Note: Descriptions are shown in the official language in which they were submitted.
12~Z~14
1 This invention relates to a process for granulat-
ing a water-absorbent resin, in particular a pxocess for
preparing a water-absorbent resin having an appropriate
particle diameter and a narrow particle size distribution.
Recently, water-absorbent resins have been
used in the field of sanitation as menstrual articles,
diapers, disposable house-cloths and the like and in the
field of agriculture and horticulture as water retentive
materials, 80il conditioners and the like. Further,
they are useful in other various fields such as coagulation
o ~ludge~, prevention of dew conden~ation on construction
material~, dehydration o oil~ and the like.
Water-absorbent resins have extensively been
u~ed part~cularly or sanitary products such as menstrual
articles, diapers and the like.
A~ such water-ab30rbent re~ins, there are known
crosslinked acrylic acid salt polymers, saponification
products of crosslinked acrylic acid ester-vinyl acetate
copolymers, crosslinked starch-acrylic acid salt graft
copolymers, saponification products o crosslinked
starch-acrylonitrile graft copolymers, crosslinked
polyvinyl alcohols grafted with maleic anhydride, cross-
li~ed polyethylene oxides and the like.
These water-ab~orbent resins are generally
produced by aynthesizing polymer~ by such a process as
~b
91~
1 inverse suspension polymerization, inverse emul~ion
polymerization, aqueous solution polymerization or
reactions in organic solvents and drying the polymers
as such or subjecting the polymers after drying to
grinding step, if necessary.
However, when a water-absorbent resin was
produced by such a process, there was usually obtained a
product having a wide range of particle size distribution
and containing finely divided particles to a considerable
extent.
- When a powdery water-absorbent resin is used
in the field of sanitation, it is frequently used by
mixing with a ground pulp, spreading uniformly on a ground
pulp layer or inserting between water-absorbent papers.
In using a water-ab~orbent resin which consists of finely
divided particles or contains a lar~e amount of finely
divided particles, it is hard to handle because it tends
to cause bridging during transfer or feeding, and
furthermore the envLn~m~nt i5 ~ deteriorated to a
very inferior level because of rising of dust, which may
cause pollution or trouble of installations. Further,
finely divided particles tend to drop off from sanitation
products.
When such a water-absorbent resin is used as a
water-retentive material for agriculture and horticulture,
it may be attached to machines or may form nonuniform
mixtures in mixing thereof with soil or sand.
The present inventors have conducted earnest
2 -
,, ,
1~9Z914
l researches with a view to overcoming the aforementioned
defects in the conventional techniques and for see~ing a
process for preparing stably and easily a water-absorbent
resin which has particle sizes depending on its applications
and a narrow particle size distribution and will not
produce dust. As a result thereof, they have found that
a water-absorbent resin having appropriate particle
sizes and a narrow particle size distributi~n and exclud-
ing finely divided particles having a particle size of
lO0 ~ or less can be obtained by adding a powdered
inorganic material in a proportion of 0.000005 - 0.2 part
by weight to 1 part by weight of a water-absorbent resin
containing therein a carboxylate as a component of the
polymer with agitation in an inert solvent in the presence
of 0.1 - 5.0 parts by weight of water and 0.005 - 0.2
part by weight of a surfactant,and then removing water
and the inert solvent by distillation. Thus, they have
accomplished the present invention.
The water-absorbent resin containing a carboxylate
as a constituent of the polymer according to ~his invention
includes crosslinked acrylic acid salt polymers, saponifica-
tion products of crosslinked acrylic acid ester-vinyl
acetate copolymers, crosslinked starch-acrylic acid salt
graft copolymers, saponification products of crosslinked
starch-acrylonitrile graft copolymers, crosslinked polyvinyl
alcohol grafted with maleic anhydride and the like. These
resins are preferably used in this invention. It is need-
less to say that a copolymer having as a main component
- 3 -
129Z914
1 thereof an acrylic acid salt such as cro~slinked
acrylic acid salt-acrylamide copolymers, crosslinked
acrylic acid salt-2-acrylamide-2-methylpropane sulfonic
acid salt copolymers or the like may be used in this
invention.
The embodiments of this invention are now
explained in detail. The water-absorbent resin containing
a carboxylate can be prepared by any one of the processes
which are disclosed in Japanese Patent Publication No.
