Radiation leak coaxial cable flame retardant jacket structure and method of manufacture

Abstract

The application discloses a radiation type leaky coaxial cable flame-retardant sheath structure and a manufacturing method. The radiation type leaky coaxial cable flame-retardant sheath structure comprises an inner sheath and an outer sheath, the outer sheath is sleeved on the inner sheath and abuts against the inner sheath, and the inner sheath is an inorganic filling type flame-retardant polyolefin sheath, and the outer sheath is a chemical expansion type flame-retardant sheath. The inner sheath combustion shell formation is greatly improved, a carbon shell is formed after the inner sheath is burned when the leaky coaxial cable is burned, the carbon shell can isolate the flame from entering the inside of the leaky coaxial cable, the outer sheath has high flame-retardant efficiency, meanwhile, good mechanical physical properties can be kept, and the flame-retardant performance of the flame-retardant sheath can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cable equipment, in particular to a radiation type leaky coaxial cable flame-retardant sheath structure and manufacturing method. BACKGROUND

[0002] The leaky coaxial cable is composed of inner conductor (copper or aluminum), polyethylene insulation layer, outer conductor and flame-retardant sheath from inside to outside, and periodic slots or holes are arranged on the outer conductor, a small part of electromagnetic energy between the inner and outer conductors is leaked through the holes, and the surrounding space electromagnetic wave also enters the inside of the leaky coaxial cable through the holes, the leaky coaxial cable is widely used in closed or semi-closed narrow spaces such as subway tunnels, high-speed railways, highway tunnels, mines, high-rise elevators and underground shopping malls, and the flame-retardant performance of the leaky coaxial cable is required to be high in these use occasions. The flame-retardant sheath of the prior art is mostly made of flame-retardant polyethylene to achieve the flame-retardant purpose, that is, inorganic flame retardants are added to the polyethylene resin. However, when a fire occurs, the flame generated by the combustion of the leaky coaxial cable can pass through the slots or holes arranged on the outer conductor to ignite the internal polyethylene insulation layer, causing the fire to spread, so the flame-retardant sheath structure of the current leaky coaxial cable cannot achieve the effective flame-retardant purpose. SUMMARY

[0003] The technical problem to be solved by the present application is that the flame-retardant performance of the existing flame-retardant sheath is low, and the present application provides a radiation type leaky coaxial cable flame-retardant sheath structure and manufacturing method, which can improve the flame-retardant performance of the flame-retardant sheath through improvement of the flame-retardant sheath.

[0004] The technical scheme adopted by the present application to solve the technical problem is that a radiation type leaky coaxial cable flame-retardant sheath structure comprises: an inner sheath and an outer sheath, the outer sheath is sleeved on the inner sheath and abuts against the inner sheath, and the inner sheath is an inorganic filling type flame-retardant polyolefin sheath, and the outer sheath is a chemical expansion type flame-retardant sheath.

[0005] Thus, the burning shell formation of the inner sheath is greatly improved, the carbon shell formed after the inner sheath burns when the leaky coaxial cable burns can isolate the flame from entering the inside of the leaky coaxial cable, the flame-retardant efficiency of the outer sheath is high, at the same time, the mechanical physical performance can be maintained well, and the flame-retardant performance of the flame-retardant sheath can be improved.

[0006] Further, the radial cross sections of the inner sheath and the outer sheath are both circular rings, the inner diameter of the inner sheath is d1, the outer diameter is d2, the inner diameter of the outer sheath is d2, and the outer diameter is d3.

[0007] Further, the thickness of the inner sheath is H1, the radial cross-sectional area is S1, the thickness of the outer sheath is H2, the radial cross-sectional area is S2, 1.5 2 H1 / H2<2.5, S1 / S2 2 H1 / H2. Wherein: H1=d2-d1, H2=d3-d2, S1=π((d2) 2 )2 / 4, S2=π((d3) 2 )2 / 4. Thus, the cost of the outer sheath flame retardant is higher than that of the inner sheath flame retardant, the thicker inner sheath and the thinner outer sheath can reduce the material cost of the flame retardant sheath on the one hand, and can improve the flame retardant performance of the flame retardant sheath on the other hand, and at the same time, the extrusion load of the inner sheath can be reduced.

