JP2005272653A - Granulating process of hydrogel and granulating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a granulating process using a screw type of extruder, where a hydrogel is granulated without deteriorating physical properties thereof and without using a special device and, further, the filling factor in the extruder has no influence on the granulation. <P>SOLUTION: The screw type of the extruder is characterized by an equipped function which prevents reverse flow of hydrogel toward a supplying port without adding a specific system. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for refining a water-containing gel, such as pulverizing a water-containing gel suitably used as a material for a water absorbent resin.

The water-absorbent resin is used as a component of sanitary materials such as paper diapers, sanitary products, simple toilets, wound protection materials, and wound healing materials, and is used in the agriculture, forestry, civil engineering, food, It is used in many fields such as medical field and housing field.
Examples of such water-absorbing resins include polyacrylic acid partially neutralized crosslinked products, starch-acrylonitrile graft polymer hydrolysates, starch-acrylic acid graft polymer neutralized products, and vinyl acetate-acrylic acid ester copolymers. Known are saponified polymers, hydrolysates of acrylonitrile copolymers or acrylamide copolymers, or cross-linked products thereof.

The above water-absorbing resin is usually obtained as a water-containing gel (hereinafter simply referred to as a water-containing gel) which is a semi-solid and highly elastic gel, but it is rarely used as it is and often has a drying efficiency. In order to increase the viscosity, it is dried after being finely divided by pulverization or the like, and further pulverized as necessary.
Then, what dried the said hydrogel and made it the powder state is used for various uses as a water absorbing resin.

  Conventionally, as a method for refining the hydrated gel, for example, a method of crushing the hydrated gel after polymerization with a screw type extruder such as a meat chopper has been used. As a technique for pulverizing a hydrogel using the screw extruder, a screw extruder provided with a perforated plate having a pore diameter of 6.5 mm to 18 mm is obtained by heating the hydrogel at a temperature of 45 ° C. to 95 ° C. A method of pulverizing the extruded hydrous gel with a roll mill or the like (see Patent Document 1), and at least an anti-reverse member for preventing the hydrous gel from returning to the supply port side. Examples thereof include a method using a screw extruder provided in the vicinity, a method of defining the filling rate of the hydrogel inside the screw extruder (see Patent Document 2), and the like.

In the method described in Patent Document 1, a particulate hydrogel having a narrow particle size distribution is obtained within an average gel particle size range of 0.5 mm to 3 mm. Therefore, the drying efficiency is greatly improved, and a water-absorbing resin with significantly less residual monomer can be obtained with high productivity.
However, the amount of water-soluble components in the finally obtained water-absorbing resin may be increased by cutting the cross-linked polymer chain in the hydrogel due to mechanical external force when the hydrogel is finely divided.
Further, according to the method described in Patent Document 2, by providing the above-described reversion preventing member, the hydrogel can be well extruded and pulverized with little mechanical external force applied.

However, it is necessary to provide a specific anti-reverse member on the screw extruder, which complicates equipment and makes it difficult to design the apparatus.
Further, according to the method described in the publication, by specifying the filling rate of the hydrogel in the screw type extruder, the hydrogel can be extruded and pulverized with little mechanical external force.
However, since the filling rate inside the extruder is defined, the pulverization speed of the crosslinked polymer is limited.
Japanese Patent Laid-Open No. 5-70597 JP 2000-67527 A

  The present invention has been made in view of the above-mentioned problems, and its purpose is due to mechanical external force when the hydrogel is refined in the hydrogel refinement process using a screw type extruder. In addition, when the cross-linked polymer chain in the hydrogel is cut, the uniform pulverization is hardly accompanied by almost no decrease in the physical properties of the hydrogel, such as the amount of water-soluble components in the finally obtained water-absorbent resin is increased. An object of the present invention is to provide a fine granulation method that can be carried out without using a device with a special mechanism such as the above, and that the rate of fine granulation of the hydrogel is not affected by the filling rate inside the extruder.

