Water-absorbing resin particle, water stop material, and cable

Abstract

Provided are: a water-absorbing resin which has excellent swelling performance and of which the gel viscosity hardly decreases even at high temperatures; a water stop material containing the water-absorbing resin particles; and a cable.　The water-absorbing resin particles according to the present invention have a median particle diameter of 250 μm or less, the water absorption rate of physiological saline is 20 seconds or less, and the water absorption ratio represented by formula (1): water absorption ratio [%] = (A / B)×100 (in formula (1), A denotes the water absorption amount [g / g] when 0.5 g of water-absorbing resin particles are stirred in 500 g of water by using a rotor at a rotation speed of 100 rpm for 30 seconds in an environment at a temperature of 25±2°C and a humidity of 50±10%, and B denotes the water absorption amount [g / g] when 0.5 g of water-absorbing resin particles are stirred in 500 g of water by using a rotor at a rotation speed of 900 rpm for 30 seconds in an environment at a temperature of 25±2°C and a humidity of 50±10%) is 80% or more.

Description

Water-absorbent resin particles, water-stopping materials and cables

[0001] The present invention relates to water-absorbent resin particles, and a water-stopping material and a cable containing the water-absorbent resin particles.

[0002] It is known that water-absorbent resin particles have excellent water absorption capacity and can exert a water-stopping effect, and therefore can be applied to various applications where water-stopping is required. For example, water-absorbent resin particles are used as a water-stopping material for communication cables such as optical cables, power cables, etc.

[0003] For example, Patent Document 1 discloses a technology in which a water-stopping material is used, which is an absorbent sheet containing a water-absorbent resin enclosed in an exterior material, to prevent the gel of the absorbent resin that swells after absorbing water from seeping out.

[0004] JP 2014-147281 A

[0005] The water-absorbent resin particles used in cable waterstop tapes are generally required to have a fast water absorption rate, so that when water penetrates into the cable, they must quickly absorb water and swell to stop the water from entering. However, after the water-absorbent resin particles in the waterstop material swell, the swollen gel is affected by the heat generated by the cable and deteriorates. Even if water-absorbent resin particles have a fast water absorption rate and excellent swelling performance, if their gel viscosity decreases at high temperatures, they will not be able to function as a waterstop material. This has been a problem when using water-absorbent resin particles as a waterstop material. In other words, water-absorbent resin particles used in waterstop materials must have excellent swelling performance and also the property of being resistant to a decrease in gel viscosity even at high temperatures.

[0006] The present invention has been made in view of the above, and aims to provide water-absorbent resin particles that have excellent swelling performance and also have the property of being resistant to a decrease in gel viscosity even at high temperatures, and a water-stopping material and a cable that contain the water-absorbent resin particles.

[0007] As a result of intensive research to achieve the above-mentioned object, the present inventors have found that, in the case of water-absorbent resin particles having a specific particle size, the ratio of the water absorption amounts under two different types of water absorption conditions contributes to suppressing a decrease in the swelling performance and gel viscosity of the water-absorbent resin particles. That is, the present inventors have found that the above-mentioned object can be achieved by setting the ratio within a specific range, and have thus completed the present invention.

[0008] That is, the present invention encompasses, for example, the subject matter described in the following items. Item 1: Water-absorbent resin particles having a median particle size of 250 μm or less, a water absorption rate for physiological saline solution of 20 seconds or less, and a water absorption ratio of 80% or more, as represented by the following formula (1): water absorption ratio [%]=(A / B)×100 (1) (in formula (1), A represents the amount of water absorption [g / g] when 0.5 g of the water-absorbent resin particles are stirred in 500 g of water at a rotation speed of 100 rpm using a rotor for 30 seconds under an environment of 25±2° C. and humidity of 50±10%, and B represents the amount of water absorption [g / g] when 0.5 g of the water-absorbent resin particles are stirred in 500 g of water at a rotation speed of 900 rpm using a rotor for 30 seconds under an environment of 25±2° C. and humidity of 50±10%). Item 2: The water-absorbent resin particles according to Item 1, having a pure water absorption of 500 g / g or less. Item 3: A water-stopping material containing the water-absorbent resin particles according to Item 1 or 2. Item 4: A cable containing the water-stopping material according to Item 3. Item 5: A method for producing the water-absorbent resin particles according to Item 1 or 2, the method comprising a step of obtaining polymer particles by a polymerization reaction using a raw material containing a water-soluble ethylenically unsaturated monomer. Item 6: The production method according to Item 5, wherein the raw material contains an internal crosslinking agent. Item 7: The production method according to Item 5 or 6, wherein the polymer particles are crosslinked with a post-crosslinking agent.

[0009] The water-absorbent resin particles of the present invention have excellent swelling properties and also have the property that the gel viscosity is unlikely to decrease even at high temperatures.

[0010] FIG. 2 is a schematic diagram of a measuring device used to measure the swelling height of water-absorbent resin particles.

[0011]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0012] In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example or a value that can be unambiguously derived from an example. In addition, in this specification, a numerical value connected with "to" means a numerical range that includes the numbers before and after "to" as the lower and upper limits.

[0013] 1. Water-absorbent resin particles The water-absorbent resin particles of the present invention have a median particle diameter of 250 μm or less, a water absorption rate for physiological saline solution of 20 seconds or less, and a water absorption ratio of 80% or more, as expressed by the following formula (1): Water absorption ratio [%] = (A / B) × 100 (1) In formula (1), A represents the amount of water absorption [g / g] when 0.5 g of the water-absorbent resin particles are stirred in 500 g of water at 100 rpm using a rotor for 30 seconds under an environment of 25±2°C and 50±10% humidity, and B represents the amount of water absorption [g / g] when 0.5 g of the water-absorbent resin particles are stirred in 500 g of water at 900 rpm using a rotor for 30 seconds under an environment of 25±2°C and 50±10% humidity.

[0014] The water-absorbent resin particles of the present invention have excellent swelling performance and also have the property that the gel viscosity is not easily reduced even at high temperatures. That is, the water-absorbent resin particles of the present invention can be said to be excellent in swelling performance and heat resistance. Therefore, the water-absorbent resin particles of the present invention can be particularly suitably used for cables.

[0015] The water-absorbent resin particles of the present invention have a median particle diameter of 250 μm or less. If the water-absorbent resin particles have a median particle diameter of more than 250 μm, there is a risk that the water-stopping effect will be reduced and the gel viscosity at high temperatures will be reduced.

[0016] The median particle diameter of the water-absorbent resin particles of the present invention is preferably 250 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less. The lower limit of the median particle diameter of the water-absorbent resin particles is, for example, preferably 5 μm or more, more preferably 10 μm or more, even more preferably 30 μm or more, and even more preferably 60 μm or more.

[0017]

[0044] A method for controlling the median particle diameter of water-absorbent resin particles is not particularly limited, and for example, known methods can be widely adopted. Among them, it is preferable to control the median particle diameter of water-absorbent resin particles by adjusting the conditions of reverse phase suspension polymerization of water-absorbent resin particles, which will be described later.

[0018] The water-absorbent resin particles of the present invention have a water-absorption rate for physiological saline solution of 20 seconds or less. If the water-absorption rate for physiological saline solution exceeds 20 seconds, the water-absorption rate is slow, and there is a risk that the water-stopping effect will be reduced when the particles are used as a water-stopping material, for example.

