A self-limiting temperature heating belt and its preparation process

Abstract

The invention relates to the technical field of electric heating belts, and provides a self-limiting temperature heating belt and a preparation process thereof, which solve the problem that the heating belt prepared by the prior art does not have the function of self-limiting temperature and the cost of raw materials is high; the invention comprises a self-limiting temperature heating belt body, the self-limiting temperature heating belt body comprises a metal conductor core, a self-limiting temperature graphene conductive layer, a metal wire mesh shielding layer, an isolation layer, and a sheath layer which are sequentially arranged from the inside to the outside, the self-limiting temperature graphene conductive layer comprises the following raw materials in parts by weight: 5-10 parts by weight of conductive particles, 70-90 parts by weight of polymer-based PTC self-limiting temperature material, 10-20 parts by weight of cationic nanocellulose, and 20-30 parts by weight of solvent; the polymer-based PTC self-limiting temperature material comprises: a skeleton support material and a temperature control material.

Description

Technical Field

[0001] The invention relates to the technical field of heating belts, in particular to a self-limiting temperature heating belt and a preparation process thereof. Background Art

[0002] The research on heating belt electric ice melting system is a new technology that can melt ice efficiently without affecting the normal working load of the system. The uniformity and controllability of temperature during the heat treatment process cannot be ignored.

[0003] PTC material is a thermistor material with a positive temperature coefficient effect. When the temperature is low, the resistance value of the material remains basically unchanged within a certain range. When the temperature reaches a certain value, its resistance value suddenly increases with the increase of temperature, usually in a very small temperature range (a few degrees Celsius to more than ten degrees Celsius) Rapidly increase to 10 of the original 3 -10 5 times, and this specific temperature is called the Curie temperature. Then it will reach a certain PTC effect termination point, at which time the resistivity remains stable or increases slowly. The difference in logarithmic resistivity between the PTC effect termination temperature and the Curie temperature is defined as the PTC strength of the material.

[0004] Chinese patent publication number CN116916477B discloses an amorphous thermal superconducting heating belt and a preparation method. The heating belt includes an electric heating layer, an insulating layer, and a protective layer; the insulating layer is coated on the outside of the electric heating layer; the protective layer is coated on the outside of the insulating layer; the electric heating layer is made of amorphous alloy material; the material of the protective layer includes the following components by weight: 60-75 parts of methyl vinyl silicone rubber, 25-45 parts of ethylene-vinyl acetate copolymer, 1-2 parts of vulcanizing agent, 0.5-1 parts of vulcanization accelerator, 1-2 parts of activator, 20-25 parts of filler, 1-2 parts of antioxidant, 3-6 parts of plasticizer, 3-4 parts of calcium para-aminosalicylate and 6-8 parts of zinc stearate. Through the above technical solution, the problem of low heat resistance and mechanical properties of the heating belt in the prior art is solved. However, the heating belt does not have the function of PTC self-limiting temperature, and the problem of excessive local temperature is prone to occur.

[0005] Chinese patent publication number CN113056044B discloses a graphene metal mesh and a preparation method thereof, as well as an electric heating belt and an application thereof. The graphene metal mesh first adds 81.2%-91.2% of nickel-chromium alloy heating wire, 17.0%-17.9% of industrial nickel powder and 1.74%-1.81% of platinum powder into a smelting furnace, and is smelted into a metal liquid at a high temperature of 1600°C. The metal liquid is then stirred and poured into a film pressing machine to press a film belt at 1100°C-1200°C; the pressed film belt is then subjected to chemical high-temperature oxidation for 3min-5min, cooled until it recovers its toughness, and then the graphene paste is evenly applied to the film belt, and the pressing is repeated for multiple times until the film belt is gray-black; finally, the obtained film belt is mesh-cut and pressed according to demand, and at least two graphene metal meshes are sandwiched between two layers of silicone rubber-coated carbon fiber cloth, and used as an electric heating belt for deicing and defrosting drainage pipes in plateau railway tunnels. The electric heating belt of the invention has the advantages of ultra-thinness, high and low temperature resistance, good toughness and insulation, high heat conversion rate and long service life. However, this method has high requirements on production equipment and a complicated process. Summary of the invention

