Medical Plastic Data Service Magazine



Our 30th Year of Publication
Page  4 of 6

Cover Story

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

(Courtesy : Celanese Chemicals The Chemistry Inside InnovationTM)



LCP resins are different but not difficult. Once their polymer characteristics are understood, they can be put to good use in pushing the envelope with advanced designs, part to part tolerance repeatability, and high volume productivity in the tens of millions of units … all with the right design, tooling and processing.


Liquid Crystal Polymer (LCP) thermoplastics are well-known in the consumer electronics industry for tight tolerance designs with high stiffness and strength, plus rapid cycle times and extreme flow to fill sub-mm wall sections. Processing benefits allow for micro-molding and replication of intricate detail in miniaturized devices for delivery of therapeutic drugs (biological and pharmaceutical) and vaccines. These same advantages are translatable to precision combination drug delivery devices which incorporate complex mechanisms and wireless connected electronics for pharma prescription adherence goals.


Specifically, LCP resins can help designers and engineers achieve more compact, intricate components through thin-wall molding even as low as 0.3mm (0.012in) nominal wall without sacrificing mechanical stiffness and strength as LCP polymer chains are inherently stiffer & stronger than many other neat thermoplastics. This can be an
advantage in wearable/on-body devices where light-weight, compact form factors add value by creating more free space for pharma container and other components which can be critical.



A. Introduction to use of LCP in Drug Delivery Devices
B. Polymer and processing characteristics of Liquid Crystal Polymers
C. Design benefits from the use of LCP
D. Case study: Vectra® MT® LCP 1305 Lowers Cost Per Part And Enables Improved Design For Wearable/On-Body Injector Chassis


A. Introduction to use of LCP in Drug Delivery Devices


Miniaturization of drug delivery devices requires careful planning of the integration of all components into a compact package. This miniaturization makes wearable devices lighter-weight, less intrusive and more comfortable for the patient. In order to provide information on patient usage for themselves and their healthcare providers, many drug delivery devices are integrating electronic circuits and transceivers, in addition to the mechanical systems to precisely dose the drug. Special materials capable of molding small and precise components enable the design of such complex devices with intricate designs and thinwalls. These benefits significantly expand the market for controlled dosing products vs. conventional self administered injections and provide reliable and precise delivery outside of a clinical setting. Production of such devices at a large volume leads manufacturing to fast-cycling injection molded plastics with high cavity tools and hot runner systems. Vectra® MT® LCP provides advantages for each requirement.


• High stiffness, strength and toughness with long flow-lengths (>150 mm @ 3.2mm) and capability for wall thicknesses as thin as 0.3 mm at common device flow lengths and even thinner with short flow length.
• Ultra-low viscosity at process temperatures for high flow in thin wall sections.
• Fast crystallization with small mold temperature excursions between melt injection and part ejection for fast cycle times and high productivity.
• Tailored dielectric strength for compact integration of electronic circuits.
• Inherent V0 UL Flammability rating



These attributes make Vectra® LCP the preferred material for micro connectors and precision optics for the miniaturization of consumer electronic devices such as mobile phone cameras and tablet bus connectors. Combined with Celanese MT® medical quality management and service package Vectra® MT® LCP brings these same benefits to the connected and wearable medical devices.


B. Polymer and processing characteristics of Liquid Crystal Polymers


LCP resins are unique in the world of engineering resins. LCP is a high heat thermoplastic, but its value for most medical devices is its exceptional flow in thin-wall designs. The morphology of LCP resin’s nematic rod-like crystalline structure is very different from amorphous & semi-crystalline resins.


Even unfilled LCP is extremely strong & stiff, behaving like a selfreinforcing polymer, similar to or exceeding mechanicals of 20- 30% glass fiber composites.


The nematic structure of LCP helps with its extremely high flow in thin-wall geometries. High flow combined with high stiffness & strength allows designers to make thinner structures without sacrificing structural performance, enabling smaller parts & freeing up more internal space for pharma or other components. LCP flows better under high shear without degrading mechanical properties. Figure 1 shows how LCP flow increases exponentially with high shear (high injection rate) compared to PPS.



Figure 2 compares spiral flow of 30%GF LCP vs other 30-40% GF resins at 3.2mm (0.125”).


Each molded at manufacturer’s recommended conditions and three injection pressures normalized to 30K psi. Cavity thickness = 0.125 in (3.2mm)


As seen in Figure 3, LCP has a low heat of fusion from its ordered molecular structure, which changes very little from molten to solid phase, it rapidly solidifies when flow ceases allowing a rapid cycle from melt injection to part ejection.


Part and tool design must provide for high enough shear to maintain a low viscosity throughout the tool. Areas where the flow speed drops, such as sharp changes in runner direction, can allow cold slugs to form.


Rapid cycling means more parts per hour, so fewer molds may be required for high volume production. Rapid solidification allows for minimal part flashing. LCP exhibits a melting range rather than a sharp melt point. The typical solidification time is a few seconds, with injection molding cycle time ranges commonly 5 to 15 seconds for small part molding, depending on the number of cavities.


Since high mechanical shear is used to thin the resin to make it flow better, high mold temperatures are not necessary as with polyphenylene sulfide (PPS) or polyetheretherketone (PEEK). LCP can be processed at mold temperatures less than 100 °C similar to many engineering resins and requiring only water based cooling. Also, contrary to intuition, smaller gates and thinner runners are better to increase shear rate and thus flow.


Other characteristics of LCP include:


• Excellent dimensional stability with low moisture absorption (0.03%) & low mold shrinkage (0.1- 0.4%)
• Inherently flame retardant without FR additives
• Very clean, low extractables & ionics, food contact compliant, biocompatible with MT® grades being FDA master file listed
• Service temperature from -190 °C up to 240°C, short term up to 340°C
• High tensile strength (to 185 MPa) & high tensile modulus (to 30000 Mpa)
• Excellent barrier property to both oxygen and moisture, one of the best resins
• Sterilizable by steam, ethylene oxide, gamma radiation or H2O2 plasma
• Excellent chemical resistance
• Natural color is opaque, off-white ivory with options for coloration.


To support customer applications in regulated medical devices, Celanese provides regulatory and quality management support to enable customer compliance to ISO 13485. This includes elements related to Celanese polymers, ingredients, manufacturing controls and supply chain management.


Celanese MT® polymers service package


• Material compliance to FDA and EU requirements
• Long-term supply assurance without change of formulation
• Animal- and latex-free formulations
• Certified biocompatibility (USP 23 Class VI / ISO 10993, etc)
• FDA Drug & Device Master Files

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