Note: Descriptions are shown in the official language in which they were submitted.
~2S8338
METHOD FOR CONTINUOUS PRODUCTION OF CROSS-LINKED POLYMER
BACKGROUND OF THE INVENTION
Field of the Inven-tion:
This invention relates to a method for the
continuous production of a cross linked polymer. More
particularly, this invention relates to a method for the
continuous production of a water-containing gel polymer
cross-linked by aqueous solution polymerization.
Discription of the Prior Art:
Heretofore, cross-linked polymers using acryl-
amide, acrylic acid or salts thereof as main components have
been known for their ability to absorb and retain large
volumes of water, effect ion exchange, and induce chelation
and have found extensive utility in various applications as
sanitary articles, soil conditioners for agronomic uses,
dehydrants, ion-exchange resins and adsorbents. For the
production of these cross-linked polymers, the method which
comprises polymerizing an aqueous monomer solution as
water-in-oil emulsified or suspended in a hydrophobic
solvent and the method which comprises cast polymerizing an
aqueous monomer solution have found recognition and accept-
ance. The method of water-in-oil emulsion polymerization
and the method of water-in-oil suspnesion polymerization
entail use of large volumes of organic solvent and, there-
fore, prove highly dangerous from the standpoint of preven-
tion of accidents and pose a serious problem of possible
:~Z5~33~
exposure of workers to toxic effects of the organic solvent.
The method which relies on the cast polymerization of an
aqueous monomer solution is excellent over the two methods
described above in the sense that it has no use for any
organic solvent. This method nevertheless requires
continual removal of heat of reaction during the course of
polymerization and inevitably entails use of an intricate
and expensive polymerization device. Further, in producing
a cxoss-linked polymer in a dry state from the produced
water-containing gel polymer by the removal of water, there
is essentially involved a step of finely dividing the water-
containing gel polymer mechancially thereby increasing the
surface area of the polymer enough for drying. In this
case, the mechanical fine division of the water-containing
gel polymer may be accomplished by cutting or extrusion, for
example. In either case, the work of fine division of the
polymer consumes a huge amount of energy because the water-
containing gel polymer possesses strong rubbery elasticity.
As a solution to the various problems described
above, the inventors have proposed in Japanese Patent
Laid-open SHO 57(1982)-34101 a method for the batchwise
radical aqueous solution polymerization by the use of a
vessel provided with a plurality of rotary stirring shafts.
Although this method has succeeded in improving productiv-
ity and workability to some extent over the conventional
methods, it still has much to be desired.
~Z5833~
An object of an aspect of this invention,
therefore, is to provide a novel method for the continuous
production of the cross-linked polymer.
An object of an aspect of this invention is to
provide a method for t~e continuous pro~uction of a water-
containing gel polymer cross-linked by aqueous solution
polymerization.
SUMMARY OF THE INVEMTION
An aspect of the invention is as follows:
A method for the continuous production of a cross-
linked polymer, comprising the steps of continuously feeding
an aqueous solution of a monomer capable of being converted
by aqueous solution polymerization into a water-containing
cross-linked gel polymer and a polymerization initiator to a
vessel provided with a plurality of mutually parallel rotary
stirring shaft each fitted with stirring blades, said
monomer comprising an a,~-ethylenically unsaturated monomer
wherein the concentration of said monomer in said aqueous
solution is in the range of 10 to 80% by weight, finely
dividing a water-containing gel polymer issuing from the
polymerization in progress by the shearing force of stirring
blades generated by the rotation of said stirring shafts
while allowing the radical aqueous solution polymerization to
proceed without interruption, and continuously discharging
the resultant finely divided water-containing gel polymer
having a size less than about 3 cm out of said vessel.
83~
BRIEF DESCRIPTION OF THE DR~WINGS
Fig. 1 is a schematic cross-sectional view illus-
trating a typical reaction device to be used for the
method of this invention,
Fig. 2 is a front view of stirring blades to be
used in the reaction device of Fig. 1,
Fig. 3 is a side view illustrating a typical
group of discharge blades.
