Application of silicone foam 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 both organic and inorganic materials, high and low temperature resistance, radiation resistance and weather resistance (no double bonds, It is not easily decomposed by ultraviolet light and ozone, water, flame retardant, physiologically inert, oil-resistant, solvent-resistant, etc. This is incomparable with other materials.

Silicone rubber foaming material (also known as: silica gel foam/foamed silica gel) is made of silicone rubber raw rubber, filler, vulcanizing agent, foaming agent, etc., after being uniformly kneaded and foamed at high temperature. A porous, low density, compressible polymeric elastomer material. Today, silicone rubber foams are becoming more widely used because of their superior properties in silicone rubber and foam. It not only has the high elasticity of rubber, but also has the properties of foams such as sound absorption and shock absorption. It is mostly used for materials with high performance requirements such as cushions, gaskets, sound insulation materials, insulating materials and aviation insulation materials.

1. The generality of silicone rubber

Silicone rubber has many excellent properties:

(1) High and low temperature resistance

Silicone rubber has excellent mechanical properties in high temperature (above 200 °C) and still has certain toughness and elasticity. The glass transition temperature (Tg) can be as low as -70 °C. In general, silicone rubbers operate at temperatures ranging from -100 °C to 350 °C. It can withstand thousands of degrees of transient high temperatures, so it is often used to make heat-resistant coatings, such as the aerospace industry.

(2) Electrical insulation

Silicone rubber has good insulation properties, and after combustion, the resulting silica is still an insulating material. In addition, silicone rubber is not easily scorched during arc discharge, because its structure has a small number of carbon atoms, and its reinforcing filler white carbon black is suitable for high pressure applications.

(3) Physiological inertia

The surface of the silicone rubber is hydrophobic, so the physical properties are reduced in a humid environment. Poor adhesion can play a role in isolation. It is non-toxic and tasteless, has 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 superior in physiological aging performance.

2. Characteristics of silicone rubber foam (foamed silica gel)

Silicone rubber foam is increasingly used in applications, because it has the excellent properties of silicone rubber and foam materials. It has the high resilience of rubber, anti-aging, and the performance of foams such as sound absorption and shock absorption. Shock absorbers, gaskets (sealing grade IP68), sound insulation, insulation, aviation insulation and other performance requirements are relatively high. According to the cell structure, the silicone rubber foam is classified into a closed cell type, an open cell type, and a mixed type.

Closed-cell foamed silicone foam material has good shock-proof cushioning, sound insulation, heat insulation and flame-retardant and explosion-proof characteristics. It is mainly used in automotive fields for thermal insulation foam pipes for automotive air-conditioning, automotive shock absorption, and new energy. Foamed silicone gaskets for automotive batteries, etc.

At present, most automotive interior materials, such as flooring, ceiling, steering wheel, and car seats, are polyurethane foams. This is because polyurethane foam technology is relatively mature and its performance meets the needs of use. On the other hand, polyurethane foam The price of the material is lower. However, polyurethane foams have poor weather resistance, are flammable, and release a large amount of toxic gases harmful to the human body during combustion. Therefore, with the promotion of foamed silica gel materials and the improvement of people's understanding, future foamed silica gel materials are expected to replace traditional polyurethane foam materials.

2.1 Density selection of foamed silica gel

The silicone rubber matrix had a density of 1.17 g/cm3. However, through the foaming treatment, the silicone rubber foam prepared in the current mature process can have a density of at least 0.16-0.20 g/cm3, which can be used for parts such as automobile seats and headrests; and conventional silicone rubber. Foam (density of 0.45 g/cm3) is widely used for gap filling in areas such as sealing and shock absorption.

2.2 Flame retardant properties of foamed silica gel

Oxygen index (OI) refers to the minimum oxygen concentration required for flaming combustion of a material in a mixed stream of oxygen and nitrogen under specified conditions. It is one of the indicators for determining the flame retardancy of a polymer. Usually: oxygen index < 22 is a flammable material; 22 27 is a flame retardant material.

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 Fig. 1 that as the amount of the flame retardant increases, the oxygen index of the silicone rubber foaming material increases remarkably. The silicone rubber without flame retardant has an oxygen index of 28, and the silicone rubber with 80 parts of flame retardant has an oxygen index of up to 43. It can be seen that the flame retardant can significantly improve the flame retardancy of the silicone rubber foaming material.

In addition to the oxygen index, vertical burning properties can also be used to characterize the flame retardant properties 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 the 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 silicone rubber with 40 parts of flame retardant has a vertical burning grade of FV-1, which has a certain self-extinguishing ability; and 80 parts of flame retardant is added. The vertical burning grade of silicone rubber has reached FV-0 level and shows good self-extinguishing performance.

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 decreased, and the dielectric constant and dielectric loss factor generally increased. It can be seen that the addition of physical fillers impairs the electrical insulation properties of silicone rubber to some extent.

3. Application of foamed silica gel in new energy vehicles

The key to the technology of new energy electric vehicles lies in the charging and discharging technology and safety performance of their high energy density lithium batteries. Lithium batteries must maintain excellent waterproof and dustproof effect during use, and easy to heat and spontaneous combustion is the first problem that affects their safe use. In extreme conditions such as heavy rain, shoal and haze, in order to meet the requirements of sealing and buffer protection of power batteries during driving, Tesla and other American car companies took the lead in applying the nitrile material of foamed silicone to the power battery. .

For example: Tesla model3 battery PACK package In order to reduce the weight of the module and improve safety, a large amount of silicone foam potting material is used to protect a single battery core. Due to the convenient benchmarking of the power battery technology, Tesla has greatly accelerated the application of silicone foaming materials in the power battery PACK package.

At the same time, foamed silica gel is widely used for anti-leakage, dust-proof, shock-absorbing, and air-tight treatment around LEDs; as well as anti-noise around the speakers and speakers, and filling gaps.