Water borne heat resistant paints: a review

Excerpt: The use of water-borne protective coatings is increasing due to legislation on the emission of solvents (volatile organic compound) from paints

Abstract

The use of water-borne protective coatings is increasing due to legislation on the emission of solvents (volatile organic compound) from paints. The aim is to reduce the content of the volatile organic compound (VOC) of the paint and subsequent emission into the atmosphere. Water-borne paints are one class of coatings that normally have VOC levels below any regulatory limits and can be used to reduce overall emissions compared to solvent-borne paints.

Due to environmental considerations, water-based systems are becoming more essential in the production of heat-resistant coatings. Compared to traditional solvent-based resins, water based silicone resins significantly reduce VOC emissions in coating formulations. The aim of water borne heat resistant paint is to reduce extensive usage of solvent in heat resistant paint for the concern of eco-system.

This review paper will talk about the water borne Heat resistant paint and their advantages over solvent based heat resistant paints.

What are waterborne coatings?

The solvent in automotive coatings thins pigment solids for smooth and even application and then evaporates.

Waterborne coatings contain water as the main solvent but also contain other solvents, such as glycol ethers, to improve application. These coatings are ideal primers because they have greater resistance to heat and abrasion and provide excellent adhesion. Waterborne primers and primer-surfacers have a VOC content as low as 1.2 lbs/gal.

Why use waterborne coatings?

Generally, consumers can choose between two types of paints:

  • Water-based paints
  • Solvent-based paints

As their name indicates, solvent-based paints, sometimes referred to as "oil-based" or "alkyd" paints, contain a significantly higher level of organic solvents than water-based paints. These solvents are responsible for the strong odor noticeable in buildings that have been freshly painted. They are also potentially hazardous for both human health and for the environment which is why concerted efforts are being made to reduce or remove their presence in paints without negatively impacting on paint performance.

Today, water-based paints dominate and account for roughly 80% of paints sold in the residential market.

The function of organic solvents in a paint relates to certain properties it brings – it facilitates the paint's application, it's drying, and the formation of a regular paint film. During application and drying, the solvent evaporates. Ideally a dry paint film no longer contains solvent. However when they evaporate, these solvents release Volatile Organic Compounds (VOCs) into the atmosphere, with a negative, toxic impact on the environment.

Fifty years ago, virtually all paint was solvent-based. Today, advances in paint technology mean that modern, water-based paints, often referred to as acrylic emulsions, are increasingly replacing organic solvents across a broad range of paint applications and surface areas (and account for 80% of architectural paints). Legislation is in place to support this trend. There are several advantages to using waterborne coatings:

  • Solvent-borne coatings contain VOCs and Hazardous Air Pollutants (HAP) including toluene, xylene, methyl ethyl ketone, and ethyl benzene.
  • Waterborne coatings are less toxic, have low VOC levels, and are less flammable. Their use will reduce air emissions, improve worker health and safety and may decrease insurance costs.
  • The products may cost less than their solvent-borne counterparts and require no thinners, additives, or hardeners.
  • Compared to solvent-borne products, less product may be needed to cover the same surface area.
  • The pot life of the waterborne products is much longer and unused coatings can be saved in a sealed container for later use.
  • Waterborne primer is best used where solvent primer would react with existing substrate materials or coatings.
  • Paint guns can be cleaned with water or water-based solutions rather than paint thinner, acetone, or methyl acetate.

Uses of Waterborne Coatings

Waterborne coatings are available for various applications. The following is a list of prominent uses for waterborne coatings:

  • Applied on copiers, fax machines, printers, typewriters, and computers
  • Automotive OEM sector
  • As a quick release coating for interiors of coal cars, fly ash hoppers, plastic pellet hoppers, refuse containers and trucks, filled with PE or Teflon extenders
  • To coat porous materials such as paper or leather
  • Emulsion waterborne paints are widely used in the architectural market sector
  • Printing Inks

How to make it work

Some adjustments will be needed when changing from solvent-borne to waterborne primers. You may need to purchase new spray application equipment designed for waterborne coatings. Spray guns must be lined with corrosion resistant materials, such as stainless steel or plastic. Work with your vendor to try new products at low or no cost and to provide hands-on training in your shop.

