Our customers have expressed the wish to acquire inkjet-capable inks for printing on polycarbonate surfaces. These inks should contain either water or ethanol as the main component. They should come in three colour directions cyan, magenta and yellow (CMY), adhere to polycarbonate and dry sufficiently fast. Currently, no inks exist that meet these requirements.
Due to the hydrophobic properties of polycarbonate (PC), coupled with the lack of pores that could absorb dye, there are only two possible approaches.
An additive that has a high chemical affinity to the PC and at the same time serves as a carrier for the dye. This can only be another organic plastic. It should also be soluble in water or ethanol. This already limits the number of candidates very much. They have to be polyamines: polyethyleneimine (PEI) or polyvinylpyrrolidone (PVP). These are available and cheap. Other polyamines are known to science but are not commercial products. Other candidates are polyvinyl alcohols (PVAL), but they are the second choice over polyamines. A combination of different candidates is also possible, and could bring advantages. It would also be possible to use a polymer that does not dissolve in water but has a low melting point and affinity to PC. It can be presented as a stabilised emulsion in the ink, melts during printing, and solidifies on the surface to form a hard film. A suitable candidate is polylactone (PL) with the melting point of 30 to 65 °C, depending on the molar mass and functionalisation.
You could add additives to the ink that attack polycarbonate. Then, during printing, pores would form in which the dye is stably embedded. However, PC is very chemically resistant and one does not want to work with strong acids or alkalis in the printing industry. Therefore, there is only one suitable class of substances here: lower amines, such as triethanolamine.
Both approaches have several development risks. For one, the adhesion of the polymer film could still be poor. One possible solution is to use the second approach together with the first, see below. Another risk is the possibility that the film is sticky after printing - and not smooth and firm. This is also related to the possibility of removing the print again with water, which is not desirable. This problem could be solved with additives that strengthen the film and make it hydrophobic. These could be layer silicates, for example. It is probably advantageous to combine both approaches.
- Selection and purchase of reagents. Design of a test system.
- Selecting a suitable ink formulation from those already available. This then serves as a starting point for development.
- Experiments with PEI - different concentrations, molar masses, etc.
- Trials with PVP - different concentrations, molecular weights, etc.
- Experiments with PVAL - different concentrations, molecular weights, etc.
- Experiments with PL - different concentrations, molecular weights etc.
- Building on the above modules - combination of different polymers, e.g. PEI and PVAL, or PL and PVP.
- Experiments with suitable lower amines - triethanolamine, triethylamine, various ethylenediamine derivatives.
- Investigation of suitable additives if the problems described under risks occur.
- Building on the above modules - combining different polymers with lower amines and additives to the final formulation.