Source: https://patents.google.com/patent/EP1191051B1/en
Timestamp: 2019-04-19 03:03:39
Document Index: 378944668

Matched Legal Cases: ['art 2', 'art 2', 'art 2', 'art 5', 'art 5', 'art 5', 'art 2', 'art 2', 'art 2', 'art 5', 'art 5']

EP1191051B1 - Production process for a water-absorbent resin - Google Patents
Production process for a water-absorbent resin Download PDF
EP1191051B1
EP1191051B1 EP20010121378 EP01121378A EP1191051B1 EP 1191051 B1 EP1191051 B1 EP 1191051B1 EP 20010121378 EP20010121378 EP 20010121378 EP 01121378 A EP01121378 A EP 01121378A EP 1191051 B1 EP1191051 B1 EP 1191051B1
EP20010121378
EP1191051A2 (en
EP1191051A3 (en
2001-09-06 Application filed by Nippon Shokubai Co Ltd filed Critical Nippon Shokubai Co Ltd
2002-03-27 Publication of EP1191051A2 publication Critical patent/EP1191051A2/en
2002-09-25 Publication of EP1191051A3 publication Critical patent/EP1191051A3/en
2010-11-03 Publication of EP1191051B1 publication Critical patent/EP1191051B1/en
2011-08-03 First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=26600356&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=EP1191051(B1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
The present invention relates a production process for a water-absorbent resin. More particularly, the present invention relates to a production process for a modified water-absorbent resin by carrying out a specific step.
As to these water-absorbent resins, the following are known as their examples: hydrolyzed copolymers of starch-acrylonitrile ( JP-B-43395/1974 ), neutralized graft polymers of starch-acrylic acid ( JP-A-125468/1976 ), saponified copolymers of vinyl acetate-acrylic acid ester ( JP-A-14689/1977 ), and hydrolyzed copolymers of acrylonitrile or acrylamide ( JP-B-15959/1978 ), or crosslinked polymers of these hydrolyzed copolymers, and partially-neutralized crosslinked poly(acrylic acid) ( JP-A-84304/1980 ).
The most important matter thought in this surface-crosslinking step is to surface-crosslink the surface of water-absorbent resin particles uniformly, and therefore, it is important that the water-absorbent resin before surface-crosslinking is uniformly blended with a surface-crosslinking agent. As to an art in which this water-absorbent resin before surface-crosslinking is uniformly blended with the surface-crosslinking agent, various methods are disclosed until now. For example, the following methods are known: a method which involves the use of crosslinking agents having a different solubility parameter together ( JP-A-184320/1994 (corresponding to USP 5,422,405 )); a method which involves the use of a specific material as the material of the inner surface of the blender, and involves add-blending an aqueous crosslinking agent liquid while being stirred in a high speed ( JP-A-235378/1997 (corresponding to USP 6,071,976 ) and JP-A-349625/1999 ); and a method involves spraying a particulate liquid drop of a surface-crosslinking agent to bring a water-absorbent resin powder in a raw state
( JP-A-246403/1992 ).
As to methods for surface-crosslinking water-absorbent resins using these crosslinking agents, the following methods are known: a method which involves directly adding a crosslinking agent to a water-absorbent resin powder, or a composition obtained by dissolving a crosslinking agent in a small quantity of water or a hydrophilic organic solvent, and heat-treating if necessary ( JP-A-180233/1983 (corresponding to USP 4,666,983 ), JP-A-189103/1984 , and JP-A-16903/1986 (corresponding to USP 4,734,478 )); a method which involves dispersing a water-absorbent resin in a mixed solvent of water and a hydrophilic organic solvent, and adding a crosslinking agent thereto to react with the water-absorbent resin ( JP-B-48521/1986 ); and a method which involves allowing a resin to react with a crosslinking agent in an inert solvent in the presence of water ( JP-B-18690/1985 (corresponding to USP 45,418,771 )).
In addition, the state of the water-absorbent resin is a powder in many cases. When the water-absorbent resin includes many particulate powders such that pass through a sieve having a mesh opening size of 150 µm, it may exercise a bad influence on the working environment due to causing dust, it may cause the blendability to decrease when blending with other substances, and it may cause formation of bridge in a hopper.
Until now, known examples of production processes for water-absorbent resins having a small amount of particulate powders include a method which involves adjusting the particle diameter by adjusting the extent of the polymerization or pulverization, or a method which involves classify-removing the particulate powders as caused. However, plenty of particulate powders (several to several tens percents) are caused in the production steps even if the above method is carried out. Therefore, the yield is greatly decreased when the particulate powders are classic-removed, and further abandoned. At the same time, there are disadvantages in view of abandoning cost.