[0008] The application also provides a manufacturing method of the radiation type leaky coaxial cable flame-retardant sheath structure, the base resin used for the inner sheath and the outer sheath is the same kind of polymer, and the base resin is one or two of LDPE, LLDPE, HDPE, PP, EVA, EEA or EBA.

[0009] Further, the inner sheath is extruded by adding 50%-60% of inorganic flame retardant by mass fraction in the base resin, and the inorganic flame retardant is magnesium hydroxide or aluminum hydroxide. Thus, the limiting oxygen index (LOI) of the inner sheath reaches 35%-45%, the vertical burning grade of the inner sheath reaches V-0, and it is not necessary to add a light aging agent resistant to sunlight aging.

[0010] Further, the outer sheath is extruded by adding 20%-30% of chemical intumescent flame retardant by mass fraction in the base resin, and the chemical intumescent flame retardant is phosphorus-ammonia intumescent flame retardant. Thus, the limiting oxygen index of the outer sheath is 30%-35%, the vertical burning grade of the outer sheath is not less than V-1, the tensile elongation of the outer sheath is not less than 250%, and the tensile breaking strength of the outer sheath is not less than 17 MPa.

[0011] Further, the inner sheath and the outer sheath are both vertically extruded in close series. Thus, the sagging can be avoided, so as to ensure that the flame-retardant sheath always keeps concentric with the cable core, and a large gap between the flame-retardant sheath and the outer conductor is avoided.

[0012] Further, the inner sheath and the outer sheath adopt two different extrusion dies.

[0013] Further, the inner sheath and the outer sheath share one extrusion head, and the two extrusion dies are respectively located on the two sides of the extrusion head and connected with the extrusion head.

[0014] Further, the cable core is immediately extruded through the extrusion die of the outer sheath after the inner sheath is extruded. Thus, the inner sheath with poor mechanical properties is not prone to breakage and cracking under the protection of the outer sheath with good mechanical properties under the action of external forces such as bending and stretching of the leaky coaxial cable, the extrusion efficiency of the inner sheath and the outer sheath can be improved, the inner sheath and the outer sheath can be bonded together, and the extrusion machines and extrusion dies with different characteristics can be selected according to the different processing requirements and processing properties of the inner sheath and the outer sheath.

[0015] Compared with the prior art, the beneficial effects of the present application are:

[0016] The present application greatly improves the shell formation of the inner sheath, and the inner sheath forms a carbon shell after burning when the leaky coaxial cable burns, which can isolate the flame from entering the inside of the leaky coaxial cable, the outer sheath has high fire-retardant efficiency, and at the same time, the mechanical and physical properties are good, and the fire-retardant performance of the fire-retardant sheath can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] The present application will be further described below in conjunction with the drawings and examples.

[0018] Figure 1 The present application is a cross-sectional structure diagram of the radiation type leaky coaxial cable fire-retardant sheath structure.

[0019] In the figure: 1, inner sheath; 2, outer sheath. DETAILED DESCRIPTION

[0020] The present application will be further described below in conjunction with the drawings and examples.

[0021] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the features defined as "first" and "second" can be explicitly or implicitly included one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] like Figure 1 As shown, a radial leaky coaxial cable flame-retardant sheath structure includes an inner sheath 1 and an outer sheath 2, with the outer sheath 2 fitted onto and abutting against the inner sheath 1. The inner sheath 1 is an inorganic-filled flame-retardant polyolefin sheath, and the outer sheath 2 is a chemically expanding flame-retardant sheath. This significantly improves the shell-forming properties of the combustible material in the inner sheath 1. When the leaky coaxial cable burns, the inner sheath 1 forms a charred shell, which can prevent flames from entering the interior of the leaky coaxial cable. The outer sheath 2 has high flame-retardant efficiency and maintains good mechanical and physical properties, thus improving the flame-retardant performance of the sheath.

