Note: Descriptions are shown in the official language in which they were submitted.
'~62723
DESCRIMETHOD FOR CONTINUOUS AGGLOMERATION OF AN ABSORBENT RESIN
POWDER AND APPARATUS THEREFOR
Technical Field
This invention relates to a method for the
continuous agglomeration of an absorbent resin powder by
ag~lomerating minute particles contained in the absorbent
resin powder thereby adjusting particle sizes of the resin
powder within a fixed range and to an apparatus for the
execution of this method.
Background Art
In recent years, the absorbent resin powder has come
to find utility in various fields specializing in such
hygienic articles as sanitary napkins and disposable diapers
and water-retaining agents. The absorbent resin of this
quality has been generally produced by polymerizing a
resinous raw material, drying the re~ultant polymer, and
pulverizing the dry polymer with a pulverizer. The absorbent
resin powder re~ultlng from the pulverization, therefore,
contain~ minute particles short of desired particle sizes.
When the absorbent resin powder containing the minute
partlcles is put to use, it ha~ the disadvantage that the
minute particle~ are drifted.
Thus, the practice of incorporating a drift-
preventing agent in the resin powder for the purpose of
improving the dry flowing property of the resin powder as
disclosed in the specification of JP-A-52-121,658 and the
practice of incorporating a dust-proofing agent in the resin
powder for the purpose of curbing the drifting of minute
particles contained in the resin powder a~ taught in the
~pecification of JP-A-63-39,93~ have been heretofore
followed.
Further, the method for effecting removal of the
minute particles from the resin powder by the use of a sieve
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and the method for enlarging only the minute particles in the
resin powder by the use of a binder have been conceived. The
former method, however, is undesirable on account of poor
economy. The latter method generally requires use of an
organic solvent type binder and, therefore, not only entails
the danger of ignition during the step of drying subsequent
to the size enlargement but also jeopardizes the biological
safety owing to the residue of the organic solvent. The
latter method is liberated from this problem when the binder
to be used therein is in the form of an aqueous solution.
Since the absorbent resin powder produced by pulverization
with a binder has the nature of quickly absorbing the aqueous
solution, however, the aqueous solution encounters
difficulty in allowing uniform disper~ion and mixture of the
minute particles therein and the agglomeration tends to form
large lumps of high density. When the large lumps are to be
pulverized, this pulverization entails occurrence of minute
particles and produces uniformly aggregated particles only
with difficulty.
For the solution of this problem, the method which
as taught in JP-A-61-97,333 and JP-A-61-101,536 comprises
uniformly mixing the absorbent resin powder and an aqueous
liquid and agglomerating the resultant mixture by the use of
a specific mixing device such as, for example, a high-speed
rotary paddle type mixer or an air current type mixer and
then crushing the produced agglomerate has been heretofore
trled.
It has been found, however, that the method which
effects the mixture of the absorbent resin powder with the
aqueou~ liquid by virtue of the shearing force of the high-
speed rotary type mixer as de~cribed above produces a powder
of an unduly small basic particle diameter. Thi~ adver~e
phenomenon may be logically explained by a qupposition that
when the resin powder iq mixed by stirring in the mixer, the
component particles of this powder undergo repetitiou~
mutual collision and, at the ~ame time, yield to
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_ _ _
20~2723
fracture due to mechanical shear. When the particles of the
resin powder having the particle surface thereof specially
treated in advance for the purpose of qualitative
improvement are fractured as described above, the fractured
particle surface poses a problem of qualitative degradation.
When the air current type mixer mentioned above is
to be adopted, it has a problem of unfitness for commercial
production of an absorbent resin powder because it is
incapable of continuous stirring. Moreover, the mixer has
another problem of practically uneasy maintenance because
the otherwise inevitable adhesion of particles of the powder
to the mixer must be prevented by keeping the resin powder
heated and meantime adding thereto the aqueous liquid
piecemeal for a long time.
JP-A-1-236,932 proposes a spray agglomerating
apparatus for effecting continuous agglomerating of a
powder. This spray agglomeration apparatus comprises a
drying chamber, a powder supply device provided with a powder
discharge outlet disposed above the drying chamber, and
spray nozzles disposed one each on the opposite sides of the
powder disoharge outlet and adapted to spout mutually
intsrsecting currents of liquid droplets.
This apparatus i~ effeotive for the purpose of
effecting oontinuous agglomeration af the powder of dextrin
or melamine resin, for example. When this apparatus is
adopted for the agglomeration of an absorbent resin powder
wlth an aqueous liquid, however, it fails to accomplish the
primary object of continuous size enlargement because
viscous agglomerate of the absorbent resin which have
acquired increased viscousness due to absorption of water
adhere to the wall of the apparatus and the deposit of
viscous agglomerate thus formed gains in volume with the
elapse of time. Further, when the absorbent resin powder and
the aqueous liquid contact each other at the position of
mutual intersection of the projeoted threads of the aqueous
liquid, the dispersion of the mixture caused by the force of
.. , . . . .. , . ... . .. . . _ _ _ _ , ~ , .. . ~ _ _ _
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collision due to the discharge of liquid droplets is
insufficient and the state of contact is ununiform. The
enlarged particles consequently obtained, therefore, contain
minute particles which have escaped the size enlargement and
suffer occurrence of wet clusters which have absorbed water
in a large amount.