[0006] Therefore, in view of the above problems, the present invention provides a self-limiting temperature heat-generating belt and a preparation process thereof, which solves the problem that the heat-generating belt prepared by the prior art does not have the self-limiting temperature function and has high production raw material costs.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A self-limiting temperature heat-generating belt comprises a self-limiting temperature heat-generating belt body, wherein the self-limiting temperature heat-generating belt body comprises a metal conductor core, a self-limiting temperature graphene conductive layer, a metal wire mesh shielding layer, an isolation layer and a sheath layer which are sequentially arranged from the inside to the outside, wherein the self-limiting temperature graphene conductive layer comprises the following raw materials in parts by weight: 5-10 parts by weight of conductive particles, 70-90 parts by weight of a polymer-based PTC self-limiting temperature material, 10-20 parts by weight of cationic nanocellulose and 20-30 parts by weight of a solvent; the polymer-based PTC self-limiting temperature material comprises: a skeleton support material and a temperature control material; the weight ratio of the skeleton support material to the temperature control material is 1:2.5-1:4; the skeleton support material is one of ethylene-vinyl acetate, water-based acrylic resin, high-density polyethylene, low-density polyethylene and linear low-density polyethylene, or a mixture of at least two of them in equal proportions; and the temperature control material is any one of modified tetradecanoic acid, n-decanoic acid, lauric acid and n-tetracosane.

[0009] Furthermore, the preparation method of the self-limiting temperature graphene conductive layer is:

[0010] a. Preparation of conductive particle dispersion: Weigh conductive particles and solvent by weight, stir and mix evenly, let stand for 24h-36h, filter, wash with deionized water 3-5 times, perform vacuum distillation and then dry, then add 2-5 parts by weight of polyvinyl pyrrolidone and 2-5 parts by weight of 1-methyl-2-pyrrolidone, stir and mix evenly, perform water bath ultrasound, and obtain conductive particle dispersion;

[0011] b. stirring and mixing the conductive particle dispersion and cationic nanocellulose uniformly, pouring into a Buchner funnel with a polytetrafluoroethylene filter membrane after water bath ultrasonic treatment, filtering, and drying to obtain a solid mixture;

[0012] c. Preparation of polymer-based PTC self-limiting temperature material: weigh the skeleton support material and the temperature control material by weight, add 20-30 parts by weight of xylene solution, heat to 60°C-80°C, stir and mix evenly, perform homogeneous dispersion treatment, and obtain a mixed solution;

[0013] d. Add the solid mixture treated in step b to the mixed solution obtained in step c, continue to stir evenly at 60° C.-80° C., and then perform water bath ultrasonic treatment to obtain a preliminary finished sample;

[0014] e. Put the above-mentioned sample preliminary product into a mold, press it into a film, and then perform two heat treatments to obtain the self-limiting temperature graphene conductive layer.

[0015] Furthermore, the preparation method of the modified myristic acid is:

[0016] 1) Weighing Ni powder in a ratio of Ni powder to tetradecanoic acid of 3:8-3:10, adding anhydrous ethanol in a ratio of Ni powder to anhydrous ethanol of 1:3-1:5, stirring and mixing, then performing water bath ultrasonic treatment, drying, and obtaining a first mixture for standby use;

[0017] 2) Weighing stearic acid and myristic acid in a mass ratio of 1:2-2:3, adding anhydrous ethanol and stirring under a water bath, performing a homogenous dispersion treatment, and then performing a water bath ultrasonic treatment to obtain a first mixed solution;

[0018] 3) The first mixture obtained in step 1) is added to the first mixed solution obtained in step 2) and ball milled to obtain the modified myristic acid.

[0019] Furthermore, the conductive particles are any one of acetylene black, graphite, graphene, carbon nanotubes and carbon fibers; and the solvent is petroleum ether or acetone.

[0020] Furthermore, the metal conductor core is composed of a plurality of copper wires; the raw material of the metal wire mesh shielding layer is copper wire, which is formed by warp and weft plain weaving; the raw material of the isolation layer is ultraviolet light cross-linked polyethylene; and the raw material of the sheath layer is polyurethane.

[0021] Furthermore, the process of the two heat treatments is: first, in a vacuum oven at 60°C-80°C, holding time is 60min-90min, after cooling to room temperature, the temperature is increased to 100°C-120°C, the heating rate is 2°C / min, and the holding time is 120min-150min.

[0022] Furthermore, the pressing is carried out in a film pressing machine at a pressure of 0.3MPa-0.5MPa, and the thickness of the self-limiting temperature graphene conductive layer after pressing is 5mm-7mm.

[0023] Furthermore, the frequency of the water bath ultrasound is 30Hz-40Hz, and the time is 10min-20min; the stirring is magnetic stirring, the speed is 100r / min-120r / min, and the time is 10min-30min; the drying is carried out in a vacuum drying oven, the temperature is 60℃-80℃, and the time is 2h-4h; the ball milling treatment is carried out in a ball mill, the speed is 200r / min-400r / min, and the time is 4h-5h; the homogenization dispersion is carried out in a disperser homogenizer, and the speed is 1000r / min-1200r / min.

