WO2024253658A1 - Method for producing a stretchable soft sheet comprising flexible circuit - Google Patents

Abstract

The present invention relates to a method for producing an electrically conductive laminated sheet comprising a soft and flexible structure having a circuitry trace. The circuitry trace has an improved design which allows multi-direction stretchability and robustness, and can be used for multi-function circuits that can perform heating and capacitive touch sensing and cabling, and making it suitable for applications that require electronic functionality on special surfaces. In further aspects, the invention provides also a flexible circuit for use in the method of the present invention.

Description

Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT} INTERNATIONAL PATENT APPLICATION UNDER THE PATENT COOPERATION TREAT ^{METHOD FOR PRODUCING A STRETCHABLE SOFT SHEET COMPRISING FLEXIBLE CIRCUIT Technical Field The present invention relates to a method for producing a laminated sheet comprising a soft and flexible structure having an electronic circuit. More particularly, the invention pertains to a method for manufacturing of an electrically conductive laminated sheet which is stretchable in} _{one or multiple directions and having a specific circuitry which supports a range of functionalties such as heating, capacitive touch sensing and cabling, and making itsuitable for applications that require electronic functionality on special surfaces. In further aspects, the invention provides also a flexible circuit for use in the method of the present invention.} ^{Background of the Invention Electric heating is used in a range of industries such as medical and automotive to bring comfort or therapy to patients and passengers. In many of these applications, it is desirable to have a heating element integrated easily into a textile. For example, in the automotive industry, one may have the desire to heat a steering wheel with a soft, flexible circuit layer that can be easily wrapped around the steering wheel. It is a requirement for many of these applications that the heating element can have 2-way or 4-way stretch of up to 50% and that the heating element can be easily integrated using bonding or sewing into the substrate good. These requirements make traditional flexible electronics and wire-based heating methods unsatisfactory for many applications.} _{Disclosures have been made, for example in US11528780B2, which describes a process for making a thin and flexible PTC hybrid heater. The heater suggested in this patent is made with a soft, flexible conductive fabric that acts as the conductor. For this purpose, conductive ink in tandem with a conductive planar material is used, which is actually not specified as a conductive fabric or textile. The electrically conductive heater lines comprise a carbon black material having an electrical resistivity with a positive temperature coefficient (PTC) in order to reduce silver usage in the conductive ink. This patent, however bears several limitations in terms of stretchability over surfaces having a complex geometry due to the production technique which requires depositing of adhesive material without masking, use of bridge members and the material used in different layers.} 1 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT Likewise, US10490507B1, US10716341B2, US10925168B2 and US11342271B2 disclose flexible circuitry layers comprising a conductive mesh including a circuitry trace and an interfacing component. Further disclosed are the specific methods for manufacturing of flexible circuitry layers comprising, for instance, providing a conductive mesh, applying a masking thereon in order to form a circuitry trace and selectively removing of the mask with mechanical or chemical means. These patents do not specify the conductive trace design as a contributor to mechanical properties, such as stretchability. WO 2014/184743 discloses a combination heater and sensor comprising: a heating layer and a sensing layer wherein the heating layer is a nonwoven layer that is comprised of a plurality of} _{metallized fibers. The combined system suggested herein can be implemented in a seat or steering wheel of a vehicle, but it relies only on a serpentine trace for stretchability, not the combination of trace patterning and a stretchable carrier, and it requires multiple layers of circuitry in order to achieve heating and sensing together, which inhibits mechanical properties. As seen above, flexible materials comprising heating elements, cabling and antenna (for capacitive touch sensing, for example) have certain limitations in creating a very thin, flexible and stretchable circuit that is soft in nature. The present invention solves existing drawbacks of the prior art with a method for producing a hybrid product comprising a polymeric film layer and a patterned conductive sheet featuring a heating circuitry according to the appended claims.