WO2024040705A1 - Method for evaluating scorching resistance of crosslinkable polyethylene insulating material used for electrical cable - Google Patents

Abstract

A method for evaluating the scorching resistance of a crosslinkable polyethylene insulating material used for an electrical cable. The method comprises: obtaining a target parameter value of a crosslinkable polyethylene insulating material containing a same amount of antioxidant, wherein the target parameter value comprises the actual measured value of a number average molecular weight; based on the actual measured value of a number average molecular weight and a preset parameter value, obtaining a first comparison result, wherein the preset parameter value comprises a preset value of a number average molecular weight and a preset value of a polydispersity coefficient; and based on the first comparison result, evaluating the scorching resistance of the crosslinkable polyethylene insulating material. The method for evaluating the scorching resistance of the crosslinkable polyethylene insulating material used for an electrical cable can avoid to a certain extent a pre-crosslinking phenomenon from occurring in the production process of the crosslinkable polyethylene insulating material, thereby improving production efficiency.

Description

Evaluation method for scorch resistance of cross-linkable polyethylene insulation materials for cables

Related applications

This application claims priority to the Chinese patent application filed on August 26, 2022, with the application number 2022110314086 and titled "Method for Evaluating the Scorch Resistance of Cross-Linkable Polyethylene Insulation Materials for Cables". The full text is here Introduced for reference.

Technical field

This application relates to the field of cable technology, and in particular to a method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables.

Background technique

Cross-linked polyethylene insulation materials are widely used as insulation materials for AC and DC land cables and submarine cable insulation layers due to their excellent electrical properties. The preparation method of cross-linked polyethylene is usually to use active free radicals generated by the decomposition of the cross-linking agent to connect cross-linkable polyethylene insulation materials with linear molecular chains into cross-linked polyethylene insulation materials with a network structure and excellent electrical properties. . In the production process of cross-linked polyethylene insulation materials, the scorch resistance of cross-linkable polyethylene insulation materials in the processing and molding process is a key link to ensure its quality and production stability. However, during the production process, cross-linkable polyethylene insulation materials usually inevitably produce pre-cross-linking, and the scorched material produced by pre-cross-linking will accumulate on the filter screen of the extrusion equipment, causing insulation extrusion. The pressure increases and the glue output decreases, which over time causes equipment shutdown and affects production efficiency.

Contents of the invention

Based on this, this application provides a method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables, aiming to reduce the occurrence of pre-crosslinking phenomena of cross-linkable polyethylene insulation materials during the production process and improve production efficiency.

This application provides a method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables, including:

Obtain the target parameter value of the cross-linkable polyethylene insulation material with the same antioxidant content, wherein the target parameter value includes the measured value of the number average molecular weight;

Obtain a first comparison result based on the actual measured value of the number average molecular weight and the preset parameter value, wherein the preset parameter value includes a preset value of the number average molecular weight and a preset value of the polydispersity coefficient; and

Based on the first comparison result, the scorch resistance of the cross-linkable polyethylene insulation material is evaluated.

According to any embodiment of the present application, the target parameter values of cross-linkable polyethylene insulation materials with the same antioxidant content are obtained, including:

Conduct a gel chromatography test on the cross-linkable polyethylene insulation material to obtain the target parameter value, where the target parameter value also includes the measured value of the polydispersity coefficient.

According to any embodiment of the present application, the first comparison result is obtained based on the actual measured value of the number average molecular weight and the preset parameter value, including:

Comparing the actual measured value of the number average molecular weight with the preset value of the number average molecular weight, the relative size of the actual measured value of the number average molecular weight and the preset value of the number average molecular weight is obtained.

According to any embodiment of the present application, based on the first comparison result, the scorch resistance of the cross-linkable polyethylene insulation material is evaluated, including:

When the actual measured value of the number average molecular weight is higher than the preset value of the number average molecular weight, it is determined that the scorch resistance of the cross-linkable polyethylene material meets the first requirement; or

When the actual measured value of the number average molecular weight is lower than the preset value of the number average molecular weight, it is determined that the scorching resistance of the cross-linkable polyethylene insulation material does not meet the first requirement.

