[0001] The present invention relates to paper and methods of making paper and more particularly,
to compositions, pulp suspensions and processing to provide for white paper production.
[0002] Paper is made from a pulp stock or suspension incorporating a number of ingredients
but principally fibres in order to provide through appropriate processing sheets or
rolls of paper. The fibres in the paper stock can be obtained from a number of sources
but are principally obtained from tree sources such as cellulose fibre. The tree fibres
are appropriately macerated in order to provide the fibres required. Unfortunately,
fibres are biologically active and inherently slightly mis-coloured such that in attempting
to form good quality white paper it is necessary to bleach that paper. It is also
a typical requirement to add a so-called optical brightness agent (OBA) which is an
ultra-violet dye which upon exposure to light radiates a bright white light hue giving
the impression of a pure white colour and masks any potential yellow white in the
fibres after bleaching. Unfortunately, OBA materials are relatively expensive and
so care must be taken with the proportion of such OBA material added to the pulp stock
for economic reasons. It will also be understood that the production of paper inherently
generates large volumes of waste water and any contamination and in particular toxic
or environmentally impacting agents such as OBA should be limited in that waste water.
[0003] There are a number of OBA and FWA additives available from suppliers such as Bayer
AG and from Ciba under their product names Tinopal VP, ABPZ and SPP. Generally, the
OBA and FWA additives are fluorescent dyes. Typically, these fluorescent dyes include
sulphonated stilbeane molecules.
[0004] Previous additives to thick pulp stock include sodium hypochlorite (bleach) and chlorine.
Hypochlorite bleaches the fibres in the pulp stock but the pH level dramatically increases
and some bi-products of the bleaching process are deemed environmentally unfriendly.
Furthermore, sodium hypochlorite is a slow acting additive at low temperatures and
residuals from the bleaching process may have adverse effects on other paper making
additives.
[0005] Hydrogen peroxide is also used for bleaching paper stock but normally at elevated
temperatures and with the hydrogen peroxide in a concentration of at least 50% in
the stock. In such circumstances, hydrogen peroxide bleaching of paper stock is very
hazardous. It is also known to provide hydrogen peroxide in combination with polydadmac
in order to act as a bleaching agent. However, such a combination only provides a
limited increase in paper stock brightness.
[0006] Hydrogen sulphite can also be added to paper stock and is a reductive "bleach" in
comparison with the sodium hypochlorite and hydrogen peroxide oxidising bleach process.
Hydrogen sulphite is generally supplied as a powder requiring on-site preparation
by dissolving the powder to form the additive solution. If wetted, hydrosulphite releases
sulphur dioxide gas with potential dangerous consequences. Hydrosulphite is also difficult
to handle as a liquid and must be kept dry in order to avoid the sulphur dioxide gas
release problem.
[0007] In view of the above, it will be appreciated that current additives to bleach paper
stock are inconvenient or even dangerous to use whilst they have limited effect upon
the brightness achieved or the proportion of fluorescent whitening agent (FWA) or,
more commonly, optical brightening agent (OBA) which is required to achieve the desired
paper brightness and tone.
[0008] In accordance with the present invention there is provided a composition for cellulose
suspensions, the composition comprising peroxyacetic acid or peracetic acid and hydrogen
peroxide in sufficient relative concentration to reduce the necessary proportion of
fluorescent whiting agent (FWA) or optical brightening agent (OBA) required to achieve
the desired brightness in finished paper or paper board products formed from the cellulose
suspension.
[0009] Alternatively, in accordance with the present invention there is provided a suspension
for paper or paper board making, the suspension including an additive comprising a
peroxyacetic and/or peracetic acid and hydrogen peroxide composition added to a cellulose
fibre stock after pulping.
[0010] Preferably, the composition comprises at least 12.5 weight percent peroxyacetic acid
and/or peracetic acid. Preferably, the composition includes a polyamine or other cationic
materials to facilitate reaction of the peroxyacetic acid and/or peracetic acid with
cellulose fibres. Typically, the composition comprises 15% peroxyacetic acid and 14%
hydrogen peroxide. Typically, the polyamine or other cationic materials are added
in the range of 1 - 20% by volume to the composition.