Then, various methods for modifying a water-absorbent resin for the purpose of solving the above problems are proposed by granulating or recovering the particulate powders to granules by use of binders such as an aqueous liquid, wherein the particulate powders are inevitably caused in the steps of producing the water-absorbent resin ( JP-A-101536/1986 (corresponding to USP 4,734,478 ) and JP-A-817200/1991 (corresponding to USP 5,369,148 )). Preferred binders for the water-absorbent resin generally include water or an aqueous liquid in view of efficiency, safety, and production costs.
JP-A-04 246403 discloses a process for the treatment of a water-absorbent resin with a liquid comprising a substance with two or more functional reactive groups by spraying the liquid from the top of a cylindrical body downwards onto the resin while the resin is falling down within the cylindrical body.
WO-A-98/49221 relates to the production of superabsorbent polymers having improved processability and discloses spraying of additive solutions onto a polymer material while being agitated in a blender.
The present inventors diligently studied to solve the problems. As a result, they found that the problems could be solved by employing a mode of spray-blending with a specific blending apparatus.
That is to say, a production process for a water-absorbent resin, according to the present invention; comprises the steps of claim 1 or 2.
In addition, the another production process for a water-absorbent resin, according to the present invention, comprises the steps of: blending a liquid material and a water-absorbent resin; and heating the resultant mixture in order to produce a modified water-absorbent resin, and further comprises the steps of: spray-blending a water-absorbent resin (A) and a liquid material (B) with a blending apparatus equipped with a spray nozzle (C); and heat-treating, with the production process being characterized in that the liquid material (B) is sprayed from the spray nozzle (C) and its spray pattern is a circular and hollow cone shape in the spray-blending step, and in that the heat-treating step is carried out under an atmosphere having a dew point of not higher than 60 °C and a temperature of not lower than 90 °C.
In addition, the production process for a water-absorbent resin, according to the present invention, comprises the steps of: blending a liquid material and a water-absorbent resin; and heating the resultant mixture in order to produce a modified water-absorbent resin, and further comprises the steps of: spray-blending a water-absorbent resin (A) and a liquid material (B) with a blending apparatus equipped with a spray nozzle (C); and heat-treating, with the production process being characterized in that the liquid material (B) is sprayed from the spray nozzle (C) and its spray pattern is a double-convex-lens and elliptic cone shape in the spray-blending step, and in that the heat-treating step is carried out under an atmosphere having a dew point of not higher than 60 °C and a temperature of not lower than 90 °C.
In addition, a water-absorbent resin, according to the present invention, is surface-crosslinked with a surface-crosslinking agent including at least a polyhydric alcohol.
Fig. 4 is a figure showing the relationship between relational humidity and temperature (°C) as to dew curves of vapor. In addition, the scope limited in the present invention claim is described in the hatching range. Td, black plots, and white plots mean a dew temperature, examples of the present invention, and comparative examples, respectively.
Examples of the above-mentioned internal-crosslinking agent include N,N'-methylenebis(meth)acrylamide, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate, glycerol tri(meth)acrylate, glycerol acrylate methacrylate, ethoxylated trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly(meth)allyloxyalkanes, (poly)ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol, propylene glycol, glycerin, pentaerythritol, ethylenediamine, polyethylenimine, and glycidyl (meth)acrylate. However, the internal-crosslinking agent is not especially limited. These internal-crosslinking agents are used either alone respectively or in combinations with each other. Among the exemplified internal-crosslinking agents, those having a plurality of polymerizable unsaturated groups per molecule are preferably used because they can give a water-absorbent resin of which the properties are more modified.
When polymerizing the hydrophilic unsaturated monomers, the following can be used: radical polymerization initiators, such as potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, and 2,2'-azobis(2-amidinopropane) dihydrochloride; and active energy lights, such as ultraviolet, and electron beam. In addition, when using the oxidative radical polymerization initiators, they may be combined with reducing agents, such as sodium sulfite, sodium hydrogen sulfite, iron (II) sulfate, and L-ascorbic acid, thereby carrying out redox polymerization. The amount of these polymerization initiators as used is preferably in the range of 0.001 to 2 mol %, more preferably 0.01 to 0.5 mol %.
