We often hear our bosses talking
about working in a paperless office. Yet everyone knows that no
office can ever be completely paperless. It is hard to conceive
of any life without paper, whether in the office or at home.
Since its invention, paper has become inseparable from our
daily lives. Closely connected to the cultural development of
mankind, it can be considered a socio economic indicator of any
Paper is normally manufactured from
vegetable fibers such as wood pulp, old rags, bagasse,
agro-waste, recycled paper and other ingredients including
inorganic non-metallic minerals such as calcium carbonate,
talc, kaolin. Some of these minerals play a very important role
and are termed as functional fillers. With the
latest advancements in technologies such as nano technology,
the role of minerals is expected to increase even more.
|Talc mine belonging to Golcha
Group, southern Rajasthan, India.
A brief history of papermaking
The basic idea of papermaking is bringing single natural fibers
together into a writable sheet. It began as a hand-crafted
system in the ancient world, gradually spreading across the
globe and becoming a mechanised process as different countries
applied their own systems and technological know-how.
Although paper is known to have
been used as far back as 3500 (BC), when it appeared in the
form of papyrus in Egypt, the first real papermaking, as we
understand it, is believed to have been attempted by Tsai
Lun in 105 AD. He was working for the Chinese Emperor, Ho Ti,
and succeeded in making paper from a combination of mulberry
bark, tow and old linen.
Further developments occurred in
Mexico, where the early Mayans and Aztecs produced a similar
material from the inner bark of the fig tree. The bark was
treated with water and lime to remove a latex- like sap, before
being beaten on stones and then felted on a board
where it was left to dry.
Papermaking in Europe appears to
have been introduced by the Moors who had mills in Spain at
Xativa, Valencia and Toledo appearing around the middle of the
12th century. The oldest recorded document on paper is a deed
of King Roger of Sicily in the year 1102.
Italian mills were first set up in
1276 in Fabriano, and the first known watermarked paper is said
to have come from a mill in Bologna about 1282, or possibly
from the Fabriano mill in 1293 or 1294.
The earliest German mills were
established in Cologne in 1320. Stromers mill at
Nuremberg was established in 1390 with the aid of Italian
workmen, and other early factories were located at Ratisbon and
Augsburg. The industry also progressed well in France, from
where it expanded into the Netherlands.
English papermaking lagged behind
the French and Dutch industries, with the first English mill
established by John Tate early in the 16th century.
Once the process was established in
Europe, different types of paper began to appear: blotting
paper, a coarse, gray product, is mentioned as early as 1465,
while the use of brown paper is first recorded 1570.
In America the first paper mill was
built in 1690 by William Rittenhouse and William Bradford in
the city of Philadelphia.
In 2004 global production of paper
touched 300m tpa, comprising of over 3,000 qualities. Some of
the more widely used examples are: writing and printing paper;
photocopying paper; art paper; coated paper; tissue paper;
newsprint; brown paper; matt finish coated; duplex; board and
The per capita consumption of paper
in 2010 is shown in table No 1.
Talc as a functional filler
There are a number of fillers which are used in paper
manufacturing. These fillers may be functional or
non-functional in character.
Non-functional fillers include
gypsum, powdered cuttlebone, wax and zinc oxide. The purpose of
using non-functional fillers is to decrease costs without
having any adverse effect on the properties of the paper.
Functional fillers, on the other
hand, are critical to achieving various properties of paper.
Such fillers include non-micronised or micronised talc, ground
calcium carbonate, wet ground calcium carbonate and processed
Of the functional fillers, talc is
the worlds softest mineral; its ores are soft, platy,
water repellant and chemically inert. Commercially the terms
steatite, soapstone and talc are applied to the same mineral
commonly referred to as talc.
Soapstone is a broad term, which is
composed essentially of talc with accessory minerals such as
dolomite, magnesite, quartzite and, rarely, with marble and
limestone. Steatite is pure form of industrial talc, which
contains CaO not more than 1.5%, MgO, 28-32%, SiO, 58-60%, grit
not more than 0.5%, Al2O3, 2-3% and other
impurities in traces.
