Note: Descriptions are shown in the official language in which they were submitted.
~z~
IMPROVEMENTS IN PAPER AND BOARD MANUFACTURE
This invention relates to paper or board
manufacture. More especially, it relates to a method of
paper or board manufacture in which an organic
polysaccharide i6 added to the mixture or applied to the
web of fibres during the process of manufacturing the
paper or board. In particular it relates to paper of
improved strength or surface characteristics
manufactured according to such a method. An improved
additive material also constitutes a feature of the
present in~ention.
It is well known to add during the early stages of paper
or board manufacture one or more additives so as to
increase the inter-fibre bonding and thus the strength
of the eventual paper or board. The additives are
usually polysaccharides including starches and cellulose
and their chemical derivatives as well as other organic
substances capable of forming chemical links with the
cellulose which forms the basis of the paper or board
web. This latter cellulose may have been modified by
the paper or board manufacturer in order to assist the
web formation during ~he early stages of manufacture
preceding the web formation.
~;~35~i4
Additives as described in the application can be
added to the pulp itself, or to ~he early stages in the
formation of the paper web ("we~-end addition"), i.e.
when the water content is reduced from about 99% to
about 30%. The additives are in such cases distributed
more or less uniformly throughout the thickness of the
paper or board. It is also known, for convenience, to
apply the additive to the formed web, on one or both
surfaces thereof in stages of manufacture subsequen~ to
web formation, as the water content is reduced to 2~ to
Z0% by weight of the web.
"Size-Press Addition" named after the relevant par~
of the paper-making machine, is an example of a known
process; application of additives may be effected at
this stage using solutions or dispersions of the
additives, or foamed liquids, or dry powders. It is
known that, whilst the size press process is a useful
method of applying substances to paper or board, the
equipment is expensive to buy and install; it also
consumes large amounts of energy to drive the machinery
and to carry out the extra drying operations conseguent
on the use of a size press.
Since the application of substances at the si~e
press is carried out using solutions or dispersions in
~Z;~6~
water, it is necessary to arrange for extra drying
equipment to be installed in addition to that used to
dry the paper or board before it i6 passed through the
size press. This extra drying requires up to 30% extra
drying eguipment and represents a further 30~ increase
in energy consumed during the manufacture of the paper
or board.
The present invention is concerned with the
transfer, handling and subsequent behaviour on heating
of ~hese dispersions or solutions of polysaccharide
additives, and is based on a consideration of the flow
characteristics thereof.
When dispersions of starch in water are subjected to
high rates of shear, e.g. high rates of flow through
restricted orifices such as those which are normally
used to produce sprays, they exhibit considerable
dilatancy. i.e. the apparent viscosity or resistance to
flow increases as the rate of shear increases. The
result of such increases i5 to restrict or stop flow.
Dilatancy is particularly noticeable in suspensions of
starch wheLe the starch represents 5% or more of the
total fluid. This stoppage is familiar to those users
of starch who wish to spray suspensions of raw or
processed starch as aids to various industrial processes
including application to paper and board during and
~z~
subsequent to manufactura.
Aqueous dispersions of starch also tend to form
sediments owing to the effect of gravity or iner~ial
forces on ~he particulate matter suspended in the
water. Such sediments are the cause o~ much failure of
equipment. In order to prevent or reduce the occurrence
of sedimentation, it has hitherto been customary to
increase the viscosity of the suspension by raising the
temperature of the s~arch above the temperature at which
~he individual par~icles rupture: the process is
generally referred to as "cooking". This enables the
starch to hydrate, forming a gel which, by increasing
the fluid viscosity, reduces the tendency of the starch
particles to sediment. Alternatively, it is customary
to add substances which, by raising the viscosity of the
aqueous phase of the suspension, reduce the
sedimentation process. Such viscosity-increasing
substances include cold-water-soluble derivatives of
starch or of cellulose and many high molecular weight
polyhydric substances such as polyethylene oxide ethers,
polyvinyl alcohols as well as "swelling clays" such as
bentonite, attapulgite, Laponite and the like which are
capable of raising the viscosi~y of the dispersion of
s~arch in cold water.
However, such procedures as described above lead to
poor spray formation since the fluids require high
pumping pressures in order to achieve a sufficiently
high degree of turbulence at the spray head to produce
the fine droplets that are desirable for application as
herein described. Such high pumping pressures
frequently lead to failure of equipment due to ~he
inherent tendency of starch suspensions to beco~e
dilatant. The presen~ invention has discovered a method
of paper or board manufacture in which one or more
further additives are present in the strength-affecting
starch suspension.
