A method for improving stable batch preparation of non-cross-linked polypropylene cable insulation material

Abstract

The present invention belongs to the technical field of cable insulation material preparation, and specifically relates to a method for improving the batch stable preparation of non-cross-linked polypropylene cable insulation material. The preparation method comprises the following steps: screening different batches of polypropylene and elastomer raw materials through a vibrating screen to ensure the uniformity of particle size; using a high-speed mixer to mix the screened raw materials at high speed, with a rotation speed of 100-500r / min and a mixing time of 10-15 minutes; preparing a masterbatch with an elastomer content of 75-85%; and melt blending the masterbatch with a polypropylene matrix for extrusion granulation. The present invention is optimized in steps, and the batch production of non-cross-linked polypropylene cable insulation material becomes more stable, and the obtained non-cross-linked polypropylene cable insulation cable material has a lower melt index volatility, stable extrusion pressure, and more stable and reliable material insulation performance, mechanical properties, etc., which meets the actual needs of high-performance cables.

Description

Technical Field

[0001] The invention belongs to the technical field of cable insulation material preparation, and in particular relates to a method for stably preparing a batch of non-cross-linked polypropylene cable insulation materials. Background Art

[0002] At present, polypropylene has been widely studied as a cable insulation material, mainly because of its excellent thermal properties, electrical properties and processing properties. However, pure polypropylene has certain deficiencies in mechanical properties, aging resistance and thermal conductivity, which limits its application in high-voltage DC cables and other fields. In order to overcome these limitations, researchers have conducted a variety of modification studies on polypropylene, including copolymerization modification, nanoparticle modification, blending modification and grafting modification, among which blending modification is one of the commonly used methods for preparing non-cross-linked polypropylene cable insulation materials.

[0003] However, there are still some problems in the batch preparation process of non-cross-linked polypropylene cable insulation materials. Traditional preparation methods are difficult to ensure the stability of the performance of each batch of materials. In the raw material mixing process, due to differences in particle size, density, etc. of different batches of raw materials, it is easy to cause uneven mixing, thus affecting the final performance of the insulation material. In terms of processing technology, fluctuations in processing parameters such as temperature and pressure will also affect the microstructure of non-cross-linked polypropylene such as crystallinity and molecular orientation, thereby affecting its insulation and mechanical properties. Moreover, the existing preparation process lacks an effective quality monitoring and feedback adjustment mechanism, and it is impossible to detect and correct deviations in the production process in a timely manner, making it difficult to ensure the stability of batch production. Summary of the invention

[0004] The present invention aims to solve the problems existing in the prior art and provides a method for improving the batch stable preparation of non-cross-linked polypropylene cable insulation material. The method makes the batch production of non-cross-linked polypropylene cable insulation material more stable and the material performance more reliable through step-by-step optimization, thus meeting the actual needs of high-performance cables.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for stably preparing a batch of non-cross-linked polypropylene cable insulation material comprises the following steps:

[0007] (1) Using a vibrating screen to screen different batches of raw polypropylene and elastomer to obtain raw materials with uniform size;

[0008] (2) mixing the screened polypropylene and the elastomer in a high-speed mixer to obtain a preliminary mixture;

[0009] (3) pre-dispersing the preliminary mixed material in a twin-screw extruder to obtain a pre-dispersed masterbatch;

[0010] (4) The pre-dispersed masterbatch is mixed with the screened polypropylene, and melt-blended and extruded in a twin-screw extruder to obtain non-cross-linked polypropylene cable insulation material particles.

[0011] Furthermore, the mesh size of the vibrating screen in step (1) is set according to the average particle diameter of the raw material.

[0012] The mesh size of the vibrating screen refers to the size of the holes on the screen, which has an important impact on the screening effect and production efficiency. The particle sizes of different raw materials are different. The selection of the mesh size should consider the following factors:

[0013] (a) Raw material particle size: Select the corresponding sieve aperture according to the particle size characteristics of the raw material. Generally speaking, the finer the raw material particle size, the smaller the required sieve aperture.

[0014] (b) Screening efficiency requirements: Select the appropriate screen mesh diameter according to the screening efficiency requirements. For example, if the screening effect of fine particles is required to be high, the screen mesh diameter should be reduced accordingly.

