A high-voltage, high-stability high-temperature PPTC material and a preparation method thereof

Abstract

This invention discloses a high-voltage-resistance, high-stability, high-temperature PPTC material and its preparation method, belonging to the technical field of circuit protection components. It comprises the following components by weight: 115-130 parts polymer matrix, 30-70 parts conductive filler, 0.5-5 parts compatibilizer, and 1-5 parts acid scavenger. The polymer matrix is ​​one or more blends of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, polyetheretherketone, and polyphenylene sulfide. The conductive filler is carbon black. The compatibilizer is a maleic anhydride-grafted polyolefin elastomer. The acid scavenger is calcium stearate. This invention also discloses a preparation method for this material, including mixing and granulation, coating, hot pressing, irradiation crosslinking, and encapsulation steps. By optimizing the polymer matrix composition, introducing compatibilizers and acid scavengers, and optionally adding maleimide-modified sensitizers, this invention significantly improves the material's voltage resistance and high-temperature stability, making it suitable for overcurrent protection in automotive electronics, communication power supplies, and other fields with voltage levels of 48V and above.

Description

Technical Field

[0001] This invention belongs to the field of circuit protection element technology, specifically relating to a high-voltage, high-stability high-temperature PPTC material and its preparation method. Background Technology

[0002] Polymer positive temperature coefficient (PPTC) thermistors are widely used in overcurrent protection. With the development of new energy vehicles, 48V communication power supplies, and industrial control, higher requirements are being placed on the voltage withstand rating of PPTC devices, such as in 48VDC systems. They also require extremely stable resistance characteristics after surface mounting and during long-term use. Traditional PPTC materials are based on polyethylene and other matrices, which have limited temperature resistance. The high temperature of approximately 270°C during soldering can easily cause material expansion and damage to the crystal structure, resulting in an irreversible and significant increase in resistance, typically exceeding two times or even higher. Furthermore, after long-term storage, factors such as internal stress relaxation, polymer aging, and changes in the filler interface can cause resistance drift, affecting the accuracy and reliability of circuit protection.

[0003] High-temperature PPTC generally refers to PPTC products that meet automotive-grade requirements, meaning they must pass the globally recognized AEC-Q200 reliability testing standard for automotive electronic passive devices. The two most important aspects are temperature resistance and voltage withstand rating. Temperature resistance requires the device to function normally after being stored at 125°C for 1000 hours. Voltage withstand requires the electrical system voltage to be no less than 48V. Furthermore, surface-mount devices must use lead-free reflow soldering processes, and resistance to soldering heat is also a fundamental requirement for high-temperature PPTC devices.

[0004] Existing technologies struggle to simultaneously resolve the contradiction between high voltage resistance and high-temperature stability. Using high-melting-point resin matrices such as PVDF is beneficial for improving weld heat resistance and high-temperature stability, but the interaction between its strong fluorocarbon polar chains and the carbon black surface is weak, resulting in poor compatibility. This leads to difficulties in dispersing carbon black in PVDF, causing it to easily agglomerate and form localized conductive enrichment areas, thus resulting in poor voltage resistance.

[0005] Therefore, developing a high-temperature PPTC material and process that can achieve a resistance change rate of less than 1.8 times after lead-free soldering at a 48V withstand voltage level, and whose resistance change rate remains stable between 0.80 and 1.20 times after long-term high-temperature storage, has significant industrial value. Summary of the Invention

[0006] (I) Technical Solution

[0007] To address the aforementioned technical problems, this invention provides a high-pressure-resistant, high-stability, high-temperature PPTC material, comprising the following components in parts by weight:

[0008] 115-130 parts polymer matrix; 30-70 parts conductive filler; 0.5-5 parts compatibilizer; 1-5 parts acid scavenger;

[0009] The polymer matrix is ​​one or more blends of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, polyetheretherketone, and polyphenylene sulfide; the conductive filler is carbon black; the compatibilizer is maleic anhydride-grafted polyolefin elastomer; and the acid scavenger is calcium stearate.

[0010] Furthermore, the polymer matrix is ​​a mixture of polyvinylidene fluoride and ethylene-tetrafluoroethylene copolymer, and the weight ratio of polyvinylidene fluoride to ethylene-tetrafluoroethylene copolymer is 100:15-30.

[0011] Furthermore, the selected carbon black has an oil absorption value of 70-150.

