GB2313124A - Water-absorbent or water-retention material - Google Patents

Description

2313124 WATER-ABSORBENT OR WATER-RETENTION MATERIAL The present invention

relates to a water-absorbent or water-retention material comprising water-absorbent resin which is excellent in stability and has salt resistance. More particularly, the present invention relates to a water-absorbent or water-retention material comprising a water- absorbent resin derived from unit components comprising hydroxyl group- containing water soluble mono-(meth)acrylate; (meth)acrylic acid and/or alkali metal salt thereof; and crosslinking agent at predetermined ratios as essential components. Herein, the term "(meth)acryl--" denotes "acryl-- " and/or "methacryl--". The same shall apply hereinafter.

Hitherto. water-absorbent resins have been widely used in hygienic materials such as sanitary materials and paper diapers, water retainers for soil and the like. Water insoluble crosslinked polymer is known as such water-absorbent resins. Examples of the above mentioned waterabsorbent resins include crosslinked polyacrylic acid salts, selfcrosslinking type polyacrylic acid salts, crosslinked copolymer of starchgrafted acrylic acid salts.

Such acrylic water-absorbent resins are highly absorbent of solutions having relatively low concentration of ions, for example water or urine, but the absorbency is much less of an aqueous solution containing a high concentration of metal ions, for example sea water or cement slurry which contains a great amount of calcium ions. Moreover, in the case where an acrylic water-absorbent resin is used in the form of hydrogel, in a condition in which free radicals are generated in a molecule, for example, by exposure to the light or by being held at a high temperature for a long time, a cleavage in the main chain of the polymer occurs due to the radicals. As a result, the gel elasticity deteriorates a lot. Furthermore, the acrylic resins cannot retain the form of gel.

As a water-absorbent resin which increases the absorbency of an aqueous solution containing metal ions, for example, sea water, cement slurry or the like, the following (1) to 3 have been suggested.

(1) A crosslinked polymer of sulfonic acid monomer (salt) or a crosslinked copolymer of sulfonic acid monomer (salt) with aclyric acid (salt) (disclosed in Japanese Laid Open Patent Application Tokkai Sho No. 56-161412, Tokkai Hei No. 61-36309 etc.). Herein, "sulfonic acid monomer (salt)" denotes sulfonic acid monomer and/or sulfonic acid salt monomer; and "acrylic acid (salt)" denotes acrylic acid and/or acrylic acid salt. Similar expressions are used hereinafter.

(g) A crosslinked copolymer of acrylic acid salt and poly (vinyl alcohol) (PVA) (disclosed in Japanese Laid Open Patent 2 Application Tokkai Sho No. 53-104691.) 3 A crosslinked copolymer of acrylamide and acrylic acid (salt) (disclosed in Japanese Laid Open Patent Application Tokkai He! No. 4- 45850.) However, in (1) above, the dissociation degree of sulfonic acid is higher than that of carboxylic acid. Therefore, the polymer of (1) above has relatively high absorbency of an aqueous solution containing a monofunctional metal salt, for example sea water, but in an aqueous solution containing polyvalent metal ion, for example in a cement slurry containing a great amount of polyvalent metal such as calcium ions, crosslinking occurs due to the polyvalent metal, so that the absorbency deteriorates.

Moreover, in general, the polymer of (1) above copolymerizes, mainly with sulfonic acid monomer. However, this sulfonic acid monomer does not polymerize sufficiently readily, cannot easily increase the molecular weight of the polymer, and the gel elasticity of the resulting polymer is not excellent. Moreover, the market price of such sulfonic acid monomer is high, and thus this type of polymer is uneconomical.

In (2) above, PVA which is a copolymerization component is a hydrophilic nonionic compound. If the compolymerization ratio of PVA is increased, the absorbency is relatively increased in the presence of a great amount of a polyvalent metal salt such as calcium. The crosslinking copolymer of PVA-acrylic acid (salt) 3 is generally produced by copolymerizaing acrylate, vinyl acetate and hydrophobic crosslinking agent and then saponifying with alcoholic alkali. Therefore, the molecular weight of the crosslinking copolymer cannot easily be increased and the gel strength of the polymer in a solution of metal salt is weak as compared with a polymer produced by the general aqueous solution polymerization.

Moreover, during saponification, excess alkali or byproduced sodium acetate or methanol must be removed by washing, thus making the process complicated.

In 3 above, since acrylic amide is a hydrophilic nonionic compound and the polymerization propensity of the monomer is excellent, the absorbency of an aqueous solution of metal salt containing a great amount of polyvalent metal and the gel strength of the polymer is relatively good as compared with the method described in the above (1) and (2). However, in the case where a great amount of alkali exists, for example in a cement composition, the acrylic amide is hydrolyzed and ammonia gas is generated. Consequently, the operation environment deteriorates, or the moulded cement composition product emits an odour of ammonia.

Moreover, in (1) and 3 above, in general, sulfonic acid monomer or (meth)acrylic acid monomer are polymerized by the method of aqueous solution polymerization or reversed phase 4 suspension polymerization after neutralization. Examples of the crosslinking agents used in (D and (1, in general, include water soluble crosslinking agents having amide groups or ester groups in the molecule, for example, NX-methylenebis acrylamide or trimethylol propane triacrylate and a crosslinking agent generating ester groups by crosslinking reaction, for example, ethylene glycol diglycidyl ether. Consequently, in a high alkaline solution such as cement slurry, amide groups and ester groups in a crosslinking agent are hydrolyzing, so that the gel elasticity of the polymer deteriorates a great deal.

The present inventors earnestly have studied the means to solve the abovementioned problems of (D-(3) above and worked out a water-absorbent resin derived from monomer unit components, at the predetermined ratio, comprising hydroxyl group-containing water soluble mono-(meth)acrylate and (meth)acrylic acid (alkaline metal salt). The water-absorbent resin of the present invention has a high absorbency of aqueous solution having large amounts of polyvalent metal, for example a cement slurry; has a high gel elasticity of the polymer; and exhibits excellent gel stability when exposed to the light. Moreover, the present inventors also found that in the case where the resin of the present invention has a structure having the resistance to alkaline hydrolysis, the gel stability is excellent if exposed to high temperature under alkaline conditions.

