JP2002284803A - Method of manufacturing highly water absorptive resin and highly water absorptive resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly water absorptive resin suitable for using as a sanitation material such as paper diaper, etc., and a method of its manufacturing. SOLUTION: In a method of manufacturing a highly water absorptive resin, where an aqueous solution of a polymerizable monomer containing a water soluble polymerizable monomer and a polymerization initiator is supplied in a hydrophobic organic solvent, and suspension polymerized batch-wise, for this method of manufacturing this highly water absorptive resin, 1-25 wt.% of the total quantity of the aqueous solution of the water soluble polymerizable monomer to be polymerized and a monomer emulsified liquid prepared by emulsifying a dispersant and the hydrophobic organic solvent are supplied in the hydrophobic organic solvent containing the dispersant, and suspension polymerized beforehand, then the rest of the aqueous solution of the water soluble polymerizable monomer is consecutively supplied and polymerized. This highly water absorptive resin particle is obtained by the suspension polymerization of the water soluble polymerizable monomer and has a pillar shape and non-smooth and uneven surface, and the ratio of the long diameter to the short diameter is 1.5-15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a superabsorbent resin, and more particularly to an improvement in a method for producing a superabsorbent resin by suspension polymerization. The superabsorbent resin obtained by the method of the present invention has a peculiar uneven surface and an elongated cocoon-like shape, and because of this peculiar shape, the liquid permeability and the pressure water absorption rate are large, so that the incontinence pad It is suitable for use in sanitary materials such as adult paper diapers and sanitary products.

[0002]

2. Description of the Related Art Recently, the demand for superabsorbent resins has been rapidly increasing. Its main use is as a sanitary material such as disposable diapers and sanitary articles, but application to various fields such as a soil water retention agent, an anti-condensation agent, a freshness retention agent, and a solvent dehydrating agent is also being studied. In hygiene materials such as incontinence pads, adult paper diapers, and sanitary products, which are the main uses of superabsorbent resins, the use of superabsorbent resins has increased and the use of diaper base materials such as pulp has decreased. is there. As the amount of resin increases, the water permeability of the superabsorbent resin before and after water absorption decreases due to the gel block of the superabsorbent resin that has absorbed water and body fluid, and the liquid permeability further deteriorates under load. May occur. As a result, water and body fluids not absorbed by the resin will return, causing discomfort to those who are using incontinence pads, adult paper diapers, and sanitary products. In addition, even for a highly water-absorbing resin, a resin fixing property that the resin is hardly moved by being fixed to a base material such as pulp has been required.
According to Japanese Patent No. 2574032, it is possible to increase the viscosity of an aqueous solution of a water-soluble polymerizable monomer to a specific viscosity with a thickener at the time of suspension polymerization and to use a specific nonionic surfactant as a dispersant to form a sausage-like product. Of highly water-absorbent resin particles. Particles of this shape are improved in fixability to the pulp substrate because of the sausage shape, but because they have a cylindrical and smooth surface with no corners, they can easily adhere to each other, and have liquid permeability, Also, the pressure water absorption rate is not satisfactory. Furthermore, the preferred major axis of the sausage-like particles obtained by this method is 1,000 to 10,000 μm, and the particles are rather large for application to a water-absorbent article of a sanitary material, which limits its use.

[0003] In order to have excellent performance not only with respect to the liquid permeation rate and the pressure water absorption rate but also with respect to the resin fixability, resin particles having large irregularities on the surface and having columnar shapes are used for mutual or pulp base material. Although it is considered to be advantageous because it easily engages with the like, the resin particles obtained by suspension polymerization are generally spherical and have a smooth surface, and thus are considered to be disadvantageous for this requirement for resin fixability. The present inventor has previously proposed a method for producing particles having an uneven surface by suspension polymerization (Japanese Patent Application Laid-Open No. 2001-11106). Particles obtained by this method have a structure in which fine particles are fused and integrated, and have irregularities on the particle surface, that is, a non-smooth and slightly obtuse angle (hereinafter, having an angle) (May also be referred to as particles). However, since the particles obtained by this method are nearly spherical, they have not been able to satisfy high demands on performance such as liquid permeability and pressurized water absorption rate.

