Method for preparing flexible stretchable conductive fiber and flexible stretchable conductive fiber

Abstract

This invention relates to the field of new materials technology, providing a method for preparing flexible and stretchable conductive fibers and the resulting flexible and stretchable conductive fibers. The method includes using a mixture containing conductive materials, a catalyst, and a two-component addition-type liquid silicone rubber as a core spinning solution, and a mixture containing a sensitizer, hydroxyl silicone oil, and methyl vinyl silicone rubber as a shell spinning solution. The fibers are extruded using a coaxial spinning process. The resulting nascent fibers are cured by gamma-ray irradiation to form a shell, and then the core spinning solution is cured by heat treatment to obtain flexible and stretchable conductive fibers. The thickness of the shell is 100–200 μm; the vulcanization temperature of the two-component addition-type liquid silicone rubber is 40–60 °C. The resistivity of the obtained flexible and stretchable conductive fibers is ≤1×10⁻⁶. ‑4 Ω·m, tensile elongation at break ≥200%, resistivity increase rate ≤5% after 100 cycles of tensile stress.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and to a flexible stretchable conductive fiber and its preparation method, particularly to a flexible stretchable core-shell structure conductive silicone rubber continuous fiber and its preparation method. Background Technology

[0002] Flexible and stretchable circuits are electronic circuits that can maintain their function under physical deformations such as bending and stretching, and have broad application prospects in wearable devices such as smart bracelets and smart clothing. Commonly used materials for flexible and stretchable circuits include liquid metals and conductive polymers. Traditional flexible circuits are mostly printed with conductive circuits on a flexible polymer matrix using screen printing. However, in this approach, the conductive silver paste in the circuit cannot effectively follow the deformation when the flexible polymer matrix is ​​stretched. Therefore, after repeated stretching cycles, the resistance of the circuit increases significantly, resulting in poor durability of the flexible circuit components. With technological advancements, patent application CN117702302A proposes a method for preparing a liquid metal composite filament, fiber film, and flexible electronic composite material based on electrospinning, which can produce low-density and highly conductive liquid metal composite materials. Because an oxide film is generated during the processing and electrospinning of liquid metal droplets, and because the elastomer coating structure has insulating properties, the electrospun liquid metal filament fiber composite material without heat treatment activation is non-conductive. By applying pressure uniformly to the surface of the composite material within a temperature range of 80–130°C, liquid metal can be uniformly connected within the composite material to achieve conductivity. However, this hot-pressing method has uncertain effects on the fiber structure, making it difficult to obtain flexible, stretchable conductive fibers with stable performance.

[0003] Therefore, this invention is proposed. Summary of the Invention

[0004] This invention provides a method for preparing flexible and stretchable conductive fibers and the flexible and stretchable conductive fibers themselves, thereby overcoming the difficulty in preparing stable flexible and stretchable conductive fibers in the prior art. Through fibers with a core-shell structure composed of specific raw materials, flexible and stretchable conductive fibers are prepared using silicone rubber as the main material and a coaxial spinning process.

[0005] Specifically, the present invention provides a method for preparing flexible and stretchable conductive fibers, comprising: using a mixture containing conductive materials, catalysts and bicomponent addition-type liquid silicone rubber as a core spinning solution, using a mixture containing sensitizers, hydroxyl silicone oil and methyl vinyl silicone rubber as a shell spinning solution, extruding the nascent fibers using a coaxial spinning process, curing the resulting nascent fibers by γ-ray irradiation to form a shell, and then curing the core spinning solution by heat treatment to obtain flexible and stretchable conductive fibers;

[0006] The shell layer has a thickness of 100–200 μm; the vulcanization temperature of the two-component addition-curing liquid silicone rubber is 40–60 °C.

[0007] Due to the characteristics of its molecular chain and high viscosity, silicone rubber presents certain technical challenges in forming continuous fibers during spinning. This invention has found that by using coaxial spinning technology combined with the principle of γ-ray irradiation curing, and further designing different curing mechanisms for the core spinning solution and the shell spinning solution, the continuous preparation of core-shell structured silicone rubber fibers can be achieved. The shell layer is primarily made of a mixture containing sensitizers, hydroxyl silicone oil, and methyl vinyl silicone rubber. This material can be cured under gamma-ray irradiation to form a shell layer with good strength, thermal conductivity, and structural stability, thus encapsulating the spinning solution of the core material and ensuring the morphological stability of the nascent fiber. The core material inside the nascent fiber is mainly composed of bicomponent addition-curing liquid silicone rubber and conductive materials. The addition of conductive materials imparts conductivity to the fiber. Before the spinning solution undergoes heat treatment, the core material spinning solution is in an uncured state, allowing the nascent fiber to continue to be stretched under traction. Since the shell layer also uses silicone rubber, which is a poor conductor of heat, this invention designs the shell layer thickness to be within a suitable range and designs the bicomponent addition-curing liquid silicone rubber to be vulcanized between 40 and 60°C. This allows for the subsequent curing of the nascent fiber using a simple heat treatment process, resulting in a flexible and stretchable conductive fiber.

