Inert Pigments

Inert Pigments: The Unseen Contributor to Improving Paint Performance

Inert pigments absorb nearly no light, and therefore, by themselves in a cured paint film, do not stand out from a color perspective. Inert pigments have a refractive index similar to that of the vehicles used in paints, so they provide very little light-scattering. However, used in conjunction with opacifying pigments, they can provide enhanced opacity at lower cost. Inert pigments are also called fillers or extenders as they are normally lower in cost and occupy volume in the paint film. Other valuable functions they provide include improved mechanical properties, rheology adjustment, gloss adjustment, and enhanced barrier protection.

Critical Characteristics of Inert Pigments that Influence Paint Performance

Mineralogy – Chemical composition, crystal structure, Hardness in Mohs (Fig. I)
Physical Characterization – Brightness, refractive index, pH, inertness, oil absorption, purity and presence of soluble salts
Particle Metrics – Particle size, shape, size distribution and aspect ratio

Per Figure I, talc would be a better filler pigment to improve sanding characteristics in a primer-surfacer, whereas a silica based pigment such as quartz (SiO₂) would provide better scrub resistance in an interior architectural wall paint due to increased hardness.

The Chemical composition of a pigment can also play an enormous role in determining the overall impact on the performance. For example, calcium carbonate in exterior latex paint can degrade in the presence of acid rain, producing carbon dioxide and calcium bicarbonate, which is water soluble. This in turn causes the film to be porous and the calcium bicarbonate to migrate to the surface of the paint film, forming a light frosting of insoluble calcium carbonate.

Pigments that have a pH of less than 7 can exacerbate corrosion when used in metal primers. Aluminum in a pigment contributes to the acidity, whereas calcium, potassium, barium, and sodium provide alkalinity. If a pigment contains soluble salts, these salts can contribute to blistering when exposed to moisture.

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Beat the Heat with Solar Reflective Coatings

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Solar Reflective Coatings- a Deep Dive

According to EPA statistics, approximately $40 billion is spent annually in the U.S. to air-condition buildings. The incorporation of solar reflective pigments in paint can decrease the cost to air condition buildings in the U.S. by more than $8 billion.

Figure1: SolarReflective — Figure1: Solar Reflective

When exposed to sunlight, it is commonly known that light colors, especially white, remain cooler than darker surfaces. Darker colors, especially black, absorb infrared light energy, resulting in warming of the substrate. The amount of light energy absorbed is dependent on color.

Other factors that determine an object’s temperature in an outside environment, in addition to it’s color and solar reflectivity, include it’s emissivity, convection and conduction. To illustrate further, Figure 1 indicates at an ambient air temperature of 20° C, a white object will remain at about 20°C, whereas a black object will be about 35° C for the coating surface of a steel building.

However this same black coating will have a surface temperature of about 65°C if the coated substrate is wood, plastic or isolated steel sheets. Key definitions follow:

Total Solar Reflectance – the amount of solar radiation that is reflected by a surface, measured as a percentage.

Thermal Emittance – the ability of a material to dissipate heat away from itself, or rather, to shed heat.

Convection – exchange of energy with air above the substrate.

Conduction – exchange of energy with the layer of the substrate directly below the surface.

To better understand the phenomena of why colors display different heating/cooling characteristics in sunlight, it is essential to examine the natural light spectrum. Solar radiation reaches the earth’s surface in three distinct wavelength packets. These packets of light include Ultra Violet light (UVA 280 – 315 nm, and UVB 315 – 400 nm), Visible light (400 nm – 700 nm) and Infrared light (near IR and far IR) between 700 and 2500 nm. The human eye sees light primarily in the visible portion of the light spectrum resulting in color. Some animal species, such as birds can see light in the UV portion of the spectrum.

