Chemically foamed fep insulating material and method for producing the same

Abstract

The application discloses a kind of chemical foaming FEP insulating material and preparation method thereof, the raw material of the insulating material is prepared from the following weight parts of raw materials: FEP resin 100 parts, chemical foaming agent compound 1.2~3 parts, modified silane coupling agent 1~3 parts, antioxidant 0.3~1 parts, lubricant 0.5~2 parts.The chemical foaming agent compound created by the application is mainly decomposed gas production temperature at 330~400 DEG C, can perfectly match the preparation processing temperature (280~380 DEG C) of current FEP communication cable, and the processing adaptability is high, and without high-end physical foaming special extrusion equipment, ordinary fluoroplastic cable extrusion equipment can be used.In addition, the cable prepared by the chemical foaming FEP insulating material of the application has higher foaming degree and good mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of cable material technology, specifically to a chemically foamed FEP insulation material and its preparation method. Background Technology

[0002] The insulation layer of communication cables needs to meet requirements such as high temperature resistance, low dielectric constant, and good mechanical properties. Fluoroplastics (such as FEP) have become the preferred insulation material for communication cables in high-temperature environments due to their excellent high temperature resistance, chemical stability, and electrical insulation properties. Currently, the insulation layer of high-temperature resistant fluoroplastic communication cables is almost entirely prepared using a physical foaming process. The principle is to form bubbles in molten FEP resin using high-pressure inert gas (such as nitrogen), thereby reducing the insulation layer density and optimizing dielectric properties.

[0003] However, physical foaming processes have significant drawbacks: First, they require extremely high-performance equipment, including specialized high-pressure foaming extrusion equipment, which is very expensive (the investment for a single unit usually exceeds one million yuan); second, the process is complex, requiring precise control of multiple parameters such as gas pressure, extrusion temperature, and traction speed, as even slight fluctuations can lead to defects such as uneven cell size and cell breakage; and third, the production cost is high, with high-pressure gas consumption and equipment maintenance costs significantly increasing the overall cost of cable manufacturing.

[0004] To address the aforementioned issues with physical foaming, the industry has attempted to employ chemical foaming processes, which involve using chemical foaming agents to decompose at high temperatures and generate inert gases to achieve foaming. However, existing chemical foaming agents are ill-suited to the processing characteristics of FEP: the decomposition temperatures of inorganic foaming agents (such as sodium bicarbonate and ammonium carbonate) are typically 70℃ to 180℃, far lower than the extrusion processing temperature of FEP (280℃ to 380℃), resulting in the foaming agent completely decomposing before the FEP melts, thus failing to form effective cells; the decomposition temperatures of organic foaming agents (such as azodicarbonamide and benzenesulfonyl hydrazine) are at most about 270℃, still lower than the minimum processing temperature of FEP, and the decomposition products easily react chemically with FEP, leading to a deterioration in the insulation layer performance.

[0005] Furthermore, even if the decomposition temperature of some foaming agents is close to the processing temperature of FEP, poor foaming uniformity still exists: bubbles easily merge to form large-diameter cells (co-formed cells), or rupture due to insufficient cell wall strength (broken cells), ultimately affecting the mechanical and electrical properties of the insulation layer. Simultaneously, the poor compatibility between chemical foaming agents and FEP resin easily leads to uneven dispersion, further exacerbating cell defects and reducing the material's mechanical properties.

[0006] Therefore, developing a chemically foamed FEP insulation material that is compatible with FEP processing temperature, has uniform foaming, good mechanical properties, and can be prepared using ordinary equipment has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a chemically foamed FEP insulation material and its preparation method. Through a specific ratio of composite raw materials and an optimized preparation process, the material achieves a synergistic improvement in its compatibility with FEP processing temperature, foaming uniformity, and mechanical properties.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A chemically foamed FEP insulation material is prepared from the following raw materials in parts by weight:

[0010]

[0011] The specific selection and parameters of each raw material are as follows:

[0012] FEP resin: The melt index, measured at 372℃ / 5kg, is 15g / 10min~25g / 10min, and the melt temperature is 260℃~280℃. FEP resin with these parameters exhibits suitable flowability, ensuring uniform mixing with other components and stable bubble growth during foaming.

