Patent Publication Number: US-2022219254-A1

Title: Method of connection to a conductive material

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to U. S. Provisional Application No. 63/136,870 filed on Jan. 13, 2021, entitled “METHOD OF CONNECTION TO A CONDUCTIVE MATERIAL,” the entire contents of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure is generally related to a method of preparing a busbar on a conductive material, particularly a conductive layer within a switchable film. 
     BACKGROUND 
     Switchable films in glass constructions may be provided for various purposes, including architectural and vehicle windows. Switchable films may include those based on liquid crystal constructions and may be selectively changed from an opaque or dark state to a transparent, or clear, state by the application of an electric field to the film. The electrical connection may be formed within the glass construction to control the switchable material. When an electric field is activated, the switchable material may transfer from an opaque state to a transparent state or vice versa. 
     Switchable materials may include polymer dispersed liquid crystal (PDLC) and polymer network liquid crystal (PNLC) constructions. PNLC materials are formed by liquid crystals dispersed throughout a liquid polymer matrix. As the polymer matrix solidifies, the liquid crystals form droplets. The random orientation of liquid crystal droplets results in the opaque, milky appearance of the PDLC in an OFF state. When an electrical current is applied to the PDLC, the liquid crystals may align parallel to the direction of the electric field. The parallel orientation allows for light to pass through, and in an ON state, PDLC is transparent relative to the OFF state. PNLC may also provide a film that may selectively switch between opaque and transparent states. PNLC films may have a higher ratio of liquid crystal to polymer and require a lower driving voltage than a PDLC. PDLC and PNLC films may also be configured to have a reverse alignment where, in a default OFF state, the PDLC or PNLC is transparent, and in an ON state with an electric voltage applied, the PDLC or PNLC is opaque. 
     To power the switchable films, electrical connections must be made to conductive layers in the switchable films. The connections may include the positioning of a busbar on the conductive layers. For efficient processing of the films and preparation of laminated glazings including such films, an efficient method for positioning busbars on conductive layers of the switchable films is needed. 
     BRIEF SUMMARY OF THE EXEMPLARS EMBODIMENTS 
     The disclosed exemplary embodiments are generally directed to a method of connection to a conductive material, particularly useful for assembling a laminated glazing with a switchable film. 
     According to an exemplary embodiment, a method of applying a busbar to a switchable film may include the steps of providing a switchable film having a first substrate, a first conductive layer, a switchable layer, a second conductive layer, and a second substrate; applying a solder material to the first conductive layer with ultrasonic application to provide a first busbar; and applying the solder material to the second conductive layer with ultrasonic application to provide a second busbar. 
     In the some embodiments, the solder material may be flux-free and/or lead-free. Each of the first and second busbars may have a length of at least 5 cm or at least 10 cm. Each of the first and second busbars may have a width of 6 mm or less. The method may include the step of removing a portion of the second substrate and the second conductive layer before applying the solder material to the first conductive layer and removing a portion of the first substrate and the first conductive layer before applying the solder material to the second conductive layer. In some embodiments, the switchable material may be cleaned off of the first conductive layer and the second conductive layer prior to applying the solder material. In some embodiments, the conductive layer may not be cleaned prior to applying the solder material to the first conductive layer and the second conductive layer such that at least part of the switchable layer remains on the first conductive layer and the second conductive layer during application of the solder material. 
     In the same or different embodiments, a first connector may be applied to the first busbar while a second connector may be applied to the second busbar. The first connector and the second connector may be applied by the solder material used tear the first busbar and the second busbar. The first connector and the second connector may be applied on the first busbar and the second busbar using a conductive adhesive. The first connector and the second connector may be flexible connectors. 
     In some embodiments, a first metallic foil may be applied over the first busbar whereas a second metallic foil may be applied over the second busbar. The first metallic foil and the second metallic foil may be formed from a copper tape. In a further embodiment, a first connector may be applied to the first metallic foil whereas a second connector may be applied to the second metallic foil. 
     In some embodiments, the ultrasonic application may include application of the solder material with an ultrasonic probe at a temperature from 230° C. to 290° C., preferably from 235° C. to 275° C. The switchable film may be a polymer dispersed liquid crystal film. Where the first conductive layer has more than one electrically isolated portion, each electrically isolated portion may include one of the first busbars. 
