Flexible heatable film printed by polylactic acid spinning fiber-based metal conductive ink

Abstract

The invention provides a flexible heatable film printed by polylactic acid spinning fiber-based metal conductive ink, a polylactic acid-based film is prepared by an electrostatic spinning process, and based on the characteristics of polylactic acid, the prepared polylactic acid electrostatic spinning film can be completely degraded in a natural environment, and has excellent flexibility and excellent air permeability; the biocompatibility is high; the conductive ink is prepared from low-melting-point liquid metal ink modified by a modifier, and through interaction of phenolic hydroxyl groups in the modifier and liquid metal, dispersity and stability of conductive particles are remarkably improved, so that the flexible film with the heating function shows stable electrothermal conversion performance when powered on, and the conductive ink is suitable for the flexible film with the heating function. Organic combination of degradability, flexibility and electric heating performance is realized, and a green and environment-friendly solution is provided for wearable heating equipment.

Description

Technical Field

[0001] This invention belongs to the field of flexible conductive materials technology, specifically relating to a flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink. Background Technology

[0002] With the increasing trend towards wearable and portable electronic products, flexible conductive materials have received widespread attention. Besides conductivity and elasticity, electrical stability is also a crucial factor for flexible conductive materials. Many practical applications, such as stretchable electronic circuits, flexible batteries, and stretchable light source devices, require conductive materials with high electrical stability to ensure good performance during deformation. However, achieving both high electrical stability and high stretchability simultaneously is quite challenging for highly stretchable elastic conductors. Furthermore, in addition to high electrical stability, the application of porous thin-film elastic conductors in wearable electronics is also urgently needed, requiring these conductive materials to possess good air permeability and vapor permeability. As wearable products evolve, future wearable electronic products will require stretchable conductive materials that support multifunctionality, small package size, and high integration to support superior product performance.

[0003] Wearable heaters have garnered significant attention due to their applications in personal heating systems and healthcare management, such as insulation and thermotherapy in textiles / clothing. Protecting heating performance from degradation under large deformations is crucial for the application of wearable heaters.

[0004] Wearable heating technology has demonstrated significant application value in personal thermal management and medical thermotherapy, such as in smart temperature-controlled clothing and rehabilitation therapy equipment. Traditional heating materials (such as the carbon fiber heating film disclosed in Chinese patent CN 110983595A) are conductive, but they suffer from problems such as non-degradability and poor breathability, and long-term use can easily cause skin discomfort and environmental pollution. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink.

[0006] The technical solution adopted in this invention is as follows: a flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink.

[0007] It comprises a composite film, which includes a polylactic acid (PLA) base film and a conductive layer coated on the surface of the PLA base film.

[0008] The polylactic acid (PLA) base film is a flexible film layer formed by electrospinning of PLA with a molecular weight of 8000-10000 g / mol. The conductive layer is an electrothermal conductor formed on the base film using liquid metal ink with a melting point below room temperature.

[0009] The liquid metal ink comprises liquid metal and a modifier, wherein the modifier has phenolic hydroxyl groups.

[0010] Using polylactic acid (PLA) as the base layer material endows the device with excellent biodegradability and environmental friendliness; the unique porous structure design of PLA achieves good air permeability and biocompatibility; by optimizing the PLA molecular weight (8000-10000 g / mol) and electrospinning process, the feasibility of large-area preparation and the stability of use are ensured.

[0011] Preferably, the modifier is tannic acid. Tannic acid has multiple phenolic hydroxyl groups, which further enhance the interaction between the phenolic hydroxyl groups and the liquid metal, thereby improving the dispersibility and stability of the conductive particles.

[0012] Preferably, the composite film further includes an insulating sealing layer, which covers the conductive layer to form a sealing layer.

[0013] Preferably, the insulating sealing layer is a flexible film layer formed on the conductive layer by electrospinning polylactic acid with a molecular weight of 8000-10000 g / mol.

[0014] Preferably, the liquid metal ink further includes a solvent, which includes at least one of deionized water, tetrahydrofuran, and ethanol.

[0015] Preferably, the mass fraction of the modifier in the conductive ink is 0.05-0.1%; and the concentration of the liquid metal is 0.1-5 g / ml.

[0016] Preferably, the solvent, modifier and liquid metal are mixed and then ultrasonicated, with an ultrasonic power of 20-150W, a time of 45-60min and a temperature of 0-10℃.

[0017] Preferably, the liquid metal ink forms a pattern on the base film by screen printing, and then is applied to the surface of the base film by a mold to form an electrothermal conductor.

[0018] Preferably, the heating conductor is a linear serpentine heating wire.

