U.S. patent application number 10/138308 was filed with the patent office on 2003-11-06 for crosslinking agent based on linear hydroxypolyallyl ether.
Invention is credited to Daniel, Thomas, Matsutomi, Tohru, Nakamura, Shin-Ichiro, Shimizu, Yasumi.
Application Number | 20030208022 10/138308 |
Document ID | / |
Family ID | 29269303 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030208022 |
Kind Code |
A1 |
Nakamura, Shin-Ichiro ; et
al. |
November 6, 2003 |
Crosslinking agent based on linear hydroxypolyallyl ether
Abstract
An allyl type crosslinking agent for use in production of a
super water-absorbent polymer comprising a polymerizable compound
having a carbon-carbon double bond or a salt thereof, comprising a
linear hydroxypolyallyl ether having at least one hydroxyl groups
and at least two allyl groups obtained by allyletherification of
hydroxyl groups in a linear polyol compound selected from the group
consisting of erythritol, xylitol and sorbitol, is provided. This
allyl type crosslinking agent is highly soluble in an aqueous
solvent, and can give an excellent super water-absorbent polymer,
which cannot be obtained in the prior arts, having high levels of
both of water absorptivity under atmospheric pressure and water
absorptivity under pressurized conditions are obtained.
Inventors: |
Nakamura, Shin-Ichiro;
(Kanagawa, JP) ; Shimizu, Yasumi; (Osaka, JP)
; Matsutomi, Tohru; (Osaka, JP) ; Daniel,
Thomas; (Waldsee, DE) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
29269303 |
Appl. No.: |
10/138308 |
Filed: |
May 6, 2002 |
Current U.S.
Class: |
526/333 ;
568/673 |
Current CPC
Class: |
C07C 43/178 20130101;
C08F 220/04 20130101; A61L 15/60 20130101 |
Class at
Publication: |
526/333 ;
568/673 |
International
Class: |
C08F 016/12; C07C
043/178 |
Claims
1. A crosslinking agent for use in the production of a super
water-absorbent polymer comprising a polymerizable compound having
a carbon-carbon double bond or a salt thereof, comprising a linear
hydroxypolyallyl ether having at least one hydroxyl group and at
least two allyl groups obtained by allyletherification of a
hydroxyl group in a linear polyol compound which has a
straight-chain carbon skeleton, which has carbon atoms each having
one hydroxyl group, and which is represented by the formula (1):
HOCH.sub.2[CH(OH)].sub.nCH.sub.2OH (1) wherein n is an integer of
from 2 to 8.
2. The crosslinking agent according to claim 1, wherein the linear
polyol compound is selected from the group consisting of
erythritol, xylitol and sorbitol.
3. The crosslinking agent according to claim 1, wherein the linear
polyol compound is sorbitol.
4. The crosslinking agent according to claim 1, wherein the linear
polyol compound is sorbitol triallyl ether or sorbitol tetraallyl
ether.
5. The crosslinking agent according to anyone of claims 1 to 4,
wherein the super water-absorbent polymer is crosslinked in an
aqueous medium.
6. The crosslinking agent according to anyone of claims 1 to 4,
wherein the polymerizable compound has also a carboxyl group.
Description
TECHNICAL FIELD
[0001] The present invention relates to a crosslinking agent for
use in the production of a super water-absorbent polymer
crosslinked in an aqueous medium and comprising a polymerizable
compound having a carbon-carbon double bond or a salt thereof.
RELATED ART
[0002] Most of super water-absorbent polymers comprising
polymerizable compounds having polymerizable double bonds (e.g.,
carbon-carbon double bonds) or salts thereof are based on acrylate
salt polymers and produced mainly by polymerization in an aqueous
solution. It is proposed to use a wide variety of materials having
reactive double bonds, such as acrylate esters, acrylic amides and
allyl ethers, as crosslinking agents for crosslinking the super
water-absorbent polymers, It is reported that particularly when
allyl compounds are used as the crosslinking agent, the polymers
excellent particularly in water absorptivity can be obtained.
Further, the reverse-phase suspension polymerization method
polymerizing a monomer and a crosslinking agent dissolved in water
suspended in an organic solvent is also industrially carried out,
and this reverse-phase suspension polymerization method can also be
regarded as the polymerization in an aqueous medium.
[0003] For example, it is reported in J. Polym. Sci. A: Polym.
Chem. 35, 799 (1977) that polymers obtained by using polyethylene
glycol diallyl ether as the crosslinking agent is superior in water
absorptivity to the polymers obtained by using an acrylic
crosslinking agent. However, the properties of the polyethylene
glycol diallyl ether as the crosslinking agent is not
satisfactory.
[0004] A method of neutralizing polymers obtained by polymerizing
acrylic acid is known. JP-A-3-174414, which uses this method,
discloses use of tetra-allyloxy ethane as a specific allyl
compound. However, this compound suffers from problems such as
deficient heat resistance, poor solubility in an aqueous solution
of a monomer, and insufficient resistance to hydrolysis. Thus there
is demand for development of crosslinking agents having higher
property.
[0005] Further, JP-A-4-246403 discloses use of triallyl amine,
trially cyanurate, triallyl isocyanurate and triallyl phosphate.
However, these crosslinking agents generally have problems such as
deficient heat resistance, adverse effects on polymerization
reaction, poor solubility in an aqueous solution of a monomer, and
insufficient resistance to hydrolysis, and thus none of these
crosslinking agents are practical.
[0006] JP-A-11-140193 discloses hydrophilic polymers optionally
containing crosslinking monomers. Trimethylol propane
tri(meth)acrylate and the like are mentioned as such crosslinking
monomers. This prior art document does not describe
hydroxypolyallyl ethers derived from erythritol, xylitol and/or
sorbitol as the crosslinking monomers.
[0007] Generally in the aqueous solution polymerization, an aqueous
solution of an acrylic acid monomer is neutralized at a degree of
about 75% with e.g., an aqueous solution of sodium hydroxide, then
a crosslinking agent is mixed therewith, the monomer is polymerized
by a polymerization initiator, and the formed solid is cut into
pieces of suitable size and then dried (hereinafter, this method is
referred to as "post-neutralization polymerization method").
However, if the crosslinking agent is sparingly soluble in the
aqueous solution after neutralization, the crosslinking agent is
dissolved in an aqueous solution of acrylic acid, and the solid
formed by polymerization is cut and neutralized (hereinafter, this
method is referred to as "pre-neutralization polymerization
method"). This method as compared with neutralization in solution
form is disadvantageous in production efficiency and uneven
neutralization of the product.
SUMMARY OF THE INVENTION
[0008] The object of the present invention is to provide a novel
allyl type crosslinking agent soluble in an aqueous solution of a
monomer (e.g., an aqueous solution of an acrylate salt) and free of
the problems possessed by the prior art, in order to produce a
super water-absorbent polymer having particularly excellent
water-absorptivity among water-absorptivity required at practical
levels.
[0009] The present inventors found that, as the allyl compound for
solving the problems described above, a linear hydroxypolyallyl
ether having at least two allyl ether groups derived from a linear
polyol compound is industrially useful not only in the
above-mentioned pre-neutralization polymerization method but also
in the above-mentioned post-neutralization polymerization method,
thus completed the present invention.
