阅读说明：本技术 一种高填充高导热聚丙烯复合材料及其制备方法 (High-filling high-thermal-conductivity polypropylene composite material and preparation method thereof ) 是由 李勇进 曹欢 顾森林 于 2020-08-05 设计创作，主要内容包括：本发明公开一种高填充高导热聚丙烯复合材料及其制备方法,包括聚丙烯、层状碳系填料、球状填料；球状填料为导热系数远低于层状碳系填料的无机氧化物。本发明在不加入增容剂的情况下,利用一定量的导热系数较低的无机氧化物球状填料改变石墨在聚丙烯基体中的取向,从而大幅度提升聚丙烯复合材料的导热率。本发明仅需使用常用的熔融混炼设备,工业制备简单,且在在提高材料导热率的同时,能够大幅度的降低材料的制备成本。(The invention discloses a high-filling high-thermal conductivity polypropylene composite material and a preparation method thereof, wherein the high-filling high-thermal conductivity polypropylene composite material comprises polypropylene, layered carbon fillers and spherical fillers; the spherical filler is an inorganic oxide having a thermal conductivity much lower than that of the layered carbon-based filler. According to the invention, under the condition of not adding a compatibilizer, a certain amount of inorganic oxide spherical filler with a low thermal conductivity coefficient is used for changing the orientation of graphite in a polypropylene matrix, so that the thermal conductivity of the polypropylene composite material is greatly improved. The invention only needs common melting mixing equipment, has simple industrial preparation, and can greatly reduce the preparation cost of the material while improving the thermal conductivity of the material.)

1. A high heat conduction polypropylene composite material is a blend and is characterized by comprising polypropylene, layered carbon fillers and spherical fillers;

the spherical filler is an inorganic oxide with a thermal conductivity coefficient lower than that of the layered carbon filler;

the layered carbon filler and the spherical filler account for 30-70 wt% of the total filling amount of the polypropylene composite material, and the spherical filler accounts for 2.5-10 wt% of the mass content of the polypropylene composite material.

2. The polypropylene composite material of claim 1, wherein the layered carbon-based filler is one or both of flake graphite and graphene.

3. The polypropylene composite material as claimed in claim 2, wherein the flake graphite has a mesh size of 500-800 mesh.

4. A highly thermally conductive polypropylene composite material according to claim 1, wherein the thermal conductivity is much lower than that of the inorganic oxide of the layered carbon-based filler, specifically one or more of alumina, calcium carbonate, and magnesium oxide.

5. The polypropylene composite material as claimed in claim 5, wherein the spherical filler is alumina with a particle size of 5-20 μm.

6. The polypropylene composite material of claim 1, wherein the spherical filler accounts for 2.5 wt% to 5 wt% of the polypropylene composite material.

7. The method for preparing the highly filled and highly heat conductive polypropylene composite material sheet as claimed in any one of claims 1 to 6, wherein the dried polypropylene, flake graphite and spherical filler are added into a melt-kneading device for melt-kneading to obtain a blend; discharging the blend from the melting and mixing equipment, and cooling to normal temperature to obtain the polypropylene composite material; and carrying out fusion tabletting on the composite material to obtain a thin sheet with a certain thickness.

8. The method according to claim 7, wherein the melt-kneading temperature is 180 to 230 ℃; the melting and mixing equipment is an internal mixer, the rotor speed of the internal mixer is 10-30 rpm/min during premixing, the melting and mixing time is 1-3 min, then the rotor speed is increased to 45-75 rpm/min, and the melting and mixing time is 5-10 min.

9. The process according to claim 7 or 8, wherein the melt-tabletting conditions are: keeping the pressure at 5-30 MPa and 190-230 ℃ for 3-10 min; then cold pressing is carried out, and the conditions are as follows: keeping the pressure at 5-30 MPa and room temperature for 1-5 min.

10. A plastic product, which is made of the highly filled and highly heat conductive polypropylene composite material as claimed in any one of claims 1 to 6.

Technical Field

The invention belongs to the field of high polymer materials, and particularly relates to a high-filling high-thermal-conductivity polypropylene composite material obtained by hybridization of spherical and lamellar thermal-conductivity fillers and a preparation method thereof.

