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

Prepolym er Curative

Polyurethane Prepolym er Processing

Dispensing

Dem old

Curing

Finishing

Post-Cure

(M elting),W arm ing &Degassing

M elting orW arm ing

(Degassing)

M etering

M olding

M ixing

Step Do’s Don’tsDegassing Degas Prepolymers

Maintain Proper Vacuum and Temperature

Try to get by Without DegassingTrust 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

Step Do’s Don’tsPrepolymer/Curative Gas Blankets

Use Dry Gas (N2, Dried Air) Use Ambient AirUse Plant AirLeave Containers open

Curative Transfer

Use GlovesUse RespiratorObserve Safety RegulationsWash up

Use Bare HandsSpill Materials

Metering Check CalculationsCheck for Proper Processing ConditionsUse Proper Size BalanceRecord Weights and Conditions

Weigh Without CalculationUse 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 = 133.5 For GR107, EW = 107

Calculation:

4202

%Theory Desired x EW x %NCO Curative pph

Mix Ratio Calculation – Example 1 IMUTHANE 22-90A cured with GR107

22-90A: %NCO = 4.15%. GR107: EW = 107 Desired %Theory: 95%

Calculation:

4202

%Theory Desired x EW x %NCO Curative pph

4202

95 x 107 x 4.15

10

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

Step Do’s Don’tsMixing Make Sure Temperatures Are Correct

Mix Quickly and ThoroughlyScrape Sides and BottomUse StopwatchProvide VentilationWear Safety Glasses and GlovesClean Tools After Mixing

Whip in AirExpose to MoistureUse Wooden SticksBreathe FumesGuess 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

Step Do’s Don’tsPouring & Casting

Pour Evenly and avoid SplashingAllow Trapped Air to Sweep outControl Temperatures (mold and Material)

Dump Material in to Save TimeFlood the Pour SpaceMove Molds too Quickly

Cure and Postcure

Control TemperaturesUse Correct Time

Use Cold Molds or InsertsUse 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.