In view of the true state of prior art described
above, we made a diligent study in search of a method for
agglomeration which comprises subjecting an absorbent resin
powder to continuous agglomeration thereby attaining
elimination of minute particles contained in the resin
powder and an apparatus for execution of the method. We
consequently acquired a knowledge that from an absorbent
resin powder containing minute particles, an absorbent resin
powder of high quality possessing particle sizes in a desired
range i9 obtained by causing the resin powder and an aqueous
liquid qeparately disperqed in advance with the current of
air to flow down a cylindrical member from the upper part to
the lower part thereof and come into parallel flow contact
during the descent thereby inducing cohesive union of the
absorbent resin powder oontalning minute particles and
optionally crushing coarse clusters possibly formed in
¢onsequence of the union. This invention has been perfected
as a result.
An object of this invention, therefore, is to
provide a method for continuous agglomeration which
accomplishes elimination of minute particles contained in an
absorbent resin powder by agglomerating the individual
particles of the absorbent resin powder by cohesive union
with an aqueou~ liquid as a binder while avoiding mutual
collision thereof and optionally crushing coarse particles
possibly formed by the oohesive union and an apparatus for
the execusion of this method.
Disclosure of Invention
The object described above is accomplished by a
method for continuou~ agglomeration of an absorbent resin
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powder characterized by introducing the absorbent resin
powder into a cylindrical member having an open lower end by
means of a current of air through a dispersing member
disposed in the upper part of the cylindrical member and, at
the same time, spraying minute droplets of an aqueous liquld
downwardly through a nozzle disposed inside the dispersing
member thereby establishing mutual parallel flsw contact
between the absorbent resin powder descending toward the
lower part of the cylindrical member as dispersed with the
current of air and the liquid droplets descending toward the
lower part of the cylindrical member as diffused in the
radial direction, removing the produced agglomerate having a
plurality of particles of the absorbent resin powder
cohesively united through the medium of the liquid droplets
through the lower part of the cylindrical member, and
optionally crushing the removed agglomerate.
The object is further accomplished by an apparatus
for continuou~ agglomeration of an absorbent resin powder,
comprising a cylindrical member provided with temperature
control means and having an open lower end~ hopper-shaped
absorbent resin powder dispersing means disposed in the
upper part of the cylindrical member and provided with air
ourrent generating means, mean~ dispo~ed at a position
inside the absorbent resin powder dispersing means and
adapted to spray droplets of an aqueous liquid parallelly to
the direction of descent of the resin powder, and means
disposed in the proximity of the open lower end of the
cylindrical member and adapted to withdraw agglomerate
having a plurality of particles of the absorbent resin powder
cohesively united through the medium of the liquid droplets.
Brief Description of the Drawing~
Fig. 1 i~ a cross section illustrating an apparatus
for working a method for continuous agglomeration of an
absorbent resin powder as one embodiment of the present
invention,
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Fig. 2 is a cross section illustrating an apparatus
as another embodiment of this invention,
Fig. 3 is a cross section illustrating an apparatus
as a control, and
Fig. 4 is a cross section illustrating a device for
determining the absorpt,on ratio of a sample kept under
pressure.
Best Mode for Carrying Out the Invention
In accordance with this invention, the cohesive
union of a plurality of particles of an absorbent resin
powder attained through the medium of droplets of an aqueous
liquid as a binder inside a cylindrical member enlarges
minute particles of the resin powder having particle sizes
below a prescribed level into a resin powder having particle
sizes above the prescribed level and consequently effects
elimination of the minute particles from the resin powder.
During the formation of agglomerate by cohesive union, the
absorbent resin powder containing the minute particles is
introduced downwardly into the cylindrical member as
dispersed with a current of air through a dispersing memeber
disposed in the upper part of the cylindrical member and, at
the ~ame time, the droplets of the aqueous liquid are sprayed
through a nozzle disposed inside the dispersing member so as
to give rise inside the cylindrical member to a region in
which the resin powder and the liquid droplets come into
mutual parallel flow contact in such a state that the
individual particles of the re~in powder avoid frequent
mutual collision. The agglomerate are formed in consequence
of the contact and cohesive union of the plurality of
particles of the resin powder through the medium of the
liquid droplets. At this time, since the absorbent resin
powder i~ fully susceptible to agglomerate, no strong
collision is required between the resin powder and the liquid
droplets or between the individual particles of the resin
powder wetted with liquid droplet~ and readied for cohesive
union into agglomerate. Aq a result, the ab~orbent powder
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acquires particle sizes above the prescribed level without
infliction of injury or fracture upon the particles of the
resin powder or damage upon the surface of the particles.
The agglomerate resulting from the cohesive union
may be put in their unmodified form to use as a finished
product as incorporated in sanitary articles and water-
retaining agents. Preferably for the purpose of improvement
of the convenience of handling, the agglomerate just
produced by the procedure described above are further
crushed preparatorily to use. This crush does not give rise
to any minute particle at all but comminutes coarse
agglomerate. Thus, the produced absorbent resin powder
compri~es particles which measure above a desired particle
size and contains no coarse particles.
