Process for the production of isotactic polypropylene material and isotactic polypropylene material

Abstract

The application provides a processing method of isotactic polypropylene material and isotactic polypropylene material. The processing method comprises the following steps: step S1: applying a tension condition to a main orientation direction or a structural feature direction of the isotactic polypropylene material; and step S2: heating the isotactic polypropylene material subjected to the tension to a specified temperature and performing a heat preservation treatment; the heating rate is less than 10 DEG C / min, and the specified temperature is not higher than the temperature of the onset of the melting phase transition of the isotactic polypropylene material. The processing method provided by the application can improve the insulation performance of the existing isotactic polypropylene material at high temperatures, is simple to operate, has a wide application range, and has a wide application space.

Description

Technical Field

[0001] This invention relates to a processing method for isotactic polypropylene material and isotactic polypropylene material, specifically to a method for treating isotactic polypropylene material using a combination of heat and tension and isotactic polypropylene material obtained by the above method, belonging to the field of materials technology. Background Technology

[0002] Isotactic polypropylene (IP) materials exhibit excellent insulation, mechanical, and processing properties, maintaining good electrical strength and dielectric loss under high voltage and high temperature environments. Currently, Isotric polypropylene is widely used in insulation materials, particularly as a capacitor insulating medium, and plays a crucial role in high-voltage cables and accessories. With the rapid development of the electrical industry and the new energy vehicle industry, the application of isotactic polypropylene insulation materials is trending towards higher insulation strength, higher application temperature, and higher safety and reliability. However, as a general-purpose plastic, polypropylene begins to show significant softening and a decrease in insulation performance at high temperatures. When used at temperatures above 90°C, the overall device rating needs to be reduced, which cannot fully meet the requirements of higher temperature applications, especially emerging applications such as electric vehicles and wind power generation where ambient temperatures may reach 125°C.

[0003] To improve the high-temperature performance of isotactic polypropylene materials, the following research has been conducted in the prior art:

[0004] Reference 1 provides a polypropylene-high-temperature resistant polymer blend film, its preparation method, and a capacitor core. The film is made from the following raw materials in parts by weight: polypropylene resin: high-temperature resistant polymer resin = 1:1 to 12:1, wherein the high-temperature resistant polymer resin is selected from poly(4-methylpentene) (TPX), cyclic olefin copolymers (COC), etc. The polypropylene-high-temperature resistant polymer blend film for capacitors prepared in this reference has a heat resistance of not less than 125°C. However, due to compatibility issues between the cyclic olefin copolymer and the polypropylene resin, the raw materials are physically stirred and then directly cast into a film using a single-screw extruder before biaxial stretching. In actual production, the film-forming properties of the material are poor, and the dielectric properties of the finished product are significantly lower than those of conventional polypropylene films.

[0005] Reference 2 provides an ultrathin, high-temperature resistant polypropylene capacitor metallized film and its preparation method. The film includes a base film and an aluminum coating and a zinc coating sequentially deposited on the base film, with a blank area left at the edge between the aluminum coating and the base film. A high-temperature resistant layer, made of polyurethane, is disposed on the zinc coating, and this high-temperature resistant layer has multiple convex thickened areas. By setting a high-temperature resistant layer with multiple convex thickened areas on the zinc coating, the adhesion between the coatings is increased, improving the temperature resistance of the capacitor. However, this method is complex and requires sophisticated equipment.

[0006] It is evident that although existing technologies have conducted some research on improving the insulation performance of isotactic polypropylene materials at high temperatures, this research cannot be considered sufficient and there is room for further improvement.

[0007] References:

[0008] Reference 1: CN115260647A

[0009] Reference 2: CN106024378A Summary of the Invention

[0010] The problem the invention aims to solve

[0011] As mentioned above, although isotactic polypropylene has excellent insulation, mechanical and processing properties, it begins to soften significantly and its insulation properties decrease at high temperatures, which affects its application range.

