CN107406542B - Method for producing aqueous liquid absorbent resin - Google Patents
Method for producing aqueous liquid absorbent resin Download PDFInfo
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- CN107406542B CN107406542B CN201680014571.8A CN201680014571A CN107406542B CN 107406542 B CN107406542 B CN 107406542B CN 201680014571 A CN201680014571 A CN 201680014571A CN 107406542 B CN107406542 B CN 107406542B
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/30—Processes for preparing, regenerating, or reactivating
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/44—Polymerisation in the presence of compounding ingredients, e.g. plasticisers, dyestuffs, fillers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
- C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
- C08F20/04—Acids, Metal salts or ammonium salts thereof
- C08F20/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F8/00—Chemical modification by after-treatment
- C08F8/44—Preparation of metal salts or ammonium salts
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
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Abstract
The invention provides a method for producing an aqueous liquid absorbent resin having a large water retention capacity and little coloration and odor. The present invention is a process for producing an aqueous liquid absorbent resin, comprising the step of radically polymerizing a radically polymerizable monomer (a) containing acrylic acid as a main component in the presence of an internal crosslinking agent (b) and water, characterized in that the radical polymerization is carried out in the presence of hypophosphorous acid (salt) (c), the upper limit of the charge concentration of the monomer (a) is less than 30% by weight based on the weight of the polymerization liquid, and the maximum reaching temperature of the polymerization liquid at the time of polymerization is lower than the boiling point thereof.
Description
Technical Field
The present invention relates to a method for producing a resin having excellent water-based liquid absorption performance. More specifically, the present invention relates to a method for producing an aqueous liquid absorbent resin having a high water retention and little odor and coloring.
Background
Conventionally, as a particulate absorbent having an ability to absorb an aqueous liquid, a hydrophilic crosslinked polymer called a water-absorbent resin has been used, and the application range thereof is expanded to various industrial fields such as sanitary products such as paper diapers and sanitary products, a dewing preventive, and a water retention agent for agriculture and horticulture. The aqueous liquid absorbent resin for these uses is expected to have a high water retention.
In general, the water absorption capacity (water retention capacity) of an aqueous liquid absorbent resin under normal pressure is conceptually proportional to "(ionic osmotic pressure + affinity of polymer chains for water)/crosslink density of the polymer". That is, the properties of the aqueous liquid absorbent resin are correlated with the crosslink density. As a method for increasing the water retention amount, a method of reducing the amount of the crosslinking agent is generally carried out, and the following methods are further proposed: when aqueous solution polymerization is performed on an aqueous monomer solution containing a radical polymerizable monomer and a crosslinking agent, a chain transfer agent is allowed to coexist (see, for example, patent document 1).
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 3-179008
Disclosure of Invention
Problems to be solved by the invention
However, although the conventional method using a chain transfer agent has a certain effect in terms of improvement in water retention, further improvement in performance is desired. In addition, the conventional method using a chain transfer agent has a problem that the resulting aqueous liquid absorbent resin particles are likely to be odorous and colored. The cause of this odor and coloration is not determined, and is believed to be derived from the residue of the chain transfer agent incorporated into the polymer chain and the low molecular weight components that increase with the use of the chain transfer agent. In particular, in the use for sanitary goods such as disposable diapers, there is a demand for an aqueous liquid absorbent resin which is further improved in absorption performance and is less likely to cause odor and coloring from the viewpoint of safety and clean feeling.
Means for solving the problems
The present inventors have intensively studied to solve the above problems and as a result, have found that an aqueous liquid absorbent resin having a high water retention and little odor and coloring can be obtained by carrying out polymerization under specific conditions in the presence of a specific chain transfer agent. That is, the present invention is a method for producing an aqueous liquid absorbent resin, comprising a step of radical-polymerizing a radical-polymerizable monomer (a) containing acrylic acid as a main component in the presence of an internal crosslinking agent (b) and water, wherein the radical polymerization is carried out in the presence of hypophosphorous acid (salt) (c), the upper limit of the charge concentration of the monomer (a) is less than 30% by weight based on the weight of the polymerization liquid, and the maximum temperature of the polymerization liquid at the time of polymerization is low and the boiling point thereof is low.
Effects of the invention
The aqueous liquid absorbent resin obtained by the production method of the present invention has a high water retention capacity and is less likely to cause odor and coloring.
Detailed Description
The process for producing an aqueous liquid absorbent resin comprises a step of radical-polymerizing a radical-polymerizable monomer (a) containing acrylic acid as a main component in the presence of an internal crosslinking agent (b) and water, wherein the radical polymerization is carried out in the presence of hypophosphorous acid (salt) (c), the upper limit of the charge concentration of the monomer (a) is less than 30% by weight based on the weight of the polymerization solution, and the maximum reaching temperature of the polymerization solution during polymerization is lower than the boiling point thereof.
The radically polymerizable monomer (a) (hereinafter also simply referred to as the monomer (a)) used in the production method of the present invention contains acrylic acid as a main component. In order to improve the absorption characteristics of the aqueous liquid absorbent resin, the acrylic acid content in the monomer (a) is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, and particularly preferably 90 to 100 mol%.