[0011] Further in accordance with the present invention there is provided a process for
preparing a suspension comprising forming a cellulose fibre pulp suspension and adding
a composition of peroxyacetic acid and/or peracetic acid and hydrogen peroxide before
any other additives are added to the suspension.
[0012] Typically, a polyamine or other cationic material is added in the range of 1 - 20%
by volume to the composition in the suspension.
[0013] Preferably, the composition is added in the process when the pulp suspension has
a consistency of at least 2% or greater of cellulose fibres. Typically, if the composition
has a concentration of at least 12.5% peroxyacetic acid or peracetic acid, then the
composition is added to the suspension in the proportion 50 millilitres of composition
per gross tonne of cellulose fibre or dry solids in the suspension. Alternately, there
is preferably 7 litres of composition to 1 tonne of pulp suspension formed from cellulose
fibres and water. Further alternatively, in the order of 50g to 7kg of composition
per tonne of gross paper is initially added then allowed to react for a pre-determined
process time and a further 50g to 7kg of composition added per tonne of gross paper
for final preparation.
[0014] Typically, the process allows for a process time of at least 30 minutes between adding
the composition to the pulp suspension and adding any further additives such as FWA
or OBA.
[0015] Typically, a polyamine or other cationic material is added in the range of 1 - 20%
by volume to the composition during the process.
[0016] Possibly, the process provides for batch processing of vats of pulp suspension or
continuous processing.
[0017] Typically, pulp suspension is calibrated at the end of the process time to determine
whether the composition has been effective against a desired brightness and further
composition added, if required, and/or a further period of processing time allowed.
Generally, FWA and OBA is added to the pulp suspension at the end of the processing
time or at least prior to paper or paper board forming from the pulp suspension.
[0018] Embodiments of the present invention will now be described by way of example only.
[0019] The process for forming paper is well known. Typically, fibrous materials, chiefly
of a vegetable origin are mixed with a large quantity of water and shredded into very
fine fibres. The suspension or pulp stock typically includes additives such as size,
OBA and filler in order to render a special property to the paper.
[0020] The fibrous material is generally obtained from trees, grasses, bamboo and cotton.
There are numerous mechanical, chemical and bio-chemical processes for pulping the
fibrous material to an appropriately thick stock or stuff for paper or paper board
formation. Various grades of paper are provided and typically comprise various combinations
of fibrous vegetable material as described previously along with other fibres such
as hemp, linen, wool, asbestos, slag wool, glass fibres and synthetic fibres along
with fillers, size and other additives in order to achieve a desired paper quality.
[0021] The present invention principally relates to providing relatively high quality white
paper and paper board. To achieve such high quality paper a so-called fluorescent
whitening agent or FWA is added. Such fluorescent whitening agents are also known
as optical brightening agents (OBA). In short, such FWA or OBA materials fluoresce
on exposure to light in order that the paper incorporating such agents appears brighter
and therefore whiter. FWA and OBA are relatively expensive additives in a typical
paper combination and so there are strong economic reasons for limiting their proportion
of the combination in terms of a weight percentage. It will also be understood that
FWA or OBA materials are considered unfriendly environmental agents such that waste
water from the paper making process must be appropriately treated to remove such FWA
or OBA agents prior to release.
[0022] As with all vegetable matter the fibres used with regard to paper making will tend
to be discoloured relative to the desired whiteness as well as biologically active.
In such circumstances, as indicated previously, it is known to bleach suspensions
or pulp stock in order to render the fibres of a whiter surface complexion as well
as reduce biological activity which may itself discolour the fibres as the paper ages.
Traditional bleaching methods, whether they be oxidising or reducing, create their
own inherent problems with respect to residuals left in the paper after forming, processing
dangers and waste water contamination.