} ^{Summary of the Invention The present invention relates to a method for producing an electrically conductive laminated sheet having a flexible circuit comprising provision of a flexible circuit comprising a planar circuitry sheet (2) having a circuitry trace (1) placed in between dielectric layers made of polymeric films having a preferable stretchability between 10% and 60%, more preferably between 20% and 50%, and most preferably between 30% and 50%. The circuitry trace (1) comprises conductive lines (11) that can be patterned to function as a resistive heater, anteanna,} _{capacitive touch sensor, or cables of the conductor tuned by the circuit design. The circuitry trace (1) for supporting heating and/or capacitive touch sensing is designed to have a pulse wave form having elongated lines (111) corresponding to pulse amplitude and extending in vertical direction (y), and shorter lines (112) corresponding to pulse length and extending in horizontal direction (x). Each wave consists of two elongated lines (111) arranged substantially parallel to eachother and one shorter line (112) perpendicular to the neighbouring elongated lines} 2 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT (111). The elongated lines (111) forming the waves in outermost edge of the circuitry trace (1) have advantageously a bending portion (20) whereby a horizontally elongated line (201)} _{extending in horizontal direction (x) is connected with said elongated line (111), and said horizontally elongated line (201) extends inwardly between the borderlines (A, A’) forming the outermost edges of the circuitry trace (1).} ^{Brief Description of the Figures Figure 1 presents a circuitry trace produced, according to the method of the present invention.} _{Figure 2 shows the circuitry trace according to another embodiment of the present invention.} ^{Detailed Description of the Invention Soft and flexible sheets containing electronic circuits for a range of applications such as heating and sensing properties are known in the art. In addition to single functions, sheets may provide multiple functionalities such as a combination of capacitive touch sensor and heating which inherently produces heat by virtue of resistors which can also be used as an antenna for capacitive touch sensing. More particularly, the circuit produces an electric field through an antenna (which can double as a heater) whereby an object (i.e. human finger or hand) interfere with said electric field lines decreasing the mutual capacitances and causing a signal to be generated based on the aforementioned change in the capacitance. This phenomena generally doesn’t require a physical touch on the circuit but it may produce a response as soon as the object approaches and interferes with electrical field lines.} _{This technology is therefore promising for the provision of functional surfaces in automotive industry such as steering wheels, seats, door trims etc. However, certain limitations render the flexible circuits inapplicable in the automotive industry. Especially, the automotive parts having higher geometric complexity such as steering wheels and seats require extra flexibility and stretchability as well as robustness of the circuitry during application in the course of the production. Therefore, it would be desirable to select appropriate materials and a production method compatible with the foregoing objectives. It is also desirable to provide a superior design of the circuitry allowing it to be stretchable enough without deterioration of the conductive lines in the circuitry.} 3 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT Thus, in one aspect of the present invention, there is provided a method for producing an electrically conductive laminated sheet having a flexible circuit, comprising the steps of: - providing a planar carrier sheet made of a polymeric film, - printing a desired circuit pattern with adhesive onto the polymeric film by using a screen, - sheeting of a flexible circuit comprising a planar circuitry sheet (2) having a circuitry trace (1) and placing the same onto the polymeric film so that it overlays the surface of the film and lays on top of the screened adhesive, said circuitry trace (1) may comprise conductive lines (11) with resistance forming resistors for producing heat, capacitive sensing means for activating resistors, and/or electrodes connected to the conductive lines (11) of the circuitry trace (1), - curing this combination to ensure bonding with the adhesive, - cutting of the planar circuitry sheet (2) so that the material not bonded by the adhesive can be removed, - placing auxiliary electronic components and connecting them with the circuitry trace (1) of the planar circuitry sheet (2), - providing a top layer polymeric film and laminating the same on the foregoing combination to obtain a stretchable product.} _{The conductive lines (11) of the circuitry trace (1) in between the polymeric planar carrier sheet and the polymeric top layer is inherently configured to function as the capacitive sensing means because the polymeric layers behave as dielectric (i.e., insulating) layers. Therefore, a control circuitry can be provided for receiving electrical signals received from the circuitry trace (1) and producing a control signal for controlling supply of electricity to the circuitry trace (1). For this purpose, the control circuitry is calibrated so that electrically conductive laminated sheet is made sensitive to a desired electromagnetic field threshold signal. The polymeric film used in the planar carrier sheet and the top layer as mentioned hereinabove is a dielectric material advantageously stretchable in multiple directions according to the objectives of the invention. More particularly, the polymer material mentioned herein is selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI), polyethylene naphthalate (PEN), polyoxymethylene (POM), polyamide (PA), polyphthalamide (PPA), polyether ether ketone (PEEK), thermoplastic olefins (TPO), silicone and polyurethane (PU). The polymer material is most preferably thermoplastic polyurethane (TPU) which is highly stretchable and flexible being also suitable for use in automotive. However, the top layer polymeric film, in any case, is selected as a dielectric polymeric film that is heat sealed to} 4 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT close the layer with auxiliary electronic components and circuitry. The film may be hot melt, or have an adhesive layer inside. Application of the desired circuit pattern with adhesive onto the planar carrier sheet by using a screen and masking is advantageous because of the controlled usage of the adhesive. Otherwise, without masking, excessive adhesive reduces stretchability and flexibility of the polymeric film. It is also noted that applying the adhesive to the planar circuitry sheet (2) and then bonding it with the planar carrier sheet causes irregularities in the polymeric film and limited stretchability of the planar circuitry sheet (2). The planar circuitry sheet (2) of the flexible circuit is preferably a conductive fabric or conductive textile which may have a polymeric core material that is woven or knit. This material is preferably electroplated with an electrically conductive material such as copper and/or nickel. Deposition of copper and/or nickel by electroplating is advantageous because of the highly intense and homogenous conductivity which is substantially not affected by the stretching forces in any direction. This also alleviates the drawbacks of the alternative techniques such as conductive ink which generally require more conductive and expensive material such as silver.} _{The adhesive used in the method mentioned above is preferable curable with UV. Alternatively, the adhesive may have been pre-applied by lining covered with a mask in a ready to use form such that the mask is removed just before bonding with the planar circuitry sheet (2). Cutting of the planar circuitry sheet for removing the material not bonded by the adhesive, can be carried out by kiss cutting which can be advantageously automatized and carry out a sensitive cutting without deteriorating the circuit. The auxiliary electronic components added to the circuit include any desired component such as terminations, wires, PCBs, switches and control circuitry necessary for the control and power supply to the flexible circuitry. In preferred embodiments, the auxiliary electronic components may include also an illumination means such as LED either for indication of functionality of heating, solely for lighting the environment or a combination thereof. The illumination means can be located in an appropriate area of the electrically conductive laminated sheet such that when the user approaches or touches a particular area on the electrically conductive sheet, illumination means are activated. A control circuitry for this purpose is designed and placed into the electrically conductive laminated sheet. The auxiliary electronic components can be fixed to the} 5 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT electrically conductive laminated sheet by using electrically conductive or non-conductive adhesive or epoxy. The electrically conductive laminated sheet according to the present invention can be formed with a multi-layer circuit by repetition of the sheeting step whereby a further planar circuitry sheet is laminated to the initial planar circuitry sheet (2). In the electrically conductive laminated sheet having a flexible circuit used in the method of the present invention, the circuit is designed to allow maximum stretchability while providing sufficient durability and circuit intensity per area. Typically, a serpentine pattern for obtaining stretch within a heating element of the circuitry consists of a sinusoidal wave shape that either snakes around a volume, or is connected by parallel bars to create several heating lines (i.e. resistors) in parallel. This technique is not suitable for this method of making a soft, flexible circuit from conductive fabric because it may not adequately fill space and trace-width for kiss cutting which results in wider conductive traces that require different space filling approaches. This invention improves on this approach with a more angular “space filling” approach to circuit design. It is possible to create space filling geometries that result in multi directional stretch (Figures 1 and 2).} _{This space filling approach can also be used to create cabling, antennas, or capacitive touch sensors within a soft, flexible circuit. It is also possible to combine functions (such as cabling and capacitive touch sensing) by designing an external electronic system to switch between the desired functions quickly. This approach is particularly useful for cost-savings and for improved mechanical features over multi-layer electronics. Referring now to Figure 1, a circuitry trace (1) is provided with electrically cunductive lines (11) and regions (12) for a plurality of electrodes according to an embodiment of the present invention. The conductive line (11) is configured to form a pulse wave form, more particularly a rectangular pulse wave form having elongated lines (111) corresponding to pulse amplitude and extending in vertical direction (y) and shorter lines (112) corresponding to pulse