An e-PTFE-based cable waterproof and breathable heat-shrinkable sealing cap and a verification method

Abstract

The application discloses a kind of e-PTFE-based cable waterproof and breathable type heat shrinkage sealing cap and verification method, belong to the technical field of wire and cable, the sealing cap includes sealing cap body, the closed end of sealing cap body is equipped with waterproof and breathable device with e-PTFE breathable film, realizes the waterproof and breathable double protection inside cable using the breathable water-blocking characteristics of e-PTFE micropore, waterproof and breathable device is installed on the thickening boss of the closed end of sealing cap body by threaded connection or interference pressure connection mode, sealing ring is arranged between device shell and boss, verification method includes water permeation test and air permeation test.The application effectively solves the safety hazard of the accumulation of flammable gas inside the sealed cap, while ensuring the long-term waterproof sealing of the end.

Description

Technical Field

[0001] This invention relates to the field of wire and cable accessories technology, specifically to a heat-shrinkable cable terminal cap with dual functions of waterproof sealing and breathable pressure relief, and a method for verifying its performance. Background Technology

[0002] As the "blood vessels" of power transmission and information communication, the reliability of the end seals of cables directly affects the long-term operational safety and service life of cable systems. During cable production, after processes such as extrusion, vulcanization, and cross-linking, residual volatile organic compounds and cross-linking byproducts within the cable insulation layer gradually precipitate inside the cable. Especially after the cable termination is manufactured, these gases continuously accumulate in the enclosed space.

[0003] Currently, the cable industry commonly uses heat-shrink caps to seal and protect cable ends, preventing the intrusion of moisture and impurities. However, existing technologies mainly fall into two categories, each with significant drawbacks: The first type is the fully sealed cap. While it achieves effective waterproof sealing, it creates a completely enclosed space at the cable end. Combustible gases and cross-linking byproduct gases (such as methane and ethane) remaining in the cable insulation layer will continuously accumulate within this confined space. During storage and transportation, these accumulated combustible gases pose a risk of combustion and explosion under certain conditions. Simultaneously, because the gases cannot escape, the gas pressure inside the cap gradually increases, keeping the heat-shrink cap under constant stress and accelerating material aging. Furthermore, during cable termination manufacturing, the fully sealed cap prevents the gases generated during the insulation baking process from escaping, prolonging the volatilization time of the insulation cross-linking agent and impacting production efficiency.

[0004] The second type is the perforated vent cap, which has vents to release internal pressure. However, the perforated structure allows external impurities such as moisture and dust to penetrate into the cap, also compromising the cable's insulation performance. To overcome this deficiency, existing solutions require dedicated personnel for regular inspections and maintenance, increasing labor costs and maintenance difficulty.

[0005] Therefore, the core technical contradiction in existing technologies lies in the inherent conflict between pursuing reliable sealing and ensuring internal safety and production efficiency—enhancing sealing fails to eliminate internal gases, while adding ventilation channels sacrifices waterproofing and dustproofing capabilities. Thus, developing a cable cap that combines both "selective ventilation" and "reliable waterproofing" has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a waterproof and breathable heat-shrinkable cap for cables that allows selective gas passage while preventing water penetration. This cap effectively blocks the intrusion of external liquid water while safely and automatically releasing internal gas from the cable, fundamentally solving the safety hazard of flammable gas accumulation and achieving automatic pressure relief without manual maintenance.

[0007] The further technical problem to be solved by the present invention is to provide a dedicated verification method for testing the waterproof and breathable performance of the above-mentioned cap, so as to ensure the reliability of the dual functions of the product.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A waterproof and breathable heat-shrinkable cap for cables includes a cap body made of heat-shrinkable material, with a hot melt adhesive layer on the inner wall of the open end of the cap body. The key feature is that the closed end of the cap body is provided with a waterproof and breathable device, which contains an e-PTFE breathable membrane that allows gas molecules to pass through while blocking liquid water from passing through.

[0009] Preferably, the waterproof and breathable device is a waterproof and breathable valve, including a housing, with the e-PTFE breathable membrane fixedly disposed inside the housing. By encapsulating the breathable membrane in an independent valve body structure, not only is standardized production and quality control facilitated, but modular installation on the cap is also convenient.

[0010] Furthermore, the closed end of the cap body is provided with a thickened boss, the wall thickness of which is greater than the wall thickness of the cap body. The waterproof and breathable valve is installed on this thickened boss. The function of the thickened boss is to provide sufficient structural strength for installation, avoid deformation due to uneven local stress during heating and shrinkage, thereby ensuring the installation accuracy and sealing reliability of the waterproof and breathable valve. Preferably, the wall thickness of the thickened boss is 4mm to 8mm.

