JP2002179791A - Cross-linked polyaspartic acid (salt) and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cross-linked polyaspartic acid (salt) having biodegradability, high absorbing rate and high productivity. SOLUTION: This cross-linked polyaspartic acid (salt) is obtained by the steps of reacting polysuccinic acid imide with a multi-valent amine compound to produce a cross-linked polysuccinic acid imide and hydrolyzing the imide ring of the cross-linked polysuccinic acid imide, and having a water absorption per 1 minute measured by tea-bag method being 30 to 150 times of polymer self-weight for physiological salt water, and being 100 to 1,500 times of polymer self-weight for distilled water. Especially the cross-linked polyaspartic acid (salt) has a structure enabling to enhance water absorption rate such as a porous structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable composition,
Also, the present invention relates to a crosslinked polyaspartic acid (salt) useful as a water absorbent resin tree.

[0002]

2. Description of the Related Art [Technical background of water-absorbent resin] A water-absorbent resin is a resin that can absorb water of several tens to several thousand times its own weight, such as sanitary products such as sanitary products, disposable diapers, and various other fields. Used in

[Prior art relating to water-absorbing resin] Examples of the water-absorbing resin used in such applications include:
Crosslinked polyacrylic acid partially neutralized product (JP-A-55-8430)
No. 4, U.S. Pat. No. 4,625,001), a partially hydrolyzed starch-acrylonitrile copolymer (JP-A-46-43).
No. 995), a starch-acrylic acid graft copolymer (JP-A-51-125468), and a hydrolyzate of a vinyl acetate-acrylic ester copolymer (JP-A-52-14689).
No.), copolymerized crosslinked product of 2-acrylamido-2-methylpropanesulfonic acid and acrylic acid (European patent 00681)
No. 89), a crosslinked polymer of a cationic monomer (US Pat. No. 4,906,717), and a hydrolyzate of a crosslinked isobutylene-maleic anhydride copolymer (US Pat. No. 4,389,513)
No.) etc. are known.

However, since these water-absorbing resins have substantially no biodegradability, disposal after use is a problem. At present, these water-absorbing resins are
Incineration and landfill methods are used.However, incineration methods may cause damage to furnace materials due to heat generated during incineration, as well as cause global warming and acid rain. It is pointed out. In addition, in the landfill method, plastic has a problem that the ground after the landfill is not stable because the volume does not bulky and rot.
A major problem is that it has become difficult to secure land suitable for land reclamation. That is, these resins are poorly biodegradable and exist substantially semipermanently in water and soil, which is a very troublesome and serious problem in view of environmental conservation in waste treatment.

For example, in the case of a resin used in disposable applications represented by sanitary materials such as disposable diapers and sanitary products, it is costly to recycle the resin, and the resin is incinerated in large quantities. Heavy load. It has also been reported that when a crosslinked polyacrylic acid resin is used as a water retention material for agriculture and horticulture, it forms a complex with polyvalent ions such as Ca ²⁺ in soil and forms an insoluble layer (Matsumoto). Et al., Polymer, Vol. 42, August, 1993
Year).

[0006] Such a layer is said to have low toxicity per se, but has not originally existed in nature at all. The long-term effects of are unknown,
It is desired to use after careful and sufficient confirmation of safety.

In the case of a nonionic resin, a complex is not formed, but since it is nondegradable, it may accumulate in the soil. The effect over a long period of time is unknown, and it is desired to use it after careful and sufficient confirmation of safety.

[0008] Further, as these polymer resins, those having high toxicity to the skin and mucous membranes of mammals are used as monomer raw materials. In order to remove these from the product after polymerization, Many considerations have been made. Usually, it is difficult to remove the unreacted polymer from the product after polymerization, and it is expected that it will be more difficult, especially in industrial-scale production.

[Technical background of water-absorbing resin having biodegradability] In recent years, biodegradable polymers have attracted attention as "earth-friendly materials", and it has been proposed to use this as a water-absorbing resin. .

[0010] Examples of the biodegradable water-absorbing resin used for such applications include cross-linked polyethylene oxide (Japanese Patent Laid-Open No. 6-157795), cross-linked polyvinyl alcohol, cross-linked carboxymethyl cellulose (US (Patent No. 4,650,716), cross-linked alginic acid, cross-linked starch, cross-linked polyamino acid and the like are known. Among these, crosslinked polyethylene oxide and crosslinked polyvinyl alcohol have low water absorption, and are usually suitable when used as materials for products requiring high water absorption such as sanitary products, disposable diapers, disposable rags, and paper towels. Not.

[0011] Further, since these compounds cannot be biodegraded unless they are produced by a special bacterium, the biodegradation is extremely slow or not decomposed at all under general conditions. When these compounds have a large molecular weight, their degradability is further extremely reduced. In addition, saccharide cross-linked products such as carboxymethyl cellulose cross-linked products, alginic acid cross-linked products, and starch cross-linked products have many strong hydrogen bonds in their molecules.
Therefore, the molecular chains cannot be widely opened, and as a result, the water absorption capacity is not high.

[Technical Background of Polyamino Acid-Based Water-Absorbent Resin] The resin obtained by crosslinking a polyamino acid is biodegradable and thus is friendly to the global environment. Since it has been shown that it does not show antigenicity and that degradation products have no toxicity, it is a material that is easy on mammals.

As a specific example of such a method for producing a resin, there is a method for producing a resin having high water absorption by irradiating poly-γ-glutamic acid with γ-rays (Kunioka et al. Vol. 50, No. 10, 755 (1993)
Year)). However, from an industrial point of view, the ⁶⁰ Co irradiation equipment used in this technology requires a large-scale equipment to shut off radioactivity, and requires sufficient consideration for its management. is not. Another problem is that polyglutamic acid as a starting material is expensive.

Another specific example of a method for producing such a resin is a method for obtaining a hydrogel by crosslinking an acidic amino acid [Akamatsu et al., US Pat. No. 3,948,863 (Japanese Patent Publication No. 52-86). 41309), Iwatsuki et al., JP-A-5-279416]. Still another specific example is a method using a crosslinked amino acid resin as a water-absorbing polymer (Sikes et al., JP-T-6-5062).
No. 44; U.S. Pat. Nos. 5,247,068 and 5,2;
No. 84,936, Suzuki et al., JP-A-7-309943,
Harada et al., JP-A-8-59820). However, these polymers do not have sufficient performance as a water-absorbing polymer.

On the other hand, a method for producing these cross-linked polyamino acids by reacting polyaspartic acid or aspartic acid with a cross-linking agent by heat is disclosed in JP-A-6-506244.
And Japanese Patent Publication No. Hei 8-504219. Also, mixing acidic and basic polyamino acids,
A method for obtaining a water-absorbing polymer by heating and crosslinking is disclosed in JP-A-8-59820. However, these methods are characterized in that the cross-linking reaction is performed in a solid state, so that the cross-linking reaction is difficult to be uniform, so that physical properties such as water absorbing ability are not sufficient, and the reaction temperature of the cross-linking reaction requires a high temperature. Therefore, there is a problem that the decomposition is remarkable and the hue changes to yellow or brown.

On the other hand, Japanese Patent Application Laid-Open No. 7-224163 discloses a method in which a polysuccinimide is crosslinked with a diamine, and the remaining imide ring is hydrolyzed with an alkali to obtain a water-absorbent resin having high salt water absorbency. . Similarly, a method of hydrolyzing a partially crosslinked product of an anhydrous polyacidic amino acid with a polyamine with an alkali metal compound is disclosed in JP-A-7-30994.
No. 3.

In these methods, polysuccinimide is uniformly and efficiently cross-linked, and the degree of cross-linking is easily controlled, so that a water-absorbing polymer having high water-absorbing ability can be obtained in a high yield. This is extremely significant in that it is a production method that is optimally used. However, in order to crosslink polysuccinimide with a diamine, the polysuccinimide is dissolved in an aprotic polar solvent, so equipment for handling the organic solvent and recovery of the organic solvent are required, and further improvement is desired.

The present inventors have also disclosed in Japanese Patent Application Laid-Open No. 11-060.
No. 729 discloses a method for producing a crosslinked polyamino acid by reacting a polyamino acid with a crosslinking agent such as a polyepoxy compound, a polyol, a polythiol, a polyisocyanate, a polyaziridine, or a polyvalent metal. This method is characterized in that no aprotic polar solvent for dissolving polysuccinimide is required, and uniform crosslinking can be performed.

Japanese Patent Application Laid-Open No. 10-298282 discloses that
A method for producing a polyamino acid-based water-absorbent resin which is crosslinked with a polyglycidyl compound or an epihalohydrin-modified amino compound in an aqueous solution of a water-soluble polyamino acid having a concentration of 2 to 40% by mass is disclosed. However, in this production method, the number of reaction sites is small, and a high-concentration reaction cannot be performed, so that a crosslinking reaction speed is slow, and a long time is required for the reaction. Cleavage occurs, the yield is low, and the performance (water absorption capacity) of the obtained polymer is very low. In addition to the side reactions, as described in this publication, since the polarity of the polymer is high, when the polymer concentration is high, many entanglements between the polymers are present or the polymer chain shrinks. Does not progress well.

That is, in this production method, since the crosslinking reaction does not proceed efficiently, the time required for the reaction is long, the polyaspartic acid is hydrolyzed, the main chain is cut, and the water-soluble component is reduced. That it is generated in large quantities and the yield is low,
It has many problems. Furthermore, since it has a low water absorption capacity, it is difficult to use it for sanitary articles such as disposable diapers. In particular, there is a strong demand for thin sheets in applications such as sanitary materials, but it is essential to reduce the amount of pulp as much as possible in order to produce thin sheets. For this purpose, there is a strong demand for the ability of the water-absorbing polymer to quickly absorb excreted body fluids (high absorption rate).

In Japanese Patent Application Laid-Open No. 10-330478,
A method for producing a crosslinked polyamino acid is disclosed in which an aqueous solution of a polyamino acid is brought into contact with a diglycidyl compound or a diaziridine compound, water is removed by freeze-drying or the like, and heat treatment is performed. However, since the crosslinking agent used does not dissolve in water, it is difficult to maintain uniform mixing when removing water by freeze-drying, and uniform crosslinking cannot be performed in a solid-state crosslinking reaction, resulting in uneven crosslinking. And the degree of cross-linking is locally increased, and conversely, there is a problem that a part which is not sufficiently cross-linked and is water-soluble is formed.

[0022]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior arts. That is, an object of the present invention is to provide a crosslinked polyaspartic acid (salt) having high productivity, biodegradability, and high absorption rate, and a method for producing the same.

[0023]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have hydrolyzed the imide ring of a crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound. With respect to the crosslinked polyaspartic acid (salt) thus obtained, the present inventors succeeded in obtaining a crosslinked polyaspartic acid (salt) exhibiting a much higher water absorption rate than conventional ones, and have completed the present invention.

That is, the present invention relates to a physiological saline solution obtained by hydrolyzing an imide ring of a crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound for one minute as measured by a tea bag method. Is a crosslinked polyaspartic acid (salt) having a water absorption of 30 to 150 times the weight of the polymer.

Further, the present invention relates to a method for hydrolyzing an imide ring of a cross-linked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound, and using distilled water for 1 minute as measured by a tea bag method. A crosslinked polyaspartic acid (salt) having a water absorption of 100 to 1500 times the weight of the polymer.