According to this invention there is provided an
aqueous suspension of starch characterised in that it
contains minor amount of a hydrophilic polymeric
viscosity increasing agent whereby the settlement of
suspended s~arch particles is prevented. There is also
provided a method of applying a viscous treating agent
in the manufacture of paper or board, characterised in
that the agent is applied by means of a rotary
atomiser.
The invention can be seen to comprise three aspects.
In one aspect, the invention provides a method for
the manufacture of paper or board in which an aqueous
suspension starch i~ applied to the paper web during or
~2~
after its formation: wherein there i6 present in the
suspension a hydratable polymer in an amount such that
the rheology of the suspension i6 altered so a to
render the suspension more pseudoplastic whereby
application to the web is facilitated since
pseudoplastic (alternatively known as visco-elastic or
shear-thinning) fluids as described in this inven~ion
are capable of having sufficien~ viscosity to prevent
sedimentation of dispersed particles such as starch
under the low rates of shear experienced during storage
or whil~t being transported; yet, when subjected to high
rates of shear such as occur when a fluid is expelled
from a narrow orifice such as the nozzle of a spray jet,
the same fluids exhibit sufficiently low viscosity to
permit the formation of droplets suitable for the
application of solutions or suspensions to paper or
board during the early stages of manufacture.
In another aspect the invention provides a method
for the manufacture of paper or board in which an
aqueous solution of a hydratable polymer is applied to
the paper web during or after forma~ion; wherein there
îs present in the solution a water-soluble polymeric
substance capable of forming a continuous film at or
near the surface of the paper or board. This polymer
may be applied alone utilising the advantages of the
atomising distributor descLibed in this invention;
alteLnatively, it may be applied together with the
starch and rheology-modifying polymer described above
In each of the above aspects, the hydratable polymer
is nonionic or ionic, preferably anionic. It may be the
sodium, potassium or ammonium salt of a polycarboxylic
acid in which the carboxylic units are attached to
long-chain polyhydroxyl polymers, e.g. polysaccharides,
whereof the polymers are based on glucose, mannose,
galac~ose, pyranose, amylose and the like and their
hybrid derivatives including such acids as glucuronic
acid. Typical polymers include the sodium, potassium
and ammonium salts of carboxymethylcellulose and ~he
complex polymer obtained by fermentation of a suitable
sugar-based medium by the organism Xanthomonas
campestris and commonly known as xanthan gum. It may
also be one of the water-soluble salts of polyacrylic
acid, polymethacrylic acid and their homologues. the
actual polysaccharides and their derivatives most
preferred will depend on which aspect of the inven~ion
is of major impor~ance.
In another aspect the invention provides a method
for the manufac~ure of paper or board in which
suspensions or solutions of substances in water or other
liguids are applied by means of a rotary atomiser.
Al~hough the a~ueous suspensions and solutions described
in this invention may be applied to the surface of the
paper by conventional, high-pressure sprays, it is pre-
ferred to use the rotary atomiser which has hitherto not
been used in the manufacture of paper although well kno~.
in the agricultural art. The atomiser is available in
several similar forms including devices sold under several
registered trade marks including those of "MICRON MICROMAX'
and "LE~Y HYDRASPIN". Such an atomiser is described in
detail in GB Patents 2,004,204B, 2,004,205B and 2,004,206B
and defined in claim 1 of those patents. These atomisers
and other similar devices comprise a truncated hollow con-
ical shell set to spin on its vertical axis with the
narrow end ~ownwards.
An illustration of the configuration of the atomiser
15 i5 shown in the accompanying drawing, which
consists of a sectional view of a twin-cone system. The
atomiser comprises a fixed inner cone 1 surrounded by an
outer cone 2 moun~ed on a bottom bearing 3 situated at
the end of a central shaft ~. A central nozzle 5 is
20 arranged to supply incoming fluid~ The outer cone 2 is
provided at the top with a top bearing 6 and drive means
comprising a belt driven pulley system 7,8 coupled with
an electric motor 9. The upper outer edge of the outer
cone 2 is provided wi~h teeth 10 and a circumferential
25 protecting ring. The fluid to be atomised is pumped
through one or more ports into the interior of the
spinning cone 2 and is subsequently carried upwards and
outwards across the inner surface of the spinning cone 2
until it leaves the cone tangentially at its widest,
upper circumference. The size of the droplets generated
by this movement of the fluid is partly controlled by
arranging for the upper edge of the cone to be serrated
in the form of teeth 10 arranged radially around its
upper surface. The cone may be driven by an electric or
air or hydraulic motor through a suitable drive and with
suitable bearings to support the cone rigidly on it~
mounting. In the case of a hydraulic motor, the driving
energy may be ~ransferred to the motor by means of a
conventional hydraulic generator pump and specialised
Qo-called "hydraulic fluid"; alternatively, the driving
energy may be transferred by arranging for the aqueous
starch suspension or other fluid, intended to be applied
to the paper, to drive a turbine connected to the
spinning cone.