[0019] Preferably, the liquid metal is selected from one or more of the following: gallium, mercury, gallium-indium alloy, gallium-indium-tin alloy, bismuth-tin alloy, and bismuth-tin-lead-indium alloy.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention provides an environmentally friendly, biodegradable, flexible heating film. It utilizes polylactic acid (PLA), a green and biodegradable material, as the matrix and is constructed by printing liquid metal ink to form a flexible, wearable heating film. The PLA-based film is prepared via electrospinning. Based on the properties of PLA, the prepared PLA electrospun film can completely degrade in the natural environment while exhibiting excellent flexibility, outstanding breathability, and high biocompatibility. The conductive ink is prepared using low-melting-point liquid metal ink modified with a modifier. Through the interaction between the phenolic hydroxyl groups in the modifier and the liquid metal, the dispersibility and stability of the conductive particles are significantly improved, enabling the flexible heating film to exhibit stable electrothermal conversion performance when energized. This achieves an organic combination of degradability, flexibility, and electrothermal performance, providing a green and environmentally friendly solution for wearable heating devices. Attached Figure Description

[0022] 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 of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0023] Figure 1 This is a flowchart illustrating the preparation process of the green wearable conductor composite film provided in Embodiment 1 of the present invention.

[0024] Figure 2 This is a digital image of ink under different concentration ink formulations in Example 1 of the present invention;

[0025] Figure 3 This is a scanning electron microscope (SEM) image of the polylactic acid electrospun fiber basement membrane in Example 1 of the present invention.

[0026] Figure 4 This is a scanning electron microscope (SEM) image of EGaIn-PLA in an inactive state in Embodiment 1 of the present invention;

[0027] Figure 5 This is a scanning electron microscope (SEM) image of EGaIn-PLA in an activated state in Embodiment 1 of the present invention;

[0028] Figure 6 Infrared images of the serpentine heating wire formed by EGaIn-PLA printing in Embodiment 1 of the present invention under different currents (0-0.3A);

[0029] Figure 7 This is a schematic diagram of the highest temperature that EGaIn-PLA can reach under different currents in Embodiment 1 of the present invention;

[0030] Figure 8 This is a schematic diagram of the temperature-time curve of the EGaIn-PLA heating patch under continuous stepped current in Embodiment 1 of the present invention;

[0031] Figure 9 This is a schematic diagram of the temperature-time curves of the EGaIn-PLA heating patch under different currents (0-0.6A) in Embodiment 1 of the present invention.

[0032] Figure 10 This is a schematic diagram of the cyclic temperature-time curves of the EGaIn-PLA heating patch in Embodiment 1 of the present invention under currents of 0.5A, 0.55A, and 0.6A.

[0033] Figure 11 This is a schematic diagram of the temperature-time curves of the EGaIn-PLA heating patch under different currents (0-0.6A) in Embodiment 1 of the present invention.

[0034] Figure 12 This is a schematic diagram showing the resistance change data of the EGaIn-PLA heating-functional flexible film before and after bending in Embodiment 1 of the present invention;

[0035] Figure 13 This is a schematic diagram showing the resistance change data of the heating-functional flexible film during the bending process of EGaIn-PLA in Embodiment 1 of the present invention;

[0036] Figure 14 This is a schematic diagram showing the resistance change data of the EGaIn-PLA heating-functional flexible thin film before and after torsion in Embodiment 1 of the present invention;

[0037] Figure 15 This is a schematic diagram showing the resistance change data of the heating-functional flexible thin film during the torsion process of EGaIn-PLA in Embodiment 1 of the present invention;

[0038] Figure 16 This is a schematic diagram showing the resistance growth rate of EGaIn-PLA under different tensile strains in Embodiment 1 of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Preparation method of the base film: This invention uses biodegradable polylactic acid (PLA) with a molecular weight of 8000-10000 g / mol as the electrospinning raw material. The PLA is dissolved in an organic solvent to prepare an electrospinning solution with a concentration of 6-10 wt%. After stirring for 24 hours, an electrospinning process is used to prepare a PLA base film with controllable thickness on a receiver. This PLA base film has fully biodegradable properties and an ideal porous structure, providing an ideal flexible substrate for the subsequent construction of the conductive layer.

[0041] Conductive layer formation process: On the surface of the prepared PLA substrate film, this invention uses liquid metal ink with a melting point below room temperature to form an electrothermal conductor layer. This liquid metal ink is mainly composed of EGaIn, with added biocompatible solvents and biodegradable small-molecule surfactants to ensure compatibility with the PLA substrate. By precisely controlling the ink formulation and coating parameters, a uniform and stable conductive network can be formed on the PLA substrate film.

[0042] Composite Structure Construction Process: This invention uses a precision coating process to uniformly coat the aforementioned liquid metal conductive ink onto the surface of a PLA base film, ultimately forming an integrated flexible electrothermal composite film. This composite structure maintains the biodegradable properties of the PLA substrate while achieving excellent electrothermal performance. The film's conductivity, tested according to national standards, is 2.71*10⁻⁶. 5 With a maximum temperature of 128℃, the S / m value fully meets the performance requirements of wearable heating flexible films.