The present invention further provides a method for producing the above-mentioned crosslinked polyaspartic acid (salt) of the present invention, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyamine compound. Is a method for producing a crosslinked polyaspartic acid (salt), comprising immersing a hydrous gel obtained by hydrolyzing a compound in a water-miscible organic solvent, and drying the obtained precipitate.

The present invention further relates to a process for producing the above-mentioned crosslinked polyaspartic acid (salt) of the present invention, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyamine compound. Is a method for producing a crosslinked polyaspartic acid (salt), which comprises lyophilizing a hydrogel obtained by hydrolyzing a poly (aspartic acid).

The present invention further relates to the crosslinked polyas of the present invention.
A method for producing paraginic acid (salt), comprising:
Crosslinking obtained by reacting succinimide with polyamine compound
Water content obtained by hydrolyzing the imide ring of polysuccinimide
Gels are 5 × 10-9 × 10 ^FourDry under reduced pressure of Pa
Crosslinked polyaspartic acid (salt) characterized by drying
It is a manufacturing method of.

Further, the present invention relates to a method for producing the above-mentioned crosslinked polyaspartic acid (salt) of the present invention, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound is provided. Is mixed with a water-miscible organic solvent to obtain a water-containing gel obtained by hydrolysis of
0 is a method for producing ⁴ Pa crosslinked polyaspartic acid, characterized by drying under a reduced pressure of (salt).

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] Water Absorbing Ability of Crosslinked Polyaspartic Acid (Salt) The crosslinked polyaspartic acid (salt) of the present invention is a resin characterized by having a high water absorption rate. That is, the resin satisfies one or both of the following two performances. (1) The amount of water absorbed in physiological saline for 1 minute measured by the tea bag method is 30 to 150 times the weight of the polymer.
Times. (2) The amount of water absorbed in distilled water per minute measured by the tea bag method is 100 to 1500 times the polymer's own weight.

The water absorbing ability other than the above-mentioned water absorbing speed is not particularly limited. However, those having excellent water absorption and water retention are preferable. In particular, when used for sanitary articles such as disposable diapers, high water absorption is required.

For example, 1 measured by the tea bag method
The amount of water absorbed in saline over time is 30-
It is preferably 200 times, more preferably 30 to 150 times, and particularly preferably 40 to 100 times. Further, the amount of water absorbed by distilled water in one hour measured by the tea bag method was 200 to 200 of the polymer.
It is preferably 0 times, more preferably 300 to 1000 times, and particularly preferably 400 to 1000 times. The specific conditions for measuring the amount of water absorption are shown in the column of Examples described later.

[2] Structure of Crosslinked Polyaspartic Acid (Salt) The structure of the crosslinked polyaspartic acid (salt) of the present invention comprises a polymer basic skeleton, a side chain portion, and a crosslinked portion. Hereinafter, these will be described in three parts.

[Basic polymer backbone of crosslinked polyaspartic acid (salt)] The polymer backbone of the crosslinked polyaspartic acid (salt) of the present invention is a main chain composed of aspartic acid (salt) as a main repeating unit. . This basic skeleton may contain another amino acid as a repeating unit as long as the function of the present invention is not hindered.

Specific examples of amino acid components other than aspartic acid include, for example, 20 kinds of protein-constituting amino acids, L-ornithine, a series of α-amino acids, β-alanine, γ-aminobutyric acid, neutral amino acids, acidic amino acids, Amino acids and amino acid derivatives such as ω-esters of acidic amino acids, basic amino acids, N-substituted basic amino acids, aspartic acid-L-phenylalanine dimer (aspartame), and aminosulfonic acids such as L-cysteic acid. be able to. The α-amino acid is an optically active form (L
, D-form) or a racemic form.

In addition, the basic skeleton may contain a monomer component other than an amino acid as a repeating unit as long as the function of the present invention is not hindered. Specific examples of the monomer component include aminocarboxylic acid, aminosulfonic acid, aminophosphonic acid, hydroxycarboxylic acid, mercaptocarboxylic acid, mercaptosulfonic acid, and mercaptophosphonic acid. In addition, polyamines, polyhydric alcohols, polythiols, polycarboxylic acids, polysulfonic acids, polyphosphonic acids, polyhydrazine compounds, polycarbamoyl compounds, polysulfonamide compounds, polyphosphonamide compounds , Polyvalent epoxy compounds, polyvalent isocyanate compounds, polyvalent isothiocyanate compounds, polyvalent aziridine compounds, polyvalent carbamate compounds, polyvalent carbamic acid compounds, polyvalent oxazoline compounds, polyvalent reactive unsaturated bond compounds, Valent metals and the like.

When the basic polymer skeleton is composed of a copolymer, it may be a block copolymer or a random copolymer. Further, it may be a graft copolymer.

The polymer basic skeleton of aspartic acid (salt) obtained by hydrolysis has an amide bond in the main chain of α.
It may be a bond or a β bond. In the present invention, there is no particular limitation, and either structure can be used. That is, the case where it is bonded to the carboxyl group at the α-position of aspartic acid is an α bond, and the case where it is bonded to the carboxyl group at the β-position of aspartic acid is a β bond. There is no particular limitation on the binding mode of the α-linkage and β-linkage.

[Structure of Side Chain Part of Crosslinked Polyaspartic Acid (Salt)] The structure of the side chain part of the crosslinked polyaspartic acid (salt) of the present invention is not particularly limited. May have a side chain structure as a substituted carboxylic acid derivative. Examples of the side chain structure include carboxylic acids, salts of carboxylic acids, esters, thioesters, and amides. Examples of the counter ion of the carboxyl group include alkali metal salts, ammonium salts, and amine salts.

In the case of esters, thioesters, amides and the like, the condensed alcohol, thiol, and amine components may have a substituent. These are called pendant groups. For example, there are an amino acid residue such as lysine, a pendant group having a carboxyl group, a pendant group having a sulfonic acid group, and a pendant group having a hydroxyl group.
Here, when it has a carboxyl group or a sulfonic acid group, the acid may be a salt.

[Structure of Crosslinked Portion of Crosslinked Polyaspartic Acid (Salt)] The crosslinked polyaspartic acid (salt) refers to a structure in which a part of a main chain or a side chain structure is crosslinked. Although this cross-link is a covalent bond, an ionic bond and a hydrogen bond may be used in combination.

In particular, the crosslinked polyaspartic acid (salt) of the present invention is obtained by hydrolyzing the remaining imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyamine compound. At least a part of the crosslinked portion has a structure in which an imide ring is opened by an amine. Although there is no particular limitation on the molecular structure of the cross-linked portion, the cross-linked portion can be understood as a “bonding portion” with the polymer basic skeleton or side chain structure and a “connecting portion” bridging them.

The crosslinked portion of the crosslinked polyaspartic acid (salt) of the present invention basically has a structure derived from a carboxyl group of polyaspartic acid as a polymer main chain. Therefore, the “bonding moiety” is generally an amide bond in which the carbonyl group of the polymer main chain is bonded by N. Further, instead of N, an ester or thioester bond bonded by O or S may be included. Further, the crosslinking group may be substituted at the α-position or β-position with respect to the amide bond of the polymer main chain.

The "linking group", which is a portion sandwiched by amide bonds and the like in the crosslinking group of the crosslinked polyaspartic acid (salt) of the present invention, is not particularly limited, but includes alkylene, aralkylene, phenylene, naphthylene and the like. No. The specific examples are listed below.

--CH _2- , --CH ₂ CH _2- , --CH ₂ CH
₂ CH _2- , -CH ₂ CH ₂ CH ₂ -,-(CH ₂ ) ₅ -,-(C
_{H 2) 6 -, - (} CH 2) 7 -, - (CH 2) 7 -, - (CH 2)
_{8 -, - (CH 2)} 9 -, - (CH 2) 10 -, - (CH 2) 11 -,
_{- (CH 2) 12 -,} - (CH 2) 13 -, - (CH 2) 14 -, - (C
_{H 2) 15 -, - (} CH 2) 16 -, - (CH 2) 17 -, - (CH 2)
_{18 -, - CH 2 CH 2} OCH 2 CH 2 -, - (CH 2 CH 2 O)
_{2 CH 2 CH 2 -, -} (CH 2 CH 2 O) 3 CH 2 CH 2 -, -
_{(CH 2 CH 2 O) 4} CH 2 CH 2 -, - (CH 2 CH 2 O) 5 CH
₂ CH ₂ -,-(CH ₂ CH ₂ O) ₆ CH ₂ CH _2- , -CH ₂ C
_{H 2 CH 2 OCH 2 CH 2} CH 2 -, - (CH 2 CH 2 CH 2 O)
_{2 CH 2 CH 2 CH 2 -} , - (CH 2 CH 2 CH 2 O) 3 CH 2 C
_{H 2 CH 2 -, - (} CH 2 CH 2 CH 2 O) 4 CH 2 CH 2 CH 2
_{-, - (CH 2 CH 2} CH 2 O) 5 CH 2 CH 2 CH 2 -, - (C
_{H 2 CH 2 CH 2 O)} 6 CH 2 CH 2 CH 2 -,

[0046]

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[0047]

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These linking groups may further contain a substituent, as in the case of the above-mentioned hydrocarbon group in the pendant group.

These connecting moieties may be unsubstituted,
It may be substituted by a substituent. Examples of the substituent include an optionally branched alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, an aralkyl group, an optionally substituted phenyl group, and an optionally substituted A good naphthyl group, an optionally branched alkoxy group having 1 to 18 carbon atoms, an aralkyloxy group, a phenylthio group, an optionally branched alkylthio group having 1 to 18 carbon atoms, An optionally branched alkylamino group, an optionally branched dialkylamino group having 1 to 18 carbon atoms, and 1 to 1 carbon atoms
8, an optionally branched trialkylammonium group,
Examples include a hydroxyl group, an amino group, a mercapto group, a carboxyl group, a sulfone group, a phosphone group and salts thereof, an alkoxycarbonyl group, an alkylcarbonyloxy group and the like.

Here, the amount of the crosslinked portion (hereinafter referred to as “crosslinking degree”) is not particularly limited, but the properties of the polymer greatly differ depending on the crosslinking degree. That is, the polymer is water-soluble up to a certain degree of cross-linking, and becomes insoluble in water when the degree of crosslinking is exceeded, resulting in a gel swollen by absorbing water. When this is expressed by an inequality, “the degree of crosslinking of the water-soluble polymer <the degree of crosslinking of the water-insoluble polymer”. However, the degree of crosslinking varies depending on the number of repeating units constituting the polymer main chain, that is, the degree of polymerization. And the crosslinked polyaspartic acid (salt) of the present invention is a substantially water-insoluble polymer.

Since the degree of polymerization can be expressed in terms of molecular weight, it can be expressed in terms of molecular weight. In general, when the molecular weight of the polymer main chain is large, it becomes insoluble in water even if the degree of crosslinking is small. On the other hand, when the molecular weight of the polymer main chain is small, the polymer does not become insoluble in water unless the degree of crosslinking increases. And the crosslinked polyaspartic acid (salt) of the present invention
Is a substantially water-insoluble polymer and may exhibit the above-described water absorption rate, and the degree of crosslinking is not particularly limited. However, based on the total number of repeating units of the whole polymer, the number of repeating units having a crosslinking group is 0.1 to 5
0% is preferable, and 0.5 to 10% is more preferable.