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~2S8~33~
Fig. 4 is a schematic cross-sectional view
illustrating another typical reaction device to be used for
the method of this invention,
Fig~ 5 is a schematic cross-sectional view
illustra-ting a typical combination of the reaction vessel of
Fig. 4 and a heating device and a drier,
Fig. 6 is a perspective view of stirring blades
fox use in the reaction devices of Figs. 4 and 5, and
Fig. 7 is a schematic cross-sectional view
illustrating yet another typical reaction device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The monomer to be used in this invention is
capable of being converted by aqueous solution polymeriza-
tion into a water-containing cross-linked gel polymer. The
cross-linked structure may be that which is obtained by the
copolymerization of a water-soluble monomer and a cross-
linking monomer possessing at least two polymerizable
double-bonds in the molecular unit thereof or that which is
obtained by subjecting a water-soluble monomer to aqueous
solution polymerization in the presence of a hydrophilic
high molecular substance such as starch, cellulose or
polyvinyl alcohol and a water soluble poly epoxide compound
thereby effecting the polymerization in combination with
graft linkage, formation of a complex or ester linkage.
The aqueous monomer solution to be used in this
invention is continuously fed into a polymerization vessel
and, therefore, is desired to contain the monomer in a
~;25~3~
concentration of 10 to 80% by weight, preferably 20 to 60~ by
weight. So long as the concentration falls within this
range, the water containing gel polymer formed with the
progress of the polymerization can be easily divided finely
by the shearing force generated by the rotation of the
stirring shafts.
Examples of the water-soluble monomer usable
advantageously in the polymerization include a,~-
ethylenically unsaturated monomers such as acrylic acid and
methacrylic acid and alkali metal salts and ammonium salts
thereof, acrylamide, methacrylamide, acrylonitrile,
2-hydroxyethyl (meth)acrylate, methyl acrylate, ethyl
acrylate, isopropyl acrylate, methyl methacrylate, ethyl
methacrylate and maleic acid. One member or a mixture of two
or more members selected from the group of monomers
enumerated above can be used.
Examples o~ the cross-linking monomer usable
ad~antageously herein include diacrylate or dimethacrylates
of ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, 1,4-butane diol, 1,5-pentanediol,
1,6-hexane diol, neopentyl glycol, trimethylol propane and
pentaerythritol; triacrylates or trimethacrylates of
trimethylol propane and pentaerythritol; tetracrylates or
tetramethacrylates of pentaerythritol; N,N'-methylene-bis-
acrylamide, N,N;-methylene-bis-methacrylamide and triallyl
isocyanurate. One member or a mixture of two or more members
selected from the group mentioned above can be used. The
~ '
:~5833~
aforementioned cross-linking monomer is used generally in
the amount of not more than 10 mol%, more desirably 0.0005
to 5 mol%, and most desirably 0.001 to 1 mol%, based on the
aforementioned water-soluble monomer.
Among numerous monomers enumarated above, a
monomer mixture of (A) one member or a combination of two or
more members selected from the grouQ consisting of acrylic
acid, methacrylic acid, alkali metal salts, ammonium salts
thereof, acrylamide and methacrylamide and (s) a cross-
linking monomer possessing at least two polymerizable
double-bond in the molecular units, with the cross-linking
monomer of (B) accounting for not more than 10 mol%, is used
particularly desirably. The cross-linking monomer (s) is
one member or a mixture of two or more members selected from
the group of cross-linking monomers enumerated above. If
the amount of the cross-linking monomer (B) to be used
exceeds 10 mol%, especially 50 mol% based on the monomer
(A), the produced cxoss-linked polymer is deficient in the
ability to absorb water or the ability to effect ion
exchange. Thus, the ratio of the cross-linking monomer (B)
is in the range of 0.0005 to 5 mol%, preferably 0.001 to 1
mol%. Further, concentration of this aqueous monomer
solution is 10 to 80% by weight, preerably 20 to 60% by
weight.
Even when the cross-linking monomer (B) is nOt
used at all, the continuous polymerization aimed at by the
1~58~31~
present invention can be carried ou-t so far as the formation
of the cross-linking structure is effected as by the use of
ammonium persulfate in a large amoun-t, for example.
The aqueous monomer solution to be used in this
invention is continuously fed into a polymerization vessel
and, therefore, is desired to contain the monomer in a
concentration of 10 to 80~ by weight, preferably 20 to 60~
by weight. So long as the concentration falls within this
range, the water containing gel polymer formed wi-th the
progress of the polymerization can be easily divided finedly
by the shearing force generated by the rotation of the
stirring shafts.