The monomer (a) may contain a monomer other than acrylic acid as required. The monomer other than acrylic acid is not particularly limited, and specific examples thereof include acrylic acid salts such as sodium acrylate, potassium acrylate, and ammonium acrylate; acid group-containing monomers such as methacrylic acid, maleic acid (anhydride), itaconic acid, cinnamic acid, allyltoluenesulfonic acid, vinyltoluenesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2-hydroxyethyl (meth) acryloylphosphate, vinylsulfonic acid, styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, and 2- (meth) acryloylpropanesulfonic acid, and salts thereof; an unsaturated monomer containing a thiol group; a phenolic hydroxyl group-containing unsaturated monomer; nonionic hydrophilic group-containing unsaturated monomers such as (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine and N-vinylacetamide; and cationic unsaturated monomers such as N, N-dimethylaminoethyl (meth) acrylate, N-diethylaminoethyl (meth) acrylate, N-dimethylaminopropyl (meth) acrylate, and N, N-dimethylaminopropyl (meth) acrylamide, and salts thereof. These monomers may be used alone, or 2 or more of them may be used in combination.
In the present invention, when a monomer other than acrylic acid is used, the amount thereof is preferably 30 mol% or less, more preferably 20 mol% or less, and particularly preferably 10 mol% or less, based on the total number of moles of the monomer (a). By using the monomer other than acrylic acid in the above-mentioned ratio, the absorption characteristics of the finally obtained aqueous liquid absorbent resin can be further improved, and the aqueous liquid absorbent resin can be obtained at a lower cost.
Examples of the internal crosslinking agent (b) used in the production method of the present invention include compounds (b1) having 2 or more radical polymerizable double bonds; a compound (b2) having at least 1 functional group capable of reacting with the functional group of the monomer (a) and having at least 1 radical polymerizable double bond; and a compound (b3) having 2 or more functional groups capable of reacting with the functional group of the monomer (a).
Examples of the compound (b1) having 2 or more radically polymerizable double bonds include bis (meth) acrylamides such as N, N' -methylenebisacrylamide; poly (meth) acrylates of polyhydric alcohols such as (poly) alkylene glycol, trimethylolpropane, glycerol, pentaerythritol, and sorbitol; divinyl compounds such as divinylbenzene; poly (meth) allyl ethers of polyhydric alcohols such as (poly) alkylene glycol, trimethylolpropane, glycerol, pentaerythritol, and sorbitol, and poly (meth) allyl compounds such as tetraallyloxyethane and triallylisocyanurate.
Examples of the compound (b2) having at least 1 functional group reactive with the functional group of the monomer (a) and having at least 1 radical polymerizable double bond include radical polymerizable compounds having a functional group reactive with a carboxylic acid (salt) group, a hydroxyl group, an amino group, or the like, and examples thereof include radical polymerizable monomers having a hydroxyl group such as hydroxyethyl (meth) acrylate and N-methylol (meth) acrylamide, radical polymerizable monomers having an epoxy group such as glycidyl (meth) acrylate, and the like.
Examples of the compound (b3) having 2 or more functional groups capable of reacting with the functional group of the monomer (a) include polyfunctional compounds having 2 or more functional groups capable of reacting with a carboxylic acid (salt) group, a hydroxyl group, an amino group, or the like, and examples thereof include glyoxal; polycarboxylic acids such as phthalic acid and adipic acid; polyols such as (poly) alkylene glycols, glycerin and sorbitol; (poly) alkylene polyamines such as ethylenediamine; polyglycidyl ethers of polyhydric alcohols such as ethylene glycol diglycidyl ether, glycerol triglycidyl ether, and sorbitol polyglycidyl ether.
Among these, the compound (b1) having 2 or more radical polymerizable double bonds is preferable, and from the viewpoint of being able to increase the water retention amount of the obtained aqueous liquid absorbent resin, a poly (meth) allyl compound is more preferable, a poly allyl compound is particularly preferable, and a poly allyl compound having 8 to 20 carbon atoms is most preferable. These internal crosslinking agents (b) may be used alone, or 2 or more kinds may be used in combination.
The amount of the internal crosslinking agent (b) is preferably 0.001 to 5% by weight, more preferably 0.01 to 2% by weight, based on the weight of the monomer (a). (b) When the amount of (b) is less than 0.001% by weight, the gel strength of the resulting resin upon absorption of water is small and the resin becomes sol, and the productivity may be deteriorated and the amount of the water-soluble component may be increased. On the other hand, if the amount exceeds 5% by weight, the gel strength becomes too high, and the water retention may decrease.
Examples of the hypophosphorous acid (salt) (c) used in the production method of the present invention include hypophosphorous acid, alkali metal salts of hypophosphorous acid (sodium hypophosphite, potassium hypophosphite, and the like), alkaline earth metal salts of hypophosphorous acid (calcium hypophosphite, barium hypophosphite, and the like), ammonium hypophosphite, and hydrates thereof. These hypophosphorous acids (salts) (c) may be used alone or in combination of 2 or more.