[0024] In this embodiment, the radial cross-sections of both the inner sheath 1 and the outer sheath 2 are annular. The inner diameter of the inner sheath 1 is d1 and the outer diameter is d2, while the inner diameter of the outer sheath 2 is d2 and the outer diameter is d3. The thickness of the inner sheath 1 is H1 and the radial cross-sectional area is S1, while the thickness of the outer sheath 2 is H2 and the radial cross-sectional area is S2. 1.5 < H1 / H2 < 2.5, S1 / S2 < H1 / H2, where: H1 = d2 - d1, H2 = d3 - d2, S1 = π(d2) / (d2) 2 -(d1) 2 S2=π((d3)) 2 -(d2) 2 Therefore, the cost of the flame retardant in the outer sheath 2 is higher than that in the inner sheath 1. The thicker inner sheath 1 and the thinner outer sheath 2 can reduce the material cost of the flame retardant sheath on the one hand, and improve the flame retardant performance of the flame retardant sheath on the other hand. At the same time, it can reduce the extrusion load of the inner sheath 1.

[0025] The application also provides a manufacturing method of the flame-retardant sheath structure of the radiation type leaky coaxial cable. The base resin used by the inner sheath 1 and the outer sheath 2 is the same kind of polymer, and the base resin is one or two of LDPE (low density polyethylene), LLDPE (linear low density polyethylene), HDPE (high density polyethylene), PP (polypropylene), EVA (ethylene-vinyl acetate copolymer), EEA (ethylene-ethyl acrylate) or EBA (ethylene-butyl acrylate). For example, the base resin of the inner sheath 1 and the outer sheath 2 is LDPE, or the base resin of the inner sheath 1 is EVA and the base resin of the outer sheath 2 is LDPE, or the base resin of the inner sheath 1 and the outer sheath 2 is the blend of EVA and LLDPE.

[0026] In the embodiment, the inner sheath 1 is extruded by adding inorganic flame retardant with mass fraction of 50%-60% in the base resin, and the inorganic flame retardant is magnesium hydroxide or aluminum hydroxide; the outer sheath 2 is extruded by adding chemical intumescent flame retardant with mass fraction of 20%-30% in the base resin, and the chemical intumescent flame retardant is phosphorus-ammonia intumescent flame retardant. Thus, the limiting oxygen index (LOI) of the inner sheath 1 reaches 35%-45%, the vertical burning level of the inner sheath 1 reaches V-0, and there is no need to add light stabilizer for resisting sunlight aging; the limiting oxygen index of the outer sheath 2 is 30%-35%, the vertical burning level of the outer sheath 2 is not lower than V-1, the tensile elongation of the outer sheath 2 is not lower than 250%, and the tensile breaking strength of the outer sheath 2 is not lower than 17 MPa.

[0027] Specifically, the phosphorus-ammonia intumescent flame retardant is composed of APP (ammonium polyphosphate), PER (pentaerythritol) and MEL (melamine).

[0028] Specifically, the inner sheath 1 is made into granular shape after mixing the base resin with the inorganic flame retardant, and then is extruded; the outer sheath 2 is made into granular shape after mixing the base resin with the chemical intumescent flame retardant, and then is extruded.

