1. Improving Manufacturability Through Part and Mold Design for Eastman Tritan™ Copolyester
Jeffrey Skelton and Krish Rajagopalan
Eastman Specialty Plastics

2. What are TritanTM Copolyesters?
dimethyl terephthalate
(DMT) monomer
cyclohexane dimethanol
(CHDM) monomer
tetramethylcyclobutanediol
(TMCD) monomer
Building block for PET, particularly when combined with ethylene glycol (EG; a basic diol)
Basis of Eastman copolyester chemistry; modification of PET with CHDM provides:
Clarity (slow crystallization)
Toughness
Chemical resistance
Slight thermal resistance
Critical to Tritan; provides
significantly increased thermal resistance 2

3. Eastman Tritan™ copolyester Balancing processing and performance properties
Clarity – balancing lively aesthetics and long-lived performance
A high level of light transmittance
A low level of haze
High gloss provides vibrant appearance in colored or tinted products
Toughness – balancing high visual impact with enduring impact resistance
Tough
Durable
Maintains functional and aesthetic integrity over product life
Toughness
Heat
Resistance
Clarity
Easy
processing
Chemical
resistance
Chemical resistance and hydrolytic stability – tipping the balance in your favor
Eastman Tritan™ copolyester can withstand many harsh chemical environments without crazing, cracking or hazing
Glass transition temperature – balancing heat resistance and easy processing
Reduced molding and sheet-thermoforming cycle times
No need for separate annealing step

4. Eastman Design and Technical Services
MATERIAL SELECTION
PART DESIGN
TOOL DESIGN
PROCESSING
SECONDARY OPERATIONS

5. Part Design

6. Part design—keys to success
Design action
Factors to consider
Design parts with reasonable fill pressure, fill pattern, and volumetric shrinkage.
Eastman Design Services uses mold-filling simulation to evaluate “moldability” of part design with a particular resin.
Design parts with gate location in mind.
Select location based on aesthetic requirements, mechanical loading requirements, and fill pattern.
Design parts with a plan for ejection.
Design part to withstand ejection forces.
Design parts to
eliminate sharp notches.
Rounded corners make tough parts.

7. Part design—predicted fill pressure
Excessive fill pressure results in:
High clamp tonnage requirements
Reduced life of mold components due to high stress loading
Higher ejection force requirements—possible part deformation or breakage
Running excessive melt temperature to reduce pressure can result in resin degradation.
Eastman Design Services uses mold-filling simulation to estimate required fill pressure.
Guideline of 15,000 psi maximum fill pressure for new part designs
MFR g/10 min, 280°C, 1.25-kg load
Tritan TX1001 7
Tritan TX2001 8
Tritan TX1501 18

8. Part design—fill pattern
Evaluate fill pattern with mold-filling simulation.
Eliminate potential fill-pattern issues, such as:
Flow-front hesitation
Air traps
Weld lines—locate in unstressed areas if possible.

9. Part design—volumetric shrinkage
Minimize volumetric shrinkage to avoid shrinkage defects such as sinks/voids.
Minimize thick sections to reduce cycle time.

10. Part design—gate location considerations
Aesthetics
Gate leaves a “witness” where the part is separated from the runner system.
This appearance defect is typically hidden in an inconspicuous location.
Mechanical properties
Gate locations typically exhibit mechanical properties inferior to the rest of the cavity.
Gates should be located in areas that are not subjected to externally applied high tensile loading.

11. Part design—eliminate sharp notches
Notches act as stress concentrations during impact loading.
Food pan with rim
Sharp “notchy” rim
Rounded rim preferred

12. Tooling Design

13. Tooling design—keys to success
Design action
Factors to consider
Proper gating selection
• Cold gating works well with copolyesters. • If hot runner is used, use valve gates.
Design tooling with good cooling/thermal control.
Copolyesters require good thermal control throughout the cavity for optimal processing.
Design tools with a plan for venting.
Poor venting can result in burn marks and incomplete fill.
Design tooling with a plan for ejection.
Adequately support parts during ejection to avoid deformation or breakage.

14. Tooling design—cold gating systems
Successful gate designs for copolyester injection molding include sub, pin, fan, edge, sprue, and diaphragm gates.
Self-degating styles (sub gate, pin gate) typically require smaller gate sizes.

15. Tooling design—sprue gating
High-heat-transfer sprue bushings recommended
Design cooling lines in close proximity.
Slight press fit between sprue bushing/tool steel
Sprue length < 3”
Reduces required ejection force
Reduced pressure losses during fill
Extended machine nozzles can be used to reduce sprue length.
Draw polish existing sprues to improve ejection.

16. Tooling design—hot gating systems
Valve gates recommended when using hot runner systems with Eastman Tritan™ copolyester.
Provide excellent thermal control around gate area
Cooling water circuit in close proximity to gate
Many gate suppliers offer water-jacketed gate.
Consider an independent water supply to control gate water temperature independent from cavity cooling circuit.
Cooling water jacket insert

17. Tooling design—need for cooling
Coefficient of friction/ejection is significantly higher as steel temperature approaches the glass transition temperature of the material.
Higher-Tᶢ copolyesters, such as Eastman Tritan™ copolyester, reduce sticking issues in tooling with cavity “hot spots” compared with lower-Tᶢ copolyesters, such as PET, PETG.

18. Tooling design—cooling techniques
Gate area
Cavity

19. Tooling design—ejection
Eastman Tritan™ copolyester is more flexible than some competitive resins.
Provide adequate support during ejection
Minimize ejection force requirements.
Polish—polish mold cavity features in the direction of draw
Cooling—no hot spots
Mold steel coatings
Part
Ejector

20. Processing

21. Molding essentials: drying Eastman Tritan™ copolyester
Drying is critical for efficient processing and retaining polymer molecular weight (IV).
Desiccant drying
Minimum 4 hours at 190°F
Aim for under 0.03% moisture content.

22. Molecular weight as measured by inherent viscosity (IV) affects many polymer properties:
Impact and tensile properties
Tensile properties
Impact properties
Heat resistance and creep
Chemical resistance
Viscosity
Heat resistance and creep
Chemical resistance
Property
Viscosity
Molecular weight/IV
Drying is absolutely necessary to maintain properties.

23. Other factors that affect inherent viscosity (IV):
Extreme heat in combination with moisture can cause excessive molecular weight (IV) loss.
Recommended processing conditions for Eastman Tritan™ copolyester:
Under normal conditions, IV loss is ≤ 0.05 or 8%.
Mold T
Melt T
Target residence time (min)
Typical IV loss
60°C
(140°F)
282°C
(540°F) 5
≤ 0.05 (8%)
Effect of melt temperature and residence time

24. Processing tips—injection molding Eastman Tritan™ copolyester
Injection molding recommendations for Tritan
Target melt temperatures in the 520–540°F range
Tool steel surface temperatures 130–150°F to reduce part stress and be below HDT for ejection
Linear part shrinkage in the 0.005–0.007 in./in. range

25. Q&A

26. Technical information disclaimer
Any technical information or assistance provided herein is given and accepted at your risk, and neither the sender, Eastman Chemical Company, nor its affiliates makes any warranty relating to it or because of it. Neither Eastman nor its affiliates shall be responsible for the use of this information, or of any product, method or apparatus mentioned, and you must make your own determination as to its suitability and completeness for your own use, for the protection of the environment, and for the health and safety of your employees and purchasers of your products. No warranty is made with respect to the merchantability or fitness of any product; and nothing herein waives or modifies any of Eastman’s conditions of sale.