Composite ceramic heat shrink tube and preparation method and application thereof

Abstract

The invention relates to the technical field of insulation protection flame-retardant materials, and discloses a composite ceramic heat shrink tube and a preparation method and application thereof. The composite ceramic heat shrink tube comprises an inner layer and an outer layer which are integrally compounded from inside to outside through co-extrusion molding, wherein the inner layer is a thermal shrinkage silica gel layer, and raw materials of the inner layer comprise vinyl silicone rubber, a hydrogen-containing silicone oil cross-linking agent, a platinum catalyst, a heat stabilizer, a flame retardant and a coloring agent; the outer layer is a ceramic silica gel layer and is prepared from the following raw materials: vinyl silicone rubber, modified ceramic micro powder, a hydrogen-containing silicone oil cross-linking agent, a platinum catalyst, a dispersing agent and a heat stabilizer; the modified ceramic micro powder is obtained by carrying out surface modification treatment on aluminum oxide-silicon dioxide composite micro powder through a silane coupling agent. The preparation method is simple and efficient, and the prepared composite ceramic heat shrink tube has excellent mechanical property, insulativity, high-temperature fire resistance and heat stability through the steps of mixing, co-extrusion, vulcanization, irradiation and expansion.

Description

Technical Field

[0001] This application relates to the field of insulating, protective, and flame-retardant materials technology, and in particular to a composite ceramicized heat shrink tubing, its preparation method, and its application. Background Technology

[0002] In fields such as new energy batteries and power transmission, the insulation protection of conductive busbars such as copper and aluminum busbars is crucial, affecting the safe and stable operation of the entire new energy system. With the rapid development of the new energy industry, the requirements for insulation and flame-retardant materials and processes are becoming increasingly stringent. Highly efficient, reliable, and well-sealed insulation and flame-retardant materials can improve the overall performance and service life of new energy equipment, reduce maintenance costs, and drive the new energy industry towards a safer and more efficient direction.

[0003] Currently, the industry commonly uses a method of manually wrapping ceramic silicone tape followed by an aluminum foil layer for protection. Ceramic silicone tape is typically made by calendering ceramic silicone through platinum vulcanization, then combining it with fiberglass cloth, and finally slitting and rolling it. This method can achieve insulation and flame retardancy for new energy systems to a certain extent, but it still has many drawbacks. First, this method relies on manual wrapping, resulting in low production efficiency and poor product consistency, easily leading to uneven wrapping thickness and overlapping gaps. Second, its sealing performance is insufficient; in harsh environments such as humidity and salt spray, moisture and corrosive media can easily penetrate, causing electrochemical corrosion and insulation failure. Third, the insulation resistance of traditional ceramic silicone tape decreases significantly under high temperatures or open flames, and its fire-retardant performance is not stable enough. While ordinary heat shrink tubing is used for insulation protection in this scenario, it typically lacks high-temperature fire resistance and ceramic-forming properties, failing to meet the stringent requirements for high-temperature fire resistance and other performance characteristics of power battery protection materials. Summary of the Invention

[0004] To at least overcome one of the problems existing in the prior art, one objective of this invention is to provide a composite ceramicized heat shrink tubing, comprising an inner layer and an outer layer integrally composited by co-extrusion molding from the inside out; wherein, the inner layer is a heat-shrinkable silicone layer, the raw materials of which include specific crosslinking agents, catalysts, etc.; the outer layer is a ceramicized silicone layer, the raw materials of which include vinyl silicone rubber, modified ceramic micro powder, etc.; the specific double-layer composite structure of this application enables the composite ceramicized heat shrink tubing to integrate the heat-shrink sealing function of the inner layer and the high-temperature ceramicized flame-retardant function of the outer layer, satisfying both the convenience of installation and meeting extreme heat protection requirements. The composite ceramicized heat shrink tubing of this application possesses excellent high-temperature resistance and flame-retardant properties, and strong thermal stability. A second objective of this invention is to provide a method for preparing the composite ceramicized heat shrink tubing. A third objective of this application is to provide applications of the composite ceramicized heat shrink tubing.

[0005] Therefore, the present invention adopts the following technical solution: A first aspect of the present invention provides a composite ceramicized heat shrink tubing, comprising an inner layer and an outer layer integrally composited from the inside out by co-extrusion molding; wherein, the inner layer is a heat-shrinkable silicone layer, the raw materials of which include vinyl silicone rubber, a hydrogen-containing silicone oil crosslinking agent, a platinum catalyst, a heat stabilizer, a flame retardant, and a colorant; the outer layer is a ceramicized silicone layer, the raw materials of which include vinyl silicone rubber, modified ceramic micropowder, a hydrogen-containing silicone oil crosslinking agent, a platinum catalyst, a dispersant, and a heat stabilizer; the modified ceramic micropowder is obtained by surface modification treatment of alumina-silica composite micropowder with a silane coupling agent.

[0006] This application's composite ceramicized heat shrink tubing adopts a co-extruded integrated composite double-layer structure, avoiding problems such as uneven thickness and poor sealing caused by traditional manual winding methods, significantly improving production efficiency, while ensuring a tight bond between the inner and outer layers and enhancing the stability of insulation protection. The inner heat-shrinkable silicone layer uses crosslinking agents and catalysts with specific compositions and ratios, giving the heat shrink tubing excellent heat-shrinkability and helping to improve the sealing effect of the composite ceramicized heat shrink tubing during use. The modified ceramic micropowder in the outer ceramicized silicone layer is obtained by surface modification treatment of alumina-silica composite micropowder with a silane coupling agent, which improves its compatibility with the vinyl silicone rubber substrate to a certain extent. The addition of modified ceramic micropowder avoids the agglomeration of inorganic powders, and at high temperatures, it can synergistically form a dense ceramicized protective layer, thereby giving the product excellent high-temperature insulation and fire resistance, enhancing the flame-retardant and fire-resistant properties and mechanical properties of the outer layer. This application's composite ceramicized heat shrink tubing has good heat-shrink sealing and high-temperature flame-retardant protection effects, meeting the stringent safety requirements of the new energy field.