[0010] The present invention provides a crosslinking agent for use
in the production of a super water-absorbent polymer comprising a
polymerizable compound having a carbon-carbon double bond or a salt
thereof, comprising a linear hydroxypolyallyl ether having at least
one hydroxyl group and at least two allyl groups obtained by
allyletherification of hydroxyl group in a lenear polyol compound
which has a straight-chain carbon skeleton, which has carbon atoms
each having one hydroxyl group, and which is represented by the
formula (1):
HOCH.sub.2[CH(OH)].sub.nCH.sub.2OH (1)
[0011] wherein n is an integer of from 2 to 8.
DETAILED EXPLANATION OF THE INVENTION
[0012] When the linear hydroxypolyallyl ether according to the
present invention is used as the crosslinking agent for high
water-absorbance, it imparts an effective water absorptivity, and
it provides a super water absorptivity crosslinking agent having
remarkably improved properties, particularly in the view point of a
high level of water absorbance under both of a normal pressure and
an increased pressure and in the view point of a low concentration
of the crosslinking agent at which said high level of water
absorbance is achieved, in comparison with other polyallyl
derivative crosslinking agents used in the conventional technology
or polyacryl derivative crosslinking agents. As the crosslinking
agent for the super water absorbent polymer, for example, a
"polyallyl ether" compound is generally described in
JP-A-10-128108, and a compound having close relation to the
crosslinking agent of the present invention is generally described
as in JP-A-11-140193 and JP-A-4-236203. However, significant
effects of the crosslinking agent of the present invention cannot
be expected from extension of the prior arts.
[0013] In the present invention, the linear hydroxypolyallyl ether
is used as a crosslinking agent for the production of super
water-absorbent polymers. The crosslinking agent comprises one
linear hydroxypolyallyl ether or a mixture of at least two linear
hydroxypolyallyl ethers. The molecule of the linear
hydroxypolyallyl ether has at least one hydroxyl group and at least
two allyl groups. The number of hydroxyl groups is at least one,
for example at least two, and specific example of the number of
hydroxyl groups is from 1 to 8, particularly from 1 to 4. The
number of allyl groups is at least 2, for example at least 3,
specifically from 2 to 8, particularly from 3 to 5. In the case of
the mixture of linear hydroxypolyallyl ethers, an average number of
hydroxyl groups is at least 0.5, for example at least 1.0,
particularly at least 1.5, and an average number of allyl groups is
at least 2.0, for example at least 2.5, particularly at least 3.0.
The numbers of hydroxyl groups and allyl groups (including the
average numbers thereof) are determined by NMR (particularly,
.sup.1H NMR). At least one allyl group may be present in a linear
hydroxypolyallyl ether molecular chain excluding molecular chain
terminals.
[0014] The linear hydroxypolyallyl ether can be obtained generally
by allyletherification of at least two hydroxyl groups among the
hydroxyl groups in a linear polyol compound. Allyletherification
can be conducted by using an allyl etherifying agent. In the
allyletherification of the linear polyol compound, a hydrogen atom
in the hydroxyl groups is replaced by an allyl group.
[0015] The linear polyol compound is a compound having a
straight-chain carbon skeleton, having carbon atoms each having one
hydroxyl group, and represented by the formula (1):
HOCH.sub.2[CH(OH)].sub.nCH.sub.2OH (1)
[0016] wherein n is an integer of from 2 to 8. In particular, n may
be from 2 to 4, and the linear polyol compound may be erythritol,
xylitol and/or sorbitol.
[0017] The allyl etherifying agent is a compound having an allyl
group and a reactive group. The allyl group may be bound to the
reactive group by means of a direct bond, but may also bound by
means of a divalent organic group (e.g., substituted or
unsubstituted hydrocarbon group (e.g., C.sub.1 to C.sub.10)).
Usually, the allyl etherifying agent comprises one allyl group and
one reactive group which are bonded by means of a direct bond.
[0018] Examples of the reactive group in the allyletherifying agent
include a halogen atom, an alkyl sulfonyloxy group (number of
carbon atoms in the alkyl group is e.g., from 1 to 10), an aryl
sulfonyloxy group (number of carbon atoms in the aryl group is
e.g., from 6 to 20), and an aralkyl sulfonyloxy group (number of
carbon atoms in the aralkyl group is e.g., from 7 to 30).
[0019] Examples of the halogen atom include chlorine and
bromine.
[0020] Examples of the alkyl sulfonyloxy group include a methyl
sulfonyloxy group, an ethyl sulfonyloxy group, a n-propyl
sulfonyloxy group, an isopropyl sulfonyloxy group, a n-butyl
sulfonyloxy group, a n-octyl sulfonyloxy group, a trifuloromethane
sulfonyloxy group, a trichloromethane sulfonyloxy group, a
2-chloro-1-ethane sulfonyloxy group, a 2,2,2-trifluoroethane
sulfonyloxy group, a 3-chloropropane sulfonyloxy group, and a
perfluoro-1-butane sulfonyloxy group.
[0021] Examples of the aryl sulfonyloxy group include a benzene
sulfonyloxy group, a 2-aminobenzene sulfonyloxy group, a
2-nitrobenzene sulfonyloxy group, a 2-methoxycarbonyl benzene
sulfonyloxy group, a 3-aminobenzene sulfonyloxy group, a
3-nitrobenzene sulfonyloxy group, a 3-methoxycarbonyl benzene
sulfonyloxy group, a p-toluene sulfonyloxy group, a 4-tert-butyl
benzene sulfonyloxy group, a 4-fluorobenzene sulfonyloxy group, a
4-chlorobenzene sulfonyloxy group, a 4-bromobenzene sulfonyloxy
group, a 4-iodobenzene sulfonyloxy group, a 4-methoxybenzene
sulfonyloxy group, a 4-aminobenzene sulfonyloxy group, a
4-nitrobenzene sulfonyloxy group, a 2,5-dichlorobenzene sulfonyloxy
group, a pentafluorobenzene sulfonyloxy group, a 1-naphthalene
sulfonyloxy group, and a 2-naphthalene sulfonyloxy group.
[0022] Examples of the aralkyl sulfonyloxy group include an
.alpha.-toluene sulfonyloxy group, a trans-.beta.-styrene
sulfonyloxy group, and a 2-nitro-.alpha.-toluene sulfonyloxy
group.
[0023] Examples of the allyletherifying agent include an allyl
halide, an alkyl sulfonyloxyallyl, an aryl sulfonyloxyallyl, and an
aralkyl sulfonyloxyallyl.
[0024] Examples of the allyl halide include allyl chloride and
allyl bromide.
[0025] Examples of the alkyl sulfonyloxyallyl include methyl
sulfonyloxyallyl, ethyl sulfonyloxyallyl, n-propyl
sulfonyloxyallyl, isopropyl sulfonyloxyallyl, n-butyl
sulfonyloxyallyl, n-octyl sulfonyloxyallyl, trifluoromethane
sulfonyloxyallyl, trichloromethane sulfonyloxyallyl,
2-chloro-1-ethane sulfonyloxyallyl, 2,2,2-trifluoroethane
sulfonyloxyallyl, 3-chloropropane sulfonyloxyallyl, and
perfluoro-1-butane sulfonyloxyallyl.
