JPS63199205A - Production of highly water absorbing polymer - Google Patents

Abstract

PURPOSE:To obtain a polymer having high water absorption properties, high strength of gel having absorbed water and excellent water absorption rate, by crosslinking a hydrophilic polymer containing a carboxyl group or carboxylate group with an amino group-containing polyfunctional epoxy compound. CONSTITUTION:A hydrophilic polymer containing carboxyl group and/or carboxylate group (preferably hydrous polymer having 40-70wt.% water content) is crosslinked with an amino group-containing polyfunctional epoxy compound (preferably compound containing one or more amino groups and 2-10 epoxy groups) to give the aimed polymer. An epoxy compound, for example, obtained by reacting a polyglycidyl compound with a low-molecular-weight amine is preferable as the epoxy compound and the amount of the epoxy compound used is preferably 0.5-5wt.% based on the hydrophilic polymer ordinarily. The polymer is widely used as body fluids absorbing agents, water retaining agent for soil, coating agent for seed, water stopping agent, condensation preventing agent, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a body fluid absorbent for sanitary napkins, disposable diapers, etc.
It is an absorbent polymer that has a wide range of uses such as soil water retention agents, seed coating agents, water stopping agents, and dew prevention agents.It has particularly high water absorption properties, has high absorbed gel strength, and has excellent water absorption speed. The present invention relates to a method for producing a polymer.

[Conventional technology]

Water-absorbing materials such as water-absorbing polymers made of hydrophilic polymers having carboxyl groups and carboxylate groups have been proposed as an alternative to paper, pulp, etc., which have been conventionally used as water-absorbing materials in the fields of sanitary materials and agriculture and horticulture. It's here. In addition, various improvements have been made to further improve the water absorption performance of these polymers. For example, in order to improve the wettability of water-absorbing polymers, when producing water-absorbing resins by polymerizing vinyl monomers by reverse-phase suspension polymerization or emulsion polymerization, water-soluble polymers (JP 57-167307) or A method of adding a surfactant (JP-A No. 58-32641) has been used. However, the performance of the polymer obtained by these methods as a water absorbing agent is still insufficient.

On the other hand, in order to improve the water absorption rate, a hydrophilic polymer having a carboxyl group (or carboxylate group) is adjusted to have a water content of 10 to 40% by weight, and then reacted with the carboxyl group (or carboxylate group). A method of crosslinking with a polyglycidyl ether, especially a polyglycidyl ether (
JP-A No. 59-62665) has been proposed. In this method, crosslinking is performed in a state in which the water content of the polymer is reduced so that the crosslinking agent does not reach inside the polymer, that is, in a semi-precipitated state of the polymer or in a state in which only the surface layer absorbs a small amount of water. It is assumed that performance is improved by increasing the crosslinking density of the polymer, that is, performing surface crosslinking, but since polymerization is usually carried out in an aqueous solution with a water content of 55% by weight or more, after polymerization, the water content is reduced to 55% by weight. Polymers containing more than a certain amount have the disadvantage that a complicated step of dehydration is required prior to crosslinking treatment. Furthermore, if the water content is too low and the polymer is in a completely precipitated state or in a solid state that has not absorbed water, the efficiency of the reaction of the crosslinking agent with the carboxyl group is extremely low, and the crosslinking effect is small. The problem is that the water content must be controlled within a narrow range of 15-35% in order to be effective. Furthermore, the reactivity of the crosslinking agent toward carboxyl groups is significantly affected by the water content, so even if the water content is within this range, the properties of the product are difficult to stabilize.

Regarding water absorption performance, although the water absorption rate and gel strength are improved, the water absorption performance is still insufficient when used for sanitary materials.

In addition, JP-A-59-189103 proposes a technique for surface crosslinking of water-absorbing resin powder using a polyvalent glycidyl ether compound, a polyvalent aziridine compound, or a polyvalent amine compound as a crosslinking agent. If the water content is such that the resin exhibits a powdery state, the reactivity of the crosslinking agent is low, there is a risk that a large amount of the crosslinking agent remains, and the improvement in water absorption is still insufficient.

[Problem that the invention seeks to solve]

Therefore, an object of the present invention is to provide a method for producing a water-absorbing polymer that has higher water absorption than conventional water-absorbing polymers and has superior water-absorbing gel strength.

