Note: Descriptions are shown in the official language in which they were submitted.
CA 02767216 2012-01-04
WRITING SUBSTANCE FOR WRITING, DRAWING AND/OR PAINTING
TOOLS
The invention relates to polymer-bound writing substances
for writing, drawing and/or painting tools.
Such writing substances for writing, drawing and/or
painting are known in principle. "Polymer-bound graphite-
based writing substances for writing, drawing and/or
painting" are understood to be writing substances which are
inserted rigidly into wood or other materials which can be
sharpened, and also writing substances which are held
displaceably in a rigid casing. Examples of this include
wood-cased pencils and writing substances for mechanical
pencils, for example `retractable pencils'. In this case
the writing substances normally have an outer diameter in
the range of approximately 0.3 mm to 6 mm.
For example, polymer-bound graphite writing substances are
known from DE 38 27 968 Cl. Such raw writing substances
contain a polymer bonding agent, lubricants and fillers.
A drawback in the production of such writing substances is
that although the writing and painting properties thereof
are very good with a high filler material content of more
than 50 wt. the viscosity of the writing substance mass
during extrusion is very high and the extrusion pressure
thus required in the die and in the extruder reaches very
high values. The head pressure is approximately 350 bar.
This is disadvantageous since a greater dimensioning of the
extruder and complex configuration are required. The
service life of the equipment and dies is much reduced by
the high extrusion pressure.
The object of the invention is therefore to provide a
writing substance for writing, drawing and/or painting
which does not have the aforementioned drawbacks and which
can be produced at low extrusion pressure.
CA 02767216 2012-01-04
- 2 -
The object is achieved for polymer-bound writing substances
for writing, drawing or painting tools, in particular for
pencils or coloured pencils, comprising at least one
polymer bonding agent, at least one wax, and at least one
filler material, in that the writing substance further
comprises 0.1 to 5 wt. % of palm kernel oil, and/or coconut
butter, and/or coconut oil and/or oleic acid.
It has surprisingly been found that an inner lubricant is
added to the formulation by the selective addition of palm
kernel oil, and/or coconut butter, and/or coconut oil
and/or oleic acid as a writing substance component,
significantly reducing the extrusion pressure in the
extruder. The addition of palm kernel oil, and/or coconut
butter, and/or coconut oil and/or oleic acid in the writing
substance composition leads in particular with extrusion to
a considerable reduction in the pressing or extrusion
pressure at the mouthpiece or head of the extruder. The
pressure decreases with increased addition of palm kernel
oil, and/or coconut oil, and/or coconut butter and/or oleic
acid, wherein a reduction in pressure by at least 30 %, in
particular by at least 50 % compared to conventional
extrudable writing substance compositions is achieved.
It has been found that other natural or synthetic oils also
reduce the pressure in the extruder, but that these are
overproportionately detrimental to the strength of the
extruded writing substance. Surprisingly, this is not the
case with use of palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid, since the pressure in
the extruder is low, yet the strength of the writing
substance is provided to the required extent.
The addition of palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid also provides a more
intense colour of the stroke of the writing substance and
improves the sliding behaviour thereof when writing. In the
CA 02767216 2012-01-04
3 -
case of pencil writing substances, a deep stroke of high
density is demonstrated, whilst coloured pencil writing
substances exhibit a deep, bright intense shade of the
stroke.
The proportion of palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid in the writing
substance composition lies in the range of 0.1 to 5 wt. %,
in particular in the range of 0.5 to 2.5 wt. If the
content of palm kernel oil, and/or coconut butter, and/or
coconut oil and/or oleic acid exceeds the aforementioned
limit of 5 wt. the strength of the writing substance
will be overproportionately reduced. The writing substances
then tend to crumble or break during use.
At 20 C, the waxes used are ductile, compact to brittle,
have a coarse to finely crystalline structure, are
translucent to opaque in terms of colour, but are not
glassy and melt above 40 C without decomposition. They are
free-flowing slightly above the melting point and have a
largely temperature-dependent consistency and solubility.
The writing substances according to the invention are raw
writing substances which can be used immediately after
extrusion without further heat treatment or impregnation.
In addition to pencil and coloured pencil writing
substances, special writing substances such as writing
substances for "carpenter's pencils" are also cited.
Advantageous embodiments emerge from the dependent claims.
It has proven to be advantageous if the polymer-bound
writing substance comprises
to 30 wt. % polymer bonding agent
2 to 25 wt. % wax
0.1 to 5 wt. % palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid
CA 02767216 2012-01-04
- 4 -
remainder filler material(s).
In particular, it is preferable if the polymer-bound
writing substance comprises
15 to 25 wt. % bonding agent
4 to 20 wt. % wax
0.5 to 2.5 wt. % palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid
remainder filler material(s).
