The general shift from an
acid-based process to an alkaline one has transformed the use
of fillers in papermaking, creating an opening for ground
calcium carbonate (GCC) and precipitated calcium carbonate
(PCC). This has allowed these minerals to increasingly replace
wood pulp and other pigments in the paper manufacturing
GCC and PCC improve paper quality
in terms of its brightness, bulk, opacity and porosity. These
mineral additives are widely used in the alkaline process,
which produces paper types such as fine printing and writing
paper. In some cases, however, paper is still manufactured in
an acid environment, and it is here that traditional paper
minerals such as kaolin are still required.
Loading paper rolls for transport at one of
factories in Finland. UPM is one of the largest paper
in the world. UPM-Kymmene Oyj
World paper scene
China has emerged as the
worlds leading paper and board producer and its global
share continues to increase year on year. In 2009 the country
produced an estimated 90m. tonnes of paper and board (P&B),
up from 78m. tonnes in 2008, and some projections indicate that
Chinas P&B share in 2010 could increase again to 98m.
This emergence has been encouraged
by the Chinese government, which has ensured that investment by
large domestic and international companies has created a modern
Chinese paper industry.
In this year alone global
engineering and process solutions provider, Metso Corp., has
won three contracts to provide or renovate new and existing
paper manufacturing equipment in Chinese paper factories.
The group also won a significant,
170m. order last year to supply a coated fine paper
production line to Shandong Huatai Paper Co. Ltd, member of
Huatai Group, in Dong Ying City, Shandong province. The
state-of-the-art production line will produce close to 500,000
tpa of coated and uncoated fine papers, within the basis weight
range of 80-200g/m2. The paper machine design speed
is 1,800 m/min and the coater design speed is 2,000 m/min.
China has a shortage of high
quality kaolin suitable for paper products. It does, however,
hold significant deposits of high quality marble near to the
main papermaking areas, and it has successfully developed these
for paper grade GCC.
GCC is now the principal industrial
mineral for paper production (Figure 1), where it can
be used as a precoat, coating pigment and as filler. As
consultant Ian Wilson discussed in his presentation at
IMs 20th Industrial Mineral
Congress & Exhibition, March 2010, topcoats previously
comprised around 70% GCC and 30% kaolin but this ratio has
swung in favour of GCC and the topcoat ratios today are around
85-90% GCC and 10-15% kaolin.
This increased proportion of GCC,
particularly in the higher coating colour solids, saves on the
energy and costs associated with drying.
Not only has the ratio of GCC used
in topcoats increased, so has the actual pigment loading:
especially in Chinese Printing and Writing paper (P&W). As
Wilson explained, pigment loadings of 40-50% are now common and
new paper machines will run, for the first time anywhere in the
world, with up to 55% pigment loading the pigment
consisting mainly of GCC.
Growth of GCC production in China from 1992-2008
One company pioneering this
increased pigment loading is Asia Pulp & Paper Co. Ltd
(APP), which plans to bring on stream a new paper machine at
its Hainan Island, China plant, that will see total loading
levels of mineral pigments (such as GCC, talc, and titanium
dioxide) overtaking those of fibre for the first time.
APPs imminent start up of
Paper Mill 2 (PM2) at the Hainan Island plant will result in
increased volume consumption of minerals in paper. Some 600,000
tpa GCC is anticipated in the first phase of production,
possibly increasing to 800,000 tpa GCC. The precoat and filler
will consist of GCC while the topcoat will comprise 90% GCC and
Supplied by Germanys Voith
Paper GmbH, PM2 will have a production capacity of 1.45m. tpa,
is 430 metres in length, and produces paper at 2,000
The PM2 will have reduction in
freshwater consumption used in papermaking and minimal use of
fresh fibres; mainly assisted through increased use of GCC .
PM2s water use will be around 5 l/kg paper produced: the
maximum allowable in China is 10.5 l/kg with comparable fine
paper machines in Europe consuming on average 8 l/kg.
APPs planned increase of
mineral pigment loading, in excess of 50% and even up to 60%,
is a significant increase from the usual filler loading levels
of 30-40%. Not only does the increased GCC loading save costs
on energy for drying purposes, it also saves significant money
on raw material costs.
The price of Northern Bleached
Softwood Kraft pulp in the USA is about $875/tonne while the
price of Chinese pulp is close to $900/tonne. Chinese precoat
GCC, meanwhile, can command price ranges of $80-160/tonne while
Chinese filler grade PCC costs about $80-90/tonne. Comparing
the mineral prices to pulp prices, it is clear that increasing
mineral loading and decreasing pulp content is certainly
advantageous for producers.
world paper and board production figures taken from the paper
by Ian Wilson and Larry Lai, Why Chinese paper is so
competitive, given at IMs
20th Industrial Minerals Congress &
Exhibition, March 2010.
Since the early 1990s the
paper-grade kaolin market has suffered increased competition
from ground calcium carbonate (GCC) and precipitated calcium
carbonate (PCC) products. At present, numerous kaolin grades
exist on the market, with much of this diversity targeting the
changing demands of the paper industry.
The growth of GCC in applications
such as paper coating has driven the development of specialised
kaolin grades, such as Hydragloss¨ 90 by US kaolin producer
KaMin LLC (formerly Huber), an example of a fine glossing, high
Paper grade kaolin must undergo a
rigorous manufacturing process, and some products may go
through as many as six processing steps. One of the principal
grades of hydrous kaolin is a water-washed
product which is taken through beneficiation processes to
remove grit and increase brightness.
This can include blunging (kaolin
is mixed with water and chemicals to form a slurry),
de-gritting, centrifuging (fine and coarse particles are
separated), brightness enhancement (bleaching, magnetic
separation, flocculation, ozonation, flotation, and oxidation),
and filtering and drying.
Advantages of water-washed kaolin
include easy dispersion, chemical inertness, neutral pH, range
of particle sizes and brightnesses, low Mohs hardness which
minimises machinery wear, rheology aid, and extender for
titanium dioxide and resins. Other kaolin types include:
coarse kaolin, the particles of which resemble
booklets when magnified, is milled to separate the
booklets into individual plates. This extra processing step
produces an engineered kaolin, suitable for lightweight coating
applications, which has additional benefits to a water-washed
product. Benefits include a high aspect ratio (HAR), improved
barrier properties, neutral pH, low machinery wear, controlled
penetration, and bridging.
kaolin is heat treated to convert the mineral into an amorphous
structure. During calcination, air voids are incorporated into
the structure. The advantages to using calcined kaolin include
chemical inertness, increased brightness, structured particles,
low moisture content, increased oil absorption, improved
reinforcement, and better optical properties.
Surface treated: kaolin is chemically
modified for enhanced coupling with polymer systems. This
affects the kaolins chemical compatibility by improving
dispersion and rheology. Also affected is the chemical coupling
of the kaolin, as surface treated kaolin grades have improved
physical and mechanical properties in addition to increased