Successfully Processing High Temperature Thermoplastics

Transcription

1 Successfully Processing High Temperature Thermoplastics Jim Kostakes Entec Polymers August 13, 2015

2 Page 2 What Are High Temperature Thermoplastics? These are thermoplastics that can be used in applications that require elevated temperature performance. However, for the purpose of our discussion these are thermoplastics that require high melt temperatures and/or high mold temperatures. These temperatures are generally higher than what is required to process commodity and/or engineering thermoplastics. Melt temperatures C ( F) Mold temperatures C ( F) These materials generally also require higher drying temperatures. Drying temperatures C ( F)

3 Page 3 High Temperature Thermoplastics Examples of High Temperature Thermoplastics include: Polysulfone (PSU) Polyethersulfone (PES) Polyphenylsulfone (PPSU) Polyphthalamide (PPA) Polyphenylene Sulfide (PPS) Liquid Crystal Polymers (LCP) Polyetherimide (PEI)* Polyetheretherketone (PEEK)* * NOTE: Entec Polymers does NOT sell PEI or PEEK

4 Page 4 Thermoplastic Pyramid PES PAI PPSU PEEK LCP We are mainly concerned with these materials in this presentation. PSU PPS PPA PC PPOm PET PBT POM SPS PA6/66 ABS PMMA PP PS PVC SAN HDPE LDPE AMORPHOUS SEMI-CRYSTALLINE

5 Page 5 Processing Considerations Drying: All of these high temperature thermoplastics require drying prior to processing. The primary difference between drying high temperature thermoplastics and commodity / engineering resins is the higher drying temperature and drying time. Depending on the resin, drying temperatures of C ( F) are required.

6 Page 6 Processing Considerations Melt Temperature: These high temperature thermoplastics require high melt temperatures ( C). Heater bands need to be able to supply enough heat so it is recommended to use ceramic heater bands with 5-8 W/cm2 of heating power. Melt temperature is the actual temperature of the polymer, not just the barrel temperature set-points. Care should be taken to avoid excessive temperatures or residence times as these can cause degradation products to form. Some of these products may be corrosive or odorous, for example with PPS.

7 Page 7 Processing Considerations Gates and Runners: All standard gates and runners can be used with high temperature thermoplastics. High viscosity thermoplastics like PSU, PES, PPSU and PEI may require larger gates and runners. Higher flowing thermoplastics like PPS and LCP can use smaller gates and runners.

8 Page 8 Processing Considerations Mold Temperature Because of the high mold temperatures used ( C / F) Molds should be made of high quality steel. Hot work tools steels (AISI H10 to H13) have been successfully used with some high temperature thermoplastics. Molds should be well insulated from the machine platens to minimize heat loss. Hot oil or pressurized water is preferred over cartridge heaters for more uniform heating. Mold temperature should be the actual steel temperature, not the mold temperature set-points. Too cold of a mold temperature can result in excessive molded in stress which can lead to premature part failure. Too cold of a mold temperature can result in incomplete crystallization (i.e. PPS) which can cause dimensional and warpage issues as well as inferior mechanical properties.

9 Page 9 Processing Considerations Mold Temperature Typically the mold is closed and allowed to normalize at it comes up to heat. Once the molding process is started, the actual steel temperature should be checked. Checking again when in normal production is prudent. The actual mold temperature can shift so temperature set points may have to be adjusted.

10 Page 10 Processing Considerations Purging (start up): In most cases, purging with low melt index PE or PP or purging compounds is acceptable. The purge compound should be run through the barrel at about 250 C (or at the melt temperature of the high temperature thermoplastic) until the barrel is cleaned. Then the barrel temperatures may be increased to the desired temperature setting appropriate for the high temperature thermoplastic. The high temperature thermoplastic material should be purged through the barrel before molding parts to ensure that all traces of purge compound are removed.

11 Page 11 Processing Considerations Purging (shut down): Empty the barrel of all of the high temperature thermoplastic. Introduce the purge compound and purge until all traces of the high temperature thermoplastic material are gone. The machine can now be shut down.

