Silver micron belt and preparation method thereof

Abstract

The invention discloses a silver micron belt and a preparation method thereof, and belongs to the technical field of micro-nano silver materials, and the preparation method comprises the following steps: carrying out silver plating treatment by taking solid columnar micron-sized polymer fibers as a sacrificial template; and removing the sacrificial template to obtain the silver micron tube. And pressing the silver micron tube to obtain the silver micron belt. According to the method, circumferential diffusion and dense filling in the silver deposition process are promoted through the geometrical characteristics of the cylindrical structure, the compactness of the silver micrometer belts in the width direction is improved, the widths of the obtained silver micrometer belts are basically consistent, and the size uniformity is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of micro-nano silver materials, and particularly relates to a silver microstrip and a preparation method thereof. BACKGROUND

[0002] Silver micro-nano strip is a special silver structure with high aspect ratio, smooth surface or nano-level roughness, a thickness of micron or nanometer, a length extending from micron to centimeter, and a width between tens of nanometers and several tens of microns. A silver microstrip is usually taken as a silver microstrip with a width of 1 micron to several tens of microns, and a silver nano strip is taken as a silver nano strip with a width of several tens of nanometers to several hundred nanometers. The silver micro-nano strip has the surface characteristics of one-dimensional silver wire and two-dimensional silver sheet, has a relatively large specific surface area, and has good mechanical flexibility and high electrical conductivity. The silver micro-nano strip and a film layer material taking the silver micro-nano strip as a basic unit have become a key functional unit for constructing flexible electronic devices, transparent conductive films, microelectrodes, and high-performance catalyst carriers.

[0003] At present, researchers have developed various methods for preparing silver nano strip or micro strip structure. For example, silver is plated on a porous alumina template (AAO), or a hydrothermal synthesis method is used to prepare silver nano strips with a surface covered with polymers under the condition of high temperature, high pressure and long reaction time (Wang Long et al. [Chinese patent CN102009185B]); Kim et al. [Nanoscale, 2017, 9, 9622] prepared micro / nano fluidic channels by crack lithography technology, and synthesized silver nano strip arrays in the channels by Tollens reaction in situ; Sun et al. [Nano Lett, 2003, 3(5): 675-679] once reported a method of continuously heating under light irradiation to convert silver nanoparticles, but only a small amount (about 5%) of silver nano strips were obtained; Huang et al. [Langmuir, 2007, 23(10), 5722-5726] successfully prepared silver nano strips by galvanic replacement (Gallvani reduction) of copper assisted by surfactant CTAC.

[0004] In the process of realizing the present application, the inventors found that at least the following problems exist in the prior art: The conventional preparation method of silver micrometer strips usually utilizes a porous alumina template with a regular pore structure to guide the growth of silver, and then removes the template by strong alkali treatment to obtain a silver strip structure. However, such a method has obvious defects. If deposition is performed on the outer surface of the template, the growth of silver is often disordered, and dendrites with loose structure and uneven morphology are easily formed, and additional steps such as ultrasonic treatment are often required to obtain a strip structure, and there are defects such as complicated process and poor uniformity of the product. While directly growing silver strips in the internal pores of the template, complex interfacial dynamics or electrochemical regulation techniques such as constructing an ion shielding layer or using a sacrificial electrode are often required. In addition, the current method is difficult to accurately and stably control the size of the product, especially difficult to control the size of the silver strip at the micrometer level and maintain high uniformity; many processes are complex, or require long-time reaction under harsh conditions of high temperature and high pressure, or rely on expensive precision instruments and equipment (such as photolithography, electron beam evaporation, etc.), resulting in high preparation cost and high energy consumption; impurities remaining in the organic stabilizer and surfactant commonly used in some wet chemical methods easily pollute the final product, affecting the purity of the silver micrometer strip, and then affecting the conductivity, catalytic activity and other key properties of the silver micrometer strip. How to obtain more compact silver micrometer strips at low cost, on a large scale and in an industrialized manner has become a problem to be solved by those skilled in the art. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a silver micrometer strip and a preparation method thereof to solve the above-mentioned problems of the prior art.

[0006] To solve the above-mentioned technical problems, the technical scheme adopted by the present application is as follows:

[0007] On the one hand, a preparation method of a silver micrometer strip is provided, comprising the following steps:

[0008] Performing silver plating treatment on the solid columnar micrometer polymer fiber as a sacrificial template;

[0009] Removing the sacrificial template to obtain a silver micrometer tube;

[0010] Pressing the silver micrometer tube to obtain a silver micrometer strip.

[0011] On the other hand, a silver micrometer strip prepared according to the above-mentioned preparation method of a silver micrometer strip is provided, and the width of the silver micrometer strip is 4-8 μm.

