Low-dielectric and high-thermal-conductivity polymer-based composite material and preparation method thereof
Technical Field
The invention belongs to the technical field of preparation of heat-conducting composite materials, and relates to a low-dielectric and high-heat-conducting polymer-based composite material and a preparation method thereof.
Background
With the rapid development of science and technology and the progress of society, the requirements of human beings on communication technology are higher and higher, and 5G communication technology with high transmission rate (>1Gpbs) and low delay time (<1ms) is produced. Compared with the 4G communication technology, the 5G communication technology has the characteristics of higher transmission rate, wider coverage range and more connections, and the advantages of the 5G communication technology are derived from higher integration degree and higher power consumption. For example, the volume of a 5G device is only about 30% of 4G, but the power consumption is more than 3 times of 4G, and the heat density of the 5G device is more than 10 times of 4G, so that the operating temperature of the 5G communication device is higher, and the thermal runaway is more likely to occur. Therefore, the heat dissipation problem of the 5G device needs to be solved urgently. In devices such as mobile phones, metal or graphite-based heat conducting materials are often used to solve the heat dissipation problem, but cannot be used in 5G devices due to their high dielectric constant. Therefore, the development of a high thermal conductive polymer composite having a low dielectric constant, a high thermal conductivity, and excellent insulating properties is urgently required.
Among various types of heat-conducting fillers (alumina, aluminum nitride, silicon dioxide, boron nitride and the like), hexagonal boron nitride has a unique two-dimensional structure, and has the advantages of low dielectric constant (4.0), high heat conductivity (300W/m.K) and excellent insulating property (volume resistivity)>1015Omega cm) is considered as an ideal filler for preparing insulating high-heat-conductivity composite materialsAnd (5) feeding. The prior art discloses application number 201910297116.9, which is named as a manufacturing process of a novel polyurethane high-thermal-conductivity insulating sheet; application No. 201911314925.2, entitled a high thermal conductivity composite material and its preparation and use; in the prior art, boron nitride is used as a heat conducting filler, but the heat conductivity of the boron nitride is lower than 10W/m.K, so that the requirement of 5G equipment on high heat conductivity cannot be met.
Disclosure of Invention
The invention aims to solve the problem of low thermal conductivity in the prior art and provides a low-dielectric and high-thermal-conductivity polymer composite material and a preparation method thereof. The polymer composite material prepared by the invention has excellent thermal conductivity, insulating property and good mechanical property.
In order to achieve the purpose, the technical scheme of the invention is as follows:
in a first aspect, the present invention provides a low dielectric, high thermal conductivity polymer composite comprised of a thermally conductive filler, a crosslinking agent, and a polymer matrix; the heat-conducting filler is hexagonal boron nitride powder; the crosslinking agent is at least one of dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, dicumyl hydroperoxide, vinyl trimethoxy silane, a polyethylenimine crosslinking agent and triallyl isocyanurate; the polymer matrix is thermoplastic polyurethane.
As an embodiment of the invention, the thermoplastic polyurethane matrix is a polyether or polyester polyurethane.
According to one embodiment of the invention, the addition amount of the heat-conducting filler in the composite material is 40-89 wt%. Preferably 70 to 80 wt%.
As an embodiment of the invention, the addition amount of the polymer matrix in the composite material is 10-60 wt%. Preferably 20 to 30 wt%.
As an embodiment of the invention, the addition amount of the cross-linking agent in the composite material is 1-4 wt%.
In one embodiment of the invention, the size of the hexagonal boron nitride is 11-100 μm. When the size is too small, the heat conduction effect is poor, and when the size is too large, the particles are easy to agglomerate and are not uniformly dispersed. It may be preferably 30 μm.
During preparation, hexagonal boron nitride powder, a cross-linking agent and thermoplastic polyurethane are mixed in an organic solvent, a wet film is obtained in a solution coating mode, a semi-finished film is obtained after drying, and then the low-dielectric and high-thermal-conductivity polymer composite material is obtained through hot pressing treatment. According to the invention, the high-thermal-conductivity composite materials with different thicknesses can be obtained by controlling the thickness of the wet film according to actual use requirements, and the thickness can be 10-1000 μm.
