Anti-water-absorption marine cable composite insulation structure and preparation method and application thereof

Abstract

The application belongs to the technical field of cables, and particularly relates to a water-absorption-resistant marine cable composite insulation structure and a preparation method and application thereof. The application discloses a water-absorption-resistant marine cable composite insulation structure, which comprises, from inside to outside, a conductor, an inner insulation layer and an outer insulation layer; wherein the material of the inner insulation layer comprises cross-linked polyethylene and is uniformly coated outside the conductor; and the material of the outer insulation layer comprises ethylene-propylene rubber insulation material and is uniformly coated outside the inner insulation layer. The cable composite insulation structure utilizes the cross-linked polyethylene inner insulation layer to form a hydrophobic barrier, prevents water from migrating to the conductor interface, significantly improves the water-absorption resistance, meets the requirements of the IEEE 1580 standard, and meanwhile maintains good flexibility, and is suitable for marine cable laying.

Description

Technical Field

[0001] This invention relates to the field of cable technology, specifically to a water-resistant composite insulation structure for marine cables, its preparation method, and its application. Background Technology

[0002] The insulation structure of cables used in ships and marine engineering is exposed to high humidity and high salt spray environments for a long time. The water resistance of the insulation layer is a key indicator affecting the service life and operational reliability of the cable insulation structure.

[0003] Ethylene propylene rubber (EPR) insulation is widely used in marine cable insulation due to its excellent electrical insulation, heat resistance, flexibility, and aging resistance. However, EPR molecules contain polar groups and are hydrophilic. In accelerated water absorption tests, water molecules reach the inner surface of the insulation layer (the conductor-insulation interface) through surface adsorption and bulk diffusion. Since the dielectric constant of water is much higher than that of EPR, the capacitance of the cable insulation structure increases significantly. Conventional EPR insulated cables often exceed the capacitance change limit of the IEEE 1580 standard in 14-day accelerated water absorption tests, failing to meet the standard requirements.

[0004] To address the poor water resistance of ethylene propylene rubber insulation, existing technologies primarily employ two approaches: one is to modify the ethylene propylene rubber formulation by adding hydrophobic fillers or improving the crosslinking system, but this is both technically challenging and costly; the other is to use crosslinked polyethylene insulation, which has extremely low water absorption, but suffers from high hardness and poor flexibility, making it prone to cracking due to mechanical stress under the frequent bending conditions of marine cable insulation structures. Therefore, there is an urgent need for a novel composite insulation structure for marine cables that can meet the IEEE 1580 water absorption requirements while maintaining the flexibility of marine cables. Summary of the Invention

[0005] The purpose of this invention is to provide a water-resistant composite insulation structure for marine cables, its preparation method, and its application, thereby solving the problem that existing composite insulation structures for marine cables cannot simultaneously meet the water-resistant performance requirements of the IEEE 1580 standard and the flexibility requirements of the marine environment.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, embodiments of the present invention disclose a water-resistant composite insulation structure for marine cables, which comprises, from the inside out: a conductor, an inner insulation layer, and an outer insulation layer; wherein, the material of the inner insulation layer comprises cross-linked polyethylene, which is uniformly coated on the outside of the conductor; the material of the outer insulation layer comprises ethylene propylene rubber insulation material, which is uniformly coated on the outside of the inner insulation layer; the thickness of the inner insulation layer is 0.15 to 0.25 mm.

[0007] Furthermore, the cross-linked polyethylene is a two-step silane cross-linked polyethylene, a one-step silane cross-linked polyethylene, or an irradiated cross-linked polyethylene.

[0008] Secondly, embodiments of the present invention disclose a method for preparing a water-resistant composite insulation structure for marine cables, comprising the following steps: S1: Cross-linked polyethylene is extruded onto the surface of a conductor and then subjected to water boiling for cross-linking to obtain a cross-linked polyethylene inner insulation layer; S2: Ethylene propylene rubber insulating material is uniformly extruded onto the surface of the cross-linked polyethylene inner insulation layer obtained in S1, thus obtaining the desired product.

[0009] Thirdly, embodiments of the present invention disclose the application of the water-resistant marine cable composite insulation structure of the first aspect in the laying of cables for marine vessels.

