CN111574766B

CN111574766B - Radiation cross-linked polyethylene foam with high heat dissipation performance and preparation method and application thereof

Info

Publication number: CN111574766B
Application number: CN202010482332.3A
Authority: CN
Inventors: 马琦入; 魏立东; 郭宇; 张新可; 孙东立
Original assignee: Shenzhen Changyuan Tefa Technology Co ltd
Current assignee: Shenzhen Changyuan Tefa Technology Co ltd
Priority date: 2020-05-29
Filing date: 2020-05-29
Publication date: 2022-09-06
Anticipated expiration: 2040-05-29
Also published as: CN111574766A

Abstract

The invention discloses radiation cross-linked polyethylene foam with high heat dissipation performance, a preparation method and application thereof, wherein the radiation cross-linked polyethylene foam is prepared from the following raw materials in percentage by weight: 52 to 93.7 percent of low density polyethylene, 2 to 15 percent of azodicarbonamide, 0.3 to 3 percent of pore-forming agent, 1 to 10 percent of heat-conducting powder, 1 to 10 percent of low dielectric filler, 1 to 5 percent of compatilizer and 1 to 5 percent of sensitizer. According to the invention, the pore-forming agent is added to form a cross-linked pore-forming structure, so that the air circulation is facilitated, and the heat dissipation of foam is improved; meanwhile, by adding the heat-conducting powder, the heat conductivity coefficient is improved, and the heat dissipation of the foam is improved. In the invention, the radiation crosslinking polyethylene foam has low dielectric constant and low loss by adding the low dielectric filler.

Description

Radiation cross-linked polyethylene foam with high heat dissipation performance and preparation method and application thereof

Technical Field

The invention relates to the field of foam, in particular to radiation cross-linked polyethylene foam with high heat dissipation performance and a preparation method and application thereof.

Background

The radiation crosslinking polyethylene foam (IXPE) material is a high-molecular foam material prepared by taking low-density polyethylene (LDPE) as a main raw material and Azodicarbonamide (AC) as a foaming agent and performing high-temperature foaming of mixing granulation, extrusion processing, radiation crosslinking and foaming molding on a plurality of chemical raw materials, and has the advantages of smooth surface, closed, fine and uniform foam holes, no water absorption, environmental protection, light weight, low cost, excellent sealing and buffering performance, high shape recovery capability and high buffering and damping capability.

However, the existing radiation crosslinking polyethylene foam product has high dielectric constant, and the existing radiation crosslinking polyethylene foam has a closed pore structure and poor heat dissipation.

Disclosure of Invention

The invention mainly aims to provide radiation cross-linked polyethylene foam with high heat dissipation performance, a preparation method and application thereof, and solves the technical problems that in the prior art, a radiation cross-linked polyethylene foam product is high in dielectric constant, the existing radiation cross-linked polyethylene foam is of a closed-cell structure and poor in heat dissipation performance, and the radiation cross-linked polyethylene foam is low in dielectric constant and good in heat dissipation performance.

The technical problem to be solved by the invention is realized by the following technical scheme:

the invention provides radiation cross-linked polyethylene foam with high heat dissipation performance, which is prepared from the following raw materials in percentage by weight: 52 to 93.7 percent of low density polyethylene, 2 to 15 percent of azodicarbonamide, 0.3 to 3 percent of pore-forming agent, 1 to 10 percent of heat-conducting powder, 1 to 10 percent of low dielectric filler, 1 to 5 percent of compatilizer and 1 to 5 percent of sensitizer.

Further, the melting point of the low-density polyethylene is 100-110 ℃, and the melt index is 1-4g/10 min; the particle size of the azodicarbonamide is 10-15nm, and the decomposition temperature is 200-220 ℃.

Further, the pore opening agent is at least one of nitroso salt derivatives, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate.

Further, the heat conducting powder is at least one of graphite powder and carbon black powder.

Further, the low dielectric filler is a fluoroplastic.

Further, the fluoroplastic is at least one of polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), ethylene chlorotrifluoroethylene copolymer (ECTFE), ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoroethylene-vinylidene fluoride copolymer (THV), and Fluorinated Ethylene Propylene (FEP).