The hypophosphorous acid (salt) (c) is used in an amount of preferably 0.001 to 1% by weight, more preferably 0.005 to 0.3% by weight, based on the weight of the monomer (a). (c) When the amount of (c) is less than 0.001% by weight, the effect of (c), that is, the effect of increasing the water retention amount of the aqueous liquid absorbent resin may be insufficient. On the other hand, if the amount exceeds 1% by weight, the polymerization rate of the monomer (a) may not be sufficiently increased or the polymerization rate may be lowered, and it may be necessary to extend the polymerization time or the aging time, resulting in poor productivity. In addition, the resulting aqueous liquid absorbent resin is likely to be odorous and colored.
In the present invention, the monomer (a) is radically polymerized in the presence of water. The upper limit of the polymerization concentration, that is, the charged concentration of the monomer (a) in the polymerization liquid is less than 30% by weight based on the weight of the polymerization liquid, that is, usually the total weight of the monomer (a), water, the internal crosslinking agent (b), and hypophosphorous acid (salt). The charging concentration of the monomer (a) is preferably 10 to 29.5% by weight, more preferably 20 to 29% by weight, from the viewpoint of drying and removing water after polymerization.
When the polymerization concentration exceeds 30% by weight, the water retention of the resulting aqueous liquid absorbent resin decreases due to low molecular weight of the resulting polymer and occurrence of side reactions such as self-crosslinking.
In the present invention, the maximum temperature of the polymerization liquid at the time of polymerization is lower than the boiling point thereof (i.e., of the polymerization liquid), and is preferably 100 ℃ or lower. When the maximum attainment temperature exceeds the boiling point of the polymerization liquid, the water retention amount of the resulting aqueous liquid absorbent resin decreases due to low molecular weight of the resulting polymer and occurrence of side reactions such as self-crosslinking, and the resulting aqueous liquid absorbent resin develops odor and coloring.
The boiling point of the polymerization liquid can be measured as a 10% distillation temperature of the non-reactive mixture obtained by removing the polymerization initiator from the polymerization liquid, and specifically, can be measured by using a known heated distillation tester specified in JIS K0066 "distillation test method of chemicals".
In addition to the above-mentioned methods, when the maximum temperature at the time of polymerization exceeds the boiling point of the polymerization liquid, water vapor is vigorously discharged from the interface of the polymerization liquid or foaming of the polymerization gel occurs, and thus, it can be judged visually.
In the present invention, the polymerization initiation temperature may be appropriately selected depending on various conditions such as the polymerization concentration, the polymerization catalyst used, and the maximum temperature at the time of polymerization, but is preferably 15 ℃ or lower, and more preferably 10 ℃ or lower.
The polymerization method in the present invention may be any conventionally known method carried out in the presence of water, and examples thereof include an aqueous solution polymerization method, a suspension polymerization method, a reversed-phase suspension polymerization method, and the like, which generally use a radical polymerization catalyst. Further, a method of starting polymerization by irradiation with radiation, electron beam, ultraviolet ray, or the like may be employed. Among these, the aqueous solution polymerization method is preferable in view of the advantage in production cost, such as the elimination of the use of an organic solvent. In particular, the aqueous solution adiabatic polymerization method is preferable because an aqueous liquid absorbent resin having a large water retention amount and a small amount of water-soluble components can be obtained and temperature control during polymerization is not necessary.
As the polymerization catalyst used in the polymerization using the radical polymerization catalyst, conventionally known catalysts can be used, examples thereof include azo compounds [ e.g., azobisisobutyronitrile, azobiscyanovaleric acid, and 2, 2' -azobis (2-amidinopropane) hydrochloride ], inorganic peroxides [ e.g., hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate ], organic peroxides [ e.g., benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide, and bis (2-ethoxyethyl) peroxydicarbonate ], and redox catalysts [ e.g., catalysts composed of a combination of a reducing agent such as alkali metal sulfite or bisulfite, ammonium sulfite, ammonium bisulfite, and ascorbic acid, and an oxidizing agent such as alkali metal persulfate, ammonium persulfate, hydrogen peroxide, and organic peroxide ]. These catalysts may be used alone, or 2 or more of them may be used in combination.
The amount of the radical polymerization catalyst to be used is preferably 0.0005 to 5% by weight, more preferably 0.001 to 2% by weight, based on the weight of the monomer (a).
In the present invention, the hydrogel polymer obtained after polymerization is usually neutralized. The degree of neutralization of acid groups in the polymer is preferably 50 to 80 mol%. When the neutralization degree is less than 50 mol%, the resultant hydrogel polymer may have high tackiness and may have poor workability during production and use. Further, the water retention amount of the resulting aqueous liquid absorbent resin may decrease. On the other hand, when the neutralization degree exceeds 80%, the pH of the obtained resin may be increased, which may cause a concern about safety to human skin.
The neutralization may be carried out at any stage after the polymerization in the production of the aqueous liquid absorbent resin, and a preferable example thereof is a method of carrying out neutralization in the state of a hydrogel polymer as a polymerization product.
In the present invention, the polymer neutralized product obtained may be further uniformly crosslinked in a state of a hydrogel by using a compound having at least 2 groups capable of reacting with a carboxylic acid (salt) group (for example, a polyglycidyl compound such as ethylene glycol diglycidyl ether, a polyhydric alcohol such as ethylene glycol, diethylene glycol, and glycerin, a (poly) alkylene polyamine such as ethylenediamine, and polyvalent metal compounds capable of forming ionic crosslinking), if necessary. By this crosslinking, an aqueous liquid absorbent resin having high gel strength and a small amount of water-soluble components can be produced.
