Composite heating sheet based on PTC thermistor and preparation process thereof

Abstract

The invention relates to the related field of heating sheets, in particular to a composite heating sheet based on a PTC (Positive Temperature Coefficient) thermistor and a preparation process thereof, and the preparation process comprises the following steps: preparing modified hydroxyl-terminated polydimethylsiloxane; preparing the low-Curie-point PTC thermistor composite material; tabletting and forming; preparing a conducting strip; and testing and packaging to obtain the composite heating sheet of the PTC thermistor. As isocyanate groups at the two ends of the diphenylmethane diisocyanate and hydroxyl have good reaction activity, the hydroxyl-terminated polydimethylsiloxane is modified by using the diphenylmethane diisocyanate, and compared with unmodified hydroxyl-terminated polydimethylsiloxane, the hydroxyl-terminated polydimethylsiloxane has the advantages that the hydroxyl-terminated polydimethylsiloxane is more stable in performance, and the service life of the hydroxyl-terminated polydimethylsiloxane is prolonged. The impact resistance of the composite heating sheet prepared by adding the modified hydroxyl-terminated polydimethylsiloxane is obviously improved, so that the water pipe can better resist the impact of external force.

Description

Technical Field

[0001] The present invention relates to the field of heating plates, and in particular to a composite heating plate based on a PTC thermistor and a preparation process thereof. Background Art

[0002] In cold weather, temperatures drop below -10°C (-10°F), causing the water inside outdoor pipes to freeze. This not only affects water delivery but can also cause ice to burst through the pipes. Electric heating is an effective way to prevent ice buildup in water pipes during winter. Currently, conventional heating elements, such as resistance wire and metal wire, lack self-regulating temperature control and continue to heat regardless of the temperature. However, continuous heating is not necessary in temperatures below -10°C, as it can easily lead to overheating and excessive power consumption. Therefore, thermistor materials with positive temperature coefficients (PTCs) have broad application prospects in the field of self-regulating heating.

[0003] When using a PTC thermistor-based heating sheet as an electric heating anti-icing element, when the heating temperature is lower than the Curie temperature of the PTC thermistor, the resistivity of the PTC thermistor remains stable. When the heating temperature exceeds the Curie temperature of the PTC thermistor, the resistivity of the PTC thermistor begins to increase rapidly, causing the heat generation of the PTC thermistor to drop rapidly and the heating power to decrease, thereby slowing down the temperature increase trend of the PTC thermistor until the heat generation and heat dissipation of the PTC thermistor reach a balance, thereby achieving adaptive temperature control and avoiding overheating.

[0004] The PTC thermistor heating sheets currently prepared mainly rely on packaging technology to ensure that they have basic impact resistance. However, when used in special scenarios for water pipe anti-icing, the PTC thermistor heating sheets are exposed to a relatively harsh external environment with wind and snow impact, so it is necessary to improve the impact resistance of the PTC thermistor heating sheets. In addition, the PTC thermistor materials currently developed generally use a single organic phase change material to regulate the Curie temperature. The atomic arrangement inside the single organic material is relatively disordered, and the lattice vibration contributes less to heat transfer. Therefore, the prepared heating sheet has poor thermal stability, and the density of the single organic material is relatively low, so the thermal conductivity of the prepared heating sheet is low. To this end, a composite heating sheet based on a PTC thermistor and a preparation process thereof are proposed, which can improve impact resistance, thermal conductivity and thermal stability. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a composite heating plate based on a PTC thermistor and a preparation process thereof.

[0006] A preparation process of a composite heating sheet based on a PTC thermistor includes the following steps: S1: Preparation of modified hydroxyl-terminated polydimethylsiloxane Separately taking solvent cyclohexanone, diphenylmethane diisocyanate, hydroxyl-terminated polydimethylsiloxane, curing agent, talc powder and zinc powder, mixing and stirring to obtain modified hydroxyl-terminated polydimethylsiloxane; S2: Preparation of low Curie point PTC thermistor composite materials n-Tetradecane and n-octanoic acid are placed in a beaker and mixed and stirred, conductive carbon black and nickel powder are added as conductive fillers, mixed and stirred again, modified hydroxyl-terminated polydimethylsiloxane is added as a matrix material, polydimethylsiloxane is added as a diluent, mixed and stirred again, and a cross-linking agent and a catalyst are added to obtain a low Curie point PTC thermistor composite material; S3: Tablet forming Compression molding the low Curie point PTC thermistor composite material to obtain a molded green sheet; S4: Preparation of conductive sheet The surface of the formed green sheet is coated with molten metal to form an electrode, and the molten metal is sintered, and then external leads are connected to the metal surface to obtain a conductive sheet; S5: Testing and Packaging Conduct relevant tests on the conductive sheets, screen out qualified products, and then package and store them.

