JP5207609B2 - Ion-sensitive water-absorbing resin - Google Patents

Description

  The present invention relates to a water absorbent resin. More specifically, the present invention relates to a water-absorbing resin used for paper diapers, sanitary napkins, etc., which absorbs body fluids but dissolves in water.

  At present, hydrophilic materials such as water absorbent resin and pulp for absorbing body fluid are widely used as sanitary materials such as paper diapers and sanitary napkins, so-called incontinence pads. Examples of the water-absorbing resin include a polyacrylic acid partial neutralized product cross-linked product, a starch-acrylonitrile graft polymer hydrolyzate or cross-linked product, a starch-acrylic acid graft polymer neutralized product or cross-linked product, and acetic acid. Saponified or cross-linked vinyl-acrylic acid ester copolymer, hydrolyzate or cross-linked product of acrylonitrile copolymer, cross-linked acrylamide copolymer, and cross-linked polymer of cationic monomer are used as main raw materials. Yes.

  Conventionally, as a method for improving the performance of the above water-absorbent resin, Patent Documents 1 and 2 have proposed a high absorption rate, an excellent absorption rate, a high liquid permeability, and the like for aqueous liquids such as body fluids. However, since the water-absorbing resins proposed to date have been prepared in a strong cross-linked form with a cross-linking agent or the like, the water-absorbing resin exhibits high absorbability with respect to aqueous solutions containing salts such as body fluids and water ( (Ion-exchanged water, distilled water, tap water) showed high absorbency, and had a problem such as the possibility of clogging the drain pipe when it was poured into a flush toilet. For this reason, there are only actual disposal methods such as incineration and landfilling, and a great deal of labor is required for disposal.

Further, according to known techniques, Patent Documents 3 to 10 propose so-called ion-sensitive films and binders in which the solubility changes depending on the difference in ion concentration.
US Pat. No. 5,601,542 US Pat. No. 5,669,894 JP-A-63-139906 Japanese Patent No. 3162696 Japanese Patent No. 3148307 US Pat. No. 4,535,098 US Pat. No. 6,291,372 US Pat. No. 6,423,804 US Pat. No. 6,683,143 US Pat. No. 6,537,663

  However, the techniques described in these publications have problems such as low absorption performance with respect to body fluids and low solubility with respect to water, and provide an absorption agent for body fluids that can be washed in a flush toilet. There wasn't. Furthermore, as a form of its use, a method of producing a high-strength absorbent core by spraying a polymer solution as a binder on a molded absorbent core web and then drying it is performed. When a large amount of polymer is introduced, there is a problem that the absorption core becomes hard or the injection rate of the liquid into the absorption core becomes slow. As a result, it can be used only as a small amount of an additive such as a binder, and the polymer has not been required to absorb water.

  Therefore, the problem to be solved by the present invention is to provide a water-absorbing resin that makes it possible to design an absorbent core and an absorbent article that can be flowed as it is in a flush toilet or the like, which is difficult to achieve with conventional water-absorbing resins. That is.

  The inventors of the present invention have intensively studied to solve the above problems, and the reason why the water-absorbent resin cannot be washed away in a flush toilet or the like is that the conventional water-absorbent resin has a high swelling property with respect to water. I paid attention to that. Since the conventional water-absorbing resin is designed as a chemical cross-linked product such as acrylate as described above, it has a very strong cross-linked form, and water (ion-exchanged water, distilled water, tap water) is hardly dissolved. Swellability several hundred times that of (water). However, the performance required for disposable diapers and sanitary napkins is to highly absorb the excretory fluid from the body. All of the fluid excreted from the body is an aqueous electrolyte solution containing about 0.4% by mass or more of salt, and the requirement can be satisfied as long as the absorbability of the aqueous electrolyte solution is ensured. In the water-absorbent resin in the prior art, chemical cross-linking is introduced in order to develop absorbability with respect to the electrolyte aqueous solution. As a result, a high degree of swellability with respect to water is developed as a secondary result. In particular, in the case where the polymer used for the water-absorbent resin has a dissociable ionic group, the water absorption capacity under no pressure is 20 g / g to 50 g / g for an electrolyte aqueous solution such as physiological saline. Increases to 200 g / g to 500 g / g for water. It has been found that the swelling degree of the water-absorbent resin is greatly increased by the decrease in the electrolyte concentration of the solution to be absorbed, thereby causing the drainage pipe to be blocked when the water-absorbent resin is flushed in the flush toilet. Of course, when the polymer used for the water-absorbent resin does not have a dissociable ionic group, there is almost no change in the absorption rate due to the electrolyte concentration in the solution, but the absorption rate and absorption rate are extremely low. Therefore, it becomes unsuitable for use on paper diapers and sanitary napkins.

  Accordingly, the present inventors have found that a water-absorbent resin mainly composed of a repeating unit having an ionic dissociation group in the main chain or side chain has a specific absorption ratio or higher than that of physiological saline, On the other hand, in order to show specific solubility, it has been found that by using such a water-absorbent resin, it is possible to design paper diapers and sanitary napkins that can be flushed in flush toilets, etc., and the present invention has been completed. It was.

  That is, the water-absorbent resin of the present invention is a water-absorbent resin mainly composed of a repeating unit having an ionic dissociation group in the main chain or side chain, and the absorption capacity under no pressure in physiological saline for 4 hours ( CRCs) is a water-absorbent resin having a solubility of 10 g / g or more and ion-exchanged water of 50% by mass or more.

  According to the water-absorbent resin of the present invention, when used in paper diapers and sanitary napkins, it exhibits excellent usability by exhibiting the ability to absorb body fluids in the same manner as in the past, and provides the convenience of being able to flow directly to a toilet or the like. It has the effect that it can be done.

  The present invention is a water-absorbent resin mainly composed of a repeating unit having an ionic dissociation group in the main chain or side chain, and has an absorption capacity (CRCs) under no pressure for 4 hours with respect to physiological saline of 10 g / g. As described above, the present invention relates to a water-absorbent resin having a dissolution rate in ion-exchanged water of 50% by mass or more. Hereinafter, in the present specification, the water-absorbent resin of the present invention is also referred to as “ion-sensitive water-absorbent resin”.

  Hereinafter, the raw materials and reaction conditions used for the water-absorbent resin of the present invention will be described. In this specification, “physiological saline” refers to a 0.90 mass% sodium chloride aqueous solution, and “water” refers to tap water, ion-exchanged water, distilled water unless otherwise specified. Unless otherwise specified, the temperature when using these is a solution having a low electrolyte concentration, such as an electrolyte concentration of less than 0.1% by mass, more preferably less than 0.05% by mass. The temperature is 25 ± 2 ° C., and the liquid temperature is 21 ± 2 ° C.

(1) Mechanism of ion-sensitive water-absorbing resin The water-absorbing resin of the present invention is a compound having a high water-absorbing property with respect to a saline solution, specifically, with respect to 0.90% by mass of physiological saline. It indicates the absorption capacity under no pressure in 4 hours of 10 g / g or more. In addition, this measuring method is prescribed | regulated in the following Example. The water-absorbent resin of the present invention may contain a small amount of additives and trace components such as water if necessary, and the content ratio of water and a small amount of additives is 0 to 30 with respect to the total mass of the water-absorbent resin. It is 0 mass%, Preferably it is 0-20 mass%, More preferably, it is 0 mass% or more and less than 10 mass%. Usually, water is mainly used as the trace component, and the additives described later are used. The water absorbent resin of the present invention is used for absorbing and solidifying an aqueous solution containing an electrolyte. The aqueous solution containing the electrolyte is an aqueous solution containing 0.4% by mass or more of electrolyte such as urine, blood, feces, body fluid, blood-containing waste liquid, seawater, etc., but preferably absorbs and solidifies urine, particularly human urine. Used for

  The mechanism by which the water-absorbent resin of the present invention develops ion sensitivity is not clear, but is considered as follows. First, it is considered that the water-absorbent resin is essential, and the main component is a repeating unit having an ionic dissociation group in the main chain or side chain.

  Thus, the osmotic pressure derived from the polymer is increased by using as a main component a repeating unit having an ionic dissociation group in the main chain or side chain. Therefore, the absorption rate with respect to physiological saline can be designed to be large, and the osmotic pressure becomes maximum when it comes into contact with water. That is, the osmotic pressure can be designed to take different values depending on the salt concentration of the liquid in contact.

  Further, as an embodiment, it is considered preferable to further have a hydrocarbon group having 4 or more carbon atoms in the side chain.

  When hydrocarbon groups are present in this way, when the salt concentration of the solution to be absorbed is high, aggregation of hydrocarbon groups (so-called salting out) is promoted against the osmotic pressure derived from the ionic dissociation group, The aggregation becomes a cross-linking point and becomes water-swellable. On the other hand, when the salt concentration of the solution to be absorbed is low, the osmotic pressure derived from the ionic dissociation group overcomes the aggregation of the hydrocarbon group, so that the solubility is considered to be exhibited.

  In another embodiment, when the polymer having a repeating unit having an ionic dissociative group in the main chain or side chain as a main component is in the form of particles or fibers, the polymer is selectively formed in the vicinity of the surface. By forming a film by introducing cross-linking (surface cross-linking treatment), swellability in physiological saline and solubility in water can be realized simultaneously. Therefore, in the present invention, chemical cross-linking (surface cross-linking treatment) may be introduced in the vicinity of the surface of the particle or fiber, but it is preferable that a solid network due to uniform chemical cross-linking is not formed in the particle or fiber. it is conceivable that.

  In other words, the present invention is a combination of an osmotic pressure derived from an ionic dissociation group, a cohesive force derived from a hydrocarbon group, chemical crosslinking only in the vicinity of the surface, and a factor of salt concentration of the liquid to be absorbed. When the absorption characteristics of the water-absorbing resin are adjusted to 10 g / g or higher in the absorption capacity (CRCs) under no pressure in physiological saline for 4 hours and the solubility in ion-exchanged water is 50% by mass or more, the water-absorbing resin is obtained. It has been found that the absorbent article to be used can be designed to flow into a flush toilet after use. The feature of the present invention is that if the water-absorbent resin satisfies such specific parameters, the drainage pipe even if the absorbent article and the absorbent core after use and the water-absorbent resin are caused to flow together with water in a drainage pipe with many bends I found out that it was boring. In particular, in a drainage pipe having a plurality of bends, the water-absorbing resin tends to accumulate at the bent portion, and in the case of a conventional water-absorbing resin, the water-absorbing resin swells and the drainage pipe is blocked. If the parameter range is satisfied, the blockage is resolved.

“Ion-sensitive” as used in the present invention is applied when a characteristic that satisfies the above parameters is exhibited based on the mechanism described above. By satisfying the above parameters, the ion-sensitive water-absorbing resin of the present invention can be applied in various applications such as being used as a water-absorbing resin that can be flowed into a drain pipe after use. As a rough guide, it shows a high degree of swelling for aqueous solutions containing 0.4 mass% or more of salts (for example, NaCl, KCl, CaCl ₂ , MgCl _2, etc.). On the other hand, it can be used practically by showing solubility.