As a result of intensive studies to solve the above problems, the present inventors have optimized the structure of the screw-type extruder used for the above pulverization treatment, and thereby added a water-containing gel without adding a specific reversal prevention member. It was found that it can be extruded well.
The inventors have also found that the above-described reversion preventing mechanism can be extruded well without being affected by the filling rate of the hydrogel inside the extruder, and have completed the present invention.
That is, the present invention
[1]
In the hydrogel refinement method in which the hydrogel is supplied from the supply port of the screw-type extruder and extruded from the extrusion port provided with the perforated plate to perform the pulverization process, from the screw end of the screw-type extruder to the tip of the supply port When the length of the nozzle is A and the length from the supply port tip to the screw tip is B, the following formula (1)
C = (B / A) × 100 (1)
Of the water-containing gel characterized by using a screw type extruder having a function of preventing the water-containing gel from returning to the supply side by making the value C defined by the above in the range of 100% to 500%. Fine graining method,
[2]
In the fine granulation method, when the length from the screw end of the screw type extruder to the tip of the supply port is A and the length from the tip of the supply port to the screw tip is B, the following formula (1)
C = (B / A) × 100 (1)
By making the value C defined in the range of 100% to 500%, the water-containing gel screw-type extruder atomizer having the function of preventing the water-containing gel from returning to the supply side,
It is.

In the hydrogel refinement method according to the present invention, the feed port of the screw extruder used is set at a specific position with respect to the screw, so that the hydrogel does not return to the feed port side and is pushed smoothly. Extruded from the exit.
For this reason, the water-containing gel does not stay in the screw case of the screw-type extruder, and it is avoided that a mechanical external force exceeding the necessary minimum is applied to the water-containing gel. That is, water content such as the amount of water-soluble components in the water-absorbent resin finally obtained is increased by cutting the cross-linked polymer chain in the water-containing gel due to mechanical external force when the water-containing gel is refined. Fine graining can be easily performed without lowering the physical properties of the gel.

And since the said objective is implement | achieved without giving a special process inside the screw type extruder, the structure of an extruder is not complicated.
In addition, since the above reversion preventing mechanism can perform fine granulation without affecting the filling rate of the hydrogel in the extruder without affecting the fine gelation rate of the hydrogel, there is a wide range of operating conditions of the extruder. It becomes possible to make it.

The method for refining a hydrogel according to the present invention will be described in detail below based on the drawings, but the present invention is not limited to this.
The water-containing gel to be finely divided in the present invention is suitably used as a water-absorbing resin, for example, and is obtained by aqueous solution polymerization of an ethylenically unsaturated monomer so as to form a crosslinked structure. Is.

  The ethylenically unsaturated monomer used as the raw material for the hydrous gel is a monomer having water solubility, and examples thereof include (meth) acrylic acid, β-acryloyloxypropionic acid, maleic acid. Acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, cinnamic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2- (meth) acrylamido-2-methylpropane Acid group-containing monomers such as sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, vinyl phosphonic acid, 2- (meth) acryloyloxyethyl phosphoric acid, and alkali metal salts and alkaline earth metal salts thereof , Ammonium salt, alkylamine salt; N, N-dimethylaminoethyl (meth) acrylate, N Dialkylaminoalkyl (meth) acrylates such as N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and the quaternized compounds thereof (for example, reaction with alkyl hydride, dialkyl sulfate N-alkylvinylpyridinium halide; hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl methacrylate and 2-hydroxypropyl (meth) acrylate; (meth) acrylamide, N-ethyl (meth) acrylamide, N -N-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide; alkoxy polyethylene such as methoxypolyethylene glycol (meth) acrylate Glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate; vinylpyridine, N-vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine; N-vinylacetamide;

Only one kind of these ethylenically unsaturated monomers may be used, or two or more kinds may be appropriately mixed.
Among the ethylenically unsaturated monomers exemplified above, it is preferable to use a monomer containing an acrylate monomer as a main component because the water absorption characteristics and safety of the resulting hydrogel are further improved. Here, the acrylate monomer refers to acrylic acid and / or water-soluble salts of acrylic acid.
The water-soluble salts of acrylic acid are alkali metal salts, alkaline earth metal salts, ammonium salts, hydroxyammonium salts, amine salts of acrylic acid having a neutralization rate in the range of 30 mol% to 100 mol%, An alkylamine salt is shown.

These acrylate monomers may be used alone or in combination of two or more. In addition, the average molecular weight (degree of polymerization) of the water absorbent resin is not particularly limited.
The water-containing gel can be obtained by polymerizing the monomer composition containing the ethylenically unsaturated monomer as a main component in the presence of a crosslinking agent. Another monomer (copolymerizable monomer) copolymerizable with the ethylenically unsaturated monomer may be included to such an extent that the hydrophilicity of the resulting hydrogel is not inhibited.

