Case Studies

Epoxy coatings are highly durable, corrosion resistant, and are commonly used as floor and metal coatings or as protective primers. They are typically 2-part coating systems and consist of an epoxy resin combined with a reactive hardener (such as amines, phenols, anhydrides or thiols). Traditional epoxy resin molecules are based on a rather rigid chemical structure, which, combined with high levels of crosslinking from the hardener, gives good mechanical properties to the final coating. The rigidity can however be a disadvantage, as high levels of crosslinking can make the coating brittle and inflexible. They are also sensitive to UV light, which causes cracking and flaking, hence they are only used in indoor applications, or as primers which are protected by a UV-resistant topcoat.

This article is the last in a 3-part series, to help you understand the relationship between rheology and paint performance. Parts 1 and 2 discussed the rheological characteristics of paints and introduced the rheometry capabilities available at PRA. In Part 3, we discuss specific rheometry experiments that can be used to measure and understand the paint properties of interest.

This article is the second in a 3-part series, to help you understand the relationship between rheology and paint performance. Part 1 discussed some characteristic rheological parameters, and how these relate to the physical properties of paints. In Part 2, we also describe the rheometry capabilities available at PRA and how you might use these to measure and predict the behaviour of your paint.

Rheology is defined as the response of a material to a force. Rheological properties can be vital in determining the success of a coating. Paints are typically viscoelastic materials, which means they exhibit a combination of liquid-like (viscous) and solid-like (elastic) behaviour, depending on the conditions.

Reducing the environmental impacts of petroleum-based products is a significant sustainability challenge. Bio-based alternatives are not always available, and integrating polar, solid biomaterials into non-polar liquids can be particularly difficult due to their inherent incompatibility.

PRA conducted a case study involving the synthesis of high solids hybrid alkyd resins for a customer’s request. The initial synthesis was based on a literature recipe, but unforeseen results led to the need for recipe optimisation. PRA successfully resolved the issues, achieving acid values within the desired range. The incorporation of hybridising resin led to faster drying times compared to standard long oil alkyd resins, as evidenced by tack-free time measurements. Additionally, coatings formulated with hybrid resins exhibited improved adhesion to both steel and aluminium substrates. The study provided valuable data for the customer’s product marketing efforts.

PRA conducted a multi-client evaluation of decorative gloss paints to help manufacturers comply with Phase II of the EU Paint Products Directive. The directive sets VOC emission limits for decorative and vehicle refinish paints. PRA invited raw material suppliers, paint manufacturers, and distributors to submit samples of 2010 compliant white gloss paints for evaluation. Various paint technology routes were evaluated, and all samples were tested for composition, performance in laboratory tests, and practical application trials. The results were reported anonymously to subscribers, with the full report available for purchase.

PRA was approached by a company seeking to replace an existing isocyanate cured coating used in a radioactive environment. The PRA conducted a comparative trial, testing two candidate replacement paint systems along with the existing system. Unfortunately, both candidates showed disappointing results, exhibiting increased brittleness, susceptibility to mechanical damage, and other weaknesses. Further development is needed before adopting the candidate coatings.

PRA assisted a client in studying the impact of molecular weight on waterborne coating properties using a specific copolymer. They analysed the process, proposed improvements, and conducted experiments. By adjusting initiator concentration and using a chain transfer agent (CTA), they achieved different molecular weights. The tests examined molecular weight distribution, particle size, glass transition temperature (Tg), and monomer-to-polymer conversion. Results revealed a relationship between molecular weight and initiator/CTA concentration, affecting film formation, stain resistance, and durability. PRA’s expertise helped the client understand coating structure-property relationships and support internal R&D.

PRA was approached by an organisation seeking to establish a knowledge base on waterborne coatings and dispersion methodologies within their scientific group. They wanted a course delivered on-site for 10 attendees over 2-3 days. PRA developed a tailored 3-day course, addressing knowledge gaps and desired outcomes. The course covered technical topics and included market intelligence from PRA’s IRFAB study. It was well-received, allowing full attendance and valuable interaction among delegates. This approach enabled the company to deliver high-quality training effectively and at a competitive rate.

PRA was approached by a client to understand the relationship between polymer molecular weight and thermal properties in styrene-acrylic copolymers. PRA utilised a “seed and feed” method to control copolymer composition throughout the reaction. Testing revealed that adjusting initiator or chain transfer agent concentrations effectively controlled molecular weight. The particle size distribution remained consistent, and thermal analysis confirmed the expected trend of lower glass transition temperature with lower molecular weight. The client utilised the provided latexes to enhance their understanding of existing formulations and pave the way for future developments.

PRA tackled the challenge of achieving deep blacks with a blue undertone using high-colour carbon black pigments. They conducted optimisation steps to determine the best dispersant among three candidates. Dispersant 1 showed the highest jetness and best colour performance, while Dispersant 2 exhibited lower oil absorption and improved viscosity reduction. Recommendations depend on customer requirements, with Dispersant 1 for maximum jetness and Dispersant 2 as a potentially more economical option. PRA offers expertise in dispersant selection and testing for optimal colour performance.