[0024] Furthermore, the particle size of the Ni powder is 2 m m-2.5 m m.

[0025] A preparation process of a self-limiting temperature heat-generating belt comprises the following steps:

[0026] S1. twisting a plurality of copper wires into a metal conductor core by a twisting device, wherein the cross section of the metal conductor core is circular;

[0027] S2, coating the self-limiting temperature graphene conductive layer on the metal conductor core to form a preliminary finished product of a self-limiting temperature heat-generating belt;

[0028] S3, sequentially covering the self-limiting temperature heat-generating belt with a metal wire mesh shielding layer, an isolation layer, and a sheath layer to obtain a self-limiting temperature heat-generating belt.

[0029] By adopting the above technical solution, the beneficial effects of the present invention are:

[0030] 1. The present invention forms a eutectic between the skeleton support material and the temperature control material to improve the overall material crystallinity, so that the prepared self-limiting temperature heat-generating belt PTC has higher self-limiting strength, can withstand higher temperatures, has better thermal stability, can generate heat stably for a long time and keep the heat-generating belt at 40°C-50°C (Curie temperature), and does not need to install an anti-overheating device, so as to avoid the problem that the local temperature is too high and affects the service life, mechanical properties and electrical properties of the heat-generating belt; and can make the heat-generating belt flexible and adaptable to road surfaces in different conditions; the traditional self-limiting temperature heat-generating belt has a high Curie temperature (above 50°C, generally 90°C-110°C), and the room temperature resistivity of the material is also high, so a larger starting voltage and higher energy consumption are required. The heat-generating belt prepared by the present invention has a Curie temperature of 40°C-50°C, which can reduce energy consumption while having high efficiency in snow melting and ice removal.

[0031] 2. The present invention adopts a solution mixing method to prepare a self-limiting temperature heat-generating belt. First, petroleum ether or acetone is added to the conductive particles as a solvent for pretreatment. Based on the principle of like dissolves like, organic substances such as oxygen-containing functional groups adsorbed on the surface of the conductive particles can be dissolved in the solvent, and then the solvent is evaporated by heating, thereby avoiding these substances from affecting the conductive properties of the conductive particles. Then, the pretreated conductive particles and the polymer-based PTC self-limiting temperature material are fully contacted with the solvent. Since the polymer-based PTC self-limiting temperature material has viscosity, it can avoid the conductive particles from settling and agglomerating after being fully contacted with the conductive particles. Therefore, the conductive material can be more evenly distributed in the matrix material, and the prepared heat-generating belt has better stability and greater PTC self-limiting temperature strength. In addition, the self-limiting temperature heat-generating belt is prepared by the solution mixing method, the process is simple, the equipment requirements are low, and it is suitable for large-scale production.

[0032] 3. The polymer-based PTC self-limiting temperature material of the present invention has a high degree of crystallinity. As the crystallization is more perfect, the difference between the size of the conductive particles and the crystal is greater, the conductive particles are less likely to remain in the nucleated crystal phase, and a continuous conductive network is easily formed. The less conductive particles are required, the better the conductive properties of the material and the higher the PTC strength. Therefore, the heat-generating belt prepared can reduce the amount of conductive material used and reduce costs without affecting the conductive properties. And by changing the temperature control material, a polymer-based PTC self-limiting temperature material with a Curie temperature of 40-50°C can be prepared.

[0033] 4. During the two heat treatments after pressing, first dry it in a vacuum oven at 60℃-80℃ to evaporate most of the solvent, then raise the temperature to 100℃-120℃ to evaporate the remaining solvent. The heating rate is 2℃ / min to ensure that no bubbles are generated during the evaporation of the solvent due to excessive evaporation of the solvent, thereby avoiding affecting the uniformity of the self-limiting temperature heating belt. DETAILED DESCRIPTION Example 1

[0034] A self-limiting temperature heat-generating belt comprises a self-limiting temperature heat-generating belt body, wherein the self-limiting temperature heat-generating belt body comprises a metal conductor core, a self-limiting temperature graphene conductive layer, a metal wire mesh shielding layer, an isolation layer, and a sheath layer which are sequentially arranged from the inside to the outside, wherein the self-limiting temperature graphene conductive layer comprises the following raw materials in parts by weight: 5 parts by weight of acetylene carbon black, 70 parts by weight of a polymer-based PTC self-limiting temperature material, 10 parts by weight of cationic nanocellulose, and 20 parts by weight of petroleum ether; the polymer-based PTC self-limiting temperature material comprises: a skeleton support material and a temperature control material; the weight ratio of the skeleton support material to the temperature control material is 1:2.5, the skeleton support material is ethylene-vinyl acetate, and the temperature control material is modified tetradecanoic acid.