When the aqueous liquid is used in a large amount
during the course of the continuous agglomeration, the
produced agglomerate formed of cohesively united particles
possibly acquire a viscous surface. The agglomerate having
a viscous surface are preferably to have this unwanted
viscosity dimin1shed by being left standing for a prescribed
duration or being heated before they are crushed. In this
case, the agglomerate do not always necessitate intentLonal
drying. This heating is preferably carried out at a
temperature in the range of from 50 to 200C ~or a period in
the range of from 3 minutes to 12 hours. Preferably, the
heating temperature is from 70 to 120C and the heating time
ls from 10 minutes to 2 hours.
The term "absorbent resin powder" as used in this
invention refers to a resin powder which shows virtually no
solubility in water, swells with absorbed water, and
possesses a water absorption ratio of not less than l,000%,
preferably not less than 5,000%. The method of this
invention is effective particularly in the agglomeration of
an absorbent resin powder having a conspicuously high water
absorption ratio.
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The absorbent resins which answer this description
include a hydrolyzed starch-acrylonitrile graft copolymer
(JP-B-49-43,395), a neutralized starch-acrylic acid graft
polymer (JP-B-53-46,199 JP-B-55-21,041), saponified acrylic
ester-vinyl acetate copolymers (JP-B-53-13,495 JP-B-55-
19,243), a modified cross-linked polyvinyl alcohol (JP-A-54-
20,093), a cross-linked partially neutralized polyacrylic
acid (JP-A-5~-84,304, JP-A-56-93,716, JP-A-56-161,408, and
JP-A-58-71,907), and a cross-linke~ isobutylene-maleic
anhydride copolymer (JP-A-56-36,504), for example.
The absorbent resin is usable in the form uniformly
cross-linked throughout the entire volume thereof or in the
form having the surface thereof cross-linked as disclosed in
JP-A-58-180,233, JP-A-58-117,222, and JP-A-58-42,602.
Though this invention makes no discrimination between the
two forms mentioned above, the latter form fits the method of
this invention.
The absorbent resin powder is desired to have a
particle size distribution such that those of the particles
of the resin powder which pass a ~tandard lO0-mesh sieve
(particles having dimeter under 0.15 mm) account for a
proportion of not more than 50% by weight, based on the total
amount of the particles. If this proportion i~ not less than
50% by weight, the amount of resin powder particles which
e~oape cohesive union in the oylindrical member increases to
an excessive extent. If the cohesive union is dared in spite
of thi~ adversity, the consumption of the aqueous liquid
inevitably increases and the faqt adhesion of resin powder to
the apparatus heavily occurs and, as a result, the continuous
size enlargement fails to proceed. Further, when the
absorbent resin powder includes the aqueou~ liquid in a large
amount, it is compelled to sacrifice its quality as a toll.
The aqueous liquid for use in this invention may be
either water in its simple form or a liquid mixture of water
with an organic colvent which iq miscible with water. The
organic solvents which exhibit miscibility with water
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include lower alcohols, tetrahydrofuran, and acetone, for
example. The water in its simple form or the liquid mixture
mentioned above may optionally incorporate therein various
compounds or mixtures as dissolved or dispersed therein
preparatorily to use. The compounds or mixtures which are
usable for this incorporation include a slurry of microfine
silica besides the deodorants and plant growth accelerators
which are enumerated in JP-A-61-97,333, for example.
The amount of the aqueous liquid to be used in this
invention need not be particularly restricted but may be
selected in a wide range. No conspicuously effective
agglomeration is easily obtained if the amount is unduly
small. Conversely, if this amount is unduly large, the
agglomerate produced in consequence of the agglomeration
possibly suffer a decline in the capacity for absorption when
no step for drying follows the step for agglomeration.
Generally, the amount of the aqueous liquid desirably falls
in the range of from 1 to 50 parts by weight, preferably in
the range of from 3 to 35 parts by weight, ba~ed on 100 parts
by weight of the absorbent resin powder.
The minute droplets of the aqueous liquid to be used
in this invention are preferable to have an average diameter
of not more than 300 ~m, preferably not more than 250 ~m.
Generally, this average diameter is in the range of from 50
to 200 ~m. If the average diameter exceeds 300 ~m, since the
aqueous liquid is uniformly diffused or dispersed only with
difficulty, the disadvantage ensues that the resin powder
forms lumps of high density and the amount of minute
particles of the resin powder which survive the
agglomeration in the cylindrical member unduly increases.
