Note: Descriptions are shown in the official language in which they were submitted.
W091/10776 PCT/GB91/~89
,. 1
REDUCING FOAMING IN PAPER MANUFACTURE
The present invention is concerned with reducing the
problems caused by foam formation during the production of
paper. Particularly paper produced under alkaline or
neutral conditions using cyclic acid anhydrides, especially
alkyl or alkenyl succinic anhydrides (ASA) as sizes.
Sizing paper with alkenyl succinic anhydrides (ASA) at or
about a neutral pH, using paper stock containing calcium
carbonate as a neutral whitening filler is a well khown
process, but it is known to produce an unacceptable amount
of foam in the paper machine white water recycle. The
foam, accumulates as white pitches in the white water
recycle and is transported with the paper stock to the
paper machine head box. Although silicones and other
anti-foam additives are sometimes added they do not give
adequate foam reduction.
Shutting down the process and cleaning up the equipment is
the technique used to alleviate the above mentioned
problems. The resulting cost, due to the lower
productivity, represents an unrecoverable process loss.
Typically the sizing is carried out by metering ASA as an
emulsion into the paper stock in the wet end of the paper
machine just before feeding the diluted paper stock to the
Fourdrinier table. The paper stock contains 20-30% (on dry
cellulose) calcium carbonate as an inert filler. More
recently it has been proposed in European Patent
S~ ,5TIT~JT SH~-
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WO91/10776 PCT/GB91/~89
Application 8930617.8 that the ASA may be applied neat or
as a solution.
Suitable technologies have been developed to produce
emulsion involving both dynamic and static mixing (US
Patent R 29960), ancillary materials, classified as
activators, promoters and stabilizers, to optimise ASA
smulsions with respect to sizing, retention and paper
machine runnability.
.,
Although the place to introduce the ASA emulsion in the
paper machine can be chosen according to various plant
needs, it is customary to select a position to minimize
hold time and where the fluid is turbulent to facilitate
ASA mixing with the paper stock
ASA are easily hydrolysable compounds which produce alkenyl
succinic acid on reaction with water. The acid is not
active in sizing paper (TAPPI Journal 70 12 117-121 1987).
Moreover, it builds up in the white water recycle to a
point when the production of foam and of white pitches
occurs with the appearance of dark spots in the paper.
Plating out of the white pitches also occurs on several
critical places of the paper machine (such as the
Fourdrinier net, the drying section's felts, the head box
and in the piping system) with a consequent productivity
decrease mainly due to press pickin~, felt soilage and
lowered drainage.
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SUBSTITUTE SH~Er
WO91/10776 PCT/GB91/~89
.
Shutting down the process and cleaning up the paper machine
is the only known technique used to prevent paper quality
problems due to foaming and white pitches formation see the
(TAPPI Papermakers Conference 1986 Publication pages
311-314) and to eliminate runnability problems.
ASA's hydrolysis kinetlcs indicate a rapid reaction whose
rate increases with temperature and pH and it is a function
of the emulsion's particle size (TAPPI Alkaline Papermaking
1985 17-20). The ASA emulsion in water is therefore
generally produced on site just before its introduction in
the paper machine to minimize hydrolysis.
Unless the ASA's first pass retention is high (f.i. 80-85%
and higher), hydrolysis of the unretained ASA and foaming
occur quite rapidly due to the high pH prevalent in the
white water recycle and its temperature being between 30 to
40 C.
A number of formulations are available to the paper
industry to prepare ASA emulsions s~e (TAPPI Alkaline
Papermaking 1985 113-133, TAPPI Sizing short course 1987
89-91). They are based on an emulsifier compound (such as
sulfosuccinates, nonylphenol adducts with ethylene and
propylene oxides and the like) and natural and synthetic
organic compounds bearing positive charges (such as
cationized starch, polyamines and the like).
An improved sizing process, which maximizes ASA first pass
retention, involves metering ASA neat or in solution, as a
fine spray,
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SUBSTIT~JT~ SI~E~T
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WO 91/10776 PCI'/GB91/00089
directly into the paper stock through a nozzle is described
in European Patent Application 8930617.8. The improved
retention obtainable with the spray-mixing technique
depends on several parameters including: ASA particle
diameter distribution, presence of ASA-soluble, inert
compounds, absence of emulsifiers, a 2-3 orders of
magnitude lower contact time with water compared with the
emulsion process, etc.
