Heat insulation type cross-linked polyolefin cable

Abstract

The invention belongs to the technical field of cable design and manufacturing, and particularly relates to a heat insulation type cross-linked polyolefin cable which is provided with a polyolefin sheath layer, the polyolefin sheath layer comprises a polyolefin base material, methyl vinyl silicone rubber raw rubber and a cross-linking agent microcapsule, a peroxide cross-linking agent is coated in the form of the microcapsule, and the cross-linking agent microcapsule is coated with a peroxide cross-linking agent. Vinyl reaction polymerization between the silicone rubber caused by exposure of the cross-linking agent in the middle-early stage of extrusion is effectively reduced; when the extrusion temperature rises to a certain degree, the capsule wall of the microcapsule is greatly molten to effectively release the cross-linking agent, and the cross-linking agent is used for initiating a polyolefin molecular chain and a silicone rubber molecular chain to jointly react and be cross-linked together, so that cross-linking aggregation between silicone rubber in a matrix is effectively reduced; and the thermal insulation contribution of the silicone rubber can be developed, and the overall mechanical property of the sheath can be guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of cable design and manufacturing, and particularly relates to a heat-insulating cross-linked polyolefin cable. Background Art

[0002] The cable layer structure mainly includes the innermost conductor core, the outer layer of the conductor core is covered with an insulation layer, a shielding layer and other functional protective layers, and the outermost layer is a sheath layer, which is directly in contact with the external use environment. When the temperature of the cable use environment is continuously too high, such as in the aerospace field, it is easy to cause cable insulation aging, and even cause safety problems such as fire.

[0003] Therefore, the protective layer of this type of cable needs to have sufficient thermal insulation to effectively block the transfer of high-temperature heat to the inside of the cable, so that the cable can still work normally in a high-temperature environment and ensure the stable transmission of signals or electrical energy. At the same time, it also reduces cable aging and insulation performance degradation caused by high temperature and extends the service life of the cable.

[0004] Silicone rubber materials can remain stable for a long time in the temperature range of -60℃ to 180℃, and also have good corrosion resistance and waterproof properties. These characteristics make silicone rubber materials have broad application prospects in thermal insulation cables. Polyolefin is a common cable sheath molding material with relatively low cost. Therefore, the applicant blends methyl vinyl silicone rubber raw rubber with polyolefin matrix resin and extrude and cross-link to obtain the cable sheath layer. However, the applicant found that the overall mechanical properties of the sheath layer after molding in this way are not ideal, and the improvement of thermal insulation effect is also limited. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a heat-insulating cross-linked polyolefin cable. The cable mainly includes a conductor core, an insulating layer, a shielding layer and a polyolefin sheath layer from the inside to the outside in terms of layer structure. The polyolefin sheath layer includes 100 parts of a polyolefin base material, 15 to 30 parts of methyl vinyl silicone rubber, 1 to 6 parts of a cross-linking agent microcapsule, 5 to 10 parts of a maleic anhydride grafted polyolefin compatibilizer, 10 to 20 parts of a polyolefin elastomer, 1 to 15 parts of an inorganic filler, and 1 to 10 parts of an additive, calculated by weight.

[0006] Wherein, the polyolefin is one or a combination of high-density polyethylene, low-density polyethylene, and polypropylene;

[0007] The molecular weight of methyl vinyl silicone rubber is 400,000 to 600,000, and the mole fraction of vinyl chain is 0.13% to 0.35%;

[0008] The crosslinking agent microcapsule comprises a peroxide crosslinking agent as a capsule core, a long-chain acrylate polymer as a capsule wall, the peroxide crosslinking agent is dicumyl peroxide or di-tert-butyl peroxide, etc., the weight ratio between the capsule core and the capsule wall is 10-90:100, and the preparation method of the crosslinking agent microcapsule comprises the following steps: fully mixing the peroxide crosslinking agent with acrylate and methacrylate as an oil phase; fully emulsifying the obtained oil phase in deionized water as an emulsion; dropping an initiator into the obtained emulsion and heating the emulsion for a period of time, purifying the solid content components therein and drying the emulsion.