[0004]

As the use of superabsorbent resin expands, further improvements in performance are required.
There is a demand for the development of a method for industrially producing a superabsorbent resin having improved resin fixability, liquid permeability and pressurized water absorption rate. Accordingly, an object of the present invention is to provide a highly water-absorbent resin having a high resin fixability, a liquid passing rate, and a high pressure water absorption rate, and a method for producing the resin by a suspension polymerization method.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a highly water-absorbent resin excellent in water-absorbing performance and resin fixability by a suspension polymerization method, and a method for producing the same. In a method for producing a superabsorbent polymer in which a polymerizable monomer aqueous solution containing a water-soluble polymerizable monomer and a polymerization initiator is supplied and suspension polymerization is performed in a batch mode, the amount used for the total polymerization of the water-soluble polymerizable monomer aqueous solution And a monomer emulsion obtained by emulsifying 1 to 25% by weight of a dispersant and a hydrophobic organic solvent is supplied to a hydrophobic organic solvent containing a dispersant to perform preliminary suspension polymerization. The present invention resides in a method for producing a superabsorbent resin, characterized in that a water-soluble polymerizable monomer aqueous solution is gradually supplied to carry out polymerization, and the other gist is a high water absorption obtained by suspension polymerization of a water-soluble polymerizable monomer. Resin particles And it has a non-smooth uneven surface lies in the superabsorbent polymer particles which major and the ratio of the minor axis of the particles, wherein it is 1.5 to 15.

[0006]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, any water-soluble polymerizable monomer known to give a superabsorbent resin can be used as a raw material. Some examples are (a) ionic monomers such as (meth)
(B) nonionic monomers such as acrylic acid or its alkali metal salt or ammonium salt, acrylamide-2-ethylsulfonic acid or its alkali metal salt, for example, (meth) acrylamide, N, N-dimethylacrylamide, 2-hydroxyethyl (Meth) acrylate, N
-(C) amino group-containing monomers and quaternized products thereof, such as methylol (meth) acrylamide, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, and the like, and these monomers may be used alone or in combination. You can also. In this specification, “(meth) acryl” means “acryl” or “methacryl”, and for example, (meth) acrylic acid represents acrylic acid or methacrylic acid.

[0007] Of these, preferred are (meth) acrylic acid or its alkali metal salts and ammonium salts,
(Meth) acrylamide and the like. As the alkali metal salt, sodium salt, potassium salt, lithium salt, rubidium salt and the like are used, the performance of the resulting super absorbent resin,
Sodium salts or potassium salts are preferred from the viewpoint of industrial availability and safety. These water-soluble monovinyl monomers are used as an aqueous solution when subjected to suspension polymerization, and the monomer concentration in the aqueous solution is usually 20% by weight.
As described above, it is preferably used in a concentration of 25% by weight to a saturated concentration. Further, the ionic monomers such as (meth) acrylic acid and acrylamido-2-ethylsulfonic acid are in a form in which at least a part thereof is neutralized with an alkali metal hydroxide, ammonium hydroxide or the like, that is, a salt. It is preferably used in the form of The degree of neutralization is usually 20 to 1
00 mol%, preferably 30 to 100 mol%.

[0008] These water-soluble monovinyl monomers, especially acrylic acid-based monomers, give rise to a highly water-absorbing resin by self-crosslinking to some extent during polymerization even without the use of a crosslinking agent. In order to obtain a functional resin, it is preferable to use a crosslinking agent in combination with the above-mentioned monovinyl monomer. As the cross-linking agent, a polyvinyl monomer or a compound having two or more functional groups that react with the functional groups of the above monomers is used. That is, the formation of the crosslinked structure
It can be roughly classified into a method of copolymerizing a polyvinyl monomer having two or more ethylenically unsaturated bonds, and a method of adding two reactive groups such as a glycidyl group to the functional groups of the water-soluble monovinyl monomer. There is a method of reacting the compound having the above. In the latter method, if the reaction between the functional groups occurs before the polymerization, the resulting monomer compound having two or more ethylenically unsaturated bonds is copolymerized, which is essentially the same as the former method. Does not change.

The crosslinking agents having two or more ethylenically unsaturated bonds include (a) di- or tri (meth) acrylates of polyols, for example, when the polyol is ethylene glycol, propylene glycol, trimethylolpropane, glycerin, (B) In (a) above, the unsaturated acid is other than (meth) acrylic acid, for example, maleic acid, fumaric acid, etc. C) bisacrylamides, such as N, N'-methylenebisacrylamide, and (d) di- or tri (meth) acrylates obtained by reacting polyepoxide with (meth) acrylic acid; Reacts hydroxy (meth) acrylate Di (meth) acrylic acid carbamyl esters, for example, those in which the polyisocyanate is tolylene diisocyanate, hexamethylene diisocyanate, etc .; , Tetraallyloxyethane, pentaerythritol triallyl ether, trimethylolpropane triallyl ether, diethylene glycol diallyl ether, triallyl trimellitate and the like.
Among them, in the present invention, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, N, N'-methylenebis (meth) acrylamide and the like are preferable.

