Chemistry ISU
THE EARLY HISTROY AND THE
MANUFACTURING
OF
Elastic Erasers
What is an Eraser?
A
eraser is an object that is used to remove marks from paper. Most erasers are
designed to remove pencil marks. There are some special pens that have erasable
ink that can be removed by special erasers.
How Do Erasers Work?
Erasers
pick up graphite particles (pencil marks), and remove them from the surface of
the paper. The molecules in erasers are 'stickier' than the paper, so when the
eraser is rubbed on top of the pencil mark, the graphite sticks to the eraser
over the paper. Some erasers damage the top layer of the paper and remove it as
well. Erasers attached to pencils absorb the graphite particles and leave a
residue which needs to be brushed away. Soft vinyl erasers are softer than the
erasers attached to pencils, but are otherwise similar. Art gum erasers are
made of soft, coarse rubber and are used to remove large areas of pencil marks
without damaging paper.
Kneaded
erasers absorb graphite and charcoal without wearing away. Kneaded erasers may
stick to the paper if they are too warm. They eventually pick up enough
graphite or charcoal that they leave marks rather than pick them up, and need
to be replaced.
The History of Erasers
The
first erasers were pieces of bread. It was the best substance for removing
pencil marks until rubber was available in the Europe. Rubber was known to the inhabitants
of Central and South America before Europeans came to the Central and South
America. As early as the 11th century, it was used to coat clothing
and to make balls. It was also used to make footwear and bottles by pouring the
liquid form on earthen molds and allowing it to dry.
In
1735, the French scientist Charles de la Condamine discovered a substance known
as caoutchouc and sent samples to
Europe. Caoutchouc came from a fluid under the bark of a tree found in tropical
areas of Central and South America. This milky liquid, known as latex, is still
used to make natural rubber. Caoutchouc was first suggested for use as an
eraser in the Proceedings of the French Academy in 1752. In 1770, the English
scientist Joseph Priestley suggested that caoutchouc should be called rubber,
because of its ability to rub away pencil marks. Until the late 19th
century, pencils and erasers were always separate. In 1858, Hyman Lipman of
Philadelphia patented a pencil with a groove in the tip, into which an eraser was
glued. By the early 1860s, the Faber company made pencils with attached
erasers.In 1858, Hymen Lipman received a patent for attaching erasers to the
ends of pencils, though the patent was later invalidated since it combined two
products rather than invented a new one.
Raw Materials
The
most important raw material in an eraser is rubber. The rubber may be natural
or synthetic. Natural rubber comes from latex produced by the rubber tree. Synthetic rubber exists in a wide
variety of forms. The most common synthetic rubber comes from the chemicals
styrene and butadiene. Styrene is a liquid derived from ethylbenzene.
Ethylbenzene is usually made from ethylene and benzene, both of which are
derived from petroleum. Butadiene is a gas, derived either directly from
petroleum or from substances known as butanes and butenes, which are derived
from petroleum.
Other
ingredients that are added to rubber include pigments that change the color of
the eraser. Zinc oxide and titanium oxide make the white color. Red can be
produced by iron oxide. Many other colors can be produced with various organic
dyes.
Sulfur
is a very important ingredient added to
almost all rubber. Sulfur allows rubber to be vulcanized. Charles Goodyear
invented this process in 1839. It uses heat and sulfur to make rubber more
durable, resistant to heat, improve the strength and resiliency. Vegetable oil
is added to the rubber to make the rubber softer and easier to shape and
pumice, a natural mineral, is added to make the eraser more abrasive.
Making Erasers
When
the rubber arrives at the eraser factory it is mixed with pigments, vegetable
oil, pumice, sulfur, and other ingredients that modify the properties of the
final product. Synthetic rubber is easier to mix because it usually arrives as
a powder or a liquid. Natural rubber usually arrives in bales and must be
pulverized (mashed up) into powder or dissolved in a solvent before it can be
mixed.
The
mixture is heated, causing the sulfur to vulcanize, making the mixture more
stable. To make plugs, which will be attached to pencils, an extrusion process
is usually used. The mixture, in the form of a soft solid, is forced through a
die to form a long cylinder. The cylinder is repeatedly cut as it emerges,
forming plugs.
To make flats, which are not attached to pencils, an
injection molding process is usually used. The mixture, in the form of a warm
liquid, is forced into molds and allowed to cool into a solid. The flats are
then removed from the molds.
The
plugs are shipped directly to pencil manufacturers where they are attached to
pencils by small, cylindrical, metal cases known as ferrules. Ferrules are made
of plain aluminum for less expensive pencils, or painted brass for more
expensive pencils. The ferrule is attached to the pencil with glue or with
small metal prongs. The plug is inserted into the ferrule and clamped around
it.
The
flats may be marked with the name of the manufacturer or other markings. This
may be done by stamping or by screen printing. Three-dimensional markings can
be made by embossing—cutting into the eraser with a sharp die. The completed
flats are packed into cardboard boxes and shipped to retailers.
The Future
Erasers
have remained mostly unchanged for many years. Improvements in eraser
technology are likely to be made in the way rubber is produced. New chemical
formulas are constantly being developed to produce synthetic rubber in ways
that are more efficient, less costly, and which result in products with more
useful properties. Genetic engineering may result in rubber trees that produce
more latex, or trees that produce latex with physical properties that would
make natural rubber production more efficient.
Bibliography:
Wikipedia.org
Google.com
Media available by Discovery
Channel's, How it's Made.
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