Liquid silicone rubber technology enhances Eastman Tritan™ copolyesters.
There’s a growing demand in today’s medical market for innovative medical devices and housings that provide a superior combination of chemical resistance and impact strength. Thanks to advancements in liquid silicone rubber (LSR) technology, manufacturers are now able to meet this demand using medical grades of Eastman Tritancopolyester. 
 
Momentive’s Silopren LSR 47×9 series provides strong in-mold adhesion with Tritan™ without the need for primers. This combination is ideal for applications that require properties like handling comfort, waterproofing, durability, and aging stability, including:
  • Respiratory devices
  • Sealing elements
  • Gaskets for joints in housings and hardware
  • Buttons and switches on electronic housings and hardware
  • Vibration reduction
  • Membranes and lenses for electronic device housings
 
Clear and opaque grades of Tritan™ have a lower Tg and require a lower processing temperature than other engineering polymers. The ability of Silopren LSR 47×9 to cure rapidly at relatively low temperatures is optimal for achieving functional performance and efficient processing with Tritan™. Incorporating LSR technology enhances the advantages of Tritan™, which include outstanding chemical resistance, excellent impact strength and durability, clarity and color retention, and design flexibility.
 
This single-step, integrated molding process can shorten cycle times and reduce input costs. Contact us to learn more about optimizing overmolding with Tritan™ medical grades. 

 
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This Old Mold 3 - Hot runner systems
Tips for optimizing existing molds to run Eastman Tritan copolyester
 
Selecting the best hot runner system for your needs can vary greatly depending on the size of the part, polyester formulation, and part design. That’s why it’s critical that runner design and selection be discussed together. When using Eastman Tritan copolyester in an existing mold, consider the following factors when designing and processing hot runner systems.
 
Design guidelines
When properly designed, hot runner systems can eliminate sprue and runner regrind, mold with lower pressures, reduce cycle times, and improve processing windows. Good hot runner systems should:
 
  • Have uniform heating and good heat control - The mold should be designed so that heat is quickly removed from the gate. This is best accomplished by the gate orifice being an integral part of the cavity steel rather than the hot runner system being an insert projecting through the cavity into the part.
  • Eliminate holdup spots - The flow channel for the plastic should be streamlined and uninterrupted. Any crevice or pocket where material can collect and degrade will probably cause defective parts.
  • Minimize shear heating - The diameter of the flow path needs to be large enough to minimize the shear heating that can be caused by sharp corners or edges in the flow path at the gate or elsewhere. Mold filling analyses can show shear heating and indicate potential problems during the design stage.
 
Hot drops
Eastman medical grade polymers work best with externally heated hot drops where the polymer is completely enclosed by a heated tube and all surfaces of the melt channel ID are maintained in the desired melt temperature. Heat flow from outside to the center results in a homogeneous melt temperature across the melt channel diameter, allowing excellent temperature control.
 
Valve gates
If possible, a valve system should be used when processing Eastman medical grade polymers. With valve gates, the melt channel is externally heated and the mechanical shutoff feature allows better gate vestige control. The gate size is generally larger when compared with other available systems. The valve pin is retracted during the filling process, resulting in a less obstructed flow, less shear heating, and pressure drop.
 
Processing conditions
In general, manifold and drop temperatures should be set near the actual on-cycle melt temperature value and should be balanced for uniform flow. Many molders use hot drops to gate into a small, cold subrunner, allowing the benefits of cold runner gates while reducing regrind or scrap. It can be beneficial to gate into noncritical areas or to gate into a post or tab that can be hidden or removed.


 
Read more detailed information on gate placement, gate size, and other hot runner system details in our Eastman polymer processing and mold design guidelines.
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Improving Medical Devices with Eastman MXF221 Copolyester
Eastman’s polymers are the key components used in many medical devices, and we’re constantly innovating our materials to help equipment achieve optimum performance and withstand the ever-changing demands of the health care industry.
 
