Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
/l0777 2 ~ a PCT/GB91/~91
PROCESS FOR SIZING PAPER AND SIMILAR PRO WCTS
This invention relates to a process and apparatus for sizing
paper or similar products, such as board, cardboard etc.,
based on cellulose or synthetic fibres. Particularly paper
produced under alkaline or neutral conditions using cyclic
acids anhydrides, especially alkyl or alkenyl succinic
anhydrides (ASA), alkyl ketene dimers (AKD), or their
mixtures as sizes.
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.
United Kingdom Patent 1492104 describes the use of
polyoxyalkylene alkyl or arylalkyl ethers, or the
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corresponding mono- and di-ester 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 siæed paper.
The sizing e~ulsion can be produced in-situ, within the
cellulose stock, or prior to 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 th~ negatively charged
surface of the cellulose fibres.
The use of nitrogen and/or oxygen containing emulsifiers to
produce emulsions of cyclic acid anhydride emulsions, in the
presence of cationic stabilizers, with a low shear energy
'~ input is generally carried out using a concentration of 2.0
to 10.0% emulsifier based on the anhydride. Concurrently,
typically 1 to 5 parts of cationic stabilizers are used for 1
part of anhydride.
,~ .
The emulsions obtained are chemically unstable in water. As
a consequence, emulsion particles with sub-micron diameters
are quickly hydrolysed. On the contrary, emulsions particles
of diameter above 3-4 microns, with too low surfacs-to-mass
ratios lack enough Coulombic attraction to be rapidly
deposited onto the cellulose and thus remain suspended in the
process water used in tXe paper making.
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Consequently, they are recycled continuously with the process
water and are eventually hydrolysed which not only wastes
sizing compounds, but causes paper machine running problems.
The emulsion-based sizing technology further produces poorly
sized paper due to re-wetting phenomena, caused by the
emulsifier, low sizing yields and foaming.
Re-wetting results from the presence of residual emulsifier
in the cyclic acid anhydride absorbed on the cellulose
fiber's surface. The emulsifier's polar groups, spread over
the surface of the anhydride particle, attract water to the
surface thus favouring the anhydride hydrolysis rather than
its reaction with the hydroxy groups in the cellulose.
Moreover, the presence of residual emulsifier on the finished
paper creates undesirable water affinity in the paper and the
consequent decrease of the hydrophobic character of the paper
produced by sizing. These difficulties are not eliminated by
reducing the emulsifier concentration to below 1.0% based on
the anhydride and by using high shear mixers in the presence
- of 1 to 5 parts of a cationic stabilizer for 1 part
anhydride. Even by using turbine-type mixers (rotating in
the range 10000 to 20000 RPM) it 1s difficult to control the
particle's diameter distribution both in the sub-micron and 3
to 4 micron ranges. The anhydride molecular weight and the
structure of its alkenyl chain have little influence on the
above behaviour.
High-shear emulsification techniques based on turbine pumps
with inlet-outlet pressure drops as high as 8 to 10 kg/cm2
are needed to obtain emulsion particle diameter distributions
for best sizing result. However, the high-shear produced
emulsions are characterized by poor stability and they tend
to phase out quickly.
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WO91t1n777 PCT/GB91/~91 !
Producing paper, with the use of cyclic acid anhydride
emulsions for sizing, requires some additional skills not
generally available to the paper industry and extra caution.
Also, operational costs are higher and foaming can cause
problems.
Foam, with its large air-liquid interface, favours
evaporation of the recycle liquids with the formation of
fatty deposits both on the paper and in the water recycle
tank. These can also cause paper machine running problems.
Thus, more frequent cleaning operations may be needed which
tend to disrupt the process and to increase the produrtion
costs. A further negative cost item is represented by the
use of the emulsion's cationic stabilizers.
A number of problems encountered by the paper industry when
using emulsions of cyclic acid anhydrides in sizing paper are
described in:
. .
1987 Sizing Short Course, April 8-10 1987, Atlanta, Ga.,
;~ TAPPI Press 1987.
:` .
1985 Alkaline Papermaking, April 17-19, 1985, Denver, CO.,
TAPPI Press 1985, ISSN 0738-1190.