[0012] Compared with the prior art, the present application has the following advantages:

[0013] 1. The present application adopts columnar solid micrometer polymer fiber as a sacrificial template, plating a silver layer with nanometer thickness on the template, decomposing and removing the sacrificial template to obtain silver micrometer tubes, and radially pressing the silver micrometer tubes to collapse them into flat strips to obtain silver micrometer strips, the present application utilizes the geometric characteristics of the cylindrical structure to promote circumferential diffusion and dense filling in the silver deposition process, improves the width direction density of the silver micrometer strips, and the obtained silver micrometer strips have a width of 4-8 microns and high size uniformity.

[0014] 2. The method for preparing the silver micrometer strips of the present application does not require high-cost, high-destructive raw materials and additional post-processing steps, has significant process advantages, and is conducive to large-scale and industrialized promotion.

[0015] The technical solutions of the present application will be further described in detail below in combination with the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The flowchart for preparing the silver micrometer strips of Example 1 is shown in the figure.

[0017] Figure 2 The scanning electron microscope diagram of the silver micrometer strips prepared in Example 1 and Example 2 is shown in the figure.

[0018] Figure 3 The thermogravimetric analysis curve of the polylactic acid short fibers of Comparative Example 1 and the silver-plated polylactic acid short fibers prepared in Example 1 is shown in the figure.

[0019] Figure 4 The XRD test result diagram of the silver-plated polylactic acid fibers and silver micrometer strips prepared in Example 1, and the polylactic acid short fibers of Comparative Example 1 is shown in the figure. DETAILED DESCRIPTION

[0020] The technical solutions will be described clearly and completely below in combination with the examples of the present application. Obviously, the described examples are part of the examples of the present application, rather than all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present application.

[0021] In the following description, the term "and / or" is used to describe the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the cases of A alone, B alone and A and B together. Wherein A and B can be singular or plural.

[0022] In the following description, the terms "include", "contain", "have" and "contain" and the like are all open terms, that is, they mean to include but not limited to.

[0023] Those skilled in the art shall understand that in the following description of the embodiments of the present application, the order of the serial numbers does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process shall be determined according to its function and inherent logic, and shall not constitute any limitation on the implementation process of the embodiments of the present application.

[0024] Those skilled in the art shall understand that the numerical range in the embodiments of the present application shall be understood as also specifically disclosing each intermediate value between the upper limit and the lower limit of the range. Each smaller range between any stated value or intermediate value in the stated range and any other stated value or intermediate value in the stated range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range.

[0025] Unless otherwise specified, the technical / scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present application. All documents mentioned in the specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of any conflict between the contents of the specification and any incorporated document, the contents of the specification shall prevail.

[0026] The present application provides a preparation method of silver micrometer belt, comprising the following steps:

[0027] Solid columnar micrometer polymer fibers are used as sacrificial templates for silver plating treatment;

[0028] The sacrificial templates are removed to obtain silver micrometer tubes;

[0029] The silver micrometer tubes are pressed to obtain silver micrometer belts.

[0030] In some specific embodiments, the micrometer polymer fibers are polymer fibers with a diameter in the micrometer scale (1 micrometer to tens of micrometers), and the solid columnar means that the polymer fibers are solid and the cross section is circular.

[0031] The present application uses solid columnar micrometer polymer fibers as sacrificial templates, which can effectively reduce the complexity of the process and avoid defects such as loose structure and uneven morphology of silver belts caused by traditional aluminum oxide templates.

[0032] The preparation method of micron-level polymer fibers is mature, whether self-made or purchased, the raw material availability is high, the process is mature, and it is easy to promote and produce stably. The diameter, orientation and length of the polymer fiber have mature control methods, which can be flexibly adjusted or selected to match the size requirements of the silver micron strip. The material and source of the micron-level polymer fiber are not limited in the present application, as long as it meets the shape and size requirements involved in the present application. It can be a commonly used sacrificial material that meets the technical requirements of the molding field, such as a sacrificial material with a stable shape that can be removed after product molding, for example, the micron-level polylactic acid fiber described in the following embodiments.

[0033] The present application first silver-plated the solid columnar micron-level polymer fiber to obtain a silver-plated polymer fiber, and then removed the polymer fiber to obtain a micron-level hollow silver micron tube. The hollow silver micron tube is collapsed into a silver micron strip by molding. This preparation method can make the plated silver layer hollow and circular. The removal of the template process is accompanied by the removal of the internal support of the silver tube material. The present application fully utilizes the geometric characteristics of the columnar structure, uniformly disperses the stress of the sacrificial template decomposition process, avoids defects such as cracking, curling, collapsing and breaking caused by stress concentration in the traditional sacrificial template removal process, and can maximize the maintenance of the hollow tubular shape of the silver tube. It provides a material basis for the final molding collapse to form a flat strip shape.

