A flexible heating film material based on nano-carbon doping and a preparation method thereof

Abstract

This application belongs to the technical field of heating film materials, specifically providing a flexible heating film material based on nano-carbon doping and its preparation method. The flexible heating film material based on nano-carbon doping comprises the following components: high-density polyethylene, PE-g-MAH, nano-carbon powder, and tannic acid-modified cobalt-aluminum co-doped oxide. The heating film material obtained in this application has the advantages of good heating performance and high mechanical properties.

Description

Technical Field

[0001] This application belongs to the field of heating film material technology, and in particular relates to a flexible heating film material based on nano-carbon doping and its preparation method. Background Technology

[0002] Flexible heating film materials have broad application prospects in fields such as battery new energy and wearable heating devices. An ideal heating film material should possess excellent electrothermal conversion efficiency, uniform surface resistivity, long-term electrical stability, and good mechanical flexibility.

[0003] Currently, the mainstream flexible heating film technologies mainly include three categories: metal wire woven mesh, conductive ink printed film, and polymer conductive composite material film. Among them, polymer conductive composite material film has attracted widespread attention due to its advantages such as light weight, large-area preparation, and good flexibility. Polyethylene, due to its excellent electrical insulation, chemical corrosion resistance, and ease of processing, has become one of the commonly used matrix resins for this type of heating film. However, pure polyethylene is an electrical insulator, and conductive fillers need to be added to impart conductive heating capabilities.

[0004] Nanomaterials, such as carbon nanopowder, carbon nanotubes, and graphene, are commonly used conductive fillers for constructing conductive polymer composites. Among them, carbon nanopowder has great potential for industrial application due to its low cost and wide availability. However, in practical applications, simply blending carbon nanopowder into the polyethylene matrix often presents the following contradictions: (1) To achieve the required conductive heating power, the amount of carbon powder added needs to be high enough to exceed the percolation threshold, but this will drastically deteriorate the mechanical flexibility and melt processability of the material; (2) Carbon powder has poor dispersion in the matrix and is prone to agglomeration, resulting in poor heating uniformity and local hot spots that can easily cause the material to melt and burn; (3) The interfacial bonding between carbon powder and polyethylene matrix is ​​weak, and the mechanical properties of the composite material are severely degraded as the carbon content increases. The flexibility and bending resistance of the membrane are insufficient, which restricts its application range.

[0005] Some technicians have attempted to introduce inorganic metal oxides as auxiliary functional fillers to improve the structure of conductive networks or endow materials with new functions. Layered bimetallic hydroxides (LDHs) and their calcined products are inorganic functional materials with adjustable composition and structure. However, when directly introduced into carbon powder / polyethylene composite systems, it is often difficult to achieve uniform dispersion and effective interfacial bonding due to the poor compatibility between the inorganic oxide surface and the organic polymer matrix; at the same time, the synergistic conductivity and reinforcement mechanism between oxides and carbon powder has not been fully explored and utilized.

[0006] Therefore, how to simultaneously achieve a low conductivity percolation threshold, high electrothermal efficiency, excellent mechanical flexibility, and long-term electrical stability in nano-carbon powder / polyethylene composite systems through component design and interface control remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the aforementioned issues, this application provides a flexible heating film material based on nano-carbon doping and its preparation method.

[0008] This application first provides a flexible heating film material based on nano-carbon doping, comprising the following components: high-density polyethylene, PE-g-MAH, nano-carbon powder, and tannic acid-modified cobalt-aluminum co-doped oxide.

[0009] Furthermore, the tannic acid-modified cobalt-aluminum co-doped oxide is prepared by calcination of a cobalt-aluminum layered double hydroxide precursor and surface modification with tannic acid.

[0010] Furthermore, the molar ratio of Co to Al in the cobalt-aluminum layered double hydroxide precursor is (2-4):1;

[0011] And / or, the calcination is performed at a constant temperature of 300-400°C in an air atmosphere.

[0012] Preferably, the molar ratio of Co to Al is (2.5-3.5):1; more preferably, the molar ratio of Co to Al is (2.8-3.2):1; for example, it can be 2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1 or 4:1.