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Thus, although sizing paper may be achieved by using
emulsified reactive synthetic products, the disadvantages ar~
sizing compound waste due to hydrolysis, poorly sized paper
due to re-wetting phenomena, low sizing yields, foaming,
fatty deposits formation in the water recycle tank and paper
machine running problems.
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In addition paper production processes based on sizing with
; emulsified products is less economic due to:
- the need for emulsifiers and emulsion stabilizers.
- a larger use of sizing compounds to compensate for the
lower sizing yields, resulting from the size's
hydrolysis, and the ensuing lower hydrophobic character
of the paper.
- the need for more frequent cleaning operations leading
to an increased number of process disruptions.
- the need for high-shear turbine pumps or static, high
pressure differential, static mixers .
It is the main purpose of this invention to reduce or
`; eliminate the technical and cost problems associated with the
paper sizing with emulsified sizing compounds especially
those based on cyclic acid anhydrides.
., .
An aim of this invention is to develop a method to interact
the sizing compounds with the cellulose stock in the absence
of an emulsifier which predetermines accurately and with
reproducibility the contact time and the sizing compound's
particle diameter as a function of other relevant process
parameters (for instance, type of cellulose, paper stock
degree of freeness, type of mineral charges, temperature of
the drying section, etc).
Another aim is to develop a method, to contact the synthetic
sizing compound with the cellulose stock which reduces
hydrolysis of the sizing compound during its residence period
in the process water.
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Yet another aim is to produce paper with an acceptable
hydrophobicity for writing and printing as indicated by the
standard tests developed for the paper industry such as the
Hercules Size Test and the Cobb Test.
It is also desirable that the method to contact the synthetic
sizing compound with the cellulose stock be readily adaptable
to existing plants producing paper, cardboard, etc.
In our European Application 89306178.8 we describe a process
or the production of paper, board, cardboard, etc., 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.
;'.
As this technology has been developed to commercial scale we
have found that the process may be improved if the size is
injected by means of a piston pump through one or more
nozzles immersed in the aqueous system. We also find that
the dispersion of the size is improved if it is preheated
` before injection into the cellulose stock/water slurry. As a
preferred feature of the invention the size is mixed into a
small amount of water prior to injection into the cellulose
stock/water slurry. This stream of water may contain
cationised starch and/or other cationizing agents such as
protiens, polamines as well as natural gums and synthetic
polyhydroxylated hydrocarbons.
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Accordingly the present invention provides a process to size
paper and similar products comprising:
- forming a cellulose water slurry;
- preheating a sizing product, either neat or in solution,
mixing the preheated sizing product with water and
injecting the mixture in droplet form into said
cellulose water slurry before, during or after the paper
web formation;
wherein the cellulose water slurry and/or the size is treated
with a cationizing compound.
- drying the paper web
The preferred temperature to which the size should be
preheated depends upon the nature of the size, where alkenyl
succinic anhydrides are used the temperature should be from
30 to 65 C preferably 35 to 50C, where alkyl ketene dimers
are used the temperature should be above their melting point,
generally above 40'C. We also prefer that the water into
which the preheated size is mixed be heated to a temperature
in the range 30-65 C.
When the slurry is cationized it is generally treated with
mineral charges after mixing with the size.
:; .
Further benefits of the use of the process of the invention
will become apparent in the detailed description of some
procedures neededLto implement it. Such procedures are
described to explain the invention and are not meant to be a
limitation thereof.
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According to the preferred procedure to implement the
invention, the reactive synthetic sizing compound mixed with
water 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
i sizing compound with the paper stock.
The sizing compound dispersion is conveniently obtained with
a spraying nozzle, which produces droplets in the water of
predetermined dimensions and a predetermined particle
diameter distribution. The spraying nozzle type and spraying
angle may change depending on the type of paper machine and
on the place, within the paper machine, where it will be
positioned for best result. The number of spraying nozzles
used may be chosen according to the type of paper machine and
the type of paper or paper product being manufactured.
' We have found that good dispersion of the size into the large- aqueous systems may be achieved by pumping the size with a
piston pump through one or more nozzles immersed in the
aqueous system.