[0026] Examples of the aryl sulfonyloxyallyl include benzene
sulfonyloxyallyl, 2-aminobenzene sulfonyloxyallyl, 2-nitrobenzene
sulfonyloxyallyl, 2-methoxycarbonyl benzene sulfonyloxyallyl,
3-aminobenzene sulfonyloxyallyl, 3-nitrobenzene sulfonyloxyallyl,
3-methoxycarbonylbenzene sulfonyloxyallyl, p-toluene
sulfonyloxyallyl, 4-tert-butyl benzene sulfonyloxyallyl,
4-fluorobenzene sulfonyloxyallyl, 4-chlorobenzene sulfonyloxyallyl,
4-bromobenzene sulfonyloxyallyl, 4-iodobenzene sulfonyloxyallyl,
4-methoxybenzene sulfonyloxyallyl, 4-aminobenzene sulfonyloxyallyl,
4-nitrobenzene sulfonyloxyallyl, 2,5-dichlorobenzene
sulfonyloxyallyl, pentafluorobenzene sulfonyloxyallyl,
1-naphthalene sulfonyloxyallyl, and 2-naphthalene
sulfonyloxyallyl.
[0027] Examples of the aralkyl sulfonyloxyallyl include
.alpha.-toluene sulfonyloxyallyl, trans-.beta.-styrene
sulfonyloxyallyl and 2-nitro-.alpha.-toluene sulfonyloxyallyl.
[0028] The following method is generally used to prepare the linear
hydroxypolyallyl ether by allyletherification of the linear polyol
compound.
[0029] One part by mol of the linear polyol compound, y part by mol
of potassium hydroxide or sodium hydroxide, and 10 to 50 wt-% of
water or an aprotic polar solvent (e.g., acetonitrile,
tetrahydrofuran, dioxane, and dimethyl formaldehyde) are introduced
into a suitable reaction vessel equipped with a stirrer, a
thermometer and a reflux condenser. The mixture is heated at about
50.degree. C. to 150.degree. C. under stirring, then y part by mol
of the allyletherifying agent is added dropwise, and the mixture is
reacted for about 2 hours to 40 hours. The amount of the alkali
(e.g., an alkali metal hydroxide such as sodium hydroxide) and the
allyletherifying agent may be considerably higher than y part by
mol. If necessary, an alcohol or a catalyst such as quaternary
ammonium salt may be present in the reaction system. After the
completion of the reaction, the resultant liquid layer is separated
from the precipitated solid and purified by conventional techniques
such as distillation, extraction, recrystallization and liquid
chromatography. Sodium hydroxide or potassium hydroxide may be
added dropwise as an aqueous solution to the reaction system,
simultaneously with adding the allyletherifying agent.
[0030] In a preferable embodiment of the present invention, the
linear hydroxypolyallyl ether is a compound obtained by
allyletherification of at least three hydroxyl groups in the linear
polyol compound.
[0031] Examples of such linear hydroxypolyallyl ether include
erythritol triallyl ether, xylitol triallyl ether, xylitol
tetraallyl ether, sorbitol triallyl ether, sorbitol tetraallyl
ether, and sorbitol pentaallyl ether.
[0032] In the present invention, a linear hydroxypolyallyl ether
having two allyl groups may be used. Examples of such linear
hydroxypolyallyl ethers include erythritol diallyl ether, xylitol
diallyl ether, and sorbitol diallyl ether.
[0033] Sorbitol polyallyl ether is preferable, in view of easy
available raw materials, and in view of a wide application range of
concentration due to high solubility of the crosslinking agent.
Sorbitol tiallyl ether and sorbitol tetraallyl ether are
particularly preferable.
[0034] In production of a super water-absorbent polymer, the
crosslinking agent of the present invention is used for the purpose
of crosslinking said polymer. Generally, a super water-absorbent
polymer is crosslinked in an aqueous medium with the crosslinking
agent of the present invention.
[0035] Generally, the crosslinking agent of the present invention
is used in the production of a super water-absorbent polymer
polymerized in an aqueous medium and comprising a polymerizable
compound having a carbon-carbon double bond or a salt thereof. In
production of the super water-absorbent polymer, said polymerizable
compound and/or a salt thereof can be used as the monomer.
[0036] A repeating unit in the super water-absorbent polymer has a
functional group. Examples of the functional group include a
carboxyl group, a hydroxyl group, an amide group and an acetamide
group.
[0037] Examples of the super water-absorbent polymer include an
acrylic acid-based polymer, a vinyl alcohol-based polymer, an
isobutylene/maleic anhydride-based polymer, an acrylamide-based
polymer, an acrylamide/acrylic acid-based polymer, and an N-vinyl
acetamide-based polymer. Generally, a monomer forming the super
water-absorbent polymer has the functional group. In production of
a certain polymer such as polyvinyl alcohol, however, a vinyl ester
such as vinyl acetate or vinyl propionate may be used as the
monomer, and then a functional group such as a hydroxyl group may
be introduced into the synthesized polymer.
[0038] Examples of the monomer forming the super water-absorbent
polymer include acrylic acid, methacrylic acid, maleic acid,
fumaric acid, itaconic acid, crotonic acid, citraconic acid,
.alpha.-hydroxyacrylic acid, aconitic acid, 2-(meth)acryloylethane
sulfonic acid, 2-(meth)acrylamide-2-methylpropane sulfonic acid and
salts thereof. Examples of the salts include metal salts. Examples
of metals in the salts are alkali metals (e.g., potassium and
sodium).
[0039] The crosslinking agent is preferably dissolved in a mixture
of the monomer and an aqueous medium. The solubility of the
crosslinking agent in 100 mL of the mixture of the monomer and the
aqueous medium is at least 0.2 g, for example at least 0.4 g,
particularly at least 1 g, especially at least 5 g. The aqueous
medium consists of water only or comprises water and a
water-soluble organic solvent (e.g., alcohol).
[0040] The super water-absorbent polymer may be based on a complete
or partial salt of carboxylic acid.
[0041] The crosslinking agent of the present invention can be used
in any methods known in the art, which are not limited. For
example, 60 to 90 mol-% of an aqueous solution of an acrylic acid
monomer is neutralized with e.g., an aqueous solution of sodium
hydroxide to form 30 to 50 weight-% aqueous solution, then the
crosslinking agent is mixed in an amount of 0.1 to 1.0 weight-%, a
redox radical polymerization initiator such as an azo compound or a
peroxide is added thereto, the monomer is polymerized usually at a
temperature of at most about 100.degree. C., and the formed polymer
is cut into pieces of suitable size and then dried, whereby the
super water-absorbent polymer can be produced (a
post-neutralization polymerization method).
[0042] Alternatively, the crosslinking agent and the polymerization
initiator are added to an aqueous solution of an acrylic acid
monomer not neutralized, then the monomer is polymerized, and the
formed solid is cut into pieces of suitable size and neutralized
with sodium hydroxide (a pre-neutralization polymerization
method).
[0043] The crosslinking agent of the present invention may consist
of the hydroxypolyallyl ether only or a liquid mixture such as an
aqueous solution of the hydroxypolyallyl ether.
[0044] The super water-absorbent polymer polymerized in the
presence of the crosslinking agent of the present invention may be
in the form of a water-absorbent polymer having higher properties
prepared by a method in which surfaces of the polymeric particles
are treated with a specified agent (for example, a surface
treatment agent) for the purpose of decreasing a blocking property
among polymeric particles prepared by comminution according to
conventional procedures such as U.S. Pat. No. 5,597,873 and
JP-A-5-138019.