[0013] Preferably, the calcination temperature is 320-380℃; more preferably, the calcination temperature is 340-360℃; for example, it can be 300℃, 320℃, 340℃, 350℃, 360℃, 380℃ or 400℃.

[0014] Furthermore, the calcination time is 2-6 hours; preferably, the calcination time is 3-5 hours; for example, it can be 2 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours or 6 hours.

[0015] Furthermore, by mass parts, it contains the following components: 70-80 parts high-density polyethylene, 6-10 parts PE-g-MAH, 10-20 parts nano carbon powder, and 8-15 parts tannic acid-modified cobalt-aluminum co-doped oxide.

[0016] Preferably, the amount of high-density polyethylene used is 72-78 parts; for example, it can be 70 parts, 72 parts, 74 parts, 75 parts, 76 parts, 78 parts or 80 parts.

[0017] Preferably, the amount of PE-g-MAH used is 7-9 parts; for example, it can be 6 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, 9 parts or 10 parts.

[0018] Preferably, the amount of the nano-carbon powder is 12-18 parts; for example, it can be 10 parts, 12 parts, 14 parts, 15 parts, 16 parts, 18 parts or 20 parts.

[0019] Preferably, the amount of the tannic acid-modified cobalt-aluminum co-doped oxide is 10-13 parts; for example, it can be 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts or 15 parts.

[0020] Furthermore, the components also include processing aids, which include antioxidants and lubricants.

[0021] Furthermore, by weight, the antioxidant is 0.3-0.8 parts and the lubricant is 0.3-0.8 parts; the antioxidant is a compound of a primary antioxidant and a secondary antioxidant, the primary antioxidant is a hindered phenolic antioxidant, and the secondary antioxidant is a phosphite antioxidant.

[0022] Preferably, the amount of antioxidant is 0.4-0.6 parts; for example, it can be 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, or 0.8 parts. Preferably, the primary antioxidant is selected from one or more of antioxidant 1010 and antioxidant 1076, and the secondary antioxidant is selected from one or more of antioxidant 168 and antioxidant 626.

[0023] Preferably, the amount of lubricant used is 0.4-0.6 parts; for example, it can be 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, or 0.8 parts. Preferably, the lubricant is selected from at least one of calcium stearate and zinc stearate.

[0024] Furthermore, the melt index of the high-density polyethylene is 1.0-5.0 g / 10 min;

[0025] And / or, the grafting rate of the PE-g-MAH is 0.5-2.5 wt%;

[0026] And / or, the average particle size of the nano-carbon powder is 20-100 nm, and the specific surface area is 200-500 m². 2 / g.

[0027] Preferably, the average particle size of the nano-carbon powder is 30-80 nm; more preferably, the average particle size of the nano-carbon powder is 40-60 nm; for example, it can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 80 nm or 100 nm.

[0028] Furthermore, the specific surface area of ​​the nano-carbon powder is 200-500 m² / g; preferably, it is 250-400 m² / g; more preferably, it is 300-380 m² / g.

[0029] This application provides a method for preparing a flexible heating film material based on nano-carbon doping, comprising the following steps:

[0030] 1) Dissolve soluble cobalt salt and soluble aluminum salt in water to prepare a mixed salt solution; dissolve alkali and carbonate in water to prepare a mixed alkali solution;

[0031] 2) The mixed salt solution and the mixed alkali solution were added dropwise simultaneously to control the pH to be stable. After the addition was completed, the temperature was raised and the mixture was aged. After separation, washing, drying and grinding, the CoAl-LDH precursor was obtained. The CoAl-LDH precursor was calcined in air to obtain cobalt aluminum co-doped oxide. Then it was dispersed in Tris-HCl buffer, and tannic acid was added for surface modification. After separation, washing and drying, tannic acid-modified cobalt aluminum co-doped oxide was obtained.

[0032] 3) After premixing high-density polyethylene, PE-g-MAH, nano carbon powder, tannic acid-modified cobalt-aluminum co-doped oxide and optional processing aids, the mixture is melt-extruded and granulated to obtain the flexible heating film material.

[0033] Furthermore, in step 1), the Co / Al molar ratio in the mixed salt solution is (2-4):1; the NaOH concentration in the mixed alkali solution is 2.0-6.0 mol / L, and the carbonate concentration is 0.2-1.0 mol / L.

