JP3699225B2 - Porous water-absorbing crosslinked polymer and process for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous water-absorbing crosslinked polymer whose water absorption speed and water absorption ratio are remarkably improved by hydrophilization.
[0002]
[Prior art]
As a porous cross-linked polymer material containing a large amount of an aqueous liquid, a cured product of a water-in-oil emulsion containing up to 90% of an internal aqueous phase is known (UK Patent No. 1458203). As applications of such a water-in-oil emulsion, Japanese Patent Application Laid-Open No. 62-250002 discloses a low density porous crosslinked polymer material having elasticity, and Japanese Patent Application Laid-Open No. 6-510076 discloses a high absorption capacity. A low density foam is disclosed.
[0003]
In general, these high-absorption capacity low-density foams are polymerized after forming a water-in-oil emulsion in a highly dispersed phase with a weight ratio of water relative oil phase exceeding 9: 1 in the presence of a surfactant. Manufactured by. However, the polymer obtained after the formation of the highly dispersed phase water-in-oil emulsion is substantially hydrophobic, and its hydrophilicity is essential for use as a water-absorbing agent.
[0004]
For example, JP-A-6-509834 discloses a method of leaving an inorganic residue such as calcium chloride on the surface of a foam containing a surfactant therein. Although the wettability of the polymer obtained by this method to the initial water is improved, the water absorption rate and the water absorption ratio are not satisfactory, and there is a problem that the water absorption characteristics after storage for a long period of time are deteriorated. there were.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide a porous water-absorbing crosslinked polymer that exhibits improved water absorption rate and water absorption capacity even after long-term storage.
[0006]
[Means for Solving the Problems]
As a result of intensive studies on a method for obtaining a porous water-absorbing crosslinked polymer having an improved water absorption rate, the present inventors have determined that a porous hydrophobic crosslinked polymer produced using a water-in-oil type highly dispersed phase emulsion It has been found that a porous water-absorbing crosslinked polymer having a remarkably excellent water absorption rate and water absorption ratio can be obtained by hydrophilizing itself, and the present invention has been achieved.
[0007]
That is, the present invention
( 1 ) Porous hydrophobic bridge containing a carboxylic acid ester group represented by the general formula -COOR (wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms) A method for producing a porous water-absorbing crosslinked polymer, wherein the polymer is hydrophilized by hydrolysis;
( 2 ) The method for producing a porous water-absorbing crosslinked polymer according to ( 1 ) above, wherein the hydrolysis of the porous water-absorbing crosslinked polymer is performed using an aqueous solution of an alkali hydroxide;
( 3 ) The porous hydrophobic group containing a carboxylic acid ester group represented by the general formula —COOR (wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms). An oil in which the cross-linked polymer contains a monomer having a solubility parameter (SP value) of 9 or less and a monomer component mainly composed of a cross-linkable monomer having at least two polymerizable unsaturated groups in the molecule. The method for producing a porous water-absorbent crosslinked polymer according to the above ( 1 ) or ( 2 ), which is obtained by curing a water-in-water emulsion at a temperature of less than 60 ° C;
(4) A porous water-absorbing crosslinked polymer obtained by the method according to any one of (1) to (3) above, wherein the water absorption rate of physiological saline (0.9% saline) is 5 seconds. A porous water-absorbing crosslinked polymer that is ˜21 seconds;
(5) A water-absorbing article comprising the porous water-absorbing crosslinked polymer of (4) above;
Is to provide.
[0008]
The present invention is described in detail below.
[0009]
The porous hydrophobic cross-linked polymer used in the present invention is, for example, a water-in-oil type using a hydrophobic vinyl monomer and a cross-linkable monomer having at least two polymerizable unsaturated groups in the molecule. It can be obtained by polymerizing after forming a highly dispersed phase emulsion. A preferred hydrophobic monomer is a monomer whose main component is a monomer having a solubility parameter (SP value) of 9 or less.