[0012] Furthermore, the maleic anhydride-grafted polyolefin elastomer used is a maleic anhydride-grafted polyethylene elastomer, and the grafting degree is 0.1-0.5%.

[0013] Furthermore, it also includes antioxidants and processing aids, wherein the antioxidant used is a hindered phenolic antioxidant, and the processing aid is a PPA aid.

[0014] Furthermore, it also includes a sensitizer, wherein the sensitizer is a maleimide-modified sensitizer, and the sensitizer is present in parts by weight of 0.3-1 parts.

[0015] Furthermore, the preparation method of the maleimide-modified sensitizer is as follows:

[0016] The amino protecting agent was dissolved in THF and slowly added to melamine under alkaline conditions. After reacting for 12-16 hours, the pH was adjusted to 4-5 and a precipitate was formed. The precipitate was then filtered and thoroughly dried.

[0017] The dried precipitate was poured into anhydrous DMF and potassium carbonate was added to obtain a suspension. Allyl bromide was slowly added dropwise under nitrogen protection. The mixture was heated to 80°C and stirred for 24 hours. The inorganic salt was removed by filtration and the solvent was removed by rotary evaporation. The product was then purified and recrystallized to obtain the dielylated product.

[0018] The dienylated product was added to dichloromethane, and excess trifluoroacetic acid was added. The mixture was stirred at room temperature for 2-4 hours. The solvent and excess raw material were removed by rotary evaporation, and the pH was adjusted to 8-9 to obtain a solid product. The solid product was then filtered, washed with water, and dried.

[0019] N-maleimide acetic acid was added to anhydrous DMF, along with a condensing agent and an activator. The solid product was then added to DMF to obtain a suspension. The suspension was added dropwise to N-maleimide acetic acid and stirred at room temperature for 18-24 hours. The reaction solution was then added to ice water to precipitate the precipitate. The crude product was collected by filtration and then purified and dried to obtain the final product.

[0020] Based on the same concept, this invention also proposes a method for preparing a high-pressure-resistant, high-stability, high-temperature PPTC material. The method includes a mixing and granulation step, as well as a coating and product packaging step. The mixing and granulation step includes the following steps:

[0021] S1: The above polymer matrix, conductive filler, compatibilizer, acid scavenger, antioxidant and processing aid are mixed in a high-speed mixer;

[0022] S2: Add the mixture from step S1 to a reciprocating single-screw extruder for melt blending;

[0023] S3: The melt from step S2 is extruded, cooled with water, and pelletized to obtain masterbatch, and the moisture in the masterbatch is removed;

[0024] The coating and product packaging steps include the following steps:

[0025] S4: The dried PPTC masterbatch is fed into a single-screw extruder. The plasticized conductive masterbatch is coated with a film by two rubber rollers. The temperature of the coating rollers is set to 220-240℃, the melt pressure is 15-25MPa, the linear speed is 0.3-2 m / min, and the final sheet thickness is 0.2-2.0 mm with a thickness tolerance of ±5%.

[0026] S5: The sheet coated with nickel-plated copper foil is hot-pressed on a press at a temperature of 220±10℃ and a pressure of 5±1Mpa. After hot pressing, it is then cold-pressed for 4 minutes each.

[0027] S6: Irradiate and crosslink the pressed PPTC sheet;

[0028] S7: Encapsulate the irradiated PPTC sheet.

[0029] Furthermore, step S1 specifically includes step S1a: adding 10 parts of ethylene-tetrafluoroethylene copolymer, 0.5 parts of compatibilizer and 0.5 parts of sensitizer to a high-speed mixer for mixing, then adding to a twin-screw extruder for melt blending, and finally extruding, water cooling, pelletizing and drying the melt;

[0030] S1b: Add the remaining polymer matrix, conductive filler, particles obtained in step S1a, and all processing aids into a high-speed mixer for mixing.

[0031] (ii) Beneficial effects

[0032] The beneficial effects of this invention are as follows:

[0033] 1. By using polyvinylidene fluoride and ethylene-tetrafluoroethylene copolymer as the polymer matrix and maleic anhydride-grafted polyolefin elastomer as a compatibilizer, the dispersion uniformity of carbon black in the matrix is ​​significantly improved, the formation of local conductive enrichment areas is avoided, and the material can work stably for a long time at 48V voltage, meeting the AEC-Q200 automotive grade requirements.