For a given atomiser and a liquid of given
rheological properties and set spinning at a given speed
of rotation, droplets of uniform size are generated. It
follows that droplet size can be selected by choosing an
appropriate ~ombination of atomiser geometry, fluid
rheology and speed of rotation in order to meet the
particular requirements o$ the user. Each of the
parameters go~erning droplet size may be adjusted
independently of the others and also independently of
~23~
the rate of flow of the suspension or solution being
applied to the paper surface, whereas with a
conventional spray nozzle as previously used in the art.
the droplet size is dependent on the pressure drop
across the nozzle which, in turn, governs the rate of
flow. Since the droplets produced by the atomiser are
of virtually uniform size, they follow similar
trajectories thus permitting a remarkably close degree
of control of the pa~tern laid down on the paper surface
and hence, uniformity of application. If the droplets
are ejected from the ro~ating atomiser set to spin on a
vertical axis, they will travel in a horizontal
trajectory; it therefore follows that they will each
travel along a path determined by the resultant of the
horizontal forces produced by the tangential motion and
the force of gravity. If the body of the atomiser is
placed so that the base of the cone is close to the
surface to which the fluid is to be applied, it follows
that the droplets will travel approximately 20
centimetres in the vertical direction under ~he force of -
gravity and so will be travelling very much more slo~ly
than would similar drople~s ejected at high velocity
from a conventional pressure-operated spray nozzle.
This is particularly advantageous when the fluid is to
~e applied to the surface of paper or board during the
early states of manufacture when the water content of
the paper is high and the strength of the paper
conseguently low.
One or more atomisers may be fixed to a boom set so
as to allow the fluid to be applied to the upper or
lower sides of the paper or board as it passes through
the paper machine. If desired, part of the
circumference of the spinning cone may be surrounded by
a shield so as ~o restrict the passage of droplets ~o
the space diametrically opposi~e the shield this
permits directional application of fluids to be made as
and when required by the user. Fluid collected by the
shield can be returned to the holding tank or in~o the
fluid circula~ing system as may be convenient.
The first aspect of the invention is concerned with
the rheology of the suspension. It is well known that
the velocity of a liquid at which i~ changes from
laminar or quiescent flow to turbulent flow is defined
by the Reynolds Equation expressed as follows:-
NR = d.v.r .K
V
12
where Nr = the Reynolds number of the fluid
d = ~he density of ~he fluid
v = the velocity of the fluid
r = radius of the pipe or orifice through
which the fluid is flowing
~ = a proportionality constant
V = the viscosity of the fluid
If the above parameters are expressed in cgs units,
it is known that turbulence occurs when the Reynolds
Number exceeds 2000. It can be seen that if the valueof V (the viscosity) for a particular fluid is low, the
Reynolds Number will be high and so turbulence will
occur in conditions in which a fluid of higher viscosity
would flow in a laminar manner; additionally, the low
viscosity will enable the fluid to flow at a higher
velocity under given circumstances and so further
increase the Reynolds Number and, hence, the turbulence
of the fluid.
It i6 well known that, for optimum efficiency of a
spray or atomising system, it is necessary for the fluid
to be in a state of turbulence at the point a~ which
break-up into droplets occurs; in other words, op~imum
droplet formation occurs when the fluid viscosity is
low. It therefore follows that, if two fluids of
different viscosities are compared under similar
~4
13
condi~ions of flow as defined by the parameters used in
the Reynolds Equation, better spray efficiency will be
obtained in the fluid with the lower ~iscosity.
Further consideration of the first aspect, ie. the
rheology of the suspension of starch, requires that the
viscosity or resis~ance to deformation within the fluid
6hould be as high as possible when the ~luid is at or
virtually at rest, i.e. under conditions of low rates of
shear. Prior art teaches that a starch or similar
suspension could be stabilised if the fluid viscosi~y is
raised by cooking at least part of the starch or by the
addition of a soluble polymeric substance as defined
earlier, i.e. the starch particles are prevented from
setting out under the forces oP gravity or inertia.
