Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
wo ~A3~ 2I 61 09~ PCT/GB94/00~2
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IMPROVEMENTS IN OR RELATING TO D~1N~1~G OF PAPER
The present invention concerns improvements in or
relating to the deinking of paper. More particularly,
the present invention is concerned with the recovery of
paper for recycling purposes, which paper has all traces,
or substantially all traces, of ink removed therefrom.
More particularly, the invention is concerned with the
recycling of high quality white paper utilised in the
production of recycled photocopier and laser print paper.
In recent times, more and more attention is being
given to the recycling of paper and paper products in an
attempt to reduce the amount of virgin pulp which is
utilised in paper production. In order to ensure that
the recycled paper is of the desired quality, it is
generally required to remove all, or substantially all,
of the print from the paper and paper products to be
recycled. This is particularly the case in connection
with laser and xerographic printed papers. In the paper
industry, such papers are normally of high quality white
paper and are normally regarded as a potentially
extremely valuable feedstock to make recycled copier and
laser print paper. However, to date, the conventional
method adopted for deinking such papers has not been
particularly successful. Chemical extractant techniques,
such as flotation and the use of dispersion aids have
primarily been used in this regard.
There are two main issues surrounding the
economic recyclability of such laser and xerographic
printed papers. Firstly, when paper and paper products
are collected for recycling, there is generally a mixture
of all types of waste paper collected. Accordingly, in
order to ensure that quality recycled copier and laser
print paper are o~tained, it is necessary to ensure that
216109~ ;
W094/~ ~ PCT/GB941~2
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only laser and xerographic printed paper or paper
products should be present. Secondly, it is necessary to
ensure, as far as possible, the complete removal of ink
from the pulped laser and xerographic printed papers in
order to eliminate both the darkening effect produced by
small particles of ink and the spot fo~àtion produced by
larger pieces of ink. ~;
In view of the fact that the above-identified
chemical techniques have not proved economically
successful, having regard to the fact that firstly the
waste paper cannot be properly separated, coupled with
the fact that when laser and xerographic printed papers
are treated then substantially complete ink removal is
not obtained, in order to obtain the required good
quality fibre, virgin pulp is being used which means that
more and more trees have to be felled with consequent
ecological problems associated therewith.
It is an object of the present invention to
provide a method for initially sorting high quality laser
and xerographic printed paper waste from other paper
waste and thereafter to remove ink therefrom in order to
provide high brightness paper which is spot free.
It is also a further object of the present
invention to utilise the method of the present invention
in the treatment of other types of printed paper
products, wherein the ink utilised for printing has been
appropriately treated.
The present invention is based on the discovery
that the ink utilised in laser and xerographic printed
papers is comprised of a thermoplastic resin (usually
PVC) containing carbon black as pigment and usually
ferric oxide to assist in handling the dry ink in the
2 1 610 9 1 ; PCT/GB~/OO~Z
printing device. Based on such discovery, we have now
found that it is possible to separate laser and
xerographic printed papers from other type of papers by
maqnetic separation and furthermore, have discovered it
is possible to s~parate ink from the fibre of such laser
and xerographic printed papers after pulping, again by
the use of a magnet.
According to one aspect of the present invention
there is provided a method of dry separating and/or
sorting laser and xerographic printed paper waste
containing ink with a magnetic component from other paper
waste products containing ink but which does not contain
any magnetic material, by the use of at least one magnet
and by applying an appropriate magnetic force.
In such aspect of the invention, any suitable
magnet may be utilised although same should be
sufficiently strong in order to separate the paper
containing ink with a magnetic component from paper
containing ink but without such magnetic component.
Suitable magnets would be an electromagnet, a permanent
magnet or a superconducting magnet.
In a preferred procedure in accordance with such
aspect, a mixture of paper waste products would be
allowed to fall substantially vertically past at least
one operating magnet and the paper waste containing ink
with a magnetic component would be magnetically drawn to
one side and collected. Any suitable procedure can be
adopted in this regard. The operating magnet(s) should
apply a magnetic force over a large area of the body of
paper being treated.
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W094~A364 21610 9 4 PCT/GB94/~
Magnetic force is a function of two variables:
1) Magnetic flux density; and
2) Field gradient. .i~
Magnetic flux density is the p ~ t of magnetic
field strength (or intensity) and pe~meability of a
material. The magnetic field strength (intensity) is the
magnitude of the field strength vector in a medium (i.e.
the magnetic strain produced by neighbouring magnetic
elements or current-carrying conductors).
It is believed that this aspect of the present
invention would be of benefit to waste paper merchants or
in mills which wish to select the particular type of
paper for one particular operation in the mill, for
example, production of recycled paper suitable for laser
or xerographic copier paper. The residual paper could
then be used for production of a lower grade of recycled
paper.
We have carried out tests in connection with
laser and xerographic printed papers and have ascertained
that same are susceptible to removal by a magnetic field.
In accordance with the above aspect of the
invention, we have been able to pick up paper having
xerographic and laser print thereon. Accordingly, given
a sheet with xerographic or laser print on it in a strong
magnetic field then same will move towards a magnet and
such procedure could be used as a means of preselecting
xerographic or laser printed paper from office waste in
the situation where there is a mixture of conventional
waste material and xerographic waste material.
Suitable magnetic forces are achieved by
utilising background magnetic fields in excess of 4000
wO 941243C4 2 1 6 1~0 9 g~ ~ ~ ^ r ~ ~ I
Gauss (4 tesla) and a field gradient in excess of 1000
Gauss/cm (10 tesla/m).
However, such high and absolute fields are not
necessary to practice the invention. A high gradient
magnetic separation device can be envisaged which will
not require such high input field strengths. It is the
magnetic field gradient that is important to effect the
separation. There are several types of high gradient
machine designs. These devices have been called "induced
pole" devices.