[0013] Chemical foaming agent complex: composed of ammonium polyphosphate, expandable graphite, and ultrafine boron nitride, which work synergistically to achieve high-temperature foaming and cell control.

[0014] Ammonium polyphosphate: degree of polymerization n≥1000, particle size D50 is 9 micrometers, it begins to decompose at 330℃ to produce ammonia and nitrogen (inert gas), and the gas production temperature matches the FEP processing temperature;

[0015] Expandable graphite: with a mesh size of 200, it begins to expand above 300℃, and its volume can expand 10 to 30 times at 300℃~400℃, forming worm-like micro-spaces to provide storage places for air bubbles and prevent gas from escaping;

[0016] Ultrafine boron nitride: with a particle size D50 of 1 micrometer, it serves as a bubble nucleation point, guiding the gas to grow uniformly into small-sized bubbles;

[0017] The ratio of ammonium polyphosphate to expandable graphite is (3-4):1; the mass of ultrafine boron nitride is 1.5 times the total mass of ammonium polyphosphate and expandable graphite.

[0018] Modified silane coupling agent: KH-792. The amino groups in its molecular structure can chemically react with the polar groups on the surface of FEP resin and the hydroxyl groups of foaming agents (ammonium polyphosphate, expandable graphite), thereby improving the compatibility between inorganic foaming agents and organic FEP resin and enhancing the mechanical properties of the material.

[0019] Antioxidant: One or a combination of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (1010), 1,2-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine (1024), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (1076), and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid (3114) can inhibit the oxidative degradation of FEP resin during high-temperature processing and extend the service life of the material.

[0020] Lubricant: Ethylene bis-stearamide, which can reduce the viscosity of FEP resin in the molten state, improve the dispersibility of each component and the flowability of extrusion processing, and prevent premature decomposition of foaming agent due to local friction overheating.

[0021] The present invention also provides a method for preparing the above-mentioned chemically foamed FEP insulation material, comprising the following steps:

[0022] S1. Raw material drying: Dry the FEP resin at 100℃ for 2-3 hours to remove moisture (to avoid moisture affecting the stability of the foam cells during processing); dry the remaining raw materials (except for the modified silane coupling agent) at 60℃ for 3-4 hours to prevent the foaming agent from becoming ineffective or unevenly dispersed due to moisture.

[0023] S2. Resin pretreatment: Add the dried FEP resin and modified silane coupling agent to a high-speed mixer and stir at 800-1200 r / min for 10-15 minutes until the mixture is uniform. Then let it stand for 30 minutes to allow KH-792 to fully penetrate and be absorbed by the FEP resin, ensuring that the coupling agent is evenly distributed and plays a compatibility improvement role.

[0024] S3. Co-extrusion: The pretreated FEP resin and the remaining dried raw materials (chemical foaming agent complex, antioxidant, lubricant) are added to a high-speed mixer and stirred at 600-800 r / min for 5-10 minutes until uniformly mixed. The mixture is then fed into a twin-screw extruder for melt blending. The extruder temperature is set to 280℃-380℃ (gradual heating along the screw direction to ensure complete melting of the FEP resin and prevent premature decomposition of the foaming agent). The screw length-to-diameter ratio is (20-25):1, and the compression ratio is 2.5-3.0 (to ensure sufficient plasticization and dispersion of the material). After the molten material is extruded through the die head, it is granulated by water-jetting. The resulting granules are dried at 100℃ for 2 hours to remove surface moisture, thus obtaining the chemically foamed FEP insulation material.

