SPRAY POLYUREA TECHNOLOGY
Polyurea spray coatings is THE BEST PRODUCT RECOMENDATION for WATERPROOFING are typically used as a coating or lining in water tanks, secondary containment and waste water management applications. Polyurea approved for direct contact with potable water. Polyurea is an organic polymer that is the reaction of isocyanate with an amine terminated polyether resin, forming a plastic-like or rubber-like compound that may be used in many of the same ways as older technologies – polyurethane, epoxy, vinyl ester, neoprene; to name a few.
What is Polyurea?
A polyurea coating/elastomer is that derived from the reaction product of an isocyanate component and a resin blend component. The isocyanate can be aromatic or aliphatic in nature. It can be monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymore. The prepolymer, or quasi-prepolymer, can be made of an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin.
The Resin blend must be made up of amine-terminated polymer resins, and/or amineterminated chain extenders. The amine-terminated polymer resins will not have any intentional hydroxyl moieties. Any hydroxyls are the result of incomplete conversion to the amine-terminated polymer resins. The resin blend may also contain additives, or non-primary components. These additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier. Normally, the resin blend will not contain a catalyst(s).
Polyurea Formulation & Raw Materials
A typical polyurea consists of a multi-ingredient chemical formulation commonly shipped in 55-gallon drum sets or 5-gallon pales. Part A is a dark colored viscous liquid called isocyanate. Part B is commonly called the amine resin blend. It is often colored, or pigmented, and normally requires agitation or stirring before use.
When the liquids are thoroughly mixed, they result in an immediate chemical reaction that becomes viscous and ultimately solid. This reaction is very fast and typically sets up dry to the touch within seconds. Ultimate cure usually takes up to 24-48 hours, however longer and shorter cure time durations are quite possible depending on specific formulation and characteristics of mix.
The use of different types, and/or different volumes, of isocyanates, polyether, or polyester amines, chain extenders and other additives can have a significant effect on the ultimate physical properties and final characteristics of the polyurea coating/lining system.
Technical Aspect of Polyurea Formulations
Polyureas have been described as the resin from a polyurethane reacted with the curative of an epoxy. This is a good description, as polyurea coatings do seem to take the best from both of these polymer technologies. They have improved chemical and solvent resistance, and higher temperature resistance compared with the polyurethanes. They also have better impact resistance and higher elongation vis-à-vis the epoxy.
A polyurea is formed when amines react (cure) with the isocyanate. This reaction is fast, auto-catalytic (that means it does not need a catalyst to react – even at cold temperatures) and leads to many of the special properties that allow polyureas to distinguish themselves from the other polymers.
There are three MAIN properties:
- Polyurea reactivity is independent of the ambient temperature. Polyurea reacts fast – and it will react at the same speed regardless of the temperature. It can be 100 F or -25 F and the reactivity is almost the same. Polyurethanes can be catalyzed to also react very fast, but a system designed for 70 F, will take forever to cure at -20 F. A polyurethane system that will cure properly (fast) at -20 F will be too fast to handle at 70 F. Epoxy cannot cure at these very low temperatures.
- Polyurea reactivity is independent of the ambient humidity. It can be 98% RH and the polyurea coating will spray bubble-free. (Be careful of the dew point – that’s a different story) A polyurethane must have catalysts to complete the reaction. These catalysts are designed to catalyze either the polymer reaction (gelation) or the “blowing” reaction (many polyurethanes use this well known use of water to react with the isocyanate to release CO2 to use as the blowing agent in polyurethane foams). Unfortunately, either types of catalyst will catalyze BOTH reactions – to some degree. The choice of a good gelation catalyst will still catalyze the ISO/water (from the humid air) reaction – and when it does you WILL have bubbles.
- Polyureas develop their physical properties FAST. This gives the polyurea “FAST RETURN TO SERVICE” — meaning you can drive on the coated floor and/or use the coated product within 12 hours of application. Polyurethanes take up to 14 days to fully develop their physical properties. Epoxy require several days.
As mentioned before, polyureas have improved chemical and solvent resistance and higher temperature resistance compared with polyurethanes. They have improved impact resistance and elongation compared with epoxies. All of the properties can be impacted by the formulating chemist.
The formulating chemist will always want to know the application for which his polyurea system is intended. The proper selection and amount of raw material components will effect the performance – both processing and physical properties.
Polyurea spray coatings The technology and latest developments
Abstract Polyurea spray coatings technology is one of the new developments of the last 20 years. This technology combines fast curing, even at very low temperatures, and water insensitivity with exceptional mechanical properties, chemical resistance and durability. The development of new raw materials and improved spray equipment has made it possible to overcome the initial problems of this technology such as substrate wetting, intercoat adhesion and surface finish quality. The latest development programs are focussing on the extension of the application fields through the introduction of MDI-prepolymers combining low viscosity with low NCOcontent, resulting in slower reactivity and/or higher flexibility. Alternatively, prepolymers with higher NCO-content produce coatings with superior hardness.
This paper details the technology, eradicates the misconceptions and provides an update on the latest developments in the field of raw materials, formulation and application performance for polyurea spray. Polyurea is a type of elastomer that is derived from the reaction product of an isocyanate component and a synthetic resinblend component through step-growth polymerization. The isocyanate can be aromatic or aliphatic in nature. It can bemonomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymer. The prepolymer, or quasi-prepolymer, can be made of an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin.