[0010] The beneficial effects of this invention are: This invention adds a 0.15-0.25 mm thick cross-linked polyethylene inner insulation layer between the conductor and the ethylene propylene rubber outer insulation layer. The cross-linked polyethylene inner insulation layer has extremely low water absorption and a dense molecular structure, which forms a hydrophobic barrier when water molecules pass through the ethylene propylene rubber body to its inner surface, preventing further migration of water to the conductor-insulator interface. This suppresses the increase in dielectric constant near the interface and significantly reduces the capacitance change rate in the accelerated water absorption test. Testing shows that the capacitance increase rate of the cable after immersion for 1-14 days is as low as 2.6%, and after 7-14 days, it is as low as 1.3%, fully meeting the requirements of the IEEE 1580 standard.

[0011] This invention first extrudes a thin layer of cross-linked polyethylene and sets it in cross-linked shape, then extrudes ethylene propylene rubber insulation material at high temperature. The high-temperature molten ethylene propylene rubber insulation material can fully wet the surface of the cross-linked polyethylene. After cooling, a tightly bonded composite interface without free voids is formed between the two, fundamentally eliminating the place where moisture accumulates.

[0012] The thickness of the cross-linked polyethylene inner insulation layer in this invention is only 0.15~0.25 mm. While forming an effective hydrophobic barrier, it almost does not increase the bending stiffness of the cable composite insulation structure, avoiding the problem of excessive rigidity and difficulty in installation caused by adding too many multi-functional layers. This thickness range can maximize the flexibility and thermomechanical reliability of the cable composite insulation structure while forming an effective hydrophobic barrier, avoiding the defect of pure cross-linked polyethylene insulation being prone to cracking under frequent bending conditions in marine cable composite insulation structures due to its high hardness and poor flexibility. Detailed Implementation

[0013] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products.

[0014] The inventors discovered that ethylene propylene rubber (EPR) contains polar groups in its molecular structure, giving it a certain degree of hydrophilicity. In the accelerated water absorption test according to the IEEE 1580 standard, the insulated core of a cable was immersed in 75°C hot water, with the conductor end exposed above the water surface. Water molecules enter the insulation layer through the following pathways: water molecules adsorb onto the outer surface of the EPR insulation layer; driven by the water concentration gradient, water molecules diffuse into the insulation layer through the free volume between the EPR molecular chains; after several days to weeks of diffusion, water molecules penetrate the entire thickness of the EPR insulation layer, reaching the inner surface (i.e., near the interface between the conductor and the insulation layer). Consequently, water accumulates near the interface. Because the dielectric constant of water is much higher than that of EPR, the equivalent dielectric constant of the cable insulation layer increases, resulting in a significant increase in capacitance.

[0015] Due to manufacturing limitations, microscopic gaps inevitably exist at the overlaps in the wrapping structure. Furthermore, the water-blocking tape and the EPDM rubber insulation layer are physically bonded but separated, making it difficult to form a tight, continuous composite structure. After prolonged immersion in water, water molecules will seep in along the gaps and accumulate in the interfacial voids. The high dielectric constant of water causes a significant increase in capacitance, failing to meet the stringent capacitance change rate requirements of the IEEE 1580 standard.

[0016] This invention employs a process of first extruding a thin layer of cross-linked polyethylene and allowing it to cross-link and solidify, followed by extruding ethylene propylene rubber insulation at high temperature. The molten ethylene propylene rubber at high temperature fully wets the surface of the cross-linked polyethylene, and upon cooling, a tightly bonded composite interface without free voids is formed between the two. This structure fundamentally eliminates the site of moisture accumulation. Even if water molecules penetrate the ethylene propylene rubber body to reach the inner layer interface, they cannot migrate laterally or accumulate there, thus effectively suppressing the increase in dielectric constant and ensuring that the capacitance change rate of the cable composite insulation structure stably meets the standard limits during accelerated water absorption tests.

