Electrical insulation in clothing

Abstract

The electrical system includes a conductive layer and an insulating layer for application to a surface of a garment, the electrical system including a first insulating layer for attachment to the garment, a second insulating layer, and the conductive layer encapsulated between the first insulating layer and the second insulating layer, the first and second insulating layers having a predetermined minimum withstand voltage and a predetermined minimum resistance.

Description

[Technical field]

[0001] The present invention relates to insulation provided to garments incorporating electrical elements. [Background technology]

[0002] Garments incorporating electrical wiring are becoming commonplace with many defined applications, such as physiological and biomechanical sensing, heating, electrical stimulation, lighting for visibility, user interfaces, etc. The basic purpose of such wiring is to conduct electrical signals or currents from one part of the garment to another, for example from a set of skin electrodes located on the chest to an electronic module located elsewhere within the garment. Obviously, such wiring and the insulation provided thereon needs to be flexible and capable of withstanding the various forces encountered in donning and doffing the garment, as well as wearing, washing, drying and storing it. Garments generally need to operate over a range of temperatures and humidities, as well as other environmental conditions such as exposure to liquids and dust. If it needs to be washed, the wiring needs to withstand the associated chemical and mechanical conditions.

[0003] Currently, there are various options for creating wiring, including copper wires between fabric layers or in seams, printed circuits using screen printed conductive inks, 3D printing, conductive threads in the form of woven yarn or fabric, thin sheets or strips of conductive polymers or elastomers, etc. The electrical resistance of such conductors is often a critical factor, particularly the stability of the resistance as it is stretched, bent, washed, etc.

[0004] In most cases, insulation between conductors is required to ensure correct functioning of the device. Many options exist for providing the insulation, including printed dielectric inks or encapsulants, extruded sheets of insulating material cut to the required shape, injection molded plastics, and 3D printed materials. The conductive yarns may be coated with an insulating film.

[0005] Of particular interest is the case when the electrical system of a garment consists of several layers applied to the surface 1 of a textile or fabric (see Figure 1), for example an adhesive layer 3 that attaches the structure to the garment fabric, an insulating layer 5, a conductive layer 7 and an insulating layer 9.

[0006] This structure may be applied to the skin-facing surface of the garment, the exterior surface, or indeed between the textile layers of the garment. One or both of the insulating layers 5, 9 may have openings 11 (see FIG. 2) to allow electrical connection to the underlying conductive layer 7. The textile may also have openings 15 to allow access to the exposed conductors.

[0007] To achieve a soft and lightweight finished garment, it is desirable for these layers to be as thin and flexible as possible, the conductive layer 7 must retain a minimum of conductivity during stretching and bending, and the insulating layers 5, 9 must have sufficient resistance and pressure resistance.

[0008] Now, conductive inks with excellent stretchability are emerging that can be printed directly onto stretchable fabrics. In addition to wiring, it is often necessary to make electrical contact with the skin using one or more electrodes. For example, in electrical stimulation, it is desirable to have a defined area of ​​skin contact to ensure that the stimulation current is distributed across the skin so that high current densities are avoided. Electrodes can be made from thin sheets of conductive elastomers, conductive inks, conductive textiles, etc. Electrodes can be formed by simply providing a window in an overlying insulating layer that exposes the conductive layer. Additional layers can be applied to the electrode area to modify its conductivity, for example to match it to that of the skin.

[0009] Insulation is necessary to restrict the flow of current to desired points in a system. Insulation provided to ensure that a device functions correctly by isolating conductors from one another may be described as functional insulation. In some cases, insulation may be required to isolate conductors from their surroundings to ensure safety. However, the prior art did not address the performance requirements of such insulation, let alone its design. This is particularly important when the conductors involved are patient connections and when they need to be isolated from earth or from contact with parts of the body they are not intended to contact. Such insulation may be referred to as protective insulation. Of course, insulation has both functional and protective purposes.

