Design of Conductive Elastomer

In EMI shielding, conductive elastomer is the most common shielding material. It is made by evenly filling conductive particles into silicone rubber or fluorosilicone rubber, combining the environmental sealing of silicone rubber itself with the high conductivity of conductive particles. It can not only meet the requirements of conductive grounding and electromagnetic shielding, but also achieve environmental sealing. This article will introduce how to design and select conductive elastomers.

1. Structuralof conductive elastomerdesign considerations

In the selection of the structural size and shape of actual conductive rubber products, the following four factors are usually considered:

◆Closing force

Conductive rubber adapts to the pressure by changing shape rather than volume, and the volume will expand under heat/pressure, so the potential expansion space must be taken into account. If you want to achieve a larger compression deformation, the required closing force will inevitably increase rapidly. The design of the product appearance is a "light and thin" metal structure, which requires a smaller closing force. When the size allows, it is necessary to give priority to the hollow section structure, such as the hollow "O" and "D" types. This increase in compression achieved by structural deformation will significantly reduce the closing force.

◆Filling ratio

Filling ratio is the ratio of the cross-sectional area of ​​the rubber pad to the cross-sectional area of ​​the groove seal. Too small or too large a filling ratio will affect environmental sealing and electromagnetic shielding. In order to meet the special requirements of electromagnetic shielding and environmental sealing, taking into account all product tolerances, a filling ratio between 93% and 98% can achieve the best electromagnetic shielding and environmental sealing effects.

◆Compression deformation design

The special structure of conductive rubber products determines that they must achieve conductivity and shielding properties through compression deformation. Recommended value of compression deformation: For conductive rubber products with non-hollow structures, the deformation should be greater than 10%, and 15% is recommended, with an upper limit of no more than 25%. For specific recommended compression values ​​for different materials and different cross-sectional shapes, please contact the company staff to meet special needs.

◆Compression permanent set

Compression permanent set is defined as the height difference of deformation that cannot be recovered after compression, expressed as a percentage. Compression permanent set is an important mechanical performance indicator of conductive rubber products. The size of the compression permanent set of conductive rubber is related to the elasticity and recovery of the rubber, and is also closely related to the sealing performance, shielding effectiveness and service life of the conductive rubber product.

2. Selection of conductive rubber materials

From the perspective of environmental sealing and electromagnetic shielding, our company's conductive rubber products can provide a series of products to meet customers' different requirements for performance and cost.

For designers, how to choose suitable conductive rubber materials mainly refers to the following points:

① Shielding effectiveness requirements;

② Material working temperature range requirements;

③ Material environmental adaptability requirements, such as corrosion resistance, salt spray resistance, mildew resistance, etc.

Taking these factors into full consideration, the company provides customers with the following materials for selection:

3. Balance between conductivity and elasticity: standards and methods

When designing conductive elastomer, the balance between conductivity and elasticity is a key factor. Too high a conductive filler content may reduce the elasticity of the material, while too low a filler content may not meet the conductivity requirements.

Conductivity refers to the ability of a material to conduct electric current, usually expressed as conductivity (S/m). The conductivity of a conductive elastomer depends mainly on the type, shape and distribution of the filler.

Elasticity is the ability of a material to return to its original shape after being deformed by an external force, usually measured by tensile strength and elongation.

①Selection and proportion of filler

Selecting the appropriate conductive filler is the first step in achieving a balance between conductivity and elasticity. Common conductive fillers include carbon black, metal powders and conductive polymers. Different fillers vary in their conductivity and impact on elasticity. For example, carbon black generally provides good electrical conductivity, but filling it too high can significantly reduce elasticity.

In practical applications, it is recommended to determine the optimal ratio of fillers through experiments. Generally speaking, the content of filler is between 10% and 30%, which is a common range, but the specific proportion needs to be adjusted according to the characteristics of the material and application requirements.

② Standards and test methods

Although there is no unified international standard specifically for the balance between conductivity and elasticity of conductive elastomers, some industry standards and test methods can be used as reference:

Conductivity test: Use the four-probe method or resistivity test instrument to measure the conductivity of the material to ensure that it meets the application requirements.

Tensile test: According to the ASTM D412 standard, the tensile strength and elongation of the material are measured to evaluate its elastic properties.

Dynamic mechanical analysis (DMA): DMA is used to test the dynamic modulus of the material at different frequencies and temperatures to understand its elastic and viscoelastic properties.

③Simulation and optimization

Computer simulation technology is also widely used in modern material design. Through methods such as finite element analysis (FEA), the effects of different filler ratios on conductivity and elasticity can be predicted. This method can be optimized before actual production, saving time and cost.

④ Conclusion

The balance between conductivity and elasticity is one of the core challenges in designing conductive elastomers. By rationally selecting fillers, determining the optimal ratio, following relevant standards and test methods, and using modern simulation technology, the balance between the two can be effectively achieved to meet the needs of different applications.

The above three points are simple opinions on the design and selection of conductive elastomers. In addition to providing customers with standard products of conductive elastomers, our company can also provide more design selections and electromagnetic safety protection solutions, and provide customized products and services according to the various needs of customers.

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