Examples of the crosslinking agent having two or more functional groups that react with the functional group of the monovinyl monomer include diglycidyl ether compounds, haloepoxy compounds, and isocyanate compounds. Among these, a diglycidyl ether compound is particularly preferred. Specific examples of the diglycidyl ether compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether,
Examples thereof include polypropylene glycol diglycidyl ether, glycerin diglycidyl ether, and polyglycerin diglycidyl ether. Among them, ethylene glycol diglycidyl ether is preferable. Examples of the haloepoxy compound include epichlorohydrin and β-methylepichlorohydrin.
4-tolylene diisocyanate, hexamethylene diisocyanate and the like. The amount of the crosslinking agent used is usually 0 to 10% by weight based on the main monovinyl monomer,
Preferably it is 0 to 5% by weight.

As the polymerization initiator, a conventional water-soluble radical polymerization initiator may be used. Some examples thereof include (a) hydrogen peroxide, (b) persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, and (c) azo-based initiators such as 2,2'-azobis-
(2-amidinopropane) dihydrochloride, 2,2'-azobis- (N, N'-dimethyleneisobutylamidine) dihydrochloride, 2,2'-azobis {2-methyl-N- [1,1
-Bis (hydroxymethyl) -2-hydroxyethyl]
And propionamide. These water-soluble radical initiators can be used alone or in combination. In addition, hydrogen peroxide and persulfate can be used as a redox initiator by combining a reducing substance such as sulfite and L-ascorbic acid, an amine salt, and the like. These polymerization initiators are suitably used in the range of 0.001 to 5% by weight, particularly 0.01 to 1% by weight, based on the water-soluble polymerizable monomer.

As the hydrophobic organic solvent used for the monomer emulsion and the reaction medium for suspension polymerization, any one can be used as long as it is basically insoluble in water and inert to polymerization. Some examples thereof include (a) aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane; and (ii) alicyclic hydrocarbons such as cyclohexane and methylcyclohexane. C) Aromatic hydrocarbons such as benzene, toluene, xylene and the like. Preferably, the hydrophobic organic solvent has a lower boiling point than water and forms an azeotrope with water. Usually, n-hexane, n-heptane or cyclohexane is used. The hydrophobic organic solvent as a reaction medium for suspension polymerization is usually used in an amount of 0.5 to 10 times by weight, preferably 0.8 to 3 times by weight, based on the aqueous monomer solution. If the ratio of the hydrophobic organic solvent is too small, the resin particles are likely to aggregate even if a dispersant is present, and it is difficult to obtain a highly absorbent resin having a desired particle size. Conversely, if this ratio is too large, productivity will decrease.

In the present invention, a phosphoric ester dispersant represented by the general formula (1) is present in a hydrophobic organic solvent as a reaction medium during suspension polymerization.

[0014]

Embedded image (Wherein, R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group, and R ² represents a hydroxyl group or R ¹ O—
(CH ₂ CH ₂ O-) represents a n- group, n represents an integer of 1 to 30)

This phosphate ester-based dispersant is a highly safe dispersant having low irritation and toxicity. In the general formula (1), R ¹ is preferably an alkyl group having 8 to 23 carbon atoms or a monoalkylphenyl group. n is 2
It is preferably 15. R ² is R ¹ O- (CH ₂ CH ₂ O
—) N-group, two R ¹ O— (CH ₂ CH ₂
The O-) n- groups are preferably identical. Representative and preferred examples of R ¹ include a nonylphenyl group, an octylphenyl group, a tridecyl group, a lauryl group, a 2-ethylhexyl group, an octadecyl group, and a dodecylphenyl group. This commercially available phosphate ester-based dispersant is usually a mixture of a phosphate monoester and a phosphate diester.

The phosphoric ester-based dispersant is usually present in a hydrophobic organic solvent in an amount of 0.01 to 5% by weight. 0.0
Preferably it is present at 5 to 2% by weight, especially 0.05 to 1% by weight. If the amount is too small, the desired dispersing effect cannot be obtained, while if it is too large, aggregation tends to occur when the produced resin particles are dried.

In the present invention, the suspension polymerization is carried out in two stages,
It consists of a staged suspension polymerization (herein referred to as a pre-suspension polymerization) and a subsequent suspension polymerization carried out in a second stage (herein referred to as a main suspension polymerization). . In the pre-suspension polymerization, a monomer emulsion obtained by emulsifying a part of the aqueous polymerizable monomer solution, the hydrophobic organic solvent and the dispersant is added to the hydrophobic organic solvent containing the dispersant. In this pre-suspension polymerization, a predetermined amount of a monomer emulsion is supplied to an organic solvent, and then the polymerization can be carried out by raising the temperature.However, the monomer is added to a hydrophobic organic solvent maintained under polymerization conditions. It is preferable to carry out suspension polymerization while sequentially supplying the emulsion. In the pre-suspension polymerization, the supply rate and stirring intensity of the monomer emulsion are controlled so that the monomer emulsion is dispersed as fine droplets. The monomer emulsion is usually supplied at the same time as the start of the suspension polymerization, but in another embodiment, a small amount of an aqueous monomer solution may be supplied at the start of the suspension polymerization, followed by the monomer emulsion. In that case, the amount of the aqueous monomer solution initially supplied is at most 5% by weight of the amount of monomer used for the total polymerization.
It is about. If the amount exceeds 5% by weight, desired columnar particles cannot be obtained.