Our latest offering, Eastman MXF221 copolyester, is a biocompatible, fully compounded medical grade polymer that is uniquely suited for medical devices and electronic device housings. Developed from Eastman Tritan copolyester, Eastman MXF221 copolyester offers superior chemical resistance to stringent disinfectants and drugs, improved durability, and greater longevity.
 
Eastman MXF221 copolyester provides many advantages for devices and brands, including:
 
  • Unsurpassed chemical resistance—Unlike polycarbonate or other polymers that lose their impact strength after contact with harsh disinfectants and chemicals, Eastman MXF221 copolyester can withstand many aggressive disinfectants without cracking, crazing, or hazing.
     
  • Durability and impact strength—Eastman MXF221 copolyester retains its impact strength after exposure to tough chemicals and harsh cleaners. In tests measuring notched Izod impact strength, Eastman MXF221 copolyester far outperforms competing polymers.
 
  • Ease of processing—Eastman MXF221 copolyester offers homogeneous pellet processing, which may result in better consistency and reduced scrap rates.  
 
  • Color consistency—Eastman MXF221 copolyester can be molded into both clear and opaque parts, creating more uniform translucence and color to comply with a brand’s color guidelines and palettes.
 
For more information about how Eastman MXF221 copolyester can enhance your devices and brands, visit www.Eastman.com/medical.




 
This Old Mold 3 - Shrinkage
Tips for optimizing existing molds to run Eastman Tritan copolyester
 
When using a mold designed for other plastics to run Eastman Tritan™ copolyester, good cooling is absolutely critical. Proper cooling helps you obtain lower cycle times and high-quality parts while reducing cost. Poor cooling, however, can lead undesirable effects, including mold shrinkage and warpage.
 
To minimize shrinkage, remember these key factors:
 
Uniform wall thickness
A uniform wall promotes even flow, minimizes shear heating, reduces molded-in stress, and tends to minimize warpage.
 
Consistent mold temperatures
A uniform mold temperature helps ensure even heat transfer from both wall surfaces. This will leave the part in a balanced condition, provided the wall thickness is uniform. The mold should be designed for adequate control of the temperature in the range required for the material being processed. This will not only decrease the amount of residual stress, but will also permit reduction of cycle time.
 
Every combination of existing mold properties and molding requirements is different. Tritan experts can review your cooling techniques to help you minimize shrinkage in your old mold.
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4 Keys to Successful Tooling Design
To develop successful injection molding applications, it’s crucial to consider all aspects of design early on in the process. Tooling design review is an important step in helping to determine what type of gating system and other factors are the right fit for your device.
 
Here are four tooling design tips for injection molding with Eastman TritanTM copolyester:
 
Proper gating selection 
  • Most conventional cold gating styles work well with TritanTM copolyesters, including sub, pin, fan, edge, sprue, and diaphragm gates. Self-degating gate styles, such as sub gates or pin gates, typically require smaller gate sizes balancing the ability to limit pressure drop with degating.
  • For hot runner systems, valve gates should be used. Critical design features of TritanTM valve gate systems include thermal control and independent water supply.
Design tooling with good cooling/thermal control 
  • Tritan™ copolyesters require good thermal control throughout the cavity for optimal processing.
  • Injection molding gates typically have the highest heat load in an injection mold.
  • Higher thermal conductivity steels allow greater heat transfer rates, potentially reducing cycle time and providing a more uniform cavity temperature.
Design tooling with a plan for venting 
  • The inability to remove air from the cavity can result in part appearance defects such as incomplete fill (or short shots) and burn marks due to heat of compression of the escaping air.
  • Suggested vent depths for Tritan™ copolyesters are typically 0.0005′′–0.0015′′.
Design tooling with a plan for ejection 
  • Parts should be adequately supported during ejection to avoid part deformation/breakage.
  • Part design features like long cores or deep ribs with minimal draft can result in high forces being placed on the molded part during this process.
  • Tritan™ copolyesters have a relatively low modulus (i.e. are more flexible) and yield strength compared to some competitive transparent resins. Contact us today.
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