According to another aspect of the present invention, there is provided a method for preparing the radiation cross-linked polyethylene foam with high heat dissipation performance, comprising the following steps:

mixing and granulating: banburying and granulating azodicarbonamide and low-density polyethylene to obtain foaming agent master batches; banburying and granulating the pore forming agent and the low-density polyethylene to obtain pore forming agent master batches; banburying and granulating the heat-conducting powder and the low-density polyethylene to obtain heat-conducting powder master batches; banburying and granulating the compatilizer and the low-density polyethylene to obtain compatilizer master batches; banburying and granulating a sensitizer and low-density polyethylene to obtain sensitizer master batches; grinding the low dielectric filler and granulating the ground low dielectric filler and low density polyethylene to obtain low dielectric filler master batches;

and (3) extrusion molding: uniformly mixing the foaming agent master batch, the pore opening agent master batch, the heat conducting powder master batch, the compatilizer master batch, the sensitizing agent master batch, the low dielectric filler master batch and the low density polyethylene in a screw extruder and extruding to obtain a substrate;

radiation crosslinking: carrying out radiation crosslinking on the substrate through a high-speed electron field to obtain a master slice;

foaming: and (3) foaming the master slice at a high temperature by a foaming furnace to generate foam.

Further, in the process of granulating the foaming agent master batch, the temperature range is 105-115 ℃, and the blending time is 8-12 min; in the process of granulating the heat-conducting powder master batch, the temperature range is 115-120 ℃, and the blending time is 10-15 min.

Further, in the step of extrusion molding, the temperatures of the first zone to the seventh zone of the barrel of the extruder are respectively 103-.

Further, the electron energy of the radiation crosslinking is 1-2MeV, and the radiation dose is 5-9 megarads;

further, in the foaming step, the master slice is foamed at high temperature through a gas-fired horizontal foaming furnace to generate foam, the temperature of the preheating section of the foaming furnace is 145-165 ℃, the temperature of the foaming section of the foaming furnace is 190-220 ℃, and the mesh belt speed is 2-4 m/min.

According to another aspect of the invention, the application of the radiation cross-linked polyethylene foam with high heat dissipation performance in the preparation of high-frequency cables is provided.

The invention has the following beneficial effects:

according to the invention, the pore-forming agent is added to form a cross-linked pore-forming structure, so that air circulation is facilitated, and the heat dissipation performance of foam is improved; meanwhile, by adding the heat-conducting powder, the heat conductivity coefficient is improved, and the heat dissipation of the foam is improved.

In the invention, the low dielectric filler is added, so that the radiation crosslinking polyethylene foam has low dielectric constant and low loss.

Detailed Description

The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.

Unless otherwise defined, terms used in the present specification have the same meaning as those generally understood by those skilled in the art, but in case of conflict, the definitions in the present specification shall control.

The use of "including," "comprising," "containing," "having," or other variations thereof herein, is meant to encompass the non-exclusive inclusion, as such terms are not to be construed. The term "comprising" means that other steps and ingredients can be added that do not affect the end result. The term "comprising" also includes the terms "consisting of …" and "consisting essentially of …". The compositions and methods/processes of the present invention comprise, consist of, and consist essentially of the essential elements and limitations described herein, as well as any of the additional or optional ingredients, components, steps, or limitations described herein.

All numbers or expressions referring to quantities of ingredients, process conditions, etc. used in the specification and claims are to be understood as modified in all instances by the term "about". All ranges directed to the same component or property are inclusive of the endpoints, and independently combinable. Because these ranges are continuous, they include every value between the minimum and maximum values. It should also be understood that any numerical range recited herein is intended to include all sub-ranges within that range.

As described in the background art, the prior art radiation crosslinked polyethylene foam product has the problems of high dielectric constant, closed cell structure and poor heat dissipation performance

In order to solve the technical problems, the invention provides radiation cross-linked polyethylene foam with high heat dissipation performance, which is prepared from the following raw materials in percentage by weight: 52 to 93.7 percent of low density polyethylene, 2 to 15 percent of azodicarbonamide, 0.3 to 3 percent of pore-forming agent, 1 to 10 percent of heat-conducting powder, 1 to 10 percent of low dielectric filler, 1 to 5 percent of compatilizer and 1 to 5 percent of sensitizer.

The inventor unexpectedly finds that the pore opening agent and the heat conduction powder are compounded, and the components are synergistic, so that the heat dissipation of the foam can be obviously improved, and an unexpected technical effect is achieved.