;
Spray-mixing will then occur due to the large pressure
differential created at the nozzle tip between the size and
the paper stock. Such differential accelerates the
disintergration of the liquid jet, issuing at high speed from
the nozzle tip, into small spherical particles by impingement
on the surrounding fluid.
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The reactive synthetic sizing compound may be delivered to
the spraying nozzle through a pressurized piping system and
the spraying pressure can be generated with metering
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micro-pumps. Alternatively, the compound may be delivered to
the spraying nozzle from storage tanks which are pressurized
with an inert dry gas, and the compound can be metered with
calibrated microvalves.
The storage tanks, the piping system, the nozzles, the valves
and the metering micro-pumps can conveniently be thermostated
to maintain the size at the desired preheating temperature.
Convient thermostating may be achieved with water at the
selected temperature.
Thermostating controls the viscosity of the sizing compound and
produces droplets with predetermined diameters when exiting the
spraying nozzle. The viscosity control which is especially
useful when reactive sizing compounds which are solid or highly
viscous at room temperature, are used. For instance, this
could be the case with cyclic anhydrides substituted with
palmityl (or heavier) or linear rather than branched groups or
the use of alkyl ketene dimers.
In the preferred process the preheated size is injected into a
stream of water at substantially the same temperature as the
size shortly before the stream of water is itself injected into
the bulk cellulose stock. This water stream can also be used
to introduce other additives into the paper stock such as
defoamers, proteins, natural gums, synthetic polyhydroxylated
hydrocarbons, alum and cationic starch. Products to
micro-encapsulate the size and thus inhibit its hydrolysis may
also be included in the water.
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The sizing product pressurization in the storage tank can be
obtained, at or about room temperature, with dried gases such
as air, nitrogen, argon, methane, propane, butane,
chlorofluoro hydrocarbons, carbon dioxide, nitrogen
protoxide. Some of said gases are soluble in the reactive
sizing compounds at the storage temperature.
The absorption of the sizing compound droplets on the
cellulosic fibres is aided by the cationizing treatment. The
fibres may have undergone previous cationization either
on-line or in the paper stock preparation tubs.
Alternatively the size itself may be applied together with
the cationizing agent. 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.
The time of contact between the process water and the
reactive synthetic sizing compound in dispersed droplet form
is very small, depending on the turbulence of the machine
wet-end and on the cationizing treatment. These factors can
be varied to obtain the desired deposition rates of the size
droplets on the fibres.
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.
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Moreover, by lowering the droplets diameter the interactions
with the cellulose fibres and the sizing compound absorption
can be improved thus increasing the sizing yield to a level
beyond that achieved with the current emulsion technology.
In another procedure to implement this invention, 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.
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The nozzle(s), or any similar device, connected with a
prsssurized piping system to the storage tank containing the
sizing compound solution, may be used to disperse the sizing
compound solutions into the cellulose-water slurry.
Preferably the injection system is controlled by the rate of
paper production and consists of a preheated vessel which
feeds a low pressure feed pump which itself feeds, preferably
through a filter, a metering pump which is conventiently a 4
.~,
- to 6 cylinder metering pump operating at pressures in the
range 50 to 300 atmospheres, preferably 120 to 200
atmospheres, the pump being controlled by a signal from the
paper stock flow to maintain constant the ratio of size to
- stock.
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The pump injects the size through one or more nozzles into
the water stream and hence into the stock at the determined
` rate to give appropriate sizing. Any gas evaporates or it is
dissolved by the process water, favouring the droplets
dispersion without affecting in any other way the paper
production process.
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Another important function of the dissolved gas is to protect
the surface of the droplets from water's hydrolytic action,
and to produce in-situ a fresh surface on the droplets as the
gas evaporates or dissolves into the process water.
A range of gas sizing compound mixtures may be used, the
preferred composition 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 l to l9~. The sizing compound gas solutions could
also be obtained by previously mixing gas types with low and
high solubility into the 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.
As a further embodiment inert gases may be dissolved in the
aprotic solvent, as previously specified (for example carbon
dioxide).