[0009] The initiator is an inorganic persulfide such as sodium persulfate or potassium persulfate. The initiator is first dispersed and dissolved in deionized water as an initiator solution, and then the initiator solution is added dropwise to the emulsion.

[0010] Inorganic fillers include magnesium hydroxide, silicon carbide, silicon dioxide, graphite, etc.;

[0011] Additives include silane coupling agents, lubricants, antioxidants, ultraviolet light absorbers, etc.;

[0012] The conductor core is coaxially coated with an insulating layer and a shielding layer in sequence from the inside to the outside, thus serving as an insulating shielding unit. Two or more insulating shielding units are twisted together and coaxially coated with a polyolefin sheath layer to form a heat-insulating cross-linked polyolefin cable.

[0013] The beneficial effects of the present invention are:

[0014] First, this scheme selects methyl vinyl silicone rubber as raw rubber, not only based on the good thermal insulation contribution of silicone rubber, but also considering that there is a small amount of vinyl distributed on its molecular chain, which can help improve the vulcanization crosslinking activity of silicone rubber, improve the efficiency of vulcanization crosslinking agent, and reduce the amount of peroxide crosslinking agent. However, this scheme is to add this type of silicone rubber raw rubber to polyolefin base material for blending and extrusion. Some types of polyolefin base materials such as polypropylene and polyethylene with large molecular weight have relatively high melting processing temperatures, generally above 150°C, so the fluidity is obviously not as good as the silicone rubber. When the extruder temperature rises to 110°C to 120°C, the peroxide crosslinking agent in the material will decompose into active free radicals in large quantities. At this time, these active free radicals will inevitably initiate the polymerization reaction of vinyl carbon-carbon double bonds on silicone rubber. At the same time, since the processing melting temperature of the polyolefin base resin is not reached, it is difficult for the polyolefin molecules to participate in the initiation polymerization reaction. Therefore, at this stage, a considerable portion of the silicone rubber in the mixture will be cross-linked due to the reaction between the vinyl groups, similar to the agglomeration of the silicone rubber, which results in the inability of this portion of silicone rubber to be effectively dispersed in the sheath matrix. This is also the reason why the applicant analyzed and summarized the experimental results mentioned in the background technology that "the cable sheath layer obtained by extruding and cross-linking methyl vinyl silicone rubber raw rubber blended in polyolefin matrix resin has limited improvement in thermal insulation effect and unsatisfactory overall mechanical properties".

[0015] On this basis, the present scheme first encapsulates the peroxide crosslinking agent in the form of microcapsules. In the early and middle stages of extrusion, the material temperature is relatively low, and the peroxide crosslinking agent in the microcapsules will not be exposed too much. Therefore, the phenomenon of crosslinking and aggregation between the silicone rubber in the material through the reaction between the vinyl groups in the early and middle stages of extrusion is effectively reduced. Since the capsule wall of the microcapsule is based on linear polyacrylate molecular chains after all, its structure is not as stable as the crosslinked network structure. Therefore, when the extrusion temperature rises to a certain level, the capsule wall will eventually melt significantly and effectively release the peroxide crosslinking agent and its free radicals. Since the temperature in the extruder at this time is sufficient to melt the matrix polyolefin resin, the release of the peroxide crosslinking agent at this time will be more conducive to the reaction of the polyolefin molecular chains and the silicone rubber molecular chains to crosslink together, thereby effectively reducing the situation of "crosslinking and aggregation only between silicone rubbers" mentioned in the previous analysis, promoting the dispersion and distribution of silicone rubber in the sheath, improving the utilization rate of the mixed silicone rubber, and better ensuring the comprehensive performance of the polymer sheath.