The solid content of the hydrogel polymer as obtained by the above-mentioned polymerization is adjusted by drying. The drying of the hydrogel polymer can be carried out by using conventional dryers and heating furnaces, such as thin blending dryers, rotary dryers, disk dryers, fluidized-bed dryers, air blow type dryers, and infrared dryers. Then, the drying temperature is preferably in the range of 40 to 250 °C, more preferably 90 to 200 °C, still more preferably 120 to 180 °C. The solid content of the dry product as obtained in the above way is usually in the range of 70 to 100 weight % (water content: 30 to 0 weight %), preferably 80 to 98 weight % (water content: 20 to 2 weight %), most preferably 90 to 98 weight % (water content: 10 to 2 weight %). Incidentally, the solid content is usually calculated from the amount as decreased by drying at 180 °C for 3 hours.
The dry product as obtained in the above drying can be used as a water-absorbent resin as it is. However, the dry product can be used as a particulate water-absorbent resin having a predetermined size by pulverization and classification. Then, the particle size is not larger than 2 mm, preferably in the range of 10 µm to 1 mm. The weight-average particle diameter may be different depending upon its use, but is in the range of 100 to 1,000 µm, preferably 150 to 800 µm, still more preferably 300 to 600 µm. In addition, the ratio of the particles passing through a sieve having a mesh opening size of 150 µm is preferably not more than 15 weight %, more preferably not more than 10 weight %, still not more than 5 weight %.
The powder temperature of the water-absorbent resin (A) as obtained in the above way before adding the liquid material (B) is preferably adjusted to the range of 80 to 35 °C, more preferably 70 to 35 °C, still more preferably 50 to 35 °C. Thereafter, the liquid material (B) is blended therewith. In case where the temperature of the water-absorbent resin (A) before adding the liquid material (B) is higher, the liquid material (B) is blended ununiformly. In addition, there are disadvantages in adjusting to lower than 35 °C, because it takes much time to forcibly or stationary cool, and besides, the agglomeration of the powder as stationary cooled is observed, and the energy loss is increased when carrying out reheating.
Examples of the above surface-crosslinking agent include: polyhydric alcohols, such as ethylene glycol, propylene glycol, glycerol, pentaerythritol, sorbitol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butane diol, 1,4-butanediol, 1,5-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2,5-hexanediol, and trimethylolpropane; polyamine compounds, such as diethanolamine, triethanolamine, ethylenediamine, diethylenetriamine, and triethylenetetramine; polyglycidyl compounds, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether, 2,4-tolylene diisocyanate, ethylene carbonate (1,3-dioxolan-2-one), propylene carbonate (4-methyl-1,3-dioxolan-2-one), 4,5-dimethyl-1,3-dioxolan-2-one, (poly-, di- or mono-) 2-oxazolidinone, epichlorohydrin, epibromohydrin, diglycol silicate, and polyaziridine compounds, such as 2,2-bis(hydroxymethylbutanol)-tris[3-(1-aziridyl)propionate]. However, the surface-crosslinking agent is not limited to these compounds. In addition, these surface-crosslinking agents are used either alone respectively or in combinations with each other. Among these, at least one kind of the surface-crosslinking agents is preferably a surface-crosslinking agent selected from the group consisting of polyhydric alcohols, polyglycidyl compounds, 1,3-dioxolan-2-on, poly(2-oxazolidinone), bis(2-oxazolidinone), and mono(2-oxazolidinone), and is more preferably a surface-crosslinking agent including polyhydric alcohols.
In addition, the liquid temperature of the liquid material (B) is preferably lower than the powder temperature of the water-absorbent resin (A), more preferably lower than the powder temperature of the water-absorbent resin (A) by 10°C, still more preferably by 20 °C, most preferably by 30 °C. Incidentally, the liquid material (B) is sprayed from the spray nozzle (C). Therefore, its liquid temperature should be higher than its melting point. In addition, when the liquid temperature of the liquid material (B) is too high, there are disadvantages in that: the liquid absorption speed is rapid, and the uniform blending of the liquid material (B) and the water-absorbent resin (A) is inhibited.
The average diameter of the liquid drop of the liquid material (B) as blended with the water-absorbent resin (A) is preferably smaller than the average diameter of the water-absorbent resin (A), and is more preferably not larger than 300 µm, still more preferably not larger than 250 µm. The average diameter of the liquid drop is usually in the range of 50 to 200 µm. In case where the average diameter is larger than 300 µm, there are disadvantages in that: it is difficult to defuse or disperse the liquid material (B) uniformly; a lump having high density is caused; and the amount of the water-absorbent resin (A) which does not come into contact with the liquid material (B), namely, the aqueous surface-crosslinking agent solution is increased in the blending apparatus.
In the present invention, the spray angle of the liquid material (B) from the spray nozzle (C) is very important, and the maximum spray angle of the liquid material (B) from the spray nozzle (C) is preferably not less than 50°.
