Research and Application of Thermal Polymer Materials

The research progress of various high thermal conductivity fillers and their application in thermal conductive polymer materials. Finally, the research direction of thermal conductive polymer materials is proposed.

(3):1999-The conventional thermal conductive materials are mostly metals such as AgCuAl and metal oxides such as Al23MgOBeO and other non-metallic materials such as graphite carbon black S3. The thermal conductivity of A1N materials is shown in Tab. 1. It is also reported that conductive organic materials include poly Acetylene, polyphenylene sulfide, polythiophene, etc. also have good thermal conductivity. The use of conductive organic materials as fillers can improve the material's compatibility, processability and thermal conductivity, and can reduce the density of the materials, and the conductive organic substances in the In the case of impurities, it will become an insulator. | With the development of industrial production and science and technology, people have put forward new requirements for thermally conductive materials. It is hoped that the materials have excellent comprehensive properties such as those used in chemical production and wastewater treatment. Heat exchangers require both the thermal conductivity of the materials used and their chemical resistance and high temperature resistance. In the field of electrical and electronics, due to the rapid development of integration technology and assembly technology, the volume of electronic components and logic circuits has shrunk thousands of times, and high heat-dissipating thermal insulating materials are required.

In recent decades, the field of application of polymer materials has been continuously expanding. The use of synthetic polymer materials instead of various materials used in traditional industries, especially metal materials, has become one of the directions of scientific research efforts in the world. Since polymer materials are mostly poor thermal conductors (see Tab. 2), in order to produce thermally conductive materials with excellent overall properties, high-thermal-conductivity metals or inorganic fillers are generally used to fill the polymer materials. The heat-conducting material thus obtained is inexpensive and easy to process and shape, and can be applied to certain special fields after appropriate process treatment or formulation adjustment. 1 Heat-conduction mechanism The heat-conduction mechanism of various materials is different. The thermal conduction mechanism of the crystal is the thermal vibration of the aligned crystal grains. Usually the concept of phonons is used to describe the movement of free electrons plays a major role in the conduction of heat. The contribution made by phonons can be neglected in most cases.

Amorphous heat transfer mechanism relies on randomly arranged molecules or atoms, thermal vibrations around a fixed position, and the energy is transferred sequentially to adjacent molecules or atoms. Since amorphous can be regarded as a crystal with very fine crystals, the concept of phonon can also be used to analyze the thermal conductivity of some crystals and non-crystals, such as glass and single crystals with good transmission properties. Obvious rejection By the above, we can see that the solid heat transfer carrier is divided into three types: electron, phonon, and photon. Due to the large amount of free electrons in the metal, its thermal conductivity is much greater than that of non-metals. Phonon plays a major role in the crystal due to the remote ordering of the particles. The thermal conductivity of crystals in non-metallic materials is much greater than that of amorphous materials.

Generally, the polymer material itself has poor thermal conductivity and is a poor conductor of heat. Only by filling the material with high thermal conductivity can the thermal conductivity of the material be added, but the addition of the filler tends to reduce the strength properties of the material. The thermal conductivity of the filler itself and its The distribution pattern in the matrix determines the thermal conductivity of the overall material. 1.1 Thermal Conductivity of Metal Materials The thermal conductivity of metals can be expressed by the following formula: In = In + Inp For pure metals, Xe is much larger than Xp, so that metal's Thermal conductivity mainly depends on the movement of free electrons. The valence electrons inherent in each metal element can run from one atom to another, that is, there is a flow of electrons between the metal atoms. This flow of electrons transfers heat from one metal atom to another. At room temperature and above room temperature, the relationship between the thermal conductivity of a pure metal and the electrical conductivity is in accordance with the Wiedman-Franz law: drop. Under low temperature conditions, the thermal conductivity of metals: Metals contain impurities or other elements, and their thermal conductivity is greatly reduced (see Fig. 1.2. Non-metal materials' thermal conduction mechanism Non-metal thermal conductivity mainly depends on phonons. Non-metal can be divided into Crystal non-metal and non-crystal non-metal.Crystal non-metal whose thermal conductivity is second only to metal Although it is a dielectric, it is still a good thermal conductor Diamond(I type) X=90W/(m' K) is the material with the highest thermal conductivity at room temperature, and the crystal non-metal with particularly high thermal conductivity is a very pure single crystal, with no defects such as impurities and dislocations, and only when the temperature of the thermal resistance caused by phonon scattering from each other decreases. The phonons are scattered and attenuated, and the thermal resistance caused by them decreases in an approximate exponential manner. When the phonon free path is limited by the interface of the single crystal, the thermal resistance rises (see Fig. 2). Compared to the ordered crystal, the amorphous Poor regularity of nonmetals causes strong inelastic scattering of phonons and a significant drop in thermal conductivity. If structurally induced phonon inelastic scattering is the only factor that causes thermal resistance, thermal conductivity should be proportional to temperature (see Fig.2) Non-metallic materials The thermal energy diffusion rate of the material mainly depends on the vibration of the adjacent atoms or groups.In the strongly covalently bonded materials, the heat transfer in the ordered crystal lattice is relatively orderly, especially at lower temperatures. Has good thermal conductivity, but with the increase of temperature, the lattice defects, thermal conductivity, so the disordered amorphous solid shows a lower thermal conductivity 3 thermal conductivity of insulating polymer materials for polycrystalline or glass Insulation materials have low thermal conductivity due to small phonon free path. For insulating polymer materials, the thermal conductivity of the material depends on the number of polar groups and the degree of polar group dipolarization. Many macromolecule materials are composed of asymmetrical polar chains, such as polyvinyl chloride, cellulose polyester, etc., all of which are crystalline or amorphous materials. The entire molecular chain cannot be completely free to move and can only occur. Vibrations of atoms, groups or chains.

