Water retention material

Abstract

The present invention relates to a water-retaining material comprising a water-absorbent resin and one or more substances selected from the group consisting of acetic acid and acetic acid derivatives.

Description

[Technical field]

[0001] The present invention relates to a water-retaining material. [Background technology]

[0002] In recent years, with the chronic depletion of water resources, attempts have been made to use agricultural water effectively and appropriately, and to maintain or increase agricultural yields even with smaller amounts of irrigation water than before (e.g., Patent Documents 1 to 3). These agricultural water retention materials are mainly composed of super absorbent polymers (SAP), and compared to, for example, peat moss used to improve the water retention of soil, they are effective in extremely small amounts, and therefore have the advantage of placing less of a burden on farmers when used. However, it has been revealed that conventional water absorbent polymers have a negative effect on seed germination or plant growth (Patent Document 4 and Non-Patent Document 1), and Patent Document 4 describes the reason for this as being that the roots cannot effectively use the water in the water absorbent polymer.

[0003] On the other hand, in order to increase the desiccation tolerance of a plant itself under dry conditions, for example, Patent Document 5 discloses administering acetic acid to the plant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 1998 / 005196 Brochure [Patent Document 2] Special Publication No. 2013-544929 [Patent Document 3] Special Publication No. 2013-540164 [Patent Document 4] JP 2009-148163 A [Patent Document 5] U.S. Patent Publication No. 2012 / 0227134 [Non-patent literature]

[0005] [Non-Patent Document 1] Norio Sugimura et al., Use of superabsorbent polymers as greening materials, Greening Technology, 9(2), 11-15, 1983 Summary of the Invention [Problem to be solved by the invention]

[0006] The water-absorbent resin has ionic functional groups, which causes an osmotic pressure difference between the inside and outside of the resin when immersed in water, allowing it to absorb a large amount of water. However, according to the study by the present inventors, it was found that if the concentration of ionic functional groups is too high, the roots cannot absorb water from the resin, and conversely, the resin absorbs water from the roots. And, when the water-absorbent resin dries, the concentration of ionic functional groups becomes even higher, so that even more water escapes from the roots, which is thought to have a negative effect on plant growth. In other words, it was found that there is a problem that adding a water-absorbent resin makes the soil less likely to dry, but once it dries, it may have a negative effect on the soil.

[0007] On the other hand, the present inventors have found that when the method of imparting drought resistance to plants described in Patent Document 5 is applied to seedling cultivation, a shallow box with holes on the bottom, called a seedling cultivation box, is generally used for seedling cultivation, so water, nutrients, etc. flow out from the bottom, and the amount that the plant can actually use is small compared to the amount administered. Therefore, the above method has the problem that the soil is easily dried and the plant cannot fully utilize acetic acid, etc., and the desired drought resistance cannot be obtained. Furthermore, it has been found that the pH of the soil temporarily decreases, suppressing plant growth.

[0008] Therefore, an object of the present invention is to solve the above problems and to provide a water-retaining material which imparts sufficient drought resistance to plants and promotes plant growth. [Means for solving the problem]

[0009] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by a water-retaining material comprising a water-absorbent resin and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives.

[0010] That is, the present invention includes the following preferred embodiments. [1] A water-retaining material comprising a water-absorbent resin and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. [2] The water-retaining material according to [1], wherein the content of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives is 0.001 mass% or more and 70 mass% or less relative to the mass of the water-retaining material. [3] The water-retaining material according to [1] or [2], wherein the acetic acid derivative is one or more compounds selected from the group consisting of sodium acetate, magnesium acetate, potassium acetate, ammonium acetate and calcium acetate. [4] The water-retaining material according to any one of [1] to [3], wherein the water-absorbent resin contains a polymer selected from the group consisting of vinyl alcohol-based polymers, acrylic acid-based polymers, acrylamide-based polymers, methacrylic acid-based polymers, and starch-based polymers. [5] The water-retaining material according to [4], wherein the vinyl alcohol-based polymer includes a copolymer containing a vinyl alcohol structural unit and a monomer structural unit having an ionic group or a derivative thereof. [6] The water-retaining material according to [4] or [5], wherein the vinyl alcohol polymer contains potassium ions or ammonium ions as counter cations of the ionic groups. [7] The water-retaining material according to any one of [4] to [6], wherein the vinyl alcohol polymer has a crosslinked structure. [8] The water-retaining material according to any one of [1] to [7], which is for agricultural use. [9] The water-retaining material according to any one of [1] to [8], which is for raising seedlings.

[10] The water-retaining material according to any one of [1] to [9], wherein the water-absorbent resin contains an element inside the resin that does not constitute the polymer backbone of the resin, and the element is one or more elements selected from the group consisting of phosphorus, potassium and nitrogen.

[11] The water-retaining material described in

[10] , wherein the content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen present inside the resin is 0.001 mass% or more and 50 mass% or less relative to the mass of the resin.

[12] The water-retaining material according to

[10] or

[11] , further containing one or more elements selected from the group consisting of phosphorus, potassium and nitrogen, which are not present inside the resin but are present in the water-retaining material.

[13] A water-retaining material according to any one of

[10] to

[12] , wherein the content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements which are not present inside the resin but are present in the water-retaining material is 0.001 mass% or more and 50 mass% or less relative to the mass of the resin.

[14] The water-retaining material according to any one of [1] to

[13] , wherein the water-absorbent resin contains therein one or more agents that kill or inhibit the growth of microorganisms in an amount of 0.00001% by mass or more and 10% by mass or less relative to the mass of the resin.

[15] The water-retaining material according to

[14] , further comprising one or more of the chemicals present in the water-retaining material but not present inside the water-absorbent resin.

[16] The water-retaining material according to

[15] , wherein the content of one or more chemicals that are not present inside the water-absorbent resin but are present in the water-retaining material is 0.00001% by mass or more and 10% by mass or less relative to the mass of the resin.

[17] A water-retaining material according to any one of [1] to

[16] , wherein the proportion of water that can be absorbed by a plant in the water-retaining material in an absorbed state, in which the water-retaining material has absorbed 50 times its mass of water, is 7.6 mass% or more based on the mass of the water-retaining material in the absorbed state.

[18] The water-retaining material has an SP value of 6.0 (cal / cm 3 ) 1 / 2 More than 30.0(cal / cm 3 ) 1 / 2 The water-retaining material according to any one of [1] to

[17] , further comprising a compound (Y) which is:

[19] The water-retaining material according to

[18] , wherein the compound (Y) is one or more compounds selected from the group consisting of water, glycerin, methanol, dimethyl sulfoxide, ethanol, acetonitrile, isopropanol, N-methyl-2-pyrrolidone, methyl acetate, tetrahydrofuran, diethyl ether, N,N-dimethylformamide and ethylene glycol.

[20] The water-retaining material according to

[18] or

[19] , wherein the content of the compound (Y) is 0.001% by mass or more and 98% by mass or less relative to the mass of the water-retaining material. Effect of the Invention

[0011] According to the present invention, it is possible to provide a water retention material that imparts sufficient drought resistance to plants and promotes plant growth. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The following is a description illustrating embodiments of the present invention and is not intended to limit the present invention to the following embodiments.

[0013] <Water retention material> The water-retaining material of the present invention comprises a water-absorbent resin and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives.

[0014] The present inventors have found that the water-retaining material of the present invention provides sufficient drought resistance to plants and promotes plant growth. The water-retaining material of the present invention has a high affinity with one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, and the compounds are easily permeated into the resin. Therefore, it is considered that the compound is prevented from flowing out from the bottom of the nursery box, and the amount available to the plant is greater than that in the case of direct administration. Furthermore, since the permeated compound is gradually released into the medium over time, it is considered that the plant was able to use the slowly released compound over a long period of time. In addition, it is considered that the plant was prevented from being exposed to a high concentration of the compound that may have a negative effect on the plant, and therefore the effect of promoting growth was obtained. However, even if the actual embodiment differs from the above assumption, it is within the scope of the present invention. In this way, it was revealed for the first time in the present invention that a water-retaining material comprising a water-absorbent resin and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives has the effect of promoting plant growth.

[0015] <Acetic acid derivatives> The acetic acid derivative is not particularly limited. For example, sodium acetate, magnesium acetate, potassium acetate, ammonium acetate, calcium acetate, methyl acetate, ethyl acetate, iron acetate, copper acetate, lithium acetate, rubidium acetate, acetic anhydride, etc. are listed, but sodium acetate, magnesium acetate, potassium acetate, ammonium acetate, and calcium acetate are preferred because they have good affinity with the water-absorbing resin.

[0016] The molecular weight of the acetic acid derivative is preferably 1000 or less, more preferably 500 or less. When the molecular weight of the acetic acid derivative is within the above range, the acetic acid derivative can easily pass through the cell membrane of the plant and can be easily utilized by the plant, which is preferable. The molecular weight of the acetic acid derivative can be measured, for example, by gas chromatography mass spectrometry, liquid chromatography mass spectrometry, etc.

[0017] The content of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, more preferably 0.01% by mass or more, more preferably 0.02% by mass or more, more preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, even more preferably 1% by mass or more, particularly preferably 5% by mass or more, and preferably 70% by mass or less, more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, even more preferably 55% by mass or less, and particularly preferably 40% by mass or less. The content of the compound can be measured by adopting an appropriate measurement method such as ion chromatography or gas chromatography depending on the type of compound. When measured by ion chromatography, the compound is detected as acetate ions, and the content of acetate ions relative to the mass of the water-retaining material is preferably 0.0005% by mass or more, more preferably 0.003% by mass or more, more preferably 0.005% by mass or more, more preferably 0.01% by mass or more, more preferably 0.03% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 3% by mass or more, and preferably 66% by mass or less, more preferably 63% by mass or less, even more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably 30% by mass or less. The content measured by gas chromatography is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, more preferably 0.01% by mass or more, more preferably 0.02% by mass or more, more preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, even more preferably 1% by mass or more, particularly preferably 5% by mass or more, and preferably 70% by mass or less, more preferably 65% ​​by mass or less, more preferably 60% by mass or less, even more preferably 55% by mass or less, and particularly preferably 40% by mass or less. When the content of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives is within the above range, it is preferable because it can provide sufficient drought resistance to the plant and is less likely to have an adverse effect on the plant.The amount can be adjusted within the above range by, for example, the amount charged during production of the water-retaining material, washing conditions, and the like.

[0018] In the above embodiment, the content of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives in the water-retaining material is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, more preferably 0.01% by mass or more, more preferably 0.02% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 1% by mass or more, more particularly preferably 5.3% by mass or more, and preferably 250% by mass or less, more preferably 200% by mass or less, even more preferably 150% by mass or less, even more preferably 130% by mass or less, and particularly preferably 70% by mass or less. The mass of the resin at this time is the mass in its dry state. In the present invention, the "dry state" may be a state in which the resin does not contain volatile components such as water or organic solvents in an amount detectable by a general method (for example, the change in mass before and after heating at 60 ° C. under vacuum) (for example, 0.1% by mass or more).

[0019] <Water absorbent resin> The water-absorbing resin in the present invention is not particularly limited. For example, acrylic acid polymers, isobutylene-maleic acid copolymers, carboxymethylcellulose polymers, saponified acrylonitrile polymers, alginic acid ester polymers, sulfonic acid polymers, vinyl acetate-maleic anhydride copolymers, N-vinylacetamide polymers, acrylamide polymers, methacrylic acid polymers, starch polymers, ethylene glycol polymers, and vinyl alcohol polymers may be used as the water-absorbing resin. These polymers may be used alone or in combination of two or more.

[0020] From the viewpoints of ease of production and water retention, the water-absorbing resin preferably includes a vinyl alcohol-based polymer, an acrylic acid-based polymer, an acrylamide-based polymer, a methacrylic acid-based polymer, or a starch-based polymer, more preferably includes a vinyl alcohol-based polymer, and in a preferred embodiment, the water-absorbing resin is a vinyl alcohol-based polymer.

[0021] <Vinyl alcohol polymer> Examples of the vinyl alcohol polymer (hereinafter sometimes referred to as vinyl alcohol polymer (A)) include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and those in which the vinyl alcohol unit is acetalized with an acetalizing agent. From the viewpoint of good affinity with one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, the vinyl alcohol polymer (A) preferably includes a copolymer containing a vinyl alcohol structural unit and a monomer structural unit having an ionic group or a derivative thereof. The ionic group or a derivative thereof is preferably a carboxyl group, a sulfonic acid group, an ammonium group or a salt thereof, and more preferably a carboxyl group or a salt thereof. The content of the vinyl alcohol polymer (A) in the water absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass. Furthermore, the content of the copolymer in the vinyl alcohol polymer (A) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass. That is, in one preferred embodiment, the vinyl alcohol polymer (A) comprises a copolymer of a vinyl alcohol constituent unit and a monomer constituent unit having an ionic group or a derivative thereof.