[0015] (c) Process parameters: Consider the influence of production process parameters and select the appropriate mesh size. If the humidity, viscosity and other parameters of the raw materials have an impact on the screening effect, these should be considered.

[0016] Furthermore, the frequency of the vibrating screen in step (1) is 35-65 Hz, and the amplitude is 2-4 mm.

[0017] Different batches of polypropylene and elastomer raw materials may contain particles of different sizes and powder attached to the surface of the raw materials in the initial state, and these oversized and undersized particles and powders will affect the stability and performance of the subsequent insulation material preparation. Use a vibrating screen to screen the polypropylene and elastomer raw materials. The vibrating screen uses a specific vibration frequency and amplitude to make the raw materials produce complex motion trajectories on the screen, which separates the particles and powder that do not meet the requirements from the qualified raw materials. The appropriate screen aperture is selected based on the precise analysis of the particle size characteristics of the polypropylene and elastomer raw materials. This analysis can be measured with the help of advanced particle analysis instruments (such as laser particle size analyzers) to ensure that the screen aperture can accurately screen out the raw material particles that meet the requirements, thereby ensuring that the raw materials entering the subsequent process have uniform particle size, laying the foundation for the preparation of non-cross-linked polypropylene cable insulation materials with stable performance.

[0018] Furthermore, the elastomer is one or more of hydrogenated styrene-butadiene-styrene (SEBS) triblock copolymer, polyolefin elastomer (POE), propylene elastomer, ethylene propylene diene monomer rubber (EPR), and ethylene propylene diene monomer rubber (EPDM).

[0019] Furthermore, the mass proportion of the elastomer in the preliminary mixture in step (2) is 75-85%.

[0020] Furthermore, in step (2), the rotation speed of the high-speed mixer is 100-500 r / min, and the mixing time is 10-15 minutes.

[0021] The speed range and mixing time set by the present invention are obtained through experimental optimization. In this speed range, the stirring paddle generates enough shear force on the raw materials, so that the raw materials are constantly turned and collided inside the mixer, thereby promoting the raw materials to be fully mixed at the microscopic level. When the speed is lower than 100r / min, the shear force generated by the stirring paddle on the raw materials is insufficient, and the turning and collision of the raw materials in the mixer are not violent enough, making it difficult to make the raw materials of different components fully contact and mix at the microscopic level, which easily leads to uneven mixing of the raw materials. When the speed is higher than 500r / min, although a large shear force can be generated, it may damage the molecular structure of the raw materials, especially for polypropylene and elastomer raw materials, which may affect their physical and chemical properties, and then affect the performance of the final non-cross-linked polypropylene cable insulation material. The setting of the mixing time ensures that the raw materials have enough time to reach a uniformly mixed state, avoiding local component differences caused by insufficient mixing, and then affecting the performance of the final insulating material. In the initial stage of mixing, the different components in the raw materials are in a relatively dispersed state. As the mixing time increases, under the action of the stirring paddle, the contact and mixing between the raw materials gradually become sufficient. If the mixing time is shorter than 10 minutes, some raw materials may not be fully mixed, resulting in uneven composition areas in the final product, affecting the product's insulation and mechanical properties. If the mixing time exceeds 15 minutes, continuing to mix after the mixture has been fully mixed will not only increase energy consumption, but may also have unnecessary effects on the raw materials due to excessive mixing.

[0022] Furthermore, the parameters of the twin-screw extruder in step (3) are set as follows: zone 1 temperature: 170-190°C, zone 2 temperature: 200-220°C, zone 3 temperature: 180-200°C, rotation speed: 200-300r / min.

[0023] Step (3) prepares a pre-dispersed masterbatch containing 75-85% of elastomer. By precisely controlling the amount of elastomer added, the masterbatch can impart specific properties to the non-cross-linked polypropylene cable insulation material when subsequently blended with a polypropylene matrix.

[0024] Furthermore, the parameters of the twin-screw extruder described in step (4) are set as follows: zone 1 temperature: 180-200°C, zone 2 temperature: 200-220°C, zone 3 temperature: 220-240°C, rotation speed: 80-150r / min.