Figure 2 illustrates the natural spectrum of solar radiation. 5% of the light energy is UV light, 46% is visible light, and the remaining 49% is infrared light energy. Pigments can absorb or reflect solar infrared energy resulting in 1) heat build-up of the coated substrate if the pigment absorbs IR energy (for example conventional darker pigments); or 2) little or no increase in temperature if the pigment reflects IR light (for example white and lighter colors).

Solar infrared energy (700 – 2,500 nm) is different than infrared energy emitted by hot objects in interior spaces, such as heaters. Infrared energy is found in the far infrared range beyond 1,200 nm.

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How to Protect Against Corrosion

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In 2013, the direct cost of corrosion was 3.1% of the 15.1 trillion in U.S. GDP, which in June 2013 is estimated to equal $500.7 billion. Corrosion is a an electrochemical process where the metal is oxidized by virtue of interaction with its environment, which results in the metal returning to its most stable oxidative state. This article will discuss those factors that influence corrosion, especially in regard to the use of coatings designed to protect the metal to which they’re applied. Accordingly, consideration of the fundamental factors that influence corrosion processes as it relates to the use of organic coatings will be considered herein.

Metals desire to be in their most thermodynamically stable state, which, in simplified terms, is the naturally occurring state of matter in its lowest energy state. Metals ordinarily exist naturally as oxides (e.g. iron oxide, aluminum oxide, zinc oxide etc.), because oxides represent their lowest energy state. Oxidation occurs at the anode (positive electrode) and reduction occurs at the cathode (negative electrode). Corrosion is normally accelerated by the presence of water, oxygen, and salts (particularly of strong acids).

Figure I lists a series of metals and their ability to resist corrosion. The most common metals used in industry include steel (cold rolled and hot rolled steel), aluminum, galvanized steel (hot dip and electrogalvanized steel) as well as galvalume. The latter two metal substrates utilize either a zinc layer or an aluminum/zinc layer respectively on the surface of the steel to enhance corrosion resistance.

Even though aluminum and zinc are less noble than steel, when not coated with an organic coating, they provide longer-term improved corrosion resistance than steel. When steel rusts, the corrosion product (ferric oxide) is loosely attached to the surface, whereas in the case of aluminum or a zinc/aluminum alloy, the corrosion products form a more tightly knit adherent layer to the metal surface that decreases the subsequent rate of corrosion (Table III).

Table III – Corrosion Loss of Uncoated Metals in microns/year in Various Environments. Exterior Durability of Organic Coatings, Eric V. Schmid, FMJ International, 1988 — **Table III – Corrosion Loss of Uncoated Metals in microns/year in Various Environments.** Exterior Durability of Organic Coatings, Eric V. Schmid, FMJ International, 1988

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Waterborne Resin Technology

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Waterborne resin technology is the largest type of coating technology used on a global basis and is expected to continue to grow as a percent of the total coatings market. By 2022, the global market size of waterborne coatings is expected to be over $146 billion USD. Growth in large part is due to increased volume in the construction and automotive markets with acrylics being the largest single type of waterborne resin system representing over 80% of the total waterborne market.

Driving forces for the increased use of waterborne coatings include:

Lower VOC
Ease of cleanup in most cases
Decreased fire hazard
Lower insurance cost
Lower energy use for baked coatings due to the need for less oven make up air
The need for decreased levels of petroleum-based materials.

As the May 2014 Prospector article on Flow, Leveling and Viscosity Control in Water-Based Coatings indicates, the two largest classes of waterborne coatings include water-reducible and latex, with the majority of baked coatings falling in the first category with most of the architectural coatings belonging to the second category. The term water-reducible is used for resins made in solvent and reduced in water to form a dispersion of resin in water. Latex resins on the other hand are prepared by emulsion polymerization in water.

