A method of fabricating a fabric-based flexible stress sensor

Abstract

The application discloses a preparation method of a fabric-based flexible stress sensor, and comprises the following steps: S1, mixing a core layer melt, a colloid and a pore-forming agent, and extruding the mixture into primary filaments through a spinneret; S2, using side blowing to cool the primary filaments, and placing the primary filaments into a dissolving agent to obtain annular core layer fibers; S3, mixing graphene with a dispersant and adding a curing agent to form a mixed medium, mixing the core layer fibers with the mixed medium, and curing and shaping; S4, taking out the sample in S3, adding water, and adjusting the position and orientation of the graphene in the sample through an external electric field in the circumferential direction of the sample, and obtaining a core layer after drying the moisture; S5, collecting the core layer obtained in S4, coating a layer of composite fibers on the core layer in the circumferential direction and curing, collecting the fixed yarn through a collection roller, and connecting the hydrophilic end and the hydrophobic end and the piezoelectric material through the fixed yarn to form the flexible stress sensor; in the application, the ordered arrangement of the graphene material in the fixed yarn improves the output signal of the sensor.

Description

Technical Field

[0001] This invention relates to the technical field of flexible stress sensors, and more particularly to a fabric-based flexible stress sensor and its fabrication method. Background Technology

[0002] With the development of science and technology, humanity has entered the era of big data and information technology. A sensor is a controllable component that can convert non-electrical signals such as electricity, light, temperature, and chemical reactions into electrical signals. The traditional and most commonly used sensors mainly use piezoelectric ceramics as materials. Although this type of sensor has a long history and mature technology, piezoelectric ceramics have disadvantages such as high brittleness, high density, and poor flexibility, which cannot meet the complex and diverse application environments. In particular, fields such as medical health, robotics, biomechanics, and smart wearables have higher requirements for the flexibility, thinness, and biocompatibility of sensor materials. Flexible stress sensors, as data acquisition and transmission devices, are thin, flexible, soft, and skin-friendly, making them an ideal and indispensable interface between the environment, electronic devices, and the human body.

[0003] In existing wearable stress sensors, sweat causes the fabric fibers to swell and deform during use, resulting in a smaller degree of material strain. This also hinders the time for the material to recover to its initial state. When the strain has not fully recovered, a new strain begins, leading to a decrease in the output voltage and output signal when pressure is subsequently applied. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a fabric-based flexible stress sensor and its preparation method. It aims to solve the problem of how to reduce the swelling deformation of fabrics caused by sweat, reduce radial swelling, and accelerate the transmission speed of sweat and the transmission speed of electrons in sweat.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a fabric-based flexible stress sensor, comprising the following steps:

[0006] S1. Base material mixing: The core layer melt, colloid and pore-forming agent are mixed in proportion and extruded through an annular spinneret to form nascent filaments;

[0007] S2, Cooling and Hole Formation: The nascent filaments are cooled using a side-blowing airflow, and the cooled nascent filaments are placed in a solvent to obtain annular core fibers;

[0008] S3, Media Introduction: Graphene and dispersion are thoroughly mixed and a curing agent is added to form a mixed media. The core fiber is then mixed with the mixed media and shaped and cured.

[0009] S4. Shaping and positioning: Take out the sample from S3, add water and adjust the position and orientation of the graphene in the sample by applying an external electric field around the sample. After drying the moisture, a moisture-wicking core layer is obtained.

[0010] S5, Skin Coating: During the process of collecting the core layer obtained in S4, a layer of composite fiber is coated around the core layer and cured. The fixed yarn is collected by the collecting roller and used to connect the hydrophilic textile material, the hydrophobic textile material and the piezoelectric material to form a flexible stress sensor.

[0011] It should be noted that composite fibers have the characteristics of small radial deformation and large axial elasticity.

[0012] In a preferred embodiment of the present invention, the mixing ratio in S1 is 4-6:1-2:1-2, and the pore-forming agent is a soluble salt such as sodium carbonate and sodium chloride, and the core layer melt is a polyester melt and a polyamide melt mixed in a 1-2:1-2 ratio.

[0013] Preferably, the core melt, colloid, and pore-forming agent are mixed in a ratio of 5:1:1, and the ratio of polyester melt to polyamide melt in the core melt is 1:1.

