JP2001226416A - Method for producing water-absorbing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a new water-absorbing resin having no problems in quality and properties by using a water-absorbing resin powder in a fine powdery state which is considered to be inferior in quality and properties. SOLUTION: This water-absorbing resin is prepared by adding the fine powdery water-absorbing resin when polymerizing a water-soluble polymerizable monomer and a cross-linkable monomer in an aqueous solution. If necessary, the water-absorbing resin is prepared while reducing the amount of the cross- linkable monomer according to the amount of the added fine powdery water- absorbing resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-absorbent resin, and more particularly, to a new method for improving quality and performance by using fine water-absorbent resin powder which is considered to be inferior in quality and performance. The present invention relates to a method for producing a new water-absorbing resin having no problem. In other words, it is a method for converting a fine water-absorbing resin powder having a problem in treatment into an effective one. It is about use. That is, the present invention belongs to the chemical product manufacturing technology.

[0002]

2. Description of the Related Art Resins that absorb a large amount of water, that is, water-absorbing resins, include partially hydrolyzed starch-acrylonitrile graft polymers, crosslinked polyacrylates, polyethylene oxides, polyacrylonitriles, polyvinyl alcohols, and the like. Water-absorbing resins are widely used, especially cross-linked polyacrylates, including partially neutralized and fully neutralized salts, are widely used due to their excellent water absorption capacity, water absorption speed, suction power, gel strength, etc. Have been. These water-absorbent resin powders are useful as body fluid absorbers for absorbing body fluids and preventing leakage in sanitary materials such as sanitary products and disposable diapers, as well as soil water retention agents, seed coating agents, water-stopping agents, It is used for applications such as thickeners, anti-condensation agents, sludge coagulants, desiccants and humectants. These water-absorbent resin powders,
In particular, the water-absorbent resin powder composed of cross-linked polyacrylate,
Generally, it is prepared by polymerizing acrylic acid or a salt thereof in an aqueous solution together with a crosslinkable monomer to obtain an aqueous polymer gel, and then drying and crushing the gel. Naturally, the water-absorbent resin powder prepared industrially, including the above-mentioned method, has a distribution in particle size, and has a particle size of 0.25 mm so as to pass through a 65-mesh sieve.
Also contains the following fines: The fine powder contained in the water-absorbent resin powder has poor water absorption performance itself and has the following major problems due to being a fine powder. That is, dust tends to be generated at the time of work, and the work environment is deteriorated, and the workability is poor.Mamako is likely to be generated at the time of absorbing water, which prevents water from diffusing and penetrating. It has the problem of making transport difficult. Therefore, in the production of the water-absorbent resin powder, the production conditions are set so that the fine powder does not occur, but since the fine powder cannot be completely eliminated under the production conditions, the prepared water-absorbent resin powder is Finally, the powder was classified and fine powder was removed. Classified fine powder is difficult to use as it is because it has many problems as described above, but disposal is a problem from the viewpoint of resource saving, and its use method is The following proposals have been made. For example, a method of granulating a fine powder using water or water to which a water-soluble polymer or an inorganic powder is added (JP-A-61-97333, JP-A-61-101536); A method in which a water-absorbent resin fine powder is added to an organic solvent containing a gel, followed by azeotropic dehydration to granulate (Japanese Patent Laid-Open No. 63-210108)
), A method in which a water-absorbent resin-containing gel containing an unpolymerized monomer and a water-absorbent resin fine powder are added and mixed, and then the unpolymerized monomer is polymerized (JP-A-5-43610). ing. However, these methods have both advantages and disadvantages, and better methods are required. That is, the granulated particles obtained by the above granulation method cannot always be said to have a sufficiently large fixing strength, and are broken during transportation or swelling due to water absorption, regenerating fine powder, The method of mixing the water-absorbent resin hydrated gel and the fine powder, which does not contribute to the improvement of the performance and may not prevent the diffusion property, requires sufficient shearing force for mixing, and requires the use of equipment such as a kneader. In addition to the necessity, a delicate and complicated operation of adjusting the polymerization rate of the monomer in the hydrogel is required.

[0003]

SUMMARY OF THE INVENTION The present invention provides a method of reusing a water-absorbent resin fine powder which does not have these problems,
It is an object of the present invention to propose a method for providing a new water-absorbing resin powder by using the same at the time of preparing a new water-absorbing resin powder.

