Colour Chronicle - June 2013

PAPER
Chemistry
Explained
How is paper manufactured?
Paper is manufactured mainly from wood
fibres which are broken down either
mechanically or chemically. These wood
fibres are then mixed with auxiliary agents
and large amounts of water to produce a
suspension which is then placed on a sieve.
As the fibres distribute themselves beside and
on top of each other on the sieve, the water
drains away. This produces a homogeneous
fibre composite – the raw paper. The paper
web is then pressed between rolls, a process
in which it is de-watered, compacted and
finally dried. In a further processing cycle,
many types of paper are coated, i.e. treated
with a very thin layer of pigments and
binders. This gives the paper a closed surface
with good printing properties.
How is paper made grease resistant?
Paper intended for use as food packaging
material has to be treated to make it grease
resistant. Two methods are practiced for this
purpose: in the first technique Cartaguard®
KHI is introduced into the fibre suspension
early in the production process so that it is
distributed evenly throughout the entire
paper. In the second method, it is the
finished paper which is impregnated with
Cartaguard® KHI; this is done, for example,
by using a “size press” in which the paper
web is passed between two rolls while
applying a mixture of Cartaguard® KHI and
starch. The impregnating agent doesn’t just
remain on the surface, but also penetrates
into the paper, creating a grease resistant
layer.
How does Cartaguard® KHI repel
grease?
Cartaguard® KHI consists of complex
molecules comprising mainly carbon,
fluorine, oxygen and hydrogen. The shape
of a single molecule can be imagined as
being rather like a comb; the handle of the
comb represents the part of the molecule
that attaches itself to the paper fibre and
combines permanently with it while each
tooth corresponds to a pendant molecular
chain. When a large number of “combs”
– Cartaguard® KHI molecules – arrange
themselves close together on the surface
of every single paper fibre, the fibre is
surrounded by a grease resistant layer. When
a droplet of oil comes into contact with this
layer, it cannot penetrate as it would into
untreated paper. Instead, it simply bounces
off – experts call this the “lotus effect”. Oil
therefore cannot enter the fibres and the
paper remains unstained.
15 COLOUR CHRONICLE__JUNE 2013