[0014] In a preferred embodiment of the present invention, the side-blowing air is segmented and the wind speed is constant at 0.5-2 m / s. The temperature of the first stage is 190-230℃ and the humidity is 30%-45%. The temperature of the second stage is 90-130℃ and the humidity is 45%-65%. The temperature of the third stage is 15℃-25℃ and the humidity is 55%-75%. The solvent is water.

[0015] Preferably, the constant wind speed of the side-blowing air is 1 m / s, the temperature in the first stage is 200°C and the humidity is 30%; the temperature in the second stage is 100°C and the humidity is 50%; and the temperature in the third stage is 15°C and the humidity is 75%.

[0016] In a preferred embodiment of the present invention, the doping concentration of the graphene is 10%-13%, and the graphene is in powder form, obtained by screening with a 100-200 mesh sieve.

[0017] Preferably, the graphene doping concentration is 12%, and the sample sieve mesh size is 100 mesh.

[0018] It should be noted that the curing agent is an acid anhydride curing agent or a diketone catalyst, and the mass ratio of curing agent to graphene is 8-10:1. Because there are multiple reaction sites between the curing agent and the core layer, it can be cured and shaped by heating after thorough mixing.

[0019] In a preferred embodiment of the present invention, the mixing ratio of the graphene to the dispersion is 1-2:2-4, and the dispersion is sugar.

[0020] Preferably, the mixing ratio of graphene and dispersion is 1:2.

[0021] In a preferred embodiment of the present invention, the strength of the applied electric field is 120-450V / cm of a DC constant voltage power supply.

[0022] Preferably, the applied electric field strength is 300V / cm.

[0023] In a preferred embodiment of the present invention, the device for coating in step S5 is L-shaped, including a long handle and a short handle connected by a coating unit.

[0024] The long handle includes several liquid supply pipes, and the short handle is equipped with a motor one and a motor two, wherein the motor one and the motor two rotate at the same speed but in opposite directions.

[0025] The covering unit includes a rotating covering ring arranged at the front and rear, and a total covering ring. The rotating covering ring includes a front covering ring and a rear covering ring, and the inner diameter of the rear covering ring is larger than the inner diameter of the front covering ring, which is larger than the outer diameter of the core layer. The front covering ring and the rear covering ring are respectively connected to motor one and motor two.

[0026] In a preferred embodiment of the present invention, a liquid outlet hole is provided on the inner wall of both the front covering ring and the rear covering ring, and the liquid outlet hole is connected to the liquid supply pipe. An annular groove is provided on the inner wall of the total covering ring, and the annular groove is connected to the liquid supply pipe.

[0027] This invention also provides a fabric-based flexible stress sensor, comprising a piezoelectric layer and hydrophilic and hydrophobic ends disposed on both sides of the piezoelectric layer.

[0028] The piezoelectric layer includes: piezoelectric yarn and a plurality of conductive yarns spaced apart and staggered on both sides of the piezoelectric yarn. The hydrophilic end and the hydrophobic end are respectively connected to the plurality of conductive yarns, and the hydrophilic end, the hydrophobic end and the piezoelectric layer are fixed together by a fixed yarn in an S-shaped trajectory.

[0029] In a preferred embodiment of the present invention, the hydrophilic end, the hydrophobic end, the piezoelectric yarn, and the conductive yarn are arranged perpendicularly, and the moving direction of the fixed yarn trajectory is consistent with the axial direction of the piezoelectric yarn.

[0030] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0031] (1) The fixed yarn with a core-sheath structure is used in this invention. The core layer is a mixture of polyester and polyamide materials. After spinning and pore making, it forms a sponge structure with a large specific surface area, attachment space and attachment points, while providing a certain degree of high water absorption. The sheath layer is made of composite fiber material with small radial deformation and large circumferential elasticity. Through the coating structure design, two continuously intersecting composite fibers are attached to the outer surface of the core layer in the axial direction, which plays a certain role in the radial constraint of the core layer. A complete sheath layer is wrapped on the two composite fibers to further reduce the swelling deformation of the core layer after moisture absorption, reduce its radial swelling, prevent the fixed yarn from increasing moisture after moisture absorption, and reduce the strain of the material when under pressure. At the same time, the sheath made of composite material has high resilience and radial constraint force, ensuring that it can recover to its original position more quickly after being compressed, and improving the signal output.

