Performance of a material may be critical in other applications, but in the medical industry where the health and lives of people are at stake, it is unequivocally critical. Thus, it becomes a challenge in medical applications to find a component that is strong enough to withstand heat, chemical exposure, and pressure.
And there is more, this material should be non-irritating when it comes in contact with the patient. Not all materials can pass these differing demands but fortunately one can stand to the challenge. It’s called liquid silicone rubber.
How important is this material in manufacturing products for the medical industry we are about to find out in this article?
LSR for medical products
What is Liquid Silicone Rubber?
Before we proceed to the discussion of the liquid silicone rubber molding, let us first know more about the liquid silicone rubber material.
The medical industry relies on liquid silicone rubber as the best material to manufacture medical-grade equipment. It has many unique properties that are compatible with the requirements of the medical industry. LSR is classified as a thermosetting plastic that has a wide range of compositions and durometers. This property allows it to match any application.
Unlike other thermoplastics that are solid at room temperature and become liquid when applied with heat, thermosetting plastics begin in liquid form. When they are cured with heat, they transform into a solid and rubbery state, as in the case of LSR. Cured LSRs will remain solid across different temperatures.
This is what makes them valuable to the medical field. A cured LSR is not affected by high temperatures and therefore can be sterilized with radiation or heat without harm. Aside from this tolerance to heat, LSR is also unaffected by chemicals. It can be used in delivering liquids and gases without risks and can be sterilized with chemical agents.
Applications of Liquid Silicone Rubber
Liquid silicone rubber is very flexible. This property is perfect for manufacturing caps, plungers, and gaskets. Given that it can withstand sterilizations, the products made from this material can be reused. It is also used in making valves and seals. Both of these items act as device components between the patients and the devices.
The durability of LSR makes its ideal from hand grips on many medical devices. While its low compression property fits for vibration dampers, tubing, and tubing couplers. Aside from its use in devices and as parts, LSR is now also present in disposables.
The use of LSR is infinite as designers are finding new and revolutionary uses for this material.
The Liquid Silicone Rubber Molding Process
The unique properties of LSR do not only benefit its applications but its molding process as well. Since it is in a liquid state, it is easy to fill the mold in the liquid silicone molding process. This allows for the material to form thin walls and intricate details.
One property of LSR that helps the molding process is being a shear-thinning fluid or what industries call pseudoplastic behavior. The term shear-thinning refers to the decrease in the viscosity of the fluid when shear stress is applied.
In liquid silicone rubber molding, the process involves injecting the material into the mold cavity. The shear-thinning of LSR enhances its flow to the thin areas of the walls in the mold. In short, this property allows the formation of small, detailed parts.
Liquid silicone rubber molding offers the advantage of fast cycle time, which can range from 30 seconds to three minutes, depending on the catalyst and the design. It is a thermoset process where two compounds are mixed.
The process is similar to plastic injection molding, the only difference is the mold is heated while the delivery system for the material is cooled. Another difference is the liquid silicone rubber molding depends on mechanical mixing while plastic injection molding uses the pressurized impingement technique.
In LSR molding the material is cross-linked using a platinum-catalyzed reaction. When cured, it cannot be repurposed or reshaped because the cross-linked material needs high energy levels to break it apart. This contributes to the structural makeup of the material making it impervious to high temperatures.
Conclusion
The invention of liquid silicone rubber is a breakthrough for manufacturing medical-grade products. It possesses high tensile strength, flexibility, and heat resistance that makes it the perfect material for medical applications. It also has another major advantage, it’s chemical inertness. This makes LSR great material to deliver chemicals and gases from the device to the patient.
The properties of LSR also provide a great benefit to the molding process itself. Its shear-thinning property helps LSR to improve its flow into the thin walls of the mold that is perfect when the mold has small and intricate details. Its fast cycle times and the properties of LSR are why the liquid silicone rubber is a good material for many medical products.