[0011] In a preferred embodiment, the thickened boss has a vent hole with internal threads on its inner wall; the outer wall of the housing has matching external threads, and the housing and the thickened boss are detachably connected via these threads. An elastic sealing ring is provided between the housing and the thickened boss to ensure a static seal at the interface. The elastic sealing ring is preferably made of fluororubber or silicone rubber, which has good temperature resistance and elastic recovery capability.

[0012] To further improve the reliability of the connection, a flange structure is provided on the upper outer wall of the housing. An elastic sealing ring is press-fitted between the lower end face of the flange structure and the upper end face of the thickened boss. A lock nut can also be provided on the upper outer side of the housing, which abuts against the thickened boss to form an anti-loosening structure and prevent the threads from loosening due to vibration during long-term use.

[0013] In another embodiment, the waterproof and breathable valve is fixedly connected to the thickened boss by an interference fit or a snap-fit ​​structure using a press-fit method. This method is suitable for applications requiring one-time installation and no disassembly, and features a simpler structure and lower cost.

[0014] The shell has at least one vent hole above or below the e-PTFE breathable membrane, serving as a channel for gas exhaust. The pore size of the e-PTFE breathable membrane is preferably 0.1 μm to 1.0 μm, a size range that ensures effective blocking of liquid water molecules (water molecule cluster diameter approximately 0.3 nm to 100 μm) while allowing gas molecules (diameter approximately 0.3 to 0.4 nm) to pass through smoothly. The e-PTFE breathable membrane is preferably a multilayer composite structure, including at least one e-PTFE microporous membrane layer and one nonwoven fabric support layer, the support layer enhancing the membrane's mechanical strength.

[0015] The cap body is preferably made of cross-linked polyethylene or polyolefin heat-shrinkable material, the thickness of the hot melt adhesive layer is 0.5mm to 1.2mm, and the melting temperature is 80℃ to 120℃.

[0016] The present invention also provides a verification method, comprising: Water permeability test procedure: Immerse the cap with the waterproof and breathable valve in water, so that the waterproof and breathable valve is below the water surface, with an immersion depth of 30mm to 50mm, and keep it for more than 30 minutes. After removing it, check whether there are water stains inside the cap and inside the e-PTFE breathable membrane. Air permeability test procedure: After the water permeability test is passed, connect the cap to a clean air source and slowly introduce clean air into the cap at a rate not exceeding 0.001 MPa / s. Observe and record the air pressure value P1 when the gas begins to stably escape from the waterproof air valve continuously. P1 should be less than 0.001 MPa.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) Intrinsic safety: Through the selective permeability of the e-PTFE microporous membrane, the combustible gas accumulated inside the cable is slowly and safely discharged automatically, eliminating the risk of explosion from the source and realizing the intrinsic safety design of "self-pressure relief".

[0018] (2) High-efficiency production: The introduction of the breathable function makes the inside of the cap no longer a closed space. The cross-linking by-product gas generated during the baking and curing process of the insulation core can be smoothly discharged, which can greatly shorten the insulation baking time and improve production efficiency and delivery speed.

[0019] (3) Zero maintenance cost: It realizes the fully automatic and unmanned "self-maintenance" ventilation function, eliminating the need for manual periodic opening of the cover to release air, and greatly reducing the labor cost and inspection difficulty of long-term operation and maintenance.

[0020] (4) Reliable structure: The thickened boss structure avoids local thermal deformation during heat shrinkage and heating. Combined with the multi-seal design (hot melt adhesive layer + elastic sealing ring + thread seal), it ensures the long-term waterproof reliability and structural stability of the product under complex working conditions such as high temperature, high humidity and vibration.

[0021] (5) Verifiability: The matching water-permeable / breathable dual-function verification method provides a reliable technical guarantee for product quality, and uses quantitative test data to ensure the coordinated realization of the contradictory functions of "waterproof" and "breathable". Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a waterproof and breathable heat-shrinkable cap for cables provided in an embodiment of the present invention.

[0023] Figure 2 This is a flowchart of the verification method in this invention.

[0024] In the diagram: 1-Cap body, 2-Hot melt adhesive layer, 3-Waterproof and breathable valve, 4-Thickened boss, 5-Locking nut, 6-e-PTFE breathable membrane, 7-Shell, 8-Sealing ring. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention.