Stokes' Law illustrates this by calculating that the
forces exerted on suspended particles by external forces
are inversely proportional to the viscosity of the
fluid. However, such treatments give rise to high
viscosities which are detrimental to the efficiency of
2~ the spraying equipment. It follows, therefore, that the
rheology of the fluid in which the starch is suspended
should exhibi~ a high viscosity at low rates of shear in
order to prevent se~tlemen~ of the starch particles; at
the same time it should exhibit low visocsity at high
rates of shear in order to ensure sufficient trubulence
to form droplets of optimum 6ize and particle siæe
~3~
14
dist~ibution.
It is well known that the viscosity of solutions of
some poly~eric substances falls off more rapidly than
others as ~he rate of shear or the rate of flow through
a given orifice i6 increased. This is illustrated in
the following Table in which the viscosities in water of
several well-known high viscosity polymeric substances
are comparPd over a range of rates of shear; the
respecti~e viscosities and rates of shear were measured
with a Broo~field Viscometer fitted with a concentric
bob and cylinder attachment sold under the designation
SC4 Small Sample Adapter:-
Shear
Rate
Polymer* Viscosit~ tcentipoises) ~ 20 deq C
CMC1~000 1300084006000 43003000 l900 1400
HEC8000 6500 50003800 2700l900 llO0
GGllO0 9100 58003900 24001500 700
XG32000 170Q0 75003800 l900llO0 450 240
~C660 550 480430 400 340 2~0 210
.
The present invention has discovered ~hat if a
minor proportion o a 6ubs~ance capable of pro~idingaqueous solutions of high pseudoplas~icity is added ~o
starch powder or incorpora~ed into a suspension of
starch, it renders the starch capable of being stored
for prolonged periods in aqueous suspension; of being
capable of being transported through re6tricted orifices
without giving rise to dilatancy; and i~s suspensions
of being readily transformed into droplets of
sufficiently small size to enable ~hem to be used as a
means of applying starch uniformly to surfaces including
surfaces of paper during manufacture.
Preferred polymers for the rheology-affecting
purpose are xanthan gum and similar polysaccharides
capable of dissolving in wa~er to produce solutions
possessing very high viscosity at low rates of shear
compared with other commerically available polymers but
a relatively low viscosity at high rate of shear; this
is illustrated in Table 1. Solutions of xanthan gum
show little variation in their physical properties.
including rheology, over temperature ranges normally
experienced in paper mills and o~har closed industrial
premises: these properties also show neglible
variations when ionic and other dissolved substances are
present with the xanthan gum. This is especially
important when water of unknown composition is used to
prepare the starch suspensions e.g. when recycled water
of differing degrees of hardness or with differing salt
contents and at varying temperature is used in such
preparations.
~z~
The rheology-affecting properties of xanthan gum are
of particular importance if it is desired to apply
starch in the form of a suspension or slurry in water
since the presence of the xanthan gum in the suspension
greatly reduces the tendency of starch particles ts
settle out or form intractable sediments. The presence
of xanthan gum in a s~arch suspension as described in
~his inven~ion allows users to store such suspensions
for prolonged psriods and enables users ~o transport the
~tarch in the form of slurry to its eventual destination
without the necessity to install special agitation
equipment in the slurry containers used for transport
and storage of the slurry. The convenience of being
able to transport and store starch suspensions by the
addition of xanthan gum is particularly importan~ in
that such suspensions are available as residues produced
;n certain food-manufacturing processes: it is
economically advantageous to be able to supply the
starch in the suspension or slurry form in which it is
produced rather than to extract and dry the starch and
subsequently have to re-form the suspension before use.
This invention procides an economic method of storing
and transporting such starch suspensions or slurries to
the benefi~ of the starch and paper industries.
This invention has also discovered that ~he presence
of xanthan gum in starch suspensions also overcomes the
tendency of such suspensions to exhibit the phenomenon
of dilatancy which can best be described as a rise in
viscosi~y or resistance to flow as the rate of shear
increases. Dilatancy is a condition to be avoided in
handling starch and other ssspensions since dilatan~
fluids tend to cease flowing under conditions of high
rates of shear such as occur inside pumps and control
valves, restrictions and bends in pipes and in the
noz~les of conventional spraying equipment. Therefore,
the presence of xanthan gum in such suspensions serves
to prevent the well-known and troublesome tendency of
suspensions to cause blockages in the equipment used to
carry them and, particularly, in the nozzles of
conventional spray equipment.