[0045] The surface treatment agent is referred to also as a
"surface crosslinking agent". Examples of the surface treatment
agent include a dihydric alcohol such as ethylene glycol, propylene
glycol, butane diol, diethylene glycol, triethylene glycol and
polyethylene glycol; a polyhydric alcohol (an alcohol having
valence of at least three) such as glycerine, polyglycerine,
trimethylolpropane, pentaerythritol, sorbitol and polyvinyl
alcohol; an amine compound such as diethanolamine, triethanolamine,
N-(hydroxyalkyl)-(meth)alanine ester, a polyamine/epichlorohydrin
adduct and a polyethylene/polyamine/epichlorohy- drin adduct; a
polyglycidyl compound such as ethyleneglycol diglycidyl ether; a
carbonate compound such as ethylene carbonate. The amount of the
surface treatment agent may be from 0.01 to 20 parts by weight,
preferably from 0.1 to 10 parts by weight, particularly preferably
from 0.1 to 5 parts by weight, based on 100 parts by weight of the
dried polymer obtained by the polymerization reaction. The polymer
contacted with the treatment agent may be thermally treated by the
use or non-use of an organic solvent or an aqueous solvent. The
heat temperature may be from 50 to 300.degree. C., preferably from
80 to 250.degree. C., more preferably from 100 to 200.degree.
C.
PREFERRED EMBODIMENTS OF THE INVENTION
[0046] Hereinafter, the present invention is illustrated with
reference to the Examples and Comparative Examples.
[0047] The water absorptivity of a powdery polymer (amount of
absorbed water (g) per 1 g of the powdery polymer) was evaluated in
the following manner.
[0048] About 0.2 g powdery polymer is accurately weighed,
introduced uniformly into a tea bag-type bag made of non-woven
fabric (6.8 mm.times.9.6 mm), and immersed in a 0.9% saline
solution, and the weight thereof after immersed for 1 hour is
measured. The procedure is conducted under atmospheric pressure (1
atm). Taking that the weight of the bag only is the blank, the
water absorptivity of the powdery polymer is calculated according
to the following equation:
Water absorptivity=[(weight (g) after water absorption)-(blank
(g))]/[weight (g) of super water-absorbent polymer]
[0049] (1) Production of Crosslinking Agent
EXAMPLE 1
[0050] 455 g (2.5 mol) of D-sorbitol, 421 g (7.5 mol) of potassium
hydroxide and 150 mL of water were introduced into a 2 L
four-necked flask equipped with an agitator, a dropping funnel, a
reflex condenser, a thermometer and a mechanical stirrer, and the
mixture was stirred under heating on a mantle heater to give a
slightly turbid pale yellow solution having a temperature of
135.degree. C. Upon the initiation of dropwise addition of allyl
bromide thereto, the refluxing was initiated and the liquid
temperature was lowered to about 95.degree. C. Thereafter, gentle
refluxing was continued while the liquid temperature was kept at
about 90 to 105.degree. C. during dropwise addition. 910 g of allyl
bromide (7.5 mol) was added dropwise over the period of 6 hours,
and the temperature of the solution was 86.degree. C. after this
addition. Thereafter, the mixture was further heated under reflux
for 4 hours and then gradually cooled, and this reaction mixture
was removed. This mixture had been separated into an organic layer,
a small amount of an aqueous layer and a large amount of
crystalline solids. This organic layer (468 g) was taken while the
crystalline solids and the aqueous layer were washed with diethyl
ether, and the washing liquids were combined with the organic
layer. This mixture was concentrated in an evaporator at 40.degree.
C. to give 434 g of a concentrated liquid. The resultant oily
liquid was analyzed by a liquid chromatography (analytical
conditions were as follows: column: ODS-120-5-AP manufactured by
Daiso Co., Ltd., column temperature: 25.degree. C., eluent:
methanol/water (4:1) at a flow rate of 1 ml/min.). The analysis
results are shown in Table 1, indicating that a mixture of
D-sorbitol ally ethers was obtained. The average degree of
allylation (that is, the average number of allyl groups) per one
molecule was about 3.0 as determined by .sup.1H NMR.
1TABLE 1 Ratio of area (%) Number of allyl by liquid Compound
groups per molecule chromatography D-sorbitol monoallyl ether 1
2.15 D-sorbitol diallyl ether 2 17.14 D-sorbitol triallyl ether 3
43.16 D-sorbitol tetraallyl ether 4 22.51 D-sorbitol pentaallyl
ether 5 13.40 D-sorbitol hexaallyl ether 6 1.01
[0051] The solubility of this mixture in an aqueous acrylate salt
solution was determined in the following manner.
[0052] 180 g of acrylic acid, 75 g of sodium hydroxide, and 424 g
of distilled water were mixed to prepare a standard aqueous
solution of acrylate salt having a monomer concentration of 32.4
wt-% and a degree of neutralization of 75 mol-%.
[0053] 10 g of the mixture obtained in the above experiment was
added to 100 g of the standard aqueous solution of acrylate salt,
then shaken vigorously and left to be separated into 2 layers, and
an aqueous layer was removed and analyzed by a liquid
chromatography (analytical conditions were as follows:
[0054] column: ODS-120-5-AP manufactured by Daiso Co., Ltd.,
column
[0055] temperature: 25.degree. C., eluent: methanol/water (4:1) at
a flow rate of 1 ml/min.), indicating that the solubility was 1.34
w/v %.
COMPARATIVE EXAMPLE 1
[0056] 10 g of trimethylol propane triacrylate was mixed with 100 g
of the above-mentioned standard aqueous solution of acrylate salt,
then shaken vigorously and left to be separated into 2 layers, and
an aqueous layer was removed and analyzed by a gas chromatography
(analytical conditions were as follows: column: 30 m, BP20-0.25
manufactured by SGE Co., Ltd., column temperature: from 100 to
200.degree. C. at an increasing temperature of 10.degree. C./min.),
indicating that the solubility was 0.20 w/v %.
[0057] The solubility in the standard aqueous solution of acrylate
salt in Example 1 and Comparative Example 1 is summarized in Table
2.
2TABLE 2 Example 1 Comparative Mixture of Example 1 D-sorbitol
Trimethylol Compound allyl ethers propane triacrylate Average
degree of allylation 3.0 -- Solubility (w/v %) in standard 1.34
0.20 aqueous solution of acrylate salt
[0058] The compound in Example 1 was superior in the solubility in
the standard aqueous solution of acrylate salt to the compound in
Comparative Example 1.
[0059] (2) Production of a Water-Absorbent Polymer
EXAMPLE 2
[0060] 180 g (2.5 mol) of acrylic acid, 75 g (1.875 mol) of NaOH,
424 mL of water and 1.44 g (4.78 mmol) of the D-sorbitol allyl
ether mixture obtained in Example 1 were introduced into a 1 L
separable flask equipped with a nitrogen inlet (for use in liquid
and gaseous phase), a thermometer, a dropping funnel and a
mechanical stirrer, and the mixture was cooled to a temperature of
5.degree. C. on ice. The mixture at this stage was a colorless
transparent liquid having a pH value of 5 to 6. The separable flask
was placed in a thermal insulating container, and then a solution
of 150 mg (0.56 mmol) 2,2'-azobis(2-amidinopropane) dihydrochloride
in 1 mL water, a solution of 20 mg (0.113 mmol) L-ascorbic acid in
1 mL water and a solution of 100 mg (0.91 mmol) of 31% aqueous
hydrogen peroxide in 1 mL water were added thereto successively
within 1 minute. Just after these materials were added, the
turbidity of the mixture was increased, and the viscosity was
increased in an exothermic reaction to terminate stirring. The
reaction mixture was left to stand and it reached the maximum
temperature (82.degree. C.) after 19 minutes. Thereafter, the
reaction mixture was left and gradually cooled to room temperature,
and the resultant colorless transparent gel was removed from the
flask. Apart (about 100 g) of this gel was removed and comminuted
by a speed cutter. When the size of the resultant particles was
reduced to about 1 mm or less, the particles were dried for 5 hours
in an oven at 180.degree. C. The resultant solids were removed from
the oven to give 28.0 g of pale yellow solids. These were ground
into powder in a sample mill, placed again in the oven (180.degree.