[0026] Example 1, referring to Figure 1 As shown, the waterproof and breathable heat-shrinkable cap for cables provided in this embodiment has a cap body 1 integrally formed from cross-linked polyolefin heat-shrinkable material through processes such as extrusion, irradiation cross-linking, and expansion molding. A polyolefin-based hot melt adhesive with a thickness of approximately 0.8 mm is pre-coated onto the inner wall of the open end of the cap body 1, forming a hot melt adhesive layer 2. This hot melt adhesive melts within a temperature range of 80℃ to 120℃, enabling it to form a strong bond and seal with the surface of the cable's outer sheath.

[0027] At the closed end of the cap body 1, a thickened boss 4 is formed by a local thickening molding process. The wall thickness of the thickened boss 4 is increased to 6.0 mm compared to the conventional wall thickness of the cap body (approximately 2.0 mm), reaching 8.0 mm, preferably 6.0 mm. A threaded vent hole of M12×1.25 specification is machined at the center of the thickened boss 4.

[0028] The waterproof and breathable valve 3 is a pre-assembled, independent functional module. The housing 7 is injection molded from POM (polyoxymethylene) engineering plastic, possessing good mechanical strength and chemical resistance. The lower outer wall of the housing 7 is machined with external threads to mate with the breathable mounting holes. The upper part of the housing 7 features an open breathable cavity structure with multiple breathable slots on the side walls to ensure unobstructed gas flow. An annular support platform is located inside the housing 7 to support the e-PTFE breathable membrane 6.

[0029] During assembly, a circular e-PTFE breathable membrane 6 with a pore size of 0.2μm is first placed on the annular support platform inside the housing 7, and then pressed and fixed with a high-temperature resistant plastic pressure ring to ensure no leakage at the edges of the membrane. Next, a fluororubber O-ring 8 is fitted into the sealing groove above the thread root of the housing 7. Finally, the pre-assembled waterproof and breathable valve 3 is screwed into the threaded hole of the thickened boss 4 and tightened. During tightening, the sealing ring 8 is pressed against the contact surface between the housing 7 and the thickened boss 4, achieving a reliable static seal.

[0030] To further improve connection reliability, a locking nut 5 can be installed on the part of the housing 7 that exposes the upper end face of the thickened boss 4. The lower end face of the locking nut 5 is in close contact with the upper end face of the thickened boss 4 to form a mechanical anti-loosening structure, ensuring that the threaded connection does not loosen under long-term use or vibration conditions.

[0031] During use, first use a hot air gun to evenly heat the cap body 1. The cap body 1 shrinks and adheres tightly to the cable outer sheath when heated. At the same time, the hot melt adhesive layer 2 melts and flows when heated, filling the tiny bumps and depressions on the surface of the cable outer sheath. After cooling, a strong adhesive seal is formed. After installation, place the waterproof and breathable valve 3 of the cap facing upwards (or towards the direction where water does not accumulate).

[0032] When residual gas or cross-linking byproduct gas in the cable insulation layer gradually accumulates inside the cap, under a slight positive pressure (less than 0.001 MPa), gas molecules reach the e-PTFE breathable membrane 6 through the breathable channels inside the shell 7. Since the micropore size (0.2 μm) of the e-PTFE breathable membrane 6 is much larger than the diameter of gas molecules (approximately 0.3–0.4 nm), gas molecules can freely diffuse into the external atmosphere through the micropores.

[0033] Conversely, when liquid water in the external environment comes into contact with the waterproof and breathable valve 3, the surface tension of the water is much greater than the driving force required for gas molecules to penetrate. The micropores of the e-PTFE breathable membrane 6 create effective capillary resistance to the liquid water—water molecule clusters cannot pass through the 0.2μm micropores and are thus blocked from the outside. Simultaneously, the sealing ring 8 between the shell 7 and the thickened boss 4 provides a second waterproof barrier, and the hot melt adhesive layer 2 provides a third waterproof barrier, forming a multi-layered waterproof sealing system.

[0034] Example 2 is essentially the same as Example 1, except for the fixing method of the waterproof and breathable valve 3. In this example, the vent mounting hole on the thickened boss 4 is a smooth straight hole without internal threads. The outer wall of the housing 7 has an annular groove. During installation, the housing 7 is pressed into the vent mounting hole, and fixed by interference fit or by the annular groove and the annular protrusion on the mounting hole wall. The sealing function is achieved by the interference fit between the annular sealing rib on the outer wall of the housing 7 and the inner wall of the mounting hole, or by pre-applying sealant. This example is suitable for one-time installation without disassembly, has a simpler structure, and lower manufacturing cost.