[0012] To improve the high-temperature performance of isotactic polypropylene materials, existing technologies mainly employ methods such as blending polypropylene with high-temperature resistant materials and coating with high-temperature resistant layers. However, the blending method suffers from compatibility and dispersion issues between the blended materials and polypropylene, which not only limits the improvement of heat resistance but also affects subsequent film-forming properties. The coating with high-temperature resistant layers, on the other hand, requires sophisticated equipment and involves complex preparation operations, making it difficult to promote and apply.

[0013] A major reason limiting the high-temperature application of isotactic polypropylene (IP) materials is that at higher temperatures, the microstructure of IIP undergoes deorientation and random reorientation, leading to a decrease in insulation and mechanical properties, and even deformation such as wrinkling, resulting in overall performance degradation. Through long-term research, the inventors of this invention have discovered that a heat treatment method using specific conditions and temperature processes can induce the structure of isotactic polypropylene materials to possess properties that suppress microscopic deorientation and random reorientation at high temperatures, thereby ultimately inhibiting the performance degradation of the material at high temperatures.

[0014] In view of the above, the present invention provides a processing method for isotactic polypropylene materials by combining heat and tension treatment, thereby improving the insulation performance of existing isotactic polypropylene materials at high temperatures.

[0015] In addition, the present invention also provides an isotactic polypropylene material, which is obtained by the above-described processing method.

[0016] Solution for solving the problem

[0017] This invention first provides a method for processing isotactic polypropylene material, comprising the following steps:

[0018] Step S1: Apply tension to the main orientation direction or structural feature direction of the isotactic polypropylene material;

[0019] Step S2: Heat the isotactic polypropylene material under tension to the specified temperature and keep it at that temperature.

[0020] The heating rate is less than 10°C / min, and the specified temperature is no higher than the melting phase transition starting point of isotactic polypropylene material.

[0021] According to the method of the present invention, the tension in the tension condition is less than 30 N / m and not 0.

[0022] According to the method of the present invention, the specified temperature is less than 125°C.

[0023] According to the method of the present invention, the heat preservation treatment time is 10 minutes or more.

[0024] According to the method of the present invention, step S2 is carried out under essentially anaerobic conditions, wherein the essentially anaerobic conditions are an environment containing less than 1% reactive oxygen species.

[0025] According to the method of the present invention, a cooling step is further included after step S2, wherein the cooling includes natural cooling or forced air cooling.

[0026] According to the method of the present invention, the isotactic polypropylene material has an isotacticity greater than 95% as measured by testing the resonance spectrum.

[0027] According to the method of the present invention, the volume resistivity of the isotactic polypropylene material at room temperature for 60 min is greater than 10. 14 Ω·m; and / or, the dielectric loss tangent of the isotactic polypropylene material is less than 0.006.

[0028] According to the method of the present invention, the isotactic polypropylene material is a film material.

[0029] Furthermore, the present invention also provides an isotactic polypropylene material, which is obtained by the processing method described in the present invention, wherein the isotactic polypropylene material satisfies at least one of the following conditions:

[0030] (1) The isotactic polypropylene material at 90°C has an electrical strength reduction rate of less than 20% compared to room temperature;

[0031] (2) The isotactic polypropylene material has a volume resistivity of 1.4 or higher at 90°C for 10 min and 1 min.

[0032] The effects of the invention

[0033] The present invention provides a processing method for isotactic polypropylene materials using a combination of heat and tension. This method employs appropriate tension conditions to suppress random deformation of the material during heat treatment, and adopts appropriate heating rates and holding times to induce the material to reach a high-temperature steady state in advance. This induces the isotactic polypropylene material structure to possess the property of suppressing microscopic deorientation and random reorientation at high temperatures, thereby improving the insulation resistance and DC breakdown field strength of the isotactic polypropylene material at high temperatures.

[0034] The processing method for isotactic polypropylene provided by this invention is simple to operate, has a wide range of applications, and has broad application potential. Attached Figure Description

[0035] Figure 1 The electrical strength of Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3 at room temperature, 50°C and 90°C are shown.

[0036] Figure 2 The Weibull distribution shape parameters of Example 2, Comparative Example 1, and Comparative Example 2 at room temperature and 90°C are shown.