:
The main purpose of the present invention is to eliminate
the technical and cost problems, as previously described,
encountered due to foam formation particularly in the
ASA-based paper sizing technology.
'
It has been observed that in papermaking operations
involving ASA sizing foam formation depends on the presence
of ASA, calcium carbonate and air microbubbles. The
absence of one of these components from the paper stock
drastically reduces or eliminates foam. Thus, ASA
hydrolysis alone cannot account for foam production.
We have found that the foam is composed of calcium
carbonate mixed with small amounts of fines and traces of
calcium succinate, an ionic surfactant. It includes also
moderate to large amounts of air. We have also found that
air microbubbles, when brought into contact with a calcium
carbonate surface, do not spontaneously adhere thereto.
However, if a hydrophobic material, such as an alkenyl
succinic moiety, coats the surface of the calcium carbonate
particle the air microbubbles may attach readily to it
floating the calcium carbonate particles typically of
diameter 0.2-0.5 microns to the surface so that they
accumulate as a frothy foam on top of the process liquid.
SUBSTITUTE ~;H~ET
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WO91/10776 PCT/GB91/~89
ASA hydrolysates are essentially alkyl or alkenyl succinic
acid dissolved in or dissolving unhydrolysed ASA. They
produce a hydrophobic material adhering by chemisorption to
calcium carbonate and in part reacting with the production
of calcium succinate.
It has been found that foam in the paper making process may
be depressed by addition to the paper stock of water
soluble salts of a polybasic acid such as sodium
hydroxide-treated polymerised silica of the general
formula NA2O.mSiO2 nH2_ where m and n are the number
; of SiO2 and H2O moles relative to one mole of Na20.
We have found that the addition of such depressants reduces
or prevents foaming and thus both reduces the paper process
runnability problems and improves paper quality. We prefer
to use from 0.02 to 2 wt% based on weight of dry cellulose
of the salt of the polybasic acid.
:;
It is believed that the effect of the addition of these
salts of polybasic acids is to block the calcium carbonate
surface and prevent the formation of the foam creating
calcium succinate. Other salts which may be used as foam
depressants include sodium derivatives of polyacids such as
polyphosphoric acids, polyphosphonic acids, ethylene
tetracetic acid, polyacrylic acids, hydrocolloids,
polysaccarides, etc.
The present invention therefore provides the use as a foam
suppressant in alkaline or neutral paper making containing
calcium carbonate of a water soluble salt of a polybasic
acid or its water colloidal dispersion.
In a further embodiment the invention provides a process
for making paper under alkaline or neutral conditions
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comprising adding thereto an amount sufficient to depress
` foam formation of a water soluble salt of a polybasic acid
or its water colloidal dispersion.
.,
In a further embodiment the invention provides such a useor such a process as previously described in which the
paper is sized with a cyclic acid anhydride particularly an
alkyl or alkenyl succinic acid anhydride.
The treatment of the calcium carbonate with the foam
dispersant is carried out either batchwise or preferably
on-line when the pigment slurry is added to the paper
stock. While the foam suppressant and calcium carbonate
introduction points could be different, we prefer they are
the same and are preferably positioned downstream of the
position at which the size is added to the paper stock
It is believed that foam depression by surface blocking
occurs because the depressants preferably bind themselves
to the calcium carbonate surface thus preventing air
microbubbles from adhering to calcium carbonate particles
and floating them upward (A.T. Taggart, Elements of ore
dressing, John Wiley & Sons Inc., New York 1951 pages 263
to 281).
As a consequence of a substantially foamless operation,
white pitches accumulation in the paper is drastically
depressed or eliminated. Thus, it is no longer necessary
to frequently shut down the papermaking process to carry
out cleaning operations to eliminate white pitches
deposited on the paper machines. As a consequence, there
is an improvement of the machine runnability and of the
production costs.
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WO91/10776 PCT/GB91/~89
This invention may be applied to the production of paper or
similar products, such as board, cardboard etc., based on
cellulose or synthetic fibres.
Paper, board, cardboard and other similar products are
produced by first dispersing the cellulose or synthetic
fibres in large quantities of water and the dispersion
passed to a paper making machine where the water is removed
to form the continuous paper web.
According to the nature of the fibres, the type of paper or
board to be produced etc, the product is treated with
various chemicals which may be injected into the aqueous
dispersion of the fibres. One particular treatment common
to most paper making processes is sizing.
Sizing of paper is well known, two typical sizing materials
are alkyl-ketene dimers and alkenyl succinic anhydrides.
