JP2018145329A - Water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-absorbing resin which has balance between excellent dynamic characteristics and degradability in addition to water absorptivity, and stably functions due to the excellent dynamic characteristics, and then is decomposed in the environment and is reduced in an influence on environment, and to provide a water-retaining material for agriculture and a sanitary material containing the water-absorbing resin.SOLUTION: A water-absorbing resin contains modified polyvinyl alcohol of which at least a part is acetalized with a glyoxylic acid and/or a glyoxylic acid derivative as a component, where when solution viscosity at 20°C of 4 mass% aqueous solution of polyvinyl alcohol being a raw material before acetalization is represented by V (mPa s), and 1,2-glycol bond content contained in the main chain is represented by G(mol%), V and G satisfy the expression 1: (100-V)*G≥86 and expression 2: V≥5 at the same time.SELECTED DRAWING: None

Description

  The present invention relates to a water absorbent resin. More specifically, the present invention relates to a water-absorbing resin that is more easily decomposable than a conventional water-absorbing resin and has an excellent balance with mechanical properties.

With the recent depletion of water resources, attempts to use agricultural water effectively and appropriately, or to maintain or increase the yield of agricultural products with a smaller amount of irrigation water than before, are the so-called agricultural water retention. It has been studied using materials (for example, see Patent Documents 1 to 5). These agricultural water-retaining materials have a superabsorbent resin (SAP) as a main component, and for example, when compared to peat moss, which is used to improve the water retention of the entire soil, it produces an effect in a very small amount. There is an advantage that the burden on the farmer is small.
Patent Documents 1 and 2 disclose that a highly water-absorbent resin mainly composed of polyacrylate gel is used as an agricultural water retention material. Patent Documents 3 and 4 disclose polymer gels obtained by grafting polyacrylic acid (salt) and / or polyacrylamide onto a readily degradable natural polymer such as starch. Patent Document 5 discloses polymer particles having a complex surface structure containing polyvinyl glyoxylic acid resin, and states that such particles can be applied to sanitary materials and agricultural water retention materials.

Japanese Patent No. 4346112 Special table 2013-544929 gazette US Patent No. 8,507,602 US Patent No. 9,181,377 Special table 2013-540164

  The polyacrylate gel disclosed in Patent Documents 1 and 2 is inferior in mechanical properties in a water-absorbed state, and tends to inhibit the air permeability of the soil due to swelling in the soil. Moreover, when the method of irrigating from underground piping is adopted, there is a problem that the polyacrylic acid gel flows out to the ground and the function of supplying water to the roots is not exhibited. Furthermore, the polyacrylate gel is not decomposed in the soil or the like, or the decomposition rate is extremely slow. Polyacrylate gels have a strong tendency to lose their water retention upon contact with divalent ions contained in the soil, and the gel itself is not decomposed even after loss of function and accumulates in the soil in the field. .

  Since the polymer gel disclosed in Patent Documents 3 and 4 has a tendency that starch, which is the main chain, degrades in the environment, improvement in soil accumulation can be expected. On the other hand, the mechanical properties are still not sufficient, and there remains a problem that the air permeability maintenance of the soil and the function of staying in the vicinity of the root are insufficient. In addition, even if the main chain is decomposed, the side chain components polyacrylic acid (salt) and polyacrylamide are not decomposed in the soil or the like. Become. In addition, since a nutrient source that is readily available to fungi is released by the decomposition of starch, there is a problem that leads to generation of fungi and mushrooms that hinder crop cultivation in the field.

The polymer particles containing the polyvinyl glyoxylic acid resin disclosed in Patent Document 5 have molds when left in a water-containing state, and degelation has occurred. Therefore, such materials have biodegradability. It has been suggested that deacetalization and main chain cleavage occur when a metal catalyst and an oxidizing agent are used in combination. On the other hand, there is no specific disclosure and teaching regarding the relationship between the molecular weight and main chain structure of polyvinyl glyoxylic acid resin and polyvinyl alcohol, the raw material of the resin, and the mechanical properties and degradability of the resulting polymer particles. There is no suggestion.
Thus, the object of the present invention is to have a good balance of mechanical properties and decomposability in addition to water absorption, and after it functions stably due to the excellent mechanical properties, it is decomposed in the environment and has an impact on the environment. Water-absorbing resin in which water is reduced, and an agricultural water-retaining material and hygiene material comprising the water-absorbing resin.

  In order to achieve the above object, the present inventors have conducted intensive studies. As a result, it has been found that the mechanical properties of the polyvinyl glyoxylic acid resin disclosed in Patent Document 5 have a correlation with the solution viscosity of an aqueous solution of polyvinyl alcohol as a raw material. On the other hand, it has been found that the degradability of polyvinyl glyoxylic acid resin strongly depends on the specific structure that the main chain of polyvinyl alcohol as the raw material can have, more specifically, the amount of 1,2-glycol bonds. Furthermore, the modification | denaturation which acetalized with the glyoxylic acid and / or the glyoxylic acid derivative using the polyvinyl alcohol with which the solution viscosity of aqueous solution and the specific structure (1,2-glycol bond amount) of a principal chain satisfy | fill a specific relationship simultaneously as a raw material The present inventors have found that a resin containing polyvinyl alcohol as a constituent component has an excellent balance between mechanical properties and decomposability in addition to water absorption.

