Formulating UV curable inkjet inks

These requirements make formulating UV curable inkjet inks more challenging than for applications where low viscosity is not mandatory. This chapter hopes to provide an introductory look at formulating UV curable inkjet inks for printing via DOD print heads. 

Formulating UV curable inkjet inks for piezoelectric print heads requires technical knowledge as well as creativity to meet the strenuous requirements that the print markets, particularly the industrial printing arena, demand. The basic components found in most inkjet ink formulas include monomers and oligomers, pigments and dyes, photoinitiators, and additives. 

The majority of the monomers and oligomers used in UV curable inkjet ink formulations are acrylates of varying functionalities, although occasionally materials such as unsaturated polyester resins are used as well. Figure 2 shows examples of the acrylate moiety. Acrylates are skin sensitizers and should be handled with caution. 

This chapter looks at the raw materials available to UV curable inkjet ink formulators. The main emphasis is on the performance trends of the raw materials, thus hopefully enabling formulators to produce inks that fulfill the greater performance demands required as the technology expands. 

In general, the acrylates classified as "oligomers" are too high in viscosity for extensive use in the very low viscosity formulations required by UV curable inkjet inks. However, acrylate oligomers do possess several properties that can be very beneficial, even when used at additive levels. 

The formulation of UV curable inkjet inks is built up from aU the raw materials described in previous sections. In order to achieve the cure speed, adhesion and other final film properties, a combination of raw materials are generally required. It is also the case that there are many patents covering this area and so formulators should respect this. 

The predominant chemistry for formulating UV curable inks is acrylate-based free radical curing. Most UV inkjet formulations are mixtures of several different acrylates chosen for their individual properties which, when combined with photoinitiators, achieve the required specification. Because of the extremely low viscosity of the... 

Figure s 4 and 5 show the sedimentation profiles for two different UV curable white inkjet ink formulations. These profiles were collected with a Turbiscan LabXpert Sedimentometer. For this experiment, a vial of each ink was prepared and the amount of backscattering was measured (the purple line in each profile, shown on the Y-axis in time) along the length of the vial (shown on the X-... 

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