The present invention provides to a water-absorbent or water-retention material comprising a water-absorbent polymer (A) derived from monomer unit components comprising 40 to 99 wt. % of a hydroxyl groupcontaining water soluble mono-(meth)acrylate (a); 1 to 60 wtA of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid alkali metal salt, and methacrylic acid alkali metal salt (b) (hereinafter, "(meth)acrylic acid (alkaline metal salt) (b) will be used.); 0.00001 to 3 wtA of crosslinking agent (c); and optionally not more than 10 wtA of another water soluble ethylenically unsaturated monomer (d). In addition, the present invention relates to a waterabsorbent or waterretention material comprising the water-absorbent resin (A) having a hydrolysis resistant crosslinking structure.

In the present invention, the hydroxyl group-containing water soluble mono-(meth)acrylate (a) need only have a hydroxyl group in the molecule and is water soluble mono-(meth)acrylate. Examples of such water soluble mono-(meth)acrylates include hydroxyalkyl mono-(meth)acrylate containing 2 to 4 carbon atoms in the alkyl group, mono(meth)acrylate of polyalkylene glycol (containing 2 or 3 carbon atoms in the alkylene group; polymerization degree: 2 to 20 or higher) such as mono(meth)acrylate of polyethylene glycol (polymerization degree: 2 to 20), mono(meth)-acrylate of polypropylene glycol (polymerization degree: 2 to 10); as well as mono-(meth)alkyl ethers of the corresponding polyalkylene glycol, and the like.

Preferred among the above is hydroxyalkyl (meth) acrylate containing 2 or 3 carbon atoms in the alkyl group and mono(meth)acrylates of polyethylene glycol (polymerization degree: 2 to 20). Specific examples of the preferred hydroxyalkyl (meth)acrylate include 8 -hydroxyethyl (meth)acrylate, 8 -hydroxypropyl (meth)acrylate, 7 -hydroxypropyl (meth)acrylate and mono(meth)acrylates of polyethylene glycol (polymerization degree: 2 to 20).

The copolymerization ratio of hydroxyl group-containing water soluble mono (meth)acrylate (a) is generally 40 to 99 wt. %, more preferably 60 to 95 wt.%. It is not preferable for the copolymerization ratio of hydroxyl group-containing water soluble mono-(meth)acrylate to be less than 40 wt. % since the absorbency of aqueous salt solutions deteriorates. In the meantime, it is not preferable for the copolymerization ratio of hydroxyl groupcontaining water soluble mono-(meth)acrylate to be more than 99 wt. % since the absorbing rate deteriorates.

In the present invention, examples of (meth)acrylic acid (alkaline metal salt)(b) used for the copolymerization include (meth)acrylic acid and (meth)acrylic acid alkali metal salts such as Na or K.

In general, the neutralization degree of the (b) unit in 7 the water-absorbent resin (A) is 40 to 100 mol%, more preferably 60 to 100 mol%. It is preferable to make the neutralization. degree 40 mol % or more since (meth)acrylic acid salts dissociate sufficiently and high absorbency and high absorbing rate can be attained.

In general, the neutralization of (meth)acrylic acid can be conducted by adding alkali metal hydroxide (for example, sodium hydroxide, potassium hydroxide, lithium hydroxide or the like).

The neutralization of (meth)acrylic acid is conducted on the monomer before polymerization, or by adding alkali metal salts into the hydrogel after polymerization. However, in the case where the below mentioned hydrolysis resistant allyl ether crosslinking agent which does not contain an amide group or an ester group is used as a crosslinking agent (c), the crosslinking agent has low hydrophilicity. Therefore, it is preferable to conduct polymerization before neutralization since the crosslinking agent can be homogeneously dissolved.

In the present invention, the copolymerization ratio of (meth)acrylic acid (alkali metal salt) (b) is usually 1 to 60 wt. %, more preferably 5 to 40 wt.%. If the ratio of (meth)acrylic acid (alkaline metal salt) (b) is less than 1 wt. %, the absorbing rate of the water-absorbent or waterretention material decreases.

8 On the other hand, if the copolymerization ratio of (meth)acrylic acid (alkali metal salt) is more than 60 wt. %, the copolymerization ratio of hydroxyl group-containing water soluble mono-(meth)acrylate (a) is deteriorated, so that the absorbency of an aqueous solution of salt deteriorates.

In the present invention, when the hydroxyl groupcontaining water soluble mono-(meth)acrylate (a) and (meth)acrylic acid (alkali metal salt) (b) are copolymerized, optionally 0 to 10 wt.% of another water soluble ethylenically unsaturated monomer (d) may be copolymerized together.

Such water soluble ethylenically unsaturated monomer need only be a water soluble ethylenically unsaturated monomer that is copolymerizable with hydroxyl group-containing water soluble mono(meth)acrylate and (meth)acrylic acid (alkaline metal salt). Examples of such water soluble ethylenically unsaturated monomers include acrylamide, sulfoalkyl (meth)acrylate or alkali metal salt thereof, 2-acryl amide-2-methyl propane sulfonic acid and alkali metal salt thereof, styrene sulfonic acid and alkali metal salt thereof, maleic acid, itaconic acid or the like. Moreover, two or more types of these water soluble ethylenically unsaturated units may be used in combination at the predetermined range of amount.

In the present invention, in order to obtain the waterabsorbent resin (A) which has excellent salt resistance, the 9 crosslinking agent (c) is used. Examples of the crosslinking agent (c). include a radical compolymerizable crosslinking agent having two or more double bonds in the molecule (cl) and a reactive crosslinking agent having two or more functional groups that react with a hydroxyl group and/or carboxyl group (c2).

In a case where (cl) is used, (cl) is added during polymerization and copolymerized in the presence of a hydroxyl group-containing water soluble mono-(meth)acrylate (a), (meth) acrylic acid (alkali metal salt) (b) and optionally another water soluble ethylenically unsaturated monomer (d).