The production process, according to the present invention, is characterized in that: the liquid material (B) is sprayed from the spray nozzle (C) and its spray pattern is a circular and hollow cone shape (a hollow cone spray shape); or the liquid material (B) is sprayed from the spray nozzle (C) and its spray pattern is a double-convex-lens and elliptic cone shape (a flat spray shape). In these processes, the maximum spray angle is preferably is not less than 50 °.
The spray nozzle (C) is necessary to be fitly selected according to the use condition so that the spray nozzle (C) has a predetermined spray angle. However, the spray angle of the liquid material (B) from the spray nozzle (C) is preferably selected at not less than 50 °, more preferably not less than 70 °, still more preferably not less than 90 °. In case where the spray angle is less than 50 °, the portion where the liquid material (B) is dispersed excessively and the portion where the liquid material (B) is dispersed in low density are caused in a dispersing state of the liquid material (B) as sprayed in the blending apparatus, and the partiality is caused in a blending state of the water-absorbent resin (A) and the liquid material (B). There are disadvantages in that the water-absorbent resin (A) as excessively brought into contact with the liquid material (B), namely, the aqueous surface-crosslinking agent solution produces a lump having high density (rigid agglomerated material) easily, and causes excessive surface-crosslinking. This lump having high density becomes a rigid lump difficult to pulverize after the heat treatment as described in the following. Therefore, the extra-pulverization is necessary in order to adjust to the particle size of the produced material (for example, all the particles have a particle size of less than 1 mm.). However, where the pulverization is carried out, there are disadvantages in that the surface-crosslinked layer as specially formed is destroyed by pulverization. Incidentally, the maximum spray angle is not more than 180 ° because of the structure of the spray.
In addition, the present invention process which involves the maximum spray angle of the liquid material (B) from the spray nozzle (C) at not less than 50°, the process which involves spraying the liquid material (B) from the spray nozzle (C) with a spray pattern of a circular and hollow cone shape (a hollow cone spray shape), or the process which involves spraying the liquid material (B) from the spray nozzle (C) with a spray pattern of a double-convex-lens and elliptic cone shape (a flat spray shape) is more preferably applied to continuous production processes. Incidentally, the maximum spray angle is not more than 180 ° because of the structure of the spray.
Furthermore, when the liquid material (B) is sprayed from the spray nozzle (C) for the purpose of adjusting to the above predetermined spray angle, the area of the spray-dispersing state of the liquid material (B) projected onto a sectional area which is perpendicular to the axis direction of the blending apparatus and includes a spraying point of the spray nozzle (C) accounts for 70 to 100 % of the sectional area perpendicular to the axis direction of the blending apparatus, preferably 80 to 100 %, more preferably 90 to 100 %. In case where the area of the spray-dispersing state of the liquid material (B) projected onto a sectional area which is perpendicular to the axis direction of the blending apparatus and includes the spraying point of the spray nozzle (C) accounts for less than 70 % of the sectional area perpendicular to the axis direction of the blending apparatus, there are disadvantages in that the portion where the liquid material (B) is dispersed excessively and the portion where the liquid material (B) is dispersed in low density are caused in a dispersing state of the liquid material (B) as sprayed in the blending apparatus, and the partiality is caused in a blending state of the water-absorbent resin (A) and the liquid material (B).
Furthermore, the inner wall temperature of the blending apparatus is preferably higher than room temperature, more preferably not lower than 40 °C. The temperature is preferably maintained in the range of 50 to 100 °C. In addition, the inner wall temperature of the blending apparatus is preferably higher than the temperature of water-absorbent resin (A). The temperature difference is preferably not more than 40 °C, more preferably not more than 20 °C. In case where the inner wall temperature of the blending apparatus is not higher than room temperature, when the liquid material (B) and water-absorbent resin (A) are blended, there is a possibility that the resultant water-absorbent resin mixture is adhered to the inner wall or piled.
When the occasion demands, the water-absorbent resin (A) is granulated to a granule by use of the liquid material (B) as a binder, and the ratio of particles passed through a mesh opening size of 150 µm can be decreased.
The powder temperature of the above water-absorbent resin (A) is preferably adjusted to the range of 80 to 35 °C, more preferably 70 to 35 °C, still more preferably 50 to 35 °C. Thereafter, the liquid material (B) is blended therewith. In case where the temperature of the water-absorbent resin (A) before adding the liquid material (B) is higher, the liquid material (B) is blended ununiformly. In addition, there are disadvantages in adjusting to lower than 35 °C, because it takes much time to forcibly or stationary cool, and besides, the agglomeration of the powder as stationary cooled is observed, and the energy loss is increased when carrying out reheating.