Thermal conductivity depends on the temperature As the temperature increases, larger groups or chain vibrations can occur, so as the temperature increases, the polymer material conducts heat conductively.

In addition, it also depends on the degree of internal binding of the molecule. In addition to the degree of tightness in the molecule itself, the degree of thermal conductivity can also be increased by external orientation stretching or molding so that the thermal conductivity of the crystalline polymer is much greater than that of the amorphous polymer. The thermal conductivity of polyethylene can even reach 2 times unstretched until it becomes a good conductor of heat, due to the formation of a considerable number of needle-like crystal lattice bridges composed of stretched molecular chains at high draw ratios. The thermal conductivity also increases with the molecular weight, degree of crosslinking, and degree of orientation.

1.4 Heat Conduction Theory Models Many researchers have proposed various models for Y.Agari et al. to fill in the heat-conducting materials and propose a new model that, in those filled polymer systems, if all filler particles aggregate to form a conductive block and polymer Conductive masses are parallel in the heat flow direction, the thermal conductivity of the composite is the highest, and if it is vertical, the thermal conductivity of the composite is the lowest (see Fig. 3). Because the particles can affect the degree of crystallinity in the preparation of the composite material And the crystal size of the polymer can change the thermal conductivity of the polymer, so he took into account the influencing factors of the particle and assumed that the dispersion state is uniform, so as to obtain the theoretical equation: the free factor for forming the thermally conductive chains of the particles, and the polymerization The thermal conductivity of the material; L is the thermal conductivity of the particle; X is the thermal conductivity of the composite; Vf is the filling volume fraction of the particle; meanwhile he compares the theoretical equations of the river 3611-Eucken, Bruggeman, and Cheng-Vochen with his The theoretical equations are compared between experimental data from low filling to ultra high filling (Fig.4, Fig.5). As can be seen from Fig.4 and Fig.5, the theoretical curve of Y.Aga basically agrees with experimental data. , Several other theoretical curves and experimental data have a 2 thermal conductive filler research progress 1 ultra-fine thermal conductive filler or chemical processing Japan's Kyowa Chemical Industry Co., Ltd. developed a high purity and fine MgO, its thermal conductivity is 50W/(m'K) It is equivalent to 4 times that of Si2 and 3 times that of Al23. It was also reported that epoxy powders were filled with metal powders with an average particle size of 5-30 Mm, and the thermal conductivity was 3 W/(rtK) with 2-tert-butyl peroxy-2 methyl-3-hex-5-ene and maleic acid. Aqueous Alkaline Aqueous Solution of Copolymer (Molecular Weight 4900~6000) can modify Al23, the content of At3 in the glue can reach 200%~250%, the thermal conductivity of the film can reach 1.6W/(mK), and the shear strength can reach 2 52MPa. It is mainly due to the formation of bridges due to the peroxide groups on the surface of the filler during the curing process. 2.2 Production of highly oriented fillers. Nagoya Industrial Technology Research Institute, Japan, etc. High-thermal-conductivity ceramics are commonly developed. The usual silicon nitride is a randomly oriented sintered structure. Low thermal conductivity, high thermal conductivity silicon nitride is added to seed powder (particle diameter less than 1m) seed particles (diameter 卟 m, length 3 - such seed particles are aligned and formed with a long orientation The 100m fibrous silicon nitride structure exhibits anisotropic thermal conductivity due to the formation of a fibrous structure with a thermal conductivity of 120 W/(rtK) in the direction of the structural orientation, which is three times that of ordinary silicon nitride and corresponds to steel. Thermal Conductivity 2.3 Preparation of Three-dimensional Structure of Carbon Fibers at the 40th International Society of Advanced Materials In the exhibition and exhibition, the thermal conductivity of the high-performance pitch graphite fiber THORNELK 1100X newly developed by AMOCO was 1200W/(mK) (copper thermal conductivity 394w/(mK)) with three-dimensional structure of carbon in Shanghai The successful research of L-90 thermal mud is based on the thermosetting resin (epoxy resin phenolic resin, polyester resin) as the basic material to be modified, adding a curing agent to crosslink the polymer resin to form a network structure. The main components of L-90 resin thermal clay are as follows: (1) modified thermosetting resin; (2) carbon black or graphite; (3) curing agent-A; (4 accelerator-. Plasticizers; A (Lin additives -9 thermal mud is a core energy-saving display of high thermal conductivity 2 thermal insulation adhesives In the wave of contemporary electronic technology revolution, the field of electrical and electronic materials urgently needed thermal insulating materials, such as semiconductor tube ceramic substrates Bonding with copper seats, protection of the tube core, sealing of the tube case, heat conduction and insulation of the rectifier, thermistor, etc. require thermal conductive insulation adhesives with different process properties.

Wang Tieru successfully developed a variety of epoxy-modified fillers filled with L-1 fillers. The main properties of adhesives cured with self-made curing agents were: thermal conductivity 1. rate >1012 μm, still >1012m after damp heat test. Surface resistivity >1014'm, still >1014'm after damp heat test; electrical strength 500N/cm2; working temperature (long-term) 200250C. The glue has a variety of functions, both for thermal esters and for adhesive coatings, Potting material. Shi Hong modified epoxy adhesive with aluminum nitride filler, its thermal conductivity is 1.20W/(mK), volume resistivity 1.34