UV curable coatings and inks are experiencing rapid growth and adoption due to the many advantages they offer. Higher productivity due to near instantaneous curing makes the UV printing and coating process more economical. The lack of heat used in curing is ideal for heat sensitive materials such as plastics. In addition UV coatings and inks can have very tough surface properties. For all of these reasons and more UV cured coatings and inks are a great option for a variety of applications.
However, there are some drawbacks that one should consider when formulating a UV curable coating or ink. The absence of solvent and speed of cure can lead to poor wetting, leveling, flow, and pigment dispersion. Due to the high cross link density UV coatings and inks can also shrink upon cure causing adhesion issues. Ultimately these issues can lead to a coating or ink with sub optimal appearance and performance.
Why Use Cellulose Esters? The Benefits are Twofold
Increased flow and leveling for fewer surface defects
Better gloss and reflection
Optimal metallic and pearlescent flake alignment
Improved pigment dispersion
Reduced shrinkage, fewer adhesion failures
Increased hardness and abrasion resistance
Improved weathering and chemical resistance
FDA approved for direct and indirect food contact
Eastman™ Cellulose esters (CE’s) with high butyryl content will dissolve in and tolerate common UV curable monomers such as styrene and acrylates. When formulated into UV curable applications such as inks and OPVs, CE's help improve the flow and leveling leading to surfaces with fewer defects and higher gloss. CEs will improve pigment orientation and flop allowing for brightly colored metallic and pearlescent finishes. CE's also act as fillers to help reduce the shrinkage of coatings and inks upon cross link and cure. In addition, Eastman’s cGMP compliance allow ink and coating formulations for direct and indirect food contact.
Cellulose Esters are typically dissolved in monomer as a masterbatch. This is then used as an additive to the UV curable formulation. Typical additive use levels are 0.1 - 2.0 wt% of the final formulation. In some instances addition levels as low as 0.1 - 0.5 wt% have shown an improvement in formulation properties. The table below lists Brookfield viscosities of the recommended grades in common monomers at 5% concentration. Cellulose esters with lower molecular weight can be used in applications where viscosity is a limitation as is shown by the data in the table below.
Value = Brookfield Viscosity at 24° C
I = Insoluble