12 Page 12 Processing Conditions PRODUCT MELT TEMPERATURE, C MOLD TEMPERATURE, C DRYING, C Ultrason S PSU (unfilled) Ultrason S PSU (reinforced) Ultrason E PES (unfilled) Ultrason E PES (reinforced) Ultrason P PPSU (unfilled) Grivory HT1 PPA (reinforced) Grivory HT2 PPA (reinforced) Fortron PPS (reinforced) Vectra "A & B" LCP (reinforced) Vectra "C" LCP (reinforced Vectra "Ei" LCP (reinforced

13 Page 13 Case Study: Isoplast RTPU Isoplast is a rigid thermoplastic polyurethane (RTPU) produced by Lubrizol. While not a high temperature thermoplastic, Isoplast is a very finicky material to process and therefore makes for a good example. Isoplast MUST be processed exactly within the recommended processing conditions. You cannot cheat with Isoplast like you can with some other thermoplastics.

14 Page 14 Case Study: Isoplast RTPU Isoplast is a live polymer. This means that is undergoes a rapid and reversible depolymerization and repolymerization during processing. This results in a very low molecular weight during processing (depolymerization) and a rebuilding of high molecular weight during cooling/solidification (repolymerization). If not dried and processed within the recommended processing conditions the repolymerization does not place, resulting in a brittle, low molecular weight polymer.

15 Page 15 Isoplast RTPU Case Study: ISOPLAST Rigid TPU 2015-M-3A

16 Page 16 Case Study: Isoplast RTPU Processing variables that affect Isoplast are: Drying Melt temperature Mold temperature Shear / Injection Speed Packing Cavity Balance

17 Page 17 Case Study: Isoplast RTPU DRYING: Because Isoplast is susceptible to hydrolysis it MUST be dried properly. Drying temperature is within 10 F of the glass transition temperature (varies with the grade). Moisture content should be 0.02% or less. Drying time of 12 hours minimum, even from sealed bags. Even 15 minutes exposure to ambient conditions can absorb moisture and cause splay.

18 Page 18 Case Study: Isoplast RTPU MELT TEMPERATURE: Melt temperature range is C, depending on the grade. Melt temperature should be closely controlled since Isoplast has a very steep viscosity temperature curve. Hot runners are OK but need tight temperature control. Manifold should have at least one temperature control zone. Each hot drop should have individual temperature control.

19 Page 19 Case Study: Isoplast RTPU MOLD TEMPERATURE: Mold temperature is critical for the repolymerization to take place. Mold temperature range is C, depending on the grade. Mold temperature MUST be a minimum of 65 C but will vary with the grade. Mold temperatures below the minimum temperature will produce parts that are brittle and may have poor surface aesthetics M-3A

20 Page 20 Case Study: Isoplast RTPU OTHER PROCESSING CONDITIONS: Isoplast does not like high shear conditions so the injection speed should be slow and the gates and runners should be large. Minimum gate size of inches Sub-gates are not recommended Splay is a sign of over-shearing Isoplast does not like to be over-packed. Over-packing (or cavity imbalance) should be avoided otherwise the parts will be brittle and require annealing M-3A

21 Page 21 Case Study: Isoplast RTPU PRODUCT MELT TEMPERATURE, C MOLD TEMPERATURE, C DRYING, C Isoplast 101 low heat Isoplst 202EZ high heat Isoplast 101LGF40 low heat long glass reinforced Isoplast 202LGF40 high heat long glass reinforced

22 Page 22 Isoplast RTPU Isoplast is shear sensitive. Slow injection speeds with little or no back pressure 200 psi max Slow screw recovery speed Screw and check ring need to be tight Independent heat on nozzle tip 2015-M-3A

23 Page 23 Isoplast RTPU If possible use a return air cooler at the drier Better dryer efficiency The air cooler can trap low melting point volatiles and plasticizers which could damage the molecular sieve material in the desiccant beds M-3A

24 Page 24 Summary High heat thermoplastics have continuous use temperature ratings of 150C+ Running hot molds is essential to insure low to no molded-in stress Molds need to be insulated from the plattens Mold and material melt temperatures should be checked with a pyrometer Don t rely on temperature set-points

25 Page 25 Thank you.