That is, the object of the present invention is achieved by providing the following [1] to [8].
[1] A water-absorbent resin comprising a modified polyvinyl alcohol at least partly acetalized with glyoxylic acid and / or glyoxylic acid derivative as a constituent component, and comprising a 4% by mass aqueous solution of polyvinyl alcohol as a raw material before the acetalization A water-absorbent resin having a solution viscosity at 20 ° C. of V (mPa · s) and a 1,2-glycol bond amount G (mol%) contained in the main chain thereof simultaneously satisfy the following formulas 1 and 2.
(100−V) * G ≧ 86 (Formula 1)
V ≧ 5 (Formula 2)
[2] The water-absorbent resin according to [1], wherein the raw material polyvinyl alcohol is obtained by saponifying polyvinyl acetate and has a saponification degree of 30 mol% or more.
[3] The water-absorbent resin according to [1] or [2], comprising glyoxylic acid and / or modified polyvinyl alcohol having a degree of acetalization by glyoxylic acid of 1 mol% to 80 mol% as a constituent component.
[4] The water-absorbent resin according to any one of [1] to [3], wherein at least a part is crosslinked.
[5] The water-absorbent resin according to [4], wherein the crosslinking site is cleaved by a hydrolysis reaction.
[6] A composition comprising the water absorbent resin according to any one of [1] to [4].
[7] An agricultural water-retaining material comprising the water-absorbing resin according to any one of [1] to [4].
[8] A sanitary material comprising the water absorbent resin according to any one of [1] to [4].

  The water-absorbent resin of the present invention has an excellent balance between mechanical properties and degradability in addition to water absorbency, and, for example, when applied as an agricultural water retention material, it can stably exhibit functions in soil and is excellent. Therefore, accumulation in field soil after use is suppressed. In addition, when used as a sanitary material, because it has excellent mechanical properties and degradability of the water-absorbent resin, it not only excels in stability and shape retention during use, but also easily decomposes after use. Accumulation in the environment is suppressed.

The present invention is described in detail below.
The water-absorbent resin of the present invention is a water-absorbent resin comprising a modified polyvinyl alcohol (hereinafter sometimes simply referred to as a modified polyvinyl alcohol) at least partially acetalized with glyoxylic acid and / or a glyoxylic acid derivative. The solution viscosity at 20 ° C. of a 4% by weight aqueous solution of polyvinyl alcohol as a raw material before acetalization is V (mPa · s), and the 1,2-glycol bond amount G (mol%) contained in the main chain. Is a water-absorbent resin that simultaneously satisfies the following formula 1 and formula 2.
(100−V) * G ≧ 86 (Formula 1)
V ≧ 5 (Formula 2)
By satisfying such a specific relationship, a modified polyvinyl alcohol having an excellent balance between mechanical properties and decomposability in addition to water absorption can be obtained, which becomes a main constituent of the water absorbent resin of the present invention.

  The modified polyvinyl alcohol constituting the water-absorbent resin of the present invention is preferably obtained by acetalizing at least a part of the hydroxyl groups possessed thereof with glyoxylic acid and / or glyoxylic acid derivatives using polyvinyl alcohol as a raw material. First, polyvinyl alcohol used as a raw material will be described.

In the present invention, it is one condition that polyvinyl alcohol used as a raw material has a solution viscosity V (mPa · s) at 20 ° C. of a 4 mass% aqueous solution of 5 or more.
It is known that the mechanical properties of polymers generally tend to improve as their molecular weight increases, while they tend to generally degrade as their molecular weight decreases. Various methods for measuring the molecular weight of a polymer are known to those skilled in the art, and there is a correlation between the solution viscosity of a solution obtained by dissolving a polymer in a solvent in which the polymer is dissolved and the molecular weight of the polymer. Are known. In the present invention, the smaller the solution viscosity V of the polyvinyl alcohol used as a raw material, the smaller the molecular weight, and the larger V, the larger the molecular weight. When polyvinyl alcohol with a high molecular weight is simply used, the mechanical properties of the resulting modified polyvinyl alcohol can be improved, but the degradability is reduced, and the desired mechanical properties and degradability of the water-absorbent resin are deviated. Resulting in.

  It is known that resins such as polyacrylic acid, polyacrylamide, polyethylene, and polypropylene have a main chain structure composed of carbon-carbon bonds, and these resins are not degradable or decompose very slowly. On the other hand, polyvinyl alcohol is also known to be a degradable resin, although its main chain structure is composed of carbon-carbon bonds. The main chain of polyvinyl alcohol has two vinyl alcohol units at the head when the methylene side of the vinyl alcohol unit (vinyl alcohol unit) is the head and the methine side to which the hydroxyl group is bonded is the tail, as shown in the following chemical structural formula. -1,3-glycol binding units mainly resulting from binding in the tail form, but 1,2-glycol binding units resulting from binding in the head-to-head or tail-to-tail form as heterogeneous bonds It is included.