[0007] Preferably, the preparation method of the modified ceramic micro powder includes the following steps: Alumina-silica composite micro powder was dried in an oven at 110℃ for 2 hours. 8-13 parts by weight of the alumina-silica composite micro powder and 0.2-0.4 parts by weight of the silane coupling agent were added to 10-12 parts by weight of an ethanol-water solution with a volume ratio of 9:1. The mixture was heated and stirred in a water bath at 60-70℃ for 2-3 hours. The mixture was then filtered, and the filter cake was washed with a small amount of anhydrous ethanol. The filter cake was transferred to an oven and dried at 100-120℃ for 2.5-3 hours. The mixture was then passed through a 200-250 mesh sieve, and the sieve-passing material was collected to obtain the modified ceramic micro powder.

[0008] Preferably, the silane coupling agent is selected from at least one of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane. More preferably, the silane coupling agent is selected from at least one of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane. Even more preferably, the silane coupling agent is selected from at least one of γ-methacryloxypropyltrimethoxysilane and vinyltriethoxysilane.

[0009] Preferably, the alumina-silica composite micropowder has a particle size of 3-8 μm, and the mass percentage of alumina in the alumina-silica composite micropowder is 60%-90%. More preferably, the alumina-silica composite micropowder has a particle size of 4-8 μm, and the mass percentage of alumina in the alumina-silica composite micropowder is 60%-90%. Even more preferably, the alumina-silica composite micropowder has a particle size of 5-8 μm, and the mass percentage of alumina in the alumina-silica composite micropowder is 70%-90%.

[0010] In the above technical solution, the compatibility between modified ceramic micropowder and vinyl silicone rubber is improved by modifying the silane coupling agent, avoiding agglomeration. At the same time, silane coupling agents such as γ-methacryloyloxypropyltrimethoxysilane contain functional groups, such as vinyl groups, that can chemically react with the vinyl silicone rubber vulcanization system. This allows the surface of the modified ceramic micropowder to be connected to the silicone rubber matrix through chemical bonds rather than just physical action, thereby significantly improving the interfacial bonding force between the inorganic filler and the organic matrix. Therefore, in the high-temperature ceramicization process, the synergistic effect between the filler and the matrix is ​​better, and the formed ceramic skeleton is more robust, thereby improving the mechanical strength, heat resistance and fire resistance of the outer layer as a whole.

[0011] In the alumina-silica composite micropowder, alumina accounts for 70% to 90% of the mass. Alumina provides a robust framework, while silica primarily acts as a binder and stress buffer. If the alumina proportion is too high, the ceramicized silica layer may become too hard and brittle, easily cracking; if the silica proportion is too high, the ceramicized silica layer may lack sufficient strength and soften, deforming. Therefore, controlling the mass proportion within the range specified in this application is beneficial for producing excellent synergistic effects at high temperatures, resulting in a ceramicized silica layer that possesses excellent strength, toughness, density, and thermal insulation properties.

[0012] Preferably, in the composite ceramicized heat shrink tubing, the thickness ratio of the inner layer to the outer layer is 1:(1~1.5). More preferably, in the composite ceramicized heat shrink tubing, the thickness ratio of the inner layer to the outer layer is 1:(1.2~1.5).

[0013] At this specific thickness ratio, the outer layer is slightly thicker than the inner layer. The sufficient thickness of the outer ceramicized silicone layer ensures a stable ceramic protective shell under high-temperature or open-flame conditions, while avoiding excessive thickness that would reduce the flexibility of the heat-shrink tubing and consequently the heat-shrinkability of the inner layer. The moderate thickness of the inner heat-shrinkable silicone layer helps provide sufficient heat-shrink stress, ensuring a tight fit between the heat-shrink tubing and the protected component. Simultaneously, at this thickness ratio, the inner layer adheres closely to the outer layer while maintaining a certain degree of heat shrinkability, preventing cracking or detachment of the outer layer during heat shrinking. This achieves a good combination of the inner layer's heat-shrinkability and the outer layer's ceramicized protective function.

[0014] Preferably, the vinyl molar content of the vinyl silicone rubber is 0.15% to 0.3%. More preferably, the vinyl molar content of the vinyl silicone rubber is 0.18% to 0.3%. Even more preferably, the vinyl molar content of the vinyl silicone rubber is 0.21% to 0.3%.

[0015] Preferably, the active hydrogen content of the hydrogen-containing silicone oil crosslinking agent is 0.5% to 1.8% by weight. More preferably, the active hydrogen content of the hydrogen-containing silicone oil crosslinking agent is 0.7% to 1.6% by weight. Even more preferably, the active hydrogen content of the hydrogen-containing silicone oil crosslinking agent is 1.1% to 1.6% by weight.

[0016] Preferably, the platinum catalyst has a platinum content of 4000-5500 ppm by weight. More preferably, the platinum catalyst has a platinum content of 4500-5500 ppm by weight. Even more preferably, the platinum catalyst has a platinum content of 5000-5500 ppm by weight.

[0017] Preferably, the heat stabilizer is selected from at least one of nano-iron oxide, nano-cerium oxide, and nano-zinc oxide, and its particle size is 45-60 nm. More preferably, the heat stabilizer is selected from at least one of nano-iron oxide and nano-cerium oxide, and its particle size is 45-60 nm. Even more preferably, the heat stabilizer is a compound of nano-iron oxide and nano-cerium oxide in a weight ratio of (2-3):(1.2-4), and its particle size is 50-60 nm.