[0034] Furthermore, in step 2), the temperature of the dripping is 55-75℃, and the pH is maintained at 9.5-11.0 during the dripping process; the temperature of the aging is 70-90℃, and the time is 8-16h; the temperature of the calcination is 300-400℃, and the calcination time is 2-6h.

[0035] Compared with the prior art, this application has the following beneficial effects:

[0036] The flexible heating film material provided in this application incorporates tannic acid-modified cobalt-aluminum co-doped oxide (m-CoAlO). x @TA), through the abundant phenolic hydroxyl groups on its surface, can form hydrogen bonds with the oxygen-containing groups on the surface of carbon nanoparticles, and chemically react with the anhydride groups on PE-g-MAH, constructing an effective "bridging" interface between the conductive network of carbon nanoparticles and the polymer matrix. This interface design promotes the dispersion of carbon nanoparticles and the formation of a three-dimensional isolated conductive network, significantly reducing the percolation threshold and achieving stable and controllable resistivity at low carbon powder addition levels; on the other hand, m-CoAlO xThe particles can serve as "physical cross-linking points" and stress transfer centers for the nano-carbon powder network, effectively transferring external forces from the flexible PE matrix to the rigid nano-carbon network, thereby improving the material's electrothermal performance while maintaining its mechanical flexibility. Furthermore, the cobalt-aluminum co-doped oxide originates from calcined CoAl-LDH precursors. The calcined products retain the lamellar structure memory and porous morphology of LDH, possessing a large specific surface area, which is beneficial for carbon powder dispersion. Simultaneously, the presence of cobalt and aluminum, two transition metals, endows the material with unique thermal stability, which helps suppress localized high-temperature oxidation of the heating film during long-term energization, thus improving long-term energization stability. Detailed Implementation

[0037] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0040] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0041] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0042] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0043] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0045] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0046] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0047] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0048] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0049] Example 1

[0050] The preparation method of the flexible heating film material based on nano-carbon doping in this embodiment includes the following steps:

[0051] 1) Dissolve 874g of cobalt nitrate hexahydrate and 375g of aluminum nitrate nonahydrate in 3L of deionized water and stir until completely dissolved to obtain a pink transparent cobalt / aluminum salt solution with a total concentration of Co and Al ions of 1.33 mol / L and a Co / Al molar ratio of 3:1.

[0052] Dissolve 320g NaOH and 106g sodium carbonate in 2L of deionized water and stir to dissolve, to obtain a mixed alkaline solution with NaOH concentration of 4 mol / L and sodium carbonate concentration of 0.5 mol / L.

[0053] 2) In a 50L stainless steel reactor equipped with a mechanical stirrer, pH electrode, and constant temperature water jacket, 5L of deionized water was added as a base solution, and the mixture was heated to 65℃ in a water bath. Under vigorous stirring, the salt solution and alkali solution were simultaneously added dropwise to the reactor using two peristaltic pumps. During the addition, the drop rate of the salt solution was maintained at 10mL / min, and the rate of the alkali solution was set to maintain the pH in the reactor at 10.0±0.5. After the addition was completed, the suspension was heated to 80℃ and aged overnight with stirring. After aging, it was naturally cooled to room temperature and filtered using a plate and frame filter press. The resulting filter cake was repeatedly washed with deionized water, then dried in an 80℃ forced-air drying oven, and ground through a 200-mesh sieve to obtain the CoAl-LDH precursor.

[0054] The obtained CoAl-LDH precursor was spread in a quartz boat and placed in a box-type muffle furnace. Under air atmosphere, the temperature was increased from room temperature to 350℃ at a rate of 5℃ / min, and calcined at 350℃ for 4 hours to obtain cobalt-aluminum co-doped oxide. 100g of the cobalt-aluminum co-doped oxide was dispersed in 500mL of Tris-HCl buffer and ultrasonically dispersed for 30min. Then, 6g of tannic acid was added, and the mixture was stirred at room temperature for 5h. After centrifugation, the precipitate was washed and dried to obtain m-CoAlO. x @TA;

[0055] 3) Take 7.5 kg of high-density polyethylene, 0.65 kg of PE-g-MAH, 1.5 kg of nano-carbon powder, and 1 kg of m-CoAlO. x @TA, 35g antioxidant 1010, 20g co-antioxidant 168, and 40g calcium stearate are premixed in a high-speed mixer, melt-extruded through a twin-screw extruder, cooled, and pelletized to obtain the final product. The temperature of the twin-screw extruder is 155℃ in the feeding section, 175℃ in the compression section, 190℃ in the plasticizing section, and 200℃ in the die. The screw speed is 150rpm, and the feed rate is 10kg / h.