[0037] Figure 3 The curves showing the change in volume resistivity as a function of temperature for Examples 1, 2, 3 and Comparative Example 1 as the temperature is continuously increased from room temperature to 90°C are shown.

[0038] Figure 4 The volume resistivity of Example 2 and Comparative Example 1 at current decay of 1 min, 10 min and 60 min under the conditions of room temperature, 50°C, 70°C and 90°C is shown. Detailed Implementation

[0039] The present invention will now be described in detail. The descriptions of the technical features described below are based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0040] In this specification, the range of values ​​referred to as "value A to value B" refers to the range including the endpoint values ​​A and B.

[0041] In this specification, the numerical range indicated by "above" or "below" refers to the numerical range that includes the stated number.

[0042] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0043] In this specification, the terms "optional" or "optional" are used to indicate the use or omission of certain substances, components, procedures, application conditions, etc.

[0044] In this manual, “room temperature” or “room temperature” refers to an indoor ambient temperature of “23±2℃”. Generally speaking, unless otherwise specified, the volume resistivity described in this manual is the volume resistivity at room temperature.

[0045] All unit names used in this manual are international standard unit names, and unless otherwise stated, the "%" used refers to weight or mass percentage content.

[0046] In this specification, the term "substantially" is used to indicate that the standard deviation from the theoretical model or theoretical data is within a range of 2%, preferably 1%, and more preferably 0.8%.

[0047] In this specification, the terms “comprising” and / or “including” are used to indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0048] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0049] This invention provides a processing method for isotactic polypropylene material, specifically a processing method that utilizes a combination of heat and tension to treat isotactic polypropylene material. By treating isotactic polypropylene material under appropriate tension conditions and at an appropriate heating rate, it can be pre-treated to reach a high-temperature steady state, thereby improving the insulation performance of isotactic polypropylene material at high temperatures.

[0050] This invention is based on the following viewpoints:

[0051] While isotactic polypropylene (IP) materials possess excellent insulation, mechanical, and processing properties, they exhibit significant softening and a decline in insulation performance at high temperatures, limiting their application range. To improve the high-temperature performance of IPS materials, existing technologies primarily employ methods such as introducing other high-temperature resistant substances into the polypropylene material, including blending with high-temperature resistant materials and applying a high-temperature resistant layer. However, these methods all have certain drawbacks.

[0052] In fact, the main reason for the performance degradation of isotactic polypropylene (IP) at high temperatures is that the microstructure of IIP undergoes deorientation and random reorientation at high temperatures, leading to a decrease in insulation and mechanical properties, and even deformation such as wrinkling, resulting in overall performance deterioration. In the field of materials science, annealing is typically used to heat materials or products to a specific temperature and then cool them in a specific manner to affect the microstructure and macroscopic properties of the material; however, annealing is usually used for metal materials. Through long-term research, the inventors of this invention have discovered that by heat-treating IIP under specific conditions and at specific temperatures, it is possible to induce the IIP structure to possess properties that suppress microscopic deorientation and random reorientation at high temperatures, thereby ultimately inhibiting the performance degradation of the material at high temperatures.

[0053] <First Aspect>

[0054] A first aspect of the present invention provides a method for processing isotactic polypropylene material, comprising the following steps:

[0055] Step S1: Apply tension to the main orientation direction or structural feature direction of the isotactic polypropylene material;

[0056] Step S2: Heat the isotactic polypropylene material under tension to the specified temperature and keep it at that temperature.

[0057] Isotactic polypropylene material

[0058] The type of isotactic polypropylene material used in this invention is not particularly limited, and may include isotactic polypropylene raw materials or pre-formed components, such as uniaxially and biaxially stretched polypropylene films, polypropylene cable sheaths, etc.