It is known that the amount of 1,2-glycol bonds affects the degradability of polyvinyl alcohol. Since this bond has a lower binding energy than the carbon-carbon bond contained in the 1,3-glycol bond unit and is relatively easily cleaved, polyvinyl alcohol is decomposed as more 1,2-glycol bonds are contained. It is thought that it is easy to do. As a result of intensive studies, the present inventors have found that the degradability of the modified polyvinyl alcohol can be controlled by the amount of 1,2-glycol bonds contained in the raw material polyvinyl alcohol, and have reached the present invention. In Patent Document 5, there is no discussion about the relationship between degradability and the amount of 1,2-glycol bond in the main chain.
Furthermore, when the solution viscosity of the aqueous polyvinyl alcohol solution that is the raw material is below a certain level, the degradability of the resulting modified polyvinyl alcohol is improved, while the mechanical properties are remarkably reduced, and it is used for agricultural water retaining materials and sanitary materials. Problems arise.

  The solution viscosity V (mPa · s) at 20 ° C. of a 4% by mass aqueous solution of polyvinyl alcohol can be measured, for example, by a method based on JIS K6726. Regarding the range of the solution viscosity V (mPa · s), it is necessary to satisfy the formula 1 and the formula 2 at the same time, and if it is less than 5, the mechanical properties of the modified polyvinyl alcohol obtained are significantly lowered. On the other hand, when it is 55 or more, the degradability of the modified polyvinyl alcohol obtained is deteriorated, and when acetalizing at least part of the hydroxyl groups of the polyvinyl alcohol with glyoxylic acid and / or glyoxylic acid derivatives, the viscosity is high and the operability is lowered. It becomes a trend. Considering these, the range of the solution viscosity V is preferably 5 or more and less than 55, more preferably 10 or more and less than 45, and further preferably 15 or more and less than 35.

There is no restriction | limiting in particular in the calculation method of the 1, 2- glycol bond amount G (mol%) contained in polyvinyl alcohol, For example, it can quantitate by using nuclear magnetic resonance spectroscopy (NMR). Specifically, it is purified and completely dried, and polyvinyl alcohol is dissolved in deuterated dimethyl sulfoxide (DMSO-d ₆ ) at a concentration of about 0.1 to 10% by mass, for example, in the range of room temperature to 150 ° C. And a method of measuring ( ¹ H-NMR) a nuclear magnetic resonance spectrum of a proton nucleus (hydrogen nucleus) at the temperature of In order to improve peak separation, an additive such as trifluoroacetic acid may be added during measurement. ^When structural analysis of polyvinyl alcohol is performed by ¹ H-NMR method, protons bonded to a methine carbon bonded with a hydroxyl group show different peaks. By quantitative analysis of this, 1, 1 contained in the main chain structure is obtained. The 2-glycol bond amount G can be determined. Specifically, the peak derived from the methine proton of the vinyl alcohol unit is 3.2 to 4.0 ppm (integrated value A), and the peak derived from one methine proton of the 1,2-glycol bond is 3.25 ppm (integrated value B). ) And the 1,2-glycol bond amount G (mol%) can be determined from the following equation.
G = (B / A) * 100 (Formula 3)

  The amount of 1,2-glycol bonds G (mol%) is not limited as long as Formula 1 is satisfied, but is usually in the range of 0.5 to 3.5 mol%. A modified polyvinyl alcohol obtained by acetalizing at least a part of a hydroxyl group thereof with glyoxylic acid and / or a glyoxylic acid derivative, using polyvinyl alcohol having a 1,2-glycol bond amount G (mol%) of less than 0.5 mol% as a raw material, It cannot be said that the decomposability is sufficient, which is not preferable. On the other hand, in order to obtain polyvinyl alcohol having a 1,2-glycol bond amount G (mol%) exceeding 3.5 mol%, measures such as radical polymerization of vinyl acetate monomer at a temperature greatly exceeding the boiling point are taken. However, a remarkable chain transfer reaction and side reaction during the polymerization cannot be avoided, and it is difficult to say that this is an industrially feasible method, which is not preferable. From the viewpoint of the balance between degradability and mechanical properties of the resulting modified polyvinyl alcohol, the range of 1,2-glycol bond amount G (mol%) is preferably 0.9 to 3.0, and from 1.4 A range of 2.5 is more preferable.

  The polyvinyl alcohol used as a raw material in the present invention may have only a vinyl alcohol unit as its constituent unit, or may contain other constituent units. Examples of other structural units include: vinyl acetate units, vinyl pivalate units and other vinyl ester derived units; ethylene, propylene, 1-butene, isobutylene and other olefin derived units; acrylic acid and its derivatives, methacryl Examples include structural units derived from acids and derivatives thereof, maleic acid and derivatives thereof, maleic anhydride and derivatives thereof, and the like. Other structural units may contain one kind or plural kinds. When the content of other structural units is too large, the reaction point with glyoxylic acid and / or a derivative thereof is reduced in the acetalization reaction, so that the effects of the present invention may not be achieved. Therefore, the content of other structural units is preferably 50% by mass or less, more preferably 30% by mass or less, and further preferably 15% by mass or less.

