Thermoset resins have been around for decades and are important components of coatings and composite materials—just as dispersants are an important part of the equation to disperse pigments and impart improved properties in end-use products.
Choosing the appropriate dispersant for the pigment can reduce the impact of curing of thermoset resins. When developing reactive thermoset dispersions of pigments in reactive systems, the wrong dispersant can increase or decrease the cure response and contribute to various types of failures. The goal is avoid adverse reactions, with the dispersant having no impact on the curing of thermosets.
The thermoset resin, such as epoxy, polyamide, polyurea, polyaspartic, polyurethane, or unsaturated polyester gelcoats, serves as the base in solvent-free reactive systems. A pigment dispersion is then added to this base. A reaction in the resin starts the curing process. Dispersants are designed to interact with the resin, but should not start the curing process before it’s ready to begin or stall the process once it begins. The resin is what delivers the cure time, which is why the functionality of the dispersant should not interact with the functionality of the resin.
The Importance of Cure Rate
Why is the cure rate important? There are two ways to think about it. If the cure rate is slowed dramatically, nothing can be done until the coating is cured, which will slow production. Door applications are a good example. Doors have to remain horizontal until finished curing. If they stay flat for four hours instead of one hour, they take up more space for a longer period, leading to lost productivity and lost money. If a coating cures faster than anticipated, there might not be enough time to produce the end product, with the polymer setting in the can before it can be used or applied.
In most cases, a manufacturer can get resins in different systems that have different cure rates to be able to pick one with an operating window that works for their application. Manufacturers are fully aware that dispersants could affect the expected cure time, so it’s not surprising they look to avoid it.
Historically, compounders and pigment dispersion houses have had to choose a polymeric dispersant that can provide either good stability or good dispersion, but not both, when creating reactive thermoset dispersions of pigments in 100% active systems. They can offer either a stable low viscosity dispersion that enables ease of use at the end customer, but poor dispersion quality (i.e. pigment float issues). Or, they can offer a good-quality, high-color strength dispersion that is unstable and difficult to compound.
In addition to that, most dispersants available today are typically designed for use in one specific system or with one specific pigment or filler, resulting in inventory control challenges and higher costs because multiple dispersant products in small quantities are needed to meet varying requirements.
One Unique Dispersant
That’s why Lubrizol developed Solplus™ D610 Hyperdispersant for wetting, dispersion and fluidization of pigments and fillers in 100% active (solvent-free reactive) systems. It provides the ability to achieve the combination of a proper balance of stability of the system and good dispersion and/or high color strength. This dispersant is also compatible with multiple reactive systems.
Solplus D610 provides good color development and improved gloss. Due to its ability to reduce the millbase viscosity, higher pigmentation may be possible for reactive resin systems
With it, compounders and pigment dispersion houses can now inventory one dispersant instead of many, smaller volume dispersants, and create one dispersion in larger volumes that can meet the different needs of their end customers.