In order to improve the heat dissipation performance of the polyethylene foam product, a heat dissipation layer is usually combined on a polyethylene foam layer to form a composite structure in the prior art. However, in the process of implementing the embodiments of the present application, the inventors of the present application found that the above-mentioned technology has at least the following technical problems: the radiation cross-linked polyethylene foam layer in this composite structure is still a closed cell structure. The composite structure is complex in process and low in production efficiency, heat is dissipated through the heat dissipation layer, and although heat can be transferred in three modes of conduction, convection and transfer of radiant heat, the heat after the conduction, the convection or the heat radiation is easy to accumulate on the foam layer or between the foam layer and the heat dissipation layer, so that the heat dissipation effect is poor. In the invention, the pore-forming agent and materials such as low-density polyethylene, azodicarbonamide and the like which conventionally form the radiation crosslinking polyethylene foam are creatively used as raw materials, and the foam is prepared by mixing, granulating, extruding, radiation crosslinking and foaming, so that the technical problems of complex process, low production efficiency and poor heat dissipation effect of the radiation crosslinking polyethylene foam product with heat dissipation in the prior art are solved; the radiation cross-linked polyethylene foam with high heat dissipation performance is formed into a cross-linked open-pore structure through one-step forming, and is simple in process, high in production efficiency and good in heat dissipation performance.

In the prior art, a pore-opening agent is directly added in the preparation of foam to form an open-pore structure. However, the foam is foamed by chemical reaction. For foam products which adopt electron radiation crosslinking foaming, the direct addition of the cell opening agent to form a cell opening structure can affect the gas retention performance of the product, and is not beneficial to the foaming process. Therefore, no report that the cell opening agent is directly added to the preparation of the radiation crosslinking polyethylene foam to form an open cell structure exists. According to the invention, the low-density polyethylene, azodicarbonamide, the pore-opening agent, the heat-conducting powder, the low-dielectric filler, the compatilizer and the sensitizer are compounded according to a certain proportion, and the components have synergistic effect, so that the pore-opening structure can be formed to facilitate the heat dissipation of foam, the normal foaming process can be ensured, and other physical properties of the product are maintained without being influenced by directly adding the pore-opening agent.

The radiation crosslinking polyethylene foam uses low-density polyethylene as a main material. The low density polyethylene is 52-93.7% by weight, with typical but non-limiting percentages by weight being 52%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 92 or 93.7%.

The melting point of the low-density polyethylene is 100-110 ℃, and the melt index is 1-4g/10 min. The melt index of the low-density polyethylene was measured at 190 ℃ under a load of 2.16 kg.

It should be noted that the source of the low density polyethylene in the present invention is not particularly limited, and the low density polyethylene meeting the requirements well known to those skilled in the art can be used; if it is commercially available, it can be prepared by itself by a method known to those skilled in the art.

The radiation crosslinking polyethylene foam takes azodicarbonamide as a foaming agent. The azodicarbonamide is present in an amount of 2-15% by weight, with typical but non-limiting amounts being 2%, 5%, 8%, 10%, 12%, or 15% by weight. The azodicarbonamide is added too little, the foam multiplying power after foaming is too low, the azodicarbonamide is added too much, and the azodicarbonamide is extruded at low temperature and is easy to decompose, so that normal foaming is influenced.

The particle size of the azodicarbonamide is 10-15nm, and the typical but non-limiting particle size of the azodicarbonamide is 10nm, 11nm, 12nm, 13nm, 14nm or 15 nm; preferably, the decomposition temperature of the azodicarbonamide is 200-220 ℃, and typical but non-limiting decomposition temperatures of azodicarbonamide are 201 ℃, 202 ℃, 203 ℃, 204 ℃, 205 ℃, 207 ℃, 209 ℃, 210 ℃, 211 ℃, 212 ℃, 213 ℃, 215 ℃, 216 ℃, 219 ℃ or 220 ℃.

It should be noted that the source of the azodicarbonamide in the present invention is not particularly limited, and azodicarbonamide satisfying conditions well known to those skilled in the art may be used; as commercially available products thereof can be used.

The cell opening agent can adjust the cell structure of the foam to form a cell opening structure. The above mentioned radiation cross-linked polyethylene foam has a cell opener 0.3-3 wt%, typically but not limited to 0.3 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, or 3 wt%. The addition of the opening agent is less than 0.3 percent, and the opening rate of the foam is not high; if the addition of the pore former is higher than 3%, the gas retention performance of the system is greatly influenced, and foaming is not facilitated.

In the embodiment of the present invention, the kind of the pore former is not particularly limited, and may be any pore former known to those skilled in the art, including but not limited to at least one of nitroso salt derivative, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate.

The radiation cross-linked polyethylene foam comprises 1-10 wt% of heat-conducting powder, typically but not limited to 1%, 2%, 5%, 7%, 8%, 9%, or 10%. The addition amount of the heat-conducting powder is lower than 1 percent, which is not beneficial to improving the heat conductivity coefficient; the addition amount of the heat-conducting powder is higher than 10%, which affects the multiplying power of the product.