[0022] When the vinyl alcohol polymer (A) has a carboxyl group, a sulfonic acid group, and an ammonium group as an ionic group, examples of the vinyl alcohol polymer (A) include (i-1) a saponification product of a copolymer of a vinyl ester and one or more selected from a monomer having a carboxyl group, a sulfonic acid group, and an ammonium group and derivatives of the monomer; (i-2) a reaction product of a vinyl alcohol polymer and a compound (B) having a functional group (b1) capable of reacting with a hydroxyl group and a carboxyl group and / or a functional group (b2) capable of being derived to a carboxyl group; and the like.

[0023] In the above (i-1), the monomer having a carboxyl group is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, itaconic acid, maleic acid, etc. In addition, examples of the derivatives of the monomer having a carboxyl group include anhydrides, esters, neutralization products, etc. of the monomer, and examples of the derivatives include methyl acrylate, methyl methacrylate, dimethyl itaconate, monomethyl maleate, maleic anhydride, etc.

[0024] In the above (i-1), the monomer having a sulfonic acid group is not particularly limited, and examples thereof include vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and p-styrenesulfonic acid. In addition, examples of the derivatives of the monomer having a sulfonic acid group include the esters and neutralized products of the monomers, and examples of the derivatives include sodium vinylsulfonate, sodium 2-acrylamido-2-methylpropanesulfonate, and sodium p-styrenesulfonate.

[0025] In the above (i-1), the monomer having an ammonium group is not particularly limited, and examples thereof include diallyldimethylammonium chloride, vinyltrimethylammonium chloride, allyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, and 3-(methacrylamide)propyltrimethylammonium chloride. In addition, examples of the derivatives of the monomer having an ammonium group include the amines of the monomers, and examples thereof include diallylmethylamine, vinylamine, allylamine, p-vinylbenzyldimethylamine, and 3-(methacrylamide)propyldimethylamine.

[0026] In the above (i-1), the vinyl ester is not particularly limited, but examples thereof include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl stearate, vinyl benzoate, vinyl trifluoroacetate, and vinyl pivalate, with vinyl acetate being preferred.

[0027] The method for producing the saponified product (i-1) above is not particularly limited, and the product can be produced by carrying out a known polymerization reaction of one or more selected from a monomer having a carboxyl group and a derivative of the monomer with a vinyl ester using a known polymerization initiator, and then carrying out a saponification reaction by a known method.

[0028] In the compound (B) used in the above (i-2) having a functional group (b1) capable of reacting with a hydroxyl group and a functional group (b2) capable of being derived to a carboxyl group, the functional group (b1) capable of reacting with a hydroxyl group is not particularly limited, and examples thereof include an aldehyde group, a carboxyl group, an amino group, and derivatives of these functional groups. Among them, from the viewpoint of ease of production or durability of the vinyl alcohol polymer, an aldehyde group and a derivative of an aldehyde group are preferred. That is, as the compound (B), an aldehyde having a carboxyl group and / or a derivative of the aldehyde are preferred.

[0029] That is, the reaction product of the above (i-2) is preferably a vinyl alcohol polymer in which at least a part of the vinyl alcohol units is acetalized with one or more selected from aldehydes having a carboxyl group and / or derivatives of the aldehydes [hereinafter, sometimes referred to as vinyl alcohol polymer (A-1)].

[0030] The aldehyde having a carboxyl group, which is the compound (B), is not particularly limited, and examples thereof include glyoxylic acid, 2-formylpropanoic acid, 3-formylpropanoic acid, and phthalaldehyde acid. Among them, glyoxylic acid is preferred from the viewpoints of availability and biodegradability. In addition, the derivative of the aldehyde having a carboxyl group, which is the compound (B), includes anhydrides, hydrates, esters, acetals, and neutralization products of the aldehyde, and examples thereof include glyoxylates, glyoxylic acid monohydrates, glyoxylic acid esters, and glyoxylic acid dimethyl acetal.

[0031] The counter cation of the glyoxylate salt may be an alkali metal ion such as sodium ion, potassium ion, or lithium ion; an alkaline earth metal ion such as calcium ion or magnesium ion; or an organic cation such as ammonium ion or alkylammonium ion. Among them, from the viewpoint of good affinity with acetic acid and acetic acid derivatives, potassium ion, ammonium ion, calcium ion, or magnesium ion is preferred. From the viewpoint of plant growth, potassium ion or ammonium ion is more preferred, and from the viewpoint of ease of production, potassium ion is even more preferred.

[0032] Examples of the glyoxylate ester include methyl glyoxylate, ethyl glyoxylate, propyl glyoxylate, isopropyl glyoxylate, butyl glyoxylate, isobutyl glyoxylate, sec-butyl glyoxylate, tert-butyl glyoxylate, hexyl glyoxylate, octyl glyoxylate, and 2-ethylhexyl glyoxylate.

[0033] The method for producing the vinyl alcohol polymer (A-1) is not particularly limited, and the vinyl alcohol polymer (A-1) can be produced by acetalizing at least a portion of the vinyl alcohol units of a vinyl alcohol polymer produced by a known method with one or more selected from an aldehyde having a carboxyl group and a derivative of the aldehyde, in the presence or absence of a catalyst.

[0034] Examples of the catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as carboxylic acid and sulfonic acid; and solid acids such as cation exchange resins and heteropolyacids. These catalysts may be used alone or in combination. Glyoxylic acid is also an acid that promotes the acetalization reaction, and therefore acts as a catalyst when producing the vinyl alcohol polymer (A-1). In other words, from the viewpoint of ease of treatment after the reaction, a method of using glyoxylic acid as an aldehyde having a carboxyl group when producing the vinyl alcohol polymer (A-1) is preferred.

[0035] The vinyl alcohol polymer used as a raw material in the production of the vinyl alcohol polymer (A-1) may be any of the following: a commercially available product produced industrially; a product produced by carrying out a known polymerization reaction using a known polymerization initiator in the presence of vinyl carboxylate such as vinyl acetate and other monomers as necessary, followed by a known method of saponification reaction; a product produced by cationic polymerization and hydrolysis reaction of vinyl ether; a product produced by direct polymerization of acetaldehyde; and the like, but a product produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is preferred. The saponification degree of the vinyl alcohol polymer used as the raw material is preferably 30 mol% or more, more preferably 60 mol% or more, and from the viewpoint of easily introducing an appropriate amount of carboxyl groups in one embodiment of the present invention, more preferably 80 mol% or more, even more preferably 90 mol% or more.

[0036] The acetalization degree of the vinyl alcohol polymer (A-1) is preferably 0.01 mol% or more and 85 mol% or less. When the acetalization degree is within the above range, it is easy to improve the water absorbency. From the above viewpoint, the acetalization degree is preferably 0.1 mol% or more, more preferably 1 mol% or more, even more preferably 5 mol% or more, even more preferably 8 mol% or more, particularly preferably 10 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, even more preferably 60 mol% or less, even more preferably 50 mol% or less, particularly preferably 45 mol% or less, and even more preferably 40 mol% or less.

[0037] From the viewpoint of easily suppressing the elution of the vinyl alcohol polymer (for example, during seedling raising), in the production of the vinyl alcohol polymer (A-1), acetalization reaction may be carried out by using other aldehydes other than the aldehyde having a carboxyl group and the derivative of the aldehyde. Examples of such other aldehydes include aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, i-butyraldehyde, sec-butyraldehyde, and tert-butyraldehyde; aromatic aldehydes such as benzaldehyde, anisaldehyde, cinnamaldehyde, 4-benzyloxybenzaldehyde, 3-benzyloxybenzaldehyde, 4-amyloxybenzaldehyde, and 3-amyloxybenzaldehyde; and the like. Among them, from the viewpoint of ease of production or water absorption and strength of the vinyl alcohol polymer obtained, formaldehyde, acetaldehyde, and n-butylaldehyde are preferred. When other aldehydes are used in combination, there is no particular limitation on the amount used, but it is usually 0.01 to 30 mol%, preferably 0.1 to 10 mol%, more preferably 1 to 5 mol% based on the total of the aldehyde having a carboxylic acid and the derivative of the aldehyde. When the amount of other aldehyde used is less than the upper limit, the water absorption of the obtained vinyl alcohol polymer tends to be excellent, and when it is more than the lower limit, it is easy to obtain the effect of suppressing the elution of the vinyl alcohol polymer during seedling growth due to the use of other aldehydes in combination. The other aldehydes may be used as derivatives such as acetals.

[0038] In one embodiment of the present invention, when the vinyl alcohol polymer (A) has an ionic group (e.g., a carboxyl group), a part or all of the ionic group may be in the form of a salt (a carboxylate when the ionic group is a carboxyl group). Examples of counter cations of the salt include alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; other metal ions such as aluminum ion and zinc ion; onium cations such as ammonium ion, imidazolium ion, pyridinium ion, and phosphonium ion; and the like. Among them, potassium ion, ammonium ion, calcium ion, and magnesium ion are preferred from the viewpoint of good affinity with acetic acid and acetic acid derivatives. Potassium ion and ammonium ion are more preferred from the viewpoint of plant growth, and potassium ion is even more preferred from the viewpoint of ease of production. Therefore, in a preferred embodiment of the present invention, the vinyl alcohol polymer (A) contains potassium ion or ammonium ion, preferably potassium ion, as a counter cation of the ionic group. When the ionic group is a carboxyl group, examples of a method for producing a vinyl alcohol polymer (A) in which some or all of the carboxyl groups are carboxylates include the method (I) using a neutralized product of a monomer having a carboxyl group in the above (i-1); the method (II) using a neutralized product of a compound having a carboxyl group and a functional group capable of reacting with a hydroxyl group in the above (i-2); and the method (III) of producing a vinyl alcohol polymer (A) having a carboxyl group by the above-mentioned various methods and then neutralizing the produced polymer; and among these, the method (III) is preferred.

[0039] In one embodiment of the present invention, when the vinyl alcohol polymer (A) has an ionic group, the amount of the ionic group in the vinyl alcohol polymer (A) is preferably 0.1 mol% or more, more preferably 1 mol% or more, particularly preferably 3 mol% or more, most preferably 5 mol% or more, and is preferably 80 mol% or less, more preferably 50 mol% or less, more preferably 40 mol% or less, more preferably 30 mol% or less, even more preferably 25 mol% or less, particularly preferably 20 mol% or less, most preferably less than 18 mol%. When the amount of the ionic group is the lower limit or more, the water absorption of the vinyl alcohol polymer used in the present invention is more excellent, and when it is the upper limit or less, decomposition by ultraviolet light is unlikely to occur, and the retention of acetic acid and acetic acid derivatives is maintained. In addition, when the vinyl alcohol polymer (A) has a carboxyl group as an ionic group, the amount of the carboxyl group derived from acrylic acid or its salt is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol% based on the total structural units of the vinyl alcohol polymer. When the amount of the carboxyl group derived from acrylic acid or its salt is the upper limit or less, it is easy to obtain better weather resistance (particularly ultraviolet resistance). In addition, when a part or all of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of a derivative (e.g., a salt), the content of the ionic group is the content of the ionic group and its derivative or the content of the derivative of the ionic group. In a preferred embodiment, more than half of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives. In a more preferred embodiment, most of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives. In a particularly preferred embodiment, all of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives.

[0040] The content of ionic groups in the vinyl alcohol polymer (A), particularly the amount of the carboxyl groups and the amount of the carboxyl groups derived from acrylic acid or a salt thereof, among the carboxyl groups, may vary depending on, for example, the solid 13 It can be measured by C-NMR (nuclear magnetic resonance spectroscopy), FTIR (Fourier transform infrared spectroscopy), acid-base titration, etc. In the present invention, the term "structural unit" refers to a repeating unit that constitutes a polymer, and for example, a vinyl alcohol unit is counted as "1 unit," and a structure in which two vinyl alcohol units are acetalized is counted as "2 units."

[0041] The content of the vinyl alcohol structural unit in the vinyl alcohol polymer (A) is preferably more than 20 mol%, more preferably 50 mol% or more, and even more preferably 60 mol% or more, and is preferably 98 mol% or less, more preferably 95 mol% or less, and even more preferably 90 mol% or less, based on the total structural units of the vinyl alcohol polymer (A). The content of the vinyl alcohol structural unit can be measured, for example, by Fourier transform infrared spectroscopy (FTIR), solid 13 It can be measured by C-NMR (nuclear magnetic resonance spectroscopy) or can be calculated from the amount of acetic anhydride consumed when reacted with a fixed amount of acetic anhydride.

[0042] The vinyl alcohol polymer (A) may contain other structural units other than the vinyl alcohol structural unit. Examples of the other structural units include structural units derived from vinyl carboxylate such as vinyl acetate and vinyl pivalate; structural units derived from olefins such as ethylene, 1-butene, and isobutylene; structural units derived from acrylic acid and its derivatives, methacrylic acid and its derivatives, acrylamide and its derivatives, methacrylamide and its derivatives, maleic acid and its derivatives, and maleimide derivatives; and the like. The other structural units may contain one type or multiple types. The content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, and even more preferably 15 mol% or less, based on the total structural units of the vinyl alcohol polymer (A), and may be 0 mol%. When the content of the other structural units is less than the upper limit, the water retention material of the present invention is more likely to have excellent water absorption and water absorption speed.

