Patent Publication Number: US-2021185827-A1

Title: Printing conductive traces

Description:
BACKGROUND 
     Many retailers, manufacturers, and distributers want access to cost effective RFID (radio frequency identification) tags to put on all of their products. Incorporating RFIDs onto product packaging can help provide product security, reduce the number of lost products, and collect data to indicate trends in the movement and sales of products. RFID technology allows for multiple products to be scanned and accounted for quickly, and at the same time. RFIDs are being implemented in an increasing variety of products due to their decreasing cost. For many products, however, the cost threshold for using RFIDs remains too high. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  shows an example of a conductive trace printing system that is suitable for generating high quality metal conductive traces on media substrates through the enhancement of printed conductive traces in an electroless metal plating process; 
         FIG. 2  shows an example of a conductive trace printing system with additional details of a conductive trace application station and a conductive trace enhancement station; 
         FIG. 3  shows a blow-up block diagram of an example conductive trace application station illustrating different example print engines suitable for implementing within a conductive trace application station; 
         FIG. 4  shows an example of a conductive trace printing system that includes an example overprint application station; 
         FIG. 5  shows examples of media substrates in various stages of having a conductive trace applied by a conductive trace printing system; 
         FIGS. 6 and 7  are flow diagrams showing example methods  600  and  700 , of applying a conductive trace to a media substrate. 
     
    
    
     Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. 
     DETAILED DESCRIPTION 
     A significant challenge to the adoption of RFIDs is their cost, which varies depending on the type of RFID being used. Active RFIDs have battery power and can broadcast their own signals, act as beacons to track product locations in real-time, and provide much longer read times than passive RFIDs, but they are much more expensive than passive RFIDs. Passive RFIDs are cheaper, but they have no internal power source and rely on energy from the RFID reader to function. Passive RFIDs are therefore used in less demanding applications such supply chain management, smart labels for packaging, access control, and so on. 
     Further still, passive RFIDs can be chipped or chipless, which also impacts their cost. The added cost to design and fabricate a microchip for passive RFIDs can make passive RFIDs too expensive for use in many low cost and low margin products. Passive chipless RFIDs are therefore the cheapest, and they are increasingly being used in low end products. However, both chipped and chipless RFID tags are mainly generated through screen printing of conductive metal particles or adhesion of conductive metal foils. These methods of fabricating passive RFIDs are cost intensive, difficult to scale, and involve additional processing steps. With these methods, passive RFIDs often have to be produced off the product and then adhered later in a subsequent step. 
     Accordingly, examples of systems and methods described herein enable the generation of high quality metal conductive traces, such as metal coil RFID tags (RFIDs), through an electroless metal plating enhancement to printed conductive traces. The production process enables the generation of high quality, low cost RFIDs and other conductive traces directly onto packaging material substrates. In some examples, a protective overprint layer can be applied to the RFIDs to enhance their durability. 
     In an example process, a conductive trace design such as a passive chipless RFID design, can be printed on the surface of a media substrate (e.g., a package substrate) using different printing technologies such as inkjet and liquid electro-photographic (LEP) printing processes. Because the conductive metal trace can have impurities and/or contaminants, its conductivity may be attenuated and it may not be sufficiently conductive to be used as an RFID directly, for example. Therefore, the conductive trace can be exposed to an electroless metal plating solution to enhance the trace through electroless deposition of metal, such as copper, onto the trace. During exposure to the metal plating solution, reactants within the solution will reduce onto the conductive trace and generate, for example, a high quality metal-plated passive chipless RFID. 
     Exposure of the conductive trace to the metal plating solution can be achieved by various methods including through the use of a saturated sponge-like material or through a sealed liquid bath. The method of exposing the trace to the metal plating solution can depend in part on the type of media substrate on which the trace is printed. For example, while the use of a liquid bath may work faster and reduce issues with transporting reactants, it may be less suitable for use with a paper substrate due to the potential for over-saturating the substrate. Delivering the plating solution through a saturated sponge may take longer, but it may also provide better control over the amount of liquid introduced to the substrate. 