[0004]

Means for Solving the Problems The present inventors have studied various methods for reusing a water-absorbent resin fine powder, and polymerized a water-soluble polymerizable monomer and a crosslinkable monomer in an aqueous solution to absorb water. When obtaining a water-soluble resin, if a water-absorbent resin fine powder generated during the preparation of the water-absorbent resin is made to coexist, a new water-absorbent resin incorporating the fine powder is obtained, which has been a concern in the past. The decrease in water absorption performance due to the graft polymerization was slight,
If the decrease is a problem, they have found that it is sufficient to reduce the amount of the crosslinkable monomer in accordance with the amount of the fine powder added, and have completed the present invention. That is, the present invention relates to a method for producing a water-absorbent resin, which is prepared by polymerizing a water-soluble polymerizable monomer and a crosslinkable monomer in an aqueous solution to which a fine-powder water-absorbent resin is added. And further relates to the method for producing a water-absorbent resin, wherein the amount of the crosslinkable monomer is reduced according to the amount of the water-absorbent resin added as a fine powder. Things.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for preparing a water-absorbing resin, particularly a water-absorbing resin comprising a crosslinked polyacrylate, by polymerizing a water-soluble polymerizable monomer and a crosslinkable monomer in an aqueous solution is well known. The method is briefly described below. The water-absorbing resin composed of a cross-linked polyacrylate is essentially an acrylic acid or an alkali metal salt such as sodium or potassium acrylate, an ammonium salt,
A water-soluble polymerizable monomer such as an amine salt (hereinafter also referred to as an acrylic acid monomer) is used as a main constituent monomer, and if desired, other water-soluble or water-miscible ethylenically unsaturated monomers, for example, , Methacrylic acid, maleic acid, vinyl sulfonic acid,
Anionic unsaturated monomers such as styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and salts thereof; (Meth) acrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-
Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol
Nonionic hydrophilic group-containing monomers such as (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine, N-vinylacetamide; N, N-dimethylaminoethyl (meth) Acrylate, N, N-diethylaminoethyl (meth) acrylate,
N, N-dimethylaminopropyl (meth) acrylate, N, N-
With one or more kinds of cationic unsaturated monomers such as dimethylaminopropyl (meth) acrylamide and quaternary salts thereof, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di ( (Meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) Acrylate,
Pentaerythitol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl Ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethyleneimine, glycidyl (meth)
It is obtained by polymerizing with a crosslinkable monomer such as acrylate, and the present invention is that the polymerization is performed in an aqueous solution. The concentration of the monomer aqueous solution in the aqueous solution polymerization is not particularly limited as long as it is an aqueous solution, but is preferably 5 to 70% by weight, more preferably 10 to 60% by weight.
It is. The reaction conditions such as the polymerization temperature and the polymerization time during the polymerization may be appropriately set according to the composition of the monomer components to be used, and are not particularly limited.
The polymerization is carried out at a temperature of 110 ° C, preferably 5 ° C to 100 ° C.

The acrylic acid monomer is preferably used in an amount of 50 to 100% by mass based on the total amount of other monomers, and the amount of the crosslinking agent used is generally based on the total amount of the monomers. 0-5
%, Preferably 0 to 2% by mass. Also,
The ratio of the acid and the salt in the acrylic acid monomer is 0.0 based on the number of moles of the acid group in the obtained water-absorbing polymer.
Preferably, 1 to 100% is neutralized, more preferably, 1 to 99% is neutralized, and still more preferably, 40 to 95% is neutralized. Neutralization may be carried out in any of the steps of a monomer or after a polymer is formed. In addition, during polymerization, starch,
Derivatives of starch, cellulose, derivatives of cellulose,
Derivatives of polyvinyl alcohol, polyacrylic acid (salt),
A hydrophilic polymer such as a crosslinked polyacrylate, a chain transfer agent such as hypophosphorous acid (salt), and a blowing agent such as an inert gas or a carbonate can also be added. For the initiation of polymerization, a thermal radical polymerization initiator or an active energy ray such as ultraviolet light or an electron beam can be used.Examples of the thermal radical polymerization initiator include radicals that generate radical species by heat, peroxides, Examples include persulfate compounds, azo compounds and redox initiators. Examples of peroxides include benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, t-
Butyl hydroperoxide and dicumyl peroxide. Examples of persulfate compounds include ammonium persulfate, potassium persulfate and sodium persulfate. Examples of the azo compound include azobisisobutyronitrile and azobis-2,4-dimethylvaleronitrile. Examples of redox initiators include hydrogen peroxide-iron (II) salts, peroxodisulfate-sodium bisulfite and cumene hydroperoxide-iron (II) salts. The amount of these used is usually 0.0005 to 1% by mass, preferably 0.001 to 0.5% by mass, based on the monomer. When the polymerization is initiated using active energy rays, a photopolymerization initiator or a photosensitizer can be used in combination. Examples of the photopolymerization initiator include benzoin and its alkyl ethers, acetophenones, anthraquinones, thioxanthones, ketals, benzophenones, and xanthones. Examples of the photosensitizer include benzoic acid-based and amine-based photosensitizers. These can be used in combination of two or more. The amount of these used is also usually 0.0005 to 1% by mass, preferably 0.001 to 0.5% by mass, based on the monomer.