[0034] 2. The introduction of ethylene-tetrafluoroethylene copolymer improves the heat distortion temperature and long-term heat resistance of the material. Combined with the neutralizing effect of acidic substances such as hydrofluoric acid generated during processing and use by the acid scavenger calcium stearate, it effectively inhibits polymer degradation and damage to the conductive network.

[0035] 3. The present invention optionally introduces maleimide-modified sensitizer and adopts a stepwise blending process to make the sensitizer preferentially enriched in the ethylene-tetrafluoroethylene copolymer phase, avoiding mutual interference with the acid scavenger, and further improving the irradiation crosslinking efficiency and the long-term stability of the material. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a TEM image of Example 1.

[0038] Figure 2 This is a TEM image of Example 7. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] To address the problems existing in the relevant prior art, please refer to the figure. This invention proposes a high-pressure-resistant, high-stability, high-temperature PPTC material, comprising the following components in parts by weight:

[0041] 115-130 parts polymer matrix; 30-70 parts conductive filler; 0.5-5 parts compatibilizer; 1-5 parts acid scavenger.

[0042] Specifically, in this embodiment, the polymer matrix is ​​a mixture of polyvinylidene fluoride (PVDF) and ethylene-tetrafluoroethylene (ethylene-tetrafluoroethylene) copolymer, with a weight ratio of PVDF to ethylene-tetrafluoroethylene copolymer of 100:15-30. The ethylene-tetrafluoroethylene has a melting point of approximately 260-270°C and can serve as a high-temperature skeleton, uniformly dispersed within the PVDF system. This improves the overall heat distortion temperature and long-term heat resistance of the material. Simultaneously, the interface region of the two-phase structure of the ethylene-tetrafluoroethylene and PVDF melt blend provides more dispersion areas for the conductive filler, preventing carbon black from being encapsulated in the single-phase region and forming agglomerates, thus affecting its conductivity. In some other embodiments, the polymer matrix may also be one or more blends of PVDF, ethylene-tetrafluoroethylene copolymer, polyetheretherketone (PEEK), and polyphenylene sulfide (PPS).

[0043] The selected conductive filler is carbon black, with an oil absorption value of 70-150. The oil absorption value is affected by the carbon black particle size and structure, ultimately directly determining its surface energy. A higher oil absorption value and higher structure result in better conductivity when used as a conductive filler, but also make it prone to agglomeration in the matrix, leading to poor dispersibility and ultimately a decrease in voltage withstand capability. Conversely, if the carbon black's oil absorption value is too low, its conductivity is poor, requiring an increase in its dosage. However, excessive conductive filler dosage can easily reduce the final PTC strength and voltage withstand capability. Therefore, to balance dispersibility, conductivity, and PTC strength, the carbon black used in this design has an oil absorption value of 70-150.

[0044] The compatibilizer is a maleic anhydride-grafted polyolefin elastomer. In this embodiment, the polymer matrix is ​​PVDF / ETFE, which has a low surface energy. However, the selected conductive filler, carbon black, contains polar functional groups such as carboxyl and hydroxyl groups on its surface, which easily leads to poor compatibility between the two and easy separation at the interface. Therefore, the compatibilizer needs to be a maleic anhydride-grafted polyolefin elastomer that improves the bonding ability between the two. The polyolefin elastomer backbone has a non-polar structure, which has good compatibility with the polymer matrix, while the grafted maleic anhydride groups are compatible with the polar functional groups such as carboxyl and hydroxyl groups on the carbon black surface. Hydrogen bonds are formed between the groups, allowing the compatibilizer to act as a bridge between the polymer matrix and the carbon black filler. This inhibits carbon black agglomeration and achieves uniform dispersion. Specifically, the maleic anhydride-grafted polyolefin elastomer used is a maleic anhydride-grafted polyethylene elastomer. During melt blending and subsequent processing, a small amount of maleic anhydride groups will undergo thermal decomposition, generating maleic acid and acrylic acid. These acidic substances will affect the function of the acid scavenger in the system. Therefore, the grafting degree of the maleic anhydride-grafted polyethylene elastomer used in this embodiment is 0.1%-0.5%.