[0016] To better achieve this, the present invention selects peroxides, such as dicumyl peroxide and di-tert-butyl peroxide, as crosslinking agents for initiating the crosslinking of resin molecular chains in the cable sheath layer. The decomposition initiation temperature of such peroxide crosslinking agents is above 100°C. When microencapsulating the active substances of this type of crosslinking agent, the initiator selected for initiating the polymerization of acrylate monomers into the microcapsule wall is inorganic persulfide, which can effectively initiate the polymerization of the wall monomers as long as the temperature is 60°C. It can be seen that this initiation temperature is much lower than the decomposition temperature of the peroxide crosslinking agent as the core of the microcapsule. Therefore, during the preparation process of the microcapsule, most of the peroxide crosslinking agent can be well retained without decomposition, so as to play an initiating role after being released in the subsequent sheath extrusion stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the radial cross-section of the heat-insulating crosslinked polyolefin cable in the present invention (taking the structure of a single-core cable as an example), where 1 - conductor core, 2 - insulating layer, 3 - shielding layer, 4 - polyolefin sheath layer. DETAILED DESCRIPTION OF THE INVENTION

[0018] Example 1

[0019] Preparation of crosslinking agent microcapsules:

[0020] At room temperature, 20 parts by weight of dicumyl peroxide are mixed with 60 parts by weight of isobutyl acrylate and 40 parts by weight of ethyl methacrylate to form an oil phase; the obtained oil phase and 1.5 parts by weight of sodium dodecylbenzenesulfonate are added to 500 parts by weight of water and stirred at room temperature until fully emulsified; while continuing to stir, the obtained emulsion system is heated to 60°C, and then a total of 50 parts by weight of an aqueous solution of sodium persulfate (where the mass concentration of sodium persulfate is 1.6%) is added dropwise thereto under heat preservation operation. After the addition is completed in 1.5 h, the stirring reaction is continued under heat preservation for 8 h, and then cooled to room temperature. The precipitate is separated by centrifugation and dried in an oven at 50°C to obtain the crosslinking agent microcapsules.

[0021] A heat-insulating crosslinked polyolefin cable, the cable has a layer structure from inside to outside in sequence as a conductor core made of metallic copper, an insulating layer coaxially coated on the conductor core, a shielding layer (metal wire mesh braided layer) coaxially coated on the insulating layer, and a polyolefin sheath layer coaxially coated on the shielding layer. Among them, the polyolefin sheath layer, calculated by weight parts, includes 100 parts of polypropylene S900 (Lanzhou Petrochemical), 20 parts of methyl vinyl silicone rubber raw rubber (110-3 A type), 6 parts of the crosslinking agent microcapsule prepared in the above-mentioned embodiment of the present invention, 8 parts of maleic anhydride grafted polypropylene compatibilizer (PO1015), 12 parts of POE thermoplastic elastomer (‌58705), 4 parts of silicon carbide, 1 part of silane coupling agent (KH560), 3 parts of lubricant (zinc stearate), and 1.5 parts of antioxidant (168).

[0022] Example 2

[0023] Preparation of crosslinking agent microcapsules:

[0024] At room temperature, 40 parts by weight of diisopropylbenzene peroxide, 30 parts by weight of isobutyl acrylate, and 90 parts by weight of ethyl methacrylate are mixed fully as the oil phase; the obtained oil phase and 3 parts by weight of sodium dodecyl sulfate are added to 600 parts by weight of water and stirred at room temperature until fully emulsified; while continuing to stir, the obtained emulsifying system is heated to 60 °C, and then an aqueous solution of sodium persulfate with a total of 40 parts by weight (wherein the mass concentration of sodium persulfate is 3%) is dropped into it under heat preservation operation. After the dropping is completed in 1 h, continue to keep stirring and reacting for 8 h under heat preservation, then cool to room temperature, and the precipitate is separated by centrifugation and dried in an oven at 50 °C to obtain the crosslinking agent microcapsules.

[0025] A heat-insulating crosslinked polyolefin cable, the cable has a layer structure from inside to outside in sequence as a conductor core made of metallic copper, an insulating layer coaxially coated on the conductor core, a shielding layer coaxially coated on the insulating layer, and a polyolefin sheath layer coaxially coated on the shielding layer. Among them, the polyolefin sheath layer, calculated by weight parts, includes 100 parts of polypropylene S900, 20 parts of methyl vinyl silicone rubber raw rubber, 5 parts of the crosslinking agent microcapsule prepared in the above-mentioned embodiment of the present invention, 5 parts of maleic anhydride grafted polypropylene compatibilizer, 10 parts of POE thermoplastic elastomer, 12 parts of magnesium hydroxide, 2 parts of silane coupling agent, 3 parts of lubricant, and 1 part of antioxidant.