[0025] Furthermore, in step (4), the mass ratio of the polypropylene to the pre-dispersed masterbatch is 1:0.1-0.5.

[0026] The masterbatch with an elastomer content of 75-85% interacts with the polypropylene matrix during the melt blending extrusion process. The presence of the elastomer can improve the flexibility, impact resistance and other properties of polypropylene, while the polypropylene matrix provides basic structural support and insulation performance for the entire insulation material. In the molten state in the extruder, the molecular chains of the two raw materials interweave and entangle with each other under the shearing and pushing action of the screw to form a uniform mixed system, which is then extruded through a specific die to form granular non-cross-linked polypropylene cable insulation material. In this process, the mixing ratio of the masterbatch and the polypropylene matrix, the extrusion temperature, the screw speed and other parameters are carefully adjusted to ensure the stable batch preparation of non-cross-linked polypropylene cable insulation materials.

[0027] In the method of the present invention, a vibrating screen is used to screen the raw materials, thereby eliminating the particle size differences existing in different batches of raw materials, and removing the powder attached to the surface of the raw material particles. The screened raw materials are more evenly distributed in the subsequent mixing and processing process, which is conducive to the consistency of material performance. At the same time, the influence of particle size differences on mixing and processing equipment can be reduced, and production stability is improved. The method of accurately selecting the mesh aperture according to the characteristics of the raw materials avoids the problem of waste of raw materials or incomplete screening due to inappropriate mesh aperture, can retain qualified raw materials to the greatest extent, and effectively remove particles that do not meet the requirements, thereby improving the efficiency and accuracy of raw material pretreatment. The pre-dispersed masterbatch preparation step makes the distribution of the elastomer in the polypropylene more uniform, enhances the toughness and mechanical properties of the material, solves the problem of poor compatibility between the elastomer and the polypropylene base material, and provides a guarantee for improving the performance of the composite material. The final mixture preparation step ensures the uniform distribution of the raw materials and further reduces the performance differences between batches.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] Each step of the method provided by the present invention is interconnected to form a complete and stable preparation process. The present invention makes the batch production of non-cross-linked polypropylene cable insulation material more stable through step-by-step optimization, and the obtained non-cross-linked polypropylene cable insulation cable material has a lower melt index fluctuation rate, stable extrusion pressure, and more stable and reliable material insulation performance, mechanical properties, etc., meeting the actual needs of high-performance cables. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It is worth noting that the methods used in the present invention are conventional methods unless otherwise specified; the raw materials and devices used are conventional commercially available products unless otherwise specified, and their sources are not specifically limited.

[0031] Example 1

[0032] This embodiment provides a method for stably preparing a batch of non-cross-linked polypropylene cable insulation material, and the raw materials used are as follows:

[0033] Polypropylene (PP): average particle size 0.5-5mm, hydrogenated styrene-butadiene-styrene (SEBS): average particle size 0.5-1mm, a small amount of powder exists on the surface of the raw material.

[0034] The method comprises the following steps:

[0035] (1) Using a vibrating screen with an aperture of 0.6 mm and 1 mm to screen polypropylene, and using a vibrating screen with an aperture of 0.2 mm and 0.9 mm to screen SEBS, to remove oversized and undersized particles, and obtain raw materials with uniform sizes. The vibration frequency of the vibrating screen is set to 50 Hz and the amplitude is 3 mm. Under this setting, the vibrating screen can effectively screen out polypropylene particles with a diameter less than 0.6 mm and greater than 1 mm, and elastomer particles with a diameter less than 0.2 mm and greater than 0.9 mm, and remove powder on the surface of the raw materials, accurately ensuring the uniformity of the raw material particle size;

[0036] (2) Mixing the screened polypropylene and SEBS in a high-speed mixer, with the mass proportion of SEBS being 80%, at a high-speed mixer speed of 300 r / min for 12 minutes to obtain a preliminary mixture; during the mixing process, sampling of the raw materials at different positions in the mixer was performed under a microscope, and it was found that the polypropylene and SEBS particles in the raw materials were uniformly distributed at the microscopic level, indicating that the setting of the speed and mixing time ensured that the raw materials were fully mixed;