[0045] The acid scavenger is either calcium stearate or zinc oxide. Specifically, in this embodiment, calcium stearate is used as the acid scavenger. During the melt extrusion, hot pressing, and long-term current cycling heating process, PVDF undergoes a defluorination reaction, releasing hydrofluoric acid. Hydrofluoric acid catalyzes the degradation of PVDF and also damages the conductive network structure, ultimately leading to a decrease in the voltage resistance and stability of the PPTC material produced. Therefore, an acid scavenger is added in this solution to neutralize the acidic substances generated in the system during production and use, mainly hydrofluoric acid generated during PVDF processing and acidic substances generated by the thermal decomposition of the compatibilizer.

[0046] In addition, it includes antioxidants and processing aids. The antioxidants used are hindered phenolic antioxidants, and the processing aids are PPA additives, which are commonly used additives in the PPTC processing process and are existing technologies, so they are not specifically limited here.

[0047] It also includes a sensitizer, which is a maleimide-modified sensitizer, with a weight of 0.3-1 parts.

[0048] The preparation method of maleimide-modified sensitizer is as follows:

[0049] Step 1: Dissolve the amino protecting agent in THF and slowly add it to melamine under alkaline conditions. After reacting for 12-16 hours, adjust the pH to 4-5 and precipitate. Filter the precipitate and dry it thoroughly.

[0050] The specific operation is as follows: Add 12.6g of melamine to a three-necked flask, add 200ml of water and 4.4g of sodium hydroxide, heat to 50℃ and stir until dissolved; dissolve 24g of Boc2O in 50ml of THF, and transfer the three-necked flask to an ice-water bath to cool to 0-5 degrees Celsius. Under low temperature conditions, add the Boc2O solution dropwise to the three-necked flask; after the addition is complete, stir the reaction at room temperature for 12-15 hours, and monitor the reaction progress by TLC. The specific developing solvent is dichloromethane:methanol = 10:1. When the spots of the raw material on the TLC plate completely disappear, stop the reaction, add hydrochloric acid to the reaction solution to adjust the pH value to 4-5, precipitate out, filter, wash and dry the filter cake to obtain N-Boc-melamine.

[0051] Step 2: Pour the dried precipitate into anhydrous DMF and add potassium carbonate to obtain a suspension. Under nitrogen protection, slowly add allyl bromide to the suspension. Heat to 80°C and stir for 24 hours. Filter to remove inorganic salts and remove solvent by rotary evaporation. Then, purify and recrystallize to obtain the dielylated product.

[0052] The specific operation is as follows: Weigh 22.6g of N-Boc-melamine from step one and add it to a three-necked flask, along with 200ml of anhydrous DMF and 30g of potassium carbonate. Stir thoroughly to obtain a suspension. Under nitrogen protection, slowly add 26.6g of allyl bromide to the suspension and heat in a water bath to 80℃ with stirring for 24h. After the reaction is complete, cool to room temperature, filter to obtain the filtrate, and then rotary evaporate the filtrate. Finally, dissolve the filtrate in ethyl acetate, wash it several times with water, dry the organic phase with anhydrous sodium sulfate, and rotary evaporate again to obtain the crude product. Recrystallize the crude product using an ethanol / water mixed solvent to obtain purified N-Boc-N',N''-diallyl melamine.

[0053] Step 3: The dielylated product is added to dichloromethane, and excess trifluoroacetic acid is added. The mixture is stirred at room temperature for 2-4 hours. The solvent and excess raw material are removed by rotary evaporation, and the pH is adjusted to 8-9 to obtain a solid product. The solid product is then filtered, washed with water, and dried.

[0054] The specific operation is as follows: Add the N-Boc-N',N''-diallyl melamine from the previous step to a three-necked flask, and add 150 ml of dichloromethane to dissolve it. Place the three-necked flask in an ice-water bath to cool it to 0-5°C, and slowly add 40 ml of trifluoroacetic acid dropwise. After the addition is complete, stir the reaction at room temperature for 2-4 hours. During the reaction, monitor the reaction by TLC. The developing solvent used is DCM:MeOH = 10:1. Stop the reaction when the raw material spot on the top disappears completely. After the reaction is complete, remove the dichloromethane and excess trifluoroacetic acid by rotary evaporation. Add cold water to the residual liquid, and add sodium hydroxide solution to adjust the pH value to 8-9. At this time, a solid will precipitate. Filter to collect the solid, wash it with water, and dry it.

[0055] Step 4: Add N-maleimide acetic acid to anhydrous DMF, along with a condensing agent and an activator. Add the solid product to DMF to obtain a suspension. Add the suspension dropwise to N-maleimide acetic acid and stir at room temperature for 18-24 hours. Add the reaction solution to ice water to precipitate the precipitate. Filter and collect the crude product, and after purification and drying, obtain the final product.

