IMUTHANE Processing

Processing of Castable Polyurethane Elastomers – Basic Considerations  Mobile liquids (2 or more parts)  Accurate ratio control needed (ratios range from 1:1 to 3:100)  Good mixing  Accurate temperature control at all stages  Moisture exclusion  Good degassing  Proper molds and filling techniques  Finishing techniques

StepDo’sDon’ts Degassing  Degas Prepolymers  Maintain Proper Vacuum and Temperature  Try to get by Without Degassing  Trust Gauges without Checking Do’s and Don’t’s of Urethane Processing III

Processing – Degassing  Degassing removes dissolved and absorbed gases, from manufacture and those generated through natural aging  Viscosity and surface tension of the prepolymer entrap air and other gases  Degassing of the prepolymer is carried out at the processing temperature: 80 – 100°C  Degassing of the prepolymer is carried out in a vacuum of 28.5” Hg

Processing – Degassing  Degassing is complete when vigorous foaming stops – the time required is dependent on:  the amount of prepolymer  the temperature of the prepolymer  the size and shape of the vessel  the degree of vacuum  the amount of entrapped gases  Use a container that is twice the volume of prepolymer to be degassed to allow for foam rise  It may be necessary to re-heat the prepolymer after degassing because of heat loss

StepDo’sDon’ts Prepolymer/ Curative Gas Blankets  Use Dry Gas (N 2, Dried Air)  Use Ambient Air  Use Plant Air  Leave Containers open Curative Transfer  Use Gloves  Use Respirator  Observe Safety Regulations  Wash up  Use Bare Hands  Spill Materials Metering  Check Calculations  Check for Proper Processing Conditions  Use Proper Size Balance  Record Weights and Conditions  Weigh Without Calculation  Use Paper Cups  Guess at Conditions Do’s and Don’t’s of Urethane Processing IV

Processing – Prepolymer Preparation  Refer to Technical Datasheet for specific processing requirements  Heat only the required amount of prepolymer to the processing temperature  Add pigment, anti-foam, other additives  Degas at the processing temperature, usually 80 – 100°C  Reheat to processing temperature if required

Processing – Curative Preparation  Refer to Technical Datasheet for specific processing requirements  Weigh the appropriate amount to cure the prepolymer, allow for residual  Heat to the required processing temperature, if required (e.g. MBCA)  Curative is always added in liquid form to hot prepolymer

Mix Ratio / Stoichiometry  What is Stoichiometry?  It is the ratio of reactive groups in the curative to reactive groups in the prepolymer  It is represented by % Theory  The best mix of properties is found between 95 and 100% Theory  Outside of this range there can be significant impact on the physical properties

Mix Ratio Calculation  %NCO is the weight per cent of reactive isocyanate groups in the prepolymer. It can be found on the drum label or CoA for each batch.  EW is the equivalent weight of the curative. It can be found in the Technical Datasheet.  For GR133.5, EW =  For GR107, EW = 107  Calculation:

Mix Ratio Calculation – Example 1  IMUTHANE 22-90A cured with GR107  22-90A: %NCO = 4.15%.  GR107: EW = 107  Desired %Theory: 95%  Calculation:

Mix Ratio – Effect on Tensile Strength & Elongation

Mix Ratio – Effect on Tear Strength

Mix Ratio – Effect on Compression Set

Do’s and Don’t’s of Urethane Processing V StepDo’sDon’ts Mixing  Make Sure Temperatures Are Correct  Mix Quickly and Thoroughly  Scrape Sides and Bottom  Use Stopwatch  Provide Ventilation  Wear Safety Glasses and Gloves  Clean Tools After Mixing  Whip in Air  Expose to Moisture  Use Wooden Sticks  Breathe Fumes  Guess at Mixing Times

Processing – Mixing  Check to ensure correct temperatures before mixing  Mixing can be achieved:  Using a plastic container & spatula  Using a drill with attachment  By machine  Thorough mixing by hand is achieved by scraping the sides and the bottom of the container and using a figure-8 stirring pattern  Mix quickly and thoroughly and avoid entraining bubbles  Pour mixing can cause poor physical properties  Degas after mixing if time permits (hand mixing)  Remember – safety – ventilation, gloves, eye wear, protective clothing

Mixing Issues – Curatives  Curatives like IMUCURE GR107 are Liquid and very easily mixed into prepolymers.

Do’s and Don’t’s of Urethane Processing VI StepDo’sDon’ts Pouring & Casting  Pour Evenly and avoid Splashing  Allow Trapped Air to Sweep out  Control Temperatures (mold and Material)  Dump Material in to Save Time  Flood the Pour Space  Move Molds too Quickly Cure and Postcure  Control Temperatures  Use Correct Time  Use Cold Molds or Inserts  Use Excessively High Temperatures

Processing – Pouring  When the prepolymer and curative are mixed, the mixture is poured into the hot mold for curing  Pouring should be carried out in a way that minimises turbulence and stops bubble entrapment in the mold  Pour evenly and avoid splashing  Other molding techniques include:  Injection  Rotational  Centrifugal  Vacuum

Processing – Temperatures  Material temperature – what does it affect?  Demold hardness and toughness  Cure consistency  Efficiency of production  Efficiency of mixing  Ratio – temperature effects viscosity which can change back pressure in machines, and cause mixing difficulties if hand mixing

Processing – Temperatures  Mold temperature – what does it affect?  Demold hardness and toughness  Cure consistency – incorrect mold temperature causes  Shrinkage  Voids, cracks  Sink marks, “christmas tree effect”  Efficiency of production  Bonding for to metal.

Processing – Molds  Mold temperature – refer to Technical Datasheet for material  Molds should be coated with a release agent to ensure easy removal of cast parts  Take care in handling molds – any damage to surfaces will be reproduced in the polyurethane part  Wide material choice for making molds – steel, aluminium, polyurethane, silicone rubber, …  Mold material must be dimensionally stable, heat resistant and inert to the chemical reaction

Processing – Cure & Post-Cure  Material in the mold must be allowed to cure before demolding – the time required depends on the material and varies from 10 minutes to several hours.  Material is then post-cured, generally for 16 hours at the specified temperature. Time and temperature will depend on the material.  Post-cure is necessary to develop physical properties.  Full property development occurs over the next 7 days at ambient conditions.