Disadvantages for the use of waterborne coatings include:

High dependence of evaporation rate on relative humidity
High heat of evaporation for water requires 2260 J/g for water and for example only 373 J/g for 2-butoxyethanol, a commonly used cosolvent
Nonlinear viscosity reduction curve for coatings using water reducible resins
High dependence of flow and appearance on relative humidity
High surface tension of water (poorer wetting) requires the addition of surfactants which in many cases detracts from humidity resistance
Waterborne coatings are more corrosive than solvent born coatings and thus require lined containers, plastic or stainless steel to avoid rust
Waterborne coatings are more prone to popping in baked applications as film formation begins to occur before water evaporates from the film (see Table I)

However the continued advancement in material science to include innovations in resin chemistry, surfactants, wetting agents and flow agents will help enable the continued growth of waterborne coatings.

Figure I represents the various stages in drying of a latex based paint system. The first stage involves the evaporation of water. The second stage includes the continued evaporation of water and cosolvent to the point where the latex particles touch and begin to coalescence to form a film that is partially dried.

The final stage involves the continued coalescence and cure (in a crosslinked system) to form a cured, dry adherent paint film.

One of the key considerations in the use of waterborne coatings is the increased role that humidity in addition to temperature plays in the application and cure of these coatings. For example, to provide acceptable application properties, both the temperature and humidity must be carefully controlled as illustrated in Figure II. The effect of humidity on coatings containing water-organic solvent can not be ignored.

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Coil Coating Explained

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Coil Coating Process Analysis

Over 800 million tons of coil-coated metal are produced and shipped annually in North America alone. Coil coating (see Diagram I) is a very efficient way to produce a uniform, high quality, coated finish over metal in a continuous automated fashion. Coil coating is also referred to as pre-painted metal, because the metal is painted prior to, rather than after, fabrication.

In the coil coating process, the metal coil is first unwound, cleaned and pre-treated, applied on a flat continuous sheet, heat cured, cooled and rewound for shipment. At the fabricator, it is then cut to the desired size and formed into its finished shape. Versus most other application methods, coil coating efficiency is nearly 100%. Application is at very high line speeds as modern coil lines can run at speeds as high as 700 feet per minute and cure the applied paint in 15 – 45 seconds. As opposed to a spray-applied coating, for example, a coil-coated, formed surface offers uniform film thickness rather than the thicker films on edges, corners and bends that is more typical of spray-applied coatings.

Coil Coating Process Explained — Diagram I – Typical Coil Coating Line. Click to view source.

Topcoats

Topcoats are applied by reverse roll coat in which the applicator roll travels in the reverse direction of the strip and thus provides a smoother film with fewer defects. Primers and backers are normally applied by direct roll coating. Some lines also apply coil coatings using an extruder or via a solid block of paint with a softening point such that it can be applied smoothly when heated.

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Green Resin Technology – The Other Approach

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Green Resin Technology Explained

In April 2015, Chemical Dynamics published an article in Prospector on green resin technology using bio-based resin building blocks in the synthesis of polymers for coatings. Another highly desirable approach to green technology is the incorporation of resins utilizing building blocks derived from recyclable materials.

Sales for resins/polyols using recycled or bio-based polyols are expected to grow twice as fast as the overall polyol market in the next four years[1]. Driving forces for the use of recycled materials in the manufacture of resins can be reduced health hazard[2] (figure 2), as well as environmental and economic factors. Other attributes include reducing the carbon footprint[3] (Figure 1), increasing sustainability, and conservation of natural resources. Green products are also growing in favor with multiple government and private agencies.

Typical recyclable material sources may include polyethylene terephthalate (PET), designated rPET for recycled PET, recovered cooking oils and recycled polyurethane foam. PET is typically used as containers for soft drinks and water, whereas polyurethane foams are used as carpet underlay and in mattresses. In the U.S. alone, there were 6.5 billion pounds of unrecycled PET-based containers in 2013.

EPA Guidelines

The U.S. Environmental Protection Agency Comprehensive Procurement Guideline Program (CPG) defines recycled material as such that the EPA deems equivalent to virgin material. RCRA Section 6002 also requires purchasing agencies to establish procurement programs for designated items that meet CPG. Scientific Certification Services (SCS) recognizes products made either in whole or in part from recycled waste material in place of virgin materials. Through its certification process, SCShelps products qualify for credits within the LEED rating system. LEED is a certified U.S. Green Building Council program. Recycled content is certified by the U.S. Green Building Council’s GreenCircle for total recycled content based on pre and post consumer recycled content in products.

