A flexible sensor and a method of manufacturing the same

Abstract

The application discloses a flexible sensor and a preparation method thereof, relates to the technical field of flexible sensors, and discloses a flexible sensor preparation method, which comprises the following steps: coating a shape memory polymer slurry on a target curved surface and solidifying to obtain a curved surface polymer; flattening the curved surface polymer and cooling to below a switching temperature of the shape memory polymer to obtain a planar polymer; coating a functional layer slurry of the flexible sensor on the planar polymer, and in the case that the functional layer slurry is semi-solidified, heating to above the switching temperature to make the planar polymer return to the curved surface polymer, and then solidifying the functional layer slurry to prepare the functional layer of the flexible sensor; and the steps of flattening the curved surface polymer and cooling to below the switching temperature of the shape memory polymer to obtain the planar polymer and subsequent steps are executed again until each functional layer of the flexible sensor is prepared, and the flexible sensor is obtained. The application overcomes the internal stress interference of the flexible sensor and improves the sensor precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible sensors, in particular to a flexible sensor and a preparation method thereof. BACKGROUND

[0002] A flexible sensor is an important mechanical sensor, which can convert mechanical signals into electrical signals and is widely used in sensing and monitoring in complex curved surface environments such as robots. Since the surface of a robot is mostly a complex curved surface, the flexible sensor and its array need to have sufficient flexibility to closely adhere to the curved surface and achieve conformal contact, thereby ensuring a good signal-to-noise ratio. Therefore, the flexible sensor is often in the form of a thin film by reducing the overall modulus or thickness to reduce the minimum bending radius and improve the conformal ability to complex curved surface environments.

[0003] A conventional flexible sensor is usually prepared on a plane and has isotropic properties. However, when the sensor is transferred to a curved surface for deployment, due to the difference in curvature and height in each direction of the curved surface, the isotropic sensor will be stretched or compressed in an undirectional manner when adhering to the anisotropic curved surface, resulting in local stress concentration and internal stress. The existence of internal stress not only reduces the accuracy of the sensor, but also can cause the adhesion between the sensor and the curved surface to fail, forming a cavity and introducing additional mechanical structures, thereby interfering with the transmission process of the mechanical signal to the sensor and producing artifacts or clutter.

[0004] The above content is only used to assist in understanding the technical solutions of the present application and does not represent the acknowledgement of the above content as prior art. SUMMARY

[0005] The main purpose of the present application is to provide a flexible sensor and a preparation method thereof, aiming to overcome the problem of internal stress interference in the flexible sensor.

[0006] To achieve the above-mentioned purpose, the present application provides a flexible sensor preparation method, comprising the following steps:

[0007] Coating a slurry of a shape memory polymer on a target curved surface and solidifying to obtain a curved surface polymer;

[0008] Flattening the curved surface polymer and cooling it below the switching temperature of the shape memory polymer to obtain a flat surface polymer;

[0009] Coating a functional layer slurry of a flexible sensor on the flat surface polymer, and in the case of semi-curing of the functional layer slurry, heating it above the switching temperature to make the flat surface polymer recover to a curved surface polymer, and then solidifying the functional layer slurry to prepare a functional layer of the flexible sensor;

[0010] The step of flattening the curved polymer and the subsequent steps of cooling to below the switching temperature of the shape memory polymer, until each functional layer of the flexible sensor is prepared, to obtain the flexible sensor.

[0011] In an embodiment, the step of flattening the curved polymer comprises:

[0012] The curved polymer is flattened by pulling and placed on a carrier plane coated with a fixing agent, wherein the failure temperature of the fixing agent is lower than the switching temperature.

[0013] The curved polymer is fixed to the carrier plane by cooling to below the onset temperature of the fixing agent.

[0014] In an embodiment, the fixing agent comprises menthol.

[0015] In an embodiment, the switching temperature is 30-50℃.

[0016] In an embodiment, the shape memory polymer comprises a shape memory resin, and the shape memory resin comprises at least one of polyurethane, polyester, polystyrene-butadiene, EVA and polyoctenamer.

[0017] In an embodiment, the shape memory polymer is cured by light curing and / or thermal curing.

[0018] In an embodiment, before the step of heating to above the switching temperature to restore the flat polymer to a curved polymer, the method further comprises:

[0019] The surface of the semi-cured functional layer slurry is uniformly coated with water-soluble crystals.

[0020] In an embodiment, the water-soluble crystals comprise at least one of inorganic salt, sugar and organic acid.

[0021] The embodiments of the present application also provide a flexible sensor prepared by the above method.