     In another aspect of this disclosure, a method of preparing a laminated glazing may include a step of laminating a switchable film prepared by the method described above between a first glass sheet and a second glass sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more example aspects of the present disclosure and, together with the detailed description, serve to explain their principles and implementations. 
         FIG. 1  illustrates a portion of a switchable film prepared by methods disclosed herein; 
         FIG. 2  illustrates a portion of a switchable film prepared by methods disclosed herein; 
         FIG. 3  illustrates a cross section of a portion of laminated glazing having switchable film prepared by methods disclosed herein; 
         FIG. 4  illustrates a cross section of a portion of a switchable film prepared by a method disclosed herein; 
         FIG. 5  illustrates a cross section of a portion of a switchable film prepared by a method disclosed herein; 
         FIG. 6  illustrates a cross section of a portion of a switchable film prepared by yet another method disclosed herein; and 
         FIG. 7  illustrates a cross section of a portion of a switchable film prepared by a further method disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, specific details are set forth in order to promote a thorough understanding of one or more aspects for the disclosure. It may be evident in some or all instances, however, that many aspects described below can be practiced without adopting the specific design details described below. 
     A switchable film may include, for example, a liquid crystal material, such as a polymer dispersed liquid crystal (PDLC) or polymer network liquid crystal (PNLC) film, an electrochromic film, or a nanoparticle material, such as a suspended particle device (SPD) film. A switchable film may particularly change between an opaque state and a relatively transparent state due to the application of an electrical field to the film. Particularly the switchable film may include a first substrate, a first conductive layer electrode, a switchable layer, a second conductive layer electrode, and a second substrate. The first and second substrates may preferably be a polymer film, such sa polyethylene terephthalate (PET) film. The conductive layers may include a conductive metal oxide, such as indium tin oxide (ITO). The switchable film may particularly be powered by connection to each of the conductive layers. A busbar may be provided on each of the conductive layers, and a connector may be applied to each busbar for connection to power source. 
     To create a suitable electrical connection to the conductive layers, busbars formed on the conductive layers must have a good electrical and mechanical connection to the conductive layers and further provide for a proper attachment of an electrical connector. Preparing such busbars on the conductive layers may create a time consuming production step. An efficient process for the application of such busbars is desirable to improve production processes and cost. Methods described herein may include providing a switchable film and applying a solder to a conductive layer of the switchable film via ultrasonic application to provide a busbar on the conductive layer. 
     Preferably, methods herein include applying a busbar to an exposed conductive layer of a switchable film. The busbar may be formed of a solder material which may preferably be applied by ultrasonic application. Ultrasonic application may particularly include applying the solder material with an ultrasonic probe for providing ultrasonic vibrations which may activate the solder material. Cavitation of the solder material by the ultrasonic soldering provides the attachment of the solder material to the underlying conductive layer. Oxides in the solder material may be mechanically disrupted by ultrasonic vibrations. The ultrasonic probe may be heated for the soldering process at least to a melting temperature of the solder material. The ultrasonic probe may be formed with a heater to increase the temperature of the soldering material. The heater may be controlled to apply suitable heat to the soldering material. If the probe is not hot enough, the solder material may not properly adhere to the conductive layer, and if the probe is too hot, a substrate layer under the conductive layer may melt or otherwise be deformed. Preferably, the probe is set to a temperature from 150° C. to 290° C., more preferably from 230° C. to 290° C., more preferably from 235° C. to 275° C. The inventors found that at a temperature of 230° C. provided suitable adhesion of the solder material to the conductive layer with Cerasolzer (registered trademark) #217 from Kuroda Techno. However, the temperature of the probe may be lowered down to 150° C., if another solder which has suitable adhesion at a temperature down to 150° C. is used. A temperature of 300° C. damaged an underlying polyethylene terephthalate substrate film. If a substrate other than polyethylene terephthalate is used, the temperature threshold may increase or decrease based on what may cause damage to the underlying substrate film. Further, a power output from 10 Watts to 13 Watts may be preferable with the ultrasonic probe during busbar application. The ultrasonic probe may preferably be used a frequency from 30 to 70 kHz. 