These products are generally used in emulsion form as
described in, for example, Japanese Patent Publications
62-231099; 61-146898; 61-160495; 52-25102; 60-20905.
Whilst the present invention is concerned with sizing in
general it is particularly concerned with sizing with
alkenyl succinic anhydrides, and alkyl ketene dimers.
United Kingdom Patent 1492104 describes the use of
polyoxyalkylene alXyl or arylalkyl ethers, or the
corresponding mono- and di-esters derivatives to produce
emulsions of cyclic acid anhydrides with a low input of
shear energy. Such emulsions are used to disperse
intimately the anhydrides into the cellulose stock to
produce sized paper. The sizing emulsion can be produced
in-situ, withir. the cellulose stock, or prior to
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WO91/10776 PCT/GB91/~89
introduction into the cellulose stock. The emulsions are
preferably prepared in the presence of cationised
stabilisers such as cationized starches, polyaminoethyl
acrylate resins, polyamide resins having free amino groups,
reacted or not with epichlorohydrin etc.
The main function of these cationic stabilizers is to
charge positively the emulsion's particles favouring their
absorption by Coulombic attraction on the negatively
charged surface of the cellulose fibres.
Whilst the present invention may be used with processes in
which size emulsions are used it is particularly suited for
use in combination with the technology described in our
European Patent Application 8930617.8 in which paper,
board, cardboard, etc are produced with a sizing process
comprised of the following steps:
,, .
- production of a cellulose stock water slurry.
- cationization of such slurry.
- dispersing the synthetic size, neat or in solution
with non active compounds such as gases or solvents,
in form of fine droplets into the cellulose stock
before, during or after the paperweb formation whether
or not said paperweb is dry or wet.
- drying the paperweb.
It is also applicable to the process in which the size is
introduced in admixture with water as described in our
United Kingdom Patent Applications 9001435, 9001436,
9008334 and 9008335. Here the water generally at 30 to 50C
is used as the vehicle to transport the synthetic size in
subdivided form.
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WO91/10776 PCT/GB91/~89
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0.2 to 4.0 cubic metres of water per ton of dry cellulose,
preferably 0.35 to 3.0 cubic metres are used.
According to these preferred procedures, the reactive
synthetic sizing compound is continuously dispersed in the
form of fine droplets into the wet-end of the paper
machine, preferably in places where the cellulose stock
- water slurry is under high turbulence, to obtain rapid and
complete contact of the sizing compound with the paper
stock. If necessary turbulence can be controlled by the
provision of baffles and stirrers in the flow of the
slurry.
The absorption of the sizing compound droplets on the
cellulosic fibres is aided by a cationizing treatment
either the fibres may have undergone such treatment either
on-line or in the paper stock preparation tubs
alternatively the size may be cationised by for example,
addition together with a cationising compound. Such
cationization is a standard technique in paper production
to favour the retention of wet-strength resins, of mineral
charges, etc, which otherwise would be in large part lost.
The cationization is generally carried out with long chain
fatty amines, synthetic polymers containing amines,
cationic modified starches, polyamide-amine resins and
other cationized products. Typically 0.02 to 3.50 wt% of
cationizing agent based on the weight of dry fibre is used
.,
In these processes the contact time with the process water
of the reactive synthetic sizing compound in dispersed
droplet form is very small, depending on the turbulence of
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WO91/10776 PCT/GB91/~89
--10--
the machine wet-end and on the cationizing treatment of the
cellulose fibre. These factors can be varied at will until
high deposition rates of the size droplets on the fibres
are achieved.
The combined action of the extremely low contact time with
the process water and the natural hydrophobicity of the
sizing compound prevent its hydrolytic degradation and the
resulting waste. Moreover, by lowering the droplets
diameter to very low values, the interactions with the
cellulose fibres and the sizing compound absorption can be
improved thus increasing the sizing yield to a level beyond
that which can be achieved with the current emulsion
technology.
In another procedure, the solutions of certain gases, such
as methane, propane, butane, chlorofluoro hydrocarbons,
carbon dioxide, etc., in the synthetic sizing compound are
sprayed in form of fine droplets directly into the wet-end
of the paper machine or onto the formed paper web before
the machine drying section, or in the size press.