Specific examples of the copolymerizable monomer include (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate; vinyl acetate, vinyl propionate, and the like. And the like. These copolymerizable monomers may be used alone or in combination of two or more.
Examples of the crosslinking agent used when polymerizing the monomer component include a compound having a plurality of vinyl groups in the molecule; a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule. And the like. These crosslinking agents may be used alone or in combination of two or more.

  Specific examples of the compound containing a plurality of vinyl groups in the molecule include N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol di (meth). Acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate , Dipentaerythritol hexa (meth) acrylate, N, N-diallylacrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallyl Min, diallyloxyacetic acid, N- methyl -N- vinyl acrylamide, bis (N- vinylcarboxamides), such as tetraallyloxyethane, and the like.

  Examples of the compound having a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule include (poly) ethylene glycol, (poly) propylene glycol, 1,3-propanediol, 2,2,4 -Trimethyl-1,3-pentanediol, (poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2- Polyhydric alcohol compounds such as cyclohexanedimethanol, trimethylolpropane, diethanolamine, triethanolamine, pentaerythritol, sorbitol; (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, diglycerol polyglycidyl ether, (poly )Professional Epoxy compounds such as lenglycol diglycidyl ether and glycidol; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyamidepolyamine, polyethyleneimine, and those polyamines and haloepoxy compounds Condensates with polyhydric acids; polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; polyvalent oxazoline compounds such as 1,2-ethylenebisoxazoline; γ-glycidoxypropyltrimethoxysilane, γ-amino Silane coupling agents such as propyltrimethoxysilane; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl- , 3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolane- 2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopane- Examples include alkylene carbonate compounds such as 2-one; haloepoxy compounds such as epichlorohydrin; hydroxides or chlorides such as zinc, calcium, magnesium, aluminum, iron, and zirconium.

The amount of the crosslinking agent used is not particularly limited, but is preferably in the range of 0.0001 mol% to 10 mol% with respect to the monomer component, and 0.001 mol. More preferably, it is in the range of% to 1 mol%.
In the present invention, the method for polymerizing the above monomer components is not particularly limited, and various conventionally known polymerization methods such as bulk polymerization, precipitation polymerization, aqueous solution polymerization, and reverse phase suspension polymerization are employed. be able to. Among them, aqueous solution polymerization using the above monomer components as an aqueous solution is preferable from the viewpoint of improving the water absorption characteristics of the obtained water absorbent resin and ease of polymerization control.
During the above polymerization reaction, it is preferable that the monomer component is allowed to stand for polymerization without stirring. Furthermore, when the above ethylenically unsaturated monomer is polymerized in an aqueous solution, any one of continuous polymerization or batch polymerization may be employed, and any of normal pressure, reduced pressure, and pressurized pressure may be employed. You may implement under pressure. The polymerization reaction is preferably carried out under an inert gas stream such as nitrogen, helium, argon, carbon dioxide.

At the start of polymerization in the polymerization reaction, for example, a polymerization initiator or activation energy rays such as radiation, electron beam, ultraviolet ray, electromagnetic ray, or the like can be used. Specific examples of the polymerization initiator include inorganic compounds such as sodium persulfate, ammonium persulfate, potassium persulfate, and hydrogen peroxide; t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, and the like. Organic peroxide; 2,2′-azobis (N, N′-methyleneisobutylamidine) or a salt thereof, 2,2′-azobis (2-methylpropionamidine) or a salt thereof, 2,2′-azobis (2 -Amidinopropane) or a salt thereof, and an azo compound such as 4,4′-azobis-4-cyanovaleric acid;
These polymerization initiators may be used alone or in combination of two or more. When a peroxide is used as the polymerization initiator, for example, redox polymerization may be performed using a reducing agent such as sulfite, bisulfite, and L-ascorbic acid (salt) in combination. .