[0019] The water-absorbing speed of the water-absorbent resin particles of the present invention for physiological saline is preferably 20 seconds, more preferably 18 seconds or less, and even more preferably 15 seconds or less. The lower limit of the water-absorbing speed of the water-absorbent resin particles for physiological saline is, for example, preferably 0.5 seconds or more, and more preferably 1 second or more.

[0020]

[0043] The method for controlling the water absorption rate of physiological saline solution of water-absorbent resin particles is not particularly limited, and for example, known methods can be widely adopted. For example, as will be described later, the water absorption rate of physiological saline solution of water-absorbent resin particles can be controlled by appropriately selecting a water-soluble ethylenically unsaturated monomer, a type of crosslinking agent, an amount of crosslinking agent used, etc., used when producing the water-absorbent resin particles.

[0021] The water-absorbent resin particles of the present invention have a water absorption ratio represented by the above formula (1) (hereinafter, sometimes simply referred to as "water absorption ratio") of 80% or more. This allows the water-absorbent resin particles of the present invention to have excellent swelling performance, and furthermore, the property of gel viscosity being less likely to decrease even at high temperatures. That is, when the water-absorbent resin particles of the present invention have a water absorption ratio of 80% or more, the water-absorbent resin particles have excellent swelling performance and heat resistance. When the water-absorbent resin particles have a water absorption ratio of less than 80%, one or both of the swelling performance and heat resistance decrease.

[0022] The water absorption ratio of the water-absorbent resin particles of the present invention is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. The upper limit of the water absorption ratio of the water-absorbent resin particles of the present invention may exceed 100%. For example, the water absorption ratio of the water-absorbent resin particles of the present invention is preferably 110% or less, more preferably 105% or less, and even more preferably 100% or less.

[0023] The meaning of the water-absorbent resin particles of the present invention satisfying the water absorption ratio represented by the formula (1) is not necessarily intended to be limited, but it can mean that the water-absorbent resin particles (group) having a small particle size as a whole are likely to uniformly absorb water. As a result, it is presumed that the water-absorbent resin particles of the present invention have excellent swelling performance and are unlikely to have a decrease in gel viscosity even at high temperatures.

[0024] Examples of materials for forming the water-absorbent resin particles of the present invention include polymers of water-soluble ethylenically unsaturated monomers. Among them, the water-absorbent resin particles are preferably formed from polymer particles having a structure in which a polymer of a water-soluble ethylenically unsaturated monomer is crosslinked with a crosslinking agent. Such polymer particles may have, for example, a structure in which a polymer of a water-soluble ethylenically unsaturated monomer is crosslinked with an internal crosslinking agent described below, or may have a structure in which a polymer of a water-soluble ethylenically unsaturated monomer is crosslinked with a post-crosslinking agent described below instead of or in addition to the internal crosslinking agent. Preferably, the water-absorbent resin particles of the present invention contain polymer particles having a structure in which a polymer of a water-soluble ethylenically unsaturated monomer is crosslinked with an internal crosslinking agent described below.

[0025] As the water-soluble ethylenically unsaturated monomer, for example, a wide range of known monomers that can be used in general water-absorbent resins can be applied. Examples of water-soluble ethylenically unsaturated monomers include (meth)acrylic acid (herein, "acry" and "methacry" are collectively referred to as "(meth)acry", the same applies hereinafter) and salts thereof; 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, and polyethylene glycol mono(meth)acrylate; and amino group-containing unsaturated monomers such as N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide, as well as quaternized products thereof. These water-soluble ethylenically unsaturated monomers may be used alone, or two or more may be used in combination (copolymerized). Among these, (meth)acrylic acid and salts thereof, (meth)acrylamide, and N,N-dimethylacrylamide are preferred from the viewpoint of industrial availability, and (meth)acrylic acid and salts thereof are more preferred.

[0026] When acrylic acid and its salts are used as the water-soluble ethylenically unsaturated monomer, the acrylic acid and its salts are used as the main water-soluble ethylenically unsaturated monomer, and specifically, it is preferable that they are used in an amount of 70 to 100 mol % based on the total number of moles of the water-soluble ethylenically unsaturated monomer.

[0027] The water-soluble ethylenically unsaturated monomer may be used in the form of an aqueous solution in order to increase the dispersion efficiency in a hydrocarbon dispersion medium when performing the reversed-phase suspension polymerization described below. The concentration of the monomer in such an aqueous solution is usually 20% by mass or more and not more than the saturated concentration, preferably 25 to 90% by mass, and more preferably 30 to 85% by mass.

[0028] When the water-soluble ethylenically unsaturated monomer has an acid group, such as (meth)acrylic acid or 2-(meth)acrylamido-2-methylpropanesulfonic acid, the acid group may be neutralized in advance with an alkaline neutralizing agent, as necessary. Examples of such alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; and ammonia. In particular, these alkaline neutralizing agents may be used in the form of an aqueous solution to simplify the neutralization operation. The alkaline neutralizing agents described above may be used alone or in combination of two or more.

[0029] Regarding the degree of neutralization of the water-soluble ethylenically unsaturated monomer with the alkaline neutralizing agent, in order to increase the osmotic pressure of the obtained water absorbent resin and thereby increase the water absorption performance, the degree of neutralization of all acid groups which the water-soluble ethylenically unsaturated monomer has is usually preferably 50 to 100 mol%, more preferably 70 to 80 mol%.

[0030] The polymer particles can be produced, for example, by a production method including a step of carrying out a polymerization reaction using a raw material containing the water-soluble ethylenically unsaturated monomer (hereinafter referred to as the "polymerization step").

[0031] Examples of the polymerization reaction carried out in the polymerization step include reverse-phase suspension polymerization, aqueous solution polymerization, and emulsion polymerization, and it is preferable to use reverse-phase suspension polymerization. Reverse-phase suspension polymerization is, for example, a method in which a poorly soluble monomer is suspended in a dispersion medium in the presence of a dispersion stabilizer and polymerized. As is well known, reverse-phase suspension polymerization may be multi-stage polymerization in which the monomer is polymerized in multiple stages, and may be, for example, two-stage polymerization. In multi-stage polymerization, the first polymerization reaction is referred to as the first stage, and the monomers added stepwise after the first stage polymerization are referred to as the second stage, third stage, etc.

[0032] In the present invention, when a reverse phase suspension polymerization method is adopted, it is preferable to produce water-absorbent resin particles by a single-stage polymerization reaction, not by a multi-stage polymerization. In this case, the water-absorbent resin particles of the present invention are likely to satisfy the above-mentioned median particle size, water-absorption rate for physiological saline, and water-absorption ratio.

[0033] A hydrocarbon dispersion medium can be used as the dispersion medium used in reversed-phase suspension polymerization. Examples of hydrocarbon dispersion media include aliphatic hydrocarbons such as n-hexane, n-heptane, n-octane, and ligroin; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbons such as benzene, toluene, and xylene. Among these dispersion media, n-hexane, n-heptane, and cyclohexane are preferred because they are easily available industrially, have stable quality, and are inexpensive. These dispersion media may be used alone or in combination of two or more. Examples of dispersion media that can be used include mixed solvents such as Exxsol Heptane (manufactured by ExxonMobil: hydrocarbons of heptane and its isomers) and Nappar 6 (manufactured by ExxonMobil: hydrocarbons of cyclohexane and its isomers).