The vessel used for this invention is required to
be provided with a plurality of rotary stirring shafts and
be required to be capable of exerting shearing force
generated by the rotation of rotary stirring shafts fitted
with stirring blades to bear upon the water-containing gel
polymer being formed by the aqueous solution of polymeriza-
tion of the monomer. The vessel is required to be provided
with a plurality of rotary stirring shafts laid parallelly
to one another. ~xamples of the vessel satisfying this
requirement include a two-arm type kneader(hereinafter
referred to simply as "kneader") and a three-shaft kneader.
When the kneader is adopted, the two rotary stirring shafts
are rotated in mutually opposite directions at equal Or
unequal rates. When the two shafts are operated at an equal
rate, they may be used in such a sates that the radii of
7--
~8~33~
rotation of the two shafts partly overlap. When the two
shafts are operated at unequal rates, they are used in such
a state that the radii of rotation thereof do not overlap.
The rotary stirring shaf-ts to be used herein may be in any
of various forms such as sigma type, S type, banbury type
and fish-tail type.
The ]cneader to be used herein is desired to have
the inner surface thereof coated with fluorine containing
resin because the coating serves to prevent the formed gel
from adhering to the inner surface. Examples of the
fluorine containing resin include -tetrafluoroethylene resin,
tetrafluoroethylene-perfluoropropylvinyl ether copolymer,
tetrafluoroethylene-hexafluoropropylene copolymer, triflu-
oromonochloroethylene resin and ethylene-tetrafluoroethylene
copolymer.
The polymerization vessel to be used for this
invention is desired to be provided in the upper portion
thereof with a lid adapted to permit displacement of the
internal gas of the polymerization vessel with an inert gas
and, consequently, enable the polymerization system to be
retained under an atmosphere inert to the reaction of
radical polymerization. Optionally, the polymerization
vessel may be provided in the upper portion thereof with a
reflux condenser for condensing, during the course of the
polymerization, the water vaporized by the heat of polymeri-
zation reaction. Otherwise, the polymerization vessel may
be adapted so that the water formed as described above will
~Z5~33~
be forced out of the vessel interior by the current of an
inert gas introduced into the vessel. For the purpose of
heating the aqueous monomer solution or partially removiny
the heat of polymerization reaction during the
polymerization, i~ is desirable to provide the polymerization
vessel with a jacket. Examples of the inert gas usable
advantageously herein include nitrogen, carbon dioxide and
argon.
Now, the reaction vessel to be used for the method
of this invention will be described below with reference to
the accompanying drawing. Fig. 1 represents one typical
reaction vessel to be used for working this invention. This
is a two-arm type kneader comprising a vessel 5 provided with
a thermometer 1, a raw material feed tube 2, an inert gas
port 3 and a lid 4. Near the bottom portion thereof, the
kneader is provided with a plurality of mutually parallel
rotary stirring shafts 6 each fitted with sigma type stirring
blades as illustrated in Fig. 2. The vessel is kept under
an atmosphere of an inert gas. Optionally, the vessel may
be provided near the bottom portion thereof with a ~acket 7
to be filled with a heat transfer medium for the control of
the reaction temperature. The vessel 5 is also provided
in the upper portion thereof with a product outlet 8 and,
further near the product outlet 8, with a mechanism for
discharge of finely divided water-containing gel polymer.
The discharge mechanism, for example, may comprise a
hori~ontal shaft 9 disposed above the plurality of rotary
stirring shafts of the reaction vessel and one or
_g_
3L~ZS833~
more paddle-shaped vanes attached to the horizontal shaft as
shown in Fig. 1 and Fig. 3. The aforementioned product
outlet 8 and a vat 10 are connected to each other with a
duct 11 made of synthetic resin such as polyethylene,
polypropylene or polyvinyl chloride. The vat lo is
contained in a heating bath.