[0025] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0026] A. Excellent processing temperature adaptability: In the chemical foaming agent compound, the decomposition and gas generation temperature of ammonium polyphosphate is 330℃~400℃, and expandable graphite expands significantly at 300℃~400℃, which perfectly matches the processing temperature of FEP (280℃~380℃). This solves the problem of the decomposition temperature of existing foaming agents being too low, eliminating the need for additional control at high temperatures and simplifying the process.

[0027] B. Significantly improved foaming uniformity: The worm-like microspaces formed by the expansion of expandable graphite provide storage space for gas, and ultrafine boron nitride acts as nucleation points to guide the uniform growth of bubbles. The two work together to suppress the phenomena of pore formation and pore breakage. The bubble diameter can be controlled within 8 to 15 micrometers, and the uniformity is improved by more than 40% compared with the existing chemical foaming technology.

[0028] C. Excellent mechanical properties: The modified silane coupling agent improves the compatibility between the inorganic foaming agent and FEP resin, so that the foamed insulation material still maintains high tensile strength (≥11.5MPa) and elongation at break (≥109%), which meets the mechanical performance requirements of communication cables.

[0029] D. Low equipment cost: The chemical foaming process eliminates the need for the high-pressure gas generation and control system required for physical foaming. Ordinary fluoroplastic extrusion equipment can be used to produce it, reducing equipment investment by 60% to 70%. Moreover, the process is simple and easy to operate, making it suitable for large-scale production. Detailed Implementation

[0030] This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. All other embodiments derived by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0031] In the following embodiments, the preparation method of the finished chemically foamed FEP cable is uniformly as follows: The chemically foamed FEP insulation material is pre-dried, and a high-temperature corrosion-resistant fluoroplastic extrusion device with a screw diameter of 35mm is used. An extrusion die is employed, with a draw ratio of 15, and the processing temperature is set at 280℃~380℃. The insulation layer is extruded onto a single rigid copper conductor with an outer diameter of 1.35mm, and the extruded insulation layer thickness is 0.30mm±0.05mm. For further details, please refer to the specific embodiments.

[0032] Example 1

[0033] This embodiment provides a chemically foamed FEP insulation material, which is composed of the following raw materials in parts by weight:

[0034] FEP resin (372℃ / 5kg melt index 18.5g / 10min, melt temperature 270℃): 100 parts;

[0035] Chemical foaming agent complex: 1.2 parts (including 0.6 parts ammonium polyphosphate, 0.2 parts expandable graphite, and 1.2 parts ultrafine boron nitride, with the mass ratio of ammonium polyphosphate to expandable graphite being 3:1 and the ultrafine boron nitride being 1.5 times the total mass of the two);

[0036] Modified silane coupling agent KH-792: 2 parts;

[0037] Antioxidant 1024: 0.5 parts;

[0038] Lubricant ethylene bis-stearamide: 1.2 parts.

[0039] Preparation method:

[0040] S1. Raw material drying: FEP resin is dried at 100℃ for 2.5 hours, and chemical foaming agent complex, antioxidant, and lubricant are dried at 60℃ for 3.5 hours;

[0041] S2. Resin pretreatment: Add the dried FEP resin and KH-792 to a high-speed mixer and stir at 1000r / min for 12 minutes, then let stand for 30 minutes.

[0042] S3. Blending and extrusion: The pretreated resin and other dry raw materials are stirred at 700 r / min for 8 minutes and fed into a twin-screw extruder (length-to-diameter ratio 25:1, compression ratio 3.0). The extrusion temperature is 280℃~310℃. After extrusion, the resin is hydrostretched and pelletized, and dried at 100℃ for 2 hours to obtain chemically foamed FEP insulation material.

[0043] Performance testing:

[0044] Melt flow index (372℃ / 5kg): 18.5g / 10min;

[0045] Tensile strength: 13.5 MPa;

[0046] Elongation at break: 135%;

[0047] Foaming rate: 30%;

[0048] Average bubble diameter: 8 micrometers.

