the leg  122  of the L-bar  114  by a threaded member  124  extending through a threaded bore  126  in the stepped bar  118  and received in a threaded blind bore  128  in the L-bar  114 . A spring  130  surrounds the threaded member  124  and biases between a hand knob  132  and the stepped bar  118 . A pair of spaced apart guide pins  134  and  136  mounted in the upper end  120  of the L-bar  114  extend through bores in the stepped bar  118  and are disposed on opposite sides of the adjustment screw  124  to guide movement of the stepped bar  118  towards and away from the L-bar  114 . The step  138  of the L-bar  114  has a cylindrical recess  140  that supports a ceramic roll pin  142 . Similarly, a cylindrical recess  144  in the step  146  of bar  118  supports a ceramic roll pin  148  directly opposite the roll pin  142 . The ceramic pins prevent the web, which may be as thin as 0.001 inches, from cutting into the guides. The adjustable guide side locates the reference edge of the web firmly against the fixed guide, and opens slightly when necessary to accommodate minor variances in web width. That way, the adjustable guides  36  and  42  precisely locate the web  12  with respect to the plate roller  38 . A guide system with a constant, fixed width could cause edge damage to the web when the web width is wider than the fixed distance between the guides. 
     The impression roller  40  is located tangential to the plate roller  38 . The impression roller  40  contacts the back side of the web  12  to cause ink to transfer from the plate roller  38  to the web  12 . FIG. 3 shows the web  12  having spaced part stripes  14  of ink laid thereon by the present apparatus  10 . FIG. 5 is a partial cross-sectional view of FIG. 3 showing the precise boundaries of one of the ink stripes  14 . The contact pressure exerted by the impression roller  40  against the web moving past the plate roller  38  is manually adjustable by turning a fine threaded screw  152  connected to a link assembly  154  to move the impression roller  40  towards the plate roller  38 . 
     Web speed can vary from about 30 feet per minute to about 1,000 feet per minute, and preferably about 300 to about 500 feet per minute. An important aspect of the present invention is that the surface speed of the plate roller  38  can be the same as, faster, or slower than the web speed, and the direction of rotation of the plate roller can be the same as the pull direction of the web, or opposed to it. By varying the relative speed of the web and the plate roller, and/or the direction of rotation of the plate roller, a wiping action is created which causes the ink to be laid down without pinholes that are common in flexographic printing. Pinholes are undesirable since they allow plating in the region where no plating is desired. 
     The thickness of the deposited ink is varied by the speed and direction of rotation of the plate roller, the contact pressure between the plate and impression rollers, the design of the anilox roller and doctoring system, and the viscosity of the ink. Obviously, the thinner the ink the lower the cost. However, it is necessary to optimize the ink thickness so the coating is continuous and free of pinholes, and so the ink has sufficient ohmic resistance to withstand the electroplating voltage that will subsequently be applied to the web. 
     The web  12  leaves the second adjustable guide  42 , moves over a third guide roller  156  and into a generally horizontal orientation. The web  12  then moves over a pair of spaced apart support rollers  158  and  160  which help to maintain the distance of the travelling web  12  past an ultraviolet light source and reflector assembly  162 . The actinic radiation is preferably provided by a halide lamp which emits ultraviolet energy of about 350 nanometers to about 450 nanometers. The power of the lamp can vary depending on the web speed and the proximity of the web to the lamp. 
     The web  12  leaves there and loops about 270° around a fourth guide roller  164  and then over the drive roller  68  powered by a motive means for moving the web  12  through the present apparatus. The masked web  12  is then taken up on a take-up recoiler  166  for storage or further immediate processing. It can optionally be run through the masking apparatus of the present invention a second time to place stripes on its opposite side. The present apparatus can also be configured to simultaneously ink both sides of the web in a single pass. This is done by substituting a second plate roller for the impression roller. The second plate roller can be directly in contact with an ink or anilox roller, or there can be an intermediate transfer roller transferring ink from the ink roller to the second plate roller, as previously described in detail. 