length extending in horizontal direction (x). In this embodiment, the shorter lines (112) are substantially perpendicular to the elongated lines (111) and said elongated lines (111) are arranged in a row being substantially parallel to eachother so that a plurality of waves can be formed in a row extending in horizontal direction (x) in order to ensure stretchability in that direction (x). Each wave consists of two elongated lines (111) arranged substantially parallel to eachother and one} 6 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT shorter line (112) perpendicular to the neighbouring elongated lines (111). The elongated lines (111) are arranged to have a length much more than the shorter lines (112) (e.g. at least two fold), and width (w) of the conductive lines (11) ranges from 0.05" to 3" (1.27 mm to 76.20 mm). Furthermore, at least one of the elongated lines (111) forming the waves in outermost edge of the circuitry trace (1) has a bending portion (20) whereby a horizontally elongated line (201) extending in horizantal direction (x) is connected with said elongated line (111). The horizontally elongated line (201) extends inwardly between the borderlines (A, A’) forming the outermost edges of the circuitry trace (1). In other words, the horizontally elongated line (201) extends in the direction of the waves and in an area thereunder. Additionally, the length of the horizontally elongated line (201) is much more than the length of the shorter lines (112). The ratio of the length of the horizontally elongated line (201) to the length of the shorter lines (112) ranges from 1.5 to 50, more preferably from 2 to 20 and most preferably from 2 to 10. Horizontally elongated line (201) is preferably a straight line but it can also be a curved line terminating at an electrode (not shown). With the foregoing arrangement, stretchability in the vertical direction (y) is improved. While the length of the shorter lines (112) are generally contemplated to be substantially equal throughout the circuitry trace, in the event that the length of the shorter lines (112) differ from eachother, above mentioned ratios are calculated based on the longest one of the shorter lines} _{(112) forming the each wave. Likewise, elongated lines (111) extending in vertical direction (y), except the ones in outermost edges in borderlines (A, A’), are designed substantially to have equal length. In another embodiment as shown in Figure 2, the circuitry trace (1) is provided on a polymeric planar carrier sheet (2) as in the previous embodiment. This embodiment also provides a plurality of electrode regions (12), and conductive lines (11) configured to form a pulse wave form, more particularly a rectangular pulse wave form having elongated lines (111) corresponding to pulse amplitude and extending in vertical direction (y) and shorter lines (112) corresponding to pulse length extending in horizontal direction (x). In this embodiment, however, at least two rows of waves are arranged one under the other with a spacing therebetween wherein the horizontally elongated line (201) extending in horizantal direction (x) is discontinued and bended towards the vertical direction (y) to form a vertical line (113) and eventually to form a complete wave with another horizontally elongated line (201) which is either connected directly to an electrode or to the other wave row. There may be two waves side by side extending in horizontal direction (x) through the length of the wave rows as shown in Figure 2. In this embodiment, again the length of the horizontally elongated line (201)} 7 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT is more than the length of the shorter lines (112). The ratio of the length of the horizontally elongated line (201) to the length of the shorter lines (112) ranges from 1.5 to 50, more preferably from 2 to 20 and most preferably from 2 to 10. Horizontally elongated line (201) is preferably a straight line but it can also be a curved line. With the foregoing arrangement, a perfect stretchability both in the vertical direction (y) and horizontal direction (x) is ensured. The flexible circuit and the method according to the present invention are perfectly convenient} _{for the applications in wellness, such as therapeutic heating pads and beds, and automotive, such as upholstery work in vehicles including trims and steering wheel. The flexible circuit and the method according to the present invention are particularly suitable for medical products or vehicle parts that require wrapping with a textile or leather such as seats, steering wheels and door panels. The flexible circuit technique is also ideal for multi-function applications, such as combining heating and capacitive touch sensing, because the functionality can be executed in a single layer, saving cost and improving mechanical properties.} 8 _{33033/002/4370661.1}

Claims

Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT 1. A method for producing an electrically conductive laminated sheet having a flexible circuit, comprising the steps of: - providing a planar carrier sheet made of a polymeric film, - printing a desired circuit pattern with adhesive onto the polymeric film by using a screen, - sheeting of a flexible circuit comprising a planar circuitry sheet (2) having a circuitry trace (1) and placing the same onto the polymeric film so that it overlays the surface of the film and lays on top of the screened adhesive, said circuitry trace (1) comprising of patterned conductive lines (11) with electrode regions (12),} - _{curing this combination to ensure bonding with the adhesive, - cutting of the planar circuitry sheet (2) so that the material not bonded by the adhesive can be removed, - placing auxiliary electronic components and connecting them with the circuitry trace (1) of the planar circuitry sheet (2), - optionally providing a secondary layer of planar circuitry sheet (2) as described by the previous steps, and - applying a top layer polymeric film, and laminating the same on the foregoing combination to obtain a stretchable product.} ^{2. The method according to claim 1 wherein the polymeric film used in the planar carrier sheet} a_{nd the top layer are dielectric polymeric films.} ^{3. The method according to claim 1 wherein polymeric film is selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI),} p_{olyethylene naphthalate (PEN), polyoxymethylene (POM), polyamide (PA), polyphthalamide (PPA), polyether ether ketone (PEEK), thermoplastic olefins (TPO), silicone and polyurethane (PU).} ^{4. The method according to claim 3 wherein polymeric film comprises thermoplastic} p_{olyurethane (TPU).} ^{5. The method according to claim 1 wherein the planar circuitry sheet (2) having the flexible} c_{ircuit comprises conductive fabric or conductive textile.} 9 _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT 6. The method according to claim 1 wherein the method comprises electroplating an} e_{lectrically conductive material onto the planar circuitry sheet (2) to form the circuitry trace (1) of the flexible circuit.} ^{7. The method according to claim 6 wherein the electrically conductive material comprises a} m_{etal selected from copper and nickel.} ^{8. The method according to claim 1 wherein cutting of the planar circuitry sheet (2) is carried} o_{ut by kiss cutting for removing the material not bonded by the adhesive.} ^{9. The method according to claim 1 wherein the conductive lines (11) are configured to have} a _{functionality of heating and/or capacitive touch sensing means.} ^{10. The method according to claim 1 or 9 wherein the electrically conductive laminated sheet} f_{urther comprises auxiliary electronic components selected from terminations, wires, PCBs, switches and a control circuitry.} ^{11. The method according to claim 10 wherein the auxiliary electronic components further} c_{omprises illumination means controlled by the control circuitry for indication of functionality of a heating and/or for illuminating the environment.} ^{12. The method according to claim 10 wherein the auxiliary electronic components comprises a control circuitry receiving electrical signals from capasitive sensing means and producing} a _{control signal based on a threshold value of the electrical signals depending on a change of the magnetic field, for controlling power supply through the electrodes and the conductive lines (11).} ^{13. The method according to claim 1 wherein the cunductive lines (11) of the circuitry trace (1)} a_{re configured to form a pulse wave form.} ^{14. The method according to claim 13 wherein the cunductive lines (11) of the circuitry trace} (_{1) are configured to form a rectangular pulse wave form.} ^{15. The method according to claim 13 wherein the cunductive lines (11) comprise elongated lines (111) corresponding to pulse amplitude and extending in vertical direction (y) and} s_{horter lines (112) corresponding to pulse length and extending in horizontal direction (x).} 1⁰ _{33033/002/4370661.1} Int’l PCT Patent Application A^{ttorney Ref: 33033-002-PCT 16. The method according to claim 15 wherein the elongated lines (111) are arranged in a row being substantially parallel to eachother so that a plurality of waves can be formed in a row} e_{xtending in horizontal direction (x), and wherein each wave consists of two elongated lines (111) and one shorter line (112).} ^{17. The method according to claim 16 wherein at least one of the elongated lines (111) forming the waves in outermost edge of the circuitry trace (1) has a bending portion (20) whereby a horizontally elongated line (201) extending in horizantal direction (x) is connected with} s_{aid elongated line (111), and said horizontally elongated line (201) extends inwardly between the borderlines (A, A’) forming the outermost edges of the circuitry trace (1).} ^{18. The method according to claim 17 wherein the length of the horizontally elongated line} (_{201) is more than the length of the shorter lines (112).} ^{19. The method according to claim 18 wherein the the ratio of the length of the horizontally} e_{longated line (201) to the length of the shorter lines (112) ranges from 1.5 to 50.} ^{20. The method according to claim 19 wherein the the ratio of the length of the horizontally} e_{longated line (201) to the length of the shorter lines (112) ranges from 2 to 10.} ^{21. The method according to claim 20 wherein at least two rows of waves are arranged one under the other with a spacing therebetween wherein the horizontally elongated line (201) extending in horizantal direction (x) is discontinued and bended towards the vertical} d_{irection (y) in said spacing to form a vertical line (113) and eventually to form a complete wave with another horizontally elongated line (201) which is either connected directly to an electrode or to another wave row.} 1¹ _{33033/002/4370661.1}