Ink is a complex mixture of ingredients that are combined in a specific
formulation to meet desired characteristics of the printing application
of the ink. This article will focus on no-heat printing ink formulations
and how some of the raw materials are derived. Ingredients in no-heat
inks fall into four major classifications: Pigments, Resins, Oils
or Carriers, and Additives.
The function of the pigment is to provide the coloristic properties
of the ink. The resin is added as a dispersion aid and also as a
binder to affix the pigment to the paper. The oil or carrier is
the medium for transferring the pigment and resin through the press
to the paper. Additives are used in no-heat inks to control pigment
wetting and dispersion, viscosity and flow characteristics, as well
as to provide a proper ink/water balance.
To review these ingredients in more detail, let us look at some
news ink formulations. Figure 2 shows typical black formulations
for both the Web Offset and Letterpress printing techniques. The
ingredients used in these types of formulations are both similar,
however, they are different in concentration.
The pigment used in news ink blacks is carbon black. Carbon black
is produced by cracking oil in a continuous furnace. These furnaces
are highly controlled in order to produce a specific grade of pigment
varying in particle size and structure. The oil used is also of
a specific grade so that certain requirements can be met.
The ink film thickness applied by the printing application dictates
the concentration of pigment needed to meet the required print density.
As you can see from the typical formulations, the web offset ink
has a higher concentration of pigment than that of the letterpress.
This is because the letterpress printing process applies a much
thicker film of ink than web offset.
Resins for news ink vary depending on the rub off quality that an
ink requires. The resins are the most expensive part of a news ink
black, so their selection and concentration are limited by economic
restraints. The oil or carriers used in today's news black are treated
napthenic petroleum oils. Since these oils are non-drying the drying
process of a news ink is by absorption of this oil into the paper
stock. Changes in the absorption characteristics of the newsprint
can drastically affect the rub off quality of the finished product
The oils are non-drying under press conditions and are designed
this way. Typically newspaper presses are not temperature controlled
nor are the rollers washed up at the end of a run. If any volatile
material was used, the ink would tend to dry on the roller train
and cause problems. The heat set printing process by contrast uses
volatile oils in their printing process. These oils are driven off
the ink film by passing the printed web through an oven, thus leaving
only the pigment and resins on the printed sheet. This explains
why heat set inks have better rub off characteristics.
Additives used in news black are from a variety of different materials.
News ink black will require different viscosity or flow characteristics
depending on the type of press used. The ink is also required to
provide a proper emulsification rate so that the web offset printing
process will work. If a formulation did not accept any fountain
solution, the ink would not transfer to the plate and stripping
would result. If an ink emulsified too much fountain solution, high
dot gain and poor print quality would result. In extreme cases,
ink would tend to go to the non-image area of a plate and scum.
Figure 3 shows a typical color ink for a newspaper ink. The pigments
used in news ink colors are what are classified as organic pigments.
Organic pigments are synthetic materials that are formed under specific
conditions to produce the desired characteristics of color and crystal
size. The typical pigments used are Phthalocyanine blue for cyan,
Lithol Rubine for magenta, and Diarylide yellow for yellow.
Pigments for the printing ink industry are supplied in the form
of heavy concentrated bases or "Flushes." In the normal
course of pigment manufacture, the color pigment is produced in
an aqueous environment resulting in a pigment suspension. After
synthesis, the color pigment is filtered from the suspension and
dried to produce dry color. In producing the flush color, the pigment
is not fully dried. The water-based slurry is concentrated to approximately
20 to 30% pigment. The slurry at this point is called a presscake.
Instead of going through the drying process, the presscake is mixed
with an oil-based varnish. The two components are kneaded together
in a mixer. The pigments have a greater affinity for the oil-based
material. The water is "flushed" out or displaced by the
varnish as the pigment migrates from the water phase into the oil.
This process is continued until all the water is removed, thus creating
the flushed color.
The resins used for colors tend to be much cleaner in color than
those used for black inks, so that the printed color can reflect
its truer color. The oils used by the newspaper market today are
from the vegetable family. The newspaper market found that the soy
bean oil type formulations produced a better product for this application.
Soy bean oil is a naturally renewable resource, which is extracted
from the bean. The food industry also uses this type of oil in some
of their products.
Color printing inks also use extender pigments. These pigments are
typically kaolin type clays and provide functional properties to
a given formulation. The additives used in color inks are similar
in nature to those in black inks.
What is ink? We learned in this article that ink is comprised of
various raw materials at specific proportions which are called formulas.
When formulating quality newspaper inks, it is not only important
to have the proper ingredients, but also the proper manufacturing
and quality control techniques. When these parameters are optimized,
the quality inks developed in the laboratory can be made on a much
larger scale in production. In future articles US Ink corporation
will discuss these topics in greater detail.