Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR MAHING MASTERBATCH
The present invention relates to a process for producing a colouring agent for
colouring a
polymer, and in particular to a process for producing a masterbatch for use in
extrusion
processes and the like.
The development of polymer chemistry and its subsequent application to the
production of
industrial and household articles is one of the great success stories of the
2011' century. The
result is that an enormous range of articles are now produced from plastics
materials.
to Some of these were previously produced from alternative materials, and the
production of
some has only been possible because of the development of polymer chemistry.
Despite the fact that this technology is more than a century old, the scale of
production of
these articles is such that research into new and improved polymers and
methods of
15 production continues apace.
The natural colour of most plastics materials is rather unattractive and
variable, and
accordingly a colouring agent has traditionally been added to the plastics
material in order
to produce a finished article of uniform colour. When the aesthetic appearance
of the
2o article is not particularly important (for example in the production of
dustbins or industrial
components), then the article is often coloured black. However, it is possible
to produce
the full range of colours simply by varying the colouring agent in order to
meet consumer
demand.
25 The colouring agent is normally prepared by adding a dyestuff to a plastics
material in
order to produce a small amount of intensely coloured plastics material, and
then by
mixing the intensely coloured plastics material with a second plastics
material (which may
or may not be the same as the first) when the second plastics material is
being formed into
the finished article. The intensely coloured first plastics material is known
as
30 "masterbatch".
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2
Black masterbatch is generally formed by mixing carbon black with an
appropriate
polymer and optionally adding chalk dust as a filler in an extrusion machine.
The
components are heated, mixed, extruded and pelletised to produce the
masterbatch, which
is then added in amounts of 0.1 to 25% by weight to the plastics material when
it is being
processed into the finished article (for example in a moulding or extrusion
process).
If it is desired to produce a masterbatch of a different colour, then an
appropriately
coloured pigment is mixed with the polymer and chalk filler (normally without
carbon
black) and the process is carried out as before.
to
Industry is always on the lookout for improved production processes,
particularly in the
field of polymer chemistry with its large scale of production and the
consequently large
cost savings available.
15 EP 0322555 (General Electric Company) discloses a method for colouring
thermoplastic
polymer resins using a masterbatch which is formed from a colorant such as
carbon black
and a polyetherimide ester elastomer. A wide variety of inorganic and organic
colorants
are disclosed. The masterbatch may be manufactured on high intensity high
shear
equipment such as compounding extruders, two-roll compounding mills and in
Banbury
20 mixers.
WO 79/00406 (Akesson et al.) discloses a method for the preparation of a
masterbatch to
be added to a thermoplastic resin. The masterbatch is in the form of a
colourant including
colour pigment particles as an additive dispersed in a vehicle.
JP 08003322 (Canon KK) discloses compositions for colouring plastics comprised
of
thermoplastic polymers and pigments. The compositions give mouldings without
unevenness or density difference of colour.
3o According to a first aspect of the present invention, there is provided a
process for
producing a colouring agent for colouring a polymer, comprising the step of
mixing a
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plastics material and waste print resin. Optionally, pure carbon black and Iow
density
polyethylene may be added.
Print resin is a specific product used by the print industry to create print
automatically and
at high speed onto paper (or another substrate) without causing smudging.
Print resin is normally provided in powder form, and generally comprises at
least some of
the following components: carbon black, ferrous oxide, carranba wax, styrene
acrylic
polymer, polyester resin, zinc stearate, nigrazine dye and oxide famerete
powder. A
1o variety of carrier polymers may be included depending on the brand. Ferrous
oxide,
carbon black and nigrazine dye are black colour enhancers, and one or two of
the three
may be omitted, depending on the shade of black or brand of powder employed.
If a
different colour to black is required, then all three are omitted, and a
pigment of
appropriate colour is added.
Without wishing to be constrained by theory, it is thought that print powder
also includes a
component or number of components which stabilises the melting point of the
composition. All waste print powders investigated by the applicants (including
waste print
powders obtained from Xerox, Canon, Ricoh, Hewlett-Packard and Osay) have a
melting
point close to 118°C.
As the temperature is raised above the melting point, the waste print powder
hardens again.
Investigations have found that this solidification point is in all cases very
close to 0.75°C
above the melting point, i.e. 118.75°C.
Print powder is normally provided in a sealed cartridge for use in computer
printers and
photocopying machines. The cartridge may have a sliding door or the like which
opens
when the cartridge is fitted into the printer in order to allow access to the
waste print
powder, and closes when the cartridge is removed from the printer in order to
prevent the
3o escape of powder.