This unduly large average diameter, therefore, is the last
thing to be desired. The methods which are effectively
usable for the formation of minute liquid droplets having an
average diameter of not more than 300 ~m include the rotary
disc method, the pressure nozzle method, and the two-phase
flow nozzle method, for example. Since this invention
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2~723
contemplates introducing the absorbent resin powder
downwardly into the cylindrical member ~rcm the top thereof,
the two-phase flow nozzle fits the method of this invention
because it is capable of precluding the possible deposition
of agglomerate on the liquid sprayer by the injection of a
gas. The two-phase flow nozzle (produced by Fuyo Seiki K.K.
and marketed under trademark designation of "Luminar") and
the spray vector (produced by Kobe Chutetsu K.K.) are typical
examples of the two-phase flow nozzle. When the absorbent
resin powder and the droplets of aqueous liquid mentioned
above are caused to flow down the interior of the cylindrical
member as diffused or dispersed from the upper part thereof,
pluralities of' resin particles are severally united
cohesively through the medium of liquid droplets to form
agglomerate large in particle diameter. Then, these
agglomerate are thrown into a crushing device and pulverized
therein by crushing. The commercially available crushing
devices which are effectively usable for this pulverization
include New Speed Mill (a proprietary product of Okada Seiko
K.K.), Flu~h Mill (a proprietary product of Fuji Powder
K.K.), and Speed Mill (a proprietary product of Showa
Engineering K.K.), which are enumerated in JA-A-61-97,333
for example. This pulverization by crushing may be carried
out immediately after the agglomeration by aohesive union
within the cylindrical member or after the elapse of a
presoribed time following the agglomeration, whichever may
be convenlent.
The introduction of the absorbent resin powder into
the cylindrical member is effected by causing this resin
powder to fall down the interior of the cylindrical member as
kept in a diffused or dispersed ~tate. For the absorbent
resin powder to be uniformly introduced into the cylindrical
member, it i3 preferable to be di~per~ed and advanced with a
current of air into the cylindrical member.
A current of compres~ed air from air current
generating mean~ is blown again~t the ab~orbent re in powder
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2~2~23
being introduced via the introducing member. The resin
powder is caused by the action of this current of compressed
air to flow down the interior of the cylindrical member.
Generally, this current is formed of air. The mixing ratio
of the absorbent resin powder to the air current in this case
is preferable to fall in the range of from 0.1 to 5 kg/Nm3,
preferably from 0.5 to 2 kg/Nm3. They must be thoroughly
dispersed before they contact the liquid droplets. If the
amount of the absorbent resin powder is such that the mixing
ratio exceeds 5 kg/Nm3, the dispersion or diffusion of the
absorbent resin powder caused by the air current is not
~ufficient and, as a result, the uniformization of the
contact between the resin powder and the droplets of aqueous
liquid is not attained as desired. Thus, the amount of
minute particles of the resin powder which remain intact
after the agglomeration is unduly large. Conversely, if the
aforementioned mixing ratio is less than 0.1 kg/Nm3, the
operation of agglomeration itself is economically
impra¢ticable because the amount of a gaseous material to be
introduced to the site of size enlargement is so huge as to
necessitate installation of an unduly large device for
discharge of the used gaseous material. If the discharge of
the used gaseous material is not sufficient, the continuous
agglomeration is attained with difficulty because of an
increase in the amount of the agglomerate of cohesively
united particles suffered to adhere to the inner wall surface
of the cylindrical member. The retention time of the air
current in the cylindrical member is fixed by controlling the
flow rate of the air current and the aforementioned mixing
ratio of the air current and the absorbent resin powder.
This retention time of the air current is preferable to be
set somewhere in the approximate range of from 0.1 to 30
seconds, preferably from 5 to 15 seconds.
The inner wall of the cylindrical member i~
preferable to be provided with warmth-retaining means
adapted to keep the temperature of the inner wall in the
2~27~3
range of from 50 to 200C, preferably from 70 to 200C. The
maintenance of the inner wall temperature in the range
mentioned above is attained, for example, by covering the
cylindrical member with a jacket and circulating steam
through this jacket. The heating with the jacket serves to
prevent agglomerate of cohesively united particles from fast
deposition on the inner surface of the cylindrical member.
The position for introducing the absorbent resin
powder and the position for spraying the aqueous liquid in
the form of minute droplets are fixed as follows. The
absorbent resin powder is introduced downwardly by means of
the air current as dispersed into the cylindrical member
through the dispersing member disposed in the upper part of
the cylindrical member and the minute droplets of the aqueous
liquid are sprayed downwardly from a nozzle dlsposed inside
the dispersing member, preferably substantially at the
center of the dispersing member.
In this case, the absorbent resin powder which has
been introduced into the cylindrical member is caused to flow
down the interior of the cylindrical member by the weight of
its own coupled with the air current for dispersion and the
air current containing the liquid droplets emanating from
the nozzle. In this case, the absorbent resln powder only
flow~ down the interior o~ the cylindrical member from the
upper part to the lower part of the cylindrical member and
avoids inducing such powerful mutual collision of the
individual particles of the resin powder as to inflict damage
to the individual particles. The minute liquid droplets
which have been sprayed from the nozzle are caused to flow
down the interior of the oylindrical member as dispersed by
the spraying force coupled with the weight of their own.
Slnce the absorbent resin powder flow~ down from the upper
part to the lower part and, at the same time, the droplets of
aqueous liquid similarly flow down the interior of the
cylindrical member as diffused at a prescribed angle
relative to the radial direction of the cylindrical member,
2~2 s23
the resin powder and the aqueous liquid come into mutual
parallel flow contact. Thus, pluralities of resin particles
are severally united cohesively through the medium of the
droplets adhering as a binder to the resin particles to give
birth to agglomerate of cohering resin particles.