[0034] The present application breaks the inert thinking that the final strip shape of the silver strip must be directly formed in the initial deposition stage, and uses the strategy of first forming a tube and then pressing a strip. An intermediate body (silver micron tube) with an anti-intuitive shape is used to reduce crack defects in the process of removing the sacrificial template, and to improve the density of the product silver micron strip.

[0035] When silver deposition is carried out on the outer surface of the traditional porous sacrificial template, the growth of silver lacks micro-geometric constraints and is a diffusion-limited random aggregation process, which is prone to form loose and uneven dendrites rather than dense strip structures. If it is directly grown in the internal channel, the internal ion mass transfer efficiency is low, and the transport of reactants and the transfer of products are limited, making it difficult to form a long-range continuous and dense coating in the entire channel. In order to obtain a strip cross-section, it must rely on extremely complex electrochemical or interfacial kinetics regulation. The present application uses a cylindrical template, and the convex surface structure of the template enables silver ions in the solution to effectively diffuse and deposit on the surface from all directions. The solid-liquid boundary layer is significantly thinned, and silver atoms performing Brownian motion are more likely to penetrate the solid-liquid boundary layer to the template surface for deposition and diffusion, laying a foundation for a dense silver layer. And because of the curvature constraint of the curved surface structure, silver atoms will preferentially diffuse in the circumferential direction to form a closed ring structure, and then extend in the axial or radial direction, wherein:

[0036] Radial diffusion: Diffusion in the radial direction is perpendicular to the surface of the cylinder (normal direction). To diffuse in the radial direction, atoms need to overcome an energy barrier. Especially in the initial stage of deposition, after atoms are adsorbed onto the surface, to form a new atomic layer on the surface, the atoms need to overcome the nucleation barrier required for secondary nucleation / formation of new layer nuclei, which is due to the high energy required for the new crystal nucleus interface and the difficulty of atoms to leave the stable lattice position. The present application makes full use of the structural characteristics of the high curvature of the surface of the solid columnar micro-scale polymer fiber. The surface energy in the radial direction is high, and the silver atoms need to overcome additional surface energy caused by the curvature in the radial direction.

[0037] Axial diffusion: Diffusion in the axial direction is parallel to the surface of the cylinder. When atoms diffuse in the axial direction, they only need to migrate in the two-dimensional plane of the surface and do not need to leave the surface. The surface of the cylinder is a continuous linear structure in the axial direction. Atoms can move smoothly along the grain boundaries, defects or adsorption sites on the surface. The barrier to be overcome is mainly the activation energy of surface diffusion, which is much lower than the energy required to leave the surface in the radial direction.

[0038] As can be seen, the axial diffusion barrier is much lower than the radial barrier. Silver atoms can migrate a long distance in the axial direction, while radial diffusion is limited to a very small scale. Therefore, silver tends to preferentially diffuse axially to form a complete tube. This long-range diffusion allows axial defects to be quickly filled by surrounding atoms, which can improve the axial density of the coating. Secondly, axial diffusion can homogenize the non-uniformity of deposition, which is more conducive to the formation of a uniform and continuous coating.

[0039] The present application uses a solid columnar polymer fiber as a sacrificial template to make atoms deposit according to the diffusion priority (diffusion priority: circumferential > axial > radial), forming a continuous coating along the surface of the cylinder, while the radial growth (such as thickness increase) is relatively slow, resulting in a circumferentially closed, axially continuous and radially thin silver microtube, while meeting the continuity and thickness requirements of the silver microtube.

[0040] In one possible implementation, the diameter of the solid columnar micro-scale polymer fiber is 1-30 μm, and the length is 3-12 mm. In one possible implementation, the polymer fiber is a polylactic acid fiber. Preferably, the polylactic acid fiber is a polylactic acid staple fiber, and the diameter of the polylactic acid staple fiber is 1-30 μm, and the length is 3-12 mm. Further preferably, the diameter of the polylactic acid staple fiber is 7-10 μm, and the length is 5 mm.

[0041] In one possible implementation, the silver plating treatment method is a silver-ammonia solution silver plating method.

[0042] In one possible implementation, before the silver plating treatment, the solid columnar micro-scale polymer fiber is subjected to surface treatment. The surface-treated solid columnar micro-scale polymer fiber is used as a sacrificial template, and the method comprises the following steps:

[0043] The solid columnar micrometer scale polymer fibers are dispersed in the surface treatment agent, stirred for 6-48 hours, preferably 36 hours, and then subjected to suction filtration, washing and drying to obtain the surface treated solid columnar micrometer scale polymer fibers. In the process of dispersing the solid columnar micrometer scale polymer fibers in the surface treatment agent, the concentration of the solid columnar micrometer scale polymer fibers in the surface treatment agent can be 0.5-5 g / L, preferably 1.5 g / L. The surface treatment agent is prepared by dissolving potassium hydroxide in a solvent, and the solvent is water, anhydrous ethanol or an ethanol aqueous solution.