[0034] The water-soluble ethylenically unsaturated monomer that can be used in the reversed-phase suspension polymerization is the same as the water-soluble ethylenically unsaturated monomer described above, and in terms of excellent reactivity, (meth)acrylic acid and its salts, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and its salts are more preferred. The water-soluble ethylenically unsaturated monomer may be neutralized so that the degree of neutralization falls within the above range.

[0035] In the polymerization reaction in the polymerization step, particularly in reversed-phase suspension polymerization, a thickener can be used as needed, such as hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, partially neutralized polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, or polyethylene oxide.

[0036] The dispersion stabilizer used in reverse suspension polymerization may be a surfactant, and examples thereof include sucrose fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, sorbitol fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropyl alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl gluconamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkyl allyl ethers. Among these, sorbitan fatty acid esters, polyglycerin fatty acid esters, sucrose fatty acid esters, and the like are preferred from the viewpoint of dispersion stability of the monomer. These surfactants may be used alone or in combination of two or more.

[0037] The amount of the surfactant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first-stage water-soluble ethylenically unsaturated monomer, in order to maintain a good dispersion state of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium and to obtain a dispersing effect commensurate with the amount used.

[0038] Furthermore, a polymeric dispersant may be used in combination with or instead of a surfactant as a dispersion stabilizer. Examples of polymeric dispersants that can be used include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified EPDM (ethylene-propylene-diene terpolymer), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, maleic anhydride-butadiene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethyl cellulose, and ethylhydroxyethyl cellulose. Among these, from the viewpoint of dispersion stability of the monomer, preferred are maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymer, etc. These polymeric dispersants may be used alone or in combination of two or more.

[0039] The amount of polymeric dispersant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, per 100 parts by mass of the first-stage water-soluble ethylenically unsaturated monomer, in order to maintain a good dispersion state of the water-soluble ethylenically unsaturated monomer in the hydrocarbon dispersion medium and to obtain a dispersing effect commensurate with the amount used.

[0040] In the polymerization step, for example, a wide variety of known polymerization initiators can be used. Examples of radical polymerization initiators include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, and hydrogen peroxide; and azo compounds such as 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, 2,2'-azobis[2-(N-allylamidino)propane] dihydrochloride, and 4,4'-azobis(4-cyanovaleric acid). The radical polymerization initiator can also be used in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, or L-ascorbic acid to form a redox polymerization initiator.

[0041] From the viewpoint of polymerization stability, the lower limit of the amount of radical polymerization initiator used in the polymerization step is preferably 0.01 millimoles or more, more preferably 0.05 millimoles or more, relative to 1 mole of the water-soluble ethylenically unsaturated monomer used. Also, from the viewpoint of polymerization stability, the upper limit of the amount of radical polymerization initiator is preferably 20 millimoles or less, more preferably 10 millimoles or less, relative to 1 mole of the water-soluble ethylenically unsaturated monomer used. By using the radical polymerization initiator within this range, the production of water-absorbent resin particles becomes easy.

[0042] In the polymerization step, a chain transfer agent may be used as needed. Examples of the chain transfer agent include hypophosphites, thiols, thiolic acids, secondary alcohols, and amines.

[0043] In the polymerization step, it is preferable to use an internal crosslinking agent. Thereby, the polymer particles obtained in the polymerization step can have a structure in which the inside thereof is crosslinked by the internal crosslinking agent. That is, the obtained water-absorbent resin particles can have an internal crosslinked structure. In this specification, the crosslinking agent used for crosslinking the inside of the polymer is referred to as an internal crosslinking agent to distinguish it from a post-crosslinking agent.

[0044] Examples of the internal cross-linking agent include compounds having two or more polymerizable unsaturated groups. Specific examples of the internal cross-linking agent include triallyl compounds; sucrose allyl ether; (poly)ethylene glycol (in this specification, for example, "polyethylene glycol" and "ethylene glycol" are collectively referred to as "(poly)ethylene glycol"). the same applies hereinafter], di- or tri(meth)acrylic acid esters of polyols such as (poly)propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly)glycerin; unsaturated polyesters obtained by reacting the above-mentioned polyols with unsaturated acids such as maleic acid and fumaric acid; bisacrylamides such as N,N'-methylenebis(meth)acrylamide; di- or tri(meth)acrylic acid esters obtained by reacting polyepoxides with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanates such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth)acrylate; allylated starch; allylated cellulose; diallyl phthalate; N,N',N''-triallyl isocyanurate; divinylbenzene, etc. These internal crosslinking agents may be used alone or in combination of two or more.

[0045] Examples of the triallyl compound include triallyl compounds having 9 to 20 carbon atoms, such as triallyl cyanurate (triallyl cyanurate), triallyl isocyanurate, triallyl phosphate, and triallylamine.

[0046] The sucrose allyl ether is synthesized by a method of allyl-etherifying sucrose using allyl bromide or the like in the presence of an alkali catalyst. Depending on the degree of etherification, an oil-soluble or water-soluble sucrose allyl ether can be obtained. When the sucrose allyl ether is oil-soluble, the degree of etherification is preferably 5.0 to 8.0. When the sucrose allyl ether is a water-soluble sucrose allyl ether, the degree of etherification is preferably 1.8 to 4, more preferably 2.0 to 3.5, and even more preferably 2.2 to 3.2. The degree of etherification is the average molar ratio of allyl ether groups to sucrose.

[0047] The internal cross-linking agent may be a compound other than the above-mentioned compound having two or more polymerizable unsaturated groups, and examples of such compounds include carbonate compounds such as ethylene carbonate; glycidyl group-containing compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerin diglycidyl ether; (poly)ethylene glycol, (poly)propylene glycol, (poly)glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth)acrylate, etc. These internal cross-linking agents may be used alone or in combination of two or more.

[0048] The internal crosslinking agent is preferably one selected from the group consisting of a triallyl compound and a sucrose allyl ether. In this case, the water-absorbent resin particles of the present invention are likely to satisfy the above-mentioned median particle size, water absorption rate for physiological saline, and water absorption ratio.

[0049] The amount of the internal crosslinking agent used is preferably 0.001 mmol or more, more preferably 0.005 mmol or more, even more preferably 0.01 mmol or more, and particularly preferably 0.1 mmol or more, relative to 1 mole of the water-soluble ethylenically unsaturated monomer used. The amount of the internal crosslinking agent used is preferably 50 mmol or less, more preferably 40 mmol or less, even more preferably 30 mmol or less, and particularly preferably 20 mmol or less, relative to 1 mole of the water-soluble ethylenically unsaturated monomer used.

[0050] In the polymerization step, the temperature of the polymerization reaction can be appropriately set depending on the type and amount of the radical polymerization initiator used, and can be, for example, 20 to 110° C., preferably 40 to 90° C. The reaction time can be set, for example, in the range of 0.1 to 4 hours.

[0051] In the polymerization step, for example, an aqueous solution containing a water-soluble ethylenically unsaturated monomer, which has been neutralized as necessary, a thickener, a radical polymerization initiator, and an internal crosslinking agent is added to a dispersion medium in which a polymer dispersion stabilizer is dissolved, and then a surfactant is added to create a suspension state, thereby carrying out the polymerization step.