The nozzle for spraying the aqueous liquid is
disposed inside the dispersing member ~or the absorbent
resin powder, preferably substantially at the center of the
dispersing member. If khe nozzle is disposed outside the
dispersing member, no uniform contact is established between
the absorbent resin powder and the aqueous liquid and the
produced agglomerate of cohering particles copiously contain
minute particles remaining intact after the size enlargement
a~ well as clusters of cohering particles wetted with
absorbed water.
The nozzle so disposed has the disadvantage that
since the droplets of aqueous liquid are diffused and
consequently suffered to wet the inner wall of the
cylindrical member, the amount of the agglomerate of
cohering particle~ of the absorbent resin powder deposited
on the inner wall increases even to the extent of obstructing
fulfilment of the primary object of continuous
agglomeration.
The agglomerate produced by oohesive union of a
plurality of particle~ of the absorbent resin powder through
the medium of the aqueous liquid are received as on a
conveyor belt installed below the cylindrical member and
conveyed as carried thereon to the next step.
As the cylindrical member, a cylinder having a
tetragonal or more polygonal cros~ section can be used.
Otherwise, a cylinder having a conical or prismatic shape can
be used. Among other cylinders, the cylinder having a
circular shape i9 used particularly desirably.
Further, the absorbent resin powder ko be used in
this invention, for the ~ake of improvement in flowability,
may preparatorily incorporate therein finely particulate
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silica or, for the purpose of enhancing lightfastness and
acquiring a deodorizing effect, may incorporate therein
carbon black and/or activated carbon in advance of the
treatment for agglomeration. The term "particulate silica"
refers to a substance formed mainly of silicon dioxide
particles not more than 50 ym in average diameter. Aerosil
200 (a proprietary product of Japan Aerosil K.K.) and Carplex
#80 (a proprietary product of Shionogi & Co., Ltd.) may be
cited as typical examples of the particulate silica.
The amount of this particulate silica to be used is
in the range of from 0 to 20 parts by weight, preferably from
0.1 to 5 parts by weight, based on 100 parts by weight of the
absorbent resin ~owder. If this amount is increased beyond
the upper limit 20 parts by weight, the excess does not bring
about any proportionate addition to the effect but rather
jeopardizes the high absorbability of the resin powder or at
times renders the agglomeration difficult.
As the carbon black and/or the activated carbon
mentioned above, ordinary particulate products available
under such designations in the market may be used.
The amount of the carbon black and/or the activated
carbon to be used is in the range of from 0 to 50 part~ by
weight, preferably from 0.1 to 10 part~ by weight, based on
100 parts by weight of the absorbent resin powder. If this
amount is increased beyond the upper limit 50 parts by
weight, the excess brings about an adverse effect of
~eopardizing the high absorbability of the produced
agglomerate of cohesively united particles.
When the absorbent resin powder containing the
particulate silica is put to use, the aqueous liquid is
preferable to be used in an amount falling in the range of
from 1 to 50 parts by weight, preferably from 3 to 35 parts
by weight, ba~ed on 100 parts by weight of the combined
amount of the two powders as when the incorporation of the
particulate silica is omitted. Similarly when the absorbent
resin powder containing the carbon black and/or the
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activated carbon is put to use, the aqueous liquid is
preferable to be used in the same amount as described above.
Now, the present invention will be described in
detail below with reference to working examples. It should
be noted, however, that the scope of this invention is not
limited to these working examples. Wherever percents and
parts are mentioned in the following working examples, they
shall be construed as percents by weight and parts by weight
respectively unless otherwise specified.
Example 1
A jacketed twin-arm type kneader of stainless steel
having an inner volume of 10 liters, containing an opening
part 220 x 260 mm in area, measuring 240 mm in depth, and
provided with two sigma type vanes 120 mm in rotary diameter
was furnished with a lid. In this kneader, 5,500 g of an
aqueous solution of an acrylic monomer mixture (monomer
concentration 37% by weight and neutralization ratio 75
mol%) comprising 4,380 g of an aqueous sodium acrylate
~olution, 414 g of acrylic acid, and 706 g of deionized water
and 3.4 g of trimethylol propane triacrylate were placed and
nitrogen gas was blown in to displace the air entrapped in
the reaction sy~tem. Then, the two sigma type vanes were set
rotating at a rate of 56 rpm, the circulation of hot water at
35C through the jacket was started to heat the kneader
content~, and 2.8 g of ammonium per~ulfate and 0.14 g of ~-
a~corbic acid were added meanwhile to the kneader as
polymerization initiators. The monomer mixture began to
polymerize 5 minutes after the addition of the initiators.
When the internal temperature of the reaction system reached
83C after the elapse of 20 minutes thence, the resultant
hydrated gel wa~ already in the form of minute particles
about 5 mm in diameter. The polymerization was completed in
60 minutes. Then, a hydrated gel-like polymer was removed
from the kneader.
The hydrated gel-like polymer was ~pread out in a
thickness of 50 mm in a hot air drier and dried therein with
2~27~3
hot air at a temperature of 150C for 90 minutes to afford a
absorbent resin having a water content of not more than 10%
by weight. This absorbent resin was pulverized with a hammer
type pulverizing device and sifted with a 20-mesh metallic
net to obtain an absorbent resin (1).
