Note: Descriptions are shown in the official language in which they were submitted.
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Field of the Invention
The present invention relates to a process for
producing starch pastes intended in particular for the
manufacture of corrugated paper and cardboard. The
invention also includes a system for the automatic and
continuous implementation of the above process.
Background of the Invention
.
At the present time starch-based pastes, in
particular those intended for the production of corrugated
paper, are generally prepaxed by the following processes:
1) Stein-Hall process, the oldest and most com-
mon process, according to which some of the starch in
aqueous suspension is gelatinized at a high temperature in
the presence of an alkaline agent, generally caustic soda,
and constitutes a primary paste acting as a support or
"carrier" for further starch added to the mixture as a
powder or in the form of an aqueous suspension. The caus-
tic soda is added only to the carrier portion or together
with the carrier portion and the crude starch portion,
which should then be in the form of a "milk", but in both
cases the total amount of caustic soda should be such that
it does not produce any swelling of the crude starch in
the final paste, which would indicate instability. After
the carrier portion has been boiled it is at a fairly high
temperature, generally above 60C, and it is necessary to
reduce this temperature to a maximum value of 45C before
adding the crude starch if one is to avoid the risk of
; swelling the latter. This objective is achieved in prac-
tice by adding cold water to the primary paste.
It is thus necessary in the whole preparation
procedure to keep a sufficient amount of cold water for
this operation, which means that the primary paste of the
carrier is relatively highly concentrated before dilution,
113~
that is to say contains of the order of 10% of starch, and
is consequently very viscous. This high viscosity is a
serious drawback as regards the design of an automatic and
continuous boiling apparatus.
2) The so-called "no carrier" process, according
to which all the starch is partially swelled under the
action of the alkaline conditions and temperature. The
degree of gelatinization o~ the starch is monitored by
measuring the viscosity, and the reaction is stopped at
the desired point by adding an acidic compound, for example
aluminium sulphate. A process of this type is difficult to
adapt to continuous production.
3) Cold processes are known which use a complete
mixture containing crude starch~ pre-gelatinized starch and
chemical additives. The paste is obtained by simply dis-
persing the pre-gelatinized starch powder in water to form
the carrier. The process can be adapted to automatic and
continuous production, but there is the disadvantage of
the high cost of the pre-gelatinized starch and mixtures,
and the lack of flexibility in the choice of paste formula-
tions.
4) The so~called "Cold Burst" process, according
to which a modified or unmodified starch in granular form
is gelatinized in an aqueous medium by an alkaline agent,
- generally caustic soda, and not by raising the temperature.
This process has a certain number of advantages, including
the fact that boiling at high temperatures or the need for
costly pre-gelatinized starch are avoided, and the length
of preparation of the paste is reduced and the temperature
monitoring procedures are simplified, and consequently the
labour costs are reduced.
This last method of preparation appears to be
most capable of implementation by means of an automatic
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and continuous arrangement, since the primary paste or
carrier does not have to be cooled and may be prepared in
a relatively low concentration, namely of the order of 5%
of starch, and thus forms a not very viscous solution that
can easily be poured.
However, the cold process when carried out using
natural starches has serious disadvantages, which include
a lack of stability of the pastes under the action of shear
forces that inevitably arise in a production unit for cor-
rugated paper, when the paste circulates between thepasting machine and the paste reservoir under the action
of circulation pumps; the modification of the paste is
further accentuated by the rise in temperature, to 35-38C,
when the paste passes over the pasting rollers. The result
is a fall in viscosity of the paste and consequently a
change in the thickness of the paste film deposited on the
cardboard, or an imperfect pasting of the latter.
In order to obviate this defect it is not suffi-
cient to subject the paste or even the carrier portion, the
most sensitive part of the paste, after gelatinization in a
conventional alkaline medium, to a mechanical action, even
to a very intensive mechanical action, such as can be
obtained with a powerful stirrer in an enclosure having
the smallest volume compatible with the desired flow rate,
and instead it is necessary to employ a starch whose resis-
tance has been strengthened by a structural modification,
namely either a fluidification or a cross-linking produced
by a polyfunctional compound such as epichlorhydrin, phos-
phorus oxychloride, sodium -trimetaphosphate, etc., this
cross-linking being able to be produced in situ by employing
the alkaline medium which catalyses the reaction. The use
of a modified starch however results in a large increase in
` the cost of the paste.
, .