  As a method of introducing a hydrocarbon group into a side chain while having as a main component a repeating unit having an ionic dissociable group in the main chain or side chain, the main component is a repeating unit having an ionic dissociative group in the main chain or side chain. Alternatively, a hydrocarbon side chain may be introduced into the polymer to be used, and a monomer having an ionic dissociation group as a main chain or a side chain and a monomer having a hydrocarbon group as a side chain may be used together. It may be a polymer obtained by polymerization.

  The ionic dissociation group referred to in the present invention is a functional group that dissociates in water to cause ionic dissociation. For example, a functional group that exhibits acidity by dissociating in an aqueous solution such as a carboxyl group, a sulfonic acid group, or a phosphoric acid group. And functional groups which dissociate in an aqueous solution such as amino groups and exhibit basicity, and salts thereof. In addition, as the form of the salt of the functional group, in the case of a carboxyl group, a sulfonic acid group, or a phosphoric acid group, an alkali metal salt such as a lithium salt, sodium salt, or potassium salt of the functional group; magnesium salt, calcium Examples thereof include alkaline earth metal salts such as salts, strontium salts and barium salts; ammonium salts. Of these, lithium salts, sodium salts, potassium salts, and ammonium salts are preferable, and sodium salts and potassium salts are more preferable in terms of the performance of the water-absorbing resin obtained, industrial availability, safety, and the like. In the case of an amino group, hydrochloride, sulfate, carboxylate, phosphate and the like can be mentioned. The water-absorbent resin of the present invention may have one kind of the ionic dissociation group alone or may have two or more kinds of ionic dissociation groups.

  The hydrocarbon group having 4 or more carbon atoms referred to in the present invention is composed of carbon and hydrogen and has 4 or more continuous chains of carbon atoms. It does not matter whether the structure is linear, branched or cyclic, saturated or unsaturated. The length of the hydrocarbon group is preferably 4 or more and 50 or less, but more preferably 8 or more and 50 or less, more preferably 10 or more and 50 or less, and particularly preferably 12 or more and 50 or less in view of the aggregation performance with respect to the aqueous salt solution. In particular, the longer the side chain of the hydrocarbon group, the smaller the amount of hydrocarbon groups to be introduced, and the more the ratio of acid groups or salts thereof that can be used increases, so that the absorption performance can be improved, which is preferable. However, it is not preferable that the length of the hydrocarbon group exceeds 50, since the handleability at the time of synthesizing the polymer is deteriorated.

  Specific examples of the hydrocarbon group having 4 or more carbon atoms include butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, tert-pentyl, neopentyl, hexyl, isohexyl, heptyl, octyl, and nonyl. , Decyl, undecyl, dodecyl, 2-ethylhexyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, docosyl and the like; Cyclic saturated alkyl groups such as cycloheptyl and cyclooctyl; butenyl, isobutenyl, sec-butenyl, tert-butenyl, pentenyl, isopentenyl, tert-pentenyl, Pentenyl, hexenyl, isohexenyl, heptenyl, octenyl, nonylenyl, decenyl, undecylenyl, dodecylenyl, 2-ethylhexenyl, tridecylenyl, tetradecylenyl, pentadecylenyl, hexadecylenyl, heptadecenyl, nonadecylenyl, nonadecylenyl Chain or branched unsaturated alkenyl groups; cyclic unsaturated alkenyl groups such as cyclohexenyl, cyclooctenyl, cyclododecenyl and the like. Of these, dodecyl, octadecyl, hexadecyl, tetradecyl and the like are preferable, and dodecyl and octadecyl are particularly preferable. In particular, when an unsaturated hydrocarbon unit such as an undecylenyl group is used, effects such as antibacterial properties can be further imparted.

  Further, the ion-sensitive water-absorbing resin of the present invention preferably contains a hydrocarbon group having 4 or more carbon atoms in the side chain. At this time, the ion-sensitive water-absorbing resin of the present invention may have other side chains in place of or in addition to the hydrocarbon group having 4 or more carbon atoms, Although it does not restrict | limit, For example, the polyoxyethylene group, the polyoxypropylene group, etc. may be included in the side chain.

(2) Method for producing ion-sensitive water-absorbent resin The method for producing the water-absorbent resin of the present invention is not particularly limited as long as the physical properties defined in the present invention are satisfied. For example, when the water absorbent resin of the present invention has an ionic dissociation group in the main chain or side chain and a hydrocarbon group having 4 or more carbon atoms in the side chain, the ion sensitive water absorbent resin is more specific. Specifically, it can be obtained by the following <Production Method 1> to <Production Method 4>.

<Production method 1>
Copolymerizes a monomer having an ionic dissociation group in the main chain or side chain with a monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain, if necessary, in water or an organic solvent or a mixed solvent thereof. Then, the obtained polymer is dried, pulverized, and surface-crosslinked as necessary to obtain an ion-sensitive water-absorbing resin.

<Production method 2>
A compound having a functional group capable of reacting with an acid group or a basic group and a hydrocarbon group having 4 or more carbon atoms has an ionic dissociation group in a side chain or main chain in water, an organic solvent or a mixed solvent thereof. A method in which an ion-sensitive water-absorbing resin is obtained by reacting with a polymer containing a repeating unit as a main component, followed by drying, pulverization, and surface cross-linking treatment as necessary.

<Manufacturing method 3>
Copolymerizes a monomer having an ionic dissociation group in the main chain or side chain with a monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain, if necessary, in water or an organic solvent or a mixed solvent thereof. In this process, polymerization is performed in the presence of a chain transfer agent, followed by drying, pulverization, and surface cross-linking treatment as necessary to obtain an ion-sensitive water-absorbing resin.

<Method 4>
Copolymerizes a monomer having an ionic dissociation group in the main chain or side chain with a monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain, if necessary, in water or an organic solvent or a mixed solvent thereof. In this process, polymerization is performed in the presence of a surfactant, followed by drying, pulverization, and surface cross-linking treatment as necessary to obtain an ion-sensitive water-absorbing resin.

  Hereinafter, the manufacturing method (production methods 1 to 4) of the water absorbent resin of the present invention and the water absorbent resin of the present invention will be described in order.

(3) Unsaturated monomer having an ionic dissociation group in the side chain When the water-absorbing resin of the present invention is obtained by copolymerization, the unsaturated group having an ionic dissociation group in the main chain or side chain, particularly in the side chain Monomers are preferably used. Among monomers having an ionic dissociation group in the side chain constituting the water-absorbent resin of the present invention, an unsaturated monomer having an acid group and / or a salt thereof in the side chain (hereinafter simply referred to as a monomer) It is preferable to use (meth) acrylic acid and / or a salt thereof as a main component, but other monomers may be used in combination, or a water-absorbing resin may be obtained from other monomers alone. Good. Further monomers used include (anhydrous) maleic acid, fumaric acid, crotonic acid, itaconic acid, vinyl sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, (meth) acryloxyalkanesulfone. Acids, styrene sulfonic acids and their alkali metal salts are preferably used.

  Among the monomers having an ionic dissociation group in the side chain, examples of the unsaturated monomer having a basic group and / or a salt thereof in the side chain include dialkylaminoalkyl (meth) acrylate and dialkylaminoalkyl (meth). Examples include acrylamide, allylamine, diallylamine and the like.

(4) Other monomers In addition, the monomer having an ionic dissociation group in the side chain, and a monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain, as long as the characteristics of the present invention are not impaired. The monomer may be used as a copolymerization component. Examples of such monomers include (meth) acrylamide, N-vinyl-2-pyrrolidone, N-vinylacetamide, N-vinylformamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth). Examples of the copolymer component include acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, isobutylene, methyl (meth) acrylate, and ethyl (meth) acrylate. However, it is not limited to these. In order to achieve the present invention, the “other monomer” described in this section is preferably 0 to 30 mol%, more preferably 0 to 20 mol%, based on the total amount of all monomers. The ratio is particularly preferably 0 to 10 mol%, and most preferably 0 to 5 mol%. Moreover, it is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, particularly preferably 0 to 10% by mass, and most preferably 0 to 5% by mass based on the total amount of all monomers. is there. Therefore, the ratio of the total amount of the monomer having an ionic dissociative group in the side chain and the monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain to the total monomer is the sum of all monomers. The ratio is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, particularly preferably 90 to 100 mol%, and most preferably 95 to 100 mol%, based on the amount. Moreover, it is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, particularly preferably 90 to 100% by mass, and most preferably 95 to 100% by mass with respect to the total amount of all monomers. is there.

(5) Unsaturated monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain The unsaturated monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain is not particularly limited, but has 4 carbon atoms. It is preferably an ethylenically unsaturated monomer having the above hydrocarbon group in the side chain, more preferably an alcohol or amine having a linear, branched or cyclic hydrocarbon group having 4 or more carbon atoms and a carboxyl group An ester or amide monomer obtained from an ethylenically unsaturated monomer containing Representative examples of such monomers include butyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, 2-ethyl-hexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth). Acrylate, isostearyl (meth) acrylate, palmityl (meth) acrylate, myristyl (meth) acrylate, capryl (meth) acrylate, cetyl (meth) acrylate, isobornyl (meth) acrylate, undecylenyl (meth) acrylate, oleyl (meth) acrylate , 2-ethyl-hexyl (meth) acrylamide, lauryl (meth) acrylamide, stearyl (meth) acrylamide, isostearyl (meth) acrylamide, palmityl (meth) acrylamide (Meth) acrylic esters such as myristyl (meth) acrylamide, capryl (meth) acrylamide, cetyl (meth) acrylamide, isobornyl (meth) acrylamide, undecylenyl (meth) acrylamide, oleyl (meth) acrylamide, alkyl substituted (meth) Mention may be made of acrylamides. Further, esters and amides of similar monomers such as maleic acid, fumaric acid, crotonic acid and itaconic acid are also included.

  Further, it may be an ester monomer obtained from an ethylenically unsaturated monomer containing a carboxylic acid having a straight chain, branched chain or cyclic hydrocarbon group having 4 or more carbon atoms and a hydroxyl group, and such a monomer. Representative examples of vinyl valerate, vinyl heptanoate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl isostearate, vinyl undecylenate, vinyl behenate, Examples thereof include vinyl esters such as vinyl naphthenate, vinyl linoleate and vinyl linolenate. Further, the above esters of similar monomers such as hydroxyalkyl (meth) acrylate, polyethylene glycol (meth) acrylate, allyl alcohol and the like are also included. Particularly, a compound having an unsaturated hydrocarbon group moiety as a hydrocarbon group having 4 or more carbon atoms can be expected to have antibacterial performance. As such an example, undecylenoxypolyethylene glycol (meth) acrylate and the like can be mentioned, and further antibacterial properties can be imparted, so that it is particularly preferably used.