  The polyvinyl alcohol used as a raw material in the present invention may be an industrially manufactured and commercially available polyvinyl alcohol monomer such as a vinyl acetate monomer, as long as the above formula 1 and formula 2 are satisfied at the same time. Even if the monomer which comprises another structural unit is made to coexist as needed, a well-known polymerization initiator is used and a well-known polymerization reaction is performed, Then, the thing manufactured by performing a saponification reaction by a well-known method may be used. Good.

  Preferably, the polyvinyl alcohol is obtained by saponifying polyvinyl acetate. The degree of progress of the saponification treatment is usually represented by the degree of saponification (unit: mol%) indicating how much of the acetate portion derived from vinyl acetate has been converted to a hydroxyl group. If the degree of saponification is too low, the number of reaction sites in the subsequent acetalization with glyoxylic acid and / or glyoxylic acid derivatives becomes too small, which is not preferable. From this viewpoint, the saponification degree of polyvinyl alcohol is preferably 15 mol% or more, more preferably 30 mol% or more.

Glyoxylic acid and / or glyoxylic acid derivatives are used for acetalization of polyvinyl alcohol. Glyoxylic acid may be used alone, or may be used together with glyoxylic acid derivatives such as glyoxylate, glyoxylic acid ester, and acetal compounds thereof, or only glyoxylic acid derivatives may be used.
Examples of the glyoxylate include alkali metal salts of glyoxylic acid such as sodium glyoxylate and potassium glyoxylate, and alkaline earth metal salts of glyoxylic acid such as calcium glyoxylate and magnesium glyoxylate. Among these, potassium glyoxylate, calcium glyoxylate, and magnesium glyoxylate are preferable, and potassium glyoxylate is more preferable from the viewpoint that the effects of the present invention can be further exerted when used as a water retention material for agriculture.
Examples of glyoxylic acid esters include methyl glyoxylate, ethyl glyoxylate, propyl glyoxylate, isopropyl glyoxylate, butyl glyoxylate, isobutyl glyoxylate, sec-butyl glyoxylate, tert-butyl glyoxylate, hexyl glyoxylate, glyoxylic acid Examples include octyl and 2-ethylhexyl glyoxylate.
Examples of acetal compounds of glyoxylic acid, glyoxylic acid salts and glyoxylic acid esters include compounds in which the aldehyde part of glyoxylic acid, glyoxylic acid salts, and glyoxylic acid esters is acetalized with alcohol compounds such as methanol, ethanol, propanol, and ethylene glycol Can be mentioned.

  There is no particular limitation on the method of acetalization reaction with glyoxylic acid and / or glyoxylic acid derivatives of polyvinyl alcohol, and it may be a homogeneous reaction or a heterogeneous reaction. Specifically, for example, a method in which a polyvinyl alcohol aqueous solution and a glyoxylic acid aqueous solution are mixed and reacted can be exemplified. A catalyst may be used for the purpose of accelerating the reaction. 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; solid acids such as cation exchange resin and heteropoly acid. Since glyoxylic acid is also an acid that can accelerate the acetalization reaction, it can be used as an autocatalyst. These catalysts may be used independently and may be used in combination of multiple types. From the viewpoint of ease of treatment after the reaction, a method using glyoxylic acid as a reaction substrate and an autocatalyst is preferable.

  In the acetalization reaction of polyvinyl alcohol with glyoxylic acid and / or glyoxylic acid derivative, the amount of glyoxylic acid and / or glyoxylic acid derivative introduced into polyvinyl alcohol can be defined by, for example, the consumption of hydroxyl groups possessed by polyvinyl alcohol. That is, when the hydroxyl group consumption is low, the introduction amount of glyoxylic acid and / or glyoxylic acid derivative is low, and when the hydroxyl group consumption is high, the introduction amount of glyoxylic acid and / or glyoxylic acid derivative is high. If the amount of glyoxylic acid and / or glyoxylic acid derivative introduced is too low, the water absorption of the resulting modified polyvinyl alcohol tends to be inferior, while if it is too high, the resulting polyvinyl alcohol tends to have poor mechanical properties during water absorption. Considering the range where the effects of the present invention are exhibited, the consumption of hydroxyl groups of polyvinyl alcohol used as a raw material is preferably in the range of 0.1 to 87 mol%, and more preferably in the range of 0.5 to 85 mol%. More preferably, it is still more preferably in the range of 1 to 80 mol%. The consumption amount of the hydroxyl group can be measured by, for example, NMR (nuclear magnetic resonance spectroscopy), FTIR (Fourier transform infrared spectroscopy) or the like.