C.), and dried for 1.5 hours. After 25.9 g of pale yellow powder
was thus obtained, the powder was sieved to give 22.1 g of powder
having a particle diameter of at least 60 .mu.m.
[0061] The powdery polymer thus prepared was evaluated for water
absorptivity. The water absorptivity under atmospheric pressure was
46 g/g.
COMPARATIVE EXAMPLE 2
[0062] A powdery polymer was prepared in the same manner as in
Example 2 except that 1.41 g (4.78 mmol) of trimethyl propane
triacrylate was used in place of 1.44 g (4.78 mmol) of the
D-sorbitol allyl ether mixture. The water absorptivity under
atmospheric pressure was 36 g/g.
EXAMPLE 3
[0063] 180 g (2.5 mol) of acrylic acid, 487 mL of water and 1.44 g
(4.78 mmol) of the D-sorbitol allyl ether mixture obtained in
Example 1 were introduced into a 1 L separable flask equipped with
a nitrogen inlet (for use in liquid and gaseous phase), a
thermometer, a dropping funnel and a mechanical stirrer, and the
mixture was cooled to a temperature of 5.degree. C. on ice. The
mixture at this stage was a colorless transparent liquid. The
separable flask was placed in a thermal insulating container, and
then a solution of 150 mg (0.56 mmol) 2,2'-azobis(2-amidinopropane)
dihydrochloride in 1 mL water, a solution of 20 mg (0.113 mmol)
L-ascorbic acid in 1 mL water and a solution of 100 mg (0.91 mmol)
of 31% aqueous hydrogen peroxide in 1 mL water were added thereto
successively within 1 minute. Just after these materials were
added, the turbidity of the mixture was increased, and the
viscosity was increased in an exothermic reaction to terminate
stirring. The reaction mixture was left to stand and it reached the
maximum temperature (83.degree. C.) after 20 minutes. Thereafter,
the reaction mixture was left and gradually cooled to room
temperature, and the resultant colorless transparent gel was
removed from the flask. Apart (about 100 g) of this gel was removed
and divided by a speed cutter. When the size of the resultant
particles was reduced to about 1 mm or less, 23.5 g of 48% aqueous
sodium hydroxide was added thereto, and the particles were further
divided for 30 minutes. The resultant divided gel mixture was dried
for 5 hours in an oven at 180.degree. C. to give 28.56 g of pale
yellow solids. These were ground into powder in a sample mill,
placed again in the oven (180.degree. C.), and dried for 1.5 hours.
After 26.2 g pale yellow powder was thus obtained, the powder was
sieved to give 23.2 g powder having a particle diameter of at least
60 .mu.m.
[0064] The powdery polymer thus prepared was evaluated for water
absorptivity, indicating that the water absorptivity was 46 g/g
under atmospheric pressure.
[0065] (I) Preparation and Solubility of Crosslinking Agent
EXAMPLE 4
Sorbitol Allyl Ether Mixture
[0066] 859 g of a 70% aqueous D-sorbitol solution, 583 g of a 48%
aqueous sodium hydroxide solution and 60 mL of allyl alcohol were
charged into a 2,000 mL reactor equipped with an agitator, a reflex
condenser, a thermometer and two dropping funnels, and the mixture
was heated. When the mixture reached 90.degree. C., the dropwise
addition of allyl chloride from one of the dropping funnels was
initiated. The dropwise addition amount was adjusted so as to
maintain the temperature to at least 70.degree. C., while whole of
a reflux liquid is returned to the reactor.
[0067] At 3.7 hours after the initiation of the reaction, the
addition of 200 g of allyl chloride was completed. Then the
addition was continued. The time required for adding 300 g of allyl
chloride was 5.5 hours after the initiation of the reaction. At
this point of time (at the time at which allyl halide was added in
the amount of 20% by mol, based on total molar number of hydroxyl
group contained in D-sorbitol), the reflux liquid is separated so
that an oil layer alone is returned to the reactor by attaching a
water metering reservoir between the reflux condenser and the
reactor. The time required for adding total amount of 459 g of
allyl chloride was 8 hours after the initiation of the reaction. At
this point of time, the dropwise addition of 333 g of 48% aqueous
sodium hydroxide solution from the other dropping funnel was
initiated. The time required for adding total amount of 842 g of
allyl chloride was 11 hours after the initiation of the reaction.
The temperature was between 70.degree. C. and 90.degree. C. After
the mixture was digested for one hour, the mixture was cooled.
[0068] A reaction product was a mixture slurry of a yellowish brown
oil and a solid particles and did not have an aqueous layer. The
oil, remaining after low-boiling point substances are distilled
off, was analyzed according to a gas chromatography and .sup.1H
NMR. The composition (% by weight) was as follows. D-sorbitol:
0.0%, D-sorbitol monoallyl ether: 0.4%, diallyl ether: 11.3%,
triallyl ether: 35.4%, tetraallyl ether: 40.5%, pentaallyl ether:
12.9%, hexaallyl ether: 0.2%. An average molar number of allyl
groups added to one molecule of D-sorbitol was 3.5.
[0069] The crosslinking agent prepared according to the present
method is referred to as "crosslinking agent (A)".
[0070] A given amount of the crosslinking agent (A) was weighed in
a screw tube, and water was added to give mixtures having a
concentration of 3.0%, 2.0%, 1.0% and 0.9%. The tube containing
each mixture was vigorously shaken and stood in a
temperature-controlled bath at 20.degree. C. The tube was removed
after 30 minutes, the tube was vigorously shaken for at most 30
seconds which was such time that the liquid temperature was kept,
and then the tube was stood again in the temperature-controlled
bath. After one hour, the tube was removed from the
temperature-controlled bath and then the liquid state was quickly
visually observed. Since the opaqueness was observed at the
concentrations of 3.0% and 2.0%, and the layer separation or
opaqueness is not observed at the concentrations of 1.0% and 0.9%,
the solubility of the crosslinking agent (A) according to the
present invention was determined to be from 1% to 2%.
COMPARATIVE EXAMPLE 3
[0071] Preparation and Solubility Measurement of Pentaerythritol
Allyl Ether Mixture
[0072] 272 g (2.0 mol) of pentaerythritol, 337 g (6.0 mol) of
potassium hydroxide and 150 mL of water were charged into a 2 L
four-necked flask equipped with an agitator, a dropping funnel, a
reflex condenser, a thermometer and mechanical stirrer, and the
mixture was heated on a mantle heater with stirring to give a
solution having 120.degree. C. The initiation of the dropwise
addition of allyl bromide gave the initiation of reflux to decrease
the temperature to about 95.degree. C. During the dropwise
addition, the mild reflux was continued while the liquid
temperature was from about 90.degree. C. to about 105.degree. C.