[0043] The viscosity average degree of polymerization of the vinyl alcohol polymer (A) is not particularly limited, but from the viewpoint of ease of production, it is preferably 20,000 or less, more preferably 10,000 or less, even more preferably 4,000 or less, and particularly preferably 3,000 or less. On the other hand, from the viewpoint of the mechanical properties and resistance to dissolution into water of the vinyl alcohol polymer (A), it is preferably 100 or more, more preferably 200 or more, and even more preferably 400 or more. The viscosity average degree of polymerization of the vinyl alcohol polymer (A) can be measured, for example, by a method according to JIS K 6726. When the vinyl alcohol polymer (A) has a crosslinked structure as described below, for example, when the vinyl alcohol polymer (A) has an acetal structure or an ester structure as a crosslinked structure, the viscosity average degree of polymerization can be measured after the crosslinked structure is cut. The cut can be performed by a general method (for example, hydrolysis using an acid or an alkali).

[0044] The vinyl alcohol polymer (A) used in the present invention preferably contains a crosslinked structure in order to prevent the vinyl alcohol polymer from eluting during seedling cultivation. When the vinyl alcohol polymer (A) used in the present invention contains a crosslinked structure, it becomes a gel state when absorbing water. There is no particular limitation on the form of the crosslinked structure, and examples thereof include crosslinked structures by ester bonds, ether bonds, acetal bonds, and carbon-carbon bonds.

[0045] An example of the ester bond is an ester bond formed between a hydroxyl group and a carboxyl group of the vinyl alcohol polymer (A) when the vinyl alcohol polymer (A) has a carboxyl group as an ionic group. An example of the ether bond is an ether bond formed by dehydration condensation between hydroxyl groups of the vinyl alcohol polymer (A). An example of the acetal bond is an acetal bond formed by acetalization reaction between hydroxyl groups of two vinyl alcohol polymers (A) and an aldehyde having a carboxyl group when an aldehyde having a carboxyl group is used in the production of the vinyl alcohol polymer (A). An example of the carbon-carbon bond is a carbon-carbon bond formed by coupling between carbon radicals of the vinyl alcohol polymer (A) when the vinyl alcohol polymer (A) is irradiated with active energy rays. These crosslinked structures may be contained alone or in multiple types. Among these, crosslinked structures based on ester bonds and acetal bonds are preferred from the viewpoint of ease of production, and crosslinked structures based on acetal bonds are more preferred from the viewpoints of maintaining water retention during seedling raising, maintaining the retention of acetic acid and acetic acid derivatives, and ultraviolet resistance. Such a crosslinked structure may be formed simultaneously with the acetalization reaction in a step of acetalizing at least a portion of the vinyl alcohol units with, for example, one or more selected from an aldehyde having a carboxyl group and an aldehyde derivative thereof, or may be formed in a separate step. In the present invention, however, it is preferable to form the crosslinked structure by further adding a crosslinking agent.

[0046] Crosslinking agents include glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, 1,9-nonanedial, adipaldehyde, malealdehyde, tartaraldehyde, citralaldehyde, phthalaldehyde, isophthalaldehyde, and terephthalaldehyde.

[0047] When a crosslinking agent is added, the amount of the crosslinking agent in the vinyl alcohol polymer (A) is, from the viewpoint of easily maintaining water retention in soil, preferably 0.001 mol % or more, more preferably 0.005 mol % or more, even more preferably 0.01 mol % or more, still more preferably 0.03 mol % or more, and is preferably 0.5 mol % or less, more preferably 0.4 mol % or less, and even more preferably 0.3 mol % or less.

[0048] <Acrylic acid polymer> Examples of the polymer that may be contained in the water-absorbent resin include acrylic acid polymers. In this specification, the acrylic acid polymer generally refers to a homopolymer of acrylic acid or an acrylic acid derivative, and an acrylic acid copolymer obtained by copolymerizing a monomer component having acrylic acid or an acrylic acid derivative as a main monomer (monomer with the highest mole percentage among the monomer components). For example, raw materials include acrylic acid, sodium acrylate, potassium acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and phenyl acrylate, and the like. Examples include copolymerization of one or more of these monomers with a crosslinking agent, or copolymerization of at least one of the monomers, a crosslinking agent, and at least one other monomer that can be further copolymerized using a known method. Specifically, for example, a crosslinked product of acrylic acid-sodium acrylate copolymer can be mentioned. Examples of commercially available products include superabsorbent polymer (acrylate type) manufactured by Wako Pure Chemical Industries, Ltd., ACRYHOPE (registered trademark) manufactured by Nippon Shokubai Co., Ltd., and SANWET (registered trademark) manufactured by Sanyo Chemical Industries, Ltd.

[0049] <Acrylamide polymer> Examples of the polymer that may be contained in the water-absorbing resin include acrylamide polymers. In this specification, the acrylamide polymer generally refers to a homopolymer of acrylamide or an acrylamide derivative, and an acrylamide copolymer obtained by copolymerizing a monomer component having acrylamide or an acrylamide derivative as the main monomer (the monomer with the highest mole percentage among the monomer components). For example, examples of the raw material include acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and N-alkylacrylamide, and the like, and examples of the copolymerization of one or more of these monomers with a crosslinking agent, or the polymerization of the at least one monomer, the crosslinking agent, and at least one other monomer that can be further copolymerized using a known method. Specific examples of the polymer include a crosslinked product of acrylamide-acrylic acid-sodium acrylate copolymer, a crosslinked product of acrylamide-acrylic acid-potassium acrylate copolymer, and the like. Examples of commercially available products include Miracle-Gro (registered trademark) Water Storing Crystal; manufactured by Scotts Miracle Gro Co., Ltd., Aquasorb (registered trademark); manufactured by SNF Co., Ltd., and the like.

[0050] <Methacrylic acid polymer> The polymer that may be contained in the water-absorbing resin includes a methacrylic acid polymer. The methacrylic acid polymer generally refers to a homopolymer of methacrylic acid or a methacrylic acid derivative, and a methacrylic acid copolymer obtained by copolymerizing a monomer component having methacrylic acid or a methacrylic acid derivative as a main monomer (monomer having the highest mole percentage among the monomer components). For example, the raw material may include methacrylic acid, sodium methacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, 2-ethylhexyl methacrylate, t-butylcyclohexyl methacrylate, benzyl methacrylate, and 2,2,2-trifluoroethyl methacrylate, and the like. The polymer may be one or more of these monomers polymerized, or the at least one monomer, a crosslinking agent, and at least one other monomer that can be copolymerized may be copolymerized using a known method.

[0051] <Starch-based polymer> Examples of polymers that may be contained in the water-absorbent resin include starch-based polymers, such as those obtained by graft-polymerizing starch with acrylic acid, sodium acrylate, potassium acrylate, acrylonitrile, and the like.

[0052] <Phosphorus, potassium and nitrogen elements> In a preferred embodiment of the present invention, the water-absorbent resin contained in the water-retaining material of the present invention may contain an element that does not constitute the polymer skeleton of the resin inside the resin, and the element is one or more elements selected from the group consisting of phosphorus, potassium and nitrogen. In this specification, the content of an element that does not constitute the polymer skeleton of the resin inside the water-absorbent resin usually refers to a value calculated by subtracting the element content (the element content constituting the polymer skeleton) of the resin cross section after water washing and drying treatment from the element content of the untreated resin cross section (the total value of the element content constituting the polymer skeleton and the element content not constituting the polymer skeleton contained inside the resin), as described in the examples below.

[0053] The phosphorus, potassium and nitrogen elements are known as the three elements of fertilizer, and their origins include compounds or ions having the above atoms, such as potassium sulfate, potassium chloride, potassium carbonate, potassium hydrogen carbonate, ammonium chloride, ammonium nitrate, ammonium sulfate, sodium nitrate, phosphoric acid, diammonium hydrogen phosphate, lime superphosphate, urea, monocalcium phosphate, potassium nitrate, potassium chloride, potassium hydroxide, ammonium ion, nitrate ion, nitrite ion, phosphate ion, dihydrogen phosphate ion, monohydrogen phosphate ion and potassium ion, and from the viewpoint of ease of utilization by plants, diammonium hydrogen phosphate, potassium sulfate, potassium chloride, potassium hydroxide, potassium nitrate, ammonium sulfate, urea and lime superphosphate are preferred.

[0054] The content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements present inside the resin is preferably 0.001% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, even more preferably 1.0% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or more, even more preferably 30% by mass or less, and even more preferably 25% by mass or less, based on the mass of the resin. The mass of the resin at this time is the mass in its dry state. If the content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements present inside the resin is within the above range, it is preferable because the element is easily released appropriately from inside the resin. The content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements present inside the resin can be measured, for example, by energy dispersive X-ray elemental analysis or ICP-AES (inductively coupled plasma atomic emission spectrometry), as described in the examples below. The elements present inside the resin may be two or more of phosphorus, potassium and nitrogen, and are preferably phosphorus and potassium, phosphorus and nitrogen, or potassium and phosphorus. Also, it is preferably all of phosphorus, potassium and nitrogen. The total content of phosphorus, potassium and nitrogen elements present inside the resin is preferably 0.002% by mass or more, more preferably 0.06% by mass or more, even more preferably 0.2% by mass or more, even more preferably 1.1% by mass or more, and is preferably 70% by mass or less, more preferably 45% by mass or less, even more preferably 32% by mass or less, even more preferably 27% by mass or less, particularly preferably 10% by mass or less, and most preferably 5% by mass or less, based on the mass of the resin. The mass of the resin in this case is the mass in its dry state. The amount can be adjusted within the above range, for example, by the amount of charge and washing conditions (number of times, time, etc.) during resin production.

[0055] The water retention material of the present invention may further contain one or more elements selected from the group consisting of phosphorus, potassium and nitrogen, which are not present inside the resin but are present in the water retention material.

[0056] One or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements that are not present inside the resin but are present in the water-retaining material may be the same as or different from the elements contained inside the resin described above.

[0057] The content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements, which are not present inside the resin but are present in the water-retaining material, is preferably 0.001% by mass or more, more preferably 0.3% by mass or more, even more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, relative to the mass of the resin. The mass of the resin at this time is the mass in its dry state. If the content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements, which are not present inside the resin but are present in the water-retaining material, is within the above range, it is preferable because the plant is less likely to suffer from root burn. The elements not present inside the resin but present in the water-retaining material may be two or more of phosphorus, potassium and nitrogen, and are preferably phosphorus and potassium, phosphorus and nitrogen, or potassium and phosphorus. Also, it is preferably all of phosphorus, potassium and nitrogen. The total content of phosphorus, potassium and nitrogen elements that are not present inside the resin but are present in the water-retaining material is preferably 0.4% by mass or more, more preferably 1.1% by mass or more, even more preferably 1.6% by mass or more, and is preferably 70% by mass or less, more preferably 25% by mass or less, even more preferably 17% by mass or less, even more preferably 11% by mass or less, and particularly preferably 5% by mass or less, relative to the mass of the resin. The mass of the resin in this case is the mass in its dry state. The amount can be adjusted within the above range, for example, by the amount of charge and washing conditions (number of times, time) during the production of the water-retaining material. In the present invention, when the water-retaining material contains phosphorus, potassium and nitrogen elements derived from one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, and phosphorus, potassium and nitrogen elements derived from a compound other than one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, the above content is the total amount.

[0058] <Drugs> In a preferred embodiment of the present invention, the water-absorbent resin contained in the water-retaining material of the present invention may contain one or more agents that kill or inhibit the growth of microorganisms in an amount of 0.00001% by mass to 10% by mass relative to the mass of the resin. Here, containing one or more agents means containing the agents exemplified below alone or in combination of two or more.

[0059] In the resin, the amount of the drug contained therein is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, particularly preferably 0.05% by mass or more, and preferably 2% by mass or less, more preferably 1% by mass or less, particularly preferably 0.1% by mass or less. When the amount of drug is within the above range, the water-retaining material is likely to have excellent stability during storage and use without inhibiting plant growth. This is thought to be because the drug is contained in an appropriate amount inside the resin, and the drug is easily released appropriately from inside the resin during use. The amount can be adjusted by the amount of drug charged and washing conditions (number of times, time) when producing the water-retaining material, and can be measured, for example, by the method described in the Examples.

[0060] The drug contained in the resin is not particularly limited as long as it has the effect of killing or inhibiting the growth of microorganisms (e.g., fungi (e.g., molds and yeasts), slime molds, protozoa, single-celled algae, rickettsia, bacteria, viruses, etc.). Examples of such drugs include preservatives, bactericides, antibacterial agents, antiseptics, and fungicides.

[0061] Examples of preservatives include sorbic acid and its salts.

[0062] Examples of the disinfectant or antibacterial agent include tetrachloroisophthalonitrile (TPN), captan, cinclozolin, brassimidone, benthazole, quaternary ammonium salts, phenolic compounds, quaternary pyridinium salts, peracids, formaldehyde, glutaraldehyde, antibiotics (e.g., penicillin, streptomycin, chloramphenicol, etc.), N-chlorosuccinimide, lime, sulfur, organic sulfur agents (e.g., zineb, maneb, thiodiazine agents, thiuram agents, etc.), monothiocarbabates, dithiocarbabates, thiodiazines, sulfonamides, phthalimides, petroleum ether, naphthoquinone, benzoquinone, disulfides, mercuric compounds, tetrahydrophthalimides, arsenates, cupric salts, organic copper agents (e.g., 8-oxyquinoline copper, etc.), guanidine salts, triazines, glyoxalidine salts, quinolinium salts, and phenylcrotonate.