[0010]
Examples of monomers having a solubility parameter (SP value) of 9 or less used in the present invention include monoalkenyl allene monomers such as styrene, α-methyl styrene, chloromethyl styrene, vinyl ethyl benzene, octyl styrene and vinyl toluene. : Methyl (meth) acrylate, ethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, phenyl (Meth) acrylate, octyl (meth) acrylate, nonylphenyl (meth) acrylate, dinonylphenyl (meth) acrylate, lauryl (meth) acrylate, isodecyl (meth) acrylate, dibutyl maleate, zido Unsaturated carboxylic esters such as decyl maleate, dodecyl rotonate, didodecyl itaconate: (di) butyl (meth) acrylamide, (di) stearyl (meth) acrylamide, (di) dodecyl (meth) acrylamide, (di) butyl (Meth) acrylamide having a hydrocarbon group such as phenyl (meth) acrylamide and (di) octylphenyl (meth) acrylamide: butadiene, isoprene, 1-hexene, 1-octene, isooctene, 1-nonene, 1-decene, 1 Α-olefin such as dodecene: alicyclic vinyl compound such as vinylcyclohexene: allyl ether having an aliphatic hydrocarbon group such as dodecyl allyl ether: vinyl caproate, vinyl laurate, vinyl stearate, vinyl palmitate, etc. Fat Vinyl esters having a family hydrocarbon group: ethyl vinyl ether, butyl vinyl ether, vinyl ether and dodecyl vinyl ether: and the like, and mixtures thereof.
[0011]
Examples of the crosslinkable monomer having at least two polymerizable unsaturated groups in the molecule used in the present invention include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and polyethylene glycol di (meth) acrylate. , Polyethylene glycol-polypropylene glycol di (meth) acrylate, propylene glycol dimethacrylate, polypropylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6 -Polyfunctional (meth) acrylates such as hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, Can be mentioned.
[0012]
The ratio of the crosslinkable monomer having at least two polymerizable unsaturated groups in the molecule used in the present invention to the total monomer component is 1 to 50% by weight in the total monomer component, Preferably it is 5-45 weight%, More preferably, it is the range of 10-40 weight%. When the amount of the crosslinkable monomer used is less than 1% by weight, the strength of the obtained porous crosslinked polymer is insufficient, and when it is more than 50% by weight, the resulting porous crosslinked polymer may be too hard. is there.
[0013]
Examples of the surfactant used for forming the water-in-oil emulsion in the present invention include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, sorbitan monostearate. Examples include sorbitan derivatives such as oleate: glycerin derivatives such as glycerol monostearate and glycerol monooleate: polyoxyethylene fatty acid esters such as polyoxyethylene lauryl ether. These oil-soluble surfactants are used alone or in admixture of two or more, and the amount used is in the range of 1 to 40 parts by weight, preferably in the range of 5 to 30 parts by weight with respect to 100 parts by weight of the monomer component. It is. When the amount is less than 1 part by weight, the water-in-oil emulsion becomes unstable, and when the amount is more than 40 parts by weight, the resulting porous crosslinked polymer may become too brittle.
[0014]
Further, in the present invention, various stabilizers can be added in addition to the above surfactant for the purpose of stabilizing the water-in-oil emulsion during polymerization. A suitable stabilizer is a water-soluble inorganic salt, which is preferably added to the aqueous phase. Examples of such water-soluble inorganic salts include water-soluble salts such as potassium, sodium, calcium, magnesium, and aluminum, and polyvalent metal salts are particularly preferable. The addition amount of the water-soluble inorganic salt is preferably in the range of 0.1 to 20 parts by weight, particularly 0.5 to 15 parts by weight with respect to 100 parts by weight of water.
[0015]
In the present invention, the method for hydrophilizing the hydrophobic porous crosslinked polymer is not particularly limited as long as the polymer itself can be hydrophilized. A preferred hydrophilization method is a method of introducing an anionic group such as a carboxylic acid (salt) into the polymer by a covalent bond. More preferably, the porous hydrophobicity includes a carboxylic acid ester group represented by the general formula —COOR (wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms). In this method, a crosslinked polymer is formed in advance, and then the polymer is hydrolyzed to produce a carboxylic acid (salt) in the polymer to make it hydrophilic.