In a case where (c2) is used, (c2) is added during and/or after polymerization and if necessary, crosslinking is conducted while heating.

The polymerizable crosslinking agent (cl) need only have two or more double bonds in the molecule and can be copolymerized with hydroxyl groupcontaining water soluble mono-(meth)acrylate (a), (meth)acrylic acid (alkaline metal salt) (b) and another water soluble ethylenically unsaturated monomer (d) which is optionally added.

Specific examples of (cl) include N,W-methylenebis acrylamide, ethylene glycol di-(meth)acrylate, trimethylol propane di-or tri-(meth)acrylate, pentaerythritol di (meth)acrylate, pentaerythritol tri-(meth)acrylate, pentaerythritol tetra-(meth)acrylate, glycerol diallylether, 1 0 glycerol triallylether, trimethylol propane diallyl ether, trimethylol propane triallyl ether, pentaery.thritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether and triallyl oxyethane.

In addition, commercially available products of water soluble hydroxyl group-containing mono-(meth)acrylate (a) usually contain approximately 0. 05 to 1.0 wtA of di-(meth)acrylate monomer which is a crosslinking component. This is the same as that of the copolymerization of (cl) component, so that the crosslinking agent need not be added, depending on the content of di-(meth)acrylate component.

These radical polymerizable crosslinking agents (cl) may be used alone, or two or more types of crosslinking agents may be used at an amount within the predetermined range.

Examples of the reactive crosslinking agent (c2) having two or more functional groups which react with hydroxyl groups and/or carboxyl group include a polyvalent glycidyl compound represented by ethylene glycol diglycidyl ether, a polyvalent isocianete compound represented by diphenylmethane-2,4'-and/or 4,4'-diisocyanates (MDI), and a polyvalent amine compound represented by ethylene diamine. These reactive crosslinking agents may be used alone, or two or more types of crosslinking agents may be used in combination at the predetermined ratio. Moreover, these reactive agents may be used in combination with the polymerizable crosslinking agents (cl).

Among these polymerizable crosslinking agents (cl) and the reactive crosslinking agents (c2), preferred are crosslinking agents providing a hydrolysis resistant crosslinking structure for the porpose of improving gel stability and hydrolysis resistnace under alkaline conditions or even at high temperature.

Such crosslinking agents include, for example, a crosslinking agents which has neither amide group nor ester group and produces neither amide group nor ester group by crosslinking reaction.

Specific examples include polyvalent allyl ethers such as glycerol diallyl ether, glycerol triallyl ether, trimethyrol propane diallyl ether, trimethylolpropane triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, and triallyl oxyethane.

The amount of crosslinking agent (c) varies depending on the absorbency, the gel elasticity of the required waterabsorbent resin (A) and a kind of the crosslinking agent, but it is generally in the range of 0.00001 to 3 wt.%, more preferably in the range of 0.0001 to 1 wt.%. If the amount is less than 0.00001 wt.%, the gel elasticity is too low. On the other hand, if the amount is more than 3 wt.%, the crosslinking density increases too much and thereby the absorbency is deteriorated.

As mentioned above, commercially available monomer of hydroxyl groupcontaining water soluble mono-(meth)acrylate (a) 12 generally contains 0.05-1.0 wtA of di-(meth)acrylate monomers which are a crosslinking components. However, if the content of di-(meth)acrylate monomers are too high, the crosslinking density is highly increased and thereby the absorbency deteriorates or the hydrolysis resistant crosslinking agent cannot be used.

Therefore, the content of di-(meth)acrylate monomers in (a) which is used in the present invention is generally not more than 0.5 wtA, preferably not more than 0.2 wt.%, more preferably not more than 0.1 wt.%. It is not preferable to make the content of di-(meth)acrylates monomer more than 0. 5 wtA since the crosslinking degree of water-absorbent resin is too high and the absorbency deteriorates, although it varies depending on the intended uses. Furthermore, in di(meth)acrylate monomer components, the ester part tends to be hydrolyzed and the crosslinking structure tends to be broken under alkaline conditions, for example in a cement composition, thus making the stability of the absorbent resin poor.

The method for decreasing the content of di-(meth)acrylate monomers in (a) can be any method to decrease the content of di(meth)acrylate monomers in (a) to below the predetermined content. Examples of the above mentioned methods include the method of using a monomer having a high refining degree by distillation; and the method of decreasing the content of di(meth)acrylate components in the monomer by adding water and 13 organic solvent (hexane, toluene, fatty acid ester or the like) and extracting di(meth)acrylate monomers to the side of the organic solvent layer.

The method of copolymerizing in the presence of hydroxyl group-containing water soluble mono-(meth)acrylate (a), (meth)acrylic acid (alkali metal salt) (b), polymerizable crosslinking agent (cl), and optionally another water soluble ethylenically unsaturated monomer (d), a conventional wellknown method can be used. Examples of such conventional copolymerization methods include polymerization adding a radical polymerizable initiators and polymerization by irradiating with radioactive ray, ultraviolet ray or electron beams.

In the method of using the radical polymerization initiator, examples of such initiators include azo compounds such as azobiscyanovaleric acid, and 2,2'-azobis (2-amidino propane) hydrochloride; inorganic peroxides such as hydrogen peroxide, potassium persulfate, ammonium persulfate and sodium persulfate; organic peroxides such as di-t-butyl peroxide and cumene hydroperoxide; and redox initiators comprising the combination of a reducing agent such as alkali metal sulfite or alkali metal bisulfite, Ammonium sulfite, ammonium bisulfite, Lascorbic acid or the like, and a peroxide such as alkali metal persulfate, Ammonium persulfate, hydrogen peroxide; and a combination of two or more of these.

14 The method of polymerizing in the presence of such initiator is not particularly limited. For example, the polymerization temperature may be varied depending on the types of initiators, but it is generally in the range of -109C to 100t A more preferable temperature for increasing a molecular weight is in the range of -10t to 80t.