[0029] In the embodiment, the inner sheath 1 and the outer sheath 2 are tightly connected and vertically extruded in series, the inner sheath 1 and the outer sheath 2 adopt two sets of different extrusion dies, the inner sheath 1 and the outer sheath 2 share one extrusion head, the two sets of extrusion dies are respectively located on the two sides of the extrusion head and connected with the extrusion head, and the cable core after the extrusion of the inner sheath 1 immediately passes through the extrusion die of the outer sheath 2 for extrusion. Thus, the sagging can be avoided, so as to ensure that the flame-retardant sheath always keeps concentric with the cable core, and the large gap between the flame-retardant sheath and the outer conductor is avoided; since the base resins used in the sheath materials of the inner sheath 1 and the outer sheath 2 are the same or similar, and the inner sheath 1 and the outer sheath 2 are attached together before cooling, the inner sheath 1 and the outer sheath 2 can keep bonded and become a whole, so that the inner sheath 1 with poor mechanical properties is not easy to be broken and cracked under the external force such as bending and stretching of the leaky coaxial cable under the protection of the outer sheath 2 with good mechanical properties, the extrusion efficiency of the inner sheath 1 and the outer sheath 2 can be improved, and the inner sheath 1 and the outer sheath 2 can be bonded together, at the same time, the extrusion machines and the extrusion dies with different characteristics can be selected according to the different processing requirements and processing properties of the inner sheath 1 and the outer sheath 2.

[0030] Specifically, the two extrusion machines used for the inner sheath 1 and the outer sheath 2 are placed on the platform 5-10 meters high from the ground, the center axis of the cable core through the center line of the extrusion head is perpendicular to the ground before and after entering and exiting the extrusion head, and the sheath material wrapped around the cable core and melted after coming out of the extrusion head is also perpendicular to the ground, which is consistent with the direction of the gravity of the sheath material itself; the sheath material of the inner sheath 1 and the outer sheath 2 after melting respectively comes out of the bore and enters different extrusion dies.

[0031] For example, the inner sheath 1 is extruded by extrusion so as to tightly fit on the outer conductor and fill the slot hole of the outer conductor, which is beneficial to improve the flame retardant performance of the leaky coaxial cable. The outer sheath 2 is extruded by tube extrusion, and the eccentricity of the extrusion is greatly reduced, which can avoid the local material loss of the outer sheath 2, ensure that the outer sheath 2 remains complete and has the minimum point thickness under the condition of reducing the average thickness, and the surface of the outer sheath 2 obtained by tube extrusion is smoother. If a co-extrusion process is used, that is, a set of extrusion dies is used to complete the extrusion of the inner sheath 1 and the outer sheath 2, the advantages of extrusion and tube extrusion cannot be considered at the same time. That is, the extrusion can make the inner sheath 1 and the outer conductor more tightly fit, the structure of the leaky coaxial cable is more compact, and it is beneficial to improve the flame retardant performance of the cable. The tube extrusion can more easily reduce the eccentricity of the sheath. During processing, since the outer sheath 2 uses a chemical expansion type flame retardant material, the melt viscosity is lower than that of the inner sheath 1 containing a large amount of inorganic filler. Therefore, the extruders used for the two are different. The compression ratio of the extrusion screw of the inner sheath 1 is low, which is 1-1.2, and the surface of the barrel has a shallow thread groove. During extrusion, the sheath material is pushed out of the barrel. The extruder for the outer sheath 2 can be used for extruding ordinary polyvinyl chloride or polyethylene, and the compression ratio of the screw is 2.5-3.

[0032] For example, the extrusion die cover of the inner sheath 1 is separated from the rear seat of the extrusion die core of the outer sheath 2 by 2-10 cm.

[0033] Example 1

[0034] An inorganic flame retardant with a mass fraction of 50% is added to the base resin, and the inorganic flame retardant with a mass fraction of 50% and the base resin are prepared into the inner sheath 1 by using a close-coupled vertical extrusion method.

[0035] An expansion type flame retardant with a mass fraction of 20% is added to the base resin, and the expansion type flame retardant with a mass fraction of 20% and the base resin are prepared into the outer sheath 2 by using a close-coupled vertical extrusion method.

[0036] Example 2

[0037] The difference from Example 1 is that the mass fraction of the inorganic flame retardant is 55%, and the mass fraction of the chemical expansion type flame retardant is 25%.

[0038] Example 3

[0039] The difference from Example 1 is that the mass fraction of the inorganic flame retardant is 60%, and the mass fraction of the chemical expansion type flame retardant is 30%.

