There is a certain correlation between the transparency and hardness of liquid silicone, but it is not a simple linear relationship. Usually, the transparency of liquid silicone with higher hardness may be relatively low, while liquid silicone with lower hardness is easier to achieve high transparency. The following is an analysis for you:
The influence of hardness on transparency
The hardness of liquid silicone is mainly determined by its molecular chain structure, cross-linking density, and the type and content of additives. Generally speaking, liquid silicone with higher hardness has a higher degree of cross-linking of its molecular chain and a tighter molecular arrangement. Although this tight molecular structure helps to improve the strength and wear resistance of silicone, it also causes more scattering and reflection of light when passing through, thereby reducing transparency.
On the contrary, the molecular chain of liquid silicone with low hardness is relatively loose, the cross-linking density is low, and the light can pass through more smoothly, so the transparency is often higher.
Transparency performance of liquid silicone with different hardness
Low hardness liquid silicone: The hardness is usually below 10 Shore A, with high transparency, which can reach more than 90% (measured in visible light transmittance). It is often used to make products that require high transparency, such as contact lenses, optical lens filling materials, transparent hoses, etc. In these applications, high transparency is a key performance indicator, and the low hardness can also ensure the softness and comfort of the product.
Medium hardness liquid silicone: The hardness range is roughly between 10-50 Shore A, and the transparency will decrease, generally between 70%-90%. This type of silicone is often used to make some products that require both certain strength and transparency, such as mobile phone cases, transparent buttons, sealing gaskets, etc. Although the transparency is not as good as low hardness silicone, it can still meet basic visual needs and has good physical properties.
High hardness liquid silicone: The hardness is usually above 50 Shore A, and the transparency is further reduced, which may be only 50%-70%. High hardness liquid silicone is mainly used to manufacture products with high strength and wear resistance requirements, such as mechanical parts, tool handles, automotive parts, etc. In these applications, transparency is usually not the primary consideration, but more attention is paid to the mechanical properties and durability of silicone.
Other factors affecting transparency
Additives: In order to improve certain properties of liquid silicone, such as enhancing toughness and improving heat resistance, some fillers or additives are usually added. These additives may affect the transparency of silicone. For example, the addition of certain inorganic fillers (such as silica) will increase the scattering of light and reduce transparency.
Processing technology: Parameters such as temperature, pressure, and time during the molding process will also affect the transparency of liquid silicone. Inappropriate processing conditions may cause bubbles and stress concentration inside the silicone, thereby reducing transparency.