Background

Heat conductive materials are widely used in heat conduction engineering, heat supply engineering, and electronic information engineering. For a long time, metal materials have been widely used in non-insulated fields due to their excellent thermal conductivity. However, the metal heat conduction material is not corrosion-resistant, has heavy material quality, can consume a large amount of energy in the processing process, has high cost, and does not meet the requirement of environmental protection. Meanwhile, the increasing demand of the basic materials for the high-speed development of national economy and science and technology cannot be met. Compared with metal materials, the high polymer material has the advantages of light weight, corrosion resistance, easy molding and processing and the like which cannot be achieved by the metal materials.

Polypropylene (PP) is a colorless, translucent, thermoplastic, lightweight, general-purpose plastic as a thermoplastic synthetic resin with excellent properties, and is widely used in many fields such as electronics, automobiles, electronic devices, packaging, and food industries. The polypropylene has excellent chemical resistance, and almost has no damage effect up to 120 ℃ except for a strong oxidizing material. It is insoluble in any solvent at room temperature, and can be used as medium of general alkane, phenol, aldehyde and ketone, so that it is specially applicable to heat-exchange equipment and container for various purposes in the fields of chemical industry, pharmaceutical industry, dyeing industry, metallurgical industry, environmental protection industry and chemical fibre industry, and can be substituted for original equipment of stainless steel, enamel, carbon steel and glass, etc. However, pure polypropylene has a thermal conductivity of only about 0.24W/(m × K), which limits its application in heat-conductive materials and the like. Therefore, the development of the polypropylene composite material with good heat conductivity has very practical application value. Carbon-based fillers are often used as heat conductive fillers because of their high thermal conductivity, but their different aspect ratios, planar orientation, etc. have a large effect on the properties of composite materials, making them unable to exhibit excellent properties in composite materials. Single-dimensional fillers tend to form a single planar orientation during processing, thereby increasing the anisotropy of the thermal conductivity of the material. For example, the flake graphite has a lamellar structure which has a large contact area with a polymer matrix, and therefore can be used as a filler to exert good heat-conducting performance. Flake graphite is a commonly used heat-conducting filler, which can transfer heat through internal electrons and phonons, and the asymmetric flake structure of the flake graphite can easily form a heat-conducting network in a matrix. However, due to the strong van der waals force and pi-pi interaction between graphite sheets, the graphite sheets are easy to agglomerate and stack, and the degree of plane orientation is high, which is not favorable for fully utilizing the high thermal conductivity. At present, the multi-dimensional filler is widely applied to improving various properties of polymers, and the addition of the multi-dimensional filler can generate a synergistic effect among the fillers, so that the comprehensive properties of the composite material can be further improved.

There have been many studies on the improvement of the thermal conductivity of polymers. Aiming at the heat-conducting property of the polymer, the poplar, the like, prepares the epoxy resin/multilayer flaky graphene/multi-walled carbon nanotube ternary composite material by a solution blending method. A three-dimensional network filler system is constructed by utilizing a two-dimensional structure of multilayer flaky graphene and a one-dimensional structure of multi-walled carbon nanotubes (MWCNTs), so that the heat conductivity of the composite material is improved. Friedel et al prepared the ternary composite material of high density polyethylene/expandable graphite/multi-walled carbon nanotube by a melt blending method. Also, a filler system with a network-network synergistic effect is obtained by combining two dimensions and one dimension, and a method for improving the thermal conductivity of the composite material is provided. Regarding the thermal conductivity of polypropylene, poplar et al prepared a PP/graphite composite material with a three-dimensional isolation structure, and when the graphite filling content was 21.2 vol%, the thermal conductivity of the composite material was significantly increased to 5.4W/(m × K). Such a large increase in thermal conductivity is attributed to the graphite flakes having large particle orientation around the PP resin particles and forming a perfect thermal conductive network. Muratov et al filled hexagonal boron nitride particles (BN) into polypropylene to increase the thermal conductivity of polypropylene composites. And the silane coupling agent is used for pretreating the surface of the filler, so that the heat-conducting property of the h-BN/PP composite material can be further improved. Others have established one-dimensional/two-dimensional filler networks by simultaneously introducing multiwalled carbon nanotubes and BN into the PP to increase the thermal conductivity of the composite.