[0016]
In the present invention, R in the carboxylic acid ester represented by the general formula —COOR is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms, and the substituent does not inhibit the reaction. If it is a thing, it will not specifically limit. Specific examples of R include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, sec-butyl group, t-butyl group, n-pentyl group, hexyl group, octyl group and nonyl. Group, saturated aliphatic hydrocarbon group such as alkyl group such as decyl group; alicyclic hydrocarbon group such as cycloalkyl group such as cyclopentyl group, cyclohexyl group, 4-methylcyclohexyl group; vinyl group, allyl group, 2- Aliphatic unsaturated hydrocarbon group such as alkenyl group such as butenyl group and 3-butenyl group; aryl such as phenyl group, 2-methylphenyl group, 3-methylphenyl group, 4-methylphenyl group, xylyl group and naphthyl group Group, 2-bromophenyl group, 2-methoxyphenyl group, 3-ethoxyphenyl group, 4-methoxyphenyl group, 3-bromophenyl group, 4-butyl group, Mophenyl group, 2-chlorophenyl group, 3-chlorophenyl group, 4-chlorophenyl group, 2-fluorophenyl group, 3-fluorophenyl group, 4-fluorophenyl group, 2-iodophenyl group, 3-iodophenyl group, 4- Iodophenyl group, 2,4-dibromophenyl group, 2,5-dibromophenyl group, 2,6-dibromophenyl group, 2,3-dichlorophenyl group, 2,4-dichlorophenyl group, 2,5-dichlorophenyl group, 2 , 6-dichlorophenyl group, 3,4-dichlorophenyl group, 3,5-dichlorophenyl group, 2,4-difluorophenyl group, 2,5-difluorophenyl group, 2,6-difluorophenyl group, 3,4-difluorophenyl Group, 2,4,6-tribromophenyl group, 2,3,4-trichlorophenyl group, 2,4 A substituted or unsubstituted aryl group such as an aryl group substituted with a halogen atom such as fluorine, chlorine, bromine or iodine such as 5-trichlorophenyl group or 2,4,6-trichlorophenyl group or a lower alkoxy group; and benzyl Groups, aralkyl groups such as 2-phenylethyl group, 4-methylbenzyl group and the like.
[0017]
In order to obtain the porous hydrophobic crosslinked polymer of the present invention, an oil phase component 1 to 1 comprising a hydrophobic vinyl monomer and a crosslinkable monomer having at least two polymerizable unsaturated groups in the molecule. 10% by weight and 99 to 90% by weight of water are mixed in the presence of 1 to 40 parts by weight of surfactant with respect to 100 parts by weight of monomer, and a water-in-oil type having a large amount of water as an internal discontinuous phase. An emulsion is formed. The mixing ratio of the oil phase component and water is preferably in the range of 99 to 90% by weight of water with respect to 1 to 10% by weight of the oil phase component, more preferably 99 to 95% by weight of water with respect to 1 to 5 parts by weight of the oil phase component. It is a range. When the amount of the oil phase component is less than 1% by weight, the strength of the obtained porous hydrophobic crosslinked polymer may be lowered, causing a problem in handling. When the amount of the oil phase component is more than 10% by weight, the water absorption rate of the obtained porous water-absorbing crosslinked polymer may be insufficient.
[0018]
In the present invention, as a method of mixing an oil phase component with water in the presence of an oil-soluble surfactant to form a water-in-oil emulsion, a water-in-oil emulsion having a large amount of water as an internal discontinuous phase is formed. If you can, don't worry. For example, 1) a method in which an oil phase in which an oil-soluble surfactant is dissolved is added to water with stirring, 2) a method in which water is added to an oil phase in which an oil-soluble surfactant is dissolved, and 3) oil solubility. Method of adding water to the oil phase in which the surfactant is dissolved and stirring, 4) Method of adding and stirring the oil phase in which the oil-soluble surfactant is dissolved in water, 5) Oil phase and water in which the oil-soluble surfactant is dissolved And a method of mixing them while continuously feeding them. In each method, the oil-soluble surfactant may be preliminarily dissolved in the oil phase as described above. Alternatively, the oil-soluble surfactant may be preliminarily dispersed in water, or the oil phase component, water, and the oil-soluble surfactant may be separated. It is also possible to feed and mix. A preferable method from an economical viewpoint is a method in which an oil-soluble surfactant is previously dissolved in the oil phase component. As a mixing or stirring device that can be used to form a water-in-oil emulsion, a conventionally known device can be used, for example, a tank-type stirring device equipped with various stirring blades, a static mixer, a mixer, a homogenizer, a magnet. A stirrer etc. can be illustrated.
[0019]
The porous hydrophobic crosslinked polymer that can be used in the present invention can be subjected to ripening polymerization, for example, in the presence of a redox initiator, preferably at a temperature of less than 60 ° C., in the presence of a redox initiator. In the polymerization, it is preferable that the water-in-oil emulsion is allowed to stand and polymerize under the condition that the internal aqueous phase is not destroyed. For example, the water-in-oil emulsion is cast-polymerized by feeding batchwise or continuously. Can do. In polymerization, by forming the polymerization vessel into an arbitrary shape, the porous hydrophobic crosslinked polymer obtained by polymerization is molded and polymerized into an arbitrary shape, for example, a particle shape, a fiber shape, a mat shape, a sheet shape, a block shape, etc. Is also possible. Of course, a continuous polymerization method can also be adopted as the polymerization method. The curing temperature is preferably in the range of less than 60 ° C, more preferably in the range of 20-50 ° C. Most preferably, the curing is performed in a temperature range of 20 to 50 ° C., and the polymerization is completed in the temperature range of 50 to 90 ° C. after curing. The polymerization curing time is suitably about 1 to 30 hours. When the polymerization temperature is less than 15 ° C., it takes a long time for the polymerization and is not industrially preferable. When the curing temperature exceeds 60 ° C., the pore size of the resulting porous hydrophobic crosslinked polymer may be uneven, Moreover, the water absorption magnification of the porous water-absorbing crosslinked polymer of the present invention finally obtained is lowered.