[3] Particle Structure of Crosslinked Polyaspartic Acid (Salt) In order to exhibit the high water absorption rate characteristic of the crosslinked polyaspartic acid (salt) of the present invention, for example, (1) it has a porous structure It is very important to satisfy at least one of the following particle structures: particles, (2) scaly particles, and (3) particles having a specific surface area of 0.1 to 1000 m ² / g. It is effective for

The size of the particles is not particularly limited.
By specifying the particle size, a higher water absorption rate can be exhibited. For example, when used in a disposable diaper, it is desired that a high absorption rate and no gel blocking occur, so that the average particle size is preferably 80 to 1000 μm, more preferably 100 to 800 μm, and 100 to 50 μm.
0 μm is particularly preferred.

[4] Method for producing crosslinked polyaspartic acid (salt) In the present invention, the remaining imide ring of the crosslinked polysuccinimide obtained by reacting polysuccinimide with a polyamine compound is hydrolyzed. To produce crosslinked polyaspartic acid (salt). That is, specifically,
(1) a step of producing polysuccinimide, (2) a step of cross-linking the polysuccinimide, and (3) a step of hydrolyzing the remaining imide ring. Hereinafter, each of those steps will be described.

[4-1] Method for Producing Polysuccinimide The method for producing polysuccinimide used in the present invention is not particularly limited. The higher the molecular weight of polysuccinimide,
It is preferable because the ability as a water retaining material is increased. The weight average molecular weight is generally 30,000 or more, preferably 50,000 or more, and more preferably 90,000 or more.

For example, J. Amer. Chem. Soc, 8
0,3361 (1958) discloses a method in which aspartic acid is used as a raw material and heat-condensed at 200 ° C. for several hours. In addition, in Japanese Patent Publication No. 48-20938, 85%
There is disclosed a method of obtaining a high molecular weight polysuccinimide by performing a reaction in the form of a thin film using a rotary evaporator using phosphoric acid as a catalyst. U.S. Pat. No. 5,057,597 discloses a method of industrially obtaining polysuccinimide by heating and condensing polyaspartic acid with a fluidized bed.

Further, as a method of polymerizing an amino acid using an acid catalyst to obtain a polysuccinimide, there are, for example, the following methods (1) to (4).

(1) The method of P. Neri et al. (Journ
al of Medicinal Chemistry,
(1973, Vol. 16, No. 8) P. Neri et al. Report the result of heating and polymerizing a reaction mixture obtained by reacting aspartic acid and phosphoric acid. By this method, in a vacuum system, the degree of polymerization n = 1100 to 1600 (molecular weight of 10.7 to 1600).
(Equivalent to 15,000). The method of heating as a thin layer performed by P. Neri et al.
g and 50 g of phosphoric acid, the paste-like reaction mixture is heated on a Teflon-coated tray having an area of 1000 cm ² .

(2) US Pat. No. 5,142,062 As a first step, a mixture of aspartic acid and phosphoric acid is reacted at a temperature of 100 to 250 ° C. and a pressure of less than 1 bar to obtain a polysuccinic acid having a molecular weight of 10,000 to 100,000. A solid reaction mixture containing the imide was prepared, and as a second step, the solid reaction mixture obtained in the first step was ground to a particle size of 0.001-2 mm and further selected from the temperature and pressure range of the first step. A technique for producing a high molecular weight polysuccinimide having a molecular weight of 100,000 to 200,000 by performing polycondensation under conditions is disclosed.

(3) JP-A-7-216084 A method is disclosed in which a mixture of aspartic acid and an acidic catalyst is heated in a normal pressure system to produce a polysuccinimide. Example 3 discloses an example in which a reaction mixture obtained by reacting aspartic acid and phosphoric acid was heated in a stainless steel pan to form a layer and polymerized in the same manner as in (1).

(4) JP-A-8-231710 Acidic catalyst 0.005 to 0.2 per mole of aspartic acid
The mixture in which 5 moles are uniformly mixed is heated in a normal pressure system,
A method for producing polysuccinimide is disclosed.
In Example 2, the paste-like mixture obtained using aspartic acid, phosphoric acid, and water was vacuum-dried at 40 to 80 ° C., and the obtained dry mixture was pulverized to 200 ° C. and a normal pressure system. Is performing the polymerization operation.

In the above methods (1) to (4), in the polymerization of aspartic acid using an acidic catalyst, a vacuum system and / or a normal pressure system reaction is carried out.

The following methods (5) to (9) are known as specific examples of the method for producing polysuccinimide in an organic solvent.

(5) U.S. Pat. No. 4,363,797 A method is disclosed in which aspartic acid is dehydrated and condensed at 200 to 230 ° C. in a high boiling solvent using an ion exchange resin as a catalyst. As an embodiment of this technique, for example, aspartic acid, an ion-exchange resin (trade name: Amberlite) as a catalyst, and diphenyl ether as a high-boiling solvent are charged into a container, and 230 to 240 ° C.
When the temperature is gradually increased, dehydration condensation starts at 200 ° C., and the reaction is further performed at 230 to 240 ° C. for 2 to 3 hours. Thereafter, the mixture is cooled and filtered to recover the ion exchange resin and polysuccinimide, and the ion exchange resin is filtered. There is described a method of obtaining a polysuccinimide by performing another treatment or the like.

(6) Japanese Patent Publication No. 52-8873 discloses a method for producing polyaspartic acid from aspartic anhydride hydrochloride as a raw material. Embodiments of this technique include, for example, a method of suspending hydrochloride of L-aspartic anhydride in xylene as an inert organic solvent, heating under reflux, cooling, and filtering. It is disclosed that when the reaction temperature is set to 200 ° C., a part of the raw material may be changed to polysuccinimide.

(7) JP-A-7-196796 A method is disclosed in which aspartic acid or the like is used as a raw material, the raw material is moistened with a solvent such as o-cresol, and polysuccinimide is produced in the presence of sodium hydrogen sulfate. .

(8) JP-A-8-176297 A method for producing polysuccinimide in the presence of condensed phosphoric acid in a mixed solvent of aspartic acid with an organic solvent and an aprotic polar solvent is disclosed. In particular, it is disclosed that phosphoric acid or the like is particularly preferable as a catalyst in order to obtain a polysuccinimide having a high molecular weight. The weight average molecular weight of the polysuccinimide obtained by this technique is relatively higher than those obtained by the methods (1) to (3).

(9) JP-A-9-143265 Polysuccinimide is produced from aspartic acid (aspartic acid, aspartic acid salt, salt of aspartic anhydride, etc.) in an organic solvent in the presence of a catalyst. A method for doing so is disclosed. This technique is extremely significant in that the obtained polysuccinimide has a high weight average molecular weight of 60,000 or more.

During the production of the polysuccinimide used in the present invention, a copolymer can be produced by adding an amino acid other than aspartic acid. Specific examples of amino acid components other than aspartic acid include, for example, 20 kinds of protein-constituting amino acids, L-ornithine, a series of α-amino acids, β-alanine, γ-aminobutyric acid, neutral amino acids, acidic amino acids, and acidic amino acids. Examples include ω-esters, basic amino acids, N-substituted basic amino acids, amino acids and amino acid derivatives such as aspartic acid-L-phenylalanine dimer (aspartame), and aminosulfonic acids such as L-cysteic acid. . The α-amino acid may be an optically active form (L-form, D-form) or a racemic form.

Further, a copolymer can be produced by adding a monomer component other than an amino acid. The copolymerization component is not particularly limited, but preferably contains at least two or more functional groups capable of reacting with the carboxyl group or amino group of the acidic amino acid.

The functional group capable of reacting with the carboxyl group of the acidic amino acid in the acidic amino acid reagent is not particularly limited, but may be an amino group, an alkylamino group, a hydroxyl group, a thiol group, a hydrazino group, a carbamoyl group, a sulphonamide group, or a phosphonic group. Examples include an amide group, an isocyanate group, an epoxy group, an oxazolyl group, and a carbodiimide group.

The functional group capable of reacting with the amino group of the acidic amino acid in the copolymerization reagent is not particularly limited, but may be a carboxyl group, a sulfonic group, a phosphonic group, an isocyanate group, an epoxy group, a reactive double bond. And a reactive triple bond. The reaction of these functional groups with aspartic acid or glutamic acid is not particularly limited, and any organic chemical reaction can be used. For example, dehydration condensation, addition, substitution reaction and the like can be mentioned.

Examples of the monomer components added during the production of the copolymer include aminocarboxylic acid, aminosulfonic acid, aminophosphonic acid, hydroxycarboxylic acid, mercaptocarboxylic acid, mercaptosulfonic acid, and mercaptophosphonic acid. .

Further, polyamines, polyhydric alcohols, polythiols, polycarboxylic acids, polysulfonic acids, polyphosphonic acids, polyhydrazine compounds, polycarbamoyl compounds, polysulfonamide compounds, polyvalent sulfonamide compounds, Phosphonamide compound, polyepoxy compound, polyvalent isocyanate compound, polyvalent isothiocyanate compound, polyvalent aziridine compound, polyvalent carbamate compound, polyvalent carbamic acid compound, polyvalent oxazoline compound, polyvalent unsaturated bond Compounds, polyvalent metals and the like.

[4-2] Crosslinking Reaction In the present invention, a crosslinked polysuccinimide is reacted with a polyamine compound to obtain a crosslinked polysuccinimide.
This crosslinking reaction is preferably performed in a state where the polysuccinimide is dissolved.

The polyamine compound functions as a crosslinking agent, and is not particularly limited as long as it is an organic compound having two or more amino groups. Examples of the amino group include a primary amino group and a secondary amino group, and a primary amino group having high reactivity with polysuccinimide and easily adjusting the degree of crosslinking is preferable. For the same reason, an amino group bonded to an aliphatic or aralkyl group and an amino group bonded to the aromatic ring via methylene (amino group at benzyl position) are more preferable than an amino group bonded directly to an aromatic ring. .

Specific examples of the polyamine compound include ethylenediamine, propylenediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, Aliphatic polyamines such as decamethylenediamine, dodecamethylenediamine, tetradecamethylenediamine, hexadecamethylenediamine, 1-amino-2,2-bis (aminomethyl) butane, tetraaminomethane, diethylenetriamine, triethylenetetramine, and norbornenediamine 1,4-diaminocyclohexane, 1,3,
Alicyclic polyamines such as 5-triaminocyclohexane and isophoronediamine, aromatic polyamines such as phenylenediamine, tolylenediamine and xylylenediamine, basic amino acids or their esters, and one molecule of a monoamino compound such as cystamine or And polyamines such as compounds and derivatives thereof, each of which is linked by one or more disulfide bonds. In addition, protein-constituting amino acids represented by lysine, cystine, and ornithine, and salts or esters thereof are also included.
In particular, alkylene diamines and basic amino acids are typical, and diamines having 2 to 12 carbon atoms, lysine, and ornithine are often used.

Further, specific examples of trifunctional or higher polyamine compounds (crosslinking agents) include 1,1,1-tris (2′-aminomethyl) ethane, tetrakis (2′-aminomethyl) methane, 1,1-tris (2'-aminoethyl)
Ethane, tetrakis (2'-aminoethyl) methane, 1,
1,1-tris (2′-aminopropyl) ethane, tetrakis (2′-aminopropyl) methane, 1,1,1-tris (2′-aminobutyl) ethane, tetrakis (2′-
Aminobutyl) methane, 1,2,3-tris (aminomethyl) benzene, 1,2,4-tris (aminomethyl) benzene, 1,3,5-tris (aminomethyl) benzene and the like.

