Patent Publication Number: US-2021185767-A1

Title: Conductive ink with enhanced mechanical fatigue resistance

Description:
FIELD 
     The present disclosure relates to a conductive ink, and more particularly, to a conductive ink with greater mechanical fatigue resistance. 
     BACKGROUND 
     Heating elements for electrothermal deicers typically use etched alloys. The etching process can have an effect on material properties of a component, such as the mechanical properties, or the like. The etching process may remove metal from the surface of a part, which may have an effect on dimensional tolerances or the like. Additionally, chemical etching may be difficult to automate and/or have waste disposal issues. 
     SUMMARY 
     A conductive ink is disclosed herein. The conductive ink may comprise: a high melting temperature thermoplastic polyurethane (TPU), the high melting temperature TPU including a melting point between 120° C. (248° F.) and 200° C. (392° F.); and a plurality of conductive particles disposed in the high melting temperature TPU, the plurality of conductive particles comprising between 60% and 95% of the conductive ink by weight. 
     In various embodiments, the conductive ink may further comprise a free radical crosslinker. The free radical crosslinker may include peroxide. The plurality of conductive particles may include at least one of silver platelet particles and nanosilver. The plurality of conductive particles may include carbon nanotubes (CNT). The CNT may comprise between 70% and 85% of the conductive ink by weight. 
     A heating trace assembly is disclosed herein. The heating trace assembly may comprise: an insulator; a ceramic positive temperature coefficient (PTC) element coupled to the insulator, the ceramic PTC element extending along a length of the insulator; a first bus bar extending along the length of the insulator; and a second bus bar extending along the length of the insulator, the ceramic PTC element coupled to the first bus bar and the second bus bar. 
     In various embodiments, the ceramic PTC element is a thin film of ceramic PTC. The first bus bar may be a first conductive ink. The second bus bar may be a second conductive ink. The first conductive ink and the second conductive ink may each include: a high melting temperature thermoplastic polyurethane (TPU), the high melting temperature TPU including a melting point between 120° C. (248° F.) and 200° C. (392° F.); and a plurality of conductive particles disposed in the high melting temperature TPU, the plurality of conductive particles comprising between 60% and 95% of each conductive ink by weight. The first conductive ink and the second conductive ink may each include a free radical crosslinker. The plurality of conductive particles may include at least one of silver platelet particles and nanosilver. The insulator may include a first flexible substrate. The ceramic PTC element may be coupled to the first flexible substrate by an adhesive. The insulator may include a second flexible substrate, and the first bus bar and the second bus bar may be coupled to the second flexible substrate by an adhesive. The insulator may include a first flexible substrate, and the first bus bar and the second bus bar may be coupled to the first flexible substrate by an adhesive. 
     A method of manufacturing a conductive ink is disclosed herein. The method may comprise: mixing a high melting temperature thermoplastic polyurethane (TPU) with a plurality of conductive particles, the high melting temperature TPU including a melting point between 120° C. (248° F.) and 200° C. (392° F.), the plurality of conductive particles comprising between 60% and 95% of a resultant mixture; and curing the high melting temperature TPU and the plurality of conductive particles. 
     In various embodiments, the mixing may further comprise mixing at least one of a free radical crosslinker with the high melting temperature TPU and the plurality of conductive particles, and wherein curing further comprises heating the resultant mixture. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the following illustrative figures. In the following figures, like reference numbers refer to similar elements and steps throughout the figures. 
         FIG. 1  illustrates a plain view showing an aircraft, in accordance with various embodiments; 
         FIG. 2  illustrates a potable water system of an aircraft, in accordance with various embodiments; 
         FIG. 3  illustrates a cross-sectional view of an internal heating trace assembly, in accordance with various embodiments; 
         FIG. 4  illustrates a potable water system of an aircraft, in accordance with various embodiments; 
         FIG. 5  illustrates a cross-sectional view of an internal heating trace assembly, in accordance with various embodiments; 
         FIG. 6  illustrates a conductive ink, in accordance with various embodiments; 
         FIG. 7  illustrates a conductive ink, in accordance with various embodiments; and 
         FIG. 8  illustrates a method of manufacturing a conductive ink, in accordance with various embodiments. 
     
    
    
     Elements and steps in the figures are illustrated for simplicity and clarity and have not necessarily been rendered according to any particular sequence. For example, steps that may be performed concurrently or in different order are illustrated in the figures to help to improve understanding of embodiments of the present disclosure. 
