Optimizing Carbon Black Applications in Adhesives and Sealants: From Selection and Formulation to Dispersion Processing

　　Carbon black is one of the important ingredients in adhesives and sealants, and is widely used in various systems such as polyurethane, acrylic, epoxy resin, polysulfide, silicone, etc. When developing new products or replacing products, there are three aspects that need to be focused on: carbon black selection, formulation design, and dispersion process.

　　Carbon black selection

　　Understanding the role of carbon black can help you choose the right carbon black. For coloring purposes, the amount of carbon black generally accounts for 2% of the formula weight. At the same carbon black concentration, if you want to increase the blackness of the product, you need a carbon black with a higher surface area. In addition, you need to consider the impact of carbon black on other performance aspects, including UV aging resistance and thermal conductivity, tensile strength and elongation, rheological properties and viscosity, curing strength and adhesion, etc. In certain cases, it is also necessary to increase the absorption of carbon dioxide. At this time, the proportion of carbon black used needs to account for more than 10% of the formula weight.

　　Formulation design

　　Some formulation engineers treat carbon black as an inert solid. If it is formulated as a pigment at 2%, there will usually be no problems. However, if the use of carbon black exceeds 10% of the formula, new product development or potential product replacement is often challenging and even frustrating. This is mainly because two carbon blacks from different sources are unlikely to be identical, even if they appear identical on paper or visually in terms of colloidal properties. Therefore, the formulator needs to be patient and learn the properties of the new carbon black, ideally with minor adjustments to the process or formulation, to see some advantages.

　　In rare cases, the formulator may discover incompatible properties in the new carbon black during the formulation process. This property is either discovered immediately or after a few days of heat aging. Once discovered, the formulator usually does not understand the reason behind this situation and anxiously changes the carbon black to eliminate the incompatibility. Understanding the reason behind the incompatibility is very important for both you and the supplier. This information may benefit you greatly and provide you with a permanent solution. If necessary, we also provide ultra-pure carbon black products to minimize or eliminate incompatibilities between carbon blacks and your formulated products.

　　Dispersion Process

　　If you need to increase the jetness of your product at the same carbon black concentration, you can try a carbon black product with a higher surface area, but it is important to understand whether the same dispersion process was used when comparing the two carbon black products. If the dispersion process is the same, then a carbon black with a higher surface area may perform equally or poorly in jetness, even if the macrodispersion (i.e., appearance or particle) or scraper fineness is the same. If this is the case, then the particle dispersion of the higher surface area carbon black is not achieved and the agglomerates of the higher surface area carbon black are not adequately opened and dispersed into the polymer system. This is either because of insufficient residence time at the same shear level or because the new carbon black requires higher shear.