[Means for solving problems]

The present invention involves producing a wood-philic polymer having a carboxyl group and/or a carboxylate group as an anion group in the molecule, and then using a crosslinking agent having an amino group and an epoxy group of divalent or higher valence in the molecule to surface the polymer. When crosslinking is performed, the amino groups in the functional groups have an ionic affinity with the anionic groups in the hydrophilic polymer, so when a crosslinking agent is added, the hydrophilic The crosslinking agent is trapped in the surface layer of the polymer and does not penetrate inside.
Since cross-linking occurs in the surface layer with polyvalent epoxy groups, it is possible to easily produce a water-absorbing polymer with a high cross-linking density on the surface of the wood-philic polymer particles, and the resulting polymer has an extremely high water absorption capacity. This was done based on the knowledge that the strength is also extremely high.

That is, the present invention provides a method for producing a superabsorbent polymer, which is characterized in that a hydrophilic polymer having a carboxyl group and/or a carboxylate group is crosslinked with a polyepoxy compound having an amino group.

The hydrophilic polymer to be used in the present invention may be any type of polymer and any polymerization method as long as it has a carboxyl group and/or a carboxylate group in its constituent units. For example, acrylic acid, methacrylic acid, which is a vinyl monomer having a carboxyl group or a carboxylate group,
Polymers obtained by polymerizing maleic acid, itaconic acid, and their salts singly or in combination, and other components such as acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, vinyl acetate, 2-hydroxyethyl methacrylate, etc. Hydrophilic copolymers copolymerized to an extent that does not reduce the effects of the present invention, starch-acrylic acid graft copolymers and salts thereof, saponified starch-acrylonitrile graft copolymers, carboxymethylcellulose, polyvinyl alcohol-acrylic Examples include acid copolymers and salts thereof. Also included are those in which a small amount of crosslinking agent is added during production or after polymerization to the extent that the effects of the present invention are not reduced, and self-crosslinking types.

Incidentally, the above-mentioned salts include sodium salts, potassium salts, ammonium salts, and the like. Further, a part of the carboxyl groups in the molecule may be carboxylate.

These wood-philic polymers are synthesized by known polymerization methods such as solution polymerization, reverse-phase suspension, and turbidity polymerization. Polymers obtained by turbidity polymerization are preferred. Particularly preferred is a porous polymer obtained by polymerizing to form O/-W/O type ethylamine in which a phase containing the monomer is arranged as an intermediate phase.

Specifically, first, a water-soluble surfactant or a water-soluble polymeric dispersant, such as partially saponified polyvinyl alcohol, is used, and the inner phase is a hydrophobic phase such as cyclohexane, and the outer phase is a carboxyl compound such as a neutralized acrylic acid. After preparing an O/W emulsion, which is an aqueous phase containing a monomer having a carboxylate group and a polymerization initiator such as ammonium persulfate, this emulsion is treated with an oil-soluble surfactant such as ethyl cellulose, or an oil-soluble polymer fraction. It is a porous polymer with many pores in the particles obtained by adding it to a hydrophobic dispersion medium such as cyclohexane containing a monomer to make an O/W10 emulsion and polymerizing the monomer. Since it is large, the effect of the present invention can be exhibited most effectively.

When performing crosslinking on the surface of the wood-philic polymer particles according to the present invention, the water content of the wood-philic polymer may be any amount;
Preferably 1.0% to 90%, more preferably 40% to
It is 70%. When the water content of the wood-philic polymer is within the above range, particularly the water absorption amount and the strength of the water-absorbing gel will be excellent. This is because in the present invention, a polyvalent epoxy compound having an amino group that has an ionic affinity with a carboxyl group or a carboxylate group is used as a crosslinking agent. In other words, when crosslinking is carried out by bringing the crosslinking agent into contact with the wood-philic polymer, if the moisture content of the wood-philic polymer is within the above range, the cross-linking agent will efficiently interact with carboxyl groups or carboxylate groups on the surface of the wood-philic polymer. It is presumed that because the polymer particles are well bonded and crosslinked, the surface of the polymer particles has a high crosslinking density and an absorbent with excellent performance can be obtained. Therefore, in the present invention, after polymerizing a hydrophilic polymer by reverse phase suspension polymerization, surface crosslinking can be performed immediately without removing water. Note that if the water content is far outside the above range, and the water content is too low, the effect will decrease; on the other hand, if the water content is too high, crosslinking will proceed, but it will take time and effort to remove the water in the subsequent drying process. It's too impractical.