[0035] Verification method examples: such as Figure 2 As shown, this embodiment provides a method for verifying the waterproof and breathable performance of the cap in the above embodiments, including the following steps: Step 1, Pre-treatment: Place the cap in a 70℃ oven for 8 minutes to preheat, simulating the heat shrink installation state.

[0036] Step 2, Water Permeability Test: Immerse the entire cap with the waterproof and breathable valve 3 in water, ensuring the valve is submerged to a depth of 40mm, for 30 minutes. After removal, wipe the outside of the cap dry, disassemble and inspect the inside of the cap and the inside of the e-PTFE breathable membrane 6; there should be no water stains or droplets.

[0037] Step 3, Air Permeability Test: After passing the water permeability test, connect the cap to a clean air source that has been dried and filtered. Slowly introduce clean air into the cap at a rate of 0.0005 MPa / s, while observing the outlet of the waterproof vent valve 3. When the gas begins to escape stably and continuously from the waterproof vent valve 3, record the pressure gauge reading P1 at this time. P1 < 0.001 MPa is required. This result indicates that a small amount of gas accumulated inside the cap can be automatically discharged, and the cap's air permeability meets the requirement of "low-resistance automatic venting".

[0038] It should be noted that the above embodiments are merely illustrative examples, and any equivalent substitutions or modifications made under the technical concept of this invention should fall within the protection scope of this invention.

Claims

1. A waterproof and breathable heat-shrinkable cap for cables, comprising a cap body (1) made of heat-shrinkable material, wherein the inner wall of the open end of the cap body (1) is provided with a hot melt adhesive layer (2), characterized in that: The sealed end of the cap body (1) is provided with a thickened boss (4), and a waterproof and breathable valve (3) is installed on the thickened boss (4). The waterproof and breathable valve (3) includes a housing (7) and an e-PTFE breathable membrane (6) disposed in the housing (7). The e-PTFE breathable membrane (6) has a microporous structure that allows gas molecules to pass through and blocks liquid water from passing through.

2. The waterproof and breathable heat-shrink cap for cables according to claim 1, characterized in that: The wall thickness of the thickened boss (4) is 4mm to 8mm.

3. The water-proof and air-permeable heat-shrinkable sealing cap for electric cables according to claim 1, characterized in that: The thickened boss (4) has a ventilated mounting hole, and the inner wall of the ventilated mounting hole has an internal thread; the outer wall of the housing (7) has an external thread that matches the internal thread, and the housing (7) and the thickened boss (4) are detachably connected by the thread.

4. The water-proof and air-permeable heat-shrinkable sealing cap for electric cables according to claim 3, characterized in that: An elastic sealing ring (8) is provided between the housing (7) and the thickened boss (4).

5. The water-proof and air-permeable heat-shrinkable sealing cap for electric cables according to claim 3, characterized in that: The outer wall of the housing (7) is provided with a flange structure, and a locking nut (5) is provided below the flange structure. The locking nut (5) abuts against the upper end face of the thickened boss (4).

6. The waterproof and breathable heat-shrink cap for cables according to claim 1, characterized in that: The waterproof and breathable valve (3) and the thickened boss (4) are fixedly connected by an interference fit or a snap-fit ​​structure in a press-fit manner.

7. The waterproof and breathable heat-shrink cap for cables according to claim 1, characterized in that: The pore size of the e-PTFE breathable membrane (6) is 0.1μm to 1.0μm.

8. The water-proof and air-permeable heat-shrinkable sealing cap for electric cables according to claim 1, characterized in that: The thickness of the hot melt adhesive layer (2) is 0.5 mm to 1.2 mm, and the melting temperature is 80°C to 120°C.

9. The water-proof and air-permeable heat-shrinkable sealing cap for electric cables according to claim 1, characterized in that: The cap body (1) is made of cross-linked polyethylene or polyolefin heat-shrinkable material.

10. A method for verifying the water-vapor permeation performance of the water-vapor permeable heat-shrinkable sealing cap for the cable according to any one of claims 1 to 9, characterized by, Includes the following steps: Water permeability test procedure: Immerse the cap with the waterproof and breathable valve (3) in water, so that the waterproof and breathable valve (3) is below the water surface and the immersion depth is 30mm to 50mm. Keep it for more than 30 minutes. After taking it out, check whether there are water stains inside the cap and inside the e-PTFE breathable membrane (6). Air permeability test procedure: After the water permeability test is qualified, connect the cap to a clean air source and slowly introduce clean air into the cap at a rate not exceeding 0.001MPa / s. Observe and record the air pressure value P1 when the gas begins to stably escape from the waterproof and breathable valve (3) continuously. P1 is required to be less than 0.001MPa.

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