[0007] Furthermore, step S1 of preparing the modified hydroxy-terminated polydimethylsiloxane comprises the following steps: 10-15 parts by volume of solvent cyclohexanone, 5-7 parts by volume of diphenylmethane diisocyanate, 10-15 parts by volume of terminal hydroxyl polydimethylsiloxane, 2-4 parts by mass of curing agent, 8-10 parts by mass of talc powder and 8-10 parts by mass of zinc powder were respectively taken and magnetically stirred for 10-15 minutes to obtain modified terminal hydroxyl polydimethylsiloxane.

[0008] Furthermore, step S2 of preparing the low Curie point PTC thermistor composite material includes the following steps: S2.1: 25 to 35 parts by volume of n-tetradecane and 25 to 35 parts by volume of n-octanoic acid are respectively taken and placed in a beaker to obtain a mixture. The mixture in the beaker is then stirred with a magnetic stirrer for 15 to 25 minutes to obtain a composite phase change material. 15 to 25 parts by mass of conductive carbon black and 15 to 25 parts by mass of nickel powder as conductive fillers are then added to the beaker containing the composite phase change material. The beaker containing the composite phase change material and the conductive filler is then fixed on a digital electric stirrer at a stirring speed of 750 to 850 r / min and stirred for 10 to 15 minutes to obtain a composite A. S2.2: Weigh 40-45 parts by weight of modified hydroxyl-terminated polydimethylsiloxane as the base material and 30-35 parts by weight of polydimethylsiloxane as the diluent, add both to the beaker containing composite A, and continue stirring at the same stirring speed for 20-25 minutes to obtain composite B. S2.3: Add 3 to 6 parts by volume of a crosslinker and 3 to 6 parts by mass of a catalyst to the beaker containing the composite B, and stir again at the same stirring speed for 10 to 15 minutes to obtain a low Curie point PTC thermistor composite material.

[0009] Furthermore, step S3 tableting includes the following steps: The low Curie point PTC thermistor composite material is poured into a production mold, pressed and formed using a vulcanizer under vacuum and room temperature conditions, and demolded after 24 to 36 hours to obtain a formed green sheet.

[0010] Furthermore, step S4 of preparing the conductive sheet includes the following steps: Conductive silver paste is coated on the surface of the formed green sheet to form an electrode, and sintered at a temperature of 150-250°C to tightly bond the conductive silver paste to the formed green sheet. External leads are then connected to the surface of the conductive silver paste to obtain a conductive sheet.

[0011] Furthermore, step S5 of testing and packaging includes the following steps: The conductive sheet is first subjected to a voltage test and then a resistance test, and is screened according to different resistance values. The screened conductive sheets are then subjected to a quality test, and unqualified conductive sheets are removed. The sheets are then classified, packaged, and stored according to different resistance values ​​to obtain composite heating sheets of PTC thermistors.

[0012] Furthermore, the molar mass ratio of n-tetradecane to n-octanoic acid in step S2.1 is (50-52): (48-50).

[0013] Furthermore, the cross-linking agent in step S2.3 is set to be epoxy resin.

[0014] Furthermore, the catalyst in step S2.3 is set to palladium.

[0015] A composite heating sheet based on a PTC thermistor is prepared by the above-mentioned process for preparing a composite heating sheet based on a PTC thermistor.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Since the isocyanate groups at both ends of diphenylmethane diisocyanate have good reactivity with hydroxyl groups, the present invention uses diphenylmethane diisocyanate to modify the terminal hydroxyl polydimethylsiloxane. Compared with the unmodified terminal hydroxyl polydimethylsiloxane, the composite heating plate prepared by adding the modified terminal hydroxyl polydimethylsiloxane has significantly improved performance in impact resistance, thereby enabling the heating plate to better resist external force impact.