[0037] (3) pre-dispersing the preliminary mixed material in a twin-screw extruder, the parameters of the twin-screw extruder are: zone 1 temperature 180° C., zone 2 temperature 210° C., zone 3 temperature 190° C., speed 250 r / min, and pelletizing after cooling to obtain a pre-dispersed masterbatch;

[0038] (4) The screened polypropylene is mixed with the pre-dispersed masterbatch in a mass ratio of 1:0.1, and the mixture is added into a twin-screw extruder for melt blending. The parameters of the twin-screw extruder are: zone 1 temperature 180°C, zone 2 temperature 200°C, zone 3 temperature 220°C, and screw speed 100r / min to obtain non-cross-linked polypropylene cable insulation material particles.

[0039] The appearance of the pellets is uniform. After testing, the fluctuations of insulation performance, mechanical properties and other indicators between different batches are within ±5%, ensuring stable batch production.

[0040] Example 2

[0041] This embodiment provides a method for stably preparing a batch of non-cross-linked polypropylene cable insulation material, and the raw materials used are as follows:

[0042] Polypropylene (PP): particle size 0.3-2mm, hydrogenated styrene-butadiene-styrene (SEBS): particle size 0.2-1.2mm, there is a lot of powder on the surface of the raw material.

[0043] The method comprises the following steps:

[0044] (1) Using a vibrating screen with an aperture of 0.4 mm and 1.8 mm to screen polypropylene, and using a vibrating screen with an aperture of 0.1 mm and 1.1 mm to screen SEBS, to remove oversized and undersized particles, and obtain raw materials with uniform size. The vibration frequency of the vibrating screen is set to 60 Hz and the amplitude is 2.5 mm. Under this setting, the vibrating screen can effectively screen out polypropylene particles with a diameter less than 0.4 mm and greater than 1.8 mm and elastomer particles with a diameter less than 0.1 mm and greater than 1.1 mm, and remove powder on the surface of the raw material, accurately ensuring the uniformity of the raw material particle size;

[0045] (2) The screened polypropylene and SEBS were mixed in a high-speed mixer, with the mass proportion of SEBS being 80%. The speed of the high-speed mixer was 100 r / min for 15 minutes to obtain a preliminary mixture. During the mixing process, the raw materials in the mixing process were analyzed using a laser particle size analyzer. The results showed that as the mixing time increased, the particle size distribution of the raw materials gradually narrowed. After 15 minutes, the mixing of the raw material particles reached a uniform state, which proved that the setting of the speed and mixing time ensured sufficient mixing.

[0046] (3) pre-dispersing the preliminary mixed material in a twin-screw extruder, the parameters of the twin-screw extruder are: zone 1 temperature 180° C., zone 2 temperature 210° C., zone 3 temperature 190° C., speed 250 r / min, and pelletizing after cooling to obtain a pre-dispersed masterbatch;

[0047] (4) The screened polypropylene is mixed with the pre-dispersed masterbatch in a mass ratio of 1:0.2, and the mixture is added into a twin-screw extruder for melt blending. The parameters of the twin-screw extruder are: zone 1 temperature 190°C, zone 2 temperature 210°C, zone 3 temperature 230°C, and screw speed 80r / min to obtain non-cross-linked polypropylene cable insulation material particles.

[0048] Testing of different batches of products revealed that the fluctuation range of mechanical properties such as tensile strength and elongation at break was within ±3%, and the dielectric constant fluctuation was within ±0.03, ensuring the stable batch preparation of non-cross-linked polypropylene cable insulation materials.

[0049] Example 3

[0050] This embodiment provides a method for stably preparing a batch of non-cross-linked polypropylene cable insulation material, and the raw materials used are as follows:

[0051] Polypropylene (PP): average particle size 0.8-2.2mm, hydrogenated styrene-butadiene-styrene (SEBS): average particle size 0.4-1.5mm, there is slight powder on the surface of the raw material.