[0035] The above-mentioned preparation process of a self-limiting temperature heating belt comprises the following steps:

[0036] (1) Selection of raw materials: The metal conductor core is composed of a plurality of copper wires; the metal wire mesh shielding layer is made of copper wire, which is woven in plain warp and weft; the isolation layer is made of ultraviolet cross-linked polyethylene; the sheath layer is made of polyurethane;

[0037] (2) Preparation of self-limiting temperature graphene conductive layer: a. Preparation of conductive particle dispersion: acetylene black and petroleum ether were weighed by weight, and magnetically stirred at a speed of 100 r / min for 10 min. After stirring and mixing evenly, the mixture was allowed to stand for 24 h, filtered, washed with deionized water for 3 times, and dried after vacuum distillation. Then, 2 parts by weight of polyvinyl pyrrolidone and 2 parts by weight of 1-methyl-2-pyrrolidone were added, and magnetic stirring was performed at a speed of 100 r / min for 10 min. The mixture was heated to 60°C and subjected to water bath ultrasound at a frequency of 30 Hz for 10 min to obtain a conductive particle dispersion.

[0038] b. Add cationic nanocellulose to the above conductive particle dispersion, maintain 60° C., perform magnetic stirring at a speed of 100 r / min for 10 min, perform water bath ultrasonic treatment at a frequency of 30 Hz for 10 min, pour into a Buchner funnel with a polytetrafluoroethylene filter membrane, perform suction filtration, and perform vacuum drying in a vacuum drying oven at a temperature of 60° C. for 2 h to obtain a solid mixture;

[0039] c. Preparation of polymer-based PTC self-limiting temperature material: Weigh the skeleton support material and the temperature control material by weight, add 20 parts by weight of xylene solution, heat to 60°C and stir to mix evenly, and perform homogenization and dispersion treatment in a dispersing homogenizer at a speed of 1000r / min to obtain a mixed solution;

[0040] d. Add the solid mixture treated in step b to the mixed solution obtained in step c, continue to stir evenly at 60° C., and then perform water bath ultrasonic treatment at a frequency of 30 Hz for 10 min to obtain a preliminary finished product of the sample;

[0041] e. Put the above-mentioned sample pre-finished product into a mold, and press it in a film press at a pressure of 0.3 MPa. The thickness of the self-limiting temperature heating belt after pressing is 5 mm. After pressing into a film, heat treatment is performed twice, first in a vacuum oven at 60°C for 60 min, and then after cooling to room temperature, the temperature is increased to 100°C at a heating rate of 2°C / min for 120 min to obtain the self-limiting temperature graphene conductive layer;

[0042] (3) Preparation of modified myristic acid:

[0043] a. According to the mass ratio of Ni powder and myristic acid of 3:8, weigh the particles with a diameter of 2 m m Ni powder, adding anhydrous ethanol in a ratio of Ni powder to anhydrous ethanol of 1:3, performing magnetic stirring at a speed of 100 r / min for 10 min, then performing water bath ultrasonic treatment at a frequency of 30 Hz for 10 min, and drying in a vacuum drying oven at a temperature of 60° C. for 2 h to obtain a first mixture for standby use;

[0044] b. According to the mass ratio of stearic acid to myristic acid of 1:2, stearic acid and myristic acid were weighed, anhydrous ethanol was added and magnetic stirring was performed under water bath conditions at a speed of 100-r / min for 10 min, homogenization and dispersion treatment was performed in a dispersing homogenizer at a speed of 10000 r / min, and then water bath ultrasonic treatment was performed at a frequency of 30 Hz for 10 min to obtain a first mixed solution;

[0045] c. adding the first mixture obtained in step 1) to the first mixed solution obtained in step 2), and performing ball milling in a ball mill at a speed of 200 r / min for 4 h to obtain the modified tetradecanoic acid;

[0046] (4) Preparation of self-limiting temperature heating belt:

[0047] S1. twisting a plurality of copper wires into a metal conductor core by a twisting device, wherein the cross section of the metal conductor core is circular;

[0048] S2, coating the self-limiting temperature graphene conductive layer on the metal conductor core to form a preliminary finished product of a self-limiting temperature heat-generating belt;

[0049] S3, sequentially covering the self-limiting temperature heat-generating belt with a metal wire mesh shielding layer, an isolation layer, and a sheath layer to obtain a self-limiting temperature heat-generating belt. Example 2

[0050] A self-limiting temperature heat-generating belt comprises a self-limiting temperature heat-generating belt body, wherein the self-limiting temperature heat-generating belt body comprises a metal conductor core, a self-limiting temperature graphene conductive layer, a metal wire mesh shielding layer, an isolation layer, and a sheath layer which are sequentially arranged from the inside to the outside, wherein the self-limiting temperature graphene conductive layer comprises the following raw materials in parts by weight: 8 parts by weight of graphite, 80 parts by weight of a polymer-based PTC self-limiting temperature material, 15 parts by weight of cationic nanocellulose, and 25 parts by weight of acetone; the polymer-based PTC self-limiting temperature material comprises: a skeleton support material and a temperature control material; the weight ratio of the skeleton support material to the temperature control material is 1:3, the skeleton support material is high-density polyethylene, and the temperature control material is lauric acid.

