Preparation method of ultra-high molecular weight polyethylene conductive composite film and conductive composite film

Abstract

The invention discloses a preparation method of an ultra-high molecular weight polyethylene conductive composite film. The preparation method comprises the following steps: S1, mixing and dissolving ultra-high molecular weight polyethylene with the molecular weight of 5-7 million g / mol, a solvent and an antioxidant to obtain a mixed solution; s2, feeding the mixed solution into a double-screw extruder to obtain a molten mass, and cooling the molten mass into a gel sheet through a cooling roller; s3, performing preliminary two-way stretching on the gel sheet, and performing extraction, drying and annealing in sequence to obtain an embryonic membrane; s4, the dried blank film is subjected to two-way stretching again, and a base film is obtained; s5, coating at least one surface of the base film with silver nanowire coating liquid, and heating to form a film to obtain a conductive composite film with a flexible conductive layer; the mass ratio of the ultra-high molecular weight polyethylene to the solvent is (5-10): (90-95). The thermal stability of the base film and the size retentivity of pores are optimized through the process, so that the connection firmness with the conductive layer is improved, and the conductivity is optimized. The invention also discloses a conductive composite film.

Description

Technical Field

[0001] This invention relates to the field of polymer nanocomposite materials technology, specifically to a method for preparing an ultra-high molecular weight polyethylene conductive composite film and the conductive composite film itself. Background Technology

[0002] Flexible transparent electrodes, gas-permeable electrodes, and water-permeable electrodes are essential materials in various fields. Flexible transparent electrodes are used in OLEDs, solar cells, and flexible sensing devices, while gas-permeable or water-permeable electrodes are used as reactors in photocatalysis or electrocatalysis. For transparent electrode materials, the most commonly used are indium tin oxide (ITO), carbon nanotubes, graphene, and metal meshes. ITO achieves high transparency and high conductivity, but its high brittleness makes it unsuitable for flexible electronic devices. While carbon materials possess high mechanical strength and conductivity, their reliance on conjugated electron conduction makes it difficult to simultaneously achieve conductivity and transparency. Metal meshes can achieve good conductivity, light transmittance, and stable mechanical properties through pore structure manipulation; however, the fabrication process for these pore structures is complex. Summary of the Invention

[0003] One of the objectives of this invention is to overcome the deficiencies in the prior art and provide a method for preparing an ultra-high molecular weight polyethylene conductive composite film. By bidirectional stretching before and after extraction of the gel film, the thickness of the base film is reduced to improve its conductivity. Combined with the annealing process, the thermal stability and pore size retention of the thinned base film are optimized, ensuring its mechanical strength and air permeability. This is beneficial to improving the thermal bonding strength between the conductive layer and the base film, thereby optimizing the conductivity and conductivity stability of the composite film.

[0004] To achieve the above-mentioned process effects, the technical solution of the present invention is: a method for preparing an ultra-high molecular weight polyethylene conductive composite film, comprising the following steps: S1: Mix and dissolve ultra-high molecular weight polyethylene with a molecular weight of 500-700 million g / mol, solvent and antioxidant to obtain a mixture; S2: The mixture is fed into a twin-screw extruder to obtain a melt, which is then cooled by a cooling roller to form a gel sheet; S3: After the gel sheet is initially biaxially stretched, it is sequentially extracted, dried and annealed to obtain a embryo membrane; S4: The dried embryo membrane is stretched biaxially again to obtain the base membrane; S5: At least one surface of the base film is coated with a nano-silver wire coating liquid and heated to form a film, thereby obtaining a conductive composite film with a flexible conductive layer. The mass ratio of ultra-high molecular weight polyethylene to solvent is (5~10):(90~95).

[0005] A preferred technical solution is that the nanosilver wire coating solution includes modified nanosilver wire, diacetone alcohol and deionized water, wherein the nanosilver wire is dissolved in deionized water to form a nanosilver dispersion of 5~10g / L, and the amount of diacetone alcohol added is 0.06%~0.09% of the nanosilver dispersion.