113~Q~i
It is known, moreover, that starch pastes may
contain a certain proportion of borax, in particular when
used to manufacture corrugated paper.
The present invention is thus directed to a
process for producing starch paste which obviates the
aforementioned disadvantages while providing a product
having the desired properties and which can be produced
economically and continuously.
- Summar~
This invention relates to a process for the con-
tinuous production of starch corrugating pastes which
comprises the steps of:
a) slurrying natural or non-gelatinized starch
in water to provide a starch suspensioni
b) continuously gelatinizing a first portion
of said starch suspension by contacting with excess alka-
line agenti
c) continuously mixing the gelatinized first
starch portion with a second portion of said starch suspen-
sion; and
d) continuously neutralizing a portion of theexcess alkali present in the gelatinized starch with boric
acid.
The process according to the invention, which is
of the type comprising the stage of producing cold a pri-
mary paste from a gelatinized starch in the presence of an
alkaline agent, is essentially characterized by the fact
that the primary paste is produced from a first portion of
an aqueous starch suspension which is subjected to the
action of an alkaline agent in excess, that the primary
paste is mixed with a second portion of the said suspension,
and that at least part of the alkaline agent present in
excess is neutralized by means of boric acid.
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According to other characteristic features, the
contact time between the gelatinized starch and the second
portion of starch suspension is prolonged, and the final
paste obtained may be diluted and completely neutralized
as desired.
Advantageously the process starts from water
heated to a temperature between about 38 and 42C and a
concentrated solution of alkaline agent is prepared, the
hot water being used both for diluting the solution of
alkaline agent to the desired concentration, for preparing
the starch suspension, and, if necessary, for diluting the
final paste.
In order to implement the above process, the
system according to this invention comprises a reservoir
of water heated to a constant regulable temperature, an
assembly of three metering pumps for producing the primary
paste from a first portion of aqueous starch suspension, a
first pump connected to the outlet of a reservoir of con-
centrated alkaline agent, a second pump connected to the
water reservoir, a third pump connected to the outlet of a
tank for preparing the aqueous starch suspension, situated
. .
opposite a feed hopper, the outlet of the three metering
pumps being connected to a means for bringing the consti-
tuents of the primary paste in contact with one another,
a fourth pump connected to the said tank and whose outlet
is connected to a mixer for the primary paste and the second
portion of aqueous suspension, the outlet of the said mixer
being itself connected to a storage tank provided with a
boric acid metering device and whose outlet is connected
to at least one final paste vat provided wi-th level probes
connected to the control means for the outlet of the four
metering pumps.
According to other characteristic features, the
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assemblies of metering pumps are prcvided with three-way
valves for returning the flow to the respective reservoirs;
the mixers are preferably of the static type; the reser-
voirs and tanks are provided with constant level control
means; the assembly of the liquid circulation means are
controlled automatically by means of level probes placed
in the final paste vats.
Other characteristic features and advantages of
the present invention will be more readily understood on
reading the following description, in conjunction with the
attached drawing which diagrammatically represents the
plant and illustrates the process according to the inven-
tion.
Description of Preferred Embodiments
In accordance with the invention, the primary
paste or carrier is made from a natural starch, gelatinized
in the presence of an amount of caustic soda or other al-
kaline agent in excess with respect to the amount contained
in a normal paste for corrugated paper or cardboard. The
excess caustic soda is then neutralized and this operation
is profitably employed to reform borax, which is always
present in this type of paste, from the boric acid added
during the mixing or immediately after the mixing of the
gelatinized starch and crude starch. The amount of borax
may be modified as desired as a function of the excess
caustic soda. Under these conditions, during the course
of the gelatinization of the carrier portion in a static
mixer and in the storage enclosure connected thereafter,
the starch is sufficiently degraded to reach the resistance
point, which enables it to retain a stable viscosity during
the various actions to which the paste is subjected.
The water reservoir preferably is kept at a con-
stant temperature of the order of 38C to 42C, and is used:
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- on the one hand to prepare, in a feed vat, an
aqueous starch suspension of constant concentration pre-
ferably fixed at a value of 30 to 436 of dry matter which
can be regulated as desired within this range;
- on the other hand to dilute caustic soda to a
preferred concentration of about 400 g/litre to a concen-
tration of about 10 g to 20 g/litre.
