Polyurethane and polyurea

Two component PU coating system

The most frequently recommended products for two-component coatings

applications arepolyisocyanates and polyols. In addition,

for some applications the polyol and aromatic polyisocyanates may also be

appropriate.

Properties

The properties of a two-component polyurethane coating depend on certain factors, such as the degree of branching of the reaction partners, the content of the reactive groups themselves, physical state of the raw materials

Properties (cont.)A further possibility for modifying the film properties is to use the same polyol and vary the quantity of thepolyisocyanate. By “undercrosslinking,” which means using an NCO to OH ratio less than 1.0 / 1.0, thepolyurethane film generally becomes softer and perhaps more flexible, less weather resistant, and lessresistant to solvent and chemicals.

Properties ( cont)

On the other hand, by “overcrosslinking,” using an NCO to OH ratiogreater than 1.0 / 1.0, the resultant films tend to be harder and more chemical resistant.

Curing of two component

the curing of two-component polyurethane coating systems can be carried out at room temperature.

The drying times can vary considerably depending on the types of polyols and polyisocyanates used.

Curing

aliphatic polyisocyanates have low reactivity by nature and longer drying times as compared to aromatic polyisocyanates. The incorporation of 0.005% dibutyltin dilaurate, 0.2% zinc octoate can shorter the drying time.

CURING POINT

The following points Should be noted 1. Both components must be mixed together thoroughly.2. The reaction which begins immediately upon mixing results in a gradual to rapid viscosity increase.3. The increase in viscosity eventually leads to a gelation of paint

Application of Two component PU Coating

Application by air, airless, orair-assisted airless spray.

electrostatic spray, brush and roller coating.

Moisture- Curing one component Pu coating

Adducts of polyisocyanate/polyol combinations with an excess of isocyanate groups (prepolymers) can crosslink with atmospheric moisture to give insoluble higher molecular weigh polyurethane. This reaction describes the curing principle for moisture-curing polyurethane coatings.

Properties of one component moisture cure pu coating

Curing or drying propertiesThe one-component coatings based on aliphatic

isocyanates(HDI, IPDI) generally need longer drying times than those based on aromaticisocyanates (TDI, MDI). The drying times depend not only on the temperature, but also on the amount ofatmospheric moisture present.

Properties of one component moisture cure Pu coating

With very low absolute moisture content, the drying times may be increased.

The aliphatic polyisocyanate based moisture-cured coatings often require metal catalysts (such as dibutyltindilaurate) to provide reasonable cure times.

Properties ( Cont.)

Weathering PropertiesIt depend on the type of isocyanate used.

Coatings based on TDI or MDI have a tendency to yellow in the light and show a relatively rapid loss of gloss on weathering.

Properties ( Cont)

those based on HDI and IPDI, are light stable. Dependingon the composition, these one-component coatings may be equivalent in gloss retention and chalk resistance to two-component polyurethane,polyurethane coatings have very good mechanical properties.

Pigmented one component Coating Due to the sensitivity of one-component coatings to moisture, a special technique

has to be followed .The formulation is divided into four step

1. Weighing2. Pre dispersing3. Dispersing in the sand mill4. Filling

Application

Moisture-curing coatings based on the De polyisocyanates are normally applied by brushing orspraying. Dip coatings and curtain coating cannot generally be used because of the extended contact between the liquid coating and atmospheric moisture.

Application (cont)

Unpigmented one-component coatings are used primarily for wood substrates such as parquet flooring andother indoor wood flooring applications. Another area of application is for the sealing or coating of concretefloors, and decorative seamless floors.

Application ( Cont)

Pigmented one-component coatings can be used for anticorrosion coatings for metal,

for the coating of concrete substrates, and for various other decorative and

protective coatings.

Formulating Aids

1- Modifiers- these are added to improve specific application

properties (levelingagents or thickeners, for example), Products such as a cellulose acetate butyrate, low molecular weight acrylicresins, and polyvinyl chloride/polyvinyl acetate copolymers are suitable modifiers.

2- Solvent aromatic hydrocarbons such as toluene, and xylene. special care should be taken when selecting the solvents.

Any solvent chosen must not contain hydroxyl groups. Solvents which contain reactive groups such as amines

should not be used since they react with isocyanate groups.

PigmentsInorganic Pigments

White: Titanium dioxide Yellow: Iron oxide yellow, nickel and chrome titanates,

chrome and cadmium yellows Brown: Iron oxide brown Red: Iron oxide red, cadmium red Black: Iron/manganese mixed metal oxide black, iron

oxide black, some carbon blacks Blue: Mixed metal oxide blue Green: Chrome oxide green

Organic Pigments

Blue: Phthalocyanine blue Green: Phthalocyanine green Red: Perylene and quinacridone red Yellow: Monoazo, isoindoline, monoarylide

yellow

Leveling Agent Cellulose acetate butyrate or low molecular weight

acrylic resins . Polyvinyl acetate, copolymers of PVC/PVAC, and

some urea resins may improve leveling properties . Silicone and polymeric fluids and fluoro chemical

additives can improve flow by lowering the surface tension of the coating material

Thickening Agent

Suitable thickening agents are copolymers of vinyl chloride and vinyl acetate, precipitated silicas,and bentonite clay.