[0017] The cross-linked polyethylene inner insulation layer of this invention has a thickness of only 0.15–0.25 mm. While forming an effective hydrophobic barrier, it increases the bending stiffness of the cable composite insulation structure almost without altering its shape. This avoids the problem of excessive rigidity and difficulty in laying caused by the addition of too many functional layers in traditional multi-layer wrapping structures. Furthermore, compared to the high-tech and high-cost approach of improving the water resistance of ethylene propylene rubber through formulation modification, the structural innovation of this application has significant advantages such as good process compatibility, controllable cost, and ease of industrialization.

[0018] This invention provides a water-resistant composite insulation structure for marine cables, comprising, from the inside out: a conductor, an inner insulation layer, and an outer insulation layer; wherein the inner insulation layer is made of cross-linked polyethylene and uniformly covers the outside of the conductor; the outer insulation layer is made of ethylene propylene rubber insulating material and uniformly covers the outside of the inner insulation layer; the thickness of the inner insulation layer is 0.15~0.25 mm. For example, the thickness of the inner insulation layer is 0.20 mm.

[0019] In some specific embodiments of the present invention, the cross-linked polyethylene is a two-step silane cross-linked polyethylene, a one-step silane cross-linked polyethylene, or an irradiated silane cross-linked polyethylene.

[0020] In some embodiments of the present invention, the thickness of the outer insulation layer is set according to the requirements of the IEEE 1580 standard. For example, for a typical marine cable composite insulation structure, the thickness can be 1.0~2.5 mm. Optionally, the thickness of the outer insulation layer is determined according to the conductor cross-sectional area and voltage rating, and the present invention does not specifically limit this.

[0021] In some specific embodiments of the present invention, the conductor can be any conductive core material known in the art suitable for composite insulation structures of marine cables, and is not limited to a specific type. For example, the conductor can be one or more combinations of tin-plated soft copper conductors, aluminum alloy conductors, copper-clad aluminum alloy conductors, lead-tin alloy plated conductors, silver-plated or nickel-plated copper conductors, non-tin-plated soft copper conductors, or tin-cerium alloy plated conductors. In some specific embodiments of the present invention, the conductor is a tin-plated soft copper conductor, such as a Type 5 tin-plated soft copper conductor. Type 5 tin-plated soft copper conductors have excellent flexibility and corrosion resistance, and are a preferred conductor type for composite insulation structures of marine cables. It is understood that any conventional copper-based, aluminum-based, or alloy conductor can be used in the present invention as long as it meets the structural and electrical performance requirements of the IEEE 1580 standard.

[0022] In addition, in order to further improve the bonding force between the conductor and the inner insulation layer and prevent conductor oxidation, the present invention uniformly wraps a layer of polyester tape around the surface of the conductor. This polyester tape not only serves as an isolation and protection but also provides a smooth interface foundation for subsequent extrusion of cross-linked polyethylene.

[0023] In a specific embodiment of the present invention, the outer insulation layer is made of ethylene propylene rubber insulation material. Ethylene propylene rubber (EPR) is a type of copolymer elastomer with ethylene and propylene as the main monomers. It has a high degree of molecular chain saturation and excellent electrical insulation properties, heat resistance, ozone resistance, weather resistance, as well as good flexibility and aging resistance. It is particularly suitable for the long-term use requirements of cable insulation structures in ships and marine engineering in humid and salt spray environments.

[0024] In this invention, ethylene propylene rubber insulation materials include, but are not limited to, ethylene propylene diene monomer (EPDM), ethylene propylene diene monomer (EPM), modified ethylene propylene rubber (such as blends of grafted maleic anhydride or blends of polyisobutylene, silicone rubber, and chlorosulfonated polyethylene), composite ethylene propylene insulation materials with added nanofillers (such as nano-montmorillonite, nano-silica, and nano-alumina), or water-resistant ethylene propylene rubber treated with organosilane coupling agents or hydrophobic plasticizers.

[0025] This invention also provides a method for preparing a water-absorbing composite insulation structure for marine cables, comprising the following steps: S1: Cross-linked polyethylene is extruded onto the surface of a conductor and then subjected to water boiling for cross-linking to obtain a cross-linked polyethylene inner insulation layer; S2: The ethylene propylene rubber insulating material is extruded onto the surface of the cross-linked polyethylene inner insulating layer obtained in S1.