In the embodiment of the present invention, the heat conductive powder is preferably at least one of graphite powder and carbon black powder. By selecting the type of the heat-conducting powder, at least one of graphite powder and carbon black powder is adopted as the heat-conducting powder, so that the heat conductivity coefficient of the prepared radiation crosslinking polyethylene foam can be greatly improved, and the heat conductivity coefficient of the prepared radiation crosslinking polyethylene foam is obviously superior to that of other heat-conducting powders.

In the invention, the radiation crosslinking polyethylene foam has low dielectric constant and low loss by adding the low dielectric filler. The low dielectric filler in the radiation crosslinked polyethylene foam is 1-10 wt%, and typically, but not limited to, 1%, 2%, 5%, 7%, 8%, 9%, or 10 wt%. The addition amount of the low dielectric filler is less than 1 percent, which is not beneficial to improving the dielectric constant; the addition of the low dielectric filler in an amount of more than 10% increases the cost and also affects the extrusion and foaming properties of the system.

In the embodiment of the present invention, the low dielectric filler is preferably fluoroplastic. By selecting the type of the low dielectric filler and adopting the fluoroplastic as the low dielectric filler, the dielectric constant of the prepared radiation crosslinking polyethylene foam is obviously superior to that of other materials. Moreover, the inventor surprisingly finds that the high temperature resistance and the tensile strength of the radiation crosslinking polyethylene foam can be greatly improved after the fluoroplastic is added.

In the embodiment of the present invention, the kind of the fluoroplastic is not particularly limited, and may be any fluoroplastic body known to those skilled in the art, including but not limited to at least one of polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoroethylene-vinylidene fluoride copolymer (THV), and fluoropolyfluoroethylene propylene (FEP). More preferably, the fluoroplastic is polyvinyl fluoride or polytetrafluoroethylene.

By adding the compatilizer and controlling the addition amount of the compatilizer, the technical problem of poor compatibility between the heat-conducting powder and the low dielectric filler and a polyethylene foam system can be solved, the compatibility among the heat-conducting powder, the low dielectric filler and the polyethylene foam system can be increased, and the uniformity of cells of a polyethylene foam product can be improved.

In the embodiment of the present invention, the compatibilizer is not particularly limited, and may be any compatibilizer known to those skilled in the art, including but not limited to ethylene-octene copolymer grafted maleic anhydride, polyethylene grafted maleic anhydride, or ethylene-vinyl acetate copolymer grafted maleic anhydride.

In the invention, the sensitizer is added to promote the foam to be foamed better. In the embodiment of the present invention, the sensitizer is not particularly limited, and may be any sensitizer known to those skilled in the art, including but not limited to one or more of zinc acetate, zinc stearate, cobalt stearate, zinc oxide, and barium stearate.

In a second aspect, a preparation method of the radiation cross-linked polyethylene foam with high heat dissipation performance is provided, which comprises the following steps:

It should be noted that, the amount of the low-density polyethylene used in the process of preparing the foaming agent master batch is not particularly limited, as long as the low-density polyethylene can be banburied with the azodicarbonamide to form master batch, and the rest low-density polyethylene is enough to prepare other master batches; the dosage of the low-density polyethylene in the process of preparing the pore former master batch is not particularly limited, as long as the low-density polyethylene can be internally mixed with the pore former to form the master batch, and the residual low-density polyethylene is enough to prepare other master batches; the dosage of the low-density polyethylene in the process of preparing the heat-conducting powder master batch is not particularly limited, as long as the low-density polyethylene can be internally mixed with the heat-conducting powder to form the master batch, and the residual low-density polyethylene can be enough to prepare other master batches; the dosage of the low-density polyethylene in the process of preparing the compatilizer master batch is not particularly limited, as long as the low-density polyethylene can be internally mixed with the compatilizer to form the master batch, and the residual low-density polyethylene is enough to prepare other master batches. The low-density polyethylene in the extrusion molding process is the low-density polyethylene remaining after the mixing and granulation of the total low-density polyethylene.

In the embodiment of the invention, the azodicarbonamide, the pore-opening agent, the heat-conducting powder and the sensitizer are all independently added in the form of master batches. By preparing the master batch, on one hand, powdery raw materials can be prepared into granules; on the other hand, the raw materials can be uniformly dispersed in the main material of the low-density polyethylene.