The group has investigated the addition of flake and spherical graphite, which have relatively high thermal conductivity, to polypropylene to improve the thermal conductivity of composites. The flaky graphite mainly has the function of improving the heat conductivity coefficient of the composite material, and the spherical graphite plays a role in regulating and controlling the orientation of the flaky graphite, so that gaps in the arrangement process of the flaky graphite can be effectively stacked. In the present invention, spherical filler is added into the polypropylene/flake graphite composite material to change the graphite orientation. Different from the original situation, the spherical graphite is used as the oval filler, so that more gaps existing in the stacked flake graphite are played in the matrix, and the vertical heat conduction of the composite material is further improved. In the invention, the orientation of the flake graphite is changed by selecting the spherical filler, so that the system filler presents a compact stacking structure, thereby fully utilizing the high heat conduction of the flake graphite in the direction of the flake layer and further improving the heat conductivity of the composite material. In addition, spheroidal graphite, which is a graphite having a structure different from flake graphite, has a high thermal conductivity by itself. In the present system, the thermal conductivity is selected to be relatively only 20-30W/mK, which is much smaller than that of spherical graphite (about 1500W/mK in the lamellar direction and about 150W/mK in the perpendicular direction). But still has great improvement on the heat conduction change in the composite material.

Disclosure of Invention

One object of the present invention is to provide a new concept of adding a filler with a much lower thermal conductivity than another filler and a relatively higher density to a hybrid filler system, which can greatly improve the thermal conductivity of the composite material when added in a small amount. Therefore, a stacking and lapping structure is provided, and the structure has important application significance in improving the thermal conductivity of the polymer matrix composite material. In the invention, the high-filling high-thermal-conductivity polypropylene composite material is prepared.

The purpose of the invention is realized by the following technical scheme:

a high heat conduction polypropylene composite material is a blend, which comprises polypropylene, layered carbon series filler and spherical filler;

the layered carbon filler is one or two of flake graphite and graphene.

The spherical filler is an inorganic oxide with a thermal conductivity far lower than that of the layered carbon filler.

Preferably, the layered carbon-based filler and the spherical filler account for 30-70 wt% of the total filling amount of the polypropylene composite material.

Preferably, the mesh number of the flake graphite is 500-800 meshes.

Preferably, the thermal conductivity is much lower than that of the inorganic oxide of the layered carbon-based filler, specifically, one or more of alumina, calcium carbonate and magnesium oxide. More preferably, the spherical filler is alumina, and the particle size of the spherical filler is 5-20 μm;

in the above technical solution, the spherical filler preferably accounts for 2.5 wt% to 10 wt%, preferably 2.5 wt% to 5 wt%, of the polypropylene composite material.

The invention also aims to provide a preparation method of the high-filling high-thermal conductivity polypropylene composite material sheet, which comprises the following steps;

step (1): vacuum drying the polypropylene, the flake graphite and the spherical filler at 80 ℃ for 12-24 h;

step (2): adding the dried polypropylene, the flake graphite and the spherical filler into a melt mixing device for melt mixing at 180-230 ℃ to obtain a blend;

and (3): discharging the blend from the melting and mixing equipment, and cooling to normal temperature to obtain the polypropylene composite material.

And (4): carrying out melt tabletting on the composite material, wherein the tabletting conditions are as follows: keeping the pressure at 5-30 MPa and 190-230 ℃ for 3-10 min; then cold pressing is carried out, and the conditions are as follows: keeping the pressure at the room temperature at 5-30 MPa for 1-5 min to obtain a sheet with the thickness of 100-1000 μm.

Preferably, the melt-kneading equipment in the step (2) is an internal mixer, the rotor speed of the internal mixer is 10-30 rpm/min during premixing, the melt-kneading time is 1-3 min, then the rotor speed is increased to 45-75 rpm/min, and the melt-kneading time is 5-10 min.

It is still another object of the present invention to provide a plastic article using the above highly filled highly thermally conductive polypropylene composite.