Talc is the purest form, which is
rarely available. Talc is a hydrated magnesium sheet silicate
with the chemical formula (Mg3SiO4
(OH)2. The elementary sheet is composed of a layer
of magnesium-oxygen hydroxyl octahedral, sandwiched between two
layers of silicon oxygen tetrahedral. The main or basal
surfaces of this elementary sheet do not contain hydroxyl
groups or active ions, which explains talcs
hydrophobicity and inertness.
Talc is practically insoluble in
water and in weak acids and alkalis. It is neither explosive
nor flammable. Although it has a very little chemically
reactivity, talc does have a marked affinity for certain
organic chemicals (i.e. it is organophilic). At above
900⁰C talc progressively losses its hydroxyl groups and
above 1,050ºC, it re-crystallises into different forms of
enstatite (anhydrous magnesium silicate). Talc melts at
The paper industry is the largest
consumer of talc and generally uses 300 mesh (53µ) in
normal writing and printing varieties with the range of
brightness varying from 80-96% in normal uncoated paper.
Talc is used in three stages of paper making:
- As a
filler. In this stage, talc generally makes up 17-20%
of every 1 tonne of paper. Use of talc increases the opacity,
porosity, smoothness and brightness of the paper. Talc is
chemically inert and remains in the paper as a cost-effective,
infinitely recyclable filler.
- To control pitch and
stickiness during the papermaking process. Oleo
resinous droplets, micro or colloidal in nature, get added to
the paper stream. These micro impurities can clog the paper
machinery. Talc, being hydrophobic absorbs these micro droplets
or, if the droplets are big, then talc lamellae stick to their
surface thus controlling their stickiness.
- In coating
formulations. Due to the platy nature of talc
particle, it functions as a soft, printable and non-abrasive
material in paper and paper coating. For high brightness
finishes, talc leads to reduction in usage of expensive
whitening and helps to control the gloss of the coat. Talc also
provides smoothness to the surface and imparts opacity to the
coat. Due to its hydrophobicity it gives printing runnability,
porosity and a barrier effect in coated paper.
Additionally, talc reduces the
friction on paper manufacturing machinery thus decreasing wear.
However, the use of filler also reduces the physical strength
of the sheet of paper, and limits sizing.
Kaolin can be used instead of talc,
although the nature of the difference between these two fillers
is mainly reflected in the whiteness achieved. While the
whiteness of talc is 90% - 96.8%, the whiteness of kaolin is
80-86%. Thus, paper types requiring a relatively high whiteness
of paper types tend to use talc. However, talc is generally
used less in the production of thin sheets of paper, such as
The development of coated paper
Despite the early developments in paper manufacture noted
above, the first paper coating was not developed until
Normal base paper needs value
addition to satisfy consumer tastes and preferences by applying
different types of coating layers. Duplex, board, coated and
specialty art and matt finish papers are some of the forms of
value added coated paper products.
A coating mixture is made up of
different adhesives and pigments. Talc is the mineral pigment
which is widely used in coating mixtures. Different properties
of paper after coating like liquid penetration, surface tension
and resistance to mechanical stress are enhanced and leads to
better surface for printing, processing, or for specific
A comprehensive definition of a
coated paper might be a base paper to which a coating of
any kind has been applied. This would include a wide
variety of papers, used for a multitude of purposes. The
majority of the demand for coated paper generally comes from
books, magazines and advertising matter.
Coated paper is generally believed
to have originated in China, but no dates are given, and it
must be assumed that any early Chinese coated papers were of a
crude type and used for wall coverings.
European wallpapers were at first
printed on uncoated paper, and an English journal states that
this kind of paper first came into use around 1650.
These early hangings were quite
crude and a marked improvement was made when a flat ground-coat
was applied to the paper which was then printed with a
decorative design. Such papers were made in the United States
in 1824, and this may be assumed as the approximate date at
which coated paper was first manufactured in North America.
It seems highly probable that the
great improvement facilitated by printing wallpaper over a
ground coat was responsible for the coating of other types of
paper to obtain similar improvements in printing.