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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 concentrations 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 l to
19% may be preferred to concentrations in the range 20 to 50%
or higher, use of these lower concentrations will also avoid
; solvent accumulation in the water recycle system.
In another preferred procedure to implement the invention,
the reactive sizing compound is dissolved in an anhydrous,
protic, water soluble compound immediately before being
sprayed and transformed in 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.
0.005 to 2.0% weight of size on dry fibres is preferably
` used. Subsequent~to application of the size, the paper web
is dried by heating to temperatures in the range 90 to 120-C
which also promotes the reaction between the reactive sizing
compound and the hydroxyl groups of the cellulose.
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This may be performed by the heated cylinders which provide
also the pressure needed to impregnate the paper web with the
reactive sizing compound.
According to an alternative procedure to implement the
invention, the synthetic sizing compound is sprayed onto the
formed paperweb with one or more nozzles having small
spraying angles. They could spray in the direction of one
side of the paperweb, or in the opposite side or on both
sides simultaneously.
With this technique, the spraying can be extended to the
whole surface of the paperweb or can be limited to some parts
of the surface, either when still wet or in a size press, or
in both positions.
When spraying in a size press, the final drying cylinders
used to dry the paper should exert enough pressure and reach
a temperature high enough to ensure both the impregnation by
the sizing compound of the paper wet thickness and the
reaction with the hydroxyl groups of the cellulose.
When the sizing compound is applied in the size press, its
concentration could reach values above 2% weight on dry
fibres. Higher concentrations are possible with consequences
on the cost.
A certain period of time will be required to achieve such
reaction when the sizing compound concentration is in the
higher ranges.
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The preferred synthetic reactive sizing compounds are cyclic
acid anhydrides of the general formula
Rl -- C - C; O
O
C - C = O
where R1 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
combination thereof. Synthetic rayon or regenerated
cellulose fibres may also be used as well as waste paper and
cardboard.
The present invention may be applied to any sizing material
examples of which include acyl halides, cyclic acid
anhydrides, alkyl ketene dimers, isocyanates, alkyl amino
chlorides, urea derivatives, carbonic acid chlorides,
chlorosulphonic and chlorophosphoric acid amides such as
those described in the 1987 Sizing Short Course Reference
mentioned above (page 4).
Alternatively mixtures of sizing materials may be used .
Where the materials are solids at room temprature, such as
alkyl ketene dimers, it may be necessary to apply them as
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solutions or in the molten state, or as mixtures with other
sizing compounds in which case the preheating temperature
should be such that the product is either molten or in its
liquid state.
An injection system which also forms part of the present
invention is illustrated schematically in Fiqure l which
shows the size being fed from storage to a preheater A from
which it is fed to a low pressure pump B through filter C to
the metering pump D which forces the size through the
injector nozzle E into a pipe F through which a water stream
flows into the main Cellulose stock G.
The operation of the low pressure pump is preferably
controlled by the rate of paper production as is the
operation of the metering pump to control the ratio of size
that is applied to the stock.
A more detailed and preferred embodiment of the invention is
illustrated by reference to Figure 2. The size is injected
through a spray-mixing device which comprises a four barrel
pump, l connected to the axle of a variable speed electric
motor, 2 with camshaft 5. Pump 1 can comprise any number of
barrels depending on the application. Low pressure pump 3 is
connected by camshaft 6 to pump l and through filter 4 by
pipes 7 and 8 to pipe ll-. It feeds liquids or melts,
filtered from solid impurities, to the l suction side of pump
l. Pump 3 is connected by pipe ll to tank 13 where the size
is stored. The pump's barrels are connected with pipes 20,
21, 22, 23 to pressure relezse safety valves 24, 25, 26 and
'27.
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Pump 1 delivers the size under pressure to nozzles 40, 41,
42, 43 with pipes 28, 29, 30, 31. The nozzles are fixed on
pipe 44 with nozzle holders 36, 37, 28 and 39.
The device is operated in the following way. Tank 13 is
filled through pipe 14 with the liquid to be mixed to water
and watery fluids flowing in pipe 44. Valve 15 is then
closed. Tank 13 i9 connected with pipe 16 to tank 17
containing silica gel, molecular sieves and similar air
drying agents. Tank 17 is connected to the atmosphere when
valve 18 is open.