[0008] According to the method for preparing the flexible stretchable conductive fiber provided by the present invention, the sensitizer is selected from one or more combinations of trimethylolpropane trimethacrylate, diethylene glycol diacrylate, and triallyl isocyanurate; preferably trimethylolpropane trimethacrylate.

[0009] The curing rate of nascent fibers obtained by coaxial spinning and the strength of the resulting shell play a crucial role in the final fiber performance. Research has found that trimethylolpropane trimethacrylate (TMT) contains three methacrylate functional groups, providing more free radicals and crosslinking points. This allows for a balance between curing rate and shell structure, contributing to the curing of the core material.

[0010] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the viscosity of the shell spinning solution is 10000-50000 mPa·s.

[0011] In coaxial spinning, moderate viscosity is beneficial for fiber formation. Simultaneously, viscosity also affects the encapsulation of the core spinning solution by the shell spinning solution, thus influencing the fiber morphology. Research has found that the viscosity range described above is more suitable for improving the overall performance of the flexible, stretchable conductive fiber of this invention.

[0012] According to the method for preparing the flexible stretchable conductive fiber provided by the present invention, the shell spinning solution further includes a thermally conductive filler; the thermally conductive filler is selected from one or a combination of two or more of boron nitride, aluminum nitride, silicon nitride and aluminum oxide.

[0013] As mentioned above, the shell layer in this invention is also made of silicone rubber, which is a poor conductor of heat. In order to facilitate the curing of the core material spinning solution, thermally conductive fillers can be introduced into the shell spinning solution to adjust the thermal conductivity of the shell layer.

[0014] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the shell spinning solution further includes a reinforcing filler; the reinforcing filler is selected from gaseous SiO2.

[0015] Meanwhile, increasing the strength of the shell layer also facilitates heat treatment, so it is preferable to further introduce reinforcing fillers into the shell spinning solution.

[0016] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the shell spinning solution is composed of 100 parts methyl vinyl silicone rubber, 10-20 parts hydroxy silicone oil, 20-30 parts reinforcing filler, 1-3 parts trimethylolpropane trimethacrylate, 0.5-2 parts pigment and 10-20 parts thermally conductive filler by weight.

[0017] The pigment can be an organic pigment or an inorganic pigment.

[0018] The particle size of the thermally conductive filler is less than 50 μm, and more preferably less than 30 μm.

[0019] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the conductive material is silver powder, preferably flake silver powder.

[0020] The flake-shaped silver powder forms line or surface contacts, resulting in relatively lower resistance compared to the point contacts of spherical silver powder. This contact method provides a more efficient conductive path, thereby improving the conductivity of flexible, stretchable conductive fibers. The average thickness of the flake-shaped silver powder is typically between 50 and 100 nm, giving it good conductivity and plasticity. This plasticity allows the flake-shaped silver powder to better adapt to various shapes and structures in flexible, stretchable conductive fibers, improving the fiber's flexibility and processability.

[0021] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the core spinning solution includes component A and component B;

[0022] Component A includes vinyl silicone rubber raw material, hydrogen-containing silicone oil, reinforcing filler, and flake silver powder;

[0023] Component B includes vinyl-terminated silicone rubber raw material, vinyl dual-end-capping agent-Pt complex, reinforcing filler, and flake silver powder;

[0024] Compared to directly mixing all raw materials, this invention pre-mixes the vinyl dual-end-capping agent-Pt complex with substances such as vinyl-terminated silicone rubber raw rubber, and then mixes it with component A. This helps the vinyl dual-end-capping agent-Pt complex to catalyze the core material spinning solution during heat treatment.

[0025] Preferably, by mass, component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 2-4 parts of hydrogen-containing silicone oil, 10-20 parts of fumed SiO2 and 10-20 parts of flake silver powder.

[0026] By mass, component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 0.2 to 1 part of vinyl-terminated Pt complex, 10 to 20 parts of fumed SiO2 and 10 to 20 parts of flake silver powder.

[0027] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, during the coaxial spinning extrusion process, the liquid supply rate of the inner cylinder is 0.3 to 0.8 ml / min, and the liquid supply rate of the outer cylinder is 0.2 to 0.4 ml / min.

