Sunday, June 1, 2014

Paint Technology: Chemistry & Performance

There’s more to paint than meets the eye. Of course, what we see of paint is of paramount importance; after all, its appearance and ability to protect surfaces are why paint has been used on buildings since antiquity. Equally important though is much of what we can’t immediately perceive: paint’s chemistry and performance.

For its May meeting, CSI’s Willamette Valley Chapter was privileged to feature a talk by Randy Tessman, CSI, CDT of Benjamin Moore & Co. on the history, composition, characteristics, and future of paint technology. With more than forty years of experience under his belt, Randy is widely regarded as a go-to resource in these parts for architects and specification writers when it comes to all things having to do with paint in building applications.

Despite having more than three decades of professional experience myself, my basic knowledge about paint and architectural coatings was woefully lacking. That’s why I found Randy’s presentation so worthwhile. He provided us with a comprehensive, informative, and at times entertaining primer (pardon the pun) on a topic of great importance to the construction industry. Without a doubt, it was the best synopsis about paint I’ve ever enjoyed.  

I’ve borrowed and abridged much of the following from Randy’s presentation. Benjamin Moore is proud to offer this free online course for full HSW credit. For course details, accreditation information, and registration, visit aecdaily at the URL below:

What is Paint?
Fundamentally, paint is a mechanical mixture or dispersion of pigments and powders within a liquid binder, which once applied converts itself into a solid form and provides not only beauty, but protection. It is capable of converting itself into solid form and is used for protection, decoration, or a special functional purpose.

Humans have not changed the basic components of paint—pigment, resin, and solvent—since the beginning. The evolution of paint and changes in the paint industry has come through new resources, technological advancements, and a growing demand from society. Originally, people created paints using inorganic pigments extracted directly from the earth or organic pigments sourced from nature’s living organisms. They ground and mixed these pigments with a binding resin (such as animal fat or egg whites) and a delicate balance of added liquids to create a mixture they could transfer to a substrate. Like architecture, the paints and colors reflected the geography and lifestyles of indigenous societies.

Over the centuries, advancements in paint technology improved the performance of paints, increased their availability, and led to the development of the paint industry we know today. The vast number of options in today’s marketplace makes specifying the correct paints and coatings for a particular application a challenge. The best assurance of desired performance is knowledge. Think about it: our satisfaction is predicated on a sophisticated product that on average is a mere one or two-thousandths of an inch in thickness (the thickness of a hair shaft). There’s a lot going on in that thin layer of protective film and it behooves us to understand what makes it work.

The four basic components of paint have not changed, only their chemistry. These components are: 1) pigments; 2) binders/resins; 3) solvents; and 4) additives.

Pigments provide color and hiding. They also provide protection to the underlying substrate, control gloss and sheen, and contribute to particular performance attributes.

Primary pigments supply whiteness and color and are the main source of the hide characteristics of the paint film. Titanium dioxide is one of the primary pigments in all paints and is known for its ability to provide exceptional whiteness by scattering light and for its outstanding hiding power. TiO2 is derived from ilmenite, a titanium containing ore. Because of the complexity of its manufacturing process, TiO2 is one of the most expensive pigments. You can also find TiO2 as an ingredient in many modern products including toothpaste, pharmaceuticals, cosmetics, paper, and plastics.

Color pigments, classified as organic or inorganic, are used either in powder form during the manufacturing process or are compounded into a liquid dispersion, becoming colorants which can be added anytime to base paints for custom colors. Today, the chemical composition of colorants is a topic of ongoing discussion relating to their contribution to VOCs and the effect of stricter environmental regulations.

Extender pigments supply many characteristics such as durability, sheen and gloss control, scrub resistance, and stain resistance. Use of the proper extender pigments assists in appropriate spacing of primary pigments, particularly in creating flat and satin finishes. Among the most common extender pigments are:

  • Clay, kaolin, or china clay (which provides good hiding characteristics)
  • Silica and silicates (which help with scrub and abrasion resistance)
  • Calcium carbonate, limestone, chalk (used as a general-purpose, low-cost pigment)
  • Talc (used as a general-purpose, soft pigment for both interior and exterior paints)

Extender pigments are essential to paint formulation and its properties. They’re also useful in controlling the cost of paint manufacturing.