[0010] For example, conductive tracks may be printed on the skin-facing side of the garment, from which leakage of current to the skin must be avoided. An insulating layer may be applied above the conductive layer, electrically isolating it from the skin. Adding an insulating layer over the printed conductive tracks reduces the flexibility of the system, so it is desirable to make this as thin and flexible as possible. On the other hand, it must be durable and withstand normal wear and tear, including washing. The breakdown voltage of a given insulating material depends on its thickness and pressure resistance, so a thickness must be selected that achieves the right balance of flexibility, weight, and insulating performance. Insulation of the backside of the electrodes is also important. Consider a skin electrode located on the skin-facing surface of the garment. The opposite side of this electrode must be insulated to prevent current from passing through the garment to the outer surface. This is to prevent leakage current to the user, who is very likely to touch the outer surface of the garment with a finger or hand. For a given application, it is not immediately clear what the pressure resistance and insulation resistance requirements are for each hazard scenario. For example, if the insulation in a body-worn battery-powered heater circuit breaks in one place, there is no danger as there is no return path for any leakage current. Two insulation breaks in different places could expose the user to leakage currents and potential harm. Design choices to achieve the required protection must take into account the voltages that will stress the insulation.

[0011] There are many recent publications describing different architectures for integrating wiring into clothing, WO 2016 / 131936 (Schwarz), US 2015 / 0359485 (Berg), US 2014 / 0318699 (Longinotti), WO 2017 / 199026 (Kai), GB 2555592 (Bungay), but no attention has been paid to the insulation challenge. It is noteworthy that even a major supplier of stretchable insulating inks (Dupont™ PE773) sold for wearable applications does not cite insulation performance.

[0012] The problem, therefore, is to determine the amount of insulation necessary to achieve a desired degree of safety and functional performance, and then provide that level of insulation while minimizing the overall stiffness, weight, and thickness of the garment.

[0013] In view of the above, it is an object of the present invention to mitigate and alleviate the above mentioned disadvantages. Summary of the Invention

[0014] According to a first aspect, the present invention provides an electrical system comprising a conductive layer and an insulating layer for application to a surface of a garment, the electrical system comprising: a first insulating layer for attachment to a garment; A second insulating layer; a conductive layer encapsulated between the first insulating layer and the second insulating layer.

[0015] Preferably, the conductive layer is attached to both the first insulating layer and the second insulating layer. Preferably, the conductive layer is attached continuously to both the first insulating layer and the second insulating layer.

[0016] Preferably, the first insulating layer has a withstand voltage of at least 200 VAC or more, and the second insulating layer has a withstand voltage of at least 100 VAC or more.

[0017] Preferably, the first insulating layer has a resistance of at least 200 kΩ when measured on a conductive surface extending over the surface of the second insulating layer. More preferably, the first insulating layer has a resistance of at least 8000 cm 2 More preferably, the first insulating layer has a resistance of at least 200 kΩ when measured on a conductive surface of more than 8000 mm 2 When measured with a probe, the device has a resistance of at least 200 kΩ.

[0018] Preferably, the second insulating layer has a resistance of at least 200 kΩ when measured on a conductive surface extending above the surface of the second insulating layer. More preferably, the second insulating layer has a resistance of at least 8000 cm 2 More preferably, the second insulating layer has a resistance of at least 200 kΩ when measured on a conductive surface of more than 8000 mm 2 When measured with a probe, the device has a resistance of at least 200 kΩ.

[0019] Preferably, the first insulating layer has a thickness of 30 μm or less and a withstand voltage of at least 200 VAC or more.

[0020] Preferably, the first insulating layer has a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more.

[0021] Preferably, the first insulating layer has a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more.

[0022] The second insulating layer may have a thickness of 30 μm or less and a withstand voltage of at least 100 VAC or more.

[0023] The second insulating layer may have a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more.

[0024] The second insulating layer may have a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more.

[0025] Preferably, the first insulating layer has a withstand voltage of at least 1500 VAC or more, and the second insulating layer has a withstand voltage of at least 100 VAC or more.

[0026] Preferably, the first and / or second insulating layers are formed from at least two separately applied and bonded layers of insulating material, the number of layers being selected to provide a cumulative thickness that gives the insulating layer the required insulating performance.

