Colorful durable surface graphics

Paul Ramsden
Technical Director of Polymer Engineering
Kolorfusion International Inc.
Centennial, Colo.

One sector of the digital-graphics industry uses phase-change sublimation dyes to impregnate color graphics into polymeric materials and polymer coatings. Key to this decoration process is the thermodynamic phase transformation of the colorants from a solid to a gaseous state under heat and pressure.

These disperse dyes penetrate organic polymer substrates and coatings moving through the polymer matrix by diffusion and returning to solid within the polymer by a secondary phase change from gas to solid. This chain of events creates a highly durable subsurface transfer decoration. The graphics won't peel and highly resist fading, scratches, chemicals, and other deleterious effects when combined with proper polymer chemistries.

Starting in the 1970s, sublimation transfer printing became a reliable method for decorating textiles, most commonly printing designs on apparel and upholstery. These early dyes were printed on paper and roll-pressed through heated cylinders transferring the dyes into synthetic textiles in a process referred to as "heat-setting."

In the 1990s more advanced sublimation technologies developed letting designers decorate flat and cylindrical hard substrates, such as ceramic mugs and tiles, sheet substrates of metal and plastics, and particleboard. These substrates usually needed a coating to make them receptive to the dyes. Synthetic organic polymer coatings including polyester, urethane, and acrylic generally sublimate well.

For small print runs and one-offs, inkjets and laser printers deposit the dyes onto transfer mediums that serve as a vehicle to get the dyes from the printer to the substrate being decorated. Traditional printing equipment such as offset presses work for medium and long runs.

The most common transfer material for textile decoration is polyester. The disperse dyes are formulated into sublimation inks, which dry after printing, leaving the solid dyestuffs on the transfer medium. In the case of phase-change laser toners the disperse dyes are already dry and therefore ready for transfer.

To be receptive to the dyes, the polymer substrate or coating must be light in color and able to withstand temperatures starting at 280°F. Heat-deflection and Vicat-softening temperature ratings for a plastic are good indicators to determine if a material is a suitable substrate for the sublimation process. Many coatings are acceptable allowing process temperatures up to 375°F.

Resin selection and process parameters are fundamental to the success and stability of the decoration. An alliance with DuPont Engineering Polymers, Wilmington, Del., was recently formed to help evaluate engineered resins suitable for the Kolorfusion sublimation process. The collaboration currently boasts a portfolio that includes DuPont's Crastin PBT (polybutylene terephthalate), Rynite PET (polyethylene terephthalate), Delrin acetals, and Zytel nylons.

These polymers can be molded, thermoformed, and extruded into substrates. Substrate color, however, must be light so the subsurface design will be visible. If a translucent polymer is used the dyes will take on that translucent hue.

Numerous variables affect the success of embedding dyes into organic polymers. Initially, the process of putting decoration on 3D parts was limited by the nature of the transfer media. Paper and foil, the most common media employed initially, creased or tore when wrapped around 3D surfaces. Heat presses were also limited to flat and cylindrical platens.

Key to overcoming the obstacles of decorating complex 3D objects with disperse-dyes is a flexible transfer medium called Kolortex. The material easily wraps around objects conforming under heat and pressure to irregular surfaces without creasing, while the dyes migrate into the polymer.

The technique has been employed to decorate everything from Moen kitchen and bathroom accessories to Polaris Industries ATVs; entire trucks and boats have also been decorated with the process. In addition to resins, there's also a line of Kolorfusion coatings including water-based and solvent-borne formulations as well as powder coatings. The designs are either four-color process or are based on spot color printing methods, so that up to 12 colors can be incorporated into a design.