[0059] In principle, there are no particular limitations on the selection of isotactic polypropylene material used in this invention. However, from the perspective of having better basic insulation properties and thus being used as an insulating material, it can have the following characteristics:

[0060] The weight-average molecular weight of the isotactic polypropylene material can be 80,000 to 250,000 Da, for example, 100,000 Da, 120,000 Da, 150,000 Da, 180,000 Da, 200,000 Da, 220,000 Da, etc. For reference, the reference value for film material is 160,000 to 250,000 Da, and the reference value for cable material is 80,000 to 150,000 Da. For example, the number-average molecular weight of polypropylene for insulating film is 80,000 to 100,000 Da, the weight-average molecular weight is 190,000 to 220,000 Da, and the distribution index is typically 2.3.

[0061] The isotactic polypropylene material has an isotacticity greater than 95% as measured by nuclear magnetic resonance spectroscopy, for example, it can be 96%, 97%, 98%, 99%, etc. Polypropylene materials with too low isotacticity have low basic insulation strength and are not suitable as insulation materials.

[0062] The isotactic polypropylene material has a volume resistivity greater than 10 Ω·cm at room temperature for 60 min. 14 Ω·m, for example, can be 2×10 14 Ω·m, 4×10 14 Ω·m, 6×10 14 Ω·m, 8×10 14 Ω·m, 10 15 The volume resistivity of isotactic polypropylene materials is low (Ω·m, etc.), which does not meet the insulation requirements for insulation applications and is therefore unsuitable as an insulating material.

[0063] The dielectric loss tangent of the isotactic polypropylene material is not particularly limited in principle, but from the perspective of material insulation, it is recommended to be less than 0.006, for example, 0.005, 0.004, 0.003, 0.0002, 0.001, etc. A large dielectric loss tangent means that the material has high DC leakage loss or AC impurity loss. Regardless of the type of loss, if the isotactic polypropylene material has high heat generation in application, it cannot well meet the requirements of high-temperature applications, and even if processed by the method of the present invention, it is still not suitable as an insulating material.

[0064] For insulation applications, materials for different applications vary significantly in terms of electrical strength. Therefore, there is no specific limitation on the electrical strength, and it can be selected according to needs. In some specific implementations, when the isotactic polypropylene material is used as cable sheath, the electrical strength of the isotactic polypropylene material can be below 80MV / m, preferably 45 to 75MV / m, for example, 50MV / m, 55MV / m, 60MV / m, 65MV / m, 70MV / m, etc.; when the isotactic polypropylene material is used as capacitor film, the electrical strength of the isotactic polypropylene material can be above 400MV / m, preferably above 500MV / m.

[0065] Preferably, the isotactic polypropylene material is used in the form of a membrane material. In principle, there is no particular limitation on the thickness of such a membrane material. For example, it can be less than 100 μm. From an effectiveness perspective, the thickness of the membrane material is preferably 0.5 to 20 μm, and more preferably 1 to 10 μm.

[0066] Step S1

[0067] Step S1 of the present invention is the step of applying tension, specifically applying tension conditions to the main orientation direction or structural feature direction of the isotactic polypropylene material.

[0068] For isotactic polypropylene materials with a single structural feature, such as uniaxially oriented films and cable sheaths, the main orientation direction or structural feature direction is the direction of stretching or extrusion; for isotactic polypropylene materials with multiple structural features, such as biaxially oriented films, the main orientation direction or structural feature direction is the longitudinal continuous production direction.

[0069] The method of applying tension is not particularly limited and can be selected as needed. In some specific implementations, tension can be applied by winding or mechanical stretching.

[0070] When the isotactic polypropylene material is subjected to stable tension, the tension is less than 30 N / m and not 0, for example, it can be 25 N / m, 20 N / m, 15 N / m, 10 N / m, 5 N / m, etc. When the tension is greater than 30 N / m, the isotactic polypropylene material is prone to plastic deformation after heating, making it difficult to ensure the material has stable performance. When the tension is 0, wrinkles will spontaneously form on the surface of the isotactic polypropylene material (such as film) after heating, resulting in poor electrical strength dispersion and being detrimental to insulation stability.

[0071] Step S2

[0072] Step S2 of the present invention is a heat treatment step, specifically, heating the isotactic polypropylene material under tension to a specified temperature and holding it at that temperature.