  The water-absorbent resin of the present invention is such that the modified polyvinyl alcohol suitably obtained by acetalization reaction with glyoxylic acid and / or glyoxylic acid derivative of polyvinyl alcohol is further crosslinked from the viewpoint of preventing elution during use, That is, it is preferably in a so-called gel state at the time of use. There is no restriction | limiting in particular in the form of bridge | crosslinking, For example, the crosslinked structure by an ester bond, an ether bond, an acetal bond, a carbon-carbon bond etc. is mentioned.

  As an example of an ester bond, the ester bond formed between the hydroxyl group derived from polyvinyl alcohol and the carboxyl group derived from glyoxylic acid (derivative) can be mentioned. As an example of an ether bond, the ether bond formed by the dehydration condensation between the hydroxyl groups derived from polyvinyl alcohol can be mentioned. As an example of an acetal bond, an acetal bond formed by the acetalization reaction of a hydroxyl group between polyvinyl alcohol molecules with glyoxylic acid can be exemplified. As an example of a carbon-carbon bond, the carbon-carbon bond formed by the coupling between the carbon radicals of modified polyvinyl alcohol, which is generated, for example, by irradiation with active energy rays, can be mentioned. These cross-linked structures may be contained singly or in plural. Among these, a crosslinked structure by an ester bond or an acetal bond is preferable, and a crosslinked structure by an ester bond is more preferable. Such a form of cross-linking may be formed simultaneously during the acetalization reaction of glyoxylic acid and / or glyoxylic acid derivative of polyvinyl alcohol, or may be formed separately.

  The carboxyl group introduced by the acetalization reaction with glyoxylic acid and / or glyoxylic acid derivative of polyvinyl alcohol may be partially or completely treated to be in the form of carboxylate. Examples of the counter cation of the carboxylate include: alkali metal ions such as sodium ion, potassium ion, rubidium ion and cesium ion; alkaline earth metal ion such as magnesium ion, calcium ion, strontium ion and barium ion; aluminum ion And other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; Especially, when using as a water retention material composition for agriculture especially, it is preferable that they are a potassium ion, a calcium ion, and an ammonium ion, and it is more preferable that it is a potassium ion. These counter cations may be contained alone or in combination of two or more.

  The water-absorbent resin of the present invention may be in the form of a composition further containing other additives as long as the effects of the present invention are not impaired. Examples of such other additives include polysaccharides such as starch, modified starch, sodium alginate, chitin, chitosan, cellulose and derivatives thereof, polyethylene, polypropylene, ethylene-propylene copolymer, polystyrene, acrylonitrile-styrene copolymer. , Acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride, polycarbonate resin, 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 terephthalamide, Polyphenylene ether Polyoxymethylene, polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, polyurethane, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyacrylic acid , Polyacrylate, polyacrylate, polymethacrylic acid, polymethacrylate, polymethacrylate, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-acrylic acid copolymer , Resins such as ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-methacrylate copolymer, natural rubber, synthetic isoprene rubber, chloroprene rubber, silicone rubber, fluoro rubber, Rubbers and elastomers such as letan rubber, acrylic rubber, styrene thermoplastic elastomer, olefin thermoplastic elastomer, ester thermoplastic elastomer, urethane thermoplastic elastomer, amide thermoplastic elastomer, kaolinite, smectite, montmorillonite, sericite And clay minerals such as chlorite, glowconite, talc, natural zeolite and synthetic zeolite, and sand. These may be used alone or in combination.

  The water-absorbent resin or composition of the present invention can be suitably used as an agricultural water retention material. There are various ways to use it as a water retention material for agriculture, a method of spraying directly on the field, a method of applying together with seeds when sowing crop seeds, a method of coating seeds once and seeding the coated seeds Etc. Moreover, you may use the mixture of the water absorbing resin or composition of this invention, and water as a culture medium. There is no restriction | limiting in particular in the crop made into application object, For example, various vegetables, root vegetables, fruits, cereals, potatoes, beans, ornamental plants, flowering plants, turf, trees etc. can be mentioned.

  When the water-absorbent resin of the present invention is used as an agricultural water retention material, it may be in the form of a composition containing a fertilizer component and / or an agrochemical component as long as the effects of the present invention are not impaired. Examples of fertilizers are three major fertilizers such as nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, calcium fertilizer; plant such as calcium, magnesium, sulfur, iron, copper, manganese, zinc, boron, molybdenum, chlorine, nickel Examples include fertilizers that contain essential elements. Examples of the agrochemical component include insecticides, fungicides, insecticide fungicides, herbicides, rodenticides, plant growth regulators and the like. These may be used alone or in combination.

  Since the water-absorbent resin of the present invention exhibits high water absorption characteristics and excellent mechanical properties, for example, as an absorbent in hygiene products such as baby diapers, infant diapers, children's diapers, adult diapers, sanitary products, protective underwear, etc. It is preferably used for sanitary materials. Since the water-absorbent resin of the present invention can be decomposed after use, it is a preferable material from the viewpoint of environmental impact.

