Manufacturing a Conductive Transfer

Abstract

A conductive transfer 101 comprises a first non-conductive ink layer 103 and a second non-conductive ink layer 104; an electrically conductive ink layer 105 positioned between the first non-conductive

Description

TECHNICAL FIELD The present invention relates to a method of manufacturing a conductive transfer and a conductive transfer comprising a substrate comprising a thermoplastic polymer. BACKGROUND OF THE INVENTION Transfer printing is traditionally used to allow printed images and designs to be applied to available surfaces, including wearable items and surfaces of articles made from fabrics, plastics or wood. The present applicant has developed technology in the field of conductive transfers which adapt processes in transfer printing to produce conductive transfers which can be utilised to form electronic products with increased functionality. Conventional transfers produced from printing involve a process in which a number of printed layers are printed directly onto a substrate or other fabric. For transfers with a large number of layers, the substrate or fabric must be able to withstand repeated applications of printing thereon and the subsequent curing and drying each ink layer requires. As part of this process, each printed ink layer is typically processed through a curing machine which applies heat to cure and dry the ink at an appropriate rate. This consequently limits the choice of materials which are suitable for a substrate of such a transfer. Thermoplastic polymers are known to be used for substrates. They are not suitable for conductive transfers having increased functionality as these types of transfers require a large number of printed layers. Consequently, with each repeated curing and drying process for each layer, a thermoplastic polymer substrate repeatedly melts and solidifies thereby increasing in overall hardness with each layer and losing its flexibility and functionality. BRIEF SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided a method of manufacturing a conductive transfer, as claimed in claim 1. According to a second aspect of the present invention, there is provided a conductive transfer as claimed in claim 15. Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings. The detailed embodiments show the best mode known to the inventor and provide support for the invention as claimed. However, they are only exemplary and should not be used to interpret or limit the scope of the claims. Their purpose is to provide a teaching to those skilled in the art. Components and processes distinguished by ordinal phrases such as “first” and “second” do not necessarily define an order or ranking of any sort. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS Figure 1 shows a conductive transfer comprising a plurality of layers; Figure 2 shows a schematic of a method of manufacturing a conductive transfer; Figure 3 shows a step of screen-printing in a method of manufacturing a conductive transfer; Figure 4 shows a step of curing in a method of manufacturing a conductive transfer; Figure 5 shows a step of heat pressing a conductive transfer to a substrate comprising a thermoplastic polymer; Figure 6 shows a cross-sectional schematic view of a conductive transfer undergoing the step shown in Figure 5; Figure 7 shows a cross-sectional schematic view of a conductive transfer comprising first and second substrates; Figure 8 shows a cross-sectional schematic view of the conductive transfer of Figure 7, having been formed into a curved article; Figure 9 shows a cross-sectional schematic of an example heated conductive transfer; Figure 10 shows a vehicle seat comprising a heated conductive transfer; Figure 11 shows a cross-sectional schematic of an example conductive transfer comprising an electrical component; and Figure 12 shows a wearable item incorporating a conductive transfer comprising an electrical component. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Figure 1 A conductive transfer in accordance with the present invention is shown in Figure 1. Conductive transfer 101 comprises a plurality of layers which provide electrical functionality and which can be utilised to form part of an electrical circuit. In the embodiment, conductive transfer 101 comprises a release film 102 onto which the remaining layers may be printed thereon. In the embodiment, conductive transfer 101 comprises a first non-conductive ink layer 103 and a second non-conductive ink layer 104. Positioned between first non-conductive ink layer 103 and second non-conductive ink layer 104 is an electrically conductive ink layer 105 which is encapsulated by non-conductive ink layers 103 and 104. An adhesive layer 106 is further provided to enable the conductive transfer 101 to be transferred from release film 102 to a substrate comprising a thermoplastic polymer in accordance with the invention. It is appreciated that, in further embodiments conductive transfer 