[0028] And / or, during the γ-ray irradiation, the dose rate is 4 × 10⁻⁶. 3 ~6×10 3 Gy / h;

[0029] And / or, the heat treatment curing of the core spinning solution involves treating the nascent fibers in a hot water bath at a temperature of 60–80°C for 3–5 minutes.

[0030] Research has found that, for the raw materials used in this invention, hot water bath treatment is easier to operate and the degree of curing is easier to control compared to other heat treatment processes.

[0031] The present invention also provides a flexible stretchable conductive fiber prepared by the method described above, which has a core-shell structure; the core material of the core-shell structure is formed by curing a spinning solution containing silver powder and a two-component addition-type liquid silicone rubber; the shell layer of the core-shell structure includes silicone rubber cured by gamma radiation.

[0032] Preferably, the resistivity of the flexible, stretchable conductive fiber is ≤1×10⁻⁶. -4 Ω·m, the tensile elongation at break of the flexible stretchable conductive fiber is ≥200%, and the resistivity increase rate of the flexible stretchable conductive fiber after 100 cycles of stretching is ≤5%.

[0033] The fiber cross-section in this invention can be circular or rectangular. Generally, the diameter of circular fibers is 1–3 mm, preferably 2 mm. The width of rectangular cross-section fibers is 1–3 mm, with a width-to-thickness ratio of 1:0.5. In this invention, the fiber structure is related to the supply rates of the shell spinning solution and the core spinning solution. The supply rates of the shell spinning solution and the core spinning solution can be calculated based on the dimensions of the fiber cross-section and the thickness of the shell.

[0034] This invention provides a method for preparing flexible, stretchable conductive fibers and the flexible, stretchable conductive fibers themselves. By employing a coaxial spinning process combined with the principle of gamma-ray irradiation curing, and further designing different curing mechanisms for the core material spinning solution and the shell spinning solution, continuous preparation of core-shell structured silicone rubber fibers can be achieved. The resulting fibers have a core-shell structure; the core material is formed by curing a spinning solution containing silver powder and a two-component addition-type liquid silicone rubber, and the shell layer includes gamma-ray radiation-cured silicone rubber. The resistivity of the flexible, stretchable conductive fibers is ≤1×10⁻⁶. -4 Ω·m, tensile elongation at break ≥200%, resistivity increase rate ≤5% after 100 cycles of tensile stress. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the preparation method of the flexible stretchable conductive fiber provided by the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] The following is combined Figure 1 The present invention describes a method for preparing flexible stretchable conductive fibers and the flexible stretchable conductive fibers thereof.

[0039] Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. Specifically, the raw materials of this invention are sourced as follows:

[0040] Vinyl-terminated silicone rubber raw material: viscosity is 850 mPa·s.

[0041] Hydrogen-containing silicone oil: viscosity is 25 mPa·s.

[0042] Vaporized SiO2: Evonik A380.

[0043] Flake silver powder: prepared according to Example 1 in patent application CN201610201224.8.

[0044] Vinyl bis-terminated Pt complex: also known as ECEE (ethylene glycol bis(2-chloroethyl) ether), wherein the vinyl bis-terminated agent accounts for 2% of the total mass of the complex.

[0045] Methyl vinyl silicone rubber: grade 110-2, molecular weight 500,000 to 600,000, vinyl content 0.15 (mole fraction), product of Sichuan Chenguang Chemical Research Institute.

[0046] Hydroxyl silicone oil: grade GY209, hydroxyl content 8%, viscosity 30 Pa·s, product of Sichuan Chenguang Chemical Research Institute.

[0047] Trimethylolpropane trimethacrylate: Jiangsu Nanjing Jinling Petrochemical Technology Development Co., Ltd.

[0048] Inorganic pigments: particle size ≤30μm.

[0049] Alumina: Particle size ≤ 30 μm.

[0050] Example 1

[0051] A method for preparing flexible and stretchable conductive fibers, comprising the following steps:

[0052] (1) Preparation of core material spinning solution:

[0053] Component A: By mass, Component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 3 parts of hydrogen-containing silicone oil, 15 parts of fumed SiO2 and 15 parts of flake silver powder.

[0054] Component B: By mass, Component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 0.5 parts of vinyl dual-end-capping agent-Pt complex, 15 parts of fumed SiO2 and 15 parts of flake silver powder.

[0055] Component A and component B are added to a high-speed mixer at a mass ratio of 1:1 and mixed thoroughly to obtain a core spinning solution. The vulcanization temperature of the core spinning solution is in the range of 40 to 60°C.