[0018] Preferably, the dispersant is selected from at least two of zinc stearate, calcium stearate, and stearamide. More preferably, the dispersant is a compound of zinc stearate and calcium stearate. Even more preferably, the weight ratio of zinc stearate to calcium stearate in the dispersant is (1~3):1.

[0019] Preferably, the flame retardant is selected from at least one of magnesium hydroxide, aluminum hydroxide, nano-montmorillonite, zinc borate, and antimony trioxide, and its particle size is 1-10 μm. More preferably, the flame retardant is selected from at least one of magnesium hydroxide, aluminum hydroxide, nano-montmorillonite, and zinc borate, and its particle size is 3-8 μm. Even more preferably, the flame retardant is selected from at least one of magnesium hydroxide, nano-montmorillonite, and zinc borate, and its particle size is 3-5 μm.

[0020] In the aforementioned technical solutions, the vinyl content range of the vinyl silicone rubber helps to control the crosslinking density of the silicone rubber. Too low a content leads to insufficient crosslinking, thereby reducing the mechanical properties and heat-shrink stability of the heat shrink tubing; too high a content easily leads to excessive crosslinking, reducing the flexibility of the heat shrink tubing. The vinyl content range of the vinyl silicone rubber in this application allows the heat shrink tubing to possess both good heat-shrinkability and mechanical strength. After heat shrinking, the inner layer can tightly adhere to the protected component, while also resisting mechanical wear and deformation during long-term use.

[0021] The active hydrogen content of hydrogen-containing silicone oil is matched with the vinyl content of vinyl silicone rubber to ensure that the addition reaction between the Si-H bond in the hydrogen-containing silicone oil molecule and the vinyl C=C bond in the vinyl silicone rubber molecule proceeds fully. Too low an active hydrogen content will lead to insufficient crosslinking density, while too high an active hydrogen content may trigger other side reactions.

[0022] Platinum catalysts with a platinum content of 4000~5500ppm can efficiently catalyze addition cross-linking reactions, avoiding incomplete cross-linking caused by insufficient catalyst dosage, while reducing cost waste caused by excessive dosage or avoiding yellowing of heat shrink tubing due to over-catalysis.

[0023] Heat stabilizers of specific types and particle sizes have excellent heat stabilization effects. Particle sizes of 45~60nm can be uniformly dispersed in rubber substrates, inhibiting the aging of heat shrink tubing during high-temperature processing or use, and extending its service life.

[0024] Preferably, the raw material of the inner layer comprises the following components in parts by weight: 100 parts vinyl silicone rubber, 1.5-3 parts hydrogen-containing silicone oil crosslinking agent, 5-18 parts platinum catalyst, 0.8-1.5 parts heat stabilizer, 1-30 parts flame retardant, and 0.5-2 parts colorant. More preferably, the raw material of the inner layer comprises the following components in parts by weight: 100 parts vinyl silicone rubber, 2-3 parts hydrogen-containing silicone oil crosslinking agent, 10-18 parts platinum catalyst, 1-1.5 parts heat stabilizer, 5-30 parts flame retardant, and 0.5-2 parts colorant.

[0025] Preferably, the raw material of the outer layer comprises the following components in parts by weight: 100 parts vinyl silicone rubber, 80-150 parts modified ceramic micro powder, 1-2.5 parts hydrogen-containing silicone oil crosslinking agent, 7-20 parts platinum catalyst, 0.5-1 part dispersant, and 0.5-1.2 parts heat stabilizer. More preferably, the raw material of the outer layer comprises the following components in parts by weight: 100 parts vinyl silicone rubber, 100-150 parts modified ceramic micro powder, 1.2-2.5 parts hydrogen-containing silicone oil crosslinking agent, 7-20 parts platinum catalyst, 0.5-1 part dispersant, and 0.5-1.2 parts heat stabilizer. More preferably, the raw material of the outer layer includes the following components in parts by weight: 100 parts of vinyl silicone rubber, 100-120 parts of modified ceramic micro powder, 1.2-2.5 parts of hydrogen-containing silicone oil crosslinking agent, 7-18 parts of platinum catalyst, 0.5-1 part of dispersant, and 0.5-1.2 parts of heat stabilizer.

[0026] Within the specified amounts of raw materials used in the inner layer of this application, the proportions of hydrogen-containing silicone oil crosslinking agent and platinum catalyst ensure sufficient crosslinking within the inner heat-shrinkable silicone layer, resulting in good thermal stability. The amount of flame retardant balances the flame-retardant effect and flexibility of the heat-shrinkable tubing. Within the specified amounts of raw materials used in the outer layer, the proportions of hydrogen-containing silicone oil crosslinking agent and platinum catalyst ensure sufficient crosslinking reaction, while maintaining synchronization with the inner layer to avoid poor bonding between the outer and inner layers. The modified ceramic micropowder in the outer layer comprises 80-150 parts by weight, providing sufficient ceramicization components to facilitate the formation of a dense ceramic shell during combustion, while also avoiding the problems of reduced flexibility and processing difficulties caused by excessive dosage. This specific formulation and proportion maximize the overall performance of the composite ceramicized heat-shrinkable tubing of this application, resulting in strong bonding between the inner and outer layers. Furthermore, the composite ceramicized heat-shrinkable tubing of this application exhibits excellent high-temperature resistance, flame retardancy, and mechanical strength.