By mixing 100 parts by weight of the absorbent resin
(1) with a liquid substance comprising of 0.5 part by weight
of glycerol, 2 parts by weight of water, and 6 parts by
weight of methanol, heat-treating the resultant mixture, and
sifting the heated mixture, an absorbent resin powder (A-1)
was obtained as a 20-mesh pass.
100 parts by weight of the absorbent resin powder
(A-l) and 6 parts by weight of water supplied thereto were
subjected to continuous agglomeration in accordance with the
following procedure.
Specifically as illustrated in Fig. 1, a cylindrical
body 10 provided at the lower end thereof with an opening
part 11 wa~ installed as erected upright. This cylindrical
body 10 was provided in the upper centra] part thereof with a
hopper-like disper3ing member 12 which comprises a tapered
part 16a radially diminishing downwardly and a straight part
16b extending downwardly from the lower end part of the
tapered part 16a.
Compressed air emanating from air current generating
means formed of a nozzle 18a at the leading terminal of an
air compressing pipe 18 was blown against the absorbent resin
powder (A-1) thrown onto the upper surface of the tapered
part 16a through an introducing member 13, with the result
that the abqorbent resin powder (A-1) was caused by dint of
the weight of its own and the action of the air current to
diffu~e in the radial direction of the cylindrical body 10
and, at the same time, flow down the interior of the
cylindrical body 10.
A pipe 14 was fixed at the central part of the
dispersing member 12. A nozzle 15 was attached to the
leading terminal of the pipe 14 as disposed below the
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2~723
dispersing member 12. Air and water were simultaneously
spouted through the nozzle 15 so that the water was sprayed
in the form of minute droplets downwardly inside the
cylindrical body lO. The qprayed water droplets flowed down
the interior of the cylindrical body 10 as kept diffusing in
the radial direction of the cylindrical body 10. By the
adjustment of the nozzle and the absorption of water in the
absorbent resin powder, the diffusion of the water droplets
in the radial direction of the cylindrical body 10 did not
exceed that of the absorbent resin powder at any position in
the direction of height of the cylindrical body 10. The
water droplets during the descent were absorbed by the
absorbent resin powder so that virtually no sign of the
presence of such water droplets was found at the lower
terminal of the cylindrical body 10. At this time, the
mixing ratio of the absorbent resin powder (A-1) to the air
current was found to be 2 kg/Nm3. The average diameter of
the water droplets was about 100 ~m. The retention time of
the absorbent resin powder in the cylindrical body 10 was 10
seconds. By externally heating the cylindrical body 10, the
temperature of the inner wall thereof was kept at 90C. The
agglomerate of oohering resin partioles oonsequently
obtained were oonveyed to a pulverizing device 17 (produced
by Fu~i Powder K.K. and marketed under trademark designation
of "Flush Mill") with a bucket conveyor 20. A hot air kept
at about 90C was blown against the bucket conveyor 20 to
lower the viscosity of the agglomerate during about 20
minutes'retention time thereof. The agglomerate of cohering
particles thrown in the pulverizing device 17 were
pulverized by orushing. The pulverized agglomerate were
sifted with a sieve 19 to obtain an aggregated powder t1) as
a 20-mesh pass. The aggregated powder was teqted for (a)
absorption ratio, (b) absorption ratio under pressure, (c)
suction power, and (d) viscoqity distribution as follows.
(a) Absorption ratio
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A sample, 0.2 g in weight, of the absorbent resin
powder (A-1) or the aggregated powder (1) was uniformly
placed in a tea bag-like pouch (40 mm x 150 mm) made of non-
woven fabric, immersed in an aqueous 0.9% saline solution for
30 minutes, and then weighed. The tea bag-like pouch empty
of the sample was weighed as a blank. The absorption ratio
of the size-enlarged powder (1) was calculated in accordance
with the ~ollowing formula.
Absorption ratio (g/g) = (Weight of wet pouch (g) -
Blank (g))/(Weight of absorbent resin (g))
(b) Absorption ratio under pressure
The absorption ratio of a sample under pressure was
determir.ed by the use of a device illustrated in Fig. 4. A
stopper 23 fitted in an upper mouth 22 of a burette 21 and a
measuring stand 24 and an air inlet 25 were set flush with
each other. On a glaqs filter (No. 1) 70 mm in diameter
disposed in the measuring stand 24, a filter paper, a sample
0.2 g in weight of the absorbent resin powder (A-1) or the
aggregated powder (1), and a paper filter 27 were superposed
and a weight 28 of 20 g/cm2 was further superposed. The
sample was left abcorbing an artificial urine (containing
1.9% of urea, 0.8% of NaCl, 0.1~ of CaC12, and 0.1% of MgS04)
for 30 minute~ thence. The amount of the artificial urin
consequently absorbed by the sample was reported in ml/g.
(c) Suction power
A substrate containing artificial urine was prepared
by adding 20 ml of artificial urine onto a tissue paper (55
mm x 75 mm). On this substrate, a sample 1.0 g in weight of
the absorbent resin powder (A-1) or the aggregated powder (1)
W 3 placed. After the elapse of 10 minutes thence, a swelled
gel con~equently formed was collected and weighed. The
weight of the swelled gel was reported as the sample's
suction power of the artificial urine from the tissue paper.