[0044] Preferably, the volume ratio of anhydrous ethanol to water in the surface treatment agent is 1:(0.5-2), and the molar concentration of potassium hydroxide in the surface treatment agent is 1-100 mmol / L. Preferably, the volume ratio of anhydrous ethanol to water is 1:1, and the molar concentration of potassium hydroxide is 10-100 mmol / L, more preferably 25 mmol / L.

[0045] Preferably, the surface treatment agent of the present application is a mixed system of ethanol and water, rather than pure water. The introduction of non-toxic, inexpensive and easily removable ethanol as a co-treatment medium is to solve the technical problems of poor treatment effect of low concentration alkaline aqueous solution and easy damage to the body of high concentration alkaline aqueous solution caused by the hydrophobicity of solid columnar micrometer scale polymer fibers. Specifically, solid columnar micrometer scale polymer fibers, especially polylactic acid (PLA), are usually hydrophobic, which makes it difficult for low concentration alkaline aqueous solution to effectively wet the fiber surface, thereby limiting the effective attack and hydrolysis of hydroxyl ions on the surface ester bond. In order to achieve sufficient surface treatment in the aqueous solution, it is often necessary to increase the concentration of alkali or prolong the treatment time, but this can easily lead to serious degradation of solid columnar micrometer scale polymer fibers, damage the structural integrity of the fibers, and affect the subsequent operation and the final performance of the product.

[0046] The present application uses low concentration alkaline solution and ethanol co-treatment, which has the following technical effects:

[0047] (1) It can significantly improve the wettability of the surface of hydrophobic solid columnar micrometer scale polymer fibers. This improved wetting effect enables hydroxyl ions to more fully and uniformly contact and act on the fiber surface. More importantly, the auxiliary role of ethanol enables the present application to achieve sufficient and uniform surface treatment under the condition of significantly reducing the concentration of potassium hydroxide (preferably 25 mmol / L in the present application, which is much lower than the possible strong alkali concentration), which lays a foundation for the adsorption of stannous ions and the firm deposition of silver nanoparticles in the subsequent chemical silver plating.

[0048] (2) In addition, it can effectively avoid the serious hydrolysis, swelling or rupture of the body of solid columnar micrometer scale polymer fibers caused by strong alkali treatment, and maintain the structural integrity of the fiber template.

[0049] (3) Low concentration of alkali is easier to be removed by washing, reducing the adverse effects of residual alkali on subsequent electroless silver plating process and purity of final product.

[0050] Further, the silver plating in the silver-ammonia solution specifically comprises: placing the sacrificial template after sensitization treatment in the silver-ammonia solution, adding dropwise a reducing agent solution, stirring for 0.5-5 h, and then filtering, washing and drying to obtain the silver-plated polymer fiber.

[0051] In some specific embodiments, the sensitization agent for sensitization is an acidified stannous chloride aqueous solution, the concentration of stannous chloride in the sensitization agent is 1-20 g / L, preferably 5-15 g / L, and more preferably 10 g / L; the ratio of the mass (g) of the sacrificial template to the volume (L) of the sensitization agent is (0.5-2): 1, preferably 1:1; the sensitization time is 10-60 min, preferably 18 min. Further preferably, the stirring time after adding dropwise the reducing agent solution is 3 h; the reducing agent solution is preferably an aqueous solution of a reducing agent, the reducing agent is selected from at least one of formaldehyde, glucose, ascorbic acid and hydrazine hydrate, and is preferably ascorbic acid. Further preferably, the silver-ammonia solution is an Ag(NH3)2OH solution formed by adding ammonia water to an aqueous silver nitrate solution, the concentration of the aqueous silver nitrate solution is 1-20 g / L, preferably 4 g / L; the ratio of the mass of the reducing agent to the mass of silver nitrate is (1-5): 1, preferably 2:1.

[0052] As described above, the method of low concentration of alkali and ethanol co-surface treatment can effectively improve the hydrophilicity and surface roughness of the surface of the solid columnar micrometer-scale polymer fiber, creating favorable substrate conditions for subsequent electroless silver plating. Thanks to this, the electroless silver plating step of the present application has more significant process advantages. For example, in a preferred embodiment, a lower initial silver nitrate mass concentration (4 g / L) is used, and a uniform, continuous, well-adhered and nanometer-thick silver coating layer is achieved, which may be attributed to the fact that the surface treatment improves the efficiency and deposition uniformity of the silver plating reaction, so that effective nucleation and growth can be achieved at a lower silver salt concentration. Although the silver salt concentration range for electroless silver plating is wide, the present application achieves efficient plating at a lower concentration on the basis of specific surface treatment, reducing the consumption of precious metals, and embodying the synergistic effect and potential cost benefit of the entire process design.

