Discussion on the application of silicone foam materials in new energy vehicles
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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), hydrophobic, flame retardant, physiologically inert, oil resistant, solvent resistant and other properties, which are unparalleled by other materials.
Silicone rubber foaming material (also known as: silicone foam/foaming silica gel) is prepared from raw silicone rubber, fillers, vulcanizing agents, foaming agents, etc., mixed evenly, and then foamed and vulcanized at high temperature A porous, low density, compressible polymer elastomer material. Nowadays, silicone rubber foam is widely used because it has the excellent properties of both silicone rubber and foam materials. It not only has the high elasticity of rubber, but also has the properties of sound-absorbing and shock-absorbing foam. It is mostly used in materials with relatively high performance requirements such as shock-absorbing pads, gaskets, sound-insulating materials, insulating materials, and aviation heat-insulating materials.
1. General properties 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°C) 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 temperature of thousands of degrees, so it is often used to make heat-resistant coatings, such as in the aviation field.
(2) Electrical insulation
Silicone rubber has good insulation, and after burning, the silicon dioxide produced 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 the structure, and its reinforcing filler, white carbon black, is suitable for high-voltage applications.
(3) Physiological inertia
The surface of silicone rubber is hydrophobic, so there is little decrease in physical properties in a humid environment. Poor adhesion, can play a role in isolation. And it itself is non-toxic and tasteless, has no harm to human health, and can only have a slight reaction with the body, which also creates its excellent physiological inertia. At the same time, it is also very superior in physiological aging performance.
2. Characteristics of silicone rubber foam (foamed silicone)
Silicone rubber foam is widely used because it has the excellent properties of both silicone rubber and foam materials. It not only has the high resilience and aging resistance of rubber, but also has the properties of sound absorption and shock absorption. It is mostly used for waterproof, 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 good shock-proof cushioning, sound insulation, heat insulation and flame-retardant and explosion-proof properties. It is mainly used in the automotive field for heat-insulating foam pipes for automotive air conditioners, automotive shock Foamed silicone gaskets for automotive batteries, etc.
At present, most automotive interior materials, such as floors, ceilings, steering wheels, and car seats, are polyurethane foam materials. Material prices are lower. However, polyurethane foam materials have poor weather resistance, are flammable and release a large amount of toxic gases harmful to human body 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 foam materials in the future.
2.1 Density selection of foamed silica gel
The density of the silicone rubber matrix is 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 car seats, headrests and other parts; while conventional silicone rubber Foam materials (density 0.45 g/cm3) are widely used for gap filling in sealing, shock absorption and other parts.
2.2 Flame retardant performance of foamed silica gel
Oxygen index (Oxygen index: OI) refers to the minimum oxygen concentration required for a material to burn flamingly in an oxygen-nitrogen mixed flow under specified conditions, and it is one of the indicators for judging the flame retardancy of a polymer. Usually: Oxygen index < 22 belongs to flammable materials; 22< Oxygen index < 27 belongs to flammable materials; Oxygen index > 27 belongs to flammable materials.
The effect of the amount of flame retardant on the oxygen index of silicone rubber is shown in Figure 1. It can be seen from Figure 1 that as the amount of flame retardant increases, the oxygen index of the silicone rubber foam material increases significantly. The oxygen index of silicone rubber without flame retardant is 28, and the oxygen index of silicone rubber with 80 parts of flame retardant is as high as 43. It can be seen that the flame retardant can significantly improve the flame retardant performance of the silicone rubber foam material.
In addition to the oxygen index, vertical burning properties can also be used to characterize the flame retardancy of polymers. Compared with the oxygen index method, the combustion mode of the vertical combustion method is closer to the actual situation of the object burning, so it can better reflect the actual flame retardant effect of silicone rubber. The effect of the amount of flame retardant on the vertical burning performance of silicone rubber is shown in Table 2. It can be seen from Table 2 that the silicone rubber without flame retardant is completely burned; the vertical combustion level of silicone rubber with 40 parts of flame retardant is FV-1, and has a certain self-extinguishing ability; the silicone rubber with 80 parts of flame retardant The vertical combustion level of silicone rubber has reached the FV-0 level, showing good self-extinguishing properties.
2.3 Electrical insulation performance of foamed silica gel
As the amount of physical filler increases, the volume resistivity and surface resistivity of silicone rubber tend to decrease, and the dielectric constant and dielectric loss factor generally increase. It can be seen that the addition of physical fillers damages the electrical insulation properties of silicone rubber to a certain extent.
3. Application of foamed silica gel in new energy vehicles
The key technology 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 an excellent waterproof and dustproof effect during use, and the easy to heat and spontaneous combustion is the number one problem affecting their safe use. Under extreme conditions such as heavy rain, shoals, and smog, in order to meet the requirements for sealing and buffering protection of power batteries during driving, Tesla and other American car companies took the lead in applying foamed silica gel, a niche material, to power batteries. .
For example: In order to reduce the weight of the module and improve the safety of the Tesla model 3 battery pack, a large number of silicone foam potting materials are used to protect a single battery cell. Due to Tesla's benchmarking role in the convenience of power battery pack technology, the application and promotion of silicone foam materials in power battery packs has been greatly accelerated.
At the same time, foamed silica gel is also widely used for light leakage prevention, dust prevention, shock absorption, and air tightness treatment around LEDs; as well as noise prevention and gap filling treatment around speakers and speakers.