According to any embodiment of the present application, the first requirement is that the gel content of the prematurely crosslinked block generated after the pre-crosslinking reaction of the crosslinkable polyethylene insulation material is less than 70%.

According to any embodiment of the present application, after it is determined that the scorch resistance of the cross-linkable polyethylene insulation material does not meet the requirements, the method further includes:

Obtain a second comparison result based on the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient; and

Based on the second comparison result, the scorch resistance of the cross-linkable polyethylene insulation material is evaluated.

According to any embodiment of the present application, a second comparison result is obtained based on the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient, including:

Comparing the actual measured value of the polydispersity coefficient with the preset value of the polydispersity coefficient, the relative magnitude of the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient is obtained.

According to any embodiment of the present application, based on the second comparison result, the scorch resistance of the cross-linkable polyethylene insulation material is evaluated, including:

When the actual measured value of the polydispersity coefficient is higher than the preset value of the polydispersity coefficient, it is determined that the scorch resistance of the cross-linkable polyethylene insulation material does not meet the second requirement; or

When the actual measured value of the polydispersity coefficient is lower than the preset value of the polydispersity coefficient, it is determined that the scorch resistance of the cross-linkable polyethylene insulation material meets the second requirement.

According to any embodiment of the present application, the second requirement is that the gel content of the prematurely crosslinked block generated after the pre-crosslinking reaction of the crosslinkable polyethylene insulation material is less than 60%.

According to any embodiment of the present application, the preset value of the number average molecular weight is 2.8×10 ⁴ .

According to any embodiment of the present application, the preset value of the polydispersity coefficient is 6.

The details of one or more embodiments of the application are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the application will become apparent from the description, drawings and claims.

Description of drawings

In order to more clearly explain the technical solutions in the embodiments of the present application or the traditional technology, the drawings needed to be used in the description of the embodiments or the traditional technology will be briefly introduced below. Obviously, the drawings in the following description are only for the purpose of explaining the embodiments or the technical solutions of the traditional technology. For the embodiments of the application, those of ordinary skill in the art can also obtain other drawings based on the disclosed drawings without exerting creative efforts.

Figure 1 is a schematic flow chart of a method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables provided in one embodiment of the present application.

Figure 2 is a test chart of the scorching resistance of the cross-linkable polyethylene insulation materials in Examples 1 to 3 of the present application.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

For simplicity, only certain numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. In addition, although not explicitly stated, every point or individual value between the endpoints of a range is included in the range. Thus, each point or single value may serve as a lower or upper limit on its own in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing specific embodiments only and is not intended to limit the application. It should be noted that, unless otherwise stated, the term "and/or" used in this article includes any and all combinations of one or more related listed items, and "above" and "below" are inclusive of this number, " The "multiple" in "one or more" means two or more.

The above summary of this application is not intended to describe each disclosed embodiment or every implementation in this application. The following description illustrates exemplary embodiments in more detail. At various points throughout this application, guidance is provided through a series of examples, which may be used in various combinations. In each instance, the enumerations are representative only and should not be construed as exhaustive.

The scorch resistance of cross-linkable polyethylene insulation material for cables refers to its ability to inhibit premature cross-linking and gel formation during the extrusion process. The scorch resistance of cross-linkable polyethylene insulation material means that it allows greater temperature fluctuations during the extrusion process, longer high-temperature processing time, wider processing window, and better processability. In addition, the scorch resistance of cross-linkable polyethylene insulation material can reduce the gel content during the production process, which on the one hand can prevent the gel product from clogging the extrusion filter, increase the cable extrusion length, and improve cable production efficiency; on the other hand , there will be less gel remaining in the main insulation of the cable, and there will be fewer local defects, which will help improve the uniformity of the internal structure of the insulation medium and improve the electrical insulation performance of the cable.