A range of gas-sizing compound compositions may be used. A
preferred composition could be experimentally determined
because it may depend from the type of paper produced in a
given machine and from the process parameters. In general,
the dissolved gas concentration may be in the range 20 to
50% on the sizing compound although for economic reasons it
is preferable that gas concentrations be kept in the range
1 to 19% if the cost factor is very important. The sizing
compound gas solutions could also be obtained by previously
mixing gas types with low and high solubility into the
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WO91/10776 PCT/GB91/~89
sizing compound, such as nitrogen and carbon dioxide,
nitrogen and methane.
In another procedure, the reactive synthetic sizing
compound is first dissolved in an anhydrous, aprotic,
water-soluble, inert solvent. The solution, is sprayed
with one or more nozzles as fine droplets directly into the
water-cellulose slurry at the paper machine wet-end. In
this case, the inert solvent is dissolved by the process
water thus protecting the reactive sizing compound droplets
from water's hydrolytic action and generating in-situ a
fresh surface in the presence of cellulose.
The presence of inert gases dissolved in the aprotic
solvent, as previously specified (for example carbon
dioxide), is claimed also for this type of procedure.
Examples of useful aprotic compounds include ketones,
esters, ethers, aromatic and aliphatic hydrocarbons, (for
example acetone, methylethyl ketone, acetonyl acetone,
methyl acetate, ethylene glycol diacetate, dioxane, etc).
A range of solvent concantrations in the solutions with the
sizing compound can be considered. The preferred
composition will be determined by experiment depending on
the process parameters. Cost considerations would indicate
that solvent concentrations in the range 1 to 19% may be
preferred to concentrations in the range 20 to 50% or
higher, also to avoid the solvents accumulation in the
water recycle system.
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WO91/107~6 PCT/GB91/~89
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In another preferred procedure, the reactive sizing
compound is dissolved in an anhydrous, protic, water
soluble compound immediately before being sprayed and
transformed into fine droplets.
:
Preferred concentrations of the protic anhydrous solvent
with the reactive sizing compound are as previously
disclosed in the case of the aprotic solvents. Classes of
such solvents include alcohols, etheralcohols,
esteralcohols (e.g. methyl alcohol, ethyl alcohol,
2-butoxyethanol, ethylene glycol monoacetate, 2-~2
butoxyethanol), etc.
Subsequent to the addition of the sizing compound to the
paper stock into the paper machine wet-end in the
concentration range of 0.005 to 2.0% weight on dry fibres,
the paper web is dried by heating to temperatures in the
range 90 to 120-C thus favouring the reaction between the
reactive sizing compound and the hydroxyl groups of the
cellulose. This may be performed by the heated cylinders
which provide also the pressure needed to impregnate the
paper web surface and thickness with the reactive sizing
compound.
The preferred synthetic reactive sizing compounds are
cyclic acid anhydrides of the general formula
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WO91/10776 PCT/GB91/~89
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where Rl is an organic hydrophobic group. More preferred
are the liquid cyclic acid anhydrides in which Rl is a
branched chain C8-C16 alkenyl group.
Typical examples of cellulose that may be treated with the
sizing compounds are derived from hardwoods and softwoods,
bleached or not bleached, semi-chemical, groundwood and
combinations thereof. Synthetic rayon or regenerated
cellulose fibres may also be used as well as waste paper
and cardboard.
The following examples illustrate the present invention in
which the content of all materials reported in the Examples
refers to weights on dr~v cellulose and the following
materials are used:
A) Bleached sulphate cellulose (60% hardwood, 40% softwood)
of freeness 35-SR and concentration 40 g per litre in tap
water (hardness 17 French degrees) is treated with 0.25 to
0.50% hydrated aluminium sulphate (alum) as a 100 g per litre
solution in tap water.
B) Cationized potato starch (Roquette Fr. HICA~ 180 brand),
of concentration around 5% in demineralized water, is cooked
at 85-90 C for 30 minutes and subsequently diluted about 5
times. Limited amounts of starch are cooked and normally
used within 12-24 hours from cooking to prevent ageing
effects.
.... .
C) Calcium carbonate (Craie Micronic O brand) is
` -pre-slurried in tap water at the concentration 350 g per
litre.
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WO91/lOM6 PCTtGB9l/~89
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D) Alkenyl succinic anhydride (Exxon Chemical Co. brand),
having a C12 branched side chain, and FIBRAN 76 (Roquette
Fr. brand), having a C16-18 side chain, are used as
sizing agents.
E) Alkyl Ketene dimer tAXD) of melting point 39-C as
measured by differential scanning calorimetry.
F) Polyacrylamide (Schimmer & Schwartz FO4550BPM brand),
dissolved in water at the concentration 0.038 %, is used as
flocculating retention aid.