[0063] Examples of preservatives or fungicides include halogen donors, particularly chlorine donors, such as chloro-cyanuric acids and their salts, particularly mono-sodium or potassium dichloroisocyanurate; hydroxyquinones, sulfites, silver salts and copper salts.

[0064] In addition, the following agents are also exemplified as agents having an effect of killing or inhibiting the growth of microorganisms: water-soluble oxidizing agents of hypochlorous acid (salts) as preservatives, bactericides, antiseptics or fungicides; phenylphenols such as o-phenylphenol (excluding methoxyphenols) as bactericides or fungicides; benzoic acid or its esters (preferably C1-C 20 , more preferably C1 to C 10 alkyl esters of hydroxybenzoic acid or its esters (preferably C1-C 20 , more preferably C1 to C 10 Among these, benzoic acid or its ester and hydroxybenzoic acid or its ester are preferred.

[0065] Examples of benzoic acid esters include methylparaben (methyl 4-hydroxybenzoate), ethylparaben (ethyl paraoxybenzoate), propylparaben (propyl paraoxybenzoate), isopropylparaben (isopropyl paraoxybenzoate), butylparaben (butyl paraoxybenzoate), isobutylparaben (isobutyl paraoxybenzoate), and benzylparaben (benzyl paraoxybenzoate). Examples of hydroxybenzoic acids include gallic acid, and examples of hydroxybenzoic acid esters include propyl gallate.

[0066] In one embodiment of the present invention, the water retention material may further comprise one or more of the above-mentioned agents that are not present inside the resin but are present in the water retention material.

[0067] In this embodiment, the content of one or more chemicals that are not present inside the resin and are present in the water-retaining material is preferably 0.00001% by mass or more, more preferably 0.001% by mass or more, particularly preferably 0.01% by mass or more, and preferably 10% by mass or less, more preferably 0.3% by mass or less, particularly preferably 0.05% by mass or less, relative to the mass of the resin. The mass of the resin in this case is the mass in its dry state. When the content is within the above range, the water-retaining material is likely to have excellent stability during storage, and is likely to have excellent stability during use not only for a short period of time but also for a long period of time without inhibiting plant growth. The content can be adjusted, for example, by the amount of chemicals charged and washing conditions (number of times, time) during the production of the water-retaining material, and can be measured by the method described in the Examples.

[0068] In a preferred embodiment of the present invention, the water retention material of the present invention in a water-absorbed state that has absorbed 50 times the mass of the water retention material has a water ratio that is absorbable by plants, based on the mass of the water retention material in the water-absorbed state, of preferably 7.6% by mass or more, more preferably 10% by mass or more, even more preferably 30% by mass or more, and particularly preferably 50% by mass or more. There is no particular upper limit to the ratio. The ratio is usually 90% by mass or less.

[0069] In the present invention, the water that can be absorbed by the plant is the water released by the water retention material that has absorbed water. When the plant absorbs the water released from the water retention material that has absorbed water, the plant can use the water for growth. Even if the water retention material has a high water absorption capacity, if the water retention material has a low ability to release the absorbed water, it is difficult for the plant to absorb a sufficient amount of water from the water retention material. In a preferred embodiment, the water retention material of the present invention has a very good water release capacity, so that the plant can sufficiently absorb water that can be used for growth from the water retention material. In addition, it is also considered that the water retention material is likely to have excellent stability during use not only for a short period of time but also for a long period of time without inhibiting the growth of the plant, by appropriately releasing each component contained in the resin with the release of water from the water retention material.

[0070] The proportion of water that can be absorbed by plants can be adjusted by the amount of crosslinked structures in the resin, the amount of structural units that form carboxylates, and the type or amount of chemicals contained in the water-retaining material. For example, the proportion can be increased by increasing the amount of crosslinked structures in the resin or decreasing the amount of structural units that form carboxylates. The proportion of water that can be absorbed by plants can be measured by the method described in the Examples below.

[0071] <Compound Y> In a preferred embodiment of the present invention, the water-retaining material of the present invention has an SP value of 6.0 (cal / cm 3 ) 1 / 2 More than 30.0(cal / cm 3 ) 1 / 2 The water retention material may further contain the following compound (Y): When the water retention material further contains compound (Y), it is possible to achieve an improvement in the water absorption rate of the water retention material and suppression of dust generation.

[0072] The SP value of the compound (Y) is preferably 9.0 (cal / cm 3 ) 1 / 2 More preferably, 11.0 (cal / cm 3 ) 1 / 2 More preferably, 13.0 (cal / cm 3 ) 1 / 2 More preferably, it is 29.0 (cal / cm 3 ) 1 / 2 Less than or equal to 26.0 (cal / cm 3 ) 1 / 2 Less than 25.0 (cal / cm 3 ) 1 / 2 When the SP value is within the above range, it is easy to improve the water absorption rate of the water retention material and to suppress the generation of dust. Here, the SP value in the present invention is an SP value calculated according to the Fedors method [SP Value Fundamentals, Applications and Calculation Methods (Published by Information Organization, Author: Yamamoto Hideki, 2005), Fedors, Polym. Eng. Sci. 14, 147 (1974)].

[0073] From the viewpoint of easily achieving an improvement in the water absorption rate of the water-retaining material and suppression of dust generation, the compound (Y) having such an SP value is preferably one or more compounds selected from the group consisting of water, glycerin, methanol, dimethyl sulfoxide, ethanol, acetonitrile, isopropanol, N-methyl-2-pyrrolidone, methyl acetate, tetrahydrofuran, diethyl ether, N,N-dimethylformamide and ethylene glycol.

[0074] When the water-retaining material contains compound (Y), the content of compound (Y) in the water-retaining material is preferably 0.001% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more (e.g. 15% by mass or more), and is preferably 98% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, particularly preferably 50% by mass or less (e.g. 40% by mass or less) relative to the mass of the water-retaining material. When the content of compound (Y) is within the above range, it is easy to achieve an improvement in the water absorption rate of the water-retaining material and suppression of dust generation.

[0075] In the above embodiment, the content of the compound (Y) in the water-retaining material is preferably 0.001% by mass or more, more preferably 1% by mass or more, even more preferably 5% by mass or more, particularly preferably 11% by mass or more (e.g. 18% by mass or more), and is preferably 4900% by mass or less, more preferably 900% by mass or less, even more preferably 400% by mass or less, particularly preferably 100% by mass or less (e.g. 67% by mass or less) relative to the mass of the resin. The mass of the resin in this case is the mass in its dry state.

[0076] In a preferred embodiment, the compound (Y) contains one or more compounds selected from the group consisting of water, glycerin, methanol, ethanol and isopropanol, and the content of the compound is preferably 3% by mass or more, more preferably 10% by mass or more, particularly preferably 15% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, particularly preferably 40% by mass or less, based on the mass of the water retention material. In this embodiment, in addition to the rapid water absorption rate and low dust generation of the water retention material, an excellent germination rate is easily obtained. In this embodiment, the content of the compound (Y) is preferably 3% by mass or more, more preferably 11% by mass or more, particularly preferably 18% by mass or more, and is preferably 900% by mass or less, more preferably 400% by mass or less, particularly preferably 67% by mass or less, based on the mass of the resin. The mass of the resin in this case is the mass in its dry state.

[0077] In a preferred embodiment, the compound (Y) comprises water or methanol. In another preferred embodiment, the compound (Y) consists of water. In yet another preferred embodiment, the compound (Y) consists of methanol. In these embodiments, in addition to low dust generation and excellent germination rate, an extremely rapid water absorption rate of the water retention material is easily obtained. The content of water or methanol is preferably 3% by mass or more, more preferably 5% by mass or more, particularly preferably 10% by mass or more (e.g. 15% by mass or more), and is preferably 90% by mass or less, more preferably 80% by mass or less, particularly preferably 40% by mass or less, based on the mass of the water retention material. In this embodiment, the content of water or methanol is preferably 3% by mass or more, more preferably 5% by mass or more, particularly preferably 11% by mass or more (e.g., 18% by mass or more), and is preferably 900% by mass or less, more preferably 400% by mass or less, particularly preferably 67% by mass or less, based on the mass of the resin. The mass of the resin in this case is the mass in its dry state.

[0078] <Additives> The water-retaining material of the present invention may contain, in addition to the water-absorbent resin and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, an optional additive. Examples of such additives include polysaccharides such as sodium alginate, chitin, chitosan, cellulose and its derivatives; polyethylene, polypropylene, ethylene-propylene copolymers, polystyrene, acrylonitrile-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, polycarbonate resins, polyethylene terephthalate, polybutylene terephthalate, polylactic acid, polysuccinic acid, polyamide 6, polyamide 6·6, polyamide 6·10, polyamide 11, polyamide 12, polyamide 6·12, polyhexamethylenediamine terephthalamide, polyhexamethylenediamine isophthalamide, polynonamethylenediamine, polyisopropyl ... Resins such as terephthalamide, polyphenylene ether, polyoxymethylene, polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, and polyurethane; rubbers and elastomers such as natural rubber, synthetic isoprene rubber, chloroprene rubber, silicone rubber, fluororubber, urethane rubber, acrylic rubber, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, ester-based thermoplastic elastomer, urethane-based thermoplastic elastomer, and amide-based thermoplastic elastomer; ultraviolet absorbers, antioxidants, light stabilizers, defoamers, thickeners, surfactants, lubricants, and antistatic agents. These additives can be used alone or in combination of two or more. When the water-retaining material contains additives, the total content of the additives may be within a range that does not impair the effects of the present invention, and is usually 20% by mass or less, preferably 15% by mass or less, based on the total mass of the water-retaining material.

[0079] The water retention material of the present invention is preferably in the form of particles. When the water retention material of the present invention is in the form of particles, the volume average particle diameter of the particles is preferably 1 μm or more, more preferably 50 μm or more, even more preferably 100 μm or more, particularly preferably 300 μm or more, and is preferably 10000 μm or less, more preferably 2000 μm or less, and even more preferably 1500 μm or less. When the volume average particle diameter is the lower limit or more, the handling property is excellent, and when the volume average particle diameter is the upper limit or less, an excellent water absorption rate is easily obtained. The volume average particle diameter can be measured by laser diffraction / scattering.

[0080] <Water retention material manufacturing method> The water-retaining material of the present invention can be produced, for example, by (ii-1) mixing one or more compounds selected from the group consisting of a water-absorbing resin, acetic acid, and acetic acid derivatives, and optionally the additives; (ii-2) spraying and mixing one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives (if solid, dissolved in any solvent such as water or alcohol) on a water-absorbing resin, or immersing the water-absorbing resin in the mixture, and optionally mixing the water-absorbing resin after mixing with the additives; (ii-3) leaving one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives during preparation of the water-absorbing resin, and optionally mixing the obtained preparation with the additives; or (ii-4) a method combining the above (ii-1) to (ii-3). In the above (ii-1) to (ii-4), the content of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives can be adjusted by adjusting the amount of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives used and the degree of washing of the water-retaining material.

[0081] When the water-retaining material of the present invention also contains one or more elements selected from the group consisting of phosphorus, potassium and nitrogen, its production method can be, for example, (iii-1) a method of mixing a compound or ion containing one or more elements selected from the group consisting of phosphorus, potassium and nitrogen in addition to one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, a water-absorbent resin and optionally the above-mentioned additives; (iii-2) a method of mixing a compound containing one or more elements selected from the group consisting of phosphorus, potassium and nitrogen in addition to one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives in a water-absorbent resin by dissolving in any solvent; The water-absorbent resin can be produced by a method of spraying and mixing a solution containing the element dissolved in a solvent or a solution containing ions containing the element, or by immersing the water-absorbent resin in the solution and mixing, and optionally mixing the water-absorbent resin after mixing with the additive, (iii-3) a method of leaving a compound and ions containing one or more elements selected from the group consisting of phosphorus, potassium and nitrogen in addition to one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives during the preparation of the water-absorbent resin, and optionally mixing the obtained preparation with the additive, or (iii-4) a method combining the above (iii-1) to (iii-3). In the above (iii-1) to (iii-4), the content of one or more compounds selected from the group consisting of phosphorus, potassium and nitrogen can be adjusted by adjusting the amount of the compound containing phosphorus, potassium and nitrogen used and the degree of washing of the water-retaining material.