  Further, it may be an amide monomer obtained from an ethylenically unsaturated monomer containing a carboxylic acid having a straight chain, branched chain or cyclic hydrocarbon group having 4 or more carbon atoms and an amino group. Representative examples of monomers include caprylic acid-N-vinylamide, capric acid-N-vinylamide, lauric acid-N-vinylamide, myristic acid-N-vinylamide, palmitic acid-N-vinylamide, stearic acid-N-vinylamide. , Isostearic acid-N-vinylamide, palmitic acid-N-vinylamide, undecylenic acid-N-vinylamide, behenic acid-N-vinylamide, naphthenic acid-N-vinylamide, linoleic acid-N-vinylamide, linolenic acid-N-vinylamide, etc. The vinyl amides can be mentioned. Furthermore, similar monomers derived from allylamine and the like are also included.

  It may be a quaternary salt monomer obtained from a halide having a linear, branched or cyclic hydrocarbon group having 4 or more carbon atoms and an ethylenically unsaturated monomer containing an amino group. Representative examples of such monomers include dialkylaminoalkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylamide, vinylamine, allylamine heptyl, octyl, 2-ethylhexyl, nonyl, lauryl, palmityl, stearyl, isostearyl, undecylenyl. And quaternary salts having behenyl, naphthyl, oleyl, cetyl, isobornyl groups, and the like.

  Further, it may be an ester monomer obtained from an ethylenically unsaturated monomer containing an alcohol having a linear, branched or cyclic hydrocarbon group having 4 or more carbon atoms and a sulfonic acid group or a phosphoric acid group. Acid, styrene sulfonic acid, 2- (meth) acrylamido-2-methylpropane sulfonic acid, heptyl ester such as (meth) acryloxyalkane sulfonic acid, octyl ester, 2-ethylhexyl ester, nonyl ester, lauryl ester, palmityl ester , Stearyl ester, isostearyl ester, undecylenyl ester, behenyl ester, naphthyl ester, oleyl ester, isobornyl ester, cetyl ester and the like.

  Further, it may be an α-olefin having a straight chain, branched chain or cyclic hydrocarbon group having 4 or more carbon atoms in the side chain, and examples thereof include 1-nonene, 1-decene, 1-octadecene and the like.

  Among these, the unsaturated monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain includes an alcohol having a linear, branched or cyclic hydrocarbon group having 4 or more carbon atoms, and (meth) acrylic. Esters obtained from ethylenically unsaturated monomers containing carboxyl groups such as acids are preferred, and are obtained from alcohols having a straight chain, branched chain or cyclic hydrocarbon group having 4 or more carbon atoms and (meth) acrylic acid. More preferred is an ester. Preferred examples of these monomers include lauryl (meth) acrylate, stearyl (meth) acrylate, myristyl (meth) acrylate, and palmityl (meth) acrylate.

  These monomers may be used independently and may mix and use 2 or more types suitably.

  When the copolymerization method is employed to obtain the water absorbent resin of the present invention, the unsaturated monomer (A) having an ionic dissociation group in the side chain and the unsaturated monomer having a hydrocarbon group in the side chain The relative ratio of the body (B) may be composed of only (A) in mass ratio (100 mass%), but preferably in the range of (A) :( B) = 50: 50 to 99: 1. More preferably (A) :( B) = 60: 40 to 98: 2 and even more preferably (A) :( B) = 65: 35 to 97: 3, Preferably, (A) :( B) = 70: 30 to 96: 4, most preferably (A) :( B) = 80: 20 to 95: 5. As long as it is within the relative ratio of (A) :( B) as described above, the resulting water-absorbent resin has only osmotic pressure derived from ionic dissociation groups, cohesive force derived from hydrocarbon groups, and the vicinity of the surface. It can have a good balance with chemical crosslinking.

  In the molar ratio, it may be composed of only (A) (100 mol%), but preferably (A) :( B) = 70: 30 to 99.7: 0.3, more preferably (A) :( B) = 80: 20 to 99.5: 0.5, most preferably (A) :( B) = 90: 10 to 99: 1. As long as it is within the relative ratio of (A) :( B) as described above, the resulting water-absorbent resin has only osmotic pressure derived from ionic dissociation groups, cohesive force derived from hydrocarbon groups, and the vicinity of the surface. It can have a good balance with chemical crosslinking.

  A side chain of a hydrocarbon group having 4 or more carbon atoms obtained by reacting a reactive group such as a carboxyl group, sulfonic acid group, phosphoric acid group or amino group of the polymer with a hydrocarbon group having 4 or more carbon atoms later The above-mentioned preferable range is also interpreted by the molar ratio of the repeating units.

  The polymer at that time is not particularly limited as long as it has as a main component a repeating unit having an ionic dissociation group in the main chain or side chain. For example, poly (meth) acrylic acid, polystyrene sulfonic acid, poly 2-acrylamido-2-methylpropanesulfonic acid, polymaleic acid, carboxymethylcellulose, carrageenan, gellan gum, xanthan gum, polyethyleneimine, polyallylamine, polydiallylamine, polydialkylaminoalkyl acrylate, polydialkylaminoalkyl acrylamide and their (parts) ) A neutralized product can be mentioned. Polyethyleneimine is a typical example having a repeating unit having an ionic dissociation group in the main chain. As a compound for introducing a hydrocarbon group having 4 or more carbon atoms, a compound having an aldehyde group, an epoxy group, an amino group, or a hydroxyl group and having a hydrocarbon group having 4 or more carbon atoms may be used. .

(6) Polymerization method and polymerization solution
In the present invention, bulk polymerization, precipitation polymerization, and solution polymerization can be performed, but it is preferable to perform solution polymerization and precipitation polymerization in terms of operational safety. The concentration of the monomer in the solution polymerization depends on the temperature of the solution and the monomer, and is not particularly limited, but is preferably 10 to 70% by mass, more preferably 20 to 60% by mass. Solvents used for the solution polymerization include water, lower alcohols such as methanol, ethanol and 2-propanol, or mixed solvents of these lower alcohols and water, lower ketones such as acetone and methyl ethyl ketone, or lower ketones thereof. A mixed solvent of water and water is used, but is not limited thereto.

  Precipitation polymerization is a polymerization method as described in JP-A-60-71623 or radical polymerization handbook P264 (NTS Corporation, published in 1999), and the monomer is dissolved in a solvent. Although it is possible, it is a polymerization method in which when a polymer is polymerized, it becomes insoluble in a solvent, precipitates as fine particles, and a polymer can be easily obtained simply by removing the solvent. The monomer concentration at which the precipitation polymerization is performed is preferably in the range of 1 to 50% by mass, more preferably 5 to 30% by mass, and most preferably 10 to 25% by mass. In particular, when the precipitation polymerization reaction is performed at a high concentration, 0.5 to 10 masses of polyoxyethylene having a molecular weight of 2000 to 20000, specifically, a copolymer of ethylene oxide and propylene oxide, etc. with respect to the monomer is used. % Is preferably used for the polymerization. Since the solvent used for precipitation polymerization varies depending on the type of monomer used, it is difficult to specify, but the monomer is soluble and the high molecular weight product produced by the polymerization does not dissolve. Solvents should be selected and typical examples of precipitation polymerization solvents include alkanes having 5 to 10 carbon atoms, such as hexane, pentane; cycloalkanes having 5 to 10 carbon atoms, such as cyclohexane; benzene or Alkyl-substituted benzenes such as toluene, xylene; alkyl carboxylates containing 1 to 6 carbon atoms in the alkyl group and having 1 to 6, preferably 2 to 6 carbon atoms in the carboxylate moiety, such as Haloalkanes having 1 to 2 carbon atoms and at least 2 or more halogen groups, such as dichloroethane, That.

  When the above polymerization is started, the polymerization initiator described later is used. In addition to the polymerization initiator described above, active energy rays such as ultraviolet rays, electron beams, and γ rays may be used alone or in combination with the polymerization initiator. The temperature at the start of polymerization depends on the type of polymerization initiator used, but is preferably in the range of 15 to 130 ° C, and more preferably in the range of 20 to 120 ° C.

  In addition, the polymerization conditions according to the present invention are not particularly limited as long as the desired water-absorbing resin can be obtained from the monomer as described above, but usually 0 to 150 ° C, more preferably 20 to 100 ° C. Polymerization is carried out at a temperature for 1 minute to 10 hours, more preferably 1 to 3 hours, in the presence of a polymerization initiator and, if necessary, a chain transfer agent and / or a surfactant.

(7) Polymerization initiator
The initiator used when polymerizing the above-described monomer to obtain the water-absorbent resin used in the present invention may be any compound having radical generating ability such as an azo compound or a peroxide, for example, Potassium persulfate, ammonium persulfate, sodium persulfate, potassium peracetate, sodium peracetate, potassium percarbonate, sodium percarbonate, benzoyl peroxide, capryl peroxide, t-butyl hydroperoxide, hydrogen peroxide, 2,2 ' -Azobis (2-amidinopropane) dihydrochloride, 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4 Radical polymerization initiators such as 2-dimethylvaleronitrile) and 2-hydroxy-2-methyl-1-phenyl-propan-1-one It can be used a polymerization initiator. These polymerization initiators may be used individually by 1 type, or may be used in combination of 2 or more type. These polymerization initiators are used in an amount of 0.001 to 2 mol%, preferably 0.01 to 0.2 mol%, based on water absorption performance, with respect to the total monomers.

  When these polymerization initiators are less than 0.001 mol%, the amount of unreacted residual monomers increases, whereas when the polymerization initiator exceeds 2 mol%, it is difficult to control the polymerization. .

(8) Chain transfer agent In this invention, a chain transfer agent is used as needed at the time of superposition | polymerization. By polymerizing in the presence of a chain transfer agent in addition to the aforementioned unsaturated monomer and polymerization initiator, the molecular weight of the resulting resin can be controlled so as not to become too large. As a result, it is possible to adjust not only the ability of the resulting water-absorbent resin to absorb physiological saline, but also the ability to show fast solubility in water. In particular, it is suitably used when the solvent used for polymerization is water or ketones.

  The chain transfer agent used for polymerization in the present invention is not particularly limited as long as it dissolves in a solvent or an ethylenically unsaturated monomer, and thiols, thiolic acids, alcohols, amines, hypophosphites. And so on. Specifically, mercaptoethanol, mercaptopropanol, dodecyl mercaptan, thioglycols, thiomalic acid, 3-mercaptopropionic acid, methanol, ethanol, isopropanol, sodium hypophosphite, formic acid, and salts thereof are used. One or more selected from the group is used, and hypophosphites such as sodium hypophosphite are preferably used because of their effects.

  The amount of chain transfer agent used varies depending on the type and amount of chain transfer agent used and the concentration of the monomer solution, but it is 0 to 1 mol%, preferably 0 to 0.3 mol, based on the total monomers. %. On the other hand, if the amount exceeds 1 mol%, the amount of components dissolved in the physiological saline increases and the absorption capacity with respect to the physiological saline is decreased.