[0056] The melt flow index (MI) of high-density polyethylene is 2.5 g / 10 min (190℃, 2.16 kg), and its density is 0.950 g / cm³. 3 The grafting rate of PE-g-MAH was 1.5 wt%, and the MI was 2.0 g / 10 min. The average particle size of the nano-carbon powder was 50 nm, and the specific surface area was 350 m². 2 / g.

[0057] Example 2

[0058] This embodiment is basically the same as Example 1, except that the Co / Al molar ratio in the cobalt / aluminum salt solution is 2.5:1.

[0059] Example 3

[0060] This embodiment is basically the same as Example 1, except that the Co / Al molar ratio in the cobalt / aluminum salt solution is 3.5:1.

[0061] Control group 1

[0062] The only difference between this control group and Example 1 is that m-CoAlO is not added. x @TA was replaced with an equal mass of nano-carbon powder. The resulting material had a volume resistivity of 2.3 × 10² Ω·cm, a tensile strength of 18.7 MPa, an elongation at break of 210%, and a resistance change rate of 16% after 1000 bends.

[0063] Control group 2

[0064] The difference between this control group and Example 1 is that in step (2), the cobalt-aluminum co-doped oxide was not modified with tannic acid, but was directly blended with nano-carbon powder and resin as the calcined product. The resulting material had a volume resistivity of 5.6 × 10¹ Ω·cm, a tensile strength of 21.5 MPa, an elongation at break of 260%, and a resistance change rate of 12% after 500 bends.

[0065] Performance testing

[0066] Flexible heating film materials from Examples 1-3 and Control Groups 1-2 were hot-pressed at 195℃ and 18MPa to obtain sample films with an average thickness of 0.2mm. Volume resistivity was tested according to GB / T 31838.2-2019; mechanical properties were tested according to GB / T1040.3-2006; and the electro-thermal radiation conversion efficiency under a constant DC voltage of 12V applied to both ends of the film was tested according to GB / T 7287-2008. A 9-point thermocouple array was attached to both sides of the film, and after applying a stable 12V DC voltage for 30 minutes, the temperature at each point was recorded. The maximum temperature difference (ΔTmax) was used to characterize the surface temperature uniformity of the film. The film was repeatedly bent at 180° 1000 times (bending radius 5mm), and the resistance change rate before and after bending was tested. A constant DC voltage of 12V was applied continuously for 720 hours, and the resistance drift rate over time was tested. The comprehensive test results are shown in Table 1.

[0067] Table 1. Comprehensive performance test data of flexible heating film materials in Examples 1-3 and Control Groups 1-2

[0068]

[0069] It can be seen that the volume resistivity of Examples 1-3 is within the ideal range for film heating materials, and the maximum surface temperature difference is controlled within 4℃. However, Control Group 1 lacks m-CoAlO₂. x Due to the dispersion bridging effect of TA, the toner is prone to agglomeration, resulting in high resistivity and extremely uneven heating (ΔTmax reaches 6.8℃). Although the oxide in control group 2 provides some dispersion, its compatibility with the matrix and toner is inferior to that of the TA-modified product due to the lack of an organic interface layer modified with tannic acid on the surface, and its uniformity is also significantly different.

[0070] In terms of mechanical properties, Examples 1-3 simultaneously achieved high tensile strength (24.8~27.5 MPa) and excellent elongation at break (340~420%), exhibiting excellent flexibility. Control Group 1, due to its high carbon black content and lack of structural reinforcement, showed significantly deteriorated mechanical properties. The strength of Control Group 2 fell between the two groups, indicating that simple oxide reinforcement is limited, while TA modification significantly improved stress transfer efficiency.