The curing time for waterborne coatings is much longer than that for solvent-borne coatings so you need to plan accordingly. Review your current procedures and schedule coating applications to allow for more drying time or use specialized drying equipment. For example, it may work best to apply primer to all cars and allow to dry overnight before applying the color and finish coatings the next day. Involve employees in planning your process scheduling and equipment changes.

Paint curing technology

Many large shops have installed spray booths with heating and air movement devices primarily to increase production by reducing curing time. These spray booths and drying equipment optimize flashing and curing conditions for both solvent-borne and waterborne coatings and will significantly reduce the time needed to cure waterborne coatings. You should consider future needs for curing waterborne and low-VOC coatings when purchasing a new spray booth or paint curing equipment. The vendor should be able to provide assistance.

Portable infrared or ultraviolet lamps may be used to considerably decrease flash and cure times after primer application. Review the paint manufacturer's guidelines for using these lamps with specific products when considering this technology. Ask the equipment distributor to provide a low cost or no cost demonstration period and training before purchasing.

Training

Waterborne coatings have different viscosity than solvent-borne coatings and require different application techniques to get the best results. Allow time for painters to attend manufacturer's training and practice new techniques. Encourage and provide incentives to employees to attend local pollution prevention and compliance training provided by local regulatory and business assistance groups.

Types of waterborne coatings

Almost all types of resins are available in a waterborne version, including vinyls, two-component acrylics, epoxies, polyesters, styrene-butadiene, amine-solubilized, carboxyl-terminated alkyd and urethanes. Waterborne coatings are classified based on how the resin is fluidized. The three main types are:

water-soluble/water-reducible (solutions), water-dispersible/colloidal (dispersions) and emulsions (latex) paints (the most commonly used form). Within each category, physical properties and performance depend on which resins are used.

Water-soluble paints are paints whose individual molecules of water-soluble resins dissolve completely in water. Water-soluble resins are generally produced via polycondensation or polymerization reactions in an organic medium. As a result, they generally contain organic co-solvents like alcohols, glycol ethers or other oxygen-containing solvents that are soluble or miscible with water (organic content less than 10 to 15%). Because of viscosity anomalies, waterborne paints made with water-soluble binders have only about 30 to 40% solids content by weight. Resins include alkyds, polyesters, polyacrylates, epoxies and epoxy esters. Despite their sensitivity to water, water-soluble paints have a high gloss and a high level of corrosion protection, along with good pigment, wetting and stabilization.

Water-dispersible paints, or colloidal coatings, are paints that have small clusters of insoluble resin particles that are suspended in water. Mechanical agitation is sufficient to suspend the clusters. Small amounts of organic solvents (usually less than 5% by weight) are used as coalescing agents that evaporate on drying. Resins used in dispersion paints include vinyl acetate copolymers, vinyl propionate copolymers, acrylate-methacrylate copolymers, and styrene-butadiene copolymers and polymers. Colloidal dispersions are used mainly to coat porous materials such as paper or leathe.

Emulsions, or as they are more commonly known, latex paints, are similar to water-dispersibles. However, resin clusters in emulsions tend to be larger, and an emulsifier is required to keep the clusters in suspension . Emulsion paints are manufactured using a variety of resins including styrene-butadiene copolymers, polyvinyl acetate (the most common), acrylics, alkyds and polystyrene. Emulsion paints are widely used in the architectural market segment. These coatings are extremely versatile because they are thinned with water to almost any viscosity.

Application methods

Application technology for waterborne coatings is comparable to that of conventional solvent-borne coatings. If a facility is using a water wash booth, overspray is easily recovered and reused if colors are appropriately segregated. Uncured waterborne coatings can be cleaned from equipment with water.

