In coloured systems dispersing agents are required to wet and disperse various types of pigments. In aqueous systems the pigments tend to be more easily dispersed, however in non-aqueous systems especially the ones utilised in UV technology, problems can be experienced. In organic pigments, these generally have a non-polar surface and more problems are seen in red, blue, yellow and orange pigments. In these systems, the UV industry has utilised two different types of products in combination to aid the stabilisation of the pigments. The standard way is to use a conventional high molecular weight dispersant or hyperdispersant and a synergist which complements the dispersant. These synergists tend to be powders and of similar chemical make-up to the pigments, they are being used in. For example, blue type pigments (PB15.3 - see diagram below) the synergist is based around the phthalocyanine moiety.
Cas No: 147-14-8
Synergists have been designed to change the non-polar surface to more polar and help the dispersant to be more adsorbed on the pigment surface. This leads to a higher stabilised system, better colour strength, improved rheology but can cause some colour fading problems in the final coating. Yellow pigments (PY13, 74, 180, 185 etc) are also a problem to disperse easily. There have been reports of designing synergists by again modifying the pigment that is to be dispersed. Below is a diagram of PY74 which is a common pigment used in UV inks and which a number of papers have been published over the years on methods to modify and stabilise the system.
Cas No: 6358-31-2
Here at Lankem, we look at the conventional way of manufacturing synergists and then using our extensive knowledge of surfactant and UV chemistries, we look at making innovative products. Over a period of time, we have undertaken an extensive programme of work and continue to do so developing new chemistries and new products.
The BioLoops are one of many that have recently been developed you will find information on these on our website or by contacting us directly.
In general of the three different types of BioLoops designed the ones with loops and tails appear to offer the best performance benefits for the UV yellows and of these Lansperse UV86 works the best.
This product appears to function as both a synergist and dispersant in one molecule and studies show that the Lansperse UV86 can be used solely to replace the industry standard of dispersant and synergist.
Typical diagram of the BioLoop and tails dispersant
A programme of work was undertaken using a typical Pigment Yellow 74 used in UV inks using the following system:
DPGDA – dipropylene glycol diacrylate (UV monomer)
The dispersant, synergist (if used) and UV monomer are initially mixed with a high-speed stirrer. The pigment is then added and mixed once again. The mixture is then transferred to an Eiger Torrance bead mill and processed for 60 minutes at 2000 rpm.
Mill-base viscosity measured over time
The above graph shows that initially, the single dispersant (Lansperse UV86) follows the viscosity closely that of the dual combination of the industry dispersant/synergist. However, over a period of storage time, the Lansperse UV86 outperforms the industry standard. With the lower viscosity profile, the use of more pigment in the formulations could help the formulator.
Further work will be done on a number of different pigments in the yellow and orange range but the initial findings are encouraging and suggest that has the added advantage of being bio-based.
As with all technical work, we would recommend a ladder series study to optimise dosage levels of the dispersants.