[0071] Regarding stability in use, in Examples 1-3, the resistance change rate was controlled within 8% after 1000 bends, and the resistance drift rate was below 4% after 720 hours of long-term power-on, proving that m-CoAlO x The flexible conductive network and interface constructed by @TA exhibit excellent fatigue and aging resistance. In contrast, the bending resistance change rate and long-term energized drift rate of control groups 1 and 2 were significantly increased, reflecting the problems of conductive network reconstruction and interface debonding.

[0072] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A flexible heating film material based on nano-carbon doping, characterized in that: It contains the following components: high-density polyethylene, PE-g-MAH, nano carbon powder, and tannic acid-modified cobalt-aluminum co-doped oxide.

2. The flexible heating film material based on nano-carbon doping according to claim 1, characterized in that: The tannic acid-modified cobalt-aluminum co-doped oxide is prepared by calcination of a cobalt-aluminum layered double hydroxide precursor and surface modification with tannic acid.

3. The flexible heating film material based on nano-carbon doping according to claim 2, characterized in that: The molar ratio of Co to Al in the cobalt-aluminum layered double hydroxide precursor is (2-4):1; And / or, the calcination is performed at a constant temperature of 300-400°C in an air atmosphere.

4. The flexible heating film material based on nano-carbon doping according to claim 1, characterized in that: By mass, it contains the following components: 70-80 parts high-density polyethylene, 6-10 parts PE-g-MAH, 10-20 parts nano carbon powder, and 8-15 parts tannic acid-modified cobalt-aluminum co-doped oxide.

5. The flexible heating film material based on nano-carbon doping according to claim 4, characterized in that: The components also include processing aids, which include antioxidants and lubricants.

6. The flexible heating film material based on nano-carbon doping according to claim 5, characterized in that: The antioxidant is 0.3-0.8 parts by weight, and the lubricant is 0.3-0.8 parts; the antioxidant is a compound of a primary antioxidant and a secondary antioxidant, the primary antioxidant is a hindered phenolic antioxidant, and the secondary antioxidant is a phosphite antioxidant.

7. The flexible heating film material based on nano-carbon doping according to claim 4, characterized in that: The melt flow index of the high-density polyethylene is 1.0-5.0 g / 10 min; And / or, the grafting rate of the PE-g-MAH is 0.5-2.5 wt%; And / or, the average particle size of the nano-carbon powder is 20-100 nm, and the specific surface area is 200-500 m². 2 / g.

8. A method for preparing a flexible heating film material based on nano-carbon doping as described in any one of claims 1-7, characterized in that: Includes the following steps: 1) Dissolve soluble cobalt salt and soluble aluminum salt in water to prepare a mixed salt solution; dissolve alkali and carbonate in water to prepare a mixed alkali solution; 2) The mixed salt solution and the mixed alkali solution were added dropwise simultaneously to control the pH to be stable. After the addition was completed, the temperature was raised and the mixture was aged. After separation, washing, drying and grinding, the CoAl-LDH precursor was obtained. The CoAl-LDH precursor was calcined in air to obtain cobalt aluminum co-doped oxide. Then it was dispersed in Tris-HCl buffer, and tannic acid was added for surface modification. After separation, washing and drying, tannic acid-modified cobalt aluminum co-doped oxide was obtained. 3) After premixing high-density polyethylene, PE-g-MAH, nano carbon powder, tannic acid-modified cobalt-aluminum co-doped oxide and optional processing aids, the mixture is melt-extruded and granulated to obtain the flexible heating film material.

9. The preparation method according to claim 8, characterized in that: In step 1), the Co / Al molar ratio in the mixed salt solution is (2-4):1; the NaOH concentration in the mixed alkali solution is 2.0-6.0 mol / L, and the carbonate concentration is 0.2-1.0 mol / L.

10. The preparation method according to claim 8, characterized in that: In step 2), the temperature of the dripping is 55-75℃, and the pH is maintained at 9.5-11.0 during the dripping process; the temperature of the aging is 70-90℃, and the time is 8-16h; the temperature of the calcination is 300-400℃, and the calcination time is 2-6h.

Images