[0023] The present invention utilises a composition added to the pulp suspension prior to
other additives. This composition comprises a mixture of peroxyacetic acid or peracetic
acid with hydrogen peroxide. One source of such composition is Crosmill Limited of
Crosmill House, Dragons Lane, Moston, Sandbach, Cheshire, United Kingdom under their
product name. Crosmill Millcide PH120 which comprises a solution including 15% peroxyacetic
acid or peracetic acid with a similar proportion of hydrogen peroxide. With such a
composition, it has been found that above a greater than 2.5 weight percent concentration
in the pulp suspension the composition provides a sufficiently active concentration
to render the fibres and more particularly the suspension stock more receptive to
FWA or OBW additives later. Typically, the pulp suspension or stock will have a so-called
thick consistency of upwards of 2 weight percent cellulose solids or fibres in the
suspension. Generally, the composition must be given an effective free period of process
time during which it can actively process the suspension. With the composition concentration
of peroxyacetic acid with hydrogen peroxide described above it has been found that
a process time of 30 minutes from addition of the composition to the suspension pulp
is normally appropriate. The composition and in particular the peroxyacetic acid and/or
peracetic acid conditions the cellulose fibre surface to render it more receptive
to association with the FWA or OBA material later.
[0024] Clearly, it is still normally necessary to add FWA or OBA materials to the suspension
stock to achieve the desired whiteness in eventual paper or paper board product. Nevertheless,
with the suspension stock processed in accordance with the present invention, the
fibres and the suspension are more receptive to such FWA or OBA materials and a significantly
lower proportion of such FWA or OBA materials is required to achieve the desired brightness
in the finished product. Normally, the present composition used in the pulp suspension
and paper making process will halve the necessary amount of FWA or OBA which needs
to be added to achieve a desired whiteness and brightness.
[0025] As indicated, in order to be effective, the proportion of fibre solids in the suspension
should be at least 2% by weight such that the composition in accordance with the present
invention is able to efficiently process these fibres. A more diluted consistency
will render the amount of composition which is required to be effective in the suspension
to be significantly increased due to inherent reduction in fibre to composition association.
The composition in accordance with the present invention itself will be relatively
costly and therefore the more composition required to process the pulp suspension
the less cost effective the process will be. Although excess composition may be recovered
from waste water during later stages of the paper making process, such recovery may
be expensive and inherently some composite will be lost through each use cycle.
[0026] As the present composition acts upon the thick suspension of cellulose fibres used,
in accordance with known techniques for paper making and paper board making, it will
be understood that the fibres themselves will have an increased whiteness or brightness.
In some circumstances, it may not be necessary to add FWA or OBA materials to achieve
the desired brightness in the finished paper or paper board product, particularly
if white fillers or additives such as chalk, gypsum or china clay are included.
[0027] In accordance with an example of the process of the present invention, a suspension
pulp will be formed in accordance with conventional techniques to a consistency of
at least 2% by weight of cellulose fibres, a composition of at least 12.5% peroxyacetic
acid with proportionate amount of hydrogen peroxide in a liquid form will then be
added in the proportion of 50 millilitres of such composition to each gross metric
tonne of cellulose fibres/solids or 7 litres of composition per metric tonne of pulp
suspension. Typically, individual vats of suspension pulp will be processed such that
the appropriate process time, normally 30 minutes, can be applied to each vat of pulp
suspension in accordance with the present invention. Alternatively, through appropriate
pipework and/or holding tanks the suspension pulp can be continuously processed such
that the pulp is at least solely exposed to the composition for the necessary process
time in accordance with the present invention between additional of the composition
to the suspension and addition of any further additives to that suspension.
[0028] In order to further improve performance but possibly with the increased cost and
recovery problems, the proportion of composition may be raised such that composition
is added to the suspension pulp with a proportion in the range of 50g to 7kg of composition
per tonne of gross paper. The suspension pulp is then allowed to act during a process
time period and then a further volume of composition added in the range of 50g to
7kg per tonne of gross paper. In such circumstances, there is a significant increase
in brightness lift to the eventual paper quality. For example, if previously there
was a one point base paper brightness lift then by these additions, the brightness
lift is increased to two points in base brightness lift.
[0029] In order to further enhance the process in accordance with the present invention,
the polyamine or other cationic material can be added to the peracetic acid or composition.
The polyamide or other cationic material will be added in the range of 1 - 20% by
volume to the composition in order to further promote the reaction processes performed
by the composition in order to prepare the paper pulp suspension for receipt of an
optical brightness agent (OBA). In such circumstances, the proportional improvement
in optical brightness relative the amount of OBA added is significantly increased.
Thus, better quality paper can be produced at a reduced cost or paper quality maintained
with lower OBA content.
[0030] At the end of the composition processing time, it is found that the effect of the
composition on the suspension will be to increase the brightness of that pulp and
the resultant finished paper is brighter than if the composition had not been added.
Generally, there is an increased brightness in the range of 1 to 3 points dependent
upon the type of fibre and initial brightness of the pulp. This increased brightness
is substantially and proportionately the same with or without the eventual addition
of FWA or OBA materials in the finished paper in accordance with normal practice.
There is also a corresponding increase in the whiteness and "L" values of the suspension
pulp or finished paper sheet. The "L" value relating to brightness within 100 = pure
white and 0 = black. The colour of the suspension pulp/finished paper also changes.
Typically, the finished paper becomes less yellow and bluer, the "b" value is ratio
between blue and yellow and is less positive; this is an advantage as less dye material
may be needed with significant economic savings whilst promoting improved brightness
in the paper itself. The "a" value (red to green ratio) of the finished paper sheet
does not change very much; if there is any change in this "a" value it is a shift
from green to red but is normally only of a slight nature.
[0031] As indicated above, after the processed time other additives will normally be incorporated
into the suspension pulp prior to final paper forming and processing. Generally, before
such further additives are incorporated into the suspension pulp there will be a calibration
test in order to determine the specific whiteness, brightness and other control values
used to determine pulp suspension quality. It will be understood that as with all
natural products, vegetable fibres and in particular cellulose solids and fibres obtained
from tree matter will vary with environment, age, season and source. Thus, the present
composition may have significantly different, or at least marginally different, effects
upon different batches of suspension pulp. Thus, if the "processed" suspension pulp
has not met the desired brightness or whiteness values for onward processing then
further FWA or OBA materials may be needed or the particular batch of suspension pulp
allowed to resume further processing by the composition or, if necessary, further
composition added to the suspension pulp to increase the concentration of the composition
in that suspension. In any event, it will be understood that temperature along with
other factors such as agitation will significantly effect the necessary processing
time to achieve the desired brightness or whiteness in the suspension pulp and subsequent
finished paper product. Operational temperatures will be in the range 5 to 50°C but
the colder temperature the longer time necessary processing time for reaction.
[0032] The present composition and resultant suspension pulp and process allow a paper manufacturer
to either maintain finished sheet brightness and colour at a low cost due to less
dye and FWA materials added or maintain current dye and FWA material content in the
finished paper sheet but produce a higher quality product with higher whiteness and
brightness. Furthermore, a paper manufacturer could specify a higher quality paper
by use of the present composition whilst at the same time reducing cost through lower
dye and FWA additive components specified for that paper.
[0033] It will be appreciated that the present composition effectively chemically conditions
the pulp suspension. Thus, in order to increase and facilitate the operational efficiency
cationic materials may be added to the composition or separately during the process.
The free radicals provided by disassociation of such cationic material will promote
processing of the suspension pulp by the composition either in terms of rate or effectiveness.
It will be understood that care will be necessary with regard to the choice of cationic
material used such that the cationic material is either dissolved in the water or
composition and there is little residual solid cationic material retained in the finished
paper with a potential reduction in the quality of that paper.