  The water-absorbent resin of the present invention is used for commonly known water-absorbent resin applications such as prevention of water penetration in underground power cables or communication cables; carriers in drug delivery systems; absorption of spilled and discharged aqueous liquids. Materials; Paints; Inks; Absorbent coatings for colorant compositions; Carriers for controlled release of insecticides, herbicides, fragrances and drugs; Flame retardant gels; Funeral pads; Surgical pads; Materials; Solid waste materials for medical use; Absorbent pads and packaging materials for foodstuffs; Cosmetic gelling agents; Sealing composites; Filtration applications; Fuel monitoring systems for aircraft and automobiles; Water supply for cage animals; It can also be used for beds, toys that grow in water, drilling fluid additives, artificial snow, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and the like, but the present invention is not limited to the examples and the like. The raw materials used and the method of evaluation analysis are shown below.

Evaluation of Properties of Modified Polyvinyl Alcohol The obtained modified polyvinyl alcohol was evaluated as follows.
(1) Water absorption capacity According to JIS K 7223, the pure water absorption of the obtained modified polyvinyl alcohol was measured, and the water absorption capacity was calculated based on the following formula.

      Water absorption magnification = [Sample mass after water absorption−Sample mass before water absorption] / Mass before water absorption

(2) Oxidative degradation test The obtained modified polyvinyl alcohol was sieved using a stainless mesh having an opening diameter of 100 µm and 1000 µm, and a powder part having a particle size of 100 to 1000 µm was subjected to an acid degradation test. About 100 mg of this powder was weighed into a glass flask, and 200 mL of 30 ppm iron (II) sulfate aqueous solution was added to swell the powder. 100 mL of 30% hydrogen peroxide aqueous solution was added here, and it processed at 40 degreeC for 2 hours. Thereafter, the contents were gravity filtered with a filter paper whose mass was measured in advance, and then the substance remaining on the filter paper was washed with 100 mL of ion exchange water and filtered three times. The filter paper and the substance remaining on the filter paper were vacuum-dried at 40 ° C. for 24 hours, the mass was measured, and the oxidative decomposition rate was determined by the following equation.
Oxidative degradation rate (%) = 100 × [(filter paper after test + mass of substance) − (mass of filter paper before test)] / (powder mass used)

(3) Mechanical property test The obtained modified polyvinyl alcohol was sieved using a stainless mesh having an opening diameter of 100 µm and 1000 µm, and a powder part having a particle size of 100 to 1000 µm was subjected to an acid decomposition test. 50 g of water was added to 1 g of this powder to uniformly absorb water to obtain a hydrogel. Next, a part (about 1 g) of this hydrogel was taken with a spatula, placed on a stainless steel mesh having an opening diameter of 2000 μm and kept at a height of 10 cm in the air, and the state after 30 minutes was visually observed. The state of the hydrogel was classified as follows and evaluated as A, B, C, D, and E from the superior side. The test was performed 5 times, and the most frequently used index was used as an index of mechanical properties.
A; remained on the stainless steel mesh after 30 minutes B; more than half of the gel remained on the stainless steel mesh after 30 minutes C; about half of the gel remained on the stainless steel mesh after 30 minutes D; Less than half of the gel remained on the stainless steel mesh after 30 minutes E; After 30 minutes, all of the gel had fallen under the stainless steel mesh

(4) Solution viscosity
According to JIS K 6726, the solution viscosity at 20 ° C. of a 4% by mass aqueous solution of each polyvinyl alcohol was measured.

Polyvinyl alcohol:
The polyvinyl alcohol used in Reference Examples 1 to 11 was a commercially available product. The polyvinyl alcohol used in Reference Examples 12 to 14 was produced according to Production Examples 1 to 3 described later. Table 1 shows the characteristics.

Production Example 1 Production of polyvinyl alcohol (XII) (1) Into a 5 L pressure reaction vessel equipped with a stirrer, a nitrogen inlet and an initiator inlet, 2940 g of vinyl acetate, 60 g of methanol and 0.088 g of tartaric acid were charged at room temperature. The reaction tank pressure was increased to 2.0 MPa while bubbling with nitrogen gas and allowed to stand for 10 minutes, and then the operation of releasing the pressure was repeated three times to replace the system with nitrogen. As an initiator, a methanol solution (concentration 0.2 g / L) of 2,2′-azobis (cyclohexane-1-carbonitrile) (V-40) was prepared, and nitrogen substitution was performed by bubbling with nitrogen gas. Next, the temperature inside the polymerization tank was raised to 120 ° C. The reaction vessel pressure at this time was 0.5 MPa. Next, 2.5 mL of the initiator solution was injected to initiate polymerization. During the polymerization, the temperature was maintained at 120 ° C., and the above initiator solution was continuously added at a rate of 10 mL / hr to carry out the polymerization. The reactor pressure during the polymerization was 0.5 MPa. After 3 hours, the polymerization was stopped by cooling. The solid concentration at this time was 24%. Subsequently, unreacted vinyl acetate monomer was removed while adding methanol occasionally under reduced pressure at 30 ° C. to obtain a methanol solution of polyvinyl acetate (solid content concentration: 33%).
(2) To 400 g of a polyvinyl acetate methanol solution (100 g of polyvinyl acetate in the solution) prepared by adding methanol to the polyvinyl acetate solution obtained in (1) so that the solid concentration is 25%, Saponification was carried out by adding 11.6 g of a 10% sodium hydroxide solution in methanol (molar ratio 0.025 to the vinyl acetate units in polyvinyl acetate). About 2 minutes after the addition, the gelled system was pulverized with a pulverizer and allowed to stand for 1 hour to allow saponification to proceed, and then 1000 g of methyl acetate was added to neutralize the remaining sodium hydroxide. After confirming the end of neutralization using a phenolphthalein indicator, 1000 g of methanol was added to white solid polyvinyl alcohol obtained by filtration and washed at room temperature for 3 hours. The washing operation was repeated three times, and then the solid obtained by centrifugal drainage was dried in a dryer at 70 ° C. for 2 days to obtain polyvinyl alcohol (XII).
(3) The saponification degree of polyvinyl alcohol (XII) was 98-99 mol%, and the solution viscosity at 20 ° C. of a 4% aqueous solution was 25.0-31.0 mPa · S.