The above antimicrobial agents are conventional disinfectant ones, and are not especially limited. Examples thereof include antimicrobial agents shown in JP-A-267500/1999 .
The average diameter of the liquid drop of the liquid material (B) as the binder and/or the additive blended with the water-absorbent resin (A), for the purpose of giving the additional functions to the water-absorbent resin, is preferably smaller than the average diameter of the water-absorbent resin (A), and is more preferably not larger than 300 µm, still more preferably not larger than 250 µm. The average diameter of the liquid drop is usually in the range of 50 to 200 µm. In case where the average diameter is larger than 300 µm, there are disadvantages in that: it is difficult to defuse or disperse the liquid material (B) uniformly; a lump having high density is caused; and the amount of the water-absorbent resin (A) which does not come into contact with the liquid material (B) is increased in the blending apparatus.
In addition, the spray nozzle (C) is necessary to be fitly selected according to the use condition so that the spray nozzle (C) has a predetermined spray angle. However, the spray angle of the liquid material (B) from the spray nozzle (C) is preferably selected at not less than 50 °, more preferably not less than 70 °, still more preferably not less than 90 °. In case where the spray angle is less than 50 °, the portion where the liquid material (B) is dispersed excessively and the portion where the liquid material (B) is dispersed in low density are caused in a dispersing state of the liquid material (B) as sprayed in the blending apparatus, and the partiality is caused in a blending state of the water-absorbent resin (A) and the liquid material (B). The water-absorbent resin (A) as excessively brought into contact with the liquid material (B) produces a lump having high density easily, and it becomes a rigid lump difficult to pulverize. Therefore, the pulverization is necessary in order to adjust to the particle size of the produced material (for example, all the particles have a particle size of less than 1 mm.). However, when the surface-crosslinking is carried out in the above process, there are disadvantages in that the surface-crosslinked layer as specially formed might be destroyed by pulverization. Incidentally, the maximum spray angle is not more than 180 ° because of the structure of the spray.
In the present invention, the modification of the water-absorbent resin (A), preferably the crosslinking of its surface neighborhood is carried out by blending the above-mentioned water-absorbent resin (A) with the liquid material (B) (preferably, and the aqueous surface-crosslinking agent solution), and thereafter heat-treating the resultant mixture. Incidentally, the modification of the water-absorbent resin means the granulation of water-absorbent resins or the addition of additives, and further, examples of its modes include the surface-crosslinking by the addition of the surface-crosslinking agent. The above mentioned heat-treatment depends upon the surface-crosslinking agent as used, but is preferably carried out at a water-absorbent resin temperature (material temperature) or heat medium temperature of 60 to 250 °C, more preferably 80 to 250 °C, still more preferably 100 to 230 °C, particularly preferably 150 to 200 °C. In case where the treating temperature is lower than 60 °C, the uniform crosslinked structure is not formed. Accordingly, there are disadvantages in that the crosslinked water-absorbent resin having high absorption capacity under a load cannot be obtained. In addition, the productivity is caused to lower because it takes much time to carry out the heat treatment. In case where the treating temperature is higher than 250 °C, the water-absorbent resin (A) is caused to deteriorate. Accordingly, there are disadvantages in that the propertied of the surface-crosslinked water-absorbent resin are lowered. Incidentally, the above-mentioned treating temperature is preferably the water-absorbent resin temperature (material temperature) in order to control the surface-crosslinking reaction exactly.
The present invention is accomplished by heat-treating the water-absorbent resin powder as obtained in the above way under an atmosphere inside of the upper space of the heat-treating apparatus having a dew point of not higher than 60 °C and a temperature of not lower than 90 °C, preferably crosslinking the water-absorbent resin powder surface in the presence of a hydrophilic solution including the aforementioned crosslinking agent or its aqueous solution to preferably carry out a crossilnking reaction. Incidentally, the atmosphere in the present invention means the temperature and dew point of the upper space inside of the heat-treating apparatus, wherein the upper space inside includes the water-absorbent resin powder, and the temperature of the heat-treating apparatus may be equal to or different from the atmosphere.
In case where the water-absorbent resin powder having a water content of not less than 10 weight % is used, there are disadvantages in that: not only the aimed properties are not obtained but also much energy is required to obtain the atmosphere having a dew point of not higher than 60 °C and a temperature of not lower than 90 °C.