As a preferred embodiment of the application, in the process of granulating the foaming agent master batch, the temperature range is 105-115 ℃, and the blending time is 8-12 min; in the process of granulating the heat-conducting powder master batch, the temperature range is 115-120 ℃, and the blending time is 10-15 min; in the process of granulating the sensitizer master batch, the temperature range is 105-115 ℃, and the blending time is 8-12 min.

By adopting the foaming mode in the invention, the processing temperature of the low-density polyethylene is about 120 ℃, the processing temperature of the fluoroplastic is above 260 ℃, and the processing temperature difference between the low-density polyethylene and the fluoroplastic is large. Due to the addition of azodicarbonamide as a foaming agent, the foaming agent is decomposed in advance in the extrusion molding process and cannot be foamed normally due to overhigh processing temperature. In order to solve the problem that radiation cross-linked polyethylene foam can not be foamed normally after fluoroplastic of low dielectric filler is directly added, the invention creatively grinds the low dielectric filler into powder and then granulates the low dielectric filler with low-density polyethylene to obtain low dielectric filler master batches, and then the low dielectric filler is extruded and molded together with other raw materials, so that the low dielectric filler is added in a mode of grinding and filling solid powder, and the low dielectric filler exists in a solid powder form all the time in a system and can not be melted, thereby not only ensuring the addition of the low dielectric filler, but also ensuring the normal foaming of the radiation cross-linked polyethylene foam.

In the embodiment of the present invention, the mesh number of the low dielectric filler after being ground is preferably, but not limited to, 2000 mesh or more.

As a preferred embodiment of the invention, in the step of extrusion molding, the temperatures of the first zone to the seventh zone of the barrel of the extruder are respectively 103-110 ℃, 105-112 ℃, 105-113 ℃, 105-115 ℃, 107-118 ℃, the connector is 100-105 ℃, the temperatures of the three zones of the mold are 110-118 ℃, and the screw rotation speed is 13-18 r/min.

The process parameters such as temperature and screw rotation speed affect the properties of the extruded coiled material in all aspects, and the following effects can be generated when the process parameters are not in the range: (1) the extrusion temperature is higher, the rotating speed of the screw is too high, the foaming agent is easy to extrude and decompose, the product multiplying power and the extrusion temperature of the foam holes (2) are influenced and too low, the rotating speed of the screw is lower, the low-density polyethylene is not melted and cannot be plasticized, and the extrusion temperature of the mass production (3) cannot be extruded and is too high.

As a preferred embodiment of the present invention, the electron energy of the radiation crosslinking is 1-2MeV, more preferably 1.9MeV, and the radiation dose is 5-9 megarads.

As a preferred embodiment of the invention, in the foaming step, the master slice is foamed at high temperature by a gas-fired horizontal foaming furnace to generate foam, the temperature of the preheating section of the foaming furnace is 145-165 ℃, the temperature of the foaming section of the foaming furnace is 190-220 ℃, and the mesh belt speed is 2-4 m/min.

The foaming temperature, the mesh belt speed and other process parameters directly influence the foam skin, foam holes, the multiplying power, the mechanical property and the like, and the following influences can be generated when the foaming temperature, the mesh belt speed and other process parameters are not in the range: (1) the mesh belt speed is slow, the foaming temperature is too high, the sheet material is foamed in advance in a furnace, the high-temperature heating time is too long, the foam is easy to age and break, and continuous production cannot be realized; (2) the mesh belt speed is fast, the foaming temperature is low, the sheet material is not completely foamed before reaching the furnace mouth, the waste is large, and the multiplying power is low.

In a third aspect, the application of the radiation cross-linked polyethylene foam with high heat dissipation performance in the aspect of preparing high-frequency cables is provided.

The radiation cross-linked polyethylene foam with high heat dissipation performance provided by the invention has the advantages of small dielectric constant and low loss, can increase the signal transmission speed, is particularly suitable for high-frequency signal transmission, is high-temperature resistant, has good tensile strength, can be well applied and developed in the field of high-frequency cables with special requirements, and widens the application field of the radiation cross-linked polyethylene foam.

In order to better understand the technical solutions, the technical solutions will be described in detail with reference to specific examples, which are only preferred embodiments of the present invention and are not intended to limit the present invention.

Example 1

The radiation cross-linked polyethylene foam with high heat dissipation performance is prepared from the following raw materials in percentage by weight: 75% of low-density polyethylene, 8% of azodicarbonamide, 1.5% of pore-forming agent, 5% of heat-conducting powder, 5% of low-dielectric filler, 3% of compatilizer and 2.5% of sensitizer.

