Color And Paint - MPI

The use of color in paints and coatings has evolved significantly over time. From natural pigments to modern processed colorants, the science behind achieving the perfect hue has advanced, but with it comes challenges, particularly when it comes to tinting. This post explores the evolution of paint colorants, the shift toward environmentally friendly options, and the potential issues that can arise when too much colorant is used in coatings.

The Evolution of Color in Paints and Coatings:
Colored paints and coatings are used on a daily basis all over the world. In the past, all colors were produced using natural pigments that were, for example, dug out of the ground or a product of a vegetable or animal. Modern colors consist of processed pigments that have many origins.  

While some manufacturers produce a range of colours during manufacturing (usually with dry pigments) Many paint manufacturers only supply white, tint and accent bases in their paint lines. This assists in managing inventories and stock in the warehouse and stores. 

Tinting and Opaque Pigments:
Paints that are generally available as white, tint, deep and accent bases can be tinted to various shades and depths by the use of liquid colorants. The level of opaque pigment (in most cases titanium dioxide) is varied to balance the value (degree of darkness or lightness) of the color. The maximum amount of colorant that is added to each base is dictated by the final color required, type and opacity of the particular colorant, and the level of opaque pigment in the base.  

 Average Compositions: 

*Note Opaque pigment level varies with manufacturer and paint type.  

The Evolution of Liquid Colorants:
Liquid colourants originally consisted of a high concentration of color pigment along with an oil liquid vehicle. The oil mix was first developed because historically paints were mainly oil based. Modern times have seen a dramatic change towards water-based coatings, these coatings could not be mixed with the older style of oil colorants. For this reason, traditional "universal” colorants were developed. 

Traditional “universal” colorants contain dispersants, surfactants, and glycols to help them mix evenly into the paint. These same additives are typically very high in VOC and can significantly increase the VOC levels present in a Low/Zero VOC product. 

While most legislation ignores or exempts the point-of-sale colorants when determining the stated VOC or limits, there is a movement in the industry to move away from “universal” colorants towards new Low/Zero VOC options. 

There are many different colorant technologies currently being used and developed to provide the same performance, appearance, and dependability as the old technology. While this is not necessarily required or mandated for manufacturers and suppliers globally, this movement is being primarily driven by them, to both get ahead of environmental legislation and to provide a greener option to a market that is increasingly environmentally conscious. 

Challenges with Tinted Paints:

For the most part, paints using small amounts of universal colorants show no major differences in their physical properties. However, where large amounts are used, properties such as curing time, early and total water resistance, abrasion resistance, resistance to cleaners, burnishing (polishing) and uniformity, are affected negatively. 

The balance of the material is comprised of surfactants, glycol and in some cases, an extender pigment. The weakness comes from the properties of the surfactants and of the glycol which effectively stay in the paint film longer maintaining water solubility and softness in the dry film. 

Exterior paints, containing high levels of universal colorants, can be prone to 'wash-out' from dew or rain for longer periods of time than 'non tints' or low level tints. Another unique problem that can arise is the appearance of surfactant bleed, which appears as a clear or yellowish material on the surface of the paint and can run down onto adjoining surfaces. Although waterborne coatings show the most problems, alkyd types can also be affected. Alkyds most often show lowered gloss levels, and some softness in the film for longer than normal. 

Paints made with the color pigments added at the manufacturing stage (although often limited in range of color) offer the benefit of being less sensitive to moist conditions than a strongly tinted base. These should be considered when painting exterior surfaces, particularly those exposed to constant damp conditions, or when application is to take place in questionable weather. 

What Can Go Wrong with Too Much Colorant:

A woman had her house painted in mid-September with a deep, maroon-colored, exterior acrylic latex stain. The weather was clear with a relative humidity of 65% (on average) during the two days of painting, and the temperatures ranged from lows of 55°F (approx. 12°C) to highs of 78°F (approx. 25°C). Two weeks later, after a day of light rain, the woman noticed that the paint had lightened and was tacky to the touch. Challenged, the painter replied that since the stain was a latex and still new, it could slightly soften when wet, but "would harden up completely in a few days". 

A few days later it began to rain and continued for three days. At the end of the storm, the newly applied stain appeared washed out in areas with many small blisters on the south exposure and felt very soft and tacky. The woman again called the painter, who called the paint supplier, who sent a representative to inspect the house and the leftover paint. 

A month later, the supplier's representative was contacted by the woman to find out the results of the inspection. She was told that there was nothing wrong with the stain and that any problems would relate to the environmental conditions during application and curing. 

Not satisfied with this answer, the woman contacted the Association. The Association assigned a certified coating inspector to examine the house and to determine the cause of the problem. 

Wet samples of the stain were taken from the remaining cans, and analyzed in the laboratory. The coating had a notably long dry time, and in gas chromatographic (GC) analysis appeared to have a large amount of propylene and ethylene glycol. The stain was then further tested using mass spectroscopy/gas chromatography (MSGC). This revealed a large percentage of surfactants relative to the pigment and polymer levels. These two components led to the slow drying and to the water sensitivity of the stain. 

It was ascertained that the stain was a tinted base that had 18 ounces of colorant per gallon added to it to arrive at the selected color. As stated above where large amounts of universal colorant are added to a coating (particularly waterborne types), properties such as the dry, water sensitivity, and film integrity can be adversely affected.