MediSilicone injection molding is a cost-effective manufacturing solution that many OEMs rely on for high-quality, efficient production. This method of manufacturing is very common within the medical sector and has several benefits compared to other molding processes. For example, silicone injection molding is a good choice for a wide range of part sizes, materials, and colors – including highly intricate and complex parts. This method produces products that are virtually identical from part to part which provides excellent brand consistency and part reliability during high volume runs, which is especially crucial for products used in the medical industry. The high reproducibility of silicone injection molding also allows for production to be scaled up to very large volumes, resulting in low costs per unit.

Common Silicones for Injection Molding: LSR and HCR

Silicone elastomers have long been a popular material for silicone injection molding due to their highly desirable mechanical and physical properties. Silicones have excellent durability, chemical inertness, high tensile strength, vast range of available durometers, low toxicity, a wide temperature range, and compatibility with many sterilization methods. Furthermore, silicone is compatible with human tissue and body fluids, has a very low tissue response when implanted, and does not support bacteria growth – making it a perfect option for implants due to its excellent biocompatibility.

Silicone elastomers are primarily available in two forms for medical manufacturing: Liquid Silicone Rubber (LSR) and High Consistency Rubber (HCR). LSR and HCR are both used in medical manufacturing. While HCR and LSR have several similarities, viscosity is a key differentiator and often impacts the decision on which material is utilized for a given silicone injection molding project. The following provides an overview of both elastomers and when each should be utilized.

What is Liquid Silicone Rubber (LSR)?

Liquid Silicone Rubber (LSR) is a platinum-cured elastomer. LSR is a newer silicone technology and starts out as a 2-part liquid that cures into a solid form when mixed. LSR generally comes in buckets and has a longer shelf life than HCR.

LSR is a versatile silicone that has a wide range of end-uses from medical devices to consumer goods to electronics to automotive. There are several types of LSR that can be manufactured such as medical, self-lubricating, conductive, flame-retardant, and radio opaque. The type of LSR produced is determined by the additives incorporated during the manufacturing process. Additionally, LSR is available in different grades, namely medical, food, and industrial. Given its versatility, it is not surprising that the worldwide demand for LSR continues to grow.

LSR has excellent properties, such as a low viscosity and low shrink rate, that make it a great choice for silicone injection molding and the manufacturing of complex products and intricate parts. One of the benefits of LSR is that it cures faster than most other rubber materials; additionally, due to the highly automated nature of silicone injection molding and the potential for 24/7 manufacturing, high volumes of LSR products can be produced in a short period of time – adding to its popularity.

A key benefit of LSR’s lower viscosity is that it is easier to mix additives into. Additives that can readily be incorporated into a batch of LSR include colorants, desiccants, barium, and pharmaceuticals such as hormones or steroids. For these reasons, LSR is a great option for medical devices such as combination products. The low viscosity of LSR and the temperatures needed to vulcanize LSR are usually low enough that significant degradation of compounded substances, like Active Pharmaceutical Ingredients (APIs) that are used in combination products, can be avoided.

While LSR has many attractive properties, its biocompatibility is outstanding. LSR has demonstrated superb compatibility with human tissue and body fluids, and is resistant to bacteria growth. Medical grades of LSR are temperature resistance and can easily sterilize, which makes them compatible with various medical devices and accessories such as implantable devices, liquid feeding bottles, dialysis filters, and oxygen mask instruments.

Looking for a proven and reliable medical manufacturing partner for your next silicone injection molding project?

Contact the professionals at ProMed to learn more about our range of medical manufacturing solutions and the various silicone materials we utilize.

What is High-Consistency Rubber (HCR)?

Another common elastomer for silicone injection molding is High-Consistency Rubber, or HCR. It should be noted that the terms HCR and HTV, which stands for High Temperature Vulcanization, are often used interchangeably and refer to the same silicone material; for the purpose of this article, we will use the acronym HCR.

HCR is a type of silicone elastomer comprised of long polymer chains with a very high molecular weight. It is cured at high temperatures with a platinum catalyst or peroxides. HCR is known for its gummy consistency that is similar to peanut butter, and mostly comes in partially vulcanized sheets.

HCR has many desirable properties such as excellent aging resistance, thermal stability, electrical properties, mechanical strength, elongation, and hardness. For these reasons, HCR is a good material for a broad range of applications within medical manufacturing. Due to its higher viscosity compared to other elastomers such as LSR, HCR is typically processed using compression and transfer molding methods, but is also utilized for silicone injection molding projects.

HCR takes longer to cure than many other molding materials. A longer cure time results in a longer silicone injection molding cycle time. To improve project economics, HCR molds often have a large number of

cavities in order to accommodate the longer cycles and still achieve the desired production volume for each cycle – resulting in a more cost-effective solution on a per unit basis.

Which Silicone is Best for My Injection Molding Project?

Medical device OEMs often face a tough decision: should we use HCR or LSR for our silicone injection molding project? For companies already using HCR to manufacture medical components, it may make sense to continue using this elastomer especially since the initial capital equipment costs have already been made. For new product development, however, LSR is often the best choice given the lower capital costs and labor associated with processing this silicone. Due to its lower cost and versatility with formulations, companies often prefer LSR over HCR – but the decision should be made on a case-by-case basis. This is why it is important to team up with an experienced partner, such as ProMed, who will guide you through the selection process to ensure the right material is chosen for your silicone injection molding project.

About ProMed

ProMed was founded in 1989 to address an industry need for cleanroom manufacturing of silicone components, specifically those having a medical application. Over time, we broadened our product offerings to include assembly, micro-molding of highly engineered plastics, and combination products. We have garnered a reputation as the world benchmark of implantable silicone components and assemblies – and are one of few companies in the world to provide contract manufacturing of drug-eluting products.

ProMed has expertise in working with the full spectrum of silicones covering a wide range of properties and characteristics. We will assist in your material selection to help ensure all design requirements are met. Our manufacturing facilities and equipment are designed for a single purpose—to mold medical and implantable silicone, combination components, and bio-material grade plastics with uncompromising quality and service. We currently have four divisions that are located within two manufacturing sites. All are certified class 10,000 / ISO Class 7 cleanrooms.

We can identify the right manufacturing solution for any project. We have extensive experience in a wide range of injection molding techniques including:

· Automated Silicone Injection Molding

· Multi-cavity tooling

· Micro molds and micro molding

· Servo-controlled de-molding capabilities

· Insert molds, overmolds, and automation integration

· Transfer molding

· Compression molding

Click here to see why ProMed is your silicone injection molding partner. Contact ProMed today at 763-331-3800 to discuss your next silicone injection molding project.

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