[0027] A second aspect of the present invention provides a method for preparing a composite ceramicized heat shrink tubing according to the first aspect of the present invention, comprising the following steps: S1. Mixing: The inner layer raw materials and the outer layer raw materials are mixed separately in an internal mixer to obtain the inner layer compound and the outer layer compound. S2. Co-extrusion: The inner layer compound and the outer layer compound are respectively added to a double-layer co-extrusion equipment and extruded through a concentric double-layer composite die to obtain a tube blank; S3. Vulcanization: The tube blank is subjected to continuous hot air vulcanization; S4. Irradiation crosslinking: The vulcanized tube blank is subjected to electron beam irradiation; S5. Expansion and shaping: The irradiated tube blank is heated and radially expanded under vacuum conditions, and then cooled to obtain the composite ceramicized heat shrink tube.

[0028] Preferably, in step S1, the mixing temperature is 60-70°C, the mixing speed is 30-40 rpm, and the mixing time is 20-25 min. More preferably, in step S1, the mixing temperature is 65-70°C, the mixing speed is 35-40 rpm, and the mixing time is 20-25 min. Even more preferably, in step S1, the mixing temperature is 67-70°C, the mixing speed is 35-40 rpm, and the mixing time is 25 min.

[0029] Preferably, in step S2, the temperature of the extrusion feed section is 60-70℃, the temperature of the extrusion compression section is 70-85℃, the temperature of the extrusion homogenization section is 85-100℃, the temperature of the extrusion die head is 100-110℃, the screw speed of the extrusion is 15-25 rpm, and the extrusion speed is 2-4 m / min. More preferably, in step S2, the temperature of the extrusion feed section is 65-70℃, the temperature of the extrusion compression section is 75-85℃, the temperature of the extrusion homogenization section is 90-100℃, the temperature of the extrusion die head is 105-110℃, the screw speed of the extrusion is 20-25 rpm, and the extrusion speed is 2-4 m / min.

[0030] Preferably, in step S3, the vulcanization temperature is 140~150℃, and the vulcanization time is 8~12 min. More preferably, in step S3, the vulcanization temperature is 145~150℃, and the vulcanization time is 10~12 min.

[0031] Preferably, in step S4, the irradiation dose is 80-150 kGy. More preferably, in step S4, the irradiation dose is 90-150 kGy.

[0032] Preferably, in step S5, the expansion temperature is 90~110℃, the expansion vacuum degree is -0.06~-0.08MPa, and the expansion ratio is 2.5~3.5 times. More preferably, in step S5, the expansion temperature is 100~110℃, the expansion vacuum degree is -0.07~-0.08MPa, and the expansion ratio is 2.5~3.5 times.

[0033] In the above technical solution, the preparation steps of mixing, co-extrusion, vulcanization, irradiation, and expansion synergistically achieve uniform dispersion in mixing, interfacial fusion in co-extrusion, and sufficient cross-linking in vulcanization. In step S1, the mixing temperature of 60~70℃ softens the vinyl silicone rubber matrix and promotes the wetting of other raw materials. This temperature is lower than the initial reaction temperature of the platinum vulcanization system, which also effectively avoids early vulcanization of the rubber compound during the mixing process, ensuring processing safety. Furthermore, mixing at a speed of 30~40 rpm ensures uniform dispersion of each component and reduces agglomeration. Step S2 employs a gradient temperature co-extrusion process, gradually increasing from the feed section to the die head. This ensures good rheological properties of the inner and outer layers at the composite die head, achieving excellent fusion of the inner and outer melt interfaces and initially forming a dense, well-bonded double-layer composite tube blank. Simultaneously, a screw speed of 15-25 rpm helps reduce shear heat generation, mitigating the risk of localized pre-vulcanization. It also reduces surface damage or agglomeration of the modified ceramic micropowder in the outer layer raw material, ensuring stable co-extrusion. Step S3, at 140-150°C, involves a hydrosilylation vulcanization reaction between the Si-H bonds of the hydrogen-containing silicone oil and the C=C bonds of the vinyl silicone rubber, catalyzed by a platinum catalyst. This results in sufficient cross-linking, forming a stable three-dimensional network structure. Under these conditions, the problems of poor mechanical strength and heat shrinkability in heat shrink tubing caused by insufficient cross-linking are avoided. In step S4, electron beam irradiation causes free radical cross-linking of the vinyl silicone rubber molecular chains, which further forms a denser network structure on the basis of the original vulcanization cross-linking, thereby improving the thermal stability, mechanical strength, and heat shrinkage memory of the heat shrink tubing. In step S5, at a temperature of 90~110℃ and a vacuum of -0.06~-0.08MPa, the tube blank is in a highly elastic state, and its tube wall is heated uniformly, allowing it to expand smoothly. The entire process is closely linked and works synergistically, ultimately resulting in a composite ceramicized heat shrink tubing with a double-layer structure that possesses excellent mechanical properties, heat shrinkage reliability, and high-temperature fire resistance.

[0034] The third aspect of this application provides the application of a composite ceramicized heat shrink tubing in insulating, protective, and flame-retardant materials, wherein the composite ceramicized heat shrink tubing is the aforementioned composite ceramicized heat shrink tubing, or is prepared by the aforementioned method.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects: 1) The composite ceramicized heat shrink tubing of this application comprises an inner layer and an outer layer integrally composited by co-extrusion molding from the inside out; wherein, the inner layer is a heat-shrinkable silicone layer, the raw materials of which include vinyl silicone rubber, hydrogen-containing silicone oil crosslinking agent, platinum catalyst, heat stabilizer, flame retardant and colorant; the outer layer is a ceramicized silicone layer, the raw materials of which include vinyl silicone rubber, modified ceramic micro powder, hydrogen-containing silicone oil crosslinking agent, platinum catalyst, dispersant and heat stabilizer; the modified ceramic micro powder is obtained by surface modification treatment of alumina-silica composite micro powder with silane coupling agent. Through the reasonable proportion of each raw material component, the resulting composite ceramicized heat shrink tubing has excellent mechanical properties, heat shrink reliability, insulation and high-temperature fire resistance.