[0026] In some specific embodiments of the present invention, in S1, a polyester tape layer is provided between the conductor and the cross-linked polyethylene inner insulation layer.

[0027] In some specific embodiments of the present invention, in S1, the extrusion speed is 5~20 m / min, and the extrusion temperature is 180-200℃.

[0028] In some specific embodiments of the present invention, in S1, the temperature of the water boiling crosslinking is 80~100℃, and the time of the water boiling crosslinking is 20~40 min.

[0029] In some specific embodiments of the present invention, in S2, the extrusion speed is 2~10 m / min, and the extrusion temperature is 70~90℃.

[0030] This invention also provides the application of a water-resistant composite insulation structure for marine cables in the laying of cables on marine vessels.

[0031] In a specific embodiment of the present invention, cables made from a water-resistant marine cable composite insulation structure are particularly suitable for cable laying projects on marine vessels and offshore floating facilities. The laying environment for this type of cable is characterized by high humidity, high salt spray, frequent vibration, confined space, and numerous bending paths, placing extremely high demands on its water resistance, flexibility, and long-term reliability. Specifically, this cable can be used in the following laying scenarios: laying power cables in humid and high-temperature areas such as the main engine room, auxiliary engine room, and pump room of ships; laying control cables and instrument cables in areas susceptible to seawater splash or salt spray corrosion, such as decks and open areas; laying main and branch cables in the ship's power distribution system; and laying fixed or flexible cables for marine engineering facilities such as offshore drilling platforms and floating production storage and offloading (FPSO) units.

[0032] The present invention will be further described in detail below with reference to specific embodiments.

[0033] Example 1 The following is a method for preparing a water-absorbing resistant composite insulation structure for marine cables: S1: Select a Class 5 tin-plated soft copper conductor (specification 3 / 0 AWG) whose structure conforms to the requirements of IEEE 1580 standard, and uniformly wrap a layer of polyester tape around the surface of the conductor to obtain a conductor wrapped with polyester tape. S2: Two-step silane crosslinked polyethylene is uniformly extruded onto the conductor surface of the wrapped polyester tape using an extruder. The extrusion temperature is 190℃, the extrusion speed is 10 m / min, and the final extrusion thickness is 0.20 mm. It is then placed in warm water at 90℃ for water boiling crosslinking for 30 min to form an inner insulation layer of crosslinked polyethylene, thus forming a three-dimensional network structure of polyethylene. S3: The ethylene propylene rubber insulating material is uniformly extruded onto the surface of the cross-linked polyethylene inner insulation layer using an extruder. The extrusion temperature is 80 ℃, the extrusion speed is 6 m / min, and the thickness is set according to the IEEE 1580 standard (1.7 mm).

[0034] Example 2 The following is a method for preparing a water-absorbing resistant composite insulation structure for marine cables: S1: Select a Class 5 tin-plated soft copper conductor (specification 3 / 0 AWG) whose structure conforms to the requirements of IEEE 1580 standard, and uniformly wrap a layer of polyester tape around the surface of the conductor to obtain a conductor wrapped with polyester tape. S2: Two-step silane crosslinked polyethylene is uniformly extruded onto the conductor surface of the wrapped polyester tape using an extruder. The extrusion temperature is 190℃, the extrusion speed is 10 m / min, and the final extrusion thickness is 0.15 mm. It is then placed in warm water at 90℃ for water boiling crosslinking for 30 min to form an inner insulation layer of crosslinked polyethylene, thus forming a three-dimensional network structure of polyethylene. S3: The ethylene propylene rubber insulating material is uniformly extruded onto the surface of the cross-linked polyethylene inner insulation layer using an extruder. The extrusion temperature is 80 ℃, the extrusion speed is 6 m / min, and the thickness is set according to the IEEE 1580 standard (1.7 mm).