Electrostatic spray can be used if the electrically conductive waterborne paint is isolated from the electrostatic system. Three methods can be used to avoid grounding out the electrostatics in a waterborne system.

The facility can (1) isolate the entire paint system from electrical grounds; (2) isolate a small part of the wetted system with a voltage blocking device; and (3) indirectly charge the paint particles away from any wetted equipment. Each method has its own advantages and disadvantages and should be evaluated for the specific application. The use of a voltage blocking device at each atomizer is often the most cost-effective method

Waterborne coatings can also be applied by electrodeposition for corrosion resistance and coating of hard-to-reach areas. However, some formulations or substrates might require special pumps and piping to prevent corrosion from water in the formulation. In addition, for product finishing, coatings need to dry or cure at elevated temperatures to ensure complete cure in a reasonable period of time. Therefore ovens are required with this process

Markets

Waterborne coatings have quickly taken hold in some product-coating market segments; for more than two decades, copiers, fax machines, typewriters, printers and computers have been painted with various combinations of waterborne emulsion and other coatings. However, waterborne coatings have been less accepted in market sectors with requirements that are exceptionally high for appearance and engineering. In recent years, however, the automotive OEM sector has increased its use of water-based paints and coatings in all but the heaviest coat applications. An estimated 20% of this sector now uses water-based paints, and that percentage is growing each year. With improved water-based paint technology, manufacturers have been able to change from solvent-borne paint systems and meet emissions regulations while maintaining their ultrahigh finish standards.

New developments

Waterborne Two-Component Technology. With this new technology, coatings manufacturers can formulate high-performance coatings without cosolvents and achieve the same appearance, properties and ease of use that manufacturers have with the solvent-borne analogs. For example, an epoxy curing agent for water-based epoxy coating formulations has been designed for use with solid epoxy dispersions. This epoxy curing agent provides corrosion resistance when used as a primer in general metal applications.

Cost and implementation issues

Waterborne coatings are more expensive than conventional coatings per unit of reactive resins. In addition, the capital costs for application equipment tends to be greater (e.g., stainless steel is required to protect against corrosion in storage tanks and transfer piping). However, water-based coatings generally use less organic solvents, reducing environmental and human health risks. Technical assistance providers should remember that, despite the use of water in waterborne formulations, discharge of wastes from coatings must still be in compliance with federal and state wastewater discharge regulations. Paint manufacturers, however, are developing methods for recycling waterborne paints collected from communities and industry.

Quality vs. Economy

Whether water-based or solvent-based in nature, there is no true economy in buying cheap paint. In terms of superior coverage, adhesion and durability, always buy the best-quality paint you can afford. If you're working on unfinished walls, metal or synthetic surfaces, it's important to apply the appropriate primer.

What is heat resistant paint?

Heat resistant polymers are that paint which can sustain high temperature environment to external and internal application. Heat resistant paints are used for chimney stack, pipes, petro-chemical & water tank, boiler fronts, duct work, piping and furnace structure. These paints give good performance in external & internal application. Due to higher reflectance value this paint has special use in coating exterior of storage tanks in oil industry.

Heat resistant paints and surface coatings must offer continuous service at temperatures between 200 and 650 °C with no discoloration or loss of adhesion. This puts extreme demands on the binder and formulation. These coatings must not degrade under severe thermal stressing and should adhere firmly, whatever the temperature range. Silicone resins have proved particularly effective even in long-term applications. This is because they have a very high inorganic content and develop their high performance perfectly in different paint and coating system.

Resins used in heat resistant paint

  1. Epoxy Resin
  2. Silicone resins

Four Types of Heat resistant coatings are generally used. Coatings are found in several related yet distinct applications:

  • High-build surface insulation coatings for industrial use and to improve the thermal efficiency of older buildings;

  • Heat-reflecting (using IR-reflective pigments, not necessarily high-build) coatings, particularly useful for roofing systems in hot climates;

  • Coatings resistant to high temperatures during service; and

  • Coatings which retard the spread of fire or minimize fire-related damage to structures.