     The coiled, masked web is then transferred to a continuous reel-to-reel plating machine. There, the web is cleaned in an acid media and then electroplated to the desired thickness with one or more metals. After electroplating, the web passes through a stripping station containing a solution to dissolve the ink. The stripping solution may be agitated by pumping action, or sprayed onto the web to increase the removal rate of the ink mask. After stripping, the web is rinsed, residual alkali is neutralized in a mild acid bath, the web is rinsed again, dried and recoiled. 
     FIG. 4 shows the web of FIG. 3 after plating and removal of the masking ink. FIG. 6 is a partial cross-sectional view of FIG. 4 illustrating the precise boundaries of the plated material  168 . In contrast, FIG. 7 illustrates an inked web according to the prior art having poorly defined boundaries  170  and pin holes  172 . FIG. 8 illustrates the web  12  of FIG. 7 after plating and removal of the masking ink. The imprecise deposition of the plate material  174  caused by the poorly defined boundaries and pinhole plate  176  is evident. 
     The following example describes the manner and process of continuously masking a web substrate according to the present invention, and it sets forth the best mode contemplated by the inventors of carrying out the invention, but it is not to be construed as limiting. 
     EXAMPLE 
     A web of copper alloy having a thickness of 0.003±0.005 inches, and a width of 1.300±0.002 inches was continuously moved through an ink masking apparatus according to the present invention at a speed of about 300 feet per minute. Two stripes of ink with a targeted width of 0.125 inches were laid down using a plate roller with a polymeric surface of 55 durometer EPDM, contoured to deposit the ink in the desired area. The ratio of the surface speed of the plate roller to the speed of the web was 1.3:1. The inked web was exposed to radiation with ultraviolet light having a wavelength of 360 to 400 nanometers. The length of the exposure window in the direction of web travel was 12 inches resulting in an exposure time of 0.2 seconds. The web was then passed through the present inking apparatus a second time using the same conditions, except that the plate roller was contoured to produce two stripes with a targeted width of 0.040 inches. The thickness of the ink maskant in both cases was approximately 0.0002 inches. 
     The stripes were well defined, having a width variation of about ±0.010 inches, with sharp edges and no apparent pinholes. It was also determined that the boundry between the ink stripe and the unmasked web wandered ±0.0005 inches along the length of the web. The coating was hard and dry and resisted abrasion by coarse paper. 
     The ink used was a blend of multifunctional acrylate monomers and oligomers, photoinitiators such as benzophenone, and surfactants. 
     After the second pair of stripes was printed, the web was coiled up and transferred to a reel-to-reel selective plating machine. The web was passed through the various cells of the machine at 35 feet per minute. The following processes were performed continuously on the plating machine: 
     (1) Clean the web in an aqueous acid media containing surfactants to remove finger prints and soils. 
     (2) Electroplate with 0.0001 to 0.00012 inches of copper from an acid bath at a cathode current density of 200 amps per square foot. 
     (3) Electroplate with 95% tin/5% lead from a methane sulfonic acid based bath at 400 amps per square foot. 
     (4) Strip the ink maskant in an aqueous solution of sodium hydroxide and surfactants. 
     (5) Neutralize, rinse and dry the web. 
     After electroplating, the web was examined to determine the accuracy of the stripe location, integrity of the plated material, i.e., the absence of pinholes, definition of the stripe edge, thickness and/or composition of the plated metal layers, and adhesion of the plating, particularly at the boundaries of the unplated/plated area. 
     There were no adhesion failures found. Lack of adhesion failures at the boundary of the plated and unplated areas demonstrates that the ink masking was sharply defined. Generally when there is a blush at the ink/substrate interface, the thinner maskant will break down under the applied plating voltage. This results in uneven and often thin, non-adherent deposits at the edges of the unplated area. 
     It is appreciated that various modifications to the present inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention as defined by the herein appended claims.