[0035] Example 3 The following is a method for preparing a water-absorbing resistant composite insulation structure for marine cables: S1: Select a Class 5 tin-plated soft copper conductor (specification 3 / 0 AWG) whose structure conforms to the requirements of IEEE 1580 standard, and uniformly wrap a layer of polyester tape around the surface of the conductor to obtain a conductor wrapped with polyester tape. S2: Two-step silane crosslinked polyethylene is uniformly extruded onto the conductor surface of the wrapped polyester tape using an extruder. The extrusion temperature is 190℃, the extrusion speed is 10 m / min, and the final extrusion thickness is 0.25 mm. It is then placed in warm water at 90℃ for water boiling crosslinking for 30 min to form an inner insulation layer of crosslinked polyethylene, thus forming a three-dimensional network structure of polyethylene. S3: The ethylene propylene rubber insulating material is uniformly extruded onto the surface of the cross-linked polyethylene inner insulation layer using an extruder. The extrusion temperature is 80 ℃, the extrusion speed is 6 m / min, and the thickness is set according to the IEEE 1580 standard (1.7 mm).

[0036] Example 4 The following is a method for preparing a water-absorbing resistant composite insulation structure for marine cables: S1: Select a Class 5 tin-plated soft copper conductor (specification 3 / 0 AWG) whose structure conforms to the requirements of IEEE 1580 standard, and uniformly wrap a layer of polyester tape around the surface of the conductor to obtain a conductor wrapped with polyester tape. S2: One-step silane crosslinked polyethylene is uniformly extruded onto the conductor surface of the wrapped polyester tape using an extruder. The extrusion temperature is 190℃, the extrusion speed is 10 m / min, and the final extrusion thickness is 0.20 mm. It is then placed in warm water at 90℃ for water boiling crosslinking for 30 min to form an inner insulation layer of crosslinked polyethylene, thus forming a three-dimensional network structure of polyethylene. S3: The ethylene propylene rubber insulating material is uniformly extruded onto the surface of the cross-linked polyethylene inner insulation layer using an extruder. The extrusion temperature is 80 ℃, the extrusion speed is 6 m / min, and the thickness is set according to the IEEE 1580 standard (1.7 mm).

[0037] Example 5 The following is a method for preparing a water-absorbing resistant composite insulation structure for marine cables: S1: Select a Class 5 tin-plated soft copper conductor (specification 3 / 0 AWG) whose structure conforms to the requirements of IEEE 1580 standard, and uniformly wrap a layer of polyester tape around the surface of the conductor to obtain a conductor wrapped with polyester tape. S2: Irradiated cross-linked polyethylene is uniformly extruded onto the conductor surface of the wrapped polyester tape using an extruder. The extrusion temperature is 190℃, the extrusion speed is 10 m / min, and the final extrusion thickness is 0.20 mm. It is then placed in warm water at 90℃ for water boiling cross-linking for 30 min to form an inner insulation layer of cross-linked polyethylene, thus forming a three-dimensional network structure of polyethylene. S3: The ethylene propylene rubber insulating material is uniformly extruded onto the surface of the cross-linked polyethylene inner insulation layer using an extruder. The extrusion temperature is 80 ℃, the extrusion speed is 6 m / min, and the thickness is set according to the IEEE 1580 standard (1.7 mm).

[0038] Comparative Example 1 The following is a method for preparing a water-absorbing resistant composite insulation structure for marine cables: S1: Select a Class 5 tin-plated soft copper conductor (specification 3 / 0 AWG) whose structure conforms to the requirements of IEEE 1580 standard, and uniformly wrap a layer of reinforced non-woven fabric around the surface of the conductor to obtain a conductor wrapped with non-woven fabric. S2: The insulating material is uniformly extruded onto the surface of the conductor wrapped with nonwoven fabric using an extruder. The extrusion temperature is 80 ℃, and the extrusion speed is 6 m / min. The thickness is set according to the IEEE 1580 standard (1.7 mm).

[0039] Comparative Example 2 The difference compared to Example 1 is that in S2, the extrusion thickness of the two-step silane crosslinked polyethylene is 0.10 mm.

[0040] Comparative Example 3 The difference compared to Example 1 is that in S2, the extrusion thickness of the two-step silane crosslinked polyethylene is 0.30 mm.