Resins available in market for water based heat resistant paints

Due to environmental considerations, water-based systems are becoming more essential in the production of heat-resistant coatings.

  • By utilizing silicone resin emulsion Silres MP 50 E, a complete range of water-based high-temperature coatings can be formulated and produced while retaining all the benefits of a silicone based coating:
    1. High heat resistance
    2. Excellent adhesion
    3. Chemical resistance
    4. Corrosion resistance

Silres MP 50 E has good compatibility with other organic resins, which in turn, provides formulators with flexibility and enables ease of compounding during the manufacturing process.

Silres MP 50 E is used in all types of coatings for oven and stove paints and for household appliances that are regularly subjected to high temperatures, such as pots, pans and toasters. Mufflers and exhaust systems on motorcycles, recreational vehicles and automotive are some of the other more popular applications in which Silres MP 50 E provides high temperature protection and performance.

  • By utilizing Silres MPF 52 E, a complete range of water-based high temperature coatings can be formulated and produced while retaining all the benefits of a silicone-based coating:
    1. High heat resistance
    2. Excellent adhesion
    3. Chemical and corrosion resistance

Silres MPF 52 E has good compatibility with other organic resins, providing formulators with flexibility and ease of compounding during the manufacturing process.

When Silres MPF 52 E is used in combination with other resin emulsions, the formulation will dry at room temperature to form a tack-free film. For moderately heat-resistant coatings (~200 – 300°C), Silres MPF 52 E can be used as a single binder or in combination with a broad range of water-based organic polymers such as acrylates, alkyds and polyesters.

Depending upon which systems Silres MPF 52 E is combined with, final curing is obtained by baking at 200 – 280 °C for 15 minutes to one hour.

Uses of heat resistant paints

Depending on the manufacturer and the intended use, each heat resistant paint has different characteristics. They differ in the ingredients used, the type of cure, minimum curing temperature, and most important to the consumer, temperature tolerance. They bring durability, and form tough corrosion proof surfaces that are resistant to weathering, to surfaces that endure a whole lot of heat.

The first fire retardant paint was made in the 1950s. This was very expensive, difficult to use and contained known carcinogens. During the 1980s, this type of paint was improved by adding intumescent reactant to the formulation. This took away the carcinogenic properties and helped it bond to different surfaces with ease.

Some of the top uses for this type of paint are:

  • Automotive engine, fan, radiator, and exhaust system
  • Fireplace
  • Grill
  • Kiln
  • Oven
  • Stove
  • Boiler
  • Steam pipes
  • Chimney

High-temperature coatings are often found in the following industries:

  • Aerospace
  • Power
  • Manufacturing
  • Petrochemical
  • Military

Specific examples of applications for high-temperature coatings include:

  • Jet Engines
  • Power/Chemical plants/Refineries
  • Offshore assets
  • OEM applications
  • Corrosion Under Insulation
  • Fireproofing
  • Buildings and Construction

Summary

Environmental regulations directed to reduce environmental degradation and public health hazards have raised a major interest in the development of ecological paints which comply the legal requirements for paint formulations with low volatile organic compounds (VOC) contents, whereas they should not be too costly to prevent them from wide use.

In particular, the emission of VOC into the environment has experienced a huge increase over the last twenty years and has led to the onset of serious problems of air pollution and, thus, health risks.

The aim of the paper is to make people aware of ecological way of painting.

References

  1. The Environmental Protection Act, ISBN 0-10-544390-5, 1990.

  2. info@wacker.com

  3. heat-resistant paint b * AcademyPublish.org- Vehicle Engineering.

    [## Author Details

Mithun Ramchandra Chalke

Kansai Nerolac Paints Ltd.

Lower Parel, Mumbai](http://encyclopedia2 .thefreedictionary.com/heat-resistant+paint)