Thermally conductive plastics refer to a type of plastic products with higher thermal conductivity, and generally their thermal conductivity is greater than 1w/(m.k).
Most metal materials have good thermal conductivity and can be used in radiators, heat exchange materials, waste heat recovery, brake pads and printed circuit boards. However, corrosion resistance of metal materials limits application in some fields, such as heat exchangers, heat pipes, solar water heaters and battery coolers in chemical production and wastewater treatment.
Corrosion resistance and mechanical properties of plastics are very good, but compared with metal materials, thermal conductivity of plastic materials is not good. Thermal conductivity of hdpe with the best thermal conductivity is only 0.44vv/(m.k).

 

Low thermal conductivity of plastic limits its scope of application. With rapid development of integration technology and assembly technology in electrical field, volume of electronic components and logic circuits has shrunk thousands of times, there is an urgent need for insulating packaging materials with high heat dissipation. However, traditional metals, metal oxides, metal nitrides and carbon-based thermal conductive materials have been unable to meet such needs, people are turning their attention to plastics with excellent comprehensive properties.
Thermal conductivity of traditional plastics is very low, thermal conductivity of different types of plastic materials can roughly follow following rules: thermal conductivity of crystalline plastics is higher than that of amorphous plastics; high-molecular-weight plastics have high thermal conductivity; orientation can increase thermal conductivity of plastics. For example, when pvc is in stretching direction of 300%, thermal conductivity is increased by 2 times; when hdpe is in stretching direction of 1000%, thermal conductivity is increased by 10 times; thermal conductivity of foam plastic is greatly reduced, generally by more than 10 times.

In matrix resin with high crystallinity, adding high thermal conductivity additives is the most effective way to improve thermal conductivity of plastics. Addition of high thermal conductivity fillers to polymers is large, which will affect mechanical properties of composite materials. The first solution is to refine thermal conductive filler, even nano-size, not only has a small impact on mechanical properties, but also improves thermal conductivity; for example, high-purity micro-mgo developed by JPN Kyowa Chemical Industry Co., Ltd. has a thermal conductivity of 36w/(m). .K) increased to 50w/(m.k). The second is to add fibrous fillers as much as possible.

Commonly used filler materials are metal powders and flakes such as aluminum, copper, tin, silver and iron, which have good thermal conductivity. Disadvantage is that it conducts heat at the same time, added amount is too large to affect performance of composite material. Among them, aluminum and copper are most used, specific examples are as follows.
① hdpe/iron powder. In hdpe resin, when 25% by volume of iron powder is added, thermal conductivity of composite material can reach 1.4w/(m.k).
②ep/copper powder. When 40% volume fraction of copper powder (50um particle size) is added to epoxy resin, thermal conductivity of composite material can reach 0.9w/(m·k).
③pp/aluminum sheet. When 18% to 22% volume fraction of aluminum sheet (40/1 aspect ratio) is filled in pp and phenolic resin, thermal conductivity is close to 80% of pure aluminum.
④PP/aluminum powder. Adding 30% aluminum powder with a particle size of 50um to pp, thermal conductivity of composite material is 3.58w/(m.k), which is 14 times that of pure pp; but the overall mechanical properties are reduced, such as tensile strength of 24mpa and impact strength of 7.3kj/m2.
⑤Epoxy resin/aluminum powder. According to epoxy resin/curing agent/aluminum powder in ratio of 100/8/34, it is cast into a product, thermal conductivity is 4.60w/(m.k), dimensional stability is good, tensile strength is 81mpa, and compressive strength is 215mpa.

Mainly copper, stainless steel, iron and other fibers, thermal conductivity is better than that of metal powder, amount of addition is less than that of metal powder, which has little effect on performance of composite materials. Disadvantage is that it conducts heat and conducts electricity at the same time, addition amount is still too large. Such as pp/copper fiber/graphite, adding copper fiber and graphite to pp, thermal conductivity of composite material can reach 8.65w/(m-k).

Mainly include carbon fiber nickel plating, carbon fiber copper plating, etc. Advantage is that proportion of added mass is greatly reduced, which affects performance of composite materials. Disadvantage is that it conducts heat at the same time.

Metal oxides include zinc oxide, copper oxide, magnesium oxide, beryllium oxide, and aluminum oxide, etc., and have advantage of conducting heat while not conducting electricity.
① ldpe/a12o3. Two kinds of a12o3 of 65um and 8um are mixed and added. When volume fraction of a12o3 reaches 70%, it is processed by melt casting method, thermal conductivity of composite material is 4.6w/(m.k). 
②Silicone rubber/a12o3 When amount of a12o3 is 3 times that of silicone rubber, thermal conductivity of composite material is 2.72w/(m·k).