The invention has the beneficial effects that:

the polypropylene composite material sheet prepared by the invention has excellent vertical heat-conducting property. According to the invention, under the condition of not adding a compatibilizer, a certain amount of inorganic oxide spherical filler with a low thermal conductivity coefficient is used for changing the orientation of graphite in a polypropylene matrix, so that the thermal conductivity of the polypropylene composite material is greatly improved. The invention only needs common melting mixing equipment, has simple industrial preparation, and can greatly reduce the preparation cost of the material while improving the thermal conductivity of the material.

Drawings

FIGS. 1(a) - (b) are the quenched cross-sectional morphologies of the composite sheets prepared in comparative example 1 and example 3, respectively.

FIGS. 2(a) - (b) are the quenched cross-sectional morphologies of the composite sheets prepared in comparative example 2 and example 6, respectively.

FIG. 3 is a graph showing the vertical thermal conductivity and mechanical properties of the composite materials prepared in comparative examples 2,5 to 6 and examples 4 to 6.

FIGS. 4(a) - (b) are the quenched cross-sectional morphologies of the composite sheets obtained in example 5 and comparative example 7, respectively.

Detailed Description

In order to enhance the understanding of the present invention, the present invention will be further described in detail with reference to the following examples, which are provided for illustration only and are not intended to limit the scope of the present invention.

Comparative example 1: 70 w% of filler and no alumina

Step (1): vacuum drying polypropylene and flake graphite at 80 deg.C for 24 hr;

step (2): adding 15g of polypropylene and 35g of flake graphite into an internal mixer for melting and mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melting and mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melting and mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.

Comparative example 2: 50 w% of filler and no alumina

Step (1): vacuum drying polypropylene and flake graphite at 80 deg.C for 24 hr;

step (2): adding 25g of polypropylene and 25g of flake graphite into an internal mixer for melting and mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melting and mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melting and mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.

Comparative example 3: 70 w% of filler, wherein the alumina is 15 w%

Step (1): vacuum drying polypropylene, flake graphite and 20 μm spherical alumina at 80 deg.C for 24 hr;

step (2): adding 15g of polypropylene, 27.5g of flake graphite and 7.5g of spherical alumina into an internal mixer for melt mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melt mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melt mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.

Comparative example 4: 70 w% of filler, wherein the alumina is 20 w%

Step (1): vacuum drying polypropylene, flake graphite and 20 μm spherical alumina at 80 deg.C for 24 hr;

step (2): adding 15g of polypropylene, 25g of flake graphite and 10g of spherical alumina into an internal mixer for melting and mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melting and mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melting and mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.

Comparative example 5: 50 w% of filler, wherein the alumina is 15 w%

Step (1): vacuum drying polypropylene, flake graphite and 20 μm spherical alumina at 80 deg.C for 24 hr;

step (2): adding 25g of polypropylene, 17.5g of flake graphite and 7.5g of spherical alumina into an internal mixer for melt mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melt mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melt mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.

Comparative example 6: 50 w% of filler, wherein 20 w% of alumina

Step (1): vacuum drying polypropylene, flake graphite and 20 μm spherical alumina at 80 deg.C for 24 hr;

step (2): adding 25g of polypropylene, 15g of flake graphite and 10g of spherical alumina into an internal mixer for melting and mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melting and mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melting and mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.

Comparative example 7: 50 w% of filler, wherein the filler is carbon material, and 5 w% of spherical graphite

Step (1): vacuum drying polypropylene, flake graphite and 20 μm spherical graphite at 80 deg.C for 24 hr;

step (2): adding 25g of polypropylene, 22.5g of flake graphite and 2.5g of spherical graphite into an internal mixer for melt mixing at 190 ℃, wherein the rotor speed of the internal mixer is 20rpm/min during premixing, the melt mixing is carried out for 2min, then the rotor speed is increased to 50rpm/min, and the melt mixing is carried out for 5min, so as to obtain a blend;

and (3) performing melt tabletting on the obtained blend, wherein the tabletting conditions are as follows: maintaining the pressure at 20MPa and 200 ℃ for 5 min; then, the pressure was maintained at 20MPa for 4min at room temperature to prepare a sheet having a thickness of 500. mu.m.