[0020]
Examples of the water-soluble oxidant used as the redox polymerization initiator include water-soluble peroxides such as hydrogen peroxide: water-soluble persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate: sodium peracetate, Water-soluble peracetates such as potassium peracetate: water-soluble percarbonates such as sodium percarbonate and potassium percarbonate. The amount of the water-soluble oxidizing agent used is preferably in the range of 0.001 mol% to 80 mol% with respect to the total number of moles of the total monomer components.
[0021]
In the polymerization, the reducing agent used together with the oxidizing agent includes bisulfites such as sodium bisulfite and potassium bisulfite: thiosulfates such as sodium thiosulfate and potassium thiosulfate: triethanolamine, diethanolamine, dimethylaniline, etc. Examples of amines: Multivalent metal salts such as: L-ascorbic acid and the like. More preferably, it is more preferable to use an amount of reducing agent such that the water-soluble oxidizing agent / reducing agent molar ratio is 1 or less.
[0022]
The most preferable form in the present invention includes a carboxylic ester group represented by the general formula -COOR (wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms). Carboxylic acid is contained in the polymer by hydrolyzing a porous hydrophobic crosslinked polymer obtained by polymerizing a monomer component containing a hydrophobic monomer as an essential component in the form of a water-in-oil emulsion. (Salt) is produced to hydrophilize the polymer.
[0023]
The hydrolysis can be performed using, for example, an aqueous solution of alkali hydroxide (for example, NaOH or KOH), preferably an aqueous solution of 0.5% to a saturated concentration. In the present invention, the hydrolysis is carried out in the temperature range of 50 to 150 ° C., and the degree of neutralization of the carboxyl group generated during the hydrolysis reaction can be changed by adding an appropriate amount of a mineral acid such as HCl. The required reaction time can be arbitrarily selected depending on the reaction temperature and the desired degree of hydrolysis. Moreover, the porous water-absorbent crosslinked polymer of the present invention after hydrolysis is subjected to a compression treatment and dried after washing with water as necessary.
[0024]
The porous water-absorbing crosslinked polymer of the present invention thus obtained has the following excellent points as compared with conventional surfactants and inorganic salt-added products because the polymer itself is hydrophilized. .
[0025]
1) The water absorption speed and the water absorption magnification are remarkably improved.
[0026]
2) There is no residual surfactant and inorganic salt, and it is safe.
[0027]
3) No change in water absorption characteristics after long-term storage due to alteration of the surfactant.
[0028]
4) Since the crosslinked polymer itself is hydrophilized, a part of the crosslinked polymer can be swollen with water, so that the water absorption / retention ability in a pressurized state is remarkably improved.
[0029]
The porous water-absorbing cross-linked polymer of the present invention may be formed into an arbitrary shape, for example, a sheet shape, a block shape, a fiber shape, a film shape, a powder shape, or the like by further cutting if necessary. Moreover, it has a large number of continuous holes through which the liquid permeates into the molded body when it comes into contact with the aqueous liquid. Although the porous water-absorbing crosslinked polymer of the present invention may be used as a water-absorbing material as it is, at least a part of the porous water-absorbing crosslinked polymer is sandwiched between films having liquid permeability, It is also possible to fill the container with a liquid-permeable material and use it as a water-absorbing article.
[0030]
【Example】
Next, although an Example is given and this invention is demonstrated in detail, this invention is not limited only to this. In the examples, unless otherwise specified, parts represent parts by weight.
[0031]
The water absorption rate and water absorption rate of the porous crosslinked polymer in the present invention were measured by the following methods.
[0032]
(Water absorption ratio)
Using a pre-weighed sample cut to a size of 1 cm square, this sample was immersed in physiological saline (0.9% saline) at a temperature of 10 ° C. After the sample that had absorbed physiological saline and expanded was left on a glass filter (# 0: Duran) with a diameter of 120 mm and a height of 5 mm for 30 seconds to drain the liquid, the weight of the absorbed sample was measured. The water absorption capacity (g / g) was determined by the following formula.
