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I recently successfully injected some 38mm neck preforms following the "EASTMAN TRITAN Drying and processing guidelines for injection molding" pdf. I am now trying some tests to blow these preforms into small bottles.

Can you please share with me some guidelines with regards to blowing the preforms?
For example, how do the required conditions vary from blowing PET bottles.

Thank you.


Hi Slanfranco,

Thank you for your question. I hope you find the following information on blow molding helpful. If you have any further questions, please feel free to contact us here so we can connect you with our technical services group. 

Comparison of Eastman Tritan™ copolyester and PET in Stretch Blow Molding
Tritan copolyester can perform well on stretch blow molding processes, both reheat blow and injection stretch blow. The primary differences between PET processing and Tritan processing relate to the higher softening point of Tritan. PET softens around 80 C. Tritan softens around 110-120 C.

Preform Stretch Ratio
PET strain hardens in the stretch blow process and benefits from very high stretch ratios. Typical planar stretch ratio for PET is 10-12. Tritan remains amorphous in the stretch blow process and does not strain harden as does PET. Therefore, typical planar stretch ratio for Tritan is 1.8 - 2.5. Higher ratios can be used, but it becomes more difficult to achieve good aesthetics and material distribution.

Preform Temperature at Blow
PET is typically processed at preform temperature of 100-110 C. Tritan® has a significantly higher softening temperature, and is typically processed at 140-155 C for sports bottles and similar applications. Tritan baby bottle processing uses preform temperatures of 180-195 C to enable making a low stress bottle.

Blow Pressure
Because of the strain hardening effect, PET benefits from very high blow pressure, upwards of 400 psi. This high pressure is unsuitable for Tritan copolyester and will cause aesthetic problems, such as orange peel or flow marks. The high pressure also creates high residual stress in the bottle, which can reduce chemical resistance and dishwasher durability.
Tritan bottles are preferably made with two-step blow. For sports bottles or similar applications, primary air is 30-40 psi, and secondary air is 80-120 psi. The blow timers should also be set to allow full inflation with primary air, and then higher pressure secondary air can help form the sharper details of the bottle.
Tritan baby bottles are a special case, using very hot preforms and very low blow pressure to create a bottle with minimal residual stress.

Blow Mold Temperature
PET bottles are typically made with blow mold temperature of 15-25 C. Because Tritan has a higher softening temperature, blow mold temperature is typically 50-55 C for sports bottles and similar applications. Tritan baby bottle processing uses blow mold temperature of 85-90 C to further reduce residual stress in the bottle.

Reheat Blow Process - Preform Storage and Moisture
Since PET uses relatively low preform temperature, the moisture absorbed from the air during storage does not cause significant problems. There may be a noticeable shift in material distribution, but no aesthetic problems.
Since Tritan uses preform temperature above 100 C (vaporization temperature of water), excessive moisture absorbed by the preforms in storage can show up as small bubbles in the bottle sidewall. To minimize this effect, preform should be used within 2-4 weeks of molding, depending on the relative humidity of the storage environment.
 

My company represents and sells pigment dosifiers, and a client That has Nissei stretch- blow machines is asking me if I can provide an adequate dosifier to dose micro granular pigments in your Tritan Copolyester.
We have a special dosifier with a refrigeration system used specifically for PET resins that need to be dried for several hours and are feed to the injection stretch blow machines at temperatures of around 110-140 °C
We suposse that your copolyester also needs to be dried and then feed o the injection machines, we will appreciate if you could give us some guide lines for dosing pigments in the Nissei machines and also in Husky, and Netsal machines.
Thanks and Regards
Eng. Francisco Ollervides