Further, when the polyamine compound (crosslinking agent) is a polymer, specific examples include dipeptides having a basic amino acid at the C-terminal such as glycine-lysine, alanine-lysine, glycine-ornithine, and alanine-ornithine. , Lysine-glycine, lysine-alanine, ornithine-glycine, ornithine-alanine, lysine-lysine,
Dipeptides having a basic amino acid at the N-terminus such as ornithine-lysine, lysine-ornithine, ornithine-ornithine, glycine-glycine-lysine, glycine-lysine-glycine, glycine-glycine-ornithine, glycine-ornithine-glycine, lysine-lysine -Lysine, ornithine-ornithine-ornithine, glycine-
Glycine-glycine-lysine, glycine-ornithine-
At least one basic amino acid such as glycine-glycine is used.
One or more polypeptides.

Further, when the polyamine compound (crosslinking agent) is a polymer having a relatively high molecular weight, specific examples thereof include polylysine, polyarginine, a copolymer of lysine and arginine, and a copolymer of lysine and aspartic acid. Copolymers, copolymers of lysine and glutamic acid, copolymers of basic amino acids and other amino acids, and the like, and further include polyethyleneimine, polyallylamine, chitosan, and peptides.

In the present invention, the degree of polymerization of these polymers is not particularly limited, and may be selected in consideration of solubility in an organic solvent used in the reaction.

Among these polyamine compounds, those having biodegradability are preferable in consideration of disposal and the like. Further, those having excellent reactivity with polysuccinimide are preferable. From these points, specifically, for example, ethylenediamine, propylenediamine, 1,4-butanediamine, heptamethylenediamine, hexamethylenediamine, lysine, ornithine, cystamine and the like are preferable.

The amount of the polyvalent amine compound used is not particularly limited. However, if the degree of cross-linking is too large, the amount of water absorption of the resin decreases. Conversely, if the degree of cross-linking is too low, the resin becomes water-soluble and does not exhibit water absorption. Therefore, the amount of the polyvalent amine compound to be used is determined in accordance with the number and molecular weight of the amino group and in consideration of the degree of crosslinking. Specifically, when the number of repeating units of polysuccinimide is 100 mol, the ratio of amino groups is as follows:
0.1 to 100 mol is preferable, and 0.5 to 50 mol is more preferable.

Further, a polyvalent amine compound having an amino group having a different reactivity may be cross-linked by reacting in a stepwise manner. Examples of the case where the reaction is performed stepwise include compounds such as lysine and ornithine.
Since these have a carboxyl group at the carbon to which the amino group is bonded, the reactivity of the α-amino group is low. In addition, the presence or absence of steric hindrance, the difference between aliphatic and aromatic amines, and the like can also be used.

Here, the compound having at least two amino groups does not necessarily require that all of the amino groups have reacted with the polysuccinimide, and can exhibit substantially high water absorption and gel strength. It does not matter if the stability of can be maintained. That is, the crosslinked polyaspartic acid (salt) of the present invention includes a crosslinked structure in which two or more amines have reacted, but may include a pendant structure in which some amino groups are unreacted.

The crosslinking reaction is not particularly limited.
A method of reacting a polyvalent succinimide solution in an organic solvent with a polyamine compound (crosslinking agent) may be used. Such a method is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-22416.
No. 3 and the like.

The organic solvent used herein is generally
It is preferable to use a good solvent that can substantially dissolve each component used. Specific examples of good solvents include N, N
-Dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N, N'-dimethylimidazolidinone, dimethylsulfoxide, sulfolane and the like. Among these, N, N-dimethylformamide and N, N-dimethylacetamide, which have high solubility of polysuccinimide, are particularly preferable. These solvents may be used alone or in combination of two or more.

For the purpose of slowing down the crosslinking reaction or dispersing the raw materials or products, if necessary, a poor solvent which does not dissolve or only slightly dissolves the polysuccinimide may be added.

The poor solvent is not particularly limited, and any solvent generally used in chemical reactions can be used. For example, water, alcohols such as methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, 2-methoxyethanol, 2-ethoxyethanol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, diethanol Glycols such as propylene glycol, methyl glycosolve, glycosolves such as ethyl glycosolve, acetone, methyl ethyl ketone, ketones such as methyl isobutyl ketone,
Examples include cyclic ethers such as tetrahydrofuran and dioxane, petroleum ether, pentane, hexane, heptane, octane, cyclohexane, benzene, toluene, ethylbenzene, xylene, decalin, diphenyl ether, anisole, cresol and the like.

The concentration of the polysuccinimide in the solution containing the polysuccinimide at the time when the crosslinking reaction proceeds is not particularly limited, but is generally 0.1 to 50% by mass.
Is preferable, and 1 to 40% by mass is more preferable.

In the crosslinking reaction, a catalyst may be used if necessary. Generally, a base catalyst is used as the catalyst. As the base catalyst, the same alkali as the alkali used for neutralization described later can be used. Further, an acid catalyst may be added to slow the crosslinking reaction.

The temperature in the crosslinking reaction is not particularly limited, and may be appropriately determined in consideration of the reactivity of the crosslinking agent and the dispersion state of the polysuccinimide. Generally, 0-2
00 ° C is preferred, and 10 to 80 ° C is more preferred.

After the completion of the cross-linking reaction, the organic solvent used for the cross-linking reaction may be directly separated and proceed to the next hydrolysis step, or separated and taken out as a cross-linked polysuccinimide to proceed to the next hydrolysis step. You may proceed. The separation of the crosslinked polysuccinimide and the organic solvent may be performed according to a conventionally known method. For example, filtration, decantation, centrifugation and the like can be adopted. In some cases, the reaction product may be dried before use.

[Hydrolysis Reaction of Imide Ring] In the present invention, after a polysuccinimide is subjected to a crosslinking reaction with a polyamine compound to obtain a crosslinked polysuccinimide, it is formed without reacting with the polyamine compound. The imide ring remaining in the main chain of the crosslinked polysuccinimide is subjected to a hydrolysis reaction (ring opening reaction) to obtain a crosslinked polyaspartic acid (salt).
This hydrolysis reaction can be carried out, for example, by reacting the crosslinked polysuccinimide with an alkali or another reaction reagent.

When the hydrolysis reaction is carried out in water, the resin gels and swells as the hydrolysis proceeds, so it is efficient to carry out the reaction while controlling the degree of swelling of the gel.

The hydrolysis of the remaining imide ring of the crosslinked polysuccinimide can be easily carried out, for example, by the method described in JP-A-11-5840. That is, the hydrolysis can be performed in a mixed solution of water and a water-miscible organic solvent, in an aqueous solution of an inorganic or organic salt, or in warm water at 40 to 100 ° C. In the hydrolysis of the imide ring, gelation becomes remarkable in water and stirring becomes difficult, and in an organic solvent, precipitates aggregate and become difficult to stir, and the progress of hydrolysis becomes slow or inadequate. In some cases, the water absorption of the washed resin may decrease. On the other hand, the above method using a mixture of water and a water-miscible organic solvent can improve those points.

The water-miscible organic solvent is not particularly limited, but generally includes alcohols such as methanol, ethanol, propanol, isopropanol, butanol, 2-methoxyethanol and 2-ethoxyethanol, ethylene glycol, diethylene glycol, triethylene glycol. Glycols such as propylene glycol, dipropylene glycol, acetone, methyl ethyl ketone, ketones such as methyl isobutyl ketone, cyclic ethers such as tetrahydrofuran and dioxane, N, N-dimethylformamide, N, N-dimethylacetamide,
N-methylpyrrolidone, N, N'-dimethylimidazolidinone, dimethylsulfoxide, sulfolane and the like. Among them, methanol, ethanol, propanol, isopropanol, and butanol are preferable because the formed resin is easily dried and the solvent hardly remains in the resin after drying.

The amount of water used is preferably 1 to 10 times by mass, particularly preferably 1 to 5 times by mass of the water-absorbing resin to be produced, in order to increase the volumetric efficiency. The ratio of water to be used is generally 5% by mass or more and less than 100% by mass of the whole liquid mixture, and preferably 20 to 80% by mass.

When an inorganic or organic salt is used to hydrolyze the imide ring, the inorganic or organic salt is not particularly limited, and may be a common salt such as a neutral salt, a basic salt, or an acidic salt. Can be used. Here, when a polyvalent metal salt is used, it is preferable that the concentration is not too high, since the polyvalent metal salt is ionically crosslinked with the carboxyl group generated by hydrolysis of the imide ring and the degree of crosslinking of the formed resin is increased.

As a method of adding the salt to be used, the salt may be dissolved in water or may be formed by neutralization in water. Further, the salt generated by the crosslinking reaction can be used as it is. The concentration of the salt used is 0.01-20.
% By mass is preferable, and 0.1 to 5% by mass is more preferable.
If the concentration is too low, the effect is small, and if the concentration is too high, salt may be mixed into the product.

The reagent used for hydrolyzing the imide ring is not particularly limited, but generally, alkaline water is used. Specific examples of alkali water include sodium hydroxide, potassium hydroxide, alkali metal hydroxides such as lithium hydroxide, sodium carbonate, potassium carbonate, alkali metal carbonates such as lithium carbonate, sodium hydrogen carbonate,
Examples thereof include alkali metal bicarbonates such as potassium bicarbonate, alkali metal acetates such as sodium acetate and potassium acetate, alkali metal salts such as sodium oxalate, and alkaline water such as aqueous ammonia. Of these, sodium hydroxide and potassium hydroxide alkaline water, which are inexpensive, are preferable.

The pH of the alkali ring-opening reaction solution varies depending on the concentration of alkaline water. The reaction becomes slow and not practical.
Generally, 7.5 to 13 is preferable, and 9 to 12 is more preferable.

Further, ammonia water and various amines may be reacted with the imide ring. In this case, one having the specific structure described in the section of "[2] Structure of crosslinked polyaspartic acid (salt)" is obtained.

The temperature of the hydrolysis reaction (ring opening reaction) of the imide ring is generally 5 to 100 ° C., preferably 10 to 60 ° C. The reaction time varies depending on the reaction temperature, the reaction concentration, the amount of the crosslinking agent used, and the like, and can be adjusted according to various conditions. Specifically, it is in the range of about 1 minute to 20 hours, and although it depends on the reaction apparatus, 5 minutes to 10 hours is preferable, 5 minutes to 5 hours is more preferable, and 5 minutes to 1 hour is particularly preferable. .

[Post-treatment after the hydrolysis reaction] The post-treatment after the hydrolysis reaction is not particularly limited. For example, treatments such as neutralization, salt exchange, drying, purification, granulation, and surface cross-linking treatment may be performed as necessary. Hereinafter, the processing of neutralization and salt exchange will be particularly described. As described above, the granulation preferably has a specific particle structure in the present invention.

The neutralization treatment after the crosslinking reaction may be performed as needed. By this neutralization treatment, the carboxyl group present in the molecule of the crosslinked polyaspartic acid (salt) can be converted into a salt or a free carboxylic acid. That is, the carboxylic acid salt in the crosslinked polyaspartic acid (salt) can be changed to a free carboxylic acid by using an acid, and the free carboxylic acid in the polymer can be converted to a carboxylic acid salt by using an alkali. Can be changed.

Although the degree of neutralization is not particularly limited, generally, the ratio of carboxyl groups forming a salt is from 0 to 50 based on the total number of all carboxyl groups in the molecule of the crosslinked polyaspartic acid (salt). % Is preferable, and 0 to 30% is more preferable.