During the research process, the inventor found that in the production process of cross-linked polyethylene insulation materials, the relative molecular weight and distribution of the cross-linked polyethylene insulation materials will have a greater impact on the scorch resistance performance, and are also related to the cross-linked polyethylene insulation materials. The electrical insulation properties of vinyl insulation are closely related. Based on this discovery of the inventor, this application proposes the following technical solution, which is to evaluate the strength of the anti-scorch performance of different cross-linkable polyethylene insulation materials by comparing the differences in relative molecular mass and distribution before production. In this way, cross-linkable polyethylene insulation materials with strong scorch resistance can be screened out, which can avoid the occurrence of pre-cross-linking phenomenon in the production process to a certain extent in the early stage and reduce the formation of gel products caused by it. Increase productivity.

The embodiment of the present application provides a method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables, which includes the following steps:

S10. Obtain target parameter values of cross-linkable polyethylene insulation materials with the same antioxidant content, where the target parameter values include the measured value of number average molecular weight;

S20. Obtain the first comparison result based on the actual measured value of the number average molecular weight and the preset parameter value, where the preset parameter value includes the preset value of the number average molecular weight and the preset value of the polydispersity coefficient;

S30. Based on the first comparison result, evaluate the scorch resistance of the cross-linkable polyethylene insulation material.

Figure 1 is a schematic flowchart of a method according to an embodiment of the present application. It should be understood that although various steps in the flowchart of FIG. 1 are shown in sequence as indicated by arrows, these steps are not necessarily executed in the order indicated by arrows. Unless explicitly stated in this article, the execution of these steps is not strictly limited in order, and they can be executed in other orders. Moreover, at least some of the steps in Figure 1 may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but may be executed at different times, and their execution order is not necessarily may be performed sequentially, but may be performed in turn or alternately with other steps or sub-steps of other steps or at least part of stages.

This application provides a method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables by comparing the target parameter values and preset parameter values of different cross-linkable polyethylene insulation materials, and evaluating the cross-linkability based on the comparison results. The scorch resistance of polyethylene insulation materials can be evaluated and screened out before production, and cross-linkable polyethylene insulation materials with better scorch resistance can be avoided to a certain extent. The pre-crosslinking phenomenon caused by the poor scorch resistance of polyethylene insulation materials can reduce the formation of gel products and improve production efficiency. In addition, the reduction of gel products can also reduce the generation of local defects in the cross-linked polyethylene insulation material, which is beneficial to improving the uniformity of the internal structure of the insulation material, thereby improving the electrical insulation performance of the cable.

It should be noted that since the amount of antioxidant added will affect the evaluation results of the scorch resistance of the cross-linkable polyethylene insulation material, the cross-linkable polyethylene insulation materials in this application must have the same properties during evaluation. antioxidant content.

In some embodiments, step S10 obtains target parameter values of cross-linkable polyethylene insulation materials with the same antioxidant content, including the following steps:

S100. Conduct a gel chromatography test on the cross-linkable polyethylene insulation material to obtain target parameter values. The target parameter values also include the actual measured value of the polydispersity coefficient.

In some embodiments, the target parameter value may also include a measured value of weight average molecular weight, and the measured value of polydispersity coefficient (PD) may be obtained by the measured value of weight average molecular weight/the measured value of number average molecular weight.

In some embodiments, the gel chromatography test in step S100 has a meaning known in the art, and can be tested using conventional instruments or equipment in the art. For example, the AgilentPL-GPC220 high-temperature gel chromatograph can be used for testing.

Specifically, in step S100, by performing a gel chromatography test on the cross-linkable polyethylene insulation material, the actual measured value of the number average molecular weight and the actual measured value of the weight average molecular weight of the cross-linkable polyethylene insulation material can be obtained. Through the actual measured value of the weight average molecular weight /The measured value of number average molecular weight can obtain the measured value of polydispersity coefficient (PD).