[0056] Preparation of shell spinning solution: A mixture consisting of 100 parts by mass of methyl vinyl silicone rubber, 15 parts by mass of hydroxyl silicone oil, 25 parts by mass of fumed SiO2, 2 parts by mass of trimethylolpropane trimethacrylate, 1 part by mass of inorganic pigment and 15 parts by mass of alumina is mixed on a two-roll mill and then degassed to obtain a shell spinning solution with a viscosity in the range of 10,000 to 50,000 mPa·s.

[0057] (2) Spinning: such as Figure 1 As shown, using a coaxial spinning method, the core spinning solution and the shell spinning solution are added to the inner and outer cylinders respectively. A constant air pressure of 1 MPa is applied above the cylinders to push the spinning solution downwards, and the drawing speed is 1 m / min. Co is arranged below the spinning needle. 60 The spinning solution, after being irradiated with gamma rays, rapidly cross-links and solidifies its shell layer, with a dose rate of 5 × 10⁻⁶. 3 The process involves heating the fibers at a speed of Gy / h, followed by immersing the cured outer shell in a water bath at 70°C. Heat is transferred through the outer shell to the core, accelerating the cross-linking of the liquid silicone rubber in the core. After 4 minutes of hot water bath treatment, continuously prepared flexible and stretchable conductive fibers are obtained. The resulting flexible and stretchable conductive fibers have a circular cross-section. Based on the aforementioned spinning speed, the supply rates of the outer shell spinning solution and the core spinning solution are adjusted to achieve a fiber diameter of 2 mm and a outer shell thickness of 150 μm.

[0058] The resistivity, elongation at break, and resistivity after 100 cycles of cyclic stretching of the obtained flexible, stretchable conductive fiber were tested. The elongation at break was tested according to GB / T528-2009, with a stretching speed of 500 mm / min. The test results showed a resistivity of 1×10⁻⁶. -3 Ω·m, tensile elongation at break is 300%, and resistivity increase rate after 100 cycles of tensile stress is ≤5%.

[0059] Example 2

[0060] A method for preparing flexible and stretchable conductive fibers, comprising the following steps:

[0061] (1) Preparation of core material spinning solution:

[0062] Component A: By mass, Component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 2 parts of hydrogen-containing silicone oil, 20 parts of fumed SiO2 and 10 parts of flake silver powder.

[0063] Component B: By mass, Component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 0.3 parts of vinyl-terminated Pt complex, 20 parts of fumed SiO2, and 10 parts of flake silver powder.

[0064] Component A and component B are added to a high-speed mixer at a mass ratio of 1:1 and mixed thoroughly to obtain a core spinning solution. The vulcanization temperature of the core spinning solution is in the range of 40 to 60°C.

[0065] Preparation of shell spinning solution: A mixture consisting of 100 parts by mass of methyl vinyl silicone rubber, 10 parts by mass of hydroxyl silicone oil, 20 parts by mass of fumed SiO2, 1 part by mass of trimethylolpropane trimethacrylate, 1 part by mass of inorganic pigment and 10 parts by mass of alumina is mixed on a two-roll mill and then degassed to obtain a shell spinning solution with a viscosity in the range of 10,000 to 50,000 mPa·s.

[0066] (2) Spinning: such as Figure 1 As shown, using a coaxial spinning method, the core spinning solution and the shell spinning solution are added to the inner and outer cylinders respectively. A constant air pressure of 1 MPa is applied above the cylinders to push the spinning solution downwards, and the drawing speed is 1 m / min. Co is arranged below the spinning needle. 60 The spinning solution, after being irradiated with gamma rays, rapidly cross-links and solidifies its shell layer, with a dose rate of 5 × 10⁻⁶. 3 The process involves heating the fibers at a speed of Gy / h, followed by immersing the cured outer shell in a water bath at 75°C. Heat is transferred through the outer shell to the core, accelerating the cross-linking of the liquid silicone rubber in the core. After 3 minutes of hot water bath treatment, continuously prepared flexible and stretchable conductive fibers are obtained. The resulting flexible and stretchable conductive fibers have a circular cross-section. Based on the aforementioned spinning speed, the supply rates of the outer shell spinning solution and the core spinning solution are adjusted to achieve a fiber diameter of 1 mm and a outer shell thickness of 100 μm.

[0067] The resistivity, elongation at break, and resistivity after 100 cycles of cyclic stretching of the obtained flexible and stretchable conductive fiber were tested. The elongation at break was tested according to GB / T528-2009, with a stretching speed of 500 mm / min.