[0040] Comparative Example 1

[0041] The difference from Example 1 is that the mass fraction of the inorganic flame retardant is 40%, and the mass fraction of the chemical expansion type flame retardant is 10%.

[0042] The test method of limiting oxygen index (LOI) is according to GB / T 2406-2009 "Determination of flammability of plastics - Part 2: burning behaviour of small specimens in contact with an igniting source - test method", the determination method of vertical burning grade is according to GB / T 18380.12-2022 "Determination of the flammability of electric cables under fire conditions - Part 12: single- insulated wires and cables - flame spread in vertical position - test method for 1 kW pre-mixed flame", the test method of breaking tensile rate and tensile breaking strength is according to YD / T 837.3-1996 "Test methods of indoor communication cables with copper conductor and polyolefin insulation and aluminum plastic composite sheath - Part 3: mechanical and physical property test methods".

[0043] The data of test by the above test methods for Example 1-3 and Comparative Example 1 are shown in Table 1.

[0044] Table 1

[0045]

[0046] According to Table 1, it can be obtained that:

[0047] Compared with Comparative Example 1, the LOI of inner sheath 1, the LOI of outer sheath 2 in Example 1-3 are higher, and the breaking tensile rate of outer sheath 2 and the tensile breaking strength of outer sheath 2 are decreased; compared with Comparative Example 1, the inner sheath 1 of Example 1 is prepared by using inorganic flame retardant with a mass fraction of 50%, and the outer sheath 2 is prepared by using chemical intumescent flame retardant with a mass fraction of 20%, which can increase the LOI of inner sheath 1 by 10%, can increase the LOI of outer sheath 2 by 10%, and the breaking tensile rate of outer sheath 2 can still be maintained at 129%, and the tensile breaking strength of outer sheath 2 can still be maintained at 20 MPa; compared with Example 1, the amount of inorganic flame retardant and intumescent flame retardant in Example 2 and 3 is increased, which can increase the LOI of inner sheath 1 by 5%-10%, and the LOI of outer sheath 2 by 2.5%-5%, and the breaking tensile rate of outer sheath 2 can still be maintained at 117%-129%, and the tensile breaking strength of outer sheath 2 can still be maintained at 14 MPa-20 MPa.

[0048] It should be added that: 1, if the sheath material added with inorganic flame retardant wants to achieve sufficient flame retardant effect, the added proportion will be extremely large, and in some special cases, it will even exceed the amount of high polymer, therefore, it will inevitably have a very large impact on the physical and mechanical properties of high polymer, which requires the inorganic flame retardant to be treated, for example: microparticulation, surface activation.

[0049] 2. Intumescent flame retardants have poor compatibility with polymers, which reduces the physical, mechanical, electrical, and insulating properties of polymers, especially tensile strength and impact resistance. Excessive use of these agents can increase the difficulty of engineering applications, necessitating modification treatment.

[0050] 3. Magnesium hydroxide or aluminum hydroxide is used as an inorganic flame retardant. Its flame retardant mechanism is that when magnesium hydroxide or aluminum hydroxide is heated, it decomposes and releases water vapor to reduce the surface temperature of the cable. At the same time, the water vapor can dilute the oxygen on the surface of the sheath. The decomposed oxides adhere to the surface of the sheath and play a barrier role, thereby achieving flame retardant performance. Therefore, its flame retardant effect is highly related to the proportion of inorganic flame retardant. To achieve a high flame retardant V-0 rating, the proportion of inorganic flame retardant needs to reach more than 50%. However, if too much inorganic flame retardant is added, it will seriously deteriorate the mechanical and physical properties of the sheath, such as the tensile strength and tensile breaking strength of the sheath.