  The weight average molecular weight required for the water-absorbent resin of the present invention depends on the nature of the ionic dissociation group, the nature of the hydrocarbon group, its ratio, the neutralization rate, etc., but is preferably in the range of 10,000 to 2,000,000. Preferably it is in the range of 20,000 to 1,000,000, most preferably in the range of 30,000 to 800,000.

  In the present invention, the weight average molecular weight of the water absorbent resin is a value measured according to the following measuring method. The weight average molecular weight is a value measured by GPC (Gel Permeation Chromatography) after dissolving a water-absorbing resin adjusted to non-neutralized (ie, neutralization rate 0%) in a soluble solvent such as methanol or ethanol. It is. In the case of a water-absorbing resin that has been neutralized, a water-absorbing resin that has been neutralized with an acidic substance or a basic substance to have a neutralization rate of 0% is used.

(9) Surfactant Since the water-absorbent resin of the present invention is a polymer mainly comprising a repeating unit having an ionic dissociation group in the main chain or side chain, and preferably having a hydrocarbon group in the side chain, The polarities of the functional groups are greatly different. Therefore, depending on the solvent used in the actual synthesis, it is preferable to disperse using a surfactant. For example, when a monomer having an ionic dissociative group in the side chain and a monomer having a hydrocarbon group in the side chain are copolymerized in water or an organic solvent or a mixed solvent thereof, or water or an organic solvent or In these mixed solvents, when introducing a hydrocarbon group into a polymer mainly composed of a repeating unit having an ionic dissociation group in the main chain or side chain, polymerization or reaction is performed in the presence of a surfactant. It is preferable to carry out.

  The surfactant used at that time is not particularly limited, but examples thereof include the following.

  Alkyl sulfate salts, fatty acid salts: for example, sodium stearate, sodium laurate, sodium dodecyl sulfate. Alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkylsulfosuccinates: for example, sodium dodecylbenzenesulfonate, sodium dialkylsulfosuccinate. Polyoxyethylene alkyl ether sulfate ester salts: For example, sodium polyoxyethylene lauryl ether sulfate. Alkaline phosphates: for example, hydrogen dodecyl phosphate, potassium polyoxyethylene alkyl ether phosphate. Fluoroemulsifier: For example, perfluoroalkyl sulfate. Alkylamine hydrochlorides: for example, dodecylamine hydrochloride, tridecylamine hydrochloride. Polyoxyethylene alkyl ethers, sorbitan fatty acid esters, polyoxyalkylene alkyl ethers, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene Examples thereof include alkylamines.

  The amount of the surfactant used may be an amount sufficient to disperse the monomer or compound (micelle formation), and the amount used is preferably 0 to 50% by mass, more preferably based on the total amount of the polymer or monomer. Is 0 to 30% by mass, particularly preferably 0 to 20% by mass, particularly preferably 0 to 10% by mass, and most preferably 0 to 5% by mass.

(10) Neutralization rate, neutralization method Although depending on the nature of the ionic dissociation group (acid group or basic group) used, in order to obtain the water-absorbent resin of the present invention, the physical properties and pH It is preferable that the acid group or the basic group is neutralized, and the neutralization rate is usually 30 to 100 mol%, more preferably 40 to 90 mol%, more preferably 50 to 50% with respect to the total ionic dissociation group. 90 mol%. The neutralization of the acid group or basic group may be performed with a monomer, a polymer, or a combination thereof. The neutralization of the acid group or basic group may be carried out at any stage before, during or after the polymerization.

  By neutralizing the acid group or the basic group, the osmotic pressure due to ionic dissociation is increased, and an improvement in the water absorption rate with respect to physiological saline and an improvement in solubility in water can be expected. In particular, the tendency becomes remarkable when a carboxyl group is used as the acid group or when an amino group is used as the basic group. Moreover, when it has a sulfonic acid group as an acid group, if it is unneutralized, the pH of the polymer will be too low, and if it is used for a diaper or the like, it will cause rough skin, such being undesirable. The pH range of the polymer of the present invention is preferably controlled to pH 4.0 to 8.0, more preferably pH 5.0 to 7.0.

  In addition, when the acid group is neutralized and takes a salt form, examples of the salt include alkali metal salts, alkaline earth metal salts, and ammonium salts. From the viewpoint of safety and the like, it is preferable to form a sodium salt, potassium salt, lithium salt, or ammonium salt.

  Alkali metal compounds used for neutralizing acid groups to partially or wholly form alkali metal salts include alkali metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.), alkalis Metal carbonate (sodium carbonate, sodium bicarbonate, etc.) etc. are mentioned.

  Moreover, when neutralizing a basic group and taking a salt form, the salt includes hydrochloride, sulfate, phosphate, carboxylate and the like. Examples of the carboxylate include acetate, propionate, lactate and the like, but are not limited thereto.

  The acid used to neutralize the basic group and partially or wholly form the salt is appropriately selected depending on the form of the desired salt. For example, hydrochloric acid, sulfuric acid, phosphoric acid, Examples include acetic acid, propionic acid, and lactic acid.

  As a method for neutralizing the polymer, it is preferable to add the above-mentioned compound for forming a salt to the polymer which is a gel-like or viscous solution or a dry solid and knead sufficiently with a kneader or meat chopper. In the present invention, when a particulate water-absorbing resin (water-absorbing agent) is obtained, the neutralization temperature is preferably 10 to 100 ° C., more preferably 20 to 90 ° C., and neutralization is carried out in US Pat. No. 6,187. No. 872, the first neutralization index (specified by the degree of neutralization of 200 particles) is preferably 10 or less. In the present invention, when obtaining a fibrous water-absorbing resin (water-absorbing agent), it is preferable to add the above-mentioned compound for forming a salt to the water-absorbing resin in the form of an aqueous solution, and carry out a neutralization reaction under standing conditions. .

(11) Drying When the polymer is a viscous solution or gel, it is subsequently dried. Drying is usually performed in a temperature range of 20 ° C to 250 ° C, preferably 40 ° C to 220 ° C, more preferably 50 ° C to 200 ° C. The drying time depends on the surface area of the polymer, the amount of volatile components, and the type of dryer, and is selected to achieve the desired amount of volatile components.

  The amount of volatile components of the water-absorbent resin of the present invention (specified by the content of volatile components such as water contained in the water-absorbent resin and measured by loss on drying at 180 ° C. for 3 hours) is not particularly limited. However, it is particles (powder) or fibers exhibiting fluidity, more preferably the amount of volatile components is in the range of 0 to 40% by mass, more preferably 0 to 30% by mass, and still more preferably 0 to 0% by mass. It is 20% by mass, and most preferably 0 to 10% by mass in a particulate or fibrous state. If the amount of the volatile component is increased, not only the fluidity is deteriorated and the production is disturbed, but the water absorbent resin may not be pulverized or may not be controlled to a specific particle size distribution. Furthermore, there is a possibility that the absorption capacity under no pressure with respect to physiological saline is lowered and the characteristics of the present invention cannot be satisfied.

  The drying method used includes heat drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, dehydration by azeotropy with a hydrophobic organic solvent, and high-humidity drying using high-temperature steam. Various methods can be adopted so that there is no particular limitation.

(12) Form of water-absorbing resin-pulverization / classification and particle size control The shape of the water-absorbing resin of the present invention obtained by the above-mentioned production method is not limited, but is preferably particulate or fibrous. At this time, as long as it can be handled in the form of particles or fibers, there are no particular limitations such as spherical, fibrous, rod-like, substantially spherical, flat, irregular, granulated, or porous particles.

  When the water-absorbent resin of the present invention has a particle shape, it is preferably adjusted to a specific particle size.

  As the particle size when the water absorbent resin of the present invention is in the form of particles, the mass average particle size is usually controlled to 150 to 3000 μm, preferably 150 to 1000 μm, more preferably 200 to 600 μm, and particularly preferably 200 to 500 μm. It is preferable. Further, it is preferable that particles having a particle size of less than 150 μm are present in the total amount of the water-absorbing resin in as small an amount as possible. %, Preferably 0-15% by mass, more preferably 0-10% by mass, most preferably 0-5% by mass.

  When the particle diameter is larger than the above range, an excessive time is required until it dissolves in water, so that the drain pipe may be clogged when flowing in a toilet or the like. Moreover, when it is less than the said range, water absorption performance may worsen, or a water absorbing resin may fall out when an absorption core is produced.

  The logarithmic standard deviation (σζ) of the particle size distribution is preferably 0.20 to 0.60, more preferably 0.20 to 0.50, and particularly preferably 0.20 to 0.40.

  When it is larger than the above range, it is not preferable because there is a possibility that undissolved part may be generated due to variations in the time until each particle is dissolved in water. Moreover, since manufacture becomes difficult when it is less than the said range, it becomes high cost.

  The particle size adjustment is adjusted to the target particle size by pulverization and classification after solution polymerization, after the neutralization step, and after drying.

  When the water-absorbent resin of the present invention is processed into a fiber form, a spinning method as described in WO 93/24684, WO 94/04724, and Japanese Patent Publication No. 2-2969 is adopted. be able to. The aqueous polymer solution of the present invention may be ejected from a nozzle and spun, dried quickly at a temperature of 150 ° C. to 250 ° C., and molded into a fiber form. At this time, the drying time depends on the surface area of the polymer, the amount of volatile components, and the type of dryer, and is preferably selected so as to have the amount of volatile components as described above. The average fiber diameter of the fiber in that case is preferable in the order of the range of 10 micrometers-1000 micrometers, 10 micrometers-800 micrometers, 10 micrometers-500 micrometers, 10 micrometers-300 micrometers, 10 micrometers-150 micrometers. Since the fiber has a long length, there is an advantage that the dropout from the absorbent core is small even if the average fiber diameter is made smaller than in the case of the particulate form. In addition, an average fiber diameter is calculated | required by the value which measured the diameter of 100 fibers under the microscope, and averaged. Further, when the water-absorbent resin of the present invention is fibrous, the length of the fiber is not particularly limited and varies depending on the application, average fiber diameter, etc., preferably 100 to 1,000,000 μm, more preferably 100 to 100,000 μm, in particular 100 to 10,000 μm.

  In the method of using a conventionally known ion-sensitive binder, a method of spraying a polymer solution as a binder on a molded absorbent core web and then drying to produce a strong absorbent core is performed. When a large amount of the polymer is introduced into the absorbent core, there is a problem that the absorbent core becomes hard or the injection rate of the liquid into the absorbent core becomes slow. However, it is not practical because it increases the load of the subsequent drying process. However, in the present invention, the hydrophilic fiber such as pulp constituting the absorbent core and the water absorbent resin can be mixed in a dry state or a humidified state by processing the form of the water absorbent resin in the form of particles or fibers. This makes it possible to introduce a water-absorbing resin efficiently and in a large amount into the absorbent core. In particular, if the water-absorbent resin is in the form of particles or fibers, a gap can be secured between the water-absorbent resin particles or between the fibers, so that it has an effect of being excellent in the rate of liquid uptake into the absorbent core.