The polymeriza-tion in the device cons-tructed as
described above is effected by feeding the aqueous monomer
solution containing the water-soluble radical polymerization
initiator via the raw material feed tube 2 into the vessel 5
and, at the same time, introducing an inert gas such as
nitrogen Via an inert gas port 3 into the vessel and
displacing the air remaining in the system, and maintaining
the temperature of the system at a prescribed level to
induce polymerization. As the polymerization proceeds and
produces a water-containing gel polymer, the produced
polymer is finely divided by the shearing force generated by
the rotation of the vanes of the rotary strirring shafts 6
without interrupting the polymerization in progress. Then,
the aforementioned feeding of the aqueous monomer solution
containing the polymerization initiator is continued to
permit continl~ation of the polymerization and, for the
purpose of maintaining the amount of the gel contained in
the system substantially at a fixed level, the particles of
the water-containing gel polymer are discharged out of the
system through the discharge mechanism. Optionally, the
discharged water-containing gel polymer is heated within the
--10--
~.f~
vat 10 to complete the polymerization still proceeding in the
discharged polymer.
Figs. 4 and 5 illustrate another typical reaction
device usable in working the present invention. This is a
three-shaft type kneader comprising a vessel 25 provided with
a thermometer 21, a raw material feed tube 22, an inert gas
port 23 and a lid 24. The vessel is provided near the bottom
portion thereof with a plurality of mutually parallel rotary
stirring shafts 26 using Banbury type stirring blades as
shown in Fig. 5 and further with a discharge screw 29. The
vessel is kept under an atmosphere of an inert gas.
Optionally, the vessel is provided near the bottom portion
thereof with a jacket 27 filled with a heat transfer medium
for the control of the reaction temperature. Near the bottom
portion of this vessel 25 is further formed a discharge
outlet 28. To this discharge outlet 28 is connected a
double-paddle feeder 30 which may be optionally provided with
a jacket 31. Below the discharge outlet 32 at one end of the
double-paddle feeder 30 is disposed a conveying device 34
such as, for example, a belt conveyor. This conveying device
34, when necessary, is provided with a drier 35. The
stirring blades are available in various forms such as are
illustrated in Fig. 6 (A) - (D).
The polymerization in the device constructed as
described above is effected by feeding the aqueous monomer
solution containing the water-soluble radical polymerization
initiator via the raw material feed tube 22 into the vessel
~Z5~33~
25 and, at the same tlme, introducing an inert gas such as
nitrogen via the inert gas port 23 into the vessel to
displace the air remaining in the system, and keeping the
inner temperature of the vessel at a prescribed level to
induce polymerization. When the polymerization proceeds and
produces a water-containing gel polymer 33, the polymer 33
is finely divided by the shearing force generated by the
rotation of the blades of the rotary stirring shafts 26
without interrupting the polymerization in progress.
Further the feeding of the aforementioned aqueous monomer
solution containing the polymerization initiator is
continued to permit continuation of the polymerization and,
at the same time for the purpose of maintaining the amount
of gel contained in the system substantially at a fixed
level, the gel is driven by the discharge screw 29 and
forced out of the discharge outlet 28 into the double-paddle
feeder 30. The discharged water-containing gel polymer,
when necessary, is heated within the feeder 30 to complete
the polymerization still proceeding within the polymer. The
water-containing gel polymer inside the feeder 30 is
discharged through the discharge outlet 32 onto the
conveying device 34 and then dried by the drier 35.
Fig. 7 illustrates yet another typical reaction
device to be used for working this invention. This device
is generally similar to the device of Fig. 1, except that
the wall on the discharge outlet 48 side of the vessel 45
has a small height enough for the produced water-containing
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~'Z~8~33~
gel polymer to depart from the vessel interior by
overflowing the wall. Optionally, this wall of the vessel
45 may be designed as a weir adjustable in height so that it
will be intermittently lowered to permit departure of the
gel polymer by overflow. The numerical symbols in Fig. 7
which are the sums of the numerical symbols found in Fig. 1
plus 40 denote the same components as those of Fig. 1. The
polymerization in this device is carried out by the same
procedure as used in the device of Fig. 1.
The term "continuous" as used herein is not
required to be interpreted as constant in the exact sense of
the word but may be interpreted as portraying the discharge
of the produced polymer in a pulsating manner or in an
intermittent manner. The discharge of the produced gel
polymer has only to be "continuous" in the sense that the
amount of the water-containing gel polymer is retained
substantially in a fixed level within the reaction vessel.
