novomatics HEMOTRONIC III, Руководство по эксплуатации

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CHEMOTRONIC III
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1.3.1. Introduction
This chapter is providing information on the basic concept of the cloud point
measurements of resins for applications in printing inks.
In lithography printing conventional oil-based paste inks perform best. These inks
consist of resins, mineral oils, pigments and additives. Therefore the performance
of these inks is highly depending on the compatibility of all these components. In
order to test the compatibility of a resin and a mineral distillate, the resin must be
dissolved in the mineral distillate at a high temperature first. When cooling this
solution, the resin will precipitate in the liquid at a specific temperature, which is
called the cloud point. The cloud point can accurately be detected by automatic
turbidity measurement with the CHEMOTRONIC.
Turbidity is defined as an optical property of a liquid caused by light scattering and
absorption. This state will be caused by unsolved particles, for instance fine
polymers or organic material. These particles solved in a liquid lead to haze or
turbidity, if the light passes through the liquid. Easily said, turbidity is the opposite
of clearness.
In case of a resin dissolved in oil, the precipitation process increases rapidly within
a small temperature interval until full solidification of the varnish. The temperature
at which this happens is the so-called solidification point which is closely related to
the cloud point. Deviations in the cloud point can lead to sedimentation in the
varnish, differences in drying speed, loss of gloss and tack stability of printing inks.
Therefore the cloud point is a characteristic value for the specification of printing
ink resins.
In the past the cloud point detection could be determined on the manual way only.
This test method had many sources of error and uncertainty due to poor
reproducibility, variances in heating and cooling of the sample, inaccurate turbidity
determination, etc.