Article written by Carol D. Klein, Manager, Technical Sales
INTRODUCTION
The types of inks manufactured and their applications are so varied. The following is a general classification of inks and the colorants used in them. As a dye supplier, Spectra Colors Corporation focuses on the following ink areas: ink jet inks, marker inks for children including highlighter and disappearing inks, writing inks, stamp pad inks, ball point pen inks, ribbon inks, permanent inks and artists’ inks. Appropriate dyes must be specifically qualified and developed for each type of ink. The dyes listed below must be tested in the ink system to conform to low insoluble levels, purity, viscosity, surface tension, strength, shade and solubility
INK JET INKS
Ink jet inks can be water or solvent based. Many dyes used in other areas mentioned in this article are also used in ink jet inks. The success of ink jet ink is extremely dependent on the relationship between the ink, the cartridge, and the substrate to be printed on. An aqueous jet ink cannot be used in all aqueous ink jet cartridges. The formulations stated in this article are good starting points for ink jet inks as well. Purity of the ink is necessary and many dyes used in ink jet inks are filtered to the sub-micron range. Many characteristics of the ink, such as surface tension, viscosity, shade, color intensity, drying time, light and water fastness, can be altered with minor modifications.
DYES USED IN AQUEOUS INK JET INKS
Some ink jet systems are based on solvent-based inks, such as Alcohol and M.E.K., and Hot-Melt Systems. Spirit-soluble, solvent-soluble, and oil-soluble dyes are generally used in these systems.
MARKER INKS FOR CHILDREN
The issue of safety is foremost in the production of any product intended for use by children. The below information is just a guide and can be altered to adjust drying time, surface tension, viscosity or any other property that is critical. The ability to wash ink from clothing and skin can be improved by replacing propylene glycol with one of the longer chain polyethylene glycols.
A typical aqueous ink formulation for use by children is as follows:
| De-ionized water | – | 70-80% |
| Propylene glycol | – | 20-30% |
| Dye | – | 1-5 % |
| Biocide | – | <0.5% |
| Surfactant(optional) | – | <0.5% |
The issue of safety is foremost in the production of any product intended for use by children. The above formulation is just a guide and can be altered to adjust drying time, surface tension, viscosity or any other property that is critical. The ability to wash ink from clothing and skin can be improved by replacing propylene glycol with one of the longer chain polyethylene glycols.
MAIN DYES USED IN CHILDREN’S INKS
The marker system itself is critical to ensure proper flow of the ink to the substrate. The ink flows by capillary forces from the reservoir, where it is held in the marker, through the nib and onto the substrate. The reservoir is generally made of synthetic fibers, polyester or cellulose acetate, and the nib can be made of bonded fibers such as polyester or acrylic, felt, extruded plastic, or molded plastic.
These dyes must meet certain specifications for this application and many other dyes are available. Spectra can make recommendations for a specific requirement. Specialty types of inks are also made for children such as: highlighter, color changing inks and disappearing inks.