101 may be transferred to any other suitable flexible or stretchable substrate that would not typically survive the traditional manufacturing process. In an embodiment, this includes alternative substrates such as substrates comprising a paper-based material or another material damageable by repeated curing processes. In the embodiment, non-conductive ink layers 103 and 104 comprise a suitable printing ink which may be a water-based printing ink, an ultraviolet cured printing ink, a solvent-based ink, or a latex printing ink. In the embodiment, electrically conductive ink layer 105 comprises any suitable conductive ink of any specified resistance and is configured to provide a conductive path on application of an electric current or voltage. In an embodiment, conductive ink 105 comprises a silver-based ink although it is appreciated that any other suitable conductive ink may be utilised depending on the application. In the embodiment, adhesive layer 106 may comprise a water-based adhesive, a solvent-based adhesive, a printable adhesive, a powder adhesive or any other suitable adhesive which is capable of adhering conductive transfer 101 to a substrate. Typically, adhesive layer 106 comprises a printed adhesive which is substantially transparent. In the embodiment, release film 102 comprises a polyester film onto which the layers 103, 104, 105, and 106 are printed thereon. Alternatively, release film 102 comprises a paper film or a coated paper film. Release film 102 is configured to be enabled to be removed from the remaining layers of material following an application of heat and / or pressure as will be described further with respect to Figures 5 and 6. It should be noted that the exploded schematic of Figure 1 illustrates the layers of the conductive transfer in a simplified form. In practice, each of the non-conductive layers 103 and 104 comprise a plurality of printed layers of the same material. This ensures that the non-conductive layers provide a solid layer of a consistent thickness and, typically, in manufacture, several layers will be overprinted to ensure a robust and durable layer. This similarly applies to conductive layer 105 which may comprise several overprinted layers of a silver-based ink to ensure the required conductivity. As will further be seen in the example illustrated in Figures 9 and 10, conductive layer 105 may further comprise layers of more than one material to enable increased electrical functionality. Similarly, it is anticipated that adhesive layer 106 may comprise a plurality of printed layers to form adhesive layer 106. Figure 2 A schematic of a method of manufacturing the conductive transfer 101 shown previously in Figure 1 is shown in Figure 2. Conductive transfer 101 comprises a first step 201 of printing a non-conductive ink onto release film 102 to produce a first non-conductive ink layer. Once the first non-conductive ink layer has been printed, non-conductive ink undergoes a curing process at step 202. The curing process ensures that the layers are fully solidified prior to the printing of a further layer thereon. This process will be described further with respect to Figure 4, however, it is to be appreciated that the step of curing comprises drying the first non-conductive ink layer typically by blowing hot air over the layers by means of a curing machine. Once the first non-conductive ink layer has been appropriately cured, at step 203, an electrically conductive ink is printed onto the first non-conductive ink layer to produce an electrically conductive ink layer. Similarly, the electrically conductive ink layer is cured at step 204 in a substantially similar manner to the curing of first non-conductive ink layer at step 202. At step 205, further printing of the non-conductive ink, which may be substantially similar to the non-conductive ink of the first non-conductive ink layer, is printed to form the second non-conductive ink layer at step 205. This is subsequently cured at step 206 in preparation of the printing of an adhesive material over the second non-conductive ink layer to produce an adhesive layer at step 207. At step 208 adhesive layer is cured via the curing machine in a substantially similar manner as described previously. Thus, by the end of step 208, the plurality of layers have been printed effectively onto the release film 102 and are ready for transfer. At step 209 therefore, the release film to which the non-conductive ink layers, electrically conductive ink layer and adhesive layer are attached thereto is applied to a substrate comprising a thermoplastic polymer. In order to adhere the conductive transfer 101 to the substrate an application of heat and / or pressure is applied to the substrate, the layers and the release film such that adhesive layer 106 adheres to the substrate. Release film 102 can then be removed from non-conductive ink layer 103 at step 210 by peeling release film 102 from non-conductive ink layer 103. Consequently, the