Hot runner molding systems #1

Introduction and advantages

Eastman receives many questions about molding Eastman Tritan copolyester with hot runner systems. It can be a complex topic, loaded with variables that include not only mold design, but also part size, polymer formulation, and part design. Success depends on early collaboration and clear communication between Eastman, molders, tool builders, and hot runner suppliers.
 
We're usingTritanMoldIt.com as a platform to jumpstart this communication between stakeholders. During the next few months, the Tritan experts will post a series of blogs, beginning with this overview and advantages of hot runners for amorphous copolyesters, including Tritan.

We invite you to help shape our series of hot runner blogs. Send your feedback. Ask your questions. Share your success stories. We look forward to hearing from you.
 

Key advantages of hot runner systems

In a hot runner molding system, the runners are within the mold. They are heated to maintain the plastic resin in a liquid state (a temperature above the material's softening temperature, Tg) within the tool until it passes through the gate into the mold cavity. Unlike a cold runner system, hot runners are not ejected with the finished part. Instead, they stay in the mold in a liquid state, ready to fill the cavity on the next shot.
 
Hot runner systems are popular for high-production runs or in high-cavity molds, where quality is critical and gate witnesses are objectionable. A hot runner system can offer these advantages:
• Less resin used because there is virtually no waste
• Shorter flow path
• Reduced injection time; reduced open-dwelling time
• Lower cost per part for high-volume production—especially small parts
• Higher part quality
• More design flexibility


 

In Part 2 of our hot runner series, we’ll start focusing on specific ways for getting the best results with Tritan in a hot runner system. 

 
TMI TIP: Help make this ongoing series on hot runners more relevant for your needs. Let us know your feedback or questions—and share your experience with hot runner systems and Tritan.  

For more information about hot runners, download the Eastman Tritan copolyester Processing Guide
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Troubleshooting Focus: Flowlines
Flowlines are wavy or rippling surface defects. They can appear as lines, streaks, or patterns, but are consistent with the material flow within the cavity of the mold. They occur when the molten plastic passes through the mold or gate and can have many causes and corrective actions.

If you have more questions about flowlines or other molding defects, talk with your Eastman technical service representative—and ask how to receive your free copy of our Injection Molding Troubleshooting Guide
 

TMI TIPFor more information about getting the best results when you mold with Tritan, watch the webinar 共聚聚酯加工解决方案
 
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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
  • Be smooth but not polished:
    • Sand the surfaces you wish to bond with a 120-grit or finer paper.
    • 金刚石砂轮抛光机、企口刨床或其他器械都可以产生极好的效果。
    • Do not use soft-polishing wheels or flame polishing, as they can round the edges, creating gaps and improper fit.
 
Before selecting an adhesive system, conduct a careful evaluation of the part application to ensure the adhesive provides both acceptable performance (bond appearance and strength) and that it meets all applicable regulatory requirements. See inset box for several recommendations.
 NOTE: This list of recommended adhesive systems does not include all products have been used successfully with Tritan. For best performance, always follow the guidelines provided by the adhesive manufacturer.
    
Recommended adhesive systems for use with Tritan
  • Dymax adhesives for medical devices 
  • Henkel adhesives for medical devices 
  • Weld-On® 55*
  • Lord® adhesives 7542 A/B*
  • Flex Welder 14345*
  • Lord adhesives 403/19*
  • Lord adhesives 406/19*
  • Lord adhesives 406/17*
  • Plastic Welder® II 14340*
*Tested according to ASTM D1002

For details about bonding Tritan to itself and to other materials, contact your Eastman technical representative. For more information about adhesive bonding as well as tips for decorating, painting, overmolding, and other tips, download a free copy of the Secondary operations guide
 
TMI TIP: Adhesives that contain a volatile component may shrink while curing.为了补偿收缩,可将接合处切割成一定的角度,从而可以留出一定空隙,以在接合处稍微多加一些粘合剂。请参考您的粘合剂供应商资料,了解有关收缩的具体信息。
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电子束灭菌如何影响伊士曼Tritan™共聚聚酯?
对医疗器械进行灭菌会对透明聚合物的光学和物理性能带来不利影响。
 
电子束(电子束)辐射是为医疗器械进行灭菌的最常用方法之一,此外还有伽马射线、环氧乙烷(EtO)、高压灭菌器以及低温等离子灭菌等其他灭菌方法。
 
Eastman开展研究以判断电子束辐射对Eastman Tritan共聚聚酯以及其他透明医用聚合物光学和物理特性的影响。
 
Formula Resin type
Eastman Tritan copolyester MX711 共聚聚酯
Eastar polyester MN052 polyester
Eastar copolyester MN211 共聚聚酯
Eastar copolyester MN006 共聚聚酯
DuraStar polymer MN611 共聚聚酯
Tenite propionate 360A40012 Cellulose acetate propionate (CAP)
Lipid resistant PC polycarbonate
TABS Transparent ABS
Medical grade acrylic Acrylic (PMMA)

The objective of sterilizing medical devices is to reduce the bioburden to a safe level with minimal effects on the desired properties of its constituent polymers.
 
Technology advances have improved the performance of e-beam radiation, making it a safe, efficient, and reliable source of energy for sterilization. High dose rates reduce the time of exposure, which can make e-beam a less costly alternative to gamma radiation.
 
To study the effect of e-beam radiation on Tritan MX711, Eastman measured color shifting and physical property retention after e-beam radiation.   

Optical properties
Samples were exposed to e-beam radiation (25 and 50 kGy), then stored in darkness and their color measured at Days 3, 7, 14, and 42 using HunterLab UltraScan Sphere 8000 and the CIE L*, a*, b* color scale. (Samples were stored in darkness and only exposed to light for color measurement.)
 
Figure 1 shows the changes in b* value, which measures the blue to yellow scale after e-beam exposure at 50 kGy. Photos of the molded samples before and after exposure are available upon request.

Figure 1. Eastman Tritan copolyester and other transparent resins after e-beam exposure at 50 kGY—b* color measurements




Figure 2 shows the difference in b* color values between unexposed samples and sterilized samples at Day 42—after e-beam radiation at both 25 and 50 kGy. 

Figure 2. Change in b* color 42 days after e-beam radiation—25 and 50 kGy  

Physical properties were measured before and after e-beam sterilization at 25 and 50 kGy. No physical property degradation was noted for Tritan MX711 or the other resins tested. The polyesters and copolyesters in the study showed no statistical change in molecular weight although Tenite propionate 360 did show a loss of molecular weight, as expected from an aliphatic polymer. 

For complete details of these studies or more information about the advantages of Eastman Tritan copolyesters, email Eastman today. 
 
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成型专业技术从未如此便捷。
Tritan Mold It现已作为移动应用发布!现在,动动手指即可了解Eastman Tritan共聚聚酯相关信息。
 
您可将这款便捷的移动应用用于:
  • 计算干燥时间
  • 计算熔融逗留时间
  • 计算注塑量利用率
  • 下载数据表
  • 观看视频
  • 获取Tritan专家建议等。

开始使用Tritan Mold It应用。
This handy processing resource helps you get the best results from Eastman Tritan copolyester—and access valuable information on other engineering polymers. 
The Tritan Mold It app’s Quick Links function also makes it easy to dive deeper into Tritan applications, successes, and the latest tips for molding Tritan. 
 
​Download the free Tritan Mold It app now.    

 
TMI TIP: After you’ve used the Tritan Mold It app, use the “App Feedback” feature to tell us how you like it—and provide any suggestions for making it an even more valuable tool for you.     
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