[0032] (2) In this invention, soluble salt is used as a pore-forming agent, combined with a water-permeable polyester material. When dissolving and forming pores, water can penetrate into the core structure through the polyester material and carry away the soluble salt, forming a sponge structure with a network structure. Then, through the in-situ sugar template method, sugar particles bring graphene into the sponge structure, so that the graphene material is evenly dispersed in the sponge structure. Then, water is used to dissolve the sugar to leave the graphene material. By adjusting the external electric field, the graphene is made to have order, which improves the water-conducting effect of graphene on the water passing through the fixed yarn and speeds up the water flow.

[0033] (3) In this invention, by increasing the transmission speed of water in sweat, the transmission speed of electrons in sweat is increased, so that the material increases the output of signals before reaching the ultimate strain; at the same time, the two ends of the fixed yarn are connected to the hydrophilic end and the hydrophobic end respectively, forming a supply and demand relationship at the two ends of the fixed yarn, and then increasing the speed of water in the fixed yarn during the transmission process, thereby improving the unidirectional hygroscopicity of water from the hydrophobic end to the hydrophilic end.

[0034] (4) In this invention, segmented cooling is used when cooling the nascent yarn to prevent rapid cooling from causing internal stress in the yarn and breakage during cooling and use; when applying an external electric field, water is added first so that the graphene material is suspended in the sponge structure, which facilitates the movement and adjustment of the graphene material in space when the electric field is applied. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the preparation method of a preferred embodiment of the present invention; Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0039] like Figure 1 The diagram shows a process flow chart for fabricating a flexible stress sensor based on a fabric substrate, including the following steps:

[0040] S1. Base material mixing: Polyester melt and polyamide melt are mixed in a ratio of 1-2:1-2 to form core layer melt, and then mixed with colloid and pore-forming agent in a ratio of 4-6:1-2:1-2. The mixture is then extruded through an annular spinneret to form nascent filaments. The pore-forming agent is a soluble salt such as sodium carbonate and sodium chloride.

[0041] S2. Cooling and pore formation: Use a constant side-blowing airflow of 0.5-2m / s to cool the nascent filaments. At the same time, adjust the temperature of the first stage to 190-230℃ and the humidity to 30%-45%, the temperature of the second stage to 90-130℃ and the humidity to 45%-65%, and the temperature of the third stage to 15℃-25℃ and the humidity to 55%-75%. Place the cooled nascent filaments in water to dissolve and obtain the annular core fiber.

[0042] S3. Medium introduction: Graphene is ground into powder particles and screened through a 100-200 mesh sieve. It is then fully mixed with the dispersion in a ratio of 1-2:2-4 and a curing agent is added to form a mixed medium. The doping concentration of graphene is 10%-13%. The core fiber is then mixed with the mixed medium and shaped and cured.

[0043] S4. Shaping and positioning: Take out the sample from S3, add water and apply an external electric field with a DC constant voltage power supply strength of 120-450V / cm around the sample to adjust the position and orientation of the graphene in the sample. After drying the moisture, a moisture-wicking core layer is obtained.

[0044] S5, Skin Coating: During the process of collecting the core layer obtained in S4, a layer of composite fiber is coated around the core layer and cured. The fixed yarn is collected by the collecting roller and used to connect the hydrophilic textile material, the hydrophobic textile material and the piezoelectric material to form a flexible stress sensor.

[0045] The device used for coating in step S5 is L-shaped, including a long handle and a short handle connected via a coating unit, wherein...

[0046] The long handle includes several liquid supply tubes, and the short handle contains motor one and motor two, with motor one and motor two rotating at the same speed but in opposite directions.

[0047] The covering unit includes a rotating covering ring arranged at the front and rear, and a total covering ring. The rotating covering ring includes a front covering ring and a rear covering ring, and the inner diameter of the rear covering ring is larger than the inner diameter of the front covering ring and larger than the outer diameter of the core layer. The front covering ring and the rear covering ring are respectively connected to motor one and motor two.