The amount of the initiator is not particularly limited, but it is preferable that the amount is in the range of 0.000001 to 3.0 wtA with respect to the total weight of the monomer. More preferably it is in the range of 0.000001 to 0.5 wt.%.

As a solvent during polymerization, a solvent having less chain transfer, that is, water is generally used; thereby an aqueous solution polymerization is conducted. However, so called reversed phase suspension polymerization can preferably be used. In the reversed phase suspension polymerization, an aqueous solution of monomer is dispersed or suspended in the hydrophobic solvent (for example, hexane, toluen, xylene or the like) in the presence of a dispersing agent if necessary.

In the present invention, the water-absorbent resin (A) is obtained optionally by drying the hydrogel which is obtained by the polymerization. As the drying method, a conventional well known method can be adopted. In case of a polymer obtained by aqueous solution polymerization, drying methods include air permeating drying or through air drying (band type drying or the 1 5 like) or ventilation drying (air circulating drying or the like), and contacting drying (drum dryer drying or the like), which are conducted after the obtained hydrogel was pulverized. In case of a polymer obtained by reverse phase suspension polymerization, drying methods include depressurization drying or ventilation drying, which are conducted after a solid-liquid separation.

The drying of the hydrogel is generally conducted at not more than 150t, more preferably at not more than 130T. If the hydrogel is dried for a long time at more than 150t, the crosslinking of hydroxyl group and carboxylic acid group proceeds excessively at the stage where water is dried out. Thus, the absorbency occasionally deteriorates.

In the present invention the dried polymer is optionally pulverized to obtain a predetermined particle size. As the pulverizing method, a conventional well known method may be adopted. Examples of a pulverizing method include using an impact pulvelizer (such as pin mill, cutter mill, pulpelyzer, centrifugal mill or the like), or an air pulverizer (such as jet mill or the like).

The particle size of the pulverized product varies depending on the intended uses, but for the purpose of the improvement of retaining the shape of the extrusion of a cement composition, the particle size is usually in the range of 1 to 1000p m, more preferably in the range of 1 to 500g m. On the 16 other hand, in the case where the pulverized product is mixed into rubber as a sealing materials for an aqueous solution containing cement solution for civil engineering, the particle size of the pulverized product is usually in the range of 0.1 to 100p m, more preferably in the range of 0. 5 to 50m m.

In the present invention, for the purpose of increasing the water abosorption rate and preventing the size-controlled water-absorbent resin from forming lumps when water is absorbed, the size controlled waterabsorbent resin, which is surface crosslinked by adding the above mentioned reactive crosslinking agents (c2) and heating thereof, may optionally be used as the absorbent resin (A).

The temperature of the surface crosslinking is generally not more than 1509C. It is preferable to make the crosslinking temperature not more than 1500C since the extreme increase of the crosslinking degree due to a reaction between hydroxyl group and carboxylic, acid group in the resin and the decrease of the absorbency can be inhibited.

The heating apparatus used for conducting the surface crosslinking may be any apparatus to heat particles homogeneously. Examples of such heating apparatus include a hotair drier, a rotary drier, a paddle drier, a rotaling disc drier, a fluidized bed drier, a belt type drier, a Nauta type heater, and an infrared drier.

1 7 The above mentioned water-absorbent resin (A) is the water-absorbent resin which is substantially water insoluble, excellent in stability, and salt resistant. In accordance with the present invention, has been provided a water-absorbent or water-retention material which is not easily subjected to the influence of salts and has high absorbency even to a high concentrated salt solution containing the high concentration of metal ion. A water-absorbent or water-retention material according to the present invention shows improved even towards polyvalent metal ion- containing aqueous solutions. Besides, water-absorbent or water-retention material of the present invention exhibits excellent stability even when the hydrogel is stored in a condition in which raidcals are generated, for example, the hydrogel is irradiated with light or heated.

The gel strength and the water absorbency of the above mentioned waterabsorbent resins can be controlled depending on the purpose of use. However, the absorbency of 10 wtA aqueous solution of calcium chloride is generally not less than 10 times as much as the water-absorbent resin, and the elasticity of the water swollen gel which absorbs 10 wtA aqueous solution of 2 calcium chloride is not less than 5000 N/m More preferably, the absorbency is not less than 15 times as much as the waterabsorbent resin, and the gel elasticity of the gel swollen with water is not less than 8000 N/m 2 18 The water absorbent resins (A) of the present invention may be applied for absorbing or retaining various aqueous liquids. Examples of suitable aqueous liquids include water (including soft water and hard water); aqueous liquids of relatively low ion content, for example, body fluids (body exudates, such as urine, menstrual discharge and wound exudates): and aqueous liquids containing larger amount of metal ion, for example, seawater and other saline waters.

The water-absorbent resins (A) of the present invention are particularly useful for absorbing or retaining aqueous dispersions containing polyvalent metal ions [ions of alkaline earth metals, such as calcium and magnesium, zinc, iron, tin, lead, copper and other transition or heavy metals], especially cement slurry having a high calcium ion content (for instance, 0.01% to 40 % by weight or more).

In adding water-absorbent resin (A) to cement slurry, the amount may vary widely according to purpose, applications and requirements therefor. The above mentioned resin (A) can be used in an amount of usually 0.01 to 10 % by weight or more, preferably 0.05 to 5 % by weight, based on the solid weight of cement contained in the slurry.

Therefore, in the case where the water-absorbent or waterretention material comprising the water absorbent resin (A) of the present invention is added into a cement slurry which is used 1 9 for extrusions moulding, such as material for cement outer walls, if too large pressure is applied during the extrusion moulding, the gel is not broken or does not generate water. Thus, the viscosity of the moulded cement slurry product can be increased or the shape of the moulded product can be kept.

Moreover, in the case where the water-absorbent resin (A) has a hydrolysis resistant crosslinking structure, if it is exposed to alkaline conditions at high temperature, the gel does not so deteriorate. Consequently, the shape of the moulded product can be maintained for a long time after extrusion.