The melting point of the low-density polyethylene is 100-110 ℃, and the melt index is 1-4g/10 min; the particle size of the azodicarbonamide is 10-15nm, and the decomposition temperature is 200-220 ℃.

The pore former is sodium bicarbonate; the heat conducting powder is graphite powder; the low dielectric filler is polytetrafluoroethylene; the compatilizer is ethylene-octene copolymer grafted maleic anhydride; the sensitizer is zinc acetate.

The preparation method of the radiation cross-linked polyethylene foam with high heat dissipation performance comprises the following steps:

mixing and granulating: banburying and granulating azodicarbonamide and low-density polyethylene to obtain foaming agent master batches; banburying and granulating the pore forming agent and the low-density polyethylene to obtain pore forming agent master batches; banburying and granulating the heat-conducting powder and the low-density polyethylene to obtain heat-conducting powder master batches; banburying and granulating the compatilizer and the low-density polyethylene to obtain compatilizer master batches; banburying and granulating the sensitizer and the low-density polyethylene to obtain sensitizer master batches; grinding the low dielectric filler and granulating the ground low dielectric filler and low density polyethylene to obtain low dielectric filler master batches; wherein, in the process of granulating the foaming agent master batch, the temperature range is 105-115 ℃, and the blending time is 8-12 min; in the process of granulating the heat-conducting powder master batch, the temperature range is 115-120 ℃, and the blending time is 10-15 min; the mesh number of the low dielectric filler after being ground is more than 2000 meshes;

and (3) extrusion molding: uniformly mixing the foaming agent master batch, the pore-opening agent master batch, the heat-conducting powder master batch, the compatilizer master batch, the sensitizer master batch, the low-dielectric filler master batch and the low-density polyethylene in a screw extruder and extruding to obtain a substrate; in the step of extrusion molding, the temperatures of the first zone to the seventh zone of the barrel of the extruder are respectively 103-110 ℃, 105-112 ℃, 105-113 ℃, 105-115 ℃, 107-118 ℃, the connector is 100-105 ℃, the temperatures of the three zones of the mold are 110-118 ℃, and the screw rotation speed is 13-18 r/min;

radiation crosslinking: carrying out radiation crosslinking on the substrate through a high-speed electronic field to obtain a master slice; the electron energy of the radiation crosslinking is 1-2MeV, and the radiation dose is 5-9 megarads;

foaming: foaming the master slice at high temperature through a foaming furnace to generate foam; in the foaming step, the master slice is foamed at high temperature through a gas-fired horizontal foaming furnace to generate foam, the temperature of the preheating section of the foaming furnace is 145-165 ℃, the temperature of the foaming section of the foaming furnace is 190-220 ℃, and the mesh belt speed is 2-4 m/min.

Example 2

Based on example 1, the difference is only that: in the embodiment 2, the material is prepared from the following raw materials in percentage by weight: 52% of low-density polyethylene, 15% of azodicarbonamide, 3% of pore-forming agent, 10% of heat-conducting powder, 10% of low-dielectric filler, 5% of compatilizer and 5% of sensitizer; the pore former is ammonium carbonate; the heat conducting powder is carbon black powder; the low dielectric filler is polyvinyl fluoride; the compatilizer is polyethylene grafted maleic anhydride; the sensitizer is zinc stearate.

Example 3

Based on example 1, the difference is only that: in example 3, the material is prepared from the following raw materials in percentage by weight: 93.7 percent of low-density polyethylene, 2 percent of azodicarbonamide, 0.3 percent of pore-opening agent, 1 percent of heat-conducting powder, 1 percent of low-dielectric filler, 1 percent of compatilizer and 1 percent of sensitizer; the pore forming agent is ammonium bicarbonate; the heat conducting powder is graphite powder; the low dielectric filler is ethylene-chlorotrifluoroethylene copolymer; the compatilizer is ethylene-vinyl acetate copolymer grafted maleic anhydride; the sensitizer is cobalt stearate.

Example 4

Based on example 1, the only differences are: in example 4, the material is prepared from the following raw materials in percentage by weight: 65% of low-density polyethylene, 11% of azodicarbonamide, 2% of pore-forming agent, 8% of heat-conducting powder, 7% of low-dielectric filler, 4% of compatilizer and 3% of sensitizer; the pore-forming agent is sodium bicarbonate and ammonium bicarbonate; the heat conducting powder is graphite powder and carbon black powder; the low dielectric filler is polyvinyl fluoride and polytetrafluoroethylene; the compatilizer is ethylene-octene copolymer grafted maleic anhydride; the sensitizer is zinc acetate and zinc stearate.