[0051] The above-mentioned preparation process of a self-limiting temperature heating belt comprises the following steps:

[0052] (1) Selection of raw materials: The metal conductor core is composed of a plurality of copper wires; the metal wire mesh shielding layer is made of copper wire, which is woven in plain warp and weft; the isolation layer is made of ultraviolet cross-linked polyethylene; the sheath layer is made of polyurethane;

[0053] (2) Preparation of self-limiting temperature graphene conductive layer: a. Preparation of conductive particle dispersion: carbon nanotubes and petroleum ether were weighed by weight, and magnetically stirred at a speed of 120 r / min for 15 min. After stirring and mixing evenly, the mixture was allowed to stand for 36 h, filtered, washed with deionized water for 3 times, and dried after vacuum distillation. Then, 5 parts by weight of polyvinyl pyrrolidone and 5 parts by weight of 1-methyl-2-pyrrolidone were added, and magnetic stirring was carried out at a speed of 120 r / min for 15 min. The mixture was heated to 80°C and subjected to water bath ultrasound at a frequency of 40 Hz for 15 min to obtain a conductive particle dispersion.

[0054] b. Add cationic nanocellulose to the above conductive particle dispersion, maintain 60° C., perform magnetic stirring at a speed of 120 r / min for 15 min, perform water bath ultrasonic treatment at a frequency of 40 Hz for 15 min, pour into a Buchner funnel with a polytetrafluoroethylene filter membrane, perform suction filtration, and perform vacuum drying in a vacuum drying oven at a temperature of 80° C. for 2 h to obtain a solid mixture;

[0055] c. Preparation of polymer-based PTC self-limiting temperature material: Weigh the skeleton support material and the temperature control material by weight, add 30 parts by weight of xylene solution, heat to 80°C and stir to mix evenly, and perform homogenization and dispersion treatment in a dispersing homogenizer at a speed of 1200r / min to obtain a mixed solution;

[0056] d. Add the solid mixture treated in step b to the mixed solution obtained in step c, continue to stir evenly at 80° C., and then perform water bath ultrasonic treatment at a frequency of 40 Hz for 15 min to obtain a preliminary finished product of the sample;

[0057] e. Put the above-mentioned sample pre-finished product into a mold, and press it in a film press at a pressure of 0.5 MPa. The thickness of the self-limiting temperature heat-generating belt after pressing is 7 mm. After pressing into a film, heat treatment is performed twice, first in a vacuum oven at 60°C for 90 min, and then after cooling to room temperature, the temperature is increased to 120°C at a heating rate of 2°C / min for 150 min to obtain the self-limiting temperature graphene conductive layer;

[0058] (3) Preparation of modified myristic acid: a. Weigh a 2-diameter particle size according to the mass ratio of Ni powder to myristic acid of 3:10. m m Ni powder, adding anhydrous ethanol in a solid-liquid ratio of Ni powder to anhydrous ethanol of 1:3, performing magnetic stirring at a speed of 120 r / min for 20 min, then performing water bath ultrasonic treatment at a frequency of 40 Hz for 15 min, and drying in a vacuum drying oven at a temperature of 80° C. for 3 h to obtain a first mixture for standby use;

[0059] b. According to the mass ratio of stearic acid to myristic acid of 1:3, stearic acid and myristic acid were weighed, anhydrous ethanol was added and magnetic stirring was performed under water bath conditions at a speed of 120 r / min for 20 min, and homogenization and dispersion were performed in a dispersing homogenizer at a speed of 1100 r / min, and then water bath ultrasonic treatment was performed at a frequency of 40 Hz for 15 min to obtain a first mixed solution;

[0060] c. adding the first mixture obtained in step a to the first mixed solution obtained in step b, and performing ball milling in a ball mill at a speed of 200 r / min for 4 h to obtain the modified tetradecanoic acid;

[0061] (4) Preparation of self-limiting temperature heating belt:

[0062] S1. twisting a plurality of copper wires into a metal conductor core by a twisting device, wherein the cross section of the metal conductor core is circular;

[0063] S2, coating the self-limiting temperature graphene conductive layer on the metal conductor core to form a preliminary finished product of a self-limiting temperature heat-generating belt;