[0022] In an embodiment, the functional layer of the flexible sensor comprises an electrode layer and a sensing layer.

[0023] The one or more technical solutions provided in the present application have at least the following technical effects: a flexible sensor preparation method is provided, a shape memory polymer slurry is coated on a target curved surface, and is cured to obtain a curved polymer; then the curved polymer is flattened, and is cooled to below the switching temperature of the shape memory polymer to obtain a flat polymer; then a functional layer slurry of the flexible sensor is coated on the flat polymer, and in the case of semi-curing of the functional layer slurry, the temperature is raised to above the switching temperature, so that the flat polymer returns to the curved polymer, and the functional layer slurry is cured to obtain the functional layer of the flexible sensor; then the steps of flattening the curved polymer and cooling to below the switching temperature of the shape memory polymer to obtain the flat polymer and the subsequent steps are re-executed until each functional layer of the flexible sensor is prepared, and the flexible sensor is obtained. The present application utilizes the characteristics of the shape memory polymer that can be restored in the high elastic state after being deformed in the glass state, first uses the shape memory polymer to copy the target curved surface shape, and then flattens the polymer after further cooling to the glass state, so that the curved surface preparation process of the flexible sensor is converted into a mature controllable flat surface preparation process. After the functional layer of the sensor is constructed on the shape memory polymer, the shape polymer is triggered to restore, so that the sensor is deformed in the restoration of the shape memory polymer, and is restored to the stress-free state of closely adhering to the curved surface, thereby effectively overcoming the internal stress interference of the flexible sensor and improving the accuracy of the prepared sensor. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A flowchart of the flexible sensor preparation method involved in the embodiment scheme of the present application.

[0025] The implementation, functional features and advantages of the present application will be further described with reference to the drawings. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased on the market.

[0027] Hereinafter, the embodiments of the flexible sensor and the preparation method thereof disclosed in the present application will be specifically described with appropriate reference to the drawings. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of matters well known and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0028] The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the range, i.e., all combinations of any two of the range limits, unless otherwise indicated. For example, a range of "1 to 10" is intended to include any number from 1 to 10, including the integers 1 and 10. Unless otherwise indicated, the use of "or" in the disclosed aspects herein is the inclusive, and not the exclusive use. Only the context, and not the number of times an item is used, can determine that it is the exclusive use. For example, the phrase "A uses B or C" means that A can use B, or A can use C, or A can use both B and C. Also, the use of the term "one" or "a" or "the" is intended to be singular as well as plural, unless only the singular form is used. For example, the phrase "one or more of A, B, and C" means that A, B, or C can be present, and that one of A, B, and C can be present, and that two of A, B, and C can be present, and that all of A, B, and C can be present.

[0029] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0030] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0031] Unless otherwise specified, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0032] Unless otherwise specified, the "includes" and "contains" mentioned in the present application are open-ended, and can also be closed. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0033] If not specifically stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0034] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the technical solutions of the present application will be further described below with reference to the drawings and embodiments. However, the present application is not limited to the listed embodiments, and should also include any known changes within the scope of the rights claimed by the present application.

[0035] The term "one embodiment" or "an embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one implementation of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are the various embodiments mutually exclusive of one another.

[0036] In order to better understand the technical solutions of the present application, the following will be described in detail with reference to the drawings and specific embodiments of the specification.

[0037] In conventional technology, flexible sensors are usually prepared on a plane such as a wafer, a flat mold, etc., and their mechanical and electrical properties are isotropic. However, when these sensors are transferred to a curved surface for deployment, due to the differences in curvature and height of the curved surface in various directions, the originally isotropic sensors will be stretched or compressed in an undirectional manner when they are attached to an anisotropic curved surface, thereby causing local stress concentration, i.e., the generation of internal stress. Ideally, the curved surface and the sensor are just complementary to each other to achieve a stress-free state of the sensor. However, the sensor is usually assembled by multiple layers or components, and needs to be processed using multiple devices and technologies. That is, direct processing on the curved surface requires the processing device to have three-dimensional processing capability, i.e., from two-axis plane processing to three-axis or even multi-axis 3D processing, which will lead to an increase in system complexity and an increase in the cost of equipment and technology. Therefore, it is difficult to directly process the flexible sensor on the curved surface.