Example 5

Based on example 1, the difference is only that: in example 5, the material is prepared from the following raw materials in percentage by weight: 80% of low-density polyethylene, 3% of azodicarbonamide, 1% of pore-forming agent, 6% of heat-conducting powder, 3% of low-dielectric filler, 3% of compatilizer and 4% of sensitizer; the pore former is ammonium carbonate; the heat-conducting powder is carbon black powder; the low dielectric filler is polyvinyl fluoride and ethylene-chlorotrifluoroethylene copolymer; the compatilizer is ethylene-vinyl acetate copolymer grafted maleic anhydride; the sensitizer is barium stearate.

Example 6

Based on example 1, the difference is only that: in example 6, the material is prepared from the following raw materials in percentage by weight: 59% of low-density polyethylene, 13% of azodicarbonamide, 2% of pore-forming agent, 9% of heat-conducting powder, 9% of low-dielectric filler, 4% of compatilizer and 4% of sensitizer; the pore former is sodium bicarbonate; the heat-conducting powder is graphite powder; the low dielectric filler is polytetrafluoroethylene; the compatilizer is polyethylene grafted maleic anhydride; the sensitizer is zinc stearate.

Comparative example 1

Based on example 1, the difference is only that: in the comparative example 1, the material is prepared from the following raw materials in percentage by weight: 75% of low-density polyethylene, 8% of azodicarbonamide, 6.5% of heat-conducting powder, 5% of low-dielectric filler, 3% of compatilizer and 2.5% of sensitizer.

Comparative example 2

Based on example 1, the difference is only that: in the comparative example 1, the material is prepared from the following raw materials in percentage by weight: 75% of low-density polyethylene, 8% of azodicarbonamide, 6.5% of a pore opening agent, 5% of a low-dielectric filler, 3% of a compatilizer and 2.5% of a sensitizer.

Comparative example 3

Based on example 1, the difference is only that: in the comparative example 1, the material is prepared from the following raw materials in percentage by weight: 80% of low-density polyethylene, 8% of azodicarbonamide, 1.5% of pore-forming agent, 5% of heat-conducting powder, 3% of compatilizer and 2.5% of sensitizer.

Comparative example 4

Based on example 1, the difference is only that: in the comparative example 1, the material is prepared from the following raw materials in percentage by weight: 75% of low-density polyethylene, 8% of azodicarbonamide, 1.5% of pore-forming agent, 5% of heat-conducting powder, 5% of low-dielectric filler and 5.5% of sensitizer.

Comparative example 5

Based on example 1, the only differences are: in the comparative example 1, the material is prepared from the following raw materials in percentage by weight: 75% of low-density polyethylene, 8% of azodicarbonamide, 1.5% of pore-forming agent, 5% of heat-conducting powder, 5% of low-dielectric filler and 5.5% of compatilizer.

Comparative example 6

Based on example 1, the only differences are: in comparative example 1, the heat conductive powder was alumina.

Comparative example 7

Based on example 1, the difference is only that: in this comparative example 1, the heat conductive powder was boron nitride.

Comparative example 8

Based on example 1, the difference is only that: the low dielectric filler is silicon dioxide.

Test example

In order to verify the performance of the product of the invention, the products prepared in examples 1 to 6 and comparative examples 1 to 8 were respectively subjected to relevant performance tests, including the following specific methods:

and (3) testing the heat conductivity coefficient: testing according to GB/T10297;

and (3) testing the dielectric constant: the sample size is 100 multiplied by 3mm, the temperature is 23 ℃, and the test resonance frequency is 2.5GHz by adopting SBJDCS-A equipment, GB/T1409-2006.

And (3) testing tensile strength: tested according to ISO 527-2 standard.

The test result shows that: for the thermal conductivity coefficient, the test values are arranged from large to small as follows: example 1 > example 4 > example 2 > example 5 > example 3 > example 6 > comparative example 8 > comparative example 3 > comparative example 4 > comparative example 5 > comparative example 6 > comparative example 7 > comparative example 2 > comparative example 1, with the test value for example 6 being 1.06W/(m.K), whereas the test value for comparative example 2 is 0.2W/(m.K) and the test value for comparative example 1 is 0.1W/(m.K). The result shows that the combination of the pore forming agent and the heat conducting powder can obviously improve the heat dissipation of the foam, and obtain unexpected technical effects; at least one of graphite powder and carbon black powder is adopted as heat-conducting powder, so that the heat conductivity coefficient of the prepared radiation crosslinking polyethylene foam can be greatly improved, and the heat conductivity coefficient of the prepared radiation crosslinking polyethylene foam is obviously superior to that of other heat-conducting powder.