[0049] Example 2

[0050] This embodiment provides a chemically foamed FEP insulation material, which is composed of the following raw materials in parts by weight:

[0051] FEP resin (372℃ / 5kg melt index 18.8g / 10min, melt temperature 265℃): 100 parts;

[0052] Chemical foaming agent complex: 2.5 parts (including 1.2 parts ammonium polyphosphate, 0.4 parts expandable graphite, and 2.4 parts ultrafine boron nitride, with the mass ratio of ammonium polyphosphate to expandable graphite being 3:1 and the ultrafine boron nitride being 1.5 times the total mass of the two);

[0053] Modified silane coupling agent KH-792: 1 part;

[0054] Antioxidant 1024: 0.3 parts;

[0055] Lubricant ethylene bis-stearamide: 2 parts.

[0056] Preparation method:

[0057] S1. Raw material drying: FEP resin is dried at 100℃ for 2 hours, and other raw materials (except coupling agent) are dried at 60℃ for 3 hours;

[0058] S2. Resin pretreatment: FEP resin and KH-792 are stirred at 1200r / min for 10 minutes and then allowed to stand for 30 minutes;

[0059] S3. Blending and extrusion: The mixed raw materials are stirred at 800 r / min for 5 minutes and fed into a twin-screw extruder (length-to-diameter ratio 25:1, compression ratio 3.0). The extrusion temperature is 300℃~340℃, and the post-extrusion treatment is the same as in Example 1.

[0060] Performance testing:

[0061] Melt flow index (372℃ / 5kg): 18.8g / 10min;

[0062] Tensile strength: 11.8 MPa;

[0063] Elongation at break: 120%;

[0064] Foaming rate: 45%;

[0065] Average bubble diameter: 12 micrometers.

[0066] Example 3

[0067] This embodiment provides a chemically foamed FEP insulation material, which is composed of the following raw materials in parts by weight:

[0068] FEP resin (372℃ / 5kg melt index 18g / 10min, melt temperature 275℃): 100 parts;

[0069] Chemical foaming agent complex: 3 parts (including 1.6 parts ammonium polyphosphate, 0.4 parts expandable graphite, and 3 parts ultrafine boron nitride, with the mass ratio of ammonium polyphosphate to expandable graphite being 4:1 and the ultrafine boron nitride being 1.5 times the total mass of the two);

[0070] Modified silane coupling agent KH-792: 3 parts;

[0071] Antioxidant 3114: 1 part;

[0072] Lubricant ethylene bis-stearamide: 0.5 parts.

[0073] Preparation method:

[0074] S1. Raw material drying: FEP resin is dried at 100℃ for 3 hours, and other raw materials (except coupling agent) are dried at 60℃ for 4 hours;

[0075] S2. Resin pretreatment: FEP resin and KH-792 are stirred at 800 r / min for 15 minutes and then allowed to stand for 30 minutes;

[0076] S3. Blending and extrusion: The mixed raw materials are stirred at 600 r / min for 10 minutes and fed into a twin-screw extruder (length-to-diameter ratio 25:1, compression ratio 3.0). The extrusion temperature is 340℃~380℃, and the post-extrusion treatment is the same as in Example 1.

[0077] Performance testing:

[0078] Melt flow index (372℃ / 5kg): 18g / 10min;

[0079] Tensile strength: 11.5 MPa;

[0080] Elongation at break: 109%;

[0081] Foaming rate: 47%;

[0082] Average bubble diameter: 15 micrometers.

[0083] Comparative Example

[0084] The chemical foaming agent composite of the present invention is replaced by an organic foaming agent (azodicarbonamide, decomposition temperature 200℃~220℃) commonly used in the prior art. The other raw materials and preparation methods are the same as in Example 1. The foaming rate of the resulting insulation material is only 5%, and a large number of cells are merged (average diameter > 50 micrometers). The tensile strength is reduced to 8.2 MPa, which cannot meet the requirements for use in communication cables.