In the present invention, the obtained hydrogel polymer is dried and pulverized into particles as necessary.
The drying method may be a method of drying with hot air at a temperature of 80 to 230 ℃, a film drying method using a drum dryer or the like heated to 100 to 230 ℃, (heating) reduced pressure drying method, freeze drying method, drying method using infrared ray, or other common methods.
The shape of the pulverized particles of the aqueous liquid absorbent resin is not particularly limited, and examples thereof include an amorphous pulverized shape, a flake shape, a pearl shape, and a granulated shape. In the case of paper diaper applications, the amorphous crushed form obtained by aqueous solution polymerization is preferable because the fiber material is well entangled with the fiber material and there is no fear of falling off from the fiber material.
The pulverization method is not particularly limited, and a common apparatus such as a hammer mill, an impact mill, a roll mill, and a jet mill can be used. The obtained pulverized product may be screened as necessary.
The average particle diameter of the pulverized aqueous liquid absorbent resin particles is usually 100 to 600 μm, preferably 200 to 500 μm. The content of fine particles is preferably small, and the content of particles having a particle size of 100 μm or less is usually 3% or less, and the content of particles having a particle size of 150 μm or less is preferably 3% or less.
The water retention capacity of the aqueous liquid absorbent resin obtained by the production method of the present invention with respect to physiological saline is preferably 50g/g or more, and more preferably 55g/g or more. The water retention amount is measured by the method described later.
In the present invention, the gel strength can be improved by surface-crosslinking the obtained aqueous liquid absorbent resin, and the water retention amount and the absorption amount under load which are expected in actual use can be satisfied.
As a method for surface-crosslinking the aqueous liquid absorbent resin, there can be mentioned a conventionally known method, for example, a method in which the aqueous liquid absorbent resin is pelletized, and then mixed with a mixed solution of the surface-crosslinking agent (d), water and a solvent, followed by a heating reaction.
Examples of the surface-crosslinking agent (d) include polyglycidyl compounds such as ethylene glycol diglycidyl ether, glycerol diglycidyl ether, and polyglycerol polyglycidyl ether, polyhydric alcohols such as glycerol and ethylene glycol, alkylene carbonates such as ethylene carbonate, polyamines, and polyvalent metal compounds such as aluminum sulfate, sodium aluminum sulfate, potassium aluminum sulfate, aluminum chloride, polyaluminum chloride, aluminum lactate, zirconium acetate, ammonium zirconium carbonate, zirconium oxychloride, zirconium nitrate, and zirconium sulfate. Among these, the polyglycidyl compounds are preferred because they can undergo a crosslinking reaction at a relatively low temperature. These surface-crosslinking agents may be used alone, or 2 or more of them may be used in combination.
The amount of the surface-crosslinking agent (d) to be used is preferably 0.001 to 5% by weight, more preferably 0.005 to 2% by weight, based on the weight of the aqueous liquid absorbent resin before crosslinking. When the amount of the surface-crosslinking agent (d) is less than 0.001% by weight, the surface-crosslinking degree is insufficient, and the effect of improving the absorption amount under load may be insufficient. On the other hand, when the amount of (d) exceeds 5% by weight, the degree of surface crosslinking becomes excessive, and the water retention amount may decrease.
The amount of water used in the surface crosslinking is preferably 1 to 10% by weight, more preferably 2 to 7% by weight, based on the weight of the aqueous liquid absorbent resin before crosslinking. When the amount of water used is less than 1% by weight, the degree of penetration of the surface-crosslinking agent (d) into the interior of the aqueous liquid absorbent resin particles is insufficient, and the effect of improving the absorption under load may be deteriorated. On the other hand, when the amount of water used exceeds 10% by weight, the surface-crosslinking agent (d) penetrates into the interior, and although an increase in the absorption under load is observed, the water retention may decrease.
As the solvent to be used in combination with hydration at the time of surface crosslinking, a conventionally known solvent can be used, and it can be appropriately selected and used in consideration of the degree of penetration of the surface crosslinking agent (d) into the aqueous liquid absorbent resin particles, the reactivity of the surface crosslinking agent (d), and the like, and hydrophilic organic solvents which can be dissolved in water such as lower alcohols (methanol, propylene glycol, 1, 3-propylene glycol, ethylene glycol, diethylene glycol, and the like) and ether alcohols (diethylene glycol and the like) are preferable, and lower alcohols are more preferable. The solvent may be used alone or in combination of 2 or more.
The amount of the solvent to be used may be appropriately adjusted depending on the kind of the solvent, and is preferably 1 to 10% by weight based on the weight of the aqueous liquid absorbent resin before surface crosslinking. The ratio of the solvent to water may be arbitrarily adjusted, and is preferably 20 to 80 wt%, and more preferably 30 to 70 wt% on a weight basis.