[0026] Comparative Example 1

[0027] The peroxide crosslinking agent was not subjected to emulsion polymerization coating, and the other components and operations were the same as those in Example 1:

[0028] At room temperature, 60 parts by weight of isobutyl acrylate and 40 parts by weight of ethyl methacrylate are mixed thoroughly as an oil phase; the obtained oil phase and 1.5 parts by weight of sodium dodecylbenzene sulfonate are added to 500 parts by weight of water and stirred at room temperature until fully emulsified; the obtained emulsified system is heated to 60° C. under stirring, and a total of 50 parts by weight of an aqueous solution of sodium persulfate (wherein the mass concentration of sodium persulfate is 1.6%) is added dropwise thereto under heat preservation operation, and after the addition is completed for a total of 1.5 hours, the mixture is kept warm and stirred for 8 hours, and then cooled to room temperature, the precipitate is separated by centrifugation and dried in an oven at 50° C. to obtain acrylate polymer microspheres.

[0029] A heat-insulating cross-linked polyolefin cable, wherein the cable comprises, from inside to outside, a conductor core made of metal copper, an insulating layer coaxially coated on the conductor core, a shielding layer coaxially coated on the insulating layer, and a polyolefin sheath layer coaxially coated on the shielding layer, wherein the polyolefin sheath layer, calculated by weight, comprises 100 parts of polypropylene S900, 20 parts of methyl vinyl silicone rubber, 5 parts of the acrylate polymer microspheres prepared in the comparative example, 1 part of diisopropylbenzene peroxide, 8 parts of a maleic anhydride grafted polypropylene compatibilizer, 12 parts of a POE thermoplastic elastomer, 4 parts of silicon carbide, 1 part of a silane coupling agent, 3 parts of a lubricant, and 1.5 parts of an antioxidant.

[0030] Comparative Example 2

[0031] The peroxide crosslinking agent was not emulsion polymerized and coated, and the remaining components and operations were the same as those in Example 2:

[0032] At room temperature, 30 parts by weight of isobutyl acrylate and 90 parts by weight of ethyl methacrylate are mixed thoroughly as an oil phase; the obtained oil phase and 3 parts by weight of sodium dodecyl sulfate are added to 600 parts by weight of water and stirred at room temperature until fully emulsified; the obtained emulsified system is heated to 60° C. under stirring, and a total of 40 parts by weight of an aqueous solution of sodium persulfate (wherein the mass concentration of sodium persulfate is 3%) is added dropwise thereto under heat preservation operation, and after the addition is completed for a total of 1 hour, the mixture is kept warm and stirred for 8 hours, and then cooled to room temperature, the precipitate is separated by centrifugation and dried in an oven at 50° C. to obtain acrylate polymer microspheres.

[0033] A heat-insulating cross-linked polyolefin cable, wherein the cable comprises, from inside to outside, a conductor core made of metal copper, an insulating layer coaxially coated on the conductor core, a shielding layer coaxially coated on the insulating layer, and a polyolefin sheath layer coaxially coated on the shielding layer, wherein the polyolefin sheath layer, calculated by weight, comprises 100 parts of polypropylene S900, 20 parts of methyl vinyl silicone rubber, 3.75 parts of the acrylic polymer microspheres prepared in the comparative example, 1.25 parts of diisopropylbenzene peroxide, 5 parts of a maleic anhydride grafted polypropylene compatibilizer, 10 parts of a POE thermoplastic elastomer, 12 parts of magnesium hydroxide, 2 parts of a silane coupling agent, 3 parts of a lubricant, and 1 part of an antioxidant.

[0034] The components of the polyolefin sheath layer in the above-mentioned embodiments and comparative embodiments were first blended in a high-speed mixer for 15 minutes until fully mixed, and then melt-extruded on the shielding layer through a twin-screw extruder (zone 1 155°C, zone 2 165°C, zone 3 175°C, zone 4 190°C, zone 5 200°C, die 195°C, screw aspect ratio 25:1, screw speed 90rpm) to obtain a polyolefin sheath layer (thickness 1.5mm), and the mechanical properties of each sheath layer before and after the heat aging test were tested and compared.