     The solder material may include a flux-free material suitable for ultrasonic application. Preferably, the solder is lead-free. For example, Cerasolzer (registered trademark) (such as #217) from Kuroda Techno may be used. These may include suitable conductive materials, such as Zn, Ti, Si, Al, Be, and Rare Earth Elements, which may react strongly with oxygen and create a strong bond with the underlying coated surface, particularly in the presence of an ultrasonically-produced cavitation field. 
     The solder material may particularly be applied in a shape desired for a busbar, such as a line of solder positioned along an edge of the conductive layer. The busbar may preferably have a width and length suitable for providing suitable electrical connection to conductive layer and providing a surface for attachment of an electrical connector. For example, a busbar may have a length of about 5 cm or more or about 10 cm or more. Further, some busbars may have a width of 6 mm or less. The width of the busbar may be 0.5 min or more to accommodate a connector, but is preferably minimized so as to take up less space on the switchable film and in a laminated glazing. Preferably the busbar does not have a width greater than 10 mm. 
     A switchable film may include two opposing conductive layers which independently connect to a power source. Thus, each conductive layer in a switchable film may require a busbar to facilitate such connections. The busbars may be formed on each conductive layer by the same process. Some switchable films may include electrically isolated segments in one or both conductive layers. Each electrically isolated portion of the coating may include a separate busbar to maintain electrical isolation. Methods disclosed herein may be used to prepare any or all of the busbars for a particular switchable film. 
     A connector may be attached onto the busbar and attached to a power source for controlling the switchable film. The connector may be a flexible connector, for example. To attach the connector to the busbar, any solder or conductive adhesive may be used. Preferably the same solder material used for preparation of the busbar may further be used for attachment of the connector. The process of attaching the connector may preferably include a soldering process which does not exceed a temperature of 290° C., more preferably 275° C. Preferably the connector is attached using a soldering process at the same temperature used daring the busbar preparation. In some preferable embodiments, the connector may be soldered to the busbar using an ultrasonic soldering probe. 
     In some embodiments, a metallic foil may be positioned over the busbar. Such a metallic foil may provide a good surface for a connector attachment. The metallic foil may include, for example, a copper tape. The metallic foil may include an adhesive, particularly a conductive adhesive, such that an electrical connection may be formed between the conductive layer and a connector soldered to the metallic foil. 
     In some methods, the switchable film may be provided without an exposed conductive layer, such that the conductive layer(s) must be exposed prior to applying a busbar thereon. Particularly, exposing the first conductive layer in an area for application of a busbar may include removing a substrate film and a second conductive layer to expose the first conductive layer. Removal may include cutting away the materials. Switchable material may remain on the first conductive layer during busbar application. In some embodiments, the first conductive layer may be cleaned with alcohol to remove the switchable material, leaving the first conductive layer ready for busbar application. The second conductive layer may be similarly prepared for a busbar by the local removal of the other substrate layer and the first conductive layer. The cutaway portion of the substrate and second conductive layer may have a width such that a distance between the busbar and the edge of the film and second conductive layer is preferably from 0.5 mm to 5 mm, more preferably from 1 mm to 3 mm. 
     The switchable film may be further laminated between first and second glass sheets. The switchable film may, for example, be laminated in an automotive glazing, such as a sunroof, a rear window, side window, or windshield. A laminated glazing may particularly include a first glass sheet, a first interlayer, a switchable film, a second interlayer, and a second glass sheet. The lamination process may include stacking the glass sheets, interlayers, and switchable film to provide a lamination stack where the switchable film is positioned between the first and second interlayers which are positioned between the first and second glass sheets. The busbars and connectors may be positioned on the conductive layers of the switchable film prior to lamination. The lamination process may include deairing the lamination stack to remove air from between the materials of the lamination stack. After deairing, the stack may be autoclaved, which includes applying heat and pressure to the lamination stack to provide a laminated glazing. Connectors attached to the switchable film may extend out of the glazing edge such that they can be connected to a power source outside of the glazing. 
     In a laminated glazing, the switchable film may be smaller than the first and second glass sheets in terms of surface area so that there is a distance between the edge of the laminated glazing and the edge of the switchable film within the glazing. Where a switchable film has a thickness of at least 0.25 mm, the laminated glazing may further include a third interlayer around the edge of the switchable film such that there is minimal to no change in thickness where the switchable film ends. 