  In the present invention, it is particularly preferable that the water-containing gel obtained by polymerizing the monomer component contains bubbles inside because the water-absorbing property of the resulting water-absorbent resin can be improved. A water-containing gel containing bubbles inside can be easily obtained by polymerizing the monomer component in the presence of a crosslinking agent so as to contain bubbles. Examples of such a polymerization method include a polymerization method in the presence of an azo-based initiator, a polymerization method using a carbonate (JP-A-5-237378 and Kaihei 7-185331) as a foaming agent, pentane and A polymerization method in which a water-insoluble blowing agent such as trifluoroethane is dispersed in a monomer (US Pat. No. 5,328,935, US Pat. No. 5,338,766), a polymerization method using a solid particulate foaming agent (international Publicly known WO96 / 17884), various conventionally known methods such as a method of polymerizing while dispersing an inert gas in the presence of a surfactant can be employed.

When the monomer component is polymerized in the presence of a cross-linking agent, in order to improve the water absorption characteristics of the resulting water absorbent resin, and when polymerizing so as to contain bubbles, foaming is performed efficiently. Therefore, it is preferable to use water or a mixed solvent of water and an organic solvent soluble in water as the solvent.
Specific examples of the organic solvent include methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, acetonitrile, ethylene glycol monomethyl ether, and the like. These organic solvents may be used alone or in combination of two or more.

The concentration of the monomer component in the aqueous solution (hereinafter referred to as the monomer aqueous solution) is more preferably in the range of 20 wt% to 60 wt%. When the concentration of the monomer component is 20% by weight or more, it is possible to suppress an increase in the amount of the water-soluble component of the obtained water-absorbent resin, and foaming by the foaming agent is sufficient, and the water absorption rate can be improved. Therefore, it is preferable. On the other hand, when the concentration of the monomer component is 60% by weight or less, it is preferable because the reaction temperature and foaming by the foaming agent can be easily controlled.
The water content of the water-containing gel obtained as described above is generally in the range of 10 to 90% by weight, and preferably in the range of 20 to 80% by weight. When the water content is 10% by weight or more, it is preferable to extrude the water-containing gel, and when the water-containing gel contains air bubbles, the air bubbles are less likely to be crushed. On the other hand, when the water content is 90% by weight or less, it is preferable that drying after extrusion does not take too much time.

The water-containing gel can be made into a water-absorbent resin by extruding to a predetermined size, then drying and pulverizing, but during the extrusion, the water-containing gel is extruded so as to be as uniform and not kneaded as possible. It is preferable. This is because the physical properties of the resulting water-absorbent resin are lowered.
Specifically, when the water-containing gel is not uniformly extruded, it becomes impossible to dry each water-containing gel uniformly, and a part of undried material may be generated. Since this undried product has a very large adhesive force, it adheres to the pulverizer in the pulverization step after drying and prevents pulverization. Moreover, when an undried product mixes in the water absorbent resin which is the final product, the physical properties of the water absorbent resin are lowered.

Furthermore, if the hydrogel is kneaded during the extrusion process, the crosslinked chains of the hydrogel are broken, leading to an increase in the amount of soluble components and reducing the physical properties of the water-absorbent resin as the final product. Further, when the hydrogel has bubbles, the bubbles are crushed during the extrusion process, and the physical properties of the water-absorbent resin are also lowered.
Therefore, it is preferable that the water-containing gel is uniformly extruded and that the water-containing gel is not kneaded during the extrusion. In order to carry out such extrusion of the hydrogel, in the present invention, a screw type extruder having a mechanism for preventing the hydrogel from returning to the supply side without a specific additional mechanism is used.

The screw extruder used in the present invention is not particularly limited as long as it has a uniaxial or multiaxial screw that rotates in a cylindrical screw case. As the screw type extruder, for example, as shown in FIG. 1, a screw case 11, a screw shaft 12, a supply port 13, a hopper 14, an extrusion port 15, a perforated plate 16, a die holder 17, a die presser 18 and the like are provided. The thing of the structure which can be used suitably can be used.
The screw case 11 has a cylindrical shape, and a screw shaft 12 is disposed along the longitudinal direction of the screw case 11. An extrusion port 15 through which the hydrogel is extruded is provided at one end of the cylindrical screw case 11, and a motor, a drive system, and the like for rotating the screw shaft 12 are provided at the other end. Provided. Above the screw case, a supply port 13 for supplying the hydrogel is provided, and preferably, a hopper 14 for facilitating the supply of the hydrogel is provided.