[0064] S3, sequentially covering the self-limiting temperature heat-generating belt with a metal wire mesh shielding layer, an isolation layer, and a sheath layer to obtain a self-limiting temperature heat-generating belt. Example 3

[0065] A self-limiting temperature heat-generating belt comprises a self-limiting temperature heat-generating belt body, wherein the self-limiting temperature heat-generating belt body comprises a metal conductor core, a self-limiting temperature graphene conductive layer, a metal wire mesh shielding layer, an isolation layer, and a sheath layer which are sequentially arranged from the inside to the outside, wherein the self-limiting temperature graphene conductive layer comprises the following raw materials in parts by weight: 10 parts by weight of carbon nanotubes, 90 parts by weight of a polymer-based PTC self-limiting temperature material, 20 parts by weight of cationic nanocellulose, and 30 parts by weight of petroleum ether; the polymer-based PTC self-limiting temperature material comprises: a skeleton support material and a temperature control material; the weight ratio of the skeleton support material to the temperature control material is 1:4, the skeleton support material is linear low-density polyethylene, and the temperature control material is n-decanoic acid.

[0066] The above-mentioned preparation process of a self-limiting temperature heating belt comprises the following steps:

[0067] (1) Selection of raw materials: The metal conductor core is composed of a plurality of copper wires; the metal wire mesh shielding layer is made of copper wire, which is woven in plain warp and weft; the isolation layer is made of ultraviolet cross-linked polyethylene; the sheath layer is made of polyurethane;

[0068] (2) Preparation of self-limiting temperature graphene conductive layer:

[0069] a. Preparation of conductive particle dispersion: graphite and acetone were weighed by weight, and magnetically stirred at a speed of 120 r / min for 15 min. After stirring and mixing evenly, the mixture was allowed to stand for 36 h, filtered, washed with deionized water for 3 times, and dried after vacuum distillation. Then, 5 parts by weight of polyvinyl pyrrolidone and 5 parts by weight of 1-methyl-2-pyrrolidone were added, and magnetic stirring was performed at a speed of 120 r / min for 15 min. The mixture was heated to 60° C. and subjected to water bath ultrasound at a frequency of 35 Hz for 15 min to obtain a conductive particle dispersion;

[0070] b. Add cationic nanocellulose to the above conductive particle dispersion, maintain 60° C., perform magnetic stirring at a speed of 120 r / min for 15 min, perform water bath ultrasonic treatment at a frequency of 35 Hz for 15 min, pour into a Buchner funnel with a polytetrafluoroethylene filter membrane, perform suction filtration, and perform vacuum drying in a vacuum drying oven at a temperature of 60° C. for 2 h to obtain a solid mixture;

[0071] c. Preparation of polymer-based PTC self-limiting temperature material: Weigh the skeleton support material and the temperature control material by weight, add 25 parts by weight of xylene solution, heat to 60°C and stir to mix evenly, and perform homogenization and dispersion treatment in a dispersing homogenizer at a speed of 1000r / min to obtain a mixed solution;

[0072] d. Add the solid mixture treated in step b to the mixed solution obtained in step c, continue to stir evenly at 60° C., and then perform water bath ultrasonic treatment at a frequency of 35 Hz for 15 min to obtain a preliminary finished product of the sample;

[0073] e. Put the above-mentioned sample pre-finished product into a mold, and press it in a film press at a pressure of 0.3 MPa. The thickness of the self-limiting temperature heating belt after pressing is 5 mm. After pressing into a film, heat treatment is performed twice, first in a vacuum oven at 60°C for 60 min, and then after cooling to room temperature, the temperature is increased to 100°C at a heating rate of 2°C / min for 120 min to obtain the self-limiting temperature graphene conductive layer;

[0074] (3) Preparation of modified myristic acid:

[0075] a. According to the mass ratio of Ni powder and myristic acid of 3:10, weigh the particles with a diameter of 2 m m Ni powder, adding anhydrous ethanol in a ratio of Ni powder to anhydrous ethanol of 1:3, performing magnetic stirring at a speed of 120 r / min for 15 min, then performing water bath ultrasonic treatment at a frequency of 35 Hz for 15 min, and drying in a vacuum drying oven at a temperature of 60° C. for 4 h to obtain a first mixture for standby use;

[0076] b. According to the mass ratio of stearic acid to myristic acid of 2:3, stearic acid and myristic acid were weighed, anhydrous ethanol was added and magnetic stirring was performed under water bath conditions at a speed of 120 r / min for 30 min, homogenization and dispersion were performed in a dispersing homogenizer at a speed of 1200 r / min, and then water bath ultrasonic treatment was performed at a frequency of 35 Hz for 15 min to obtain a first mixed solution;