In a second aspect, the present invention relates to a method for preparing a low dielectric, high thermal conductivity polymer composite, the method comprising the steps of:
s1, blending the heat-conducting filler, the cross-linking agent and the organic solvent;
s2, adding a polymer matrix into the mixed solution obtained in the step S1, and blending;
s3, coating the mixed liquid obtained in the step S2 on the surface of a base material, and drying to obtain a semi-finished film;
and S4, cutting the semi-finished film, and sequentially carrying out hot pressing and cold pressing to obtain the finished film.
As an embodiment of the present invention, in step S1, the organic solvent is selected from: one of N, N-dimethylformamide, N-dimethylacetamide and N, N-diethylformamide.
In one embodiment of the present invention, in step S1, the blending is mechanical stirring blending, the stirring time is 0.5 to 5 hours (preferably 1 hour), and the stirring speed is 1000 to 2000rpm/min (preferably 1500 rpm/min).
In one embodiment of the present invention, in step S2, the blending is mechanical stirring blending, the stirring time is 1 to 24 hours (preferably 2 hours), and the stirring speed is 1000 to 2000rpm/min (preferably 1500 rpm/min).
As an embodiment of the present invention, in step S3, the substrate is PET or PI.
In an embodiment of the present invention, in step S3, the drying temperature is 100 to 180 ℃ and the drying time is 10 to 60 min.
In step S3, a coating machine is used to coat the mixed solution obtained in step S2 on the surface of the substrate, and the substrate is dried at 130-150 ℃ for 20-30 min to obtain a semi-finished heat-conducting film.
In step S4, the semi-finished heat conductive film obtained in step S3 is cut and then hot-pressed by a press vulcanizer.
In one embodiment of the present invention, in step S4, the hot pressing temperature is 160 to 240 ℃ (preferably 180 to 200 ℃), the hot pressing time is 1 to 10min (preferably 2 to 4min), the hot pressing pressure is 10 to 30MPa (preferably 15 to 20MPa), and a PTFE film with a thickness of 0.5 to 10mm (preferably 1 to 3mm) is arranged between the substrate and the hot pressing plate during the hot pressing.
According to one embodiment of the invention, the cold pressing temperature is 5-25 ℃, the cold pressing pressure is 1-10 MPa, preferably 5-7 MPa, and the cold pressing time is 1-5 min, preferably 2-3 min.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention has low dielectric constant (3.7, 1MHz), high thermal conductivity (40W/m.K) and excellent insulating property (resistivity)>1013Omega cm, the breakdown strength is 116MV/m), can be used for the heat management of 5G communication equipment, does not influence the transmission of 5G signals, and can be used as a thermal interface material for the purposes of heat dissipation, heat soaking and the like of various electronic devices.
2. The heat-conducting composite material disclosed by the invention is simple in preparation process, economical and practical, and can be used for large-scale industrial production.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a microscopic topography of the prepared thermally conductive composite; wherein, FIG. 1a is a surface topography of the heat-conducting composite material, FIG. 1b is a cross-sectional topography of the heat-conducting composite material, and the addition amount of boron nitride is 80 wt%;
FIG. 2 is an electrical property of a thermally conductive composite containing 80 wt% BN: wherein, fig. 2a is the variation of the dielectric constant of the heat-conducting composite material with frequency, fig. 2b is the variation of the electrical conductivity (resistivity) of the heat-conducting composite material with frequency, and fig. 2c is the statistical result of Weibull breakdown strength of the heat-conducting composite material;
FIG. 3 is the thermal conductivity of a thermally conductive composite containing 80 wt% BN.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The test sample of the present invention was molded by hot pressing and cold pressing in sequence in a flat vulcanizing machine (XH-407C, Xihua detection Instrument Co., Ltd.) and a flat vulcanizing machine (YX-25 type, Shanghai Simma Weili rubber machinery Co., Ltd.).