The shape and size of the screw case 11 is not particularly limited as long as it has a cylindrical inner surface corresponding to the shape of the screw shaft 12, but is supplied from the screw end of the screw extruder. When the length to the tip of the mouth is A and the length from the tip of the supply port to the tip of the screw is B, the following formula (1),
C = (B / A) × 100 (1)
The value C defined by is preferably in the range of 100% to 500%.
Here, if the value of C is less than 100%, the hydrous gel is not properly extruded and stays in the screw case, which is unsuitable. If the value of C is greater than 500%, the hydrous gel is contained during extrusion. This is unsuitable because the gel is kneaded, the crosslinked chain of the hydrous gel is broken, the amount of soluble components is increased, and the physical properties of the water-absorbent resin as the final product are lowered.

Further, the rotational speed of the screw shaft 12 is preferably 1 to 300 rpm, more preferably 1 to 240 rpm, and particularly preferably 1 to 180 rpm. Within the range of 1 to 300 rpm, an excessive mechanical external force is not applied to the hydrous gel due to the rotation of the screw shaft 12, and the physical properties are not deteriorated.
A perforated plate 16 having a plurality of holes is disposed at the extrusion port 15. Further, the perforated plate 16 is detachably fixed to the die holder 17 by a die presser 18. This is because the thickness of the string-like hydrogel is determined by the diameter of the holes opened on the porous plate 16, so that the porous plate 16 has a different hole diameter in order to adjust the thickness of the string-like hydrogel. This is because it will be necessary to replace it appropriately.

The thickness of the porous plate 16 is in the range of 1 mm to 20 mm. The hole diameter is preferably in the range of 1 mm to 28 mm, and more preferably in the range of 2 mm to 20 mm. If the pore diameter is in the above range, excessive mechanical external force is suppressed from being applied to the water-containing gel during extrusion, so that the water-containing gel can be satisfactorily extruded.
Here, in the conventional method, when extruding the hydrous gel with a screw type extruder, it has been considered preferable that the pore diameter of the perforated plate is in the range of 6.5 mm to 18 mm. This is because, in a conventional screw-type extruder that does not include a reversal prevention mechanism, the water-containing gel cannot be favorably extruded when the diameter of the hole is out of the above range.

Specifically, if the pore diameter is smaller than the above range, the conventional method requires a very large force to extrude the hydrogel from the perforated plate, and the hydrogel is kneaded in the screw case and the physical properties And productivity decreases due to retention. On the other hand, when the pore diameter is larger than the above range, the thickness of the resulting string-like hydrogel is not uniform, and drying after extrusion is not performed uniformly during the production of the water absorbent resin, Reduces physical properties.
On the other hand, in the method for refining the hydrogel according to the present invention, since the hydrogel does not reverse, the hydrogel is smoothly pushed out, and the productivity is not lowered due to retention. Moreover, even when the hole diameter is large, more uniform and efficient pulverization is possible.

The aperture ratio of the porous plate 16 is preferably 5% or more, more preferably in the range of 10% to 40%, and particularly preferably around 20%. When the open area ratio is less than 5%, the hydrogel is difficult to be extruded and the productivity is lowered. Moreover, since it becomes difficult to extrude a hydrogel, it is not preferable because the hydrogel is excessively and finely crushed at the pumping site to the perforated plate 16. The aperture ratio refers to the ratio of the total area of all the holes to the total area of the porous plate 16.
The string-like hydrogel obtained by the above-described screw-type extruder is of a high quality with no extra mechanical external force applied during pulverization. Here, the average diameter of the string-like hydrogel is preferably within a range of 1 mm to 28 mm, more preferably within a range of 2 mm to 20 mm, and particularly preferably within a range of 3 mm to 10 mm when the hydrous gel is hard. .

In the method for refining the water-containing gel according to the present invention, the water-containing gel can be extruded and refined without being affected by the filling rate and without being retained in the screw case 11. The range of 100% is preferable because an excessive mechanical external force accompanying rotation of the screw shaft 12 is not applied.
In addition, the said filling rate is the same rotation speed as this time with respect to the processing amount per unit time when the screw case 11 of the said screw-type extruder is completely filled with a hydrous gel and a fine granulation process is performed. The ratio of the supply amount of the hydrogel supplied with the screw shaft 12 rotating is indicated.