[0053] In one possible implementation, after the silver plating treatment and before the removal of the sacrificial template, a pre-pressing step is further included, specifically as follows:

[0054] The silver-plated polymer fiber is dispersed in a dispersion solvent, followed by vacuum suction filtration to obtain a retentate layer, the retentate layer is dried and pressed to obtain a fiber thin layer; the thickness of the fiber thin layer is 10-100 μm, and the fiber density is 1-3 g / cm 3 , preferably 1.3-2.3 g / cm3 .

[0055] By vacuum filtration, most of the dispersion solvent is removed, and a retentate layer is obtained, which is formed by the accumulation of silver-coated polymer fibers. The present application improves the compactness of the retentate layer through the dispersion-filtration-pressurized pre-pressing, and gives it a compact flat layer shape with uniform fiber accumulation.

[0056] The inventors found in the research process that the silver-coated polymer fibers obtained by the silver-ammonia solution method form irregular agglomerates. The fibers in these agglomerates are chaotic, and the shape and size are not uniform. It is difficult to obtain a regular silver micron strip by direct pressing. The present application disperses the fiber aggregation by including dispersion-filtration-pressurized pre-pressing, so that the fibers are uniformly dispersed in the dispersion solvent first, and then uniformly deposited on the surface of the filter membrane during subsequent filtration as the dispersion solvent is drawn out. The appearance shows a retentate layer with uniform thickness. The present application includes dispersion-filtration-pressurized pre-pressing, which can effectively comb the chaotic silver-coated polymer fibers and improve the disordered agglomeration state of the silver-coated polymer fibers, providing homogeneous raw materials for subsequent pressing.

[0057] In some specific embodiments, the dispersion solvent is one or more of water, anhydrous ethanol, and isopropyl alcohol; the dispersion method includes one or more of ultrasonic treatment, mechanical stirring, and vortex mixing; preferably vortex mixing; the applied pressure is 5-15 MPa, preferably 10 MPa. In some embodiments, the applied pressure in the pressure application is uniaxial pressure perpendicular to the plane of the retentate layer, which can be applied by flat plate mechanical molding.

[0058] This pressure application method can effectively compress the voids between the silver-coated polymer fibers or fiber aggregates in the retentate layer, forcing the silver-coated polymer fibers to closely contact in the plane. Especially when the applied pressure is 5-15 MPa, it can be achieved on the basis of promoting the close combination of silver-coated polymer fibers to avoid the rupture of the silver layer or the breakage of the internal polymer fibers.

[0059] In the present application, the method for removing the sacrificial template of the polymer fiber can be solution method (alkaline hydrolysis, organic solvent dissolution), biological degradation, and thermal decomposition method, preferably thermal decomposition removal. Thermal decomposition treatment can be carried out in a heat treatment equipment (such as a tubular furnace, a box furnace, or a muffle furnace). The temperature of the heat treatment should be set to ensure that it is higher than the complete decomposition temperature of the sacrificial template under the condition, and lower than the melting point of silver. The thermal decomposition treatment should also consider and inhibit the oxidation reaction of silver, such as by vacuum, inert gas or nitrogen atmosphere protection, so that there is no air or oxygen involved in the thermal decomposition process. In one possible implementation, the sacrificial template is removed by thermal decomposition under the protection of air, vacuum environment, inert gas or nitrogen atmosphere, preferably nitrogen atmosphere.

[0060] In some specific embodiments, the thermal decomposition treatment for removing the micrometer-scale polylactic acid fiber comprises: heating from room temperature to a thermal decomposition temperature and keeping; the heating rate is 2-10℃ / min, preferably 5℃ / min; the thermal decomposition temperature is 400-800℃, preferably 400℃; and the keeping time is 1-4h, preferably 2h.

[0061] The thermal decomposition treatment comprises a heating stage and a keeping stage after the temperature is raised to the thermal decomposition temperature. The heating stage not only decomposes the polymer fiber, but also sinters the silver layer to densify it. Especially when the heating rate is 2-10℃ / min, the thermal decomposition temperature is 400-800℃, and the keeping time is 1-4h, the degree of solid-phase sintering of silver particles can be controlled to achieve a moderate sintering state, preventing brittle fracture caused by excessive sintering and preventing insufficient sintering that leads to insufficient strength of the silver tube wall, forming surface defects during the process of being pressed into a belt. The silver micrometer tube after removing the polymer fiber template can not only provide the required mechanical strength of the silver micrometer belt, but also maintain good plasticity as a subsequent pressing precursor.