     In a particular example, Cerasolzer (registered trademark) #217 from Kuroda Techno was applied to a conductive layer of a polymer dispersed liquid crystal film using an ultrasonic soldering probe at a temperature of 250° C. and at 12.5 W power. The conductive layer of the examples included indium tin oxide. A portion of the second substrate and second conductive layer were removed to reveal the first conductive layer. The solder material was then applied to provide a busbar on the first conductive layer. In some additional examples, the switchable material that remained on the first conductive layer was removed with alcohol prior to busbar application. Connectors were then soldered to the busbars and the switchable films were laminated between first and second glass sheets. In some examples, a copper tape was applied over the busbars prior to attachment of a connector. In some examples, the copper tape, which is connected to the first busbar or to the second busbar can be wrapped around the edge of the switchable film, to allow connection of first and second busbars from the same side of the switch able film. 
       FIG. 1  illustrates a portion of a switchable film  12  having a busbar  18  prepared thereon according to methods disclosed herein.  FIG. 2  illustrates a portion of the switchable film  12  having a connector  20  attached to a busbar  18  prepared according to methods disclosed herein.  FIG. 3  illustrates a laminated glazing  30  having a switchable film  12  laminated therein. In  FIG. 1  to  FIG. 3 , the switchable film  12  and the laminated glazing shows only a part of the film for an illustrative purpose. In  FIG. 1 , the switchable film  12  may be provided in a sheet-like rectangular shape, and a substrate cutaway  14  may be formed to open an edge of the switchable film  12  in a longitudinal shape to expose a first conductive layer  16  of the switchable film  12 . The substrate cutaway  14  may be formed by partly removing a second substrate, a second conductive layer, and a switchable material layer at the same area. Attachment of the busbar  18  to the exposed first conductive layer  16  is made by application of the soldering material with the ultrasonic oscillations. The busbar  18  may be formed of the solder material. Substantially the same process, not shown, may be used to provide a busbar on the second conductive layer by removing the first substrate, the first conductive layer, and the switchable material layer. 
     In  FIG. 2 , a connector  20  may be attached to the surface of the busbar  18 . The connector  20  may be attached to the busbar  18  by ultrasonic application or by bonding with a solder without ultrasonic application, depending on the design or structural materials of the busbar  18  and the connector  20 . Alternatively, the connector  20  may be adhered to the busbar  18  by a conductive adhesive. A first connector  20  may be attached to the first busbar  18 , while a second connector, not shown, may be attached to a second busbar, not shown. The first and second connectors may be attached to the busbars simultaneously or sequentially. 
     After attaching the connector  20  to the switchable film  12 , the switchable film  12  may be laminated between a first glass sheet  22  and a second glass sheet  24  as shown in  FIG. 3 . The switchable film  12  may be sandwiched between a first interlayer  26  and a second interlayer  28  and laminated between the first and second glass sheets  22 ,  24  to produce a laminated glazing  30 . The connectors  20  project from the edge of the laminated glazing  30  to easily connect a power source. For simplicity, the details of the switchable film  12  layers are not shown in  FIG. 3 . The glass sheets  22 ,  24  and interlayers  26 ,  28  may extend past an edge of the switchable film  12 . A third interlayer  27  may be provided around the edge of the switchable film between the first interlayer  26  and the second interlayer  28 . 
       FIG. 4  shows details of the switchable film  12  according to methods disclosed herein. The switchable film  12  may be placed between the first and second interlayers  26 ,  28  and be laminated between the first and second glass sheets  22 ,  24 . The switchable film  12  may be typically formed of a first substrate  40 , a first conductive layer  38 , a switchable material layer  36 , a second conductive layer  34 , and a second substrate  32 . To switch between the opaque state and the transparent state, a change in voltage may be applied to the first conductive layer  38  and the second conductive layer  34  via busbars  42 ,  44  from a first connector  46  and a second connector  48 . Particularly, some switchable films may switch to a transparent state when a voltage is applied. An alternating current voltage may be used. 