[0033]
Water absorption ratio = (sample weight after water absorption−sample weight before water absorption) / sample weight before water absorption (water absorption speed)
At the time of measuring the water absorption magnification, the time until the sample finished absorbing the physiological saline was measured, and the time required for absorption was taken as the water absorption rate.
[0034]
Reference Example A 1000 ml cylindrical polypropylene container was charged with 50 parts of calcium chloride, 0.7 part of sodium persulfate and 450 parts of pure water as an aqueous phase. Subsequently, 1.73 parts of styrene, 5.21 parts of 2-ethylhexyl acrylate, 1.73 parts of 55% divinylbenzene, and sorbitan monolaurate (trade name: Rheodor Super SP-L10, manufactured by Kao Corporation) as the oil phase 1 A solution consisting of .31 parts was added into the vessel with stirring at room temperature. After confirming that the mixture became yogurt-like and a good emulsion was obtained, a solution prepared by dissolving 0.7 part of sodium bisulfite in 10 parts of pure water was added, and stirred again until the emulsion became uniform. After completion of the stirring, the container was kept at 40 ° C. for 3 hours polymerization and curing to complete the polymerization to obtain a porous hydrophobic crosslinked polymer (a).
[0035]
Example 1
The porous hydrophobic cross-linked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration twice to be washed. Next, 10 parts of the washed porous crosslinked polymer was immersed in 100 parts of a 48% aqueous sodium hydroxide solution and heat-treated at 130 ° C. for 1 hour in a 500 mL separable flask equipped with a reflux condenser. After completion of the treatment, the porous crosslinked polymer hydrophilized from the flask is taken out, the alkali is removed by washing with pure water, dried in a hot air drier at 60 ° C. for 1 hour, and the porous water absorption of the present invention. Crosslinkable polymer (1) was obtained. The porous water-absorbing crosslinked polymer (1) of the present invention had a water absorption rate of 67 g / g and a water absorption rate of 5 seconds. Further, the water absorption rate and the water absorption magnification of this product did not change even after aging for 2 weeks in a hot air dryer at 60 ° C.
[0036]
Example 2
The porous hydrophobic cross-linked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration twice to be washed. Next, 10 parts of the washed porous crosslinked polymer was immersed in 100 parts of a 48% aqueous sodium hydroxide solution and heat-treated at 120 ° C. for 30 minutes in a 500 mL separable flask equipped with a reflux condenser. After completion of the treatment, the porous crosslinked polymer hydrophilized from the flask is taken out, the alkali is removed by washing with pure water, dried in a hot air drier at 60 ° C. for 1 hour, and the porous water absorption of the present invention. Crosslinkable polymer (2) was obtained. The porous water-absorbing crosslinked polymer (2) of the present invention had a water absorption rate of 60 g / g and a water absorption rate of 7 seconds. Further, the water absorption rate and the water absorption magnification of this product did not change even after aging for 2 weeks in a hot air dryer at 60 ° C.
[0037]
Example 3
The porous hydrophobic cross-linked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration twice to be washed. Next, 10 parts of the washed porous crosslinked polymer was immersed in 100 parts of a 48% aqueous sodium hydroxide solution and heat-treated at 130 ° C. for 2 hours in a 500 mL separable flask equipped with a reflux condenser. After completion of the treatment, the porous crosslinked polymer hydrophilized from the flask is taken out, the alkali is removed by washing with pure water, dried in a hot air drier at 60 ° C. for 1 hour, and the porous water absorption of the present invention. Crosslinkable polymer (3) was obtained. The porous water-absorbing crosslinked polymer (3) of the present invention had a water absorption rate of 75 g / g and a water absorption rate of 5 seconds. Further, the water absorption rate and the water absorption magnification of this product did not change even after aging for 2 weeks in a hot air dryer at 60 ° C.
[0038]
Example 4
The porous hydrophobic cross-linked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration twice to be washed. Next, 10 parts of this washed porous crosslinked polymer was immersed in 100 parts of a 40% aqueous sodium hydroxide solution, and heat-treated at 130 ° C. for 5 hours in a 500 mL separable flask equipped with a reflux condenser. After completion of the treatment, the porous crosslinked polymer hydrophilized from the flask is taken out, the alkali is removed by washing with pure water, dried in a hot air drier at 60 ° C. for 1 hour, and the porous water absorption of the present invention. Crosslinkable polymer (4) was obtained. The porous water-absorbing crosslinked polymer (4) of the present invention had a water absorption rate of 57 g / g and a water absorption rate of 13 seconds. Further, the water absorption rate and the water absorption magnification of this product did not change even after aging for 2 weeks in a hot air dryer at 60 ° C.