[0052] The method comprises the following steps:

[0053] (1) Using a vibrating screen with an aperture of 0.6 mm and 2 mm to screen polypropylene, and using a vibrating screen with an aperture of 0.3 mm and 1.4 mm to screen SEBS, to remove oversized and undersized particles, and obtain raw materials with uniform sizes. The vibration frequency of the vibrating screen is set to 40 Hz and the amplitude is 3.5 mm. Under this setting, the vibrating screen can effectively screen out polypropylene particles with a diameter less than 0.6 mm and greater than 2 mm, and elastomer particles with a diameter less than 0.3 mm and greater than 1.4 mm, and remove powder on the surface of the raw materials, accurately ensuring the uniformity of the raw material particle size;

[0054] (2) The screened polypropylene and SEBS were mixed in a high-speed mixer, with the mass proportion of SEBS being 80%. The speed of the high-speed mixer was 500 r / min for 10 minutes to obtain a preliminary mixture. During the mixing process, differential scanning calorimetry (DSC) analysis was performed by sampling, and it was found that after 10 minutes of mixing, the thermal property curves of the raw materials tended to be consistent, indicating that the raw materials had been fully mixed at the microscopic level, proving that the settings of the speed and mixing time met the requirements of full mixing.

[0055] (3) pre-dispersing the preliminary mixed material in a twin-screw extruder, the parameters of the twin-screw extruder are: zone 1 temperature 180° C., zone 2 temperature 210° C., zone 3 temperature 190° C., speed 250 r / min, and pelletizing after cooling to obtain a pre-dispersed masterbatch;

[0056] (4) The screened polypropylene is mixed with the pre-dispersed masterbatch in a mass ratio of 1:0.3, and the mixture is added into a twin-screw extruder for melt blending. The parameters of the twin-screw extruder are: zone 1 temperature 185°C, zone 2 temperature 205°C, zone 3 temperature 225°C, and screw speed 120 r / min to obtain non-cross-linked polypropylene cable insulation material particles.

[0057] After testing, the fluctuation range of the product's electrical performance indicators such as volume resistivity and dielectric loss between different batches is within ±4%, ensuring the stable batch preparation of non-cross-linked polypropylene cable insulation materials.

[0058] Example 4

[0059] This embodiment provides a method for stably preparing a batch of non-cross-linked polypropylene cable insulation material, and the raw materials used are as follows:

[0060] Polypropylene (PP): average particle size 0.4-1.8 mm, hydrogenated styrene-butadiene-styrene (SEBS): average particle size 0.3-1.3 mm, there are some powder impurities on the surface of the raw materials.

[0061] The method comprises the following steps:

[0062] (1) Using a vibrating screen with an aperture of 0.5 mm and 1.7 mm to screen polypropylene, and using a vibrating screen with an aperture of 0.2 mm and 1.2 mm to screen SEBS, to remove oversized and undersized particles, and obtain raw materials with uniform sizes. The vibration frequency of the vibrating screen is set to 55 Hz and the amplitude is 3 mm. Under this setting, the vibrating screen can effectively screen out polypropylene particles with a diameter less than 0.5 mm and greater than 1.7 mm and elastomer particles with a diameter less than 0.2 mm and greater than 1.2 mm, and remove powder on the surface of the raw materials, accurately ensuring the uniformity of the raw material particle size;

[0063] (2) The screened polypropylene and SEBS were mixed in a high-speed mixer, with the mass proportion of SEBS being 80%. The speed of the high-speed mixer was 200 r / min, and the time was 13 minutes to obtain a preliminary mixture. During the mixing process, a rheological test was performed on the raw materials in the mixer, and it was found that with the increase of mixing time, the rheological properties of the raw materials tended to be stable. At 13 minutes, the raw materials were fully mixed at the microscopic level, indicating that the setting of the speed and mixing time can ensure that the raw materials are fully mixed.

[0064] (3) pre-dispersing the preliminary mixed material in a twin-screw extruder, the parameters of the twin-screw extruder are: zone 1 temperature 180° C., zone 2 temperature 210° C., zone 3 temperature 190° C., speed 250 r / min, and pelletizing after cooling to obtain a pre-dispersed masterbatch;

[0065] (4) The screened polypropylene is mixed with the pre-dispersed masterbatch in a mass ratio of 1:0.4, and the mixture is added into a twin-screw extruder for melt blending. The parameters of the twin-screw extruder are: zone 1 temperature 195°C, zone 2 temperature 215°C, zone 3 temperature 235°C, and screw speed 90r / min to obtain non-cross-linked polypropylene cable insulation material particles.