~ s the water-soluble radical polymerization initi-
ator to be used for effecting the radical aqueous solution
polymerization of the monomer of this invention, any of the
water-souble radical polymerization initiators known to the
art may be used. Ex,amples of the polymerization initiator
include persulfates, hydrogen peroxide, and water-soluble
azo compounds. Such a polymerization initiator may be used
alone or used as a redox type initiator in combination with
a sulfite, a hydrogen sulfite, a thiosulfate~ an L-ascorbic
acid or a ferrous salt. The amount of the radical
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33~
polymerization initiator to be used is in -the range of 0.001
to 1~ by weight, preferably 0.005 to 0.5% by weight, based
on the total amount of the reactants.
The reaction temperature is variable with the kind
of the monomer to be used. When a monomer mixture of (A)
one member or a combination of two or more members selected
from the group consisting of acrylic acid, methacrylic acid,
alkali metal salts, ammonium salts thereof, acrylamide and
methacrylamide and (B) a cross-linking monomer possessing at
least two polymerizable double-bonds in the molecular unit
is used, for example, the reaction temerature falls
generally in the range of 60to 110C, preferably in the
range of 70to 100C. When necessary, the polymerization
product is subjected to an aging at a temperature in the
range of 50to 120C, preferably 60to 100C.
When the polymerization is carried out in accord-
ance with the method of this invention, finely divided
water-containing gel polymer particles each possessing a
cross-linked structure can be continuously produced with
ease.
Although the particle diameter of the produced
polymer is variable with the reaction conditions actually
involved, polymer particles are obtainable in diameters
generally not exceeding 3 cm, preferaly falling in the range
of 0.05 to 1 cm.
In accordance with the method of this invention,
since the monomer is continuously fed to the vessel and the
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produced water-containing gel polymer is continuously
discharged out of the vessel, the method enjoys an extremely
high operational efficiency. In contrast to the method for
batchwise polymerization which necessitates manual works in
the steps of introducing the monomer, causing the polymeri-
zation, and discharging the produced polymer, the continuous
method of this invention had an advantage that virtually no
manual work is required after the reaction has reached its
constant state.
Further by the method of this invention, the
generation of the heat of polymerization reaction is uniform
along the course of time because the finely divided water-
containing gel polymer retained within the reaction vessel
and the freshly supplied aqueous monomer solution are
uniformly m xed and the polymerization of the monomer occurs
on the surface of polymer gels. Thus, the removal of the
heat of the polymerization reaction and the maintenance of
the temperature of the polymerization system at a constant
level are easy. Consequently, the rate of polymerization
can be increased and the productivity of the polymerization
can be enhanced and the maintenance of the product quality
at a fixed level is easy to obtain. Unexpectedly, the
polymer obtained by the continuous method of this invention
exhibits a high ability of absorption as compared with the
polymer obtained by the batchwise method. Further, the
method of this invention has an effect of producing
water-containin~ gel polymer particles in substantially
~S~333~
uniform particle diameters and in a state easy to dry. In
the case of the batchwise polymerization, since the heat of
polymerization reaction is evolved concentrically, the
elimination of the heat is relatively difficult and, as the
result, the increase of the rate of polymerization and the
enhancement of the productivity of polymerization are
difficult to obtain. Moreover, the produced polymer suffers
from dispersion of quality and relatively poor ability of
absorption. The finely divided water-containing gel polymer
particles have widely dispersed particle diameters and some
of these particles are not easily dried.
The method of this invention is entirely different
in operating principle from the method of Japanese Patent
Laid-Open SHO 56(1981)-32514 which causes the materials to
be moved in the manner of piston flow from the entrance to
the exit. The aqueous monomer solution introduced into the
vessel is uniformly mixed with the finely divided water-
containing gel polymer particles and, in that state,
subjected to polymerization and part of the produced polymer
is discharged out of the vessel. As the result, the amount
of the water-containing gel polymer retained inside the
reaction vessel is large for the amount of heat generated.
Thus, the removal of the heat is easy.
In contrast, in the case of the method which
involves the movement of materials in the manner of piston
flow, the removal of heat is difficult. An attempt to
enhance the productivity of the polymerization, therefore,
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~ Z~833~
has a fair possibility of elevating the temperature of the
materials and degrading the quality of the product.