[0017] 2. The composite phase change material obtained by the present invention using n-tetradecane and n-octanoic acid, compared with the single addition of n-tetradecane as a phase change material, the composite heating plate prepared by adding the composite phase change material can not only combine the advantages of multiple single organic phase change materials, but also use high thermal conductivity fillers to form an effective heat conduction network in the composite phase change material, so that heat can be transferred from one part of the material to another more quickly, thereby enhancing the thermal conductivity of the heating plate and improving the thermal stability of the heating plate.

[0018] 3. The present invention uses modified end-hydroxy polydimethylsiloxane as the matrix material, adds dimethylsiloxane as a diluent, and adds a composite phase change material to lower the Curie temperature. At the same time, conductive carbon black and nickel powder with excellent conductive properties are used as conductive fillers. A low-Curie-point PTC material with a Curie temperature of 1 to 5°C is prepared by an in-situ polymerization method. The heating plate processed based on this material is used for electric heating and anti-icing of water pipes in winter. It not only has certain energy-saving properties, but also can make the water pipes heat evenly, avoid burning of the water pipes, and has certain safety and controllability. DETAILED DESCRIPTION

[0019] The following describes in detail a composite heating sheet based on a PTC thermistor and its preparation process provided by the present invention in conjunction with specific embodiments. It is also noted that, in order to make the embodiments more detailed, the following embodiments are best and preferred embodiments, and those skilled in the art may also adopt other alternative methods for implementing certain known technologies. Furthermore, the embodiments are merely for the purpose of describing the embodiments in more detail and are not intended to limit the present invention in any specific way. Example 1:

[0020] A preparation process of a composite heating sheet based on a PTC thermistor comprises the following steps: S1: Preparation of modified hydroxyl-terminated polydimethylsiloxane 10 parts by volume of solvent cyclohexanone, 5 parts by volume of diphenylmethane diisocyanate, 10 parts by volume of terminal hydroxyl polydimethylsiloxane, 2 parts by mass of curing agent, 8 parts by mass of talc and 8 parts by mass of zinc powder were taken respectively and magnetically stirred for 10 minutes to obtain modified terminal hydroxyl polydimethylsiloxane.

[0021] S2: Preparation of low Curie point PTC thermistor composite materials S2.1: 25 parts by volume of n-tetradecane and 25 parts by volume of n-octanoic acid, respectively, with a molar mass ratio of n-tetradecane to n-octanoic acid being 51:49, are placed in a beaker to obtain a mixture, and the mixture in the beaker is stirred with a magnetic stirrer for 15 minutes to obtain a composite phase change material. 15 parts by mass of conductive carbon black and 15 parts by mass of nickel powder as conductive fillers are then added to the beaker containing the composite phase change material. The beaker containing the composite phase change material and the conductive filler is then fixed on a digital electric stirrer at a stirring speed of 750 r / min and stirred for 10 minutes to obtain a composite A; S2.2: Weigh 40 parts by mass of modified hydroxyl-terminated polydimethylsiloxane as the base material and 30 parts by mass of polydimethylsiloxane as the diluent, add both to the beaker containing composite A, and continue stirring at the same stirring speed for 20 minutes to obtain composite B; S2.3: Add 3 parts by volume of epoxy resin as a crosslinking agent and 3 parts by mass of palladium as a catalyst to the beaker containing compound B, and stir again at the same stirring speed for 10 minutes to obtain a low Curie point PTC thermistor composite material.

[0022] S3, tableting The low Curie point PTC thermistor composite material is poured into a production mold, pressed into shape using a vulcanizer under vacuum and room temperature conditions, and demolded after 24 hours to obtain a formed green sheet.

[0023] S4. Preparation of conductive sheet Conductive silver paste is coated on the surface of the formed green sheet to form an electrode, and sintered at a temperature of 150°C to tightly bond the conductive silver paste to the formed green sheet. External leads are then connected to the surface of the conductive silver paste to obtain a conductive sheet.

[0024] S5. Testing and packaging The conductive sheet is first subjected to a voltage test and then a resistance test, and is screened according to different resistance values. The screened conductive sheets are then subjected to a quality test, and unqualified conductive sheets are removed. The sheets are then classified, packaged, and stored according to different resistance values ​​to obtain composite heating sheets of PTC thermistors. Example 2:

[0025] A preparation process of a composite heating sheet based on a PTC thermistor comprises the following steps: S1: Preparation of modified hydroxyl-terminated polydimethylsiloxane 15 parts by volume of solvent cyclohexanone, 7 parts by volume of diphenylmethane diisocyanate, 15 parts by volume of terminal hydroxyl polydimethylsiloxane, 4 parts by mass of curing agent, 10 parts by mass of talc and 10 parts by mass of zinc powder were taken respectively and magnetically stirred for 10 minutes to obtain modified terminal hydroxyl polydimethylsiloxane.