For the dielectric constant, the test values are arranged from large to small as follows: comparative example 3 > comparative example 8 > comparative example 1 > comparative example 2 > comparative example 6 > comparative example 7 > comparative example 4 > comparative example 5 > example 2 > example 3 > example 6 > example 4 > example 5 > example 1, with the test value for example 2 being 2.04, the test value for comparative example 3 being 4.56 and the test value for comparative example 8 being 4.05.

For tensile strength, the test values are arranged from large to small as: example 4 > example 1 > example 5 > example 2 > example 3 > example 6 > comparative example 7 > comparative example 2 > comparative example 4 > comparative example 5 > comparative example 6 > comparative example 1 > comparative example 8 > comparative example 3, with the test value for example 6 being 18MPa, the test value for comparative example 8 being 12MPa and the test value for comparative example 3 being 10 MPa.

The results show that: the fluoroplastic is used as a low dielectric filler, and the dielectric constant of the prepared radiation crosslinking polyethylene foam is obviously superior to that of other materials. And after the fluoroplastic is added, the tensile strength of the radiation crosslinking polyethylene foam can be greatly improved.

The foam in examples 1-6 and comparative examples 1, 6-8 can be foamed and molded normally, while the foam in comparative examples 2-5 can not be molded or foamed and can not retain air.

The above-mentioned embodiments only express the embodiments of the present invention, and the description is more specific and detailed, but not understood as the limitation of the patent scope of the present invention, but all the technical solutions obtained by using the equivalent substitution or the equivalent transformation should fall within the protection scope of the present invention.

Claims

1. The radiation cross-linked polyethylene foam with high heat dissipation performance is characterized by being prepared from the following raw materials in percentage by weight: 52 to 93.7 percent of low-density polyethylene, 2 to 15 percent of azodicarbonamide, 0.3 to 3 percent of pore-forming agent, 1 to 10 percent of heat-conducting powder, 1 to 10 percent of low-dielectric filler, 1 to 5 percent of compatilizer and 1 to 5 percent of sensitizer; the pore former is at least one of sodium bicarbonate, ammonium carbonate and ammonium bicarbonate; the heat conducting powder is at least one of graphite powder and carbon black powder; the low dielectric filler is fluoroplastic, and the fluoroplastic is at least one of polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoroethylene-vinylidene fluoride copolymer and fluoropolymerized perfluoroethylene propylene.

2. The radiation cross-linked polyethylene foam with high heat dissipation performance as claimed in claim 1, wherein the melting point of the low density polyethylene is 100-110 ℃, and the melt index is 1-4g/10 min; the particle size of the azodicarbonamide is 10-15nm, and the decomposition temperature is 200-220 ℃.

3. The method for preparing the radiation cross-linked polyethylene foam with high heat dissipation performance as set forth in any one of claims 1-2, characterized in that the method comprises the following steps:

radiation crosslinking: carrying out radiation crosslinking on the substrate through a high-speed electronic field to obtain a master slice;

foaming: and (3) foaming the master slice at a high temperature through a foaming furnace to generate foam.

4. The method for preparing the radiation cross-linked polyethylene foam with high heat dissipation performance as claimed in claim 3, wherein in the process of granulating the foaming agent master batch, the temperature range is 105-115 ℃, and the blending time is 8-12 min; in the process of granulating the heat-conducting powder master batch, the temperature range is 115-120 ℃, and the blending time is 10-15 min.

5. The method as claimed in claim 3, wherein the temperatures of the first zone, the second zone, the third zone, the fourth zone, the fifth zone, the sixth zone, the seventh zone, the fifth zone, the sixth zone, the seventh zone, the sixth zone, the seventh zone, the sixth zone, the seventh zone, the fifth zone, the sixth zone, the seventh zone, the sixth, the fourth, the sixth, the.

6. The method of claim 3, wherein the electron energy of the radiation cross-linking is 1-2MeV, the radiation dose is 5-9 Mrad; in the foaming step, the master slice is foamed at high temperature through a gas-fired horizontal foaming furnace to generate foam, the temperature of the preheating section of the foaming furnace is 145-165 ℃, the temperature of the foaming section of the foaming furnace is 190-220 ℃, and the mesh belt speed is 2-4 m/min.

7. Use of the high heat dissipating radiation crosslinked polyethylene foam according to any one of claims 1-2 for the production of high frequency cables.