(13) Surface cross-linking treatment In the present invention, a so-called surface cross-linking treatment may be performed in which a cross-linked structure is further introduced in the vicinity of the surface of the obtained water absorbent resin. By the surface crosslinking treatment, it is possible to improve the diffusibility, the dry feeling, and the absorbency under pressure when the water absorbent resin absorbs the liquid. The cross-linking introduced by the surface cross-linking treatment may be cross-linking based on chemical bonds, but since the cross-linking is only near the surface of the particle, the above characteristics can be improved without impairing the characteristics of the present invention. . The degree of surface cross-linking may be appropriately adjusted depending on the type and amount of cross-linking agent, reaction temperature, time, and the like.

  Although it does not specifically limit as a surface crosslinking agent which can be used by this invention, For example, it illustrates to U.S. Patent 6,228,930, 6,071,976, 6,254,990 etc. The surface cross-linking agent that has been used can be used. For example, mono, di, tri, tetra or polyethylene glycol, monopropylene glycol, 1,3-propanediol, dipropylene glycol, 2,3,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin , 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, etc. Alcohol compounds; epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polyamide polyamine, etc. Haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin; condensates of the polyvalent amine compounds and the haloepoxy compounds; oxazolidinone compounds such as 2-oxazolidinone; ethylene carbonate And the like, and only one of these may be used, or two or more may be used in combination. In order to sufficiently exhibit the effects of the present invention, it is preferable to use a polyhydric alcohol as an essential component among these surface crosslinking agents. As a polyhydric alcohol, a C2-C10 thing is preferable and a C3-C8 thing is more preferable.

  The amount of the surface cross-linking agent used depends on the compounds to be used and combinations thereof, but is preferably in the range of 0.001 to 10% by mass, and in the range of 0.01 to 5% by mass with respect to the water absorbent resin. Is more preferable.

  When performing surface crosslinking in the present invention, it is preferable to use water. At this time, although the amount of water used depends on the amount of volatile components of the water absorbent resin to be used, it is preferably within a range of 0.5 to 20% by mass with respect to the water absorbent resin, more preferably 0.5. It is in the range of -10% by mass. In addition to water, a hydrophilic organic solvent may be used. The hydrophilic organic solvent that can be used in this case is not particularly limited. For example, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, and t-butyl alcohol; acetone, Ketones such as methyl ethyl ketone; ethers such as dioxane, alkoxy (poly) ethylene glycol, tetrahydrofuran; amides such as ε-caprolactam and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; ethylene glycol, diethylene glycol, Propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentane All, glycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, Polyhydric alcohols such as 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, pentaerythritol, sorbitol, and the like, and one or more of these can be used. . When a hydrophilic organic solvent is used, the amount used is preferably in the range of 0 to 10% by mass, more preferably in the range of 0 to 5% by mass, and still more preferably 0 to 3% by mass with respect to the water absorbent resin. Is within the range.

  In the case of performing surface crosslinking in the present invention, it is preferable to mix water and / or a hydrophilic organic solvent and a surface crosslinking agent in advance, and then spray or drop-mix the aqueous solution onto the water-absorbent resin. The method is more preferred. The size of the droplets to be sprayed is preferably in the range of 0.1 to 300 μm, more preferably in the range of 0.1 to 200 μm, in terms of average particle diameter.

  As a mixing device used when mixing the water-absorbent resin, the surface cross-linking agent, water, and a hydrophilic organic solvent, it is preferable to have a large mixing force in order to uniformly and reliably mix the two. Examples of the mixing apparatus include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, a double-arm kneader, and a pulverizing kneader. Rotating mixers, airflow mixers, turbulators, batch-type Redige mixers, continuous-type Redige mixers, and the like are suitable.

  It is preferable that the water-absorbent resin after mixing the surface cross-linking agent is heat-treated. The heating temperature (heating medium temperature or material temperature) is preferably in the range of 50 to 250 ° C, more preferably in the range of 100 to 250 ° C, and the heating time is preferably in the range of 1 minute to 2 hours. Preferable examples of the combination of the heating temperature and the heating time are 0.1 to 1.5 hours at 180 ° C. and 0.1 to 1 hour at 200 ° C.

(14) Other additives In the present invention, components as exemplified in the following (A) to (F) are further added as trace components, thereby imparting various functions to the water absorbent resin of the present invention. You can also. In addition, the components (A) to (F) below may be used alone or in the form of a mixture of two or more, or one or more of each component may be used. You may use it combining suitably.

(A) Plant component The water-absorbent resin according to the present invention can be blended with plant components in the following amounts in order to exert deodorant properties. The plant component that can be used in the present invention is preferably at least one selected from polyphenols, flavones and the like, caffeine, tannin, tannic acid, pentaploid, gallic acid and gallic acid.

  Examples of plants containing plant components that can be used in the present invention include camellia, cypress, mokoku and the like for camellia plants, and rice, sasa, bamboo, corn, wheat and the like for grasses. For example, in the plant of Rubiaceae, there are coffee.

  Examples of plant components that can be used in the present invention include extracts extracted from plants (essential oils), plants themselves (plant powders), plant meals and extracted meals produced as by-products in the manufacturing process of the plant processing industry and food processing industry. Although it is mentioned, it is not specifically limited.

(B) Multivalent metal salt The water-absorbent resin according to the present invention contains a polyvalent metal salt, particularly an organic acid polyvalent metal salt, in the following amounts in order to improve powder flowability and prevent blocking during moisture absorption. be able to.

  The organic acid polyvalent metal salt used and the mixing method are exemplified in, for example, WO 2004/069936. What is an organic acid polyvalent metal salt having 7 or more carbon atoms in the molecule that can be used in the present invention? It consists of metal salts other than alkali metal salts such as fatty acids, petroleum acids and polymer acids.

  Examples of the organic acid constituting the organic acid polyvalent metal salt include caproic acid, octylic acid, octic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, stearic acid, bovine fatty acid, castor fatty acid, etc. Examples include long-chain or branched fatty acids, benzoic acid, myristic acid, naphthenic acid, naphthoic acid, petroleum acids such as naphthoxyacetic acid, and high molecular acids such as poly (meth) acrylic acid and polysulfonic acid. It is preferably an organic acid having a group, more preferably caproic acid, octylic acid, octic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, oleic acid, stearic acid, bovine fatty acid, castor fatty acid, castor fatty acid and the like. It is. More preferred are fatty acids having no unsaturated bond in the molecule, such as caproic acid, octylic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, and stearic acid. Most preferably, it is a long chain fatty acid having 12 or more carbon atoms in the molecule and having no unsaturated bond in the molecule, such as lauric acid, myristic acid, palmitic acid, and stearic acid.

(C) Inorganic fine particles The water-absorbent resin according to the present invention may contain inorganic fine particles, particularly water-insoluble inorganic fine particles, for preventing blocking during moisture absorption. Specific examples of the inorganic powder used in the present invention include metal oxides such as silicon dioxide and titanium oxide, silicic acid (salts) such as natural zeolite and synthetic zeolite, kaolin, talc, clay, bentonite and the like. It is done. Among these, silicon dioxide and silicic acid (salt) are more preferable, and silicon dioxide and silicic acid (salt) having an average particle diameter measured by the Coulter counter method of 0.001 to 200 μm are more preferable.

(D) Composite Hydrous Oxide The water-absorbent resin according to the present invention exhibits excellent moisture-absorbing fluidity (powder fluidity after the water-absorbent resin absorbs moisture) and further exhibits excellent deodorizing performance. A composite hydrous oxide containing zinc and silicon, or zinc and aluminum (for example, exemplified in WO2005 / 010102) can be blended with the above.

(E) Addition of chelating agent A chelating agent, particularly a polyvalent carboxylic acid and a salt thereof can be blended with the water-absorbent resin of the present invention. Thereby, decomposition | disassembly of the water absorbing resin by the component contained in urine or blood can be suppressed.

  The chelating agent that can be used for the particulate water-absorbing agent of the present invention is preferably a chelating agent having a high ion sequestering ability and chelating ability for Fe and Cu, specifically, a stability constant for Fe ions of 10 or more, preferably Is preferably 20 or more chelating agents, more preferably aminopolycarboxylic acids and salts thereof, particularly preferably aminocarboxylic acids having 3 or more carboxyl groups and salts thereof.

  Specific examples of these polycarboxylic acids include diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl etherdiaminetetraacetic acid, ethylenediaminetetraacetic acid. Examples include propionacetic acid, N-alkyl-N′-carboxymethylaspartic acid, N-alkenyl-N′-carboxymethylaspartic acid, and alkali metal salts, alkaline earth metal salts, ammonium salts, or amine salts thereof. Of these, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, N-hydroxyethylethylenediaminetriacetic acid and salts thereof are most preferable.

  In the present invention, the amount of the chelating agent, particularly the amino polyvalent carboxylic acid, is preferably a very small amount with respect to 100 parts by mass of the water-absorbent resin as the main component, and usually 0.00001 to 10 parts by mass, particularly preferably. 0.0001 to 1 part by mass. When the amount used exceeds 10 parts by mass, not only an effect commensurate with the use cannot be obtained, but also the problem arises that the amount of absorption decreases. On the other hand, when the amount is less than 0.00001 part by mass, a sufficient addition effect cannot be obtained.

(F) Others Other additives such as antibacterial agents, water-soluble polymers, water-insoluble polymers, water, and organic fine particles are optional as long as the water-absorbent resin of the present invention is obtained.
In particular, it is possible to form so-called granulated particles in which a plurality of particles are aggregated to form one particle by adding and mixing water or a water-soluble polymer to the water absorbent resin of the present invention.

  Although the usage-amount of these (A)-(F) additives changes also with the objective and an additional function, 0-10 mass parts with respect to 100 mass parts of water-absorbing resin as one kind of addition amount normally, Preferably it is 0.001-5 mass parts, More preferably, it is the range of 0.002-3 mass parts. Usually, if it is less than 0.001 part by mass, sufficient effects and additional functions cannot be obtained, and if it exceeds 10 parts by mass, an effect commensurate with the addition amount may not be obtained, or the absorption performance may be lowered.

(15) Water-absorbent resin of the present invention The ion-sensitive water-absorbent resin of the present invention using the above production methods 1 to 4 and the like as an example of the production method is a novel water-absorbent resin that exhibits novel performance that has not existed before.

  That is, the water-absorbent resin of the present invention is a water-absorbent resin mainly composed of a repeating unit having an ionic dissociation group in the main chain or side chain, and a) under no pressure for 4 hours against physiological saline Absorption capacity (CRCs) is 10 g / g or more, b) An ion-sensitive water-absorbing resin, preferably a particulate or fibrous ion-sensitive water-absorbing resin, having a solubility in ion-exchanged water of 50% by mass or more Resin.