[0056] The specific operation is as follows: Add 17.1g N-maleimide acetic acid, 23.0g EDC·HCl, 13.8g NHS and 150mL anhydrous DMF to a three-necked flask, and stir and activate at room temperature for 30 minutes; add the product from the previous step to 20mL DMF to obtain a suspension, and add the suspension to the three-necked flask; stir and react at room temperature in the dark for 18-24 hours. After the reaction is completed, slowly pour the reaction solution into 1L of ice water, and a large amount of precipitate will precipitate; filter and collect the precipitate, and recrystallize it using DMF / water to remove unreacted raw materials and byproducts, and further purify it by silica gel column chromatography. The final product is dried under vacuum in the dark at 50°C to obtain the maleimide modified sensitizer.

[0057] This invention also proposes a method for preparing a high-pressure-resistant, high-stability, high-temperature PPTC material. The method includes a mixing and granulation step, a coating molding step, and a product packaging step. The mixing and granulation step includes the following steps:

[0058] S1: The above polymer matrix, conductive filler, compatibilizer, acid scavenger, antioxidant and processing aid are mixed in a high-speed mixer;

[0059] S2: Add the mixture from step S1 to a reciprocating single-screw extruder for melt blending;

[0060] S3: The melt from step S2 is extruded, cooled with water, and pelletized to obtain masterbatch, and the moisture in the masterbatch is removed;

[0061] The coating and product packaging process includes the following steps:

[0062] S4: The dried PPTC masterbatch is fed into a single-screw extruder. The plasticized conductive masterbatch is coated with a film by two rubber rollers. The temperature of the coating rollers is set to 220-240℃, the melt pressure is 15-25MPa, the linear speed is 0.3-2 m / min, and the final sheet thickness is 0.2-2.0 mm with a thickness tolerance of ±5%.

[0063] S5: The sheet coated with nickel-plated copper foil is hot-pressed on a press at a temperature of 220±10℃ and a pressure of 5±1Mpa. After hot pressing, it is then cold-pressed for 4 minutes each.

[0064] S6: Irradiate and crosslink the pressed PPTC sheet;

[0065] S7: Encapsulate the irradiated PPTC sheet.

[0066] The following are specific examples:

[0067] Example 1

[0068] S1: By weight, mix 100 parts PVDF, 20 parts ETFE, 50 parts carbon black, 3 parts compatibilizer, 3 parts acid scavenger, 0.3 parts antioxidant, and 0.1 parts fluoropolymer processing aid in a high-speed mixer at room temperature, adjusting the speed range to 500-1500 rpm, and premix for 5-30 minutes.

[0069] S2: Add the premix to a reciprocating single-screw extruder for melt blending, wherein the temperatures of the first to fourth zones are set to 205-215℃, 225-235℃, 240-250℃, and 230-235℃, respectively.

[0070] S3: The melt is extruded, water-cooled, and pelletized to obtain PPTC masterbatch. The masterbatch is then vacuum-dried at 80-100℃ for 4-6 hours to remove moisture.

[0071] The coating and product packaging process includes the following steps:

[0072] S4: The dried PPTC masterbatch is fed into a single-screw extruder. The plasticized conductive masterbatch is coated by two rubber rollers. The roller temperature is set within the range of 230±10℃, the melt pressure is 15-25MPa, the linear speed is 0.3-2 m / min, and the final sheet thickness is 0.2-2.0mm with a thickness tolerance of ±5%.

[0073] S5: The sheet is laminated with nickel-plated copper foil on both sides and then hot-pressed on a press. The hot-pressing temperature is 220±10℃, the pressure is 5±1Mpa, the hot-pressing / cold-pressing time is 4 minutes each, and Teflon is used as a buffer layer for sheet pressing.

[0074] S6: The pressed PPTC sheet is cross-linked by irradiation with gamma rays at a dose of 20-50 kGy.

[0075] S7: Encapsulate the irradiated PPTC sheet.

[0076] The following tests were performed on the products respectively:

[0077] Initial resistance R0 test: 5.0±2.5mΩ, meeting the current requirement of 3A at 25℃ and 0.9A at 125℃.