[0062] Preferably, the present application further comprises, after heating to the thermal decomposition temperature and keeping for a preset time, cooling to room temperature, and the cooling rate of the cooling is 5-10℃ / min. The cooling method can be programmed cooling or natural cooling by keeping the thermal decomposition treatment device sealed and the heating turned off.

[0063] The inventors found during the research that the cooling method after the thermal decomposition temperature is kept for a preset time also affects the morphology of the silver micrometer belt. When the cooling rate is too fast, a large temperature difference between the inner and outer surfaces of the silver micrometer tube is formed, inducing internal stress of the silver micrometer tube and causing microcracks. When the cooling rate is controlled to be 5-10℃ / min, the impact of thermal shock on the structure can be effectively slowed down, a low internal stress dense structure is obtained, and the process cycle is appropriate and the production efficiency is high.

[0064] The preferred embodiment of the present application is not a single breakthrough, but the result of the mutual correlation and synergistic optimization of the four steps of surface treatment (improving the silver plating basis), chemical silver plating (forming a uniform silver shell), thermal decomposition treatment (precise template removal and sintering control to obtain a stable hollow tube), and pressing (realizing belt transformation and avoiding damage).

[0065] In one possible implementation, the pressure for pressing the silver micrometer tube after removing the sacrificial template is 1-5MPa, preferably 3MPa.

[0066] The purpose of pressing the silver micrometer tube after removing the polymer fiber is to cause the silver micrometer tube to collapse and form a belt structure. When the pressure is 1-5MPa, the hollow micrometer tube can be uniformly and fully collapsed.

[0067] Specifically, the pressing of the hollow micrometer tube is performed after the hollow silver micrometer tube is cooled to room temperature after the removal of the sacrificial template. Both the sufficient removal of the sacrificial template and the pressing of the fully sintered silver coating can be achieved, the process and operation are fully simplified, and the repeatability is high.

[0068] Another aspect of the present application provides a silver micrometer tape, which is prepared by the above-mentioned method for preparing a silver micrometer tape, and preferably has a width of 4-8 μm.

[0069] In order to enable the above-mentioned implementation details and operations of the present application to be clearly understood by those skilled in the art, and the progress of the embodiments of the present application to be significantly embodied, the above-mentioned technical solutions are illustrated by the following examples.

[0070] The following examples relate to the source of raw materials:

[0071] Poly lactic acid short fiber: purchased from Advansa GmbH, Germany; model: 1.7-771NBT; linear density: 1.55-1.81 dtex; density: 1.24 g / cm 3 ; in the form of a solid column, with an average diameter of 10 μm and a length of 5 mm, and a length-diameter ratio of 500;

[0072] Potassium hydroxide, absolute ethanol, ammonia, hydrochloric acid, stannous chloride dihydrate, silver nitrate, ascorbic acid, purchased from Chengdu Kolon Chemical Co., Ltd.

[0073] Example 1

[0074] The present application provides a method for preparing a silver micrometer tape, and a flowchart is shown as Figure 1 , which specifically comprises the following steps:

[0075] Step one, surface treatment of poly lactic acid short fiber, specifically comprising:

[0076] Step 101, 14 g of potassium hydroxide is placed in a mixed solution of 5 L of absolute ethanol and 5 L of deionized water, and stirred until completely dissolved to obtain a surface treatment agent;

[0077] Step 102, 15 g of poly lactic acid short fiber is added to the surface treatment agent, and the stirring is continued for 36 h, then the system after stirring is suction filtered, washed, and dried to obtain surface-treated poly lactic acid short fiber;

[0078] Step two, silver plating treatment by silver-ammonia solution plating method, specifically comprising:

[0079] Step 201, 10 g of stannous chloride is placed in 1 L of deionized water, and 10 mL of hydrochloric acid is added to obtain an acidified stannous chloride aqueous solution;

[0080] Step 202, 1 g of the surface-treated polylactic acid short fiber in step one is added into the acidified stannous chloride aqueous solution, and stirring is continued for 18 min. The stirred system is suction filtered and washed to obtain a sensitized polylactic acid short fiber;

[0081] Step 203, 4 g of silver nitrate is placed in 1 L of deionized water, and stirring is performed until it is completely dissolved. Then, ammonia water is added dropwise into the solution until the generated precipitate is completely dissolved to obtain a silver ammonia solution;

[0082] Step 204, 8 g of ascorbic acid is placed in 50 mL of deionized water, and stirring is performed until it is completely dissolved to obtain a reducing agent;

[0083] Step 205, the sensitized polylactic acid short fiber is placed in the silver ammonia solution, and stirring is performed for 3 min. Then, the reducing agent is slowly added dropwise into the solution, and stirring is continued for 3 h. The stirred system is suction filtered and washed, and drying is performed at 50°C to obtain a silver-plated polylactic acid short fiber. The obtained silver-plated polylactic acid short fiber is in the form of a silver-plated polylactic acid short fiber accumulation;

