Method of producing hydrophilic resin

A method of producing hydrophilic resin by pulverizing and drying a hydrogel polymer, in which, during pulverization of the hydrogel polymer, the hydrogel polymer is sheared between two spiral rotary blades with different respective feed rates, provided opposite one another. Due to the difference in feed rates of the two rotary blades, one rotary blade overtakes the other, and the hydrogel polymer is caught therebetween and sheared. It is preferable if the temperature of the hydrogel polymer at this time is no less than 40.degree. C.

FIELD OF THE INVENTION 
The present invention relates to a method of producing hydrophilic resin, 
which may be suitably used for various purposes such as sanitary materials 
for disposable diapers and pads for incontinence, water-retaining 
materials for sandbags, materials for maintaining food freshness, and 
water-retaining materials for agriculture and gardening, in which method 
lumps of a hydrogel polymer having high adhesion and elasticity are 
pulverized without kneading and crushing. 
BACKGROUND OF THE INVENTION 
In recent years, water-absorbent resin, which is a type of hydrophilic 
resin, has been widely used as, for example, a constituent material of 
sanitary materials for disposable diapers, sanitary napkins, pads for 
incontinence, etc., in order to prevent contamination of clothing, etc., 
by bodily fluids such as urine and blood, by absorbing and retaining these 
bodily fluids. 
Further, recently, in order to make such sanitary materials thinner and 
improve their performance, the trend is to decrease the amount of fiber 
base materials (such as pulp) and increase the amount of water-absorbent 
resin used therein. Accordingly, further improvement of the water 
absorbing performance of such water-absorbent resin is needed. 
Such water-absorbent resins can be obtained by polymerizing monomers such 
as acrylic acid, sodium acrylate, etc. in an aqueous solution in the 
presence of a crosslinking agent, yielding lumps of a hydrogel polymer, 
which are pulverized to a suitable particle size, dried, and then further 
pulverized as necessary. 
One conventional method of pulverizing the foregoing hydrogel polymer is 
pulverizing by feeding between a two-shaft roller-type cutter. 
However, when pulverizing the hydrogel polymer using the foregoing 
conventional method, even if the foregoing hydrogel polymer is fed into 
the roller-type cutter, it is not easy to bite into the hydrogel polymer, 
because it is a semi-solid gel having elasticity, and the hydrogel polymer 
may be kneaded during pulverizing. For this reason, if the foregoing 
conventional method is used, the hydrogel polymer is subject to great 
mechanical external force, and there are cases in which, for example, 
crosslinked polymer chains are broken, thus increasing the content of 
water-soluble components therein. 
Further, in order to improve the water absorbing performance (especially 
absorbing capacity and absorption rate) of the water-absorbent resin, the 
foregoing hydrogel polymer is often made to contain bubbles by 
polymerizing the constituent monomers in an aqueous solution in the 
presence of a crosslinking agent. In this case, with the foregoing 
conventional pulverization method, the bubbles contained in the hydrogel 
polymer are squashed and reduced in number. Accordingly, in a 
water-absorbent resin obtained in this way, since the reduced number of 
bubbles leads to decreased surface area, it may not be possible to ensure 
sufficient liquid infiltration spaces necessary for movement of the 
aqueous liquid, thus impairing permeability to and dispersion of the 
aqueous liquid. For this reason, a problem with water-absorbent resins 
obtained by the conventional methods is that, during the production 
process, not only is the content of water-soluble components increased, 
but performance, such as absorbing capacity, is also impaired. These 
problems are not limited to water-absorbing resins, but are common to all 
hydrophilic resins. 
SUMMARY OF THE INVENTION 
The present invention was created in view of the foregoing problems with 
the conventional methods, and it is an object hereof to provide a method 
of producing hydrophilic resin which, by pulverizing a hydrogel polymer 
with minimal kneading and crushing, is capable of obtaining a hydrophilic 
resin having few water-soluble components and having superior performance, 
such as absorbing capacity. 
As a result of close investigations to attain the foregoing object, the 
present inventors discerned that, by pulverizing a hydrogel polymer by 
shearing between two spiral rotary blades with different feed rates, 
provided opposite one another, kneading and crushing during pulverization 
of the hydrogel polymer could be held to a minimum, and a hydrophilic 
resin having few water-soluble components and having superior performance, 
such as absorbing capacity, could be easily produced. Thus the present 
invention was completed. 
In other words, in order to attain the foregoing object, the method 
according to the present invention is a method of producing hydrophilic 
resin by pulverizing and drying a hydrogel polymer, and includes the step 
of pulverizing the hydrogel polymer by shearing between two spiral rotary 
blades with different respective feed rates, provided opposite one 
another. 
With the foregoing method, the hydrogel polymer gets in between the two 
spiral rotary blades with different respective feed rates, and, due to the 
feed effect thereof, is easily fed into the rotary blades. Further, with 
the foregoing method, due to the different respective feed rates of the 
rotary blades, one rotary blade overtakes the other, and the hydrogel 
polymer is caught therebetween and sheared. For this reason, with the 
foregoing method, the hydrogel polymer can be pulverized by shearing, thus 
holding kneading and crushing to a minimum. Accordingly, with the 
foregoing method, a hydrophilic resin having few water-soluble components 
and having superior performance, such as absorbing capacity, can be easily 
obtained. 
Additional objects, features, and strengths of the present invention will 
be made clear by the description below. Further, the advantages of the 
present invention will be evident from the following explanation in 
reference to the drawings.

DESCRIPTION OF THE EMBODIMENTS 
In what follows, one embodiment of the present invention will be explained 
in detail with reference to FIGS. 1 through 4. The method of producing 
hydrophilic resin according to the present invention is a method which, by 
pulverizing a hydrogel polymer with minimal kneading and crushing, is 
capable of producing a hydrophilic resin with low water-soluble component 
content, and having superior performance, such as absorbing capacity. For 
this purpose, in the present invention, the hydrogel polymer is pulverized 
by shearing between two spiral rotary blades with different respective 
feed rates, provided opposite one another. 
The foregoing hydrogel polymer to be pulverized in the present invention is 
a hydrogel polymer obtained, for example, by polymerization of monomer 
substances including a water-soluble, ethylenically unsaturated monomer in 
the presence of, as necessary, a crosslinking agent. The foregoing 
hydrophilic resin according to the present invention can be obtained by 
pulverizing, drying, and, as needed, further pulverizing of the foregoing 
hydrogel polymer. A specific example of a hydrophilic resin according to 
the present invention is a resin made of a water-soluble, ethylenically 
unsaturated monomer which has an internal crosslinked structure, and which 
is partially neutralized, for example, a water-absorbent resin. 
The ethylenically unsaturated monomer used as raw material for the 
foregoing hydrogel polymer is a water-soluble monomer. Specific examples 
of such monomers include monomers containing acid groups, such as 
(meth)acrylic acid, .beta.-acryloyloxypropionic acid, maleic acid, maleic 
anhydride, fumaric acid, crotonic acid, itaconic acid, cinnamic acid, 
2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, 
2-(meth)acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, 
styrenesulfonic acid, allylsulfonic acid, vinylphosphonic acid, 
2-(meth)acryloyloxyethyl phosphate and (meth)acryloxyalkanesulphonic acid, 
and alkaline metal salts, alkaline earth metal salts, ammonium salts, and 
alkyl amine salts thereof; dialkylaminoalkyl (meth)acrylates, such as 
N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl 
(meth)acrylate and N,N-dimethylaminopropyl (meth)acrylamide, and 
quaternary compounds thereof (for example, a product of a reaction with 
alkyl hydride, a product of a reaction with dialkyl sulfate, etc.); 
dialkylaminohydroxyalkyl (meth)acrylates and quaternary compounds thereof; 
N-alkylvinylpyridinium halide; hydroxyalkyl (meth)acrylates, such as 
hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 
2-hydroxypropyl (meth)acrylate; acrylamide, methacrylamide, N-ethyl 
(meth)acrylamide, N-n-propyl (meth)acrylamide, N-isopropyl 
(meth)acrylamide, and N,N-dimethyl (meth)acrylamide; alkoxypolyethylene 
glycol (meth)acrylates and polyethylene glycol mono(meth)acrylates, such 
as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and 
methoxypolyethylene glycol (meth)acrylate; vinylpyridine, N-vinylpyridine, 
N-vinylpyrrolidone, and N-acryloyl piperidine; and N-vinylacetamide. A 
single one of the foregoing ethylenically unsaturated monomers may be used 
alone, or two or more may be used in combination. 
Among the foregoing examples of ethylenically unsaturated monomers, 
monomers containing an acrylic acid salt monomer as chief constituent are 
preferred because absorption characteristics and safety of the resulting 
hydrogel polymer can be further improved. Here, "acrylic acid salt 
monomer" means acrylic acid and/or water-soluble salts thereof. Further, 
water-soluble salts of acrylic acid are alkaline metal salts, alkaline 
earth metal salts, ammonium salts, hydroxy ammonium salts, amine salts and 
alkyl amine salts of acrylic acid having a neutralization ratio within a 
range from 30% to 100% by mole, preferably from 50% to 99% by mole; among 
these, sodium salts and potassium salts are especially preferred. A single 
one of the foregoing acrylic acid salt monomers may be used alone, or two 
or more may be used in combination. Incidentally, the average molecular 
weight (degree of polymerization) of the hydrophilic resin is not limited 
to any particular average molecular weight. 
Further, the monomer substances may also include, to an extent that does 
not substantially interfere with the hydrophilic nature of the resultant 
hydrogel polymer, other monomers which are copolymerizable with the 
ethylenically unsaturated monomer (copolymerizable monomers). Specific 
examples of such copolymerizable monomers include (meth)acrylic esters 
such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl 
(meth)acrylate; and hydrophobic monomers such as vinyl acetate and vinyl 
propionate. A single one of the foregoing copolymerizable monomers may be 
used alone, or two or more may be used in combination. 
Specific examples of the crosslinking agent which may be used as necessary 
when polymerizing the foregoing monomer substances include compounds 
having in their molecular structure a plurality of vinyl groups, and 
compounds having in their molecular structure a plurality of functional 
groups capable of reacting with carboxyl groups, sulfonic groups, etc. 
Specific examples of compounds having in their molecular structure a 
plurality of vinyl groups include N,N'-methylene bis(meth)acrylamide, 
(poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol 
di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane 
di(meth)acrylate, glycerin tri(meth)acrylate, glycerin acrylate 
methacrylate, ethylene oxide denaturated trimethylolpropane 
tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol 
hexa(meth)acrylate, N,N-diallylacrylamide, triallyl cyanurate, triallyl 
isocyanurate, triallyl phosphate, triallylamine, diallyloxyacetic acid, 
N-methyl-N-vinylacrylamide, bis(N-vinylcarboxyamide), and 
poly(meth)allyloxyalkanes such as tetraallyloxyethane. 
Specific examples of compounds having in their molecular structure a 
plurality of functional groups capable of reacting with carboxyl groups, 
sulfonic groups, etc. include polyhydric alcohol compounds, such as 
(poly)ethylene glycol, diethylene glycol, triethylene glycol, 
tetraethylene glycol, propylene glycol, 1,3-propanediol, dipropylene 
glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, 
(poly)glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 
1,6-hexanediol, 1,2-cyclohexane-dimethanol, 1,2-cyclohexanol, 
trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, 
oxyethylene-oxypropylene block copolymer, pentaerythritol, and sorbitol; 
epoxy compounds, such as (poly)ethylene glycol diglycidyl ether, 
(poly)glycerol polyglycidyl ether, diglycerol polyglycidyl ether, 
(poly)propylene glycol diglycidyl ether, and glycidol; polyamine compounds 
such as ethylenediamine, diethylenetriamine, triethylenetetramine, 
tetraethylenepentamine, pentaethylenehexamine, polyamidepolyamine, and 
polyethylenimine, and condensates of these polyamines and haloepoxy 
compounds; compounds having two or more isocyanate groups, such as 
2,4-tolylene diisocyanate and hexamethylene diisocyanate; compounds having 
two or more oxazoline groups, such as 1,2-ethylene bisoxazoline; silane 
coupling agents, such as .gamma.-glycidoxypropyltrimethoxysilane and 
.gamma.-aminopropyltrimethoxysilane; alkylene carbonate compounds, such as 
1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 
4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 
4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolan-2-one, 
1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 
4,6-dimethyl-1,3-dioxan-2-one, and 1,3-dioxopan-2-one; haloepoxy 
compounds, such as epichlorohydrin, epibromohydrin, and 
.alpha.-methylepichlorohydrin; and hydroxides and chlorides of polyvalent 
metals such as zinc, calcium, magnesium, aluminum, iron and zirconium. 
The amount of crosslinking agent used is not limited to any particular 
amount, but is preferably within a range from 0.0001% to 10% by mole, more 
preferably from 0.001% to 1% by mole, with respect to the monomer 
component. 
The method of producing the foregoing hydrogel polymer to be used in the 
present invention, i.e., the method of polymerizing the foregoing monomer 
substances, is not limited to any method in particular; various known 
conventional polymerization methods, such as bulk polymerization, 
precipitation polymerization, polymerization in an aqueous solution, and 
reversed-phase suspension polymerization, may be used. However, the method 
of polymerizing the foregoing monomer substances is preferably 
polymerization in an aqueous solution, in which an aqueous solution of the 
monomer substances is prepared, because, in this case, the absorption 
characteristics of the resultant hydrophilic resin can be improved, and 
polymerization can be controlled easily. When the polymerization method 
adopted is polymerization in an aqueous solution, polymerization may be 
performed while stirring the aqueous solution containing the monomer 
substances (hereinafter referred to as the "aqueous monomer solution"), or 
with the aqueous monomer solution at rest. Further, when polymerizing 
while stirring the aqueous monomer solution, stirring may be continued 
from the beginning of polymerization through the completion thereof, or 
stirring may be suspended during polymerization. When polymerizing with 
the aqueous monomer solution at rest, on the other hand, batch 
polymerization in a polymerization vessel, or continuous polymerization on 
a driven belt, may be performed. Among these options, it is preferable to 
perform continuous polymerization with the aqueous monomer solution at 
rest, by supplying the aqueous monomer solution to a driven belt. 
A hydrogel polymer obtained by one of the foregoing polymerization methods 
is a semi-solid body having high elasticity, in the form of a gel, and is 
used in a dry powder form as a hydrophilic resin. However, hydrogel 
polymers obtained by the foregoing polymerization in an aqueous solution, 
or by bulk polymerization or precipitation polymerization, are gelatinous 
substances in the form of lumps, and thus the efficiency of drying is 
extremely poor. Accordingly, in order to improve the efficiency of drying, 
it is necessary to pulverize the hydrogel polymer to a suitable particle 
size. Again, reverse-phase suspension polymerization usually results in a 
hydrogel polymer in particulate form, but there are also cases in which 
part or all of the hydrogel polymer is a gelatinous substance in the form 
of lumps. Accordingly, in cases like the foregoing, application of the 
present invention is extremely effective. In other words, the present 
method is a method which, when it is necessary to pulverize a hydrogel 
polymer in producing a hydrophilic resin, pulverizes the hydrogel polymer 
with minimal kneading and crushing, and is thus capable of obtaining a 
hydrophilic resin having few water-soluble components and having superior 
performance, such as absorbing capacity. 
In the present invention, when commencing polymerization, it is possible to 
use, for example, a polymerization initiator, or activation energy 
radiation such as radioactive rays, electron rays, ultraviolet rays, or 
electromagnetic rays. Specific examples of polymerization initiators 
include radical polymerization initiators, such as inorganic peroxides 
like sodium persulfate, ammonium persulfate, potassium persulfate, and 
hydrogen peroxide; organic peroxides like t-butyl hydroperoxide, benzoyl 
peroxide, and cumene hydroperoxide; and azo compounds like 
2,2'-azobis(N,N'-dimethyleneisobutylamidine) and salts thereof, 
2,2'-azobis(2-methylpropionamidine) and salts thereof, 
2,2'-azobis(2-amidinopropane) and salts thereof, and 4,4'-azobis-4-cyano 
valeric acid. A single one of the foregoing polymerization initiators may 
be used alone, or two or more may be used in combination. When a peroxide 
is used as the polymerization initiator, redox polymerization may be 
performed using a reducing agent, such as sulfite, bisulfite, or 
L-ascorbic acid. 
In the present invention, when the hydrogel polymer obtained by 
polymerization of the foregoing monomer substances is a water-absorbent 
resin, the hydrogel polymer preferably contains bubbles, because in this 
case, absorption characteristics can be improved. 
With the method according to the present invention, the bubbles contained 
in the hydrogel polymer are not kneaded and crushed, and decrease of 
surface area due to decreased number of bubbles can be prevented. Thus a 
water-absorbent resin can be obtained which has superior absorption 
characteristics, such as absorption rate and absorbing capacity. 
As the polymerization method for obtaining the foregoing hydrogel polymer 
containing bubbles, various known conventional methods may be used, such 
as polymerization in the presence of an azo initiator; polymerization 
using carbonate as a foaming agent (Japanese Unexamined Patent Publication 
Nos. 5-237378/1993 (Tokukaihei 5-237378) and 7-185331/1995 (Tokukaihei 
7-185331)); polymerization performed by dispersing a water-insoluble 
foaming agent such as pentane or trifluoroethane in a monomer (U.S. Pat. 
Nos. 5,328,935 and 5,338,766); polymerization using a solid particulate 
foaming agent (Publication of International Patent Application No. 
WO96/17884); and polymerization performed while dispersing an inert gas in 
the presence of a surfactant. 
When polymerizing the monomer substances in the presence of a crosslinking 
agent, in order to improve absorption characteristics of the resulting 
hydrophilic resin and effectively perform foaming using a foaming agent, 
it is particularly preferable to use, of the various polymerization 
methods mentioned above, polymerization in an aqueous solution. In this 
case, the concentration of the monomer substances in the aqueous monomer 
solution may be within a range from 10% to 90% by weight, but is 
preferably from 20% to 60% by weight. If the concentration of the monomer 
substances is less than 20% by weight, the content of water-soluble 
components in the resulting hydrophilic resin is increased, and, due to 
insufficient foaming by the foaming agent, it may not be possible to 
improve the absorption rate. On the other hand, if the concentration of 
the monomer substances exceeds 60% by weight, it may be difficult to 
control the reaction temperature and foaming by the foaming agent. 
For the solvent for the aqueous monomer solution, a combination of water 
and a water-soluble organic solvent may be used. Specific examples of such 
an organic solvent include methyl alcohol, ethyl alcohol, acetone, 
dimethyl sulfoxide, ethylene glycol monomethyl ether, glycerin, 
(poly)ethylene glycol, (poly)propylene glycol, and alkylene carbonate. A 
single one of these organic solvents may be used alone, or two or more may 
be used in combination. 
The foaming agent may be a compound which is dispersible or soluble in the 
aqueous monomer solution. Specific examples of such foaming agents include 
volatile organic compounds, such as n-pentane, 2-methylbutane, 
2,2-dimethylpropane, hexane, heptane, benzene, substituted benzene, 
chloromethane, chloroethane, chlorofluoromethane, 
1,1,2-trichlorotrifluoroethane, methanol, ethanol, isopropanol, acetone, 
azodicarbonamide, azobisisobutyronitrile, barium azodicarboxylate, 
dinitrosopentamethylenetetramine, 4,4'-oxybis(benzenesulfonyl hydrazide), 
paratoluenesulfonyl hydrazide, diazoaminobenzene, 
N,N'-dimethyl-N,N'-dinitrosoterephthalamide, nitrourea, 
acetone-p-toluenesulfonyl hydrazone, p-toluenesulfonylazide, 
2,4-toluenedisulfonyl hydrazide, p-methylurethane benzenesulfonyl 
hydrazide, trinitrosotrimethylenetriamine, p-toluenesulfonyl 
semicarbazide, oxalyl hydrazide, nitroguanidine, hydrazo dicarbonamide, 
trihydrazinotriamine, azobisformamide, benzenesulfonyl hydrazide, 
benzene-1,3-disulfonyl hydrazide, diphenylsulfone-3,3'-disulfonyl 
hydrazide, 4,4'-oxybis(benzenesulfonyl hydrazide), sulfone hydrazide, 
malonic acid and salts thereof, and carbamic acid and salts thereof; 
carbonates, such as sodium bicarbonate, ammonium carbonate, ammonium 
bicarbonate, ammonium nitrite, basic magnesium carbonate, and calcium 
carbonate; acrylic acid salts of azo compounds containing one or more 
amino groups, represented by general formulae (1) and (2) below; and dry 
ice. 
##STR1## 
(Here, X.sub.1 and X.sub.2 each independently represents an alkylene group 
having 1 to 4 carbon atoms, and R.sub.1, R.sub.2, R.sub.3, R.sub.4, 
R.sub.5, and R.sub.6 each independently represents a hydrogen atom, an 
alkyl group having 1 to 4 carbon atoms, an aryl group, an allyl group or a 
benzyl group.) 
##STR2## 
(Here, X.sub.3 and X.sub.4 each independently represents an alkylene group 
having 1 to 4 carbon atoms, X.sub.5 and X.sub.6 each independently 
represents an alkylene group having 2 to 4 carbon atoms, and R.sub.7 and 
R.sub.8 each independently represents a hydrogen atom or an alkyl group 
having 1 to 4 carbon atoms.) 
When a carbonate such as sodium carbonate is used as the foaming agent, it 
is preferable to also use a surfactant or dispersant. By using a 
surfactant or dispersant, it is possible to prevent the average diameter 
of the bubbles in the resulting hydrogel polymer from becoming too large, 
and the absorption rate from being lowered. 
A single one of the foregoing foaming agents may be used alone, or two or 
more may be used in combination. Among the foregoing examples of foaming 
agents, acrylic acid salts of azo compounds containing one or more amino 
groups are preferred. Such an acrylic acid salt of an azo compound 
containing one or more amino groups has superior dispersibility with 
respect to acrylic acid salt monomers, and functions both as foaming agent 
and as radical polymerization initiator. Thus, such an acrylic acid salt 
can be uniformly dispersed in the aqueous monomer solution while at rest, 
while maintaining a predetermined average particle diameter, without using 
a surfactant or a dispersion stabilizing agent such as a water-soluble 
polymer, and without stirring the aqueous monomer solution. Moreover, such 
an acrylic acid salt does not cause sedimentation, flotation or 
separation. Accordingly, by polymerizing the monomers in the presence of 
an acrylic acid salt of an azo compound containing one or more amino 
groups, a hydrophilic resin (water-absorbent resin) can be obtained which 
has an even lower content of water-soluble components, and of residual 
monomers. 
In the present invention, the foaming agent may be added to the aqueous 
monomer solution before polymerization or during polymerization, or may be 
added to the hydrogel polymer resulting from polymerization of the aqueous 
monomer solution. Further, a foaming agent prepared in advance may be 
added to the aqueous monomer solution, or a foaming agent may be prepared 
in the aqueous monomer solution by dissolving a foaming agent precursor 
therein, and then adding, as needed, carbon dioxide gas or acrylic acid 
salt. In other words, the foaming agent may be precipitated in the aqueous 
monomer solution by causing a reaction between the foaming agent precursor 
and the carbon dioxide gas or acrylic acid salt. 
In the present invention, the quantity of foaming agent used with respect 
to the monomer substances is not limited to any particular quantity, and 
may be set in accordance with the combination of monomer substances and 
foaming agent used, etc., but is preferably within a range from 0.001 
parts to 10 parts by weight of foaming agent to 100 parts by weight of the 
monomer substances. If the amount of foaming agent used is not within the 
foregoing range, the resulting hydrophilic resin (water-absorbent resin) 
may have unsatisfactory absorption characteristics. 
The water content of a hydrogel polymer obtained as above is within a range 
from 10% to 90% by weight, preferably from 20% to 80% by weight. If the 
water content is less than 10% by weight, it may be difficult to pulverize 
the hydrogel polymer, and when the hydrogel polymer contains bubbles, the 
bubbles may be squashed. On the other hand, a water content greater than 
90% by weight is not economical, because drying after pulverization 
requires too much time. 
In the present invention, a hydrophilic resin can be obtained by 
pulverizing and drying the lumps of hydrogel polymer resulting from the 
foregoing polymerization. In the present invention, "pulverization" of the 
hydrogel polymer means disintegration of the lumps of hydrogel polymer to 
a suitable particle size smaller than their original size, and thus, in 
the present invention, pulverization includes cracking, granulation, 
cutting, shredding, etc. 
In the method of producing hydrophilic resin according to the present 
invention, a pulverizer, provided with a pair of spiral rotary blades 
(feeding blades) with different respective feed rates, is used in 
pulverizing the hydrogel polymer. 
The foregoing pulverizer, as shown, for example, in FIG. 1, includes two 
rotary blades 6 and 7 provided in the shape of spirals around rotary 
shafts 3 and 4, respectively. In a pulverizing chamber 2 provided with a 
hopper 1 (intake) in the upper part thereof, the rotary shafts 3 and 4 are 
provided parallel to one another with a predetermined interval 
therebetween, and are rotated independently by driving motors 9 and 10. 
Further, the rotary blade 6 and the rotary blade 7 are provided such that 
respective facing surfaces 6c and 7c thereof (shearing surfaces; see FIG. 
4) are substantially parallel to each other with a uniform interval 
therebetween. 
The rotary blade 6 is made up of two rotary blades 6a and 6b, having the 
same spiral pitch P.sub.1 but spiral structures of opposite direction, 
separated at the center of the rotary shaft 3 with respect to the 
longitudinal axis thereof (the rotary shaft direction). Further, the 
rotary blade 7 is made up of two rotary blades 7a and 7b, having the same 
spiral pitch P.sub.2 but spiral structures of opposite direction, 
separated at the center of the rotary shaft 4 with respect to the 
longitudinal axis thereof (the rotary shaft direction). Further, in the 
rotary blades 6 and 7, the rotary blades 6a and 7a (opposite one another) 
and the rotary blades 6b and 7b (opposite one another) are provided so as 
to have spiral structures of opposite direction. 
Accordingly, by rotating the rotary shafts 3 and 4 in opposite directions, 
the rotary blades 6a and 6b and the rotary blades 7a and 7b perform a 
feeding action moving toward the center of the rotary shafts 3 and 4 with 
respect to the longitudinal direction thereof (i.e., toward the place 
where the direction of the respective spiral structures of the rotary 
blades 6 and 7 changes). Thus the hydrogel polymer introduced into the 
hopper 1 is collected at the center of the rotary shafts 3 and 4 with 
respect to the longitudinal direction thereof. In this way, the spiral 
directions of the rotary blades 6 and 7 and the rotation directions of the 
rotary shafts 3 and 4 are set so that the rotary blades 6 and 7 have the 
same directions of feed due to a screw action, so as to perform a feeding 
action moving from the ends toward the center of the rotary shafts 3 and 4 
with respect to the longitudinal direction thereof. 
Further, although the feed directions of the rotary blades 6 and 7 are the 
same, they are set to different respective feed rates. In other words, the 
foregoing pulverizer is set such that the feed rate of the rotary blade 6 
is greater than the feed rate of the rotary blade 7. 
Some methods of attaining the foregoing structure, in which the rotary 
blade 6 overtakes the rotary blade 7, are, for example, (1) setting the 
spiral pitch P.sub.1 of the rotary blade 6 so as to be greater than the 
spiral pitch P.sub.2 of the rotary blade 7, and rotating the rotary shafts 
3 and 4 at the same speed (peripheral speed); (2) setting the spiral pitch 
P.sub.1 of the rotary blade 6 so as to be greater than the spiral pitch 
P.sub.2 of the rotary blade 7, and setting the rotation speed (peripheral 
speed) of the rotary shaft 3 so as to be greater than the rotation speed 
(peripheral speed) of the rotary shaft 4; and (3) setting the spiral 
pitches P.sub.1 and P.sub.2 of the rotary blades 3 and 4 to the same 
value, and setting the rotation speed (peripheral speed) of the rotary 
shaft 3 so as to be greater than the rotation speed (peripheral speed) of 
the rotary shaft 4. Among the foregoing methods, (1) and (2) are 
preferred, and when pulverizing a hydrogel polymer in a large mass (for 
example, one in the form of a sheet, obtained by polymerization at rest), 
method (2) is more preferred, since it is easier to feed the hydrogel 
polymer between the rotary blades 6 and 7. 
Further, the directions of feed of the rotary blades 6 and 7 do not 
necessarily have to be the same; in order to increase shearing force, a 
structure may be used in which the rotary shafts 3 and 4 are rotated so 
that the directions of feed of the rotary blade 7 and the rotary blade 6 
are opposite, and the extruding force of the rotary blade 6 is set so as 
to be greater than the extruding force of the rotary blade 7, so that the 
hydrogel polymer is transported toward the center of the rotary shafts 3 
and 4 with respect to the longitudinal direction thereof. 
In the present invention, the spiral pitches P.sub.1 and P.sub.2 of the 
rotary blades 6 and 7 are not limited to any particular pitches, and may 
be set as needed in accordance with the pulverization conditions other 
than spiral pitch, such as size of the pulverizer (diameters of the rotary 
shafts 3 and 4), rotation speed of the rotary shafts 3 and 4, which of the 
foregoing methods (1) through (3) is used, etc., so that the feed rate of 
the rotary blade 6 is greater than that of the rotary blade 7. However, in 
consideration of particle size of the pulverized hydrogel polymer and the 
efficiency of pulverization, the spiral pitch P.sub.1 of the rotary blade 
6 is preferably within a range from 5 mm to 300 mm per revolution, more 
preferably from 10 mm to 250 mm per revolution, and even more preferably 
from 20 mm to 200 mm per revolution. The spiral pitch P.sub.2 of the 
rotary blade 7, on the other hand, is preferably within a range from 3 mm 
to 250 mm per revolution, more preferably from 5 mm to 200 mm per 
revolution, and even more preferably from 10 mm to 150 mm per revolution. 
If the respective spiral pitches P.sub.1 and P.sub.2 of the rotary blades 
6 and 7 are less than the respective ranges mentioned above, there are 
cases in which the hydrogel polymer is not pulverized, but is caught 
within the respective rotary blades making up the rotary blades 6 and 7, 
i.e., within the spiral pitch. Accordingly, in consideration of the 
efficiency of pulverization, it is preferable to set the pulverization 
conditions, such as pulverizer size (diameters of the rotary shafts 3 and 
4), rotation speed of the rotary shafts 3 and 4, etc., such that the 
spiral pitches P.sub.1 and P.sub.2 fall within the respective ranges 
mentioned above. 
Further, in the present invention, when using either of the methods in (1) 
or (2) above, in consideration of efficiency of pulverization, it is 
preferable to set the spiral pitch P.sub.1 of the rotary blade 6 within a 
range, for example, from more than 1 time to no more than 10 times the 
spiral pitch P.sub.2 of the rotary blade 7, more preferably within a range 
from 1.1 times to 5 times the spiral pitch P.sub.2 of the rotary blade 7. 
Further, the respective rotation speeds of the rotary shafts 3 and 4 are 
preferably within a range from 0.05 rpm to 100 rpm, more preferably from 
0.1 rpm to 50 rpm. When, as in the methods in (2) and (3) above, the 
rotary blades 6 and 7 have different respective rotary shaft rotation 
speeds, a ratio between the peripheral speeds of the rotary blades 6 and 
7, i.e., a ratio of the peripheral speed of the rotary shaft 3 to that of 
the rotary shaft 4 (peripheral speed of rotary shaft 3/peripheral speed of 
rotary shaft 4) is preferably within a range from 1.1/1 to 50/1, more 
preferably from 1.1/1 to 20/1. Incidentally, when the rotary shafts 3 and 
4 are rotated at the same speed, a structure may be used in which, using a 
single driving motor, one rotary shaft is rotated in synchronization with 
the rotation of the other rotary shaft. 
In the present invention, in the process of collecting the hydrogel polymer 
at the center of the rotary shafts 3 and 4 with respect to the 
longitudinal direction thereof, due to the difference in feed rates of the 
rotary blades 6 and 7, the rotary blades 6a and 6bcross and overtake the 
rotary blades 7a and 7b. Thus the rotary blades 6 and 7 bite into and 
shear the hydrogel polymer. 
Further, in the foregoing pulverizer, as shown in FIGS. 1, 3, and 4, it is 
preferable to provide a further spiral rotary blade, for example, between 
the rotary blades 6 and 7 and an outlet 12 provided at the bottom end of 
the pulverizing chamber 2 (in the direction of discharge of the hydrogel 
polymer); in particular, a rotary blade 8 having a grid shape made up of 
rotary blades with different respective spiral directions, provided on a 
rotary shaft 5 in the pulverizing chamber 2 below the place where the 
rotary blades 6 and 7 face one another. In other words, the foregoing 
pulverizer preferably has a multi-shaft (in the present embodiment, 
3-shaft) structure. The spiral pitch of the rotary blade 8, i.e., the 
length of one side of each square in the grid pattern, is preferably from 
5 mm to 200 mm. The rotary blade 8 is provided opposite the rotary blades 
6 and 7 such that a facing surface 8a (shearing surface) thereof facing 
the rotary blades 6 and 7 has a predetermined interval with the 
corresponding facing surfaces 6c and 7c (shearing surfaces) of the rotary 
blades 6 and 7. The rotary blade 8 is rotated independently of the rotary 
blades 6 and 7 by a driving motor 11. Further, the rotary blade 8 and the 
rotary blades 6 and 7 are provided such that respective facing surfaces 
thereof (the facing surfaces 8a and 6c, and the facing surfaces 8a and 7c) 
are substantially parallel to each other with a uniform interval 
therebetween. By this arrangement, hydrogel polymer which has passed 
between the rotary blades 6 and 7, in the process of being transported 
toward the center of the rotary shaft 5 with respect to the longitudinal 
direction thereof, is caught between the rotary blade 8 and either the 
rotary blade 6 or the rotary blade 7, and is sheared even more finely 
where the respective rotary blades cross. 
When the foregoing pulverizer has a 3-shaft structure, if the rotary shafts 
3 and 4 are rotated at the same rotation speed, a ratio between the 
peripheral speed of the rotary blade 8 and the peripheral speed of the 
rotary blades 6 and 7, i.e., a ratio of the peripheral speed of the rotary 
shaft 5 to that of the rotary shafts 3 and 4 (peripheral speed of rotary 
shaft 5/peripheral speed of rotary shafts 3 and 4) is preferably within a 
range from 1/1 to 100/1, more preferably from 3/1 to 50/1. If, on the 
other hand, the rotary shafts corresponding to the rotary blades 6 and 7 
have different respective rotation speeds, a ratio between the peripheral 
speeds of the rotary blades 8 and 7, i.e., a ratio of the peripheral speed 
of the rotary shaft 5 to that of the rotary shaft 4 (peripheral speed of 
rotary shaft 5/peripheral speed of rotary shaft 4) is preferably within a 
range from 1.1/1 to 100/1, more preferably from 2/1 to 50/1. 
In the present invention, an interval D.sub.1 between the respective facing 
surfaces 6c and 7c of the rotary blades 6 and 7 (i.e., the interval where 
the rotary blades 6 and 7 cross), an interval D.sub.2 between the 
respective facing surfaces 6c and 8a of the rotary blades 6 and 8 (i.e., 
the interval where the rotary blades 6 and 8 cross), and an interval 
D.sub.3 between the respective facing surfaces 7c and 8a of the rotary 
blades 7 and 8 (i.e., the interval where the rotary blades 7 and 8 cross) 
are each preferably set within a range from 0.01 mm to 2 mm, more 
preferably from 0.05 mm to 0.5 mm. Further, intervals D.sub.4 and D.sub.5 
between the inner walls of the pulverizing chamber 2 and the facing 
surfaces 6c and 7c of the rotary blades 6 and 7, respectively, and 
intervals D.sub.6 and D.sub.7 between the inner walls of the pulverizing 
chamber 2 and the facing surface 8a of the rotary blade 8 are each 
preferably set within a range from 0.1 mm to 50 mm, more preferably from 1 
mm to 20 mm. The size of the pulverized hydrogel polymer is determined by 
the intervals D.sub.1, D.sub.2, and D.sub.3. If the intervals D.sub.1, 
D.sub.2, and D.sub.3 are too large, the hydrogel polymer cannot be finely 
pulverized. If, on the other hand, the intervals D.sub.1, D.sub.2, and 
D.sub.3 are less than 0.01 mm, the pulverized hydrogel polymer may be too 
fine, and pulverization takes too long. For these reasons, it is 
preferable to set the intervals D.sub.1, D.sub.2, and D.sub.3 within the 
foregoing range. The intervals D.sub.4, D.sub.5, D.sub.6, and D.sub.7 are 
set so that only the hydrogel polymer pulverized by the rotary blades 6, 
7, and 8 can be discharged from the outlet 12 provided at the bottom of 
the pulverizing chamber 2. Further, of the intervals D.sub.6 and D.sub.7 
between the inner walls of the pulverizing chamber 2 and the rotary blade 
8, in order to perform pulverizing and discharge smoothly, it is 
preferable to set the interval D.sub.7 on the side where, in order to 
further pulverize the hydrogel polymer between the rotary blade 8 and the 
rotary blades 6 and 7, the rotary blade 8 pushes the hydrogel polymer up, 
to be smaller than the interval D.sub.6 on the side where the rotary blade 
8 rotates in the direction of discharge of the hydrogel polymer. 
Next, with regard to the sizes of the rotary blades 6, 7, and 8, in 
consideration of the efficiency of pulverization, it is preferable to set 
thicknesses W.sub.1, W.sub.2, and W.sub.3 of the rotary blades 6, 7, and 
8, respectively (i.e., the respective widths of the facing surfaces 6c, 
7c, and 8a; see FIGS. 1 and 3) within a range from 1 mm to 50 mm, more 
preferably from 2 mm to 30 mm. Further, it is preferable to set heights 
S.sub.1, S.sub.2, and S.sub.3 of the rotary blades 6, 7, and 8, 
respectively (i.e., the respective differences between the outer diameters 
of the rotary blades 6, 7, and 8 and the outer diameters of the rotary 
shafts 3, 4, and 5; see FIG. 4) within a range from 2 mm to 100 mm, more 
preferably from 5 mm to 50 mm. 
Further, in the vicinity of the area where the rotary blade 8 is provided, 
it is preferable to further provide, as shown in FIG. 5, a scraper 13 
and/or fixed blades 14 and 15. By providing the scraper 13 in the vicinity 
of the area where the rotary blade 8 is provided, pulverized hydrogel 
polymer attached to the rotary blade 8 can be separated therefrom and 
efficiently discharged from the pulverizer. Further, by providing the 
fixed blades 14 and 15 in the vicinity of the area where the rotary blade 
8 is provided, pulverized hydrogel polymer pulverized by the rotating 
blades 6, 7, and 8 can be further pulverized prior to discharge, by 
shearing between the rotating blade 8 and the fixed blades 14 and 15. 
Accordingly, by providing the fixed blades 14 and 15 in the vicinity of 
the area where the rotary blade 8 is provided, the hydrogel polymer can be 
pulverized even more finely. When the scraper 13 and/or the fixed blades 
14 and 15 are provided in the vicinity of the area where the rotary blade 
8 is provided, the size of the pulverized hydrogel polymer is determined 
by the intervals D.sub.1, D.sub.2, and D.sub.3, and also by an interval 
D.sub.8 between the rotary blade and the scraper 13, an interval D.sub.9 
between the rotary blade 8 and the fixed blade 14, and/or an interval 
D.sub.10 between the rotary blade 8 and the fixed blade 15. Accordingly, 
it is preferable to set each of the intervals D.sub.8, D.sub.9, and 
D.sub.10 within a range from 0.01 mm to 2 mm, more preferably from 0.05 mm 
to 0.5 mm. Incidentally, either of the fixed blades 14 and 15 may be 
omitted. 
In the present invention, the temperature of the hydrogel polymer during 
pulverization is preferably no less than 40.degree. C., and, in view of 
such considerations as the temperature of the hydrogel polymer during 
polymerization and temperature change and temperature maintenance of the 
hydrogel polymer from polymerization to pulverization, the temperature of 
the hydrogel polymer during pulverization is more preferably within a 
range from 40.degree. C. to 100.degree. C., and even more preferably from 
50.degree. C. to 80.degree. C. 
At 40.degree. C. and over, adhesion of the hydrogel polymer is decreased. 
For this reason, if the hydrogel polymer is pulverized at a temperature 
within the foregoing range, its adhesion to the rotary blades 6, 7, and 8 
is markedly decreased, which minimizes deformation of the hydrogel polymer 
during shearing, and thus the hydrogel polymer can be pulverized without 
kneading and crushing, and while retaining more of the bubbles contained 
therein than in the past. 
Further, when the temperature of the hydrogel polymer is within the 
foregoing range, water vapor is produced from the surface thereof. 
Consequently, this water vapor becomes attached to the surface of the 
rotary blades 6, 7, and 8, which further suppresses adhesion of the 
hydrogel polymer to the rotary blades 6, 7, and 8. 
Accordingly, if the hydrogel polymer is caught and sheared between the 
rotary blades 6 and 7, or between the rotary blade 6 or 7 and the rotary 
blade 8, within the foregoing temperature range, kneading and crushing of 
the hydrogel polymer can be markedly decreased, and a hydrophilic resin 
(water-absorbent resin) can be provided which has even better absorbing 
performance, such as absorbing capacity. Further, with the foregoing 
method, since attachment of the hydrogel polymer to the rotary blades 6, 
7, and 8 can be suppressed, the hydrogel polymer can be pulverized 
efficiently and continuously over a long period of time, and deterioration 
of the rotary blades 6, 7, and 8 can be minimized. 
Consequently, in the present invention, it is preferable to pulverize the 
hydrogel polymer immediately after polymerization, without allowing its 
temperature to decrease. Further, in order to prevent decrease of the 
temperature of the hydrogel polymer to less than 40.degree. C., the 
hydrogel polymer after polymerization may be maintained in a heat 
retaining chamber wrapped with insulation, etc., or in a chamber or vessel 
maintained at no less than 40.degree. C. The method of maintaining the 
temperature of the hydrogel polymer within the foregoing range is not 
limited to any particular method. 
Further, in the present invention, when the temperature of the hydrogel 
polymer prior to placing in the pulverizer is less than 40.degree. C. 
(when, for instance, its temperature has decreased to less than 40.degree. 
C.), it is preferable to adjust the temperature of the hydrogel polymer, 
by raising its temperature, prior to pulverization. The method of 
increasing the temperature of the hydrogel polymer is not limited to any 
particular method; examples of methods which may be used include (1) 
raising the temperature of the hydrogel polymer in advance using a heating 
device, etc., and then placing it in the pulverizer and pulverizing; and 
(2) heating the rotary blades 6, 7, and 8 using a heating device, etc. 
such as a heater, thus raising the temperature of the hydrogel polymer as 
it is transported. However, the method in (1) above is preferred, because 
in this case it is easier to attach water vapor to the rotary blades 6, 7, 
and 8, and easier to uniformly increase the temperature of the hydrogel 
polymer. 
As the heating device used when heating the hydrogel polymer in advance, a 
typical dryer or furnace may be used. The dryer is not limited to any 
particular type; specific examples include channel mixing dryers, rotary 
dryers, desk dryers, fluidized-bed dryers, gas flow dryers, and infrared 
dryers. 
As discussed above, in the present invention, the hydrogel polymer is 
pulverized while adjusting and controlling its temperature to no less than 
40.degree. C. For this reason, in order to suppress adhesion (attachment) 
of the hydrogel polymer to the rotary blades 6, 7, and 8, and to prevent 
deformation of the rotary blades 6, 7, and 8 by heat, it is preferable to 
form the rotary blades 6, 7, and 8 of a material such as carbon steel, 
Swedish steel, bearing steel, ceramic, spring steel, powdered high-speed 
steel, alloy tool steel, cemented carbide, high-speed steel, stellite, 
stainless steel, or ferrotic steel. Furthermore, in order to suppress 
adhesion (attachment) of the hydrogel polymer, it is particularly 
preferable to perform surface treatment (surface treatment to prevent 
attachment of the hydrogel polymer) of the surfaces of the rotary blades 
6, 7, and 8, in particular the surfaces thereof other than the facing 
surfaces 6c, 7c, and 8a (i.e., sides 6d, 7d, and 8b of the rotary blades 
6, 7, and 8, respectively), and of the outer surfaces of the rotary shafts 
3, 4, and 5. 
The method of surface treatment is not limited to any particular method; 
specific examples include carbonizing, nitriding, dichromic treatment, 
atomlloy treatment, redux treatment, polytetrafluoroethylene coating 
(so-called Teflon coating), tef-lock, tungsten spraying, hard chrome 
plating, ceramic spraying, and mirror surfacing. Among these, Teflon 
coating is preferred. 
Further, in order to suppress adhesion of the hydrogel polymer and prevent 
deformation by heat, it is preferable to provide the inner wall (inner 
surface) of the pulverizing chamber 2 with a base material having a heat 
deformation temperature higher than the temperature during pulverization 
of the hydrogel polymer. 
Examples of such a base material for the inner surface of the pulverizing 
chamber 2 include synthetic resins such as polyethylene, polypropylene, 
polyester, polyamide, fluorine resin, polyvinyl chloride, epoxy resin and 
silicone resin; and the foregoing synthetic resins strengthened by 
formation of a complex with an inorganic filler such as glass, graphite, 
bronze, or molybdenum sulfide, or with an organic filler such as 
polyimide. 
Among the foregoing substances, fluorine resins such as 
polyethylenetetrafluoride, polyethylenetrifluoride, 
polyethylenetrifluorochloride, ethylenetetrafluoride-ethylene copolymer, 
ethylenetrifluorochloride-ethylene copolymer, 
propylenepentafluoride-ethylenetetrafluoride copolymer, 
perfluoroalkylvinylether-ethylenetetrafluoride copolymer, and polyvinyl 
fluoride are especially preferred. 
Further, in order to suppress adhesion (attachment) of the hydrogel 
polymer, it is more preferable to also perform surface treatment (surface 
treatment to prevent attachment of the hydrogel polymer) of the inner wall 
(inner surface) of the pulverizing chamber 2. In other words, it is 
preferable that surface treatment to prevent attachment of the hydrogel 
polymer be performed on all areas where the hydrogel polymer may become 
attached. 
Further, in the present invention, in order to further suppress attachment 
of the hydrogel polymer to the rotary blades 6, 7, and 8, in addition to 
the water vapor produced by the hydrogel polymer, water may be attached to 
the rotary blades 6, 7, and 8. 
Various methods may be adopted to attach water to the rotary blades 6, 7, 
and 8, such as using an atomizer, etc. to atomize or spray water onto the 
rotary blades 6, 7, and 8 from above or to the side(s) thereof. Such 
atomizing, etc. of water may be performed continuously, or at regular 
intervals. 
The following will explain, with reference to FIGS. 2(a) through 2(d), 
operations for pulverizing the hydrogel polymer using the foregoing 
pulverizer. First, as shown in FIG. 2(a), a lump of hydrogel polymer 21 
introduced into the pulverizing chamber 2 through the hopper 1 is 
transported toward the center of the rotary shaft 3 with respect to the 
longitudinal direction thereof by the rotation of, for example, the rotary 
blade 6a. Due to the difference in feed rates of the rotary blades 6a and 
7a, the rotary blade 6a catches up to the rotary blade 7a. For this 
reason, in the process of transporting the hydrogel polymer 21, the 
distance between the rotary blade 6a and the rotary blade 7a lying in 
front of the rotary blade 6a is gradually shortened, and, as shown in FIG. 
2(b), the hydrogel polymer 21 is caught between the rotary blades 6a and 
7a. Then, since the rotary blade 6a crosses (as shown in FIG. 2(c)) and 
then overtakes (as shown in FIG. 2(d)) the rotary blade 7a, the hydrogel 
polymer 21 is sheared in two. Then the pieces produced by shearing of the 
hydrogel polymer 21, for example, pulverized hydrogel polymer pieces 21a 
and 21b, depending on their orientation during transportation, are either 
discharged (fall) from between the rotary blades 6a and 7a toward the 
outlet 12 at the bottom of the pulverizing chamber 2, or are again sheared 
as the rotary blade 6a behind the pulverized hydrogel polymer pieces 21a 
and 21b again overtakes the rotary blade 7a, and are then discharged 
(fall) from between the rotary blades 6a and 7a toward the outlet 12 at 
the bottom of the pulverizing chamber 2. 
Next, the hydrogel polymer which falls between the rotary blades 6 and 7 is 
further sheared by the rotary blade 8 provided between the rotary blades 6 
and 7 and the outlet 12, and is then discharged from the outlet 12. In 
this way, by adopting the foregoing method, the hydrogel polymer can be 
sheared a plurality of times prior to discharge, and can thus be 
efficiently pulverized. Moreover, by first pulverizing the hydrogel 
polymer to a desired size by the foregoing shearing, drying of the 
hydrogel polymer can be performed more easily and quickly. 
Further, when the temperature of the hydrogel polymer is 40.degree. C. or 
more, adhesion of the hydrogel polymer is decreased, and water vapor 
becomes attached to the rotary blades 6, 7, and 8. Consequently, with the 
foregoing method, the hydrogel polymer, which has high flexibility and is 
difficult to pulverize, can be pulverized without kneading and crushing, 
and thus the increase of water-soluble components can be held to a 
minimum, and transparent pulverized hydrogel polymer can be obtained. 
Further, if the hydrogel polymer has a crosslinked structure, the 
resulting high hardness and viscosity can better prevent attachment of the 
hydrogel polymer to the interior of the pulverizing chamber 2, the surface 
of the rotary blades 6, 7, and 8, etc., thus making pulverizing even 
easier. Moreover, with the present invention, even if the hydrogel polymer 
contains bubbles, these bubbles are not squashed, and thus a 
water-absorbent resin with a high rate of bubble retention, and with 
superior absorption characteristics, can be obtained as the hydrophilic 
resin according to the present invention. 
In the present invention, when the hydrogel polymer after pulverization 
(pulverized matter) is to be dried without further pulverization, the 
pulverized hydrogel polymer may have any particle diameter at which the 
particles can be sufficiently dried to their center during the drying 
step, and is preferably within a range from 0.1 mm to 30 mm, more 
preferably from 1 mm to 15 mm. Even more preferably, not less than 90% of 
the pulverized hydrogel polymer has a particle diameter within a range of 
1 mm to 5 mm. It is not preferable for the particle diameter of the 
pulverized hydrogel polymer to be less than 0.1 mm, because silting is 
likely during drying, which decreases drying efficiency, and because the 
internal bubbles are squashed. On the other hand, if the particle diameter 
of the pulverized hydrogel polymer exceeds 30 mm, it is difficult to dry 
the particles of hydrophilic resin to the center thereof. Incidentally, 
when a hydrogel polymer obtained by polymerization in an aqueous solution 
is in the form of lumps, it is preferable to pulverize this hydrogel 
polymer into a powder having a predetermined particle diameter. 
Again, when the foregoing pulverized hydrogel polymer is to undergo further 
pulverization (fine pulverization) prior to drying, the pulverized 
hydrogel polymer is not limited to any particular particle diameter, 
provided it is of a size which can be introduced into the device used for 
the further pulverization (fine pulverization), for example within a range 
from 0.1 mm to 500 mm. As the method of further pulverizing the foregoing 
pulverized hydrogel polymer, for example, a screw-type extruder such as a 
meat chopper (Hiraga Kosakusho Co., Ltd. product) or a Dome-Gran (Fuji 
Paudal Co., Ltd. product), or a cutting mill such as a Rotoplex (Hosokawa 
Micron Co., Ltd. product) may be used. The particle diameter of the 
pulverized hydrogel polymer after further pulverization is generally 
within a range from 0.1 mm to 30 mm, preferably from 1 mm to 15 mm. Even 
more preferably, not less than 90% of the pulverized hydrogel polymer has 
a particle diameter within a range of 1 mm to 5 mm. 
In the present invention, the pulverized hydrogel polymer obtained by the 
foregoing pulverization step(s) can be made into hydrophilic resin 
particles by means of a drying step and, if necessary, a further 
pulverization step. 
The method of drying the hydrogel polymer is not limited to any particular 
method; various known drying methods may be used, such as hot-air dying, 
infrared drying, microwave drying, drying using a drum dryer, and 
azeotropic dehydration in a hydrophobic organic solvent. Moreover, drying 
conditions may be set as desired so that the solid content of the 
hydrophilic resin is within a desired range, preferably so that the water 
content is not more than 10% by weight. 
Furthermore, the particle size of the hydrophilic resin according to the 
present invention may be adjusted by further pulverization or granulation 
after drying the hydrogel polymer. The average particle diameter of the 
hydrophilic resin is not limited to any particular diameter, but is 
preferably within a range from 10 .mu.m to 2000 .mu.m, more preferably 
from 100 .mu.m to 1000 .mu.m, and even more preferably from 300 .mu.m to 
600 .mu.m. It is preferable for the hydrophilic resin to have a narrow 
particle size distribution. By adjusting the particle size of the 
hydrophilic resin to within the foregoing range, the various 
characteristics, such as absorbing performance, can be further improved. 
Incidentally, the hydrophilic resin particles may have any of various 
forms, such as spherical, scale-shaped, irregularly broken, and granular. 
Further, it is preferable to increase the density of crosslinking near the 
surface of the hydrophilic resin particles obtained by the foregoing 
method, by secondary crosslinking of the surface thereof using a surface 
crosslinking agent. By treating the hydrophilic resin produced by the 
method according to the present invention using a surface crosslinking 
agent, liquid permeability, absorption rate, absorbing capacity under 
pressure, etc. can be further improved. 
The surface crosslinking agent may be any compound which has a plurality of 
reactive groups and is reactive with the functional groups, such as 
carboxyl groups, of the hydrophilic resin; known surface crosslinking 
agents generally used for such applications may be used. Specific examples 
of such surface crosslinking agents include polyhydric alcohols, such as 
(poly)ethylene glycol, diethylene glycol, (poly)propylene glycol, 
triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene 
glycol, 2,2,4-trimethyl-1,3-pentanediol, (poly)glycerin, 
2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 
1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, 
diethanolamine, triethanolamine, polyoxypropylene, 
oxyethylene-oxypropylenene block copolymer, pentaerythritol, sorbitol, 
polyvinyl alcohol, glucose, mannitol, sucrose, and glucose; compounds 
having two or more epoxy groups, such as ethylene glycol diglycidyl ether, 
polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, 
diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and 
(poly)propylene glycol diglycidyl ether; polyamine compounds, such as 
ethylenediamine, diethylenetriamine, triethylenetetramine, 
tetraethylenepentamine, pentaethylenehexamine, and polyethylene imine; 
compounds having two or more isocyanate groups, such as 
2,4-tolylenediisocyanate and hexamethylenediisocyanate; compounds having 
two or more oxazoline groups, such as 1,2-ethylenebis(oxazoline); alkylene 
carbonate compounds, such as 1,3-dioxolan-2-one, 
4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3-dioxolan-2-one, 
4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 
4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 
4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, and 
1,3-dioxopan-2-one; haloepoxy compounds, such as epichlorohydrin, 
epibromohydrin, and .alpha.-methylepichlorohydrin; and polyvalent metal 
compounds, such as hydroxides and chlorides of polyvalent metals like 
zinc, calcium, magnesium, aluminum, iron, and zirconium. However, the 
surface crosslinking agent is not limited to the foregoing examples. A 
single one of the foregoing surface crosslinking agents may be used alone, 
or two or more may be used in combination, as needed. 
By giving the hydrophilic resin secondary crosslinking using the foregoing 
surface crosslinking agent, absorbing capacity under applied pressure can 
be further improved. Further, the content of components which, when they 
contact the aqueous liquid, elute therein, i.e., so-called water-soluble 
components, can be held to a minimum. Incidentally, the quantity of the 
surface crosslinking agent and the temperature and duration of treatment 
are not particularly limited, and may be set as desired in accordance with 
the hydrophilic resin, the type or combination of surface crosslinking 
agents, the desired degree of surface crosslinking, etc. 
As discussed above, the method of producing hydrophilic resin according to 
the present invention is a method of producing hydrophilic resin by 
pulverizing and drying a hydrogel polymer, in which the hydrogel polymer 
is pulverized by shearing between two spiral rotary blades with different 
respective feed rates, provided opposite one another. In the present 
invention, the temperature of the hydrogel polymer is preferably not less 
than 40.degree. C. With the foregoing method, the hydrogel polymer gets in 
between the two spiral rotary blades with different respective feed rates, 
and, due to the feeding action thereof, is easily fed into the rotary 
blades. Further, with the foregoing method, due to the different 
respective feed rates of the rotary blades, one rotary blade overtakes the 
other, and the hydrogel polymer, caught therebetween, is sheared. For this 
reason, with the foregoing method, the hydrogel polymer can be pulverized 
by shearing, thus holding kneading and crushing to a minimum. Accordingly, 
with the foregoing method, a hydrophilic resin having few water-soluble 
components and having superior performance, such as absorbing capacity, 
can be easily obtained. Further, if the temperature of the hydrogel 
polymer is within the foregoing range, adhesion of the hydrogel polymer is 
less than when the temperature is outside the foregoing range, and water 
vapor is produced from the surface of the hydrogel polymer. For these 
reasons, if the temperature of the hydrogel polymer is adjusted and 
controlled to within the foregoing range, deformation of the hydrogel 
polymer can be minimized, thus allowing the hydrogel polymer to be 
pulverized without destroying its three-dimensional network structure. 
Consequently, particulate hydrophilic resin can be obtained which has 
superior absorption characteristics, such as absorbing capacity, 
absorption rate, and absorbing capacity under applied pressure, and which 
has a low content of water-soluble components, residual monomers, etc. 
In particular, when the hydrogel polymer contains bubbles, destruction of 
the many bubbles (pores) formed throughout the interior of the hydrogel 
polymer can be held to a minimum, and thus a porous hydrophilic resin can 
be obtained by drying and, as necessary, further pulverization. 
Accordingly, with the method according to the present invention, since a 
hydrophilic resin can be obtained which has a high bubble content and a 
larger surface area, a higher absorbing capacity, faster absorption rate, 
etc. can be attained. 
Hydrophilic resins produced by the method according to the present 
invention have superior absorbing performance, and thus can be suitably 
used for a variety of purposes, for example sanitary materials (bodily 
fluid absorbing articles), such as disposable diapers, sanitary napkins, 
pads for incontinence, wound protecting material, and would healing 
material; articles for absorbing urine, etc., of pets, for example; 
construction and building materials, such as building materials and 
water-retaining material for sandbags, waterproofing material, packing 
material, and gel water-bags; articles for food, such as drip absorbing 
material, freshness maintaining material, and cold reserving material; 
various industrial articles, such as oil/water separating material, 
material for preventing dew condensation, and coagulant; and agricultural 
and gardening articles, such as water-retaining material for plants and 
sandbags. 
The following will explain the present invention in further detail by means 
of concrete Examples and a Comparative Example, but the present invention 
is not limited in any way thereby. In what follows, performance of 
water-absorbent resin, as the hydrophilic resin according to the present 
invention, was measured by the following methods. 
(a) Absorbing Capacity 
Approximately 0.2 grams of water-absorbent resin was accurately weighed and 
placed in a 5 cm square tea bag made of non-woven fabric, which was then 
sealed by heat sealing. Next, the tea bag was submerged in synthetic urine 
at room temperature. One hour later, the tea bag was removed from the 
synthetic urine, and, after eliminating a liquid component by placing in a 
centrifugal separator at 1,300 rpm (equivalent to 250 G) for 3 minutes, 
the weight W.sub.1 (g) of the tea bag was measured. The same operations 
were performed using a tea bag in which no water-absorbent resin was 
sealed, and the weight W.sub.0 (g) of the tea bag was measured and used as 
a blank. Absorbing capacity was calculated based on the following 
equation. 
##EQU1## 
The composition of the synthetic urine and the content of each component 
were as follows. 
______________________________________ 
Composition Content 
______________________________________ 
Sodium sulfate 0.200% 
Potassium chloride 0.200% 
Magnesium chloride hexahydrate 0.050% 
Calcium chloride dihydrate 0.025% 
Ammonium dihydrogen phosphate 0.035% 
Diammonium hydrogen phosphate 0.015% 
Deionized water 99.475% 
______________________________________ 
(b) Content of Water-Soluble Components 
0.5 g of water-absorbent resin was dispersed in 1,000 ml of deionized 
water, stirred for 16 hours, and then filtered using filter paper. The 
water-soluble component content (%) was found by colloid-titrating the 
resulting filtrate using a cationic colloid reagent and measuring the 
amount of colloid of the water-absorbent resin dispersed in the filtrate. 
EXAMPLE 1 
A hydrogel polymer made of 75% partially neutralized crosslinked sodium 
acrylate, with a water content of 39% by weight and a temperature of 
55.degree., was introduced into the pulverizer shown in FIG. 4, and 
continuously pulverized. 
The foregoing hydrogel polymer was pulverized continuously for 24 hours, 
but almost no attachment of the hydrogel polymer to the rotary blades 6, 
7, and 8 was observed, and the pulverized hydrogel polymer was pulverized 
without kneading. 
Then, using a circulating hot air dryer, the pulverized hydrogel polymer 
was dried for 1 hour at 160.degree. C. Next, the dried hydrogel polymer 
was further pulverized by a predetermined method, yielding, as a 
hydrophilic resin according to the present invention, a water-absorbent 
resin with a predetermined particle diameter. Upon measuring the absorbing 
capacity and water-soluble component content of the foregoing 
water-absorbent resin, the absorbing capacity was found to be 42 g/g, and 
the water-soluble component content was found to be 12.5% by weight. 
EXAMPLE 2 
First, an aqueous monomer solution was prepared by mixing 134 parts of an 
aqueous solution containing 37% sodium acrylate by weight, 20 parts 
acrylic acid, 0.2 parts polyethylene glycol diacrylate (average ethylene 
oxide (EO) added mol number 8), and 44 parts water. Next, by bubbling 
nitrogen gas into the aqueous monomer solution, dissolved oxygen was 
eliminated therefrom. 
Then, in a nitrogen gas flow atmosphere, the foregoing aqueous monomer 
solution was continuously supplied to a driven steel belt polymerizer 
capable of heating and cooling of the belt surface, such that the depth of 
the aqueous monomer solution supplied to the top of the belt was 25 mm. 
The temperature of the aqueous monomer solution at this time was 
18.degree. C. Next, as polymerization initiators, an aqueous solution 
containing 5% 2,2'-azobis(2-methylpropionamidine) dihydrochloride by 
weight, an aqueous solution containing 0.1% L-ascorbic acid by weight, and 
an aqueous solution containing 0.07% hydrogen peroxide by weight, were 
added to the aqueous monomer solution in quantities of 2.0 parts/minute, 
1.8 parts/minute, and 2.0 parts/minute, respectively, and mixed therewith 
by line mixing. 
The aqueous monomer solution supplied to the belt commenced polymerization 
immediately after the foregoing polymerization initiators were added, 
forming a thick gelatinous substance. Here, the surface of the belt was 
cooled in a zone thereof up to a point reached when polymerization 
temperature reached its maximum. Maximum polymerization temperature was 
87.degree. C. Thereafter, the gelatinous substance was ripened in a zone 
heated to 80.degree. C., yielding a transparent hydrogel polymer. 
Next, the hydrogel polymer in the form of a sheet, obtained by the 
foregoing polymerization, was continuously pulverized by continuously 
introducing it into the pulverizer shown in FIG. 4 at 0.14 m/min. The 
temperature of the hydrogel polymer prior to pulverization was 60.degree. 
C. Further, the rotation speed of the rotary blades 6 and 7 was 0.6 
rotations/min, and that of the rotary blade 8 was 10 rotations/min. 
As a result, almost no attachment of the hydrogel polymer to the rotary 
blades 6, 7, and 8 was observed during pulverization, and the hydrogel 
polymer was pulverized without kneading. The average particle diameter of 
the pulverized hydrogel polymer was within a range from 1 mm to 100 mm, 
and over 70% thereof was within a range from 50 mm to 100 mm. 
Next, the pulverized hydrogel polymer was further pulverized in a meat 
chopper with a grating of holes 9.5 mm in diameter, and dried in a hot air 
dryer at 160.degree. C. for 65 minutes. The average particle diameter of 
the hydrogel polymer after pulverizing in the meat chopper was 2.5 mm. 
Thereafter, the dried hydrogel polymer was further pulverized by a 
predetermined method, yielding, as a hydrophilic resin according to the 
present invention, a water-absorbent resin with a predetermined particle 
diameter. Upon measuring the absorbing capacity and water-soluble 
component content of the foregoing water-absorbent resin, the absorbing 
capacity was found to be 60 g/g, and the water-soluble component content 
was found to be 10% by weight. 
EXAMPLE 3 
A hydrogel polymer was obtained and continuously pulverized by the same 
operations as in Example 2 above, except that its temperature after 
polymerization, i.e., temperature prior to introducing into the 
pulverizer, was 20.degree. C. 
As a result, 2 hours after commencement of pulverization, the hydrogel 
polymer was attached to the rotary blades 6, 7, and 8, and began to 
accumulate in the pulverizing chamber 2. Part of the accumulated hydrogel 
polymer had been kneaded to a dough-like consistency. 
The hydrogel polymer discharged from the outlet 12, i.e., the hydrogel 
polymer pulverized by the foregoing method, was dried and further 
pulverized by the same method as in Example 1 above, and upon measuring 
the absorbing capacity and water-soluble component content of the 
resulting water-absorbent resin, the absorbing capacity was found to be 59 
g/g, and the water-soluble component content was found to be 10% by 
weight. 
As the foregoing results show, when the temperature of the hydrogel polymer 
was low, stable pulverization could be performed, provided the duration of 
pulverization was short, and the resulting water-absorbent resin had a low 
water-soluble component content, and superior absorbing capacity. 
EXAMPLE 4 
First, in a reaction vessel provided with a thermometer, a nitrogen gas 
introducing pipe, etc., an aqueous monomer solution was prepared by mixing 
2286 g of an aqueous solution containing 37% sodium acrylate by weight, 
216 g acrylic acid, 5.8 g polyethylene glycol diacrylate (average ethylene 
oxide (EO) added mol number 8), and 1038 g water. Next, by bubbling 
nitrogen gas into the aqueous monomer solution, dissolved oxygen was 
eliminated therefrom. 
Then 0.5 g of a fluoride surfactant (Fluorad FC-135, a Sumitomo 3M Co., 
Ltd. product) was added to the aqueous monomer solution, which was then 
stirred at high speed in a homodisper in a nitrogen gas flow atmosphere, 
yielding an aqueous monomer solution with nitrogen gas bubbles dispersed 
therein. The volume of the aqueous monomer solution after dispersing 
bubbles therein was 1.5 times that of the aqueous monomer solution before 
dispersion of bubbles. Next, as polymerization initiators, 14 g each of an 
aqueous solution containing 10% sodium persulfate by weight and an aqueous 
solution containing 10% sodium hydrogensulfite by weight were added to the 
aqueous monomer solution. 
The aqueous monomer solution commenced polymerization immediately after 
addition of the foregoing polymerization initiators, and the 
polymerization temperature reached 90.degree. C. after 15 minutes. 
Thereafter, the reaction vessel was submerged in a 60.degree. C. hot-water 
bath for 20 minutes, yielding a hydrogel polymer with bubbles dispersed 
therein. 
Next, the foregoing hydrogel polymer was immediately introduced into the 
pulverizer shown in FIG. 5, and pulverized. Upon measuring the temperature 
of the hydrogel polymer prior to introduction into the pulverizer, the 
temperature thereof was approximately 70.degree. C. 
As a result, almost no attachment of the hydrogel polymer to the rotary 
blades 6, 7, and 8 was observed during pulverization, and the hydrogel 
polymer was pulverized without kneading. The average particle diameter of 
the pulverized hydrogel polymer was within a range from 1 mm to 25 mm. 
Bubbles in the pulverized hydrogel polymer were not squashed, but were 
retained. 
Next, the pulverized hydrogel polymer was dried in a hot air dryer at 
160.degree. C. for 1 hour. Thereafter, the dried hydrogel polymer was 
further pulverized by a predetermined method, yielding, as a hydrophilic 
resin according to the present invention, a water-absorbent resin with a 
predetermined particle diameter. Upon measuring the absorbing capacity and 
water-soluble component content of the foregoing water-absorbent resin, 
the absorbing capacity was found to be 50 g/g, and the water-soluble 
component content was found to be 12% by weight. The water-absorbent resin 
obtained was a porous hydrophilic resin and had a superior absorption 
rate. 
EXAMPLE 5 
First, an aqueous monomer solution was prepared by mixing 180 parts of an 
aqueous solution containing 37% sodium acrylate by weight, 20 parts of an 
aqueous solution containing 80% acrylic acid by weight, 0.3 parts 
polyethylene glycol diacrylate (average ethylene oxide (EO) added mol 
number 8), and 30 parts water. Next, by bubbling nitrogen gas into the 
aqueous monomer solution, dissolved oxygen was eliminated therefrom. 
Then, the aqueous monomer solution was continuously supplied, in a nitrogen 
gas flow atmosphere, to a driven steel belt polymerizer capable of heating 
and cooling of the belt surface, such that the depth of the aqueous 
monomer solution supplied to the top of the belt was 25 mm, and, as 
polymerization initiators, 1.3 parts of an aqueous solution containing 10% 
sodium persulfate by weight and 1.3 parts of an aqueous solution 
containing 0.05% L-ascorbic acid by weight were added to and mixed with 
the aqueous monomer solution by line mixing. The temperature of the 
aqueous monomer solution at the time of adding the polymerization 
initiators was 25.degree. C. 
The aqueous monomer solution supplied to the belt commenced polymerization 
immediately after the foregoing polymerization initiators were added, 
forming a thick gelatinous substance. Here, the surface of the belt was 
cooled in a zone thereof up to a point reached when polymerization 
temperature reached its maximum. Maximum polymerization temperature was 
90.degree. C. Thereafter, the gelatinous substance was ripened in a zone 
heated to 80.degree. C., yielding a transparent hydrogel polymer. 
Next, the hydrogel polymer in the form of a sheet, obtained by the 
foregoing polymerization, was continuously pulverized by continuously 
introducing it into the pulverizer shown in FIG. 5 at 1 mm/min. The 
temperature of the hydrogel polymer prior to pulverization was 65.degree. 
C. Further, the rotation speeds of the rotary blades 6, 7, and 8 were 7 
rotations/min, 5 rotations/min, and 12 rotations/min, respectively. 
As a result, almost no attachment of the hydrogel polymer to the rotary 
blades 6, 7, and 8 was observed during pulverization, and the hydrogel 
polymer was pulverized without kneading, yielding transparent pulverized 
hydrogel polymer. The average particle diameter of the pulverized hydrogel 
polymer was within a range from 1 mm to 50 mm. 
Next, the pulverized hydrogel polymer was further pulverized in a meat 
chopper with a grating of holes 13 mm in diameter, and dried in a hot air 
dryer at 170.degree. C. for 40 minutes. The average particle diameter of 
the hydrogel polymer after pulverizing in the meat chopper was 2 mm. 
Thereafter, the dried hydrogel polymer was further pulverized in a roll 
mill. Particles that passed through an 850-.mu.m mesh screen but did not 
pass through a 150-.mu.m mesh screen were collected, yielding, as a 
hydrophilic resin according to the present invention, a water-absorbent 
resin with a predetermined particle diameter. Upon measuring the absorbing 
capacity and water-soluble component content of the foregoing 
water-absorbent resin, the absorbing capacity was found to be 52 g/g, and 
the water-soluble component content was found to be 5% by weight. 
COMATIVE EXAMPLE 1 
The hydrogel polymer of Example 1 was pulverized using a two-shaft 
roller-type cutter. The rollers were for the most part unable to bite into 
the hydrogel polymer, and thus pulverization was nearly impossible. 
Further, it took time for the rollers to bite into the hydrogel polymer. 
As a result, the hydrogel polymer obtained by the foregoing method was 
kneaded to a dough-like consistency throughout. 
The resulting hydrogel polymer was dried and further pulverized by the same 
method as in Example 1, yielding, as a comparative hydrophilic resin, a 
comparative water-absorbent resin with a predetermined particle diameter. 
Upon measuring the absorbing capacity and water-soluble component content 
of the foregoing comparative water-absorbent resin, the absorbing capacity 
was found to be 40 g/g, and the water-soluble component content was found 
to be 18.5% by weight. 
The embodiments and concrete examples of implementation discussed in the 
foregoing detailed explanation of the present invention serve solely to 
illustrate the technical contents of the present invention, which should 
not be narrowly interpreted within the limits of such concrete examples, 
but rather may be applied in many variations without departing from the 
spirit of the present invention and the scope of the patent claims set 
forth below.