     In a particular example, a conductive trace printing system includes a conductive trace application station to apply a conductive trace onto a media substrate. The printing system also includes a conductive trace enhancement station to expose the conductive trace to an electroless metal plating solution to generate an enhanced conductive trace. 
     In another example, a non-transitory machine-readable storage medium stores instructions that when executed by a processor of a conductive trace printing system, cause the system to apply a conductive trace to a media substrate, and then expose the conductive trace to an electroless metal plating solution to enhance the conductive trace. In some examples, an insulating layer can be applied to the media substrate prior to applying the conductive trace, and the conductive trace can be applied on the insulating layer. 
     In another example, a conductive trace printing system includes a printing device to print a preliminary conductive trace onto a media substrate, and a solution applicator to expose the preliminary conductive trace to an electroless metal plating solution to generate an enhanced conductive trace. The printing system also includes a memory device comprising print instructions and print data, and a processor programmed to execute the print instructions to control the printing device to print the preliminary conductive trace in a pattern according to information in the print data. 
       FIG. 1  shows an example of a conductive trace printing system  100  that is suitable for generating high quality metal conductive traces on media substrates through the enhancement of printed conductive traces in an electroless metal plating process. As shown in  FIG. 1 , a media substrate  102  can travel through the printing system  100  in a direction taking it from a conductive trace application station  104  to a conductive trace enhancement station  106 . A media substrate  102  can include a variety of printable media substrates such as substrates used in product packaging. Examples of media substrates  102  include, but are not limited to, various plastics such as polyolefin, polyester, polyethylene terephthalate, and polyvinyl chloride; papers such as kraft paper, sulfite paper, and greaseproof paper; and, single and multi-layer paperboards such as white board, solid board, chipboard, fiberboard, and corrugated cardboard. 
     As the media substrate  102  passes through the conductive trace application station  104 , a preliminary conductive trace can be applied to the substrate  102 . The conductive trace can be applied, for example, as a nickel (Ni) trace or an iron (Fe) trace, or as a trace comprising another metal. The conductive trace can be applied in any design to achieve a conductive purpose, such as in the design of an RFID tag. After the conductive trace is applied to the media substrate  102  the substrate  102  passes through the conductive trace enhancement station  106 . As the conductive trace passes through the conductive trace enhancement station  106 , it is exposed to an electroless metal plating solution such as a copper solution (e.g., CuSO4 in acidic, basic, or neutral environments). During exposure to the metal plating solution, a process of electroless deposition of metal onto the conductive trace is driven by reactants within the metal plating solution. The metal deposited onto the conductive trace from the metal plating solution is generally spontaneous with a metal of higher nobility than the metal comprising the conductive trace. The use of a reducing agent in the electroless plating solution is needed if the metal in the plating solution is lower or around the same nobility as the conductive trace metal. Examples of reducing agents can include sodium hypophosphite, sodium borohydride, hydrazine, and so on. Deposition of additional metal onto the conductive trace generates an enhanced conductive trace that has improved conductivity compared to that of the preliminary conductive trace applied by the conductive trace application station  104 . 
       FIG. 2  shows an example of a conductive trace printing system  100  with additional details of a conductive trace application station  104  and a conductive trace enhancement station  106 . As shown in  FIG. 2 , a conductive trace application station  104  can include a print engine  108  and a print controller  110 , while a conductive trace enhancement station  106  can include or be implemented as a variety of different metal plating solution applicators  112  (illustrated as applicators  112   a ,  112   b ,  112   c ).  FIG. 3  shows a blow-up block diagram of an example conductive trace application station  104  illustrating different examples of print engines  108  (illustrated as print engines  108   a ,  108   b ,  108   c ) suitable for implementing within the conductive trace application station  104 .  FIG. 3  additionally shows an example print controller  110  for controlling a print engine  108  to print a conductive trace onto a media substrate  102 . 