25045/85, Japanese Patent Application No. 210198/84,
Japanese Patent Application Kokai (Laid-Open) Nos.
158210/82 and 21405/82, ~apanese ~atent Publication No.
46199/78, Japanese Patent Application Kokai (Laid-Open)
Nos. 71907/83 and 84304/80 and the like.
Typical preparation examples of the water-
absorbent resin are illustrated below.
Preparation Example 1
A process which compxises suspending an aqueous
solution of an ,~-unsaturated carboxylic acid and an
alkali metal salt thereof in a petroleum hydrocarbon
solvent containing a saccharose fatty acid ester in the
presence or absence of a crosslinking agent and subjecting
the suspension to polymerization in the presence of a
radical polymerization initiator.
Preparation Example 2
; A process which comprises suspending an aqueous
- 4 -
1~9Z91~
1 solution of acrylic acid and an alkali salt of acrylic
acid in an alicyclic or aliphatic hydrocarbon solvent
containing a surface active agent havingan HLB value of
8 - 12 and su~jecting the suspension to polymerization
in the presence of a water soluble radical polymerization
initiator.
Preparation Example 3
A process which comprises suspending an aqueous
solution of a monomer in a hydrophobic liquid inert to
lO ~ the polymerization by using as a protective colloid a
reaction product obtained by grafting l - 20% by weight
of an ,~-unsaturated polyvalent carboxylic acid or an
anhydride thereof to a monoolefin polymer having a
molecular weight of 750 - lO,000 or a product obtained
by oxidizing said monoolefin polymer to a final acid
value of lO - lO0, and subjecting the suspension to
polymerization in the presence of a water soluble radical
polymerization initiator.
Preparation Example 4
A process which comprises dispersing or suspend-
ing an aqueous solution of a water soluble ethylenically
unsaturated monomer, the concentration of said solution
being 40% by weight to the saturation concentration, in
a hydrocarbon or a halogenated aromatic hydrocarbon by
using a cellulose ester or cellulose ether which is oil
soluble at the.polymerization temperature as a protective
lZ~Z9 1~
1 colloid, and subjecting the mixture to polymerization
using a persulfate as a polymerization initiator.
Preparation Example 5
A ~rocess for preparing a polymer which comprises
polymerizing (A) at least one of starch and cellulose,
(B) at least one of monomers having a double bond being
capable of causing addition polymerization which are
water soluble or become water soluble by hydrolysis and
(C) a crosslinking agent as the essential constituents,
10- and subjecting the polymerization product to hydrolysis,
if necessary.
Preparation Example 6
A process for preparing a water-absorbent resin
which comprises adding a polymerization initiator to a
warmed aqueous solution containing potassium acrylate and
a water miscible or water soluble divinyl compound, the
concentration of said monomers being in the range of
55 - 80% by weight, subjecting the mixture to polymeri-
zation without external heating, and vaporizing the
water.
; The water-absorbent resin used in this invention
may be prepared by any producing process without limitation
to those mentioned above.
According to this invention, when these water-
absorbent resins are granulated, they are allowed tocontain a certain amount of water. However, the effects
.
~ - 6 -
.;,
12~ i4
1 of this invention vary greatly depending upon the
proportion of water to be contained. Thus, in this
invention, the amount of water to be contained should be
varied within the ran~e of 0.1 - 5.Q parts by weight
S to 1 part by weight of water-absorbent resins.
If the amount of water is 0.1 part by weight
or less, no granulation is o~tained or the effect of
granulation, even if obtained, is poor. On the other
hand, if the amount of water is 5.0 parts by weight or
more, bulk materials are obtained in place of granules,
or the granules, even if obtained, are unfavorably
coarse.
From such relationships, more preferable
results are obtained in the case of particularly 0.2 -
3.0 parts by weight of the amount of water. Further, itis also possible to obtain particles having no finely
divided particles of 100 ~ or less and having appropriate
particle sizes, the distribution of which is narrow, by
changing the amount of water within the range mentioned
above.
As the surface active agent used in this inven-
tion, there may be cited sorbitan fatty acid esters or
sorbitan fatty acid ester ethers having an ~LB of 8 - 12
such as sorbitan monolaurate or oxyethylene sorbitan
monostearate ether; saccharose fatty acid esters having
an HLB of 2 - 16; cellulose esters or cellulose ethers;
low molecular weight monoolefin polymers or low molecular
weight diolefin polymers grafted with maleic anhydride;
- 7 -
Z~
1 monoolefin polymers having an acid value of 10 - 10
or the like.