Specific examples of the acid include hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfurous acid, nitric acid, nitrous acid, and the like.
Carbonic acid, phosphoric acid, formic acid, acetic acid, propionic acid, oxalic acid,
Examples thereof include carboxylic acids such as benzoic acid, sulfonic acids such as methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, and toluenesulfonic acid, and phosphonic acids such as benzenephosphonic acid.

Specific examples of the alkali include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide; alkali metal carbonates such as sodium carbonate, potassium carbonate and lithium carbonate; sodium hydrogen carbonate; Examples include alkali metal bicarbonates such as potassium, alkali metal acetates such as sodium acetate and potassium acetate, alkali metal salts of organic carboxylic acids such as sodium oxalate, and tertiary amines such as triethylamine and triethanolamine.

When the carboxyl group present in the molecule of the crosslinked polyaspartic acid (salt) is converted into a salt by the neutralization treatment, the salt can be replaced with another type of salt, if necessary.

Specific examples of the reagent used for this salt exchange include, for example, alkali metal salts, ammonium salts, amine salts and the like. More specifically, sodium, potassium, alkali metal salts such as lithium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium,
Tetrapentylammonium, tetrahexylammonium, ethyltrimethylammonium, trimethylpropylammonium, butyltrimethylammonium, pentyltrimethylammonium, hexyltrimethylammonium, cyclohexyltrimethylammonium,
Ammonium salts such as benzyltrimethylammonium, triethylpropylammonium, triethylbutylammonium, triethylpentylammonium, triethylhexylammonium, cyclohexyltriethylammonium, benzyltriethylammonium, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine , Triethanolamine, tripropanolamine, tributanolamine, tripentanolamine, trihexanolamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine, dibenzylamine, ethylmethylamine , Methylpropylamine, spot Methylamine, methyl pentyl amine, methyl hexyl amine, methyl amine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, decylamine,
Examples thereof include amine salts such as dodecylamine and hexadecylamine.

Among these, the higher the molecular weight, the higher the molecular weight per monomer unit and the smaller the water absorption per unit mass. Therefore, the smaller the molecular weight, the better.

[5] Method for Producing Cross-Linked Polyaspartic Acid (Salt) Particles The cross-linked polyaspartic acid (salt) of the present invention is obtained by using the particles described in the column of “[3] Particle structure of cross-linked polyaspartic acid (salt)”. It preferably has a shape. To obtain such a particle structure, “[4] Crosslinked polyaspartic acid (salt)
The method can be realized by producing the crosslinked polyaspartic acid (salt) by the method described in the section of “Production method”, and particularly by hydrolyzing the remaining imide ring, and then performing the granulation method described below.

[5-1] Method for Producing Particles Having Porous Structure The method for producing particles having a porous structure is not particularly limited, and examples thereof include the following methods. (1) A method of freeze-drying a hydrogel of cross-linked polyaspartic acid (salt) obtained by hydrolyzing the imide ring of cross-linked polysuccinimide obtained by reacting polysuccinimide with a polyvalent amine compound. (2) A hydrogel of cross-linked polyaspartic acid (salt) obtained by hydrolyzing the imide ring of cross-linked polysuccinimide obtained by reacting polysuccinimide with a polyvalent amine compound,
A method of drying under reduced pressure of × 10 to 9 × 10 ⁴ Pa. (3) A water-miscible organic solvent is mixed with a water-containing gel of crosslinked polyaspartic acid (salt) obtained by hydrolyzing the imide ring of crosslinked polysuccinimide obtained by reacting polysuccinimide with a polyvalent amine compound. And drying under reduced pressure of 5 × 10 to 9 × 10 ⁴ Pa. (4) A hydrogel of cross-linked polyaspartic acid (salt) obtained by hydrolyzing the imide ring of cross-linked polysuccinimide obtained by reacting polysuccinimide with a polyvalent amine compound is immersed in a water-miscible organic solvent. , A method of drying the obtained precipitate.

Hereinafter, each of these methods will be described.

[5-1-1] Method for Freeze-Drying a Hydrogel A method for freeze-drying a hydrogel is generally to freeze the hydrogel and distill water from the frozen product under reduced pressure. Is the way. By the cavity after distilling this frozen water,
A porous structure is formed.

As the hydrogel, a hydrogel of crosslinked polyaspartic acid (salt) obtained by reacting polyaspartic acid (salt) with a polyvalent amine compound is used. For example,
The hydrogel after the cross-linking reaction described in the section of “[3] Particle structure of cross-linked polyaspartic acid (salt)” may be used as it is, or post-treatment such as neutralization and salt exchange may be performed after the cross-linking reaction. A hydrogel may be used, or a gel obtained by drying the gel and absorbing water to form a gel may be used. In particular, it is preferable to use a hydrogel after the cross-linking reaction or a hydrogel that has been subjected to post-treatment such as neutralization and salt exchange, because it has no impurities and can efficiently produce particles.

The water content of the water-containing gel of crosslinked polyaspartic acid (salt) is not particularly limited. However, a higher water content is preferable because the surface area of the porous body becomes larger, but conversely, if the water content is too high, the volumetric efficiency becomes poor or a large amount of energy used for freezing or drying is required, which is uneconomical. It is. From such a point, the water content based on the mass of the entire gel is preferably 20 to 99% by mass, and 40 to 99% by mass.
95 mass% is more preferable, and 50 to 90 mass% is particularly preferable.

The polymer content of the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, but is preferably from 1 to 80% by mass, more preferably from 5 to 60% by mass, and preferably from 10 to 60% by mass, based on the total mass of the gel. 50% by weight is particularly preferred.
The lower limits of these preferred ranges are significant in terms of volumetric efficiency, economy of energy used for freezing, and the like. The upper limit is significant in that the surface area of the porous structure is increased.

The composition of the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, but basically comprises a crosslinked polyaspartic acid (salt) and a medium that causes gelation such as water. In addition, other substances may be contained in addition to the crosslinked polyaspartic acid (salt) and water. However, if the other substance is not a solvent that can be removed by drying, it is preferable to remove as much as possible before freeze-drying. Basically, non-volatile substances cannot be removed by lyophilization,
This is because the product quality often deteriorates. However,
This does not apply if other substances can be removed after this step. Further, even if the solvent can be removed by drying, an organic solvent other than water is basically not economical when the degree of pressure reduction is high because it needs to be trapped at a low temperature.

The size of the hydrogel used for producing the porous structure particles is not particularly limited. However, in consideration of the easiness of removing water from the gel and the pulverization in the subsequent step, the size (average particle size) of the hydrogel is preferably 1 μm to 10 mm, more preferably 10 μm to 5 mm, and more preferably 50 μm to 5 μm.
3 mm is particularly preferred. The upper limits of these preferred ranges are also significant in terms of drying efficiency and drying time.

The temperature for freezing the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, and any temperature at which water freezes can be selected.

The temperature at which the hydrogel of the crosslinked polyaspartic acid (salt) is freeze-dried is not particularly limited. The pressure for freeze-drying is not particularly limited, and a pressure at which drying can be sufficiently performed may be appropriately selected. However, the freeze-drying pressure may be low, but if it is too low, the energy efficiency is industrially low. Considering such points, the freeze-drying pressure is preferably 5 × 10 to 9 × 10 ⁴ Pa, and 1 × 10 ² Pa.
１1 × 10 ⁴ Pa is more preferable, and 5 × 10 ² -9 × 10
³ Pa is particularly preferred.

[0124] If the freeze-drying alone does not provide sufficient drying, ordinary drying methods such as normal-pressure drying, ventilation drying, and reduced-pressure drying may be used in combination.

[5-1-2] The hydrated gel was mixed with 5 × 10 to 9 ×
Method of drying under reduced pressure of 10 ⁴ Pa In the method of drying a hydrogel under a reduced pressure of 5 × 10 to 9 × 10 ⁴ Pa, a liquid (mainly water) in the gel that evaporates under reduced pressure is distilled off. Forms a porous structure.

The type, composition, water content, polymer content, size, etc. of the hydrogel are the same as those described in the section of "[5-1-1] Method for freeze-drying hydrogel".

When the hydrogel is dried under reduced pressure, the pressure and temperature are important. The temperature and pressure of the drying under reduced pressure determine the size and number of pores to be formed, which affect the specific surface area. When drying under reduced pressure at high temperature and low pressure (high decompression degree),
Although the hydrated gel foams rapidly and the solvent is removed quickly, the specific surface area does not increase because the pores increase. On the other hand, if the temperature is too low and the pressure is too high, it is not preferable because the formed pores are crushed and the removal of the solvent becomes too slow.
On the other hand, if the pressure is too low, the energy efficiency becomes industrially poor.

In consideration of such points, the drying temperature under reduced pressure is preferably 10 to 200 ° C., more preferably 20 to 150 ° C., and particularly preferably 20 to 100 ° C. The pressure for drying under reduced pressure is 5 × 10 to 9 × 10 ⁴ Pa.
10 ² -1 × 10 ⁴ Pa is preferred, and 5 × 10 ² -9 × 1
0 ³ Pa is more preferred.

Further, as the reduced pressure drying step, a multi-step method in which fine holes are formed at a low temperature and a high pressure and then a higher temperature and a lower pressure can be employed. If drying is not sufficient only by drying under reduced pressure, ordinary drying methods such as normal pressure drying and ventilation drying can be used together.

[5-1-3] A method in which a water-miscible organic solvent is mixed with a water-containing gel and dried under reduced pressure of 5 × 10 to 9 × 10 ⁴ Pa. A water-miscible organic solvent is mixed with the water-containing gel, 5 × 10-9 ×
In the method of drying under a reduced pressure of 10 ⁴ Pa, a liquid (mainly an organic solvent) in a gel mixed with a water-miscible organic solvent or a slurry produced by the mixing is vaporized under reduced pressure, and the liquid (mainly After the organic solvent is distilled off, a porous structure is formed.

The difference between this method and the above-mentioned method (5-1-2) of drying the hydrogel as it is under reduced pressure of 5 × 10 to 9 × 10 ⁴ Pa is that the latter method has In contrast to water distillation, the former method is to distill off an organic solvent which is relatively easily distilled out of the gel or slurry. That is, the latter method is excellent in that it does not require the recovery of an organic solvent or the like, and the former method is excellent in that pore formation is easy.

As the hydrogel, a hydrogel of crosslinked polyaspartic acid (salt) obtained by reacting polyaspartic acid (salt) with a polyvalent amine compound is used. For example,
In the hydrogel after the crosslinking reaction described in the section of “[3] Particle structure of crosslinked polyaspartic acid (salt)”, or in the hydrogel after post-treatment such as neutralization and salt exchange after the crosslinking reaction, A water-miscible organic solvent may be mixed to form a gel or a slurry, or a dried gel may be absorbed with water to form a hydrous gel, and simultaneously mixed with a water-miscible organic solvent to form a gel or a slurry. You may.

The water content of the hydrogel of crosslinked polyaspartic acid (salt) before mixing with the water-miscible organic solvent is not particularly limited. A higher water content is preferable because the surface area of the porous body becomes larger. On the other hand, if the water content is too high, the volumetric efficiency deteriorates and a large amount of energy used for drying under reduced pressure is required, which is uneconomical.