Totally 726 g (6.0 mol) of allyl bromide was dropwise added for 8
hours. After the completion of dropwise addition of allyl bromide,
the liquid temperature was 93.degree. C. After the completion of
dropwise addition of allyl bromide, the liquid was heated for 4
hours with stirring. Then the liquid was kept stand without heating
and the reaction mixture was removed. The reaction mixture had
separated phases of an organic phase, an aqueous phase and a large
amount of crystalline solid. The organic phase was removed. This
mixture was concentrated in an evaporator at 40.degree. C. to give
458 g of an oil. A gas chromatography analysis [analysis conditions
are as follows: Column: BP20-0.25 (trade name, manufactured by SGE
Corp.), column temperature: 100.degree. C. to 200.degree. C.,
temperature increase rate: 10.degree. C./min.] of the resultant oil
gave results (area ratio) as follows. A pentaerythritol allyl ether
mixture was obtained. An average allylation amount per one molecule
according to .sup.1H NMR was about 3.0.
3TABLE I Value of y Area ratio according (number of ally groups to
gas Compound per one molecule) chromatography (%) Pentaerythritol
diallyl 2 11.4 ether Pentaerythritol triallyl 3 80.7 ether
Pentaerythritol 4 7.4 tetraallyl ether
[0073] The solubility of this mixture in an aqueous acrylate salt
solution was determined as follows. 10 g of the mixture obtained in
the above experiment was added to 100 g of the above-mentioned
standard aqueous solution of acrylate salt, then shaken vigorously
and left to be separated into 2 layers, and an aqueous layer was
removed and analyzed by a gas chromatography [analysis conditions
are as follows: Column: BP20-0.25 (trade name, manufactured by SGE
Corp.), column temperature: 100.degree. C. to 200.degree. C.,
temperature increase rate: 10.degree. C./min.]. The solubility was
0.40 w/v %.
REFERENCE EXAMPLE 1
[0074] Crosslinking Agent (a) (P-30, Pentaerythritol Triallyl
Ether)
[0075] 10.0 mg, 21.4 mg or 61.8 mg of P-30 (pentaerythritol
triallyl ether manufactured by Daiso Co., Ltd.) was weighed into
each of three 30 mL screw tubes and 20.0 g of water was added to
each tube to give mixtures each having a concentration of 0.05%,
0.11% or 0.31%. The mixtures were treated in a
temperature-controlled bath at 20.degree. C. as in Example 4.
[0076] No opaqueness was observed in the concentration of 0.05%,
slight opaqueness was observed in the concentration of 0.11%, and
opaqueness was observed in the concentration of 0.31%. The
solubility of the crosslinking agent P-30 in water was determined
as "from 0.05% to 0.11%".
REFERENCE EXAMPLE 2
[0077] Synthesis of Crosslinking Agent (b): Ethyleneglycol Diallyl
Ether
[0078] Into 500 mL three-necked flask equipped with a dropping
funnel, a thermometer, a reflux condenser and magnetic stirrer, 180
g of acetonitrile, 48.0 g (1,200 mmol) of NaOH pellets and 12.4 g
(200 mmol) of ethyleneglycol were charged with stirring to give an
opaque mixture having a temperature of 60.degree. C. 96.8 g (800
mmol) of allyl bromide was further dropwise added, and the stirring
was continued for 4 hours. After left and gradually cooled to room
temperature, the mixture was filtered and the filtered solid was
washed with a small amount of ether. A filtrate and a washing
liquid were combined. The resultant solution was distilled at
atmospheric pressure. After a large amount of acetonitrile was
filtered off at the beginning of distillation, 22 g of a
distillation fraction having a boiling temperature of 132 to
140.degree. C. was obtained. This distillation fraction contained
78%, 6% of monoallyl product according to a gas chromatography.
This fraction was distilled again to give the objected product
(b).
[0079] (II) Preparation of Water-Absorbent Polymer
[0080] Hereinafter, the water absorptivity of the super
water-absorbent polymer was evaluated as follows:
[0081] a) Measurement of Water Absorption Amount at Atmospheric
Pressure (AC: Absorbency Capacity)
[0082] About 0.2 g of Highly water-absorbent resin particles are
precisely weighed (Ws (g)). The resin particles are uniformly
charged into a tea bag-type bag (size: 6.8 mm.times.9.6 mm for
enclosure part) made of non-woven fabric. The bag is immersed into
a 0.9% saline solution. After one hour immersion, the bag is
removed from the solution. The bag is placed on a paper board and
left for one minute so that the paper board roughly absorbs water.
The bag is transferred and placed on another new paper board and
left for 30 minutes. Then the weight (W1 (g)) of the bag is
measured. W0 (g) is a blank weight wherein a bag containing no
resin sample is immersed into a 0.9% saline solution. The above
procedure was conducted using two bags containing the same resin
and two blank bags containing no resin. An average of two numerical
values is taken as a measurement value. The experiment is conducted
at room temperature (about 20.degree. C.).
[0083] A previous experiment reveals that good repetition can be
obtained since a weight decrease is most stable at the time of 20
minutes to 40 minutes in the conditions left on the board
paper.
[0084] The AC value is calculated by the following equation:
AC (g/g)=(W1-W0)/Ws
[0085] b) Measurement of Water Retention Amount in Centrifugally
Treated Water-Absorbed Polymer (CRC: Centrifuge Retention
Capacity)
[0086] About 0.5 g of a gel having absorbed water in the above AC
measurement test is charged into a 1.5 mL sample vessel having a
inner diameter of 7 mm which has a mesh screen at a bottom so as to
filter off the dehydrated water. The weight of the gel contained in
the vessel is precisely measured. The gel is dehydrated with a high
speed micro-centrifuge separator (MTX-160, TOMY) for 20 minutes at
10.degree. C. and 15,000 rpm. The weight of the gel after the
dehydration treatment is measured so that a weight decrease ratio D
(% by weight) to the weight before the dehydration treatment is
determined. The CRC is calculated according to the following
equation:
CRC (g/g)=AC(g/g).times.(100-D)/100
[0087] c) Measurement of Water Absorption Amount Under Pressurized
Conditions (AUP: Absorbency Under Pressure)
[0088] About 0.2 g of SAP particles are charged into an acryl tube
having an inner diameter of 30.7 mm and a length of 100 mm wherein
one end of the tube is capped with a metal mesh having 325 mesh.
The SAP particles (Ws(g)) contained in the tube are precisely
weighed and are almost uniformly spread. An acryl rod (inner tube)
having an outer diameter of 30 mm is inserted into the
above-mentioned acryl tube so that the inner tube reaches the
bottom end. Then the weight (W1) is measured. Lead weights are
positioned on the inner tube so that the total weight of the inner
tube and the lead weights is 346 g. 3 sets of this measurement
instrument and one set of blank instrument containing no sample are
provided. Four sets are positioned on a vat, and a 0.9% saline
solution is poured into the vat so that the mesh is sufficiently
immersed in the saline solution. After left for one hour, the lead
weights are took away and water drops attached to the tube are
wiped off and the weight of tubes is measured. A weight difference
between the sets after and before immersion, that is, gel weight
(W1)(g) is determined. An average weight of gel (W1 (g)) in three
sets is taken as the measurement value for the sample set. In the
same manner, the weight difference for the blank is measured and
taken as W0 (g).