However, if the process according to this
invention is carried out with a sorbitan fatty acid
S ester having a low HLB value such as sorbitan monostearate
(HLB = 4.7) among sorbitan fatty acid esters, there are
obtained the only granules that will be finely divided
by applying a little force. Thus, such a case does not
attain the object of this invention.
~ When the amount of the surface active agent used
is 0.005 part by weight or less to 1 part by weight of
a water-absorbent resin, it is difficult to obtain products
having an appropriate particle size and coarse particles
or bulk products are obtained. ThU5, the case is not
preferred. When the amount of the surface active agent
is 0.2 part by weight or more, it contributes little to
granulation. Further, it influences adversel~ the
performanc~ of a water-absorbent resin and such case
is not economical. Thus, the case is not preferred
either.
The inert solvent used in this invention may
be any one that will not influence adversely the polymer
and its constituents. Particularly, when a petroleum oil
solvent or a lower alcohol is used, a preferable result
is obtained.
The petroleum oil solvent includes aliphatic
hydrocarbons, alicyclic hydrocarbons and aromatic hydro-
carbons. As the aliphatic hydrocarbons, there are cited
- 8 -
12~914
1 normal pentane, normal hexane, normal heptane, ligroin
and the like. As the alicyclic hydrocarbons, there are
cited cyclopentane, methylcyclopentane, cyclohexane,
methylcyclohexane and the like. As the aromatic hydro-
carbons, there are cited benzene, toluene, xylene andthe like.
As the lower alcohols, there are cited methanol,
ethanol, isopropa~ol and the like. Particularly, normal
hexane, normal heptane, cyclohexane, toluene, xylene and
methanol are industrially stable in their qualities.
Furthermore, they are easily available and inexpensive,
so that they can be used advantageously.
When the water-absorbent resin and the inert
solvent are used generally in a ratio of 1 - 100 parts
by weight, preferably 2 - 50 parts by weight of the
inert solvent to 1 part by weight of the water-absorbent
resin, a preferred result is obtained. The less the
amount of the inert solvent, the better the volumetric
efficiency. However, the dispersion of the water-
absorbent resin in a water-containing state is deteriorated,
and a bulk product is often produced upon addition of a
powdery inorganic material. On the other hand, when the
amount of the inert solvent is too much, said water-
~; absorbent resin is easily dispersed and granulation is
carried out homogeneously, so that the range of the particlesize distribution becomes narrow. However, the volumetric
efficiency is lowered. Thus, it is preferred to conduct
granulation within the aforementioned range of the ratio.
:
_ g _
2~?19t
1 As the powdery inorganic materials which can
be used in this invention, there are mentioned, for
example, silicon dioxide, aluminum oxide, titanium
dioxide, calcium phosphate, calcium carbonate, talc,
magnesium phosphate, calcium sulfate, diatomaceous
earth, bentonite, zeolite, other metal oxides and the
like. In particular, silicon dioxide, aluminum oxide
and titanium dioxide are preferred. There are preferably
used these powdery inorganic materials having a particle
size of generally 200 ~ or less, particularly 100 ~ or
- less.
If the amount of the powdery inorganic material
added is used in a proportion of generally 0.000005 - 0.2
part by weight, preferably 0.000005 - 0.1 part by weight
to the water-absorbent resin, a preferable result is
obtained. Generally when the amount of the powdery
inorganic material added is less than 0.0000~5 part by
weight, no effect of addition appears. When it exceeds
0.2 part by weight, the performance of the water-absorbency
is unfavorably deteriorated.
Particles having an appropriate particle size,
the distribution of which is in a narrow range, can be
obtained by changing the amount to be added within the
aforementioned ranges. In order to obtain stable granules
having a narrow particle size distribution, it is necessary
to use an apparatus wherein homogeneous dispersion can be
accomplished for the entire suspension.
The embodiments of this invention include various
, . -- 1 0
291~
1 processes. For example, a water-absorbent resin having
a suitable particle size can be o~tained by dispersing
a water-absorbent resin in an inert sol~ent containing
a surface active agent, adding water with agitation to
S the dispersion for uniform absorption of water into the
water-absorbent resin, adding a powdery inorganic material
therein and then evaporating water and said solvent in a
usual manner, or by oonduct~g a polymerization reaction
for getting a water-absorbent resin by use of the afore-
mentioned inert solvent, controlling, if necessary, the
- ratio of the three, that is, the water-absorbent resin,
water and the surface active agent in the polymerization
liquid obtained from said reaction step, adding a powdery
inorganic material to the mixture, and finally evaporating
water and the solvent.
In the conventional processes for producing
water-absorbent resins, final products contained finely
divided particles, especially those having a particle
size of 100 ~ or less in a considerable proportion, and
products having a wide particle size distribution were
usually obtained.
When the granulation process according to this
invention is used, it is possible to obtain a water-
absorbent resin which contains none of the finely divided
particles and has an appropriate particle size depending
on its application and a narrow particle size distribution.
Thus, no dust will be caused on transfer or packaging
cperations, and it is possible to prevent the deterioration
L,~
12~'~914
1 of working en~ironment and the contamination or trouble
of apparatuses.
The water-absorbent resin according to this
invention, when used as sanitary products or agricultural
or horticultural products, does not drop off fine
powders. Moreover, a water-absorbent resin having a
suitable particle size depending on its applications can
be obtained according to this invention, so that the
spreadability, mixing property, water-retentive property
and the like of the resin can be remarkably improved
according to this invention.
This invention will be actually illustrated by
the following Examples and Comparative Examples.
Comparative Example l
In a 500 ml four-neck round bottom flask
equipped with a stirrer, a reflux condenser, a dropping
unnel and a nitrogen gas introducing tube was charged
280 ml of n-heptane, and then 0.75g of saccharose di- and
tri-stearate having an HLB value of 3 was dispersed in
the soivent. Oxygen dissolved in the dispersion was
purged by blowing nitrogen gas, and the temperature of
the mixture was raised up to 50C to dissolve with
agitation the saccharose di- and tri-stearate. The
resultant ~olution was then cooled to 30C.
In a 200 ml Erlenmeyer flask was separately
placed 37.5 g of 80~ by weight aqueous acrylic acid
solution, and subsequently 75 molar ~ neutralization was
- 12 -
12~914
1 carried out with external ice-cooling by dropping 49.3g of
2S.4% by weight aqueous sodium hydroxide solution, and
then 0.045g of potassium persulfate was added and dis-
solved therein.
me partially neutralized aqueous acrylic acid
salt solution was added in the four-neck flask to disperse
it, and the system was sufficiently purged with nitr~gen
again, and then the temperature was raised to maintain
the temperature of the bath at 55 - 65C. The polymeriza-
tion reaction was conducted for 1 hour to obtain the
~ polymerization liquid product of a water-absorbent resin.
Water and n-heptane were removed by distillation, and
the residue was dried to obtain 41.0g of polymer beads
having a particle size of 150 - 400 ~.
Examples 1 - 11
A powdery inorganic material was added with
stixring to the polymerization liquid product mentioned
above and those stated hereinafter which contain water-
absorbent resins, water, inert solvents and surface
active agents. The water and the inert solvents were
removed by distillation and drying was conducted to
obtain granulated water-absorbent resins. me results
are shown in Table 1 below. The amounts and particle
sizes of the water-absorbent resins obtained in the
Comparative Example 1 mentioned above and Comparative
Examples 2, 3, and 4 stated hereinafter are also shown
in the right column of Table 1 for comparison.
- 13 -
129~
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-- 14 --
lZ92~914
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-- 15 --
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129Z9i4
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-- 17 --
1~329~
1 Comparative Example 2
In the same 500 ml four-neck round flask as
used in Comparative Example 1 was charged 213 g of
cyclohexane, and then 0.8 g of sorbitan monolaurate
having an HLB value of 8.6 was added and dispersed in the
solvent. Oxygen dissolved in the dispersion was purged
by blowing nitrogen gas, and the sorbitan monolaurate
was dissolved with agitation at room temperature.
In a 200 ml Erlenmeyer flas~ was separately
placed 39.1 g of acrylic acid having a purity of 99.8~ by
weight, and 80 molar % of the acrylic acid was neutralized
with external ice-cooling by dropping ?6.5 g of 22.6~ by
wéight of aqueous sodium hydroxide solution, and then
0.13 g of potassium persulfate was added and dissolved
therein.
The partially neutralized aqueous acrylic acid
salt solution was added in the four-neck flask to disperse
it, and the system was sufficiently purged with nitrogen
again, and then the temperature was raised to maintain
the temperature of the bath at 55 - 60C. The polymer-
ization reaction was conducted for 3 hours to obtain the
polymerization liquid product of a water-absorbent resin.
The water and the cyclohexane were removed by distillation,
and the residue was dried to obtain 48.0 g of a dried
polymer in the form of fine particles having a particle
size of 50 - 350 ~.
- 18 -
1~9Z9~ `
1 Comparative Example 3
In the same 500 ml four-neck round flask as
used in Comparative Example 1 was charged 280 ml of n-
heptane and then 2.3 g of modified polyethylene wax
(trademark~ Wax 1105A', manufactured by Mitsui Petro-
chemical Industries, Ltd., molecular weight: 2700, density:
0.94, acid value: 30) was added and dispersed in the
solvent. Oxygen dissolved in the dispersion was purged
by blowing nitrogen gas, and the modified polyethylene
wax was dissolved with agitation by raising the tempera-
~ ture up to 65~C.
In an Erlenmeyer flask was separately placed
37.5 g of 80% by weight aqueous acrylic acid solution and
75 molar ~ of neutralization was carried out with external
ice-cooling by dropping 44.5 g of 28.1% by weight of
aqueous sodium hydroxide solution, and then 0.045 g of
potassium persulfate was added and dis301ved therein.
The partially neutralized aqueous acrylic acid
salt golution was added in the four-neck flask to disperse
it, and the system was sufficiently purged with nitrogen
again, and the temperature was raised to maintain the
temperature of the bath at 60 - 65C. me polymerization
reaction was conducted for 1 hour to obtain the polymer-
ization liquid product of a water-absorbent resin. The
water and the n-heptane was removed by distillation, and
the residue was dried to obtain 40 g of polymer beads
having a particle size of 50 - 350 ~.
-- 19 --
12929~
1 Comparative Example 4
In the same 500 ml four-nec~ round flask as
used in Comparative Example 1 was charged 280 ml of
cyclohexane, and then 1~86 g of ethylcellulose (trade-
name; Ethylcellulose N-200, manufactured by ~ercules)
was added and dispersed in the solvent. Oxygen dissolved
in the dispersion was purged by blowing nitrogen gas, and
the ethylcellulose was dissolved by raising the tempera-
ture up to 75C.
Inan Erlenmeyer flask was separately placed
37.5 g of 80% by weight aqueous acrylic acid solution,
and 75 molar % of neutralization was carried out with
external ice-cooling by dropping 44.5 g of 28.1% by
weight of aqueous sodium hydroxide solution and then
0.045 g of potassium persulfate was added and dissolved
therein.
The partially neutralized aqueous acrylic
acid salt solution was added in the four-neck flask to
disperse it, and the system was again sufficiently
purged with nitrogen, and then the temperature was
raised to maintain the temperature of the bath at
- 60 - 65C. The polymerization reaction was conducted
for 1 hour to obtain the polymerization liquid product of
a water-absorbent resin. The water and cyclohexane were
removed by distillation, and the residue was dried to
obtain 40.5 g of polymer beads having a particle size of
50 - 350 ~.
- 20 -
,~,
1~92~14
1 Example 12
In a 500 ml four-neck r~und b~ttom flask
equipped with a stirrer, a reflux condenser, a water-
s~_parator, a dropping funnel and a nitrogen gas introduc-
ing tube was charged 50 g of a commercial water-absorbent
resin, crosslinked starch-acrylic acid salt graf~ polymer
(trademark: SANWET IM-1000, manufactured by Sanyo Chemical
Ind., Ltd.; particle size; 30 - 840 ~, water content:
9.0~), and then 300 ml of n-heptane and 2.5 g of sorbitan
10 ~monolaurate were added, and 45.5 g of water was slowly
- added with agitation from the dropping funnel.
To the suspension was added 0.68 g of silica
(trademark: TOKUSIL P. manufactured by Tokuyama Soda
Co., Ltd.), and then the water and n-heptane were removed
by distillation, and the residue was dried to obtain
53.5 g of granules having a particle size of 350 - 900 ~.
Example 13
In the same ~pparatus as used in Example 12 was
charged 50 g of a commercial water-absorbent resin,
crosslinked acrylic acid salt polymer (trade~ark:
'Arasorb 720', manufactured by ARAKAWA KAGAKU; particle
size: 50 - 900 ~, water content: 10%), and then 300 ml
of n-heptane and 2.5 g of sorbitan monolaurate were added,
and 20 g of water was slowly added with agitation from
the dropping funnel. To the suspension was added 0.45 g
of silica (trademark: TOKUSIL P, manufactured by Tokuyama
Soda Co., Ltd.), and then the water and n-heptane were
- 21 -
,~
i~9 ~91~
1 removed by distillation, and the residue was dried to
obtain 53.0 g of granules having a particle size of
3~0 - 1000 y.
Example 14
In the same apparatus as used in Example 12
was charged 30 g of the water-absorbent resin ~water
content: 5.0%) obtained in Comparative Example 1, and
then a liquid mixture of 60 g of methanol, 60 g of water
and 1.7 g of sorbitan monolaurate was added and mixed
well. To the suspension was added 0.25 g of silica
(trademark: TOKUSIL P, manufactured by Tokuyama Soda
Co., Ltd.). The water and methanol were subsequently
removed by distillation, and the residue was dried to
obtain 30.5 g of granules having a particle size of
500 - 1000 ~.
Example 15
In the same apparatus as used in Example 12
was charged 50 g of a commercially available water-
absorbent resin, crosslinked polyvinyl alcohol grafted
with maleic anhydride (Trademark:"KI Gel", manufactured by
Kuraray Co., Ltd., particle size: 30 - 1000 ~, water
content: 8.0%), and then 300 ml of cyclohexane and 1.0 g
of sorbitan monolaurate were added, and 46 g of water was
slowly added with agitation from the dropping funnel.
To the suspension was added 0.23 g of silica ~trad~E~k :
"Aerosil 380', manufactured by Nippon Aerosil Co., Ltd.).
- 22 -
;:~
~29Z9i~
1 The water and cyclohexane were subsequently removed by
distillation, and the residue was dried to obtain 51.5 y
o~ granules having a particle size of 500 - 140~ ~.
Example 16
In the same apparatus as used in Example 12
was charged 50 g of a commercially a~ailable water-
absorbent resin, saponification product of crosslinked
acrylic acid ester-vinyl acetate copolymer (Trademark:
"Sumikagel S-50', manufactured by Sumitomo Chemical Co.,
Ltd., particle size: 80 - 400 ~, water content: 5.0%),
and then 300 ml of cyclohexane and 1.0 g of sorbitan
monolaurate were added, and 47.5 g of water was slowly
added with agitation from the dropping funnel. To the
suspension was added 0.5 g of silica (trademark:'~erosil
130', manufactùred by Nippon Aerosil Co., Ltd.). The
water and cyclohexane were subsequently removed by dis-
tillation, and the residue was dried to obtain 52.5 g of
granules ha~ing a particle ~ize of 300 - 800 ~.
Comparative Example 5
In the same apparatus as used in Example 12
was charged 30 g of the water-absorbent resin, obtained
in Comparative Example 2 (water content: 5.0%), and then
280 ml of n-heptane was added and the mixture was mixed
well. Then, 0.75 g of silica (trademark: TOKUSIL P,
~;~ 25 manufactured by Tokuyama Soda Cs., Ltd.) was added therein
with agitation. The n-heptane ~as subsequently removed
- 23 -
.~, .
3Z~
1 by distillation, and the residue was dried to obtain 29.5
g ~f a particulate polymer ha~ing the same particle size
as the original one of S0 - 350 ~.
Comparative Example 6
In the same apparatus as used in Example 12
except the volume of 2 liters was charged 50 g of a
commercially available water-absorbent resin (trademarX:
~QUALIC CA, manufactured by Nippon Shokubai Kagaku ~ogyo
Co., Ltd., water content: 9.0%), and then 1000 ml of n-
heptane and 2.5 g of sorbitan monolaurate were added and
314 g of water was slowly added with agitation from the
dropping funnel. Then, 0.68 g of silica (trademark:
TO~USIL P, manuactured by Tokuyama Soda Co., Ltd.) was
added to the suspension. me water and n-heptane were
subsequently removed by distillation, and the residue
was dried to obtain only 10 g of granules with the rest
being bulk.
Comparative Example 7
Experiment was conducted in the same manner as
in Example 12 except that no sorbitan monolaurate was
used. Most of th0 product was bulk with granules being
obtained only in an amount of 5 g.
- 24 -