[0082] When the water-retaining material of the present invention also contains one or more agents that kill or inhibit the growth of microorganisms, the water-retaining material can be produced, for example, by (iv-1) spraying a solution in which one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives and the agent are dissolved in any solvent onto a water-absorbent resin, or by immersing a water-absorbent resin in the solution, mixing, and then washing and removing the solvent as necessary. When producing a water-retaining material that also contains additives, for example, in the above (iv-1), (iv-2) a solution containing additives in addition to the drug is used, or (iv-3) the additives are mixed in together during the above mixing, or (iv-4) the water-retaining material and the additives are mixed after the solvent has been removed, or (iv-5) two or more of the above (iv-2) to (iv-4) can be combined to produce the material. When producing a water-retaining material containing the compound (Y), the water-retaining material can be produced, for example, by a method of mixing the water-retaining material with the compound (Y), a method of spraying the compound (Y) onto the water-retaining material and mixing it or a method of immersing the water-retaining material in the compound (Y) and mixing it, a method of allowing the compound (Y) to remain during the preparation of the water-absorbent resin, or a combination of two or more of the above methods.

[0083] When the water-retaining material of the present invention contains all of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen, one or more agents that kill microorganisms or inhibit their growth, and the compound (Y), the manufacturing method thereof can be any combination of the above manufacturing methods. There is no particular restriction on the order in which one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, compounds or ions containing one or more elements selected from the group consisting of phosphorus, potassium and nitrogen, agents that kill microorganisms or inhibit their growth, compound (Y) and any additives are mixed.

[0084] In the above-mentioned production method, the mixing may be carried out sequentially or simultaneously in a general device (for example, a reaction vessel equipped with an agitating blade, a mixer, etc.). In the above-mentioned (ii-3) and (iii-3), the one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives to be left behind include compounds that can be used in the preparation of a water-absorbent resin, such as acetic acid, sodium acetate, potassium acetate, etc., and the compounds and ions to be left behind include compounds that can be used in the preparation of a water-absorbent resin, such as potassium hydroxide, nitric acid, ammonium nitrate, ammonium sulfate, ammonia, potassium hydrogen sulfate, phosphoric acid, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, potassium diammonium hydrogen phosphate ion, ammonium ion, phosphate ion, hydrogen phosphate ion, dihydrogen phosphate ion, nitrate ion, etc. In addition, when a water-retaining material containing the compound (Y) is produced, if a method of leaving the compound (Y) during the preparation of the water-absorbent resin is selected, the compound (Y) to be left behind includes compounds that can be used in the preparation of a water-absorbent resin, such as water, acetonitrile, ethanol, and methanol.

[0085] The production method of the present invention may include a step of pulverizing and / or sieving the water-absorbent resin and / or the water-retaining material, if necessary. For example, the water-absorbent resin and / or the water-retaining material obtained after removing the solvent may be subjected to a pulverizing and / or sieving step, or the acrylic acid structural unit-containing polyvinyl alcohol, which is an intermediate product obtained during the preparation of the water-absorbent resin, may be subjected to a pulverizing and / or sieving step.

[0086] In a preferred embodiment, the water retention material of the present invention is for agricultural use. In a more preferred embodiment, the water retention material of the present invention is for raising seedlings. Therefore, in one embodiment of the present invention, the water retention material can be used as a medium for raising seedlings. The medium may contain optional components other than the water retention material.

[0087] <Optional ingredients> Examples of such optional components include resins other than the water-absorbent resin contained in the water-retaining material, culture soil, other optional components described below, and combinations thereof. In the following description of the preferred content of the optional components when the medium contains the optional components, the mass of the medium components other than one or more compounds selected from acetic acid and acetic acid derivatives (water-absorbent resin contained in the water-retaining material, additives when contained in the water-retaining material, and optional components when contained) is the mass in a dry state.

[0088] <Resins other than water-absorbent resins> Examples of resins other than water-absorbent resins include polyethylene, polypropylene, alkyd resins, phenolic resins, polyethylene glycol, and polyurethane. These resins can be used alone or in combination of two or more. When the medium contains the above resins, the total content is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, based on the total mass of the medium.

[0089] <Cultivating soil> When the medium contains culture soil, the roots grow in the gaps of the culture soil, so that the roots tend to intertwine appropriately, and the medium tends to have excellent drainage and breathability. The culture soil is not particularly limited, and one type of commercially available culture soil can be used alone or in combination of two or more types. In addition, the optional components described below can be attached to the culture soil by a conventional method (for example, a method of spraying a solution or dispersion of the optional components on the culture soil and then drying it) and used.

[0090] From the viewpoint of obtaining better drainage and breathability, the soil is preferably granular. The particle size of the granular soil is preferably 0.2 to 20 mm, more preferably 0.5 to 10 mm, and particularly preferably 1 to 5 mm. In order to adjust the particle size of the granular soil within the above range, commercially available granular soil for paddy rice can be used after sieving. Granular soil can be produced by granulation methods such as compression granulation, extrusion granulation, rolling granulation, and fluidized bed granulation. The particle size of the granular soil can be measured by the following method. Thirty particles are randomly selected from the granular soil, and the diameter of each particle is measured using a caliper, and the average value is taken as the particle size of the granular soil. In addition, if the particle is not spherical, the average value of the longest side and the shortest side is taken as the diameter of the particle.

[0091] When the medium contains culture soil, the content of the culture soil is preferably 20 to 99.9999 mass%, more preferably 70 to 99.95 mass%, particularly preferably 80 to 99.9 mass%, and most preferably 90 to 99.8 mass%, based on the total mass of the medium.

[0092] <Other optional ingredients> Other optional components include peat, grass peat, peat, peat moss, coco peat, rice husk, humus material, charcoal, calcined diatomaceous earth granules, shell fossil powder, shell powder, crab shell, VA mycorrhizal fungi, microbial material, and other animal and plant materials; vermiculite, perlite, bentonite, natural zeolite, synthetic zeolite, gypsum, fly ash, rock wool, kaolinite, smectite, montmorillonite, sericite, chlorite, glauconite, talc, and other minerals; fertilizers, and combinations thereof. These may be disinfected or sterilized as necessary, and may be used together with a pH adjuster or pesticide. When the medium contains other optional components, the total content of the components may be within a range that does not impair the effects of the present invention, and is usually 50% by mass or less, preferably 30% by mass or less, based on the total mass of the medium.

[0093] Examples of fertilizers include the three major fertilizers, nitrogen fertilizers, phosphorus fertilizers, and potassium fertilizers; fertilizers containing elements essential to plants, such as calcium, magnesium, sulfur, iron, copper, manganese, zinc, boron, molybdenum, chlorine, and nickel; compost such as bark compost, cow dung, pig manure, chicken manure, food waste, and pruning waste. Nitrogen fertilizers include ammonium sulfate, ammonium chloride, ammonium nitrate, sodium nitrate, lime nitrate, humic acid ammonia fertilizer, urea, lime nitrogen, ammonia nitrate lime, ammonia nitrate soda, and magnesium nitrate fertilizer. Phosphorus fertilizers include superphosphate, double superphosphate, molten phosphorus fertilizer, humic acid phosphate fertilizer, burnt phosphorus, double burnt phosphorus, phosphorus starch, magnesium superphosphate, mixed phosphate fertilizer, by-product phosphate fertilizer, and high-concentration phosphoric acid. Potassium fertilizers include potassium sulfate, potassium chloride, magnesium sulfate, potassium carbonate, potassium bicarbonate, and potassium silicate. These fertilizers may be used in the form of a solid, paste, liquid, solution, or the like, or may be used as a coated fertilizer. Examples of pesticides include insecticides, fungicides, insecticides and fungicides, herbicides, rodenticides, preservatives, and plant growth regulators.

[0094] When the water-retaining material of the present invention is combined with a fertilizer to prepare a medium, in a preferred embodiment, the fertilizer is used as a coated fertilizer. The coated fertilizer is a fertilizer coated with a resin. Examples of the resin include polyolefin. When the coated fertilizer is used, the fertilizer can be continuously supplied to the soil as the resin decomposes. In addition, when a mat seedling is prepared using a granular coated fertilizer, the strength of the obtained mat seedling tends to be high. The particle size of the coated fertilizer is preferably 1 mm to 10 mm, more preferably 3 mm to 6 mm. When the coated fertilizer is used, the content of the coated fertilizer in the medium is preferably 10 to 99.99% by mass, more preferably 15 to 90% by mass, particularly preferably 20 to 80% by mass, and most preferably 30 to 60% by mass.

[0095] When the water retention material of the present invention is used in combination with an optional component, the water retention material and the optional component can be mixed and used, or the water retention material can be sprinkled on the medium after germination. When the water retention material is mixed and used, the mixing method is not particularly limited. A medium for raising seedlings can be prepared by mixing the water retention material and the optional component by a general method. When the water retention material is sprinkled on the medium after germination, the time of sprinkling is not particularly limited, but it is preferable to use the water retention material during the seedling raising period (approximately one month after sowing) when the plants are vulnerable to drying.

[0096] The amount of the water-retaining material of the present invention used in combination with optional components will vary depending on the culture soil and other components to be combined, but is usually 0.0001% by mass to 20% by mass, preferably 0.05% by mass to 15% by mass, and more preferably 0.1% by mass to 10% by mass relative to the total mass of the culture medium.

[0097] When the medium is for raising rice seedlings, rice seeds can be sown in the medium. Seed rice is often sown in a rice seedling box in which the medium for raising rice seedlings has been introduced. Usually, the amount of seed rice is 100 to 500 g per rice seedling box (length 28 cm × width 58 cm). The medium may be used as either bed soil (soil introduced into the rice seedling box before sowing the seeds) or cover soil (soil that covers the seeds after sowing), or it may be used for both. When used for both, the composition of the medium may be the same for the bed soil and the cover soil, or it may not be the same. The medium may also be spread on top of the culture soil after germination. EXAMPLES

[0098] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0099] <Evaluation items and evaluation methods> (1) Survival rate (9, 14 or 21 days after sowing) Nine days (Examples 13-22, Comparative Examples 6-10), 14 days (Examples 1-12, Comparative Examples 1-5), or 21 days (Examples 23-33, Comparative Examples 11-14) after sowing, the number of seedlings that were not dead (less than 1 on the color scale) was visually counted, and the survival rate was calculated as the ratio to the total number of seedlings.

[0100] (2) Moisture content 14 days after sowing, the seedling sheet (including the soil and water-retentive material) was removed from the rice seedling box and cut into 10 cm x 6 cm pieces to measure the mass w1. The cut seedling sheet was dried with hot air at 105°C for 24 hours, and the mass w2 was measured again. The moisture content was measured based on the following formula. Moisture percentage (mass%)={(w1-w2) / w1}×100

[0101] (3) Content of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives 100 mg of the water-retaining material was added to 1 L of pure water and stirred for 24 hours at 23° C. The liquid phase was filtered through a 0.45 μm filter, and the content was calculated by ion chromatography (Dionex ICS-1600, manufactured by Thermo Fisher Scientific). When the content was low, the amount of water-retaining material added was increased to 1000 mg, and the liquid phase was concentrated using an evaporator before being measured by ion chromatography.

[0102] (4) Plant height (9, 14 or 21 days after sowing) 9 days (Examples 13-22, Comparative Examples 6-10), 14 days (Examples 1-12, Comparative Examples 1-5), or 21 days (Examples 23-33, Comparative Examples 11-14) after sowing, 10 seedlings randomly sampled in a rice seedling raising box were measured for length from the top of the medium to the top of the seedlings, and the average value was taken as plant height. If the sampled seedlings were wilted, they were stretched and their length was measured.