[0006] A preferred technical solution is as follows: The modified silver nanowires are prepared by preheating 10 ml of ethylene glycol to 160-170°C, and adding 2.5 ml of a 0.008 g / 10 ml solution of copper chloride ethylene glycol seed inducer to obtain an induction solution; mixing a 0.1 g / 10 ml solution of AgNO3 ethylene glycol and a 0.3 g / 10 mL solution of polyvinylpyrrolidone ethylene glycol stabilizer, and slowly adding 10 ml of the mixture to the induction solution to obtain a silver nanowire suspension; reacting for 20-30 min; centrifuging the suspension; and washing and purifying it sequentially with acetone, distilled water, and anhydrous ethanol to obtain a silver nanowire preform; immersing the silver nanowire preform in a 0.3-0.5 mol / L glutaric acid ethanol solution as a surface treatment agent for 15-20 min; and removing the surface treatment agent to obtain the modified silver nanowires.

[0007] The preferred technical solution is that, in S3, the initial bidirectional stretching is an asynchronous bidirectional stretching that first proceeds longitudinally and then laterally, with the longitudinal stretching ratio being n, where 4 ≤ n ≤ 6, and the lateral stretching ratio being m, where 4 ≤ m ≤ 8, and 1 ≤ m / n ≤ 1.35.

[0008] The preferred technical solution is that, in step S4, the second bidirectional stretching includes a first bidirectional stretching and a second bidirectional stretching. Both the first bidirectional stretching and the second bidirectional stretching are asynchronous bidirectional stretching, first longitudinal and then transverse. The longitudinal stretching ratio of the first bidirectional stretching is a, 2≤a≤3, and the transverse stretching ratio is b, 1≤b≤2, and b≤a. The longitudinal stretching ratio of the second bidirectional stretching is x, 1≤x≤2, and the transverse stretching ratio is y, 1≤y≤2, and y≤x.

[0009] The preferred technical solution is that the stretching temperature of the initial biaxial stretching is 115-120℃; the stretching temperature of the first biaxial stretching step in the second biaxial stretching step is 130-135℃, and the stretching temperature of the second biaxial stretching step is 135-140℃.

[0010] The preferred technical solution is that, in step S3, the drying temperature is 65~75℃ and the annealing temperature is 105~110℃.

[0011] A preferred technical solution is that, in step S5, the heating temperature of the base film is 140~150℃.

[0012] The preferred technical solution is that the antioxidant is antioxidant 1010, and the amount added is 0.5% to 1% of the total mass of ultra-high molecular weight polyethylene and solvent; the solvent is white oil; and the diluent is n-hexane.

[0013] The second objective of this invention is to overcome the deficiencies in the prior art and provide a conductive composite film prepared by the above-mentioned method for preparing ultra-high molecular weight polyethylene conductive composite film.

[0014] The advantages and beneficial effects of this invention are as follows: The conductive composite film is obtained by preliminary biaxial stretching before gel extraction and secondary biaxial stretching after gel extraction, resulting in a base film with a thickness of less than 1 μm, which is beneficial to improving its conductivity. Combined with the annealing process after preliminary biaxial stretching, the thermal stability and pore size retention of the base film are optimized, ensuring its mechanical strength and air permeability, while laying the foundation for the strong thermal connection between the conductive layer and the base film. Detailed Implementation

[0015] The specific embodiments of the present invention will be further described below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0016] Flexible ultra-high molecular weight polyethylene conductive composite film The conductive composite film includes a base film and a conductive layer disposed on at least one surface of the base film. The base film is an ultra-high molecular weight polyethylene layer, the conductive layer is a silver nanowire layer, and the thickness of the base film is 0.5~1μm.

[0017] To ensure the strength and processability of the base film, the molecular weight of ultra-high molecular weight polyethylene is 5 million to 7 million g / mol.