The dispersibility of the filler in the composite material prepared by the present invention was observed by a field emission Scanning Electron Microscope (SEM) (Nova NanoSEM 450 type, FEI corporation, usa).
The dielectric properties of the samples prepared according to the invention were determined using a broadband dielectric spectrometer (GmbH Concept 40, Novocontrol, germany).
The breakdown strength of the sample prepared by the invention is measured by using a direct current high voltage generator (Shanghai Jia extra high voltage electrical equipment Co., Ltd.).
The heat conductivity of the sample prepared by the invention is measured by a laser heat conduction instrument (LFA 467HT HyperFlash @, NanoFlash, Netzsch).
Example 1
The embodiment relates to a low dielectric and high thermal conductivity polymer composite material and a preparation method thereof, wherein the composite material is prepared from 78 wt% of boron nitride (with the average particle size of 30 microns), 20 wt% of a polyurethane matrix and 2 wt% of dicumyl peroxide, and is prepared by the following steps:
step 1, adding 96g of boron nitride, 2.4g of dicumyl peroxide and 240mL of N, N-diethylformamide into a 1L stirring container, and stirring at the rotating speed of 1500rpm for 1 hour at normal temperature;
step 2, adding 24g of polyurethane (BASF 1185A10) into the mixed solution obtained in the step 1, and stirring at the rotating speed of 1500rpm/min at normal temperature for 2 hours to obtain a uniformly mixed solution;
step 3, coating the solution obtained in the step 2 on the surface of PET by using a coating machine, and drying for 30min at the temperature of 150 ℃ to obtain a semi-finished film;
and 4, cutting the semi-finished film, preheating the cut semi-finished film for 2min in a flat vulcanizing machine at the temperature of 200 ℃, then hot-pressing the cut semi-finished film for 5min under the pressure of 15MPa (a PTFE film with the thickness of 2mm is adopted between the base material and the hot plate), then placing the cut semi-finished film in a flat vulcanizing machine at the temperature of 20 ℃, keeping the cut semi-finished film for 2min under the pressure of 5MPa, and then taking down the sample.
The implementation effect is as follows: as shown in fig. 1, the low dielectric and high thermal conductivity polymer composite material prepared in this embodiment has a dense microstructure, and boron nitride is connected inside the composite material and arranged along the film direction. As shown in FIG. 2, the composite material had a low dielectric constant (3.7, 1MHz) and excellent insulating properties (resistivity)>1013Ω · cm, breakdown strength 116 MV/m). Meanwhile, as shown in FIG. 3, the thermal conductivity of the composite material was over 40W/m.K in all of the 5 tests, and the average value was 41.3W/m.K.
Example 2
This example relates to a low dielectric, high thermal conductivity polymer composite and a method of making the same, the composite being made from 78 wt% boron nitride (average particle size 31 μm) and 20 wt% polyurethane matrix (hensmyl 5836P) and 1 wt% dicumyl hydroperoxide and 1 wt% triallyl isocyanurate. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the invention prepares a polymer composite material with low dielectric constant and high thermal conductivity, wherein the dielectric constant of the composite material is 3.8(1MHz), and the thermal conductivity is 40W/m.K.
Example 3
This example relates to a low dielectric, high thermal conductivity polymer composite and a method of making the same, the composite being made from 78 wt% boron nitride (average particle size of 21 μm) and 20 wt% polyurethane matrix (feldt 3021) and 2 wt% of 1 wt% di-t-butyl peroxide and 1 wt% vinyltrimethoxysilane. The preparation procedure was the same as in example 1.
The implementation effect is as follows: this example prepares a low dielectric, high thermal conductivity polymer composite, the composite having a dielectric constant of 3.9(1MHz) and a thermal conductivity of 36W/m · K.