The water-containing gel polymer particles
obtained by the method of polymerization of this invention
can be used in their unmodified form as adsorbents, water-
retaining agents, ion-exchange resins and absorbents. When
they are dried, however, they can be handled more conven-
iently. The water-containing gel polymer particules
obtained by the method of polymerization of this invention
have an advantage that they can be dried very easily. To be
specific, the water-containing gel polymer particles
produced by this invention have a large surface area such
that they will be quickly and easily dried as by exposure to
blast of hot air.
The method of this invention for the continuous
polymerization enjoys an advantage that a continuous drier
can be effectively utilized in the drying of the product.
The device used for the batchwise polymerization necessi-
tates use of a hopper, for example, for the connection of a
continuous drier to the device itself. The device of this
invention has no use for such extra implement.
In the actual working of this invention, the
conversion of the monomer to the polymer can be improved by
heating the water-containing gel polymer freshly discharged
from the polymerization vessel befoxe the polymer is dried.
For this particular embodiment of this invention, union of a
continuous heater and a continuous drier may be
-~Z~333~3
contemplated.
Now, the method of this invention will be
described more specifically below with reference to working
examples.
Example 1
A jacketed two-arm type stainless steel kneader
(hereinafter called "kneader" for short) constructed as
illustrated in Fig. 1, having an inner volume of 2 liters,
incorporating an opening 160 mm x 150 mm, having a depth of
135 mm, and provided with two sigma type stirring blades of
a rotational diameter of 70 mm, and having a coating of
tetrafluoroethylene-perfluoropropylvinyl ether copolymer
formed on surfaces exposed to contact with the solution was
fitted with a discharge device and a lid. An aqueous
monomer solution containing 399 g of partially neutralized
acrylic acid having a 75 mol% portion thereof neutralized
with caustic soda, 0.036 g of N,N'-methylene-bis-acrylamide,
and 600 g of water was fed into the kneader and nitrogen was
blown into the kneader to purge oxygen from of the reaction
system. Then the two sigma type stirring blades were
rotated at respective rates of 67 and 56 r.p.m. and hot
water at 45 C was circulated through the jacket, and a
solution of 0.23 g of 2,2'-azo-bis-(2-amidinopropane)-
dihydrochloride (produced by Wako Junyaku Kabushiki Kaisha
and marketed under trademark designation V-50) in 10 g of
water was added thereto as a polymerization initiator.
Polymerization began to proceed 15 minutes after the
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addition of the polymerization initiator. With the progress
of the polymerization, the aqueous monomer solution gave
rise to a soft water-containing gel, which was gradually
divided finely by the rotation of the stirring shafts. The
inner temperature of the reaction system reached 80C within
35 minutes of the addition of the polymerization initiator.
At this point, the temperature of the hot water circulated
to the jacket was raised to 94C. Then, an aqueous monomer
solution containing 14.36 kg of partially neutralized
acrylic acid haivng a 75 mol~ portion thereof nuetralized
with caustic soda, 1.3 g of N'N-methylene-bis-acrylamide and
21.6 kg of water and purged of dissolved oxygen by the
blowing of nitrogen gas and a solution of 8.2 g of V-50 in
360 cc of water were separately forwarded by constant rate
pumps to a mixing tank. The resultant homogeneous mixture
was fed into the kneader over a period of 24 hours.
The aqueous monomer solution thus fed cotinuously
to the kneader was converted into finely divided water-
containing gel polymer and, in that form, continuously
discharged by a discharge vane. In this while, the inner
temperature of the system was kept substantially constant at
C. The discharged water-containing gel polymer was
further kept under an atmosphere of nitrogen at 90C for 20
minutes to complete the polymerization still proceeding
within the polymer.
The discharged water-containing gel polymer was in
the form of finely divided particles 2 to 7 mm in diameter.
--19--
~5~
They lacked cohesiveness and enjoyed ease of handling and
could be easily dried.
The discharged water-containing gel polymer was
spread on a wire gauze of 50 mesh, dried in a hot air drier
at 150 C, and then pulverized with a vibrating mill.
A 0.2 g portion of the pulverized product (herein-
after referred to as "absorbent (1)") was evenly placed in a
bag (40 mm x 150 mm) of non woven fabric shaped after a tea
bag, immersed in a 0.9% saline solution for lo minutes,
removed from the water, and weighed. The absorbency of this
specimen was calculated in accordance with the following
formula, using as a blank the bag lacking its content.