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4
It is impractical to design a system which uses alI of the powder in a
cartridge and
inevitably somewhere in the region of 5% of the powder remains inaccessible in
the
cartridge when the printer shows the cartridge as having expired.
Even though the amount of powder remaining in a spent cartridge is relatively
small, the
total number of spent cartridges and therefore the total amount of waste
powder produced
by industry is substantial and growing rapidly.
The powder left in expired cartridges is a waste product which is very
difficult to dispose
l0 of. The powder is so finely divided (with particle sizes being in the order
of 15~,m) that it
tends to escape from landfill sites and find its way to the water supply, with
serious
environmental consequences. This is now of world-wide concern.
The inventive realisation of the present realisation is that this waste print
powder can be
15 used to make masterbatch. Thus, a waste product which is extremely
difficult to dispose of
in an environmentally friendly way can be employed in the production of an
industrially
useful product.
A substantial amount of surplus or imperfect waste print powder is produced by
print
2o manufacturers, and often this is difficult or expensive for the
manufacturer to dispose o~
Accordingly, the powder employed in the present invention may be obtained from
spent
cartridges as described above, or may be obtained directly from the print
manufacturer,
who may have supplies which could not otherwise be used in print cartridges.
For
example, waste powder for printer cartridges must be produced with having
narrow
25 particle size distribution. Powder having particles which axe too small (in
the order of 2
~m or less) or too large (in the order of 10 ~m or more) cannot be employed in
printer
cartridges and is surplus to requirements. It is however perfectly suitable
for the purposes
of the present invention.
30 The preferred proportion by weight of the components in the inventive
process is as
follows:
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Plastics materials - preferably from 5 to 95%, more preferably at least from
20 to 50%,
most preferably about 25%.
Carbon black - preferably from 0.5 to 80%, more preferably from 20 to 40%,
most
5 preferably about 25%.
Waste print powder - preferably from 5 to 80%, more preferably from 25 to 50%,
most
preferably about 40%.
to The ratio of plastics material to carbon black depends on the particle size
of the carbon
black. Thus the ratios of particularly preferred embodiments of the present
invention are
given in Table 1 below:
TABLE 1
CARBON BLACK
DBP STRUCTURE CARBON BLACK PLASTICS WASTE PRINT
MATERIAL POWDER
170 20 35 45
137 22.5 32.5 45
115 25 30 45
70 30 25 45
65 32 23 45
55 35 20 45
The term "Carbon Black DBP Structure" refers to the grade of carbon black and
is a
definition well known in the industry.
If these ratios are not adhered to, the likelihood is that:
(1) the end product will be too brittle to be effective
(2) the product will overheat during the process and the mixture will oxidise
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(3) if oxidation does occur the pigment transportation qualities of the
product are
reduced to below commercial value.
It has been found that the use of waste print powder on its own results in an
end product
which is too brittle to be effective.
The relative proportions of the various components is varied depending on how
dark the
masterbatch is required to be (the so-called "cover"). For example, if heavier
cover is
required than that given by the preferred proportions of 50% waste print
powder, 25%
to carbon black and 25% polymer, then 45% waste print powder, 30% carbon black
and 25%
polymer may be used. Ideally, the polymer is included at 25% by weight or
more, which
prevents the final product becoming brittle and difficult to handle during
extrusion.
Other additives may be included to create and/or enhance the required end-
product
15 specification.
In order to produce a non-black colouring agent, the appropriate coloured
pigment (e.g.
coloured waste print powder) is mixed with the plastics material in accordance
with the
invention. The coloured powder may be supplemented with additional pigment
and/or
20 other additives, in order to produce the desired final colour.
An effective masterbatch can be prepared by the following preferred process:
I. The components are mixed loosely in a drum.
25 2. The components are transferred by a variable speed feeder at a defined
rate to a
mixer and grinder where they are mixed, ground and amalgamated.
3. The resulting materials exit the pre-mixer in a rope form which is then fed
by a
time-sequenced pusher device at a constant rate into an extruder.
4. The mixture is mixed and extruded as a series of strands.
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In a preferred embodiment, the components are mixed together and heated in a
mixing
machine such as a twin screw extruder, a single screw extruder, a two roll
mill, or,
preferably, a Farrel CP machine, a Banbury mixer, or any suitable mixer.