[0103] (5) Phosphorus, potassium and nitrogen content (5)-1. The total content of elements constituting the polymer skeleton of the water-absorbent resin and elements not constituting the polymer skeleton but contained within the water-absorbent resin (Fa) The water-retaining materials or the water-absorbent resin contained in the mixture produced in the Examples and Comparative Examples were embedded in epoxy resin, and then cut to prepare a cross section of the water-absorbent resin. The cross section was introduced into a scanning electron microscope equipped with an energy dispersive X-ray analyzer, and three points, a point 5 μm from the surface of the resin, the center, and the midpoint between them, were measured as a part of the inside of the resin, and the average value was calculated to obtain the content Fa (mass%) of each element. (5)-2. Content of elements contained in the polymer skeleton of the water-absorbent resin (Fb) 0.1 g of the water-absorbent resin contained in the water-retaining material or mixture produced in the Examples and Comparative Examples was washed five times with 100 g of pure water to remove the phosphorus element, potassium element, and nitrogen element contained in the resin that do not constitute the polymer skeleton. The washed resin was vacuum-dried at 40°C for 12 hours, embedded in epoxy resin, and then cut to prepare a cross section of the water-absorbent resin. The cross section was introduced into a scanning electron microscope equipped with an energy dispersive X-ray analyzer, and elemental analysis of the water-absorbent resin cross section was performed in the same manner as in (5)-1., and the content Fb (mass%) of each element constituting the polymer skeleton of the water-absorbent resin was measured. (5)-3. Content of elements in water-retentive material (Fc) The nitrogen element content was measured by burning the water-retentive material using an organic element analyzer. For phosphorus and potassium elements, nitric acid was added to the water-retentive material, which was then decomposed using microwaves, after which the contents were measured using ICP-AES. The contents of phosphorus, potassium and nitrogen elements contained in the water-retentive material were defined as Fc (mass%). The contents Fi of the phosphorus element, potassium element and nitrogen element contained inside the water absorbent resin, which do not constitute the polymer skeleton, were calculated from the following formula. Fi=Fa-Fb The phosphorus, potassium and nitrogen elements Fo that are not contained within the resin but are contained in the water-retaining material were calculated using the following formula. Fo=Fc-Fa

[0104] (6) Germination rate (2 days after sowing) The number of sprouts (N1) that had emerged above the soil cover in the rice seedling box was counted visually. The number of sown germinated rice seeds (N2) was used to calculate the emergence rate according to the following formula. Germination rate [%]=(N1 / N2)×100

[0105] (7) Drug content (7)-1. Amount of chemical not present inside the resin but present in the water-retaining material (Eo) 1 g of the water-retaining material or mixture (in the case of Examples 32 and 33, the water-retaining material was replaced with the water-retaining material, which was heated at 60°C for 12 hours in a vacuum and dried) produced in the examples or comparative examples was placed in a cylindrical filter paper (Advantec (registered trademark) #84, manufactured by Toyo Roshi Kaisha, Ltd., inner diameter 25 mm, outer diameter 28 mm, length 100 mm) and immersed in 0.1 L of acetone for 10 seconds. Next, the cylindrical filter paper containing the water-retaining material was taken out, and the concentration Co of the drug in the acetone solution was measured by a liquid chromatography mass spectrometer (LC-MS), and Eo was calculated from the following formula. Eo (mass%)=[{Co(g / L)×0.1(L)} / 1(g)]×100 When the drug concentration was low, the acetone solution was concentrated using an evaporator before LC-MS measurement. (7)-2. Amount of chemicals present in the water-retentive material (Ea) 1 g of the water-retaining material or mixture produced in the examples or comparative examples (in the case of Examples 32 and 33, the water-retaining material was replaced with the material after heating and drying at 60°C for 12 hours under vacuum) was placed in a cylindrical filter paper (manufactured by Toyo Roshi Kaisha, Ltd., Advantec (registered trademark) #84, inner diameter 25 mm, outer diameter 28 mm, length 100 mm) and subjected to Soxhlet extraction for 24 hours using 0.2 L of acetone. After the extraction, acetone was further added to the acetone solution to make the total volume 0.3 L, and the concentration Ca of the drug in the acetone solution was measured by LC-MS, and Ea was calculated from the following formula. Ea (mass%)=[{Ca(g / L)×0.3(L)} / 1(g)]×100 When the drug concentration was low, the acetone solution was concentrated using an evaporator before LC-MS measurement. (7)-3. Amount of drug contained inside the resin (Ei) Ei was calculated from the following formula. Ei=Ea-Eo

[0106] (8) The percentage of water that can be absorbed by plants In the present invention, the "proportion of water that can be absorbed by plants" [W (unit: mass %) means the proportion of water that can be absorbed by plants based on the mass of the water-retentive material in a state in which the water-retentive material has absorbed 50 times its own weight in water. This proportion W can be easily calculated by the centrifugation method. In the present invention, W was calculated by the following method. As a sample, 2.4 g of water-retaining material that had absorbed 50 times the mass of the water-retaining material produced in the examples or comparative examples was introduced into a syringe, and this syringe was fixed inside a centrifuge tube at a position 10.2 cm from the center of a small centrifuge "H-36" manufactured by Kokusan Co., Ltd. The centrifuge was rotated at 2200 rpm for 60 minutes, and the proportion of water that the plant can absorb (W) (unit: mass%) was calculated based on the following formula. However, when the water-retaining material could not absorb 50 times the mass of water, 2.4 g of water-retaining material that had absorbed to saturation was introduced into the syringe. W = [{(sample mass before centrifugation) - (sample mass after centrifugation)} / (sample mass before centrifugation)] x 100

[0107] (9) Water absorption speed (vortex method) The water-retaining material was weighed so that the mass excluding the mass of the compound (Y) was 0.5 g, and the water-absorption time was measured using the weighed water-retaining material and 50 g of pure water in accordance with JIS K 7224. The shorter the water-absorption time measured by this method, the faster the water-absorption speed of the water-retaining material.

[0108] (10) Powder scattering rate A stainless steel pipe with an inner diameter of 2.9 cm and a length of 44 cm was set vertically, and a petri dish with an inner diameter of 4.1 cm was placed 15 cm below the bottom of the pipe. 2 g of the water-retentive material sample was poured into the top of the pipe over a period of 3 seconds, and the mass of the sample that remained in the petri dish without scattering was measured, and the powder scattering rate was calculated based on the following formula. The lower the powder scattering rate, the lower the health risk to the person handling the water-retentive material from inhaling it, and the less likely dust explosions are to occur.

number

[0109] (11) SP value The SP value was calculated by the Fedors method [SP Value Fundamentals, Applications and Calculation Methods (Published by Information Organization, Author: Hideki Yamamoto, 2005), Fedors, Polym. Eng. Sci. 14, 147 (1974)]. The SP value of water was set to 23.4. The SP values ​​of the compound (Y) used in the examples and comparative examples, determined by the above method, are shown in Table 1 below. [Table 1]

[0110] (12) Content of compound (Y) relative to the mass of the water-retaining material 1 g of the water-retentive material was placed in a cylindrical filter paper (Advantec (registered trademark) #84, manufactured by Toyo Roshi Kaisha, Ltd., inner diameter 25 mm, outer diameter 28 mm, length 100 mm) and subjected to Soxhlet extraction for 24 hours using 0.2 L of methanol. After extraction, the solid remaining in the cylindrical filter paper was vacuum dried at 40°C for 16 hours, and then the mass W2 was measured and the content of compound (Y) relative to the mass of the water-retentive material was calculated using the following formula. Content of compound (Y) relative to the mass of water-retentive material = [{1(g)-W2(g)} / 1(g)] x 100

[0111] (13) Volume average particle size Measurements were performed using a laser diffraction / scattering particle size distribution analyzer (LA-950V2, manufactured by Horiba, Ltd.). No dispersion medium was used for the measurements, and the volume average particle size was measured in a dry state. The volume average particle size is the particle size at which the cumulative volume is 50%.

[0112] <Synthesis of water-absorbent resin> [Synthetic raw materials] Glyoxylic acid monohydrate, 40% by weight glyoxal aqueous solution, 25% by weight glutaraldehyde aqueous solution, acetonitrile, methanol, vinyl acetate, sodium hydroxide, methyl acrylate, and azobisisobutyronitrile, acetic acid, sodium acetate, and crosslinked product of acrylic acid-sodium acrylate copolymer (product name: superabsorbent polymer (acrylate salt type)); manufactured by Wako Pure Chemical Industries, Ltd. Crosslinked acrylamide-acrylic acid-potassium acrylate copolymer (composition ratio (mol) 67:11:22) (product name: Miracle-Gro (registered trademark) Water Storing Crystal); manufactured by Scotts Miracle-Gro Polyvinyl alcohol A: ELVANOL (registered trademark) 71-30 manufactured by Kuraray America, Inc.

[0113] [Synthesis of water-absorbent resin a-0] In a 500mL four-necked separable flask equipped with a reflux condenser and a stirring blade, 12.55g of glyoxylic acid monohydrate, 0.11g of 40% by mass glyoxal aqueous solution, 12.55g of ion-exchanged water, 150mL of acetonitrile, and 40.0g of polyvinyl alcohol A (sodium acetate content 1.0% by mass) were introduced and stirred at 23°C for 1 hour. The mixture obtained was heated to 70°C, and then 16.87g of 25% by mass sulfuric acid aqueous solution was added dropwise over 10 minutes, and the mixture was reacted for 6 hours while maintaining the temperature at 70°C. After cooling to 30°C, 150mL of ion-exchanged water was added, and the resin was taken out by filtration. The resin thus taken out was then washed five times using 200mL of methanol each time (washing 1). The washed resin was introduced into a 500mL four-necked separable flask equipped with a reflux condenser and a stirring blade, and 180mL of methanol, 11.6mL of ion-exchanged water, and 16.8mL of 8mol / L potassium hydroxide aqueous solution were added and reacted under reflux for 2 hours. The resin was taken out by filtration, washed six times using 200mL of methanol each time (washing 2), and vacuum dried at 40°C for 6 hours to obtain the target water-absorbing resin (hereinafter referred to as "water-absorbing resin a-0"). The volume average particle diameter of the vinyl alcohol polymer a-0 measured using a laser diffraction / scattering type particle size distribution measuring device was 142μm.

[0114] [Synthesis of water-absorbent resin b-0] Into a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, and an initiator addition port, 602 g of vinyl acetate, 1.21 g of methyl acrylate, and 254 g of methanol were introduced, and the inside of the reactor was replaced with inert gas for 30 minutes while bubbling with nitrogen. The reactor was heated using a water bath, and when the internal temperature of the reactor reached 60°C, 0.16 g of azobisisobutyronitrile (AIBN) was added as an initiator to start polymerization. Sampling was performed appropriately, and the progress of polymerization was confirmed from the solid content concentration, and the consumption rate, which is the total mass of vinyl acetate and methyl acrylate consumed by polymerization relative to the total mass of vinyl acetate and methyl acrylate introduced, was calculated. When the consumption rate reached 4%, the internal temperature of the reactor was cooled to 30°C to stop the polymerization. The reactor was connected to a vacuum line, and the remaining vinyl acetate was distilled off under reduced pressure at 30°C together with methanol. While visually checking the inside of the reactor, when the viscosity increased, methanol was appropriately added and distillation was continued, and polyvinyl acetate containing 5.2 mol % of acrylic acid constituent units was obtained. The content of acrylic acid constituent units was 13 Measurements were performed using C-NMR. Next, 1 g of the obtained polyvinyl acetate containing acrylic acid structural units and 18.2 g of methanol were added to the same reactor as above, and the polyvinyl acetate containing acrylic acid structural units was dissolved. The reactor was heated using a water bath, and the reactor was heated with stirring until the internal temperature reached 70°C. 0.78 g of a methanol solution of sodium hydroxide (methacuum, concentration 15% by mass) was added thereto, and saponification was carried out at 70°C for 2 hours. The obtained solution was filtered to obtain polyvinyl alcohol containing 5.2 mol% of acrylic acid structural units (hereinafter referred to as "polyvinyl alcohol b"). The obtained polyvinyl alcohol b contained 1.2% by mass of sodium acetate. 58.9g of acetonitrile, 6.28g of ion-exchanged water, 0.171g of 25% by mass glutaraldehyde aqueous solution, and 20g of polyvinyl alcohol B were introduced into a three-necked separable flask equipped with a reflux condenser and a stirring blade, and the mixture was stirred at 23°C to disperse polyvinyl alcohol B. 12.38g of 16.9% by mass sulfuric acid aqueous solution was added dropwise over 15 minutes, and the mixture was heated to 65°C and reacted for 6 hours. After the reaction, the resin was removed by filtration, and the filtered resin was washed six times using 160g of methanol each time (washing 3). The washed resin was introduced into a three-necked separable flask equipped with a reflux condenser and a stirring blade, and 71g of methanol, 13.3g of ion-exchanged water, and 5.7g of potassium hydroxide were added, followed by reaction at 65°C for 2 hours. After the reaction, the resin was taken out by filtration, and the filtered resin was washed six times using 160 g of methanol each time (washing 4), and vacuum dried at 40° C. for 12 hours to obtain the target water-absorbing resin (hereinafter referred to as “water-absorbing resin b-0”). The volume average particle diameter of the vinyl alcohol polymer b-0 measured using a laser diffraction / scattering type particle size distribution measuring device was 135 μm.

[0115] [Example 1] A water absorbent resin (hereinafter referred to as "water absorbent resin a-1") was synthesized in the same manner as the water absorbent resin a-0, except that the number of washings 1 was changed from 5 times to 1 time, and the number of washings 2 was changed from 6 times to 1 time. The water absorbent resin a-1 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin a-1 corresponds to a water retention material (hereinafter referred to as "water retention material a-1"). Granular soil (containing 0.5-1.5-0.5g / kg N-P2O5-K2O as fertilizer, average particle size 2.7mm) was spread in a rice seedling box with inner dimensions of 58cm x 28cm and 56 holes with a diameter of 2mm on the bottom, and 1000mL of water was sprayed for 5 seconds with a watering can. After uniformly spreading 200g of germinated rice (variety: Koshihikari), 1200g of granular soil was spread evenly on top of it to prepare a rice seedling box. The above operation was repeated two more times to prepare three rice seedling boxes with the same rice seedling soil and water. After germination for two days in a germination chamber at 30℃ and 100% humidity, the seedlings were removed from the chamber and raised in a chamber equipped with LEDs at 25℃ and 50% humidity. Nine days after sowing, 20 g of water-retentive material a-1 was spread on the cover soil and 1 L of water was irrigated. After the seedlings were raised, the survival rate and water content were measured 14 days after sowing. The results are shown in Table 2.