The crosslinking agent used in the present invention may be any polyvalent epoxy compound containing an amino group in the molecule, but a compound having at least one amino group and 2.10 epoxy groups in the molecule may be used. preferable. Amino groups are primary, secondary,
Either a tertiary or quaternary ammonium salt may be used. Examples of such compounds include compounds obtained by reacting polyvalent epoxy compounds and amines. Particularly preferred are compounds obtained by reacting a polyglycidyl compound with a low molecular weight amine. Examples of polyglycidyl compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerol polyglycidyl ether, trimethylol propane polyglycidyl ether, ethylene glycol polyglycidyl ether, polyethylene glycol polyglycidyl ether, and bisphenol A. Examples include those having two or more epoxy groups in the molecule, such as type epoxy resins. Examples of low molecular weight amines include primary or secondary amines such as methylamine, dimethylamine, monoethanolamine, jetanolamine, ethylamine, diethylamine, and ethylenediamine, and imidazoles such as 2-methylimidazole. Since tertiary amines promote polymerization of epoxy groups, primary or secondary amines are preferred from the viewpoint of viscosity after reaction.

In order to obtain the crosslinking agent used in the present invention, both the polyglycidyl compound and the amine may be mixed and heated if necessary. Amine is added almost quantitatively to the epoxy group of the polyglycidyl ether, the epoxy group disappears, and an amino group is generated. The amine to be reacted with the divalent epoxy compound must have two or more active hydrogens in one molecule, and primary amines are suitable.

For the polyvalent epoxy compound, any of primary amines, secondary amines, both primary and secondary amino groups, or amines having a large number of groups may be used.

The mixing ratio should be determined based on the number of epoxy groups per molecule of polyglycidyl ether (average value) and the number of active hydrogens of the amine, so that the crosslinking agent as a reactant has two or more epoxy groups per molecule. Although it differs depending on the type of both types and because there is a distribution in the number of epoxy functional groups in the polyglycidyl compound, it is preferably 0.05 to 00 g as active hydrogen of the amine per epoxy equivalent of the polyglycidyl compound.
It is appropriate to use an equivalent amount. More preferably 0.1-0
．． It is preferable to use 7 equivalents. Incidentally, the reaction is preferably carried out at 40°C to 90°C for several minutes to about 2 hours. If the reaction time is long, some polymers will mix and the epoxy content will decrease, but a solvent such as water may be added to an extent that does not interfere with the effect of the crosslinking agent.
After the reaction, hydrochloric acid or the like may be added to an extent that does not reduce the epoxy group to form an amine salt. In the present invention, in addition to the above-mentioned compounds, polyepoxy compounds disclosed in JP-A-60-199010 can be used. That is, after reacting an imidazole with a halomethyloxirane compound such as epichlorohydrin, a jepoxy compound is obtained by an alkali treatment. In addition, it is also used as a component of epoxy resin.

In the present invention, the amount of the crosslinking agent used for surface crosslinking is arbitrary, but it is usually 0.01 to
10%, preferably 0.05-5%. That is,
If the amount of the crosslinking agent added is less than 0.01%, sufficient effects will not be achieved, while if it is more than 10%, the amount of water absorption tends to decrease, which is not preferable.

There are various methods for obtaining a water-absorbing polymer by reacting a hydrophilic polymer with the above-mentioned crosslinking agent. In the case of a hydrophilic polymer obtained by reverse phase suspension polymerization or a porous hydrophilic polymer obtained by suspension polymerization using a ○/W/○ emulsion,
Since the water content during polymerization is usually about 55% by weight or more, the crosslinking agent of the present invention may be added, further heated at 40° C. or higher to effect crosslinking, and then dried using a known drying method.

In the case of thin film polymerization using solution polymerization, the resulting polymer gel is crushed, a crosslinking agent is added, heat treatment is performed, and then drying is performed. In addition, it can be used after being subjected to pulverization and granulation treatment if necessary.

〔Effect of the invention〕

According to the present invention, it is possible to produce a superabsorbent polymer that is highly water absorbent, has a high gel strength after absorbing water, and has an excellent water absorption rate.

Therefore, it can be suitably used as a water-absorbing agent for sanitary materials such as disposable diapers and sanitary napkins that need to quickly absorb large amounts of urine and blood, as well as water-retaining agents for agriculture and horticulture, water-stopping agents for civil engineering and construction, and the like.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto.

[Example 1] In actual ARPI, water absorption amount, water absorption rate, and strength of water absorption gel were measured as follows.