[0052] In the polymerization step, the water-soluble ethylenically unsaturated monomer is polymerized to produce polymer particles. For example, in reversed-phase suspension polymerization, a slurry in which a polymer of the water-soluble ethylenically unsaturated monomer is dispersed is obtained. When an internal crosslinking agent is used, the polymer obtained in the polymerization step has a structure crosslinked by the internal crosslinking agent.

[0053] In the case of the above-mentioned multi-stage polymerization in the polymerization step, after the first-stage reversed-phase suspension polymerization is carried out by the above-mentioned method, the water-soluble ethylenically unsaturated monomer is added to and mixed with the reaction mixture obtained in the first-stage polymerization step, and the second-stage and subsequent reversed-phase suspension polymerizations are carried out by the same method as in the first stage.In the reversed-phase suspension polymerization in each stage from the second stage onwards, in addition to the water-soluble ethylenically unsaturated monomer, a radical polymerization initiator and an internal crosslinking agent added as needed are added within the range of the molar ratio of each component to the water-soluble ethylenically unsaturated monomer mentioned above, based on the amount of the water-soluble ethylenically unsaturated monomer added during the reversed-phase suspension polymerization in each stage from the second stage onwards, and the reversed-phase suspension polymerization is carried out under the same conditions as in the above-mentioned method.In addition, when the reversed-phase suspension polymerization is carried out in multiple stages, from the viewpoint of facilitating the production of the desired water-absorbing resin, it is preferable that the total amount of the polymerization initiator and the total amount of the internal crosslinking agent used as needed per mole of the water-soluble ethylenically unsaturated monomer used in the reversed-phase suspension polymerization are each set to be within the above-mentioned range.

[0054] The polymer particles obtained by the polymerization step can also include a drying step, if necessary. That is, the method for producing polymer particles can also include a drying step in addition to the polymerization step. The drying step is a step of removing water from the polymer obtained in the polymerization step or the polymer crosslinked with an internal crosslinking agent by applying energy such as heat from the outside to the polymer. For example, in the case of reversed-phase suspension polymerization, in the drying step, water, hydrocarbon dispersion medium, etc. can be removed from the polymer by performing azeotropic distillation while the polymer (hydrous gel) obtained in the polymerization step is dispersed in a hydrocarbon dispersion medium. By performing the drying step, the water content of the polymer or the polymer crosslinked with an internal crosslinking agent can be adjusted. The drying step may be performed simultaneously with the post-crosslinking step described below.

[0055] The drying step may be carried out under normal pressure or under reduced pressure, and may be carried out under a stream of nitrogen or the like to increase drying efficiency. When the drying step is carried out under normal pressure, the drying temperature is preferably 70 to 250°C, more preferably 80 to 180°C, even more preferably 80 to 140°C, and particularly preferably 90 to 130°C. When the drying step is carried out under reduced pressure, the drying temperature is preferably 40 to 160°C, more preferably 50 to 120°C.

[0056] The polymer obtained in the polymerization step (including a polymer crosslinked with an internal crosslinking agent) or the polymer obtained in the drying step (including a polymer crosslinked with an internal crosslinking agent) can be treated with a post-crosslinking agent. This allows the polymer to have a structure crosslinked with the post-crosslinking agent, and the crosslink density near the surface of the water absorbent resin increases. The step of treating the polymer with a post-crosslinking agent is referred to as a "post-crosslinking step."

[0057] The type of post-crosslinking agent can be exemplified by various crosslinking agents of the same type as the internal crosslinking agent described above. Among them, the post-crosslinking agent is preferably a carbonate compound such as ethylene carbonate. In this case, the water-absorbent resin particles of the present invention are likely to satisfy the above-mentioned median particle size, water absorption rate for physiological saline, and water absorption ratio. The post-crosslinking agent may be used alone or in combination of two or more types.

[0058] The amount of the post-crosslinking agent used is preferably 0.01 mmol or more, more preferably 0.05 mmol or more, and even more preferably 0.1 mmol or more, relative to 1 mol of the water-soluble ethylenically unsaturated monomer constituting the polymer to be post-crosslinked, and is preferably 20 mmol or less, more preferably 15 mmol or less, and even more preferably 10 mmol or less.

[0059] The reaction temperature in the post-crosslinking step (i.e., the temperature at which the polymer is treated with the post-crosslinking agent) is preferably 50 to 250° C., more preferably 60 to 230° C., and even more preferably 60 to 200° C. The reaction time of the post-crosslinking (i.e., the time at which the polymer is treated with the post-crosslinking agent at the reaction temperature) cannot be determined in general because it differs depending on the reaction temperature, the type and amount of the post-crosslinking agent used, etc., but is usually 1 to 300 minutes, and preferably 5 to 200 minutes.

[0060] In the production of polymer particles, a metal chelating agent may be added before, during, or after the post-crosslinking step. Examples of the metal chelating agent include known metal chelating agents. Examples of types of metal chelating agents include phosphonic acid-based metal chelating agents and metal chelating agents having an aminocarboxylic acid moiety.

[0061] The polymer particles may also contain silica. In this case, for example, silica may be present in a state of being coated on the surface of the polymer particles. When the water-absorbent resin particles of the present invention contain silica, the content ratio thereof is, for example, 0.01 to 5 parts by mass, and preferably 0.02 to 3 parts by mass, per 100 parts by mass of the water-absorbent resin particles. The water-absorbent resin particles of the present invention may contain other components other than silica, and examples thereof include various components contained in known water-stopping materials.

[0062] Incidentally, "100 parts by mass of water-absorbent resin particles" may include, in addition to polymer particles, an initiator, a crosslinking agent, a thickener, a surfactant, and a polymer-based dispersant used in a polymerization step, and may further include moisture contained in the water-absorbent resin particles. In addition, it may also include various additives added after the polymerization step.

[0063] The water-absorbent resin particles of the present invention may be formed only from the polymer particles, or may contain components other than the polymer particles. The water-absorbent resin particles of the present invention preferably contain 50% by mass or more of the polymer particles, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0064] The water-absorbent resin particles preferably have a pure water absorption capacity of 500 g / g or less. In this case, the gel viscosity after 18 hours in an environment of 90±2° C. is high, and the particles can be more suitably used as a water-stopping material. The pure water absorption capacity of the water-absorbent resin particles can be measured according to the measurement method described in the Examples section.

[0065] The pure water absorption of the water-absorbent resin particles is preferably 500 g / g or less, more preferably 400 g / g or less, even more preferably 300 g / g or less, and even more preferably 250 g / g or less.

[0066] The water-absorbent resin particles preferably have a bulk density of 0.4 g / mL or more, more preferably 0.5 g / mL or more, and the upper limit may be 1 g / mL or less, or may be 0.9 g / mL or less.

[0067] The water-absorbent resin particles preferably have a centrifuge retention capacity (CRC) of 30 g / g or less, more preferably 27 g / g or less, and even more preferably 25 g / g or less, and the lower limit may be 5 g / g or more, or may be 10 g / g or more.

[0068] The water-absorbent resin particles preferably have a 30-second swelling height of 3 mm or more. In this case, the water-absorbent resin particles can have excellent swelling performance and can be more suitably used as a water-stopping material. The 30-second swelling height of the water-absorbent resin particles can be measured according to the measurement method described in the Examples section.