remaining conductive transfer comprising the non-conductive ink layers, electrically conductive ink layer and the adhesive layer are retained on the substrate. Figure 3 An example embodiment of the printing steps for each layer material is shown in Figure 3. In this illustrated embodiment, Figure 3 shows a method of a screen-printing process which can be utilised to produce each of the layers. While this illustrated example shows an example of screen-printing, it is appreciated that alternative methods of printing may be utilised to produce the conductive transfer which involve any one of the following forms of printing: reel to reel printing; dot matrix printing; laser printing; cylinder press printing; inkjet printing; flexographic printing; lithographic printing; offset printing; digital printing; gravure printing; or xerographic printing. It is further appreciated that the invention is not intended to be limited to these specific methods. In the embodiment, release film 102 is placed by operative 103 onto a surface 302 of a screen-printing machine 303. In the embodiment, release film 102 comprises a sheet of appropriate film which is positioned to be aligned with the screen-printing stencil 304. Once positioned, the screen 305 onto which stencil 304 sits, can be lowered such that the required ink may be released onto release film 102 and printed in the appropriate design or pattern corresponding to that of the stencil 304. It is noted that for each printing step in the method shown in Figure 2, release film 102 may initially be free of ink, however, with further steps of printing release film 102 will comprise additional layers of ink depending on the stage in the process. Figure 4 Following the printing of each layer, the release film, which includes at least one printed layer, is then processed by means of a curing machine 401 as depicted in Figure 4. In the embodiment, curing machine 401 comprises a dryer which provides a hot air flow onto sheets 402, 403 and 404 such that any printed layers can be cured effectively and the respective inks appropriately dried. In the embodiment, the blown air temperature inside the dryer of the curing machine for a worn is often between around one hundred and twenty degrees Celsius and one hundred and fifty degrees Celsius (120°C and 150°C). Consequently, it is appreciated that if the printed ink layers were printed directly onto a substrate comprising a thermoplastic polymer, this would have a significant effect on the quality of the substrate. Thus, the release film is provided of an alternative material to ensure the curing process can be conducted effectively and repeatedly even in the cases of complex conductive transfers in which several layers including layers with a plurality of overprint are required. The curing process is important as, to ensure effective electrical circuits in many applications, it is important to avoid cross-contamination of the layers particularly those between the non-conductive ink layers and the electrically conductive ink layer. Figure 5 A step of applying the release film comprising the first non-conductive ink layer, electrically conductive ink layer, second non-conductive ink layer and the adhesive layer to a substrate is shown in Figure 5. The release film comprising the conductive transfer is positioned on a lower plate 501 of a heat press 502. A substrate comprising a thermoplastic polymer is also positioned on the plate 501 of the heat press 502 such that the conductive transfer is positioned appropriately in relation to the substrate. Once aligned, an operative 503 activates heat press 502 to provide heat and pressure to the conductive transfer to enable release and removal of the release film and, the addition of the conductive transfer to the thermoplastic polymer substrate. In this way, the adhesive layer adheres to the thermoplastic polymer substrate. In an embodiment, the heat press applies a pressure substantially within a range of one hundred and forty-five and one hundred and eighty degrees Celsius (145°C to 180°C). This temperature may vary dependent on the type of heat press utilised however, it is appreciated that in the method of manufacture described herein, this is the only application of heat and pressure for which the thermoplastic polymer substrate is required to withstand. Figure 6 A cross-sectional schematic view of conductive transfer 101 being applied to a first substrate in line with the method previously described with respect to Figure 5 is shown in Figure 6. Conductive transfer 101 is shown comprising first non-conductive ink layer 103, second non-conductive ink layer 104 and electrically conductive ink layer 105. Conductive transfer 101 further comprises adhesive layer 106. Each of the layers are shown attached to release film 102. In the embodiment of Figure 6, a substrate 601 is shown such that conductive transfer 101 can be transferred to substrate 601. Thus, conductive transfer 101 is