Water Based Polyurethane Dispersions (PUD's)
- Water-based Polyurethane dispersions (PUDs) are a rapidly growing segment of the polyurethane coating industry due to environmental legislations such as the clean air act and also due to technological advances, that has made them an effective substitute for the solvent-based analogs. They are versatile and environmentally friendly coating materials that are available in a wide range of hardness and solid content. Their zero to low volatile organic content facilitate their formulation into a compliant coating for many different substrates. Their versatility and wide range of superior properties, such as abrasion resistance, impact strength and low temperature flexibility are the driving forces to their continuously expanding usage in many applications.
- Polyurerthane dispersions are fully reacted polyurethane/ polyureas of small and discrete polymer particles ranging in sixe from 0.01-5.0 microns in a continuous water phase. They are free of isocyanate residues and have a zero or a very low volatile organic content (VOC). They are safe to handle and are a good choice for compliant coatings. PUDs can be made to have 30-65% solid content and a wide range of film hardness.
- One of the drawbacks of PUDs is their relatively higher cost. To compensate for the higher cost and in some cases, to improve adhesion to certain substrates, the PUDs are blended with other low cost dispersions. Acrylic emulsions are the most commonly used blending materials due to the familiarity of the formulators with their properties.
- Solvent-based coatings are being replaced with eco-friendly water-based polyurethane dispersions
- Stringent production standards required in the food, pharmaceutical and personal hygiene industry, the world over, dictate that the actual formulating area must be sterile and clean from bacteria and pathogens. These rooms are generally airconditioned, sealed environments, under pressure of two isobars. Inside, the floors, walls and ceilings are coated with a tough resilient seamless coating to prevent biological contamination such as germs or viral infestation which would find a hold in the cracks or joints in the tiles or canters.
- Epoxy coating and solvent-based polyurethane coatings which are used in developing countries such as India for cleanrooms, are highly toxic in nature and therefore fraught with health hazards. The solvent added to the above coatings for better finish and to bring down the cost of these coatings, is the proverbial nail in the coffin due to its negative long-term effects on human health.
- In the developed world, especially Europe and the Americas, the use of solventbased coatings are being phased out. These are being replaced with waterbased Polyurethane dispersions (PUDs). PUDs are waterborne systems, ecofriendly, having all the properties of the solvent-based systems, minus the hazards. PUDs can be formulated to not only make floor coatings but also for the walls which arte tough and resilient with scratch resistance and stability.
- The PUDs have a life of 10 years even in exposed areas as they have excellent UV resistance against yellowing, cracking or peeling. They enjoy enhanced penetration into the substrate and offer better bonding viz a viz water based acrylics. They can also be formulated into coatings for glass, clear glossy finishes for wood and veneers, anti-corrosive coatings for metals, even in exposed areas with an enhanced life span. Technology is moving rapidly as also awareness levels, with the advanced countries already having phased out solvent-based systems in their work places and living environments for health reasons.
- Cleanrooms in Indian pharmaceutical companies are not all designed with waterbased PUDs. Epoxy and solvent-based coatings are still used in cleanrooms. Hardeners used in solvent-based polyurethane coatings contain MDI, the health hazards of which can result in skin rashes, cornea damage, asthma like reactions, allergies. Isocyanates are also known to cause tumours in rats and are therefore classified as human carcinogens.
- 3)Solvents are also used in many items like Paints, varnishes, lacquers, paint removers, etc. They include commonly used chemicals such as alcohol, mineral spirits, petroleum distillates, turpentine, benzene, perchloroethylene, toluene, xylene, trichloroethylene, gasoline, kerosene, butyl acetate, acetone, metyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK). The list goes on.
- As per OSHA (Occupational Safety and Health Administration, US Department of Labour), health hazards associated with solvent exposure include cancer, skin infections and reproductive damage. The smell of solvents hangs in the air, days and weeks after the application of Epoxy solvent-based polyurethane coatings.