[0089] The AUP is calculated according to the following
equation:
AUP (g/g)=(W1-W0)/Ws
EXAMPLES 5 to 10
[0090] (II)-1 Polymerization Reaction (Pre-Neutralization
Polymerization Method);
EXAMPLES 5 to 7
[0091] Synthesis of Super Water-Absorbent Polymer
[0092] 180 g (2.5 mol) of acrylic acid and 487 g of water are
charged into a 1 L separable flask equipped with a nitrogen
introducing tube, a thermometer, a dropping funnel and a stirrer,
and stirred and cooled with ice under nitrogen atmosphere to have a
temperature of about 10.degree. C. The crosslinking agent (A) was
added in a concentration shown in Table 3 and nitrogen was bubbled
for 30 minutes in the mixture while stirred and cooled with ice to
give a mixture temperature of about 5.degree. C.
[0093] After the reaction flask was placed into a vessel filed with
a thermally insulating material, a solution of 200 mg (0.74 mmol)
of 2,2'-azobis(2-amidinopropane) dihydrochloride in 1 mL of water,
a solution of 33.4 mg (0.19 mmol) of L-ascorbic acid in 1 mL of
water, and a solution of 108 mg (0.98 mmol) of 31% aqueous hydrogen
peroxide in 1 mL water were added. The mixture increasingly had
higher viscosity with evolving heat. At the time of stirring the
mixture with difficulty, the stirring is discontinued. The mixture
became a gel, which was allowed to stand. The reaction temperature
reached a maximum temperature of 65.degree. C. to 75.degree. C.
after about 10 to 20 minutes, depending on the conditions. The
mixture was allowed to stand so as to be gradually cooled and was
kept to stand for one night.
[0094] About 100 g of the resultant gel was placed into a rotary
cutter, and comminuted to have particle size of about 1 mm. The
rotary comminution was conducted by adding a solution in 20 mL
water of NaOH (11.2 g) corresponding to 75% based on equivalent of
free carboxylic acid contained in the gel calculated from charged
acrylic acid amount.
[0095] The resultant comminuted gel was dried at 140.degree. C. for
6 hours in an air flow oven with confirming a constant weight to
give a dry solid. The resultant dry solid was treated with a sample
mill, and sieved. The particles having the particle size of at
least about 63 .mu.m were taken as a super water-absorbent polymer
without surface crosslinking treatment. The results of water
absorptivity of the resultant super water-absorbent polymer without
surface crosslinking treatment are shown in Examples 5 to 7 in
Table 3.
[0096] (II)-2 Surface Crosslinking Treatment; Examples 8 to 10
[0097] 10.0 g of the powder having the particle size of at least 63
.mu.m obtained in (II)-1 was charged into a 200 mL improved coffee
mill vessel and sprayed for several seconds with an aqueous
solution of the following surface crosslinking agent by an air
brush (OLYMPOS HP-83C). Then the powder was thermally treated and
dried at 155.degree. C. for 30 minutes to give surface
crosslink-treated particles.
[0098] Aqueous solution of surface crosslinking agent: aqueous
solution of 0.25 g of propylene glycol and 0.01 g of ethylene
glycol diglycidyl ether in 0.25 g of deionized water.
[0099] The improved coffee mill was prepared by making two holes
having a diameter of 1 cm on a top of a commercially available
coffee mill, fixing with an adhesive tape, to one hole, a net
having 325 mesh as a gas flow exit filter, and using the other hole
as an introducing port for an air brush.
[0100] The results of the resultant super water-absorbent polymer
with surface crosslinking treatment are shown in Examples 8 to 10
in Table 3.
COMPARATIVE EXAMPLES 4 to 17
[0101] The polymerization and the optional surface crosslinking
treatment were conducted to give polymers with or without surface
crosslinking treatment in the same manner as in Examples 5 to 10,
except that the crosslinking agent (A) was replaced with
crosslinking agent (a), (b) and (c) in the concentration shown in
Table 3. The water absorptivity is shown in Comparative Examples 4
to 17 in Table 3.
EXAMPLES 11 to 16
[0102] (II)-3 Polymerization Reaction (Post-Neutralization
Polymerization Method)
[0103] 180 g (2.5 mol) of acrylic acid and 100 mL of water were
charged into a 1 L separable flask equipped with a nitrogen
introducing tube, a thermometer, a dropping funnel and a stirrer,
and stirred and cooled with ice under nitrogen atmosphere to have a
temperature of about 10.degree. C. A solution of 75 g (1.875 mol)
of NaOH in water was dropwise added. The speed of dropwise adding
the NaOH solution was adjusted so that the mixture temperature did
not exceed 20.degree. C. After the completion of addition of the
NaOH solution, water was added so that the total amount of water
was 424 g to give an aqueous solution having a monomer
concentration of 32.4% and a neutralization ratio of 75% by mol. A
crosslinking agent in the amount shown in Table 4 was added. The
mixture was further cooled to about 5.degree. C. while blowing
nitrogen for at least 30 minutes.
[0104] After the reaction vessel was placed into a vessel filled
with a thermally insulating material, a solution of 200 mg (0.74
mmol) of 2,2'-azobis(2-amidinopropane) dihydrochloride in 1 mL of
water, a solution of 33.4 mg (0.19 mmol) of L-ascorbic acid in 1 mL
of water, and a solution of 108 mg (0.98 mmol) of 31% aqueous
hydrogen peroxide in 1 mL water were successively added within 30
seconds. The mixture increasingly had higher viscosity with
evolving heat, and the stirring is discontinued after about 0.5 to
10 minutes. The reaction temperature reached a maximum temperature
of 65.degree. C. to 75.degree. C. after about 10 to 20 minutes. The
resultant gel was allowed to stand so as to be gradually cooled and
was kept to stand for one night.
[0105] 100 g of the resultant gel was placed into a rotary cutter,
and comminuted to have particle size of about 1 mm.
[0106] The resultant comminuted gel was dried at 140.degree. C. for
6 hours in an air flow oven with confirming a constant weight to
give a dry solid. The resultant dry solid was treated with a sample
mill, and sieved. The particles having a particle size of at least
about 63 .mu.m were taken as a super water-absorbent polymer
without surface crosslinking treatment. The results of water
absorptivity of the resultant super water-absorbent polymer without
surface crosslinking treatment are shown in Examples 11 to 13 in
Table 3.
[0107] (II)-4 Surface Crosslinking Treatment
[0108] 10.0 g of the powder having the particle size of at least 63
.mu.m obtained in (II)-3 was charged into a 200 mL improved coffee
mill vessel and sprayed for several seconds with an aqueous
solution of the following surface crosslinking agent by an air
brush (OLYMPOS HP-83C). Then the powder was thermally treated and
dried at 180.degree. C. for 30 minutes to give surface crosslinking
treatment particles.
[0109] Aqueous solution of surface crosslinking agent: aqueous
solution of 0.33 g of ethylene carbonate in 0.150 g of deionized
water.
[0110] The results of the super water-absorbent polymer with
resultant surface crosslinking treatment are shown in Examples 11
to 16 in Table 4.
COMPARATIVE EXAMPLES 18 to 29
[0111] The polymerization and the optional surface crosslinking
treatment were conducted to give polymers with or without surface
crosslinking treatment in the same manner as in Examples 11 to 16,
except that the crosslinking agent (A) was replaced with
crosslinking agent (a), (b) and (c) in the concentration shown in
Table 4. The results of water absorptivity are shown in Comparative
Examples 18 to 29 in Table 4.
[0112] The water absorptivity under pressurized conditions is a
scale of still exhibiting absorption property against a body weight
when the polymer is used for, for example, a diaper. The water
absorption property under pressurized conditions has a trade-off
relationship with the CRC property which is a scale of water
absorptivity under atmospheric pressure. The super water-absorbent
polymer having high level of both properties has the preferable
water absorptivity.