For the surface crosslinking, a mixed solution of the surface crosslinking agent (d), water and a solvent is mixed with the aqueous liquid absorbent resin particles by a conventionally known method and heated to react. The reaction temperature is preferably 100 to 230 ℃, and more preferably 120 to 160 ℃. The reaction time may be appropriately adjusted according to the reaction temperature, and is preferably 3 to 60 minutes, and more preferably 10 to 40 minutes. The particulate aqueous liquid absorbent resin obtained by surface crosslinking may be further surface-crosslinked using a surface-crosslinking agent of the same type as or different from the surface-crosslinking agent used initially.
The particulate aqueous liquid absorbent resin obtained by surface crosslinking is screened as necessary to adjust the particle size. The average particle diameter of the obtained particles is preferably 100 to 600 μm, and more preferably 200 to 500 μm. The content of fine particles is preferably small, and the content of particles having a particle size of 100 μm or less is preferably 3% by weight or less, and more preferably the content of particles having a particle size of 150 μm or less is 3% by weight or less.
In the present invention, an antiseptic agent, a fungicide, an antibacterial agent, an antioxidant, an ultraviolet absorber, an antioxidant, a coloring agent, an aromatic agent, a deodorant, an inorganic powder, an organic fibrous material, and the like may be added as needed at any stage of the production method of the present invention, and the amount thereof is usually 5% by weight or less based on the weight of the obtained aqueous liquid absorbent resin. If necessary, the method of the present invention may be carried out at any stage to form a foamed structure, or may be granulated or molded.
Examples
The present invention will be further illustrated by the following examples, which are not intended to limit the scope of the inventionIn these embodiments. Hereinafter, unless otherwise specified, parts means parts by weight and% means% by weight. The water retention capacity of the aqueous liquid absorbent resin was 40g/cm2Or 60g/cm2The absorption amount under load, whiteness and odor of (b) were measured by the following methods.
[ method for measuring Water Retention amount ]
A tea bag (length: 20cm, width: 10cm) made of a 250 mesh nylon net was impregnated with 1.000G of an aqueous liquid absorbent resin for 60 minutes, then the bag was immersed in physiological saline (an ion exchange aqueous solution having a NaCl concentration of 0.90%) and then pulled up, suspended for 15 minutes to remove water, and then the bag was put into a centrifugal dehydrator together with the tea bag and centrifuged at 150G for 90 seconds to remove the remaining water, and the weight of the bag (h1) was measured. The weight of the tea bag after the centrifugal dehydration (h2) was measured in the same manner as described above except that the measurement sample was not used, and the water retention amount was determined from the following equation. The temperature of the physiological saline used and the temperature of the measurement atmosphere were set to 25 ℃. + -. 2 ℃.
Water retention (g/g) ═ h1 (h2)
[ method for measuring absorption under load ]
0.160g of an aqueous liquid absorbent resin was charged into a plastic cylinder (inner edge 25mm, height 30mm) having a bottom surface to which a 250-mesh nylon net was attached, and uniformly flattened, and a 200g weight having an outer edge 25mm and smoothly placed on the cylinder was placed on the aqueous liquid absorbent resin. The load at this time was about 40g/cm2。
A plastic cylinder to which an aqueous liquid absorbent resin and a weight were added was dipped into a dish (diameter: 12cm) to which 60ml of physiological saline was added, with the nylon mesh side as the lower side, and left to stand. The weight gain of the aqueous liquid absorbent resin due to absorption of physiological saline after 60 minutes was measured, and the value was converted to a value of 40g/cm per 1g of the aqueous liquid absorbent resin2The amount of absorption under load. 60g/cm2The absorption amount under load of (2) was determined by the same measurement using a 300g weight having the same outer diameter.
[ method for measuring whiteness (WB value) ]
The ease of initial coloring (coloring immediately after production) of the aqueous liquid absorbent resin and coloring in long-term storage or application products were evaluated by measuring the whiteness (WB value) before and after the accelerated test using a digital colorimeter (ND-1001 DP type manufactured by japan electro-chromatic industries, ltd.). The larger the value of the Whiteness (WB), the more suppressed the coloring. The procedure of the coloring acceleration test is as follows.
10g of an aqueous liquid absorbent resin was put into a glass plate having an inner diameter of 90mm, and leveling was uniformly performed to flatten the surface. The obtained extract was stored in a constant temperature and humidity machine at 60 + -2 deg.C and 80 + -2% R.H. for 14 days. Then, the plate was taken out from the constant temperature and humidity apparatus, and returned to room temperature, and the whiteness (WB value) after the accelerated test was measured.
[ method of odor test ]
The odor of the aqueous liquid absorbent resin was evaluated by the following test method.
1g of the aqueous liquid absorbent resin was put into a 100ml beaker, and 20g of a 0.9 wt% aqueous sodium chloride solution was added thereto, and then the beaker was sealed with a membrane and left at 37 ℃ for 1 hour. Then, an off-flavor sensory test was performed on 10 adult subjects, and an average score was calculated based on the following scores.