The assemblies of metering pumps consist of a
four-head metering pump which ensures a perfect synchroni-
zation and enables a constant relationship between theflow rates of the various constituents of the paste to be
maintained, or, by way of variation, consists of an assembly
of four variable flow metering pumps operating continuously,
the liquids being recycled automatically outside the pro-
duction. The following simultaneous operations may accord-
ingly be realized:
1) Metering of the solution of concentrated
caustic soda;
2) Metering of the water of dilution for the
caustic soda, the mixing being effected in a pipe arrange-
ment by means of a T or, better, by means of a static mixer;
3) Metering of the amount of starch suspension
necessary to produce the carrier part or primary paste;
4) Metering of the amount of starch suspension
necessary to form the crude starch part of the paste. This
secondary starch suspension is mixed with the carrier paste
in a second static mixer; homogenization is completed by
passing the suspension through a pump connected in series
and operating in counter-current, as will be explained in
detail hereinafter.
The flow rate of the secondary starch suspension
to the static mixer is controlled by a probe located in the
outlet of the storage vessel in which the gelatinization of
~3~05
the primary starch takes place; the supply of crude starch
may also be effected by means of a timing system.
The final mixture of primary starch and secondary
starch is then passed to a storage vat where it remains for
a specific duration determined by means of an overflow level
device.
The storage tank located at the end of the circuit
results in a good homogenization of the paste and brings it
to its final equilibrium state. A11 the desired additives,
for example resins intended to make the paste resistant to
moisture, can easily be added to this tank.
With reference to the accompanying drawing, the
starch is distributed from a hopper or silo 1 and, via a
volumetric metering device 2, to the starch milk prepara
tion vat 3. This vat is provided with a high speed stirrer
4 and is connected via a line 5 to the water reservoir 6
maintained at the desired temperature by means of, for
example, a steam coil 7. The vat 3 constitutes the device
for preparing the starch milk, and i5 able to deliver con-
tinuously an aqueous suspension within a wide range of con-
stant and regulable concentration, of the order of 30 to
43~ by weight of dry matter.
The water reservoir 6 provides depending on
requirements, and via automatic stopcocks (not shown),
water at a fixed chosen temperature, generally of the or-
der of 38 to 42C, using a thermostatic regulation of the
heating by means of the steam coil 7. The temperature of
the water is adjusted so as to obtain a final mixture which
arrives at a temperature of about 38C at the storage tank
8.
A reservoir 9 for caustic soda having a concen-
tration of about 400 g/l is connected via a line 10 to a
meteri.ng pump Pl, forming part of an assemhly Pl, P2, P3,
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~136~305
P4, described hereinafter.
This assembly may consist of a single four-head
metering pump or of four metering pumps each driven by a
variable transmission motor, having the general reference
numeral 11, and it enables the flow rate for each liquid
to be chosen within a defined range, the flow rate being
read on a flow meter in a manner known per se. The pumps
operate continuously, and the liquids are recycled, outside
production, to their respective vats or reservoirs by a set
of automatic three-way valves, namely the valve 12 con-
nected to the concentrated caustic soda reservoir 9 via the
line 13, the valve 14 connected to the water reservoir 6
via the line 15, and the valves 16 and 17 connected to the
vat 3 via the lines 18 and 19 respectively.
The inlet of the pump P2 is connected to the out-
let 20 of the water reservoir 6 via the line 21, and the
inlets of the pumps P3 and P4 are connected to the outlet
of the vat 3 via the line 22.
The pumps Pl and P2 inject their liquid flows
through the lines 23 and 24 respectively to a first point
A, and then the pump P3 injects a first portion of starch
suspension through the line 25 to a second point B up-
stream of a first static mixer 26 intended to homogenize
the various constituents and gelatinize the starch. This
gelatinization is prolonged and completed by contact with
a coil 27 connected to the outlet of the static mixer 26
via a line 28 whose dimensions are such that the storage
time is at least one minute.
The pump P4 injects the second portion of starch
suspension into the primary paste at a third point C, via
the line 29, just upstream of a second static mixer 30,
and at the outlet of the coil 27~ The simultaneous arrival
of the two flows at the point C is regulated by a probe
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(not shown) located at the outlet of the coil 27 or, more
simply, by a suitable timing device. The static mixer 30
homogenizes the primary paste/crude starch mixture, this
homogenization being completed for example by an in-line
pump 31 operating in a counter-current manner.