[0026] S2: Preparation of low Curie point PTC thermistor composite materials S2.1: 35 parts by volume of n-tetradecane and 35 parts by volume of n-octanoic acid, respectively, with a molar mass ratio of n-tetradecane to n-octanoic acid being 51:49, are placed in a beaker to obtain a mixture, and the mixture in the beaker is stirred with a magnetic stirrer for 15 minutes to obtain a composite phase change material. 25 parts by mass of conductive carbon black and 25 parts by mass of nickel powder as conductive fillers are then added to the beaker containing the composite phase change material. The beaker containing the composite phase change material and the conductive filler is then fixed on a digital electric stirrer at a stirring speed of 750 r / min and stirred for 10 minutes to obtain a composite A; S2.2: Weigh 45 parts by mass of modified hydroxyl-terminated polydimethylsiloxane as the matrix material and 35 parts by mass of polydimethylsiloxane as the diluent, add both to the beaker containing composite A, and continue stirring at the same stirring speed for 20 minutes to obtain composite B; S2.3: Add 6 parts by volume of epoxy resin as a crosslinking agent and 6 parts by mass of palladium as a catalyst to the beaker containing compound B, and stir again at the same stirring speed for 10 minutes to obtain a low Curie point PTC thermistor composite material.

[0027] S3, tableting The low Curie point PTC thermistor composite material is poured into a production mold, pressed into shape using a vulcanizer under vacuum and room temperature conditions, and demolded after 24 hours to obtain a formed green sheet.

[0028] S4. Preparation of conductive sheet Conductive silver paste is coated on the surface of the formed green sheet to form an electrode, and sintered at a temperature of 150°C to tightly bond the conductive silver paste to the formed green sheet. External leads are then connected to the surface of the conductive silver paste to obtain a conductive sheet.

[0029] S5. Testing and packaging The conductive sheet is first subjected to a voltage test and then a resistance test, and is screened according to different resistance values. The screened conductive sheets are then subjected to a quality test, and unqualified conductive sheets are removed. The sheets are then classified, packaged, and stored according to different resistance values ​​to obtain composite heating sheets of PTC thermistors. Example 3:

[0030] A preparation process of a composite heating sheet based on a PTC thermistor comprises the following steps: S1: Preparation of modified hydroxyl-terminated polydimethylsiloxane 10 parts by volume of solvent cyclohexanone, 5 parts by volume of diphenylmethane diisocyanate, 10 parts by volume of terminal hydroxyl polydimethylsiloxane, 2 parts by mass of curing agent, 8 parts by mass of talc and 8 parts by mass of zinc powder were taken respectively and magnetically stirred for 15 minutes to obtain modified terminal hydroxyl polydimethylsiloxane.

[0031] S2: Preparation of low Curie point PTC thermistor composite materials S2.1: 25 parts by volume of n-tetradecane and 25 parts by volume of n-octanoic acid, respectively, with a molar mass ratio of n-tetradecane to n-octanoic acid being 50:51, are placed in a beaker to obtain a mixture, and the mixture in the beaker is stirred with a magnetic stirrer for 25 minutes to obtain a composite phase change material. 15 parts by mass of conductive carbon black and 15 parts by mass of nickel powder as conductive fillers are then added to the beaker containing the composite phase change material. The beaker containing the composite phase change material and the conductive filler is then fixed on a digital electric stirrer at a stirring speed of 850 r / min and stirred for 15 minutes to obtain a composite A; S2.2: Weigh 40 parts by mass of modified hydroxyl-terminated polydimethylsiloxane as the matrix material and 30 parts by mass of polydimethylsiloxane as the diluent, add both to the beaker containing composite A, and continue stirring at the same stirring speed for 25 minutes to obtain composite B; S2.3: Add 3 parts by volume of epoxy resin as a crosslinking agent and 3 parts by mass of palladium as a catalyst to the beaker containing composite B, and stir again at the same stirring speed for 15 minutes to obtain a low Curie point PTC thermistor composite material.