In case where the dew point is not higher than 60 °C and the temperature is not higher than 90 °C, even if the water-absorbent resin temperature (material temperature) or heat medium temperature is sufficient, the crosslinking reaction between the carboxyl group on the surface of the water-absorbent resin powder and the crosslinking agent is not carried out sufficiently, and the amount of the unreacted crosslinking agent might be increased. In addition, in case where the dew point is not lower than 60 °C even if the temperature is not lower than 90 °C, even if the water-absorbent resin temperature (material temperature) or heat medium temperature is sufficient, the crosslinking agent permeates into the internal portion of the water-absorbent resin powder particles, and it might be difficult to carry out the crosslinking reaction between the carboxyl group on the surface of the water-absorbent resin powder and the crosslinking agent, because the water content is slowly evaporated from the water-absorbent resin powder. Therefore, as is shown in Fig. 4, the dew point and the temperature are adjusted to not higher than 60 °C and not lower than 90 °C respectively in order to maintain the permeation of the crosslinking agent into the surface neighborhood of the water-absorbent resin powder particles in an optimum state, and to make the surface of the water-absorbent resin powder a necessary and adequate crosslinking state. It is found that the influence of the temperature and the dew point in the atmosphere especially has a great influence on the heat treatment in the surface-crosslinking, especially the heat treatment with the above-mentioned specific crosslinking agent, and further the heat treatment with the polyhydric alcohol.
As to the heat-treating apparatus to treat the water-absorbent resin powder in the above condition, conventional dryers or furnaces equipped with a gas supplying or exhausting apparatus to make the predetermined atmosphere can be used. The usable gas is vapor, air, and nitrogen, and is preferably air. The amount as supplied is fitly determined. The gas for adjusting the temperature or dew point may fitly be under reduced or compressed pressure, or may fitly be heated or cooled. Air having a nearly room temperature (for example, 0 to 50 °C) may be supplied at a substantially ordinary pressure (1.013 × 10 5 Pa (1 atm) ± 10 %, preferably ± 5 %, more preferably ± 1 %). For example, conductive-heat-transfer-type, radiative-heat-transfer-type, hot-wind-heat-transfer-type, or dielectric-heating-type dryers or furnaces equipped with a gas supplying or exhausting apparatus are favorable. Examples thereof include belt-type, channel-blending-type, rotary-type, disk-type, kneading-type, fluidized-bed-type, air-blow-type, infrared-type, or electron-beam-type dryers or furnaces equipped with an apparatus for supplying a mixed gas of air and/or an inert gas. The temperature of these heat-treating apparatuses may be equal to or different from that of the atmosphere of the upper space inside of the heat-treating apparatus, but is usually adjusted to the range of 110 to 250 °C, preferably 150 to 210 °C. In addition, the heat-treating apparatus is heated and its temperature is adjusted higher than the temperature of the atmosphere of the upper space inside of the heat-treating apparatus by 0 to 120 °C, preferably 30 to 100 °C.
The effect of the present invention can be displayed if the mode includes the step of spray-blending the liquid material and the step of heat-treating.
The water-absorbent resin, according to the present invention, is obtained by the production process according to the present invention.
The water-absorbent resin, according to the present invention, is surface-crosslinked with a surface-crosslinking agent including at least a polyhydric alcohol, has a particle size distribution such that the ratio of particles having particle diameters of smaller than 150 µm is not more than 5 weight %, and exhibits an absorption capacity without a load of not less than 30 g/g, with the water-absorbent resin being characterized in that: the single-layer absorption capacity (10 min.) of particles having particle diameters of 600 to 300 µm is not less than 30 g/g under a load; the single-layer absorption capacity (60 min.) of particles having particle diameters of 600 to 300 µm is not less than 30 g/g under a load; the single-layer absorption capacity (10 min.) of particles having particle diameters of 300 to 150 µm is not less than 30 g/g under a load; and the single-layer absorption capacity (60 min.) of particles having particle diameters of 300 to 150 µm is not less than 30 g/g under a load.
It is necessary that the water-absorbent resin according to the present invention has a particle size distribution such that the ratio of particles having particle diameters of smaller than 150 µm is not more than 5 weight %. In case where the water-absorbent resin has a particle size distribution such that the ratio of particles having particle diameters of smaller than 150 µm is more than 5 weight %, an opening in absorbing materials is clogged with the particles having particle diameters of smaller than 150 µm when the water-absorbent resin is used as sanitary materials such as diapers. Therefore, liquids are inhibited from diffusing, and the properties of the product are caused to lower.
For example, among the conventional measurement methods, the absorption capacity under a load described in the present specification was an estimate for the entirety of water-absorbent resin particles having a particle size distribution. Therefore, it is difficult to estimate capacities of each particle. In addition, even if the absorption capacity under a load was measured after adjustment of particle diameters (for example, in the range of 600 to 300 µm), the estimate was for a single particle diameter range ( USP 5147343B1 , EP 532002B1 , and USP 5601542B1 ). Therefore, the surface-crosslinking state of the single particle diameter range could not be compared to that of other particle diameter ranges.