[0018] To ensure high tensile stress in the base membrane, achieve high-ratio uniform stretching, and obtain a controllable self-supporting porous base membrane, the mass ratio of ultra-high molecular weight polyethylene (UHMWPE) to solvent is (5~10):(90~95). Further, the mass ratio of UHMWPE to solvent is (6~9):(92~95).

[0019] To obtain a high-porosity base membrane, in step S3, the initial biaxial stretching is an asynchronous biaxial stretching process, first longitudinally and then laterally. The longitudinal stretching ratio is n, where 4 ≤ n ≤ 6, and the transverse stretching ratio is m, where 4 ≤ m ≤ 8, and 1 ≤ m / n ≤ 1.35. A higher transverse stretching ratio helps improve the lateral connectivity of the pores. Further, combinations of the longitudinal stretching ratio n and the transverse stretching ratio m are 4*4, 4*5, 5*5, 5*6, 6*6, 6*7, and 6*8. Even further, combinations of the longitudinal stretching ratio n and the transverse stretching ratio m are 4*5, 5*6, and 6*7.

[0020] To obtain a base film with a thickness of 0.5~1μm, ensuring both mechanical strength and porosity above 70%, in step S4, the biaxial stretching process includes a first-step biaxial stretching and a second-step biaxial stretching. Both the first and second steps are asynchronous biaxial stretching, first longitudinally and then laterally. The longitudinal stretching ratio of the first step is 'a', where 2 ≤ a ≤ 3, and the transverse stretching ratio is 'b', where 1 ≤ b ≤ 2, and b ≤ a. The longitudinal stretching ratio of the second step is 'x', where 1 ≤ x ≤ 2, and the transverse stretching ratio is 'y', where 1 ≤ y ≤ 2, and y ≤ x. Furthermore, the combinations of the longitudinal stretching ratio 'a' and the transverse stretching ratio 'b' in the first step are 2*1, 2*2, 3*1, and 3*2; the combinations of the longitudinal stretching ratio 'x' and the transverse stretching ratio 'y' in the second step are 1*1, 2*1, and 2*2.

[0021] Flexible conductive layer A flexible conductive layer is obtained by slit-coating a silver nanowire coating solution onto a heated base film surface, followed by solvent evaporation.

[0022] The nano-silver wire coating solution comprises modified nano-silver wires, diacetone alcohol, and deionized water. The nano-silver wires are dissolved in deionized water to form a nano-silver dispersion of 5-10 g / L. The amount of diacetone alcohol added is 0.06%-0.09% of the nano-silver dispersion. Diacetone alcohol acts as a leveling agent to increase the surface tension of the nano-silver wire coating solution, improve the compatibility of the modified nano-silver wires in deionized water, enhance film uniformity, and reduce the sheet resistance of the composite film.

[0023] Preparation of modified silver nanowires: Preheat 10 ml of ethylene glycol to 160-170 °C, and add 2.5 ml of 0.008 g / 10 ml copper chloride ethylene glycol solution as a seed inducer to dissolve and obtain an induction solution; mix 0.1 g / 10 mL AgNO3 ethylene glycol solution and 0.3 g / 10 mL polyvinylpyrrolidone (M = 1300000) ethylene glycol solution as a stabilizer, and slowly add 10 ml of the mixture to the induction solution to obtain a silver nanowire suspension. React for 20-30 min, then centrifuge the suspension and wash and purify it sequentially with acetone, distilled water, and anhydrous ethanol to obtain silver nanowire preforms; immerse the silver nanowire preforms in 0.3-0.5 mol / L glutaric acid ethanol solution as a surface treatment agent for 15-20 min, and remove the surface treatment agent to obtain modified silver nanowires.

[0024] The diameter of the silver nanowire preform is 30~35nm and the length is 50~55μm.