[0048] Both the front and rear covering rings have a liquid outlet hole on their inner walls, and the liquid outlet hole is connected to the liquid supply pipe. The inner wall of the main covering ring has an annular groove, and the annular groove is connected to the liquid supply pipe.

[0049] The present invention also provides a fabric-based flexible stress sensor, including a piezoelectric layer and hydrophilic and hydrophobic ends disposed on both sides of the piezoelectric layer. The piezoelectric layer includes piezoelectric yarns and a plurality of conductive yarns disposed at intervals and staggered on both sides of the piezoelectric yarns. The hydrophilic and hydrophobic ends are respectively connected to the plurality of conductive yarns, and the hydrophilic ends, hydrophobic ends and piezoelectric layer are fixed together by fixing yarns in an S-shaped trajectory.

[0050] The hydrophilic end, hydrophobic end, piezoelectric yarn, and conductive yarn are arranged vertically, and the direction of movement of the fixed yarn trajectory is consistent with the axial direction of the piezoelectric yarn.

[0051] Example 1

[0052] S1. Base material mixing: Polyester melt and polyamide melt are mixed in a 1:1 ratio to form core layer melt, and then mixed with colloid and pore-forming agent in a 5:1:1 ratio. The mixture is then extruded through an annular spinneret to form nascent filaments. The pore-forming agent is a soluble salt such as sodium carbonate and sodium chloride.

[0053] S2. Cooling and pore formation: The nascent filament is cooled using a constant side-blowing airflow of 1 m / s. At the same time, the temperature of the first stage is adjusted to 200℃ and the humidity to 30%; the temperature of the second stage is 100℃ and the humidity to 50%; and the temperature of the third stage is 15℃ and the humidity to 75%. The cooled nascent filament is then dissolved in water to obtain the annular core fiber.

[0054] S3. Medium introduction: Graphene is ground into powder particles and screened through a 100-mesh sieve. It is then fully mixed with the dispersion in a 1:2 ratio and a curing agent is added to form a mixed medium. The doping concentration of graphene is 12%. The core fiber is then mixed with the mixed medium and shaped and cured.

[0055] S4. Shaping and positioning: Take out the sample from S3, add water and apply an external electric field with a DC constant voltage of 300V / cm around the sample to adjust the position and orientation of the graphene in the sample. After drying the moisture, a moisture-wicking core layer is obtained.

[0056] S5, Skin Coating: During the process of collecting the core layer obtained in S4, a layer of composite fiber is coated around the core layer and cured. The fixed yarn is collected by the collecting roller and used to connect the hydrophilic textile material, the hydrophobic textile material and the piezoelectric material to form a flexible stress sensor.

[0057] Comparative Example 1

[0058] S1. Base material mixing: Polyester melt and polyamide melt are mixed in a 1:1 ratio to form core layer melt, and then mixed with colloid and pore-forming agent in a 5:1:1 ratio. The mixture is then extruded through an annular spinneret to form nascent filaments. The pore-forming agent is a soluble salt such as sodium carbonate and sodium chloride.

[0059] S2. Cooling and pore formation: The nascent filament is cooled using a constant side-blowing airflow of 1 m / s. At the same time, the temperature of the first stage is adjusted to 200℃ and the humidity to 30%; the temperature of the second stage is 100℃ and the humidity to 50%; and the temperature of the third stage is 15℃ and the humidity to 75%. The cooled nascent filament is then dissolved in water to obtain the annular core fiber.

[0060] S3, Skin Coating: During the process of collecting the core layer obtained in S2 by the collecting roller, a layer of composite fiber is coated around the core layer and solidified to form a fixed yarn. The fixed yarn is used to connect the hydrophilic textile material, the hydrophobic textile material and the piezoelectric material to form a flexible stress sensor.

[0061] Liquid transferability tests were conducted on Example 1 and Comparative Example 1 using tap water, which contains chloride ions, the same components found in sweat. The optical images of the test results show that the time required for a droplet in Example 1 to immerse from the hydrophobic end to the hydrophilic end is 0.27 s, while the time required for Comparative Example 1 is 4.6 s. This indicates that ordered graphene can effectively improve the moisture wicking properties of textiles.