[0078] Withstand voltage test: Force PPTC into a high-resistivity state and apply a constant voltage of 48V across its terminals for 168 hours. If there is no breakdown, it is considered a pass; otherwise, it is considered a fail.

[0079] Resistor R1 after reflow soldering: After two reflow soldering cycles according to the standard lead-free reflow soldering process, measure the ratio of resistance R1 to R0. The ratio should be between 1.5 and 1.7.

[0080] Resistance after long-term storage: After being stored at 125℃ for 1000 hours, measure the ratio of resistance R2 to R0. The ratio should be between 0.8 and 0.9.

[0081] Current withstand test: Apply a large current of 40A to the PPTC at a constant voltage of 48V, allow it to cool naturally and return to a low resistance state 1000 times, and then measure the ratio of resistance R3 to R0. The ratio should be between 1.2 and 1.8.

[0082] The operation steps of Examples 2 to 8 are the same as those of Example 1, except that the selected components are different and the testing methods are the same.

[0083] Examples 9 and 10 also include a maleimide-modified sensitizer, and the specific operating steps are as follows:

[0084] Step S1 specifically includes step S1a: adding 10 parts of ethylene-tetrafluoroethylene copolymer, 0.5 parts of compatibilizer and 0.5 parts of sensitizer to a high-speed mixer and mixing them, then adding them to a twin-screw extruder for melt blending, and finally extruding, water cooling, pelletizing and drying the melt;

[0085] S1b: Add the remaining polymer matrix, conductive filler, particles obtained in step S1a, and all processing aids into a high-speed mixer for mixing.

[0086] The other steps S2-S7 are the same as in Example 1, and the testing method is also the same as in Example 1.

[0087] The component selections of Examples 1 to 10 are statistically analyzed and tabulated as follows:

[0088] Furthermore, the test results for Examples 10 to 19 are as follows:

[0089] Based on the data in the two tables above, it can be seen that Examples 1-6, 9, and 10 passed the test, while Examples 7 and 8 failed the test. Please refer to [link / reference needed]. Figure 1 and Figure 2 High-magnification TEM microscopy analysis showed that carbon black was irregularly spherical or near-spherical with a porous or rough surface. It appeared as a dark gray-black color in the image, with relatively shallow contrast due to its low carbon atomic number and weak electron scattering ability. The particle size was approximately 20-100 nm. The acid absorber, similar to carbon black, was irregularly spherical, but due to differences in crystal structure, it exhibited sharp edges and variations in internal contrast. Containing elements with higher atomic numbers, its particle contrast was slightly deeper than carbon black, and its particle size was greater than 100 nm. In the samples of Examples 1 and 7, carbon black and the acid absorber calcium stearate were uniformly dispersed. In Example 1, the acid absorber calcium stearate was relatively concentrated in certain areas. The acid absorber neutralizes the hydrofluoric acid produced by PVDF at high temperatures. If HF is not removed in time, it will lead to polymer decomposition and a significant decrease in the pressure resistance rating. Because PVDF is more polar than ETFE, the acid absorber is mainly dispersed in PVDF, and its enrichment in PVDF is beneficial for improving the pressure resistance rating. The main difference between the formulations in Example 1 and Example 7 lies in the ratio of PVDF to ETFE. A higher content of ETFE is beneficial for increasing the effective concentration of the acid scavenger in PVDF.

[0090] Furthermore, in Examples 9 and 10, a maleimide-modified sensitizer was added, and the sensitizer was pre-blended with ETFE and a compatibilizer to obtain a sensitizer complex. This complex was mainly enriched in the ETFE phase and could form a monolayer covering at the PVDF / ETFE interface, acting as both a "molecular bridge" connecting the two phases and a free radical initiation site. Through stepwise blending, the acid absorber was mainly dispersed in PVDF, while the sensitizer was mainly distributed in ETFE. This also reduced the impact of the maleimide-modified sensitizer on the acid absorber, ensuring that it could effectively adsorb hydrofluoric acid generated during processing and use, and reducing the impact of its own acidic groups and the acidic groups generated by the decomposition of a small amount of raw materials during processing on the performance of the acid absorber itself.

[0091] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-pressure-resistant, high-stability, high-temperature PPTC material, characterized in that, The components include the following parts by weight: 115-130 parts polymer matrix; 30-70 parts conductive filler; 0.5-5 parts compatibilizer; 1-5 parts acid scavenger; The polymer matrix is ​​one or more blends of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, polyetheretherketone, and polyphenylene sulfide; the conductive filler is carbon black; the compatibilizer is maleic anhydride-grafted polyolefin elastomer; and the acid scavenger is calcium stearate.