[0069] The 30-second swelling height of the water-absorbent resin particles is more preferably 4 mm or more, and even more preferably 5 mm or more, and the upper limit may be 25 mm or less, or may be 20 mm.

[0070] The water-absorbent resin particles of the present invention preferably have a gel viscosity (mPa·s) of 5,000 mPa·s or more, more preferably 6,000 mPa·s or more, even more preferably 7,000 mPa·s or more, and particularly preferably 8,000 mPa·s or more after 18 hours in an environment of 90±2° C. The upper limit of the gel viscosity after 18 hours in an environment of 90±2° C. is, for example, preferably 70,000 mPa·s or less, more preferably 60,000 mPa·s or less, even more preferably 30,000 mPa·s or less, and particularly preferably 15,000 mPa·s or less.

[0071] The water-absorbent resin particles of the present invention have a high water absorption rate, a large 30-second swelling height, and a high gel viscosity after 18 hours in an environment of 90±2° C., and thus combine water absorption properties, swelling performance, and heat resistance. Conventionally, when the median particle diameter is a small particle diameter of 250 μm or less, there is variation in water absorption between particles, making it difficult to achieve both swelling performance and heat resistance, but in the present invention, the water-absorbent resin particles are adjusted to satisfy formula (1), and thereby it is possible to achieve both swelling performance and heat resistance.

[0072] Therefore, the water-absorbent resin particles of the present invention are suitable for various uses, and can be widely applied to various fields, for example, industrial materials such as water-stopping materials and dew-preventing agents, agricultural and horticultural materials such as water-retention agents and soil conditioners, sanitary materials such as disposable diapers and sanitary products, etc. In particular, the water-absorbent resin particles of the present invention are suitable for use in water-stopping materials, since they can maintain the water-stopping effect for a long period of time.

[0073] 2. Water-Stopping Material and Cable The present invention includes a water-stopping material. Such a water-stopping material comprises the water-absorbent resin particles of the present invention described above, and other configurations can be the same as those of known water-stopping materials, for example. The water-stopping material can be formed from water-absorbent resin particles alone, or can be formed by molding a mixture of water-absorbent resin particles with rubber and / or thermoplastic resin, etc. Examples of water-stopping materials include water-stopping tapes and water-stopping yarns.

[0074] A water-stop tape can be obtained, for example, by holding water-absorbent resin particles in a liquid-permeable sheet. Alternatively, a water-stop tape can be obtained by sandwiching water-absorbent resin particles between two or more liquid-permeable sheets. Specifically, a water-stop tape can be obtained by fixing water-absorbent resin particles and a liquid-impermeable sheet using an adhesive to form a sheet. Examples of liquid-permeable sheets that can be used include nonwoven fabrics, woven fabrics, and films made of synthetic resins such as polyolefin, polyester, polyamide, nylon, and acrylic.

[0075] The water-blocking yarn can be obtained, for example, by coating or impregnating a substrate with water-absorbent resin particles. Examples of such a substrate include long synthetic fibers or plastic yarns (substrate yarns), and more specifically, long synthetic resin fibers or plastic yarns such as polyolefin, polyester, polyamide, nylon, and acrylic are used.

[0076] In the production of a water-blocking yarn, the method of applying or impregnating a substrate with water-absorbent resin particles can be, for example, by applying or impregnating the substrate with a dispersion liquid in which water-absorbent resin particles are dispersed in an organic solvent, thereby fixing the water-absorbent resin particles to the substrate. When the fixing strength of the water-absorbent resin particles to the substrate is weak, the fixing strength can be improved by using an adhesive in combination.

[0077] Examples of the adhesive include rubber-based adhesives such as natural rubber, butyl rubber, and polyisoprene; styrene-based elastomer adhesives such as styrene-isoprene block copolymer (SIS) and styrene-butadiene block copolymer (SBS); ethylene-vinyl acetate copolymer (EVA) adhesives; ethylene-acrylic acid derivative copolymer-based adhesives such as ethylene-ethyl acrylate copolymer (EEA); ethylene-acrylic acid copolymer (EAA) adhesives; polyamide-based adhesives such as copolymerized nylon; polyolefin-based adhesives such as polyethylene and polypropylene; polyester-based adhesives such as polyethylene terephthalate (PET) and copolymerized polyester; and acrylic adhesives.

[0078] The water-stopping material of the present invention contains the water-absorbent resin particles of the present invention, and since the water-absorbent resin particles have excellent swelling properties, they can be particularly suitably used for cables.

[0079] The waterstop material of the present invention can be used in a variety of applications, for example, in various cables such as communication cables such as optical cables and power cables, and specifically, can be suitably used in power cables used underground or under the sea. In particular, the above-mentioned waterstop tape, waterstop yarn, etc. are particularly suitable as waterstop materials for power cables.

[0080] The optical cable may have a configuration similar to that of a known optical cable. Like a typical optical cable, the optical cable may have a structure including an optical fiber unit in which a plurality of optical fiber cores are bundled, an optical fiber assembly in which a plurality of optical fiber units are assembled, and a coating layer provided on the outer periphery of the optical fiber unit assembly. To prevent water entering from the outside from running along the length of the cable, a waterproof tape is disposed between the optical fiber unit assembly and the coating layer. Furthermore, the waterproof tape may be housed inside the optical fiber unit assembly.

[0081] The power cable may have a configuration similar to that of a known power cable. Like a typical power cable, the power cable may have a structure in which an inner semiconductive layer, an insulating layer, an outer semiconductive layer, and a coating layer are sequentially provided around the outer periphery of a central conductor. To prevent water entering from the outside from running along the length of the cable, a waterproof tape is disposed between the outer semiconductive layer and the coating layer. Furthermore, the waterproof tape may be disposed between the inner semiconductive layer and the insulating layer. A waterproof yarn may also be housed in the central conductor.

[0082] In specifying the inventions included in the present disclosure, the components (properties, structures, functions, etc.) described in each embodiment of the present disclosure may be combined in any manner. In other words, the present disclosure includes all subject matter consisting of all combinations of the components that can be combined as described in this specification.

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the embodiments of these examples. The water-absorbent resin particles obtained in the following examples and comparative examples were evaluated by various test methods described below. Unless otherwise specified, measurements were carried out in an environment of a temperature of 25±2°C and a humidity of 50±10%.

[0084] [Production of water-absorbent resin particles] (Example 1) [Polymerization step] A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm as a stirrer. 293 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymer dispersant. The mixture was heated to 80 ° C. with stirring to dissolve the dispersant, and then cooled to 50 ° C. Meanwhile, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in a 300 mL beaker, and while cooling with ice water, 147.7 g of a 20.9 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization, followed by adding and dissolving 0.0736 g (0.27 mmol) of potassium persulfate as a water-soluble radical polymerization agent and 1.4365 g (10.47 mmol) of triallylamine as an internal crosslinking agent to prepare a first-stage aqueous liquid. The aqueous solution prepared above was then added to a separable flask and stirred for 10 minutes. A surfactant solution was then added to a 20 mL vial, in which 0.736 g of sucrose stearate ester with an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi Chemical Foods Corporation) was dissolved in 6.62 g of n-heptane as a surfactant under heating. The mixture was then thoroughly purged with nitrogen while stirring at a stirrer speed of 500 rpm. The flask was then immersed in a 70°C water bath and heated. Polymerization was carried out for 60 minutes, yielding hydrogel-like polymer particles. [Dehydration Step] The flask was then immersed in an oil bath set at 125°C, and 114.57 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. [Drying Step] The n-heptane was evaporated at 125°C to dry the mixture, and the mixture was then passed through a sieve with 850 μm openings to obtain polymer particles. 100 parts by mass of the polymer particles were mixed with 2 parts by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) to obtain 93.5 g of water-absorbent resin particles of Example 1.