Example 4
The present embodiment relates to a low dielectric and high thermal conductive polymer composite material and a method for preparing the same, wherein the composite material is prepared from 78 wt% of boron nitride (with an average particle size of 100 μm), 20 wt% of polyurethane matrix (basf 1185A10) and 2 wt% of benzoyl peroxide. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the invention prepares a polymer composite material with low dielectric constant and high thermal conductivity, wherein the dielectric constant of the composite material is 3.6(1MHz), and the thermal conductivity is 32W/m.K.
Example 5
The embodiment relates to a low dielectric and high thermal conductivity polymer composite material and a preparation method thereof, wherein the composite material is prepared from 78 wt% of boron nitride (the average particle size is 100 mu m), 20 wt% of a polyurethane matrix (Phillips 3021), 1 wt% of di-tert-butyl peroxide and 1 wt% of a polyethylenimine crosslinking agent. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the invention prepares a polymer composite material with low dielectric constant and high thermal conductivity, wherein the dielectric constant of the composite material is 3.8(1MHz), and the thermal conductivity of the composite material is 31.6W/m.K.
Comparative example 1
The present comparative example relates to a highly thermally conductive polymer composite material prepared from 78 wt% boron nitride (average particle size of 30 μm), 20 wt% polyurethane matrix (basf 1185a10) and 2 wt% polyethylene glycol, and a method for preparing the same. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the composite material had a dielectric constant of 5.2(1MHz) and a thermal conductivity of 22W/m.K.
Comparative example 2
The present comparative example relates to a highly thermally conductive polymer composite material prepared from 78 wt% boron nitride (average particle size of 5 μm), 20 wt% polyurethane matrix (basf 1185a10) and 2 wt% dicumyl peroxide, and a method for preparing the same. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the thermal conductivity of the composite material is 15W/m.K.
Comparative example 3
The present comparative example relates to a highly thermally conductive polymer composite material prepared from 78 wt% boron nitride (average particle size 150 μm) and 20 wt% polyurethane matrix (basf 1185a10) and 2 wt% benzoyl peroxide, and a method for preparing the same. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the thermal conductivity of the composite material is 12W/m.K.
Comparative example 4
The present comparative example relates to a highly thermally conductive polymer composite material prepared from 78 wt% boron nitride (average particle size of 30 μm) and 20 wt% polyurethane matrix (basf 1185a10) and 2 wt% diallyl phthalate, and a method for preparing the same. The preparation procedure was the same as in example 1.
The implementation effect is as follows: the composite material had a dielectric constant of 4.6(1MHz) and a thermal conductivity of 20W/m.K.
Comparative example 5
The present comparative example relates to a polymer composite and a method for preparing the same, the composite being prepared from 80 wt% boron nitride (average particle size of 6 μm) and 20 wt% polyurethane matrix, prepared by the steps of:
step 1, adding 96g of boron nitride and 240mL of N, N-diethylformamide into a 1L stirring container, and stirring at the rotating speed of 1500rpm for 1 hour at normal temperature;
step 2, adding 24g of polyurethane (BASF 1185A10) into the mixed solution obtained in the step 1, and stirring at the rotating speed of 1500rpm/min at normal temperature for 2 hours to obtain a uniformly mixed solution;
step 3, coating the solution obtained in the step 2 on the surface of PET by using a coating machine, and drying for 30min at the temperature of 150 ℃ to obtain a semi-finished film;
and 4, cutting the semi-finished film, placing the cut semi-finished film in a vulcanizing press at 200 ℃, preheating for 2min, then hot-pressing for 5min under the pressure of 15MPa (the substrate is in direct contact with a hot plate), then placing the film in a vulcanizing press at 20 ℃, keeping the film for 2min under the pressure of 5MPa, and then taking down the sample.
The implementation effect is as follows: the thermal conductivity of the composite material was 21.8W/m.K.
The above-mentioned embodiments only express some embodiments of the present invention, and the description thereof is more detailed, and therefore, the present invention should not be construed as limiting the scope of the present invention. It is understood that any modifications of the invention, equivalent substitutions of the raw materials of the product of the invention and the addition of auxiliary components, selection of specific modes and the like, by those skilled in the art, are within the scope and disclosure of the invention.