It should be noted that under normal circumstances, the number average molecular weight range of cross-linkable polyethylene insulation materials for cables is 2.5×10 ⁴ to 5×10 ⁴ , and the weight average molecular weight range is 20×10 ⁴ to 30×10 ⁴ . Usually It is believed that cross-linkable polyethylene insulation materials for cables within the above range can meet the production conditions. This application improves the scorch resistance and electrical properties of the cross-linkable polyethylene insulation material by regulating the number average molecular weight and weight average molecular weight of the cross-linkable polyethylene insulation material within the above range.

In some embodiments, step S20 obtains the first comparison result based on the actual measured value of the number average molecular weight and the preset parameter value, including the following steps:

S200. Compare the actual measured value of the number average molecular weight with the preset value of the number average molecular weight, and obtain the relative size of the actual measured value of the number average molecular weight and the preset value of the number average molecular weight.

In some embodiments, the preset number average molecular weight value is a preset number average molecular weight parameter value, and the preset number average molecular weight parameter value is 2.8×10 ⁴ .

It should be noted that the preset value of the number average molecular weight in this application is 2.8×10 ⁴ . This value was obtained after the inventor discovered that the relative molecular weight and distribution of the cross-linkable polyethylene insulation material will affect its scorch resistance. It is obtained through a large number of repeated experimental studies based on the laws that have a greater impact.

Specifically, in step S200, the relative size between the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material and the preset value of the number average molecular weight may be compared.

In some embodiments, step S30 evaluates the scorch resistance of the cross-linkable polyethylene insulation material based on the first comparison result, including the following steps:

S300. Evaluate the scorch resistance of the cross-linkable polyethylene insulation material based on the relative size between the actual measured value of the number average molecular weight and the preset value of the number average molecular weight.

Specifically, in step S300, the scorch resistance of the cross-linkable polyethylene insulation material can be evaluated based on the relative size between the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material and the preset value of the number average molecular weight.

In some embodiments, step S300 includes the following steps:

S3000. When the actual measured value of the number average molecular weight is higher than the preset value of the number average molecular weight, evaluate the scorch resistance of the cross-linkable polyethylene material and determine that the scorch resistance of the cross-linkable polyethylene material meets the first requirement.

Specifically, in step S3000, when the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material is higher than the preset value of the number average molecular weight, that is, when the actual measured value of the number average molecular weight is higher than 2.8×10 ⁴ , it can be determined that it can be cross-linked. The scorch resistance of polyethylene material meets the first requirement.

In some embodiments, the first requirement is that the gel content of the prematurely crosslinked block generated after the pre-crosslinking reaction of the crosslinkable polyethylene insulation material is less than 70%. Furthermore, when the gel content of the prematurely cross-linked block generated after the pre-crosslinking reaction of the cross-linkable polyethylene insulation material is less than 70%, it can be determined that the cross-linkable polyethylene insulation material has relatively low scorch resistance. good.

S3100. When the actual measured value of the number average molecular weight is lower than the preset value of the number average molecular weight, evaluate the scorch resistance of the cross-linkable polyethylene material and determine that the scorch resistance of the cross-linkable polyethylene material does not meet the first requirement.

Specifically, in step S3100, when the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material is lower than the preset value of the number average molecular weight, that is, when the actual measured value of the number average molecular weight is lower than 2.8×10 ⁴ , it can be determined that it can be cross-linked. The scorch resistance of polyethylene material does not meet the first requirement.

In some embodiments, the first requirement is that the gel content of the prematurely crosslinked block generated after the pre-crosslinking reaction of the crosslinkable polyethylene insulation material is less than 70%. Furthermore, when the gel content of the premature cross-linked block generated after the pre-cross-linking reaction of the cross-linkable polyethylene insulation material is not less than 70%, the scorch resistance of the cross-linkable polyethylene insulation material can be determined Poor.