     DETAILED DESCRIPTION 
     The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosures, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. 
     The scope of the disclosure is defined by the appended claims and their legal equivalents rather than by merely the examples described. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to tacked, attached, fixed, coupled, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. 
     Disclosed herein is a conductive ink for enhanced mechanical fatigue resistance. The conductive ink may comprise conductive particles and a high melting temperature polyurethane (TPU). In various embodiments, the conductive ink may further comprise a free radical crosslinker, such as peroxide The conductive ink may be configured for greater fatigue resistance performance in bending cycle fatigue tests. 
     With reference to  FIG. 1 , an aircraft  10  is provided with a fuselage  20 , a left side wing  12  and a right side wing  14 . The left side wing  12  and right side wing  14  are designed to provide lift to the aircraft and enable it to fly. The fuselage  20  may house passengers, as well as various components configured to operate aircraft  10 . In various embodiments, the fuselage  20  may comprise a water system  100 . Water system  100  may be a potable water system, a gray water system, or the like. Water system  100  may be disposed in an area of fuselage  20  that is susceptible to outside temperature control. As such, at high altitudes, water system  100  may be exposed to temperatures below freezing. Water system may be temperature controlled by an internal heating trace assembly. 
     Referring now to  FIG. 2 , a schematic view of a portion of a water system  100  for use on an aircraft  10 , in accordance with various embodiments, is illustrated. The water system  100  comprises a first tube  110 , a second tube  120 , an electrical interface  130 , and an internal heating trace assembly  140 . The first tube  110  may comprise a wye shape, a tee shape, or the like. The first tube  110  may comprise a water inlet  112 , a water outlet  114 , and a heating trace inlet  116 . The second tube  120  may comprise a water inlet  122  and a water outlet  124 . The water inlet  122  of the second tube  120  may be coupled to the water outlet  114  of the first tube  110  by any method known in the art. For example, water inlet  122  of the second tube  120  may be coupled to the water outlet  114  of the first tube  110  by a coupling  118 , such as two-ferrule fitting, a single ferrule fitting, a ferrule-less push-fit connector, a collar fitting, or the like. The water system  100  may flow in a first direction B from water inlet  112  from first tube  110  through water outlet  124  of second tube  120 . 
     In various embodiments, electrical interface  130  is disposed at the heating trace inlet  116  of the first tube  110 . The electrical interface  130  may be any electrical interface  130  known in the art, such as a junction box or the like. The electrical interface  130  may be in electrical communication with a controller and/or a monitoring system. The electrical interface  130  is coupled to the internal heating trace assembly  140 . The internal heating trace assembly  140  is in electrical communication with the electrical interface  130 . A first end  142  internal heating trace assembly  140  is fixed at the electrical interface  130  and the second end  144  is free within the water system  100 . For example, second end  144  may be free in second tube  120  or an upstream tube in water system  100 . The internal heating trace assembly  140  may be configured to control a temperature of water disposed in water system  100  during normal operation. In various embodiments, bus wires disposed in the internal heating trace assembly  140  may conduct current from the electrical interface  130  through the length of the internal heating trace assembly  140  during normal operation. 
     Although water system  100  is disclosed with respect to an aircraft  10 , any water system with temperature control is within the scope of this disclosure. 
     Referring now to  FIG. 3 , a cross-sectional view of internal heating trace assembly  140  along section A-A from  FIG. 2 , in accordance with various embodiments, is illustrated. Internal heating trace assembly  140  comprises a ceramic Positive Temperature Coefficient (PTC) element  210 , a first bus bar  220 , a second bus bar  230 , and an insulator  240 . In various embodiments, the ceramic PTC element  210  may extend along the length of the internal heating trace assembly  140 . The ceramic PTC element  210  may be disposed between, and coupled to, the first bus bar  220  and the second bus bar  230 . In various embodiment, the ceramic PTC element is in electrical communication with the first bus bar  220  and the second bus bar  230 . The first bus bar  220  and the second bus bar  230  may be any conductive element known in the art. For example, the first bus bar  220  and the second bus bar  230  may be a conductive ink as disclosed herein. The first bus bar  220  and the second bus bar  230  may be electrically coupled to the electrical interface  130  from  FIG. 2 . The first bus bar  220  and the second bus bar  230  may be configured to carry an electrical current in internal heating trace assembly  140 . 