[0039]
Example 5
The porous hydrophobic cross-linked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration twice to be washed. Next, 10 parts of the washed porous crosslinked polymer was immersed in 100 parts of a 20% aqueous sodium hydroxide solution and heat-treated at 130 ° C. for 5 hours in a 500 mL separable flask equipped with a reflux condenser. After completion of the treatment, the porous crosslinked polymer hydrophilized from the flask is taken out, the alkali is removed by washing with pure water, dried in a hot air drier at 60 ° C. for 1 hour, and the porous water absorption of the present invention. Crosslinkable polymer (5) was obtained. The porous water-absorbing crosslinked polymer (5) of the present invention had a water absorption rate of 47 g / g and a water absorption rate of 21 seconds. Further, the water absorption rate and the water absorption magnification of this product did not change even after aging for 2 weeks in a hot air dryer at 60 ° C.
[0040]
Comparative Example 1
The porous hydrophobic crosslinked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration four times and washed. Subsequently, it dried for 1 hour in a 60 degreeC hot-air dryer, and the comparative porous water-absorbing crosslinked polymer (1) was obtained. The comparative porous water-absorbing crosslinked polymer (1) had a water absorption rate of 42 g / g and a water absorption rate of 120 seconds.
[0041]
Comparative Example 2
The porous hydrophobic crosslinked polymer (a) sliced to a thickness of 10 mm was swollen with a 1% calcium chloride aqueous solution at 60 ° C. and subjected to compression dehydration twice and washed. Subsequently, it dried for 1 hour in a 60 degreeC hot air dryer, and the comparative porous water-absorbing crosslinked polymer (2) was obtained. The comparative porous water-absorbing crosslinked polymer (2) had a water absorption rate of 34 g / g and a water absorption rate of 1 hour.
[0042]
Comparative Example 3
The porous hydrophobic cross-linked polymer (a) sliced to a thickness of 10 mm was swollen with pure water at 60 ° C. and subjected to compression dehydration twice to be washed. Subsequently, it was further swelled with a 0.5% sorbitan monolaurate aqueous solution and subjected to compression dehydration twice and dried in a hot air dryer at 60 ° C. for 1 hour to obtain a comparative porous water-absorbing crosslinked polymer (3). . The comparative porous water-absorbing crosslinked polymer (3) had a water absorption rate of 42 g / g and a water absorption rate of 20 minutes.
[0043]
【The invention's effect】
According to the present invention, it is possible to provide a novel porous water-absorbing crosslinked polymer that can significantly improve the water absorption characteristics such as the water absorption rate and the water absorption ratio and can maintain the water absorption characteristics even after long-term storage.
[Brief description of the drawings]
FIG. 1 is an IR of a porous hydrophobic crosslinked polymer (a).
FIG. 2 is an IR of the porous water-absorbing crosslinked polymer (1) of the present invention after hydrolysis.

Claims (5)

  A porous hydrophobic crosslinked polymer containing a carboxylic acid ester group represented by the general formula -COOR (wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms) A process for producing a porous water-absorbing crosslinked polymer that is hydrophilized by hydrolysis. The method for producing a porous water-absorbent crosslinked polymer according to claim 1 , wherein the hydrolysis of the porous water-absorbent crosslinked polymer is performed using an aqueous solution of an alkali hydroxide. The porous hydrophobic crosslinked polymer comprising a carboxylic acid ester group represented by the general formula -COOR (wherein R is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 30 carbon atoms) Is a water-in-oil type comprising a monomer having a solubility parameter (SP value) of 9 or less and a monomer component mainly composed of a crosslinkable monomer having at least two polymerizable unsaturated groups in the molecule. The method for producing a porous water-absorbent crosslinked polymer according to claim 1 or 2 , which is obtained by curing the emulsion at a temperature of less than 60 ° C. A porous water-absorbing crosslinked polymer obtained by the production method according to any one of claims 1 to 3, wherein the water absorption rate of physiological saline (0.9% saline) is 5 to 21 seconds. Water-absorbent crosslinked polymer. A water-absorbing article comprising the porous water-absorbing crosslinked polymer according to claim 4.

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