[0035] Table 1

[0036]

[0037] In the above table, the heat aging test was carried out in accordance with "8.1 Air oven aging" in GB / T 2951.12-2008, the oven temperature was 80°C, the aging treatment time was 360h (lasting 15 days), and the oven air circulation rate was 600L / h; the tensile strength was tested in accordance with GB / T 2951.11-2008; the decline = (tensile strength before heat aging test - tensile strength after heat aging test) ÷ tensile strength before heat aging test × 100%. The smaller the decline, the less the sheath is affected by the heat test, that is, the better the thermal insulation effect.

[0038] As can be seen from Table 1, whether it is the overall mechanical properties of the sheath after molding or the influence of the sheath on the heat aging test, the present solution is better than the comparative example. This is because the emulsion coating method of the present solution effectively delays the interaction between the peroxide crosslinking initiator and the methyl vinyl silicone rubber raw rubber, thereby effectively avoiding the situation of "only the silicone rubber reacts and crosslinks prematurely and aggregates together". In the present solution, after the silicone rubber is more dispersedly crosslinked in the matrix polyolefin resin, it not only better exerts its contribution to heat insulation, but also is beneficial to the overall mechanical properties of the sheath.

Claims

1. A heat-insulating cross-linked polyolefin cable, characterized in that: The cable comprises a conductor core, an insulating layer, a shielding layer and a polyolefin sheath layer from the inside to the outside in terms of layer structure, wherein the polyolefin sheath layer comprises, by weight, 100 parts of a polyolefin base material, 15 to 30 parts of methyl vinyl silicone rubber, 1 to 6 parts of a crosslinking agent microcapsule, 5 to 10 parts of a maleic anhydride grafted polyolefin compatibilizer, 10 to 20 parts of a polyolefin elastomer, 1 to 15 parts of an inorganic filler and 1 to 10 parts of an auxiliary agent, and the crosslinking agent microcapsule has a peroxide crosslinking agent as a capsule core and a long-chain acrylate polymer as a capsule wall.

2. The heat-insulating crosslinked polyolefin cable according to claim 1, characterized in that: The polyolefin is one or a combination of high-density polyethylene, low-density polyethylene, and polypropylene.

3. The heat-insulating crosslinked polyolefin cable according to claim 1, characterized in that: The molecular weight of the methyl vinyl silicone rubber raw rubber is 400,000 to 600,000, and the mole fraction of the vinyl chain segment is 0.13% to 0.35%.

4. The heat-insulating crosslinked polyolefin cable according to claim 1, wherein: The weight ratio between the capsule core and the capsule wall is 10-90:

100.

5. The heat-insulating crosslinked polyolefin cable according to claim 1, wherein: The preparation method of the crosslinker microcapsules is as follows: the peroxide crosslinker is fully mixed with acrylate and methacrylate to form an oil phase; the obtained oil phase is fully emulsified in deionized water to form an emulsion; an initiator is added dropwise to the obtained emulsion and the temperature is raised to react for a period of time, and then the solid content components therein are purified and dried to form the crosslinker microcapsules.

6. The heat-insulating cross-linked polyolefin cable according to claim 5, characterized in that: The peroxide crosslinking agent includes dicumyl peroxide and di-tert-butyl peroxide; the initiator includes sodium persulfate and potassium persulfate.

7. The heat-insulating crosslinked polyolefin cable according to claim 1, characterized in that: The inorganic filler includes magnesium hydroxide, silicon carbide, silicon dioxide and graphite.

8. The heat-insulating crosslinked polyolefin cable according to claim 1, wherein: The auxiliary agents include silane coupling agents, lubricants, antioxidants and ultraviolet light absorbers.

9. The heat-insulating crosslinked polyolefin cable according to claim 1, wherein: The conductor core is coaxially coated with the insulating layer and the shielding layer in sequence from the inside to the outside, thereby serving as an insulating shielding unit. Two or more insulating shielding units are twisted together and coaxially coated with the polyolefin sheath layer to form the thermal insulation cross-linked polyolefin cable.

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