[0038] The application provides a solution, in particular, a flexible sensor preparation method is provided. By utilizing the characteristic of shape memory polymer that can be restored in high elastic state after being deformed in glass state, the target curved surface shape is first copied by using shape memory polymer, and then the polymer is flattened after further cooling to glass state, so that the curved surface preparation process of the flexible sensor is converted into a mature controllable planar preparation process. After the functional layer of the sensor is constructed on the shape memory polymer, the shape polymer is triggered to recover, so that the sensor is deformed in the recovery of the shape memory polymer and is recovered to a stress-free state close to the curved surface, thereby effectively overcoming the internal stress interference of the flexible sensor and improving the accuracy of the prepared sensor.

[0039] Reference Figure 1 The first aspect of the embodiment of the application provides a flexible sensor preparation method, comprising the following steps:

[0040] In step S10, a slurry of shape memory polymer is coated on the target curved surface and solidified to obtain a curved polymer.

[0041] In an available embodiment, a slurry of shape memory polymer is provided and coated on the surface of the target curved surface, and then the solidification of the slurry of shape memory polymer is induced to obtain a curved polymer copying the shape of the target curved surface.

[0042] For example, the slurry of shape memory polymer can be coated on the surface of the target curved surface by brushing, dipping or the like.

[0043] In an available embodiment, the slurry of shape memory polymer comprises a shape memory resin, and the shape memory resin comprises at least one of polyurethane, polyester, polystyrene-butadiene, EVA and polyoctenamer.

[0044] The shape memory material based on polyurethane can realize double or multiple stimulus response, such as shape memory effect under the stimulation of heat, light, chemistry, etc., by using two or more than two fillers to synergistically enhance the performance, and it also has the advantages of good elasticity, good biocompatibility, biodegradability, etc., and is suitable for application in various fields.

[0045] Polyester is a transparent, high-density polymer with excellent strength and waterproofness, and is suitable for shape memory polymer applications that require high strength and waterproofness. In addition, polyester material is easy to process, and can be easily prepared into shape memory polymer products of various shapes and sizes. Compared with other polymers, polyester (such as PET) has moderate price and cost-effectiveness, and is suitable for large-scale production.

[0046] EVA has good flexibility and elasticity, which can adapt to various complex curved surfaces and deformation environments, and is suitable for preparing shape memory polymer products that need to withstand multiple deformations and recoveries. EVA material also has good resistance to various chemicals and weather conditions, which helps to protect shape memory polymer products from environmental factors.

[0047] Polyoctenamer is a high-elasticity material with excellent tensile and rebound performance. This enables it to provide stable support and recovery in shape memory polymers, which are suitable for application scenarios that require large deformation and rapid recovery. Polyoctenamer also has good resistance to various chemicals and high-temperature environments, which helps to maintain the stability and reliability of shape memory polymer products in harsh environments.

[0048] In a feasible implementation, the curing method of the shape memory polymer includes light curing and / or thermal curing. Light curing refers to the process of irradiating the slurry with a light source such as ultraviolet (UV) or visible light to cause the photosensitive components in the slurry to undergo chemical reactions, thereby achieving curing. Thermal curing refers to the process of heating the material to cause the heat-sensitive components in the material to undergo chemical reactions, thereby achieving curing.

[0049] It should be understood that the specific curing method of the shape memory polymer can be determined according to the specific components in its slurry.

[0050] For example, the shape memory polymer needs to have a large deformation capacity, where the deformation capacity is greater than 100%.

[0051] Step S20, flatten the curved polymer and cool it to below the switching temperature of the shape memory polymer to obtain a flat polymer;

[0052] In a feasible embodiment, the curved polymer in the curved state is peeled off from the target curved surface, and the temperature is raised to convert the curved polymer into a high-elasticity state to flatten it, and then the temperature is lowered to below the switching temperature of the shape memory polymer. As the temperature decreases, the chain segment motion in the shape memory polymer is gradually restricted, and below the switching temperature, the chain segment motion becomes very slow and almost freezes, forming a stable temporary shape, i.e., shape fixation, to obtain a flat polymer (i.e., a flat polymer).

[0053] In a feasible implementation, the switching temperature is 30-50°C; for example, 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, etc. By using a shape memory polymer with a switching temperature of 30-50°C, energy can be effectively saved, and the process complexity of the temperature raising and lowering operations can be reduced, for example, the cooling process can even be performed in an air-conditioned room.

[0054] It should be understood that the final flexible sensor can retain the shape memory polymer or can remove it for use. In the case of a flexible sensor retaining the shape memory polymer, it is necessary to keep the shape memory polymer in a high elastic state at the daily use temperature. This is because the flexible sensor is mainly applied to the sensing of the surface of a human or a robot, and in such applications, the flexible sensor needs to deform along with the deformation of the curved surface (for example, the skin at the joint will elongate and shorten with the movement of the joint, and the sensor attached to the skin also needs to change accordingly). Therefore, its switching temperature is preferably 30-50℃, i.e. near the human body temperature or room temperature.