     Referring generally to  FIGS. 2 and 3 , one example of a suitable print engine  108  for implementation within a conductive trace application station  104  comprises a liquid electro-photographic (LEP) printer  108   a . The LEP printer  108   a  shown in  FIG. 3  is a partial illustration of an LEP printer intended to supplement the following brief description of how an LEP printer can function to print a conductive trace onto a media substrate  102 . An LEP printer  108   a  can receive a printable media substrate  102  in various forms including cut-sheet paper from a stacked media input mechanism (not shown) or a media web from a media paper roll input mechanism (not shown). An LEP printer  108   a  includes a photo imaging component, or photoreceptor  114 , sometimes referred to as a photo imaging plate (PIP). The photoreceptor  114  is mounted on a drum or imaging cylinder  116 , and it defines the outer surface of the imaging cylinder  116  on which images can be formed. In some examples, images comprise designs and patterns for conductive traces. A charging component such as charge roller  118  generates electrical charge that flows toward the photoreceptor surface and covers it with a uniform electrostatic charge. A laser imaging unit  120  exposes image areas on the photoreceptor  114  by dissipating (neutralizing) the charge in those areas. 
     Exposure of the photoreceptor  114  creates a ‘latent image’ in the form of an invisible electrostatic charge pattern that replicates the conductive trace or other image to be printed. After the latent/electrostatic conductive trace image is formed on the photoreceptor  114 , it is developed by a binary ink development (BID) roller  122  to form a conductive ink image on the outer surface of the photoreceptor  114 . As noted above, the conductive trace can be applied using a variety of different conductive materials. Examples of conductive materials are metal materials that can include nickel (Ni), iron (Fe) trace, and others. In general, there is a wide range of materials that can be used for conductive inks. Examples of these material can include metal-based materials, carbon-based materials such as graphite and carbon nanotubes, and nanoparticles of metals. 
     In general, each BID roller  122  develops a single ink component or color (i.e., a single color separation) of the image, and each developed ink component separation corresponds with one image impression. The four BID rollers  122  shown, indicate a four component process, such as a four color process (i.e., C, M, Y, and K). In the present example, the four BID rollers  122  can include a conductive ink formulation for developing a conductive trace. The four BID rollers  122  may additionally include insulator and/or dielectric material ink formulations to be developed onto the photoreceptor  114 , as well as other material ink formulations associated with the application of a conductive trace onto a media substrate  102 . In some examples, an LEP printer can include additional BID rollers  122  corresponding to additional ink colors and/or ink formulations. 
     After a single ink component separation impression of an image is developed onto the photoreceptor  114 , it is electrically transferred from the photoreceptor  114  to an image transfer blanket  124 , which is electrically charged through an intermediate drum or transfer roller  126 . The image transfer blanket  124  overlies, and is securely attached to, the outer surface of the transfer roller  126 . The transfer roller  126  is can heat the blanket  124 , which causes the liquid in the ink to evaporate and the solid particles to partially melt and blend together, forming a hot adhesive liquid plastic that can be transferred to a print media substrate  102 . 
     In other examples, a conductive trace application station  104  may implement an inkjet based print engine  108  ( 108   b ,  108   c ) to apply a conductive trace to a media substrate  102  using an inkjet printhead  128 . An inkjet based print engine enables a drop-on-demand construction of a conductive trace onto a transfer roller  130  as shown with inkjet print engine  108   b , or directly onto a media substrate  102  as shown with inkjet print engine  108   c . A conductive ink trace applied to a transfer roller  130  may be exposed to heat or other radiation from a heat/radiation device  132  to help cure the ink prior to transferring to conductive trace onto a media substrate  102 . When applied directly to a media substrate, as shown with inkjet print engine  108   c , a conductive ink trace may be exposed to heat or another curing or drying mechanism in a subsequent step (not shown). Various formulations of jettable conductive inks may include nickel (Ni), iron (Fe) trace, and others. As noted above, various materials can be used for conductive inks such as metal-based materials, carbon-based materials such as graphite and carbon nanotubes, and nanoparticles of metals. 