[0025] Glutaric acid, a surface treatment agent, is adsorbed onto the surface of silver nanowires, not only protecting the surface but also improving conductivity. This promotes the interconnection and bonding of the silver nanowires, forming a conductive network. It also improves the dispersibility of the modified silver nanowires and enhances the hydrophilicity of the conductive layer surface, facilitating contact between the electrode reaction solution and the conductive layer of the catalytically active silver nanowires. Heating the base film at 140-150℃ optimizes the solvent evaporation rate, improves the uniformity and smoothness of the conductive layer, enhances conductivity, and prevents the desorption of glutaric acid from the silver nanowire surface. Furthermore, it induces slight softening of the surface molecular chains of the base film, improving the thermal bonding strength between the conductive layer and the base film.

[0026] Example 1

[0027] A method for preparing an ultra-high molecular weight polyethylene conductive composite film includes the following steps: S1: Mix and dissolve 6 million g / mol ultra-high molecular weight polyethylene, white oil and antioxidant 1010 to obtain a mixture, wherein the mass ratio of ultra-high molecular weight polyethylene to solvent is 8:92, and the amount of antioxidant added is 0.6% of the total mass of ultra-high molecular weight polyethylene and solvent.

[0028] S2: The mixture is fed into a twin-screw extruder to obtain a melt at a melting temperature of 250°C. It is then cooled by a cooling roller to form a gel sheet at a temperature of 25°C. S3: The gel sheet is initially biaxially stretched. The initial biaxial stretching is an asynchronous biaxial stretching, first longitudinal and then transverse. The stretching temperature is 118℃, the longitudinal stretching ratio is 5, and the transverse stretching ratio is 6. After the initial biaxial stretching, it is successively extracted, dried and annealed to obtain the embryo film. The extractant is n-hexane, the drying temperature is 70℃, and the annealing temperature is 108℃.

[0029] S4: The dried embryo film is subjected to biaxial stretching again, which includes a first biaxial stretching and a second biaxial stretching. The stretching temperature of the first biaxial stretching is 135℃, and the stretching temperature of the second biaxial stretching is 140℃. Both the first and second biaxial stretching are asynchronous biaxial stretching, first longitudinal and then transverse. The longitudinal stretching ratio of the first biaxial stretching is 2, and the transverse stretching ratio is 2; the longitudinal stretching ratio of the second biaxial stretching is 2, and the transverse stretching ratio is 1, to obtain the base film. S5: Coating a nano-silver wire coating liquid onto one surface of the base film at a coating speed of 40 m / min, heating to form a film at a temperature of 145℃, and obtaining a conductive composite film with a flexible conductive layer. The nano-silver wire coating solution includes modified nano-silver wire, diacetone alcohol and deionized water. The nano-silver wire is dissolved in deionized water to form an 8 g / L nano-silver dispersion. The amount of diacetone alcohol added is 0.075% of the nano-silver dispersion.

[0030] Preparation of modified silver nanowires: 10 ml of ethylene glycol was preheated to 165 °C, and 2.5 ml of a 0.008 g / 10 ml solution of copper chloride ethylene glycol seed inducing agent was added to dissolve and obtain an induction solution; 0.1 g / 10 mL of AgNO3 ethylene glycol solution and 0.3 g / 10 mL of polyvinylpyrrolidone (M = 1300 K) ethylene glycol solution were mixed, and 10 ml of the mixture was slowly added to the induction solution to obtain a silver nanowire suspension. The suspension was reacted for 30 min, and then the suspension was centrifuged and purified by washing with acetone, distilled water and anhydrous ethanol in sequence to obtain silver nanowire preforms; the silver nanowire preforms were dissolved in a 0.42 mol / L glutaric acid ethanol solution as a surface treatment agent and immersed for 17 min. After removing the surface treatment agent, modified silver nanowires were obtained.

[0031] A conductive composite film is prepared by the above-described method for preparing ultra-high molecular weight polyethylene conductive composite film.

[0032] Example 2

[0033] Example 2 is based on Example 1, except that the silver nanowires in the silver nanowire coating solution were not surface-treated with glutaric acid ethanol solution, while the other components and processes remained unchanged.