[0027] Preferably, each of the separately applied and bonded layers has a breakdown voltage of 15-20 kV / mm.

[0028] Preferably, each of the separately applied and bonded layers has a thickness of 8-10 μm and provides a nominal withstand voltage of 120-200 V per layer.

[0029] Preferably, each of said separately applied and bonded layers is a layer of dielectric ink.

[0030] Preferably, the at least two separately applied and bonded layers are formed from at least two separately applied coatings of insulating material, each of which is allowed to cure before the next coating is applied, the number of coatings being selected to provide a cumulative thickness that gives the insulating layer the required insulating performance.

[0031] Preferably the coating is a coating of a dielectric ink.

[0032] Preferably, an attachment device is provided for attaching the first insulating layer to the garment. The attachment device may comprise an adhesive. Other configurations for attaching the first insulating layer to the garment will be apparent to those skilled in the art. According to a second aspect, the present invention provides a method for testing an electrical system comprising a conductive layer and an insulating layer for application to a surface of a garment, the electrical system comprising: a first insulating layer for attachment to a garment; A second insulating layer; a conductive layer encapsulated between a first insulating layer and a second insulating layer; Equipped with Here, the insulating performance of the first and / or second insulating layers is tested by applying a test voltage between a probe connected to the conductive layer and a conductive plate having a defined area disposed on the associated insulating layer, and by measuring the resistance or breakdown voltage therebetween.

[0033] Preferably, the conductive plate is at least 1000 mm 2 The conductive plate has a defined area of ​​at least 8000 mm 2 The defined area may be:

[0034] Preferably, the conductive plates are shaped to substantially conform to the shape of the associated insulating layer.

[0035] Preferably, the conductive plate is longer and wider than the insulating layer being tested.

[0036] Preferably, the conductive plate is provided as a 3D body shape with a conductive surface to which the insulating layer to be tested is applied. Preferably, prior to testing, the associated insulating layer is attached to a garment, and the garment is attached to the body shape such that the insulating layer to be tested faces the body shape.

[0037] Features of the first aspect of the invention may be incorporated in the second aspect of the invention as appropriate, and vice versa. [Brief description of the drawings]

[0038] The invention will now be described, by way of example only, with reference to the accompanying drawings, which show embodiments of the invention, in which: [Figure 1] 1 shows an electrical system attached to a textile substrate. [Diagram 2] 2 illustrates an opening in an insulating layer of the system of FIG. 1 to expose a conductive layer. [Diagram 3]FIG. 1 is an insulation diagram showing the insulation on conductive tracks in the garment that are connected to the skin electrodes and the potential error currents ie that can flow on the arm if the wearer touches the faulty insulation. [Figure 4] 1 shows an equivalent circuit for two skin electrodes with contact impedances of Z1 and Z2, respectively. [Diagram 5] 1 shows a test fixture for testing the insulation of the insulation layers of the system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] To more fully explain the invention, it is useful to consider a particular example, namely transcutaneous electrical stimulation. However, it should be understood that the invention is not limited to such uses only. Various other applications will become apparent to those skilled in the art. The invention is described with reference to Figs. 1-5. Transcutaneous electrical stimulation is a widely used therapy in which electrical pulses are generated within an electronic control module 17 (see Fig. 3) and delivered to a subject 19 by at least two leads 21 and corresponding skin electrodes 23 of application portion A in Fig. 3. The leads 21 include embedded wiring or conductive tracks (see conductive layer 7 in Figs. 1 and 2) that run from the control module 17 to the skin electrodes 23 and are insulated to prevent leakage currents on the way to the skin electrodes 23. These conductive layers may typically be laminated to the skin-facing side 25 of a garment 27. An insulating layer 9 on the skin-facing side 7a of the conductive layer ensures that current does not leak onto the underlying skin when worn down, thus causing stimulation at the wrong skin location. This insulation failure may cause discomfort, skin irritation or burns. The insulating layer 5 and the electrodes on the garment-facing side 7b of the conductive layer 7 prevent leakage current into the garment 27. The garment 27 is typically made of woven or knitted textile fabric made of insulating yarns, which when wet can provide a conductive path to the outer surface 27a of the garment 27. If the user touches their hand to that part of the wet garment 27 during stimulation and the insulating layer 5 is damaged, the current i ecan flow in the hand, arm, and torso areas (see Figure 3). The magnitude of the current that flows in this case depends on the relative impedance of the electrode contact and the hand contact, since they are electrically parallel. The effects of current on the human body are specified in IEC 60479, so it is necessary to ensure that any current that occurs due to insulation failure is well below the limits that would cause significant harm.