The resin blend may be made up of amine-terminated polymer resins, and/or amine-terminated chain extenders. The amine-terminated polymer resins will not have any intentional hydroxyl moieties. Any hydroxyls are the result of incomplete conversion to the amine-terminated polymer resins. The resin blend may also contain additives, or non-primary components. These additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier. Normally, the resin blend will not contain a catalyst(s)
The word polyurea is derived from the Greek words πολυ- - poly- meaning "many"; and ουρίας - oûron meaning "to urinate". The latter term refers to the substance urea, found in urine, rather than urine itself. Urea or carbamide is anorganic compound with the chemical formula (NH2)2CO. The molecule has two amine groups (–NH2) joined by a carbonylfunctional group (C=O). In a polyurea, alternating monomer units of isocyanates and amines react with each other to form urea linkages. Ureas can also be formed from the reaction of isocyanates and water which forms a carbamic acid intermediate. This acid quickly decomposes by splitting off carbon dioxide and leaving behind an amine. This amine then reacts with another isocyanate group to form the polyurea linkage. This two step reaction is used in what is commonly but improperly called polyurethane foams. The carbon dioxide that is liberated in this reaction is the primary blowing (foaming) agent especially in many polyurethane foams which more precisely should be called polyurethane/urea foams
The choice between the different polyurethane (PU) technologies is based upon different parameters (Figure 2). Polyurethane presents the best compromise between cost and quality, but is limited by the application performance. The polyurethane system is susceptible to blistering when the substrate contains more than 5% humidity. This is due to the competition between hydroxyl-polyols and water for the reaction with an isocyanate group. Humidity content of the environment and the application temperature are limiting factors for polyurethanes and other chemically reacting systems. Hybrid systems already have a larger scope of application conditions, but the presence of catalysts in hybrids makes them more sensitive to humidity than “pure” polyurea systems. Moreover, because the catalysed polyol/isocyanate reaction behaves differently from the amine/isocyanate reaction to changing application temperatures, the system becomes less robust. Polyurea can be used in extreme conditions. When it is used on substrates almost saturated with water, polyurea will not provoke blistering nor will blistering occur when the air contains high amounts of humidity. Even at very low temperatures (as low as minus 20°C) the polyurea coating will still cure. Polyurea coatings combine high flexibility with hardness. They are the most suitable coatings when the following is required: · high curing speed, · application under high humidity and/or at low temperatures, · extreme abrasion resistance, · impermeable membranes, · high thickness build up, · chemical resistance.
Polyurea and polyurethane are copolymers used in the manufacture of spandex, which was invented in 1959.
Polyurea was originally developed to protect tabletop edges which lead to the development of two-component polyurethane and polyurea spray elastomers took place in the 1990s by Mark S Barton and Mark Schlichter US 5534295 patent. Its fast reactivity and relative moisture insensitivity made it useful for coatings on large surface area projects, such as secondary containment, manhole and tunnel coatings, tank liners, and truck bed liners. Excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. They can also be used for spray molding and armor. Some polyureas reach strengths of 6000psi (40MPa) tensile and over 500% elongation making it a tough coating. The quick cure time allows many coats to be built up quickly.
In 2014 a polyurea elastomer-based material was shown to be self-healing, melding together after being cut in half, without the addition of catalysts or other chemicals. The material also includes inexpensive commercially available compounds. The elastomer molecules were tweaked, making the bonds between them longer. The resulting molecules are easier to pull apart from one another and better able to rebond at room temperature with almost the same strength. The rebonding can be repeated. Stretchy, self-healing paints and other coatings recently took a step closer to common use, thanks to research being conducted at the University of Illinois. Scientists there have used "off-the-shelf" components to create a polymer that melds back together after being cut in half, without the addition of catalysts or other chemicals.
Polyurea has become a preferred long term solution for narrow boats. The traditional coating with bitumen, known as "blacking" is being replaced with the practice of polyurea coatings. The clearest advantage is that it is not necessary to reapply a coat every 3–4 years. It is thought that Polyurea coatings last 25–30 years.
Fast property development
Polyurea coatings are mainly used in applications were fast curing is needed. When used as a corrosion protection on pipes, storage of high volumes of coated pipes is difficult and, because of the weight, the coating needs to be fully cured before being transported. Polyurea used for pier protection needs to be fully cured before high tide. A polyurea coating builds up high internal stress during the initial phase of the curing due to the high reactivity. The stress has a negative influence on the development of the physical properties of the freshly applied polyurea film. By modifying the MDIprepolymer, it is possible to improve the relaxation of the coating and thereby reduce the waiting period before the applied coating can be put in service. The improved relaxation results in: · less stress build up; · no deformation; · improved adhesion, and · faster physical properties development. For this study the cold impact resistance was tested, along with standard physical properties (table 8a). Cold impact testing within the hour after application proved to be a very reliable measurement of property development as a function of time. The goal was to develop the properties faster without compromising the end properties
polyurea COATING SYSTEMS benefits
- Trained application teams
- Professional equipment
- Proper preparation of surface area
- Polyurea formulations including additional products MORE..
POLYUREA APPLICATION FIELDS
HIGH PRESSURE TWO COMPONENT SYSTEM
SPRAY POLYUREA high pressure systems: Two-component, high pressure systems (typically 800-1600 psi) use 55-gallon drums and are more often used when insulating larger areas on new construction or major renovations on walls and roofs. These products are intended for professional use. These products require special training and the use of specialized personal protective equipment (PPE), including respirators.
For a typical high pressure SPRAY POLYUREA application, a spray rig (truck) which houses the SPRAY POLYUREA ingredients, air supply and other items is parked near the home or building to be sprayed. Hoses (up to about 300 ft. in length) are carried to the application area and installers wearing proper protective equipment spray the POLYUREA.