[0041] The performance of the water-resistant composite insulation structures for marine cables prepared in Examples 1-5 and Comparative Examples 1-3 was tested. Specifically, the insulated cores prepared above were immersed in hot water at 75°C with the conductor ends exposed above the water surface for 14 days, according to the accelerated water absorption test method specified in IEEE 1580 standard. The capacitance value of the insulation layer was measured on the 1st, 7th and 14th day of immersion, and the capacitance increase rate from 1 to 14 days and the capacitance increase rate from 7 to 14 days were calculated.

[0042] Bending durability testing is conducted according to IEEE 1580 requirements. Test method: The sample is placed in a -25°C refrigerator for 4 hours, and then wound around a 12D diameter cylinder at this temperature (3 turns clockwise, 3 turns counterclockwise, repeated 9 times for a total of 10 times). Requirements: The insulation and sheath should not crack, and the sample should pass the withstand voltage test.

[0043] The test results are shown in Table 1.

[0044] Table 1 Performance test results of each embodiment and comparative example

[0045] As shown in Table 1, the water resistance of the insulated wire core is significantly improved by implementing this scheme. However, when the cross-linked polyethylene layer is too thin, microscopic defects occur, causing the water barrier to fail and resulting in little improvement in water resistance. When the cross-linked polyethylene layer is too thick, it is difficult to pass the bending durability test.

[0046] The thickness of the cross-linked polyethylene inner insulation layer needs to be controlled within the range of 0.15~0.25mm: Below 0.15mm, the extrusion process cannot guarantee complete interlayer density, easily leading to microscopic defects and causing the water barrier to fail; above 0.25mm, the bending stiffness of the cable composite insulation structure increases significantly, and the interlayer thermal expansion mismatch stress increases, which is detrimental to the flexibility and long-term service stability of the marine cable composite insulation structure. Therefore, this thickness range can maximize the flexibility and thermomechanical reliability of the cable composite insulation structure while forming an effective hydrophobic barrier, with 0.2mm being the optimal value, achieving the best balance between water-blocking performance and mechanical properties.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A water-resistant composite insulation structure for marine cables, characterized in that, It comprises, from the inside out, a conductor, an inner insulating layer, and an outer insulating layer; wherein, the material of the inner insulating layer comprises cross-linked polyethylene, which is uniformly coated on the outside of the conductor; the material of the outer insulating layer comprises ethylene propylene rubber insulating material, which is uniformly coated on the outside of the inner insulating layer; The thickness of the inner insulation layer is 0.15–0.25 mm.

2. The water-resistant composite insulation structure for marine cables according to claim 1, characterized in that, The cross-linked polyethylene is a two-step silane cross-linked polyethylene, a one-step silane cross-linked polyethylene, or an irradiated cross-linked polyethylene.

3. The water-resistant composite insulation structure for marine cables according to claim 1, characterized in that, The conductor is one or more of the following: tin-plated soft copper conductor, aluminum alloy conductor, copper-clad aluminum alloy conductor, lead-tin alloy plated conductor, silver-plated or nickel-plated copper conductor, non-tin-plated soft copper conductor, or tin-cerium alloy plated conductor.

4. The method for preparing the water-resistant composite insulation structure for marine cables according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Cross-linked polyethylene is extruded onto the surface of a conductor and then subjected to water boiling for cross-linking to obtain a cross-linked polyethylene inner insulation layer; S2: The ethylene propylene rubber insulating material is extruded onto the surface of the cross-linked polyethylene inner insulating layer obtained in S1.

5. The preparation method according to claim 4, characterized in that, In S1, a polyester tape layer is provided between the conductor and the cross-linked polyethylene inner insulation layer.

6. The method for preparing the water-resistant composite insulation structure for marine cables according to claim 4, characterized in that, In S1, the extrusion speed is 5~20 m / min, and the extrusion temperature is 180-200℃.

7. The method for preparing the water-absorbing composite insulation structure for marine cables according to claim 4, characterized in that, In S1, the temperature for water boiling crosslinking is 80~100℃, and the time for water boiling crosslinking is 20~40 min.

8. The method for preparing the water-absorbing composite insulation structure for marine cables according to claim 4, characterized in that, In S2, the extrusion speed is 2~10 m / min, and the extrusion temperature is 70~90℃.

9. The application of the water-resistant composite insulation structure for marine cables as described in claims 1 to 3 in the laying of cables for marine vessels.

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