subject: Printing Inks [print this page] A printing ink, especially a printing ink for newsprint, comprises essentially pigment and binder portions. The binder portion consists entirely of a tall oil based agent. The tall oil is chemically processed, e.g. polymerized, esterified, fortified and/or phenolated for bringing it into a form suitable for use as a binder portion and/or a binder component.
Particularly newsprint covers a considerable part of the current consumption of paper. In terms of national economy it is naturally advisable to use recycled fibre at least partially in the production of newsprint. Recycled fibre is obtained from waste paper subjected to a deinking process for removing previous printing ink and soil. Waste paper is decomposed in the deinking process by a vigorous agitation in the presence of chemicals. The printing ink particles thus removed are separated at the flotation stage of a deinking process. It is obvious that the qualities, particularly whiteness and yield of the recycled fibres obtained from a deinking process are dependent on how effectively the printing ink can be detached from recycled fibres. It is also obvious that the degree of removal of printing ink from waste paper has an effect on the feasibility of the actual deinking process as well as on its enviromental impact.
The currently available types of printing ink, which are applicable to offset, flexo, gravure, silk screen and letterpress printing techniques, are identical in their basic composition. They essentially include pigment and binder components. In most practical cases, the actual binder and a solvent are also separated from each other. In any case, it should be noted that the binder component of the currently employed printing inks includes as its major constituents a resin component as well as a solvent component, particularly a vegetable oil and/or a mineral oil. A characterizing feature in all these printing inks is that the deinking thereof is relatively simple in fresh state. However, especially the recovery of newsprint with all its collection stages e.g. from households to a deinking plant with intermediate storages therebetween leads to the fact that the paper arriving at a deinking plant is in most cases several months old. The performed tests have indicated that all available printing inks, which contain vegetable oils and/or mineral oils, are difficult to deink in aged state. It has been discovered that the problems are due to the chemical changes of a binder as well as to a change in the composition of a printing ink during the aging period caused by the collection process.