positioned such that adhesive layer 106 is placed in contact with substrate 601 with release film 102 being positioned furthest away from a top surface 602 of substrate 601. In accordance with the method described herein an application of heat and / or pressure is applied to a top surface 604 of conductive transfer 101 which corresponds with the top surface of release film 102. Thus, as adhesive layer 106 is brought into contact with surface 602 and heat and pressure 603 is applied, adhesive layer 106 responds to heat and pressure 603 and adheres to substrate 601. Subsequently, release film 102 can be removed from conductive transfer 101 by peeling away release film 102 from non-conductive ink layer 103. In this way, transfer 101 becomes attached to substrate 601. In the embodiment, substrate 601 comprises a thermoplastic polymer. In an embodiment, the thermoplastic polymer comprises a thermoplastic polyurethane (TPU). In an alternative embodiment, the thermoplastic polymer comprises polycarbonate. Thus, the process described herein enables the conductive transfer to be provided with a thermoplastic polymer substrate which can be incorporated into more complex articles such as those described with respect to Figures 8 to 12. Figure 7 Conductive transfer 101 may further be combined with a second substrate 701 in addition to substrate 601. In the embodiment, substrate 701 is substantially similar to substrate 601 and comprises a thermoplastic polymer as previously described. In the embodiment, substrate 701 is attached to conductive transfer 101 such that conductive transfer 101 is positioned between first substrate 601 and second substrate 701. In this way, substrates 601 and 701 encapsulate conductive transfer 101 providing a first outer surface 702 and a second outer surface 703. The nature of the outer surfaces 702 and 703 are dependent on the thermoplastic polymer and the nature of its material. As indicated previously, in an embodiment, thermoplastic polymer substrates 601 and 701 may comprise thermoplastic polyurethane (TPU) or polycarbonate. In use, these materials provide a number of advantages when being utilised in combination with conductive transfers which are suitable for many applications. For example, TPU provides a solid wipeable and washable surface such that the outer surfaces 702 and 703 can easily be cleaned while, in addition, also provide protection to conductive transfer 101 which, in the embodiment, is contained therein. In addition, the outer surfaces 702 and 703 present a robust solid surface which is also substantially transparent which provides an additional advantage in terms of incorporating the conductive transfer into practical applications. For example, in an embodiment, at least one of the substrates 601 and 701 comprises a printed graphical element. Such a printed graphical element can be positioned between substrate 601 and substrate 701 outside conductive transfer 101 such that the printed graphical element can be viewed from the outer surface(s) 702 and / or 703. In an example embodiment, in automotive applications, this may be suitable to create a desirable finish to a dashboard in a vehicle. Figure 8 In an embodiment, conductive transfer 101 in combination with substrates 601 and 701 can be adapted to produce a curved article 801 as shown in Figure 8. In the embodiment, an application of heat and pressure is applied to substrates 601 and 701 and, taking advantage of the thermoplastic properties of the thermoplastic polymer substrate, substrates 601 and 701 can be shaped into curved article 801. Conductive transfer 101 is thin enough and flexible enough to ensure that it forms a radius of curvature in line with the curved substrates 601 and 701, thus allowing for a conductive transfer to be utilised in curved applications. Again, one such example would be in automotive applications and could be utilised, for example, to provide a functional dashboard surface in an automotive vehicle or similar. In order to obtain a curved article from conductive transfer 101 and substrates 601 and 701, a process utilising injection moulding and high pressure forming can be conducted. The high pressure forming involves an application of high pressure and heat and in which substrates 601 and 701 are bonded together and curved into an appropriate moulding. This process allows for in-mould electronics to be produced. Such a moulding can be provided as an interior or exterior moulding on an automotive vehicle, for example. Figure 9 A cross-sectional schematic view of an example conductive transfer configured to provide a heating element is shown in Figure 9. As shown, conductive transfer 901 comprises release film 902, first non-conductive ink layer 903, and second non-conductive ink layer 904. In the embodiment, conductive transfer 901 further comprises conductive ink layer 905 which forms a heating element and utilises an electrically conductive ink having a positive temperature coefficient