[0085] (Example 2) 91.2 g of water absorbent resin particles was obtained in the same manner as in Example 1, except that the internal crosslinking agent used in the polymerization step was changed to 0.221 g (0.52 mmol) of sucrose allyl ether, and the amount of water extracted to the outside of the system in the dehydration step was changed to 116.30 g.

[0086] Example 3 Polymer particles passed through a sieve with an opening of 850 μm were obtained in the same manner as in Example 1, except that the amount of internal crosslinking agent used in the polymerization step was changed to 0.958 g (6.98 mmol) and the amount of water extracted from the system in the dehydration step was changed to 115.80 g. 10 g of these polymer particles were weighed into a round-bottomed cylindrical separable flask with an inner diameter of 11 cm and equipped with an anchor-shaped stirring blade made of fluororesin. Next, while stirring at 500 rpm, an aqueous surface crosslinking agent solution obtained by mixing 0.10 g of ethylene carbonate as a post-crosslinking agent, 0.54 g of 2-propanol, and 0.36 g of water was sprayed onto the mixture. The mixture obtained by spraying was uniformly spread on a metal dish with a diameter of 12 cm and then heated at 200°C for 30 minutes. After cooling to room temperature, the mixture was passed through a sieve with an opening of 850 μm to obtain polymer particles. 100 parts by mass of the polymer particles were mixed with 2 parts by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) to obtain 7.9 g of water-absorbent resin particles of Example 3.

[0087] (Comparative Example 1) [Polymerization step] A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm. 293 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymeric dispersant. The mixture was heated to 80 ° C. with stirring to dissolve the dispersant, and then cooled to 50 ° C. Separately, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in a 300 mL beaker, and while cooling with ice water, 147.7 g of a 20.9 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization. Thereafter, 0.092 g of hydroxyl ethyl cellulose (Sumitomo Seika Chemicals Co., Ltd., HECAW-15F) as a thickener, 0.0736 g (0.27 mmol) of potassium persulfate as a water-soluble radical polymerization agent, and 0.0100 g (0.057 mmol) of ethylene glycol diglycidiether as an internal crosslinking agent were added and dissolved to prepare a first-stage aqueous liquid. The aqueous liquid prepared above was then added to a separable flask and stirred for 10 minutes. A surfactant solution prepared by heating and dissolving 0.736 g of a sucrose stearate ester with an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi-Kagaku Foods Corporation) as a surfactant in 6.62 g of n-heptane in a 20 mL vial was then added. The system was thoroughly purged with nitrogen while stirring at a stirrer rotation speed of 500 rpm, and the flask was immersed in a water bath at 70°C to raise the temperature, and polymerization was carried out for 60 minutes, thereby obtaining a first-stage polymerization slurry.

[0088] Separately, 128.8 g (1.44 mol) of an 80.5 wt% aqueous acrylic acid solution was placed in a separate 500 mL Erlenmeyer flask, and 160.0 g of a 27 wt% aqueous sodium hydroxide solution was added dropwise with ice cooling to neutralize 75 mol% of the acrylic acid. To the resulting partially neutralized acrylic acid salt solution, 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent and 0.09 g (0.33 mmol) of potassium persulfate as a radical polymerization initiator were added to prepare the second-stage aqueous solution. After completion of the first-stage polymerization, the first-stage polymerization slurry was cooled to 50°C, and while the surfactant was dissolved, the second-stage aqueous solution was added dropwise to the system. While maintaining the temperature at 50°C, the system was thoroughly purged with nitrogen gas. The system was then heated to 70°C to carry out the second-stage polymerization, yielding a hydrogel-like polymer. [Dehydration step] The flask was then immersed in an oil bath set at 125°C, and 260.1 g of water was extracted by azeotropic distillation of n-heptane and water, after which 4.42 g (0.51 mmol) of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether was added as a surface crosslinking agent, and the mixture was maintained at 83°C for 2 hours. [Drying step] The n-heptane was evaporated at 125°C to dry the mixture, and the mixture was further passed through a sieve with an opening of 850 μm to obtain polymer particles. 2 parts by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with 100 parts by mass of the polymer particles to obtain 230.5 g of water-absorbent resin particles.

[0089] (Comparative Example 2) [Polymerization step] A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a capacity of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm. 293 g of n-heptane was added to this flask as a hydrocarbon dispersion medium, and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hiwax 1105A) was added as a polymeric dispersant. The mixture was heated to 80 ° C. with stirring to dissolve the dispersant, and then cooled to 50 ° C. Meanwhile, 92.0 g (1.03 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in a 300 mL beaker, and while cooling with ice water, 147.7 g of a 20.9 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization, followed by adding and dissolving 0.0736 g (0.27 mmol) of potassium persulfate as a water-soluble radical polymerization agent and 1.4365 g (10.47 mmol) of triallylamine as an internal crosslinking agent to prepare a first-stage aqueous liquid. The aqueous liquid prepared above was then added to a separable flask and stirred for 10 minutes. A surfactant solution prepared by heating and dissolving 0.736 g of a sucrose stearate ester with an HLB of 3 (Ryoto Sugar Ester S-370, Mitsubishi-Kagaku Foods Corporation) as a surfactant in 6.62 g of n-heptane in a 20 mL vial was then added. The system was thoroughly purged with nitrogen while stirring at a stirrer rotation speed of 500 rpm, and the flask was immersed in a water bath at 70°C to raise the temperature, and polymerization was carried out for 60 minutes, thereby obtaining a first-stage polymerization slurry. On the other hand, 128.8 g (1.44 mol) of an 80.5 mass% aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was placed in another 500 mL beaker, and while cooling with ice water, 160.0 g of a 27 mass% aqueous sodium hydroxide solution was added dropwise to carry out 75 mol% neutralization, and then 0.103 g (0.38 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 2.0110 g (14.66 mmol) of triallylamine as an internal crosslinking agent were added and dissolved to prepare a second-stage aqueous liquid.While stirring at a stirrer speed of 1000 rpm, the contents of the separable flask system were cooled to 22°C, and the entire amount of the second-stage aqueous liquid was added to the first-stage polymerization slurry liquid. The system was then purged with nitrogen for 30 minutes, and the flask was again immersed in a 70°C water bath to raise the temperature. A polymerization reaction was carried out for 60 minutes to obtain a hydrogel-like polymer. [Dehydration Step] The flask was then immersed in an oil bath set at 125°C, and 229.7 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane. [Drying Step] The n-heptane was evaporated at 125°C to dry the mixture, and the mixture was then passed through a sieve with 850 μm openings to obtain polymer particles. 2 parts by mass of amorphous silica (Toxil NP-S, Oriental Silicas Corporation) was mixed with 100 parts by mass of the polymer particles to obtain 234.7 g of water-absorbent resin particles of Comparative Example 2.