[0040] Figure 4 shows the equivalent circuit of two skin electrodes 23 with contact impedances of Z1 and Z2, respectively. Electrical stimulation is applied between nodes 1 and 2. Zc represents the impedance of the body core between the two skin electrodes 23 and is usually much smaller than the contact impedance of the skin. Zh represents the contact impedance of the hand with one of the conductive layers 7 during an injury condition and will usually be higher than Z1 or Z2. To ensure safety, an error current i flowing in this branch is e should be as low as possible.

[0041] The inventors have discovered that the voltage exerted across this insulation between the conductive layer 7 and the hand is approximately half the voltage between the two skin electrodes 23 in series, since the potential at the hand is substantially the same as at the body core as shown. See the equivalent circuit in FIG. 4, which represents the electrical impedance of the two skin electrodes 23 in series with the body core resistance. It is known that the overall circuit impedance is dominated by the contact impedance of the skin. For a typical electrical stimulation device outputting up to 20Vrms, the peak voltage can be up to 50V, but the voltage at the insulation is 10Vrms (the electrical stimulation waveform is usually in the form of a pulse train with a low duty ratio, and the peak pulse amplitude is often a multiple of the root mean square value of the pulse train).

[0042] The choice of safety factor to be applied in the design of insulation depends on the risk associated with failure. For low-risk applications, a factor of 2 may be sufficient, resulting in a withstand voltage of 20VAC or a peak withstand voltage of 100V. More preferably, a higher safety factor of 5 may be used, even for low-risk applications. The insulation resistance may be selected to limit the current flow in normal operation to an upper limit of 100μArms in the absence of breakdown, thus 50V / 100μA=500kΩ.

[0043] For high-risk situations, the safety factor for the breakdown voltage can be increased by 5, 10, or 20 times as needed. For currents that can flow through the chest where there is a risk of fibrillation, the withstand voltage can be set as high as 500 VAC or even 1000 VAC, depending on the risk estimate.

[0044] Since the risks associated with insulation failures are different for the skin side and the clothing side, it may be appropriate to have different insulation performance for each side. Since an insulation failure facing the skin would only result in skin discomfort, a withstand voltage of 200VAC may be specified, which is more than 20 times the working voltage. For the clothing side, where there is a greater likelihood of harm, a withstand voltage of 500VAC is appropriate. Safety standard IEC 60601 (3rd Edition) specifies withstand voltage levels for insulation at various working voltages. To provide two means of patient protection, it may be necessary to provide insulation with a breakdown voltage of 1000VAC.

[0045] It should be noted that withstand voltage testing is almost always performed on machines operating at mains frequencies where the use of "VAC" is appropriate and sufficient. In NMES (Neuromuscular Electrical Stimulation), the current is pulsed so the use of "Vrms" becomes more accurate.

[0046] For example, common dielectric inks such as SE3102 from ACI Materials have a breakdown voltage in the range of 15-20 kV / mm. Specialized inks with higher breakdown voltages are available, but may not be flexible and stretchable enough. For a material with a strength of 20 kV / mm, one screen printing pass is typically 10 μm thick, resulting in a nominal strength of 200 V per layer, so at least three passes are required to build a 500 V breakdown capacity. Flexible inks that can be printed at thicker thicknesses per layer can be utilized by using different print screen meshes and squeegee parameters.

[0047] Screen printing has inherent variations due to variations in mesh marking, mesh stretching, squeegee pressure, angle, speed, and ink viscosity. Air bubbles can also be present which impair the insulating performance. Therefore, multiple layers are required which cumulatively give the required insulating performance. As few layers as possible are desirable because multiple layers usually require curing times between layers which slows down the manufacturing process.