such that the electrically conductive ink exhibits an increase in resistance in response to an increase in temperature. In the embodiment, heating element 905 is comprised of the first electrically conductive ink layer 906 which comprises an electrically conductive ink having a positive temperature coefficient. In addition, the electrically conductive ink layer 907 comprises a further metallic material, such as a silverbased ink. Conductive transfer 901 further comprises an adhesive layer 908 which enables conductive transfer 901 to be adhered to a thermoplastic polymer substrate. Thus, it should be appreciated that in the embodiment, conductive transfer 901 with heating element 905 introduces a more complex arrangement of conductive layers which requires additional stages of curing that would damage a thermoplastic polymer substrate should the inks be printed directly onto that substrate. Figure 10 A heated conductive transfer such as that described in Figure 9 can be utilised in an application to provide a heated seat. Heated seat 1001 comprises a plurality of conductive transfers 1002, 1003, 1004 and 1005. Such heated conductive transfers are able to be incorporated into a seat for an automotive vehicle and may also, due to the properties of the thermoplastic polymer substrate, provide a wipeable, easy to clean surface on top of the seat. This may be particularly desirable for children’s seating, for example, where spillages may occur. Figure 11 A cross-sectional schematic view of a further example embodiment of a conductive transfer 1101 in accordance with the present invention is shown in Figure 11. Conductive transfer 1101 illustrates a conductive transfer comprising a release film 1102, a first non-conductive ink layer 1103 and a second non-conductive ink layer 1104. Between first non-conductive ink layer 1103 and second non-conductive ink layer 1104 is electrically conductive ink layer 1105. In the embodiment, a plurality of electrical components 1106 are provided in contact with electrically conductive ink layer 1105. In the embodiment, electrical components 1106 comprise an illuminating device such as a light-emitting diode (LED). Illuminating devices 1106 are positioned in contact with electrically conductive ink layer 1105 and extend through non-conductive ink layer 1104 and adhesive layer 1107. In the embodiment, conductive transfer 1101 is attached to thermoplastic polymer substrate 1108. As shown, electrical components 1106 are in contact with an inner surface 1109 of substrate 1108. As noted previously, one of the advantages of thermoplastic polymer materials is that these may be substantially transparent in nature. Consequently, in embodiments where the electrical components 1106 are illuminating devices, the transparent nature of substrate 1108 is particularly beneficial in ensuring that the illuminating devices are effectively seen in their application. At the same time, the harder substrate 1108 also provides additional protection to electronic components 1106 that is not true of other previously known substrates such as fabrics or flexible films. In alternative embodiments, it is appreciated that the electrical components may be any other suitable electrical component. In one example embodiment, the electrical component comprises an audio device which is configured to emit an audible signal, for example, when conductive transfer 1101 is touched. In a further embodiment, conductive transfer 1101 is configured to provide both an illuminating device and an audio response in response to a touch from a user. Figure 12 Conductive transfer 1101 may therefore be incorporated into a wearable item 1201. In the embodiment of Figure 12, wearable item 1201 is shown as a high-visibility jacket worn by an operative 1202. Wearable item 1201 comprises a plurality of conductive transfers 1101 which comprise illuminating devices 1106 as described previously in Figure 11. Due to the properties of substrate 1108, the brightness of the illuminating devices is increased compared to previously known substrates. In 5 addition, the washable and wipeable nature of the thermoplastic polymer surface means that this part of the wearable item 1201 can be effectively cleaned between uses. Further, substrate 1108 further acts to provide additional protection to conductive transfer 1101 when wearable item 1201 is washed. Consequently, 10 wearable item 1201 can be subjected to conventional washing practices such as use in conventional washing machine while ensuring that the electrical components and conductive elements within the conductive transfer are adequately protected by means of substrate 1108. It is further appreciated that this advantage could be emphasised further 15 by the inclusion of a second substrate in this embodiment in a substantially similar manner to that previously described in Figure 7. This is true irrespective of whether the conductive transfer 1101 is required to be curved or otherwise.