In the case where the water absorbent resin (A) is used for producing a water swelling rubber by mixing with a rubber substrate such as EPDM (ethylene-propylene-diene terpolymer), chloroprene rubber, SBR (stylenebutadiene rubber) or the like with water absorbent-resin (A), a sealing material comprising salt resistant water-swellable rubber which has a high absorbing rate, high absorbency can be produced because the water absorbent resin (A) can swell by overcoming the elasticity and by absorbing a salt solution. Moreover, since the gel is excellent in stability in the state in which water is contained, the recontracting after swollen with water or deterioration of performance in preventing water-penetration can be inhibited.

The water-absorbent resin (A) may be added to a rubber or rubber-like base material in such an amount as to provide a 2 0 sealing composition containing the above mentioned resin (A) in an amount of 1 to 50% by weight or more, preferably 5 to 40% b_v weight, based on the weight of the above mentioned base material.

Moreover, the water-absorbent or water retention material of the presentinvention can preferably be used in applications requiring a high swelling rate, high swelling pressure, durability in sea water, for example, water-sealing material for optical fiber to be used on the bottom of the sea.

Furthermore, stability under irradiation by light in the hydrogel state is extremely good. Therefore, the water-absorbent resin of the present invention can be used for water retainers for soil, or cold insulation material, which are exposed to the direct sunlight.

In the present invention, the water-absorbent or waterretention materials may be added to, at an arbitrary step of producing water-absorbent resin (A), with additives such as antiseptic agents, antimould agents, disinfectants, antioxidants, ultraviolet-absorbers, coloring agents, perfume agents, and deodourants.

The present invention will be further illustrated with reference to Examples and Comparative Examples hereinafter. However, the present invention is not limited to the embodiments illustrated in the Examples and Comparative Examples herein.

The water-absorbent resin was evaluated in terms of the 2 1 following points (D-(9):

(I) absorbency of 10 wtA aqueous solution of calcium chloride; absorbency of artificial sea water; gel elasticity after absorbing 10 wt.% aqueous solution of calcium chloride and gel stability after heated; and 9) gel stability after irradiation with light.

Each value is calculated by the following procedure. Hereinafter, % represents wt.% unless otherwise noted. Absorbency of 10 % Aqueous Solution of Calcium Chloride (Q1):

2.Og of waterabsorbent resin powder and 500g of 10 wt.% aqueous solution of calcium chloride (pH = 10 to 11) were placed in a one-litre beaker and stirred at the rate of 50Orpm for one hour with a stirrer.

After the stirrer of a stirrer piece was removed, the entire solution was placed in a 330-mesh JIS standard sieve (size of mesh hole: 50gm, hole diameter: 20cm). Excess calcium chloride solution was drained off for 30 minutes. Then excess calcium chloride solution retained between the screen and waterabsorbent resin was removed with tissue paper through the mesh of the sieve. Then, the total weight of the water swollen waterabsorbent resin and the sieve was measured. The absorbency of 10 % aqueous solution of calcium chloride (Q1) was calculated from 2 2 the below-mentioned formula.

Q1.= [(total weight of a water-absorbent resin swollen with water and sieve) - (weight of the sieve)] / 2.0 Thus, the absorbency of 10 % aqueous solution of calcium chloride (Q1) is the weight (unit: g) of 10 % aqueous solution calcium chloride which was absorbed by 1g of the water- absorbent resin powder.

(2) Absorbency of Artificial Sea Water (Q2):

2.Og of water-absorbent resin powder and 500g of artificial sea water C'Mqamarine", the product by YASHIMA YAKUMN CO., LTD.) were placed in a one-litre beaker and stirred at the rate of 50Orpm for one hour by the use of a stirrer.

After a stirrer piece of the stirrer was removed, the entire solution was placed in a 330-mesh JIS standard sieve (size of mesh hole: 50m m, hole diameter: 20cm). Excess artificial sea water was drained off for 30 minutes.

Then excess artificial sea water retained between the sieve and waterabsorbent resins was removed with tissue paper through the net hole of the sieve. Then, the total weight of the water-swollen water-absorbent resin and the sieve was measured. The absorbency of artificial sea water (Q2) was calculated from the below-mentioned formula.

Q2 = [(total weight of water-absorbent resin swollen with water and sieve) - (weight of sieve)] 2.0 2 3 Thus, the absorbency of artificial sea water means that the weight (unit: g) of artificial sea water absorbed by 1g of water-absorbent resin powder.

(5) Gel Elasticity (E 0) and Stability of Heated Gel of 10% Aqueous Solution of Calcium Chloride:

When the absorbency of 10 % aqueous solution of calcium chloride was measured, 0.2g of hydrogel left on the sieve was taken out and placed on a polytetrafluoroethylene measurement board of a creep meter (the product of YAMADEN CO., LTD) equipped with plunger No. 1.

This plunger was advanced towards the measurement board at the rate of 0. 5mm/second, and the gel was pressed evenly on the measurement board until 10 g of load was applied to the plunger, and the distance (H 0) between the plunger and the measurement board under 10g of load was measured.

The load on the plunger was set to be 50g and the gel was further pressed until 50 g of load was applied to the plunger. The distance (H 1) when the shape of gel instantaneously changed was measured by the use of an attached automatic analyzer. The Hookean elasticity (E 0) was calculated from the below-mentioned formula; the value was the gel elasticity.

gel elasticity (E 0 p 0 /H 1 /H 0 (dyne/cm 2) [(P 0 /H 1 /H 0)x(l/10)] (N/m 2 p 0 (stress) = F X 980/S (dyne/cm 2 [(F X 980/S)X(l/10)l(N/m 2 2 4 F (load)(g)= 50 S (sectional area)(cm 2 V/(H 0 - H 1) V (volume of sample)(cm3 sample weight(g) / relative density (g/cm 3) (1.15) 5g of the hydrogel left on the sieve was placed in a 6 X 8cm polyethylene bag having fastener, heated thereof at 90t for 10 hours and then cooled down to room temperature. 0.2 g of the heated hydrogel was taken out and the gel elasticity was measured through a procedure similar to that mentioned above, followed by calculation of the stability of the heated gel from the below mentioned formula.