Absorbency = Wel~ht after absorption (q) - blank (~)
Welght of absorbent tg)
The results shown in Table 1. The data given in
the table represent the absorbency obtained of the
pulverized products from the lots of water-containing gel
polymer sampled a~ intervals of three hours from the start
of the continuous supply of the aqueous monomer solution.
- Table 1
. _ _
Time elapsed 0 3 6 9 12 15 18 21 24
Absorbency 66 70 72 70 71 71 69 71 71
From the data, it is noted that the cross-linked
polymer obtained by the method of this invention was
effectively usable as absorbent.
Example 2
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~'~5~33~3
A jacketed stainless steel three-shaft kneader
(hereinafter called ~Ikneader~ for short) constructed as
illustrated in Figs. 4 and 5, having an inner volume of 10
liters, incorporating an opening 240 mm x 22U mm, having a
depth of 260 mm and provided with two Banbury type stirring
blades of a rotational diameter of 110 mm and one discharge
screw 35 mm in diameter had a coating of trifluoromono-
chloroethylene resin formed on the inner surface thereof.
This kneader was fitted with a nitrogen inlet tube, a
monomer inlet tube and a thermometer.
An aqueous monomer solution containing 1995 g of
partially neutralized acrylic acid having a 75 mol% portion
thereof neutralized with caustic soda, 3.3 g of trimethylol
propane triacrylate and 3000 g of water was fed into the
kneader and nitrogen gas was blown into the kneader to purge
oxygen from the reaction system. Then, the Banbury stirring
blades were rotated to a rate of 30 r.p.m., hot water at 40
C was circulated to the jacket, and 2.25 g of ammonium
persulfate and 2.25 g of sodium hydrogen sulfite were added
thereto as polymerization initiators. Polymerization began
to proceed 15 minutes after the addition of the polymeriza-
tion initiators. With the progress of the polymerization,
the aqueous monomer solution gave rise to a soft water-
containing gel. By the rotation of the stirring shafts, the
soft water-containing gel was gradually divided finely. The
inner temperature of the reaction system rose to 90 C within
25 minutes of addition of the polymerization initiators. At
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this point, the temperature of the hot water circulated to
the jacket was raised to 87C. Then, an aqueous monomer
solution containing 359 kg of partially neutralized acrylic
acid having a 75 mol% portion thereof neutralized with
caustic soda, 594 g of trimethylolpropane triacrylate, and
540 kg of water and purged of dissolved oxygen by the
blowing of nitrogen gas, a solution of 405 g of ammonium
persulfate in 10 kg of water and a solution of 405 g of
sodium hydrogen sulfite in 10 kg of water were supplied to
the over a period of 5 days. After the start of the
addition of the monomer, the rotation of the discharge screw
was controlled so that the amount of the water~containing
gel polymer retained within the kneader would become
constant.
The aqueous monomer solution continuously fed into
the kneader was converted into a finely divided
water-containing gel polymer and, in that form, continuously
discharged out of the kneader. In this while, the inner
temperature of the system was substantially constant at
about 83C.
The water-containing gel polymer discharged by the
rotation of the discharge screw was led into a double paddle
feeder (made by Kabushiki Kaisha Nara Kikai Seisakusho)
heated by a jacket filled with hot water at 90 C and heated
therein for an average retention time of 15 minutes. The
water-containing gel polymer discharged from the paddle
feeder was dried with a blast of hot air at 160C within a
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~ZS~33~
continuous through-circulation band drier. The dried
polymer thus obtained was sampled at intervals o~ one half
day. Each test specimen was pulverised and the pulverised
product (hereinafter referred to as "absorbent (2)") was
tested for absorbency. The results are shown in Table 2.
Table 2
Number of days elapsed 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Absorbency 65 66 65 65 65 64 65 66 66 65
Erom the data, it is noted that the absorbent (2)
was also an excellent absorbent.
Example 3
For visual observation of the behavior of the
continuously added aqueous monomer solution, 5cc of the
deaerated aqueous monomer solution containing 0.2 g of
fluorescent pigment in pink color (made by Nippon Shokubai
Kagaku Kogyo Co., Ltd and marketed under trademark
designation of "Epocolor") and the initiator was added to
the polymerization system during the course of the
continuous polymerization of Example 1 and placed under
visual observation.