The amount of weight of xanthan gum can vary between
0.025% and 1.0% of the water used to prepare the starch
suspensions: in the case of suspensions prepared from
dried, pow~er starch, the xanthan gum can be
incorporated in the starch powder ~ogether with such
other polymeric substances as may be desired so as to be
present in the aforementioned proportions in the slurry
during use. In the case of starch already prepared in
suspension form a~ previously described, it is
convenient to add the xanthan gum at an early stage in
order to facilitate transport and prolonged storage.
The second aspect of this invention is concerned
with ~he film-forming properties of certain polymers
when dissolved or otherwise dispersed in water and
applied in droplet form in a manner similar to that
already described for the application of starch
suspensions to paper or ~oard during manufacture. The
preferred polymers are polysaccharides such as the
alkali metal salts of carboxymethyl starches or of
carboxymethyl celluloses or of alginic acid or of
polyacrylic acid and their homologues, or (more
preferably) the sodium salt of carboxymethyl cellulose
commonly known as SCMC or CMC. The polymers may be
applied with or without starch as herein described in
order to provide different benefits to suit the
requirements of users.
The carboxymethyl celluloses can have a degree of
carboxyme~hylation of from 0.35 to 104 (i.e. related to
the three labile hydroxy groups theoretically available
for substitution in each anhydroglucose ring within the
cellulose molecule chain) and total molecular weights
from 15,000 to 80~,000, preferably 50,000 to 250,000.
It has been discovered in this invention that the
presence of SCMC or the other polymers described in an
aqueous starch dispersion has the effect of reducing the
temperature a~ which starch particles rupture and form a
gel (the gelation Temperature) as exemplified by a rapi~
increase in visc06ity. For example, 4 parts of SCMC of
molecular weight approximately lO0,000 and degree of
carboxymethylation of 0.85 were added to 16 parts of
wheat starch. The effect was to reduce the gelation
temperature of a 20% by weight starch suspension from 64
degreees Celsius to 59 degrees Celsius. This reduction
in gelation temperature is important in the paper or
board making processes in that it is known that low
~emperature gelation of starch improves the beneficial
effects of adding starch to cellulose. Thus, the
addition of such SCMC to starch is an important and
hitherto unexpected method of improving the economy of
operating the paper or board manufacturing processes.
The amount of these polymers, or mixtures thereof.
can vary up to 10% of the weight of the water used to
carry the additives through a conventional spray or ~he
atomisillg distributor as herein described, but is more
usually 0.25% ~o 7.5%.
The presence of xanthan gum as part of the agueous
dispersion ~f starch or o$her water-soluble polymers
such as SCMC increases the resistance to flow of the
dispersion and thus serves to control the rate at which
the dispersion penetrates the paper after application.
It follows, therefore, that the presence of xanthan gum
will keep the dispersion at or close ~o the surface of
the paper ~ven when the paper contains high proportions
of water such as occurs during the early s~ages of paper
manufacture.
In the method of the invention it is envisaged that
s~arch may be applied to paper or board by the method~
described herein so as to represen~ from 0.5% to 10% of
the weight of ~he dried paper. It is also envisaged
~hat a rheology-affecting material, e.g. xanthan gum,
may be present in sufficient quantity to prevent ~he
starch settling out or i~s dispersions becoming dilatant
and thus unsuitable for transportation through
restricted orifices. It is also envisaged that
so-called water-soluble polymers as described above may
be applied to paper or board by the methods described
herein in order to provide improvements to the paper or
board or to augment the benefits of applying starch. It
is envisaged that the starch and polymers may be blended
~ogether in the dry form; or by mixing together their
respec~ive dispersions or solutions and then applying
the resultan~ mixture by the methods herein described:
or by arranging for disperions or solutions of the
respective ~aterials to be applied severally through two
or more atomising distributors set so as to apply the
respec~ive ma~erials a~ ~he most appropriate points of
the paper- or board-making process.
While the invention has been defined above as a
method of manufacture of paper or board, it will be
appreciated ~hat the paper or board so manufactured is a
further aspect of the invention. Such paper or board
has been shown to have increased strength and improved
surface qualities, as described below in the Examples
given, which make it a more valuble commodity.
The invention also extends to intimate particulate
mixtures of starch and one or more of the addi~ives as
set forth above, capable of being jointly suspended or
hydrated for use in the method. The starch/xanthan gum
mixture is capable of long-term storage and reliable
passage through application equipment described above
and the SCMC solutions used alone or jointly with starch
are particularly valuable.
The invention will be further described with
reference to the following Examples:
ExamPle 1
(a~ Prior Art
100 grams of wheat starch were dispersed in 1000 ml
water to form a slurry containing 10% starch solids at
room temperature.