[0090] (Median particle diameter of water-absorbent resin particles) 5 g of water-absorbent resin particles were sieved using an ultrasonic vibration sieving measuring instrument (Robot Sifter RPS-01, manufactured by Seishin Enterprise Co., Ltd.), sieves with JIS standard openings of 400 μm, 250 μm, 180 μm, 150 μm, 106 μm, 75 μm, and 45 μm, and a tray. The mass of the particles remaining on each sieve was calculated as a mass percentage with respect to the total amount. The mass percentages of the particles remaining on each sieve were integrated in order from the largest particle diameter, and the relationship between the sieve opening and the integrated value of the mass percentage of the particles remaining on the sieve was plotted on logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to an integrated mass percentage of 50 mass% was determined, and this was taken as the median particle diameter of the water-absorbent resin particles.

[0091] (Measurement of gel viscosity) The gel viscosity of the water-absorbent resin particles was measured by adjusting the temperature of the swollen gel to 25±0.5°C using a Vismetron (Shibaura Systems Co., Ltd. VDH2 type, rotor No. 5 or 7, rotation speed 10 rpm). This gel viscosity measurement was performed with the gel placed in a 200 mL glass beaker with an inner diameter of 64 mmΦ and filled to a height of 65 mm. 100 g of ion-exchanged water was added to the 200 mL beaker, and the mixture was stirred at 1000 rpm using a magnetic stir bar (cylindrical, diameter 8 mm x length 30 mm, no ring). 2.0 g of water-absorbent resin particles were added to the vortex generated by this stirring, and the mixture was stirred until the magnetic stirrer stopped due to the gel produced. This operation was performed twice in total to obtain a swollen gel equivalent to 4.0 g of water-absorbent resin particles before swelling. The gel viscosity of the resulting swollen gel was then immediately measured and designated as "initial gel viscosity A". After this measurement, 200 g of the swollen gel was immediately placed in a 250 mL glass heat-resistant bottle with a bottom outer diameter of 70 mm and a mouth outer diameter of 42 mm, and allowed to stand in a hot air dryer (LH21-11M, manufactured by Nagano Science Co., Ltd.) at 90±2°C for 18 hours, after which the gel viscosity B of the swollen gel was measured. Note that measurements were taken using rotor No. 5 for gel viscosities less than 40,000 mPa s, and rotor No. 7 for gel viscosities of 40,000 mPa s or more.

[0092] (Measurement of Water Absorption Ratio) The water absorption ratio of the water-absorbent resin particles was measured in an environment of 25±2°C and 50±10% humidity according to the following procedure. First, 500 g of ion-exchanged water was weighed into a 1000 mL beaker (9 cm diameter x 14.5 cm height). Next, 0.5 g of water-absorbent resin particles was dispersed while stirring at 100 rpm using a magnetic stir bar (8 mm diameter x 50 mm length, without ring), and stirred for 30 seconds to obtain a dispersion containing a swollen gel. Immediately thereafter, the entire dispersion was passed through a standard sieve with a mass of Wa (g) and a mesh size of 38 μm. Then, after leaving the sieve tilted at an angle of approximately 30 degrees relative to the horizontal for 30 minutes, the mass Wb (g) of the sieve on which the swollen gel remained was measured. The water absorption amount A (g / g) was calculated using the following formula (4): The water absorption amount A was measured five times using the same procedure as above, and the average value was used to calculate the water absorption ratio. Water absorption amount A (g / g) = (Wb - Wa) / 0.5 (4) Meanwhile, 500 g of ion-exchanged water was weighed into a 1000 mL beaker (9 cm diameter x 14.5 cm height). Next, 0.5 g of water-absorbent resin particles was dispersed while stirring at 900 rpm using a magnetic stir bar (8 mm diameter x 50 mm length, no ring), and stirred for 30 seconds to obtain a dispersion containing a swollen gel. Immediately thereafter, the entire dispersion was passed through a standard sieve with a 38 μm mesh size and a mass of Wc (g). Then, after leaving the sieve tilted at an angle of approximately 30 degrees relative to the horizontal for 30 minutes, the mass Wd (g) of the sieve with the swollen gel remaining was measured. The water absorption amount B (g / g) was calculated using the following formula (5): The water absorption amount B was measured five times in the same manner as above, and the average value was used to calculate the water absorption ratio. Water absorption amount B (g / g) = (Wd - Wc) / 0.5 (5) Using the values ​​obtained from these measurements, the water absorption ratio We (%) was calculated according to the following formula (6): Water absorption ratio We (%) = (A / B) × 100 (6)

[0093] (Pure Water Absorption) The pure water absorption of water-absorbent resin particles was measured in an environment of 25±2°C and 50±10% humidity according to the following procedure. 1500 g of ion-exchanged water was weighed into a 2000 mL beaker. Next, 0.5 g of water-absorbent resin particles was dispersed in pure water while stirring at 600 rpm using a magnetic stir bar (8 mm diameter x 30 mm length, without ring) to prevent the formation of lumps. The mixture was left to stand for 60 minutes while stirring to allow the particles to fully swell, thereby obtaining a dispersion containing a swollen gel. Next, the mass Wa (g) of a 38 μm standard sieve was measured, and the particles were passed through this standard sieve. The sieve was then tilted at an angle of approximately 30 degrees relative to the horizontal and left to stand for 30 minutes to remove excess water. The mass Wb (g) of the sieve on which the swollen gel remained was measured, and the pure water absorption Wd (g / g) was calculated by the following formula (5): Pure water absorption Wd (g / g) = (Wb - Wa - Wc) / Wc (5) Wc (g) is the precisely weighed value of a mass of 0.5 g of the water-absorbent resin particles used in the measurement.

[0094] (Water absorption rate of physiological saline solution) The water absorption rate test by the Vortex method was carried out at room temperature. 50±0.1 g of physiological saline solution was weighed into a 100 mL beaker. A magnetic stirrer bar (8 mmφ×30 mm without ring) was added, and the beaker was immersed in a thermostatic water bath to adjust the liquid temperature to 25±0.2°C. Next, the beaker was placed on a magnetic stirrer, and the rotation speed was set to 600 rpm to generate a vortex in the physiological saline solution. 2.0 g of water-absorbent resin particles were then quickly added to the beaker. Using a stopwatch, the time (seconds) from the time the water-absorbent resin particles were added to the time the vortex on the liquid surface converged was measured, and this was taken as the water absorption rate of the water-absorbent resin particles.

[0095] <Bulk Density> The bulk density of the water-absorbent resin particles was measured using a "bulk specific gravity measuring device" described in JIS-K-6720-2. Approximately 120 mL of water-absorbent resin particles were placed in a funnel part of the device whose bottom was blocked with a damper, and in a state where a 100 mL capacity (cylindrical, inner diameter 40 mmφ) receiver was placed 38 mm below the damper, the damper of the device was quickly pulled out, and the water-absorbent resin particles were dropped into the receiver. The water-absorbent resin particles that had risen from the receiver were scraped off with a flat plate, and then the mass W1 of the receiver together with the receiver was measured. Separately, a mass W0 of a measured empty receiver was subtracted from the mass W1 to obtain a mass of water absorbent resin particles, and the resultant mass was divided by a volume V mL of the receiver (V of the receiver = 100 mL) to obtain a value Sa (g / mL) by the following formula (6): Sa (g / mL) = [W1 - W0] (g) / V (mL) (6) Sa was measured three times in total by the same procedure, and the average value thereof was regarded as the bulk density of the water absorbent resin particles.