Main varieties are aluminum nitride, silicon nitride, and boron nitride (bn, etc.), which are emerging heat-conducting materials. Advantage is that they conduct heat at the same time, but disadvantage is that they are expensive.
①Epoxy/a1n. Novolac epoxy resin is used for epoxy resin. When volume fraction of ain is 70%, thermal conductivity of composite material is 14w/(m·k), dielectric constant is very low, linear expansion coefficient is small, which can be used as electronic packaging materials.
②Phenolic resin/ain. When volume fraction of ain reaches 78.5%, thermal conductivity of composite material is 32.5w/(m.k), which can be used for electronic packaging materials.
③pe/ain When volume fraction of ain reaches 30.2%, thermal conductivity of composite material is 2.44w/(m.k).
④ uhmwpe/ain. By adding 30.2% ain fiber to uhmwpe resin, thermal conductivity of composite material can reach 2.44w/(m.k).
⑤ep/ceramic. In epoxy resin, add 30: volume fraction of ceramic (ba-tio3, si, sic, stio2, tio2, zno), and add 0.3% doped metal (ai, cr, li, ti), etc., thermal conductivity of composite material is 2.06w/(m,k).
⑥bn/pb (polybenzoxazine). When content of bn is 88%, conductivity of composite is 32.5w/(m.k). Moreover, bn has high insulation and is an ideal thermally conductive electronic packaging material. Advanced Ceramics and Epic have developed packaging materials with a thermal conductivity of 20～35w/(m.k), which can be compression molded and have been used in electronic packaging, integrated circuit board electronic control components, etc.
⑦ain/pvdf. 7um a1n particles and whiskers are mixed in a ratio of 25/1, and when the total added amount reaches 60% volume fraction, thermal conductivity is 11. 5w/(m.k).
⑧a1n/pf. When addition of ain reaches 78.5% volume fraction, thermal conductivity is 32.5w/(m.k).

There are mainly silicon carbide, etc., which are emerging heat-conducting materials. Advantage is that it conducts heat at the same time, but disadvantage is that it is expensive.

Mainly include silicon and boron.

Specific varieties are carbon black, carbon fiber, graphite, and carbon nanotubes, which conduct heat and conduct electricity at the same time.
By adding carbon fiber, thermal conductivity of composite material can reach 10w/(m.k). Surface treatment of graphite with titanate coupling agent ndz101 can obtain ldpe/graphite composite materials with good thermal conductivity, electrical conductivity and mechanical properties.
① hdpe/graphite When volume fraction of graphite reaches 20%, thermal conductivity is 1.53w/(m·k). When mass fraction of graphite reaches 40%, thermal conductivity is 11.6-23.0w/(m.k), and tensile strength is 40-60mpa. When mass fraction of graphite 60 reaches 50%, thermal conductivity is 47.4w/(m·k).
②Epoxy resin/natural phosphor flake graphite. When mass fraction of natural phosphor flake graphite reaches 60%, thermal conductivity of composite material is 10w/(m.k), which is about 50 times higher than pure ep.
③cf/ep. When content of cf reaches 56%, thermal conductivity is 695w/(m.k) and relative density is 1.48.
④ldpe/graphite. In ldpe resin, adding 25% of volume fraction of graphite, mixing powder, thermal conductivity can reach 2w/(m.k).
⑤PP powder. Using pp powder (brand name 1 300 or 1 330), melt flow index is not more than lg/l0min, adding 75um flake graphite 30%, thermal conductivity of composite material can reach 2.4w/(m.k).
⑥cpvc/graphite. In cpvc [thermal conductivity of 0.166w/(m.k) resin, with increase of amount of graphite added, its thermal conductivity changes. When 50% graphite is added, thermal conductivity can reach 3.2w/(m.k), which is increased by as much as 20 times.

Mainly include barium sulfate, lead sulfide and mica. For example, pp/mica, although thermal conductivity of mica is not high, ability to form an interconnection network in plastics is much higher than that of copper powder, so thermal conductivity of pp/copper powder is 1.25w/ (m.k), and thermal conductivity of pp/mica is 2.5w/(m.k).

Commonly used thermally conductive polymers include polyacetylene, polyaniline, polypyrrole, polythiophene and other polymers with excellent electrical conductivity. Its advantages are good overall performance and low relative density; its disadvantages are high price.