0: has no unpleasant odor
1: slightly unpleasant off-flavor
2: has unpleasant odor
3: the unpleasant odor is particularly strong
< example 1>
270 parts of acrylic acid, 0.88 parts of pentaerythritol triallyl ether (manufactured by Daiso) as a crosslinking agent, and 712 parts of ion-exchanged water were mixed to prepare an aqueous monomer solution, and the mixture was charged into a polymerization vessel capable of adiabatic polymerization. The amount of dissolved oxygen in the solution was controlled to 0.2ppm or less by introducing nitrogen gas into the solution, and the solution temperature was controlled to 5 ℃. To the polymerization solution were added 0.14 part of sodium hypophosphite monohydrate, 1.1 parts of 1% aqueous hydrogen peroxide solution, 2.0 parts of 2% aqueous ascorbic acid solution and 13.5 parts of 2% aqueous 2, 2' -azobisamidinopropane dihydrochloride solution and mixed (monomer concentration 27%). After the temperature rise indicating the initiation of polymerization was confirmed, the gel was allowed to equilibrate at 80 ℃ for about 2 hours, and was further aged for 5 hours to obtain a hydrogel polymer. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 102 ℃.
The hydrogel polymer was chopped into small pieces using a meat chopper, and about 72 mol% of the carboxyl groups in the polymer were formed into sodium salts by adding 220 parts of 49% aqueous NaOH solution. The neutralized hydrogel was subjected to aeration-drying using an aeration-hot air dryer (manufactured by metal works on the ground) at a supply air temperature of 150 ℃ and an air speed of 1.5 m/s until the water content reached 4%. The dried product was pulverized with a juicer mixer (Osterizer BLENDER), and sieved to adjust the particle size to 710 to 150 μm, thereby obtaining an aqueous liquid absorbent resin (A1-1).
< example 2>
An aqueous liquid absorbent resin (a1-2) was obtained in the same manner as in example 1, except that the amount of sodium hypophosphite monohydrate in example 1 was changed from 0.14 parts to 0.20 parts. The monomer concentration during polymerization was 27%, and the temperature reached at equilibrium was 80 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 102 ℃.
< example 3>
An aqueous liquid absorbent resin (a1-3) was obtained in the same manner as in example 1, except that the amount of pentaerythritol triallyl ether in example 1 was changed from 0.88 parts to 1.2 parts. The monomer concentration during polymerization was 27%, and the temperature reached at equilibrium was 80 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 102 ℃.
< example 4>
An aqueous liquid absorbent resin (a1-4) was obtained in the same manner as in example 1, except that the solution temperature at the start of polymerization was changed from 5 ℃ to 15 ℃ in example 1. The monomer concentration during polymerization was 27%, and the attainment temperature at equilibrium was 89 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 102 ℃.
< example 5>
An aqueous liquid absorbent resin (a1-5) was obtained in the same manner as in example 1, except that the amount of ion-exchanged water in example 1 was changed from 712 parts to 643 parts. The monomer concentration during polymerization was 29%, and the temperature reached at equilibrium was 90 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 103 ℃.
< example 6>
An aqueous liquid absorbent resin (a1-6) was obtained in the same manner as in example 1, except that the amount of ion-exchanged water was changed from 712 parts to 643 parts, the amount of sodium hypophosphite monohydrate was changed from 0.14 parts to 0.20 parts, and the solution temperature at the start of polymerization was changed from 5 ℃ to 15 ℃. The monomer concentration during polymerization was 29%, and the temperature reached at equilibrium was 99 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 103 ℃.
< comparative example 1>
222g of acrylic acid and 582g of water were mixed, and 181g of a 49% NaOH aqueous solution was slowly added to the mixture so that the solution temperature did not exceed 35 ℃ while externally cooling the mixture, thereby neutralizing about 72 mol% of acrylic acid. Subsequently, 0.88 parts of pentaerythritol triallyl ether (manufactured by Daiso) was mixed as a crosslinking agent to prepare an aqueous monomer solution, and the mixed solution was charged into a polymerization vessel capable of adiabatic polymerization. The amount of dissolved oxygen in the solution was controlled to 0.2ppm or less by introducing nitrogen gas into the solution, and the solution temperature was controlled to 5 ℃. To the polymerization solution were added 0.14 part of sodium hypophosphite monohydrate, 1.1 parts of 1% aqueous hydrogen peroxide solution, 2.0 parts of 2% aqueous ascorbic acid solution and 13.5 parts of 2% aqueous 2, 2' -azobisamidinopropane dihydrochloride solution and mixed (monomer concentration 27%). After the temperature rise indicating the initiation of polymerization was confirmed, the gel was allowed to equilibrate at 80 ℃ for about 2 hours, and was further aged for 5 hours to obtain a hydrogel polymer. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 103 ℃.
The hydrogel polymer was minced into small pieces by a meat chopper, and then subjected to aeration-drying at an air temperature of 150 ℃ and an air speed of 1.5 m/s by an aeration-hot air dryer (manufactured by metal on the well) until the water content reached 4%. The dried product was pulverized with a juicer mixer (Osterizer BLENDER), and sieved to adjust the particle size to 710 to 150 μm, to obtain a comparative aqueous liquid absorbent resin (R1-1).
< comparative example 2>
An aqueous liquid absorbent resin for comparison (R1-2) was obtained in the same manner as in comparative example 1, except that in comparative example 1, 0.88 parts of ethylene glycol diglycidyl ether was used instead of 0.88 parts of pentaerythritol triallyl ether. The monomer concentration during the polymerization was 27%, and the temperature reached at equilibrium was 78 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 103 ℃.
