Application of Silicone Foaming Materials in New Energy Vehicles
The main chain of the silicone material contains a "silicon-oxygen-silicon" structure, and the side chain contains a small amount of organic groups, so it has the dual advantages of organic and inorganic materials, high and low temperature resistance, radiation resistance and weather resistance (no double bonds, It is not easy to be decomposed by ultraviolet light and ozone), hydrophobicity, physiological inertness, oil resistance, solvent resistance and other properties, which are unmatched by other materials.
Silicone rubber foam material (also known as: silicone foam/foamed silica gel) is made of raw silicone rubber, filler, vulcanizing agent, foaming agent, etc., after mixing uniformly, foaming and vulcanizing at high temperature A porous, low density, compressible polymeric elastomer material. Today, silicone rubber foam is increasingly used because it combines the excellent properties of silicone rubber and foam materials. It not only has the high elasticity of rubber, but also has the properties of sound-absorbing, shock-absorbing and other foams.
The generality of silicone rubber
Silicone rubber has many excellent properties:
(1) High and low temperature resistance
Silicone rubber has excellent mechanical properties under high temperature (above 200 ℃) environment, and still has certain toughness and elasticity. The glass transition temperature (Tg) can be as low as -70 °C. In general, the working temperature of silicone rubber is -100 ℃ to 350 ℃. It can withstand instantaneous high temperatures of thousands of degrees, so it is often used to make heat-resistant coatings, such as in the aerospace field.
(2) Electrical insulation
Silicone rubber has good insulating properties, and after combustion, the generated silica is still an insulating substance. In addition, silicone rubber is not easy to scorch during arc discharge, because of its small number of carbon atoms in its structure, and its reinforcing filler silica, which is suitable for high-voltage applications.
(3) Physiological inertia
The surface of silicone rubber is hydrophobic, therefore, the physical properties decrease little in wet environment. Poor adhesion, can play a role in isolation. And it is non-toxic and tasteless, no harm to human health, and can only react slightly with the body, which also creates its excellent physiological inertia, and at the same time, it is also very superior in terms of physiological aging performance.
Characteristics of silicone rubber foam (foamed silicone)
Silicone rubber foam is widely used, because it has the excellent properties of silicone rubber and foam materials at the same time, not only has the high resilience and aging resistance of rubber, but also has the properties of sound absorption, shock absorption and other foams. Shock absorption, gasket (sealing grade IP68), sound insulation, insulation, aviation heat insulation and other performance requirements are relatively high. According to the cell structure, silicone rubber foam is divided into three types: closed cell type, open cell type and mixed type.
The closed-cell foamed silicone foam material has the characteristics of good shockproof buffer, sound insulation, heat insulation, flame retardant and explosion-proof. Foamed silicone gaskets for automobile batteries, etc.
At present, most automotive interior materials, such as floors, ceilings, steering wheels, car seats, etc. are polyurethane foam materials, because on the one hand, the technology of polyurethane foam materials is relatively mature, and the performance meets the needs of use; on the other hand, polyurethane foam materials Material prices are lower. However, polyurethane foams have poor weather resistance, are flammable, and release a large amount of toxic gases that are harmful to humans during combustion. Therefore, with the promotion of foamed silicone materials and the improvement of people's understanding of them, foamed silicone materials are expected to replace traditional polyurethane foamed materials in the future.
2.1 Density of foamed silica gel Select the density of silicone rubber matrix as 1.17g/cm3. However, through foaming treatment, the density of the silicone rubber foam material prepared in the current mature process can be as low as 0.16-0.20 g/cm3, which can be used for parts such as car seats and headrests; while conventional silicone rubber Foam material (density 0.45 g/cm3) is widely used for gap filling in sealing, shock absorption, etc.
2.2 The flame retardant performance of foamed silica gel One of the test methods commonly used to characterize the flame retardant performance of polymers is the vertical combustion method, and its combustion mode is very close to the actual burning of objects, so it can well reflect the actual flame retardant effect of silicone rubber . The influence of the amount of flame retardant on the vertical combustion performance of silicone rubber, the silicone rubber without flame retardant is completely burned; the vertical combustion grade of silicone rubber with 40 parts of flame retardant reaches FV-1 level, which has a certain self-extinguishing ability; The vertical combustion grade of silicone rubber with 80 parts of flame retardant has reached the FV-0 grade, showing good self-extinguishing properties.
2.3 Electrical insulation properties of foamed silica gel
With the increase of the amount of physical filler, the volume resistivity and surface resistivity of silicone rubber tend to decrease, and the dielectric constant and dielectric loss factor generally tend to increase. It can be seen that the addition of physical fillers impairs the electrical insulating properties of silicone rubber to a certain extent.
The application of foamed silica gel in new energy vehicles
The technical key of new energy electric vehicles lies in the charging and discharging technology and safety performance of its high energy density lithium battery. Lithium batteries must maintain excellent waterproof and dustproof effects during use, and easy to heat and spontaneous combustion is the first problem that affects their safe use. Under extreme conditions such as heavy rain, shoal, and haze, in order to meet the requirements of sealing and buffering protection of power batteries during driving, American car companies such as Tesla took the lead in applying foam silicone, a niche material, to power batteries.
For example, in order to reduce the weight of the module and improve the safety of the Tesla model3 battery pack, a large number of silicone foam potting materials are used to protect a single cell, which can limit the heat transfer from the upper part of the battery pack to the cell for a certain period of time. Thermal runaway. Due to Tesla's convenient benchmarking role in power battery pack technology, the application and promotion of silicone foam materials in power battery packs has been greatly accelerated. At present, there are mature liquid silicone foamed silicone sheets with comparable performance in China.
At the same time, foamed silica gel is also widely used for anti-leakage, dust-proof, shock absorption, and air-tightness treatment around LEDs, as well as anti-noise and gap-filling treatments around speakers and speakers.