High Volume Manufacture Of Thinwall Medical Device Components
With Liquid Crystal Polymer Thermoplastics

(Courtesy : Celanese Chemicals The Chemistry Inside InnovationTM)

LCP exhibits a melting range rather than a sharp melt point. The typical cure time is a few seconds, with injection molding cycle time range of ~5 to ~15 seconds for small part molding (depending on # of cavities)

• Individual analytical tests per lot / delivery (purity control) where appropriate
• Expanded certificate of inspection
• Change management aligned with GMP principles
• Support in Regulatory Approval

C. Design benefits from the use of LCP

Medical designers are looking for advanced and proven polymer solutions to pack more technology into tighter and lighter spaces for patient utility, comfort and concealment. LCPs are valuable for wearable, portable injector designs, diagnostic devices, injector pen internals, surgical staple cartridges, surgical instruments,
and microneedle arrays.

Vectra® LCP polymers are a natural fit for pushing the envelope on thin wall designs to free up more internal space without sacrificing product strength, stiffness, and dimensional control. LCP resins increase in strength & stiffness with thin wall designs due to their unique rod-like molecular orientation. It’s a paradigm shift in thinking, since thinner wall design drives the final material properties to their performance capable levels. Sub-1mm thickness wall sections are the sweet spot for optimum mechanical properties.

High stiffness and strength make LCP a candidate for stainless steel or other specialty metal replacement, where metal may be over-engineered for the application. VLCP resins are available in a variety of resin types and fillers for fine tuning strength, shrinkage and tribology (wear & friction) properties. See Fig 4 & 5 for how key mechanicals such as modulus (stiffness) and tensile strength change as a function of molded wall thickness.

Vectra LCP compounds are formulated in a variety of polymer, reinforcement and additive compositions for optimal mechanical, dimensional, thermal and tribological properties.

Due to LCP extreme shear flow behavior, complex thin wall designs that can’t be filled with other resins can be filled with LCP and high micro-replication of mold surface achieved, one reason why LCP is useful for micro molded parts. Thin wall design enables fast cycle times for higher productivity & reduced material use & thus cost economy, important for single/limited use products. Minimal molecular reorganization during solidification not only leads to faster cycle times but to low shrinkage for high precision, tighter tolerance parts.

One caution with LCP is its lower weld-line strength vs other composite resins like PPS so designs need to be reviewed for weld-line locations. Butt welds should be avoided as strength can be compromised as much as 90%. Gradually merging weld-lines are recommended. If necessary, designers should relocate weldlines away from high stress, critical areas or redesign those areas for less stress in use.

D. Case study: Vectra® MT® LCP 1305 Lowers Cost Per Part And Enables Improved Design For Wearable/On-Body Injector Chassis

Customer challenge

Our OEM drug delivery customer had designed a wearable injector that allowed patients to manage their diabetes with an effective low maintenance treatment approach. The designers were searching for material solutions that optimized functionality while managing overall device costs; especially critical since components of the device were disposable.

The specific requirements for a lightweight, cost-efficient wearable device called for excellent mechanical performance including dimensional stability, high stiffness and tight part tolerances for the internal chassis. From previous experience we were confident that such properties would increase production efficiency by allowing for higher cavity molds or shorter cycle times. Additionally, materials that could allow for space savings inside the device housing would provide opportunities to add connectivity features or other electronics, and generally increase design flexibility.

Our Field Development Engineers and Product Specialists worked with the customer to replace a Polycarbonate device chassis with a higher performing, smaller component produced with one of Celanese Medical’s medically compliant Liquid Crystal Polymer grades.

After careful thought and collaboration, Vectra® MT® LCP 1305 was selected. This is a 15% glass-reinforced, higher-flow grade of LCP, enabling medical device designers to develop a thinnerwalled, reducedweight chassis and accelerate cycle times.