     In various embodiments, insulator  240  is disposed around the first bus bar  220 , the second bus bar  230 , and the ceramic PTC element  210 . The insulator  240  may be any electrical insulator known in the art (e.g., polyethylene, cross linked polyethylene-XLPE, polyvinyl chloride PVC, Teflon, silicone, polyolefin, fluoropolymer, etc.). The insulator  240  may be configured to insulate the electricity generated from the first bus bar  220 , the second bus bar  230 , and the ceramic PTC element  210  from the water disposed in water system  100  from  FIG. 2 . 
     In various embodiments, an adhesive is disposed between the insulator  240  and the ceramic PTC element  210 . In various embodiments, an adhesive is disposed between the insulator  240  and the first bus bar  220  and the second bus bar  230 . The insulator  240  may include a first flexible substrate  242 . In various embodiments, when the first bus bar  220  and the second bus bar  230  are conductive inks, the conductive inks are deposited on the first flexible substrate  242  running down the length of the flexible substrate  242 . The first bus bar  220  and the second bus bar  230  are a thermoset-based ink, such as a silver conductor sold under the trademark DuPont® 5025 which is available from DuPont of Midland, Mich., a conductor sold under the trademark Loctite® ECI 1010 E&amp;C which is available from Henkel Corporation of Dusseldorf, Germany. In various embodiments, the ceramic PTC element  210  may include a thin film of ceramic PTC. In various embodiments, the thin film of ceramic PTC may be printed on the second flexible substrate  244  along the length of the second flexible substrate  244 . In various embodiments, a liquid closeout may be coated on the second substrate  244  prior to printing the ceramic PTC element  210  and cured after the ceramic PTC element  210  is printed on the second substrate  244 . In various embodiments, a solid film closeout of the PTC element  210  is bonded on with adhesive. 
     Referring now to  FIG. 4 , a schematic view of a portion of a water system  400  for use on an aircraft  10 , in accordance with various embodiments, is illustrated. The water system  400  comprises a tube  410 , an electrical interface  430 , and a heating trace assembly  440 . The tube  410  may be configured to carry a fluid, such as gray water, or the like. The tube  410  may comprise a water inlet  412  and a water outlet  414 . The water system  100  may flow in a first direction C from water inlet  412  from tube  410  through water outlet  114  of tube  410 . 
     In various embodiments, electrical interface  430  is disposed proximate the tube  410 . The electrical interface  430  may be any electrical interface  430  known in the art, such as an electrical connector or the like. The electrical interface  430  may be in electrical communication with a controller and/or a monitoring system. The electrical interface  430  is coupled to the heating trace assembly  440 . The heating trace assembly  440  is in electrical communication with the electrical interface  430 . A first end  442  internal heating trace assembly  440  is fixed at the electrical interface  430  and the second end  444  is fixed to an outer surface of tube  410 . For example, second end  144  may be fixed to the outer surface of tube  410  by any method known in the art, such as an adhesive or the like. The heating trace assembly  440  may be configured to control a temperature of water disposed in water system  100  during normal operation. In various embodiments, bus wires disposed in the heating trace assembly  140  may conduct current from the electrical interface  430  through the length of the heating trace assembly  440  during normal operation. 
     Although water system  400  is disclosed with respect to an aircraft  10 , any water system with temperature control is within the scope of this disclosure. 
     Referring now to  FIG. 5 , a cross-sectional view of heating trace assembly  440  coupled to an outer surface of a tube, in accordance with various embodiments, is illustrated. Heating trace assembly  440  comprises a ceramic PTC element  210 , a first bus bar  220 , a second bus bar  230 , and an insulator  240 . In various embodiments, the ceramic PTC element  210  may extend along the length of the heating trace assembly  440 . The ceramic PTC element  210  may be disposed between, and coupled to, the first bus bar  220  and the second bus bar  230 . In various embodiment, the ceramic PTC element is in electrical communication with the first bus bar  220  and the second bus bar  230 . The first bus bar  220  and the second bus bar  230  may be any conductive element known in the art. For example, the first bus bar  220  and the second bus bar  230  may be a conductive ink as disclosed herein. The first bus bar  220  and the second bus bar  230  may be electrically coupled to the electrical interface  430  from  FIG. 4 . The first bus bar  220  and the second bus bar  230  may be configured to carry an electrical current in internal heating trace assembly  140 . 
