STORMS - Key Processing Points For Dow PU Systems June 2014 Andrew Davies /Paul Fitzgerald Dow.com
Introduction • 2010 REACH presented the PU world a challenge with the need to move away from Mercury as a catalyst • Now we have 2 nd Generation materials with processing and performance similar to those of Hg catalyst products • Revert to basic principles that we all used when we started to process polyurethane • Help-Guide to process PU today we call it STORMS PURe Competency Workshop 2
WHAT IS STORMS? It’s a memory aid we have to help process polyurethane elastomers 3
STORMS - The Definition Stir Polyol Temperature Control Operator Engagement Ratio Control Moisture Tolerance Stir Components Together PURe Competency Workshop 4
Stir Polyol The polyol / curative component of the urethane system has always required mixing prior to use. This is the same today because: • homogeneous mixing is needed to realise the full range of properties • this will help ensure the polyol component is fully effective Drums and kegs must be handled as follows: • Melted and conditioned to correct temperatures as indicated on the current Technical Data Sheet (TDS) • Rolled/tumbled or mixed with collapsible/helicoidal stirrer for minimum 30 mins. ensuring minimum air entrapment (see next slide) The machine tank handling the polyol will require degassing and then constant slow agitation by either: • recirculation at a rate so as not to introduce air • keeping the agitator on, again so as not to introduce air PURe Competency Workshop 5
Types of Drum Mixer Drum Attach Drum Roller Drum Tumbler Mixer Bung Mixer/Transfer Pump PURe Competency Workshop 6
Temperature Check Good temperature control is important because the polyurethane catalysts are temperature sensitive. Polyol, prepolymer and mould temperatures are detailed on the Technical Data sheet and these should be followed. Time at temperature can also be detrimental to the product components. Check that you have the most up-to-date technical datasheet Systems processed at temperatures lower than datasheet recommendation can lead to some of the following effects : • Longer pot-life • Slower demould • In-complete cure • Sticky surface effects – most critical for open casting that requires flaming • Reduced physical properties • Duller surface finish • Shrinkage effects PURe Competency Workshop 7
Temperature Continued Systems processed at temperatures higher than datasheet recommendations can result in : •Faster gel times so restricting casting size •Inability to fill the mould •Air entrapment/bubbles •Difficulties when hand casting HYPERLAST™ HYPERLAST™ HHYPERLAST™ DIPRANE™ 530 DIPRANE™ 590 System 201 101 152 Polyol 20-30 35-40 40 - 45 50 – 55 45 – 55 Temperature O C Prepolymer 20-30 25-40 25 - 40 50 – 55 45 – 55 Temperature O C Mould 80 - 90 80 - 95 80 - 110 80-100 80-100 Temperature O C Demould Time 15-25 20 - 30 30 - 40 15 - 40 15 - 40 (Minutes) Typical properties – not to be construed as specifications PURe Competency Workshop 8
Operator Engagement Successful product implementation starts with your production personnel. It is important that they are made fully aware of the process requirements and understand the differences between old and new materials. Attention should be given to the product documentation and drum labelling. Material Safety Data Sheet (MSDS) should be available and read by production operators and supervisors. Data sheet information on material conditioning, handling should be understood. Data sheet information on temperature for materials and moulds must be adhered to. Data sheet information for ratio of components must be adhered to. PURe Competency Workshop 9
Ratio Check The ratio is the relationship between active Hydrogen (e.g. OH, NH)from the curative and the NCO groups of the Isocyanate to achieve a full cure and property realisation of the moulded product. This ratio has been calculated and is detailed on the Technical Data Sheet. • ALWAYS CONSULT THE TECHNICAL DATASHEET – NEVER ASSUME . • Ensure you have the current Technical Data Sheet The materials should be mixed together to a ratio tolerance no greater than 1% by weight Engineering Elastomer datasheets usually quote ratios as ‘parts’ polyol to 1 part prepolymer – be sure to check. Polyol rich castings can lead to a soft end product with reduction in physical properties and poor output. Isocyanate rich castings may make the reactive mixture more susceptible to moisture, leading to bubbles, slow demould, increased post hardening and poor physical properties of the end product. PURe Competency Workshop 10
Moisture Polyols tend to be hydroscopic and therefore will absorb atmospheric moisture. Moisture contamination leads to bubbles or foaming in the casting caused by the release of CO 2 and so care needs to be taken as follows: • Polyol containers must be kept sealed until required • Replace lids on part filled drums – especially in regions where humidity is high • Polyols may be more susceptible to moisture ingress at the elevated temperatures required for processing • Containers for mixing must be clean and dry before use when mixing plugs or decanting samples. Some polyols contain a moisture scavenger – this must be totally mixed prior to decanting to keep it efficient. Machine tanks for all components MUST have a dry air supply and also be sealed. PURe Competency Workshop 11
Moisture Contamination 2 nd Isocyanate Group (R” NCO ) Unstable Isocyanate intermediate Group product (R” NCO) Substituted Urea R” HN - C(O) - NH – R [harder segment than urethane] Water (H - O - H) Bubble Carbon Formation Dioxide (O - C – O) GAS PURe Competency Workshop 12
Stir components together The polyol and isocyanate must be thoroughly mixed together to achieve a homogeneous material at the correct ratio to realise full physical properties. Stir the material either: By hand – depending on pot-life and size of casting using following guidelines: • Condition as per datasheet temperatures • Weigh out appropriate amounts of polyol and prepolymer • Mix between 30 seconds to 1 minute depending on casting size with stirrer/spatula • Transfer mix to another container and mix again • Vacuum degas to remove air (minus 1 bar for 30 sec to 1 minute depending on gel time) • Pour into suitable mould at preconditioned temperature as indicated on TDS. By machine • Condition and vacuum in accordance to TDS and machine specification. PURe Competency Workshop 13
Help overcome those processing frustrations remember STORMS PURe Competency Workshop 14
Thank You 15
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