[0007] The water-absorbing polymer obtained by polymerization as described above is a gel-like material (water-absorbing swelled body) that has absorbed water, and is dried, pulverized, and then classified to remove fine powder. It is considered to be a water absorbent resin powder as a product. Also,
A water-absorbing resin having further improved water-absorbing properties has been also obtained by further performing a cross-linking treatment (hereinafter also referred to as a surface cross-linking treatment) on the surface of the water-absorbing resin powder particles having a cross-linked structure by the internal cross-linking. The surface cross-linking treatment is usually performed using a cross-linking agent capable of reacting with a functional group such as a carboxyl group, a hydroxyl group, or an amino group that the water-absorbing polymer has,
Examples of the crosslinking agent capable of reacting with a functional group include, for example, polyglycidyl ether compounds, polyol compounds, polyamine compounds, polyimine resins, carbonate compounds, haloepoxy compounds, polyaldehyde compounds, and the like. A surface crosslinked structure can be obtained by mixing with a hydrophilic polymer and subjecting to heat treatment. These surface crosslinking agents may be used alone or in combination of two or more. As a device used for the surface cross-linking treatment, a mixing device using mechanical force, specifically, a kneader,
Nauta type mixer, ball mill, V type mixer, Loedige mixer, turbulizer, ribbon type mixer, conical blender, Henschel mixer, Raikai, paddle type mixer, screw type mixer, rotating disk type mixer,
Examples of a mixer such as a high-speed rotary paddle-type mixer, a stirrer-type dryer, and the like, and a fluidized-mixing device using a gas include a fluidized-bed dryer and a spray dryer. Since a solvent containing water is usually used for the surface cross-linking treatment, the water-absorbing resin after the surface cross-linking treatment can be used as a drying device for drying again after the treatment. Thin-type mixing dryers, disk dryers, fluidized-bed dryers, air-flow dryers, infrared dryers and the like are used. These surface cross-linking treatment and drying are usually performed at 40 ° C to 250 ° C, preferably 40 ° C to 200 ° C, more preferably 80 ° C to 2 ° C.
It is performed in a temperature atmosphere of 00 ° C. Further, in the water-absorbent resin, if necessary, in any step, as an extender or an additive, an organic powder (e.g., pulp powder, cellulose derivative, natural polysaccharide, etc.), an inorganic powder (zeolite, silica,
(Alumina, bentonite, activated carbon, etc.), antioxidants,
Preservatives, antibacterial agents, deodorants, fragrances, coloring agents and the like may be added.

As described above, in the process of preparing the water-absorbent resin powder, the fine powder has been removed as being unfavorable, and various proposals have been made as described above regarding the handling thereof. Next, when the water-soluble polymerizable monomer and the crosslinkable monomer are polymerized in an aqueous solution to prepare a water-absorbent resin, the fine powder is added to the aqueous solution to prepare a newly prepared water-absorbent resin. The method of taking it into the resin is adopted. The fine particles used in the present invention are generally classified fine powder having a particle size of about 0.25 mm or less. Can also be used in the present invention. As a method of adding the water-absorbent resin fine powder to the aqueous solution of the water-soluble polymerizable monomer and the crosslinkable monomer,
An aqueous solution in which the water-soluble polymerizable monomer and the crosslinkable monomer are dissolved while adding and dissolving the water-soluble polymerizable monomer and the crosslinkable monomer to the water in which the water-absorbent resin fine powder is dispersed. Although it is possible to add and disperse the water-absorbent resin fine powder while stirring it inside, it is easy for the water-absorbent resin fine powder to become `` mamako '' when it comes into contact with water. A small amount of the water-absorbent resin fine powder is added to an aqueous solution that is in a fluid state when transferring an aqueous solution of a water-soluble polymerizable monomer, such as when an aqueous solution of a body or a mixed aqueous solution of a water-soluble polymerizable monomer and a cross-linkable monomer is added. It is preferable to add them one by one. The amount of the water-absorbent resin fine powder to be added is preferably up to 20% of the total mass of the water-soluble polymerizable monomer and the crosslinkable monomer. If it is added in an amount of 20% by mass or more, it may be difficult to improve the performance of the water-absorbent resin, which decreases in proportion to the amount of the fine powder, and it is desirable to avoid it. When there is a concern that the performance of the water-absorbent resin obtained by the addition of the fine powder is reduced, it is desirable to reduce the amount of the crosslinkable monomer in accordance with the amount of the water-absorbent resin fine powder added. As the amount of addition, when the amount of the crosslinkable monomer when there is no addition of the fine powder is 100, it is sufficient to add 20 to 80, and it is appropriately set according to the addition amount of the fine powder, the target value of the performance, and the like. Just do it.