[0032] S3, tableting The low Curie point PTC thermistor composite material is poured into a production mold, pressed into shape using a vulcanizer under vacuum and room temperature conditions, and demolded after 36 hours to obtain a formed green sheet.

[0033] S4. Preparation of conductive sheet Conductive silver paste is coated on the surface of the formed green sheet to form an electrode, and sintered at a temperature of 250°C to tightly bond the conductive silver paste to the formed green sheet. External leads are then connected to the surface of the conductive silver paste to obtain a conductive sheet.

[0034] S5. Testing and packaging The conductive sheet is first subjected to a voltage test and then a resistance test, and is screened according to different resistance values. The screened conductive sheets are then subjected to a quality test, and unqualified conductive sheets are removed. The sheets are then classified, packaged, and stored according to different resistance values ​​to obtain composite heating sheets of PTC thermistors.

[0035] Comparative Example 1 Compared with Example 1, the difference of Comparative Example 1 is that the step of modifying the terminal hydroxyl polydimethylsiloxane in step S2.1 is removed, and the modified terminal hydroxyl polydimethylsiloxane in step S2.2 is replaced with terminal hydroxyl polydimethylsiloxane. The other steps remain unchanged to prepare a composite heating plate of a PTC thermistor, which is recorded as Comparative Example 1.

[0036] Comparative Example 2 Compared with Example 1, Comparative Example 2 is different in that the addition of n-octanoic acid in step S2.1 is removed, and the other steps remain unchanged to prepare a PTC thermistor composite heating sheet, which is recorded as Comparative Example 2.

[0037] Impact resistance test Example 1 Example 2 Example 3 Comparative Example 1 Impact energy / J 12.2 16.4 13.8 6.3 Table 1 As can be seen from Table 1, the PTC thermistor composite heating sheets prepared in Examples 1-3 have significantly greater impact work of fracture than that of Comparative Example 1, indicating that the modification of hydroxy-terminated polydimethylsiloxane can improve the impact resistance of the PTC thermistor composite heating sheet, thereby helping to extend the service life of the PTC thermistor composite heating sheet in relatively harsh environments.

[0038] Thermal conductivity test and thermal stability test Example 1 Example 2 Example 3 Comparative Example 2 <![CDATA[Thermal conductivity before cycling / W·(m·K) -1 > 453.67 453.58 452.96 430.13 Table 2 Example 1 Example 2 Example 3 Comparative Example 2 <![CDATA[Thermal conductivity after cycling / W·(m·K) -1 > 453.66 453.58 452.95 415.26 Table 3 As can be seen from Tables 2 and 3, the thermal conductivity of the PTC thermistor composite heating sheet prepared in Examples 1-3 is significantly greater than that of Comparative Example 2, indicating that compounding n-tetradecane and n-octanoic acid as phase change materials can improve the thermal conductivity of the PTC thermistor composite heating sheet. By comparing the changes in thermal conductivity before and after the cycle, the thermal conductivity of the PTC thermistor composite heating sheet prepared in Examples 1-3 hardly changes much before and after the cycle, while the thermal conductivity of Comparative Example 2 changes significantly before and after the cycle, indicating that compounding n-tetradecane and n-octanoic acid as phase change materials can improve the thermal stability of the PTC thermistor composite heating sheet. It can be concluded that the PTC thermistor composite heating sheet has good thermal conductivity and thermal stability, which is beneficial to better anti-icing of water pipes.

[0039] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A preparation process of a composite heating sheet based on a PTC thermistor, characterized in that: The following steps are included: S1: Preparation of modified hydroxyl-terminated polydimethylsiloxane Separately taking solvent cyclohexanone, diphenylmethane diisocyanate, hydroxyl-terminated polydimethylsiloxane, curing agent, talc powder and zinc powder, mixing and stirring to obtain modified hydroxyl-terminated polydimethylsiloxane; S2: Preparation of low Curie point PTC thermistor composite materials n-Tetradecane and n-octanoic acid are placed in a beaker and mixed and stirred, conductive carbon black and nickel powder are added as conductive fillers, mixed and stirred again, modified hydroxyl-terminated polydimethylsiloxane is added as a matrix material, polydimethylsiloxane is added as a diluent, mixed and stirred again, and a cross-linking agent and a catalyst are added to obtain a low Curie point PTC thermistor composite material; S3: Tablet forming Compression molding the low Curie point PTC thermistor composite material to obtain a molded green sheet; S4: Preparation of conductive sheet The surface of the formed green sheet is coated with molten metal to form an electrode, and the molten metal is sintered, and then external leads are connected to the metal surface to obtain a conductive sheet; S5: Testing and Packaging Conduct relevant tests on the conductive sheets, screen out qualified products, and then package and store them.