[0077] 3) adding the first mixture obtained in step a to the first mixed solution obtained in step b, and performing ball milling in a ball mill at a speed of 300 r / min for 5 h to obtain the modified tetradecanoic acid;

[0078] (4) Preparation of self-limiting temperature heating belt:

[0079] S1. twisting a plurality of copper wires into a metal conductor core by a twisting device, wherein the cross section of the metal conductor core is circular;

[0080] S2, coating the self-limiting temperature graphene conductive layer on the metal conductor core to form a preliminary finished product of a self-limiting temperature heat-generating belt;

[0081] S3, sequentially covering the self-limiting temperature heat-generating belt with a metal wire mesh shielding layer, an isolation layer, and a sheath layer to obtain a self-limiting temperature heat-generating belt.

[0082] Comparative Example 1

[0083] The difference from Example 1 is that only commercially available carbon black is used as the raw material, and the self-limiting temperature heating belt is prepared by a melt mixing method instead of a solution mixing method, and the steps of the method are melt mixing, stirring, pressing and cooling. The other technical schemes are the same as those of Example 1.

[0084] The test data of the products of Example 1, Example 2, Example 3 and Comparative Example 1 are shown in Table 1.

[0085] Table 1

[0086]

[0087] Resistance-temperature test: Put the self-limiting temperature heating belt sample after insulation wrapping into an iron container, place it in a constant temperature circulating water tank, adjust the internal temperature of the constant temperature water tank to change the ambient temperature of the self-limiting temperature heating belt sample, and use a multimeter and thermocouple to record the surface temperature of the sample and the change of resistance at both ends. Set the initial temperature of the constant temperature circulating water tank to 5℃. After the sample reaches thermal equilibrium with the environment, set the constant temperature circulating water tank to heat up at a rate of 1.5℃ / min. Stop heating when the surface temperature of the sample stabilizes at about 150℃. Record the change of resistance with temperature and calculate the volume resistivity of the material.

[0088] Thermal cycle test: put the self-limiting temperature heating belt sample after insulation wrapping into an iron container, place it in a constant temperature circulating water tank, adjust the internal temperature of the constant temperature circulating water tank to change the ambient temperature of the self-limiting temperature heating belt sample, set the initial temperature of the constant temperature circulating water tank to 5℃, and after the thermal equilibrium between the sample and the environment is reached, set the constant temperature circulating water tank to heat up at a rate of 1.5℃ / min. Stop heating when the temperature on the surface of the sample stabilizes at about 150℃, cool to room temperature, and repeat the above heating steps ten times. Record the PTC strength values ​​before and after ten thermal cycle tests.

[0089] Flexibility test: The flexibility test of composite materials was carried out according to GB T 1731-1993 Determination of paint film flexibility.

[0090] According to the test data in Table 1, it can be seen that the Curie temperatures of the products of Example 1, Example 2, and Example 3 are 47°C, 40°C, and 45°C, respectively, in the range of 40-50°C, and are room temperature PTC control materials; when the temperature is low, the resistivity is low, and the resistivity is lower than 1.93, indicating good conductivity; when the temperature is increased to 90 degrees or above, the resistivity changes significantly, and after the temperature reaches the Curie temperature point of each material, the conductive path is completely destroyed, resulting in a PTC effect; compared with Comparative Example 1, they all have higher PTC strength, and the PTC strength changes less before and after the thermal cycle test, indicating that the products of the present invention have good thermal stability; compared with Comparative Example 1, they all have lower radius of curvature, indicating that the products of the present invention have better flexibility.