[0048] In addition to being able to withstand a given voltage, it is necessary that the insulating layer provides an adequate insulation resistance below the breakdown voltage. The IEC 60601 standard requires that the auxiliary current in normal use should be less than 100 μA. Thus, at a standard operating voltage of 20 Vrms, the insulation should be greater than 200 kΩ. The resistance to contact with a hand or finger depends on the area of ​​contact. The IEC 60479 standard considers the effect of electric current on the human and animal body and defines a test contact area that emulates finger and hand contact. Fingertip contact should be 250 mm 2 The area of ​​the hand can be simulated at 8000mm 2 Also, it is equivalent to 1000mm 2 A contact area of ​​1000 mm 2 may be used to simulate finger contact. Thus, a suitable insulation test for garment insulation for finger contact would be a 1000 mm 2 contact area of ​​1000 mm 2 placed on the conductive layer 7 and the insulating layers 5, 9. 2The objective of the present invention is to measure the resistance (e.g., using an insulation tester 37) at the maximum operating voltage between a surface probe 35 having an area of ​​8000 mm 2 A test using a surface probe having an area of ​​0.1 mm can be performed to test the insulation of clothing against hand contact.

[0049] To ensure that the insulating layer 5,9 meets the voltage withstand requirements, the breakdown voltage of the structure must be tested after fabrication. The entire surface of the insulating layer 5,9 must be tested, necessitating the use of a probe that can contact all points of the insulating layer 5,9. The probe or plate can be molded to match the shape of the insulating layer 5,9 so that the insulating layer 5,9 can be tested in one go without having to repeat the test multiple times while repositioning smaller probes. Alternatively, a convenient and rapid means of testing the garment is to attach it to a conductive body form or mannequin and test the resistance between each terminal of the conductive layer 7 on the garment and the conductive body form. Such a body form can be made of wood, plastic, or foam products with a conductive coating such as metal foil, conductive fabric, conductive paint or ink. It is even faster to connect all the terminals of the conductive layer 7 together to form a single electrical node and test the resistance and breakdown voltage between that node and the conductive body form. The garment can be turned inside out to test the performance of the insulating layer 5 on the outward facing side of the laminate circuit. Several body shapes may be provided or the body shapes may be adjusted to test different sizes of garments.

[0050] In garments made of stretchable fabrics, the electrical system can preferably stretch and relax so that the performance of the garment is not compromised. Stretching the electrical system necessarily reduces the cross-sectional dimension perpendicular to the stretch direction, which may reduce the dielectric withstand voltage. Therefore, it may be necessary to stretch the test sample on the body shape during testing. The size of the test body shape should be selected to match the size of the garment so that the expected stretchability is achieved.

[0051] Garments may become wet during use and washing. The insulating layers 5, 9 must be able to withstand moisture and prevent water from penetrating into the layered structure. It may therefore be necessary to test wet garments to ensure safety that voltage endurance and insulation resistance are maintained.

[0052] The insulating layers 5, 9 may have openings 11 to purposefully expose portions of the conductive layer 7. The openings 11 may be formed to allow connection to the skin or to a connector or another conductor. In a manner similar to a multi-layer printed circuit board, it may be useful to have multiple conductive layers 7 separated by insulating layers 5, 9, but with selective openings 11 that allow the conductive layers 7 to contact at specific points. The openings 11 in the insulating layers 5, 9 may also be made to allow attachment of a connector (not shown) to the conductive layer 7. Such connection means may be, for example, a stud compression fastener, crimping, adhesive, welding, soldering, a simple screw-in fastener or another suitable connector. After such a connection is made, it must be insulated. Another layer may be laminated above the joint, such layer having the same insulating properties as the insulating layer to which it is attached. Other means may include overmolding or a resin injected or sprayed into the joint.