It has been found that it is advantageous to keep the entrance into the mixer
relatively cool
in order to avoid softening the waste print powder (which softening begins at
about 90°C).
Keeping the entrance below about 90°C, preferably from 40 to
90°C and most preferably
about 45°C, enables the waste print powder to be transported into a
mixer in a stable
condition. It is particularly desirable to control this temperature carefully
in the case of
mixers other than Banbury or Farrel CP machines. The advantage of using a
Banbury or
Farrel machine is that mixing of the components is more thorough and the
entrance
temperature is not so critical.
Processing temperatures within the mixer are fairly flexible, but preferably
range from 135
to 230°C and are most preferably at about 150°C. At
approximately 118°C, the waste print
powder melts and then very rapidly hardens as the temperature rises by another
degree or
so. It is therefore necessary to use a mixer which is sufficiently powerful to
grind the
powder continuously to prevent it from conglomerating and hardening. The mixer
should
2o be sufficiently powerful to mix the waste print powder and the carbon black
into the Garner
resin homogeneously. It has been discovered that the Banbury and Farrel
machines are
particularly effective at achieving this aim.
In a preferred embodiment, the components are mixed at a mixing rate of from
150 to 500
miri 1, preferably from 350 to 400 miri 1.
Because the processing temperature tends to range from 135 to 230°C,
heat is transferred
from the main body of the mixer to the mixer entrance. Accordingly, the mixer
entrance
may be artificially cooled, for example by circulating cooled water in a j
acket around the
3o entrance, in order to maintain the entrance at the temperatures outlined
above.
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The components are fed into the mixer until the maximum safe operational
amperage is
reached. In the case of a Farrel CP 500, the maximum amperage is in the region
of 90 to
95 amps and this equates to a rate of addition of the mix of from 500 to 550
kg per hour.
The plastics material may be selected by a skilled person to match the
plastics material
which is to be coloured by addition of the masterbatch. Suitably plastics
material include
polyethylene, polypropylene, EVA, EEA, ABS, PVC or any other type of polymer.
After the components have been mixed to form the masterbatch, the masterbatch
may be
to extruded and divided into pellets for use in the colouring of a second
plastics material.
In accordance with a second aspect of the invention, there is provided a
colouring agent for
colouring a polymer which agent is obtainable by means of a process defined
above.
15 In accordance with a third aspect of the invention, there is provided a
process for forming a
coloured object from a plastics material, comprising the steps of mixing said
plastics
material with a colouring agent obtainable by means of a process as defined
above, and
forming the coloured plastics material into said object. The object may be
formed by
means of an extrusion or moulding process.
The amount of masterbatch added to the plastics material generally varies from
1 to 25%
by weight. The precise amount will depend on the level of cover required, and
from what
the plastics material is formed. For example, if the plastics material is
clear, then a
relatively low amount of masterbatch is required (perhaps 1- 2%) in order to
produce a
good level of cover. If however plastics material is used which has been
coloured white
(with e.g. titanium dioxide), then perhaps 15-20% of masterbatch may be
required in order
to achieve the same level of cover. Cover is usually assessed by eye and the
components
of the subsequent process adjusted accordingly.
3o In a fourth aspect of the invention, there is provided an object formed
from a plastics
material, which material has been coloured by the addition of a colouring
agent obtainable
by means of a process as defined above.
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The invention will now be illustrated by means of the following examples.
Example 1
Carbon black, print powder from expired printer cartridges and manufacturer's
waste and
polyethylene resin were weighed and loaded into a blender above an extruder in
the
following amount:
1o Carbon black - 25%
Print powder - 50%
Polyethylene - 25%
After being blended the mixture was fed into a Farrel CP 500 mixer at a feed
rate of from
1s 350 to SSOKgph.
The entrance to the mixer as surrounded with a water-cooled jacket in order to
maintain the
temperature at about 60 to 70°C.
2o The components were mixed at high pressure within the Farrel CP S00 at
approximately
150°C and at a mixing speed of from 350 to 400 revolutions per minute.
The resultant mix was discharged from the mixer in the form a continuous hot
rope into a
single screw extruder. It was then pushed through a dye to form separate
strands, which
25 were fed into a pelletiser where pellets were formed and cooled.
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Example 2
The process of Example 1 was carried out except that the proportions of the
components
were altered to the following in order to provide rnasterbatch with a heavier
cover:
Carbon black - 30%
Waste print powder- 45%
Polyethylene - 25%
to Machine settings are within parameters as defined in Example 1.