69~
~ ml of the above slurry were placed in the
cylindrical container of a Brookfield SC-4 Adapter
fitted ~ith the appropriate bob which was set to rotate
at 20 revolutions per minute (rpm) and the temperature
to rise from 20 degrees Celsius at a rate of 2 degree~
per minute by means of a thermos~atically controlled
water circulator. Dial readings were taken continuously
until the viscosity of the suspension had undergone a
rapid rise indicating gelation. The dial readings were
plotted on graph paper. By extrapolation, the gelation
temperature wa~ judged to be 64 degrees Celsius.
(b) Addition of SCMC of_low DS
To 250 ml of the starch slurry prepared for the above
were added 1.25 grammes of SCMC of molecular weight
approximtely 100,000 and degree of carboxymethyl
substitution 0.65, representing 5% by weight of the
starch solids and 0.5% the total slurry/solution
combination. The mixture was stirred mechanically for
one hour. 8 ml of the mixture were placed in the
cylinder of the BrooXfield SC-4 and the procedure
described above was repeated. The extrapolated gelation
temperature was judged to be 60 degrees C.
(c) Addition of SCMC of hiqher DS
To a further 250 ml of the original starch slurry
were added 1.25 grammes of SCMC of similar molecular
~3~
weight to the SCMC used in Example (b) but with
degree of substitution of 0.8 and ~he experiment
repeated. In ~hi~ case the extrapolated gelation
temperature was judged to be S9 degrees C.
(d) Addition of extra SCMC
To a further 250 ml of the original starch slurry
were added 2.5 grammes of the SCMC used in Example (c),
representing 10% by weight of the starch solids and 1.0
o the total dispersion. The experiment was repeated
and the gelation temperature judged to be ~8 degrees C.
~ .
The above experiments have indicated an unexpected
reduction in the gelation temperature or starch
suspension as exemplified ~y the rapid rise in
viscosity over a narrow range of temperature. This is
interpreted as a form of co-solvency which is more
apparent when the SCMC has a grea~er degree of
6ubstitution and so possesses a greater affinity for
20 water. Thus, when water plus such SCMC enters starch
sranules during the early stages of granule rupture, the
natural tendency of SCMC molecules to uncoil and expand
assists the rupture of ~he granules at lower
temperatures ~han would happen if SCMC were not present.
~23~i~
24
A redu~ion in ~he temperature at which starch gels
and so is rendered capable of formi~g a more or less
continuous film within the structure of the paper ~eb is
a benefit to ~hose making paper since it is to be
expected that the hea~ energy required to attain
gelation will be reduced; addi~ionally, ~he gelation
will ~ake place at an earlier stage in the drying
section of the pape~-making process, thus allowing more
time for the beneficial interactions between starch and
cellulose fibres to take place.
ExamP1~ 2
Rheoloaical Effect of Xanthan Gum (SusPension Stabilit
(a) 38% Starch Solids SlurrY
Z50 ml quantities of a commercial starch slurry
know~ as Tenstar AB manufactured by Ranks Hovis
MacDougall Ltd., by wet-milling of wheat and constituting
a never-dried starch slurry containing 38% by weight of
wheat starch solids were treated with several additions of
xanthan gum. The amount of settlement or sedimentation of
the starch was judged by noting the volume of clear liquid
appearing in the upper part of the fluid when stored in
250 ml graduated glass cylinders over periods of several
days. The results were noted and shown in Table 2 below.
r~~ k
~z~
Table 2 38% Tenstar Starch Slurry
Per cent xanthan gum Volume of Clear Liguid (ml)
(on total volume) 1 day 8 daY5 7 davs 14 davs
0.0 0 5 10 25
0.10 0 0 5 10
0.15
0.20 0 0 0 0
(b) 18% Starch Solids Slurrv
The procedure described in Example 2(a) was repeated
with another never-dried commercial starch slurry known a~
Staper Starch obtained by wet-milling cereals and contain-
ing 18% starch solids. The results are shown in Table 3.
Table ~
Per cent Xanthan Gum Volume of Clear Liquid (ml)
15 (on total volume) 1 daY3 days 7 days 14 daYs
0.0 120 140 170 180
0.10 50 70 110 150
0.15 20 40 60 70
0.20 0 0 0 0
(Note: The slurries used in the above experiments were
treated with 0.2% dichlorophen in order to prevent
microbiological interference with the starch and polymer
dispersions).
The results of the above experiments indicate that
xanthan gum addi~ion to commercial slurries of starch
~5864
has the beneficial effect of preventing settlement of
the starch particles and so provides the benefi~ of
long-term storage without the neeessity for continuou~
agitation as is the case of the prior art.