(d) Particle size distribution
2~6272~
On a olassifier formed by superposing 20-mesh, 50-
mesh, and 100-mesh standard sieves 70 mm in diameter on a
receptacle plate underlaid by a classifying plate, a sample
30 g in weight of the absorbent resin powder (A-1) or the
aggregated powder (1) was placed and shaken with a
classifying device for 10 minutes. The fractions of the
sample consequently clas~ified were weighed and reported in
% by weight.
Fig. 2 illustrates an apparatus identical with the
apparatus of Fig. 1 except for the incorporation of
temperature controlling means 33 formed of an insulating
member 32 of glass wool, phenol resin wool, or asbestos
having embedded therein a coil 31 for conveying a thermal
medium 9uch as steam. The other numerical references used in
Fig. 2 are identical to those used in Fig. l.
Control 1
In a high-speed rotary paddle type mixer (produced
by Hosokawa Micron K.K. and marketed under trademark
designation of "Turburizer"), 100 parts by weight of the
absorbent resin powder (A-1) obtained by the procedure of
Example 1 and 6 parts by weight of water were mixed. From
the resultant agglomerate of cohering particles, an
aggregated powder (1) as a 20-mesh pass for comparison was
obtained by following the prooedure of Example 1. The
aggregated powder (1) for compari~on was tested in the same
manner as in Example l.
Examples 2 to 5
Size-enlarged powders (2) to (5) were produced by
following the procedure of Example 1, except that the
temperature of the inner wall of the cylindrical body, the
mixing ratio of the absorbent re~in powder (A-1) to the air
ourrent, the retention tlme of the air current in the
cylindrical body, and the average diameter of the water
droplets were varied as shown in Table 2. They were tested
in the same manner as in Example 1. The results are ~hown ln
Table 2.
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2~2723
Example 6
In a reaction vessel provided with a stirrer, a
nitrogen gas inlet tube, and a thermometer, 50 parts by
weight of corn starch, 200 parts by weight of water, and
1,000 parts by weight of methanol were placed, stirred as
swept with nitrogen gas at 50C for 1 hour, and cooled to
30C. The resultant mixture and 25 parts by weight of
acrylic acid, 75 parts by weight of sodium acrylate, 0.5 part
by weight of methylene bisacrylamide, 0.1 part by weight of
ammonium persulfate as a polymerization catalyst, and 0.1
part by weight of sodium hydrogen sulfite as an accelerator
added thereto were left reacting at 60C for 4 hours.
Consequently, a white suspension was obtained.
The powder obtained by filtering this white
suspension was washed with a water-methanol mixed solution
(weight ratio of water to methanol 2 : 10), vacuum dried at
60C for 3 hours, then pulverized, and sifted through a 20-
meqh metallic sieve, to obtain a 20-mesh pass (absorbent
resin (2)).
100 part~ by weight of the absorbent resin (2) was
mixed with a liquid mixture comprising 1 part by weight of
glycerol and 8 parts by weight of methanol. The resultant
mixture was heat-treated and subjected to the procedure of
Example 1, to afford an absorbent resin powder (A-2) as a 20-
mesh pass.
From this absorbent resin powder (A-2), an
aggregated powder (6) was obtained as a 20-mesh pas~ by
foilowing the procedure of Example 1, except that 20 parts by
weight of water was supplied to 100 parts by weight of the
resin powder (A-2). The aggregated powder (6) was left
drying at 105C for 3 hours and then tested.
Example 7
A copolymer was produced by preparing a mixture
comprising 60 part~ by weight of vinyl acetate and 40 parts
by weight of methyl acrylate, adding 0.5 part by weight of
benzoyl peroxide as an initiator to the mixture, dispersing
-20-
'
.~
2~2723
the re~ultant product of addition in 300 parts by weight of
water containing 3 parts by weight of partially saponified
polyvinyl alcohol and 10 parts by weight of sodium chloride,
subjecting the resultant dispersion to suspension
polymerization at 65C for 6 hourq, separating the resultant
polymer by filtration, and drying the separataed copolymer.
The copolymer thus obtained was saponified, washed, dried,
pulverized, and classified, to afford a 20-mesh pass
(absorbent resin (3)).
The absorbent resin (3) obtained consequently was
heat-treated in the same manner as in Example 6, to afford an
absorbent resin powder (A-3). An aggregated powder (7) was
obtained as a 20-me~h pass by subjecting the absorbent resin
powder (A-3) to the procedure of Example 1, except that 35
parts by weight of water was supplied to 100 parts by weight
of the absorbent resin powder (A-3). The aggregated powder
(7) was left drying at 105C for 3 hours and then tested.
Example 8
The absorbent resin powder (A-1) was subjected to
the procedure of Example 1, except that an aqueous solution
oontalning 15~ of the extract of a plant of family Theaceae
(produced by Shiraimatsu Shinyaku K.K. and marketed under
trademark designation of "NI Fleska 800 M0") as a deodorant
was used in the place of the water in the same amount, to
afford a size-enlarged powder (8).