[0084] Step three, pre-pressing, specifically comprising:

[0085] Step 301, 0.03 g of the above silver-plated polylactic acid short fiber is dispersed in 40 mL of anhydrous ethanol by vortex mixing (2500 rpm, 10 min);

[0086] Step 302, the silver-plated polylactic acid short fiber dispersed in the ethanol solution is poured into a sand core funnel with an inner diameter of 4 cm, and a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm is laid in the sand core funnel. A vacuum pump is started, and vacuum suction filtration is performed at a vacuum degree of 0.09 MPa until the filtrate stops dripping to stop the suction filtration to obtain a retentate layer;

[0087] Step 303, the retentate layer is transferred to a 50°C oven for drying to remove residual ethanol solvent to obtain a dried retentate layer. The dried retentate layer is placed in a flat mold, and pressing is performed to 10 MPa and maintained for 5 min to make it compact to obtain a fiber thin layer. The thickness of the fiber thin layer is about 13 μm, and the fiber density is about 2.1 g / cm 3 ;

[0088] Step four, thermal decomposition to remove the sacrificial template, specifically comprising:

[0089] Step 401, the fiber thin layer is placed in a box furnace, and the temperature is raised from room temperature to 400°C at a heating rate of 5°C / min under the protection of a nitrogen atmosphere and maintained for 2 h. The furnace body is kept closed, and natural cooling is performed to obtain a silver micrometer tube thin layer;

[0090] Step five, pressing the silver micrometer tube, specifically comprising:

[0091] Step 501: Place the silver microtube thin layer in the above-mentioned flat mold, apply pressure to 3MPa and hold for 5 minutes to flatten the hollow silver microtube and obtain silver microband.

[0092] Example 2

[0093] Example 2 of this application is the same as Example 1, except that the mass of the silver-plated polylactic acid short fiber in step 301 is 0.05g.

[0094] Comparative Example 1

[0095] Polylactic acid short fiber was used as comparative example 1.

[0096] Performance evaluation:

[0097] Microstructure: The surface morphology of the silver microribbons prepared in Examples 1 and 2 was analyzed using a scanning electron microscope (SEM, Nova Nano SEM 450, FEI, USA) with an accelerating voltage of 5.0 kV. The characterization results are as follows: Figure 2 a and Figure 2 As shown in b, in Examples 1 and 2, the silver microribbons have a width of 4–8 μm, uniform morphology, and complete structure. The electron microscope reveals a functional network of interconnected and stacked silver microribbons. This invention successfully prepared silver microribbons. (Comparison) Figure 2 a and Figure 2 As can be seen from b, adjusting the amount of silver-plated polylactic acid short fiber can control the packing density of silver microbands.

[0098] Thermogravimetric analysis: The mass changes of polylactic acid short fibers from Comparative Example 1 and the silver-plated polylactic acid short fibers prepared in Example 1 were measured in the range of 30–800 °C using a thermogravimetric analyzer (TGA, TG 209F1, NETZSCH, Germany) at a constant heating rate of 10 °C / min under a nitrogen atmosphere (50 mL / min). The experimental results are as follows: Figure 3 As shown, the polylactic acid short fibers of Comparative Example 1 were almost completely decomposed after 400°C. The silver-plated polylactic acid short fibers of Example 1 had a relative mass reduction of about 50% at around 400°C and remained constant during subsequent heating. This indicates that the thermal decomposition of the present invention can effectively remove the sacrificial template and successfully coat the polylactic acid short fibers with silver at a mass ratio of about 1:1.

[0099] Qualitative characterization: The silver-coated polylactic acid fibers prepared in Example 1 and the polylactic acid staple fibers of Comparative Example 1 were analyzed by X-ray diffractometer (XRD, Rigaku Ultima IV, Japan) in 2Theta / Theta continuous scanning mode, with a scanning range of 5-70° and a step size of 0.02°. The test results are shown in FIG. 1. Figure 4 As shown in FIG. 1, it can be seen that the polylactic acid staple fibers of Comparative Example 1 and the silver-coated polylactic acid staple fibers of Example 1 both have a diffraction peak at about 16.86°, which belongs to the (110) crystal plane of polylactic acid. Meanwhile, the silver-coated polylactic acid staple fibers also have diffraction peaks at about 38.13°, 44.31° and 64.46°, which belong to the (111), (200) and (220) crystal planes of silver, proving the successful coating of silver on the polylactic acid staple fibers. In the spectrum of the silver microribbon, the diffraction peaks representing polylactic acid disappear, confirming the successful removal of the polylactic acid fiber template, while the diffraction peaks belonging to silver are enhanced, and the peak shape becomes sharp, indicating that the silver crystal structure is more perfect, and the silver microribbon is successfully prepared.