In the embodiments of this application, by comparing the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material with the preset value of the number average molecular weight, the scorch resistance of the cross-linkable polyethylene insulation material can be evaluated. Among them, when the actual measured value of the number average molecular weight of the pre-crosslinked polyethylene material is lower than the preset value of the number average molecular weight, it means that the pre-crosslinked polyethylene material contains more short molecular chains, because the short molecular chains are difficult to introduce into the cross-linked polyethylene material. in the combined system, thereby reducing the possibility of obtaining a high gel content, resulting in poor scorch resistance.

Furthermore, the smaller the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material is, the more small molecule polymers there are in the cross-linkable polyethylene insulation material, and more cross-linking agents are needed in the cross-linking process. Pre-crosslinking occurs when the peroxide radicals generated by the thermal decomposition of dicumyl peroxide (DCP) cross-linking agent take away the hydrogen atoms of the polymer molecular chain to form polymer radicals and promote the molecular chain cross-linking network. The formation of structures produces charred material. Therefore, the lower the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulation material, the more cross-linking agent is needed, the more likely the pre-cross-linking phenomenon will occur, and the worse its scorch resistance will be. On the contrary, it means that the cross-linkable polyethylene insulation material has better scorch resistance.

In some embodiments, after it is determined in step S3100 that the scorch resistance of the cross-linkable polyethylene insulation material does not meet the requirements, the following steps are also included:

S3200: Obtain the second comparison result based on the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient;

S3300. Based on the second comparison result, evaluate the scorch resistance of the cross-linkable polyethylene insulation material.

Specifically, in step S3200, when the actual measured value of the number average molecular weight of the cross-linkable polyethylene insulating material is lower than the preset value of the number average molecular weight, that is, when the actual measured value of the number average molecular weight is lower than 2.8×10 ⁴ , then continue to compare more The actual measured value of the dispersion coefficient and the preset value of the polydispersity coefficient are used to evaluate the scorch resistance of cross-linkable polyethylene insulation materials.

In some embodiments, step S3200 obtains the second comparison result based on the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient, including the following steps:

S3210. Compare the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient, and obtain the relative size of the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient.

Specifically, in step S3210, the actual measured value (PD) of the polydispersity coefficient and the preset value of the polydispersity coefficient can be compared to obtain the relative magnitude of the two.

Specifically, in step S3220, the scorch resistance of the cross-linkable polyethylene insulation material can be evaluated based on the relative size of the actual measured value (PD) of the polydispersity coefficient and the preset value of the polydispersity coefficient.

In some embodiments, step S3300 evaluates the scorch resistance of the cross-linkable polyethylene insulation material based on the second comparison result, including the following steps:

S3310. When the actual measured value of the polydispersity coefficient is higher than the preset value of the polydispersity coefficient, it is determined that the scorch resistance of the cross-linkable polyethylene insulation material does not meet the second requirement.

In some embodiments, the preset polydispersity coefficient value is a preset polydispersity coefficient parameter value, and the preset polydispersity coefficient parameter value is 6.

It should be noted that the preset value of the polydispersity coefficient in this application is 6. This value was obtained after the inventor discovered that the relative molecular weight and distribution of the cross-linkable polyethylene insulation material will have a greater impact on its anti-scorch performance. It is obtained through a large number of repeated experimental studies on the basis of the law of influence.

Specifically, in step S3310, when the actual measured value (PD) of the polydispersity coefficient of the cross-linkable polyethylene insulation material is higher than the preset value of the polydispersity coefficient, that is, when the actual measured value (PD) of the polydispersity coefficient is higher than 6, it can be determined The scorch resistance of the cross-linkable polyethylene material does not meet the second requirement.

