Selecting Medical Grade Polymers

Making the grade—selecting the right medical grade polymer

Eastman understands that the stakes are high when selecting the material for your next fluid management component, blood contact device, or electronic medical device housing. That’s why we want to help make this complicated process simpler when you consider Eastman Tritan copolyester, beginning with two criteria:
•  Making the grade. Selecting medical grade polymers helps ensure your device complies with quality and biocompatibility standards—and that you have reliable support for regulatory approvals.   
•  Matching the application. Each medical grade of Tritan offers a different combination of desirable strengths that help ensure performance in specific medical applications.  

Matching a medical grade of Eastman Tritan copolyester to your needs

Troubleshooting focus: Sinks and voids

Sink marks appear as surface depressions (seen as dimples or grooves); voids are less obvious and may appear as bubbles in clear parts. Both compromise aesthetics and can reduce the confidence a customer has in a part-but the impact is much greater on applications such as fluid management, where leakage from a Luer or stopcock can result in loss of sterility and contamination.

In opaque medical device housing applications where aesthetic is critical, the matte finish and pastel colors that are often used make sinks and voids obvious.   

Sinks and voids are caused by localized shrinkage of the resin at thick sections during the following steps:   
  1. When excessively heated material expands to fill the mold cavity, it results in excess space between the plastic molecules.
  2. The skin of the material in the mold solidifies (freezes) first.
  3. As the remaining resin core cools and shrinks, it pulls the solidified skin with it away from the main mold wall.
  4. If the skin is sufficiently stiff, core shrinkage may not cause surface deformation but a void can form within the core of the resin as it shrinks.

Many Medical hardware housing complaints. One new technology solution.


The increased use of aggressive cleaners, medical disinfectants, and disinfectant wipes is taking its toll on traditional plastics. Many handheld and bedside devices are becoming sticky, wearing thin in high-touch areas, or even cracking, crumbling, or shattering after only a few months of service.
 
The problem is that device housings that were designed just a few years ago are often made with materials that lack the right combination of impact strength and chemical resistance for today’s demanding medical environments.
 
In one of our most popular webinars, from November 15, 2016, we discussed the chemistry and stress behind these premature failures as well as how Eastman Tritan™ copolyester for medical housings is helping to prevent costly repairs and replacements. By replacing traditional housing materials with Tritan, you can improve patient safety and customer satisfaction.

Hot runner molding systems #2

Collaborate early to avoid false starts 
False starts are costly-especially when setting up a hot runner system. Making changes after a hot runner mold is released for building are difficult, extremely expensive, and can have lasting effects on system efficiency.
 

See how early collaboration improves hot runner success.

Early collaboration between Eastman and OEMs, part designers, tool designers, molders, and the hot runner supplier is one of the greatest benefits of molding with Eastman Tritan copolyester. This teamwork helps:
  • Reduce product development time
  • Ensure processing efficiency
  • Improve end-product quality

Troubleshooting Focus: Sprue Sticking

Material sticking can bring processing to a standstill, regardless of its source. When troubleshooting, keep in mind that the location of a sticky part in the mold is not necessarily the area of the mold that is the cause. Different sections of the mold can hang onto the part and exerted force can cause the part to bind in another section. Carefully evaluate what happens as the mold opens with special attention to four possible causes for sticking at the sprue.

Secondary Operations: Adhesive Bonding

与溶剂会挥发不同,粘合层会作为一个功能性部分留在成品组件上。 Therefore, the characteristics of the adhesive layer play a key role in the performance and appearance of the finished part.
 
Consider these characteristics when selecting an adhesive:
  • Chemical compatibility with parts being joined
  • 成品接头的美观性
  • Expansion/contraction with temperature changes (NOTE: if expansion/contraction are a major concern, consider mechanical fasteners.)
  • 脆性,刚性,柔软性
  • 耐用性/使用寿命
  • 粘合强度(与塑料的粘合力)
  • 内聚强度(抗内撕裂)
  • 最终使用要求
 
Eastman Tritan copolyester offers outstanding chemical resistance and has been studied with many adhesives and different bonding procedures. 
Adhesive bonding procedures for Eastman Tritan copolyester     
When adhesive bonding parts made with Tritan, joining surfaces should:
  • Fit well without forcing
  • Have no visible gaps

二次加工:包胶成型


二次成型软触材料的使用通常用于为刚性热塑性弹性体(TPE)增加功能性和装饰元素。Eastman Tritan共聚聚酯展现出与市售的TPE牌号之间具有优异的附着力。在选择使用的TPE牌号之前,请与TPE供应商或Eastman合作选择一种配方适合共聚聚酯基材的牌号,并设计您的零件以取得成功成果。

产品设计考虑因素:                 

  • 优化零件厚度和TPE的厚度,确保附着力和尺寸稳定性。如果TPE的厚度超过Eastman Tritan共聚聚酯零件的厚度,则可能导致从模具中取出时产生翘曲。根据一般经验,建议基材厚度为TPE的两倍。
  • 可以结合机械互锁提高TPE的附着力,促进零件的耐用性。机械互锁对于较薄的TPE层或非常苛刻的适用性要求尤为重要。
  • 对于在多个表面上采用软触功能的设计,应采用流通式设计,以提高附着力和耐用性。
  • 为了最大限度降低剥离或脱层的可能性,TPE的边缘应低于刚性基材非二次注塑部分的高度或与之齐平。

Early collaboration pays long-term rewards

You can increase the chances of success in injection molding projects with early involvement of all major stakeholders. The many rewards of early collaboration include:

  • Reduced product development time
  • Optimized part performance
  • Optimized cycle time
  • Lower scrap rate

Part design: Gate location

 

  


Gates are the belly buttons of the injection molding world-every molded part has one. The big difference is that molders can control the location of the gate. The location should be selected based on an evaluation of part aesthetic requirements, mechanical loading requirements, and fill pattern.

Designing for Manufacturability Webinar Tomorrow!

The Tritan experts at Eastman are hosting a live webinar on December 10, 2015, from 11:00 to 12:00 EST. This webinar will cover these important considerations to help you design for manufacturability:

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