Specialty pigments supply specific characteristics such as waterproofing (Portland cement), mildew control, and UV protection (zinc oxide). Manufacturers use specialty pigments in many industrial maintenance coatings to provide extended protection from environmental and chemical attack. 

Ever wonder why barns were painted red? Iron oxide pigment is easily accessible on a farm from equipment (iron oxide is rust); iron oxides help in controlling mold and mildew and therefore protect the wood substrate from damage. It has also been said that the red color keeps the barn warmer.

A binder can be called a resin, vehicle, or polymer. The purpose of a binder is to hold or bind the pigments together, promote adhesion to the substrate, and resist peeling, blistering, and cracking. Binders form the paint film and in so doing affect the amount of flexibility as well as application properties (flow and leveling, film build). Binders also help determine gloss, durability, scrub-ability, and resistance to chalking and fading.

Paint makers have used linseed, soy, tung, and other oils in their natural or modified form as binders for centuries. Today, they also widely use alkyds, epoxies, urethanes, and combinations of these, especially in specialized and high-performance paints/coatings.

Latex resin, a synthetic polymer, is a plastic-like material that is dispersed in water. The basic types include acrylic, vinyl acrylic, polyvinyl acetate, styrene acrylic, and others. The term latex comes from the synthetic products’ milky white resemblance to natural latex from the rubber tree, originally introduced to the market in the 1940's.

Each type of binder or resin has features and benefits which impact a paint system. These benefits may include better adhesion, flexibility, water-resistance, alkali-resistance, breathability, and resistance to yellowing.

Although common, alkyd (oil-based) systems are disappearing due to VOC (volatile organic compounds) regulations (they’re usually thinned with VOC-containing hydrocarbon solvent paint thinners). Alkyds produce harder films, develop excellent penetration, and exhibit desirable flow and leveling characteristics. Urethanes create hard and abrasion-resistant films. Epoxy esters are valued for their durability, hardness, and chemical resistance, while silicones provide excellent chemical and high heat resistance.

Solvents allow a thin coating for easy spreading and application; they evaporate as the coating dries. Solvents serve two principal purposes, which are indispensable for most types of paint: 1) to transfer the paint from the applicator to the substrate; and 2) to control the viscosity of the paint in order to increase its workability. Solvents also help in maintaining a wet edge. Their differing characteristics impact drying time and performance.

Thinners for alkyd/oil-based systems include mineral spirits, hi-flash naptha, and xylol. Thinners for latex/water-based systems include water, ethylene glycol, and propylene glycol.

Note: Many solvents also contain VOCs. This is creating a demand for alternatives and new formulations that are more environmentally acceptable.

The introduction of additives improves paint quality, durability, and performance. Specific additives can improve water repellency, stability, viscosity, adhesion, flow and leveling, spatter resistance, mildew resistance, and stain resistance. The various types of additives include:

  • Driers (used to help some binders, especially alkyds, dry properly
  • Anti-skinning agents (used mainly in alkyd paints to chemically inhibit the drying process)
  • De-foamers (used primarily in latex paints to help reduce foaming or break bubbles when the paint is applied)
  • Coalescing agents (used to help latex form a film)
  • Biocides (used to keep mildew from growing on the surface  to which the paint is applied or as preservative to keep bacteria from growing in the can)
  • Thickeners and rheology modifiers (used to increase the viscosity of the paint and affect application properties)
  • Dispersants/surfactants (used like soap to help incompatible materials work together)
  • Anti-settling agents (used to keep binder and pigment from separating)

Putting It All Together: The Cake Analogy
Balancing and choosing the best quality of the four main components of paint (pigment, resin, solvents, and additives) creates the best quality of the coating. Just as with baking (which likewise is a science that uses specific proportions and ingredients) we know the better the ingredients we use the richer, more flavorful the end results will be.