[0068] Example 3

[0069] A method for preparing flexible and stretchable conductive fibers, comprising the following steps:

[0070] (1) Preparation of core material spinning solution:

[0071] Component A: By mass, Component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 4 parts of hydrogen-containing silicone oil, 10 parts of fumed SiO2 and 15 parts of flake silver powder.

[0072] Component B: By mass, Component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 1 part of vinyl dual-end-capping agent-Pt complex, 10 parts of fumed SiO2 and 15 parts of flake silver powder.

[0073] Component A and component B are added to a high-speed mixer at a mass ratio of 1:1 and mixed thoroughly to obtain a core spinning solution. The vulcanization temperature of the core spinning solution is in the range of 40 to 60°C.

[0074] Preparation of shell spinning solution: A mixture consisting of 100 parts by mass of methyl vinyl silicone rubber, 20 parts by mass of hydroxyl silicone oil, 30 parts by mass of fumed SiO2, 3 parts by mass of trimethylolpropane trimethacrylate, 1 part by mass of inorganic pigment and 15 parts by mass of alumina is prepared by mixing and degassing on a two-roll mill to obtain a shell spinning solution with a viscosity in the range of 10,000 to 50,000 mPa·s.

[0075] (2) Spinning: such as Figure 1 As shown, using a coaxial spinning method, the core spinning solution and the shell spinning solution are added to the inner and outer cylinders respectively. A constant air pressure of 1 MPa is applied above the cylinders to push the spinning solution downwards, and the drawing speed is 1 m / min. Co is arranged below the spinning needle. 60 The spinning solution, after being irradiated with gamma rays, rapidly cross-links and solidifies its shell layer, with a dose rate of 5 × 10⁻⁶. 3 The process involves heating the fibers at a speed of Gy / h, followed by immersing the cured outer shell in a water bath at 65°C. Heat is transferred through the outer shell to the core layer, accelerating the cross-linking of the liquid silicone rubber within the core. After 5 minutes of hot water bath treatment, continuously prepared flexible and stretchable conductive fibers are obtained. The resulting flexible and stretchable conductive fibers have a circular cross-section. Based on the aforementioned spinning speed, the supply rates of the outer shell spinning solution and the core spinning solution are adjusted to achieve a fiber diameter of 3 mm and a outer shell thickness of 200 μm.

[0076] The resistivity, elongation at break, and resistivity after 100 cycles of cyclic stretching of the obtained flexible and stretchable conductive fiber were tested. The elongation at break was tested according to GB / T528-2009, with a stretching speed of 500 mm / min.

[0077] Example 4

[0078] A method for preparing flexible and stretchable conductive fibers, comprising the following steps:

[0079] (1) Preparation of core material spinning solution:

[0080] Component A: By mass, Component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 3 parts of hydrogen-containing silicone oil, 10 parts of fumed SiO2 and 15 parts of flake silver powder.

[0081] Component B: By mass, Component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 1 part of vinyl dual-end-capping agent-Pt complex, 10 parts of fumed SiO2 and 15 parts of flake silver powder.

[0082] Component A and component B are added to a high-speed mixer at a mass ratio of 1:1 and mixed thoroughly to obtain a core spinning solution. The vulcanization temperature of the core spinning solution is in the range of 40 to 60°C.

[0083] Preparation of shell spinning solution: A mixture consisting of 100 parts by mass of methyl vinyl silicone rubber, 20 parts by mass of hydroxyl silicone oil, 25 parts by mass of fumed SiO2, 3 parts by mass of trimethylolpropane trimethacrylate, 1 part by mass of inorganic pigment and 20 parts by mass of alumina is prepared by mixing and degassing on a two-roll mill to obtain a shell spinning solution with a viscosity in the range of 10,000 to 50,000 mPa·s.

[0084] (2) Spinning: such as Figure 1 As shown, using a coaxial spinning method, the core spinning solution and the shell spinning solution are added to the inner and outer cylinders respectively. A constant air pressure of 1 MPa is applied above the cylinders to push the spinning solution downwards, and the drawing speed is 1 m / min. Co is arranged below the spinning needle. 60 The spinning solution, after being irradiated with gamma rays, rapidly cross-links and solidifies its shell layer, with a dose rate of 5 × 10⁻⁶. 3 The process involves heating the fibers at a speed of Gy / h, followed by immersing the cured outer shell in a water bath at 80°C. Heat is transferred through the outer shell to the core, accelerating the cross-linking of the liquid silicone rubber in the core. After 4.5 minutes of hot water bath treatment, continuously prepared flexible and stretchable conductive fibers are obtained. The resulting flexible and stretchable conductive fibers have a rectangular cross-section. Based on the aforementioned spinning speed, the supply rates of the outer shell spinning solution and the core spinning solution are adjusted to achieve a fiber diameter of 2 mm and a width-to-thickness ratio of 1:0.5. ， The shell thickness is 160 μm.