[0055] In an embodiment, the step S20 of flattening the curved polymer includes:

[0056] In step S21, the flattened curved polymer is placed on a carrier plane coated with a fixing agent, wherein the failure temperature of the fixing agent is lower than the switching temperature of the shape memory polymer.

[0057] In an embodiment, the flattened curved polymer is placed on a carrier plane coated with a fixing agent by pulling along the plane, wherein the failure temperature of the fixing agent is lower than the switching temperature of the shape memory polymer, and the fixing agent can quickly sublimate, volatilize and completely remove, thereby avoiding the influence of the fixing agent on the shape memory polymer, such as dissolution, swelling and polymerization, or taking away the filler in the polymer.

[0058] In a conventional way, a metal flat plate is often used to flatten the curved surface, i.e. the curved surface is forced to flatten by pressure in the up-down direction, but the flexible sensor usually includes a multi-layer assembly (i.e. a multi-layer functional layer), so it is easy to cause damage to the processed assembly. At the same time, the curved material will inevitably move to the surrounding during the sliding process of the contact point during the pressing process until it cannot change, i.e. it is flattened. However, the flexible sensor uses a material with certain viscoelasticity and softness, and the friction is large during compression and the material itself is prone to buckling, so the whole curved surface may be squeezed into a ball instead of being flattened as desired. After the compression is completed, the flat material pressed from the curved surface is used without support; this is because the shape memory polymer is still relatively soft after the glass transition, and it is still easy to lose stability and cause unevenness under mechanical processing, making it difficult to achieve high-precision processing of the flexible sensor. The embodiment of the present application can apply force along the plane by fixing the curved polymer with menthol, thereby reducing the damage to the constructed assembly in multi-layer processing, and easily flattening the curved polymer without being affected by the modulus or viscoelasticity of the material.

[0059] In an embodiment, the fixing agent comprises menthol. The menthol has a moderate volatility, which is neither too fast to cause poor fixing effect nor too slow to affect production efficiency. The moderate volatility allows the menthol to uniformly cover the surface to be fixed and form a stable fixed layer. The menthol has a moderate melting point, which allows it to remain in a stable state between solid and liquid at room temperature, thereby facilitating its application in the fixing agent.

[0060] In step S22, the temperature is lowered to below the effective temperature of the fixing agent, so as to fix the curved polymer to the carrier plane.

[0061] In an embodiment, the temperature is lowered to below the effective temperature of the fixing agent (for example, 40°C), the fixing agent (for example, menthol) is converted into a crystal, and the curved polymer is firmly fixed to the carrier plane.

[0062] For example, the curved polymer can be tightly stretched to approach the plastic deformation region by the preset frame device, and fixed to the carrier plane coated with the fixing agent. Then, after the curved polymer is fixed to the carrier plane by lowering the temperature to below the effective temperature of the fixing agent, the frame device is removed, and the functional layer of the flexible sensor is processed.

[0063] In the embodiment, compared with the conventional method of forcing the curved surface to flatten by a metal flat plate, the curved polymer fixed by the menthol can apply force along the plane, thereby reducing the damage to the built assembly in multi-layer processing, and easily flattening without being affected by the modulus or viscoelasticity of the material.

[0064] In step S30, the functional layer slurry of the flexible sensor is coated on the planar polymer, and in the case of semi-curing of the functional layer slurry, the temperature is raised to above the switching temperature of the shape memory polymer, so as to restore the planar polymer to the curved polymer, and then the functional layer slurry is cured to obtain the functional layer of the flexible sensor.

[0065] In an embodiment, the functional layer slurry of the flexible sensor is coated on the surface of the planar polymer, and the functional layer slurry is induced to cure. Then, in the case of semi-curing of the functional layer slurry, the temperature is raised to above the switching temperature of the shape memory polymer, at which time the curing agent (for example, menthol solution) melts and volatilizes, and the planar polymer returns to the curved shape, i.e., the curved polymer. Then, the functional layer slurry is continuously cured, so that the functional layer also assumes the curved state, thereby obtaining the functional layer of the flexible sensor.

[0066] In an embodiment, before the step of raising the temperature to above the switching temperature of the shape memory polymer to restore the planar polymer to the curved polymer in step S30, the method further comprises:

[0067] In step S31, a water-soluble crystal is uniformly coated on the surface of the semi-cured functional layer slurry.