Formula: stability of heated gel (%) = (gel elasticity after heating / gel elasticity before heating) X 100 (A) Gel Stability after Light Irradiation 1.0 g of water-absorbent resin and 49.Og of deionized water were placed in a 100m1 beaker to produce a hydrogel containing 50 times as much water.

0.2 g of this hydrogel was taken out and the gel elasticity before light irradiation was measured by the use of a creep meter under the following conditions. The value was the gel elasticity.

gel elasticity (E 0 p 0 /H,/H, (dyne/cm 2 [(P 0 /H 1 /H 0)x(l/10)] (N1m 2 p 0 (stress) = F X 980/S (dyne/cm 2 [(F X 980/S)X(1/10)](N/m 2 2 5 F (load)(g)= 50 S (sectional area)(cm 2 V/(H 0 - H 1) V (volume of sample)(cm 3 sample weight(g) / relative density (g/cm 3) (1.0) 10g of the hydrogel containing 50 times as much water was placed in a 6 X 8 cm polyethylene bag having fastener, and irradiated with xenon light from a distance of 15cm. The irradiation was conducted at the blackboard temperature of 409C for 10 hours by the use of high energy xenon weatherometer [SUGA SHIKENKI Ind.].

After irradiation, the hydrogel was cooled down to room temperature. Then, 0.2 g of the irradiated hydrogel was taken out and the gel elasticity was measured by the use of a creep meter through the procedure similar to mentioned above, followed by calculation of the gel stability when light was irradiated from the below mentioned formula.

Formula: gel stability at the time of light irradiation (gel elasticity after irradiation / gel elasticity before irradiation) x 100 Example 1 260g (80 mol%) of commercially available 2hydroxyethylacrylate (the content of di-(meth)acrylate monomer is 0.15 %, the product of OSAKA YUMKAGMU Ind.), 40g (20 moM of acrylit acid, 44g of 48 % aqueous solution of sodium hydroxide, 2 6 and 656g of water were placed in a one-litre beaker and cooled down to 10t This solution was placed in a polymerizing vessel which allows adiabatic polymerization. By introducing nitrogen gas thereto, the amount of dissolved oxygen in the solution was reduced to 0.1ppm. Then 0.007 g of 35 % aqueous solution of hydrogen peroxide, 0.0025 g of L-ascorbic acid, and 0.125 g of 4X-azobis (2-amidinopropane) dihydrochloride were added thereto.

After approximately 30 minutes, the initiation of polymerization was observed. After approximately 2 hours, the solution reached the peak temperature, 660C. After 5 hour maturation at this temperature, the polymerization was completed.

The obtained polymer had a hydrogel.

This obtained hydrogel was pulverized with a meat grinder.

Then, the pulverized hydrogel was neutralized by adding and kneading in the presence of an aqueous solution of sodium hydroxide. The neutralized hydrogel was dried at 1200C for one hour by the use of a band type drier (air permeating drier, the product by INOUE KINZM Ind.). The dried product was pulverized to obtain the absorbent resin (1) having a particle size of 50500p m. The analyzed results of the quality of this product was shown in Table 1. Example 2 2 7 260g (80 mol%) of commercially available 2hydroxyethylacrylate [the content of di(meth)acrylate monomer is. 0.15 %, the product of OSAKA YUM- KAGAW Ind.], 700g of water and 50g of toluene were placed in a one-litre separating funnel. The water layer was separated by extracting di- (meth)acrylate monomer into the toluene layer, and then an aqueous solution of 2hydroxyethyl acrylate was obtained by removing di(meth)acrylate monomer.

960g of this aqueous solution of 2-hydroxyethylacrylate, 40g of acrylic acid, and 0.05g of pentaerythritol triallyl ether [the product of DAISO Co. Ltd.] as a crosslinking agent were placed in a one-litre beaker and cooled to 10t - This solution was placed in a polymerizing vessel which allows adiabatic polymerization. By introducing nitrogen gas thereto, the amount of. dissolved oxygen in the solution was reduced to 0.1ppm. Then, 0.007 g of 35 % aqueous solution of hydrogen peroxide, 0.0025 g of L-ascorbic acid, and 0.125 g of 4Xazobis (2-amidinopropane) dihydrochloride were added thereto.

After approximately 30 minutes, the initiation of polymerization was observed. Approximately after 2 hours, the solution reached the peak temperature, 66t. After 5 hour maturation at this temperature, the polymerization was completed.

The obtained polymer was in a hydrogel state. This 2 8 obtained hydrogel was pulverized with a meat grinder. Then, the pulverized hydrogel was neutralized by adding and kneading in the presence of 44g of 48% aqueous solution of sodium hydroxide. The neutralized hydrogel was dried at 120t for one hour by the use of a band type drier (air permeation drier, the product by INOUE KINZM Ind.). The dried product was pulverized to obtain the absorbent resin (2) having the particle size of 50 to 50Omm. The analyzed results of the product quality are shown in Table 1. Example 3 243.6g (70 moM of commercially available 2hydroxyethylacrylate [the content of di-(meth)acrylate monomer is 0.05 %, the product by OSAKA YUMKAGMU Ind.], 60.5g (28 mol %) of acrylic acid, 10.7g of sulfoethyl acrylate, 0.03g of glycerol diallyl ether (the product by DAISO Co. Ltd.) and 685g of water were placed in a one-litre beaker and cooled to 10T This solution was placed in a polymerizing vessel which allows adiabatic polymerization. By introducing nitrogen gas thereto, the amount of dissolved oxygen in the solution was reduced to 0.1ppm. Then 0.07 g of 35 % aqueous solution of hydrogen peroxide, 0.025 g of L-ascorbic acid and 0. 15 g of potassium persulfate were added thereto. The nitrogen purge was continued till the viscosity of the monomer solution increased.