[0051] 4. A phosphorus-nitrogen chemically intumescent flame retardant is used, whose main components are APP (ammonium polyphosphate), PER (pentaerythritol), and MEL (melamine). APP can act as both an acid source and a gas source, PER as a char source, and MEL as a gas source. When the sheath burns at a lower temperature, APP releases acidic substances. Then, at a temperature slightly higher than the temperature at which the acid is released, APP and PER undergo an esterification reaction. During the esterification process, the esterification products dehydrate to form char, creating a char layer, and the sheath layer begins to melt. Simultaneously, the water vapor, ammonia, and other gases produced by the esterification reaction, along with the non-flammable gases generated by the APP and MEL gas sources, fill the char layer, causing the sheath layer to expand and foam. When the reaction is nearing completion, the generated char layer solidifies, finally forming a porous foamed char layer, thus achieving the purpose of flame retardancy. Because phosphorus-nitrogen chemically intumescent flame retardants have high flame retardant efficiency, a flame retardant rating of V-1 can be achieved as long as the addition ratio reaches 20%-30%. However, this type of flame retardant is expensive, which will increase the overall production cost. The dosage needs to be considered in combination with actual needs.

[0052] In summary, the inner sheath 1 of the present invention has greatly improved the shell-forming properties of combustible materials. When the leaky coaxial cable is burning, the inner sheath 1 forms a carbon shell after combustion, which can prevent the flame from entering the interior of the leaky coaxial cable. The outer sheath 2 has high flame retardant efficiency and can maintain good mechanical and physical properties, thereby improving the flame retardant performance of the flame retardant sheath.

[0053] The above description is based on the preferred embodiments of the present invention. Through the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the contents of the specification, but must be determined by the scope of the claims.

Claims

1. A radiation leakage coaxial cable flame retardant jacket construction comprising, The utility model relates to a kind of cable sheath, including: Inner sheath (1), and Outer sheath (2), the outer sheath (2) is set on the inner sheath (1), and is in abutment with the inner sheath (1); Wherein: the inner sheath (1) is inorganic filling type flame-retardant polyolefin sheath, the outer sheath (2) is chemical expansion type flame-retardant sheath; The radial section of the inner sheath (1), the outer sheath (2) is all circular ring, the inner diameter of the inner sheath (1) is d1, outer diameter is d2, the inner diameter of the outer sheath (2) is d2, outer diameter is d3; The inner sheath (1) has a thickness H1 and a radial cross-sectional area S1, the outer sheath (2) has a thickness H2 and a radial cross-sectional area S2, 1.5 < H1 / H2 < 2.5, S1 / S2 < H1 / H2, wherein: H1 = d2 - d1, H2 = d3 - d2, S1 = π ((d2) 2 - (d1) 2 ), S2 = π ((d3) 2 - (d2) 2 ); The base resin used in inner sheath (1), outer sheath (2) is the same kind of polymer, and the base resin is one or two of LDPE, LLDPE, HDPE, PP, EVA, EEA, EBA; The inner sheath (1) is extruded by adding 50%-60% inorganic flame retardant in base resin by mass fraction, and the outer sheath (2) is extruded by adding 20%-30% chemical expansion type flame retardant in base resin by mass fraction.

2. The radiation leak coaxial cable flame retardant jacket structure of claim 1, wherein, Inorganic flame retardant is magnesium hydroxide or aluminum hydroxide.

3. The radiation leak coaxial cable flame retardant jacket structure of claim 1, wherein, Chemical expansion type flame retardant is phosphorus-nitrogen expansion type flame retardant.

4. A method of manufacturing a flame-retardant jacket structure for a radiating leaky coaxial cable as claimed in any one of claims 1 to 3, characterized in that, The inner sheath (1), the outer sheath (2) are tightly connected in series and vertically extruded, and in the tightly connected in series and vertically extruded, the inner sheath (1), the outer sheath (2) adopt two different extrusion dies, the inner sheath (1), the outer sheath (2) share an extrusion head, and the two extrusion dies are respectively located on the two sides of the extrusion head and connected with the extrusion head, the cable core after the extrusion of the inner sheath (1) is immediately extruded by the extrusion die of the outer sheath (2), and the inner sheath (1), the outer sheath (2) are adhered together without cooling.

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