  The water-absorbent resin of the present invention has an absorption capacity of 10 to 100 g / g, more preferably 12 to 80 g / g, still more preferably 15 to 60 g / g, particularly preferably 18 to 4 hours with respect to physiological saline under no pressure. 60 g / g, most preferably 20 g / g to 60 g / g. The absorption ratio may be controlled by controlling the length, introduction rate, neutralization rate, polymerization conditions, drying conditions, and surface crosslinking treatment conditions of the hydrocarbon groups. If the absorption ratio is lower than 10 g / g, a large amount to be used for the absorbent core is required, which is uneconomical and undesirable. In addition, the absorption capacity | capacitance under non-pressurization (CRCs) in 4 hours with respect to the physiological saline of a) means the value measured by the method as described in the following Example.

  The dissolution rate of b) in ion-exchanged water will be described later in Examples, but within a predetermined time when an operation of dispersing the water-absorbing resin in ion-exchanged water under stirring and transferring it to a 150 μm wire mesh after 30 minutes is performed. The ratio of the polymer that could pass through the wire mesh. Thereby, the polymer amount to melt | dissolve is specified and the ease of flowing through a drain pipe etc. can be determined. The range of the dissolution rate with respect to ion-exchanged water is 50% by mass to 100% by mass, preferably 70% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and still more preferably 90% by mass. The content is from 100% by mass to 100% by mass, and most preferably from 95% by mass to 100% by mass.

  If the dissolution rate with respect to ion-exchanged water is out of the above range, the water-absorbing resin swells in the drainage pipe when it flows in a flush toilet or the like, which is not preferable.

  The present invention further has the following characteristics.

c) Absorption capacity under non-pressurization with respect to ion exchange water in 4 hours (CRCw)
In the water-absorbent resin of the present invention, the absorption capacity without load (CRCw) with respect to ion-exchanged water in 4 hours is preferably not more than the absorption capacity (CRCs) of physiological saline in 4 hours, and more preferably, the above conditions are satisfied. While satisfying, the absorption capacity under no pressure with respect to ion-exchanged water in 4 hours is 0 to 20 g / g, more preferably 0 to 15 g / g, particularly preferably 0 to 10 g / g, most preferably 0 to 5 g. / G or less.

  If the composition of the water-absorbent resin can be controlled so that the water absorption ratio is within this range, there is no further concern about blockage even if it is flushed with a flush toilet.

d) pH
The water absorbent resin of the present invention preferably has a pH (specified in 400.1-99) defined by EDANA (European Disposable And Nonwoven Association) in the range of 4.0 to 8.0, and is preferably 4.5 to 7. A range of 5 is more preferable, and a range of 5.0 to 7.0 is most preferable.

  In the pH range exceeding this range, when the water-absorbent resin is used for a paper diaper or a sanitary napkin, rough skin and fogging occur, which is not preferable.

(16) Absorbent article / absorbent core The water-absorbent resin of the present invention is used as an ion-sensitive absorbent in absorbent articles due to its unique performance, as well as an ion-sensitive thickener and ion-sensitive agent. The use thereof is not particularly limited, but preferably it is used in absorbent articles of feces, body fluids, particularly urine or blood, such as disposable diapers and sanitary napkins. Used in absorbent cores.

  The absorbent core of the present invention is obtained using the above water-absorbent resin. In the present invention, the absorbent core is an absorbent material formed mainly of a water absorbent resin and hydrophilic fibers, and the absorbent core of the present invention comprises a water absorbent resin and hydrophilic fibers. The content (core concentration) of the water-absorbent resin with respect to the total mass is preferably 5 to 100% by mass, more preferably 10 to 100% by mass, particularly preferably 15 to 100% by mass, and most preferably 20 to 100% by mass. is there.

  Moreover, the thickness of the absorption core of the present invention is preferably 0.1 to 10 mm.

  Furthermore, the absorbent article of the present invention is an absorbent article comprising the above-described absorbent core of the present invention, a top sheet having liquid permeability, and a back sheet having liquid impermeability.

In the method for producing an absorbent article of the present invention, for example, an absorbent core is prepared by blending or sandwiching a fiber base material and a water-absorbent resin, and the absorbent core is made of a liquid-permeable base material (surface sheet) and a liquid. Sandwiched with an impermeable base material (back sheet) and equipped with an elastic member, diffusion layer, adhesive tape, etc. as necessary, it can be used as absorbent articles, especially adult paper diapers and sanitary napkins. That's fine. Such an absorbent core is compression molded to a density of 0.06 to 0.50 g / cc and a basis weight of 0.01 to 0.20 g / cm ² . Examples of the fiber base used include hydrophilic fibers such as pulverized wood pulp, cotton linters and cross-linked cellulose fibers, rayon, cotton, wool, acetate, and vinylon. Preferably, they are airlaid. In particular, in order to utilize the characteristics of the present invention, it is preferable that the absorbent core or the absorbent article is made of a material dispersible in water.

  For convenience, if all of the absorbent articles are dispersible in water, they can be poured directly into the toilet after use. If only the absorbent core is dispersible in water, after use, only the absorbent core may be taken out and poured into the toilet, and the top sheet and back sheet may be designed to be recyclable.

  The water-absorbing resin of the present invention exhibits unique and novel absorption characteristics. The absorbent article containing such a water-absorbent resin is not particularly limited, and specifically includes sanitary materials such as adult paper diapers, children's diapers, sanitary napkins, so-called incontinence pads, and the like. It is done. Due to the effect of the water-absorbent resin of the present invention present in the absorbent article, the amount of leakage of the absorbent article is small, the feeling of use and dryness are excellent, and the burden on the wearer and the caregiver is greatly reduced. In addition to the convenience of being able to flow to the toilet.

  EXAMPLES Examples and comparative examples of the present invention will be specifically described below, but the present invention is not limited to the following examples. In the following examples, “part” represents “part by mass” unless otherwise specified.

  Various performances of the water absorbent resin and the absorbent article were measured by the following methods. Moreover, all the electric equipments used in the examples were used under conditions of 100 V and 60 Hz. Furthermore, unless otherwise specified, the water-absorbent resin and absorbent articles were used under conditions of 25 ° C. ± 2 ° C. and a relative humidity of 50% RH. Moreover, 0.90 mass% sodium chloride aqueous solution was used as physiological saline. As ion-exchanged water, water having a conductivity of 1 to 50 μS / cm was used. The physiological saline or ion-exchanged water used for the measurement was adjusted to 21 ° C. ± 2 ° C. before use.

  In addition, as a comparison, when a comparative test is performed with a commercially available water-absorbing resin, diaper, or a water-absorbing resin in a diaper, moisture may be absorbed in the distribution process. The amount of volatile components of the water-absorbent resin may be dried to equilibrium (around 5% by mass, 2 to 8% by mass) and then compared.

(A) Absorption capacity without load (CRCs) with respect to physiological saline (0.90 mass% sodium chloride aqueous solution)
0.200 g of the water-absorbent resin was uniformly put in a bag (60 mm × 85 mm) made of a non-woven fabric (made by Nankoku Pulp Industries Co., Ltd .: Heaton Paper: product number GS-22) and sealed. 1 L of physiological saline adjusted to 21 ± 2 ° C. was placed in a polypropylene container (diameter: 85 mm, with a 5 cm long stirrer (50 mm long, 8 mm diameter cylinder type Teflon (registered trademark) stirrer). (Height: 200 mm). One non-woven fabric containing a water absorbent resin was immersed under stirring at 100 rpm. After 4 hours, the bag was pulled up and drained for 3 minutes at 250 G (250 × 9.81 m / s ² ) using a centrifuge (model K-san, model H-122 small centrifuge). Mass W ₂ (g) was measured. Moreover, the same operation was performed without using a water absorbent resin, and the mass W ₁ (g) at that time was measured. And from these masses W ₁ and W ₂ , the absorption capacity (g / g) was calculated according to the following formula.

(B) Absorption capacity under non-pressurization with respect to ion-exchanged water (CRCw)
0.050 g of the water-absorbent resin was uniformly put into a bag (60 mm × 85 mm) made of a nonwoven fabric (Nanoku Pulp Industries Co., Ltd .: Heaton Paper: Product No. GS-22) and sealed. 1 L of ion-exchanged water adjusted to 21 ± 2 ° C. was placed in a polypropylene container (diameter: 85 mm, with a 5 cm long stirrer (50 mm long, 8 mm diameter cylinder type Teflon (registered trademark) stirrer). (Height: 200 mm). One non-woven fabric containing a water absorbent resin was immersed under stirring at 100 rpm. After 4 hours, the bag was pulled up and drained for 3 minutes at 250 G (250 × 9.81 m / s ² ) using a centrifuge (model K-san, model H-122 small centrifuge). Mass W ₄ (g) was measured. Moreover, the same operation was performed without using a water absorbent resin, and the mass W ₃ (g) at that time was measured. From these mass _W 3, _{W 4,} in accordance with the following equation to calculate the absorption capacity (g / g).

(C) Volatile component amount Airless resin was uniformly dispersed in an aluminum dish (mass W ₅ [g]) having a diameter of 60 mm and a mass of known water-absorbing resin and heated to 180 ° C. (Tokyo Rika Machinery Co., Ltd.) Leave for 3 hours in EYELA natural aven NDO-450 made by company. After 3 hours, the aluminum dish was taken out, allowed to cool in a desiccator for 20 minutes, and then the mass (W ₆ [g]) was measured. The amount of volatile components was calculated by the following formula.

(D) Solubility test in 30 minutes in ion-exchanged water 500 mL of ion-exchanged water was placed in a 1 L polypropylene container (diameter: 85 mm, height: 200 mm), and a 5 cm long stirrer (length: 50 mm, diameter) Stirring is performed at a speed of 400 rpm with an 8 mm cylinder type Teflon (registered trademark) stirrer. Thereto is added 0.500 g of a water-absorbing resin. Time measurement is started at 0 minutes as the time of charging, and the time until dissolution is visually measured (visual dissolution time). After 30 minutes, the above contents were placed on a 150 μm stainless steel screen mesh (a wire mesh of 150 μm opening as defined in JIS-Z-8801, and frame dimensions: diameter 200 mm, depth 45 mm, manufactured by The IIDA TESTING SIEVE). Pour all, collect the entire amount of the solution that has passed through the wire mesh in 2 minutes, and determine the mass (W ₇ [g]).

Of the collected solution, 200 g (W ₈ [g]) was weighed into a 500 ml round bottom flask and concentrated to about 5 ml with a rotary evaporator. However, when the amount of the solution passing through the wire mesh did not reach 200 g, the total amount was used as W ₈ [g].

The obtained concentrate is transferred to an aluminum dish (mass W ₉ [g]) having a diameter of 60 mm, which has a known mass, and further the residue inside the flask is transferred to the aluminum dish using 5 ml of ion-exchanged water. This washing operation is performed three times.