[0096] (Centrifuge Retention Capacity (CRC)) The centrifuge retention capacity (CRC) was measured using the following procedure with reference to the EDANA method (NWSP 241.0.R2(15), pages 769-778). The measurement was performed in an environment with a temperature of 25±2°C and a relative humidity of 50±10%. A nonwoven fabric measuring 60 mm x 170 mm (product name: Heat Pack MWA-18, manufactured by Nippon Paper Papylia Co., Ltd.) was folded in half longitudinally. A nonwoven fabric bag measuring 60 mm x 85 mm was prepared by heat-sealing the nonwoven fabric at 5 mm-wide edges along each of the two long sides. Approximately 0.2 g of precisely weighed particles to be measured was placed in the nonwoven fabric bag. The nonwoven fabric bag was closed by heat-sealing the nonwoven fabric at the open short edge. Multiple nonwoven fabric bags containing water-absorbent resin particles were floated on 1,000 g of saline solution contained in a stainless steel tray (240 mm x 320 mm x 45 mm) without overlapping each other, thereby completely wetting the entire nonwoven fabric bag. One minute after floating the nonwoven fabric bag in the saline solution, the entire nonwoven fabric bag was immersed in the saline solution using a spatula. After 30 minutes from the start of floating the nonwoven fabric bag in the saline solution, i.e., a total of 1 minute of floating time and 29 minutes of immersion time, the nonwoven fabric bag containing the formed gel was removed from the saline solution. The removed nonwoven fabric bag was dehydrated for 3 minutes at a centrifugal force of 250 G using a centrifuge (manufactured by Kokusan Co., Ltd., model number: H-122). After dehydration, the mass Ma [g] of the nonwoven fabric bag including the mass of the gel was weighed. The above-mentioned operation was performed on a nonwoven fabric bag containing no particles to be measured, and the mass Mb [g] of the nonwoven fabric bag after dehydration was measured. CRC [g / g] was calculated according to the following formula (7): CRC [g / g] = {(Ma - Mb) - Mc} / Mc (7) Mc [g] is the precisely weighed value of the mass of 0.2 g of the water-absorbent resin particles to be measured.

[0097] (Measurement of 30-Second Swelling Height) The swelling height of water-absorbent resin particles was measured using a swelling height measuring device X shown in FIG. 1 . The swelling height measuring device X shown in FIG. 1 includes a movement distance measuring device 1, a concave circular cup 2 (height 45 mm, outer diameter 90 mm, recess depth 40 mm, inner diameter of the recess 80 mm), a plastic convex circular cylinder 3 (outer diameter 79 mm, with 60 through-holes 7 each having a diameter of 2 mm evenly arranged on the surface that contacts the water-absorbent resin particles), and a nonwoven fabric 4 (a liquid-permeable nonwoven fabric with a basis weight of 10 g / m2). The swelling height measuring device X can measure the displacement of the distance moved by the convex circular cylinder 3 to an accuracy of 0.01 mm using a laser beam 6. The concave circular cup 2 can uniformly spray a predetermined amount of water-absorbent resin particles. The convex circular cylinder 3 can uniformly apply a load of 90 g to the sample water-absorbent resin particles 5.

[0098] First, 0.2 g of a sample (water-absorbent resin particles 5) was uniformly spread in a concave circular cup 2, and a nonwoven fabric 4 was laid thereon. Then, a convex circular cylinder 3 was gently placed on the nonwoven fabric 4, and the device was set so that the laser light 6 of the sensor of the movement distance measuring device 1 was located at the center of the cylinder 3. Ion-exchanged water previously adjusted to 20°C was poured into the concave circular cup 2 through the through-holes 7 of the convex circular cylinder 3, and the water-absorbent resin particles 5 were caused to swell. The time when the laser detected that the water-absorbent resin particles 5 had swelled and pushed up the convex circular cylinder 3 was defined as the start of water absorption (0 seconds) (automatic measurement started when the water-absorbent resin particles 5 were displaced 0.5 mm), and the distance by which the convex circular cylinder 3 was pushed up due to the swelling of the water-absorbent resin particles 5 (the difference in displacement of the convex circular cylinder 3 in the direction perpendicular to the bottom surface of the recess of the concave circular cup 2) was measured. The level of the ion-exchanged water was checked every 3 seconds from the start of the addition of the ion-exchanged water, and the addition of ion-exchanged water was continued intermittently so as to maintain the water level at approximately the height of the flat surface of the flat plate part of the convex circular cylinder 3. 30 seconds after the moment when the water-absorbent resin particles 5 started to absorb water (more precisely, the moment when the water-absorbent resin particles absorbed a very small amount of ion-exchanged water and the cylinder 3 was pushed up by 0.5 mm), the distance by which the convex circular cylinder 3 was pushed up (including the height (0.5 mm) by which the cylinder 3 was pushed up at the moment when water absorption started) was recorded as the 30-second swelling height.

[0099]

[0133] Table 1 shows the evaluation results of the pure water absorption amount, water absorption rate of physiological saline, median particle size, bulk density, water absorption ratio, CRC, initial gel viscosity A, gel viscosity B after 18 hours, and 30-second swelling height of the water-absorbent resin particles obtained in each of the Examples and Comparative Examples.

[0100] From Table 1, it was found that the water-absorbent resin particles obtained in Examples 1 to 3 had a median particle diameter of 250 μm or less, a saline water absorption rate of 20 seconds or less, and a water absorption ratio of 80% or more, and that the decrease in gel viscosity at high temperatures (90°C) was suppressed and that they also had high swelling performance. On the other hand, the water-absorbent resin particles obtained in Comparative Example 1 had a water absorption ratio of less than 80%, and the decrease in gel viscosity at high temperatures (90°C) was significant. The water-absorbent resin particles obtained in Comparative Example 2 had a water absorption ratio of 80% or more, but had a large median particle diameter and a slow saline water absorption rate, resulting in low swelling performance and a significant decrease in gel viscosity. From the above, it was found that water-absorbent resin particles having a median particle diameter of 250 μm or less, a saline water absorption rate of 20 seconds or less, and a water absorption ratio of 80% or more not only have excellent swelling performance but also have the property of being less likely to decrease in gel viscosity even at high temperatures.

[0101]

Claims

1. Water-absorbent resin particles having a median particle diameter of 250 μm or less, a water absorption rate for physiological saline solution of 20 seconds or less, and a water absorption rate of 80% or more, as expressed by the following formula (1): water absorption rate [%] = (A / B) × 100 (1) (in formula (1), A represents the amount of water absorption [g / g] when 0.5 g of the water-absorbent resin particles are stirred in 500 g of water at 100 rpm using a rotor for 30 seconds under an environment of 25±2°C and 50±10% humidity, and B represents the amount of water absorption [g / g] when 0.5 g of the water-absorbent resin particles are stirred in 500 g of water at 900 rpm using a rotor for 30 seconds under an environment of 25±2°C and 50±10% humidity).

2. The water-absorbent resin particles according to claim 1, which have a pure water absorption of 500 g / g or less.

3. A water-stopping material containing the water-absorbent resin particles according to claim 1 or 2.

4. A cable containing the waterproofing material according to claim 3.

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