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STORMS - Key Processing Points For Dow PU Systems

June 2014 Andrew Davies /Paul Fitzgerald

2 PURe Competency Workshop

• 2010 REACH presented the PU world a challenge with the need to move away from Mercury as a catalyst

• Now we have 2nd 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

Introduction

WHAT IS STORMS?

It’s a memory aid we have to help process polyurethane elastomers

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STORMS - The Definition

Stir Polyol Temperature Control Operator Engagement Ratio Control Moisture Tolerance Stir Components Together

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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

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Types of Drum Mixer

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Drum Roller Drum Tumbler Drum Attach Mixer

Bung Mixer/Transfer Pump 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

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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

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System HYPERLAST™ 201

HYPERLAST™ 101

HHYPERLAST™ 152

DIPRANE™ 530 DIPRANE™ 590

Polyol Temperature OC

20-30 35-40 40 - 45 50 – 55 45 – 55

Prepolymer Temperature OC

20-30 25-40 25 - 40 50 – 55 45 – 55

Mould Temperature OC

80 - 90 80 - 95 80 - 110 80-100 80-100

Demould Time (Minutes)

15-25 20 - 30 30 - 40 15 - 40 15 - 40 Typical properties – not to be construed as specifications

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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.

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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.

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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 CO2 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.

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Moisture Contamination

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Isocyanate Group

(R” NCO)

Unstable intermediate

product

Substituted Urea R” HN - C(O) - NH – R

[harder segment than urethane] Water

(H - O - H) Carbon Dioxide

(O - C – O) GAS

2nd Isocyanate

Group

(R” NCO)

Bubble Formation

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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.

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Help overcome those processing frustrations

remember

STORMS

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Thank You

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