ExamPle 3
(a) ffec~ on Strenath of Hand Made PaPer
Blends of starch combined with sodium carboxymethyl
cellulose and/or xanthan gum were prepared as shown in
Table 4.
Table 4
BLEND Starch SCMC DS 0.65 SCMC DS 0.85 Xanthan Gum
A 100 0 0 0
B 96 4 0 0
C 96 0 4 0
15 D 99.6 0 0 0.4
E 95.6 0 4 0.4
F 95.6 4 0 0.4
~ S0 Grammes of each blend were mixed into 750 ml
water so as to form 25% w/v slurries which were used to
spray on to hand-made paper as it was being formed. The
spray was arranged so as to deliver 0.7 ml on each
occasion which, on paper sheets of nominal 3.7 grammes
dry weight, is equivalent to 4.7% add-on of dry starch
or blend to dry paper.
Z7
The paper furnish was bleached kraft with neutral
ca~ionic retention aid. Af~er drying and calendering,
the sheets were tested for burst strength with a Mullen
Tester~ The mean of 10 tests was recorded and compared
with untreated paper made at ~he same time but sprayed
with water in place of the starch slurry.
Table 5 Bleached kraft; 3.7 gramme ~heets; 4.7% starch
add-on
BLENDMullen Burst (PSi) % Chanqe
NIL 14.2 0.0
A 15.7 +10.5
B 16.5 +16.5
C 17.0 +19.7
D 17.0 ~19.7
E 17.2 +21.1
F 17.5 +23.2
~s~
28
The results of the experiments shown in Table 5
illustrate the beneficial effects of increasing the
bursting strength of paper by adding starch; they
further show the additional benefits derived from the
addition of small proportions of polymers as described
in this invention to the starch. The additional costs of
making these additions are greatly outweighed by the
commercial advantages to be gained by paper-makers
making use of this invention.
Example 4
USE OF ATOMISING DISTRIBUTOR
An atomiser as described in ~his invention was set
above the wire part of a Foudrinier paper-making machine
so as to distribute a slurry prepared by dilution of a
commercial starch slurry into which had been introduced
SMCM and xanthan gum immediately following manufacture
of the slurry as a by-product of a process to extract
other components of milled whea~. The proportions of
materials used in this Example were:
20 Stàrch Slurry
Wheat starch solids 380 Kg
SCMC 18 Kg
Xanthan gum 2 Kg
Water 600 Kg
~6~
29
The paper-making machine had been set to produce 40
Kg of paper of a weight of 35 grammes per square metre
per minute at a speed of 400 metres per minute. The
paper-making machine furnish contained 1.5% dry basis of
a commercial cationic stalch acting partly as a me~hod
of providing the required burst s~reng~h and par~ly to
aid drainage as well as retention of fibres on the wire
part of ~he machine. Slurry of the above composition
was pumped through a flowmeter at 1.5 litres per minute,
representing 0.57 Kg starch solids per minute, i.e. 1.4
of the paper dry weight. The slurry passed through an
in-line diluter in which it was mixed wi~h water
separately pumped at 5 litres per minute. The resultant
6.5 li~res per minute of diluted slurry was passed
through an atomiser as herein described driven by an air
motor set to run at 5000 revolutions per minute
producing droplets of 500 micrometres mean diameter.
The slurry was applied to the paper over a 30 hour
period, samples being taken at approximately hourly
intervals. During the period, ~he cationic starch
addition to the furnish was progressively reduced to
zero in order to make a comparison of this invention
with a well-known and hither~o acceptable method of
improving paper guality by the addition of a
starch-based product to the paper-making machine
furnish. Random results of this experiment are shown in
Table 6.
Table 6 Selec~0d waste + bleached kraft; 50 grammes/sg.
metre; 1.4% starch add-on
SAMPLE MULLEN BURST % CHANGE TENSILE STRENGTH ~ CHANGE
RATI0* (psi) (Psi)
cationic starch 1.~%
LlankZ.80 0.0 56 0.0
3.~0 +14 57 +1.8
cationic starch reduced to 0.8~
B3.41 +22 60 +6.7
C3.36 +20 62 +g.7
D3.33 ~19 59 +5.4
Cationic starch reduced to zero
E3.46 ~24 56 0.0
F3.52 ~26 56 0.0
_
* The parameter "~ullen Burst Ratio" (MEiR) is defined
as:-
MB
~qBR = GSM
where: MB = the pres6ure in pounds per square inchrequired to burst a sample of paper in the ~ell-known
Mullen Tester used throughout the paper-making industry;
GSM = the weight in gramme o~ one square metre of
paper .