In some embodiments, the second requirement is that the gel content of the prematurely crosslinked block generated after the pre-crosslinking reaction of the crosslinkable polyethylene insulation material is less than 60%. Furthermore, when the gel content of the premature cross-linked block generated after the pre-cross-linking reaction of the cross-linkable polyethylene insulation material is not less than 60%, the scorch resistance of the cross-linkable polyethylene insulation material can be determined. It is poor, and its electrical performance can also be evaluated to a certain extent.

S3320. When the actual measured value of the polydispersity coefficient is lower than the preset value of the polydispersity coefficient, determine that the scorch resistance of the cross-linkable polyethylene insulation material meets the second requirement.

Specifically, in step S3320, when the actual measured value (PD) of the polydispersity coefficient of the cross-linkable polyethylene insulation material is lower than the preset value of the polydispersity coefficient, that is, when the actual measured value (PD) of the polydispersity coefficient is lower than 6, it can be determined The scorch resistance of the cross-linkable polyethylene material meets the second requirement.

In some embodiments, the second requirement is that the gel content of the prematurely crosslinked block generated after the pre-crosslinking reaction of the crosslinkable polyethylene insulation material is less than 60%. Furthermore, when the gel content of the prematurely cross-linked block generated after the pre-crosslinking reaction of the cross-linkable polyethylene insulation material is less than 60%, it can be determined that the scorch resistance of the cross-linkable polyethylene insulation material is relatively low. Good, and at the same time, its electrical performance can also be evaluated to a certain extent.

In the embodiments of this application, by comparing the actual measured value (PD) of the polydispersity coefficient (PD) of the cross-linkable polyethylene insulation material with the preset value of the polydispersity coefficient, further evaluation can be obtained based on the evaluation of the number average molecular weight. Scorch resistance of cross-linkable polyethylene insulation. Among them, when the measured value of the polydispersity coefficient (PD) of the pre-crosslinked polyethylene material is higher than the preset value of the polydispersity coefficient, it means that the number average molecular weight of the cross-linked polyethylene insulation material is lower and the weight average molecular weight is higher. . The lower number average molecular weight indicates that the cross-linkable polyethylene insulation material contains more short molecular chains. Since short molecular chains are difficult to introduce into the cross-linking system, it will reduce the possibility of obtaining high gel content, resulting in its burn resistance. The focus becomes worse. The higher weight average molecular weight indicates that the cross-linkable polyethylene insulation material contains more molecular chains with larger mass and higher degree of long-chain branching. These molecular chains will increase the binding and entanglement in the cross-linked network structure. Moreover, because molecular chain coils with high degree of long chain branching occupy a small volume, they tend to undergo cross-linking reactions inside the coils to form intramolecular cross-linking points, which do not contribute to the effective cross-linked network and will weaken the cross-linked polymer. network, more DCPs will be added. The higher DCP content makes it more likely to produce scorch substances, resulting in poor scorch resistance of cross-linkable polyethylene insulation materials.

In addition, cross-linkable polyethylene insulation materials with lower measured polydispersity coefficients (PD) have fewer crystal points within their molecules, which means they have low internal impurity content, higher cleanliness, and higher crystallinity; The higher crystallinity means that it has higher melting enthalpy and higher breakdown field strength, indicating that it has more stable electrical properties.

Example

The following are specific examples. The following examples more specifically describe the content disclosed in the present application. These embodiments are only used for illustrative purposes, because various modifications and changes can be made within the scope of the disclosure of the present application. It's obvious. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be directly were used without further processing and the equipment used in the examples is commercially available.

Example 1

(1) Take 20 mg of cross-linkable polyethylene insulation material with an antioxidant content of 0.2%, conduct a gel chromatography test on it, and obtain the number average molecular weight and polydispersity coefficient;

(2) Compare the number average molecular weight obtained in step (1) with the preset value of the number average molecular weight;

(3) Evaluate the scorch resistance and electrical properties of the cross-linkable polyethylene insulation material based on the comparison results in step (2);

(4) Conduct actual performance tests on cross-linkable polyethylene insulation materials to obtain test results of scorch resistance and electrical properties.