The aqueous monomer solution used as the monomer emulsion for the pre-suspension polymerization is usually 1 to 2 parts of the total aqueous monomer solution.
5% by weight. If the supply amount is less than 1% by weight, columnar particles cannot be obtained. If the content is more than 25% by weight, the polymerization system becomes unstable and desired particles cannot be obtained. The aqueous monomer solution used in the pre-suspension polymerization may not be of the same composition as the aqueous monomer solution used in the main suspension polymerization, but from the viewpoint of economy, operability, and reality, the same composition is better. preferable.

The amount of the hydrophobic organic solvent used in the monomer emulsion is 0.1 to 15 times by weight, preferably 0.1 to 10 times by weight of the aqueous monomer solution to be emulsified.
If the amount is less than 0.1 times by weight, desired columnar particles having corners on the surface cannot be obtained. It is economically disadvantageous to add more than 15 times by weight, and a large amount of a dispersant is used for emulsification, so that the polymerization system becomes unstable. The type and composition of the hydrophobic organic solvent used in the monomer emulsion of the previous suspension polymerization and the hydrophobic organic solvent used in the suspension polymerization as the reaction medium may be changed, but the type and composition are changed. As a result, the boiling point changes and the polymerization temperature changes, thereby changing the quality of the resulting superabsorbent resin. Therefore, it is preferable to use the same hydrophobic organic solvent.

The dispersant used in the monomer emulsion is 0.1% by weight to 15% by weight based on the aqueous monomer solution to be emulsified.
Add and emulsify. Preferably it is 0.1 to 10% by weight. If it is less than 0.1% by weight, emulsification does not work well,
Columnar particles cannot be obtained. Conversely, 15% by weight
If the amount is larger, the dispersing agent becomes excessive and the polymerization system becomes unstable. Although it depends on other conditions, it is generally difficult to produce resin particles having desired properties outside this range. The dispersant is appropriately selected from the phosphate dispersants represented by the general formula (1). At this time, the dispersant of the monomer emulsion may be of a different type from the dispersant present in the reaction medium of the suspension polymerization, but is the same in terms of the stability of the polymerization reaction and the quality of the obtained superabsorbent resin. It is preferred to use a dispersant of

As a method of emulsification, basically, a method of obtaining a stable emulsion by liquid-liquid dispersion with a shearing force can be generally used. For example, for an emulsifier, the fluid
A homomixer or the like, a propeller stirrer, a disperser, an anchor type mixer, a paddle mixer, an ultra mixer for emulsifying by a shearing force generated when passing through a gap between a rotor and a stator that rotates at a high speed from 00 rpm to 12000 rpm, that is, a so-called external shearing force. Known mechanical emulsification equipment such as a mixer and a pipeline mixer can be used.

In the method of the present invention, the main suspension polymerization is carried out subsequent to the preliminary suspension polymerization. At this time, after the monomer emulsion in the preliminary suspension polymerization is introduced, the holding time between the start of the main suspension polymerization and the main suspension polymerization is appropriately adjusted. By adjusting, the irregularities and the shape of the surface of the generated resin particles can be arbitrarily controlled. If the holding time is lengthened, columnar particles having relatively large surface irregularities and a small minor axis can be obtained.If the main suspension polymerization is performed immediately after the preceding suspension polymerization, the surface irregularities may be increased. Columnar particles having a slightly larger diameter can be obtained.

The main suspension polymerization is usually carried out after the polymerization rate of the monomer subjected to the preliminary suspension polymerization reaches at least 10%. For that purpose, although it depends on the polymerization conditions of the pre-suspension polymerization, the main suspension polymerization is usually carried out at least 3 minutes, especially at least 5 minutes after the supply of the aqueous monomer solution in the pre-suspension polymerization is completed. It is preferable to start. In addition,
If this time is long, the productivity is reduced.
The main suspension polymerization is started within minutes, usually within 30 minutes. If the pre-suspension polymerization is carried out under polymerization conditions such that the polymerization rate of the monomer subjected to the reaction at the end of the supply of the monomer emulsion reaches 10% or more, the main suspension is continued after the completion of the supply of the monomer emulsion. Suspension polymerization can be initiated. In that case, larger columnar resin particles are generated.