Production Example 2 Production of Polyvinyl Alcohol (XIII) (1) A 5 L pressure reaction vessel equipped with a stirrer, a nitrogen inlet and an initiator inlet was charged with 2850 g of vinyl acetate, 150 g of methanol and 0.086 g of tartaric acid at room temperature. The reaction tank pressure was increased to 2.0 MPa while bubbling with nitrogen gas and allowed to stand for 10 minutes, and then the operation of releasing the pressure was repeated three times to replace the system with nitrogen. As an initiator, a solution of 2,2′-azobis (N-butyl-2-methylpropionamide) in methanol (concentration 0.1 g / L) was prepared, and nitrogen substitution was performed by bubbling with nitrogen gas. Next, the temperature inside the polymerization tank was raised to 150 ° C. The reaction vessel pressure at this time was 0.5 MPa. Next, 15 mL of the initiator solution was injected to initiate polymerization. During the polymerization, the temperature was maintained at 150 ° C., and the above initiator solution was continuously added at a rate of 15.8 mL / hr to carry out the polymerization. The reactor pressure during the polymerization was 1.0 MPa. After 4 hours, the polymerization was stopped by cooling. The solid concentration at this time was 35%. Subsequently, unreacted vinyl acetate monomer was removed while adding methanol occasionally under reduced pressure at 30 ° C. to obtain a methanol solution of polyvinyl acetate (solid content concentration: 33%).
(2) To 400 g of a polyvinyl acetate methanol solution (100 g of polyvinyl acetate in the solution) prepared by adding methanol to the polyvinyl acetate solution obtained in (1) so that the solid concentration is 25%, Saponification was carried out by adding 11.6 g of a 10% sodium hydroxide solution in methanol (molar ratio 0.025 to the vinyl acetate units in polyvinyl acetate). After the addition, the gelled system in about 3 minutes was pulverized with a pulverizer and allowed to stand for 1 hour to allow saponification to proceed, and then 1000 g of methyl acetate was added to neutralize the remaining sodium hydroxide. After confirming the end of neutralization using a phenolphthalein indicator, 1000 g of methanol was added to white solid polyvinyl alcohol obtained by filtration and washed at room temperature for 3 hours. The washing operation was repeated three times, and then the solid obtained by centrifugation was dried in a dryer at 70 ° C. for 2 days to obtain polyvinyl alcohol (XIII).
(3) The saponification degree of polyvinyl alcohol (XIII) was 98-99 mol%, and the solution viscosity at 20 ° C. of a 4% aqueous solution was 10.2-11.8 mPa · S.

Production Example 3 Production of Polyvinyl Alcohol (XIV) (1) A 5 L pressure reaction vessel equipped with a stirrer, nitrogen inlet and initiator inlet was charged with 2700 g of vinyl acetate, 300 g of methanol and 0.081 g of tartaric acid at room temperature. The reaction tank pressure was increased to 2.0 MPa while bubbling with nitrogen gas and allowed to stand for 10 minutes, and then the operation of releasing the pressure was repeated three times to replace the system with nitrogen. As an initiator, a methanol solution (concentration 0.05 g / L) of 2,2′-azobis (N-butyl-2-methylpropionamide) was prepared, and nitrogen substitution was performed by bubbling with nitrogen gas. Next, the temperature inside the polymerization tank was raised to 180 ° C. The reaction vessel pressure at this time was 1.6 MPa. Then, 0.4 mL of the above initiator solution was injected to initiate polymerization. During the polymerization, the temperature was maintained at 180 ° C., and the above initiator solution was continuously added at a rate of 10.6 mL / hr to carry out the polymerization. The reactor pressure during the polymerization was 1.6 MPa. After 4 hours, the polymerization was stopped by cooling. The solid concentration at this time was 27%. Subsequently, unreacted vinyl acetate monomer was removed while adding methanol occasionally under reduced pressure at 30 ° C. to obtain a methanol solution of polyvinyl acetate (solid content concentration: 33%).
(2) To 333 g of a polyvinyl acetate methanol solution (100 g of polyvinyl acetate in the solution) prepared by adding methanol to the polyvinyl acetate solution obtained in (1) so that the solid content concentration becomes 25%, Saponification was carried out by adding 11.6 g of a 10% sodium hydroxide solution in methanol (molar ratio 0.025 to the vinyl acetate units in polyvinyl acetate). After the addition, the gelled system in about 3 minutes was pulverized with a pulverizer and allowed to stand for 1 hour to allow saponification to proceed, and then 1000 g of methyl acetate was added to neutralize the remaining sodium hydroxide. After confirming the end of neutralization using a phenolphthalein indicator, 1000 g of methanol was added to white solid polyvinyl alcohol obtained by filtration and washed at room temperature for 3 hours. After the washing operation was repeated three times, the solid obtained by centrifugal drainage was dried in a dryer at 70 ° C. for 2 days to obtain polyvinyl alcohol (XIV).
(3) The saponification degree of polyvinyl alcohol (XIII) was 98-99 mol%, and the solution viscosity at 20 ° C. of a 4% aqueous solution was 5.2-6.0 mPa · S.