[0085] The resistivity, elongation at break, and resistivity after 100 cycles of cyclic stretching of the obtained flexible and stretchable conductive fiber were tested. The elongation at break was tested according to GB / T528-2009, with a stretching speed of 500 mm / min.

[0086] The test results of the flexible stretchable conductive fibers obtained in Examples 2-4 are as follows: resistivity ≤ 1×10⁻⁶ -4 Ω·m, tensile elongation at break ≥200%, resistivity increase rate ≤5% after 100 cycles of tensile stress.

[0087] Those skilled in the art will understand that the present invention provides a method for preparing flexible and stretchable conductive fibers, comprising: using a mixture containing conductive materials, catalysts and bicomponent addition-type liquid silicone rubber as a core spinning solution, using a mixture containing sensitizers, hydroxyl silicone oil and methyl vinyl silicone rubber as a shell spinning solution, extruding the nascent fibers using a coaxial spinning process, curing the resulting nascent fibers by γ-ray irradiation to form a shell, and then curing the core spinning solution by heat treatment to obtain flexible and stretchable conductive fibers;

[0088] The shell layer has a thickness of 100–200 μm; the vulcanization temperature of the two-component addition-curing liquid silicone rubber is 40–60 °C.

[0089] Due to the characteristics of its molecular chain and high viscosity, silicone rubber presents certain technical challenges in forming continuous fibers during spinning. This invention has found that by using coaxial spinning technology combined with the principle of γ-ray irradiation curing, and further designing different curing mechanisms for the core spinning solution and the shell spinning solution, the continuous preparation of core-shell structured silicone rubber fibers can be achieved. The shell layer is primarily made of a mixture containing sensitizers, hydroxyl silicone oil, and methyl vinyl silicone rubber. This material can be cured under gamma-ray irradiation to form a shell layer with good strength, thermal conductivity, and structural stability, thus encapsulating the spinning solution of the core material and ensuring the morphological stability of the nascent fiber. The core material inside the nascent fiber is mainly composed of bicomponent addition-curing liquid silicone rubber and conductive materials. The addition of conductive materials imparts conductivity to the fiber. Before the spinning solution undergoes heat treatment, the core material spinning solution is in an uncured state, allowing the nascent fiber to continue to be stretched under traction. Since the shell layer also uses silicone rubber, which is a poor conductor of heat, this invention designs the shell layer thickness to be within a suitable range and designs the bicomponent addition-curing liquid silicone rubber to be vulcanized between 40 and 60°C. This allows for the subsequent curing of the nascent fiber using a simple heat treatment process, resulting in a flexible and stretchable conductive fiber.

[0090] According to the method for preparing the flexible stretchable conductive fiber provided by the present invention, the sensitizer is selected from one or more combinations of trimethylolpropane trimethacrylate, diethylene glycol diacrylate, and triallyl isocyanurate; preferably trimethylolpropane trimethacrylate.

[0091] The curing rate of nascent fibers obtained by coaxial spinning and the strength of the resulting shell play a crucial role in the final fiber performance. Research has found that trimethylolpropane trimethacrylate (TMT) contains three methacrylate functional groups, providing more free radicals and crosslinking points. This allows for a balance between curing rate and shell structure, contributing to the curing of the core material.

[0092] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the viscosity of the shell spinning solution is 10000-50000 mPa·s.

[0093] In coaxial spinning, moderate viscosity is beneficial for fiber formation. Simultaneously, viscosity also affects the encapsulation of the core spinning solution by the shell spinning solution, thus influencing the fiber morphology. Research has found that the viscosity range described above is more suitable for improving the overall performance of the flexible, stretchable conductive fiber of this invention.

[0094] According to the method for preparing the flexible stretchable conductive fiber provided by the present invention, the shell spinning solution further includes a thermally conductive filler; the thermally conductive filler is selected from one or a combination of two or more of boron nitride, aluminum nitride, silicon nitride and aluminum oxide.

[0095] As mentioned above, the shell layer in this invention is also made of silicone rubber, which is a poor conductor of heat. In order to facilitate the curing of the core material spinning solution, thermally conductive fillers can be introduced into the shell spinning solution to adjust the thermal conductivity of the shell layer.

[0096] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the shell spinning solution further includes a reinforcing filler; the reinforcing filler is selected from gaseous SiO2.