[0043] The solvent is selected as ethanol.

[0044] The insulating seal completely covers the conductive layer to provide electrical isolation protection.

[0045] The electrospinable elastomer used in the insulating seal layer can be made of the same material or a different material than that used in the base film.

[0046] In one embodiment of the present invention, polylactic acid is used for electrospinning to form a base film and an insulating sealing layer. During the spinning process, the receiver is an aluminum foil wrapped around and covered on a roller, and the spinning solution is electrospun along the circumference of the roller onto the outer wall of the roller. The liquid supply rate during electrospinning is 0.01 ml / min-0.05 ml / min, the applied voltage is 2-18 KV, and the distance between the electrospinning nozzle and the receiver substrate or the liquid metal wire / spinning base film composite layer is 8-20 cm.

[0047] The liquid metallic ink also includes a solvent. Ethanol is selected as the solvent.

[0048] The conductive ink contains 0.05-0.1% by mass of modifier; the concentration of liquid metal is 0.1-5 g / ml, preferably 2-4 g / ml, and most preferably 3 g / ml.

[0049] The solvent, modifier, and liquid metal are mixed and then ultrasonicated. The ultrasonic power is 20-150W, the time is 45-60min, and the temperature is 0-10℃.

[0050] The liquid metal ink forms a serpentine heating wire pattern on the substrate film through a coating method, and the serpentine heating wire is then formed by scraping the coating onto the substrate film surface using a mold. The coating method can be one or more combinations of scraping, brushing, screen printing, and inkjet printing. It should be understood that the coating method is not limited to the various methods described above; any coating method that does not differ substantially in that it can coat the substrate film surface with a coating material to form an alloy layer is considered a technical solution protected by this invention.

[0051] In a preferred embodiment of the present invention, the conductive layer is formed using screen printing technology, specifically including the following steps: first, a screen printing plate with a predetermined pattern is prepared by photochemical etching or manual engraving; then, a squeegee is used to precisely transfer liquid metal functional ink through the opening area of ​​the screen to the surface of a pre-prepared electrospun base film; this process can directly form a functional conductive layer with a specific pattern on the substrate. The mesh size and aperture ratio of the screen printing plate can be optimized according to the thickness and resolution requirements of the conductive layer to ensure that the liquid metal ink can be uniformly and completely transferred to the base film surface.

[0052] In a preferred embodiment of the present invention, the conductive layer is prepared using the following special process: First, EGaIn liquid metal ink is transferred to the surface of the base film by screen printing to form a pre-deposited layer. This pre-deposited layer exhibits non-conductive properties in its initial state (see Appendix). Figure 4 The microstructure shown is due to the liquid metal droplets being coated with surfactant molecules to form an insulating barrier. To establish a continuous conductive path, the pre-deposited layer needs to undergo a conductive post-treatment, specifically a mechanical activation method: a rigid auxiliary tool is used to gently mechanically wipe the printed area, causing the coated liquid metal droplets to break up and fuse together to form a conductive network (its activated microstructure is shown in the attached figure). Figure 5 (As shown). The key to this activation process is controlling the appropriate mechanical force to ensure the formation of a continuous conductive path while avoiding damage to the underlying substrate structure.

[0053] The liquid metal is selected from gallium, mercury, gallium-indium alloy, gallium-indium-tin alloy, bismuth-tin alloy, and bismuth-tin-lead-indium alloy; the liquid metal is a gallium-indium eutectic alloy.

[0054] Example 1

[0055] like Figure 1As shown, the electrothermal composite film used as a heater is prepared through the following steps:

[0056] Step S1: Dissolve polylactic acid in water to form a polymer solution. The mass percentage concentration of polylactic acid in the resulting polymer solution is 6wt%-10wt%. For the preparation of the electrospun base film, aluminum foil is placed on a roller to collect the electrospun fibers. The thickness of the base film is controlled by adjusting the collection time and the mass of the electrospun polymer solution. The electrospinning process is stopped once the preset thickness is reached. See the microscopic diagram below. Figure 2 It exhibits excellent breathability. The base film is removed from the aluminum foil. The tensile stress-strain curve of the base film is shown below. Figure 3 ;

[0057] Step S2: Mix the tannic acid aqueous solution and the liquid metal and sonicate to obtain conductive ink. The liquid metal is a gallium-indium eutectic alloy (EGaIn), wherein the mass ratio of gallium and indium is 75:25.

[0058] Step S3: Apply conductive ink to the surface of the substrate film by screen printing to form a conductive ink such as... Figure 6 The serpentine heating wire shown is then coated with conductive ink by tweezers, and a liquid metal conductive substrate film (EGaIn-PLA) is formed by combining the substrate film and the conductive layer.