A gel or a slurry obtained by mixing a water-miscible organic solvent contains water and an organic solvent. Here, the difference between the gel and the slurry is determined by the water absorbing ability of the crosslinked polyaspartic acid (salt) and the mixing ratio and amount of water and the organic solvent. When the water-absorbing ability of the crosslinked polyaspartic acid (salt) is high, the range of showing a gel state is wider than that of a slurry, and as for the mixing ratio of water and an organic solvent, the range of showing a gel state is higher as the mixing ratio of water is higher. wide. In addition, the smaller the amount of water and the amount of the organic solvent, the wider the range of showing a gel state than the slurry. However, these are not determined by one factor, but also by the type of other contained substances in addition to the above three factors.

The water content of the gel or slurry is not particularly limited, but may be 10 to 10 relative to the total weight of the gel or slurry.
90 mass% is preferable, 20-80 mass% is more preferable, and 30-70 mass% is especially preferable.

The water-miscible organic solvent contained in the gel or slurry preferably has a high affinity for the crosslinked polyaspartic acid (salt) and can sufficiently swell.
In addition, those which can be easily removed by drying under reduced pressure to form porous pores efficiently are preferable. Specific examples include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, 2-methoxyethanol and 2-ethoxyethanol, ethylene glycol,
Glycols such as diethylene glycol, triethylene glycol, propylene glycol and dipropylene glycol; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; and cyclic ethers such as tetrahydrofuran and dioxane. Among them, methanol, ethanol, propanol, isopropanol, and acetone are preferred because they are particularly easy to dry. Further, methanol, ethanol and acetone are more preferable. The solvent content is not particularly limited, but is preferably from 10 to 50% by mass, more preferably from 20 to 50% by mass, and more preferably from 30 to 50% by mass, based on the total mass of the gel or slurry.
~ 50 mass% is preferred. Further, not only the content but also the ratio of water to the organic solvent is important. The ratio of organic solvent / water is preferably 0.05 to 5, more preferably 0.1 to 2, and particularly preferably 0.2 to 1.

The polymer content of the gel or slurry of the crosslinked polyaspartic acid (salt) is not particularly limited, but is preferably 1 to 80% by mass, more preferably 5 to 60% by mass, based on the total mass of the gel or slurry. Preferably, 10 to 50
% By weight is particularly preferred. The lower limits of these ranges are significant in terms of volumetric efficiency and economy of energy used for drying under reduced pressure. The upper limit is significant in terms of the surface area of the porous structure and the like.

The gel or slurry may contain other substances in addition to the crosslinked polyaspartic acid (salt) and water and a water-miscible organic solvent. However, when the other substance is not a solvent that can be removed by drying, each of the above methods (5-1)
-1) As in the case of (5-1-2), it is preferable to remove as much as possible before drying under reduced pressure.

The size of the gel after mixing with the water-miscible organic solvent is not particularly limited. However, considering the ease of removal from the gel, it is preferable that the gel is not so large. For example, the size (average particle size) of the gel is 1 μm to 10 mm.
Is preferably 10 μm to 5 mm, more preferably 50 μm.
m to 3 mm are particularly preferred. The upper limits of these preferred ranges are significant in terms of drying efficiency and drying time.

When the gel or slurry is dried under reduced pressure,
The pressure and temperature are important, and this is the method described above (5-
This is the same reason as in 2-2).

The temperature for drying under reduced pressure is preferably from 10 to 200 ° C.
20 to 150 ° C is more preferable, and 20 to 100 ° C
Is particularly preferred. The pressure for drying under reduced pressure is 5 × 10-9.
× 10^FourPa, but 1 × 10^Two~ 1 × 10^FourPa is good
Better 5 × 10^Two~ 9 × 10 ^ThreePa is more preferred.

Further, as a reduced-pressure drying step, a multi-step method in which fine holes are formed at a low temperature and a high pressure and then a higher temperature and a lower pressure can be employed. Further, when water is not sufficiently dried only by drying under reduced pressure, ordinary drying methods such as normal pressure drying and ventilation drying can be used together.

[5-1-4] Method of immersing hydrated gel in water-miscible organic solvent and drying the obtained precipitate The hydrated gel is immersed in water-miscible organic solvent (reprecipitated) to obtain Particles having a porous structure can also be obtained by a method of drying the precipitate. In this method, a water-containing gel of cross-linked polyaspartic acid having absorbed water is immersed in a water-miscible organic solvent, and the water in the gel is extracted with the water-miscible organic solvent.

It is preferable that the size of the porous structure of the particles is large, the number is large, and the depth is large because the surface area of the particles is large. To obtain such a preferred porous structure, the size of the hydrogel, the water content of the gel, the content of the polymer, and the type and amount of the organic solvent used are important. In addition, this point is the same in each of the above-mentioned methods (5-1-1) to (5-1-3).

The kind of the hydrogel to be used is described in "[5-1-
1] Method for Freeze-Drying Hydrous Gel ".

The size (average particle size) of the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, but may be 1 μm.
It is preferably from 10 to 10 mm, more preferably from 10 to 5 mm, particularly preferably from 50 to 3 mm. The lower limits of these preferred ranges are significant in terms of sufficiently forming a porous structure. The upper limit is significant in suppressing problems such as poor extraction of water with an organic solvent and long time required for water extraction.

The water content of the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, but is preferably 20 to 99% by mass, more preferably 40 to 95% by mass, and more preferably 50 to 90% by mass with respect to the total mass of the gel. % By weight is particularly preferred. The lower limits of these preferred ranges are significant in preventing problems such as a small shrinkage due to extraction and the inability to form an effective porous structure. Further, the upper limit is significant in suppressing problems such as poor volumetric efficiency and a large amount of the organic solvent used for extraction, which is uneconomical.

The polymer content of the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, but is preferably 1 to 80% by mass, more preferably 5 to 60% by mass, and more preferably 50% by weight is particularly preferred.
The significance of the upper and lower limits of these preferred ranges corresponds to the significance of the lower and upper limits of the preferred range of water content described above.
If the contraction rate of the gel (here, the ratio of the volume of the polymer after contraction to the volume of the swollen gel) is large, large pores are easily formed, and the water absorption rate of the polymer increases. If the medium for swelling the gel, such as water, is increased to increase the volume, the volumetric efficiency and the amount of the solvent to be used increase, which is not industrially preferable.

The composition of the hydrogel of crosslinked polyaspartic acid (salt) is not particularly limited, but basically comprises a crosslinked polyaspartic acid (salt) and a medium that causes gelation such as water. Further, in addition to the crosslinked polyaspartic acid (salt) and water, other substances may be contained. Other substances include:
There are substances that come from the reaction system and substances that are intentionally added after the reaction.

Examples of the substance coming from the reaction system include inorganic salts generated by neutralization and the like, aspartic acid and salts derived from aspartic acid, polyaspartic acid and salts derived from polyaspartic acid, and organic solvents.

As the substance intentionally added after the reaction,
Water, an organic solvent and the like can be mentioned. The organic solvent is used for the purpose of decreasing the viscosity of the reaction mixture or increasing the shrinkage of the gel. The organic solvent used here is preferably a water-miscible organic solvent which will be described as an organic solvent used in reprecipitation. The amounts and ratios of the organic solvent and water used are not particularly limited as long as the crosslinked polymer does not precipitate. The ratio of water used is generally preferably 5 to 100% by mass,
-80 mass% is more preferable.

The organic solvent used for reprecipitation is not particularly limited as long as it is a water-miscible organic solvent. Generally, methanol,
Alcohols such as ethanol, propanol, isopropanol, butanol, 2-methoxyethanol and 2-ethoxyethanol, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc. Ketones, cyclic ethers such as tetrahydrofuran and dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N, N′-
Examples include dimethylimidazolidinone, dimethylsulfoxide, and sulfolane. Among them, alcohols and ketones having 1 to 6 carbon atoms are preferable. In particular, it is easy to dry,
From the viewpoint that no solvent remains after drying, methanol, ethanol, propanol, isopropanol and butanol are more preferred, and methanol is most preferred.

[0153] The method of mixing the organic solvent and the gel is not particularly limited. For example, a method of charging a gel in an organic solvent or a method of adding an organic solvent to a gel or a slurry may be used. However, in the method in which the gel is charged into the organic solvent, unless the gel is charged little by little, the gel may precipitate in a lump state, and stirring may be difficult. Also,
The same may occur even when the organic solvent is added to the gel or slurry.

The number of times the gel shrinks due to the mixing of the organic solvent and the gel is not particularly limited, and may be any number of times. From the second time on, the treatment may be repeated by adding water or a water-miscible organic solvent to the precipitated solid, gel, or slurry to regel or slurry. By repeating this process, it is possible to remove the inorganic salt and the like contained therein.

The polymer shrunk and precipitated by the organic solvent as described above can be subjected to post-treatment such as drying to produce a product. Post-processing such as drying will be described later.

[5-2] Method for producing flake-like particles The method for producing flake-like particles is not particularly limited. For example, the residue of crosslinked polysuccinimide obtained by reacting polysuccinimide with a polyvalent amine compound There is a method in which a hydrogel of cross-linked polyaspartic acid (salt) obtained by hydrolyzing an imide ring is sheared, cast and dried. In this method, for example, after the crosslinked polyaspartic acid (salt) is swollen with water or a water / water-miscible organic solvent, shearing is performed, or shearing is performed while mixing.

The water-miscible organic solvent can be prepared according to the method (5-1) described above.
The organic solvent described in -3) can be used, and the preferable mixing ratio of water and the organic solvent is also the same.

The device used for shearing is not particularly limited as long as it can shear a suspension containing a gel, but a device in which a stirring blade rotates at a high speed (for example, 500 to 20,000 rpm), and a blade with a blade rotates at a high speed. Yes (for example, 500-
20,000 rpm) type is preferred. More specifically, a mixer with a blade, a pipeline mixer, a homomix mixer, a disintegrator, a spike mill, a Golator pump and the like can be mentioned.

Polyaspartic acid (salt) to be cast
When the viscosity is too low, the mixture flows unnecessarily, so that it is not preferable. Those having a high viscosity are likely to entrain the gas, but in the present invention, it is preferable to form a porous structure, so this does not matter. The viscosity of the mixture is
It depends on polymer concentration, polymer molecular weight, other additives and the like.

The substrate to be used for casting is not particularly limited, but preferably a thin film (film, sheet, scale) of the resulting crosslinked polyaspartic acid (salt) is easily peeled off.
Examples of the shape of the substrate include a plate, a film, and a sheet. The material of the base material greatly affects the adhesion and peelability of the cross-linked polyaspartic acid (salt). For example, a base material made of a resin such as polypropylene, polyethylene, polyethylene terephthalate, or a fluororesin (trade name: Teflon) Is preferred.

[0161] The thickness at the time of casting is not particularly limited, but a thinner one is preferable because the water absorption rate of the obtained flaky particles becomes faster.

In the method for producing scaly particles, it is also preferable to produce scaly particles having a porous structure by forming holes by distilling off the solvent in order to make some of the particles porous. The temperature and pressure for distilling off the solvent are not particularly limited, and any method may be used as long as the holes can be efficiently formed.
The temperature at which the solvent is distilled off is preferably from 10 to 200 ° C., and from 20 to 200 ° C.
150 ° C is more preferable, and 20 to 100 ° C is particularly preferable. The pressure of the solvent distilled off, preferably 5 × 10~9 × 10 ⁴ Pa, more preferably ^{1 × 10 2 ~1 × 10 4} Pa, 5
× 10 ^{2 to} 9 × 10 ³ Pa is particularly preferred. Further, in the drying step, a multi-step method in which fine pores are formed at a low temperature and a high pressure followed by a higher temperature and a lower pressure can be employed.