Claims

The invention claimed is:

1. A method of manufacturing a conductive transfer, comprising the steps of:printing a non-conductive ink onto a release film to produce a first non-conductive ink layer;curing said first non-conductive ink layer;printing an electrically conductive ink onto said first non-conductive ink layer to produce an electrically conductive ink layer;curing said electrically conductive ink layer;printing said non-conductive ink over said electrically conductive ink layer to produce a second non-conductive ink layer;curing said second non-conductive ink layer;printing an adhesive material over said second non-conductive ink layer to produce an adhesive layer;curing said adhesive layer;placing said adhesive layer in contact with a first substrate that comprises a thermoplastic polymer, said adhesive layer being coupled to said first non-conductive ink layer, said electrically conductive ink layer and said second non-conductive ink layer when said adhesive layer is placed in contact with said first substrate;after placing said adhesive layer in contact with said first substrate, applying at least one of heat or pressure to said release film such that said adhesive layer adheres to said first substrate such that said first substrate provides an outer surface of said conductive transfer; andafter applying at least one of heat or pressure to said release film, removing said release film; whereinafter removing said release film and after said adhesive layer is adhered to said first substrate, said conductive transfer comprising said first substrate is incorporated into a complex article or wearable item.

2. The method of claim 1, wherein said thermoplastic polymer comprises thermoplastic polyurethane.

3. The method of claim 1, wherein said thermoplastic polymer comprises polycarbonate.

4. The method of any preceding claim, wherein said first substrate is substantially transparent.

5. The method of any preceding claim, further comprising the step of:after removing said release film, injection moulding said conductive transfer.

6. The method of any preceding claim, further comprising the step of:attaching a second substrate comprising a thermoplastic polymer to said conductive transfer.

7. The method of claim 6, further comprising the step of:applying heat and pressure to said first substrate and said second substrate; andshaping said first substrate and said second substrate into a curved article.

8. The method of claim 6 or claim 7, wherein at least one of said first substrate or second substrate comprises a printed graphical element.

9. The method of any preceding claim, wherein each said step of printing comprises one or more of the following: screen-printing; reel-to-reelprinting; dot matrix printing; laser printing; cylinder press printing; ink jet printing; flexographic printing; lithographic printing; offset printing; digital printing; gravure printing; xerographic printing.

10. The method of any preceding claim, wherein each said step of curing comprises drying each said layer.

11. The method of any preceding claim, wherein said step of printing an electrically conductive ink comprises the step of:producing a heating element from said electrically conductive ink, said electrically conductive ink having a positive temperature coefficient such that said electrically conductive ink exhibits an increase in resistance in response to an increase in temperature.

12. The method of any preceding claim, further comprising the step of:attaching an electrical component in contact with said electrically conductive ink layer.

13. The method of claim 12, wherein said electrical component comprises an illuminating device.

14. The method of claim 12, wherein said electrical component comprises an audio device.

15. A conductive transfer for incorporation into a complex article or wearable item; said conductive transfer comprising:a first non-conductive ink layer and a second non-conductive ink layer;an electrically conductive ink layer positioned between said first non-conductive ink layer and said second non-conductive ink layer;an adhesive layer with a first side and a second side opposite to saidfirst side, said first side coupled to said second non-conductive layer; anda first substrate comprising a thermoplastic polymer and adhered to said second side of said adhesive layer to provide an outer surface for said conductive transfer, said adhesive layer completely separating the first substrate from the first non-conductive ink layer, the second non-conductive ink layer, and said electrically conductive ink layer.

16. The conductive transfer of claim 15, wherein said thermoplastic polymer comprises thermoplastic polyurethane.

17. The conductive transfer of claim 15, wherein said thermoplastic polymer comprises polycarbonate.

18. The conductive transfer of any one of claims 15 to 17, wherein said first substrate is substantially transparent.

19. The conductive transfer of any one of claims 15 to 18, further comprising a second substrate comprising a thermoplastic polymer.

20. The conductive transfer of claim 19, wherein said first substrate and said second substrate are shaped to form a curved article.

21. The conductive transfer of claim 19 or claim 20, wherein at least one of said first substrate or second substrate comprises a printed graphical element.

22. The conductive transfer of any one of claims 15 to 21, wherein said conductive transfer further comprises an electrical component in contact with said electrically conductive ink layer.

23. The conductive transfer of claim 22, wherein said electricalcomponent comprises an illuminating device.

24. The conductive transfer of any one of claims 15 to 23, said conductive transfer being utilised to form any one of the following:5 a printed heater; a capacitive touch sensor; a printed pressure sensor.

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