A flexible electronic skin and its encapsulation method

Abstract

The present invention relates to a flexible electronic skin and its encapsulation method, belonging to the technical field of sensors. The encapsulation method of the present invention includes the following steps: sequentially layering a first substrate layer, a porous dielectric layer, and a second substrate layer, and encapsulating both sides of the first substrate layer, the porous dielectric layer, and the second substrate layer together by laser welding technology to obtain the flexible electronic skin; silver nanowires are coated on the welding regions on the sides of the first substrate layer and the second substrate layer that are in contact with the porous dielectric layer. This encapsulation method uses silver nanowires as absorbents, and uses polydimethylsiloxane, polyurethane, polystyrene, etc. as porous dielectric materials, and combines laser welding technology to achieve high-precision welding of the flexible electronic skin.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a flexible electronic skin and a packaging method thereof. Background Art

[0002] In wearable technology, the core device for real-time and accurate monitoring of various human functions is the sensor. The working principle of the sensor is to convert the received external signals (such as force, deformation, temperature, and humidity) into electrical signals with certain rules for output. Traditionally, sensor materials are generally hard materials with poor flexibility and low biocompatibility, which are not suitable for the field of wearable technology. Therefore, researchers began to consider using flexible materials with excellent performance to replace hard materials for preparing sensors, so as to ensure signal acquisition and transmission while being able to adhere to the human skin surface to the greatest extent without any discomfort. This new type of sensor is called a flexible sensor. As an indispensable key component in the next-generation wearable flexible electronic products, flexible sensors are usually called flexible electronic skins, which show broad application prospects in health monitoring, intelligent recognition, human-computer interaction, virtual reality, etc.

[0003] Flexible electronic skins have simple structures, low energy consumption, and good stability, so they have been more developed and applied. Capacitive flexible pressure sensors usually present a "sandwich" structure, that is, electrode layer - dielectric layer - electrode layer. Both the electrode layer and the porous dielectric layer need to have good flexibility and ductility. To ensure the normal operation of the flexible electronic skin, packaging is required after the flexible electronic skin is prepared. The materials of each layer of the sensor are fixed to form a closed space, so the packaging quality is crucial for the normal use of the sensor. The standard of packaging is to ensure the connection strength between the materials of each layer, prevent external gases, liquids, etc. from entering the sensor interior, and ensure that the sensor structure is not affected during the packaging process and there is no potential pollution source. The traditional flexible electronic skin packaging technology mainly performs single packaging treatment on micro-samples, and it is difficult to achieve large-scale, high-efficiency, and non-destructive packaging, which affects the actual application range of flexible electronic skins. Therefore, it is of great exploratory significance to find a flexible electronic skin packaging technology with green processing, good sealing, high efficiency, and precision.

[0004] However, due to the differences in the properties of materials, the joining of dissimilar materials usually encounters problems such as poor material compatibility and joining performance. The joining methods of dissimilar materials are mainly divided into mechanical joining, welding, adhesive bonding, and hot pressing joining. Mechanical joining is a joining method that uses connectors such as bolts and screws to join materials. Mechanical joining has defects such as poor sealing after joining and the introduction of connectors will increase the weight of the materials. Therefore, it is not suitable for the encapsulation of flexible electronic skin. Welding includes ultrasonic welding, friction welding, etc. The welded joints of ultrasonic welding are prone to high-frequency mechanical vibration, which may cause edge fatigue failure and is only suitable for joining a few types of plastics. Friction welding has the characteristic of achieving welding by workpiece rotation and is also not suitable for the joining and encapsulation of flexible electronic skin. Therefore, the existing fixing and encapsulation of flexible electronic skin still mainly adopt adhesive bonding and hot pressing joining. Adhesive bonding is suitable for the bonding of metal to metal, metal to non-metal, and non-metal to non-metal. However, it has problems such as low bonding strength and easy corrosion and aging. At the same time, for the encapsulation process using chemical adhesive reagents, there is further a safety risk of reagent volatilization. Hot pressing joining is suitable for the encapsulation of flexible electronic skin with a thermoplastic substrate material. However, its experimental operation is time-consuming, and the continuous high temperature is likely to affect the internal parts of the sensor. Therefore, the sensor materials all need to have high thermal stability, increasing the material cost of flexible electronic skin. Laser transmission welding has the advantages of good sealing, non-contact with materials, small heat-affected zone of the weld, high quality of the welded joint, and high welding efficiency, which makes its joining and fixing encapsulation with dissimilar materials in the micro-system field show a high degree of matching. Therefore, developing its application in the field of flexible electronic skin encapsulation has very important advantages and significance.

