surface treatment stage is incorporated using rolls
to apply a sizing solution. This is known as surface
sizing and is used to improve the strength, feel,
fluid penetration and printability of the sheet.
used is a film press, this uses metering devices that
result in a thin film of the sizing solution being
applied to the surface of the paper. Traditional
sizing solutions are very simple, typically consisting
of starch in a water solution. It is becoming
increasingly common to include white pigments
in sizing solutions. This is known as pigmented
sizing. The enhanced light scatter from the pigment
increases the brightness and opacity of the paper.
Pigmented size usually has a 1:1 ratio of mineral
pigment to starch, or sometimes higher. The solids
of pigmented sizes are typically 2 to 3 times
higher than "clear" starch only sizes.
either precipitated calcium carbonate (PCC) or
ground calcium carbonate (GCC) as a filler. Size
press pigmentation normally utilises the same
type of pigments as they are available at the mill
and the most commonly used is GCC because of
its good rheology, high brightness, and bluish
colour.
pulp are causing paper and board manufacturers
to look at ways to reduce their fibre consumption.
will enable this to be achieved, but to be
successful, detrimental effects on sheet
properties must be overcome.
are used as filler and coating pigments in the
manufacture of paper and board to improve the
physical, surface and printing properties of the
finished product. A further advantage of minerals
used as fillers is the replacement of fibre. This is
because, although fibre is the most important
component in papermaking, its availability and
cost, are becoming an increasing concern for our
customers in the paper industry.
sheet of paper, or piece of board is not a new idea,
but generally, most producers have maximised the
amount of fibre replacement they can accept
without detriment to paper properties. Adding
further filler to these products is desirable from a
cost point of view. Doing so would however have
a negative impact on paper physical properties,
such as strength and rigidity (stiffness), because
fibre to fibre bonding is interrupted by the physical
presence of the mineral.
REPLACING FIBRE WITH MINERAL
is at present considerable activity in developing
ways to improve sheet strength and stiffness. This
is generally focused on ways to improve `fibre to
fibre' and `fibre to filler' bonding and IMERYS
researchers are actively involved in these studies
as part of our "FibreLean" initiative. However,
an alternative way to look at this problem, is to
consider the impact of minerals on strength and
stiffness when used in other areas of the
papermaking process instead of as fillers.
free sheet (uncoated woodfree) paper, for example,
the paper we commonly use in photocopiers and
office or home printers.
Free Sheet Papers
surface sizing to improve the sheet properties.
improves sheet stiffness, therefore allowing
replacement of fibre with mineral.
chemical additive performance are also seen.