As described above, since the range of the filling rate that can be finely divided so that excessive mechanical external force is not applied without staying in the screw case 11, the fineness of the hydrogel is reduced. The setting of conditions becomes easy, and the operation of the atomization apparatus can be facilitated.
In the method for refining the hydrogel according to the present invention, the hydrogel may be extruded from the screw-type extruder, and then the string-like hydrogel may be appropriately cut using a rotary blade or the like to be finely granulated. . As a result, the drying efficiency can be further increased and the productivity can be improved.
In the hydrogel refinement method according to the present invention, the massive hydrogel may be crushed before supplying the hydrogel to the screw extruder. This makes it easy to supply the hydrogel and to fill the screw case 11. The crushing means used for the coarse pulverization is not particularly limited as long as it can be crushed so as not to knead the hydrogel, and examples thereof include a guillotine cutter.

The size of the coarsely pulverized product of the hydrogel obtained by performing the above crushing treatment can be supplied from the supply port 13 and can be sent to the extrusion port 15 by the screw shaft 12. Although not particularly limited, in general, it is preferably 5 mm or more, and more preferably 10 mm or more. If it is less than 5 mm, it is not preferable because the meaning of crushing with a screw extruder is lost.
The water-absorbent resin obtained by drying the finely divided water-containing gel obtained by the finely divided method according to the present invention as described above is, for example, a paper diaper, a sanitary napkin, an incontinence pad, Sanitary materials (body fluid absorbing articles) such as wound protection materials and wound healing materials; Absorbing articles such as urine for pets; Construction materials such as building materials, soil water retaining materials, water-stopping materials, packing materials, gel water sacs, etc .; Food products such as drip absorbers, freshness-keeping materials, and cold insulation materials; various industrial products such as oil-water separators, anti-condensation materials, and coagulants; various agricultural and horticultural products such as water retention materials such as plants and soil It is suitable for use.
In addition, the method for finely granulating the water-containing gel according to the present invention is not only applicable to the production of the water-absorbent resin, and when the step of pulverizing the water-containing gel so as to be uniform and not kneaded is necessary. This method is preferably used.

The method for refining the hydrogel according to the present invention will be described more specifically based on the following examples and comparative examples, but the present invention is not limited to these examples and comparative examples.
In the following Examples and Comparative Examples, the water-containing gel atomization method according to the present invention is applied to the production of a water-absorbent resin. First, various physical properties in the water-absorbent resins obtained in the following examples and comparative examples and the measurement of the state of the string-like hydrogel were performed as follows. In addition,% described in the following Examples and Comparative Examples represents% by weight.

[Water absorption ratio]
First, after weighing the water absorbent resin, it was immersed in a 0.9% aqueous sodium chloride solution (physiological saline) for 60 minutes. Thereafter, after removing the water-absorbing resin and draining it, the weight of the water-absorbing resin was weighed, and the water absorption ratio was determined by comparing with the weight before absorbing the physiological saline.
[Water-soluble matter]
In a 100 mL beaker, 1 g of the water-absorbent resin was swollen in 25 mL of physiological saline, capped, and left at 25 ° C. for 16 hours. The swollen gel was then dispersed in 975 mL of deionized water, stirred for 1 hour, and then filtered through filter paper. The obtained filtrate was titrated by colloid titration, and the soluble content (%) of the water absorbent resin was calculated.

[Example 1]
An aqueous monomer solution containing 70% neutralized sodium acrylate and 0.04 mol% N ', N'-methylenebisacrylamide (relative to sodium acrylate) was prepared. The concentration of sodium acrylate at this time was 40% by weight. Nitrogen was blown into the aqueous monomer solution to adjust the dissolved oxygen concentration in the aqueous solution to 0.1 ppm or less.
Subsequently, 0.01 mol% of ammonium persulfate (based on sodium acrylate monomer) and 0.03 mol% of L-ascorbic acid (based on sodium acrylate monomer) were sequentially added to perform polymerization. The polymerization initiation temperature was 25 ° C., and after 12 minutes the temperature reached 85 ° C.
After the polymerization, the obtained hydrogel was crushed into a 15 to 55 mm lump, and then charged into a screw-type extruder as shown in FIG. Extrusion was performed at 60 rpm.
As the screw type extruder, a screw case 11 having an inner diameter of 53 mm and a length of 220 mm was used. The screw shaft 12 was 51 mm in diameter and 191 mm in length. Further, as the porous plate 16, a plate having a thickness of 8 mm, a hole diameter of 4.5 mm, and an aperture ratio of 35% was used.
Moreover, the said screw type extruder used what has the structure which can adjust the length A from a screw terminal part to an opening part front-end | tip, A was 55 mm in the present Example.
Using the screw type extruder, the hydrogel was extruded to obtain a string-like hydrogel. The extruded hydrogel was a glassy transparent string. Table 1 shows the extrusion conditions at that time, the occurrence of retention in the extruder, and the values of A, B, and C.
The string-like water-containing gel was dried at 180 ° C. for 30 minutes and then pulverized to obtain a water absorbent resin (1) in the present invention. Table 2 shows the physical properties of the water absorbent resin (1).