< comparative example 3>
An aqueous liquid absorbent resin for comparison (R1-3) was obtained in the same manner as in comparative example 1, except that in comparative example 1, 0.88 parts of N, N' -methylenebisacrylamide was used in place of 0.88 parts of pentaerythritol triallyl ether. The monomer concentration during polymerization was 27%, and the temperature reached at equilibrium was 80 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 103 ℃.
< comparative example 4>
An aqueous liquid absorbent resin for comparison (R1-4) was obtained in the same manner as in example 1, except that sodium hypophosphite monohydrate was not added in example 1. The monomer concentration during polymerization was 27%, and the temperature reached at equilibrium was 80 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 102 ℃.
< comparative example 5>
A comparative aqueous liquid absorbent resin (R1-5) was obtained in the same manner as in example 1, except that 0.14 part of triethylene glycol dithiol was used instead of 0.14 part of sodium hypophosphite monohydrate in example 1. The monomer concentration during polymerization was 27%, and the temperature reached at equilibrium was 80 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 102 ℃.
< comparative example 6>
A comparative aqueous liquid absorbent resin (R1-6) was obtained in the same manner as in example 1, except that the solution temperature at the start of polymerization in example 1 was changed from 5 ℃ to 30 ℃. The monomer concentration during polymerization was 27%, and during the polymerization, the temperature of the mixture reached the boiling point, causing foaming.
< comparative example 7>
An aqueous liquid absorbent resin for comparison (R1-7) was obtained in the same manner as in example 1, except that the amount of ion-exchanged water was changed from 712 parts to 643 parts, the amount of sodium hypophosphite monohydrate was changed from 0.14 parts to 0.20 parts, and the solution temperature at the start of polymerization was changed from 5 ℃ to 25 ℃. The monomer concentration at the time of polymerization was 29%, and during the polymerization, the temperature of the mixture reached the boiling point, causing foaming.
< comparative example 8>
A comparative aqueous liquid absorbent resin (R1-8) was obtained in the same manner as in example 1, except that the amount of ion-exchanged water in example 1 was changed from 712 parts to 583 parts. The monomer concentration during polymerization was 31%, and the temperature reached at equilibrium was 97 ℃. The boiling point of the polymerization solution was measured using a heated distillation tester and found to be 104 ℃.
< example 7>
While stirring 100g of the aqueous liquid absorbent resin (A1-1) (high-speed paddle mixer manufactured by Hosokawamicon: rotational speed 2000rpm), a solution composed of 0.14g of ethylene glycol diglycidyl ether, 4g of water and 6g of methanol was added and mixed, and the mixture was heated at 140 ℃ for 40 minutes to effect surface crosslinking, thereby obtaining an aqueous liquid absorbent resin (A2-1).
< examples 8 to 12>
Aqueous liquid absorbent resins (A2-2) to (A2-6) were obtained in the same manner as in example 7, except that the aqueous liquid absorbent resins (A1-2) to (A1-6) were used in place of the aqueous liquid absorbent resin (A1-1).
< example 13>
While stirring 100g of the aqueous liquid absorbent resin (A1-1) (high-speed paddle mixer manufactured by Hosokawamicon: rotational speed 2000rpm), a solution composed of 0.14g of ethylene glycol diglycidyl ether, 3.6g of water, and 2.8g of propylene glycol was added and mixed, and the mixture was heated at 140 ℃ for 40 minutes to effect surface crosslinking, thereby obtaining an aqueous liquid absorbent resin (A2-1P).
< example 14>
An aqueous liquid absorbent resin (a2-2P) was obtained in the same manner as in example 13, except that the aqueous liquid absorbent resin (a1-2) was used in place of the aqueous liquid absorbent resin (a 1-1).
< comparative examples 9 to 16>
Comparative aqueous liquid absorbent resins (R2-1) to (R2-8) were obtained in the same manner as in example 7, except that comparative aqueous liquid absorbent resins (R1-1) to (R1-8) were used in place of the aqueous liquid absorbent resin (A1-1).
< comparative example 17>
A comparative aqueous liquid absorbent resin (R2-4P) was obtained in the same manner as in example 13, except that the comparative aqueous liquid absorbent resin (R1-4) was used in place of the aqueous liquid absorbent resin (A1-1).
The evaluation results of the water retention capacities, whiteness degrees and odor of the obtained aqueous liquid absorbent resins (A1-1) to (A1-6) and the aqueous liquid absorbent resins for comparison (R1-1) to (R1-8) are shown in Table 1.
The evaluation results of the water retention amounts, absorption amounts under load, whiteness, and odor of the obtained aqueous liquid absorbent resins (A2-1) to (A2-6), (A2-1P), (A2-2P) and the aqueous liquid absorbent resins for comparison (R2-1) to (R2-8), (R2-4P) are shown in Table 2.