Thus, the "Mullen Burst Ratio" can be used to
elimina~e minor variations in paper weight which ~ould
0 otherwise affec~ the results of the burst test.
The results show tha~ the addition sf starch
increa6ed the burst strength of paper already containing
a streng~h-increasing additi~e; furthermore, the Mullen
Burst Strength Ratio increased still further as the
15 previously used strength-increasing additive was
progressively reduced to zero. Therefore, the addition
of starch modif ied as described in this invention and
applied in the form of small droplets to paper during
p oduction on a paper-making machine can produce better
20 results ~han another ~ype of starch hitherto regarded as
acceptable by ~chose skilled in the art of manufacturing
paper .
32
The results also show that the addition of starch
modified as described above and applied to paper during
the early stages of manufacture enhances the tensile
strength of paper to which had already been added a
tensile streng~h incrasing additive, i.e. cationic
starch.
ExamPle 5
Addition of SCMC to Paper durinq manufacture usina the
atomiser
A dispersion of SCMC was applied to paper using the
atomiser and flowmetering equipment described in Example
4. In this Example the modified starch slurry used in
Example 4 was replaced by an aqueous solution of SCMC of
molecular weight approximately 100,000 and degree of
carboxymethyl substitution of 0.85, containing 20
grammes of dry SCMC per litre of solution. As in
Example 4, the paper-making machine was set ~o produce
40 Kg of dry paper per minute. The rate of flow of the
SCMC solution was adjusted to 5 litres per minute,
representing an addi~ion rate of 0.25% of SCMC ~o the
dry paper produced.
Results of this experiment are shown in Table 7:-
~z::3586;4
33
Table 7
Sele~ted wa~t~ t blaached kraft; 50 grammes/sg. metre;
0.25% SCMC add-on; no starch
-
SCMC MULL~N BURST RATI0 ~ CHANGE TENSILE STRENGTH %CHANGE
% (psi! (Psil
0.0 2.80 0.0 56 0.0
0.~5 3.46 +23.6 57 +1.~
The results shown in Table 7 illustrate the benefits
of applying as little as 0.25% SCMC of relatively low
molecular weight and h;gh degree of carboxymethyl
6ubst~tution to paper by means oE the atomiser herein
described during the early stages o~ manuEacture.
v~ri~ m~ t.lv~ d ~dditl~ m~y b~ made to
the invention as defined above.
For example, the incorporation of the special
atomisers into the machinery used in the manufacture of
paper or board (as described above in relation to the
spraying sf starch suspensions and solutions such as
34
those of SCMC) gives the possibility of the operation of
the machinery by the selective or additional use of such
atomisers in respect of other suspensions or solutions.
For example, such atomisers may be used with sizing
agents whether in the form of solutions, emulsions or
suspensions. They may also be used with colouring
materials whether in the form of soluble dyes or
insoluble pigment suspensions. They may also be used
with oil~ materials, e.g. as applied to waterproof or
otherwise mo~ify ~he paper. They may also be used with
liquid forms of reactive resins as added to paper in
order to increase the wet strength or resistance to
water of the dried paper: in this aspect the use of two
or more atomisers arranged above the wire part of a
paper-making machine permits the application of several
materials which may, by physical or chemical interaction
with each other and the paper to which they are applied,
provide further benefits.
By adjusting the position of the atomiser along the
wire part of the paper-making machine it is envisaged
that the degree of penetration of the applied ma~erial
may be controlled. For example, applying the material
at positions where the water content of the paper is
high allows such materials to penetrate the body of the
paper and so become an integral part of the paper:
~23~
conversely, application at points where the water
content has been reduced by drainage, suction or the
application of heat allows the materials to be held at
the surface of the paper and 50 become concen~rated at
or near the surface.
It is also envisaged that the atomisers may be used
to apply coatings to paper after the end of the drying
part of the process: in this case, the atomiser6 could
form part of the specialised machinery used to apply
pigments, resins, waxes, colouring matter or various
solu~ions to the surface of the paper.
The advantage of separating the size of droplets
from the rate of flow, once incorporated into ~he
machinery in respect of the starch suspensions and SCMC
solutions as described, is of general utility throughout
the process of making paper of commercial value. It is
envisaged that the atomisers in question will either be
connec~ed for selective alternative use, or that a
succession of atomise{s will be provided at different
points of the flow path in paper production and that the
necessary solutions or suspensions will be in permanent
communication wi~h such atomisers for instant use when
desired.