[5-3] Crosslinked polyaspartic acid (salt)
Specific Surface Area of Particles The particles of the crosslinked polyaspartic acid (salt) of the present invention preferably have a specific surface area of 0.1 to 1000 m ² / g.
By having such a specific surface area, the water absorbing ability of the crosslinked polyaspartic acid (salt) is improved. Further, such a specific surface area can be favorably realized by the above-described various particle structures such as a porous structure. Furthermore, the specific surface area of the particles, more preferably from 0.1 to 10 m ² / g, particularly preferably 0.2 to 10 m ² / g. Specific conditions for measuring the specific surface area will be described in the examples section below.

[5-4] Crosslinked polyaspartic acid (salt)
Post-treatment of particles The crosslinked polyaspartic acid (salt) particles obtained by the above various granulation methods may be further dried, purified, pulverized, if necessary.
Processing such as sizing, further granulation, and surface cross-linking treatment can be performed. For example, the method for drying the crosslinked polyaspartic acid (salt) particles is not particularly limited. Specifically, hot air drying, drying with specific steam, microwave drying, drying under reduced pressure,
Various conventionally known methods such as drum dryer drying and drying by azeotropic dehydration in a hydrophobic organic solvent can be employed.

[6] Form of use of crosslinked polyaspartic acid (salt) The form of use of crosslinked polyaspartic acid (salt) is not particularly limited, and may be used alone or in combination with other materials. Is also good. However, basically, a method in which the high water absorption rate can be utilized in a bulk state is preferable.

The molded product of the crosslinked polyaspartic acid (salt) is not particularly limited, and can be used as a solid, a sheet, a film, a fiber, a nonwoven fabric, a foam, and the like. Also, the molding method is not particularly limited.

When a crosslinked polyaspartic acid (salt) is used as a composite in combination with another material, the structure of the composite is not particularly limited. For example, a method of sandwiching a pulp layer, a nonwoven fabric, or the like to form a sandwich structure The composite can be obtained by, for example, a method of forming a multilayer structure using a resin sheet or a film as a support, or a method of casting a resin sheet to form a two-layer structure. For example, if the crosslinked polymer is formed into a sheet, a water-absorbing sheet (including a water-absorbing film) can be obtained.

The crosslinked polyaspartic acid (salt) may be used by mixing with one or more other water-absorbing resins, if necessary. If necessary, an inorganic compound such as salt, colloidal silica, white carbon, ultrafine silica, titanium oxide powder, or an organic compound such as a chelating agent may be added. In addition, oxidizing agents, antioxidants, reducing agents, ultraviolet absorbers, antibacterial agents, bactericides, fungicides, fertilizers, fragrances, deodorants,
Pigments and the like may be mixed.

The crosslinked polyaspartic acid (salt) can be used as a gel or as a solid. For example, when used as a water retention material for agricultural and horticultural use, a cut flower life-promoting agent, a gel fragrance, a gel deodorant, etc., it is used as a gel, and an absorbent for disposable diapers is used as a solid.

[7] Use of Cross-Linked Polyaspartic Acid (Salt) The use of cross-linked polyaspartic acid (salt) is not particularly limited, and it can be used in any of the applications where conventional water-absorbing resins can be used.

For example, sanitary articles such as sanitary articles, disposable diapers, breast milk pads, disposable rags, dressings for protecting wounds, medical articles such as medical underpads, cataplasms,
Pet seats, portable toilets, gel air fresheners, gel deodorants, sweat absorbing fibers, household items such as disposable warmers, toiletries such as shampoos, gels for setting, moisturizers, water retention materials for agriculture and horticulture, Agricultural and horticultural supplies, food trays, etc., for life extension of cut flowers, floral foam (fixed material for cut flowers), nursery beds, hydroponic vegetation sheets, seed tapes, fluid seeding media, dew condensation prevention agricultural sheets, etc. Food packaging materials such as freshness preservation materials, drip absorbent sheets, cold insulation materials,
Transportation materials such as water-absorbent sheets for transporting fresh vegetables, building materials for preventing dew condensation, sealing materials for civil engineering and construction, anti-sedimentation agents for shield methods, concrete admixtures, civil engineering construction materials such as gaskets and packing, and electronic equipment , Sealing materials such as optical fibers, waterproofing materials for communication cables, electrical equipment related materials such as ink jet recording paper, sludge coagulants, gasoline, dehydration of oils, water treatment agents such as water removing agents, printing pastes, Water-swellable toys, artificial snow, sustained-release fertilizers, sustained-release pesticides,
Sustained-release drugs, humidity control materials, antistatic agents, and the like.

Of these, sanitary articles, disposable diapers, breast milk pads, sanitary articles such as disposable rags, dressings for protecting wounds, medical underpads, pet sheets, portable toilets that require particularly high water absorption rates Applications such as water-absorbing fibers, cold insulators, sludge coagulants, gasoline, dehydration of oils, and water treatment agents such as water removers are preferred. In particular, sanitary products such as sanitary products, disposable diapers, breast milk pads, disposable rags, medical underpads, pet sheets, portable toilets, and sludge coagulants are more preferable.

[0173]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. Hereinafter, “parts” means “parts by mass”.

(1) Measurement of weight average molecular weight Weight average molecular weight (Mw) of polyaspartic acid (salt)
Was measured by GPC (gel permeation chromatography) using polyethylene oxide as a standard. Apparatus: Shodex GPC SYSTEM-11 Detector: Shodex RI SE-61 Column: Shodex OHpak SB-804 Solvent: 0.1M-KCl aqueous solution Concentration: 0.1% Injection amount: 100 μl Flow rate: 1.0 ml / min.

(2) Measurement of Water Absorption Rate and Saturated Water Absorption The water absorption rate and the saturated water absorption were measured for distilled water and physiological saline using the tea bag method. That is, about 0.05 part of the dry water-absorbent resin in the case of distilled water and about 0.1 part of the dry water-absorbent resin in the case of physiological saline are put into a non-woven tea bag (80 mm × 50 mm), and placed at 20 ° C.
Immerse in excess distilled water or saline in
After the resin was swollen for 1 minute or 1 hour, the tea bag was pulled out and drained for 1 minute, and the mass of the tea bag containing the swollen resin was measured. In addition, assuming that the same operation was performed using only the tea bag as a blank, the value obtained by subtracting the mass of the blank and the mass of the water absorbent resin from the mass of the tea bag containing the swollen resin was divided by the mass of the water absorbent resin. This value was taken as the water absorption (g / g of resin). In this operation, the amount of water absorption when the time for swelling the resin by immersing it in an excessive amount of distilled water or physiological saline is 1 minute is expressed as the “water absorption rate” of the resin, The water absorption was expressed as the “saturated water absorption” of the resin. The physiological saline is a 0.9% by mass aqueous sodium chloride solution.

(3) Measurement of specific surface area The specific surface area of the polymer particles was determined by QUANTACHROME.
It was measured by AUTOASORB-3 manufactured by KK. Specifically, a sample which had been subjected to heating and vacuum degassing at 100 ° C. and 1 × 10 ³ Pa for 1 hour was placed in liquid nitrogen, nitrogen was evaporated, and the vapor pressure was measured. That is, the equilibrium pressure / saturated vapor pressure of the adsorption isotherm of N ₂ is determined at −196 ° C., and the BET
The specific surface area was determined by plotting.

(4) Observation of Surface Structure The surface structure of the polymer particles was measured by a scanning electron microscope (SEM).
(JSM5410-LV manufactured by JEOL Ltd.).
That is, the sample was fixed to the sample table with epoxy resin, and the acceleration voltage was 15 kV, the WD was 20 mm, and the degree of vacuum was 20 P.
a or at 40 Pa.

[Compound Production Example 1] L-aspartic acid 1
50 parts and 75 parts of 85% phosphoric acid were mixed, and the mixture was heated at 2.67 × 10 ³ Pa and 200 ° C. using a rotary evaporator.
The reaction was performed for 0 hours. The reaction mixture was dissolved in 1000 parts of dimethylformamide (DMF) and discharged into 5000 parts of water. The obtained precipitate was separated by filtration, washed with water until the washing liquid became neutral, and dried at 60 ° C. to obtain 108 parts of polysuccinimide having Mw of 106,000.

100 parts of this polysuccinimide was added to DMF
Dissolved in 200 parts, added 1.20 parts of hexamethylenediamine, stirred vigorously until gelation, and after gelation, stopped stirring and continued the reaction for 20 hours to obtain a gel of crosslinked polysuccinimide. . The gel was transferred to a mixer equipped with a blade with stirring blades, 900 parts of distilled water and 400 parts of methanol were added, and the mixture was ground at 8000 rpm for 5 minutes.

Further, 165 parts of a 25% by mass aqueous solution of caustic soda was added to the mixture of the crosslinked polysuccinimide at a pH of 165.
Was dropped so as not to exceed 12. After the dropwise addition, the mixture was further stirred for 2 hours, and then neutralized to pH 7 by adding 7% by mass aqueous hydrochloric acid. After neutralization, add 5 more methanol
By adding 00 parts, the precipitate was separated from the liquid by decantation to obtain 210 parts (145 parts of solid content) of a cross-linked sodium polyaspartate precipitate.

[Example 1] This example is an example of particles having a porous structure.

72.4 parts of a precipitate of the crosslinked sodium polyaspartate obtained in Compound Preparation Example 1 (50 in terms of solid content)
Parts), add 200 parts of distilled water and 200 parts of methanol,
This was discharged into 600 parts of methanol. The resulting precipitate was collected by suction filtration, and 500 parts of distilled water was added to gel for 5 hours. The obtained hydrogel is frozen with liquid nitrogen,
Drying at 1.33 × 10 ³ Pa gave 48 parts of crosslinked polyaspartic acid (sodium). Further, this polymer was pulverized and passed through a mesh so as to have a particle size of 100 to 500 μm to obtain particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was 2.87 m ² / g. When the particle structure was observed by SEM, it had a porous structure as shown in FIG. 1 (× 100) and FIG. 2 (× 1000). The saturated water absorption is 490 times that of distilled water and 58 times that of physiological saline.
The water absorption rate was 280 times higher for distilled water and 46 times higher for physiological saline.

[Example 2] This example is an example of particles having a porous structure.

First, a hydrogel was prepared in the same manner as in Example 1. This hydrogel was placed in a vacuum dryer, and the temperature was 20 ° C.
Foaming was performed under a reduced pressure of 1.33 × 10 ³ Pa for 5 hours. The temperature was further raised to 60 ° C. and dried at 60 ° C. for 10 hours to obtain 47 parts of crosslinked polyaspartic acid (sodium). Further, the polymer is pulverized, and
The mixture was passed through a mesh so as to have a particle size of 0 μm, thereby obtaining particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was 1.48 m ² / g. When the particle structure was observed by SEM, it had a porous structure as shown in FIG. 3 (× 100) and FIG. 4 (× 1000). The saturated water absorption is 422 times that of distilled water and 50 times that of physiological saline.
The water absorption rate was 198 times higher than that of distilled water and 40 times higher than that of physiological saline.

Example 3 This example is an example of particles having a porous structure.