     An example print controller  110  enables control over the printing and patterning of conductive traces and other images generated by a print engine  108 . The controller  110  can also control various other operations of the conductive trace printing system  100  to facilitate the application and enhancement of a patterned conductive trace, such as an RFID tag, onto a media substrate  102 . As shown in  FIG. 3 , an example controller  110  can include a processor (CPU)  134  and a memory  136 . The controller  110  may additionally include other electronics (not shown) for communicating with and controlling various components of the conductive trace printing system  100 . Such other electronics can include, for example, discrete electronic components and/or an ASIC (application specific integrated circuit). Memory  136  can include both volatile (i.e., RAM) and nonvolatile memory components (e.g., ROM, hard disk, optical disc, CD-ROM, magnetic tape, flash memory, etc.). The components of memory  136  can comprise non-transitory, machine-readable (e.g., computer/processor-readable) media that can provide for the storage of machine-readable coded program instructions, data structures, program instruction modules, PDL (page description language), PCL (printer control language), JDF (job definition format), 3MF formatted data, and other data and/or instructions executable by a processor  134  of the conductive trace printing system  100 . 
     An example of executable instructions to be stored in memory  136  include instructions associated with a print module  138 , while examples of stored data can include print data  140 . In general, print module  138  can include programming instructions executable by processor  134  to cause the print engine  108  to apply a conductive trace to a media substrate  102  according to information defined within print data  140  by any of several printing techniques as discussed above with regard to example print engines  108   a ,  108   b , and  108   c . Print data  140  can include information about patterns and/or designs of conductive traces such as RFIDS, in addition to text and other images to be printed on a media substrate  102 . 
     Referring again to  FIG. 2 , as mentioned, a conductive trace enhancement station  106  can include or be implemented as a variety of different metal plating solution applicators  112  (illustrated as applicators  112   a ,  112   b ,  112   c ). In one example, a metal plating solution applicator  112  can comprise a sponge applicator  112   a  capable of absorbing metal plating solution and distributing it onto a preliminary conductive trace applied to a media substrate  102  by the conductive trace application station  104 . A sponge applicator  112   a  can be formed of a variety of sponge materials including cellulose wood fibers or foamed plastic polymers. In some examples, a metal plating solution applicator  112  can comprise a liquid bath applicator  112   b  capable of soaking a conductive trace in a bath of metal plating solution as the media substrate  102  passes the conductive trace enhancement station  106 . Various other types of metal plating solution applicators are possible and contemplated herein, including a roll-to-roll applicator, and others. As noted above, the type of applicator  112  used to expose the conductive trace to the metal plating solution can depend in part on the type of media substrate  102  on which the trace is printed. 
       FIG. 4  shows an example of a conductive trace printing system  100  that includes an example overprint application station  142 . In some examples of a conductive trace printing system  100 , an overprint application station  142  can apply a protective overprint layer to a conductive trace and/or to the full surface of a media substrate  102 . An overprint application station  142  can be implemented by any of a variety of coating application devices including, for example, flexographic coating devices, gravure coating devices, reverse roll coating devices, knife-over-roll coating (“gap coating”) devices, metering rod (meyer rod) coating devices, slot die (slot, extrusion) coating devices, immersion coating devices, curtain coating devices, and air-knife coating devices. An overprint layer can include various transparent or opaque protective coatings such as OPV (over print varnish) coatings, UV coatings with matte or gloss finishes, electrically insulating coatings, dielectric coatings, aqueous coatings, and so on. Such coatings can be applied to conductive traces on media substrates  102  and/or to the entire surface of media substrates  102 . Such overprint layers can help protect conductive traces such as RFIDs applied to a media substrate  102 , as well as help protect, enhance, and strengthen the media substrate itself. 