G) Sodium polysilicate Na2Si3O7,.3H2O as a 42%wt
water solution is added without modifications. Colloidal
polymerized silica containing 0.3% Na20 as a 15% water
dispersion (EKA-KEMI Compozil BMA Brand) is added without
modification.
H) Diethylene triaminopertamethylene phosphonic acid
(Monsanto Dequest 2060 S) containing 0.1 wt% Na20 as a 20
wt% water solution. The product is believed to be of the
formula
~,,H03PCH2 CH2P03H
~N-cH2-cH2-N-cH2-cH2 N
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`., H03PCH2 CH2 CH2P03H
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In the Examples all concentrations refer to dry cellulose
unless otherwise stated.
COMPARATIVE EXAMPLE 1
An amount of the paper stock A previously treated with 0.25%
alum is fed to a 5 m3 feed tub and it is treated with 0.5~
cooked cationic potato starch B. The paper stock amount is
limited to about l hour of machine feed to prevent unwanted
ageing effects.
A piston metering pump connected to a spraying nozzle is used
to spray-mix neat FIBRAN 76 D into a stream of tap water at
40-50 C and the mixture is fed at the rate of 0.5m3 Ton~l
dry cellulose to the suction side of the pump feeding the
alum-treated paper stock to the paper machine. FIBRAN 76 is
fed at the rate of 0.25% to maximize foaming effects, if any.
... .
- The paper machine is constructed by SICMA, Terni, Italy. It
is fitted with a Fourdrinier net width 0.56m and a series of
22 steam-heated drying cylinders, running at the speed of 40
- m.min~l and producing about lOO kg paper per hour. The
~ grammage is kept at about 80-85 g.m2.
:,
25% calcium carbonate slurried in water is metered on-line
into the paper stock on the suction side of the fan pump The
paper stock pH after calcium car~onate addition is in the
range 7.2-7.6.
. .
0.038% polyacrylamide F is finally added to the paper stock
just before it enters the head box.
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-16-
COMPARATIVE EXAMPLE l Cont....
The paper web is dried in the machine drying section, whose
steam-heated cylinders are programmed to reach temperatures
in the range 50-llO 7 C, before being wound up.
The following paper machine parameters are observed at
equilibrium.
Head box paper stock concentration g.l-l 3.5
First pass retention all solids %94.3
First pass retention calcium carbonate % 80.5
Ashes at 425C % l9.7
Zeta potential white waters mV +l.l
Felt+wire/2 Cobb 60" (50% RH, 23 C) l9
Grammage g.m2 80
Severe foaming is observed in the white waters recycle and
white pitches formation. An average 830 dark spots per m2
; is counted in the paper produced making it totally unsuitable
for sale.
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Comparative Example l is repeated by using a branched chain
Cl2 alkenyl succinic anhydride D (EXXON CHEMICAL CO) as the
sizing agent.
The following paper machine parameters are observed at
equilibrium.
Head box paper stock concentration g.l-l 3.6
First pass retention all solids %92.7
First pass retention calcium carbonate % 75.7
Ashes at 425C ~ 16.4
Zeta potential white waters mV +2
Felt+Wire/2 Cobb 60" (50~ RH, 23C)21
Grammage g,m2 80
SUBSTITUTE SHEET
WO91/10776 PCT/GB91/~89
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-17-
Severe foaming is also observed and formation of white
pitches. An average 950 dark spots per m2 is counted in
the paper produced making it totally unsuitable for sale.
EXAMPLE 1
Comparative Example 2 is repeated in runs 1, 2, 3 and 4.
Sodium polysilicate G is metered on-line into the paper stock
on the suction side of the fan pump together with calcium
carbonate slurried in water. The paper stock pH after
addition is in the range 7.2 to 7.6.
Runs 3 and 4 were carried out with a paper stock pretreated
with 0.5% al~m and ~un 4 with 0.3% of the size to maximise
~oaming and white pitches, if any.
. .
J The following paper machine parameters are observed when
equilibrium is attained.
. .
