Soft feel coatings are desired in many industries, but the primary applications can be basically broken down in two: graphic arts applications like packaging, advertising, and print media; and durable coatings for consumer electronics and automotive. However, each industry requires coatings with very different property needs. Graphic arts applications tend to prioritize achieving a soft feel at a budget-friendly cost over long-term durability, since many targeted applications are disposable products. The automotive and consumer electronics markets are more concerned with durability and physical properties, but still need to achieve the soft feel. In general, here are 3 basic steps to creating a soft-feel formulation:
Define the Targeted “Soft-feel” Profile:
Creating a UV-curable soft-feel coating can be a big challenge for formulators, due to the subjectivity of “soft-feel” and the challenge of creating a soft yet durable UV coating. The term “soft-feel” means different things in different industries. It can refer to a slippery smooth surface, a velvety surface, or a rubbery surface. These are subjective, tactile properties that cannot be measured directly - the only way to evaluate them is by feel. Establishing which “soft-feel” profile is desired for the application is critical during raw material selection.
Select the Appropriate Oligomer Backbone:
Selecting the correct backbone oligomer is critical to achieving a soft feel. An oligomer backbone that is too soft will result in a coating that is not durable or is tacky, while too hard of an oligomer will prevent you from achieving a pliable, grippy finish. Since many soft feel applications require a lower gloss, oligomers that are inherently lower in gloss in addition to being soft and flexible may be preferable. Also, different soft oligomers can tend to favor certain “soft-feel” profiles. One oligomer may work well for a rubbery surface, but not work well for a velvety surface, so defining your targeted “soft-feel” and working closely with your oligomer supplier will help focus your oligomer selection. Also, in order to enhance the durability of the coating, consider adding highly functional oligomers in additive levels in the formulation to reduce marring.
Balance Feel with Durability Through Monomer and Additive Selection:
The primary challenge of soft-feel UV coatings is that they need to have a soft finish, while also maintaining good abrasion and mar resistance. Some applications also require solvent and stain resistance, and most applications are looking for a low gloss surface. Oligomers and monomers will not yield a soft feel on their own; they will provide the basis for a soft and rubbery feel, but monomers and additives will need to be used to accomplish the final feel. While looking for reactive diluents for your formulation, target a monomer that would promote the flexible feel but would keep the strength of the film to prevent marring, such as an ethoxylated TMPTA. Reducing the Coefficient of Friction (CoF) is important to achieving velvety or slippery finishes, for which you can use materials such as waxes, acrylated dimethylsiloxanes, and acrylated silicones. The goal is to reduce the CoF without hurting mar resistance.
Formulating a UV soft-feel coating is a balancing act; there isn't a silver bullet for every application. Working closely with technical resources at your raw material suppliers will help speed up your development timelines and narrow your focus to the materials optimized for your desired results.