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Opening valve 12 on pipe 11 thus connecting tank 13 to pistonpump 1 through low pressure pump 3, pipe 7, filter 4 and pipe
8, lets the size flow into the pump's barrels. Closing
valves 32, 33, 34, 35, hand-rotating camshaft 5 and opening
pressure release safety valves 24, 25, 26, 27 facilitates
filling the barrels.
Starting-up electric motor 2, opening valves 32, 33, 34, 35
and closing safety valves 24, 25, 26 and 27 initiate metering
and spray-mixing the size into pipe 44 (containing water or
watery fluids flowing therein) through nozzles 40, 41, 42, 43
fixed on pipe 44 with nozzles 36, 37, 38, 39, 40. We have
found that pintle nozzles such as those used for the
injection of diesel fuel into diesel motors are particularly
useful.
. .
Safety release valves 24, 25, 26, and 27 connected to the
pump's barrels with pipes 20, 21, 22, 23 and to nozzles 40,
41, 42,-43 with pipes 28, 29, 30, 31, will open when the
pressure in the system will increase above a safe set value.
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In the preferred embodiment of the invention, the size is
spray-mixed into flowing water or watery liquids in pipes,
simi}ar to 44, to which the nozzles are fized in any
preferred position (for instances~ all nozzles in a row along
the pipe length or spaced around the pipe diameter with
preferred angles etc). The number of nozzles to be utilized
is at will depending upon the volumes of liquid to be
spray-mixed, the number of barrels of the pump used and the
number of pumps.
In the preferred embodiment of the invention, pumps 1 and 3,
filter 4, valves 12, 24, 25, 26, 27, 32, 33, 34, 35, tank 13,
pipes 8, 11, 20, 21, 22, 23, 28, 29, 30, 31 and nozzles 40,
41, 42, 43 are electrically heated to change the temperature
and thermostating of the liquids contained in them. A
temperature higher than ambient temperature may have
beneficial effects on pumping and spray-mixing especially
during winter operations or if strong mixing is performed
with substances melting at temperatures in the range 20 to
100 C .
In the preferred embodiment of the invention, tank 13 may be
weighed continously to record the flow and to accurately
meter the size.
The spray mix device can be constructed with low carbon
steel, stainless steel or with other materials depending on
the type of fluid being spray mixed. While pipes 20, 21, 22,
23, 28, 29, 30, 31 and valves 24, 25, 26, 27, 32, 33, 34, 35
need to resist to pressures in excess of 200 kg/cm2, pipes
11, 7, 8 and filter 4 need to resist to only 3-10 kg/cm2.
.. .
In the preferred embodiment of the invention, the speed of
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electric motor 2 is varied by means of an electronic
connection to the circuitry of the pump which generates the
flow of water or watery fluids in pipe 44. With this
arrangement, positive or negative flow variations in pipe 44
will automatically modify pump 1 outputs.
The device previously described has been used to meter and
spray-mix, at pressures in the range 100 to 250 kg/cm2,
C12 and C16_18 alkenyl succinic anhydrides (ASA) into
paper pulp during paper making operations. Paper pulp to ASA
ratios in the range 40,000 to 100,000 have been successfully
demonstrated with a spray-mix pressure of 200 kg/cm2 and
with the production of Gaussian ASA dispersions having
particle diameters centered around 1-2 microns.
The quality of the paper produced during such industrial runs
indicated that its hydrophobic character, as determined by
Cobb and ink penetration sizing tests, has been constant and
in the range of accepted industrial and commercial standards.
The present invention is ~urther illustrated by the following
Examples in which the content of all materials refers to
weights on dry cellulose. The following materials are used:
A) Bleached sulphate cellulose (60% hardwood, 40% softwood)
of freeness 35-SR and concentration 40g/litre in tap water
(hardness 17 French degrees) is treated with 0 to 0.5%
hydrated aluminium sulphate (alum) as a lOOg/litre solution
in tap water.