[0097] Meanwhile, increasing the strength of the shell layer also facilitates heat treatment, so it is preferable to further introduce reinforcing fillers into the shell spinning solution.

[0098] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the shell spinning solution is composed of 100 parts methyl vinyl silicone rubber, 10-20 parts hydroxy silicone oil, 20-30 parts reinforcing filler, 1-3 parts trimethylolpropane trimethacrylate, 0.5-2 parts pigment and 10-20 parts thermally conductive filler by weight.

[0099] The pigment can be an organic pigment or an inorganic pigment.

[0100] The particle size of the thermally conductive filler is less than 50 μm, and more preferably less than 30 μm.

[0101] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the conductive material is silver powder, preferably flake silver powder.

[0102] The flake-shaped silver powder forms line or surface contacts, resulting in relatively lower resistance compared to the point contacts of spherical silver powder. This contact method provides a more efficient conductive path, thereby improving the conductivity of flexible, stretchable conductive fibers. The average thickness of the flake-shaped silver powder is typically between 50 and 100 nm, giving it good conductivity and plasticity. This plasticity allows the flake-shaped silver powder to better adapt to various shapes and structures in flexible, stretchable conductive fibers, improving the fiber's flexibility and processability.

[0103] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, the core spinning solution includes component A and component B;

[0104] Component A includes vinyl silicone rubber raw material, hydrogen-containing silicone oil, reinforcing filler, and flake silver powder;

[0105] Component B includes vinyl-terminated silicone rubber raw material, vinyl dual-end-capping agent-Pt complex, reinforcing filler, and flake silver powder;

[0106] Compared to directly mixing all raw materials, this invention pre-mixes the vinyl dual-end-capping agent-Pt complex with substances such as vinyl-terminated silicone rubber raw rubber, and then mixes it with component A. This helps the vinyl dual-end-capping agent-Pt complex to catalyze the core material spinning solution during heat treatment.

[0107] Preferably, by mass, component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 2-4 parts of hydrogen-containing silicone oil, 10-20 parts of fumed SiO2 and 10-20 parts of flake silver powder.

[0108] By mass, component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 0.2 to 1 part of vinyl-terminated Pt complex, 10 to 20 parts of fumed SiO2 and 10 to 20 parts of flake silver powder.

[0109] According to the preparation method of the flexible stretchable conductive fiber provided by the present invention, during the coaxial spinning extrusion process, the liquid supply rate of the inner cylinder is 0.3 to 0.8 ml / min, and the liquid supply rate of the outer cylinder is 0.2 to 0.4 ml / min.

[0110] And / or, during the γ-ray irradiation, the dose rate is 4 × 10⁻⁶. 3 ~6×10 3 Gy / h;

[0111] And / or, the heat treatment curing of the core spinning solution involves treating the nascent fibers in a hot water bath at a temperature of 60–80°C for 3–5 minutes.

[0112] Research has found that, for the raw materials used in this invention, hot water bath treatment is easier to operate and the degree of curing is easier to control compared to other heat treatment processes.

[0113] The present invention also provides a flexible stretchable conductive fiber prepared by the method described above, which has a core-shell structure; the core material of the core-shell structure is formed by curing a spinning solution containing silver powder and a two-component addition-type liquid silicone rubber; the shell layer of the core-shell structure includes silicone rubber cured by gamma radiation.

[0114] Preferably, the resistivity of the flexible, stretchable conductive fiber is ≤1×10⁻⁶. -4 Ω·m, the tensile elongation at break of the flexible stretchable conductive fiber is ≥200%, and the resistivity increase rate of the flexible stretchable conductive fiber after 100 cycles of stretching is ≤5%.

[0115] The fiber cross-section in this invention can be circular or rectangular. Generally, the diameter of circular fibers is 1–3 mm, preferably 2 mm. The width of rectangular cross-section fibers is 1–3 mm, with a width-to-thickness ratio of 1:0.5. In this invention, the fiber structure is related to the supply rates of the shell spinning solution and the core spinning solution. The supply rates of the shell spinning solution and the core spinning solution can be calculated based on the dimensions of the fiber cross-section and the thickness of the shell.