The main suspension polymerization is carried out by maintaining a hydrophobic organic solvent containing a polymer produced in the preceding suspension polymerization under polymerization conditions, and sequentially supplying the remaining amount of the polymerizable monomer aqueous solution thereto. The supply of the polymerizable monomer aqueous solution in the main suspension polymerization is usually performed over a period of at least 10% of the total polymerization time of the main suspension polymerization, and is preferably 40% or more, particularly 60% or more of the total polymerization time. It is preferable to supply the monomer aqueous solution over a period of time. The total polymerization time means that the degree of polymerization of the resin particles generated from the start of the main suspension polymerization is 98.
%, Preferably 98.5%, or the time to complete the polymerization operation, whichever is shorter.

The supply of the polymerizable monomer aqueous solution is usually performed continuously at a constant rate, but the supply rate may be changed if desired. Also, the supply of the monomer aqueous solution can be temporarily interrupted on the way. In the main suspension polymerization, the supplied monomer aqueous solution is absorbed by the polymer already existing in the hydrophobic organic solvent and grows it, or the polymer generated from the supplied monomer aqueous solution is already present. It is thought that it grows in combination with the existing polymer. Therefore, it is preferable that the supply rate and the stirring intensity of the aqueous monomer solution are set so that the aqueous monomer solution is sufficiently dispersed. Although the polymerization reaction depends on the polymerization initiator, it is usually carried out at 40 to 150 ° C.
If the temperature is too high, self-crosslinking becomes active, and the water absorption capacity of the resin particles produced is reduced. On the other hand, when the temperature is too low, not only long time is required for polymerization, but also sudden polymerization may be caused to form lumps. Suitable polymerization temperatures are between 60 and 9
The polymerization is preferably carried out at 0 ° C., particularly under the reflux condition of a hydrophobic organic solvent.

After completion of the polymerization, the resin particles generated by filtration or centrifugation are collected, surface-treated and dried by a conventional method to obtain a product. When a hydrophobic organic solvent that forms an azeotropic mixture with water is used, it is preferable to dehydrate the resin particles by azeotropic distillation before collecting the resin particles by filtration or the like. In the suspension polymerization according to the method of the present invention, the polymerization conditions for producing the desired resin particles are wide and the adhesion of the resin to the walls of the polymerization vessel is small, so that the polymerization operation is easy. Further, the resin particles obtained by the method of the present invention, unlike the true spherical particles obtained by the ordinary suspension polymerization method, has a columnar, and has a structure such that fine particles are fused and integrated, Particles having irregularities on the particle surface, that is, particles having a non-smooth and slightly near obtuse angle (hereinafter sometimes referred to as having an angle).

The resin particles having such a unique shape of the present invention can be produced by dropping an aqueous monomer solution as an emulsified solution and then dropping the remaining monomer aqueous solution after the polymerization rate becomes 10% or more. Can be obtained by fusing and forming a structure of integrated columnar particles. Then, by appropriately controlling the supply timing of the residual monomer aqueous solution, and the method, the shape and structure of the columnar particles to be generated can be arbitrarily changed, and the ratio of the major axis to the minor axis of the columnar particles is usually 1.5 to Fifteen. The average particle size is usually 30
It is as large as 0 to 1000 μm, which is a problem in handling.
Almost no fine powder of less than μm is contained. Therefore, the resin particles obtained by the method of the present invention have a high liquid passing rate and a high pressure water absorption rate, and have high resin fixability before and after water absorption. The average particle diameter referred to here is a value measured by applying the method for measuring the average particle diameter of true spherical particles for convenience in order to show the outline of the size of the columnar resin particles of the present invention.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to the following Examples without departing from the scope of the invention. In addition, the performance of the water-absorbent resin particles, that is, the water-absorbing ability, the pressure absorption rate, the average particle diameter, the bulk density, and the fixability of the water-absorbent resin were measured as follows.

(1) Water absorbency A 250-mesh nylon bag (20 cm × 10 cm) is immersed in 500 cc of artificial urine for 30 minutes. The nylon bag is pulled up, suspended in the air and drained for 15 minutes, and the weight (w ₁ (g)) is measured. About 0.5 g of resin particles are collected, and the weight (w ₂ (g)) is precisely weighed and placed in the above nylon bag. This was immersed in 500 cc of artificial urine for 30 minutes, then the nylon bag was pulled up, suspended in air and drained for 15 minutes, and then weighed (w).
₃ ) Measure (g)).

[0030]

## EQU1 ## Water absorption capacity = (w ₃ −w ₁ ) / w ₂ (g / g)

The artificial urine used had the following composition by weight. Urea 1.94% Sodium chloride 0.80% Calcium chloride 0.06% Magnesium sulfate 0.11% Pure water 97.09%

(2) Water absorption speed According to JIS K-7224, 1.0 g of resin particles were placed on a nonwoven fabric laid on a support plate having small holes so as to have a uniform thickness. The lower surface of the resin particle layer was brought into contact with the artificial urine, and the amount of the resin particles absorbing the artificial urine was measured. The amount of artificial urine absorbed for 2 minutes after the start was defined as the water absorption rate.