[Example 2]
In Example 1, the water-absorbent resin (2) in the present invention was obtained in the same manner except that the hydrogel was added so that the filling rate was approximately 50%. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (2).

Example 3
In Example 1, the water-absorbent resin (3) in the present invention was obtained in the same manner except that the hydrogel was added so that the filling rate was approximately 25%. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (3).

Example 4
In Example 1, the water-absorbent resin (4) in the present invention was obtained in the same manner except that the screw rotation speed was 120 rpm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (4).

Example 5
A water absorbent resin (5) according to the present invention was obtained in the same manner as in Example 1 except that the screw rotation speed was changed to 30 rpm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (5).

Example 6
In Example 1, the water-absorbent resin (6) according to the present invention was obtained in the same manner except that the perforated plate having a thickness of 8 mm, a hole diameter of 3.0 mm, and an aperture ratio of 37% was used. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (6).

Example 7
In Example 1, the water-absorbent resin (7) in the present invention was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was 40 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (7).

Example 8
In Example 1, the water-absorbent resin (8) in the present invention was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was set to 70 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (8).

Example 9
In Example 1, the screw extruder used was the same as that of the screw case 11 having an inner diameter of 53 mm and a length of 283 mm, and the screw shaft 12 having a diameter of 51 mm and a length of 254 mm was used. The water absorbent resin (9) in the invention was obtained. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (9).

Example 10
In Example 9, the water-absorbent resin (10) in the present invention was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was set to 70 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (10).

Example 11
In Example 9, the water-absorbent resin (11) in the present invention was obtained in the same manner except that the length A from the screw end of the screw type extruder to the tip of the opening was set to 100 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (11).

Example 12
In Example 1, the present invention is the same except that the screw type extruder used has an inner diameter of 53 mm and a length of 156 mm, and the screw shaft 12 has a diameter of 51 mm and a length of 127 mm. The water absorbent resin (12) in the invention was obtained. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (12).

Example 13
In Example 12, the water-absorbent resin (13) in the present invention was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was 40 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the water absorbent resin (13).

[Comparative Example 1]
In Example 1, a comparative water-absorbent resin (1) was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was set to 100 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the comparative water absorbent resin (1).

[Comparative Example 2]
In Example 9, a comparative water-absorbent resin (2) according to the present invention was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was 40 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the comparative water absorbent resin (2).

[Comparative Example 3]
In Example 13, a comparative water absorbent resin (3) was obtained in the same manner except that the length A from the screw end of the screw extruder to the tip of the opening was set to 70 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the comparative water absorbent resin (3).

[Comparative Example 4]
In Example 13, a comparative water absorbent resin (4) was obtained in the same manner except that the length A from the screw terminal to the tip of the opening was set to 100 mm. Table 1 shows the atomization conditions and the state in the extruder at this time. In addition, Table 2 shows the physical properties of the comparative water absorbent resin (4).

As described above, in Examples 1 to 13 using the atomization method according to the present invention, a screw type equipped with a mechanism for preventing the water-containing gel from returning to the supply side without the presence of a specific anti-reverse member. Since the pulverization process is performed using an extruder, efficient processing can be performed without causing stagnation in the screw-type extruder, and mechanical external force exceeding the minimum necessary is applied in the extruder. Thus, it was confirmed that a string-like hydrous gel that was easy to dry was obtained.
In particular, as in Examples 2 and 3, it was confirmed that the pulverization method according to the present invention can finely hydrate the water-containing gel regardless of the filling rate in the screw type extruder. .
In addition, as in Examples 4 and 5, it was confirmed that good atomization was possible regardless of the rotational speed of the screw shaft 12.
Furthermore, as in Example 6, it was also confirmed that favorable fine graining was possible regardless of the hole diameter of the perforated plate.

