Mold Design

  1. What is the preferred gating style for copolyester resins using injection molds equipped with hot runner systems?

    Answer: Valve gates
  2. Are cold sprues an acceptable gating method for use with copolyester resins in injection molding tooling?

    Answer: Yes, when cold sprues are the gating style of choice, a high-heat transfer sprue bushing is recommended. Keep sprue length less than 3 in. Provide cooling lines in close proximity. Use a slight press fit to ensure good thermal contact between the sprue bushing and surrounding tool steel.
  3. What is a key design feature of injection molds constructed for copolyester resins?

    Answer: Cooling. All steel surfaces within the cavity should be well cooled. If there are surface areas of the cavity that approach or exceed the glass transition temperature of the resin during rapid cycling, the resin can become sticky and difficult to eject.
  4. What are common methods of cooling long cores in injection molds constructed for copolyester resins?

    Answer: Bubblers, baffles, and spiral cooling channels are effective methods of cooling long cores. In cases where it is not possible to get cooling water close to the end of a long core, consider the use of high-heat transfer alloys to increase thermal conductivity.
  5. Why is cooling in the gate area important?

    Answer: During the injection molding filling phase, all of the heat going into the cavity passes through the gate, resulting in a high heat load in this area. Mold construction should focus on providing good thermal control in this region of the tool with either a cooling circuit in close proximity or a water jacketed gate insert. It is often desirable to construct this gate cooling circuit such that it can be plumbed independently, such that cooling in the gate area can be optimized independently of cavity cooling.

Secondary Operations

  1. What are acceptable methods for joining and assembly of Tritan parts?

    Chemical–adhesive bonding
    Mechanical–screws, inserts and snap-fit joints
    Thermal–ultrasonic welding, spin welding, laser welding and hot plate welding
  2. Ultrasonic welding–what type of joints work best?

    Answer: Tongue-and-groove and step-joints work best with an appropriately sized energy director.
  3. Can Tritan be decorated?

    Answer: Yes painting, overmolding, printing, labels, and decals can be applied to Tritan with superior results.
  4. What inks can be used to print on Tritan?

    Answer: Eastman has worked with Nazdar and Sun Chemical to optimize ink formulations for use with Tritan.
  5. Does adhesive bonding work well with Tritan?

    Answer: Yes Weld-On® 55, Plastic Welder II™ 14340, Flex Welder 14345, and Lord® adhesives 7542 A/B, 403/19, 406/19, and 406/17 have been demonstrated to form suitable bonds.

Part Design

  1. How much mold shrinkage should I design for with the Eastman Tritan copolyester family of materials?

    Answer: The typical value as determined by ASTM D955 is 0.005–0.007 in./in. (0.005–0.007 mm/mm).
  2. I am designing a box with a "living hinge" for the lid. The living hinge will see multiple cycles in the products life cycle. Does Tritan work well for living hinges?

    Answer:  No. Tritan isn't suggested for living hinge applications.
  3. I am designing a part with multiple ribs. How thick should the base of the rib be to avoid visible sinks on the opposite side?

    Answer: A general guideline range is that the base of the rib be approximately 40%-60% of the nominal wall section.  If the part has a nominal wall of 0.100 in. (2.5 mm), a reasonable range for the thickness at the base of the rib would be 0.040-0.060 in. (1.0-1.5 mm).
  4. What is the minimum wall section that can be molded in Tritan?

    Answer:  There is no real straight forward answer here. The minimum wall section for a part molded out of Tritan will be dependent on manufacturing considerations as well as end-use fitness-for-use requirements.  First, the part has to be thick enough to be filled with reasonable fill pressures. Second, the part must be able to meet any real world end-use physical requirements.  Eastman Design Service Engineers have the experience and tools in place to evaluate your particular design and provide feedback regarding a reasonable part thickness with multiple factors considered.
  5. What is the minimum draft angle suggested for a part designed to be molded out of Tritan?

    Answer:  The suggested reasonable range is 1.0–1.5 degrees per side.  Parts with 0.5 degrees or less have been molded, but this is not suggested due to difficulties that may be encountered such as sticking, drag marks, and extended cycle time requirements.
  6. I am designing an electrical housing that needs to have V0 flammability rating and I want the housing to be clear. Would Tritan be a viable candidate?

    Answer: No. Tritan does not meet the UL V0 flammability requirements. However, a special grade of Tritan with V2 flammability is available for use with some electronic housings.