[0116] This invention provides a method for preparing flexible, stretchable conductive fibers and the flexible, stretchable conductive fibers themselves. By employing a coaxial spinning process combined with the principle of gamma-ray irradiation curing, and further designing different curing mechanisms for the core material spinning solution and the shell spinning solution, continuous preparation of core-shell structured silicone rubber fibers can be achieved. The resulting fibers have a core-shell structure; the core material is formed by curing a spinning solution containing silver powder and a two-component addition-type liquid silicone rubber, and the shell layer includes gamma-ray radiation-cured silicone rubber. The resistivity of the flexible, stretchable conductive fibers is ≤1×10⁻⁶. -4 Ω·m, tensile elongation at break ≥200%, resistivity increase rate ≤5% after 100 cycles of tensile stress.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a flexible, stretchable conductive fiber, characterized in that, include: A mixture containing conductive materials, catalysts and bicomponent addition-type liquid silicone rubber is used as the core spinning solution, and a mixture containing sensitizers, hydroxyl silicone oil and methyl vinyl silicone rubber is used as the shell spinning solution. The nascent fibers are extruded using a coaxial spinning process, and the resulting nascent fibers are cured by γ-ray irradiation to form a shell. The core spinning solution is then cured by heat treatment to obtain flexible and stretchable conductive fibers. The shell layer has a thickness of 100–200 μm; the vulcanization temperature of the two-component addition-curing liquid silicone rubber is 40–60 °C.

2. The method for preparing the flexible, stretchable conductive fiber according to claim 1, characterized in that, The sensitizer is selected from one or more of trimethylolpropane trimethacrylate, diethylene glycol diacrylate, and triallyl isocyanurate; preferably trimethylolpropane trimethacrylate.

3. The method for preparing flexible stretchable conductive fiber according to claim 1 or 2, characterized in that, The viscosity of the shell spinning solution is 10,000 to 50,000 mPa·s.

4. The method for preparing the flexible stretchable conductive fiber according to any one of claims 1 to 3, characterized in that, The shell spinning solution also includes a thermally conductive filler; the thermally conductive filler is selected from one or more combinations of boron nitride, aluminum nitride, silicon nitride, and aluminum oxide.

5. The method for preparing the flexible stretchable conductive fiber according to any one of claims 1 to 4, characterized in that, The shell spinning solution also includes reinforcing fillers; the reinforcing fillers are selected from fumed SiO2.

6. The method for preparing the flexible stretchable conductive fiber according to any one of claims 1 to 5, characterized in that, The shell spinning solution, by weight, consists of 100 parts methyl vinyl silicone rubber, 10-20 parts hydroxyl silicone oil, 20-30 parts reinforcing filler, 1-3 parts trimethylolpropane trimethacrylate, 0.5-2 parts pigment, and 10-20 parts thermally conductive filler.

7. The method for preparing the flexible stretchable conductive fiber according to any one of claims 1 to 6, characterized in that, The conductive material is silver powder, preferably flake silver powder.

8. The method for preparing the flexible stretchable conductive fiber according to any one of claims 1 to 7, characterized in that, The core material spinning solution comprises component A and component B; Component A includes vinyl silicone rubber raw material, hydrogen-containing silicone oil, reinforcing filler, and flake silver powder; Component B includes vinyl-terminated silicone rubber raw material, vinyl dual-end-capping agent-Pt complex, reinforcing filler, and flake silver powder; Preferably, by mass, component A consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 2-4 parts of hydrogen-containing silicone oil, 10-20 parts of fumed SiO2 and 10-20 parts of flake silver powder. By mass, component B consists of 50 parts of vinyl-terminated silicone rubber raw rubber, 0.2 to 1 part of vinyl-terminated Pt complex, 10 to 20 parts of fumed SiO2 and 10 to 20 parts of flake silver powder.

9. The method for preparing the flexible stretchable conductive fiber according to any one of claims 1 to 8, characterized in that, During the coaxial spinning process, the liquid supply rate of the inner cylinder is 0.3–0.8 ml / min, and the liquid supply rate of the outer cylinder is 0.2–0.4 ml / min. And / or, during the γ-ray irradiation, the dose rate is 4 × 10⁻⁶. 3 ~6×10 3 Gy / h; And / or, the heat treatment curing of the core spinning solution involves treating the nascent fibers in a hot water bath at a temperature of 60–80°C for 3–5 minutes.

10. The flexible stretchable conductive fiber prepared by the method of any one of claims 1 to 9, characterized in that, It has a core-shell structure; the core material of the core-shell structure is formed by curing a spinning solution containing silver powder and a two-component addition-type liquid silicone rubber; the shell layer of the core-shell structure includes silicone rubber cured by gamma-ray radiation; Preferably, the resistivity of the flexible, stretchable conductive fiber is ≤1×10⁻⁶. -4 Ω·m, the tensile elongation at break of the flexible stretchable conductive fiber is ≥200%, and the resistivity increase rate of the flexible stretchable conductive fiber after 100 cycles of stretching is ≤5%.

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