To read the rest of the article by Ron Lewarchik, President of Chemical Dynamics, please click here.

Hydrophobic Coatings Explained

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Coatings that offer a hydrophobic (EU) or superhydrophobic surface can impart multiple advantages to the coating surface and substrate they are applied to. Advantages may include decreased dirt retention, self-cleanability, improved moisture and corrosion resistance, as well as extended life expectancy of the coating and substrate. To fully explain and quantify hydrophobicity, it is necessary to define the relationship between contact angle and the hydrophobic/hydrophilic (EU) character of a surface.

Figure 1 – Contact Angle for Hydrophobic Coating Surface and a Hydrophilic Coating Surface

hydro1 — Hydrophobic Surface Contact Angle ≥ 120°

hydro2 — Hydrophilic Surface Contact Angle ≤ 30°

Figure 2 – Contact Angle and Superhydrophobicity

Accordingly, the surface characteristics of a coating can range from being hydrophilic (water-loving) to superhydrophobic (or highly water repellent). Several factors impact the contact angle of a water drop on the surface of a coating. These include the macro, micro, nano-surface profile, and the surface tension of the coating on which the water droplet is resting. Surface tension is the elastic tendency of liquids that make them acquire the least surface area possible.

To read the full article written by Ron Lewarchik, Chemical Dynamics President, on UL Prospector, click here.

Nanoparticles – When Smaller is Better

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Nanoparticles (EU) are normally defined as those particles that have a dimension of between 1 and 100 nm. The use of nanoparticles in coatings has provided a means to further improve performance such as scratch resistance, hardness, antistatic properties and UV resistance. These performance attributes are derived from the property profiles of nanoparticles.

Nanoparticles provide the inherent properties of the material they are derived from. For example, nano alumina (EU)maintains the properties of alumina, such as hardness and scratch resistance, but only on a nanoscale. Likewise, nano silica(EU) provides hardness, nano titanium dioxide provides a high refractive index and UV stabilization, and nano zinc oxide(EU) remains a UV light absorber (EU), even if the zinc oxide particles are nano-sized. The benefits of these materials are imparted to the coatings that they are used in.

The most pronounced property that is influenced by the particle size is the change in light scattering. For example, nano-sized particles may produce transparent coatings as light-scattering decreases with decreasing particle size. Most objects are visible due to light scattering from their surfaces. Scattering of light depends on the wavelength or frequency of the light being scattered as well as the size, shape and type of particle.

Table I – Particle Size Perspective

Since visible light has a wavelength on the order of micrometers, most particles much smaller than this, such as nano particles, are mostly transparent as their ability to scatter light diminishes with their size. However, light scattering is also dependent on the Refractive Index (RI) and the difference in RI between the interface of the particle and the surrounding medium. For example, if the surrounding medium has an RI similar to that of the RI of the particle, then the mixture of the two materials will be more transparent. To illustrate, silica has an RI of about 1.5 and polymethylmethacrylate (EU) has an RI of about 1.5, so a coating comprised of nano silica and an pMMA will be nearly transparent. The properties of nanoparticles based on their dimension can be quite dramatic.

To read the full article written by Ron Lewarchik, Chemical Dynamics President, on UL Prospector, click here.

Bio-based Resins for Coatings

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In recent years, there has been a growing interest in the use of bio-based resin building blocks in the synthesis of polymers for use in coatings. Bio-based products are derived from plants and other renewable agricultural, marine, and forestry materials and provide an alternative to conventional petroleum derived products.