So, what is important when building a paint or coating from the ground up and what is the information you need to know when specifying and comparing products? Variables such as the proportion of volume solids (VS), weight per gallon, pigment volume concentration (PVC), desired gloss and sheen, as well as the specific components used are keys to specifying the right product for a particular application. Here are definitions for some of this terminology:
  • Volume Solids (VS): VS is an expression of how much paint film remains after the thinner has evaporated. It is the relationship seen in wet film compared to dry film thickness (DFT). Pigment and non-volatile portions of the resin determine the percentage of volume solids.
  • Weight per Gallon: Weight is expressed as a ratio of a material’s weight (or mass) to the volume it takes up. Weight is represented in either pounds or grams on a Technical Data Sheet.
  • Pigment Volume Concentration (PVC): Volume of all pigment (TiO2 and extender) divided by the volume of all the total non-volatile portion of the paint (pigment and resin) expressed as a percentage. Gloss depends on pigment volume concentration. The higher the PVC and the less binder, the flatter the finish will be. Note how the pigment particles are completely below the latex surface in the gloss paint, but exposed to the surface in the matte finish. The pigment in the matte finish scatters light which reduces gloss, but this also makes the paint more vulnerable to abrasion, moisture and dirt. Pigment Volume + Binder/Resin Volume = % of Volume Solids
  • Gloss: Gloss is used to describe the relative amount and nature of mirror-like (specular) reflection. For paints, gloss is typically measured at a 60 degree angle of incidence for satin, semi-gloss, and high-gloss finishes.
  • Sheen: Sheen is also used to describe the relative amount and nature of mirror-like (specular) reflection. For paints, sheen is typically, but not always, measured at an 85 degree angle of incidence. It is most useful when measuring lower gloss finishes such as eggshell or flat.
We classify and compare paints in a number of ways:
  • By binder type or chemical/generic name: latex, acrylic, vinyl, alkyd, lacquer, epoxy, urethane
  • By curing mechanism: coalescence (evaporation of water), oxidation, solvent evaporation, chemical cure, cross-linking, moisture cure
  • By function: primer, sealer, varnish
  • By thinner type: waterborne, solvent
  • By use: interior, exterior, floors, industrial, OEM 
We specify particular types of paint finishes on the basis of the durability and aesthetics we desire:
  • A flat finish is for general use on walls and ceilings and is well suited to low traffic areas. It has high pigment and low binder content, which provides a uniform non-reflecting surface appearance that hides surface imperfections. It is excellent for touch-ups.
  • An eggshell finish is for general use on flat areas of walls and ceilings. It has more resin and less pigment than flat paints, so it provides a more lustrous appearance and better stain resistance.
  • A pearl (or satin) finish is for general use on walls and trim. It has a low-luster pearlescent finish, which provides increased durability and easy stain release.
  • A semi-gloss finish is for use on woodwork, trim, doors, and walls in high traffic areas. It contains more binders, which creates a harder film. Semi-gloss finishes require less maintenance than finishes with lower gloss, are more stain resistant, and provide easy stain removal. Semi-gloss paints are frequently used in industrial and commercial applications because of their durability and ease of maintenance.
  • A gloss finish is for use in high traffic and high use areas. It is an easy-to-clean, impact-resistant finish which is best used on substrates with minor imperfections. Given its water-resistant characteristics, paint with a gloss finish is the best selection for use in areas where there is a need for frequent washing or in areas of high humidity.
  • Opacity in paint is generated by two mechanisms: light scattering (differences in refractive index between the formulation ingredients); and light absorption (absorption of specific colors). Most inert pigments have a very different refractive index than air; this is why they appear white as a dry powder. Light is highly refracted in the dry pigment, and the result is high opacity. A paint made with very little binder, like a whitewash, can have excellent hiding with no TiO2. Likewise, paints with a high porosity refract and bounce light around within the paint film, resulting in hiding. White and lighter colors have very little absorption and must rely on light scattering to achieve opacity. Titanium dioxide is used in white and light tints because it has a very high refractive index. This is not the case for darker colors, which depend on color pigments for their hue and opacity. TiO2 also needs a certain amount of extender pigments to avoid clumping and also for exterior applications; too much TiO2 in a recipe can cause paint to chalk. Darker colors absorb light. Think about the color black: it absorbs all the colors of light that strike it and the result is excellent hiding. Black paints have excellent opacity using no titanium dioxide. Similarly, colors other than black absorb specific wavelengths of light corresponding with the color we see. For example, yellow pigments absorb all of the colors of the rainbow except yellow, which is reflected out of the paint film. The same with reds and greens and combinations of color pigments. When the likelihood of a ray of light reaching the surface and coming back out of the paint film is low, we have good hiding.
Other criteria used for specifying a particular paint system include:
  • Cost: What’s the available budget?
  • The type of substrate involved: Is it wood, cement board, sheetrock, or wet concrete, etc.?
  • Surface preparation requirements:  Adhesion is critical to paint performance; some paints are better than others in certain situations.
  • Desired durability: Should the finished surface be resistant to chemical attack or moisture, washable, scrub-able, etc.?
  • Environmental conditions: High humidity, extreme sun, and excessive dampness can all drive our product choices.
  • Application restrictions: Is spraying an option? Is there room for rolling?
  • Ease of maintenance: Who will be responsible for general upkeep? Some coatings can only be applied by a professional.
  • Sustainability: Paint manufacturers are increasingly introducing products that are more environmentally responsible. Programs such as LEED®, CHPS, Green Globes, NAHB, MPI Green Performance™, GreenSure® and Green Seal are driving environmentally friendly specifications for paints and coatings, most notably to decrease the amount and sources of VOCs.
A paint coating system most often includes the following three components:

  • primer, which prepares and seals surfaces, promotes adhesion, enables easier color transition, optimizes quality characteristics (uniformity, touch-up, gloss/sheen, color, coverage, and specialty performance characteristics) and supports longevity of the coating.
  • An intermediate coat, which is the first coat of the finish coat or a barrier coat for the finish coat.
  • A finish coat, which is the final coat of finish.

The use of a three-part coating system is important because each part meets specific needs. They are critical to ensuring the product’s compatibility with the surface being coated, building the film thickness to maximize protection and performance, and extending the system’s longevity.

The specification of the right products and paint system along with appropriate preparation and application are keys to the performance and longevity of a paint/coating. What you choose to specify also depends on the type and complexity of the project, applicable industry standards, the availability of equivalent products, and whether the Owner demands a specific product from a particular manufacturer.

Simply put, a complete and precise paint specification is like a prize-winning cake recipe: the means to achieving a desired end result.  

Randy identified and dispelled a number of myths that are commonly repeated in the industry. One of them is the misconception that thicker paints are the best paints. The truth is thick paints may simply have a lot of cellulose in them. Cellulose thickeners were once the primary way water-based paints were thickened. However, while cellulose thickeners provide good sag-resistance, they also possess poor leveling characteristics. And while they also make paints easier to apply, this too often translates to poor film build (affecting hide). Today, in high-quality coatings, synthetic polymers do the job. Called “rheological modifiers,” they provide unique and marketable combinations of brush-ability, sag resistance, and low/leveling characteristics. So paint thickness is important but it is the right thickness, and not just “thickness,” that is the true measure of quality.

The upshot is the importance of educating yourself about paints and coatings before you select and specify them. Part of knowing is being able to ferret out the myths and untruths, as well as understanding enough to be able to ask the right questions of someone like Randy.

What’s in the Future?
Research continues to create new polymers and new resin systems for both improved performance and low emissions, as well as an array of additives like thickeners, dispersants, and coalescing agents which contain little or no VOCs.

Additionally, the paints and coatings industry is advancing some radical concepts. For example, imagine a paint that has the ability to change its color. It isn’t science fiction: companies are developing thermochromic paints that change color when heat is applied, and also photochromic paints and coatings, which when subjected to UV light, change colors much like the technology used in eyeglasses. There are also electrochromic paints that change color when you apply an electrical current. Envision changing the color of a wall with a flip of a switch. Finally, there are paint concepts based on structural color (think of colorful birds and butterflies) utilizing microscopic polymer technology based on magnetochromatic microspheres. This is mind-blowing stuff.

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If I had to cite one takeaway from Randy’s presentation about paint technology it’s that, like so much about the construction industry today, there is an increasingly broad and deep body of knowledge on the subject. Of course, our clients expect us to be in command of this information. The problem is we simply cannot know it all. That’s why we’re fortunate to be able to lean upon industry experts like Randy, who is more than happy to quickly answer our technical questions and assist us with our specifications. The same is true for all product representatives who regard education, rather than sales, as their primary objective. Be smart and take advantage of the free expertise they have to offer.

Want to reach Randy? Here’s his contact information:  

Randy E. Tessman, CSI, CDT
Benjamin Moore & Co.
Cell Number: 

Office Number: 1-800-642-5678 x2217

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