If an increase in viscosity is desired, copolymers of vinyl chloride and vinyl acetate can be added to thepolyol solution in quantities of 5-10% based on solid binder.

Thickening agent(Cont)

Bentonite clay thickeners are used in additions of up to 1.5% on solid binder to prevent the settling of pigments and extenders. These agents are best suspended with solvents into a gel before use.

Air Release Agent

Air release agents are particularly useful for the prevention of blistering during application by brush or rollercoating. Modified polysiloxanes and other types of polymeric additives are commonly used as defoamers and air release agents.

Catalysts Catalysts are used in one- and two-component

polyurethane coatings to shorten the curing time,especially in those containing aliphatic polyisocyanates.

Various metal compounds such asdibutyl tin dilaurate and zinc octoate are commonly used catalysts in both two-component coatings and one component

Catalyst ( Cont)

Excessive catalyst levels can also have a detrimental effect on filmappearance, property development, and on exterior durability.

Polyurethanes

Polyurethanes are formed by the reaction between a polyisocyanate and hydroxyl (-OH) containing resin blend

Polyurethanes

Disocyanate can be aromatic or aliphatic

Wide variety of formulations

Polyurethanes

Conventional 2-part (thin film) Waterborne formulations

Moisture cure polyurethane single component End product can be polyurethane or

polyurea chemistry 100% Solids/Elastomeric

Polyurethanes

Conventional 2-part (thin film) Slower cure, longer pot life

Waterborne formulations Use water dispersible polyisocyanates

Paint Specification “Two-Component Weatherable Aliphatic

Polyurethane Topcoat, Performance-Based”

Polyurethane Paint

Weathering levels for color and gloss Level 1 (<1000 hrs or <24 months) Level 2 (<2000 hrs or < 48 months) Level 3 (>2000 hrs or > 48 months)

Color: max 2.0 ∆E, Gloss: max loss 30

Polyurethanes

Typically aliphatic Slower cure Excellent color and gloss retention Good chemical/solvent resistance Good hardness/abrasion resistance

Polyurethanes

100% Solids/Elastomeric Typically aromatic Fast cure Hi build, up to 100+ mils

Polyurethanes

100% solids polyurethane properties: Elongation/flexibility Excellent chemical/solvent resistance Moisture sensitive application Can be applied in low temperatures (below

freezing) Low VOC

Polyureas

Formed by the reaction between an isocyanate component and an amine-terminated (-NH2) resin blend

Polyureas

Isocyanate can be aromatic or aliphatic Aromatic resins will yellow but not crack Aliphatic resins have excellent

weatherability Wide variety of formulations possible

through particular resin blend Typically 100% solids

Polyureas

100% solids polyurea properties: Elongation/flexibility Excellent chemical/solvent resistance Not sensitive to moisture during application Can be applied in low temperatures (below

freezing) Thermal shock resistance Minimize down time Low VOC

Polyureas

Polyaspartic ester based polyureas are a newer technology Resin blend based on aliphatic

polyaspartic ester Can have much slower reaction time Thinner film application Typical use is analagous to conventional

polyurethanes

Polyurethane/Polyurea Hybrids

Hybrid coatings are formed by the reaction between an isocyanate component and a resin blend component Resin blend may contain amine-terminated

and/or hydroxyl-terminated polymers Wider range for reaction time and

performance properties

Polyureas

Fast cure Moderate cure Hybrid systems Paint Specification

“Two-Component Aliphatic Polyurea Topcoat Fast or Moderate Drying, Performance Based”

Polyurea Paint

Type 1: Fast Drying (less than 30 minutes)

Type 2: Moderate Drying (30 minutes to 2 hours)

Weathering levels

Polyurea Paint

Weathering Levels Accelerated weathering levels

1A – 500 hours, max 2.0 ∆E, 20% gloss loss 2A – 1000 hours, max 3.0 ∆E, 30% gloss loss 3A – 2000 hours, max 3.0 ∆E, 40% gloss loss

Outdoor weathering levels 1N – 12 months, max 2.0 ∆E, 35% gloss loss 2N – 24 months, max 3.0 ∆E, 50% gloss loss

Polyurea Paint

Other tests Solvent Resistance

No visible topcoat removal (100 double rubs) Pull-Off Adhesion

Average (3 pulls) ≥ 600 psi Minimum 500 psi

Polyurethane vs Polyurea

Polyureas are faster cure, e.g. seconds Polyureas not moisture sensitive Polyurethanes cure slower but are

moisture sensitive May have fewer adhesion problems

with polyurethanes

Surface Preparation

Steel Abrasive blast cleaning t Angular surface profile

Surface Preparation

Concrete Abrasive blast cleaning Profile/roughening required Specialized primer may be necessary Check moisture content

Application Equipment

Thin film polyurethanes and polyureas (polyaspartics) Conventional or airless spray