Claims

1. A method for preparing silver microbands, characterized in that, Includes the following steps: Solid columnar micron-sized polymer fibers were used as sacrificial templates for silver plating. Remove the sacrificial template to obtain silver microtubes; The silver microtubes are pressed to obtain silver microribbons.

2. The method for preparing silver microribbons according to claim 1, characterized in that, The solid columnar micron-sized polymer fibers have a diameter of 1–30 μm and a length of 3–12 mm; and / or, the silver plating treatment is silver ammonia plating; and / or, the removal of the sacrificial template is thermal decomposition treatment to remove the sacrificial template; and / or, the pressing pressure of the silver microtubes is 1–5 MPa.

3. The method for preparing silver microribbons according to claim 1, characterized in that, Prior to the silver plating process, the solid columnar micron-sized polymer fibers are surface-treated to serve as a sacrificial template; and / or, after the silver plating process and before removing the sacrificial template, pre-pressing is performed, the pre-pressing comprising: dispersing the silver-plated polymer fibers in a dispersion solvent, followed by vacuum filtration to obtain a retentate layer, drying the retentate layer, and applying pressure to obtain a fiber thin layer.

4. The method for preparing silver microbands according to claim 3, characterized in that, The surface treatment includes: dispersing solid columnar micron-sized polymer fibers in a surface treatment agent, stirring for 6–48 h, followed by filtration, washing, and drying to obtain surface-treated solid columnar micron-sized polymer fibers; and / or, the thickness of the fiber thin layer is 10–100 μm, and the fiber density is 1–3 g / cm³. 3 ; and / or, the dispersing solvent is one or more of water, anhydrous ethanol and isopropanol; and / or, the pressure applied to the dried retentate layer is 5 to 15 MPa.

5. The method for preparing silver microbands according to claim 4, characterized in that, In the surface treatment, the concentration of solid columnar micron-sized polymer fibers in the surface treatment agent is 0.5–5 g / L; and / or, the surface treatment agent is potassium hydroxide dissolved in a solvent, the solvent being water, anhydrous ethanol, or an aqueous ethanol solution, and the molar concentration of potassium hydroxide in the surface treatment agent is 1–100 mmol / L.

6. The method for preparing silver microbands according to claim 5, characterized in that, In the surface treatment, the concentration of solid columnar micron-sized polymer fibers in the surface treatment agent is 1.5 g / L; and / or, the solvent of the surface treatment agent is an aqueous ethanol solution, wherein the volume ratio of anhydrous ethanol to water in the aqueous ethanol solution is 1:(0.5-2), and the molar concentration of potassium hydroxide in the surface treatment agent is 10-100 mmol / L.

7. The method for preparing silver microribbons according to any one of claims 2 to 6, characterized in that, The silver ammonia solution silver plating includes: first sensitizing the sacrificial template, then placing it in a silver ammonia solution, adding a reducing agent solution dropwise, stirring for 0.5 to 5 hours, filtering, washing, and drying to obtain silver-plated polymer fibers; and / or, the thermal decomposition treatment to remove the sacrificial template includes: heating from room temperature to the thermal decomposition temperature and holding it, wherein the heating rate is 2 to 10 °C / min, the thermal decomposition temperature is 400 to 800 °C, and the holding time is 1 to 4 hours.

8. The method for preparing silver microribbons according to claim 7, characterized in that, The sensitizer used for sensitization is an acidified stannous chloride aqueous solution, wherein the concentration of stannous chloride in the sensitizer is 1 g / L to 20 g / L; and / or, the ratio of the mass (g) of the sacrificial template to the volume (L) of the sensitizer is (0.5 to 2):1; and / or, the sensitization time is 10 to 60 min; and / or, the reducing agent in the reducing agent solution is one or more of formaldehyde, glucose, ascorbic acid, and hydrazine hydrate; and / or, the silver ammonia solution is an Ag(NH3)2OH solution formed by adding ammonia to a silver nitrate aqueous solution, wherein the concentration of the silver nitrate aqueous solution is 1 to 20 g / L; and / or, the mass ratio of the reducing agent to the mass of silver nitrate in the silver ammonia solution is (1 to 5):1; and / or, the heating rate in the thermal decomposition removal of the sacrificial template is 5 °C / min, the thermal decomposition temperature is 400 °C, and the holding time is 2 h.

9. The method for preparing silver microribbons according to claim 7, characterized in that, The thermal decomposition process for removing the sacrificial template further includes: after heating to the thermal decomposition temperature and holding it for a preset time, cooling to room temperature, wherein the cooling rate is 5-10℃ / min.

10. A silver microribbon prepared by the method according to claim 1, characterized in that, The width of the silver microband is 4–8 μm.

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