72.4 parts of a precipitate of the crosslinked sodium polyaspartate obtained in Compound Preparation Example 1 (50 in terms of solid content)
Parts), add 200 parts of distilled water and 200 parts of methanol,
This was discharged into 600 parts of methanol. The resulting precipitate was collected by suction filtration, and 250 parts of water and 160 parts of methanol were added to gel for 5 hours. The obtained hydrogel was placed in a vacuum drier and foamed at 20 ° C. under a reduced pressure of 1.33 × 10 ³ Pa for 5 hours. Further, foaming was continued while the temperature was raised to 60 ° C., followed by drying at 60 ° C. for 10 hours to obtain 46 parts of crosslinked polyaspartic acid (sodium). Further, the polymer is pulverized, and
The mixture was passed through a mesh so as to have a particle size of 0 μm, thereby obtaining particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was 1.66 m ² / g. Further, when the particle structure was observed by SEM, it had a porous structure similar to that of Example 2. The saturated water absorption was 406 times higher than that of distilled water and 49 times higher than that of physiological saline, and the water absorption rate was 210 times that of distilled water and 42 times that of physiological saline. .

Example 4 This example is an example of particles having a porous structure.

72.4 parts of a precipitate of the crosslinked sodium polyaspartate obtained in Compound Preparation Example 1 (50 in terms of solid content)
) Was added with 400 parts of distilled water and gelled for 5 hours.
Next, 1000 parts of methanol was added to shrink the gel, and the liquid was separated by decantation. Further, the same operation was performed twice on the separated and obtained crosslinked sodium polyaspartate. To the obtained precipitate, 20 parts of distilled water and 20 parts of methanol were added to form a slurry, and this slurry was gradually discharged into 200 parts of methanol. The resulting precipitate was collected by suction filtration and dried at 60 ° C. to obtain 45 parts of crosslinked polyaspartic acid (sodium). Further, this polymer was pulverized and passed through a mesh so as to have a particle size of 100 to 500 μm to obtain particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was 0.384 m ² / g. When the particle structure was observed with a SEM, it had a porous structure as shown in FIG. 5 (× 100) and FIG. 6 (× 1000). The saturated water absorption is 523 times that of distilled water and 55 times that of physiological saline.
The water absorption rate was 250 times higher than that of distilled water and 44 times higher than that of physiological saline.

[Embodiment 5] This embodiment is an example of scaly particles.

Crosslinked polyasparagide obtained in compound production example 1
72.4 parts of sodium phosphate precipitate (50 in terms of solid content)
Parts), add 200 parts of distilled water and 200 parts of methanol,
This was discharged into 600 parts of methanol. The resulting precipitate
Is collected by suction filtration, and 300 parts of water and 200 parts of methanol are collected.
And put it in a mixer with a blade at 5000 rpm
Sheared for 5 minutes. The resulting slurry is mixed with polyethylene
0.5 m thick on a terephthalate (PET) resin plate
m. At 20 ° C., 1.33 × 10 ^ThreePa
And dried at 60 ° C. for 10 hours.
To obtain scaly matter. This scaly material is added to 50 parts of water
Swell for 2 hours and remove water by decantation
After that, put in 200 parts of methanol and decant
After removing the liquid, it is crosslinked by drying at 60 ° C.
44 parts of polyaspartic acid (sodium) were obtained.
Further, the polymer is pulverized to a size of 100 to 500 μm.
Make a mesh pass so that the crosslinked polyasparagine
The scaly particles of the acid (sodium) were obtained.

The saturated water absorption of these particles is as high as 337 times that of distilled water and 45 times that of physiological saline, and the water absorption rate is 268 times that of distilled water and 39 times that of physiological saline.
It was twice as fast.

[Comparative Example 1] This comparative example is an example of particles having few irregularities on the surface.

450 parts of gel (50 parts in terms of solid content) of crosslinked sodium polyaspartate obtained by hydrolysis, neutralization and decantation obtained in Compound Production Example 1 were cut into small pieces in a mixer. To obtain 49 parts of crosslinked polyaspartic acid (sodium). Further, this polymer was pulverized and passed through a mesh so as to have a particle size of 100 to 500 μm to obtain particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was as small as 0.078 m ² / g. When the particle structure was observed by SEM, as shown in FIG. 7 (× 100) and FIG. 8 (× 1000), it had a structure with few irregularities on the surface. Also,
The saturated water absorption was 322 times for distilled water and 43 times for physiological saline, but the water absorption rate was as low as 77 times for distilled water and 23 times for physiological saline.

[Comparative Example 2] 72.4 parts (50 parts in terms of solid content) of the precipitate of the crosslinked sodium polyaspartate obtained in Compound Production Example 1 were dried at 60 ° C to obtain
46 parts of crosslinked polyaspartic acid (sodium) were obtained.
Further, this polymer was pulverized and passed through a mesh so as to have a particle size of 100 to 500 μm to obtain particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was as small as 0.098 m ² / g. In addition, when the particle structure was observed by SEM, it had a structure with few irregularities on the surface as in Comparative Example 1. The saturated water absorption is 2 to distilled water.
It is not so high at 71 times and 33 times over saline,
The water absorption rate was as low as 37 times for distilled water and 20 times for physiological saline.

[Comparative Example 3] 72.4 parts (50 parts in terms of solid content) of the precipitate of the crosslinked sodium polyaspartate obtained in Compound Production Example 1 were cut into pieces in a mixer and dried at 60 ° C. 48 parts of crosslinked polyaspartic acid (sodium) were obtained. Further, this polymer was pulverized and passed through a mesh so as to have a particle size of 100 to 500 μm to obtain particles of crosslinked polyaspartic acid (sodium).

The specific surface area of the particles was as small as 0.069 m ² / g. In addition, when the particle structure was observed by SEM, it had a structure with few irregularities on the surface as in Comparative Example 1. The saturated water absorption is 822 with respect to distilled water.
The water absorption rate was 45 times higher than that of distilled water and 15 times lower than that of physiological saline.

[0203]

As described above, according to the present invention,
A crosslinked polyaspartic acid (salt) having high productivity, biodegradability, and high absorption rate, and a method for producing the same can be provided.
More specifically, according to the present invention, for example, the following effects (1) to (4) can be obtained. (1) Since the crosslinked polyaspartic acid (salt) of the present invention exhibits a very fast water absorption rate, for example, sanitary materials, etc.
It is very useful in various applications that require rapid absorption of aqueous liquids. (2) According to the method for producing a crosslinked polyaspartic acid (salt) of the present invention, a crosslinked polyaspartic acid (salt) exhibiting a very high water absorption rate can be produced by an industrially easy method. It can be applied to a wide range of applications. (3) Since the crosslinked polyaspartic acid (salt) of the present invention has high biodegradability, it can be decomposed in compost or soil, and easily decomposed by microorganisms when released into the environment. And the accumulation in the environment is prevented. (4) Since the crosslinked polyaspartic acid (salt) of the present invention exhibits a high water absorption, it is very useful for various uses that need to absorb a large amount of aqueous liquid.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph (×) of the particles obtained in Example 1.
100).

FIG. 2 is a scanning electron micrograph (×) of the particles obtained in Example 1.
1000).

FIG. 3 is a scanning electron micrograph (×) of the particles obtained in Example 2.
100).

FIG. 4 is a scanning electron micrograph (×) of the particles obtained in Example 2.
1000).

FIG. 5 is a scanning electron micrograph (×) of the particles obtained in Example 4.
100).

FIG. 6 is a scanning electron micrograph (×) of the particles obtained in Example 4.
1000).

FIG. 7 is a scanning electron micrograph (×) of the particles obtained in Comparative Example 1.
100).

FIG. 8 is a scanning electron micrograph (×) of the particles obtained in Comparative Example 1.
1000).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // A61F 13/53 A61F 13/18 307A A61L 15/60 F term (Reference) 4C003 AA24 4G066 AB06D AC27B AC35B AD10B AE20B BA01 BA26 BA36 CA43 DA11 EA05 FA11 4J001 DA10 DB01 DB09 DC12 DD10 EA36 EE27C EE44B FA03 FC03 GD08 GE04 JA20 JB17 JB50 JC02 JC03 4J043 PA15 PC076 PC166 PC186 QB06 RA34 SA05 SA62 SB01 UA761 YB12 XA YB12 XA YB13

Claims (15)

[Claims] 1. An amount of water absorption in physiological saline for one minute, which is obtained by hydrolyzing an imide ring of a crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound and measured by a tea bag method. Is 30 to 150 times the weight of the polymer, crosslinked polyaspartic acid (salt). 2. The water absorption of distilled water in one minute as measured by a tea bag method, obtained by hydrolyzing an imide ring of a crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound. 1 of polymer's own weight
A crosslinked polyaspartic acid (salt) that is 00 to 1500 times. 3. The crosslinked polyaspartic acid (salt) according to claim 1, wherein the specific surface area is 0.1 to 1000 m ² / g. 4. The crosslinked polyaspartic acid (salt) according to claim 1, which has a porous structure. 5. The crosslinked polyaspartic acid (salt) according to claim 1, which is scaly in shape. 6. The crosslinked polyaspartic acid (salt) according to claim 1, wherein the polyvalent amine compound is an alkylenediamine or a basic amino acid. 7. The crosslinked polyaspartic acid (salt) according to claim 1, wherein the polyvalent amine compound is a diamine having 2 to 12 carbon atoms, lysine or ornithine. 8. The polymer according to claim 1, wherein the amount of water absorbed in physiological saline for one hour is from 30 to 200 as measured by the tea bag method.
The crosslinked polyaspartic acid (salt) according to any one of claims 1 to 7, which is twice as large. 9. The water absorption of distilled water in one hour measured by a tea bag method is 200 to 2,000.
The crosslinked polyaspartic acid (salt) according to any one of claims 1 to 8, which is twice as large. 10. A method for producing a crosslinked polyaspartic acid (salt) according to claim 1 or 2, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound. Producing a crosslinked polyaspartic acid (salt) by immersing a hydrogel of crosslinked polyaspartic acid (salt) obtained by hydrolyzing the product in a water-miscible organic solvent and drying the resulting precipitate. Method. 11. The method for producing a crosslinked polyaspartic acid (salt) according to claim 10, wherein the water-miscible organic solvent is an alcohol or ketone having 1 to 6 carbon atoms. 12. The method for producing a crosslinked polyaspartic acid (salt) according to claim 11, wherein the water-miscible organic solvent is methanol. 13. The method for producing a crosslinked polyaspartic acid (salt) according to claim 1 or 2, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyamine compound. A method for producing a cross-linked polyaspartic acid (salt), comprising freeze-drying a hydrogel of cross-linked polyaspartic acid (salt) obtained by hydrolyzing the product. 14. A method for producing a crosslinked polyaspartic acid (salt) according to claim 1 or 2, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound. Hydrogel of crosslinked polyaspartic acid (salt) obtained by hydrolysis of
A method for producing a crosslinked polyaspartic acid (salt), characterized by drying under reduced pressure of up to 9 × 10 ⁴ Pa. 15. A method for producing a crosslinked polyaspartic acid (salt) according to claim 1 or 2, wherein the imide ring of the crosslinked polysuccinimide obtained by reacting a polysuccinimide with a polyvalent amine compound. A water-miscible organic solvent is mixed with a water-containing gel of crosslinked polyaspartic acid (salt) obtained by hydrolyzing the product, and the mixture is dried under reduced pressure of 5 × 10 to 9 × 10 ⁴ Pa. A method for producing aspartic acid (salt).