[0005] Wang Yuying directly welded medical plastics without light-absorbing materials, low-density polyethylene (LDPE) and polyethylene terephthalate (PET), using a fiber laser with a wavelength of 1940 nm. The heat-affected zone formed by the welding without light-absorbing additives is a penetration type. Pelsmaeker et al. used a 1940 nm fiber laser to study the welding of transparent plastics such as COC, PLLA, PMMA, and PS. The shear force of the welds of several materials exceeded 5 MPa. In addition, it was proved that the laser of this wavelength can be used for the bonding of microfluidic devices. Schkutow et al. found that compared with traditional laser transmission welding with a wavelength of 1000 nm, a 2000 nm laser can reduce the sensitivity of stress cracking. This is because it is difficult to control the energy density distribution of the light beam with a single-wavelength laser, and a larger temperature gradient is more likely to cause high residual stress in transparent materials. Therefore, a suitable laser wavelength or a combination of multiple light beam sources can effectively reduce the occurrence of high residual stress and achieve reliable connection. Although the above scholars successfully used laser transmission welding to achieve the joining of dissimilar materials, however, the joining strength of the connectors is still not ideal enough.

[0006] To address the above problems, some scholars have attempted to solve the issue of welding failure caused by insufficient material absorption by adding absorbers. Absorbers can be roughly divided into two types: one is metal materials, and the other is carbon materials. Among metal materials, metal particles such as gold (Au) and copper (Cu) and their nanowires are common conductive materials. However, due to their high cost and difficulty in mass production, their use has been gradually phased out. Among carbon materials, carbon black (CB), carbon nanotubes (CNTs), and graphene have become the most commonly used conductive materials due to their strong conductivity. However, this also adds additional processes and raises operational requirements. In addition, in some application scenarios, there are high requirements for the color of the material, which also prevents the addition of colored absorbers. Therefore, the commonly used absorbers are not suitable for the encapsulation of flexible electronic skins made of multi-layered porous heterogeneous transparent plastics.

[0007] Therefore, there is an urgent need for a new encapsulation method to solve the above problems. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a flexible electronic skin and its encapsulation method, which uses silver nanowires as absorbers, and polydimethylsiloxane, polyurethane, polystyrene, etc. as porous dielectric materials, and combines laser welding technology to achieve high-precision and high-precision welding of flexible electronic skins.

[0009] The first object of the present invention is to provide an encapsulation method for a flexible electronic skin, comprising the following steps:

[0010] Lay the first substrate layer, the porous dielectric layer, and the second substrate layer in sequence, and encapsulate both sides of the first substrate layer, the porous dielectric layer, and the second substrate layer together through laser welding technology to obtain the flexible electronic skin; the areas to be welded on the sides of the first substrate layer and the second substrate layer that are in contact with the porous dielectric layer are coated with silver nanowires.

[0011] In an embodiment of the present invention, the silver nanowires have a length of 20μm - 50μm, a diameter of 70nm - 150nm, and an aspect ratio of 1500 - 3000.

[0012] In an embodiment of the present invention, the process parameters of the laser welding technology are: wavelength of 1500nm - 2000nm, power of 22W - 24W, scanning speed of 1.8mm / s - 2.2mm / s, spot diameter of 1.9mm - 2.1mm, and the welding trajectory is a straight line; by controlling the wavelength, power, and speed of the laser, etc., the heat input during welding can be controlled, and high-quality welding of flexible electronic skins can be achieved in a short time, which can improve the welding quality and speed, and has broad application prospects in the high-precision and high-speed welding applications of flexible electronic skins.

[0013] In one embodiment of the present invention, the wavelength, power, and scanning speed of laser welding are determined according to the welding requirements and the material properties of the flexible electronic skin; the light output position of the laser welding is adjusted according to the preset welding area and the preset welding track.

[0014] In one embodiment of the present invention, the material of the first substrate layer is selected from polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polycarbonate (PC), or polyimide (PI).