2. A process for preparing a composite heating sheet based on a PTC thermistor according to claim 1, characterized in that: Step S1: preparing the modified hydroxy-terminated polydimethylsiloxane comprises the following steps: 10-15 parts by volume of solvent cyclohexanone, 5-7 parts by volume of diphenylmethane diisocyanate, 10-15 parts by volume of terminal hydroxyl polydimethylsiloxane, 2-4 parts by mass of curing agent, 8-10 parts by mass of talc powder and 8-10 parts by mass of zinc powder were respectively taken and magnetically stirred for 10-15 minutes to obtain modified terminal hydroxyl polydimethylsiloxane.

3. A process for preparing a composite heating sheet based on a PTC thermistor according to claim 2, characterized in that: Step S2 of preparing the low Curie point PTC thermistor composite material includes the following steps: S2.1: 25 to 35 parts by volume of n-tetradecane and 25 to 35 parts by volume of n-octanoic acid are respectively taken and placed in a beaker to obtain a mixture. The mixture in the beaker is then stirred with a magnetic stirrer for 15 to 25 minutes to obtain a composite phase change material. 15 to 25 parts by mass of conductive carbon black and 15 to 25 parts by mass of nickel powder as conductive fillers are then added to the beaker containing the composite phase change material. The beaker containing the composite phase change material and the conductive filler is then fixed on a digital electric stirrer at a stirring speed of 750 to 850 r / min and stirred for 10 to 15 minutes to obtain a composite A. S2.2: Weigh 40-45 parts by weight of modified hydroxyl-terminated polydimethylsiloxane as the base material and 30-35 parts by weight of polydimethylsiloxane as the diluent, add both to the beaker containing composite A, and continue stirring at the same stirring speed for 20-25 minutes to obtain composite B. S2.3: Add 3 to 6 parts by volume of a crosslinker and 3 to 6 parts by mass of a catalyst to the beaker containing the composite B, and stir again at the same stirring speed for 10 to 15 minutes to obtain a low Curie point PTC thermistor composite material.

4. The process for preparing a composite heating sheet based on a PTC thermistor according to claim 3, wherein: Step S3 tableting comprises the following steps: The low Curie point PTC thermistor composite material is poured into a production mold, pressed and formed using a vulcanizer under vacuum and room temperature conditions, and demolded after 24 to 36 hours to obtain a formed green sheet.

5. The process for preparing a composite heating sheet based on a PTC thermistor according to claim 4, characterized in that: Step S4 of preparing the conductive sheet includes the following steps: Conductive silver paste is coated on the surface of the formed green sheet to form an electrode, and sintered at a temperature of 150-250°C to tightly bond the conductive silver paste to the formed green sheet. External leads are then connected to the surface of the conductive silver paste to obtain a conductive sheet.

6. The process for preparing a composite heating sheet based on a PTC thermistor according to claim 5, characterized in that: Step S5 testing and packaging includes the following steps: The conductive sheet is first subjected to a voltage test and then a resistance test, and is screened according to different resistance values. The screened conductive sheets are then subjected to a quality test, and unqualified conductive sheets are removed. The sheets are then classified, packaged, and stored according to different resistance values ​​to obtain composite heating sheets of PTC thermistors.

7. The process for preparing a composite heating sheet based on a PTC thermistor according to claim 6, characterized in that: The molar mass ratio of n-tetradecane to n-octanoic acid in step S2.1 is (50-52):(48-50).

8. The process for preparing a composite heating sheet based on a PTC thermistor according to claim 7, characterized in that: The cross-linking agent in step S2.3 is set to epoxy resin.

9. The process for preparing a composite heating sheet based on a PTC thermistor according to claim 8, characterized in that: The catalyst in step S2.3 is set to palladium.

10. A composite heating sheet based on a PTC thermistor, characterized in that: The composite heating sheet is prepared by the preparation process of a PTC thermistor-based composite heating sheet according to any one of claims 1 to 9.