[0034] Example 3

[0035] Example 3 is based on Example 1, except that the biaxial stretching in S4 is a one-step biaxial stretching, the stretching temperature of the one-step biaxial stretching is 135°C, the one-step biaxial stretching is an asynchronous biaxial stretching first longitudinally and then transversely, and the longitudinal stretching ratio of the one-step biaxial stretching is 2, and the transverse stretching ratio is 2. Other processes remain unchanged.

[0036] Example 4

[0037] Example 4 is based on Example 1, except that in S5, the heating temperature of the base film is 140°C. Other processes remain unchanged.

[0038] Example 5

[0039] Example 5 is based on Example 1, except that in S5, the heating temperature of the base film is 130°C. Other processes remain unchanged.

[0040] Example 6

[0041] Example 6 is based on Example 1, except that in S5, the heating temperature of the base film is 160°C. Other processes remain unchanged.

[0042] Comparative Example 1 Comparative Example 1 is based on Example 1, except that in S5, the base film is not heated, and a nano-silver wire coating solution is applied to one surface of the film and dried at room temperature to obtain a conductive composite film with a flexible conductive layer. Other processes remain unchanged.

[0043] Comparative Example 2 Comparative Example 2 is based on Example 1, except that in S3, the gel sheet was initially biaxially stretched and then sequentially extracted and dried to obtain a preform film, without annealing. Other processes remained unchanged.

[0044] Performance testing of conductive composite film samples in the examples and comparative examples: 1. Tensile strength: Cut 1cm×4cm specimens and test them using a universal testing machine at a temperature of 25℃ and a tensile rate of 5mm / min. 2. Water contact angle: The water contact angle of the conductive layer surface was measured at room temperature using an optical contact angle meter (DSA25). 3. Resistance: The surface resistance is measured using a four-probe tester; 4. Air permeability: Measured using an air permeability meter (NO.4110N, USA) according to ASTM D726 standard and expressed as Gurley value; Gurley value is defined as the time required for 100 ml of air to pass through a specific area (1 square inch) of the composite membrane under a pressure of 1.12 kPa; the smaller the Gurley value, the better the air permeability; 5. Bending resistance: Inner bending: 1 mm radius, bending towards the silver nanowire conductive layer 100,000 times; Outer bending: 3 mm radius, bending towards the base film 100,000 times.

[0045] The performance test results of the examples and comparative examples are as follows:

[0046] Compared to Example 1, Example 3 only involves one step of biaxial stretching, resulting in decreased mechanical strength and a base film thickness of over 1 μm, which negatively impacts the resistivity of the composite film.

[0047] Compared to Example 1, Example 5 shows that the heating temperature of the base film is too low, which has a negative impact on the film-forming properties of the conductive layer, thereby affecting the uniformity and flatness of the conductive layer, and negatively impacting both tensile strength and conductivity. Furthermore, the bonding strength between the conductive layer and the base film decreases, and delamination occurs during the bending test.

[0048] Compared to Example 1, Example 6 shows that the heating temperature of the base film is too high, which has a negative impact on the tensile strength of the base film, a greater degree of surface softening, an increased interfacial embedding depth between the conductive layer and the base film, and the appearance of local closed pores at the interface, which has a negative impact on air permeability; in addition, the desorption of glutaric acid on the surface of the silver nanowires has a negative impact on conductivity.

[0049] Compared to Example 1, in Comparative Example 1, without heating the base film, the base film and the conductive layer did not form an intercalation interface. Although the composite film had good air permeability, it had a negative impact on the conductivity of the conductive layer and the bending resistance of the composite film. In the bending test, delamination also occurred.