When the colored aqueous monomer solution was
added, the entire system assumed a pink color. This fact
evinces that the aqueous monomer solution was uniformly
mixed with the crushed water-containing gel polymer and was
caused to form a thin coat on the surface of the
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water-containing gel polymer.
When the uncolored aqueous monomer solution was
further added to continue the polymeriztion, there were
produced water-containing gel polymer particles pink at the
cores and transparent in -the outer parts. This fact evinces
that the water-containing gel polymer was pulverized within
the kneader, the aqueous monomer solution deposited on the
surface of crushed polymer and underwent polymerization in
that state, the gel particles therefore gained in particle
diameter, and the grown particles were again pulverized, and
this procedure repeated.
Example 4
The kneader used in Example 1 was modified to a
construction of Fig. 7 by having a section 150 mm x 50 mm
cut off the upper portion of one wall thereof to facilitate
the overflow of the water-containing gel polymer.
The kneader was fitted with a lid. An aqueous
monomer solutlon (35~ by weight of concentration) containing
250 g of acrylamide, 97 g of potassium acrylate, 3 g of
N,N'-methylene-bis-acrylamide and 650 g of water was fed to
the kneader and nitrogen gas was blown in the kneader to
purge oxygen from the reaction system.
Then, the two sigma type stirring blades were
rotated at respective rates of 44 and 24 r.p.m., hot water
at 40C was circulated to -the jacket to heat the kneader,
and 0.5 g of an aqueous 35% hydrogen peroxide solution and
0.006 g of L-ascorbic acid were added as polymerization
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~ ,~5~3~
initiators thereto. Poymerization began to proceed one
minute after the addition of the polymerization initiators.
With the progress of the polymerizaiton, the aqueous monomer
soluiton gave rise to a soft water-containing gel. The gel
was gradually divided finely by the rotation of the stirring
shafts. Within 15 minutes of the addition of the polymeri-
zation initiators, the inner temperature of the reaction
system reached 64 C and the water-containing gel polymer was
divided finely into particles about 3 mm in diameter. At
this point, the temperature of the hot water circulated to
the jacket was raised to 90C. Then~ an aqueous monomer
solution containing 12 kg of acrylamide, 4.66 kg of potas-
sium acrylate, 144 g of N,N'-methylene-bis-acrylamide and
29.2 kg of water and purges of dissolved oxygen by blowing
nitrogen gas, a solution of 24 g of an aqueous 35~ hydrogen
peroxide solution in 1 kg of water, and a solu~ion of 0.288
g of L-ascorbic acid in 1 kg of water were separately
forwarded by constant rate pumps to a mixing tank, there to
be uniformly mixed. The resultant uniform mixture was
supplied to the kneader over a period of 24 hours.
The aqueous monomer solution thus continuously fed
to the kneader was ~onverted into a finely divided water-
containing gel polymer and, in that state, was allowed to
overflow the shorter wall and depart continuously from the
kneader. In this while, the inner temperature of the system
was kept substantially constant at about 85C.
The discharged water-containing gel polymer was
further kept in an atmosphere of nitrogen at 85 C for 20
minutes to complete the polymerization which was still in
progress in the polymer. The discharged water-containing
gel polymer was in the form of particles divided finely to
the order of 1 to 5 mm in diameter~ The particles lacked
cohesiveness and enjoyed ease of handling and could be
easily dried. The water-containing gel polymer was spread
on a wire gauze of 50 mesh and dried with blast of hot air
at 180 C for one hour. The dried product (hereinafter
referred to as "water-retainer (1)") was in a granular form
and had a water content of 5% by weight.
A 0.5-g portion of the water-retainer (1) was
mixed with 100 g of silica sand, No. 7. The mixture was
spread on a wire gauze of 100 mesh, wetted with tap water
until saturation, left standing under the conditions of 20 C
and 65% RH, and tested for water retaining capacity along
the course of time. The change in the amount of water
retained by the mixture is shown in Table 3.
Table 3
Number of days of standing 0 2 4 6 8
Mixture of water-ratainer with sand 80g 51g 36g 20g 15g
Sand alone 30g 9g lg Og Og
From the data, it is noted that the cross-linked
polymer obtained by the method of this invention is
effectively usable as a water retainer.
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