[0116] [Example 2] In [Synthesis of water absorbent resin a-0], in addition to the aqueous sulfuric acid solution, 1.0 g of acetic acid was added as a catalyst for acetalization, the number of washings 1 was changed from 5 to 1, the number of washings 2 was changed from 6 to 1, and the 8 mol / L potassium hydroxide aqueous solution was changed from 16.8 mL to 18.8 mL. Except for this, the synthesis of a water absorbent resin (hereinafter referred to as "water absorbent resin a-2") was performed in the same manner as in the synthesis of water absorbent resin a-0. The water absorbent resin a-2 contained 1.1 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin a-2 corresponds to a water retention material (hereinafter referred to as "water retention material a-2"). Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0117] [Example 3] In [Synthesis of water absorbent resin a-0], in addition to the aqueous sulfuric acid solution, 10.0 g of acetic acid was added as a catalyst for acetalization, the number of washings 1 was changed from 5 to 1, the number of washings 2 was changed from 6 to 1, and the 8 mol / L potassium hydroxide aqueous solution was changed from 16.8 mL to 33.6 mL. Except for this, the synthesis of a water absorbent resin (hereinafter referred to as "water absorbent resin a-3") was performed in the same manner as in the synthesis of water absorbent resin a-0. The water absorbent resin a-3 contained 6.2 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin a-3 corresponds to a water retention material (hereinafter referred to as "water retention material a-3"). Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0118] [Example 4] 21 g of water-absorbent resin a-0 was mixed with 4 g of acetic acid to prepare water-retentive material a-4. Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0119] [Example 5] 21 g of the water-absorbent resin a-0 was mixed with a solution in which 24 g of sodium acetate was dissolved in 150 g of pure water, and the mixture was vacuum-dried at 40° C. for 6 hours to obtain a water-retentive material a-5. Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0120] [Example 6] In [Synthesis of water absorbent resin b-0], a water absorbent resin (hereinafter referred to as "water absorbent resin b-1") was synthesized in the same manner as in the water absorbent resin b-0, except that the number of washings 3 was changed from 6 to 4, and the number of washings 4 was changed from 6 to 3. The water absorbent resin b-1 contained 0.01 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-1 corresponds to a water retention material (hereinafter referred to as "water retention material b-1"). Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0121] [Example 7] In [Synthesis of water absorbent resin b-0], a water absorbent resin (hereinafter referred to as "water absorbent resin b-2") was synthesized in the same manner as in the water absorbent resin b-0, except that the number of washings 3 was changed from 6 times to 1 time, and the number of washings 4 was changed from 6 times to 1 time. The water absorbent resin b-2 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-2 corresponds to a water retention material (hereinafter referred to as "water retention material b-2"). Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0122] [Example 8] In [Synthesis of water absorbent resin b-0], in addition to the aqueous sulfuric acid solution, 0.5 g of acetic acid was added as a catalyst for acetalization, the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. Except for this, a water absorbent resin (hereinafter referred to as "water absorbent resin b-3") was synthesized in the same manner as in the water absorbent resin b-0. The water absorbent resin b-3 contained 0.9 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-3 corresponds to a water retention material (hereinafter referred to as "water retention material b-3"). Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0123] [Example 9] 21 g of the water-absorbent resin b-0 was mixed with 4 g of acetic acid to prepare water-retaining material b-4. Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0124] [Example 10] 21 g of the cross-linked acrylic acid-sodium acrylate copolymer was mixed with 4 g of acetic acid to prepare water-retaining material c-1. Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0125] [Example 11] 21 g of the cross-linked acrylamide-acrylic acid-potassium acrylate copolymer was mixed with 4 g of acetic acid to prepare water-retaining material d-1. Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0126] [Example 12] 10 g of polyvinyl alcohol b was dissolved in 500 g of water, and then dropped into 10 kg of methanol to precipitate the resin. Using this precipitated resin, a water absorbent resin (hereinafter referred to as "water absorbent resin b-5") was synthesized in the same manner as water absorbent resin b-0, except that the number of washings 3 was changed from 6 to 0, and the number of washings 4 was changed from 6 to 0. Water absorbent resin b-5 contained 0.004 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. In other words, water absorbent resin b-5 corresponds to a water retention material (hereinafter referred to as "water retention material b-5"). Except for using this water-retentive material, the rice seedling raising boxes were prepared and measurements were performed in the same manner as in Example 1. The results are shown in Table 2.

[0127] [Example 13] In [Synthesis of water absorbent resin b-0], a water absorbent resin (hereinafter referred to as "water absorbent resin b-6") was synthesized in the same manner as in the water absorbent resin b-0, except that the number of washings 3 was changed from 6 to 5. The water absorbent resin b-6 contained 0.08 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-6 corresponds to a water retention material (hereinafter referred to as "water retention material b-6"). 48g of water-retentive material b-6 and 600g of granular soil A (no fertilizer, average particle size 3.0mm) were mixed uniformly to prepare rice seedling soil. 60% by mass of this rice seedling soil was spread in a rice seedling box with inner dimensions of 58cm x 28cm and 56 holes with a diameter of 2mm on the bottom, and 1000mL of water was watered for 5 seconds with a watering can. After uniformly spreading 200g of germinated rice (variety: Koshihikari), the remaining rice seedling soil (40% by mass of the prepared rice seedling soil) was uniformly spread on top of it to prepare a rice seedling box with rice seedling soil and water introduced. The above operation was repeated two more times to prepare three rice seedling boxes with the same rice seedling soil and water introduced. The seedlings were allowed to germinate for two days in a germination chamber at 30°C and 100% humidity, after which the germination rate was measured. The seedlings were then raised in a chamber equipped with LEDs at 25°C and 60% humidity, and the plant height and survival rate were measured nine days after sowing. Measurements were performed in each of the three seedling raising boxes, and the average values ​​were used. The results are shown in Table 3.

[0128] [Example 14] In [Synthesis of water absorbent resin b-0], a water absorbent resin (hereinafter referred to as "water absorbent resin b-7") was synthesized in the same manner as in the water absorbent resin b-0, except that the number of washings 3 was changed from 6 to 1. The water absorbent resin b-7 contained 0.2 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-7 corresponds to a water retention material (hereinafter referred to as "water retention material b-7"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0129] [Example 15] In [Synthesis of water absorbent resin b-0], a water absorbent resin (hereinafter referred to as "water absorbent resin b-8") was synthesized in the same manner as water absorbent resin b-0, except that the number of washings 3 was changed from 6 to 2, and then potassium sulfate was mixed. Water absorbent resin b-8 contained 0.1 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, water absorbent resin b-8 corresponds to a water retention material (hereinafter referred to as "water retention material b-8"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0130] [Example 16] In [Synthesis of water absorbent resin b-0], a water absorbent resin (hereinafter referred to as "water absorbent resin b-9") was synthesized in the same manner as water absorbent resin b-0, except that the number of washings 3 was changed from 6 to 1, and then diammonium hydrogen phosphate was mixed. Water absorbent resin b-9 contained 0.2 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. In other words, water absorbent resin b-9 corresponds to a water retention material (hereinafter referred to as "water retention material b-9"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0131] [Example 17] In [Synthesis of water absorbent resin b-0], 5.0 g of diammonium hydrogen phosphate was added in addition to sulfuric acid to react with polyvinyl alcohol b and glutaraldehyde, and then the number of washings 3 was changed to three. In the same manner as in the synthesis of water absorbent resin b-0, a water absorbent resin (hereinafter referred to as "water absorbent resin b-10") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium sulfate were mixed. The water absorbent resin b-10 contained 0.08 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. In other words, the water absorbent resin b-10 corresponds to a water retention material (hereinafter referred to as "water retention material b-10"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0132] [Example 18] In [Synthesis of water absorbent resin b-0], 5.0 g of diammonium hydrogen phosphate was added in addition to sulfuric acid to react polyvinyl alcohol b with glutaraldehyde, and then the number of washings 3 was set to one. In the same manner as in the synthesis of water absorbent resin b-0, a water absorbent resin (hereinafter referred to as "water absorbent resin b-11") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium sulfate were mixed. The water absorbent resin b-11 contained 0.2 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. In other words, the water absorbent resin b-11 corresponds to a water retention material (hereinafter referred to as "water retention material b-11"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0133] [Example 19] In [Synthesis of water absorbent resin b-0], 12.38 g of 16.9 mass% sulfuric acid aqueous solution was changed to 16.32 g of 10 mass% hydrochloric acid, and 5.0 g of diammonium hydrogen phosphate was added to react with polyvinyl alcohol b and glutaraldehyde. The number of washings 3 was changed to three times, and the synthesis of a water absorbent resin (hereinafter referred to as "water absorbent resin b-12") was performed in the same manner as in the water absorbent resin b-0. After the synthesis, diammonium hydrogen phosphate and potassium chloride were mixed. The water absorbent resin b-12 contained 0.07 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-12 corresponds to a water retention material (hereinafter referred to as "water retention material b-12"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0134] [Example 20] In [Synthesis of water absorbent resin b-0], 12.38 g of 16.9 mass% sulfuric acid aqueous solution was changed to 27.06 g of 10 mass% nitric acid, and 5.0 g of diammonium hydrogen phosphate was added to react with polyvinyl alcohol b and glutaraldehyde, and the number of washings 3 was changed to three. In the same manner as in the synthesis of water absorbent resin b-0, except that, a water absorbent resin (hereinafter referred to as "water absorbent resin b-13") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium nitrate were mixed. The water absorbent resin b-13 contained 0.07 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. In other words, the water absorbent resin b-13 corresponds to a water retention material (hereinafter referred to as "water retention material b-13"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0135] [Example 21] In [Synthesis of water absorbent resin b-0], 2.3 g of urea was added in addition to sulfuric acid to react polyvinyl alcohol b with glutaraldehyde, and then the number of washings 3 was set to one. In the same manner as in the synthesis of water absorbent resin b-0, a water absorbent resin (hereinafter referred to as "water absorbent resin b-14") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium sulfate were mixed. The water absorbent resin b-14 contained 0.2 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. In other words, the water absorbent resin b-14 corresponds to a water retention material (hereinafter referred to as "water retention material b-14"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0136] [Example 22] In [Synthesis of water absorbent resin a-0], a water absorbent resin (hereinafter referred to as "water absorbent resin a-6") was synthesized in the same manner as the water absorbent resin a-0, except that the number of washings 1 was changed from 5 times to 2 times, and then potassium sulfate was mixed. The water absorbent resin a-6 contained 0.1 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin a-6 corresponds to a water retention material (hereinafter referred to as "water retention material a-6"). Except for using this water-retentive material, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 13. The results are shown in Table 3.

[0137] [Example 23] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.0022 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-15"). The water absorbent resin b-15 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-15 corresponds to a water retention material (hereinafter referred to as "water retention material b-15"). 8g of water-retentive material b-15 and 100g of granular soil (containing N-P2O5-K2O=0.5-1.5-0.5g / kg as fertilizer, average particle size 2.7mm) were mixed uniformly to prepare a rice seedling medium. 3.6 times the amount of this rice seedling medium (360g) was spread in a rice seedling box with inner dimensions of 58cm x 28cm and 56 holes with a diameter of 2mm on the bottom, and 1000mL of water was watered for 5 seconds with a watering can. 200g of germinated rice (variety: Koshihikari) was evenly spread, and then 2.4 times the amount of the rice seedling medium (240g) was evenly spread on top of it to prepare a rice seedling box containing the rice seedling medium, germinated rice, and water. The above operation was repeated two more times to prepare three identical rice seedling boxes. The seeds were allowed to germinate for two days in a germination chamber at 30°C and 100% humidity, after which the germination rate and occurrence of mold, etc. were evaluated. The seedlings were then raised in a chamber equipped with LEDs at 25°C and 70% humidity, and 21 days after sowing, the occurrence of mold, etc., plant height, and survival rate were evaluated. Evaluations were made for each of the three rice seedling raising boxes, and the average values ​​were used. The results are shown in Table 4.

[0138] [Example 24] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.011 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-16"). The water absorbent resin b-16 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-16 corresponds to a water retention material (hereinafter referred to as "water retention material b-16"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-16 was used instead of the water retention material b-15. The results are shown in Table 4.

[0139] [Example 25] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.022 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-17"). The water absorbent resin b-17 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-17 corresponds to a water retention material (hereinafter referred to as "water retention material b-17"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-17 was used instead of the water retention material b-15. The results are shown in Table 4.

[0140] [Example 26] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.11 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-18"). The water absorbent resin b-18 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-18 corresponds to a water retention material (hereinafter referred to as "water retention material b-18"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-18 was used instead of the water retention material b-15. The results are shown in Table 4.

[0141] [Example 27] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 1.9 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-19"). The water absorbent resin b-19 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-19 corresponds to a water retention material (hereinafter referred to as "water retention material b-19"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-19 was used instead of the water retention material b-15. The results are shown in Table 4.

[0142] [Example 28] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.022 g of potassium sorbate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-20"). The water absorbent resin b-20 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-20 corresponds to a water retention material (hereinafter referred to as "water retention material b-20"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-20 was used instead of the water retention material b-15. The results are shown in Table 4.

[0143] [Example 29] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a mixture of 0.10 g of 25 mass% glutaraldehyde aqueous solution and 60 g of methanol, and vacuum dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-21"). The water absorbent resin b-21 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-21 corresponds to a water retention material (hereinafter referred to as "water retention material b-21"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-21 was used instead of the water retention material b-15. The results are shown in Table 4.