[0036] 2) In the preparation method of the composite ceramicized heat shrink tubing of this application, the composite ceramicized heat shrink tubing is obtained through the steps of mixing, co-extrusion, vulcanization, irradiation, and expansion. This preparation method has simple steps, does not require complex equipment, is suitable for large-scale production, and helps to form uniform and stable composite ceramicized heat shrink tubing. Detailed Implementation

[0037] The present invention will be further described in detail below through specific embodiments, comparative examples and tables, but is not limited to all the discussions and data.

[0038] Vinyl silicone rubber was purchased from Wacker Chemie AG, model VQM 110-2, with a vinyl content of 0.15%~0.3%; hydrogen-containing silicone oil crosslinking agent was purchased from Dow Corning, model MHX-1107, with an active hydrogen content of 1.6% by weight; platinum catalyst was purchased from Shenzhen Tianqi New Materials Technology Co., Ltd., model SK-P050, with a platinum content of 5000ppm by weight; nano iron oxide and nano cerium oxide were purchased from Aladdin Reagent, with a particle size of 50nm; magnesium hydroxide was purchased from Shandong Laiyu Chemical Co., Ltd., with a particle size of 4±1μm; carbon black colorant was purchased from Cabot Chemical Company, model VXC72; alumina-silica composite powder was purchased from Shanghai Xiangtian Nanomaterials Co., Ltd., with a particle size of 5μm, of which alumina accounted for 87% by mass; zinc stearate, calcium stearate, and γ-methacryloyloxypropyltrimethoxysilane were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] It is particularly important to emphasize that, unless otherwise specified, the raw materials, reagents or devices used in this invention can be obtained from conventional commercial sources.

[0040] Preparation Example 1: Preparation of Modified Ceramic Micropowder The preparation method of a modified ceramic micro powder has the following steps: The alumina-silica composite micro powder was dried in an oven at 110℃ for 2 hours. 100g of the alumina-silica composite micro powder and 3g of γ-methacryloyloxypropyltrimethoxysilane were weighed and added to 100g of an ethanol aqueous solution with a volume ratio of 9:1. The solution was heated and stirred in a water bath at 65℃ for 2.5 hours. The mixture was filtered, and the filter cake was washed with a small amount of anhydrous ethanol. The filter cake was transferred to an oven and dried at 110℃ for 3 hours. The mixture was then passed through a 200-mesh sieve, and the sieve-passing material was collected to obtain the modified ceramic micro powder.

[0041] Preparation of Comparative Example 1: Preparation of Modified Ceramic Micropowder The preparation method of a modified ceramic micro powder has the following steps: The alumina-silica composite micro powder was dried in an oven at 110℃ for 2 hours. 100g of alumina-silica composite micro powder and 5g of γ-methacryloyloxypropyltrimethoxysilane were weighed and added to 100g of an ethanol aqueous solution with a volume ratio of 9:1. The solution was heated and stirred in a water bath at 65℃ for 2.5 hours. The solution was filtered, and the filter cake was washed with a small amount of anhydrous ethanol. The filter cake was transferred to an oven and dried at 110℃ for 3 hours. The solution was passed through a 200-mesh sieve, and the sieve-passing material was collected to obtain the modified ceramic micro powder.

[0042] Examples of composite ceramicized heat shrink tubing: A composite ceramicized heat shrink tubing is prepared by the following steps: S1. Mixing: The inner layer raw materials (100g vinyl silicone rubber, 1.5~3g hydrogen-containing silicone oil crosslinking agent, 5~18g platinum catalyst, 0.8~1.5g heat stabilizer, 1~30g flame retardant, 0.5~2g colorant) and the outer layer raw materials (100g vinyl silicone rubber, 80~150g modified ceramic micro powder, 1~2.5g hydrogen-containing silicone oil crosslinking agent, 7~20g platinum catalyst, 0.5~1g dispersant, 0.5~1.2g heat stabilizer) are mixed in an internal mixer at a temperature of 60~70℃ and a speed of 30~40 rpm for 20~25 minutes to obtain the inner layer compound and the outer layer compound. S2. Co-extrusion: The temperature of the feeding section of the double-layer co-extrusion equipment is set to 60~70℃, the temperature of the compression section to 70~85℃, the temperature of the homogenization section to 85~100℃, the temperature of the die head to 100~110℃, the screw speed to 15~25 rpm, and the extrusion speed to 2~4 m / min. The inner layer compound and the outer layer compound are added to the double-layer co-extrusion equipment respectively, and extruded through a concentric double-layer composite die to obtain a double-layer composite tube blank. S3. Vulcanization: The tube blank is continuously vulcanized with hot air, wherein the vulcanization temperature is 140~150℃ and the vulcanization time is 8~12min; S4. Irradiation crosslinking: The vulcanized tube blank is irradiated with an electron beam, wherein the irradiation dose is 80~150kGy; S5. Expansion and shaping: The irradiated tube blank is heated at 90~110℃ and radially expanded under vacuum conditions of -0.06~-0.08MPa, with an expansion ratio of 2.5~3.5 times. After cooling, the composite ceramic heat shrink tube is obtained.