Suitable devices in this connection are for
example:-
Frantz FerrofilterCarpco Separator
Jones Separator
Kolm-Marston separator
suitably modified for utilisation with pulping
techniques.
Further tests have been carried out in connection
with suspending the ink utilised in xerographic and laser
printed papers in water using a surfactant due to the
fact that the ink is hydrophobic. We have been able to
recover such ink using a magnet.
According to a further aspect of the present
invention there is provided a method of removing magnetic
ink from pulp stock formed from xerographic and laser
printed paper waste to provide high brightness paper
which is spot free, comprising feeding such pulped paper
waste past at least one magnet for removal of all or
substantially all of such magnetic ink.
W094~4K4 2 1 6 1 0 9 ~ : ~ PCT/GB94/~842
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Assuming all the print is xerographic (there may
be some conventional printing on the paper such as
headings, logos etc.), then such method would allow for
recycling of the ash present in the paper as well as the
fibre, thereby increasing the yield. A~itionally, if
the ink which is normally melted on to ~ paper has not
separated fully from the fibre of~ he paper after
treatment in the pulper, then those ~bres with ink still
attached thereto would also be removed with such ink by
the magnet(s). Accordingly, the spot removal efficiency
is improved since when recycling paper to produce high
quality paper one does not require bits of fibre which
have ink attached thereto.
The arrangement of the at least one magnet will
be so designed in order to exert a magnetic force
comprising a background magnetic field of preferably at
least 4000 Gauss and a field gradient preferably of at
least 1000 Gauss/cm.
Preferably, a plurality of magnets are utilised
and the pulp stock is fed along an elongate channel-type
container housing. The magnetic force is presented to
the pulp in such a way that it will allow small magnetic
particles to be captured or deflected.
We have discovered that incredibly fine particle
magnetic separation can be obtained by presenting the
appropriate magnetic force to virtually every magnetic
particle. The magnetic force applied must be
sufficiently high and strong to overcome the fluid drag
as the pulp is fed along the elongate housing.
We have also discovered that by application of a
very strong magnet to the outside of the wall of a beaker
containing pulp, then it is possible to drag the magnetic
W094~364 21 C 109~ r~ PCT/GB94/00842
particles to the inside of the wall of the beaker.
Thus, in order to recover magnetic material from
the pulp, it is possible to utilise a capture-type system
wherein the~ ~agnets are dropped into the pulp or are
located adjace~tly above the pulp. Alternatively, it is
possible to utilise a deflection-type system wherein the
magnets are located adjacent the outer walls of the
channel-shaped housing and a sufficiently large magnetic
force is applied to drag the magnetic particles to the
inner walls of the channel-shaped housing.
It is also possible to utilise a plurality of
steel balls of selected size and shape, which balls are
magnetised and thereafter introduced into the pulp.
Magnetic particles and the like will become attached to
the steel balls which may then be recovered from the pulp
and de-magnetised, whereupon the metallic particles will
become detached therefrom. The steel balls can
thereafter be magnetised again and the above described
process be carried out again.
By utilising the procedures outlined above,
separation of magnetic material for the pulp may be
achieved. However the binders, fillers and white
pigments contained in the pulp are not separated and
therefore can be reused in producing recycled paper.
It is necessary to overcome gravity and fluid
drag forces (intensity of pulp) when utilising the
magnetic separation system in accordance with the present
invention.
Savings can be achieved in that previously
utilised separation procedures in procedures for
recycling paper which involve costly materials, e.g.
W094/~U~ 2 1 6 1 o b ~ PCT/GB94/~&~
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china clay, can be avoided.
In a further aspect of the present invention, a
method is provided for improving the recyclability of
paper waste having ink thereon which does~not normally
contain a magnetic component, by utilis~ g one or more
magnetic carriers in the formulations o~ ~he printing ink
utilised, to enable same to be rem~ved by use of at
least one magnet in accordance with the procedures
outlined above.
In this aspect of the invention, where carbon
black is the primary pigment, it is possible to
incorporate in such ink metallic iron or its oxides or
some other paramagnetic material in order to make the ink
magnetic. Such process would facilitate the removal of
other types of inks such as flexographic inks were the
carrier matrix is an alkali soluble polymer
(polyacrylate).
In a still further aspect of the present
invention there is provided a method of enabling adhesive
material to be removed from paper pulp containing same,
by incorporating a magnetic filler or carrier in said
adhesive and removing such adhesive by magnetic means.
Thus, adhesive can be removed from the water phase after
pulping of paper containing adhesive used in the book
binding field.
It will thus be seen that the present invention
contemplates the use of a magnet of suitable strength to
enable a particular type of printed paper to be separated
from other types of paper and for ink contained on such
paper to be removed during the pulping process, both
processes utilising a magnet such as an electromagnet, a
WO94~K4 PCT/GB94/00842
2 1 6 1 0 9 4
permanent magnet or a superconducting magnet. It is also
envisaged within the present invention to incorporate one
or more magnetic carriers or fillers into other types of
inks and adhesive or materials utilised in the paper
manufacturing industry, so as to enable such inks and
other types of materials to be removed from the paper
pulp when recycling is taking place, again by magnetic
means.
The use of a magnet would be economic as compared
to known processes and would be ecologically friendly in
that no chemicals are being utilised. In view of the
believed advantages obtained utilising such magnetic
techniques, the amount of virgin pulp which would be
required could be substantially reduced.
As indicated above, any suitable magnet can be
utilised providing same has sufficient field strength and
intensity of field force. It is believed that a power of
10-20 kw would be sufficient to enable magnetic particles
and the like to be removed as required.