The water-absorbent resin obtained by the present invention is
It is composited with a fiber base material such as cotton and pulp, and is suitably used as one of materials constituting sanitary materials such as disposable diapers, sanitary napkins and incontinence pads. Other applications include soil water retention agents, seed coating agents, water blocking agents, thickeners, anti-condensation agents, sludge coagulants, desiccants, humidity regulators, gels for heat storage agents, gels for fragrances, artificial It can also be used for snow gels.

[0010]

The newly obtained water-absorbing resin is obtained even if the fine powder removed during the preparation of the water-absorbing resin powder is added to the aqueous solution of the water-soluble polymerizable monomer and the crosslinkable monomer to be polymerized in an aqueous solution. Does not significantly decrease, and the observed decrease is of an extent that can be prepared by reducing the amount of the crosslinking monomer.

[0011]

The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. Trimethylolpropane triacrylate (TMP) was added to a 40 wt% aqueous solution consisting of 25 mol% of acrylic acid and 75 mol% of sodium acrylate.
Was added to an amount shown in Table 1 below to prepare a monomer aqueous solution. 2,2 as a photoinitiator
120 pp of dimethoxy-2-phenylacetophenone
m and ammonium persulfate were added at 1500 ppm, and further, a water-absorbent resin fine powder having a particle size distribution shown in Table 2 was added, respectively, and then irradiated with ultraviolet rays on a belt to polymerize to form a polymer aqueous gel. The aqueous polymer gel was cut with a meat chopper and dried with hot air at 150 ° C. on a band dryer. The dried polymer aqueous gel was pulverized with a roll pulverizer to obtain a water-absorbent resin. The retained water absorption of the obtained water-absorbent resin was measured by the following method and is shown in Table 1.

Method for measuring retained water absorption About 0.5 g of water-absorbing resin powder was precisely weighed (S (g)) into a 150 ml polycup, 100 ml of brine (0.9 w / w%) was added, and the mixture was stirred for 30 minutes or more with a stirrer. The liquid was poured into a glass filter (17 G2) attached to a suction bottle that could be suctioned by an aspirator equipped with a pressure control valve, immediately adjusted to a suction force of 20 g / cm ² , and suctioned for 10 minutes, after which the water-absorbent resin swelled gel was contained. The weight of the glass filter is measured (X (g)). The retained water absorption was determined by the following equation. In the formula, B is the weight (g) of the glass filter.

[0013]

[Formula 1] Retained water absorption (g / g) = (X-B) / S

According to the method for measuring the retained water absorption determined as described above, simply measuring the gel swollen by absorbing water will not only remove the water adsorbed on the gel but also the water retained between the gel particles in addition to the actually absorbed water. This is a method of avoiding counting as absorbed water, and a method of measuring the pure water absorption of the water absorbent resin.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

According to the present invention, the fine powder of the water-absorbent resin which has a problem in the treatment is reused without any problem, and the performance of the water-absorbent resin produced by using the fine powder is also compared with that of the general product. There is no problem, which is an excellent effect on the reuse of the water absorbent resin fine powder, and greatly contributes to resource saving.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinzo Narimatsu 23rd, 17-Showa-cho, Minato-ku, Nagoya-shi, Aichi F-term in the Nagoya Plant of Toagosei Co., Ltd. 4J002 AA00W BG01X 4J011 PA53 PA67 PA69 PA78 PA90 PB08 PC02 QA02 QA03 QA06 QA08 QA09 QA13 QA21 QA23 QA24 QA27 QA33 QA34 QA35 QA37 QA38 QA39 QA40 QA42 QA43 QB16 SA02 SA22 SA32 SA34 SA52 SA63 SA64 UA03 UA06 4J026 AA02 BAA BA18 BA20 BA20 BA20 DB36 GA02 GA06

Claims (2)

[Claims] 1. A method for producing a water-absorbent resin, which is prepared by polymerizing a water-soluble polymerizable monomer and a crosslinkable monomer in an aqueous solution to which a fine powder of a water-absorbent resin has been added. 2. The method for producing a water-absorbent resin according to claim 1, wherein the amount of the cross-linkable monomer is reduced according to the amount of the water-absorbent resin added as a fine powder.