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.
So in case you missed it—our medical device housing webinar is available on-demand.
- Understand what is actually causing part failures and how to address it
- Learn how to improve your medical device reliability, reduce repair costs, and extend product life
- See test results comparing Tritan with traditional housing materials based on their ability to retain impact strength after exposure to common medical disinfectants and stress
|TMI Tip: When designing opaque housings for today’s medical environment, always consider both chemical resistance and impact strength. The combination of these two properties is critical for success.|
Hot runner valve-gated systems have been used successfully with amorphous copolyesters like Eastman Tritan™ copolyester for several years. One benefit of the low mold temperature required by Tritan is shorter molding cycle times—but this benefit depends on good management of both heating and cooling.
Best results come from designing a mold that allows good temperature management throughout the drops, mold, sprues, and gates to keep the material in the tool above the glass transition temperature (Tg) until it passes through the gate into the mold cavity—and is ready to fill the cavity on the next shot.
Uniform heating and proper cooling improve success by:
• Eliminating holdup spots that can degrade the material
• Avoiding excessive heat that can lead to sticking
• Minimizing shear heating
• Improving processing efficiency
• Improving part quality
Early collaboration when designing the hot runner system will pay lasting dividends when molding Tritan in a hot runner system.
Elements of effective temperature management for Tritan
A hot runner system allows you fast cycle times while making parts with good surface appearance. When molding Tritan in a hot runner mold, this means cleanly separating the hot and cold areas of the mold with good insulation systems so that melt temperature is kept uniform within the material’s working range of 500°–540°F and the well-cooled mold is maintained at its uniform surface temperature of (100°–150°F)—especially including the area around the gate—to prevent the formation of heat induced sink marks in the molded part.
Planning thermal management early in the design process helps make sure you achieve this combination of mold heating and cooling.
The melt should be maintained at the same temperature generated at the discharge of the screw all the way through the machine nozzle, mold sprue, hot runner manifold, and hot runner drops and tips.
Hot drops and tips
Eliminate holdup spots
(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 potential shear heating areas of concern and indicate potential problems during the design stage. For more information about mold filling simulations, contact Eastman Design Services.
Eastman Tritan™ copolyester requires colder molds than some other plastics, so planning cooling design features in advance pays dividends in cycle time and processability. High mold temperatures, even in small areas of the mold, can cause sticking.
Ample mold cooling channels, uniform wall thickness design, good cooling of pins and thin steel areas, good cooling near hot spots such as sprues or hot runners, insulating areas around hot runners, good water supply with few flow restrictions, and thermolators with exact control settings of water temperature all help ensure efficient production of high quality parts.
A cooling circuit or water jacket in close proximity to the gate is also required for heat removal. Plumbing this circuit independent from other cavity cooling channels can be beneficial, as separate water temperature control can be used to optimize molding performance in both the gate area and the mold cavity.
We suggest separate cooling loops with individual flow and temperature control for hot drop gate cooling.
Well-cooled molds require good water flow throughout. Chillers should be considered to cool the water as relying on tower water may prove to be insufficient.
It is important to maintain suggested surface mold temperatures at the interface with the part. An independent cooling circuit in close proximity is always suggested. Another viable solution for temperature control is a water-jacketed insert. These are sometimes custom fabricated but are also available as standard items from some manufacturers. They usually result in a witness line around the gate, which may need to be considered.
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. Some hot runner suppliers offer gate-cooling inserts.
In Part 4 of our hot runner series, we’ll focus on gate design—specifically valve gates—when molding Tritan in a hot runner system.
We've added more ways to calculate your processing parameters when using Eastman Tritan™ copolyester. In addition to drying time, you can now instantly calculate residence time and volume—with all results based on your specific operation and production goals.
It's all about more results for you.
The examples shown here demonstrate the inputs that can be factored into your calculations—and the results that will be
calculated from these inputs. It’s easy. Just enter your specifications—such as your cold runner weight and cycle time—and get
instant results for drying time, residence time, and volume.
Calculates dryer size and material processing rate
Calculates shot utilization and weight, processing time, hot runner residence time, and much more
Calculates part output per minute, hour, day, week, month, and year
|TMI TIP: Try the new calculators now.|
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.
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
Eastman works with Tritan customers to help ensure efficient processing and product performance are part of your polymer solution.
Eastman Design Services help you receive hot runner benefits by supplying expertise in:
• Knowledge of the molding and performance properties of Tritan
• Injection mold tooling design reviews
• Mold-filling simulation
• Part design reviews
• Stress analysis
Early collaboration helps you move forward.
Early involvement of Eastman can help at critical steps in the project development flow—and help prevent false starts throughout the process. For more information about hot runners, download the Eastman Tritan™ copolyester Processing guide. Or talk with your Eastman technical service representative.
In Part 3 of our hot runner series, we’ll focus on the importance of heat management when molding Tritan in a hot runner system.
|TMI Tip: Help make this ongoing series on hot runners more relevant for your needs. Send feedback. Ask questions. Share your success stories. We look forward to hearing from you.|
Food for thought—compatibility with cleansers and disinfectants used in the food industry
Chemical cleaning and disinfecting are critical steps to guarantee food products have safe, below threshold levels of microorganisms that can reduce product shelf life and cause foodborne illness if too high.
Food contact parts are generally cleaned before disinfecting. This helps reduce microbial contamination but serves the more important purpose of increasing the effectiveness of the powerful disinfectant that follows.
Both sanitizing steps rely on chemicals that can crack and break plastic parts and even lead to their premature failure. Chemical attack also can cause surface etching that creates a favorable environment for microbe growth.
Testing demonstrates Eastman Tritan™ copolyester is significantly more compatible with cleansers and disinfectants than other polymers used in the food industry.
Double-check disinfectant compatibility—with cleansers and with surface materials.
Disinfectants approved for food contact surfaces have different modes of action—and levels of biocidal effectiveness. They also have different levels of compatibility with cleansers and surface materials.
- If incompatible with a cleanser or sanitizer, any chemical agent left on the surface may neutralize the activity of the disinfectant.
- If incompatible with the surface material, the resulting chemical attack can compromise the functionality of the surface.
Be sure to read the labels of all disinfectants to confirm compatibility with your cleanser of choice and surface material.
Tritan is compatible with many common cleansers and disinfectants
Table 1 shows the results of compatibility tests measuring impact properties retained after contact with common products.
Let us know if you have questions about the chemical resistance of Tritan to a specific disinfectant, cleanser, or sanitizer.
|TMI TIP: To learn more about the chemical compatibility of Tritan, view a free webinar, "Chemical Resistance to disinfectants."|