Water Absorption Amount 0.3 g of water-absorbent resin was sealed in a non-woven fabric bag, and the bag was held horizontally so that the sample was evenly sprinkled on it. Next, the sample was immersed horizontally in a petri dish containing 300 g of physiological saline for 10 minutes, then pulled out and drained on a wire mesh for 1 minute, and its weight was measured. On the other hand, the weight obtained by testing a non-woven bag that does not contain water absorbent resin in the same manner is used as a blank, and the value obtained by subtracting the blank from the above measurement value and converting it to the weight per 1 g of water absorbent resin. was taken as the water absorption amount. The larger the number, the higher the water absorption.

Polymer 0.3 in a paper tea bag type bag with an initial water absorption rate of 5 x 3 cm
g, the bag was stood up, and the bottom was lightly stuffed with polymer.

This was immersed in physiological saline in a 30 (ltf!) beaker for 1 minute with the bag upright. After immersion for 1 minute, the water was drained off and the weight was measured. From this value, the amount of water absorbed by the tare was subtracted. The amount of water absorbed was converted to the amount of water absorbed per gram of polymer.

Measurement of Gel Strength 2 g of a water absorbent resin was placed in a 100-mm beaker, and 2 g of methanol was added to sufficiently wet the water absorbent resin. 40 g of ion-exchanged water was added to the mixture at once, and the mixture was shaken to avoid clumping, and the mixture was uniformly absorbed to prepare a sample. Next, using a rheometer (manufactured by Fudo Kogyo, NRM-2002J), this sample was raised at a rate of 2ca+/min, and the stress was measured 10 seconds after the adapter (Φ10 mm, on a disc) and the gel surface came into contact. This was taken as the gel strength. The larger this value is, the stronger the water-absorbing gel is.

Example 1 In 11 four-bottle flasks equipped with a stirrer, reflux condenser, dropping funnel and nitrogen gas inlet tube, 300 g of cyclohexane was added.
0 g and 3 g of ethyl cellulose (manufactured by Vercules, trade name N-50) were added, stirred, nitrogen gas was blown in to drive out dissolved oxygen, and the temperature was raised to 70°C. In addition, in another flask, 43 g of sodium hydroxide was dissolved in 130 g of water, and 100 g of acrylic acid (AA) was added to the resulting aqueous solution. 1.2 g of GH-17 (manufactured by Co., Ltd., trade name) and 122 mg of ethylene glycol diglycidyl ether (EGDG) were dissolved in 34 g of water, and then 80 g of cyclohexane was added and stirred. Nitrogen gas was blown in to drive out dissolved oxygen. A monomer aqueous solution (0/W emulsion) was prepared (7mer concentration: 40% vs. aqueous phase). Next, while thoroughly stirring the dispersion medium in the four-loaf flask at a speed of 40 Orpm,
W emulsion was added dropwise over 1 hour, and polymerization was continued for a further 3 hours.

On the other hand, 40m1! In a sample bottle, add sorbitol polyglycidyl ether (epoxy equivalent: 180, average epoxy groups in the molecule: 3.6: Denacol 61 manufactured by Nagase Chemical Industries, Ltd.).
4B) 6.14 g and jetanolamine 1.08 g were added, stirred, mixed and reacted at 80°C for 30 minutes,
Cool to room temperature, add 22.78g of water, and add crosslinking agent solution (
1) was prepared.

3 g of solution (I) was added to the above polymerized wood-philic polymer slurry (polymer water content 60%) and heated at an external temperature of 80° C. for 2 hours to cause surface crosslinking.

After that, the dispersion medium was removed using a decanter and heated to 110°C.
The polymer was dried for 4 hours to obtain a porous water-absorbing polymer with an average particle size of 200 μm.

The crosslinking agent solution (I) is a compound obtained by reacting 0,630 equivalents of amine per equivalent of epoxy, and has an average of 1.1 amino groups in the molecule.

Example 2 In a four-necked flask similar to Example 1, cyclohexane 3
00g! : 3 g of ethyl cellulose (manufactured by Harkiniless, trade name N-50) was added, stirred, nitrogen gas was blown in to drive out dissolved oxygen, and the temperature was raised to 70°C. In addition, in another flask, 43 g of sodium hydroxide was dissolved in 130 g of water, and 100 g of acrylic acid (AA) was added to the resulting aqueous solution, and 0.16 g of ammonium persulfate (APS) was added.
g, ethylene glycol diglycidyl ether (EGD
G) Add 61 mg and blow nitrogen gas to drive out dissolved oxygen to prepare a monomer aqueous solution. Monomer concentration 4
5%).

