How to control the softness and hardness of silicone products?

The softness and hardness of silicone products directly determine their sealing effect, tactile comfort, and compressive strength. Whether it is the need for extremely soft maternal and child products or the requirement for high hardness industrial seals, precise control of hardness is the core challenge in production.

Formula design: the underlying logic for regulating hardness
The softness and hardness of silicone products first depend on the formula design of the base material. The type of base polymer determines the initial range of hardness, while the ratio of filler to plasticizer is the key to fine-tuning. Adding inorganic fillers such as gas-phase white carbon black can effectively fill molecular gaps, restrict molecular chain movement, and significantly improve hardness and modulus; On the contrary, if it is necessary to reduce hardness, it can be achieved by adding an appropriate amount of plasticizers such as silicone oil. For example, adding 10% silicone oil to liquid silicone can reduce its hardness by approximately 2 to 5 degrees. However, it should be noted that excessive addition of silicone oil can damage the molecular weight, leading to a decrease in tear resistance and even frost spraying. Therefore, scientific proportioning must be carried out while ensuring physical properties.

Blending and compounding: a clever way to quickly respond to non-standard demands
In actual production, customers often request non-standard special hardness requirements (such as 45 degrees or 55 degrees). At this point, directly mixing raw rubber materials of different hardness in proportion is an efficient and economical solution. For example, mixing 50 degree silicone with 70 degree silicone in a 1:1 ratio theoretically yields a rubber material of approximately 60 degrees. This method is widely used in sampling or small batch non-standard orders, which can significantly reduce inventory models. However, Weishun Silicone reminds that after mixing, it is necessary to fully thin and test the vulcanization curve, and the tensile strength of the blended material may be slightly lower than that of the raw material. Products with high performance requirements should be used with caution.

Sulfurization process and post-treatment: a crucial step in determining final performance
In addition to the formula, the influence of vulcanization process on hardness cannot be ignored. The three elements of vulcanization temperature, time, and pressure need to be accurately matched. Appropriately increasing the vulcanization temperature or prolonging the vulcanization time can accelerate the crosslinking reaction rate and increase the hardness by 1 to 2 degrees Celsius; However, if the temperature is too high or the time is too long, it can lead to excessive vulcanization, making the product brittle. In addition, secondary vulcanization (heat treatment) is also an effective means of adjusting hardness. By extending the treatment time at a specific temperature, the molecular structure of silicone can be further crosslinked, thereby stabilizing and improving the overall hardness.

The control of the softness and hardness of silicone products is a systematic engineering involving material science and process optimization.