[0062] Continuous pressure rebound tests were then conducted on Example 1 and Comparative Example 1. A pressure of 10N was applied to the flexible stress sensors obtained in both cases. Example 1 required 1.36ms, 1.39ms, and 1.43ms to rebound to its original state, respectively, while Comparative Example 1 required 2.86ms, 2.88ms, and 2.96ms, respectively. It can be seen that the fixing yarn in this invention can improve the resilience of the sensor under pressure and prevent the deformation from not fully recovering before the next strain begins under continuous pressure. The deformation formed by continuous pressure is relatively small, resulting in a smaller output voltage.

[0063] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for fabricating a flexible stress sensor based on a fabric substrate, characterized in that, Includes the following steps: S1. Base material mixing: The core layer melt, colloid, and pore-forming agent are mixed in a ratio of 4-6:1-2:1-2 and extruded through an annular spinneret to form nascent filaments; wherein, the pore-forming agent is sodium carbonate and sodium chloride, and the core layer melt is a mixture of polyester melt and polyamide melt in a ratio of 1-2:1-2; S2. Cooling and Hole Formation: The nascent filament is cooled using segmented side-blowing air with a constant air velocity of 0.5-2 m / s. The temperature of the first stage is 190-230℃ and the humidity is 30%-45%. The temperature of the second stage is 90-130℃ and the humidity is 45%-65%. The temperature of the third stage is 15℃-25℃ and the humidity is 55%-75%. The cooled nascent filament is then placed in water to obtain annular core fiber. S3. Medium introduction: Graphene and dispersion are thoroughly mixed and a curing agent is added to form a mixed medium. The core fiber is mixed with the mixed medium and shaped and cured. The doping concentration of the graphene is 10%-13%. The graphene is a powder obtained by screening with a 100-200 mesh sieve. The mixing ratio of the graphene to the dispersion is 1-2:2-4. The dispersion is sugar. S4. Shaping and positioning: Take out the sample from S3, add water, and adjust the position and orientation of the graphene in the sample by applying a DC constant voltage external electric field with an intensity of 120-450V / cm around the sample. After drying the moisture, a moisture-wicking core layer is obtained. S5, Skin Coating: During the process of collecting the core layer obtained in S4, a layer of composite fiber is coated around the core layer and solidified by an L-shaped coating device. The fixed yarn is collected by a collecting roller and then used to connect the hydrophilic textile material, the hydrophobic textile material, and the piezoelectric material to form a flexible stress sensor. The L-shaped coating device includes a long handle and a short handle connected by a coating unit. The long handle includes several liquid supply pipes, and the short handle contains a motor 1 and a motor 2, which rotate at the same speed but in opposite directions. The coating unit includes a rotating coating ring arranged at the front and rear, and a main coating ring. The rotating coating ring includes a front coating ring and a rear coating ring, and the inner diameter of the rear coating ring is larger than the inner diameter of the front coating ring, which is larger than the outer diameter of the core layer. The front coating ring and the rear coating ring are respectively connected to motor 1 and motor 2. Each of the inner walls of the front coating ring and the rear coating ring has a liquid outlet hole, which is connected to the liquid supply pipe. The inner wall of the main coating ring has an annular groove, which is connected to the liquid supply pipe.

2. A fabric-based flexible stress sensor, based on the fabric-based flexible stress sensor fabrication method according to claim 1, comprising a piezoelectric layer and hydrophilic and hydrophobic ends disposed on both sides of the piezoelectric layer, characterized in that: The piezoelectric layer includes piezoelectric yarn and a plurality of conductive yarns spaced apart and staggered on both sides of the piezoelectric yarn. The hydrophilic end and the hydrophobic end are respectively connected to the plurality of conductive yarns, and the hydrophilic end, the hydrophobic end and the piezoelectric layer are fixed together by the fixed yarn prepared in claim 1 in an S-shaped trajectory.

3. A fabric-based flexible stress sensor according to claim 2, characterized in that: The hydrophilic end, the hydrophobic end, the piezoelectric yarn, and the conductive yarn are arranged perpendicularly to each other, and the moving direction of the fixed yarn trajectory is consistent with the axial direction of the piezoelectric yarn.

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