The water-absorbent resin according to the present invention is obtained by the production process for a water-absorbent resin according to the present invention. The production process is characterized in that: the treatment, preferably surface-crosslinking treatment of each water-absorbent resin particle is carried out highly uniformly. Therefore, the estimate represented by the single-layer absorption capacity under a load can exactly reflect capacities of the water-absorbent resin according to the present invention.
The water-absorbent resin, according to the present invention, is characterized in that: the single-layer absorption capacity (10 min.) of particles having particle diameters of 600 to 300 µm is not less than 30 g/g under a load; the single-layer absorption capacity (60 min.) of particles having particle diameters of 600 to 300 µm is not less than 30 g/g under a load; the single-layer absorption capacity (10 min.) of particles having particle diameters of 300 to 150 µm is not less than 30 g/g under a load; and the single-layer absorption capacity (60 min.) of particles having particle diameters of 300 to 150 µm is not less than 30 g/g under a load. The above-mentioned respective single-layer absorption capacities are preferably not less than 31 g/g under a load, more preferably not less than 32 g/g. In case where the above-mentioned respective single-layer absorption capacities are less than 30 g/g under a load, there are disadvantages in that the uniform treatment might not be carried out sufficiently.
The water-absorbent resin, according to the present invention, has a particle size distribution such that: the ratio of particles having particle diameters of 600 to 300 µm is preferably in the range of 65 to 85 weight %, more preferably 70 to 80 weight %; and the ratio of particles having particle diameters of 300 to 150 µm is preferably in the range of 10 to 30 weight %, more preferably 15 to 25 weight %.
In the water-absorbent resin according to the present invention, the time variation of the single-layer absorption capacity of particles having particle diameters of 600 to 300 µm under a load is preferably not less than 0.80.
Then, the time variation of the single-layer absorption capacity of particles having particle diameters of 600 to 300 µm under a load is calculated according to the following equation, and a value representing swellability under a load. This time variation is more preferably not less than 0.85, still more preferably not less than 0.90. That is to say, if the time variation is close to 1, there are advantages in reaching saturated swell in a short time.
Time variation of single-layer absorption capacity of particles having particle diameters of 600 to 300 µm under a load = (single-layer absorption capacity (10 min.) of particles having particle diameters of 600 to 300 µm under a load) / (single-layer absorption capacity (60 min.) of particles having particle diameters of 600 to 300 µm under a load).
In the water-absorbent resin according to the present invention, the time variation of the single-layer absorption capacity of particles having particle diameters of 300 to 150 µm under a load is preferably not less than 0.90.
Then, the time variation of the single-layer absorption capacity of particles having particle diameters of 300 to 150 µm under a load is calculated according to the following equation, and a value representing swellability under a load. This time variation is more preferably not less than 0.92, still more preferably not less than 0.95. That is to say, if the time variation is close to 1, there are advantages in reaching saturated swell in a short time.
Time variation of single-layer absorption capacity of particles having particle diameters of 300 to 150 µm under a load = (single-layer absorption capacity (10 min.) of particles having particle diameters of 300 to 150 µm under a load) / (single-layer absorption capacity (60 min.) of particles having particle diameters of 300 to 150 µm under a load).
Variation between particles of the single-layer absorption capacity (10 min.) under a load = (single-layer absorption capacity (10 min.) of particles having particle diameters of 300 to 150 µm under a load) / (single-layer absorption capacity (10 min.) of particles having particle diameters of 600 to 300 µm under a load).
Variation between particles of the single-layer absorption capacity (60 min.) under a load = (single-layer absorption capacity (60 min.) of particles having particle diameters of 300 to 150 µm under a load) / (single-layer absorption capacity (60 min.) of particles having particle diameters of 600 to 300 µm under a load).
The water-absorbent resin, according to the present invention, is surface-crosslinked with a surface-crosslinking agent including at least a polyhydric alcohol, has a particle size distribution such that the ratio of particles having particle diameters of smaller than 150 µm is not more than 5 weight %, and exhibits an absorption capacity without a load of not less than 30 g/g, with the water-absorbent resin being characterized in that the index of uniform surface-treatment is not less than 0.70.
Index of uniform surface-treatment = (time variation of single-layer absorption capacity of particles having particle diameters of 600 to 300 µm under a load) x (time variation of single-layer absorption capacity of particles having particle diameters of 300 to 150 µm under a load) x (variation between particles of the single-layer absorption capacity (10 min.) under a load) x (variation between particles of the single-layer absorption capacity (60 min.) under a load).