2. The high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 1, characterized in that, The polymer matrix is ​​a mixture of polyvinylidene fluoride and ethylene-tetrafluoroethylene copolymer, and the weight ratio of polyvinylidene fluoride to ethylene-tetrafluoroethylene copolymer is 100:15-30.

3. The high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 1, characterized in that, The selected carbon black has an oil absorption value of 70-150.

4. The high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 1, characterized in that, The maleic anhydride-grafted polyolefin elastomer used is a maleic anhydride-grafted polyethylene elastomer with a grafting degree of 0.1-0.5%.

5. The high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 1, characterized in that, It also includes antioxidants and processing aids, wherein the antioxidants used are hindered phenolic antioxidants and the processing aids are PPA additives.

6. The high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 1, characterized in that, It also includes a sensitizer, wherein the sensitizer is a maleimide-modified sensitizer, and the sensitizer is present in parts by weight of 0.3-1 parts.

7. The high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 6, characterized in that, The preparation method of the maleimide-modified sensitizer is as follows: The amino protecting agent was dissolved in THF and slowly added to melamine under alkaline conditions. After reacting for 12-16 hours, the pH was adjusted to 4-5 and a precipitate was formed. The precipitate was then filtered and thoroughly dried. The dried precipitate was poured into anhydrous DMF and potassium carbonate was added to obtain a suspension. Allyl bromide was slowly added dropwise under nitrogen protection. The mixture was heated to 80°C and stirred for 24 hours. The inorganic salt was removed by filtration and the solvent was removed by rotary evaporation. The product was then purified and recrystallized to obtain the dielylated product. The dienylated product was added to dichloromethane, and excess trifluoroacetic acid was added. The mixture was stirred at room temperature for 2-4 hours. The solvent and excess raw material were removed by rotary evaporation, and the pH was adjusted to 8-9 to obtain a solid product. The solid product was then filtered, washed with water, and dried. N-maleimide acetic acid was added to anhydrous DMF, along with a condensing agent and an activator. The solid product was then added to DMF to obtain a suspension. The suspension was added dropwise to N-maleimide acetic acid and stirred at room temperature for 18-24 hours. The reaction solution was then added to ice water to precipitate the precipitate. The crude product was collected by filtration and then purified and dried to obtain the final product.

8. A method for preparing a high-pressure-resistant, high-stability, high-temperature PPTC material as described in any one of claims 1-7, characterized in that, The method includes a mixing and granulation step, as well as a coating and product packaging step. The mixing and granulation step includes the following steps: S1: The above polymer matrix, conductive filler, compatibilizer, acid scavenger, antioxidant and processing aid are mixed in a high-speed mixer; S2: Add the mixture from step S1 to a reciprocating single-screw extruder for melt blending; S3: The melt from step S2 is extruded, cooled with water, and pelletized to obtain masterbatch, and the moisture in the masterbatch is removed; The coating and product packaging steps include the following steps: S4: The dried PPTC masterbatch is fed into a single-screw extruder. The plasticized conductive masterbatch is coated with a film by two rubber rollers. The temperature of the coating rollers is set to 220-240℃, the melt pressure is 15-25MPa, the linear speed is 0.3-2 m / min, and the final sheet thickness is 0.2-2.0 mm with a thickness tolerance of ±5%. S5: The sheet coated with nickel-plated copper foil is hot-pressed on a press at a temperature of 220±10℃ and a pressure of 5±1Mpa. After hot pressing, it is then cold-pressed for 4 minutes each. S6: Irradiate and crosslink the pressed PPTC sheet; S7: Encapsulate the irradiated PPTC sheet.

9. The method for preparing a high-pressure-resistant, high-stability, high-temperature PPTC material according to claim 8, characterized in that: The specific steps of step S1 include step S1a: adding 10 parts of ethylene-tetrafluoroethylene copolymer, 0.5 parts of compatibilizer and 0.5 parts of sensitizer to a high-speed mixer and mixing them, then adding them to a twin-screw extruder for melt blending, and finally extruding, water cooling, pelletizing and drying the melt; S1b: Add the remaining polymer matrix, conductive filler, particles obtained in step S1a, and all processing aids into a high-speed mixer for mixing.

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