The aluminum dish is left in a windless dryer (Tokyo Rika Machine Co., Ltd., EYELA natural of NDO-450) heated to 180 ° C. for 3 hours to 5 hours until it reaches a constant weight. Then allowed to cool in a desiccator for 20 minutes to measure the mass of the aluminum dish (W ₁₀ [g]).

  Separately, the above operation (c) was performed, and the solid content was determined from the amount of volatile components.

  The dissolution rate at 30 minutes was calculated by the following formula.

(E) Mass (weight) average particle diameter (D50), logarithmic standard deviation (σζ), and mass percentage of particle diameter less than 150 μm Water-absorbing resin, for example, 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm , 106 μm, 45 μm, and sieving with JIS standard sieves, mass percentages with particle diameters of less than 150 μm were measured, and residual percentage R of each particle size was plotted on logarithmic probability paper. Thereby, the particle size corresponding to R = 50% by mass was read as the mass average particle size (D50). In addition, the logarithmic standard deviation (σζ) is expressed by the following equation, and the smaller the value of σζ, the narrower the particle size distribution.

In the above formula, X ₁ is the particle size when R = 84.1% by mass, and X ₂ is the particle size when R = 15.9% by mass.

  In addition, classifying sieving is performed by charging 10.00 g of the water-absorbing resin into the above-mentioned JIS standard sieve (The IIDA TESTING SIEVE: inner diameter 80 mm), and a low tap type sieve shaker (manufactured by Iida Seisakusho, ES-65 type). Classification for 5 minutes using a sieve shaker).

  In addition, when more than half of the particles of the water-absorbent resin used for the measurement are out of the range of the sieve (for example, when exceeding 850 μm, when passing through 45 μm), the sieve opening may be appropriately changed.

  The mass average particle size (D50) is a standard sieve particle size corresponding to 50% by mass of the whole particle with a standard sieve having a constant mesh as described in US Pat. No. 5,051,259. It is.

(F) pH
The pH is measured by a method defined by EDANA (European Disposable And Nonwoven Association) in 400.1-99.

  That is, 100 ml of a 0.9 mass% sodium chloride aqueous solution and a stirrer were placed in a 250 ml beaker and stirred at an appropriate speed so that air did not enter the solution. To this solution, 0.5 ± 0.01 g of a water absorbent resin was added and stirred for 10 minutes. After 10 minutes, stirring was stopped and the mixture was allowed to stand for 1 minute. Then, a pH electrode was inserted into the solution, and the pH value of the supernatant was read.

(G) Absorbency test with absorbent core Uniform water absorbent resin 0.5g on water dispersible toilet paper (trade name: Swan, manufactured by Kawamura Paper Co., Ltd.) having a width of 5.5cm and a length of 11cm. It was sprayed and another toilet paper same as the above was placed thereon to produce a sandwich type absorbent core. On top of that, a plate (mass: 72 g) in which a pipe having a diameter of 1.5 cm is inserted in the center with an acrylic plate having a width of 7 cm and a length of 15 cm is installed as a liquid charging device, and 3.0 g of physiological saline is added. It was put into the absorption core via a pipe. After 10 minutes, remove the liquid charging device and place 4 paper towels (made by Crecia Co., Ltd., trade name: Kim Towel Wiper) with a known mass (W ₁₁ [g]) on top of each other to cover the absorbent core. An acrylic plate (mass: 70 g) having a length of 7 cm and a length of 15 cm and a weight (mass: 460 g) were sequentially installed. After 30 seconds, the acrylic board and the weight were removed, the weight of the paper towel (W ₁₂ [g]) was measured, and the return amount and the ratio of the return amount to the liquid input amount were calculated by the following equations.

(H) Occlusion test with a simulated drain pipe The apparatus shown in FIG. 1 in which a funnel is installed on one side of a silicon tube having an inner diameter of 1.2 cm and an outer diameter of 1.6 cm is used as a simulated drain pipe apparatus, and an absorption core is used. The blockage of the pipe when it was flowed was evaluated.

  That is, the simulated drainage pipe device has a funnel portion whose inner diameter at point A is 14 cm and the height from point A to point B is 12 cm, and a silicon tube portion (length is 100 cm, inner diameter connecting point B and point C). Is 1.2 cm and the outer diameter is 1.6 cm). Furthermore, the point B and the point C are fixed at the same height, and the distance between the center of the tube at the point B and the center of the tube at the point C is 25 cm.

  In a 600 ml polypropylene container (inner diameter: 85 mm, height: 120 mm), a 5 cm long stirrer (length: 50 mm, diameter: 8 mm cylinder-type Teflon (registered trademark) stirrer) and 100 ml of ion-exchanged water. Insert. The absorption core after completion | finish of said (g) absorption core test was thrown in there, and it stirred at 1200 rpm for 5 seconds. Thereafter, the stirring bar was immediately removed, and the dispersion liquid of the absorbent core was added from the point A of the simulated drainage pipe device and left for 60 minutes. After 60 minutes, 500 ml of ion-exchanged water was poured from the point A of the funnel part, and the state discharged from the point C was observed.

Example 1
A reaction solution was prepared by dissolving 51 g of acrylic acid (AA), 9 g of lauryl acrylate (LA) (purchased from Aldrich Chemical Company), 90 g of ethanol, and 0.2 g of 2,2′-azobisisobutyronitrile. The reaction solution was put into a 500 ml separable flask equipped with a stirring blade, a motor for driving the stirring blade, and a cooling tube, and the dissolved oxygen was purged by blowing nitrogen gas for 30 minutes. Then, under a flow of nitrogen gas, the separable flask is immersed in a 60 ° C. hot water bath and allowed to undergo a polymerization reaction for 2 hours with stirring. Thereafter, the temperature of the water bath is raised to 80 ° C. and the polymerization reaction is further carried out for 1 hour. A viscous solution was obtained. The resulting solution was vacuum dried at 60 ° C. for 16 hours. The obtained white lump was pulverized and a precursor resin (A) was obtained through a 850 μm mesh. The mass average particle diameter of the precursor resin (A) was 415 μm, and the logarithmic standard deviation was 0.47.

  100 parts of the precursor resin (A) and 49.6 parts of sodium hydrogen carbonate (corresponding to 50 mol% neutralization with respect to acrylic acid part) were mixed, and 400 parts of water was added thereto while stirring and left for 20 hours. Thereafter, vacuum drying was performed for 16 hours at 60 ° C., followed by pulverization, and particles that passed through 850 μm and did not pass through 150 μm were selected to obtain a water-absorbent resin (1). The obtained water-absorbent resin (1) had a mass average particle diameter of 410 μm, a logarithmic standard deviation of 0.45, and a volatile component amount of 4% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the water absorbent resin (1) and the test results of the water absorbent core using the water absorbent resin (1), respectively.

Example 2
The same as in Example 1 except that 48 g of acrylic acid, 12 g of lauryl acrylate (purchased from Aldrich Chemical Company), 90 g of ethanol, and 0.2 g of 2,2′-azobisisobutyronitrile were dissolved to form a reaction solution. The precursor resin (B) was obtained by the operation. The mass average particle diameter of the precursor resin (B) was 420 μm, and the logarithmic standard deviation was 0.45.

  100 parts of the precursor resin (B) and 70 parts of sodium hydrogen carbonate (corresponding to 75 mol% neutralization with respect to acrylic acid part) were mixed, and 400 parts of water was added thereto with stirring and left for 20 hours. Thereafter, vacuum drying was performed for 16 hours at 60 ° C., followed by pulverization, and particles passing through 850 μm and not passing through 150 μm were selected to obtain a water absorbent resin (2). The obtained water absorbent resin (2) had a mass average particle diameter of 417 μm, a logarithmic standard deviation of 0.43, and a volatile component amount of 5% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the water absorbent resin (2) and the test results of the water absorbent core using the water absorbent resin (2), respectively.

Example 3
Other than dissolving 54 g of acrylic acid, 6 g of stearyl acrylate (StA) (purchased from Wako Pure Chemical Industries, Ltd.), 90 g of ethanol, and 0.2 g of 2,2′-azobisisobutyronitrile, respectively, to prepare a reaction solution Obtained precursor resin (C) by the same operation as Example 1. The mass average particle diameter of the precursor resin (C) was 404 μm, and the logarithmic standard deviation was 0.46.

  100 parts of the precursor resin (C) and 52.5 parts of sodium hydrogen carbonate (corresponding to 50 mol% neutralization with respect to acrylic acid part) were mixed, and 400 parts of water was added thereto with stirring and left for 20 hours. Thereafter, vacuum drying was performed for 16 hours at 60 ° C., followed by pulverization, and particles passing through 850 μm and not passing through 150 μm were selected to obtain a water-absorbent resin (3). The water-absorbent resin (3) obtained had a mass-average particle diameter of 423 μm, a logarithmic standard deviation of 0.41, and a volatile component amount of 4% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the water absorbent resin (3) and the test results of the water absorbent core using the water absorbent resin (3), respectively.

Example 4
A reaction solution was prepared by dissolving 52.5 g of acrylic acid, 7.5 g of stearyl acrylate (purchased from Wako Pure Chemical Industries, Ltd.), 90 g of ethanol, and 0.2 g of 2,2′-azobisisobutyronitrile. Except for the above, a precursor resin (D) was obtained in the same manner as in Example 1. The mass average particle diameter of the precursor resin (D) was 429 μm, and the logarithmic standard deviation was 0.42.

  100 parts of the precursor resin (D) and 76.6 parts of sodium hydrogen carbonate (corresponding to 75 mol% neutralization with respect to the acrylic acid part) were mixed, and 400 parts of water was added thereto while stirring and left for 20 hours. Thereafter, vacuum drying was performed for 16 hours at 60 ° C., followed by pulverization, and particles passing through 850 μm and not passing through 150 μm were selected to obtain a water absorbent resin (4). The obtained water-absorbent resin (4) had a mass average particle diameter of 436 μm, a logarithmic standard deviation of 0.49, and an amount of volatile components of 4% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the water absorbent resin (4) and the test results of the water absorbent core using the water absorbent resin (4), respectively.

Example 5
51 g of acrylic acid and 9 g of stearyl acrylate (purchased from Wako Pure Chemical Industries, Ltd.), 90 g of ethanol, and 0.2 g of 2,2′-azobisisobutyronitrile were added and dissolved to obtain a reaction solution. Obtained precursor resin (E) by the same operation as Example 1. The mass average particle diameter of the precursor resin (E) was 419 μm, and the logarithmic standard deviation was 0.45.

