When choosing a polymer for a medical device, it’s crucial to understand how the material will perform in the real world. Eastman’s 4-step test helps show how plastics hold up when exposed to frequent disinfection, but it’s also important to see how that translates into actual performance in the field.

 
That’s why we developed the housing drop test. This test can be used alongside the 4-step method to understand how a well-designed device will respond to impact after being disinfected.

 

We often receive great questions about molding with Eastman medical grade polymers and are always glad to provide answers and more information. Here is a response to a recent query from our inbox:
 
“What is the heat deflection temperature for Eastman MXF221 copolyester?”
 
Heat deflection temperature (HDT) is the temperature at which a polymer or plastic deforms under a specified load. The HDT of our latest offering, Eastman MXF221 copolyester, is outlined here.
 

Thermal properties
Deflection temperature
	@ 0.455 MPa (66 psi)	ASTM D 648	94°C (201°F)

Eastman Tritan^™ copolyester offers a unique blend of processing and performance properties, including clarity, toughness, and heat and chemical resistance. It can also often be substituted into existing molds with minimal adjustments to processing parameters. This total balance of performance and processing gives Tritan advantages and design flexibility over many other commonly used polymers. Some qualities that make Tritan an excellent choice when it comes to molding parts for the medical market include:
 

• Toughness: Exceptional toughness and durability. Medical device housings made with Tritan are impact- and shatter-resistant and have the ability to withstand extreme conditions.
• Clarity: Outstanding clarity and color retention before and after gamma and e-beam sterilization.

Parts made from Eastman Tritan^™ copolyester can be assembled using a variety of joining techniques, including chemical, mechanical, or thermal methods. The choice of assembly method will depend on the end-user requirements of your application. With whatever method you choose, however, the assembly process can cause stress in devices.
 
The good news is that Tritan is an inherently tough material and can stand up to these stresses. Consider mechanical joining methods. In this technique, molded-in bosses are commonly used to accept screws or threaded inserts, while molded-in or postmold inserts are commonly used where a plastic cover or part must be removed repeatedly.
 

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:
 

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

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 Tritan^TM copolyester:
 
Proper gating selection 

• Most conventional cold gating styles work well with Tritan^TM 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 Tritan^TM 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.

Tips for optimizing existing molds to run Eastman Tritan^™ copolyester
 
Eastman Tritan™ copolyester provides excellent gloss and picks up mold finish very well. When using it in a mold designed for other plastics, however, there are factors you need to consider in order to achieve success.
 
Here are some guidelines for polishing Eastman Tritan^™ copolyester:

• Specify SPI mold finish standards.
• Specify surfaces smooth enough to minimize ejection force.
• Specify final polish in the direction of draw to minimize scuffing.
• Add a light 320 dry grit blasting (SPI B3 finish) to drafted walls to reduce the possibility of a vacuum forming during ejection.

 
It’s important to keep in mind that surfaces polished smoother than required for ejection add to mold cost. In most cases, highly polished surfaces can hinder ejection if there is a vacuum drawn in low or no draft areas. Where no vacuum is drawn, polished surfaces generally eject better.
 

 
Each medical grade of Eastman Tritan^™ copolyester offers a different combination of superior strengths that help optimize performance for specific medical applications. Depending on the needs of your device, you may need a clear or opaque material.
 

Clear applications
If your device is clear, such as fluid management and IV components, renal devices, or dialyzer housings, you’ll need a material with the following properties: