Hydrophilic polymer and method for production thereof

A hydrophilic polymer having the water absorption capacity thereof 1 to 30 times to its own weight by a process of manufacture which comprises preparing a monomer component comprising (a) 2 to 25 mol % of a hydroxyl group-containing alpha,beta-ethylenically unsaturated monomer, (b) 5 to 30 mol % of a carboxyl group-containing alpha,beta-ethylenically unsaturated monomer, and (c) 93 to 45 mol % of a carboxylate group-containing alpha,beta-ethylenically unsaturated monomer, providing that the total of (b) and (c) is in the range of 98 to 75 mol %, radically polymerizing said monomer component, and heat-treating the resultant polymer thereby causing the hydroxyl group and carboxyl group possessed by the polymer to react with each other and form a crosslinked structure, a method for the production thereof, and uses found therefor including a cation sequestrating resin, a coolant and a coating material.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a hydrophilic polymer, a method for the 
production thereof, and uses found therefor. More particularly, this 
invention relates to a hydrophilic polymer assuming hygroscopicity owing 
to the inclusion in its molecular unit of a carboxyl group, a carboxylate 
group, and a hydroxyl group and nevertheless having its own water 
absorption ratio being 1 to 30 times to the own weight owing to the mutual 
reaction of the carboxyl group and hydroxyl group, a method for the 
production thereof, and uses found therefor. 
2. Description of the Prior Art 
In recent years, the so-called water-absorbing polymer, i.e. such polymers 
which are insoluble in water and capable of absorbing water, have come to 
be used widely in the field of civil engineering, the field of agriculture 
and forestry, the field of sanitary articles, etc. which by nature are 
allowed to take full advantage of the polymers' ability to absorb and 
retain water. 
For the production of these water-absorbing polymers, a method which 
simultaneously polymerizes and self-crosslinks a hydrophilic monomer in 
the presence of a crosslinking agent (Japanese Patent Publication SHO 
54(1979)-30,710), a method which polymerizes a hydrophilic monomer in the 
presence of a small amount of a crosslinking monomer (Japanese Patent 
Laid-Open SHO 58(1983)-71,907), a method which polymerizes partially 
neutralized acrylic acid in the presence of a water-soluble polyhydric 
alcohol and a surfactant (Japanese Patent Laid-Open SHO 55(1980)-108,407), 
a method which causes a polyepoxy compound to react with a copolymer 
comprising an alpha-olefin and/or a vinyl compound and maleic anhydride 
(Japanese Patent Laid-Open SHO 56(1981)-36,504), and a method which 
polymerizes a monomer containing 2-hydroxyethyl acrylate and acrylic acid 
or a metal salt thereof in the presence of a crosslinking agent with the 
monomer concentration kept over 35% by weight and, during the course of 
the polymerization, causes self-crosslinking of the monomer in process of 
polymerization (Japanese Patent Laid-Open SHO 56(1981)-161,413), for 
example, have been proposed. 
The water-absorbing polymers obtained by these known methods have water 
absorption ratios so large as to take up and hold purified water 
approximately to 200 to 1,000 times their own volume and, therefore, are 
uses for which these polymers prove to be totally unfit because their 
characteristically large water absorption ratios are rather detrimental 
than otherwise. When these water-absorbing polymers are used in sheets for 
preventing dew condensation, sheets for regulating moisture, or fabrics 
for absorbing perspiration and moisture as attached fast to their fibers 
by a suitable means, they are often swelled to an unduly large extent and 
take a long time before they release the absorbed water by evaporation and 
resume their former dry state. At time, they are overswelled possibly to a 
point where sheets sustain fracture or the polymers come off the sheets or 
fibers. This phenomenon is particularly conspicuous when the 
water-absorbing polymers are amply used for the enhancement of 
hygroscopicity and ability to prevent dew condensation. 
When water-absorbing polymers of high absorption ratios are used in water 
stop packings which comprise rubber and a water-absorbing polymer 
incorporated in the rubber, the packings absorb water possibly in such a 
large volume as to swell their rubber matrixes excessively and require a 
very long time before they are fully dried. In an extreme case, the 
abosorbed water may cause fracture of the rubber matrixes and deprive the 
packings of usefulness. 
Water-absorbing polymers are generally handled in the form of powder and, 
therefore, are prone to entail a disadvantage that the powder is caked 
with absorbed moisture or drifted readily in the form of dust. This 
disadvantage can be eliminated in the case of water-absorbing polymers 
which are capable of being handled in the form of aqueous dispersion or 
aqueous slurry. Unfortunately, however, the conventional water-absorbing 
polymers of high water absorption ratios are not easily transformed into 
an aqueous dispersion or aqueous slurry. In the circumstances, a 
hygroscopic polymer which has the water absorption ratio thereof lowered 
to a point where the polymer used in a water stop sheet, for example, does 
not suffer the moisture or water absorbed therein to cause either fracture 
of the matrix of sheet or component fibers thereof or separation of the 
polymer from the sheet and which is capable of being transformed into an 
aqueous dispersion has a prospect of finding a great demand. 
A water-absorbing polymer having the capacity for water absorption 
repressed ideally as described above could be obtained from the 
conventional water-absorbing polymer by suitably increasing the 
crosslinking degree thereof. When this increase of the crosslinking degree 
is effected by a method using a polyhydric alcohol in a large amount, the 
treatment must be performed at an elevated temperature for a long time for 
the polymerization degree to be sufficiently heightened. Further, the 
polyhydric alcohol suffers from low crosslinking efficiency because it 
readily vaporizes or passes into the ambient air. When the increase of the 
crosslinking degree is performed by a method using in a large amount a 
crosslining monomer possessing two or more unsaturated groups in the 
molecular unit thereof, the crosslinking proceeds unevenly and the 
crosslinking monomer which is noxious inherently remains in its unaltered 
form because the crosslinking monomer is sparingly soluble in a 
water-soluble (hydrophilic) monomer. Thus, this method suffers from poor 
safety and high cost. In the case of a method which effects the desired 
increase of the crosslinking degree by the reaction of a polyepoxy 
compound with a water-soluble polymer, there arises a possibility of the 
polyepoxy compound remaining after the reaction and inducing the drawbacks 
of toxicity and high cost. 
As builders for detergents, phosphates, water-soluble high molecular 
electrolytes, and zeolites have been known heretofore to the art. Of these 
detergent builders, phosphates and water-soluble high molecular 
electrolytes are soluble in water and excellent in ability to sequestrate 
polyvalent metal ions in hard water, ability to purge fabrics of solid 
particulate stain, and ability to prevent removed defiling particles from 
adhering again to fabrics in process of cleaning. From the standpoint of 
preserving water from pollution, the phosphates have disadvantage that 
they possibly form a cause for the phenomenon of eutrophication of water. 
The water-soluble high molecular electrolytes which may be represented by 
sodium salts of carboxylate such as polyacrylic acid, polymaleic acid, and 
acrylic acid-maleic acid copolymer are deficient in biodegradability and, 
to be sufficiently effective, must be used in a large amount and 
inevitably are disadvantageous in that they entail environmental 
pollution. In contrast, the zeolites which are a water-insoluble inorganic 
particulate substance do not cause so heavy water pollution as the 
aforementioned phosphates and water-soluble high molecular electrolytes 
but are deficient in ability to sequestrate polyvalent metal ions. 
Recently, the problems such as undue abrasion of washing machines by 
zeolites have come to arouse serious concern. 
In the circumstances, several water-insoluble organic detergent builders 
improved in ability to sequestrate polyvalent metal ions have been 
proposed. For example, West German Patent No. 2,055,423 discloses a method 
which uses a polymer crosslinked as with divinylbenzene, West German 
Patent No. 2,216,467 discloses a method which uses a cation exchanger 
obtained by impregnating a flat fibrous matrix as with a polymer 
containing a carboxyl group, and West German Patent No. 2,307,923 
discloses a method which uses what is obtained by impregnating a porous 
matrix with a mixed monomer of a crosslinking agent containing two or more 
double bonds and an ethyleic double bond and subsequently polymerizing the 
mixed monomer lodged in the matrix. The polymers involved in these 
proposed methods are invariably water-impregnable crosslinked polymers 
obtained by using as a comonomer a crosslinked monomer containing two or 
more double bonds. 
These water-impregnable crosslinked polymers, however, have a disadvantage 
that they exhibit a weak gel strength in an impregnated state and, during 
the course of laundering, undergo disintegration and induce unwanted 
adhesion to laungered articles when the crosslinking monomer is used in an 
unduly small amount. If the amount of the crosslinking monomer to be used 
is unduly large, they have a disadvantage that for a certain unknown 
cause, the crosslinking monomer survives the reaction possibly to a point 
where the safety of polymer is jeopardized. Further, since not so large 
amount of the crosslinking monomer is soluble in water, a method which 
comprises conducting the polymerization in the state of an aqueous 
solution of unneutralized carboxylic group-containing monomer having the 
crosslinkable monomer dissolved therein, and after the completion of the 
polymerization, neutralizing the resultant polymer has been proposed. This 
method, however, inevitably grows heavily in intricacy. The crosslinking 
monomer itself is very expensive. Thus, these polymers have not been fully 
developed to a practicable level. 
Moreover, such water-soluble organic high molecular compounds as agar, 
gelatin, polyvinyl alcohol, polyethylene glycol, and partially crosslinked 
derivatives thereof which have been heretofore used as a coolant have a 
nature such that when they are cooled below 0.degree. C. in their 
water-containing state, the resultant gels are frozen hard and deprived 
totally of flexibility. Thus, they have a disadvantage that when they are 
used in cooling human bodies and foodstuffs, they exhibit a poor ability 
to come into close contact with the contours of the objects being cooled. 
During their use on human bodies, the frozen gels impart unpleasant 
sensation due to the hardness. When the frozen gels are used on 
foodstuffs, they inflict injuries to the foodstuffs or their wrappers. A 
proposal has been made to use as a coolant a hydrated gel of a highly 
absorbent resin such as slightly crosslinked sodium polyacrylate which 
takes up water approximately to 100 to 1,000 times its own weight. The 
hydrated gel has found favorable utility in products such as paper diaper, 
sanitary napkin, and agricultural-horticultural coolants which require a 
large capacity for water absorption. For the function as a coolant, the 
hydrated gel's large ability to absorb water is not utilized to advantage. 
Conversely, the hydrated gel is not fully satisfactory in the flexibility 
in a frozen state which is an important requirement for a coolant. 
Regarding the function to be expected of a coolant, the capacity for 
absorption of water is not required to be very large. The hydrated gel, 
however, is not fully satisfactory in flexibioity, an important 
requirement to be satisfied by the hydrated gel destined to be used in a 
frozen state as a coolant. 
For the elimination of these drawbacks of the conventional products as 
described above, there has been proposed a method which produces a gel 
incapable of freezing by causing the aforementioned water-soluble high 
molecular compound or highly absorbent resin to absorb an aqueous solution 
containing a polyhydric alcohol. This gel is deficient in the quality of a 
coolant because it is incapable of utilizing the latent heat of melting of 
ice. The coolants using the conventional highly absorbent resins have a 
disadvantage that when they are left standing under the sunlight or at 
elevated temperature for a long time, they gain much in viscidity and lose 
softness in a great measure during the course of freezing. 
As a coating material for proofing a given substrate against dew 
condensation, there has been proposed a product which is vested with a 
water-absorbing property by the addition of an absorbent body pigment such 
as diatomaceous earth, pearlite, or zeolite beside such ordinary paint 
components as synthetic resin emulsion, coloring pigment, pigment 
dispersant, tackifier, fungicide, and antiseptic (Japanese Patent 
Laid-Open SHO 57(1982)-151,661). This coating material is deficient in 
ability to prevent dew condensation because it has no satisfactory ability 
to absorb water. If the absorbent body pigment is used in a large amount 
for the purpose of enhancing the ability to absorb water, the coating 
material is no longer capable of forming a film rich in strength. 
For the elimination of the drawbacks suffered as described above by the 
coating material capable of proofing a substrate against dew condensation 
owing to the use of an absorbent body pigment, there has been proposed a 
coating material adapted to proof a substrate against dew condensation by 
the incorporation of a highly absorbent resin (Japanese Patent Laid-Open 
SHO 62(1987)-205,171 and SHO 62(1987)-265,364). This coating material for 
proofing substrates against dew condensation owing to the incorporation of 
a highly absorbent resin enjoys an improved ability to absorb water and 
consequently exhibits an improved ability to preclude dew condensation. 
The highly absorbent resin has a capacity for taking up water 
approximately to 50 to 1,000 times its own weight. Since it absorbs water 
excessively, it requires a long time in releasing the absorbed moisture. 
Since it is swelled greatly with absorbed water, the film formed with the 
coating material is deprived of surface smoothness by addition of only a 
small amount of water. The film sustains cracks because the difference of 
swelling and contraction of the film during the repeated cycles of 
admission and release of water is large. In the case of a water paint, if 
this paint incorporates therein the highly absorbent resin in a required 
amount, it acquires unduly high viscosity or undergoes heavy gelation to a 
point where the produced paint is effectively applied to a given surface 
only with difficulty. 
An object of this invention, therefore, is to provide a novel hydrophilic 
polymer, a method for the production thereof, and uses for the polymer. 
Another object of this invention is to provide a hydrophilic polymer having 
1 to 30 times of absorption ratio to the own weight. 
Yet another object of this invention is to provide a novel cation 
sequestrating resin, a coolant, and a coating material for proofing a 
substrate against dew condensation. 
SUMMARY OF THE INVENTION 
The objects described are attained by a hydrophilic polymer having the 
water absorption capacity thereof 1 to 30 times its own weight by a 
process of manufacture which comprises preparing a monomer component 
comprising (a) 2 to 25 mol % of a hydroxyl group-containing 
alpha,beta-ethylenically unsaturated monomer, (b) 5 to 30 mol % of a 
carboxyl group-containing alpha, beta-ethylenically unsaturated monomer, 
and (c) 93 to 45 mol % of a carboxylate group-containing 
alpha,beta-ethylenically unsaturated monomer, providing that the total of 
(b) and (c) is in the range of 98 to 75 mol %, radically polymerizing the 
monomer component, and heat-treating the resultant polymer thereby causing 
the hydroxyl group and carboxyl group possessed by the polymer to react 
with each other and form a crosslinked structure. 
The objects are also accomplished by a method for the production of a 
hydrophilic polymer having the water absorption capacity thereof 1 to 30 
times its own weight, which method comprises preparing a monomer component 
comprising (a) 2 to 25 mol % of a hydroxyl group-containing 
alpha,beta-ethylenically unsaturated monomer, (b) 5 to 30 mol % of a 
carboxyl group-containing alpha,beta-ethylenically unsaturated monomer, 
and (c) 93 to 45 mol % of a carboxylate group-containing 
alpha,beta-ethylenically unsaturated monomer, providing that the total of 
(b) and (c) is in the range of 98 to 75 mol %, aqueous solution 
polymerizing the resultant monomer component in the presence of a radical 
polymerization initiator, and subjecting the resultant polymer to a heat 
treatment at a material temperature in the range of 130.degree. to 
250.degree. C. for a period in the range of 10 minutes to 20 hours thereby 
causing the hydroxyl group and carboxyl group possessed by the polymer to 
react with each other and form a crosslinked structure. 
These objects are further accomplished by a cation sequestrating resin 
formed of a hydrophilic polymer having the water absorption property 
thereof 1 to 30 times its own weight. 
These objects are accomplished by a coolant formed of a hydrophilic polymer 
having the water absorption property thereof in the range of 1 to 30 times 
its own weight. 
These objects are also accomplished by a coating material for proofing a 
substrate against dew condensation, comprising a hydrophilic polymer 
having the water absorption property thereof in the range of 1 to 30 times 
its own weight and a synthetic resin emulsion.

EXPLANATION OF THE PREFERRED EMBODIMENT 
The hydroxyl group-containing alpha,beta-unsaturated ethylenically 
unsaturated monomer [hereinafter referred to as "monomer (a)"] to be used 
in the present invention may be a water-soluble monofunctional monomer 
containing a sole hydroxyl group in the molecular unit thereof or a 
polyfunctional monomer containing two or more hydroxyl groups in the 
molecular unit thereof. As typical examples of the monomer (a), allyl 
alcohol; hydroxyalkyl esters of vinyl carboxylic acid monomers such as 
2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl 
acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 
2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and 
4-hydroxybutyl methacrylate; di- and tri-alkylene glycol 
momo(meth)acrylates such as diethylene glycol momoacrylate, triethylene 
glycol momoacrylate, dipropylene glycol momoacrylate, tripropylene glycol 
momoacrylate, diethylene glycol monomethacrylate, triethylene glycol 
monomethacrylate, dipropylene glycol monomethacrylate, and tripropylene 
glycol monomethacrylate; polyalkylene glycol mono(meth)acrylates 
(providing that the number of repeating units of alkylene is in the range 
of 4 to 50); mono(meth)acrylates of polyhydric alcohols such as glycerol 
mono(meth)acrylate, neopentyl glycol mono(meth)acrylates, and 
pentaerythritol mono(meth)acrylates may be mentioned. These monomers (a) 
may be used either singly or jointly in the form of a mixture of two or 
more members. Of course, a monomer such as vinyl alcohol which, though 
incapable of existing by itself, is enabled to form a hydroxyl group by 
being polymerized with vinyl acetate and subsequently saponified can be 
used as a monomer (a). 
The carboxyl group-containing alpha,beta-ethylenically unsaturated monomer 
[hereinafter referred to as "monomer (b)"]is soluble in water. Typical 
examples of the monomer (b) include acrylic acid, methacrylic acid, maleic 
acid, and itaconic acid. .Among other monomers (b) mentioned above, 
acrylic acid and methacrylic acid prove to be particularly preferable. One 
member or a mixture of two or more members selected from the monomers (b) 
cited above may be used. 
The carboxylate group-containing alpha,beta-ethylenically unsaturated 
monomer [hereinafter referred to as "monomer (c)"]is soluble in water. As 
typical examples of the monomer (c), alkali metal salts and ammonium salts 
of the carboxyl group-containing alpha,beta-ethylenically unsaturated 
monomers (b) may be cited. One member or a mixture of two or more members 
selected from the monomers (c) mentioned above may be used. 
When the polymer obtained by the aqueous solution polymerization of the 
monomer component mentioned above is subjected to the heat treatment, the 
hydroxyl group and carboxyl group contained in the molecular unit of the 
polymer undergo a reaction of esterification and consequent crosslinking 
to give a three-dimensional structure to the polymer. For the produced 
polymer to be hydrophilic and to exhibit a water absorption ratio of 1 to 
30 times its own weight, the content of the monomer (a) is required to be 
in the range of 2 to 25 mol %, preferably 5 to 20 mol %, the content of 
the monomer (b) in the range of 5 to 30 mol %, preferably 10 to 30 mol %, 
and the content of the monomer (c) in the range of 93 to 45 mol %, 
preferably 85 to 5 mol %, providing that the total of the monomer (b) and 
the monomer (c) is in the range of 98 to 75 mol %, preferably 95 to 80 mol 
%. If the amount of the monomer (a) is less than 2 mol % and/or that of 
the monomer (c) is less than 5 mol %, the produced polymer has an 
insufficient crosslinking density, accordingly the produced polymer has 
too high water absorption ratio to be difficult to accomplish the object 
of the present invention. Because the water absorption capacity which the 
polymer acquires after the formation of the crosslinked structure is 
mainly originated in the carboxylate group possessed by the crosslinked 
polymer in the molecular unit thereof, when the amount of the monomer (c) 
is less than 45 mol %, it is difficult for the produced polymer to acquire 
a proper water absorption ratio, outstanding hygroscopicity and excellent 
cation exchangeability, being the characteristics of the present 
invention. Conversely, if the amount of the monomer (a) is more than 25 
mol % and that of the monomer (b) is more than 30 mol %, though the 
polymer possessing the water absorption ratio not less than once to the 
own weight may be obtained, such polymer has few need from the practical 
viewpoint. It is preferable for the sake of promoting the ester 
crosslinking reaction more efficiently, in the proportion of the monomer 
(a) to the monomer (b), to use the monomer (b) more than the monomer (a). 
The monomer component of the present invention may additionally incorporate 
therein other alpha,beta-ethylenically unsaturated monomer 
copolymerization with the monomer component in a ratio not so high as to 
impair the ester crosslinking density or the water absorption ratio. This 
additional monomer is desired to be soluble in water. Examples of this 
additional monomer include 2-acrylamide-2-methylpropane sulfonic acid, 
sulfoethyl (meth)acrylates, 2-(meth)acryloylethane sulfonic acid, 
acrylamide, N-methylol acrylamide, acrylonitrile, methyl (meth)acrylates, 
ethyl acrylate, isopropyl acrylate, butyl acrylate, dimethyl maleate, 
diethyl maleate, dibutyl maleate, and vinyl acetate. The amount of this 
additional monomer to be used is desired to be less than 29 mol %, 
preferably to be in the range of 0 to 20 mol %, per the total amount of 
the monomers mentioned above. 
Further, the monomer component may incorporate therein a crosslinking 
monomer containing two ore more unsaturated groups in the molecular unit 
thereof. This crosslinking monomer is desired to be soluble in water. 
Typical examples of this crosslinking monomer include ethylene glycol 
diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, 
diethylene glycol dimethacrylate, triethylene glycol monoacrylate, 
triethylene glycol dimethacrylate, polyethylene glycol di(meth)acrylates, 
polypropylene glycol di(meth)acrylates, glycerol di(meth)acrylates, 
glycerol tri(meth)acrylates, trimethylol propane diacrylate, trimethylol 
propane dimethacrylate, trimethylol propane triacrylate, trimethylol 
propane trimethacrylate, neopentyl glycol di(meth)acrylates, 
N,N'-methylene bisacrylamide, and N,N'-methylene bismethacrylamide. When 
the crosslinking monomer is used in the monomer component, it lends itself 
to shorten the time required for the heat treatment performed for the 
ester crosslinking of the monomer component, preclude the otherwise 
possible degradation of the polymer due to a protracted heating at an 
elevated temperature, ensure formation of a polymer of high quality. A 
gel-like polymer obtained without crosslinking monomer has markedly 
adherence of the surface thereof and, hence, such handling as finely 
cutting for the sake of making dry easy or filtering suspended substances, 
it difficult. For this reason, use of the crosslinking agent in a small 
amount makes the adherence of the gel polymer surface lower and handling 
thereof easy, so that it is preferable. The amount of this crosslinking 
monomer is in the range of 0.001 to 0.5 mol %, preferably 0.01 to 0.3 mol 
%, based on the monomer component. 
The hydrophilic polymer having the water absorption capacity repressed 
advantageously as contemplated by the present invention possesses a water 
absorption ratio of 1 to 30 times its own weight, preferably falling in 
the range of 2 to 20 times its own weight. If the water absorption ratio 
exceeds 30 times the own weight, the gel of the polymer swelled with 
absorbed water is poor in strength, liable to be deteriorated by 
ultraviolet light, and difficult of dispersion in an aqueous medium. 
For the radical polymerization of the monomer component, the method of 
aqueous polymerization heretofore employed for the polymerization of a 
water-absorbing polymer can be used in its unmodified form. This radical 
polymerizaiton can be easily carried out, for example, by a method which 
comprises forming a plurality of cavities by superposing compressively a 
plurality of horizontal frames adapted to form tightly closed cavities on 
being joined by superposition and provided with heat transfer surfaces and 
bult-in heat medium passages adapted to manifest the function of a 
polymerization reaction temperature regulator, charging the cavities with 
at least one monomer or a monomer solution, passing a heat medium through 
the plurality of heat medium passages thereby keeping the temperature of 
the polymerization reaction system through the medium of the heat transfer 
surfaces at a level within a desired range and polymerizaing the monomer, 
and on completion of the polymerization, relieving the joined horizontal 
frames of the pressure and removing the produced polymer therefrom as 
disclosed in Japanese Patent Publication SHO 48(1973)-42,466, a method 
which effects radical aqueous solution polymerization of a monomer 
destined to form a hydrated polymer by continuing the polymerization in a 
container provided with a plurality of rotary stirring shafts and, with 
the advance of the polymerization, finely dividing the polymer as formed 
by virtue of the shearing force generated by the rotation of the stirring 
shafts as disclosed in Japanese Patent Laid-Open SHO 57(1982)-34,101 and 
U.S. Pat. No. 4,625,001, or a reverse phase suspension polymerization 
method as disclosed in Japanese Patent Publication SHO 59(1984)-37,003. 
The polymerization initiator to be used in the present invention may be any 
of the water-soluble radical polymerization initiators heretofore known in 
the art. As examples of the polymerization initiator, persulfates such as 
potassium persulfate, sodium persulfate, and ammonium persulfate, and 
water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane) 
hydrochloride (produced by Wako Junyaku K. K. and marketed under product 
code of "V-50") may be cited. A redox type initiator is also available for 
the same purpose. Examples of the redox type initiator include 
combinations of those compounds mentioned above as examples of 
water-soluble radical polymerization initiator with such reducing agents 
as hydrogensulfites like sodium hydrogensulfite and potassium 
hydrogensulfite, sulfites like sodium sulfite and potassium sulfite, 
thiosulfates like sodium thiosulfate and potassium thiosulfate, L-ascorbic 
acid, and ferrous salts. The amount of the polymerization initiator to be 
used is in the range of 0.001 to 0.5% by weight, preferably 0.002 to 0.3% 
by weight, based on the total amount of the monomers. The temperature of 
the aqueous solution polymerization is in the range of 10.degree. to 
120.degree. C., preferably 30 to 100.degree. C. The concentration of the 
monomer component in the aqueous solution is 10 to 70% by weight, 
preferably 20 to 60% by weight. 
The polymer which is obtained as described above is subjected, either 
during or after the course of drying to a heat treatment at a material 
temperature in the range of 130.degree. to 250.degree. C., preferably 
150.degree. to 250.degree. C., for a period in the range of 10 minutes to 
20 hours, preferably 10 minutes to 10 hours, so that the polymer is 
enabled to induce ester crosslinking of the hydroxyl group and the 
carboxyl group contained in the molecular unit thereof. As the result, 
there is obtained a crosslinked hydrophilic polymer possessing a desired 
water absorption ratio in the range of 1 to 30 times to its own weight. By 
the method of the present invention, since the monomer component 
containing no crosslinking monomer or containing such a monomer in an 
irreducibly minimum amount required is subjected to the aqueous solution 
polymerization and the produced polymer is heated for crosslinking 
reaction, the aqueous solution polymerization can be carried out at a high 
monomer concentration and the degree of crosslinking can be controlled as 
desired by suitable selection of the conditions of the heating to permit 
easy manufacture of a hydrophilic polymer possessing a water absorption 
ratio of 1 to 30 times to its own weight. In this case, the temperature 
conditions for the drying or the heat treatment are as described above. If 
the temperature is lower than 130.degree. C., since the reaction between 
the hydroxyl group and the carboxyl group does not easily proceed, it is 
difficult to obtain a hydrophilic polymer possessing a water absorption 
ratio of 1 to 30 times to its own weight. Conversely, if the temperature 
exceed 250.degree. C., the produced hydrophilic polymer is poor in 
quality. Since the method of the production in accordance with the present 
invention, which has caused the carboxylic group-containing monomer to 
neutralize during the state of monomer, does not involves such complicated 
steps as step for post-neutralization of the polymer after polymerization 
and after heat treatment, it is excellent method capable of producing the 
product with good productability. 
The hydrophilic polymer of this invention is obtained by the polymerization 
of a monomer component of a specific composition and this polymer is 
allowed to acquire a crosslinked structure owing to the esterification of 
the hydroxyl group and the carboxyl group contained in the molecular unit 
thereof. Thus, the polymer possesses hygroscopicity and, at the same time, 
has the water absorption ratio in the range 1 to 30 times to its own 
weight. Owing to the carboxylate group contained in a specific amount in 
the monomer component, the polymer notably abounds in hygroscopicity and 
enjoys an advantageously repressed water absorption ratio of 1 to 30 times 
to its own weight. The hydrophilic polymer of this invention, therefore, 
can be dispersed in an aqueous medium to form an aqueous dispersion. It 
suffers from only a small decline of gel strength even when it is exposed 
to a large volume of water. Owing to this behavior, the polymer can be 
favorably used in sheets proofed against dew condensation, 
moisture-regulating sheets, perspiration-absorbing fibrous products, etc. 
The hydrophilic polymer of this invention excels in durability and 
lightproofness and possesses a proper water absorbing property and, 
therefore, is favorably used in water-retaining material for soil, 
water-swelling separating agent, agent for imparting hydrophilicity to 
plastic materials, antistatic agent, viscous fluid for electric 
appliances, static crushing agent, artificial snow, and chemical pocket 
warmer. Further the hydrophilic polymer of this invention enjoys extremely 
high safety because it has a notably small water-soluble polymer portion 
and contains unaltered crosslinking agent in a small amount. Owing to this 
quality, the polymer can be favorably used in sanitary absorbent or for 
drying fresh foodstuffs or preserving foodstuffs in a fresh state. The 
hydrophilic polymer of this invention further exhibits an excellent 
ability to sequestrate cations such as metal ions. It is capable of 
sequestrating calcium ions in a ratio of no less than 200 mg-CaCO.sub.3/ 
g, for example. The polymer, on exhaustion of the sequestrating capacity, 
can be easily regenerated with a mineral acid such as hydrochloric acid. 
Owing to this behavior, the polymer can be favorably used for softening 
hard water, treating waste water prior to release into bodies of water, 
recovering polyvalent metal ions, and refining water through removal of 
impurities. It is also useful as a detergent builder. 
Further, in accordance with the method of this invention, from the polymer 
obtained by the polymerization performed under fixied conditions, the 
hydrophilic polymer possessing a varying water absorption ratio can be 
produced by suitably controlling the conditions to be used during the heat 
treatment. Thus, the method of this invention is highly advantageous even 
from the standpoint of productional efficiency. 
The cation sequestrating resin (water conditioning agent) according to this 
invention, when incorporated in a detergent or added to the water in the 
washing machine, permits a saving in the amount of the detergent builder 
such as a phosphate, a water-soluble high molecular electrolyte, or 
synthetic zeolite which is the cause for the eutrophication or 
contamination of the water in rivers, lakes, etc. without a sacrifice of 
the deterging power. This water-conditioning agent excels in safety 
because a crosslinking agent containing two or more ethylenic double bonds 
in the molecular unit thereof is not used at all or used only in a very 
small amount and further because unaltered monomer or unalterd 
crosslinking agent remains in a very small amount in the produced polymer. 
Since this water-conditioning is insoluble in water, it can be removed 
easily by filtration or sedimentation from the waste water under treatment 
and it can be prevented from flowing into rivers or lakes by using the 
water-conditioning agent as contained in a water-pervious bag or packed in 
a water inlet conduit. Since the water absorption ratio is 1 to 30 times 
to its own weight, the water-conditioning agents absorbs water at a very 
high speed sequestrates cations also at a high speed. 
The coolant of this invention exhibits softness even below 0.degree. C. and 
excels in the ability to preserve coolness and fully endures the impacts 
of repeated use through freezing and thawing cycles. It also exhibits 
excellent shelf life when it is stored long in its unfrozen state. When 
the coolant of this invention is packed in a closed bag of polyvinyl 
chloride resin, polyethylene, or rubber and then cooled in a refrigerator, 
for example, the cooled bag can be used as a cooling pillow for man, a 
cooling mat for animal, or an efficient coolant for foodstuffs. It can be 
used repeatedly for this purpose. To be used effectively as a coolant, the 
hydrophilic polymer is desired to possess a water absorption ratio of 1 to 
30 times, preferably 5 to 20 times, to its own weight. 
For the hydrophilic polymer of this invention to be effectively used as a 
dew-preventing coating material, the coating material is required to 
contain the hydrophilic polymer and a synthetic resin emulsion as 
essential components. 
The synthetic emulsion to be used in the coating material in an O/W type 
emulsion. Examples of the O/W type emulsion include the emulsions of acryl 
resin, urethane resin, chloroprene rubber, ethylene-vinyl acetate 
copolymer, styrene-butadiene rubber, and epoxy resin. These emulsions may 
be used singly or jointly as a blend of two or more members. 
The hydrophilic polymer to be used in the present invention, in an 
atmosphere having a temperature of 20.degree. C. and a relative humidity 
of 90%, exhibits a hygroscopicity of 30 to 130% by weight, preferably 50 
to 130% by weight, and a water absorption ratio in the range of 1 to 30 
times, preferably 2 to 20 times, to its own weight. If the hygroscopicity 
is less than 30% by weight, the film formed of the coating material 
absorbs water at an unduly low speed and exhibits no satisfactory ability 
to prevent dew condensation by a certain unknown mechanism. 
If the water absorption ratio of the hydrophilic polymer is less than 1 
time to its own weight, the hydrophilic polymer suffers from poor economy 
because it has a small capacity for water absorption and, therefore, must 
be used in an unduly large amount. If the water absorption ratio exceeds 
30 times to its own weight, the film formed of the coating material 
possibly sustains cracks or loses surface smoothness by the impacts of 
repeated use through cycles of swelling and contraction. The film also has 
a disadvantage that it absorbs water excessively, takes much time in 
releasing absorbed moisture, and gathers mold. Depending on the water 
absorption ratio of the hydrophilic polymer and the amount of the polymer 
to be added, the synthetic resin emulsion coating material using this 
hydrophilic polymer may suffer from aggravation of viscosity and 
consequent gelation. 
The particle diameter of the hydrophilic polymer is not specifically 
restricted. For the sake of surface smoothness of the film to be formed of 
the coating material, however, the particle diameter is desired to be no 
more than 200 microns, preferably no more than 100 microns. The ratio of 
the synthetic resin emulsion to the hydrophilic polymer in the coating 
material contemplated by the present invention may be suitably selected to 
fit the conditions of the intended use and the physical properties to be 
expected. It is generally such that the proportion of the hydrophilic 
polymer is in the range of 10 to 200 parts by weight, preferably 20 to 100 
parts by weight, based on 100 parts by weight of the solids of the 
synthetic resin emulsion. 
The dew-preventing coating material of the present invention can be used in 
various types of paper, plastics, woven fabrics, non-woven fabrics, 
inorganic building materials, ALC plates, steel sheets, and composites 
thereof as applied to either or both of the surfaces thereof or allowed to 
impregnated them. 
The dew-preventing coating material can be prepared without requiring any 
special process. It is produced by sequentially adding the ingredients of 
the coating material to a suitable dispersing machine such as, for 
example, a ball mill, a sand mill, or a high speed mill and homogeneously 
mixing and dispersing them in the machine. On the surface of a substrate, 
the produced dew-preventing coating material can be applied in the form of 
a film by any of the known coating methods such as, for example, spraying, 
brushing, roller coating, trowel coating, flow coating, application with a 
flow coater, and application with a roller coater. Otherwise, it can be 
incorporated in the substrate by impregnation. 
The dew-preventing coating material of this invention is characterized by 
the fact that it exhibits an outstanding ability to prevent condensation 
when it is in the form of a film and also by the fact that the film of 
this coating material releases absorbed moisture quickly, retains high 
surface smoothness during the course of water absorption, and avoids 
sustaining any crack during repeated use through cycles of absorption and 
release of moisture. 
Since the coating material of this invention contains a polymer of high 
hygroscopicity, it exhibits a highly satisfactory moisture-controlling 
function when it is used in the linings of warehouses, closets, and other 
containers such as clothes boxes which require relatively high 
airtightness. 
Now, the present invention will be described more specifically below with 
reference to working examples. This invention is not limited to the 
working examples so cited but may be practiced otherwise without departing 
from the spirit of the invention disclosed herein. 
Example 1 
A jacketed stainless steel twin-arm kneader having an inner volume of 2.5 
liters, an opening 150 mm .times.150 mm in area, and a depth of 150 mm, 
and provided with two sigma type vanes 90 mm in diameter of rotation was 
fitted with a lid. In this kneader, 1,200 g of an aqueous solution of a 
monomer component comprising 67.5 mol % of sodium acrylate, 22.5 mol % of 
acrylic acid, 9.95 mol % of hydroxyethyl acrylate, and 0.05 mol % of 
N,N'-methylene bisacrylamide (monomer concentration 37% by weight) was 
placed and nitrogen gas was blown into displace the internal gas of the 
reaction system. Then, the two sigma type vanes were rotated at speeds of 
67 and 56 rpm, hot water at 35.degree. C. was passed through the jacket to 
heat the interior of the reaction system, and 0.5 g of ammonium persulfate 
and 0.5 g of sodium hydrogensulfite were added as polymerization 
initiators. After 5 minutes following the addition of the polymerization 
initiators, the monomer component began to polymerize. The temperature of 
the interior of the reaction system reached 83.degree. C. after 20 minutes 
following the addition of the polymerization initiators. The gel polymer 
was divided into minute particles about 5 mm in diameter. The stirring of 
the contents of the reaction system was further continued. After 60 
minutes following the start of the polymerization, the lid was removed 
from the kneader and the hydrated gel polymer was removed from the 
kneader. The hydrated gel polymer was dried in an ordinary hot air drier 
at 100.degree. C. for 2 hours and then comminuted to obtain a powdered 
polymer (1). Part of this polymer (1) was heat-treated in a still drier at 
180.degree. C., one of the two aliquot parts thereof for one hour and the 
other aliquot part for 3 hours, to produce hydrophilic polymer (1) and 
(2). 
The powdered polymer (1) and the hydrophilic polymers (1) and (2) were 
tested for water absorption ratio, residual amount of unaltered 
crosslinking agents, and hygroscopicity by the following methods. Further, 
water insoluble content (% by weight) of the hydrophilic polymer was 
determined by colloid titiation method. The results are shown in Table 1. 
Water absorption ratio: A tea bag-like pouch (40 mm.times.60mm) made of 
nonwoven fabric was packed evenly with 0.5 g of a powdery sample polymer 
was impregnated with deionized water and, after elapse of 60 minutes, 
dried on 10 sheets of tissue paper 120.times.200 mm in area (produced by 
Jujo Kimbary and marketed under trademark designation of "Kimwipe Wiper") 
to drain excess water, and weighed. The water absorption ratio was 
calculated by the following formula. 
##EQU1## 
Residual amount of unaltered crosslinking agents: A powdery sample 
polymer, 1.0 g , was dispersed in 1,000 ml of deionized water, stirred for 
2 hours, and passed through a Wattman filter paper GF/F (particle 
retaining capacity 0.7 .mu.m). The filtrate was analyzed for the content 
of unaltered crosslinking agents by liquid chromatography. 
Hygroscopicity: A powdery sample polymer, 0.2 g, was placed in an aluminum 
cup 50 mm in diameter and 10 mm in height and left standing for one week 
in a constant temperature constant-humidity container adjusted to a 
temperature of 20.degree. C. and a relative humidity of 90%. The powder 
thus allowed to absorb moisture was weighed. The hygroscopicity of the 
sample was calculated by the following formula. 
##EQU2## 
Example 2 
A powdered polymer (2) was repeating the procedure of Example 1, except 
that the monomer component as composed of 60 mol % of sodium acrylate, 20 
mol % of acrylic acid, and 20 mol % of hydroxyethyl acrylate. From part of 
the powdered polymer (2), hydrophilic polymers (3) and (4) were similarly 
produced, providing that the drying time was changed to 5 hours, because 
the polymer before drying has low crosslinking degree, so it was soft and 
was difficult to treat it and took 5 hours. These polymers were tested by 
following the procedure of Example 1. The results are shown in Table 1. 
Control 1 
When the procedure of Example 1 was repeated with a monomer component 
composed of 67.5 mol % of sodium acrylate, 22.5 mol % of acrylic acid, and 
10 mol % of N,N'-methylene bisacrylamide, a uniform aqueous solution of 
the monomer component was not obtained because N,N'-methylene 
bisacrylamide was not dissolved. 
Control 2 
A comparative polymer (2) was obtained by following the procedure of 
Example 1, except that the monomer component of the same composition was 
contained in a concentration of 15% by weight in the aqueous solution. 
From this comparative polymer (2), comparative hydrophilic polymers (1) 
and (2) were produced. These polymers were tested by following the 
procedure of Example 1. The results are shown in Table 1. 
Example 3 
A powdered polymer (3) was obtained by following the procedure of Example 
1, except that a monomer component composed of 67.5 mol % of sodium 
acrylate, 22.5 mol % of acrylic acid, 9.95 mol % of hydroxyethyl 
methacrylate, and 0.05 mol % of N,N'-methylene bisacrylamide was used 
instead. From the powdered polymer (3), hydrophilic polymers (5) and (6) 
were similarly produced. These polymers are shown in Table 1. 
Example 4 
A powdered polymer (4) was obtained by following the procedure of Example 
1, except that a monomer component composed of 72 mol % of sodium 
acrylate, 23 mol % of acrylic acid, 4.95 mol % of hydroxyethyl 
methacrylate, and 0.05 mol % of N,N'-methylene bisacrylamide was used 
instead. Hydrophilic polymer (7) was similarly produced. These polymers 
are shown in Table 1. 
It is clearly noted from Table 1 that the hydrophilic polymers produced by 
the method of this invention permitted aqueous solution polymerization at 
high monomer concentrations and showed satisfactory behaviors in terms of 
residual amount of unaltered cross-linking agents as compared with the 
comparative hydrophilic polymers (1) and (2) which were caused to lower 
the water absorption ratio below 20 times its own weight by a method not 
fulfilling the scope of this invention. 
TABLE 1 
__________________________________________________________________________ 
Example 1 
Example 2 
Example 3 
Example 4 
Control 
Control 
__________________________________________________________________________ 
2 
Composition 
Sodium acrylate 
67.5 60 67.5 
72 67.5 
67.5 
of monomer 
Acrylic acid 22.5 20 22.5 
23 22.5 
22.5 
component 
Hydroxyethyl acrylate 
9.95 
20 4.95 
(mol %) 
Hydroxyethyl methacrylate 9.95 
N,N'-methylene 
acrylamide 0.05 0.05 
0.05 
10.0 
10.0 
Monomer concentration in aqueous 
37 37 37 37 37 15 
solution of monomer component 
(% by weight) 
Time for 
No heat treatment 
heat Powdery polymer 
(1) (2) (3) (4) -- comparative (2) 
treatment 
Water absorption ratio 
62 53 64 68 -- 10.1 
at 180.degree. C. 
(times) 
Hygroscopicity 85 82 86 89 -- 84 
(% by weight) 
1 hour's heat treatment 
Hydrophilic polymer 
(1) (3) (5) -- -- comparative (1) 
Water absorption ratio 
7.8 3.5 8.1 -- -- 10.3 
(times) 
Hygroscopicity 84 81 84 -- -- 83 
(% by weight) 
3 hour's heat treatment 
Hydrophilic polymer 
(2) (4) (6) (7) -- comparative (2) 
Water absorption ratio 
4.8 2.5 4.3 17 -- 10.5 
(times) 
Amount of unaltered 
ND (Note 2) 
ND ND ND -- 130 
crosslinking agent 
(ppm) (Note 1) 
Hygroscopicity 85 81 84 87 -- 84 
(% by weight) 
Content of water- 
0.1 1.3 0.1 0.1 -- -- 
solubles (% by weight) 
Gel handling (Note 3) 
.largecircle. 
X .largecircle. 
.largecircle. 
-- -- 
__________________________________________________________________________ 
(Note 1) Amount of unaltered crosslinking agent total amount of 
hydroxyethyl acrylate, hydroxyethyl methacrylate, and methylene 
bisacrylamide remaining in unaltered state. 
(Note 2) ND Not detectable 
(Note 3) The gel handling was determined by twopoint scale, wherein 
.largecircle. stands for good X for bad. 
Example 5 
The hydrophilic polymers (1 ) to (7) and the powdered polymers (1) to (4) 
obtained in Examples 1 to 3 and a commercially available highly absorbent 
polymer (produced by Nippon Shokubai Kagaku Kogyo Co., Ltd. and marketed 
under trademark designation of "Aqualic CA") were each mixed with purified 
water to a varying concentration indicated in Table 2. The resultant 
liquids were left standing for 60 minutes and then examined visually by 
way of testing for dispersibility in aqueous medium. The results are shown 
in Table 2. 
The dispersibility was rated on a two-point scale, wherein: 
.circle. stands for the state of mixture remaining in a liquid state and 
retaining fluidity. 
X stands for the state of mixture remaining in a wholly gelled state and no 
longer retaining any fluidity. 
It is clearly noted from Table 2 that the hydrophilic polymers of this 
invention possessing water absorption ratios of no more than 30 times to 
their own weight possessed hygroscopicity equal to that of polymers 
possessing water absorption ratios exceeding 30 times their own weight and 
nevertheless were dispersible in an aqueous medium. 
TABLE 2 
______________________________________ 
Concen- 
tration of 
Polymer 
disper- Powdered 
sion (% 
Hydrophilic polymer 
polymer Aqua- 
by eight) 
(1) (2) (3) (4) (5) (6) (7) (1) (2) (3) (4) 
lick 
______________________________________ 
1 .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
X X X X 
X 
3 .largecircle. .largecircle. .largecircle. .la 
rgecircle. .largecircle. .largecircle. .largeci 
rcle. -- -- -- -- -- 
5 .largecircle. .largecircle. .largecircle. .la 
rgecircle. .largecircle. .largecircle. X -- -- 
-- -- -- 
10 X .largecircle. .largecircle. .largecircle. 
X .largecircle. X -- -- -- -- -- 
20 X X .largecircle. .largecircle. X X X -- -- 
-- -- -- 
______________________________________ 
(Note) The hygroscrpicity of Aqualick CA was 88% by weight (at 20.degree. 
C. and R.H. 90%). The values of hygroscopicity of hydrophilic polymers (1 
to (6) and powdered polymers (1) to (3) were as shown in Table 1. 
Example 6 
The powdered polymer (1) obtained in Example 1 was heat-treated for 3 hours 
at a varying temperature indicated in Table 3. The hydroscopic polymer 
consequently obtained was tested for water absorption ratio in the same 
manner as in Example 1. The results are shown in Table 3. It is noted from 
the table that the heat treatment at 100.degree. C. brought about 
virtually no discernible change in the water absorption ratio and the heat 
treatment at 130.degree. C. or over was effective in enhancing the water 
absorption ratio. 
TABLE 3 
______________________________________ 
Temperature (.degree.C.) 
100 130 150 200 250 
______________________________________ 
Water absorption 
62 18.9 12.3 4.0 4.0 
ratio (times) 
______________________________________ 
Example 7 
In a flask having an inner volume of 5,000 ml, provided with a reflux 
condenser, and having the inner gas displaced with nitrogen gas, 2,130 g 
of cyclohexane and 19 g of sorbitan monolaurate were placed and stirred at 
room temperature for solution of the surfactant. In the resultant solution 
in the flask, an aqueous monomer solution prepared by adding 1.3 g of 
potassium persulfate to 1,200 g of an aqueous solution containing 22.5 mol 
% of acrylic acid, 67.5 mol % of sodium acrylate, 9.95 mol % of 2- 
hydroxyethyl methacrylate, and 0.05 mol % of N,N'-methylene bisacrylamide 
(monomer component concentration 40% by weight) was added dropwise and 
suspended therein. The inner gas of the reaction system was again 
displaced thoroughly with nitrogen. Then, the contents of the flash were 
heated to and kept at temperatures in the range of 55.degree. to 
60.degree. C., leaving the monomer component polymerizing for 3 hours. The 
formed polymer solution was passed through a filter. The polymer was dried 
in an ordinary hot air drier at 100.degree. C. and then comminuted to 
obtain beads of polymer (A). Two aliquot parts of this polymer were dried 
in a still drier at 180.degree. C. for 1 hour and 3 hours, to obtain 
hydrophilic polymer (B) and (C). The speherical polymer (A) and the 
hydrophilic polymers (B) and (C) were tested for residual amount of 
unaltered crosslinking agents and hygroscopicity in the same manner as in 
Example 1. The results are shown in Table 4. 
TABLE 4 
______________________________________ 
Polymer 
Hydrophilic 
Hydrophilic 
(A) polymer (B) 
polymer (C) 
______________________________________ 
Water absorption ratio 
60 8.2 5.2 
(times) 
Amount of unaltered 
6 N.D. N.D. 
crosslinking agent 
(ppm) 
Hygroscopicity 
85 87 87 
(% by weight) 
______________________________________ 
N.D.: not detectable 
Example 8 
The hydrophilic polymer (2) possessing a water absorption ratio of 4.8 
times to its own weight (time of heat-treatment 3 hours) obtained in 
Example 1 was tested for the ability to sequestrate polyvalent metal ions, 
Cu.sup.2+, CR.sup.3+, Hg.sup.2+, and Ca.sup.2+ by the following method. 
The results are shown in Table 5. Method for testing ability to 
sequestrate polyvalent metal ions: 
A sample, 0.3 g, was placed in 1,000 ml of an aqueous solution containing 
100 ppm of Cu.sup.2, Cr.sup.3+, Hg.sup.2+, or Ca.sup.2+ (prepared by using 
the reagent of CuCl.sub.2, CrCl.sub.3. 6H.sub.2 O, HgCl.sub.2, or 
CaCl.sub.2. 2H.sub.2 O), stirred for 2.0 hours. The resultant aqueous 
solution was tested for the unsequentrated metal ion concentration with an 
atomic absorption meter. 
The results are shown in Table 5. 
It is clearly noted from this table that the hydrophilic polymer (2) of 
this invention possessed an outstanding ability to sequestrate these 
polyvalent metal ions. 
TABLE 5 
______________________________________ 
Ability of hydrophilic polymer (2) 
to sequestrate polyvalent metal ions 
______________________________________ 
Cu.sup.2+ 520 
Cr.sup.3+ 340 
Hg.sup.2+ 260 
Ca.sup.2+ 152 
(as CaCO.sub.3) 
(380) 
______________________________________ 
Example 9 
The test for detergency was performed as shown below for the purpose of 
examining the effectiveness of the hydrophilic polymer of this invention 
as a water-conditioning agent (resin for sequestration of cations). 
In the test for detergency, soiled cloths of cotton were used as natural 
soiled cloth. The rating of the detergency obtained was conducted with 
unaided eyes by the Scheffe's one pair comparison method repeatedly using 
four samples (as symmetrized laterally). As a control, commercially 
available sodium tripolyphsphate was used with respect to each of the 
plots involved. 
The conditions of detergency and the composition of a detergent used were 
as follows. 
______________________________________ 
i) Detergency: 
Concentration of detergent 
0.12% 
Temperature of detergent 
25.degree. C. 
Time of detergency 8 minutes 
Washing machine used Household grade 
swirling electric 
washing machine 
Bath ratio 1:30 
Water used 3.degree. DH tap water 
ii) Rinsing: 
Water temperature 25.degree. C. 
Time of use of washing 
3 minutes 
machine for rinsing 
iii) Detergent composition: 
Sodium alkylbenzene sulfonate 
20% 
(LAS MW 346) 
Builder (water-conditioning agent) 
25% 
Sodium silicate, No. 2 
5% 
Anhydrous sodium carbonate 
3% 
Carboxymethyl cellulose 
0.5% 
Anhydrous sodium sulfate 
46.5% 
______________________________________ 
The results of the test for detergency are shown in Table 6. The rating was 
made on a 10-point scale, using the effect with sodium oxadiacetate taken 
as 0 and that with sodium tripolyphosphate as 10. 
TABLE 6 
______________________________________ 
Bilder 
Hydrophilic 
Commercrally available 
polymer Detergency 
bilder (% by weight) 
(% by weight) 
rated 
______________________________________ 
Sodium tripolyphosphate 
100% -- 10 
" 50 (2) 50 11 
" 50 (4) 50 12 
" 50 (6) 50 11 
" 50 (7) 50 13 
" 25 (2) 75 10 
" 25 (4) 75 10 
" 25 (6) 75 9 
" 25 (7) 75 11 
-- 0 (2)100 8 
-- 0 (4)100 9 
-- 0 (6)100 8 
-- 0 (7)100 9 
Sodium polyacrylate 
100 -- 9 
Mw 10000 50 (7) 50 9 
25 (7) 75 9 
0 (7)100 8 
______________________________________ 
Example 10 
The hydrophilic polymer (water-conditioning agent) of the present invention 
was tested for chelating ability by the following method. 
In a beaker having an inner volume of 50 ml and provided with a rotor, 10 
mg of a builder (water-conditioning agent) placed therein and 50 ml of an 
aqueous 1.0.times.10.sup.-3 M clacium chloride solution added thereto were 
stirred for solution. Then, the resultant solution was adjusted to an ion 
strength, .mu., of 0.08 by addition thereto of 1 ml of an aqueous 4.0M 
potassium chloride solution and stirred in a constant temperature bath at 
50.degree. C. for 10 minutes. The solution resulting from the stirring was 
tested for calcium ion strength with an ion meter (produced by Toa Dempa 
Kogyo K. K. and marketed under product code of "IM-20E") using a calcium 
ion electrode (produced by Orion K. K. and marketed under model number 
"93-20"). The chelating ability was reported by the amount of calcium ion 
sequestrated with lg of a given builder, as reduced to the calcium 
carbonate content (mg). The results are shown in Table 7. 
TABLE 7 
______________________________________ 
Water-conditioning agent 
Chelating ability 
or builder (Mg of CaCO.sub.3 /g) 
______________________________________ 
Hydrophilic polymer (2) 
320 
(4) 240 
(6) 320 
(7) 350 
Sodium tripolyphosphate 
250 
Sodium polyacrylate 
230 
Synthetic zeolite 200 
______________________________________ 
Example 11 
A powdered polymer was obtained by following the procedure of Example 4, 
except that the proportion of N,N'-methylene bisacrylamide was changed 
from 0.05 mol % to 0.03 mol % and that of hydroxyethyl acrylate from 4.95 
mol % to 4.97 mol %. This powdered polymer was heat-treated in a still 
drier at 180.degree. C. for 3 hours to obtain a coolant grade polymer. 
This polymer was found to possess a water absorption ratio of 18.5 times 
to its own weight A coolant was produced by placing 100 parts by weight of 
the coolant grade polymer in 500 parts by weight of water and allowing the 
polymer to be swelled with water. A simple cooling material was produced 
by placing the coolant in a bag of polyethylene 18 cm.times.27 cm in area 
and closing the open end of the bag. 
Example 12 
A coolant was produced by mixing 100 parts by weight of the same coolant 
grade polymer as obtained in Example 11 with 500 parts by weight of water 
and 25 parts by weight of ethylene glycol and allowing the polymer to be 
swelled with the water and ethylene glycol. A simple cooling material was 
produced by placing the coolant in a bag of polyethylene 18 cm.times.27 cm 
in area and closing the open end of the bag. 
Example 13 
A coolant grade polymer was obtained by following the procedure of Example 
11, except that a monomer component composed of 72 mol % of sodium 
acrylate, 22.5 mol % of acrylic acid, 5.48 mol % of hydroxyethyl 
methacrylate, and 0.02 mol % of N,N'-methylene bisacrylamide was used 
instead. This polymer was found to possess a water absorption ratio of 
15.5 times to its own weight. A simple cooling material was produced from 
this polymer by following the procedure of Example 11. 
Example 14 
A coolant grade polymer was obtained by following the procedure of Example 
11, except that a monomer component composed of 70 mol % of sodium 
acrylate, 20 mol % of acrylic acid, 9.95 mol % of hydroxyethyl acrylate, 
and 0.05 mol % of diethylene glycol diacrylate was used instead and the 
conditions of the heat treatment conducted on the powdered polymer were 
changed to 200.degree. C. and 30 minutes. This polymer was found to have a 
water absorption ratio of 8.3 times to its own weight. A simple coolant 
material was produced from the polymer by following the procedure of 
Example 11. 
Example 15 
A coolant grade polymer was obtained by repeating the procedure of Example 
11, except that a monomer component composed of 68 mol % of sodium 
acrylate, 22.5 mol % of acrylic acid, 9.48 mol % of hydroxyethyl acrylate, 
and 0.02 mol % of N,N'-methylene bisacrylamide was used instead. This 
polymer was found to possess a water absorption ratio of 5.5 times to its 
own weight. A simple coolant material was produced from this polymer by 
following the procedure of Example 11. 
Control 3 
A coolant grade polymer was obtained by following the procedure of Example 
11, except that a monomer component composed of 74.9 mol % of sodium 
acrylate, 25 mol % of acrylic acid, and 0.1 mol % of N,N'-methylene 
bisacrylamide was used instead and the heat treatment given to powdered 
polymer was omitted. This polymer was found to possess a water absorption 
ratio of 152 times to its own weight. A simple coolant material was 
produced from this polymer by following the procedure of Example 11. 
Control 4 
A coolant grade polymer was obtained by following the procedure of Example 
11, except that a monomer component composed of 67.5 mol % of sodium 
acrylate, 22.5 mol % of acrylic acid, and 2 mol % of methylene 
bisacrylamide was used in the form of an aqueous solution containing the 
monomer component in a concentration of 15% by weight and the heat 
treatment performed on the powdered polymer was omitted. This comparative 
polymer was found to possess a water absorption ratio of 35.5 times to its 
own weight. A simple coolant material was produced from this polymer by 
following the procedure of Example 11. 
Control 5 
A coolant grade polymer was obtained by repeating the procedure of Example 
11, except that a monomer component composed of 45 mol % of sodium 
acrylate, 15 mol % of acrylic acid, 40 mol % of hydroxyethyl acrylate, and 
0.03 mol % of N,N'-methylene bisacrylamide was used instead. This 
comparative polymer was found to possess a water absorption ratio of 0.7 
times to its own weight. A hydrated gel was obtained by causing 200 parts 
by weight of this comparative polymer to be swelled with 700 parts by 
weight of water. A simple coolant material was produced from the hydrated 
gel by following the procedure of Example 11. 
Control 6 
A coolant grade polymer was obtained by following the procedure of Example 
11, except that the heat treatment performed on the powdered polymer was 
omitted. This comparative polymer was found to possess a water absorption 
ratio of 90.2 times to its own weight. A simple coolant material was 
produced from this polymer by following the procedure of Example 11. 
Example 16 
The coolant grade polymers obtained in Examples 11 to 15 and Controls 3 to 
6 were tested for residual amount of unaltered crosslinking agents. The 
simple coolant materials produced respectively from these polymers were 
placed in a refrigerator kept at -18.degree. C., left standing therein 
overnight, removed from the refrigerator into a room kept at 24.degree. 
C., and examined them for softness by the touch with hands. The coolant 
materials were each subjected to 30 cycles of The freezing and thawing 
treatments mentioned above. After the last cycle, they were examined for 
softness. The results are shown in Table 8. 
It is clearly noted from Table 8 that the coolant materials of Examples 11 
to 15 retained softness during the course of freezing and possessed 
outstanding durability in the repeated use through the cycles mentioned 
above. In constract, the coolant grade polymer obtained by polymerizing a 
monomer component containing no hydroxyl group-containing monomer (Control 
3) and the coolant grade polymer which had not undergone the heat 
treatment for crosslinking the hydroxyl group and the carboxyl group 
(Control 6) possessed water absorption ratios exceeding 50 times to their 
own weights and exhibited poor softness during the course of freezing. The 
coolant grade polymer which omitted the inclusion of the hydroxyl 
group-containing monomer and instead contained the cross-linking agents in 
an increased amount (Control 4) was found to contain a harmful amount of 
residual cross-linking agents. The coolant material using a coolant grade 
polymer possessing a water absorption ratio of no more than 3 times to its 
own weight (Control 5) was found to exhibit inferior softness during the 
course of freezing. 
TABLE 8 
______________________________________ 
Amount of State after 
Water unaltered Softness repeated use 
absorption crosslinking 
during the 
through 30 
ratio (Note 1) course of through cycles 
(times) agent (ppm) 
freezing (Note 3) 
______________________________________ 
Example 
11 18.5 N.D. Soft .largecircle. 
(Note 2) 
12 18.5 " " .largecircle. 
13 15.5 " " .largecircle. 
14 8.3 " " .largecircle. 
15 5.5 " " .largecircle. 
Control 
3 152 " Hard X 
4 35.5 300 Slightly 
X 
hard 
5 0.7 N.D. Hard X 
6 90.2 " " X 
______________________________________ 
(Note 1) Amount of unaltered crosslinking agent: Amount of residual 
N,Nmethylene bisacrylamide detected in dry polymer. 
(Note 2) N.D. Not detectable 
(Note 3) The state after 30 cycles of the alternative freezing and thawin 
treatment was rated on a twopoint scale, wherein: .largecircle. Stands fo 
substantial absence of change in softness during the course of freezing 
from the level during the first cycle. X Stands for hardness during the 
course of freezing. 
Example 17 
The coolants obtained in Examples 11 to 15 and Controls 3, 4 and 6 were 
each placed in an Erlenmeyer flask fitted with a ground stopper and having 
an inner volume of 1 liter, stoppered airtightly, placed in a drier kept 
at 50.degree. C., and left standing therein for one month. Simple coolant 
materials were produced by placing the coolants each in a bag of 
polyethylene 18 cm .times.27 cm in area and closing the open end of the 
bag. The coolant materials were tested for softness during the course of 
freezing and examined for the behavior of softness after 30 cycles of the 
alternating freezing and thawing treatment by following the procedure of 
Example 14. The results are shown in Table 9. 
It is clearly noted from the results of Table 9 that the coolant materials 
of Example 11 to 15, even after one month's standing at 50.degree. C., 
retained their outstanding properties i.e. softness, cooling property, and 
durability in the repeated use through 30 cycles of the treatment. In 
contrast, the coolant materials of Controls 3, 4, and 6 had their contents 
deteriorated to the state of honey. 
Example 18 
The coolants of the polymers obtained in Examples 11 to 15 and Controls 3, 
4, and 6 were each placed in an Erlenmeyer flask having an inner volume of 
1 liter, stoppered airtightly, and left standing for one month on a 
concrete base coated in white. The concrete base was located where no 
obstacle was allowed to intercept the direct sunlight impinging on the 
flask. After the standing, simple coolant materials were produced by 
placing the coolants each in a bag of polyethylene 18 cm.times.27 cm in 
area and closing the open end. The coolant materials were tested for 
softness during the course of freezing, cooling property, and the state of 
coolant after 30 cycles of the alternative freezing and thawing treatment 
by following the procedure of Example 16. The results are shown in Table 
10. 
It is clearly noted from the results of Table 10 that the coolants of 
Examples 11 to 15, even after the exposure to the sunlight, retained their 
outstanding properties, i.e. softness during the initial stage of freezing 
and durability after the repeated use, intact in much the same manner as 
in Example 16. In contrast, the coolant materials of Controls 3, 4, and 6 
had their contents degraded to the state of honey. 
TABLE 9 
______________________________________ 
Softness during the 
State after repeated use 
course of freezing 
through 30 cycles 
______________________________________ 
Example 
11 Soft .largecircle. 
12 " .largecircle. 
13 " .largecircle. 
14 " .largecircle. 
15 " .largecircle. 
Control 
3 Hard X 
4 " X 
6 " X 
______________________________________ 
*The softness and the state indicated in this table are examined in the 
same manner as those of Table 8. 
TABLE 10 
______________________________________ 
Softness during the 
State after repeated use 
course of freezing 
through 30 cycles 
______________________________________ 
Example 
11 Soft .largecircle. 
12 " .largecircle. 
13 " .largecircle. 
14 " .largecircle. 
15 " .largecircle. 
Control 
3 Hard X 
4 " X 
6 " X 
______________________________________ 
*The softness and the state indicated in this table are examined in the 
same manner as those of Table 8. 
Example 19 
A hydrophilic polymer (I) was obtained by following the procedure of 
Example 1, except that a monomer component composed of 75 mol % of sodium 
acrylate, 20 mol % of acrylic acid, 4.95 mol % of 2-hydroxyethyl acrylate, 
and 0.05 mol % of N,N'-methylene bisacrylamide was prepared in the form of 
an aqueous solution containing the monomer component in a concentration of 
37% by weight and the time for the heat treatment performed on the polymer 
was changed to 2 hours. This polymer was found to possess a water 
absorption ratio of 21 times to its own weight and a moisture absorption 
ratio of 105% by weight. 
Example 20 
A hydrophilic polymer (II) was obtained by preparing a hydrated gel by 
following the procedure of Example 1, except that a monomer component 
composed of 67.5 mol % of sodium acrylate, 22.5 mol % of acrylic acid, 
9,95 mol % of 2-hydroxyethyl acrylate, and 0.05 mol % of N,N'-methylene 
bisacrylamide was used in the form of an aqueous solution containing the 
monomer component in a concentration of 37% by weight, drying the hydrated 
gel in an ordinary hot air drier at 100.degree. C. for 2 hours, 
comminuting the dried gel, and heat treating the polymer powder in a still 
drier at 180.degree. C. for 3 hours. The polymer (II) was found to possess 
a water absorption ratio of 5 to times its own weight and a moisture 
absorption ratio of 95% by weight. 
Examples 21 and 22 and Controls 7 to 9 
Coating materials of working examples and controls were prepared by mixing 
varying raw materials in varying proportions indicated in Table 11. 
They were obtained by sequentially adding the raw materials to a high-speed 
mill set to rotation from the beginning. 
The coating materials and the films formed of the coating materials were 
tested for varying physical properties indicated in Table 11. 
TABLE 11 
______________________________________ 
Exam- Exam- Con- Con- Con- 
ple 21 
ple 22 trol 7 trol 8 
trol 9 
______________________________________ 
Acryl emulsion (1) 
100 100 100 100 100 
Dispersant (2) 
0.5 0.5 0.5 1.0 1.0 
Hydrophilic polymer 
2.0 -- -- -- -- 
II 
Hydrophilic polymer I 
-- 12 -- -- -- 
Highly absorbent resin 
-- -- 4 -- -- 
A (3) 
Highly absorbent resin 
-- -- -- -- 10 
B (4) 
Diatomaceous earth 
-- -- -- 100 -- 
(5) 
Heavy calcium car- 
50 50 50 30 50 
bonate (6) 
Titanium dioxide (7) 
20 20 20 20 20 
Tackifier (8) 
2 2 1 2 2 
Film-forming auxiliary 
5 5 5 5 5 
(9) 
Defoaming agent (10) 
1 1 1 1 1 
Water 83 104 1265 110 152 
Concentration (%) 
52 47 9 56 40 
Viscosity (CPS) (11) 
38,000 42,000 187,000 
41,000 
32,000 
Dew-preventing prop- 
.circleincircle. 
.circleincircle. 
.circleincircle. 
X X 
erty 
Speed of water ab- 
.circleincircle. 
.circleincircle. 
.circleincircle. 
X X 
sorption 
Water absorption ratio 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.largecircle. 
.circleincircle. 
Moisture-releasing 
.circleincircle. 
.largecircle. 
X .circleincircle. 
.largecircle. 
ratio 
Durability .circleincircle. 
.circleincircle. 
X .circleincircle. 
X 
Surface smoothness of 
.circleincircle. 
.largecircle. 
X .circleincircle. 
.largecircle. 
film 
______________________________________ 
Notes: 
(1) Acryl emulsion: Product of Nippon Shokubai Kagaku Kogyo Co., Ltd. 
marketed under trademark designation of "Acryset 
(2) Dispersant: Product of Nippon Shokubai Kagaku Kogyo Co., Ltd. markete 
under trademark designation of "Acrylic 
(3) Highly absorbent resin A: Product of Nippon Shokubai Kagaku Kogyo Co. 
Ltd. marketed under trademark designation of "Aqualic CA" having a water 
absorption ratio of 250 times to its own weight and a hygroscopicity of 
110% by weight 
(4) Highly abosrbent resin B: Product of Sumitomo Chemical Industries Co. 
Ltd. marketed under trademark designation of "Sumicagel R30" having a 
water absorption ratio of 25 times to its own weight and a hygroscopicity 
of 6% by weight 
(5) Diatomaceous earth: Marketed by Tokyo Kogyo Boeki Shokai under 
trademark designation of "Sellaite 
(6) Heavy calcium carbonate: Product of Nitto Funka Kogyo K.K. marketed 
under product code of "NS #30 
(7) Titanium dioxide: Product of Teikoku Kaka K.K. marketed under product 
code of "JR701 
(8) Tackifier: Product of Union Carbide marketed under trademark 
designation of "Cellosize OP4400" in the form of an aqueous 2.5% solution 
(9) Filmforming auxiliary: Marketed by Nagase Sangyo under trademark 
designation of "Texanol 
(10) Defoaming agent: Product of Shinetsu Silicon K.K. marketed under 
trademark designation of "Silicon 
(11) Viscosity: BL type viscosimeter, No. 4 roller, 6 rpm at 25.degree. C 
 
The times of test involved and the procedures therefor are as shown below. 
(A) Dew-preventing property 
A sample was applied on an aluminum juice can in an amount calculated to 
produce a dry film 1 mm in thickness and dried at room temperature for 7 
days. Then, the juice can was cooled to about 5.degree. C. by filling the 
can with water and ice. The coated juice can was kept standing in a 
constant temperature and constant humidity bath kept at a temperature of 
20.degree. C. and a relative humidity of 90% and held under continued 
visual observation as to the occurrence of dew on the surface of the film. 
The formation of dew was rated on a three-point scale, wherein: 
.circleincircle. stands for tatal absence of dew condensation in 30 
minutes. 
.circle. stands for slight dew condensation in 30 minutes. 
X stands for dew condensation and consequent fall of water drops in 30 
minutes. 
(B) Speed of water absorption 
A dry sheet (2 mm in thickness) was prepared from a sample coating 
material. One drop (about 0.05 cc) of water was dropped through a pipet 
onto the dry sheet. The time was clocked between the landing of the water 
drop on the dry sheet and the disappearance of the water drop due to 
absorption by the dry sheet. The speed of water absorption was rated by a 
three-point scale, wherein: 
.circleincircle. stands for no more than 2 minutes. 
.circle. stands for 2 to 9 minutes. 
X stands for no less than 9 minutes. 
The dry sheet was produced by setting a frame adapted to mold a dry film 2 
mm in thickness on a mold release paper, casing a given sample of coating 
material in the cavity of the frame, smoothening the surface of the cast 
sample with a glass rod, and allowing the cast sample to dry at room 
temperature for 7 days. 
(C) Water absorption ratio 
A dry sheet (2.0 mm thick.times.50 mm.times.100 mm) was prepared from a 
given sample coating material, immersed in water at 20.degree. C. for 3 
hours. The wet sheet was then tested for water content. The water 
absorption ratio was rated on a three-point scale, wherein: 
.circleincircle. stands for no less than 80% by weight of absorption ratio. 
.circle. stands for 50 to 80% by weight of absorption ratio. 
X stands for no more than 50% by weight of absorption ratio. 
##EQU3## 
(D) Moisture releasing ratio 
A sample sheet which had undergone the test for water absorption ratio was 
left standing in a constant temperature constant-hyumidity bath kept at a 
temperature of 20.degree. C. and a relative humidity of 40%. The sheet was 
then tested for water content. The moisture releasing ratio was rated on a 
three-point scale, wherein: 
.circleincircle. stands for no more than 2% by weight of water content. 
.circle. stands for 2 to 10% by weight of water content. 
X stands for no less than 10% by weight of water content. 
##EQU4## 
(E) Durability 
A film of a given sample polymer was subjected to 10 cycles of the 
alternative absorption and moisture release treatment. After each cycle, 
the film surface was visually examined for possible abnormal phenomenon 
before it was subjected to the subsequent cycle. The durability was rated 
on a three-point scale, wherein: 
.circleincircle. stands for absence of abnormal phenomenon after 10 cycles. 
.circle. stands for softening of film and slight occurrence of crack 
after 10 cycles. 
X stands for separation of the polymer during immersion in water after the 
second cycle. 
(F) Surface smootheness of film 
A given sample coating material was applied on a slate plate in an amount 
calculated to produce a dry film 1 mm in thickness. The applied coating 
material was dried at room temperature for 7 hours. Then, the produced 
film was immersed in water at 20.degree. C. for 24 hours. The film removed 
from the water was visually examined for surface smoothness. The surface 
smoothness was rated on a three-point scale, wherein: 
.circleincircle. stands for satisfactory smoothness free from crack. 
.circle. stands for slightly poor surface smoothness accompanied by 
slight occurrence of cracks. 
X stands for inferior surface smoothness accompanied by occurrence of 
cracks and separation of polymer.