3 Run No. _ 1 2 3 4
Sodium polysilicate % 0.08 0.160.080.08
Size % 0.25 0.250.250.30
Head box paper stock concentration g.l~l3.63.6 3.6 3.6
First pass retention all solids % - 95.0 - 96.6
First pass retention calcium carbonate % - 91.1 - 93.8
Ashes at 425 C % 22.4 21.6 22.5 22.0
Zeta potential white waters mV - +4.4 -+5.3
Felt+Wire/2 Cobb 60" (50~ RH, 23 C)21 21 19 20
-~ Grammage g.m2 80 80 80 80
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WO91/10776 PCT/GB91/~89
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Small amounts or no foam is produced and absence of white
pitches are observed in all runs. The presence of dark spots
in the paper produced averaged about 30-35 units per m2
indicated that the treatment with sodium polysilicate has
drastically decreased white pitches formation.
EXAMPLE 2
Comparative Example 2 is repeated in Runs 5, 6, 7, 8 and 10.
Run 9 is carried out with FIBRAN 76 as sizing agent for
comparison. In all cases, the size concentration is 0.25%.
; Sodium Polysilicate G or polyphosphonic acid H are metered
on-line into the paper stock on the suction side of the fan
pump together with calcium carbonate slurried in water. The
paper stock pH after addition is in the range 7.2 to 7.6.
Runs 6, 7, 8, 9 and 10 are carried out with decreasing amount
of polyacrylamide (from 0.038% as in Comparative Example 1 to
0.019 and 0.0~).
, .
- The following paper machine parameters are observed when
equilibrium is attained.
'''
Run No 5 _6 7 8 9 10
Sodium Polysilicate % 0.67 0.67 0.67 0.67 0.33 0.00
Polyphosphonic acid % 0.00 0.00 0.00 0.00 0.00 0.25
Polyacrylamide % 0.038 0.019 0.0 0.0 0.019 O.oO
Head box paper stock
conc. g,l-l 3.6 3.6 3.6 3.6 3.6 3.6
First pass retention
all solids % 97.9 92.9 88.8 89.7 91.7 90.2
First pass retention
Calcium carbonate % 95.9 83.6 75.4 76.3 88.3 79.8
Ashes at 425C % 22.3 21.8 21.7 21.8 22.0 21.6
Zeta potential white
waters +11.1 +1.1 - +0.7 - +0.6
Felt+Wire/2 Cobb 60"
(50% RH, 23C) 20 22 23 23 20 24
Grammage g.m2 80 80 80 80 80 80
SUBSTITUTE SHEET
WO9ltlO776 PCT/GB91/~89
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--19--
Small amounts or no foam is produced and absence of white pitches
are observed in all runs. The presence of dark spots in the
paper produced averaged about 25-30 units per m2 indicating
that the treatment with COMPOZIL or Dequest 2060 S has
drastically decreased white pitches formation. It is worth
mentioning that COMPOZIL alone without any polyacrylamide added
has shown a good flocculating action.
EXAMPLE 3
Example 2 is repeated in runs 11 and 12 by using respectively
branched chain C12 alkenyl succinic anhydride D (EXXON Chemical
Company) and mixture of 92.7% wt of the same with 7.3% wt alkyl
ketene dimer E as sizing agents both at the concentration of
0.15%.
. ,
In both runs, paper stock A is not previously treated with alum
and cationized potato starch B.
:
A piston metering pump, connected to a spraying nozzle, is used
to spray-mix neat C12 alkenyl anhydride D or its mixture with
alkyl ketene dimer E into a stream of cationized potato starch in
demineralized water at the concentration of 1.3~ at the rate of
0.38 m3.Ton~1 dry cellulose.
Sodium polysilicate G (COMPOZIL) is metered on-line into the
paper stock at the rate of 0.33 parts of commercial material per
100 parts of cellulose on the suction side of the fan pump
together with calcium carbonate slurried in water.
Finally, 0.25 parts of alum are metered into the paper stock just
before the head box and no polyacrylamide is added.
SUB~;TITUTE SHEET
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WO91/10776 PCT/GB91/~8
-20-
The following paper machine parameters are observed when
equilibrium is attained.
Run No. 11 12
Head box paper stock conc. g.l~1 3.6 3.6
First pass retention all solids % 96.5 97.1
First pass retention Ca carbonate % 83.8 88.3
Ashes at 425C % 21.5 22.8
Zeta potential white waters mV +1.9 +2.8
Felt+Wire/2 Cobb 60" (50% RH, 23~C) 19 17
Hercules Sizing Test 287 350
Grammage g,m2 80 80
.. . .
: .:
No foam is produced and no white pitches are observed in both
runs. Moreover, the presence of dark spots in the paper
produced is drastically reduced to 1-5 per lOm2.
'
:`~
~,
,,
.
SU~STITlJTE SHEET