[0043] Regarding step S1, in some specific embodiments, the vinyl molar content of the vinyl silicone rubber can be 0.15%, 0.2%, 0.25%, or 0.3%; the active hydrogen weight content of the hydrogen-containing silicone oil crosslinking agent can be 0.5%, 0.9%, 1.2%, 1.5%, or 1.8%; the platinum weight content of the platinum catalyst can be 4000 ppm, 4500 ppm, or 5500 ppm; the heat stabilizer can be selected from at least one of nano-iron oxide, nano-cerium oxide, and nano-zinc oxide, and its particle size is 45-60 nm; the heat stabilizer can be a compound of nano-iron oxide and nano-cerium oxide in a weight ratio of 2:4, 2.5:3.2, 3:2.6, or 3:1.2, and its particle size can be 50 nm, 55 nm, or 60 nm. The flame retardant can be selected from at least one of magnesium hydroxide, aluminum hydroxide, nano-montmorillonite, zinc borate, and antimony trioxide, and its particle size can be 1 μm, 5 μm, or 10 μm. The modified ceramic micropowder is obtained by surface modification of alumina-silica composite micropowder with a silane coupling agent. The dispersant can be selected from at least two of zinc stearate, calcium stearate, and stearamide. The dispersant can be a mixture of zinc stearate and calcium stearate, wherein the weight ratio of zinc stearate to calcium stearate in the mixture can be 1:1, 2:1, or 3:1. Regarding step S1, in some specific embodiments, the mixing temperature can be 60℃, 65℃, or 70℃, the mixing speed can be 30 rpm, 35 rpm, or 40 rpm, and the mixing time can be 20 min, 23 min, or 25 min.

[0044] Regarding step S2, in some specific implementations, the temperature of the feeding section of the double-layer co-extrusion equipment can be 60℃, 65℃, or 70℃; the temperature of the compression section can be 70℃, 72℃, 80℃, or 85℃; the temperature of the homogenization section can be 85℃, 90℃, or 100℃; the die head temperature can be 100℃, 105℃, 108℃, or 110℃; the screw speed can be 15, 20 rpm, or 25 rpm; and the extrusion speed can be 2m / min, 3m / min, or 4m / min.

[0045] For step S3, in some specific implementations, the vulcanization temperature can be 140°C, 145°C or 150°C, and the vulcanization time can be 8 min, 10 min or 12 min.

[0046] Regarding step S4, in some specific implementations, the irradiation dose can be 80 kGy, 100 kGy, 120 kGy, or 150 kGy.

[0047] Regarding step S5, in some specific implementations, the expansion temperature can be 90℃, 100℃ or 110℃, the expansion vacuum degree can be -0.06MPa, -0.07MPa or -0.08MPa, and the expansion ratio can be 2.5 times, 3 times or 3.5 times. Example 1

[0048] A composite ceramicized heat shrink tubing is prepared by the following steps: S1. Mixing: The inner layer raw materials: 100g vinyl silicone rubber, 2g hydrogen-containing silicone oil crosslinking agent, 10g platinum catalyst, 1.2g nano iron oxide and nano cerium oxide (heat stabilizer) in a weight ratio of 1:1, 16g magnesium hydroxide (flame retardant), and 1g colorant; the outer layer raw materials: 100g vinyl silicone rubber, 100g modified ceramic micro powder of Preparation Example 1, 1.5g hydrogen-containing silicone oil crosslinking agent, 15g platinum catalyst, 0.8g zinc stearate and calcium stearate (dispersant) in a weight ratio of 2:1, and 1g nano iron oxide and nano cerium oxide (heat stabilizer) in a weight ratio of 1:1 are mixed in an internal mixer at a temperature of 65°C and a speed of 35rpm for 25min to obtain the inner layer compound and the outer layer compound. S2. Co-extrusion: The temperature of the feeding section of the double-layer co-extrusion equipment is set to 65℃, the temperature of the compression section to 80℃, the temperature of the homogenization section to 90℃, the temperature of the die head to 105℃, the screw speed to 20rpm, and the extrusion speed to 3m / min. The inner layer compound and the outer layer compound are added to the double-layer co-extrusion equipment and extruded through a concentric double-layer composite die to obtain a double-layer composite tube blank. S3. Vulcanization: The tube blank is subjected to continuous hot air vulcanization, wherein the vulcanization temperature is 145℃ and the vulcanization time is 10min; S4. Irradiation crosslinking: The vulcanized tube blank is irradiated with an electron beam at a dose of 120 kGy; S5. Expansion and shaping: The irradiated tube blank is heated at 100°C and radially expanded under a vacuum of -0.07MPa with an expansion ratio of 3 times. After cooling, the composite ceramic heat shrink tube is obtained. Example 2

[0049] The preparation method of a composite ceramic heat shrink tubing is the same as in Example 1, except that in Example 2, the amount of hydrogen-containing silicone oil crosslinking agent in the inner layer raw material is changed to 1.5g. Example 3

[0050] The preparation method of a composite ceramic heat shrink tubing is the same as in Example 1, except that in Example 3, the amount of hydrogen-containing silicone oil crosslinking agent in the inner layer raw material is changed to 3g. Example 4

[0051] The preparation method of a composite ceramicized heat shrink tubing is the same as in Example 1, except that the amount of modified ceramic micro powder from Example 1 used in the outer layer raw material of Example 4 is changed to 80g. Example 5

[0052] The preparation method of a composite ceramicized heat shrink tubing is the same as in Example 1, except that the amount of modified ceramic micro powder from Example 1 used in the outer layer raw material of Example 5 is changed to 130g. Example 6

[0053] The preparation method of a composite ceramic heat shrink tubing is the same as in Example 1, except that the amount of heat stabilizer in the outer layer raw material of Example 6 is changed to 0.6g. Example 7

[0054] The preparation method of a composite ceramic heat shrink tubing is the same as in Example 1, except that the amount of heat stabilizer in the outer layer raw material of Example 7 is changed to 1.2g.

[0055] Comparative Example 1: The preparation method of a composite ceramic heat shrink tubing is the same as in Example 1, except that the amount of hydrogen-containing silicone oil crosslinking agent in the inner layer raw material of Comparative Example 1 is changed to 4g.