Next, the monomer aqueous solution was added dropwise over 1 hour while thoroughly stirring the dispersion medium in the four-hole flask at a speed of 40° rpm, and the mixture was further polymerized for 3 hours.

On the other hand, 4.91 g of polyglycerol polyglycidyl ether (epoxy equivalent: 183, average 56.3 epoxies in molecule: Denacol 521 manufactured by Nagase Chemical Industries) and 0.0 g of monoethanolamine were placed in a 40 rnl sample pin.
14 g was added, stirred and mixed, and the viscosity became high after 5 minutes of reaction at 60°C, so 2 g of water was added and the mixture was stirred and mixed.
The reaction was carried out at ℃ for 155 minutes. Next, cool to room temperature and add 22.
95 g was added to prepare a crosslinking agent solution (n).

3 g of solution (II) was added to the above polymerized hydrophilic polymer slurry (polymer water content 55%) and heated at an external temperature of 80° C. for 2 hours to cause surface crosslinking.

Thereafter, the dispersion medium was removed by decantation, and the mixture was dried at 110° C. for 4 hours to obtain a polymer having an average particle size of 150 μm.

In addition, the crosslinking agent solution (n) contains 0 amine per epoxy equivalent.
．． 16 equivalents were reacted, and the compound has an average of 1.0 amino groups in the molecule.

Example 3 43g of sodium hydroxide was added to 208g of water in an Erlenmeyer flask.
0.3 g of ammonium persulfate (APS) is added to an aqueous solution prepared by adding 100 g of acrylic acid (AA) to this solution.
, ethylene glycol diglycidyl ether (EGDG)
) was added and nitrogen gas was blown in to drive out the dissolved oxygen to prepare a monomer aqueous solution (monomer concentration 35%).
).

This aqueous monomer solution was poured onto a Teflon plate, formed into a thin film, and held at 120° C. for 1 hour to polymerize.

The rubbery polymer gel produced was cut into pieces of about 2 ma+.

Meanwhile, in a 40 ml sample bottle, sorbitol polyglycidyl ether (Denacol 614B manufactured by Nagase Chemical Industries, Ltd.)
)? 7 g of J and 1.31 g of diethylamine were added, mixed with stirring, and reacted at 50° C. for 1 hour, cooled to room temperature, and 21.32 g of water was added to prepare a crosslinking agent solution (I).

Polymer gel after the above polymerization (polymer water content 65%)
3 g 1 liter of solution (I [I) was sprayed onto the solution, and the mixture was heated at 80° C. for 3 hours to cause surface crosslinking. Thereafter, it was further dried at 110° C. for 4 hours to destroy the polymer particles having an average particle size of 2.

The crosslinking agent solution (III) is a compound obtained by reacting 0.44 equivalents of amine per equivalent of epoxy, and has an average of 1.6 amino groups in the molecule.

Comparative Example 1 Polymerization was carried out according to Example 1. However, crosslinking agent solution (1
) instead of sorbitol polyglycidyl X--f (
A solution of 0.614 g of Te+:)-l 514 B) in 3 g of water was added to the polymer slurry after polymerization, and the same treatment as in Example 1 was carried out.

Comparative Example 2 Polymerization was carried out according to Example 2. However, the crosslinking agent solution (I
Instead of I), 0.491 g of polyglycerol polyglycidyl ether (Bunacol 521) dissolved in 3 g of water was added to the polymer slurry after polymerization, and the same treatment as in Example 2 was carried out.

Comparative Example 3 Polymerization was carried out according to Example 3. However, the crosslinking agent solution (I
) The same treatment as in Example 3 was carried out, except that instead of spraying 0.74 g of sorbitol polyglycidyl ether (Bunacol 614B) dissolved in 3 g of water.

The performances of the water-absorbing polymers produced in Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1.

Table 1 From the results in Table 1, it can be seen that when surface crosslinking of a wood-philic polymer is performed using a crosslinking agent that has an amino group and an epoxy group in the molecule, compared to when an epoxy compound that does not have an amino group is used. It can be seen that a water-absorbing polymer having a high water absorption amount, a fast water absorption rate, and excellent strength of a water-absorbing gel can be obtained.

Claims (2)

[Claims] (1) A method for producing a superabsorbent polymer, which comprises crosslinking a hydrophilic polymer having a carboxyl group and/or a carboxylate group with a polyepoxy compound having an amino group. (2) The manufacturing method according to claim (1), wherein the hydrophilic polymer is a water-containing polymer and has a water content of 40 to 70% by weight.