After approximately 60 minutes, the initiation of the polymerization was observed. After approximately 6 hours, the 2 9 solution reached the peak temperature, 739C and the polymerization was completed. The obtained polymer was in a hydrogel state. This obtained hydrogel was pulverized with a meat grinder. Then the pulverized hydrogel was neutralized by adding and kneading in the presence of 66g of 48% aqueous solution of sodium hydroxide. The neutralized hydrogel was dried at 130t for five minutes by the use of a drum drier. The dried product was pulverized to obtain the absorbent resin (3) having a particle size of 50 to 500,a m. The analyzed results of the quality of the product was shown in Table 1. Example 4 240g of commercially available monoacrylate of polyethylene glycol (polymerization degree: 6 to 8), 60g of acrylic acid, 66g of 48 % aqueous solution of sodium hydroxide, and 656g of water were placed in a one- litre beaker and cooled down to 10t.

This solution was placed in a polymerizing vessel which allows adiabatic polymerization. By introducing nitrogen gas thereto, the amount of dissolved oxygen in the solution was reduced to 0.1ppm. Then 0.007 g of 35 % aqueous solution of hydrogen peroxide, 0.0025 g of L-ascorbic acid, and 0.125 g of 4,4'-azobis (2-amidinopropane) dihydrochloride were added thereto.

After approximately 30 minutes, the initiation of 3 0 polymerization was observed. After approximately 2 hours, the solution reached the peak temperature, 66t. After 5 hour maturation at this temperature, the polymerization was completed.

The obtained polymer had a hydrogel.

This obtained hydrogel was pulverized with a meat grinder.

Then, the pulverized hydrogel was neutralized by adding and kneading in the presence of an aqueous solution of sodium hydroxide. The neutralized hydrogel was dried at 1209C for one hour by the use of a band type drier (air permeating drier, the product by INOUE KINZOKU Ind.). The dried product was pulverized to obtain the absorbent resin (4) having a particle size of 50500m m. The analyzed results of the quality of this product was shown in Table 1. Comparative Example 1 The commercially available "SANWET IM-500OW [acrylic acid/sodium acrylate type water-absorbent resin, the product by Sanyo Chemical Industries, Ltd. ] was used as a comparative resin (1). The analyzed result of the quality of the product was shown in Table 1. Comparative Example 2 172.8g (0.80 mol) of sodium salt of sulfoethyl acrylate, 3.6g (0.05 mol) of acrylic acid, 14.1g (0.15 mol) of sodium acrylate, 0.154g (0.001 mol) of N,N'-methylenebisacrylamide and 260g of water were placed in a 500m1 separation flask. The 3 1 solution was stirred to dissolve thereof homogeneously. After the displacement by nitrogen, the solution,was heated by means of the hot water bath at 40t 1.Og of 10% aqueous solution of ammonium persulfate and 5g of 1% aqueous solution of L-ascorbic acid were added threrto. Then, stirring was stopped and the contents were polymerized.

After the initiation of polymerization, the generation of heat was observed. After 40 minutes, the temperature was 680C. After a temperature decrease of polymerization was observed, it was further heated for one hour by raising the temperature of a hot water bath to 90T - The hydrogel of the water-absorbent resin was pulverized. Then, the pulverized hydrogel was heated by the use of an air circulating drier at the temperature of 1500C for 5 hours, and the dried product was pulverized to obtain the comparative waterabsorbent resin (2). The analyzed results of this product quality was shown in Table 1. Comparative Example 3 3g of partially saponified poly(vinyl alcohol) as a dispersion stabilizer and 300m1 of water were placed in a onelitre separable flask. Then, 60g of vinyl acetate, 40g of methyl acrylate, 0.1g of divinylbenzene as a crosslinking agent and 0.5g of benzoyl peroxide as a polymerization initiator were added to the aqueous solution and stirred to disperse.

3 2 By introducing nitrogen gas, the dissolved oxide was displaced. Then the solution was heated to 65T by means of a hot water bath, and the suspension polymerization was conducted for approximately six hours to obtain the crosslinked copolymer.

10g of the obtained crosslinked copolymer was dispersed in 300m1 of methanol, and 70m1 of aqueous solution of sodium hydroxide of 5M (molar concentration) was added and saponified for five hours at the temperature of 609C.

After saponification, the saponified copolymer was washed with methanol and filtered repeatedly. Free sodium hydroxide and sodium acetate which was a by-product of saponification were removed. By drying under reduced pressure, the comparative waterabsorbent resin (3) was obtained. The analyzed result of the quality of the product was shown in Table 1. Comparative Example 4 31.Og of 80% of aqueous solution of acrylic acid was placed in the cylindrical circular four-neck flask having stirrer, circulating type cooler, dropping funnel and glass nitrogen introducing tube, and cooled from the outside while 95.5g of 13.0% aqueous solution of sodium hydroxide was dropped thereto to neutralize 90 mol% of acrylic acid.

Then, 293.9g of 25 wt.% of aqueous solution of acrylamide and 0.02g of NXmethylenebisacrylamide were added and the mixture stirred to homogeneously dissolve them.

3 3 0.1g of ammonium persulfate and 0.025g of sodium hydrogensulfite were added thereto and dissloved. followed by deaeration by introduction of nitrogen for 30 minutes.

The above mixed solution was heated to 509C by a hot water bath and then heated to 90t has the heat of the mixed solution itself. Then polymerization was completed after storage at 909C for one hour. The polymer was cracked, dried and pulverized to obtain a comparative waterabsorbent resin (4). The analyzed result of the quality of the product is shown in Table 1.

X c-ib 1 (-- 1 absorbency of aqueous solution of 1OwtA gel stability artificial calcium choloride after light sea water absorbency gel elasticity gel stability irradiation (g/g) (g/g) (N/m 2) after heated(%) Example 1 28 22 6000 35 80 Example 2 27 17 13500 95 85 Example 3 24 16 10800 95 86 Example 4 26 18 12800 94 81 Comparative 8 1 800 35 0 Example 1

Comparative 28 13 2300 11 0 Example 2

Com%parati 21 10 2600 90 75 Example 3

Comparative 26 16- 3600 21 0 Example 4 (odour of ammomi was emitted) 34 The following points are apparent from Table 1.