[0059] Step S4: The electrospun polymer solution obtained in step S1 is used to prepare an insulating sealing layer by electrospinning, resulting in an electrothermal composite film. The conductivity of this film, tested according to national standards, is 2.71*10⁻⁶. 5 S / m.

[0060] Figure 12 and Figure 14 The resistance curves of EGaIn-PLA as a function of bending and torsional strain are shown respectively. Figure 2 The good electrical stability exhibited by the elastic conductor composite film provided in this embodiment during stretching is attributed to the deformation of the mesh pores and the extension of the secondary gaps in the electrospun fibers. Figure 12 and Figure 14 The curves showing the change of resistance of EGaIn-PLA with the number of stretching cycles under different bending and torsional strains are presented respectively. The composite film can withstand up to 500 bending and torsional cycles without significant change in resistance.

[0061] Performance testing

[0062] The performance of the elastic conductor composite film in Example 1 was tested;

[0063] First, the sample is fixed on the test platform, and an excitation current of 0-0.3A is applied. Temperature data is acquired in real time using an infrared thermal imager. During the test, each current application lasts for at least 60 seconds to ensure the temperature reaches a stable state. Monitoring is terminated after the sample cools to room temperature. Figure 11 The temperature response curve shown and Figure 6 Infrared thermal images show that the film reached thermal equilibrium within 30 seconds in all five repeated tests.

[0064] To further evaluate the heating characteristics, a dynamic loading mode was used for testing: the current was gradually increased by 0.05A at 60-second intervals, and the current was immediately switched to the next level after the temperature stabilized, until all tests were completed and the sample was allowed to cool. Figure 8 The temperature-current relationship curve shown indicates that the composite membrane can reach a maximum temperature of 128°C under a current drive of 0.3A, confirming its precise temperature control capability.

[0065] For durability testing, cyclic current loads of 0.5A, 0.55A, and 0.6A were applied to the samples, with each cycle including heating to steady state and natural cooling. Figure 10 The data from the four cycles shown demonstrate that the composite membrane maintains excellent thermal stability during repeated heating and cooling processes, verifying its reliable recyclability.

[0066] By adjusting the tannin concentration (TA) at different concentrations, the optimal modification ratio was found to ensure the dispersion performance of the liquid metal. The results showed that at a concentration of 5% wt, an ultrasonic time of 45-60 minutes resulted in uniform dispersion with no sedimentation tendency, achieving the best effect while requiring less TA and reducing costs.

[0067] Table 1. Dispersion effect of liquid metal under different concentrations of tannic acid and ultrasonic time.

[0068]

[0069] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A flexible, heatable thin film printed with polylactic acid spun fiber-based metal conductive ink, characterized in that: It comprises a composite film, which includes a polylactic acid (PLA) base film and a conductive layer coated on the surface of the PLA base film. The polylactic acid (PLA) base film is a flexible film layer formed by electrospinning of PLA with a molecular weight of 8000-10000 g / mol. The conductive layer is an electrothermal conductor formed on the base film using liquid metal ink with a melting point below room temperature. The liquid metal ink comprises liquid metal and a modifier, wherein the modifier has phenolic hydroxyl groups.

2. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 1, characterized in that: The modifier is tannic acid.

3. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 1, characterized in that: The composite film also includes an insulating sealing layer, which covers the conductive layer to form a sealing layer.

4. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 3, characterized in that: The insulating sealing layer is a flexible film layer formed on the conductive layer by electrospinning polylactic acid with a molecular weight of 8000-10000 g / mol.

5. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 1, characterized in that: The liquid metal ink also includes a solvent, which includes at least one of deionized water, tetrahydrofuran, and ethanol.

6. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 5, characterized in that: The conductive ink contains 0.05–0.1% by mass of modifier and 0.1–5 g / ml of liquid metal.

7. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 6, characterized in that: The solvent, modifier, and liquid metal are mixed and then ultrasonicated. The ultrasonic power is 20-150W, the time is 45-60min, and the temperature is 0-10℃.

8. The flexible heatable film printed with polylactic acid spun fiber-based metal conductive ink according to claim 5, characterized in that: The liquid metal ink forms a pattern on the base film through screen printing, and then is applied to the surface of the base film using a mold to form an electrothermal conductor.

9. A flexible, heatable film printed with polylactic acid spun fiber-based metal conductive ink according to any one of claims 1-8, characterized in that: The heating conductor is a linear, serpentine heating wire.

10. A flexible, heatable film printed with polylactic acid spun fiber-based metal conductive ink according to any one of claims 1-8, characterized in that: The liquid metal is selected from one or more of the following: gallium, mercury, gallium-indium alloy, gallium-indium-tin alloy, bismuth-tin alloy, and bismuth-tin-lead-indium alloy.

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