[ TABLE 1 ]
[ TABLE 2 ]
As is clear from the results in tables 1 and 2, the aqueous liquid absorbent resin obtained by the production method of the present invention has a higher water retention capacity and reduced coloring and odor as compared with the aqueous liquid absorbent resin of the comparative example. In particular, from the results in table 2, it is understood that the water retention capacity is improved and the absorption performance is significantly improved, while the absorption capacity under load is equal to or higher than that of the aqueous liquid absorbent resin of the comparative example.
Industrial applicability
The aqueous liquid absorbent resin having a large water retention capacity and little coloration or odor can be obtained by the production method of the present invention. Further, the particulate aqueous liquid absorbent resin obtained by surface crosslinking exhibits a high water retention amount and also exhibits a high absorption amount under load, and therefore has a characteristic of having an excellent balance between the water retention amount and the absorption amount under load.
The aqueous liquid absorbent resin obtained by the method of the present invention can be suitably used for aqueous liquid absorbent articles, particularly sanitary products such as disposable diapers, because of the above-described effects.
Claims (8)
1. A process for producing an aqueous liquid absorbent resin, which comprises a step of radically polymerizing a radically polymerizable monomer (a) comprising acrylic acid as a main component in the presence of an internal crosslinking agent (b) and water, wherein the acrylic acid content in the radically polymerizable monomer (a) is 90 to 100 mol%,
the free radical polymerization is carried out in the presence of hypophosphorous acid (salt) (c), the upper limit of the charge concentration of the monomer (a) is less than 30% by weight based on the weight of the polymerization liquid, and the maximum reaching temperature of the polymerization liquid at the time of polymerization is lower than the boiling point of the polymerization liquid.
2. The production process according to claim 1, wherein the hypophosphorous acid (salt) (c) is contained in an amount of 0.001 to 1% by weight based on the weight of the monomer (a).
3. The production process according to claim 1 or 2, wherein the maximum reaching temperature of the polymerization liquid is 100 ℃ or lower.
4. The production process according to claim 1 or 2, wherein the polymerization initiation temperature is 15 ℃ or lower.
5. The production process according to claim 1 or 2, wherein the internal crosslinking agent (b) is a polyallyl compound.
6. The production process according to claim 1 or 2, further comprising a step of neutralizing the hydrogel polymer obtained by radical polymerization.
7. The manufacturing method according to claim 1 or 2, further comprising: a step of granulating the aqueous liquid absorbent resin; and a step of surface-crosslinking the aqueous liquid absorbent resin particles with a surface-crosslinking agent (d).
8. The production process according to claim 1 or 2, wherein the water retention capacity of the obtained aqueous-liquid-absorbent resin for physiological saline is 50g/g or more.
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| JP2015046968 | 2015-03-10 | ||
| PCT/JP2016/056959 WO2016143734A1 (en) | 2015-03-10 | 2016-03-07 | Method for producing aqueous liquid-absorbing resin |
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| CN1043720A (en) * | 1988-12-08 | 1990-07-11 | 日本触媒化学工业株式会社 | The production method of absorbent resin excelling in durability |
| CN102603946A (en) * | 2012-03-16 | 2012-07-25 | 广州埃文森生物科技有限公司 | Method for preparing super absorbent resin |
| CN102892795A (en) * | 2010-03-15 | 2013-01-23 | 巴斯夫欧洲公司 | Method for producing water-absorbent polymer particles having improved color stability |
| CN103492422A (en) * | 2011-04-21 | 2014-01-01 | 住友精化株式会社 | Method for producing water-absorbing resin |
| CN103502287A (en) * | 2011-04-21 | 2014-01-08 | 住友精化株式会社 | Water-absorbent resin, absorbent body and absorbent article |
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| JPH0826085B2 (en) * | 1988-12-08 | 1996-03-13 | 株式会社日本触媒 | Method for producing water-absorbent resin having excellent durability |
| JP2922216B2 (en) * | 1989-05-16 | 1999-07-19 | 三菱化学株式会社 | Super absorbent polymer production method |
| JP2877255B2 (en) * | 1989-12-08 | 1999-03-31 | 株式会社日本触媒 | Manufacturing method of water absorbent resin with excellent durability |
| JP2000026510A (en) * | 1998-07-06 | 2000-01-25 | Sanyo Chem Ind Ltd | Production of resin and water-absorbing resin |
| JP2002284805A (en) * | 2001-03-27 | 2002-10-03 | Mitsubishi Chemicals Corp | Method of manufacturing highly water absorptive polymer |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1043720A (en) * | 1988-12-08 | 1990-07-11 | 日本触媒化学工业株式会社 | The production method of absorbent resin excelling in durability |
| CN102892795A (en) * | 2010-03-15 | 2013-01-23 | 巴斯夫欧洲公司 | Method for producing water-absorbent polymer particles having improved color stability |
| CN103492422A (en) * | 2011-04-21 | 2014-01-01 | 住友精化株式会社 | Method for producing water-absorbing resin |
| CN103502287A (en) * | 2011-04-21 | 2014-01-08 | 住友精化株式会社 | Water-absorbent resin, absorbent body and absorbent article |
| CN102603946A (en) * | 2012-03-16 | 2012-07-25 | 广州埃文森生物科技有限公司 | Method for preparing super absorbent resin |
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| CN107406542A (en) | 2017-11-28 |
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