[0068] In an embodiment, water-soluble crystals, such as inorganic salts, sugars and / or organic acids, are uniformly coated on the surface of the semi-solid functional layer paste. The surface of the semi-solid functional layer has not yet been completely solidified and has certain viscosity, which can better adhere to the water-soluble crystals. During the further solidification process, the water-soluble crystals can form microstructures on the surface of the functional layer. These microstructures can increase the contact area between the functional layer (such as the electrode layer) and the touching object, thereby improving the sensitivity and accuracy of the flexible sensor.

[0069] In step S40, the curved polymer is flattened again, and the temperature is lowered to below the switching temperature of the shape memory polymer to obtain a planar polymer. Subsequent steps are performed until each functional layer of the flexible sensor is prepared, and the flexible sensor is obtained.

[0070] In an embodiment, since the flexible sensor includes multiple functional layers (such as the upper electrode layer, the sensing layer, the lower electrode layer, etc.), and each functional layer has good elasticity, when the first functional layer of the flexible sensor is prepared, the curved polymer is flattened again, and the temperature is lowered to below the switching temperature of the shape memory polymer to obtain a planar polymer. Then, the paste of the next functional layer of the flexible sensor is coated on the planar polymer, and when the functional layer paste is semi-solidified, the temperature is raised to above the switching temperature, so that the planar polymer returns to a curved polymer. The functional layer paste is solidified to prepare the second functional layer of the flexible sensor, and the above steps are repeatedly performed until each functional layer of the flexible sensor is prepared. The curved polymer is removed to obtain the flexible sensor.

[0071] In this embodiment, by using the feature that the shape memory polymer can return to the high-elastic state after being deformed in the glass state, the target curved surface shape is first copied by using the shape memory polymer, and then the polymer is flattened after being further cooled to the glass state. Thus, the curved surface preparation process of the flexible sensor is converted into a mature and controllable planar preparation process. After the functional layer of the sensor is constructed on the shape memory polymer, the shape polymer is triggered to return, so that the sensor is deformed in the return of the shape memory polymer and returns to the stress-free state close to the curved surface. Thus, the internal stress interference of the flexible sensor is effectively overcome, and the accuracy of the prepared sensor is improved.

[0072] The above is only a preferred embodiment of the present application, and does not limit the patent scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the patent protection scope of the present application.

Claims

1. A method for fabricating a flexible sensor, characterized in that, The method comprises the following steps: coating a slurry of shape memory polymer on a target curved surface and curing to obtain a curved polymer; flattening the curved polymer and cooling below the switching temperature of the shape memory polymer to obtain a flat polymer; coating a functional layer slurry of a flexible sensor on the flat polymer and, in the case of semi-curing of the functional layer slurry, heating above the switching temperature to make the flat polymer return to a curved polymer, and curing the functional layer slurry to obtain the functional layer of the flexible sensor; repeating the steps of flattening the curved polymer and cooling below the switching temperature of the shape memory polymer to obtain a flat polymer and the subsequent steps until each functional layer of the flexible sensor is prepared to obtain the flexible sensor.

2. The flexible sensor manufacturing method of claim 1, wherein, The step of flattening the curved polymer comprises: flattening the curved polymer by pulling and placing on a carrier plane coated with a fixing agent, wherein the failure temperature of the fixing agent is lower than the switching temperature; cooling below the onset temperature of the fixing agent to fix the curved polymer on the carrier plane.

3. The flexible sensor manufacturing method of claim 2, wherein, The fixing agent comprises menthol.

4. The flexible sensor manufacturing method of claim 1, wherein, The switching temperature is 30-50℃.

5. The flexible sensor manufacturing method of claim 1, wherein, The slurry of the shape memory polymer comprises a shape memory resin, and the shape memory resin comprises at least one of polyurethane, polyester, polystyrene-butadiene, EVA and polyoctenamer.

6. The flexible sensor manufacturing method of claim 1, wherein, The curing mode of the shape memory polymer comprises photocuring and / or thermal curing.

7. The flexible sensor manufacturing method of claim 1, wherein, Before the step of heating above the switching temperature to make the flat polymer return to a curved polymer, it further comprises: uniformly covering the surface of the semi-cured functional layer slurry with water-soluble crystals.

8. The flexible sensor manufacturing method of claim 7, wherein, The water-soluble crystals comprise at least one of inorganic salt, sugar and organic acid.

9. A flexible sensor, characterized by The flexible sensor is prepared by the method according to any one of claims 1-8.

10. The flexible sensor of claim 9, wherein, The functional layer of the flexible sensor comprises an electrode layer and a sensing layer.

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