     In various embodiments, insulator  240  is disposed around the first bus bar  220 , the second bus bar  230 , and the ceramic PTC element  210  and coupled to an outer surface  550  of tube  410 . The insulator  540  may be any electrical insulator known in the art (e.g., polyethylene, cross linked polyethylene-XLPE, polyvinyl chloride PVC, polytetrafluorethylene (PTFE), silicone, polyolefin, fluoropolymer, etc.). The insulator  540  may be configured to insulate the electricity generated from the first bus bar  220 , the second bus bar  230 , and the ceramic PTC element  210  from external components in water system  400  from  FIG. 4 . 
     Referring now to  FIG. 6 , a conductive ink  600 , in accordance with various embodiments, is illustrated. The conductive ink  600  may be configured for enhanced mechanical fatigue resistance. In various embodiments, first bus bar  220  and second bus bar  230  may comprise conductive ink  600 . Although described with respect to an internal heating trace assembly  140 , conductive ink  600  may be used for rotor blades and/or fixed wing electrothermal ice protection. For example, conductive ink  600  may be utilized as a bus bar for an electrothermal ice protection system in a rotor blade and/or fixed wing. By utilizing the conductive ink  600 , the ice protection system may be more robust (i.e., the conductive ink may provide mechanical fatigue resistance during vibration of the rotor blade or fixed wing). 
     The conductive ink comprises a high melting temperature thermoplastic polyurethane (TPU)  610  and a plurality of conductive particles  620 . A “high melting temperature TPU,” as disclose herein is a TPU with a melting point between 120° C. (248° F.) and 200° C. (392° F.), or between 140° C. (284° F.) and 190° C. (374° F.), or between 140° C. (284° F.) and 185° C. (365° F.). In various embodiments, the high melting temperature TPU may be any high melting temperature TPU known in the art, such as that sold under the trademark Pearlbond® 960 EXP, Pearlbond® 95AB0 NAT, 021 Pearlbond® HMS EXP which is available from Lubrizol of Wickliffe, Ohio, USA, IROGRAN® A 98 P 4535 which is available from Huntsman Corporation of The Woodlands, Tex., USA, ELASTOLLAN® 785 A 10 HPM polyester, or the like. 
     In various embodiments, the plurality of conductive particles  620  may be any conductive particles known in the art. For example, the plurality of conductive particles may comprise silver particles, silver platelet particles, nanosilver, or any combination of the three. In various embodiments, the plurality of conductive particles  620  may comprise carbon nanotubes (CNT) graphene, or the like. 
     Referring now to  FIG. 7 , a conductive ink  700 , in accordance with various embodiments, is illustrated. The conductive ink comprises mixture  710  and a plurality of conductive particles  620 . In various embodiments, the mixture  710  includes a high melting temperature thermoplastic polyurethane (TPU) and a free radical cross linker, such as peroxide. In various embodiments, the conductive particles  620  may be disposed within the urethane elastomer. 
     In various embodiments, the conductive inks  600 ,  700  may comprise the plurality of conductive particles  620  in an amount of 60% to 95%, or between 65% and 90% by weight of the conductive ink. In various embodiments, when the conductive particles comprise CNT, the amount of CNT particles may be between 70% and 85%. 
     In various embodiments, the conductive inks  600 ,  700  may show provide enhanced fatigue resistance performance in four point bending cycle fatigue tests compared to chemical etching, or the like. The conductive inks  600 ,  700  may be used for external heated composite structures, such as rotor blades, fixed wings, faring, engine lip electrothermal ice protection, or the like. 
     Referring now to  FIG. 8 , a method  800  for manufacturing a conductive ink, in accordance with various embodiments, is illustrated. The method  800  comprises mixing a high melting temperature TPU with a plurality of conductive particles (step  802 ). In various embodiments, the mixing may further comprise mixing a free radical crosslinker, such as peroxide. The mixture may be in accordance with conductive inks  600 ,  700 , as disclosed above. The method may further comprise curing the mixture of high melting temperature TPU with the plurality of conductive particles (step  804 ). In various embodiments, the curing may comprise heating the mixture, resulting in crosslinking between the high melting temperature TPU and the free radical crosslinker. In various embodiments, the curing may comprise adding an additive which acts as a reinforcing agent and an adhesive promoter, such as titanium dioxide particles. 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosures. The scope of the disclosures is accordingly to be limited by nothing other than the appended claims and their legal equivalents, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “various embodiments”, “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element is intended to invoke 35 U.S.C. 112(f), unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.