     The first connector  46  may be coupled to the first conductive layer  38  through the busbar  42  whereas the second connector  48  may be coupled to the second conductive layer  34  through the second busbar  44 . The busbars  42 ,  44  and the connectors  46 ,  48  may be connected upon removing the substrates  32 ,  40  and the conductive layers  34 ,  38 . The connections between the connectors and the conductive layers may be done by various methods as shown from  FIG. 5  to  FIG. 7 . In  FIG. 5  to  FIG. 7 , although only a first conductive layer  38  is illustrated to be connected to a connector  46 , the second conductive layer  34  may be connected subsequently to another connector, which is omitted here for the sake of simplicity. 
       FIG. 5  shows a method of connecting the connector  46  and the first conductive layer  38 . The surface of the first conductive layer  38  may be exposed by removing the second substrate  32 , the second conductive layer  34 , and the switchable material layer  36 . A solder material  50  may be provided on the exposed surface of the first conductive layer  38 . The solder material  50  may melt with application of heat from an ultrasonic probe, not shown, and may be adhered to the surface of the first conductive layer  38 , enhanced with the help of ultrasonic oscillation. This ultrasonic application may be done quickly, such as within 10 seconds, and the probe may be heated with a heater attached to the probe. The solder material  50  may be strongly adhered to the surface of the first conductive layer  38 . The solder material  50  may be provided in an extended shape on the conductive layer&#39;s surface as to constitute “a busbar”  16 ,  42 ,  44  for connection. 
     After the solder material  50  is provided, a connector  46  may be attached to the solder material  50  by ultrasonic application or regular soldering application. During ultrasonic application, the ultrasonic probe may be used to heat the solder material  50  for attachment of the connector  46 . In the regular soldering application, the solder material  50  is heated again to adhere the connector  46 . 
       FIG. 6  shows another method of connection between the first connector  46  and the first conductive layer  38 . In this method, after the solder material  50  is applied with ultrasonic application, the connector  46  may be coupled to the surface of the solder material  50  via another solder material  52 . The solder material  52  may have a melting temperature less than the busbar solder material  50  such that the busbar solder material  50  does not melt with application of the connector  46 . The connector  46  may be prepared with the solder material  52  on a back side of the connector  46  in advance, and the solder material  52  may be soldered to the surface of the solder material  50 . The solder material  52  may be a conventional solder containing flux, which may be soldered with heat application. Furthermore, the solder material  52  may be formed of the same material as the solder material  50 , and the solder material  52  may be subject to ultrasonic application to connect the connector  46  to the solder material  50 . The connector  46  may have a conductive adhesive in lieu of the solder material  52 , and the connector  46  may be attached to the solder material  50  by pressure application without applying heat to the substrate  40 . Alternatively, such the solder material  52  or conductive adhesive may be applied first to the surface of the solder material  50  and then may be adhered to the connector  46 . 
       FIG. 7  shows yet another method of connecting the first connector  46  and the first conductive layer  38 . In this method, after the solder material  50  is applied with ultrasonic application, a metal foil  54  with a conductive adhesive  56  in the form of a tape may be provided on the solder material  50  serving as the busbar. Subsequently, a connector  46  having a solder material  52  may be provided on the surface of the metal toil  54 . The surface of the metal toil  54  may be smooth, such that the connector  46  may easily adhere to the surface of the metal foil  54 . Where the metal foil  54  is provided, the metal foil  54  may prevent heat applied to the solder material  52  from reaching the first substrate  40 , so that the heat may not affect the first substrate  40 . Further as a matter of course, the solder material  52  may be formed of the same material as the solder material  50 . Moreover, the connector  46  may have a conductive adhesive in lieu of the solder material  52 . 
     The ultrasonic probe may be formed with an ultrasonic oscillator for generating ultrasonic oscillations, a horn transmitting the generated ultrasonic oscillations, a tip serving as an applicator of the ultrasonic oscillations, and a heater for heating the tip of the probe. To operate the ultrasonic probe, a signal is given from a controller to the ultrasonic oscillator, and a current from the controller flows the heater to apply heat of controlled temperature. A solder material may receive the ultrasonic oscillations and the heat from the heater via the tip, thereby melting and strongly bonding to the surface of the underlying layer. 
     The above description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the common principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Further, the above description in connection with the drawings describes examples and does not represent the only examples that may be implemented or that are within the scope of the claims. 
     Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and/or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.