[0050] Compared to Example 1, Comparative Example 2 did not involve annealing the base film, which negatively impacted its thermal stability, resulting in a decrease in the tensile strength of the composite film; it also negatively impacted the retention of pore size, resulting in a decrease in the air permeability of the composite film.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an ultra-high molecular weight polyethylene conductive composite film, characterized in that, Includes the following steps: S1: Mix and dissolve ultra-high molecular weight polyethylene with a molecular weight of 500-700 million g / mol, solvent and antioxidant to obtain a mixture; S2: The mixture is fed into a twin-screw extruder to obtain a melt, which is then cooled by a cooling roller to form a gel sheet; S3: After the gel sheet is initially biaxially stretched, it is sequentially extracted, dried and annealed to obtain a embryo membrane; S4: The dried embryo membrane is stretched biaxially again to obtain the base membrane; S5: At least one surface of the base film is coated with a nano-silver wire coating liquid and heated to form a film, thereby obtaining a conductive composite film with a flexible conductive layer. The mass ratio of ultra-high molecular weight polyethylene to solvent is (5~10):(90~95).

2. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 1, characterized in that, The nanosilver wire coating solution includes modified nanosilver wire, diacetone alcohol and deionized water. The nanosilver wire is dissolved in deionized water to form a nanosilver dispersion of 5~10 g / L. The amount of diacetone alcohol added is 0.06%~0.09% of the nanosilver dispersion.

3. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 2, characterized in that, Preparation of the modified silver nanowires: Preheat 10 ml of ethylene glycol to 160-170°C, and add 2.5 ml of 0.008 g / 10 ml copper chloride ethylene glycol solution as a seed inducer to dissolve and obtain an induction solution; mix 0.1 g / 10 mL AgNO3 ethylene glycol solution and 0.3 g / 10 mL polyvinylpyrrolidone ethylene glycol solution as a stabilizer, take 10 ml and slowly add it to the induction solution to obtain a silver nanowire suspension, react for 20-30 min, then centrifuge the suspension, and wash and purify it sequentially with acetone, distilled water and anhydrous ethanol to obtain silver nanowire preforms; The silver nanowire preform was dissolved in a 0.3-0.5 mol / L glutaric acid ethanol solution as a surface treatment agent and immersed for 15-20 minutes. After removing the surface treatment agent, the modified silver nanowire was obtained.

4. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 1, characterized in that, In S3, the initial bidirectional stretching is an asynchronous bidirectional stretching that first proceeds longitudinally and then laterally. The longitudinal stretching ratio is n, where 4 ≤ n ≤ 6, and the lateral stretching ratio is m, where 4 ≤ m ≤ 8, and 1 ≤ m / n ≤ 1.

35.

5. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 4, characterized in that, In step S4, the bidirectional stretching includes a first-step bidirectional stretching and a second-step bidirectional stretching. Both the first-step bidirectional stretching and the second-step bidirectional stretching are asynchronous bidirectional stretching, first longitudinal and then transverse. The longitudinal stretching ratio of the first-step bidirectional stretching is a, 2≤a≤3, and the transverse stretching ratio is b, 1≤b≤2, and b≤a. The longitudinal stretching ratio of the second-step bidirectional stretching is x, 1≤x≤2, and the transverse stretching ratio is y, 1≤y≤2, and y≤x.

6. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 5, characterized in that, The initial biaxial stretching temperature is 115-120℃; the first biaxial stretching temperature in the second biaxial stretching is 130-135℃, and the second biaxial stretching temperature is 135-140℃.

7. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 1, characterized in that, In step S3, the drying temperature is 65~75℃, and the annealing temperature is 105~110℃.

8. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 1, characterized in that, In step S5, the heating temperature of the base film is 140~150℃.

9. The method for preparing the ultra-high molecular weight polyethylene conductive composite film according to claim 1, characterized in that, The antioxidant is antioxidant 1010, and the amount added is 0.5% to 1% of the total mass of ultra-high molecular weight polyethylene and solvent; the solvent is white oil; and the diluent is n-hexane.

10. A conductive composite film, characterized in that, The conductive composite film of ultra-high molecular weight polyethylene is prepared by the method described in any one of claims 1 to 9.

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