[0034] Whilst endeavouring in the foregoing specification to draw attention to those features
of the invention believed to be of particular importance it should be understood that
the Applicant claims protection in respect of any patentable feature or combination
of features hereinbefore referred to whether or not particular emphasis has been placed
thereon.
1. A composition for cellulose suspensions, the composition comprising peroxyacetic acid
or peracetic acid and hydrogen peroxide in sufficient relative concentration to reduce
the necessary proportion of fluorescent whiting agent (FWA) or optical brightening
agent (OBA) required to achieve the desired brightness in finished paper or paper
board products formed from the cellulose suspension.
2. A composition as claimed in claim 1, wherein the composition comprises at least 12.5
weight percent peroxyacetic acid and/or peracetic acid.
3. A composition as claimed in claim 1 or claim 2, wherein the composition includes a
polyamine or other cationic materials to facilitate reaction of the peroxyacetic acid
and/or peracetic acid with cellulose fibres.
4. A composition as claimed in claim 3, wherein the polyamine or other cationic material
are added to the composition in the range 1 - 20% by volume.
5. A composition as claimed in any preceding claims, wherein the composition comprises
15% peroxyacetic acid and 14% hydrogen peroxide.
6. A suspension for paper or paper board making, the suspension including an additive
comprising a peroxyacetic and/or peracetic acid and hydrogen peroxide composition
added to a cellulose fibre stock after pulping.
7. A suspension as claimed in claim 6, wherein the composition comprises at least 12.5
weight percent peroxyacetic acid and/or peracetic acid.
8. A suspension as claimed in claim 6 or claim 7, wherein the composition includes a
polyamine or other cationic material to facilitate reaction of the peroxyacetic acid
and/or peracetic acid with cellulose fibres.
9. A suspension as claimed in claim 8, wherein the polyamine or other cationic material
is added to the composition in the range 1 - 20% by volume.
10. A suspension as claimed in any of claims 6 to 9, wherein the composition comprises
15% peroxyacetic acid and 14% hydrogen peroxide.
11. A process for preparing a suspension comprising forming a cellulose fibre pulp suspension
and adding a composition of peroxyacetic acid and/or peracetic acid and hydrogen peroxide
before any other additives are added to the suspension.
12. A process as claimed in claim 11, wherein the composition is added in the process
when the pulp suspension has a consistency of at least 2% or greater of cellulose
fibres.
13. A process as claimed in claim 11 or claim 12, wherein if the composition has a concentration
of at least 12.5% peroxyacetic acid or peracetic acid, then the composition is added
to the suspension in the proportion fifty millilitres of composition per gross tonne
of cellulose fibre or dry solids in the suspension.
14. A process as claimed in any of claims 11 to 13, wherein seven litres of composition
is added to 1 tonne of pulp suspension formed from cellulose fibres and water.
15. A process as claimed in any of claims 11 to 14, wherein the process allows for a process
time of at least 30 minutes between adding the composition to the pulp suspension
and adding any further additives such as FWA or OBA.
16. A process as claimed in any of claims 11 to 15, wherein the process provides for batch
processing of vats of pulp suspension or continuous processing.
17. A process as claimed in any of claims 11 to 16, wherein the pulp suspension is calibrated
at the end of a process time to determine whether the composition has been effective
against a desired brightness and further composition added, if required, and/or a
further period of processing time allowed.
18. A process as claimed in claim 17, wherein FWA and OBA is added to the pulp suspension
at the end of the processing time or at least prior to paper or paper board forming
from the pulp suspension.
19. A process as claimed in any of claims 11 to 18, wherein a polyamine or other cationic
materials are added to the composition in the proportion 1-20% by volume of the composition.
20. A process as claimed in any of claims 11 to 19, wherein in the order of 50g to 7kg
of composition per tonne of gross paper is initially added then allowed to react for
a pre-determined process time and a further 50g to 7kg of composition added per tonne
of gross paper.
21. Any novel subject matter or combination including novel subject matter disclosed herein,
whether or not within the scope of or relating to the same invention as any of the
preceding claims.