(3) Pressurized water absorption rate Measured using the apparatus shown in FIG. 1 according to JIS K-7224. A support cylinder (2.5 cm in inner diameter) was placed on a nonwoven fabric laid on a support plate having small holes so that the small holes were at the center, and 1.0 g of resin particles were placed thereon to have a uniform thickness. Then, a weight is placed on the resin particles, and the uniform load is 1
It was placed so as to apply ² g / cm ² . The lower surface of the resin particle layer was brought into contact with the artificial urine, and the amount of the resin particles absorbing the artificial urine was measured. The amount of artificial urine absorbed 10 minutes after the start was defined as the water absorption rate.

(4) Flow rate Bio column BC (manufactured by Geberal, CF-30K; inner diameter 2)
A glass filter is attached to the lower part of a cylinder having a length of 5.6 mm and a length of 500 mm, and a cock is provided at the lower end; After putting 200 ml of 0.9% by weight saline solution into the column, 0.50 g of resin particles are slowly charged. Put a rubber stopper in the upper end opening, and after 5 minutes, reciprocate up and down three times to shake. After standing for an additional 25 minutes after standing upright, the cock is released, the liquid is allowed to flow until the liquid level drops to the 100 ml weighing line, and the cock is closed. While paying attention not to allow the resin to rise, 0.9% by weight saline solution is supplied until the liquid level reaches the 200 ml balance line. After confirming that the resin particles have sufficiently settled out, open the cock and let the liquid flow out, and measure the time required for the liquid surface to pass through the 150 ml balance line and the 100 ml balance line.

## EQU2 ## Flow rate (ml / min) = 50 × 60 / hour (second) The temperature of the saline solution is room temperature. When no resin is present, the time required for the liquid surface to pass between the 150 ml weighing line and the 100 ml weighing line is 6.8 seconds.

(5) Average particle size The ASTM type standard sieve was screened from the top to 8, 12, 20, 32, 40, 60 meshes.
The mesh, 80 mesh, 100 mesh, 120 mesh, 150 mesh, and the tray were combined in this order, and about 50 g of the resin particles were put into the uppermost sieve, and shaken with a low tap automatic shaker for 1 minute. The weight of the resin particles remaining on each sieve was weighed, and the total weight was taken as 100%, the particle size distribution was determined from the weight fraction, and the 50% particle size on a weight basis was taken as the average particle size. In addition, the measurement of the minor axis and major axis of the particles was performed by scanning electron micrographs (SE) of the resin particles as schematically shown in FIG.
From M), 100 particles were arbitrarily sampled, and the maximum length in the longitudinal method of each particle was defined as the major axis, and the maximum length orthogonal to the major axis line was measured as the minor axis. The average of the measured values was defined as the ratio of the major axis / minor axis of the resin particles.

(6) Bulk density The bulk density was measured in accordance with JIS K-6721. The measurement was performed three times, and the average value was obtained. (7) Fixing property of water-absorbed resin particles 2.5 g of resin particles were added to fluff pulp (basis weight: 150 g /
m ² , size 19 × 7.5 cm).
A fluff pulp of the same size was overlaid on the resin particle / fluff pulp composite to prepare a simple water-absorbing pad. This water-absorbing pad is put on a hydraulic press at room temperature for 100
After applying a load of kg for 20 minutes, 0.9% physiological saline 1
25 g of water was absorbed by a water-absorbing pad. A 3.5 kg iron weight is placed on the water-absorbing pad, and is placed in a horizontal direction with respect to the water-absorbing pad for 3 minutes using a universal shaker (manufactured by Inuchi Seieido, model number MS-1) (number of shaking: 100). Times /
Min) Shake. The load was removed, and the resin particles existing in the pulp and the resin particles that had come out of the pulp by vibrating were respectively recovered, and their weights were measured. Resin particle fixability was calculated by the following equation.

[0037]

## EQU3 ## Fixability (%) of water-absorbed resin particles = {resin particles in pulp (g)} resin particles outside pulp (g) + resin particles in pulp (g)} × 100

EXAMPLE 1 145.4 g of acrylic acid was diluted with 9.4 g of water and, while cooling, 242.3% aqueous sodium hydroxide solution 242.3
g was added for neutralization. To this solution, 0.0727 g of ethylene glycol diglycidyl ether (manufactured by Nagase Kasei Kogyo Co., Ltd., Denacol EX810), 0.0146 g of sodium hypophosphite monohydrate and 0.1% of potassium persulfate were added.
0727 g was added and dissolved to obtain an aqueous monomer solution.