[0085] The above embodiments and comparative examples show that the chemically foamed FEP insulation material of the present invention is superior to the prior art in terms of foaming rate, cell uniformity and mechanical properties, and has strong processing adaptability, thus having significant technical advantages.

[0086] Currently, high-temperature resistant fluoroplastic communication cables are almost entirely manufactured using physical foaming methods. This method requires highly sophisticated equipment, involves complex processes, and is very expensive. This invention utilizes chemical foaming fluoroplastic technology, allowing for the production of foamed FEP cables using ordinary fluoroplastic extrusion equipment. The processing is simple, and the equipment investment is low. Compared to other inorganic or organic foaming agents, the composite foaming agent used in this invention has a high decomposition gas generation temperature, which matches the processing temperature of FEP fluoroplastics, demonstrating strong adaptability. Other inorganic or organic foaming agents generally have lower decomposition temperatures, with the highest decomposition temperature not exceeding approximately 270℃.

[0087] This invention utilizes boron nitride as a nucleation site and expandable graphite as a storage site for bubbles, suppressing the formation or breaking of pores between bubbles, and generating uniform pores with smaller diameters after reaching the decomposition temperature.

[0088] This invention utilizes a modified silane coupling agent to pretreat FEP resin, thereby improving the compatibility between FEP resin and ammonium polyphosphate, expandable graphite, and boron nitride. Therefore, the chemically foamed FEP insulation material of this invention exhibits superior mechanical properties.

[0089] Any aspects not described in this invention are applicable to existing technologies.

[0090] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A chemically foamed FEP insulation material, characterized in that, It consists of the following raw materials in parts by weight: 100 parts FEP resin 1.2 to 3 parts of chemical foaming agent complex 1-3 parts of modified silane coupling agent Antioxidant 0.3 to 1 part Lubricant 0.5 to 2 parts The chemical foaming agent composite is composed of ammonium polyphosphate, expandable graphite, and ultrafine boron nitride, and satisfies the following conditions: The mass ratio of ammonium polyphosphate to expandable graphite is (3-4):1; The mass of ultrafine boron nitride is 1.5 times the total mass of ammonium polyphosphate and expandable graphite; The degree of polymerization of ammonium polyphosphate is ≥1000, and the particle size D50 is 9 micrometers; The mesh size of expandable graphite is 200 mesh; The particle size D50 of the ultrafine boron nitride is 1 micrometer.

2. The chemically foamed FEP insulation material according to claim 1, characterized in that, The FEP resin has a melt index of 15-25 g / 10 min and a melting temperature of 260-280 °C at 372 °C / 5 kg.

3. The chemically foamed FEP insulation material according to claim 1, characterized in that, The modified silane coupling agent is KH-792.

4. The chemically foamed FEP insulation material according to claim 1, characterized in that, The antioxidant is at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,2-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid.

5. The chemically foamed FEP insulation material according to claim 1, characterized in that, The lubricant is ethylene bis-stearamide.

6. A method for preparing the chemically foamed FEP insulation material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Raw material drying: Dry the FEP resin at 100℃ for 2-3 hours, and dry the chemical foaming agent complex, antioxidant and lubricant at 60℃ for 3-4 hours; S2. Resin pretreatment: Mix the dried FEP resin with the modified silane coupling agent at high speed and let it stand for 30 minutes to allow the coupling agent to be fully absorbed by the resin. S3. Blending and extrusion: The pretreated resin is mixed with the remaining dried raw materials, melt-blended at 280-380℃ using a twin-screw extruder, extruded and granulated, and then dried at 100℃ for 2 hours to obtain the desired chemically foamed FEP insulation material.

7. The preparation method according to claim 6, characterized in that, The twin-screw extruder has a screw length-to-diameter ratio of (20-25):1 and a compression ratio of 2.5-3.0.

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