[0056] Comparative Example 2: The preparation method of a composite ceramicized heat shrink tubing is the same as in Example 1, except that the amount of modified ceramic micro powder used in the outer layer raw material of Comparative Example 2 is changed to 70g.

[0057] Comparative Example 3: The preparation method of a composite ceramicized heat shrink tubing is the same as that of Example 1, except that the modified ceramic micro powder of Example 1 in the outer layer raw material of Comparative Example 3 is replaced by the modified ceramic micro powder of Comparative Example 1.

[0058] Comparative Example 4: The preparation method of a composite ceramicized heat shrink tubing is the same as in Example 1, except that the modified ceramic micro powder in the outer layer raw material of Comparative Example 4 is replaced in equal amounts with unmodified ceramic micro powder, namely alumina-silica composite micro powder.

[0059] Comparative Example 5: The preparation method of a composite ceramic heat shrink tubing is the same as in Example 1, except that the amount of heat stabilizer in the outer layer raw material of Comparative Example 5 is changed to 1.4g.

[0060] Material performance testing: The composite ceramicized heat shrink tubing obtained in Examples 1-7 and Comparative Examples 1-5 were subjected to various performance tests, and the test methods are as follows: 1. Inner layer thickness and outer layer thickness: tested using a digital micrometer.

[0061] 2. Tensile strength and elongation at break: Tested in accordance with GB / T 528-2009 standard.

[0062] 3. High-temperature (300℃) insulation volume resistivity: Referring to GB / T 3048.5-2007 "Test Methods for Electrical Properties of Wires and Cables Part 5: Insulation Resistance Test", a 10 cm long heat-shrink tubing is placed on a clean copper rod, heated to shrink it tightly, and then placed in a 300℃ oven for 30 minutes. Using a high-resistivity meter at 500V DC, the volume resistance R between the copper rod and the ring electrode wrapped around it in close contact is measured. The volume resistivity ρ (Ω·cm) is calculated according to the following formula: ρ = 2πL·R / In(D / d), where L is the effective contact length of the ring electrode (cm), D is the outer diameter of the heat shrink tubing (cm), and d is the diameter of the copper rod (cm).

[0063] 4. Flame retardancy rating: Tested according to UL-94.

[0064] 5. Self-extinguishing time of 750℃ flame: A 750℃ flame is sprayed onto the sample and held for 30 seconds before being removed. The time it takes for the sample to self-extinguish after the flame is removed is recorded.

[0065] 6. Tensile strength retention rate after heat aging: Place the sample in a 200℃ heat aging chamber for 168 hours, remove it and cool it to room temperature. Test the tensile strength according to the tensile strength test method. Calculate the tensile strength retention rate after heat aging using the following formula: Tensile strength value after aging / Tensile strength value before aging × 100%. The larger the value, the better the heat aging resistance.

[0066] The test performance of the composite ceramicized heat shrink tubing of Examples 1-7 and Comparative Examples 1-5 is shown in Table 1 below:

[0067] The composite ceramicized heat shrink tubing in Examples 1-7 comprises an inner layer and an outer layer integrally composited by co-extrusion molding from the inside out. The inner layer is a heat-shrinkable silicone layer, and the outer layer is a ceramicized silicone layer. By controlling the specific components and proportions of the raw materials for the inner and outer layers, especially the modified ceramic micropowder in the outer layer raw material, the resulting composite ceramicized heat shrink tubing possesses excellent mechanical properties, insulation, high-temperature fire resistance, and thermal stability. Its tensile strength is ≥11.2 MPa, elongation at break is ≥250%, and volume resistivity at 300℃ is ≥5.2 × 10⁻⁶. 13With a flame retardancy rating of V-0 or V-1, a flame self-extinguishing time of ≤7s at 750℃, and a tensile strength retention rate of ≥91% after thermal aging, it fully meets the stringent requirements for conductive busbar insulation and protection materials in fields such as new energy batteries and power transmission.

[0068] Compared with Example 1, Comparative Example 1 was prepared using the same method, except that the amount of hydrogen-containing silicone oil crosslinking agent in the inner layer material was changed to 4g, exceeding the range specified in this application. The results showed that although the tensile strength of Comparative Example 1 increased to 12.9MPa, its elongation at break decreased significantly, and the tensile strength retention rate after heat aging was only 86%. This may be because the excessive crosslinking agent in the inner layer material resulted in an excessively high crosslinking density, causing stress concentration within the silicone rubber matrix and a significant decrease in flexibility. Simultaneously, excessive crosslinking enhanced the rigidity of the molecular chains, making them prone to chain segment breakage during heat aging and leading to a decline in heat aging resistance.

[0069] In Comparative Example 2, the amount of modified ceramic micropowder used in the outer layer was reduced to 70g. The results showed that its flame retardant rating was reduced to V-2, the self-extinguishing time at 750℃ was >30s, and the volume resistivity at 300℃ was only 2.1×10⁻⁶. 13 Ω·cm. This may be because the insufficient amount of modified ceramic micropowder prevents the formation of a continuous ceramic skeleton on the outer layer of the heat shrink tubing, resulting in its inability to block the transfer of heat and oxygen at high temperatures, thus causing the flame retardant to fail. At the same time, as an inorganic filler, its reinforcing effect also decreases, increasing the spacing between insulating particles and making it easier for charges to migrate, so its insulation performance drops sharply at high temperatures.