Driving forces include a growing public and private awareness and interest in the use of renewable raw materials that can meet sustainability expectations and certifications such as Green Seal and Green Guard as well as the USDA BioPreferred Program for product labeling. Green Seal and Green Guard are environmentally driven, whereas the USDA BioPreferred Program functions to encourage the use of renewable agricultural raw materials in products. ASTM d6866 was developed to standardize, certify and classify the bio-based content of materials. Minimum renewable carbon content categories (MRCC) have been established for purchasing by Federal agencies and their contractors.

Table I – BioPreferred Coatings Categories[1]

Bio-based resins for coatings are normally referred to as alkyds (EU). Alkyds are comprised of fatty acid modified polyester resins. These resins are sometimes modified to include a urethane (EU) linkage and thus called uralkyds or oil modified urethanes. The fatty acid portion is derived from naturally occurring or renewable oils derived from sunflower (EU), safflower,soybean (EU), castor (EU), tall (EU) and others. Polyesters (EU) are derived from the reaction product of a polyol (EU) and a di or multifunctional acid or carboxylic acid and anhydride (EU) to form multiple ester linkages in a polymer chain.

To read the full article written by Ron Lewarchik, Chemical Dynamics President, on UL Prospector, click here.

Paint Cost Calculations

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Paint Cost Calculations

How to Get the Most Mileage Out of Your Paint

Determining the effective cost of paint that can be made from naturally occurring elements involves several issues that must be considered. These include the volume solids of the paint, application method, and the geometry of the object to be painted. For example, a paint that sells for $20 per gallon at 20% volume solids is actually more expensive on an applied cost basis than a paint that sells for $40 per gallon at 45% volume solids.

Theoretical coverage	=	Volume Solids
		Dry mils required

To illustrate the cost of paint to apply one mil (0.001 inch) per 100 square foot of the $20 paint is as follows:

If a gallon of paint weighs 10 pounds and is $20/gallon at 20% volume solids = 10# of the 20 $/Gallon X 0.20 pounds of volume solids = 2.0 pounds of solid or dry paint per gallon of liquid paint for $20. Accordingly the cost of each dry pound of paint is $10. The square foot coverage of a paint is 1604 square feet per mil at 100% volume solids. Since our paint is 20% volume solids, at one mil dry film thickness, one gallon of paint will cover 1604 square feet/mil X 0.20 % volume solids = 320.8 square feet/gallon at a cost of $20. Accordingly the cost to paint 100 square feet of surface is $20 X 100/320.8 = $6.23

To illustrate the cost of paint to apply one mil (0.001 inch) per 100 square foot of the $40 paint is as follows:

A gallon of this paint weighs 12 pounds and is $40/gallon at 45% volume solids = 12# of the 40 $/Gallon X 0.45 pounds of volume solids = 5.14 pounds of solid or dry paint per gallon of liquid paint for $40. Accordingly the cost of each dry pound of paint is $7.78. The square foot coverage of a paint is 1604 square feet per mil at 100% volume solids. Since our paint is 45% volume solids, at one mil dry film thickness, one gallon of paint will cover 1604 square feet/mil X 0.45 % volume solids = 721.8 square feet/gallon at a cost of $40. Accordingly the cost to paint 100 square feet of surface is $40 X 100/721.8 = $5.54

Accordingly, in this illustration, the $40 paint provides more value than the $20 paint as it provides lower cost coverage at equal dry film thickness. The table below illustrates paint coverage per mil for paint applied at 100% volume solids.

Theoretical coverage	=	Volume Solids
		Dry mils required

Inert Pigments: The Unseen Contributor to Improving Paint Performance

Solar Reflective Coatings- a Deep Dive

Driving forces for the increased use of waterborne coatings include:

Disadvantages for the use of waterborne coatings include:

Coil Coating Process Analysis

Topcoats

Green Resin Technology Explained

EPA Guidelines

Table I – Particle Size Perspective

Paint Cost Calculations

How to Get the Most Mileage Out of Your Paint

Theoretical coverage

=

Volume Solids

Dry mils required

Theoretical coverage

=

Volume Solids

Dry mils required