Lightfast Inkjet Inks

While direct bond cleavage can occur, the spectral energies involved suggest that this is not a primary mechanism of photolysis of the colorants. 

The chemical properties of the colorant are critical to its lightfastness. Generally, a more chemically stable colorant fades less upon exposure to sunlight or artificial light. Most colorants are believed to be extremely resistant to photolysis in vacuo. This belief emphasizes the relationship of the chemical environment of the printed colorant to its lightfastness. 

The nature of the substrate may determine, in part, how much of the colorant is held on the surface. The porosity of the substrate can also affect the penetration of moisture and gases into the colorant (4). The components of the ink can also have an effect on the colorant s chemical environment, and can thus play a role in the lightfastness of the final print (4). 

Other various environmental factors can also affect the fading rates of printed colors. These include but are not limited to temperature, humidity, and pollutants or gaseous reactants such as oxygen, sulfur dioxide, and nitrogen dioxide. Also of great importance to the fading rate is the spectral distribution of the radiation incident on the printed colorant. 

---

Several compositions with inks with improved lightfastness have been detailed (55). The lightfastness of the printed samples was tested with an Atlas SUNTEST CPS device or an Atlas Q3000 weath-erometer. The printing medium was a glossy inkjet paper, such as UVGlossy available from the American Ink Jet Corporation. 

---