B) Cationized potato starch (Roquette Fr. HICAT 180 brand),
of concentration around 5% in demineralizewd water is cooked
at 85-90C for 30 minutes and subsequently diluted
approximately 5 times. The starch is normally used within
12-24 hours from cooking to prevent unwanted ageing.
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WO91/10777 2 r~ 3 PCT/GB91/~91 ~i
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C) Calcium Carbonate (Craie Micronic O brand) is
pre-slurried in tap water at the concentration 350 g/litre.
D) Alkenyl succinic anhydride (EXXON CHEMICAL CO), having a
C12 branched side chain, and FIBRAN 76 (Roquette Fr.
brand), having a C16-l8 side chain, are used as sizing
agents.
E) Polyacrylamide (Schimmer & Schwartz FO4550BPM brand),
dissolved in water at the concentration 0.038 ~, is used as
flocculating retention aid.
F) 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.
G) Diethylene tetra amino pentamethylene phosphonic acid
(MONSANTO DEQUEST 2060S) containing 0.1% Na20 as a 20%
water solution.
EXAMPLE 1
An amount of a 0.25% alum-treated paper stock from bleached
sulphate cellulose (60% hardwood, 40% softwood~, is fed to a
5 m3 feed tub and it is treated with 0.5% cooked cationic
potato starch. The paper stock amount is limited to about 1
hour of machine feed to prevent unwanted ageing.
A piston metering pump connected to a spraying nozzle is used
` to spray-mix neat branched chain C12 alkenyl succinic
anhydride D preheated to 35 C into a stream of tap water at
40-50-C and the mixture is fed at the rate of
0.5m3.Ton1
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to the suction side of the pump feeding the alum-treated
paper stock to the paper machine.
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 lO0 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 carbonate addition is in the
range 7.2-7.6.
0.038~ polyacrylamide E is finally added to the paper stock
just before it enters the head box.
Sodium polysilicate F is metered on-line into the paperstock
on the suction side of the fan pump together with calcium
carbonate slurried in water. The paperstock pH after
addition is in the range 7.2 to 7.6.
Runs 3 and 4 were carried out with a paperstock pretreated
with 0.5% alum and Run 4 with 0.3% sizing agent
concentration.
The following paper machine parameters are observed when
equilibrium is attained.
-. .
- Run No. l 2 3 4
Sodiu~ polysilicate % 0.08 0.16 0.08 0.08
Size% 0.25 0.25 0.25 0.30
Head box paper stock
concentration g.l-l 3.6 3.6 3.6 3.6
First pass retention
all solids % - 95.0 - 96.6
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Run No. 1 2 3 4
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
The paper web is dried in the machine drying section, whose
steam-heated cylinders are programmed to reach temperatures
in the range 50-110C, before being wound up.
The Cobb 60" results show that the paper is properly sized
and has a commercially acceptable hydrophobicity for writing
and printing.
EXAMPLE 2
Example 1 is repeated in Runs 5, 6, 7 and 8. Run 9 is
carried out with FIBRAN 76 as sizing agent. In all cases,
the size concentration is 0.25%.
The Sodium polysilicate F is metered on-line into the
paperstock on the suction side of the fan pump together with
calcium carbonate slurried in water. The paperstock pH after
addition is in the rangé 7.2 to 7.6. Runs 5 to 8 are carried
out with decreasing amounts of polyacrylamide (from 0.038%
as in Example 1 to 0.019 and 0.0%).
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The following paper machine parameters are observed whenequilibrium is attained.
Run No. 5 6 7 8 9
SODIUM POLYSILICATE % O.67 0.67 0.67 0.67 0.33
Polyacrylamide % 0.038 0.019 0.0 0.0 0.019
Head box paper stock
concentration g.l-l 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
First pass retention
calcium carbonate % 95.9 83.6 75.4 76.3 88.3
Ashes at 425C % 22.3 21.8 21.7 21.8 22.0
Zeta potential white waters +11.1 +1.1 - +0.7
Felt+Wire/2 Cobb 60"
(SO% RH, 23C) 20 22 23 23 20
" Grammage g.m2 80 80 80 80 80
Here again the Cobb 60" shows that the paper is properly sized and
has a commercially acceptable hydrophobicity for writing and
printing.
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