[0070] Compared with Example 1, Comparative Example 3 differs in that the modified ceramic powder of Preparation Example 1 in the outer layer of Comparative Example 3 is replaced by an equal amount of the modified ceramic powder of Preparation Example 1, while the silane coupling agent used in the preparation of the modified ceramic powder of Preparation Example 1 is excessive. Compared with Example 1, Comparative Example 4 differs in that the modified ceramic powder of Preparation Example 1 in the outer layer of Comparative Example 4 is replaced by an equal amount of unmodified ceramic powder, i.e., alumina-silica composite powder. The results show that the flame retardant rating of Comparative Example 3 is V-1, and the self-extinguishing time is 16s; the tensile strength of Comparative Example 4 is only 8.9MPa, and the volume resistivity at 300℃ is 1.0×10⁻⁶. 12 The flame retardant test failed due to direct combustion (Ω·cm). This may be because excessive silane coupling agent during the preparation of modified ceramic micropowder leads to the easy aggregation of organic groups on the surface of the modified ceramic micropowder, while the compatibility between the unmodified ceramic micropowder and the silicone rubber matrix deteriorates. These factors result in uneven dispersion of the micropowder in the system, making it impossible to synergistically form a dense ceramicized silicone layer at high temperatures. The increase in internal defects in the matrix also leads to a decrease in the mechanical and insulation properties of the heat shrink tubing.

[0071] Comparative Example 5 differs from Example 1 in that the amount of heat stabilizer in the outer layer of Comparative Example 5 is changed to 1.4g. The results show that the tensile strength retention rate of Comparative Example 5 after heat aging is reduced to 87%. This may be because when the heat stabilizer is excessive, the agglomeration phenomenon between particles is more obvious, and the internal uniform dispersion effect is poor, which leads to a significant decrease in the heat aging performance of its heat shrink tubing.

[0072] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A composite ceramicized heat shrink tubing, characterized in that, It includes an inner layer and an outer layer that are integrally composited through co-extrusion molding from the inside out; The inner layer is a heat-shrinkable silicone layer, the raw materials of which include vinyl silicone rubber, hydrogen-containing silicone oil crosslinking agent, platinum catalyst, heat stabilizer, flame retardant and colorant. The outer layer is a ceramicized silicone layer, the raw materials of which include vinyl silicone rubber, modified ceramic micro powder, hydrogen-containing silicone oil crosslinking agent, platinum catalyst, dispersant and heat stabilizer; The modified ceramic micro powder is obtained by surface modification treatment of alumina-silica composite micro powder with silane coupling agent.

2. The composite ceramicized heat shrink tubing according to claim 1, characterized in that, The thickness ratio of the inner layer to the outer layer is 1:(1~1.5).

3. The composite ceramicized heat shrink tubing according to claim 1, characterized in that, The silane coupling agent is selected from at least one of γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

4. The composite ceramicized heat shrink tubing according to claim 1, characterized in that, The alumina-silica composite micro powder has a particle size of 3~8μm, and the mass ratio of alumina in the alumina-silica composite micro powder is 60%~90%.

5. The composite ceramicized heat shrink tubing according to claim 1, characterized in that, The vinyl molar content of the vinyl silicone rubber is 0.15% to 0.3%.

6. The composite ceramicized heat shrink tubing according to claim 1, characterized in that, The active hydrogen content of the hydrogen-containing silicone oil crosslinking agent is 0.5%~1.8% by weight; And / or, the platinum catalyst has a platinum content of 4000~5500 ppm by weight; And / or, the heat stabilizer is selected from at least one of nano iron oxide, nano cerium oxide, and nano zinc oxide, and its particle size is 45~60nm; And / or, the dispersant is selected from at least two of zinc stearate, calcium stearate, and stearamide; And / or, the flame retardant is selected from at least one of magnesium hydroxide, aluminum hydroxide, nano-montmorillonite, zinc borate, and antimony trioxide, and its particle size is 1~10μm.

7. The composite ceramicized heat shrink tubing according to any one of claims 1 to 6, characterized in that, The raw materials of the inner layer include the following components in parts by weight: 100 parts vinyl silicone rubber, 1.5 to 3 parts hydrogen-containing silicone oil crosslinking agent, 5 to 18 parts platinum catalyst, 0.8 to 1.5 parts heat stabilizer, 1 to 30 parts flame retardant, and 0.5 to 2 parts colorant; The outer layer comprises the following components by weight: 100 parts vinyl silicone rubber, 80-150 parts modified ceramic micro powder, 1-2.5 parts hydrogen-containing silicone oil crosslinking agent, 7-20 parts platinum catalyst, 0.5-1 part dispersant, and 0.5-1.2 parts heat stabilizer.

8. A method for preparing a composite ceramicized heat shrink tubing as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Mixing: The inner layer raw materials and the outer layer raw materials are mixed separately in an internal mixer to obtain the inner layer compound and the outer layer compound. S2. Co-extrusion: The inner layer compound and the outer layer compound are respectively added to a double-layer co-extrusion equipment and extruded through a concentric double-layer composite die to obtain a tube blank; S3. Vulcanization: The tube blank is subjected to continuous hot air vulcanization; S4. Irradiation crosslinking: The vulcanized tube blank is subjected to electron beam irradiation; S5. Expansion and shaping: The irradiated tube blank is heated and radially expanded under vacuum conditions, and then cooled to obtain the composite ceramicized heat shrink tube.

9. The method for preparing the composite ceramicized heat shrink tubing according to claim 8, characterized in that, In step S3, the vulcanization temperature is 140~150℃ and the vulcanization time is 8~12min; in step S4, the irradiation dose is 80~150kGy; in step S5, the expansion temperature is 90~110℃, the expansion vacuum degree is -0.06~-0.08MPa, and the expansion ratio is 2.5~3.5 times.

10. The application of a composite ceramicized heat shrink tubing as described in any one of claims 1 to 7, or a composite ceramicized heat shrink tubing prepared by the preparation method as described in any one of claims 8 to 9, in insulating, protective, and flame-retardant materials.

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