Early coated papers were made sheet
by sheet, brushing on the coating mixture by hand. Many of the
papers were used for highly glazed labels or for colored box
coverings, and the mixture applied became known as
colour. In many plants this name persists to this
day, even when the coating contains only enough colouring
matter to give the paper some tone of white.
It appears that the first paper to
be coated on both sides was made in either 1874 or 1875 and
this is also apparently the first application of coated paper
for book printing. This paper was coated on each side
separately. In later years the coating was applied on both
sides of the paper in a single operation using machines.
Today, coated paper is made in two
different ways. The first method to be developed was carried
out by transferring the base paper, or raw stock,
as it is sometimes called, to a separate plant and completing
the work there. Coated papers of the highest quality are still
produced in this way, which is generally called
The second method is called
machine coating because it is carried out as a part
of paper machine operation and at the regular speeds of paper
production. Machine coated paper was at first quite inferior to
that made by conventional methods, but with the skill and
experience developed during the last fifteen years its quality
is becoming much nearer to that of the good grade conventional
The essential feature of a coated
paper which makes it superior for printing is the smoothness of
its nearly plane surface.
No matter how heavily uncoated
paper is calendared, or how smooth its surface appears to be,
there are always roughnesses which prevent perfect contact of
the halftone dots of the printing plate and which injure the
appearance of the illustration.
When a coating is applied it fills
in the irregularities of the base paper surface and, after
calendaring, presents a much more uniform surface to the
printing plate, thus permitting a far more accurate
reproduction of the dots of the halftones.
Talc, with or without other
minerals combined with one or more adhesives, is used in
coating mixture. Adhesives cause the pigments to stick to the
surface of the paper firmly enough to withstand the pull of the
The selection of pigment and
adhesive combinations is responsible to a great extent for the
resulting characteristics of the finished paper and its
suitability for printing. It can influence such properties as
colour, brightness, gloss, opacity, and surface smoothness, ink
receptivity, rate of ink drying and the folding characteristics
of the paper.
Among the oldest mineral components
used in coating pigments are ground bone ash, white lead,
calcium carbonate, gypsum, powdered cuttlebone, wax, zinc
oxide, titanium dioxide, acrylic gesso, clay, talc and satin
white (aluminium hydroxide, calcium hydroxide and calcium
sulphate), barium sulphate, and calcium sulphate, sulphite and
These have been combined with the
traditional binders such as starch, mucilage and gums, gelatin
and animal glues (such as hide glue), and casein, as well as
modern latexes and synthetic resins (like acrylic emulsions)
and peanut and soybean proteins.
In modern times, kaolin, calcium
carbonate, whiting, talc and titanium dioxide are some of the
preferred coating pigments.
Talc as a coating pigment
Talc is a very unique coating pigment that helps improve the
tactile properties and printability of rotogravure paper,
producing a silky, soft feel to the finished product. Since
talc is a soft and platy pigment, it increases compressibility
and maximises ink transfer, thus reducing missing dots and
print mottle and improving the opacity of the printing.
The improved ink setting results in
a lower smearing tendency. It also lowers the surface friction
of the paper, and significantly reduces core bursts and crepe
wrinkles at the paper mill and the printing plant, and improves
runnability in rotogravure printing.
Any waste due to breaks during reel
changes is reduced. The soft talc also prevents the blades of
roll cutting and finishing machines from wearing out. All these
factors improve efficiency, leading to cost savings.
In matt and silk offset papers,
some grades of talc products improve delta gloss. This
attractively emphasises the difference between printed and
unprinted areas. Talc coatings also support lower print and
In addition, talc can serve as a
carrier for optical brighteners. These are used in many papers,
and result in a reflection of light with a bluish tinge that
suppresses yellow. Talc prevents the optical brightening agents
from soaking into the sheet. It remains on the surface for
In barrier applications, the platy
structured, hydrophobic talc improves the barrier
coatings sealing effect by blocking water vapor
transmission. The coating is oxygen, aroma and oil resistant -
even liquid resistance is possible. With the use of talc, the
product can be made printable, compostable and recyclable.
Processing efficiency is increased due to improved runnability
- for example, by preventing the blocking of reels.