[0091] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A self-limiting temperature heat-generating belt, comprising a self-limiting temperature heat-generating belt body, wherein the self-limiting temperature heat-generating belt body comprises a metal conductor core, a self-limiting temperature graphene conductive layer, a metal wire mesh shielding layer, an isolation layer and a sheath layer arranged in sequence from inside to outside, characterized in that: The self-limiting temperature graphene conductive layer comprises the following raw materials in parts by weight: 5-10 parts by weight of conductive particles, 70-90 parts by weight of polymer-based PTC self-limiting temperature material, 10-20 parts by weight of cationic nanocellulose and 20-30 parts by weight of solvent; the polymer-based PTC self-limiting temperature material comprises: a skeleton support material and a temperature control material; the weight ratio of the skeleton support material to the temperature control material is 1:2.5-1:4; the skeleton support material is one or a mixture of at least two of ethylene-vinyl acetate, water-based acrylic resin, high-density polyethylene, low-density polyethylene and linear low-density polyethylene in equal proportions, and the temperature control material is any one of modified tetradecanoic acid, decanoic acid, lauric acid and n-tetracosane; The preparation method of the self-limiting temperature graphene conductive layer is: a. Preparation of conductive particle dispersion: Weigh conductive particles and solvent by weight, stir and mix evenly, let stand for 24h-36h, filter, wash with deionized water 3-5 times, perform vacuum distillation and then dry, then add 2-5 parts by weight of polyvinyl pyrrolidone and 2-5 parts by weight of 1-methyl-2-pyrrolidone, stir and mix evenly, perform water bath ultrasound, and obtain conductive particle dispersion; b. stirring and mixing the conductive particle dispersion and cationic nanocellulose uniformly, pouring into a Buchner funnel with a polytetrafluoroethylene filter membrane after water bath ultrasonic treatment, filtering, and drying to obtain a solid mixture; c. Preparation of polymer-based PTC self-limiting temperature material: weigh the skeleton support material and the temperature control material by weight, add 20-30 parts by weight of xylene solution, heat to 60°C-80°C, stir and mix evenly, perform homogeneous dispersion treatment, and obtain a mixed solution; d. Add the solid mixture treated in step b to the mixed solution obtained in step c, continue to stir evenly at 60° C.-80° C., and then perform water bath ultrasonic treatment to obtain a preliminary finished sample; e. Put the above-mentioned sample preliminary product into a mold, press it into a film, and then perform two heat treatments to obtain the self-limiting temperature graphene conductive layer.

2. A self-limiting temperature heating belt according to claim 1, characterized in that: The preparation method of the modified myristic acid is: 1) Weighing Ni powder in a ratio of Ni powder to tetradecanoic acid of 3:8-3:10, adding anhydrous ethanol in a ratio of Ni powder to anhydrous ethanol of 1:3-1:5, stirring and mixing, then performing water bath ultrasonic treatment, drying, and obtaining a first mixture for standby use; 2) Weighing stearic acid and myristic acid in a mass ratio of 1:2-2:3, adding anhydrous ethanol and stirring under a water bath, performing a homogenous dispersion treatment, and then performing a water bath ultrasonic treatment to obtain a first mixed solution; 3) The first mixture obtained in step 1) is added to the first mixed solution obtained in step 2) and ball milled to obtain the modified myristic acid.

3. A self-limiting temperature heating belt according to claim 1, characterized in that: The conductive particles are any one of acetylene black, graphite, graphene, carbon nanotubes and carbon fibers; and the solvent is petroleum ether or acetone.

4. A self-limiting temperature heating belt according to claim 1, characterized in that: The metal conductor core is composed of a plurality of copper wires; the metal wire mesh shielding layer is made of copper wires, which are woven in plain warp and weft; the isolation layer is made of ultraviolet cross-linked polyethylene; and the sheath layer is made of polyurethane.

5. A self-limiting temperature heating belt according to claim 2, characterized in that: The process of the two heat treatments is: firstly, the temperature is set in a vacuum oven at 60°C-80°C for 60min-90min, then, after cooling to room temperature, the temperature is raised to 100°C-120°C at a heating rate of 2°C / min and the holding time is 120min-150min.

6. A self-limiting temperature heating belt according to claim 1, characterized in that: The pressing is carried out in a film pressing machine at a pressure of 0.3MPa-0.5MPa, and the thickness of the self-limiting temperature graphene conductive layer after pressing is 5mm-7mm.

7. A self-limiting temperature heating belt according to claim 2, characterized in that: The frequency of the water bath ultrasound is 30Hz-40Hz, and the time is 10min-20min; the stirring is magnetic stirring, the speed is 100r / min-120r / min, and the time is 10min-30min; the drying is carried out in a vacuum drying oven, the temperature is 60℃-80℃, and the time is 2h-4h; the ball milling treatment is carried out in a ball mill, the speed is 200r / min-400r / min, and the time is 4h-5h; the homogenization dispersion is carried out in a dispersion homogenizer, and the speed is 1000r / min-1200r / min.

8. A self-limiting temperature heating belt according to claim 2, characterized in that: The particle size of the Ni powder is 2 μ m-2.5 μ m.

9. A process for preparing a self-limiting temperature heating belt, characterized in that: The following steps are involved: S1. twisting a plurality of copper wires into a metal conductor core by a twisting device, wherein the cross section of the metal conductor core is circular; S2. Wrapping the self-limiting temperature graphene conductive layer according to claim 1 on the outside of the metal conductor core to form a preliminary finished product of the self-limiting temperature heat-generating belt; S3, sequentially covering the self-limiting temperature heat-generating belt with a metal wire mesh shielding layer, an isolation layer, and a sheath layer to obtain the self-limiting temperature heat-generating belt.

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