(D The water-absorbent resins (1) to (3) obtained from Examples 1 to 3 are better than the comparative water-absorbent resins (1) to (3) obtained from Comparative Examples 1 to 3 in terms of the absorbency of 10 wtA concnetration of aqueous solution of calcium chloride and of artificial sea water and the gel elasticity of 10 wtA aqueous solution of calcium chloride.

(2) The water-absorbent resins (1) to (3) obtained from Examples 1 to 3 are much better than the comparative waterabsorbent resins (1), (2), and (4) obtained from the Comparative Examples 1, 2, and 4 in terms of the gel stability after heating and the gel stability after light irradiation.

(5) Unlike the comparative water-absorbent resin (4) obtained from the Comparative Example 4, the water-absorbent resins (1) to (4) obtained from Examples 1 to 4 do not emit an odour of ammonia even if stored at high temperature under alkaline conditions.

The effect of the water-absorbent or water-retention material of the present invention will be explained as follows.

(1) The water-absorbent or water-retention material of the present invention comprises the water-absorbent resin (A). The water-absorbent resin (A) is not readily subject to the influence of salts and the absorbency does not deteriorate even if the ion concentration of the salt solution is increased, because it is 3 5 mainly comprised of a hydroxyl group-containing water soluble mono7(meth)acrylate which is a hydrophilic nonionic compound.

(2) The water-absorbent or water-retention material of the present invention contains a great numbers of hydroxyl groups. The hydroxyl groups trap radicals. Therefore, the gel hardly deteriorates, even if stored in a condition in which radicals are generated, for example, if the gel is exposed to light or heated. Thus the gel has excellent stability.

3 In the case where the water-absorbent or waterretention material of the present invention has the alkali hydrolysis crosslinking structure as its main structure, if the hydrogel is stored at a high temperature under alkaline conditions, the gel does not deteriorate and exhibits excellent stability.

(1) The present invention can provide an inexpensive salt resistant waterabsorbent resin since it is mainly comprised of a monomer whose market price is not unduly high and whose manufacturing process is simple.

(5) The water-absorbent or water-retention material of the present invention has excellent absorbency of aqueous solutions having a high calcium ion content, for example, cement slurry or the like. Consequently if the water-absorbent or water-retention material is added to cement slurry, the property of keeping shape of a moulded product of cement slurry is improved because of the 3 6 viscosity increase of the cement slurry. Moreover, the gel.elasticity is high, so that even if high.pressure is applied to a cement slurry by an extruder or the like, the hydrogel does not release the water component, thus exhibiting excellent waterretention property. In addition, when a cement or the like is matured under alkaline conditions at high temperature: the gel in the cement slurry hardly deteriorates and the shape is not easily lost during maturation.

Moreover, in the case where the cement slurry moulded product is a dried hardened product, the portion where waterabsorbent resin is present becomes closed cells (foam), so that the water-absorbent and waterretention material of the present invention can lose weight while maintaining the strength of the cement product.

(3) In the case where the water-absorbent or waterretention material of the present invention is kneaded into rubber or the like to produce a water swellable rubber, it has high absorbency of highly concentrated solution of salt. Consequently, the water-absorbent or waterretention material can absorb sea water or water bled out from moulded cement material. Since the gel elasticity after swelling water is high, the gel quickly swells by overcoming the elasticity of the rubber and can quickly achieve sealing in sea water and bled water. Moreover, since the waterabsorbent or water-retention material of the 3 7 present invention has excellent compatibility with rubber, the water- absorbent resin dose not easily fall out of the water swellable rubber. In addition, the gel is very stable even in the state of containing water, so that once the water swellable rubber swells, it does not easily re- contract due to deterioration of the gel, thus exhibiting good water- sealing performance.

(7) Since the hydrogel of the waterabsorbent or waterretention material of the present invention is excellent in stability to light, if it is used as a water-retainer for soil or as cold insulation which is subject to irradiation by sunlight.

As mentioned above, the water-absorbent or water-retention material of the present invention has various uses, for example admixture in the cement slurry, a waterretainer for plant or soil, a coagulant for hedoro (muddy sediment), a water-sealing material or packing material for construction, a water-sealing material for electric cable or optical fiber cable, and cold insulation.

38

Claims (11)

1. A water-absorbent or water-retention material comprising a waterabsorbent resin (A) derived from monomer unit components comprising 40 to 99 wtA of hydroxyl group-containing water soluble mono-(meth)acrylate (a); 1 to 60 wtA of at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, acrylic acid alkali metal acrylate, and alkali metal methacrylate (b); 0.00001 to 3 wtA of crosslinking agent (c); and optionally not more than 10 wtA of another water soluble ethylenically unsaturated monomer (d).

2. A water-absorbent or water-retention material according to claim 1, wherein said hydroxyl group-containing water soluble mono-(meth)acrylate (a) is hydroxy alkyl (meth)acrylate having 23 carbon atoms in the alkyl group.

3. A water-absorbent or water-retention material according to claim 1 or 2, wherein the neutralization degree of the monomer (b) unit in said water-absorbent resin (A) is in the range from 60 to 100 %.

4. A water-absorbent or water-retention material according to any of claims 1 to 3, wherein said water-absorbent resin (A) has a hydrolysis resistant crosslinking structure.

5. A waterabsorbent or water-retention material according to claim 4, wherein the crosslinking agent is polyallyl ether 3 9 compound.

6. A water-absorbent or water-retention material according to any of claims 1 to 5, wherein the absorbency of the waterabsorbent resin of 10 wtA concentration of aqueous solution of calcium chloride is not less than 10 g/g and the gel elasticity 2 of water-absorbent resin (A) is not less than 5000 N/m

7. A water-absorbent or water-retention material substantially as described with reference to the Examples.

8. A process for absorbing or retaining aqueous liquid, characterized in that a water-absorbent or water-retention material according to any of the preceding claims.

9. A process according to claim 8, wherein the aqueous liquid is water, a body fluid, sea water or other saline water, or a polyvalent metal ioncontaining aqueous dispersion.

10. A water-absorbent or water-retention material substantially as described with reference to the examples other than the comparative examples.

11. A process substantially as described with reference to the examples other than the comparative examples.