Example 2

(1) Take 20 mg of cross-linkable polyethylene insulation material with an antioxidant content of 0.2%, conduct a gel chromatography test on it, and obtain the number average molecular weight and polydispersity coefficient;

(2) Compare the number average molecular weight and polydispersity coefficient obtained in step (1) with the preset value of number average molecular weight and polydispersity coefficient respectively;

(3) Evaluate the scorch resistance and electrical properties of the cross-linkable polyethylene insulation material based on the comparison results in step (2);

(4) Conduct actual performance tests on cross-linkable polyethylene insulation materials to obtain test results of scorch resistance and electrical properties.

Example 3

(1) Take 20 mg of cross-linkable polyethylene insulation material with an antioxidant content of 0.2%, conduct a gel chromatography test on it, and obtain the number average molecular weight and polydispersity coefficient;

(2) Compare the number average molecular weight and polydispersity coefficient obtained in step (1) with the preset value of number average molecular weight and polydispersity coefficient respectively;

(3) Evaluate the scorch resistance and electrical properties of the cross-linkable polyethylene insulation material based on the comparison results in step (2);

(4) Conduct actual performance tests on cross-linkable polyethylene insulation materials to obtain test results of scorch resistance and electrical properties.

The relevant parameters of the cross-linkable polyethylene insulation materials in the above-mentioned Examples 1 to 3 are shown in Table 1 below.

Table 1

The cross-linkable polyethylene insulation materials in Examples 1 to 3 were subjected to relevant performance tests, and the test results are shown in Table 2 below and Figure 2.

test part

(1) Gel chromatography test

In accordance with the regulations of ASTM D6474-2012 and SH/T1759-2007, the number average molecular weight and polydispersity coefficient of cross-linkable polyethylene insulation materials were measured using Agilent PL-GPC220 high-temperature gel chromatograph. The solvent was 1,2,4 trichlorobenzene ( TCB), the measuring temperature is 150°C, and the flow rate is 1.0mL/min.

(2) Scorch resistance test

A torque rheometer was used to test the torque and material temperature changes of the insulation material under shearing action at 140°C. According to the test of GB/T16584-1996, weigh 40g of insulation material sample and put it into the mold cavity of the torque rheometer. Conduct a rheology test on the insulation material at a temperature of 150°C and a rotation speed of 35r/min. Record the torque and material temperature. relationship with time. When the insulation material begins to be vulcanized and cross-linked, the shear modulus of the sample increases. When the torque recorded by the rheometer rises to the maximum value and becomes stable, the relationship curve between torque and time is obtained, as shown in Figure 2.

(3) Electrical performance test

A domestic HMTC-10kVA voltage breakdown tester was used to conduct power frequency breakdown experiments on XLPE samples. The voltage boosting rate was also selected to be 1kV/s, and a ball-ball electrode with a diameter of 20mm was used. Each sample obtained 12 effective breakdown field strengths, as shown in Table 2 below.

Table 2

​ Shape parameters 50% probability of breakdown field strength Example 1 18.18330 98.94711 Example 2 32.59525 104.21154 Example 3 22.06887 104.55625

It can be seen from Figure 2 that at 150°C, among the three cross-linkable polyethylene insulation materials, Example 1 (PE1) has the largest torque change rate and balance torque, followed by Example 3 (PE3), and Example 2 ( The torque change rate and balance torque of PE2) are smaller, indicating that the cross-linkable polyethylene insulation material in Example 2 has the best scorch resistance, followed by Example 3, and Example 1 has the worst scorch resistance. This echoes the scorch resistance results evaluated in Table 1 by the evaluation method provided in this application.