[0073] During heat treatment, the heating rate is less than 10℃ / min, for example, it can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, etc. Based on the structure and morphology of the material being treated and the structural principle of the heating device, and fully considering the low thermal conductivity of isotactic polypropylene, when the heating rate is less than 10℃ / min, the isotactic polypropylene material can achieve a uniform heating rate at all locations during the heating process, thereby suppressing deformation and wrinkling caused by thermal stress gradients.

[0074] During the heat treatment process, the specified temperature is no higher than the melting phase transition initiation temperature of isotactic polypropylene. This initiation temperature can be obtained through differential calorimetry analysis. By controlling the temperature to be no higher than the melting phase transition initiation temperature of isotactic polypropylene, the high-temperature performance of the material can be improved without altering its state, while also preventing localized overheating during heating. In some preferred embodiments, considering the improved applicability of the method to the material, the specified temperature is less than 125°C, preferably 40–125°C, for example, 120°C, 110°C, 100°C, 90°C, 80°C, 70°C, 60°C, 50°C, etc.

[0075] In some preferred embodiments, the device that applies tension conditions, such as a winding or stretching mechanism, remains in a fixed position during the heat treatment process.

[0076] In some specific implementations, when the specified temperature during the heat treatment process is higher than 80°C, it is necessary to perform heat treatment on the material under essentially oxygen-free conditions through a deoxidation method. Specifically, the essentially oxygen-free conditions mean that the concentration of active oxygen is less than 1%. The deoxidation method is not particularly limited and can be selected as needed, such as constructing a vacuum environment or sealing the material in an inert atmosphere of nitrogen or carbon dioxide.

[0077] The heat preservation time can be 10 minutes or more, preferably 10 minutes to 120 hours, more preferably 10 minutes to 48 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 24 hours, 36 hours, etc.

[0078] Other steps

[0079] After the heat preservation treatment is completed, a cooling step may also be included. The cooling method is not particularly limited and can be selected as needed, such as natural cooling or forced air cooling.

[0080] <Second aspect>

[0081] A second aspect of the present invention provides an isotactic polypropylene material, which is obtained by the processing method described in the first aspect.

[0082] The isotactic polypropylene material satisfies at least one of the following conditions:

[0083] (1) The isotactic polypropylene material at 90°C has an electrical strength reduction rate of less than 20% compared to room temperature;

[0084] (2) The isotactic polypropylene material has a volume resistivity of 1.4 or more at 90°C for 10 minutes and a volume resistivity of 1.45 or more for 1 minute.

[0085] Example

[0086] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0087] In the following embodiments, biaxially oriented isotactic polypropylene films with excellent performance and stability are used as examples, intended to demonstrate the effects of the embodiments and comparative examples of the present invention with the highest repeatability, and not to represent a limitation on the scope of the present invention.

[0088] The biaxially oriented isotactic polypropylene film used had a thickness of 4.8 μm, an isotacticity of 98.3%, and a volume resistivity of 1.05 at room temperature for 60 min. 15 The dielectric loss tangent is 0.002 Ω·m. Comparative examples and proportions are used at the same thickness to avoid interference caused by insulation size effects. The basic raw materials comply with GB / T 3682-2018 standard, and also meet ISO1133-1 and ASTM1238 standards. The melt flow index is 3.3 g / 10 min (230℃ / 2.16 kg).

[0089] Example 1

[0090] A pair of parallel plates are driven to move in opposite directions using a screw and linkage structure to fix the isotactic polypropylene film between the two plates. The screw is adjusted to make the film tension 20 N / m. After fixing the mechanical structure, the whole thing is placed in an electric heating box and heated at a rate of 1℃ / min. After reaching 90℃, it is kept at that temperature for 6 hours. Then the material and tension mechanism are taken out as a whole and allowed to cool naturally.

[0091] Example 2

[0092] The difference from the technical solution of Example 1 is that: during the process before and after heat treatment, the film is placed on a rough surface, and the film is kept taut by pressure fixation and the weak tension provided by friction, and the temperature is set to rise at a rate of 2°C / min.

[0093] Example 3

[0094] The difference from the technical solution in Example 2 is that the temperature is increased at a rate of 5°C / min.