[0015] In one embodiment of the present invention, the thickness of the first substrate layer is 0.1 mm - 0.3 mm.

[0016] In one embodiment of the present invention, the material of the porous dielectric layer is selected from polydimethylsiloxane (PDMS), polyurethane (PU), polystyrene (PS), or polyethylene terephthalate (PET).

[0017] In one embodiment of the present invention, the thickness of the porous dielectric layer is 1 mm - 3 mm.

[0018] In one embodiment of the present invention, the material of the second substrate layer is selected from polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polycarbonate (PC), or polyimide (PI).

[0019] In one embodiment of the present invention, the thickness of the second substrate layer is 0.1 mm - 0.3 mm.

[0020] In one embodiment of the present invention, after silver nanowires are coated on the welding areas of the first substrate layer and the second substrate layer, the substrate needs to be irradiated with ultraviolet light or air-dried naturally.

[0021] The second object of the present invention is to provide a flexible electronic skin prepared by the encapsulation method described above.

[0022] The technical solution of the present invention has the following advantages compared with the prior art:

[0023] (1) In the encapsulation method of the present invention, silver nanowires are used as absorbents and coated on the welding areas on the surface of the substrate. During welding, the flow of the material melt will cause the silver nanowire particles to be randomly distributed at the interface. After cooling, strong mechanical bonding is formed at the weld joint by the holes of the substrate material, silver nanowires, and dielectric material; in addition, new chemical bonds can be formed between silver atoms and polymer chains, which play a strengthening role in the welded joint, thereby realizing low-cost and high-strength welding of the flexible electronic skin; furthermore, the addition of pure silver nanowires will not cause pollution to the surface of the workpiece, and at the same time, it improves the conductivity of the flexible electronic skin to a certain extent.

[0024] (2)The encapsulation method of the present invention realizes high-precision welding of the flexible electronic skin by regulating the wavelength, power, scanning speed, etc. of the laser welding technology. Description of the Drawings

[0025] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the drawings, wherein:

[0026] Figure 1 It is the super-depth-of-field optical microscope image of the silver nanowires of the present invention;

[0027] Figure 2 It is the SEM image of the substrate layer after coating with silver nanowires of the present invention;

[0028] Figure 3 It is the physical image of the weld seam of the present invention. Detailed Embodiments

[0029] The following further illustrates the present invention with specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited do not limit the present invention.

[0030] In the present invention, unless otherwise specified, the technologies and scientific terms used in the present invention have the same meanings as those generally understood by those skilled in the technical field to which the present invention belongs.

[0031] In the present invention, unless otherwise specified, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0032] In the present invention, unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods without special instructions, and the materials, reagents, etc. used can be obtained from commercial channels without special instructions. Example 1

[0033] The flexible electronic skin of the present invention and its preparation method specifically include the following steps:

[0034] S1. Add 0.55 g of polyvinylpyrrolidone (PVP) powder to 50 mL of ethylene glycol solution, stir evenly to obtain a polyvinylpyrrolidone solution; add 0.55 g of silver nitrate powder and 0.55 mg of copper chloride dihydrate powder to 10 mL of ethylene glycol solution respectively to obtain a silver nitrate solution and a copper chloride dihydrate solution; pour all the polyvinylpyrrolidone solution into a three-necked flask, then add dropwise the copper chloride dihydrate solution, place it in a magnetic stirrer, carry out an oil bath at 160 °C and stir; use a dropping funnel to continue adding dropwise the silver nitrate solution to the three-necked flask, continue heating and stirring at a temperature of 160 °C for 2 h to obtain a gray-green oily liquid, then carry out centrifugal separation and drying to obtain silver nanowires, and then redissolve them in water to obtain a silver nanowire solution;

[0035] S2. Cut a PC film with a thickness of 0.125 mm into 50 mm × 20 mm as the substrate layer, and then coat 30 mL of silver nanowires on the surface of the area to be welded of the substrate layer and let it dry naturally;

[0036] S3. Cut a PET film with a thickness of 2 mm into 50 mm × 20 mm as the porous dielectric layer, and then stack the substrate layer, the porous dielectric layer and the substrate layer in sequence (the side of the substrate layer with silver nanowires is attached to the porous dielectric layer), and clamp and fix it with a clamp;