It has been proven to be useful if the at least one bonding
agent is formed of at least one polymer of the group
comprising polystyrene (PS), styrene acrylonitrile (SAN),
styrene-butadiene (SB), polyolefins (PO) and acrylonitrile
butadiene styrene (ABS).
Mixtures of two or more bonding agents may also be used.
It has also proven to be useful if the at least one wax is
at least one wax from the group comprising stearates,
montan waxes, amide waxes and paraffins.
Mixtures of two or more waxes may also be used.
It is particularly preferable if the at least one wax is
formed of calcium stearate or comprises calcium stearate.
The at least one filler material is advantageously formed
of at least one filler material of the group comprising
graphite, soot, hexagonal boron nitride, layered silicates,
chalk, baryte, coloured pigments and uncoloured pigments.
For pencil writing substances, graphite or graphite in
combination with soot as a chromophoric filler material is
preferred in particular. For coloured pencil writing
substances, combinations of white or colourless filler,
such as hexagonal boron nitride, layered silicates, etc.,
with chromophoric pigments such as azo pigments,
CA 02767216 2012-01-04
-
phthalocyanines, dioxazines, quinacridones, iron oxides,
soot, graphites, ultramarine or iron cyano complexes have
proven to be of use.
A preferred composition for a pencil writing substance
comprises:
to 25 wt. % bonding agent
4 to 12 wt. % wax
0.5 to 2 wt. % palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid
remainder graphite or graphite and soot.
In particular, a pencil writing substance comprises:
15 to 25 wt. % polystyrene (PS)
4 to 12 wt. % calcium stearate
0.5 to 2 wt. % palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid
remainder graphite or graphite and soot.
An exemplary formulation 1 for a pencil writing substance
comprises:
polystyrene (PS) 21 wt. %
calcium stearate 6 wt. %
oleic acid 1.0 wt. %
graphite remainder.
An exemplary formulation 2 for a pencil writing substance
comprises:
polystyrene (PS) 20.5 wt. %
calcium stearate 6 wt. %
coconut oil 1.5 wt. %
graphite remainder.
The reduction in extrusion pressure in the extruder head
during production of a pencil writing substance according
to the invention in accordance with formulation 1 compared
to an extruded pencil writing substance according to the
prior art is illustrated in the Table below.
CA 02767216 2012-01-04
6 -
Pencil writing Writing substances
substance of according to the
formulations 1 and prior art
2
Pressure in the < 200 350-450
extruder head (in
bar)
It can clearly be seen that writing substances which are
formed in accordance with the inventive composition require
much lower extrusion pressures for production. Equipment
and die service life is extended and equipment design is
simplified.
An exemplary formulation 3 for a pencil writing substance
comprises:
styrene-acrylonitrile (SAN) 15 wt. %
aluminium stearate 10 wt. %
coconut oil 2 wt. %
graphite remainder.
An exemplary formulation 4 for a pencil writing substance
contains:
polystyrene (PS) 15 wt. %
aluminium stearate 10 wt. %
coconut oil 1 wt. %
palm kernel oil 1 wt. %
graphite remainder.
A preferred composition for a coloured pencil writing
substance comprises:
15 to 25 wt. % bonding agent
4 to 12 wt. % wax
0.5 to 2 wt. % palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid
remainder layered silicate(s) and/or hexagonal
boron nitride as well as at least one
CA 02767216 2012-01-04
7 -
coloured pigment and/or an uncoloured
pigment.
In particular, a coloured pencil writing substance
comprises:
15 to 25 wt. % polystyrene (PS)
4 to 12 wt. % montan wax
0.5 to 2 wt. % palm kernel oil, and/or coconut butter,
and/or coconut oil and/or oleic acid
remainder talc and/or hexagonal boron nitride as
well as at least one coloured pigment
and/or an uncoloured pigment.
Extrusion has proven to be a useful method for producing a
polymer-bound writing substance according to the invention.
The writing substance according to the invention is
produced in particular by carrying out the steps detailed
below:
mixing and granulating all formulation components of
the writing substance to form a writing substance
granulate;
extruding the writing substance granulate at a
temperature in the range of 130 to 200 C on an
extruder by a suitable mouthpiece to form endless
writing substance strands.
cooling and hardening the endless writing substance
strand; and
cutting the endless writing substance strand to final
lengths, in particular to the required pencil length;
Depending on the extrusion head, the cross-section of the
writing substance may adopt any shape - round, square or
combinations thereof. Furthermore, it is possible using
multiple coextrusion to combine different writing substance
formulations in one extrusion head to form a multi-
component writing substance.