[0095] Comparative Example 1

[0096] An untreated isotactic polypropylene film was used as a blank control.

[0097] Comparative Example 2

[0098] The difference with respect to the technical solution of Example 2 is that the device is kept in a tension-free state of natural placement throughout the process before and after heat treatment.

[0099] Comparative Example 3

[0100] The difference with respect to the technical solution of Example 2 is that instead of using a slow heating rate, the sample is directly placed in a target temperature environment of 90°C.

[0101] Performance testing

[0102] Insulation performance: Insulation performance tests were conducted on the biaxially oriented isotactic polypropylene films processed in the examples and comparative examples. Volume resistivity and electrical strength tests were mainly conducted according to GB / T 13542.2-2021 standard. Furthermore, Weibull distribution fitting analysis was performed on the electrical strength test results to characterize the stability of the electrical strength in detail. Since the film thickness was selected as 4.8 μm, which is less than the standard recommended aluminum foil electrode thickness, and to avoid interference from differences in the thermal effects of different evaporation or vacuum sputtering metal processes, gallium indium tin liquid metal paste was used as a substitute electrode. The electrical strength test used a 6 mm diameter upper electrode and a large-area flat plate lower electrode system. The electrical strength test results are as follows: Figure 1 As shown; the Weibull distribution fitting results are as follows Figure 2 As shown; the volume resistivity test results are as follows. Figure 3 and Figure 4 As shown.

[0103] The Weibull distribution used in electrical strength dispersion analysis is a statistical method for describing the probability of electrical breakdown failure of materials, and its cumulative probability function is as follows:

[0104] 1-10^(-(E / E0)^k)

[0105] Here, E0 is a dimensional parameter reflecting the overall electrical strength of the test sample; k is a shape parameter representing the dispersion of the test sample. When k values ​​are 15, 20, and 40, the corresponding standard deviations are approximately 8.2%, 6.2%, and 3.2% of the electrical strength, respectively. It is worth noting that the dimensional parameter E0 here differs from the electrical strength described in the GB / T 13542.2-2021 standard. According to the principle of statistical probability, E0 multiplied by the coefficient Γ(1+1 / k) is numerically consistent with the electrical strength in the standard, where Γ is the gamma function.

[0106] from Figure 1As can be seen, Comparative Example 1 represents the untreated raw film, which exhibits excellent electrical strength at both room temperature and high temperature. At 90°C, the electrical strength generally decreases by about 23% compared to room temperature, indicating a high performance baseline. Example 2 represents the processing method of the present invention, which still maintains good electrical strength at room temperature. Furthermore, at 90°C, the electrical strength decreases by 19.4% compared to room temperature. The comparison between Example 2 and Comparative Example 1 shows that the processing method of the present invention can significantly improve the electrical strength at 90°C for materials with a high performance baseline, even with only a slight impact on the electrical strength at room temperature. Comparative Example 2 represents heat treatment under non-tension conditions, while Comparative Example 3 represents heat treatment under non-slow heating conditions. Neither Comparative Example 2 nor Comparative Example 3 improves the electrical strength of the material at any temperature.

[0107] from Figure 2 It can be seen that the Weibull distribution shape parameter k of Example 2 and Comparative Example 1 is not significantly different, being approximately 39 at room temperature and approximately 19 at 90°C, indicating that the isotactic polypropylene material obtained by the processing method of the present invention in Example 2 can maintain the electrical strength stability of the raw material. The shape parameter of Comparative Example 2 is approximately 20 at room temperature and 13 at 90°C, which is approximately 49% and 32% lower than that of Example 2 and Comparative Example 1 at room temperature and 90°C, respectively, indicating that the tension-free processing conditions used in Comparative Example 2 reduce the stability of the material's electrical strength.

[0108] from Figure 3 It can be seen that at high temperatures above 60°C, Examples 1, 2, and 3 all exhibit higher volume resistivity than the untreated material represented by Comparative Example 1, indicating that the method of the present invention can effectively improve the volume resistivity of isotactic polypropylene at high temperatures. The curve of Example 1 shows that, within the scope of the method of the present invention, the volume resistivity of isotactic polypropylene at high temperatures can be significantly improved with minimal sacrifice of volume resistivity at temperatures near room temperature. However, it must be pointed out that the deorientation effect at high temperatures cannot be completely avoided, and the resulting decrease in surface resistivity is unavoidable.