The final mixture flows via the line 32 from the
outlet of the pump 31 to the storage tank of vat 8 provided
with an efficient stirrer 33. This vat 8 is furthermore
provided with an automatic volumetric metering device 34
for metering the boric acid in the desired amount, as well
as with an overflow level device 35 intended to allow the
paste to remain in the vat 8 for 30 to 40 minutes, while
being stirred, before the paste is distributed.
To this end the outlet of the vat 8 is connected
via a line 36 containing a suitable circulation pump 37 to
at least two storage vats 38 and 39. These vats are fed
with fresh paste under instructions from a probe S situated
at a low level and which initiates the production procedure,
a three-way valve 40 arranged in the line 36 directing the
distribution by a rocking or tilting action to the required
position.
Advantageously, and particularly in the case
where the starch paste is produced for corrugated paper,
the vat 38 receives directly the final starch, which has
the characteristics of so-called "double face" paste. The
vat 39 may be allocated for the so-called "simple face"
paste and, in this case, its feed inlet 41 is connected to
the valve 40 via a line 42 comprising an inlet 43 for water
of dilution, which may be connected to the reservoir 6 and,
if necessary, an inlet 44 for the addition of an acid such
as hydrochloric acid, these additives being mixed by means
of a third static mixer 45 whose outlet forms the feed 41
for the vat 39, the hydrochloric acid being contained in a
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~t~80S
vat 46.
Suitable probes 47 and 48 placed at a high level
in the vats 38 and 39 respectively are intended to stop
the distribution and interrupt the whole production cycle,
the assembly of pumps Pl to P4 then being in the recycling
position via the valves 12, 14, 16 and 17, until produc-
tion is restarted by one of the low level probes S~
The following examples, which are given by way
of illustration and are in no way meant to be limiting,
will provide a better understanding of the scope and value
of the invention. In these examples all the percentages
are given by weight unless otherwise indicated.
Example 1
Preparation of a paste for corrugated paper, having a
starch_concentration of 20%
This test is carried out using a natural maize
starch containing 12.5% moisture. The temperature of the
water in the reservoir is maintained at 40C and the starch
milk is prepared in a concentration of 40% of commercial
starch, i.e. 35% of dry matter.
The afore-described system is used, in conjunc-
tion with the following regulation of the pumps:
The pump Pl delivers a solution of caustic soda
in a concentration of 420 g/litre at a rate of 36 litres/
hour.
The pump P2 delivers water from the reservoir at
a rate of 1200 litres/hour.
The pump P3 feeds the circuit with starch milk
for the formation of the carrier, at a rate of 140 litres/
hour.
The pump P4 provides the crude starch or secon-
dary starch at a rate of 940 litres/hour.
The boric acid is fed to the paste arriving at
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V5
the storage tank at a rate of 5 kg/hour.
The characteristics of the components employed
are as follows:
Concentration of dry matter in the starch of
the carrier paste= 4.05%;
Ratio of carrier starch to total starch = 13%;
Concentration of the caustic soda after dilution
= 12.2 grams/litre.
The flow rate of final, undiluted paste is 2320
litres/hour and the characteristics of this paste on arri-
val at the storage vat for the double face paste are as
follows:
Concentration of starch = 20.1%
Temperature = 38C
Stein-Hall viscosity at 35C = 50 s
Brookfield viscosity at 35C
(20 revs./min.) = 3000 mPas
Alkalinity in % NaOH/starch = 2.70
Borax as % Na2B407, 10 H2O/starch = 1-5
Stability of the paste: no notable change in
viscosity at 35C after shear forces produced by a turbine
blade rotating at 600 revs./minute for 4 hours. On
settling at ambient temperature for 96 hours, the Stein-
Hall viscosity normally increases to a value of the order
of 70 s, but re-adopts its initial value after stirring
and adjusting the temperature to 35C.
Gelatinization temperature of the paste = 58C.
The simple face paste is obtained by dilution
wi~h cold water at a flow rate of 280 litres of water per
0 hour, and has the following characteristics:
Flow rate = 2600 litres/hour
Concentration of starch = 18%
Temperature = 35~C
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Stein-Hall viscosity at 35C = 36 s
~ alkalinity/starch = 2.7
Borax in % Na2B4O7, 10 H2O/starCh = 1.5
Gelatinization temperature = 60C
Stability of the paste: same remarks as
for the double face paste.
Example 2
-
Pre~aration of a paste for corrugated paper, having a
starch concentration of 25%
The test is carried out as previously, using
natural maize starch containing 12.5% moisture.