In addition, as in Examples 7 to 13, when the length from the screw-type extruder screw end to the feed port tip is A and the length from the feed port tip to the screw tip is B, the following formula (1),
C = (B / A) × 100 (1)
When the value C defined by is in the range of 100% to 500%, it was confirmed that the hydrogel can be finely divided.
Furthermore, the water-absorbing resins (1) to (6), (8), (11) to (14) obtained in Examples 1 to 6, 8, and 11 to 14 in which the value of C is 100 <C <300. ) Was confirmed to be of a high quality having very good physical properties with little soluble and deteriorated soluble components.
On the other hand, in Examples 7 and 9 in which the value of C is 300 ≦ C ≦ 500, the quality is slightly decreased as compared with the water absorbent resins (1) to (6), (8), and (11) to (14). However, it was confirmed that good physical properties were exhibited.

On the other hand, in Comparative Example 2 where the value of C is C> 500, stagnation and reversion do not occur in the screw extruder, but a mechanical external force exceeding the minimum necessary is applied in the extruder. As a result, it was confirmed that the water-soluble gel contained in the string-like water-containing gel was increased and the quality of the water-absorbent resin was low.
Further, in Comparative Examples 1, 3, and 4 in which the value of C is C <100, stagnation and reversal occur in the screw extruder, and a mechanical external force exceeding the minimum necessary is applied in the extruder. As a result, it was confirmed that the water-soluble gel contained in the string-like water-containing gel was increased and the quality of the water-absorbent resin was low.

The method for refining a water-containing gel according to the present invention is a method of pulverizing a water-containing gel using a screw-type extruder having a function of preventing the water-containing gel from returning to the supply side without a specific additional mechanism. .
At this time, in the pulverization treatment by the screw type extruder, the value C defined by the formula (1) is preferably in the range of 100% to 500%.
According to the above method, excessive mechanical external force is prevented from being applied to the hydrated gel, and uniform pulverization is possible, so that it can be easily finely granulated without deteriorating the properties of the hydrated gel. Can do.

In addition, since the retention of the hydrogel does not occur in the extruder, the efficiency of fine granulation can be greatly improved.
Furthermore, if the value C is within this range, it can be finely granulated without being affected by the filling rate of the hydrogel inside the extruder, so that the operating conditions of the extruder can be widened. It becomes possible.
Because of the above advantages, the method for finely granulating a water-containing gel according to the present invention is not only applicable to the production of a water-absorbent resin, and requires a step of crushing the water-containing gel so as not to be uniformly and kneaded. It can be suitably used in such cases.

  The water-absorbent resin obtained by drying the finely divided hydrous gel obtained by the fine granulation method according to the present invention has excellent water absorption performance, such as paper diapers, sanitary napkins, incontinence pads, wound protection materials, Hygiene materials such as wound healing materials (body fluid absorbing articles); absorbent articles such as urine for pets; civil engineering and building materials such as building materials, water retention materials for soil, water-stopping materials, packing materials, gel water sacs; Suitable for various applications such as food products such as freshness-retaining materials and cold insulation materials; various industrial products such as oil-water separators, anti-condensation materials, and coagulants; and agricultural and horticultural products such as water-retaining materials such as plants and soil It is to be used.

The schematic diagram which shows the structure of the screw type extruder used for the refinement | miniaturization method of the hydrogel concerning one Embodiment of this invention.

Explanation of symbols

11 Screw case 12 Screw shaft 13 Supply port 14 Hopper 15 Extrusion port 16 Perforated plate 17 Die holder 18 Die presser

Claims (2)

In the hydrogel refinement method in which the hydrogel is supplied from the supply port of the screw-type extruder and extruded from the extrusion port provided with the perforated plate to perform the pulverization process, from the screw end of the screw-type extruder to the tip of the supply port When the length of the nozzle is A and the length from the supply port tip to the screw tip is B, the following formula (1)
C = (B / A) × 100 (1)
Of the water-containing gel characterized by using a screw type extruder having a function of preventing the water-containing gel from returning to the supply side by making the value C defined by the above in the range of 100% to 500%. Fine graining method. In the fine granulation method, when the length from the screw end of the screw type extruder to the tip of the supply port is A and the length from the tip of the supply port to the screw tip is B, the following formula (1)
C = (B / A) × 100 (1)
A screw-type extruder for refining a water-containing gel having a function of preventing the water-containing gel from returning to the supply side by setting the value C defined by the above to be in the range of 100% to 500%.

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