Example 9
A mixed powder P was obtained by thoroughly mixing
100 parts by weight of the abqorbent resin powder (A-1)
~ obtained in Example 1 with 1 part by weight of a finely
particulate silica (produced by Nippon Aerosil K.K. and
marketed under trademark designation of "Aerosil 200"). The
mixed powder P was subjected to the procedure of Example l,
except that 10 parts by weight of water was supplied to 100
parts by weight of the mixed powder P, to afford an
aggregated powder (9).
Example 10
-21-
;.
., .
, .
.,
2~62~23
A mixed powder Q was obtained by thoroughly mixing
100 parts by weight of the absorbent resin powder (A-1)
obtained in Example 1 with 4 parts by weight of carbon black
(produced by Mitsubishi Chemical Industries, Ltd. and
marketed under trademark designation of "Mitsubishi Carbon
Black #600").
The mixed powder Q was subjected to the procedure of
Example 1, except that 10 parts by weight of water was
supplied to 100 parts by weight of the mixed powder Q, to
afford a size-enlarged powder (10).
Control 2
By following the procedure depicted in Fig. 3, 100
parts by weight of the absorbent resin powder (A-1) obtained
in Example 1 and 6 parts by weight of water were subjected to
size enlargement. Fig. 3 illustrates an apparatus which is
identical with the apparatus of Fig. 1, except two nozzles 15
for simultaneous injection of air and water were disposed at
two poqitions outside the dispersing member 12 as posed
obliquely in a downward direction. The other reference
numerals uqed in Fig. 3 are identical to those used in Fig.
1. In thi~ apparatus, the continuou~ agglomeration could not
be attained beoause a deposit 34 formed on the wall was quite
large. By sub~ecting the resultant agglomerate of cohering
particle3 to the same treatment as in Example 1, a an
aggregated powder (2) for comparison was obtained as a 20-
me~h pa~s. The size-enlarged powder (2) for comparison was
tested. The results are shown in Table 3.
~2723
3 ~ o ~ o ~ço, ~o ~o
-
_ ~0 d' ~o O ~ ~ ~
~ a~ ~ ~ 0~
~o 3 ~
-23-
~2723
¦ 0 0 ~ ,0~ O O ~ e D
e _ ~ O ~ O O ~ O
C>
-¦ e ~ ~ 1~ e~ ,, O ~ ,, D ~ D~
c~ 3
~ ~ ~ 1 ~ O C'~ r~ ,o~ ,~
D~ o ~ ~ ~ e
'~ Q, ¢ ~ ¢ ~
-24-
~8~2723
~. L.~ o~
c ~ ~ c. ~ - 3 R o ~ ~ j ~ R
R "~ ~ o~ o o C~ ~ o j
æ V ~ ~ ~ O
_
R o ~ ~" ,D x _~ R
~I E 3 ~ ~ O ~ ,, u, 'a
R
E x O x
B
~_ CD ~ ~' C~ ~ ~ '~
Cq
R
~ a 3 _ co oo ,~ o ~
æ ~ , O ~ ~ ~ ~ ~ R
;~ 3 ~ ;~ R ~ 5 ;1~ El ~ a) a
¢ O ~ , h c~ ~ ~, ~ O
-25-
2 ~ 2 3
Industrial Applicability
In accordance with this invention, an absorbent
resin powder and aqueous liquid droplets both dispersed with
a current of air were caused to flow down the interior of a
cylindrical member erected upright from the upper end
thereof and the resin powder and the liquid droplets during
their descent toward the lower part of the cylindrical member
are therefore brought into mutual parallel flow contact and,
as a result, groups of a plurality of particles of the resin
powder are coherently joined through the medium of the liquid
droplets while avoiding mutual collision of the individual
particles of the resin powder and not relying on any
mechanical shearing force. The formation of agglomerate of
cohering particles, therefore, proceeds without causing fine
division of the resin powder or infliction of fracture on the
qurface of the resin powder. Thus 9 the produced absorbent
resin powder contains no minute particle and enjoys an ideal
quality. Further, since the agglomerate of cohering
particles can be obtained by simply causing the absorbent
re~in powder to ~low continuously down the interior of the
cylindrical member and ~ince the produced agglomerate can be
subjected to pulverization by crushing without preparatorily
undergoing a drying step, the absorbent resin powder can be
continuously produced with a high operational efficiency.
In accordance with the method of this invention, the
occurrence of dust and the degradation of a working
environment which generally are not avoidable in the use of a
re~in powder can be precluded because the absorbent resin
powder of this invention is not suffered to contain minute
particles. Particularly when the resin powder has the
surface thereof subjected to a cross-linking treatment for
the sake of improvement of the quality thereofl the surface
layer formed on the resin powder in consequence of the cross-
linking treatment remain~ intact and the produced absorbent
re~in powder enjoys high quality becau3e the individual
particles of the resin powder are prevented from colliding
-26-
- 2~62723
against one another and sustaining damage due to a mechanical
shearing force during the ~ormation of agglomerate of
cohering particleq within the cylindrical member.
The product of the agglomeration of the absorbent
resin powder which is obtained as described above can be
extensively utilized in sanitary articles such as sanitary
napkins and disposable diapers, water-retaining agents for
agriculture, and desiccants, for example.
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