As can be seen from Table 2 above, among the three cross-linkable polyethylene insulation materials, the 50% probability breakdown field strength of Example 1 (PE1) is lower than that of Example 2 (PE2) and Example 3 (PE3). This shows that the AC breakdown strength test value of Example 1 is inferior to that of Example 2 and Example 3; at the same time, although the 50% probability breakdown field strength of Example 3 is similar to that of Example 2, the breakdown of Example 2 is The strength stability is the best (the shape parameter is the largest), the product consistency is the best, and the electrical performance of Example 2 is better, which also echoes the electrical performance results evaluated by the evaluation method provided by this application in Table 1.

The technical features of the above-described embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, All should be considered to be within the scope of this manual.

The above-described embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims (10)

A method for evaluating the scorch resistance of cross-linkable polyethylene insulation materials for cables, including: Obtain the target parameter value of the cross-linkable polyethylene insulation material with the same antioxidant content, wherein the target parameter value includes the measured value of the number average molecular weight; Obtain a first comparison result based on the actual measured value of the number average molecular weight and the preset parameter value, wherein the preset parameter value includes a preset value of the number average molecular weight and a preset value of the polydispersity coefficient; and Based on the first comparison result, the scorch resistance of the cross-linkable polyethylene insulation material is evaluated. The evaluation method according to claim 1, wherein obtaining target parameter values of cross-linkable polyethylene insulation materials with the same antioxidant content includes: Conduct a gel chromatography test on the cross-linkable polyethylene insulation material to obtain the target parameter value, where the target parameter value also includes the measured value of the polydispersity coefficient. The evaluation method according to claim 1 or 2, wherein obtaining the first comparison result based on the actual measured value of the number average molecular weight and the preset parameter value includes: Comparing the actual measured value of the number average molecular weight with the preset value of the number average molecular weight, the relative size of the actual measured value of the number average molecular weight and the preset value of the number average molecular weight is obtained. The evaluation method according to claim 3, characterized in that, based on the first comparison result, evaluating the scorch resistance of the cross-linkable polyethylene insulation material includes: When the actual measured value of the number average molecular weight is higher than the preset value of the number average molecular weight, it is determined that the scorch resistance of the cross-linkable polyethylene insulation material meets the first requirement; or When the actual measured value of the number average molecular weight is lower than the preset value of the number average molecular weight, it is determined that the scorching resistance of the cross-linkable polyethylene insulation material does not meet the first requirement. The evaluation method according to claim 4, wherein the first requirement is that the gel content of the premature cross-linked block generated after the pre-cross-linking reaction of the cross-linkable polyethylene insulation material is less than 70%. The evaluation method according to claim 4 or 5, wherein after determining that the scorch resistance of the cross-linkable polyethylene material does not meet the first requirement, it further includes: Based on the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient, obtain a second comparison result; and Based on the second comparison result, the scorch resistance of the cross-linkable polyethylene insulation material is evaluated. The evaluation method according to claim 6, wherein obtaining the second comparison result based on the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient includes: Comparing the actual measured value of the polydispersity coefficient with the preset value of the polydispersity coefficient, the relative magnitude of the actual measured value of the polydispersity coefficient and the preset value of the polydispersity coefficient is obtained. The evaluation method according to claim 6 or 7, wherein said evaluating the scorch resistance of the cross-linkable polyethylene insulation material based on the second comparison result includes: When the actual measured value of the polydispersity coefficient is higher than the preset value of the polydispersity coefficient, it is determined that the scorch resistance of the cross-linkable polyethylene insulation material does not meet the second requirement; or When the actual measured value of the polydispersity coefficient is lower than the preset value of the polydispersity coefficient, it is determined that the scorch resistance of the cross-linkable polyethylene insulation material meets the second requirement. The evaluation method according to claim 8, wherein the second requirement is that the gel content of the premature cross-linked block generated after the pre-cross-linking reaction of the cross-linkable polyethylene insulation material is less than 60%. The evaluation method according to any one of claims 2-9, wherein the evaluation method satisfies at least one of the following conditions (1) to (2): (1) The preset value of the number average molecular weight is 2.8×10 ⁴ ; (2) The preset value of the polydispersity coefficient is 6.

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