       FIG. 5  shows examples of media substrates  102  in various stages of having a conductive trace applied by a conductive trace printing system  100 . As shown in part (a) of  FIG. 5 , a media substrate  102  has had a preliminary conductive trace  144  applied at the conductive trace application station  104 . In some examples, as shown in part (b) of  FIG. 5 , prior to applying a preliminary conductive trace  144 , an insulating layer  146  can be applied to the media substrate  102  by the conductive trace application station  104 . In these examples, the preliminary conductive trace  144  can be applied to the insulating layer  146  instead of directly to the surface of the media substrate  102 . As shown in part (c) of  FIG. 5 , a the preliminary conductive trace  144  has been exposed to an electroless metal plating solution in the conductive trace enhancement station  106  to generate an enhanced conductive trace  148 . An enhanced conductive trace  148  can include additional metal material formed on the trace making it thicker and more highly conductive. As shown in part (d) of  FIG. 5 , a protective overprint layer  150  has been applied by the overprint application station  142  over the enhanced conductive trace  148 . As shown in part (e) of  FIG. 5 , a protective overprint layer  150  has been applied over the entire surface of the media substrate  102 , including the enhanced conductive trace  148 . 
       FIGS. 6 and 7  are flow diagrams showing example methods  600  and  700 , of applying a conductive trace to a media substrate. Methods  600  and  700  are associated with examples discussed above with regard to  FIGS. 1-5 , and details of the operations shown in methods  600  and  700  can be found in the related discussion of such examples. The operations of methods  600  and  700  may be embodied as programming instructions stored on a non-transitory, machine-readable (e.g., computer/processor-readable) medium, such as memory  136  shown in  FIG. 3 . In some examples, implementing the operations of methods  600  and  700  can be achieved by a processor, such as a processor  134  of  FIG. 3 , reading and executing the programming instructions stored in a memory  136 . In some examples, implementing the operations of methods  600  and  700  can be achieved using an ASIC and/or other hardware components alone or in combination with programming instructions executable by a processor  134 . 
     The methods  600  and  700  may include more than one implementation, and different implementations of methods  600  and  700  may not employ every operation presented in the flow diagrams of  FIGS. 6 and 7 . Therefore, while the operations of methods  600  and  700  are presented in a particular order, the order of their presentation is not intended to be a limitation as to the order in which the operations may actually be implemented, or as to whether all of the operations may be implemented. For example, one implementation of method  700  might be achieved through the performance of a number of initial operations, without performing one or more subsequent operations, while another implementation of method  700  might be achieved through the performance of all of the operations. 
     Referring now to the flow diagram of  FIG. 6 , an example method  600  of applying a conductive trace to a media substrate begins an block  602  with applying a conductive trace to a media substrate. The method  600  also includes exposing the conductive trace to an electroless metal plating solution to enhance the conductive trace, as shown at block  604 . 
     Referring to the flow diagram of  FIG. 7 , another example method  700  of applying a conductive trace to a media substrate begins an block  702  with applying a conductive trace to a media substrate. In some examples, as shown at block  704 , applying a conductive trace to a media substrate can include applying an insulating layer onto the media substrate before applying the conductive trace, and then applying the conductive trace on the insulating layer. In some examples, applying a conductive trace to a media substrate can include printing the conductive trace in a printing process selected from the group consisting of a liquid electro-photographic printing process and an inkjet printing process, as shown at block  706 . 
     The method  700  can continue at block  708  with exposing the conductive trace to an electroless metal plating solution to enhance the conductive trace. In some examples, as shown at block  710 , exposing the conductive trace to an electroless metal plating solution comprises exposing the conductive trace to a solution of copper sulfate (CuSO4), a reducing agent, and sodium hydroxide (NaOH). In some examples, exposing the conductive trace to an electroless metal plating solution comprises exposing the conductive trace through a solution applicator selected from the group consisting of a sponge applicator, a bath applicator, and a roll-to-roll applicator, as shown at block  712 . The method  700  can continue as shown at block  714 , with applying a protective overprint layer over the enhanced conductive trace.