Reference Example 1: Production and characterization of modified polyvinyl alcohol (I) A 500 mL four-necked separable flask equipped with a reflux condenser and a stirring blade was charged with 200.0 g of ion-exchanged water and 40.0 g of the polyvinyl alcohol (I). Was dissolved by heating to 90 ° C. with stirring. The system was cooled to 80 ° C., 15.9 g of a 50% aqueous solution of glyoxylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was added over 5 minutes, and then reacted at the same temperature for 1 hour. The contents of the flask were taken out and dried at 105 ° C. for 3 hours using a hot air dryer (manufactured by YAMATO, DKM400). The obtained resin was cooled to room temperature, immersed in 300 mL of 50% potassium hydroxide solution for 3 hours, and then washed with ion-exchanged water to obtain modified polyvinyl alcohol (I). The obtained modified polyvinyl alcohol (I) was subjected to water absorption properties, acid degradation test, oxidative degradation test, and mechanical property test. The results are shown in Table 2.

Reference Examples 2 to 14: Production and Characterization of Modified Polyvinyl Alcohols (II) to (XIV) References except that polyvinyl alcohols (II) to (XIV) were used instead of polyvinyl alcohol (I) as polyvinyl alcohols, respectively. Reaction was carried out in the same manner as in Example 1 to obtain modified polyvinyl alcohols (II) to (XIV). The obtained modified polyvinyl alcohols (II) to (XIV) were subjected to water absorption properties, acid degradation tests, oxidative degradation tests, and mechanical property tests. The results are shown in Table 2.

  The modified polyvinyl alcohol produced using polyvinyl alcohol that satisfies the requirements of the present invention has a performance comparable to that of conventionally known water-absorbent resins in water absorption performance, has an excellent balance between decomposability and mechanical properties, and absorbs water. It is useful as a functional resin.

  Since the water-absorbent resin of the present invention has an excellent balance between decomposability and mechanical properties in addition to water-absorbing properties, it can be suitably used for, for example, agricultural water retaining materials and sanitary material applications. When used as a water retention material for agriculture, it is decomposed in the environment after functioning stably due to excellent mechanical properties, and accumulation in the field soil is also suppressed. Moreover, when using as a sanitary material, it is excellent in a usability | use_condition etc., is easy to decompose | disassemble compared with the conventional material, and the influence on an environment is reduced.

Claims (8)

A water-absorbent resin comprising a modified polyvinyl alcohol at least partially acetalized with glyoxylic acid and / or a glyoxylic acid derivative as a constituent component, and at 20 ° C. of a 4% by mass aqueous solution of polyvinyl alcohol as a raw material before the acetalization A water-absorbent resin having a solution viscosity of V (mPa · s) and a 1,2-glycol bond amount G (mol%) contained in the main chain thereof simultaneously satisfy the following formulas 1 and 2.
(100−V) * G ≧ 86 (Formula 1)
V ≧ 5 (Formula 2)   The water-absorbent resin according to claim 1, wherein the raw material polyvinyl alcohol is obtained by saponifying polyvinyl acetate and has a saponification degree of 30 mol% or more.   The water-absorbent resin according to claim 1 or 2, comprising glyoxylic acid and / or modified polyvinyl alcohol having a degree of acetalization by glyoxylic acid of 1 mol% or more and 80 mol% or less.   The water-absorbent resin according to any one of claims 1 to 3, wherein at least a part thereof is crosslinked.   The water-absorbent resin according to claim 4, wherein the cross-linking site is in a binding mode that is cleaved by a hydrolysis reaction.   The composition containing the water absorbing resin as described in any one of Claim 1 to 4.   An agricultural water-retaining material comprising the water-absorbent resin according to any one of claims 1 to 4.   A sanitary material comprising the water absorbent resin according to any one of claims 1 to 4.