Part 4 of the aqueous monomer solution prepared above
0.0 g was placed in a 100 ml beaker, and polyoxyethylene octylphenyl ether phosphate (a product of Daiichi Kogyo Seiyaku Co., Price Surf A210G,
An average degree of polymerization of oxyethylene groups of about 7) 0.30 g and cyclohexane 10.0 g were added, and the mixture was emulsified by a mechanical emulsifier (Hiscotron, manufactured by Nichion Medical Science Instruments Co., Ltd.) at 15,000 rpm for 3 minutes to obtain a monomer emulsion.

624 g of cyclohexane was placed in a three-liter four-necked round-bottomed flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen gas inlet tube, and polyoxyethylene octyl phenyl ether phosphate (No. A product from Ichigyo Seiyaku Co., Ltd., Plysurf A210G, an average degree of polymerization of oxyethylene groups of about 7)
The mixture was dispersed by stirring at 20 rpm. After the flask was purged with nitrogen, the temperature was raised to 80 ° C. to reflux cyclohexane. The above monomer emulsion was dropped at 6.6 g / min for 8 minutes. After being left at the same temperature for 10 minutes after the completion of the dropping, the remaining monomer aqueous solution was dropped at 6.6 g / min over 54 minutes. After the completion of the dropwise addition, the temperature was maintained at 75 ° C. for 30 minutes.
Dehydration was performed until the water content of the resin particles generated by azeotropic distillation with cyclohexane became 7%.

When the stirring was stopped after the completion of the dehydration, the resin particles settled at the bottom of the flask, and were separated by decantation. The obtained resin particles were heated to 90 ° C. to remove attached cyclohexane and some water. The obtained dried resin particles had irregular and columnar particles on the surface having an average particle diameter of 405 μm. The results are shown in Table 1, and the scanning micrograph of the particles is shown in FIG.

Example 2 In Example 1, the amount of the aqueous monomer solution to be emulsified was 25
g, the amount of cyclohexane was 25 g, and the amount of dispersant used for emulsification was 0.20 g, and polymerization was carried out in exactly the same manner as in Example 1. Table 1 shows the results.

Example 3 In Example 1, the amount of the aqueous monomer solution to be emulsified was 1
Polymerization was carried out in the same manner as in Example 1 except that 0.0 g, the amount of cyclohexane was changed to 40.0 g, and the amount of the dispersant was changed to 0.10 g. Table 1 shows the results.

Example 4 In Example 1, the monomer aqueous solution to be emulsified was
0 g, the amount of cyclohexane is 2.5 g, and the amount of dispersant is 0.1 g.
Polymerization was carried out in the same manner as in Example 1 except that the amount was changed to 08 g. Table 1 shows the results.

Example 5 In Example 1, the monomer aqueous solution to be emulsified was 5.0
g, the amount of cyclohexane was 45.0 g, and the amount of dispersant was 0.1 g.
Polymerization was carried out in the same manner as in Example 1 except that the amount was changed to 50 g. Table 1 shows the results.

Example 6 In Example 1, the stirring rotation speed of the polymerization tank was changed to 350 rpm.
The polymerization was carried out by the same operation except that the above was changed. Table 1 shows the results.

Example 7 Polymerization was carried out in the same manner as in Example 1, except that the addition of the remaining monomer aqueous solution was started immediately after the completion of the dropping of the monomer emulsion. The results are shown in Table 1, and a scanning micrograph of the generated resin particles is shown in FIG.
Shown in

Comparative Example 1 The procedure of Example 1 was repeated, except that the monomer emulsion was not mechanically emulsified when preparing the monomer emulsion, but was dispersed by stirring the monomer aqueous solution and cyclohexane lightly. The polymerization was carried out in exactly the same manner as in Example 1.
The results are shown in Table 1, and a scanning micrograph of the generated resin particles is shown in FIG.

Comparative Example 2 Polymerization was carried out in the same manner as in Example 1 except that the amount of the monomer emulsion was changed to 2.0 g, the amount of cyclohexane was changed to 0.60 g, and the amount of the dispersant was changed to 0.02 g. Was. Table 1 shows the results.

Comparative Example 3 The procedure of Example 7 was repeated, except that the monomer emulsion was not mechanically emulsified when preparing the monomer emulsion, but the monomer aqueous solution and cyclohexane were lightly stirred and dispersed to form a dispersion. Polymerization was carried out in the same manner as in Example 7. The results are shown in Table 1, and a scanning micrograph of the generated resin particles is shown in FIG.

[0051]

[Table 1]

[0052]

According to the method of the present invention, desired resin particles can be produced by suspension polymerization in which the polymerization operation is simple, and the obtained resin particles can be obtained by a usual suspension polymerization method. Unlike a true sphere, it has a columnar shape and an irregular particle surface, has a high liquid passing rate and a high pressure water absorption rate, and has excellent resin fixability before and after water absorption.
Therefore, it is extremely useful as water-absorbing resin particles for sanitary materials requiring high water-absorbing performance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an apparatus for measuring a pressure water absorption rate.

