VINNOL® Produces Brilliant Colors
Suitability for Mild Solvents
In the last few years, a further requirement has come to the fore: to reduce employees’ exposure to smelly solvent fumes, the printing sector is looking for inks that are formulated with the mildest-possible solvents. The fumes of mild or “eco” solvents are neither harmful to health nor noticeably malodorous. Examples are certain glycol ethers and glycol esters. Such “eco-solvent printing inks” are intended for print shops or advertising agencies that use DOD printers. In the case of inks for CIJ printers, the odor is a minor problem as these printers are used exclusively in an industrial production environment where solvent vapors are extracted as necessary.
There are two types of inkjet printing process: discontinuous (drop on demand or DOD) and continuous inkjet (CIJ)
DoD – Drop on Demand: In this technology, the ink droplets are generated and then ejected from the print-head nozzles as required, i.e. only if they are needed to produce a dot. The print heads found in professional DOD printers typically have 256 nozzles of 20 to 50 micrometers in diameter per color. The droplet volume varies from 2 to 40 picoliters in accordance with the print-head technology. The pigment particles of the ink must not be larger than 5 to 8 micrometers. A filter is installed in front of each nozzle, blocking the passage of large particles. 2-Butoxyethyl acetate is currently the principal solvent used for DOD printers.
CIJ – Continuous Inkjet: This process ejects a continuous jet of electrically conducting ink from a nozzle located in the print head. The flow of inkjet disintegrates into individual microscopic droplets with a volume of between 10 picoliters and 1 nanoliter. From 60,000 to 100,000 such droplets are formed every second. The droplets move through two electric fields. The first provides them with an electrostatic charge. The second determines the trajectory of the droplets and is itself controlled by the digital print data: depending on whether the field is switched on or off, the droplets are either deflected toward the substrate with varying degrees of force to produce a color dot or they are allowed to pass by the substrate without deflection. The non-deflected droplets are collected and returned to the printer’s ink reservoir. Methyl ethyl ketone is a common solvent for CIJ printer inks.
Mild solvents have their downsides too: a great many binders are not very soluble in them. In addition, inkjet inks formulated with mild solvents are less likely to adhere to plasticized PVC and other polymeric substrates, with the result that the print image is less resistant to abrasion. This is also true of the VINNOL® E grade, which has been available for use in digital printing inks for some considerable time. Dr. Lauter and his team therefore set out to fashion a new vinyl chloride-vinyl acetate copolymer from this product which would offer the best compromise between the somewhat contradictory requirements. Their efforts resulted in the new VINNOL® E 18/38.
This new grade not only improves solubility in mild solvents, but also yields a polymer solution that has particularly low viscosity. In addition, VINNOL® E 18/38 is resistant to water, alcohol and weakly basic cleaning agents.
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