[0113] In the comparison of water absorptivity in the
pre-neutralization polymerization method, when the water
absorptivity of the super water-absorbent polymer after the surface
treatment shown in Table 3 is focused, the super water-absorbent
polymer prepared by using the crosslinking agent (A) according to
the present invention (Examples 8, 9 and 10) exhibits better
properties particularly under both of normal and pressurized
conditions at the crosslinking agent concentration of 0.4% and
better properties under pressurized conditions at the crosslinking
agent concentration of 0.2% so as to be the super water-absorbent
polymer having good balance of properties, in comparison with the
polymer prepared according to Comparative Examples.
[0114] In comparison of the crosslinking agent of the present
invention with the pentaerythritol trially ether (crosslinking
agent (a)) which has been practically used as the allyl-based
crosslinking agent and is recognized to have high properties, the
crosslinking agent (a) has relatively poor water absorptivity
particularly under pressurized conditions and can have similar
property under pressurized conditions but has deteriorated water
absorptivity under atmospheric pressure by increasing the
crosslinking agent concentration to 1.0%. Additionally, the
crosslinking agent (a) disadvantageously needs a large amount of
used crosslinking agent.
[0115] Ethyleneglycol diallyl ether (crosslinking agent (b)) has
further poor water absorptivity under pressurized conditions than
the crosslinking agent (a).
[0116] The acryl-based trimethylolpropane triacrylate crosslinking
agent (the crosslinking agent (c)) has significantly poorer water
absorptivity than the crosslinking agent (a).
[0117] In the comparison of water absorptivity in the
post-neutralization polymerization method, when the water
absorptivity after the surface treatment shown in Table 4 is
focused, the super water-absorbent polymer prepared by using the
crosslinking agent (A) according to the present invention (Examples
14, 15 and 16) exhibits relatively poorer properties particularly
under pressurized conditions in comparison with the polymer
prepared by the pre-neutralization polymerization method, but
exhibits better properties in comparison with the crosslinking
agents (a), (b) and (c). That is, the present invention has better
water absorptivity in comparison within the same preparation
method.
4TABLE 3 Pre-neutralization polymerization method: Water
absorptivity of SAP crosslink- cross- ing agent SAP without surface
SAP with surface crosslinking treatment link- concentra-
crosslinking treatment 0.7 AUP 0.7 AUP ing tion AC (g/g) CRC (g/g)
AC (g/g) CRC (g/g) (g/g) (g/g) agent (%) after 1 hr after 1 hr
after 1 hr after 1 hr after 1 hr after 24 hr (A) 0.20 Ex. 5 48.0
44.3 Ex. 8 41.9 38.1 24.1 29.0 0.40 Ex. 6 42.1 39.0 Ex. 9 39.4 35.6
26.7 28.1 0.80 Ex. 7 41.4 37.7 Ex. 10 38.6 33.8 25.9 30.9 (a) 0.40
Com. Ex. 4 38.1 35.3 Com. Ex. 11 38.0 35.1 15.5 24.7 0.80 Com. Ex.
5 39.2 36.2 Com. Ex. 12 37.9 35.1 19.9 30.3 1.00 Com. Ex. 6 36.2
33.6 Com. Ex. 13 33.7 31.3 25.2 27.9 (b) 0.40 Com. Ex. 7 47.3 43.5
Com. Ex. 14 41.3 37.7 13.1 -- (c) 0.20 Com. Ex. 8 47.5 43.6 Com.
Ex. 15 41.2 38.0 16.3 25.1 0.40 Com. Ex. 9 40.8 37.8 Com. Ex. 16
39.8 36.7 13.0 24.0 0.80 Com. Ex. 10 37.3 34.7 Com. Ex. 17 35.6
33.1 14.6 25.8 SAP: Super water-absorbent polymer AC: Absorbency
Capacity Crosslinking agent concentration: % by weight based on
charged acrylic acid at the polymerization reaction Crosslinking
agent (A): S-30 (Product in Example 4) Crosslinking agent (a):
P-30: Pentaerythritoltriallyl ether [Daiso Co. Ltd.] Crosslinking
agent (b): Ethyleneglycoldiallyl ether Crosslinking agent (c):
Trimethylolpropane triacrylate Water absorbance amount under
atmospheirc pressure CRC: Centrifuge Retention Capacity Water
retention amount of water-absorbed polymer after centrifugal
separation treatment 0.7 AUP: Absorbency under Pressure Water
absorption amount under pressurized condition (0.7 psi)
[0118]
5TABLE 4 Post-neutralization polymerization method: Water
absorptivity of SAP crosslink- cross- ing agent
Non-post-crosslinked Post-crosslinked SAP link- concentra- SAP 0.7
AUP 0.7 AUP ing tion AC (g/g) CRC (g/g) AC (g/g) CRC (g/g) (g/g)
(g/g) agent (%) after 1 hr after 1 hr after 1 hr after 1 hr after 1
hr after 24 hr (A) 0.20 Ex. 11 51.0 46.5 Ex. 14 48.1 44.2 11.6 26.8
0.40 Ex. 12 41.8 38.3 Ex. 15 40.3 36.9 15.7 26.7 0.80 Ex. 13 38.1
35.3 Ex. 16 37.1 33.4 20.8 27.2 (a) 0.40 Com. Ex. 18 30.9 29.4 Com.
Ex. 24 43.8 40.3 11.1 24.0 0.80 Com. Ex. 19 38.6 36.2 Com. Ex. 25
41.0 37.9 10.7 24.7 1.00 Com. Ex. 20 24.8 23.1 Com. Ex. 26 41.4
38.2 9.5 26.2 (b) 0.40 Com. Ex. 21 -- -- Com. Ex. 27 41.0 38.1 11.9
-- (c) 0.20 Com. Ex. 22 42.8 39.8 Com. Ex. 28 41.9 38.4 10.7 26.5
0.40 Com. Ex. 23 24.2 23.3 Com. Ex. 29 28.1 26.5 12.5 22.9 SAP:
Super water-absorbent polymer Crosslinking agent concentration: %
by weight based on charged acrylic acid at the polymerization
reaction Crosslinking agent (A): S-30 (Product in Example 4)
Crosslinking agent (a): P-30: Pentaerythritoltriallyl ether [Daiso
Co. Ltd.] Crosslinking agent (b): Ethyleneglycoldiallyl ether
Crosslinking agent (c): Trimethylolpropane triacrylate AC:
Absorbency Capacity Water absorbance amount under atmospheric
pressure CRC: Centrifuge Retention Capacity Water retention amount
of water-absorbed polymer after centrifugal separation treatment
0.7 AUP: Absorbency under Pressure Water absorption amount under
pressurized condition (0.7 psi)
[0119] Effect of the Invention
[0120] The crosslinking agent of the present invention can be used
for the production of a super water-absorbent polymer comprising a
polymerizable compound having a polymerizable double bond or a salt
thereof. The crosslinking agent of the present invention is
satisfactory in the solubility in an aqueous acrylate salt solution
and can give an excellent super water-absorbent polymer which
cannot be obtained in the prior arts, in view that high levels of
both of water absorptivity under atmospheric pressure and water
absorptivity under pressurized conditions are obtained and that the
properties are obtained at the low concentration of the
crosslinking agent. The crosslinking agent of the present invention
can be practically used not only in the pre-neutralization
polymerization method but also in the post-neutralization
polymerization method.
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