FIG. 2 is a schematic diagram showing a flow rate measuring device.

FIG. 3 is a schematic diagram showing a major axis and a minor axis of resin particles.

FIG. 4 is a scanning electron micrograph of the resin particles obtained in Example 1.

FIG. 5 is a scanning electron micrograph of the resin particles obtained in Example 7.

FIG. 6 is a scanning electron micrograph of the resin particles obtained in Comparative Example 1.

FIG. 7 is a scanning electron micrograph of the resin particles obtained in Comparative Example 3.

Claims (14)

[Claims] 1. A process for producing a superabsorbent resin in which a polymerizable monomer aqueous solution containing a water-soluble polymerizable monomer and a polymerization initiator is supplied to a hydrophobic organic solvent and subjected to suspension polymerization in a batch system. A monomer emulsion obtained by emulsifying 1 to 25% by weight of the amount used for the total polymerization of the polymerizable monomer aqueous solution and the dispersant and the hydrophobic organic solvent is supplied to the hydrophobic organic solvent containing the dispersant. A method for producing a super water-absorbent resin, wherein pre-suspension polymerization is performed, and then the remaining amount of an aqueous solution of a water-soluble polymerizable monomer is gradually supplied to perform polymerization. 2. The weight ratio of the hydrophobic organic solvent to the aqueous solution of the water-soluble polymerizable monomer in the monomer emulsion is from 0.1 to 15%.
The method for producing a highly water-absorbent resin according to claim 1, wherein 3. The method according to claim 1, wherein the weight ratio of the dispersant to the aqueous solution of the water-soluble polymerizable monomer in the monomer emulsion is 0.1 to 15. . 4. The method according to claim 1, wherein the dispersant represented by the general formula (1) is used as a dispersant contained in the monomer emulsion and the hydrophobic organic solvent. 3. The method for producing a superabsorbent resin according to 1. Embedded image (Wherein, R ¹ represents an alkyl group which may be substituted with a phenyl group having 8 to 30 carbon atoms or an aryl group which may be substituted with an alkyl group, and R ² represents a hydroxyl group or R ¹ O
- (CH ₂ CH ₂ O-) represents a n- group, n represents an integer of 1 to 30) 5. The method according to claim 1, wherein the supply of the remaining aqueous solution of the water-soluble polymerizable monomer is started after the conversion of the water-soluble polymerizable monomer in the preliminary suspension polymerization reaches 10% or more. 5. The method for producing a superabsorbent resin according to any one of the above items 4. 6. An interval from the end of the supply of the monomer emulsion for performing the preliminary suspension polymerization to the start of the supply of the remaining aqueous solution of the water-soluble polymerizable monomer is 3 minutes or more. The method for producing a superabsorbent resin according to any one of claims 1 to 5. 7. The method according to claim 1, wherein the supply of the remaining amount of the aqueous solution of the water-soluble polymerizable monomer is started immediately after the completion of the supply of the monomer emulsion for performing the preliminary suspension polymerization.
The method for producing a superabsorbent resin according to any one of the above. 8. The supply time of the remaining aqueous solution of the water-soluble polymerizable monomer is 10 times the total polymerization time for polymerizing the remaining monomer.
% Of the superabsorbent resin according to any one of claims 1 to 7. 9. The superabsorbent water according to claim 1, wherein the hydrophobic organic solvent used for emulsification is equivalent to the hydrophobic organic solvent used for main suspension polymerization. Method of manufacturing resin. 10. The water-soluble polymerizable monomer is acrylic acid,
Acrylate, methacrylic acid, methacrylate, acrylamide and methacrylamide are mainly composed of a water-soluble monovinyl monomer selected from the group consisting of, and any one of claims 1 to 9 characterized by the above-mentioned. Production method of super absorbent resin. 11. An aqueous solution of a water-soluble polymerizable monomer is composed of the above-mentioned water-soluble monovinyl monomer and a compound having a small proportion thereof and a plurality of functional groups which react with the functional groups of the water-soluble monovinyl monomer. The method for producing a highly water-absorbent resin according to any one of claims 1 to 10, further comprising a crosslinking agent selected from the group. 12. The superabsorbent resin according to claim 1, wherein the superabsorbent resin has columnar and non-smooth uneven surfaces.
A method for producing a highly water-absorbent resin, wherein the ratio of the major axis to the minor axis is 1.5 to 15. 13. Highly water-absorbent resin particles obtained by suspension polymerization of a water-soluble polymerizable monomer, having a columnar and non-smooth uneven surface, and having a ratio of the major axis to the minor axis of 1.5 to 1.5. 15. Highly water-absorbent resin particles having a particle size of 15. 14. The superabsorbent resin particles according to claim 13, which is obtained by any one of the production methods according to claim 1.