[0037] S4. Preset the welding track as a straight track connecting one end to the other end of the welding area, set the near-infrared laser wavelength to 1710 nm according to the characteristics of the material to be welded and the preset welding track, the near-infrared laser wavelength is 1710 nm, the power is 20 W, the spot diameter is 2 mm, and the welding speed is 2 mm / s. Adjust the laser light output position to ensure that the laser beam falls within the welding area; use a pulsed laser to encapsulate both sides of the substrate layer, the porous dielectric layer and the substrate layer together to obtain a flexible electronic skin. Comparative Example 1

[0038] The flexible electronic skin and its preparation method in this comparative example specifically include the following steps:

[0039] S1. Cut a PC film with a thickness of 0.125 mm into 50 mm × 20 mm as the substrate layer, and cut a PET film with a thickness of 2 mm into 50 mm × 20 mm as the porous dielectric layer, and then stack the substrate layer, the porous dielectric layer and the substrate layer in sequence, and clamp and fix it with a clamp;

[0040] S2. The preset welding trajectory is a straight line trajectory connecting one end of the welding area to the other end. According to the characteristics of the material to be welded and the preset welding trajectory, the near-infrared laser wavelength is set to 1710 nm, the near-infrared laser wavelength is 1710 nm, the power is 20 W, the spot diameter is 2 mm, and the welding speed is 2 mm / s. Adjust the laser light output position to ensure that the laser beam falls within the welding area. Using a pulsed laser to encapsulate the substrate layer, the porous dielectric layer, and both sides of the substrate layer, it is impossible to fabricate a flexible electronic skin.

[0041] Test Example 1

[0042] Based on Example 1, the silver nanowires, the substrate layer coated with silver nanowires, and the weld seam were characterized, and the results are as Figures 1 - 3 shown. As can be seen from Figure 1 it, the length of the silver nanowires is about 20 μm - 50 μm, the diameter is about 70 nm - 150 nm, and the aspect ratio is about 1500 - 3000. In addition, the lengths and curvatures of the silver nanowires are different, and this morphology makes the silver nanowires coated more tightly entangled with each other. Figure 2 It can be seen that the silver nanowires coated on the substrate are tightly entangled, which helps the silver nanowires to be evenly heated and melted during welding. As can be seen from Figure 3 it, the heat affected zone of the weld seam after welding is uniform and defect-free, because the silver nanowires are fully melted and play a role in connecting the substrate layer and the porous dielectric layer.

[0043] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A packaging method for flexible electronic skin, characterized in that: The following steps are involved: The first substrate layer, the porous dielectric layer and the second substrate layer are stacked in sequence, and the two sides of the first substrate layer, the porous dielectric layer and the second substrate layer are packaged together by laser welding technology to obtain the flexible electronic skin; the first substrate layer and the second substrate layer are attached to the welding area on one side of the porous dielectric layer and are coated with silver nanowires; the length of the silver nanowires is 20μm-50μm, the diameter is 70nm-150nm, and the aspect ratio is 1500-3000; the process parameters of the laser welding technology are: wavelength is 1500nm-2000nm, power is 22W-24W, scanning speed is 1.8mm / s-2.2mm / s, spot diameter is 1.9mm-2.1mm, and the welding trajectory is a straight line.

2. The packaging method of flexible electronic skin according to claim 1, characterized in that: The material of the first substrate layer is selected from polydimethylsiloxane, polyethylene terephthalate, polycarbonate or polyimide.

3. The packaging method of flexible electronic skin according to claim 1, characterized in that: The thickness of the first substrate layer is 0.1 mm-0.3 mm.

4. The packaging method of flexible electronic skin according to claim 1, characterized in that: The material of the porous dielectric layer is selected from polydimethylsiloxane, polyurethane, polystyrene or polyethylene terephthalate.

5. The packaging method of flexible electronic skin according to claim 1, characterized in that: The thickness of the porous dielectric layer is 1 mm-3 mm.

6. The packaging method of flexible electronic skin according to claim 1, characterized in that: The material of the second substrate layer is selected from polydimethylsiloxane, polyethylene terephthalate, polycarbonate or polyimide.

7. The packaging method of flexible electronic skin according to claim 1, characterized in that: The thickness of the second substrate layer is 0.1 mm-0.3 mm.

8. The flexible electronic skin prepared by the packaging method according to any one of claims 1 to 7.

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