For food packaging board and paper,
talc may amount to a significant share of the coating
dispersion. As regards cost efficiency, this means a lower
demand for binder in the formulation.
High brightness talc pigments,
including calcium carbonate, are also used in coating
formulations in paper mills operating under alkaline
conditions. Studies comparing the affinity of different
minerals such as talc, ground calcium carbonate, bentonite,
clay and diatomaceous earth to different contaminants, showed
talc to have the best affinity.
In fact, talc was the only mineral
to have an affinity to all the contaminants studied: adhesive,
wax, toner ink and hot melt.
Talc therefore cannot be termed as
just filler in the paper coating: it has been well established
that it is a functional filler. Its bluish tone improves
whiteness, and the right level of gloss, matt or silk finish
can be achieved by simply fine-tuning talc particle size.
Expected increase in coated paper
Worldwide consumption of paper and board is set to grow by
approximately 2-2.5 % for at least the next two decades. The
development and fast worldwide expansion of electronic media
has led to a certain shift in paper qualities and challenged
the development of new paper and board qualities. In
particular, pigment coated grades have participated most in
this new competition in the area of communication and
Because of their significantly
enhanced printability, added aesthetic attractiveness and more
valuable feel, the growth of coated paper and board will be
twice as high as that of paper and board in general.
Additionally, printed paper is a cost efficient medium with a
high capacity for information, easily available and fully
Most recently, pigments have become
significantly cheaper than chemical pulps. Therefore,
increasing the proportion of coating layers compared to fibers
is an important economic factor in cost-efficient
According to the production figures
in 2004, coated paper and board together contributed about 17%
of total global paper production. This is expected to increase
to 21% by 2014. The volume of paper will be much higher
compared to the weight per area by 2014 due to the increased
coating to pulp ratio.
In coated paper, the proportion of
coated layers per cm² of the base paper is between 30-65%,
which is significantly higher than board for which coated
layers make up roughly 5-20%.
The magnified image above shows the
base paper and two coating layers.
Global trends in paper manufacturing
Future trends for coated papers will involve more specific
paper products. Further advances in coating and printing
technology, environmental factors, the development of coating
colour, availability of raw materials and the globalisation of
paper companies will all contribute to the evolution of the
According to the Confederation of
European Paper Industries (CEPI), Germany is the largest paper
producer in Europe, followed by Finland, Sweden, Italy and
France. The main pulp-producing countries are Finland and
Over the last 15 years, paper and
board consumption in Europe has increased by an average of 2.6%
per annum. In 2006, CEPI member countries produced more than
100m tonnes of paper and board, of which 18m tonnes were
exported. In volume terms, graphic paper grades account for
around 48% of European paper production while packaging paper
grades account for 40%, and hygiene and speciality papers for
Europes papermaking economic
cluster generates an annual turnover of more than Û375bn
($461), or 6.5% of the European manufacturing industrys
total annual turnover. This figure is dwarfed by the
industrys presence in other parts of the world, however:
in North America papermaking accounts for 28% of manufacturing
turnover, and for Asia it is 35%.
One of Asias notable success
stories in the field of papermaking has been Asia Pulp &
Paper Co. Ltd (APP), one of the Sino-Indonesian Widjaya family
of companies. Before 1995, APP was a relatively modest sized
company but has risen to become the seventh largest paper
producer in the world, exporting final products to 65
countries, according to Alex Goh, head of the firms
Perhaps unsurprisingly, China is
poised to become the worlds largest paper producer. But
Chinas ambitions for this industry are causing serious
deforestation in the country and across South East Asia. Modern
paper production in China only developed during the last
decade, but has grown aggressively in line with the rest of
Chinas economic boom.
Nick Harambasic, manager of the US
natural solutions and paper producer Penford Products
Corporation said: At first, China had many small
factories of low quality, which produced for the domestic
market. In the nineties, it started installing paper mills of
international standard. The growth has been
He predicted that China would
become the worlds largest producer of paper, a position
currently occupied by the US.
Contributor: Ajay Kulshreshtha, consultant, AK
Minerals Consultancy Services, India.