[0109] from Figure 4 It can be seen that, compared with Comparative Example 1, Example 2 has better volume resistivity and polarization index at 90℃ (long-time volume resistivity: short-time volume resistivity, national standard recommends insulation resistance of 10min: 1min). Specifically, at 90℃ for 1min, the volume resistivity of Example 2 and Comparative Example 1 are 8.97×10⁻⁶. 13 Ω·m and 3.44×10 13 Ω·m, an increase of approximately 160%, reaching 1.31 × 10 at 10 min. 14 Ω·m and 5.38×10 13The Ω·m increased by 143%, corresponding to polarization indices of 1.46 and 1.56, respectively. Meanwhile, at the same temperature for 60 min, the volume resistivity was 2.51 × 10⁻⁶. 14 Ω·m and 1.31×10 14 The volume resistivity of both materials is approximately 91.9% higher than that of Comparative Example 1, with an improvement of approximately 91.9% in Ω·m. At intermediate temperatures (50°C and 70°C), their volume resistivity performance is comparable, and their steady-state insulation resistance is similar at room temperature, but the polarization index is slightly worse than that of Comparative Example 1. Due to the deorientation effect at high temperatures, the material is more susceptible to electrode carrier injection under the influence of temperature and electric field at room temperature, thus slowing down the polarization process and resulting in a slower decay of the polarization current and a worse polarization index. Once the polarization current has completely decayed, the material regains its original high volume resistivity. At high temperatures, the processing method of the present invention, represented by Example 2, suppresses further deorientation of the material at high temperatures and limits the slowing effect of carrier injection on polarization, thereby exhibiting superior volume resistivity and polarization index at 90°C.

[0110] It should be noted that although the technical solution of the present invention has been described with specific examples, those skilled in the art will understand that the present invention should not be limited thereto.

[0111] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for processing isotactic polypropylene material, characterized in that, Includes the following steps: Step S1: Apply tension to the main orientation direction or structural feature direction of the isotactic polypropylene material; Step S2: Heat the isotactic polypropylene material under tension to the specified temperature and keep it at that temperature. The heating rate is less than 10°C / min, and the specified temperature is no higher than the melting phase transition starting point of isotactic polypropylene material.

2. The method according to claim 1, characterized in that, The tension condition is less than 30 N / m and not 0.

3. The method according to claim 1 or 2, characterized in that, The specified temperature is less than 125°C.

4. The method according to any one of claims 1 to 3, characterized in that, The heat preservation treatment time is more than 10 minutes.

5. The method according to any one of claims 1 to 4, characterized in that, Step S2 is carried out under essentially anaerobic conditions, wherein the essentially anaerobic conditions are an environment containing less than 1% reactive oxygen species.

6. The method according to any one of claims 1 to 5, wherein step S2 is followed by a cooling step, wherein the cooling includes natural cooling or forced air cooling.

7. The method according to any one of claims 1 to 6, characterized in that, The isotactic polypropylene material has an isotacticity greater than 95% as measured by the resonance spectrum test.

8. The method according to any one of claims 1 to 7, characterized in that, The isotactic polypropylene material has a volume resistivity greater than 10 Ω at room temperature for 60 min. 14 Ω·m; and / or, the dielectric loss tangent of the isotactic polypropylene material is less than 0.

006.

9. The method according to any one of claims 1 to 8, characterized in that, The isotactic polypropylene material is a film material.

10. An isotactic polypropylene material, characterized in that, The isotactic polypropylene material obtained by the processing method according to any one of claims 1 to 9 satisfies at least one of the following conditions: (1) The isotactic polypropylene material at 90°C has an electrical strength reduction rate of less than 20% compared to room temperature; (2) The isotactic polypropylene material has a volume resistivity of 1.4 or higher at 90°C for 10 min and 1 min.

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