The temperature of the water in the reservoir is
maintained at 39C and the starch milk is prepared having
a concentration of 40% of commercial starch, i.e. 35% of
dry matter.
The pump Pl delivers a solution of caustic soda
in a concentration of 415 g/litre, at a rate of 43 litres/
hour.
The pump P2 delivers water at a rate of 940
litres/hour.
The pump P3 feeds starch milk for the carrier at
a rate of 156 litres/hour.
The pump P4 feeds crude starch milk at a rate of
1260 litres/hour.
The boric acid is added to the storage tank at a
rate of 6.55 kg/hour.
Concentration of dry starch matter in the carrier
paste = 5.4%.
Ratio of carrier starch/total starch = 11%
Concentration of caustic soda after dilution =
18.16 g/l
The flow rate of undiluted final paste is 2400 l/h
Characteristics of the double face paste:
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~13ti~5
Starch concentration = 25%
Temperature = 38C
Stein-Hall viscosity at 35C = 52 s
Alkalinity in % NaOH/starch = 2.4
sorax in % Na2B407, 10 H2O/starch = 1-5
Gelatinization temperature of the paste = 58C
Stability of the paste: no notable change in
the viscosity at 35C after the action of shear forces
produced for 4 hours or after settling at ambient tempera-
ture for 2 to 4 days.
Simple face paste: obtained by dilution with
cold water at a rate of 290 litres/hour and by adding hy-
drochloric acid, density 1.16 (content of pure acid equal
to 370 g/l) at a flow rate of 6.46 litres/hour.
The characteristics of this simple face paste
are as follows:
Flow rate = 2690 litres/hour
Starch concentration = 22.5%
Temperature = 34C
Stein-Hall viscosity at 35C = 33 5
% alkalinity/starch = 2.0%
Borax in % Na2B407, 10 H20/starch = 1.5
Gelatinization temperature = 64C
Stability of the paste: identical to that of
the double face paste during exposure to shear forces at
35C, and is even improved as regards the viscosity
behaviour when the paste is allowed to settle at ambient
temperature.
The process and plant according to the invention
provide a really continuous and automatic production of
starch pastes, and permit a considerable reduction in the
storage capacity.
The plant is simple and reliable, and the constant
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1~3~i8~S
relationship between the flow rates of the various consti-
tuents of the paste ensures a constancy of the characteris-
tics of the pastes obtained from a given starch. It is not
necessary to subject the operation of the plant to control
by a device comprising a viscosimeter.
The various operating parameters can be regulated
precisely and rapidly.
The gelatinization of the carrier in the cold
constitutes an economy in the use of steam and requires
only expanded steam to maintain the water at a temperature
of about 40C. It also enables a carrier with a low starch
concentration and which is thus not very viscous and can
flow easily, to be obtained.
The system according to the invention is highly
flexible in operation, and is capable of producing pastes
having regulable starch concentrations of between 18 and
30% by varying the alkalinity as desired. The hydrochloric
acid neutralization device enables the alkalinity of the
simple face paste to be adjusted independently of that of
the double face paste.
The replacement of borax by boric acid also has
several advantages, and represents a device for increasing
_ _ _ . , _ _ . . . . . . . .. . . _
~L~3~i~05
the de~ree of degradation of the c2rrier starch in orcer to
reach its resistan_e poin~, by using an amount of âdditioncl
caustic sodc e~uivalent to the caustic SOdâ necessary to
reform the borax. It is easier to meter dry th~n borax,
~ince the flow behaviour of the powder is better and, above
allJ it dissolves more rapidly in the st2rch paste.
The storage tank located at the end of the cir-
cuit enables the paste to be well homogenised and brings the
latter to its final equilibrium state. All the desirable
additives, for example resins intended to make the p2ste
resistant to moisture, can easily be added to this tank.,
~s regards the properties of the paste, the pro- --
cess accordirg to the invention enables the followinG fe~-
tures in particular to be obtained:
- a constant viscosity at the desired level;
- a good stability with regârd to temperature
and shear forces;
- a good stability over time, without any no-
ticeable change between 35C and ambient te~perature, for a
storage period as long as 96 hours; no irreversible retro-
de&radation
- good water retention, and no separation on
storage or settling. --
It should of course be understood that the present
invention has been described and illustrated only by wcy of
example, which is in no way limiting, and any modifications -~
within the field of technical e~uivalence may be madè to the
invention without goinG beyond its scope.