[0053] There are several methods available for creating insulating and conductive layers on a garment. WO 2017 / 199026 (Kai et al.) describes a process of screen printing successive layers onto a textile fabric. GB 2555592 (Bungay et al.) describes an alternative method in which multiple layers are placed on a transfer printing substrate and then applied to the garment using heat or pressure. Similarly, layers may be formed by placing molded layers of insulating and conductive materials on top of each other and adhesively bonding or welding. For example, a first insulating layer, e.g., insulating layer 5, may be an insulating TPU having a thickness on the order of 100-200 μm. Conductive layer 7 may be a conductive yarn, a conductive textile, a metal foil, or may be a conductive ink pattern printed onto insulating layer 5. A second insulating layer, e.g., insulating layer 9, may be another molded layer of insulating TPU or other polymer or printed dielectric ink having a thickness of less than 100 μm. The entire assembly may be adhesively bonded to the textile fabric via adhesive layer 3.

[0054] While much of the above describes a layered structure of insulating layers 5, 9 and conductive layers 7 applied to the skin-facing side 25 of the garment, it is also possible for the structure to be applied to the outer surface 27a of the garment or as a layer between two garments 27. The insulation adjustments need to take into account the risk characteristics of the particular application.

[0055] Those skilled in the art will understand that variations and modifications can be made without departing from the scope of the invention, which is defined in the appended claims.

Claims

1. 1. An electrical system comprising a conductive layer and an insulating layer for application to a surface of a garment, the electrical system comprising: a first insulating layer for attachment to a garment; A second insulating layer; the conductive layer encapsulated between the first insulating layer and the second insulating layer; Equipped with The electrical system, wherein the first insulating layer has a withstand voltage of at least 200 VAC or more and the second insulating layer has a withstand voltage of at least 100 VAC or more.

2. The first insulating layer is 8000 mm ２ 13. The electrical system of claim 1, having a resistance of at least 200 kΩ when measured across a conductive surface greater than 100 mm.

3. 3. The electrical system of claim 1 or claim 2, wherein the second insulating layer has a resistance of at least 200 kΩ as measured on a conductive surface extending above a surface of the second insulating layer.

4. 4. The electrical system of claim 1, wherein the first insulating layer has a thickness of 30 μm or less and a withstand voltage of at least 200 VAC or more.

5. 4. The electrical system of claim 1, wherein the first insulating layer has a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more.

6. 4. The electrical system of claim 1, wherein the first insulating layer has a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more.

7. 7. The electrical system of claim 1, wherein the second insulating layer has a thickness of 30 μm or less and a withstand voltage of at least 100 VAC or more.

8. 7. The electrical system of claim 1, wherein the second insulating layer has a thickness of 50 μm or less and a withstand voltage of at least 600 VAC or more.

9. 7. The electrical system of claim 1, wherein the second insulating layer has a thickness of 100 μm or less and a withstand voltage of at least 1500 VAC or more.

10. 2. The electrical system of claim 1, wherein the first insulating layer has a withstand voltage of at least 1500 VAC or more and the second insulating layer has a withstand voltage of at least 100 VAC or more.

11. 11. The electrical system of claim 1, wherein the or each of the first and second insulating layers is formed from at least two separately applied and bonded layers of insulating material, the number of layers being selected to provide a cumulative thickness that imparts a required insulating performance to the insulating layer.

12. 12. The electrical system of claim 11, wherein each of the separately applied and bonded layers has a withstand voltage of 15-20 kV / mm.

13. 13. The electrical system of claim 12, wherein each of the separately applied and bonded layers has a thickness of 8-10 μm and provides a nominal withstand voltage of 120-200 V per layer.

14. 14. The electrical system of claim 11, wherein each of the separately applied and bonded layers is a layer of dielectric ink.

15. 15. The electrical system of claim 1, wherein the conductive layer is attached to both the first insulating layer and the second insulating layer.

16. 16. The electrical system of claim 15, wherein the conductive layer is continuously attached to both the first insulating layer and the second insulating layer.

17. 17. The electrical system of claim 1, wherein an attachment device is provided for attaching the first insulating layer to the garment.

18. The electrical system of claim 17 , wherein the mounting device comprises an adhesive.

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