[0066] Testing of the product revealed that the fluctuation range of its mechanical properties such as hardness and flexibility, and electrical properties such as dielectric strength between different batches was within ±2%, ensuring the stable batch preparation of non-cross-linked polypropylene cable insulation materials.

[0067] Comparative Example 1

[0068] This comparative example provides a method for the stable batch preparation of non-cross-linked polypropylene cable insulation material. The difference from Example 1 is that the method does not include step (1), that is, the raw materials are not screened.

[0069] Larger particles are prone to stratification and agglomeration during the mixing process, resulting in reduced mixing uniformity and poor compatibility of the elastomer in the polypropylene matrix. The mechanical and electrical properties of the prepared polypropylene cable insulation material are reduced compared to those in Example 1.

[0070] Comparative Example 2

[0071] This comparative example provides a method for the stable batch preparation of non-cross-linked polypropylene cable insulation material. The difference from Example 1 is that in step (2), the speed of the high-speed mixer is 600 r / min and the time is 20 minutes.

[0072] Mixing time that is too long will lead to over-mixing, causing separation and accumulation of components, deterioration of the physical properties of the blend, and decreased thermal stability; mixing speed that is too fast will generate a large amount of frictional heat, causing the material temperature to rise, and further leading to changes in the molecular structure and properties of the resin.

[0073] Comparative Example 3

[0074] This comparative example provides a method for the stable batch preparation of non-cross-linked polypropylene cable insulation material. The difference from Example 1 is that when polypropylene and SEBS are mixed in step (2), the mass proportion of SEBS is 60%.

[0075] The toughness of the polypropylene cable insulation material prepared in this comparative example is significantly lower than that in Example 1.

[0076] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for stably preparing a batch of non-cross-linked polypropylene cable insulation materials, comprising the following steps: (1) Using a vibrating screen to screen different batches of raw polypropylene and elastomer to obtain raw materials with uniform size; (2) mixing the screened polypropylene and the elastomer in a high-speed mixer to obtain a preliminary mixture; (3) pre-dispersing the preliminary mixed material in a twin-screw extruder to obtain a pre-dispersed masterbatch; (4) The pre-dispersed masterbatch is mixed with the screened polypropylene, and melt-blended and extruded in a twin-screw extruder to obtain non-cross-linked polypropylene cable insulation material particles.

2. The method according to claim 1, characterized in that: The mesh size of the vibrating screen in step (1) is set according to the average particle diameter of the raw material.

3. The method according to claim 1, characterized in that: The frequency of the vibrating screen in step (1) is 35-65 Hz, and the amplitude is 2-4 mm.

4. The method according to claim 1, characterized in that: The elastomer is one or more of hydrogenated styrene-butadiene-styrene (SEBS) triblock copolymer, polyolefin elastomer (POE), propylene elastomer, ethylene propylene diene monomer rubber (EPR), and ethylene propylene diene monomer rubber (EPDM).

5. The method according to claim 1, characterized in that: The mass proportion of the elastomer in the preliminary mixture in step (2) is 75-85%.

6. The method according to claim 1, characterized in that: The rotation speed of the high-speed mixer in step (2) is 100-500 r / min, and the mixing time is 10-15 minutes.

7. The method according to claim 1, characterized in that: The parameters of the twin-screw extruder in step (3) are set as follows: zone 1 temperature: 170-190°C, zone 2 temperature: 200-220°C, zone 3 temperature: 180-200°C, rotation speed: 200-300r / min.

8. The method according to claim 1, characterized in that: The parameters of the twin-screw extruder described in step (4) are set as follows: zone 1 temperature: 180-200°C, zone 2 temperature: 200-220°C, zone 3 temperature: 220-240°C, and rotation speed: 80-150r / min.

9. The method according to claim 1, characterized in that: The mass ratio of the polypropylene to the pre-dispersed masterbatch in step (4) is 1:0.1-0.5.