[0144] [Example 30] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.022 g of sodium dichloroisocyanurate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40°C for 12 hours to obtain a water absorbent resin (hereinafter referred to as "water absorbent resin b-22"). The water absorbent resin b-22 contained 0.3 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-22 corresponds to a water retention material (hereinafter referred to as "water retention material b-22"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-22 was used instead of the water retention material b-15. The results are shown in Table 4.

[0145] [Example 31] In the synthesis of water absorbent resin a-0, the number of washings 1 was changed from 5 to 1, and the number of washings 2 was changed from 6 to 1, and the mixture immediately after washing 2 was weighed and used. The mixture (content of water absorbent resin: 20 g) was mixed with a solution in which 0.022 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40° C. for 12 hours to obtain a water absorbent resin (hereinafter referred to as “water absorbent resin a-7”). The water absorbent resin a-7 contained 0.3 mass % of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin a-7 corresponds to a water retention material (hereinafter referred to as “water retention material a-7”). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material a-7 was used instead of the water retention material b-15. The results are shown in Table 4.

[0146] [Example 32] In [Synthesis of water absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1. The mixture immediately after washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 0.022 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and dried under reduced pressure at 40° C. using an evaporator until the content of methanol became 20% by mass, to obtain a water absorbent resin (hereinafter referred to as “water absorbent resin b-23”). The water absorbent resin b-23 contained 0.2% by mass of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water absorbent resin b-23 corresponds to a water retention material (hereinafter referred to as “water retention material b-23”). The content of the water absorbent resin in the water retention material b-23 was 79.9% by mass. The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-23 was used instead of the water retention material b-15. The results are shown in Table 4.

[0147] [Example 33] In [Synthesis of water-absorbent resin b-0], the number of washings 3 was changed from 6 to 1, and the number of washings 4 was changed from 6 to 1 to obtain a water-absorbent resin. 22 g of this water-absorbent resin was prepared, and a solution in which 0.028 g of ethyl paraoxybenzoate was dissolved in 5 g of water was sprayed onto it to obtain a water-absorbent resin (hereinafter referred to as "water-absorbent resin b-24"). The water-absorbent resin b-24 contained 0.2 mass% of one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. That is, the water-absorbent resin b-24 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-24"). The content of the water-absorbent resin in the water-retaining material b-24 was 82.4 mass%, and the content of water was 17.5 mass%. The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the water retention material b-24 was used instead of the water retention material b-15. The results are shown in Table 4.

[0148] [Comparative Example 1] Except for using the water-absorbent resin a-0 instead of the water-retentive material a-1, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0149] [Comparative Example 2] Except for using the water-absorbent resin b-0 instead of the water-retentive material a-1, the rice seedling raising box was prepared and measurements were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0150] [Comparative Example 3] A rice seedling raising box was prepared in the same manner as in Example 1, and the seedlings were raised for 9 days after sowing. Then, without spreading a water-retentive material, 3.2 g of acetic acid was dissolved in 1 L of pure water and given to the seedlings. After that, the seedlings were raised for 14 days after sowing, and then measurements were performed. The results are shown in Table 2.

[0151] [Comparative Example 4] A rice seedling raising box was prepared in the same manner as in Example 1, and the seedlings were raised for 9 days after sowing. After that, the seedlings were raised for 14 days after sowing, and then measurements were performed. The results are shown in Table 2.

[0152] [Comparative Example 5] A rice seedling raising box was prepared in the same manner as in Example 1, and the seedlings were raised for 9 days after sowing. Then, without spreading a water-retentive material, 1.1 g of acetic acid was dissolved in 1 L of pure water and given to the seedlings. Then, 10 days and 12 days after sowing, 1.1 g of acetic acid was dissolved in 50 mL of pure water and given to the seedlings. After raising the seedlings for 14 days after sowing, measurements were performed. The results are shown in Table 2.

[0153] [Comparative Example 6] Except for using the water-absorbent resin b-0, the rice seedling raising box was prepared and measurements were performed in the same manner as in Example 13. The results are shown in Table 3.

[0154] [Comparative Example 7] 48 g of water-absorbent resin b-0 was mixed with 1.2 g of potassium sulfate. The rice seedling raising box was prepared and measured in the same manner as in Example 13, except that this mixture (hereinafter referred to as "mixture b-1") was used. The results are shown in Table 3.

[0155] [Comparative Example 8] 48 g of water-absorbent resin b-0 was mixed with 3.1 g of diammonium hydrogen phosphate and 1.2 g of potassium sulfate. The rice seedling raising box was prepared and measured in the same manner as in Example 13, except that this mixture (hereinafter referred to as "mixture b-2") was used. The results are shown in Table 3.

[0156] [Comparative Example 9] 48 g of water-absorbent resin a-0 was mixed with 1.2 g of potassium sulfate. The rice seedling raising box was prepared and measured in the same manner as in Example 13, except that this mixture (hereinafter referred to as "mixture a-1") was used. The results are shown in Table 3.

[0157] [Comparative Example 10] The rice seedling raising box was prepared and measured in the same manner as in Example 13, except that no water-retaining material was used and only 3000 g of granular culture soil B (containing 0.33-0.42-0.5 g / kg of phosphorus, potassium and nitrogen as fertilizer, average particle size 3.0 mm) was used. The results are shown in Table 3.

[0158] [Comparative Example 11] Except for using the water-absorbent resin b-0 instead of the water-retentive material b-15, the rice seedling raising box was prepared and evaluated in the same manner as in Example 23. The results are shown in Table 4.

[0159] [Comparative Example 12] 20 g of the water absorbent resin b-0 and 0.04 g of ethyl paraoxybenzoate were mixed to obtain a mixture (hereinafter, referred to as "mixture b-3"). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the mixture b-3 was used instead of the water-retentive material b-15. The results are shown in Table 4.

[0160] [Comparative Example 13] In [Synthesis of water absorbent resin b-0], the mixture immediately after the washing 4 (content of water absorbent resin: 20 g) was mixed with a solution in which 5 g of ethyl paraoxybenzoate was dissolved in 60 g of methanol, and the mixture was vacuum-dried at 40° C. for 12 hours, thereby obtaining a mixture (hereinafter, referred to as “mixture b-4”). The rice seedling raising box was prepared and evaluated in the same manner as in Example 23, except that the mixture b-4 was used instead of the water-retentive material b-15. The results are shown in Table 4.

[0161] [Comparative Example 14] The rice seedling raising box was prepared and measured in the same manner as in Example 23, except that the water-absorbent resin a-0 was used instead of the water-retentive material b-15. The results are shown in Table 4.

[0162] [Table 2]

[0163] [Table 3]

[0164] [Table 4]

[0165] As in Examples 1 to 12, the survival rate of plants is high even under dry conditions in the water-retaining material containing a water-absorbent resin and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives. Also, it can be seen that when acetic acid is directly administered to plants as in Comparative Examples 3 and 5, the growth of plants tends to be poorer than in Examples 1 to 12.

[0166] Furthermore, when the water-retaining materials of Examples 13 to 22, which contain a water-absorbent resin, one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, and one or more elements selected from the group consisting of phosphorus, potassium, and nitrogen, which do not constitute the polymer skeleton of the resin, are used, the values ​​of the germination rate (growth index of the early stage of plant growth) and plant height (growth index of the later stage of plant growth) in addition to the survival rate under dry conditions are excellent. On the other hand, in Comparative Examples 6 to 9, in which the water-retaining materials do not contain one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives and do not contain the elements in the resin, and in Comparative Example 10, which does not contain a water-retaining material and contains fertilizer components in the medium, the survival rate, germination rate, and plant height are all low values.

[0167] Furthermore, when a water-retaining material containing a water-absorbent resin, one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, and a predetermined amount of a drug was used (Examples 23 to 33), the survival rate under dry conditions was good, and the occurrence of mold and the like was suppressed not only in short-term but also in long-term use, and plant growth was also good. Furthermore, the water-retaining material of the present invention was also excellent in stability during storage. On the other hand, from the results of Comparative Examples 11 to 14 in which the water-retaining material does not contain one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, it was found that the survival rate under dry conditions was not good and the following was also found. When a water-absorbent resin containing no drug was used (Comparative Examples 11 and 14), the occurrence of mold and the like was not suppressed even for a short period after the seedlings were raised. In addition, when a mixture b-3 in which the drug was contained in the water-retaining material but not inside the water-absorbent resin was used (Comparative Example 12), the occurrence of mold and the like could not be suppressed for a long period of time. This is thought to be because the drug, which was present in the water-retaining material but not inside the water-absorbent resin, flowed out of the rice seedling raising box due to watering during the seedling raising. Furthermore, when mixture b-4 containing an excessive amount of the drug inside the resin was used (Comparative Example 13), plant growth was inhibited. When a water-retaining material further containing compound (Y) was used in addition to the drug (Examples 32 and 33), the growth of mold and the like was inhibited and plants grew well, and in addition, the water absorption rate was improved and dust generation was reduced. [Industrial Applicability]

[0168] The water-retaining material of the present invention can provide plants with sufficient drought resistance and promote plant growth, and therefore can be suitably used in agriculture, particularly for raising seedlings.

Claims

1. A water-retaining material comprising a water-absorbent resin (excluding those containing an ethylene-vinyl alcohol copolymer having an ethylene content of 20 mol % or more based on all constituent units of the ethylene-vinyl alcohol copolymer in an amount of 3 mass % or more based on the total mass of the water-absorbent resin) and one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives, wherein the water-absorbent resin contains a polymer selected from the group consisting of vinyl alcohol-based polymers, acrylamide-based polymers, and methacrylic acid-based polymers, and the vinyl alcohol-based polymer contains a copolymer containing a vinyl alcohol constituent unit and a monomer constituent unit having an ionic group or a derivative thereof.

2. The water-retaining material according to claim 1 , wherein the content of the one or more compounds selected from the group consisting of acetic acid and acetic acid derivatives is 0.001% by mass or more and 70% by mass or less relative to the mass of the water-retaining material.

3. 3. The water-retaining material according to claim 1, wherein the acetic acid derivative is one or more compounds selected from the group consisting of sodium acetate, magnesium acetate, potassium acetate, ammonium acetate and calcium acetate.

4. 4. The water-retaining material according to claim 1, wherein the vinyl alcohol polymer contains potassium ions or ammonium ions as counter cations of the ionic groups.

5. The water-retaining material according to any one of claims 1 to 4, wherein the vinyl alcohol polymer has a crosslinked structure.

6. The water-retaining material according to any one of claims 1 to 5, which is for agricultural use.

7. The water-retaining material according to any one of claims 1 to 6, which is for raising seedlings.

8. The water-retaining material according to any one of claims 1 to 7, wherein the absorbent resin contains an element inside the resin that does not constitute the polymer skeleton of the resin, and the element is one or more elements selected from the group consisting of phosphorus, potassium and nitrogen.

9. The water-retaining material according to claim 8, wherein the content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen present inside the resin is 0.001 mass% or more and 50 mass% or less relative to the mass of the resin.

10. The water-retaining material according to claim 8 or 9, further comprising one or more elements selected from the group consisting of phosphorus, potassium and nitrogen, which are not present inside the resin but are present in the water-retaining material.

11. A water-retaining material according to any one of claims 8 to 10, wherein the content of one or more elements selected from the group consisting of phosphorus, potassium and nitrogen elements which are not present inside the resin but are present in the water-retaining material is 0.001 mass% or more and 50 mass% or less relative to the mass of the resin.

12. The water-retaining material according to any one of claims 1 to 11, wherein the water-absorbent resin contains one or more agents that kill or inhibit the growth of microorganisms in an amount of 0.00001% by mass or more and 10% by mass or less relative to the mass of the resin.

13. The water retention material according to claim 12, further comprising one or more of said agents present within the water retention material but not within the water absorbent resin.

14. The water retention material according to claim 13, wherein the content of the one or more chemicals present in the water retention material but not in the water absorbent resin is 0.00001% by mass or more and 10% by mass or less with respect to the mass of the resin.

15. A water retention material according to any one of claims 1 to 14, wherein in the water-absorbed state of the water retention material, which has absorbed 50 times the mass of the water retention material, the proportion of water that can be absorbed by plants is 7.6 mass% or more based on the mass of the water retention material in the water-absorbed state.

16. The water-retentive material has an SP value of 6.0 (cal / cm ３ ) １／２ or more 30.0 (cal / cm ３ ) １／２ The water-retaining material according to any one of claims 1 to 15, further comprising a compound (Y) which is:

17. The compound (Y) is one or more compounds selected from the group consisting of water, glycerin, methanol, dimethyl sulfoxide, ethanol, acetonitrile, isopropanol, N-methyl-2-pyrrolidone, methyl acetate, tetrahydrofuran, diethyl ether, N,N-dimethylformamide and ethylene glycol. The water-retaining material according to claim 16.

18. The water-retaining material according to claim 16 or 17, wherein the content of the compound (Y) is 0.001% by mass or more and 98% by mass or less with respect to the mass of the water-retaining material.

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