  100 parts of the precursor resin (E) and 74.4 parts of sodium hydrogen carbonate (corresponding to 75 mol% neutralization with respect to acrylic acid part) were mixed, and 400 parts of water was added thereto while stirring and left for 20 hours. Thereafter, vacuum drying was performed for 16 hours under conditions of 60 ° C., followed by pulverization, and particles passing through 850 μm and not passing through 150 μm were selected to obtain a water-absorbent resin (5). The water-absorbent resin (5) obtained had a mass average particle diameter of 413 μm, a logarithmic standard deviation of 0.46, and a volatile component amount of 6% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the water absorbent resin (5) and the test results of the water absorbent core using the water absorbent resin (5), respectively.

Example 6
Water absorption produced in the same manner as in Example 3 by mixing 0.05 part of ethylene glycol diglycidyl ether (manufactured by Nagase Chemical Co., Ltd., Denacol EX-810), 1 part of propylene glycol, 3 parts of water and 1 part of isopropyl alcohol. After spraying to 100 parts of the functional resin (3) with stirring, the mixture was heated with a dryer at 140 ° C. Thereafter, particles passing through 850 μm and not passing through 150 μm were selected to obtain a surface-crosslinked water-absorbing resin (6). The obtained water-absorbent resin (6) had a mass average particle diameter of 430 μm, a logarithmic standard deviation of 0.42, and a volatile component amount of 2% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the water absorbent resin (6), and the test results of the water absorbent core using the water absorbent resin (6), respectively.

Comparative Example 1
To 5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% (monomer concentration 38% by mass), 6.25 g of polyethylene glycol diacrylate (average number of added moles of ethylene oxide 9) was dissolved to obtain a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma-shaped blades, and the system was nitrogenated while maintaining the reaction solution at 30 ° C. The gas was replaced. Subsequently, while stirring the reaction solution, 29.8 g of a 10% by weight aqueous solution of sodium persulfate and 1.5 g of a 1% by weight aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. A polymerization peak temperature of 86 ° C. was exhibited 17 minutes after the start of the polymerization, and a hydrogel polymer was taken out 60 minutes after the start of the polymerization. The obtained hydrogel polymer was fragmented into particles of about 1 to 4 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried with hot air at 160 ° C. for 60 minutes. Next, the dried product was pulverized by a roll mill, and particles that passed through 850 μm but did not pass through 150 μm were selected to obtain a comparative water absorbent resin (1). The comparative water absorbent resin (1) thus obtained had a mass average particle diameter of 407 μm, a logarithmic standard deviation of 0.43, and a volatile component amount of 7% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the comparative water absorbent resin (1) and the test results of the water absorbent core using the comparative water absorbent resin (1), respectively.

Comparative Example 2
A comparative water absorbent resin (2) was obtained in the same manner as in Example 5 except that the amount of sodium hydrogen carbonate added to the polymer was 24.8 g (25 mol% with respect to the acrylic acid moiety). . The comparative water absorbent resin (2) thus obtained had a mass average particle diameter of 436 μm, a logarithmic standard deviation of 0.45, and a volatile component amount of 5% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the comparative water absorbent resin (2), and the test results of the water absorbent core using the comparative water absorbent resin (2), respectively.

Comparative Example 3
In a 1 L polypropylene container, 1.05 g of lauryl methacrylate (LMA), 12.5 g of a 30% aqueous solution of sodium lauryl sulfate, 270 g of water, 36.0 g of acrylic acid, 0.024 g of 2,2′-azobisisobutyronitrile After dissolving 1 g of a polyethylene glycol surfactant (Emulgen 108), the dissolved oxygen was purged by blowing nitrogen gas for 30 minutes. Then, it was immersed in a 60 degreeC hot water bath under nitrogen stream, and the polymerization reaction was performed for 4 hours.

  After 4 hours, it was cooled to room temperature and the gel was crushed with scissors. Thereafter, 23 g of a 28% by mass aqueous ammonia solution was uniformly added to the crushed gel and mixed.

  After standing for 3 hours, the gel was dried at 120 ° C. for 2.5 hours, and further vacuum dried at 60 ° C. for 16 hours to obtain a comparative water-absorbent resin (3). The comparative water absorbent resin (3) thus obtained had a mass average particle diameter of 421 μm, a logarithmic standard deviation of 0.43, and a volatile component amount of 5% by mass. Tables 1, 2 and 3 show the composition and water absorption performance of the comparative water absorbent resin (3) and the test results of the water absorbent core using the comparative water absorbent resin (3), respectively.

Comparative Example 4
A reaction solution was prepared by dissolving 65 g of acrylic acid, 10 g of lauryl acrylate (purchased from Aldrich Chemical Company), 25 g of ethyl acrylate (EA), 106 g of acetone, and 38 g of distilled water. The reaction solution was put into a 500 ml separable flask equipped with a stirring blade, a motor for driving the stirring blade, and a cooling tube, and the dissolved oxygen was purged by blowing nitrogen gas for 30 minutes. An aqueous solution obtained by dissolving 0.88 g of 2,2′-azobis (2-amidinopropane) dihydrochloride in 5 g of distilled water was added, and the separable flask was immersed in a 70 ° C. water bath under a flow of nitrogen gas. The polymerization reaction was performed for 6 hours. After cooling to room temperature, 10.5 g of a 48 mass% sodium hydroxide aqueous solution (corresponding to 14 mol% neutralization relative to acrylic acid portion) and 380 g of distilled water were added to neutralize. The neutralized product was dried in a vacuum dryer at 60 ° C. for 16 hours and then pulverized, and particles passing through 850 μm and not passing through 150 μm were selected to obtain a comparative water absorbent resin (4). The comparative water absorbent resin (4) thus obtained had a mass average particle diameter of 411 μm, a logarithmic standard deviation of 0.47, and a volatile component amount of 5% by mass. Tables 1 and 2 show the composition and water-absorbing performance of the comparative water-absorbing resin (4), and the test results of the water-absorbing core using the comparative water-absorbing resin (4), respectively.

Comparative Example 5
43.3 g of acrylic acid, 10.7 g of AMPS (2-acrylamido-2-methylpropanesulfonic acid), 35.2 g of butyl acrylate (BA), 20 g of 2-ethylhexyl acrylate (2-EHA) were added to 55 g of acetone / water (70 / 30) After dissolving in the mixed solution, nitrogen gas was blown for 30 minutes to purge the dissolved oxygen to obtain a monomer solution. Separately, 0.51 g of initiator 2,2′-azobisisobutyronitrile was dissolved in 20 ml of acetone, and then the dissolved oxygen was purged by blowing nitrogen gas for 30 minutes to obtain an initiator solution. Into a 1000 ml separable flask equipped with two dropping funnels, a stirring blade, a motor for driving the stirring blade, and a cooling tube, 120 g of an acetone / water (70/30) mixed solution was put, and nitrogen gas was blown into the flask. The dissolved oxygen was purged. Thereafter, the reaction vessel was immersed in a water bath and heated to 60 ° C., and the monomer solution and the initiator solution were slowly dropped from two dropping funnels simultaneously over 2 hours under a flow of nitrogen gas. After completion of the dropping, the polymerization reaction was further carried out for 2 hours. To the obtained polymer, 4.3 g of a 48% aqueous sodium hydroxide solution (8 mol% neutralization equivalent to acid group-containing monomer portion) was added dropwise and dried in vacuo at 60 ° C. for 16 hours. The obtained white lump was pulverized, and particles passing through 850 μm and not passing through 150 μm were selected to obtain a comparative water absorbent resin (5). The comparative water absorbent resin (5) thus obtained had a mass average particle diameter of 407 μm, a logarithmic standard deviation of 0.44, and a volatile component amount of 5% by mass. Tables 1 and 2 show the composition and water absorption performance of the comparative water absorbent resin (5) and the test results of the water absorbent core using the comparative water absorbent resin (5), respectively.

  As shown in Tables 1 to 3, the water-absorbent resin of the present invention exhibits a high absorption ratio with respect to physiological saline (0.9 mass% sodium chloride aqueous solution) and also exhibits excellent solubility in water. . For this reason, if the water absorbing resin of this invention is used, it will become possible to design the paper diaper and sanitary napkin which can be poured with a flush toilet.

  Since the water-absorbent resin obtained by the present invention has absorption characteristics different from conventional ones, when used in paper diapers and sanitary napkins, it has excellent absorption performance and usability for body fluids as in the past. There is an effect that it is possible to provide convenience that can be used as it is in a toilet or the like.

It is the schematic of the apparatus used for the obstruction | occlusion test with a simulation drain pipe.

Claims (8)

A water-absorbent resin mainly composed of a repeating unit having an ionic dissociation group in the main chain or side chain,
Absorption capacity under no pressure (CRCs) in physiological saline for 4 hours is 10 g / g or more, dissolution rate in ion-exchanged water is 50% by mass or more,
The ionic dissociation group is a group selected from a carboxyl group, a sulfonic acid group, a phosphoric acid group or a salt thereof;
A water-absorbing resin having a neutralization rate of the ionic dissociation group of 30 to 100 mol% ,
The water absorbent resin is a particulate water absorbent resin having a mass average particle diameter of 150 to 3000 μm or a fiber having an average fiber diameter of 10 to 1000 μm,
The repeating unit is (meth) acrylic acid and / or a salt thereof;
Furthermore, it has a hydrocarbon group having 4 or more carbon atoms in the side chain, and in this case, it has a repeating unit derived from a monomer having an ionic dissociation group in the side chain and a hydrocarbon group having 4 or more carbon atoms in the side chain. A water-absorbent resin in which the monomer-derived repeating units are in a mass ratio of 50:50 to 99: 1 . The water-absorbent resin according to claim 1, wherein the solubility in ion-exchanged water is 70% by mass or more. The water absorbent resin according to claim 1 or 2 , wherein the salt is selected from a lithium salt, a sodium salt, a potassium salt, and an ammonium salt. The water-absorbent resin according to any one of claims 1 to 3 , wherein the ionic dissociation group has a neutralization rate of 50 to 90 mol%. The water-absorbent resin according to any one of claims 1 to 4 , wherein an absorption capacity under non-pressure (CRCw) with respect to ion-exchanged water in 4 hours is equal to or less than an absorption capacity under non-pressure (CRCs) with respect to physiological saline. Among the repeating units of the water-absorbent resin, the mass of the repeating unit derived from a monomer having an ionic dissociation group in the side chain and the repeating unit derived from a monomer having a hydrocarbon group having 4 or more carbon atoms in the side chain is its mass. ratio, 50: 50 to 99: 1 range der is, the monomer having a hydrocarbon group of the 4 or more carbon atoms in the side chain, having 4 or more carbon atoms linear or branched chain or cyclic hydrocarbon The water-absorbent resin according to any one of claims 1 to 5, which is an ester or amide monomer obtained from an ethylenically unsaturated monomer containing an alcohol or amine having a group and a carboxyl group . The water absorbent resin according to any one of claims 1 to 6 , wherein the pH of the water absorbent resin is in a range of 4.0 to 8.0. An absorbent core or absorbent article for feces, urine or blood, the absorbent core or absorbent article formed by containing the water-absorbent resin according to any one of claims 1 to 7 and hydrophilic fibers.

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