100% solids polyurethanes and polyureas Plural component spray


Plural component spray equipment Heats and mixes resin (part A) and curing

agent (part B) components automatically in correct proportions

Paint mixture travels directly to spray gun for immediate application

Some coatings may be brush/roller applied


Plural component spray equipment Storage to deliver unmixed material Proportioning Device Pressure Pump Mixing Device

Static mixer or air impingement Delivery system (spray gun) Flushing system


Plural component application Equipment as recommended by coating

manufacturer Requires trained/licensed applicators Involve coating manufacturer technical

representative for projects Single application (multiple passes)




Polyurethane Applications

Roof coatings Pipe Tank interior/exterior Truck bed liners Railcars Parking decks Anti-graffiti coatings Caulk/joint/sealant materials

Polyurea Applications

Roof coatings Pipe Tank linings Truck bed liners Railcars Parking decks Caulk/joint/sealant materials

Polyurethane Systems

Conventional polyurethane for steel structures (exterior tank, bridges) Surface preparatiion Application:

Zinc primer @ 3 – 5 mils DFT Epoxy intermediate @ 4 – 6 mils DFT Aliphatic polyurethane @ 3 – 5 mils DFT


Waterborne polyurethane for steel /concrete (anti-graffiti coating) Surface preparation: abrasive blast cleaning Application:

Sealer/primer for concrete 2 coats waterborne urethane primer @ 2 – 3 mils

DFT/coat 2 coats waterborne urethane finish @ 2 – 3 mils

DFT/coat


Waterborne polyurethane properties Tensile strength: 5950 psi Elongation: 150% Taber abrasion: <45 mg loss/1000 cycles Graffiti resistance: Level 3, ASTM D6578


Waterborne polyurethane chemical resistance MEK double rubs, 300+ cycles Gasoline: no effect after 7 days 50% NaOH: no effect after 24 hours 10% HCl: no effect after 24 hours Toluene: no effect after 4 hours


Steel pipe (exterior) coating Surface preparation: SP 10, profile 2.5 mils

minimum Application:

100% solids polyurethane @ 13 – 15 mils DFT


Concrete tank lining Surface preparation: ASTM D4259/ ICRI

03732, CSP 5 Application:

Epoxy primer @ 5 – 7 mils DFT 100% solids elastomeric polyurethane @ 60 – 80

mils DFT


Elastomeric polyurethane properties Shore A hardness: 60 Adhesion to concrete: 350 psi Elongation: 400% Tear strength: 150 psi Tensile strength: 900 psi


Elastomeric polyurethane chemical immersion Acetic acid, 10% Hyrdochloric acid, 10% Methanol Nitric acid, 10% Phosphoric acid, 10% Sulfuric acid, 30%

Polyurea Systems

Steel tank lining Surface preparation: SP 10, profile 3 mils Application: 100% solids aromatic

elastomeric polyurea @ 60 – 80 mils DFT

Polyurea Systems

Elastomeric polyurea properties Shore D hardness: 50 Elongation: 250% Tensile strength: 2125 psi Tear strength: 390 psi

Polyurea Systems

Elastomeric polyurea chemical immersion: Acetic acid, 10% Ammonium hydroxide, 20% Hydrochloric acid, 10% Phosphoric acid, 10% Sulfuric acid, 10%

Polyurea Systems

Concrete tank lining Surface preparation: SP 13 / ICRI 03732,

CSP 3-5 Application:

Epoxy primer @ 3 – 5 mils DFT 100% solids aromatic polyurea @ 60 – 100 mils

DFT

Polyurea Systems

Steel structures (exterior tank, bridges) Surface preparation: SP 10, profile 2-3 mils Application:

Zinc primer @ 3 – 4 mils DFT Aliphatic polyaspartic @ 6 – 9 mils DFT

Polyurea Systems

Polyaspartic properties Abrasion resistance: 90 mg loss/1000 cycles Adhesion: 825 psi Corrosion weathering: 15 cycles ASTM

D5894, Rating 10 blistering/corrosion Freeze/thaw: 30 cycles, no adhesion loss

Polyurea Hybrid Systems

Concrete floor coating Surface preparation: abrasive

blasting/mechanical roughening Application:

Epoxy primer @ 3 – 5 mils DFT 100% solids elastomeric polyurea hybrid @

30+ mils DFT

Polyurea Hybrid Systems

Elastomeric polyurea hybrid properties Shore D hardness: 60 Tensile strength: 2300 psi Elongation: 100% Tear resistance: 330 psi Taber abrasion: 25 mg/1000 cycles

Summary of Key Points

Polyurethanes Thin film conventional and waterborne Single component moisture cure 100% solids thick film

Polyureas 100% solids thick film No moisture sensitivity Thin film polyaspartics

Summary of Key Points (cont.)

Blast cleaning generally required Plural component application for 100%

solids polyurethane/polyurea May allow for low temperature applications Minimize down time

Polyurethane and Polyurea coating

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Polyurethane and polyurea