Improving Manufacturability Through Part and Mold Design for Eastman Tritan™ Copolyester Jeffrey Skelton and Krish Rajagopalan Eastman Specialty Plastics jskelton@eastman.com| 423-224-9694 krish@eastman.com| 919-717-2420

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

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

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

Part Design

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.

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

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.

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

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.

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

Tooling Design

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.

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.

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.

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

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.

Tooling design—cooling techniques Gate area Cavity

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

Processing

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.

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.

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

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

Q&A

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