In the water-absorbent resin according to the present invention, the L value of light index measured with such as a spectrophotometer is preferably not less than 85, and the a value and b value representing chromaticness index are preferably in the range of -2 to 2, and 0 to 9 respectively. In case where the L, a, and b values is beyond these ranges, there are disadvantages in that the uniform treatment which is a characteristic of the present invention might not be carried out.
Water-absorbent resins are generally produced or used as powders. Therefore, there was a problem such that the properties of the resultant sanitary material varied due to bias (segregation) of particle diameters of the powders, and the properties values were changed depending upon the absorption time. However, the present invention water-absorbent resin includes the polyhydric alcohol, and have higher properties (higher absorption capacity), and further, there is no difference of the properties between particle diameters or absorption times. Therefore, it is favorable when the water-absorbent resin is use as a sanitary material. When using the water-absorbent resin as a sanitary material, it was found that the properties values (single-layer absorption capacity under a load for a specific particle diameter or specific absorption time) of the present invention are critically important values. The present invention water-absorbent resin has higher properties, and can be used in higher resin concentration such that the core concentration defined by fiber material/water-absorbent resin is in the range of 30 to 100 %, preferably 40 to 100 %, more preferably 50 to 100 %.
A nonwoven fabric bag (60 mm × 60 mm), in which about 0.20 g of a water-absorbent resin was put uniformly, and was immersed into an aqueous sodium chloride solution of 0.9 wt % (physiological saline solution) at room temperature (25 ±2 °C). After 30 minutes, the bag was drawn up and then drained at 250 × 9.81 m/sec2 (250 G) with a centrifuge for 3 minutes. Then, weight W1 (g) of the bag was measured. In addition, the same procedure as the above was carried out using no water-absorbent resin, and weight W2 (g) of the resultant bag was measured.
Thus, the absorption capacity (g/g) without load was calculated from these weights W1 and W2 in accordance with the following equation: Absorption capacity g / g without load = weight W 1 g - weight W 2 g / weight of water - absorbent resin g .
The vessel 2 has an opening part 2a on the top and an opening part 2b on the side, respectively. The air-inhaling pipe 3 is inserted in the opening part, and the introducing tube 4 is fitted to the opening part 2b. Incidentally, the vessel 2 contains a predetermined amount of an aqueous sodium chloride solution of 0.9 wt % (physiological saline solution, liquid temperature: 25 ± 2 °C) 11.
The measurement part 5 comprises: a filter paper 7; a supporting cylinder 8; a wire net 9 as attached to the bottom of the supporting cylinder 8; and a weight 10. The measurement part 5 is formed by mounting the filter paper 7 and the supporting cylinder 8, namely a wire net 9, in this order on the glass filter 6 and further mounting the weight 10 inside the supporting cylinder 8, namely on the wire net 9. The supporting cylinder 8 is formed in an internal diameter of 60 mm. The wire net 9 is made of stainless steel and formed in a mesh size of 38 µm (400 mesh). An arrangement is made such that a predetermined amount of water-absorbent resin can uniformly be spread on the wire net 9. In addition, the weight 10 is adjusted in weight such that a load of 20 g/cm2 (about 1.96 kPa) can uniformly be applied to the water-absorbent resin.
Then, the absorption capacity (g/g) under the load in 60 minutes from the absorption initiation was calculated from the above-mentioned W3 (g) and the weight of the water-absorbent resin (0.900 g) in accordance with the following equation. Absorption capacity g / g under load
= weight W 3 g / weight g of water - absorbent resin
As is shown in Fig. 3, the measurement apparatus comprises: a balance 1; a vessel 2 of a predetermined capacity as mounted on the balance 1; an air-inhaling pipe 3; an introducing tube 4; a glass filter 6; and a measurement part 5 as mounted on this glass filter 6. The vessel 2 has an opening part 2a on the top and an opening part 2b on the side, respectively. The air-inhaling pipe 3 is inserted in the opening part, and the introducing tube 4 is fitted to the opening part 2b. In addition, the vessel 2 contains a predetermined amount of synthetic urine 11. The lower part of the air-inhaling pipe 3 is submerged in the synthetic urine 11. The glass filter 6 is formed in a diameter of 70 mm. The vessel 2 and the glass filter 6 are connected to each other through the introducing tube. In addition, the upper portion of the glass filter 6 is fixed so that the position of the upper surface of the glass filter 6 would be slightly higher than the lower end of the air-inhaling pipe 3. The measurement part 5 comprises: a filter paper 7; a supporting cylinder 8; a wire net 9 as attached to the bottom of the supporting cylinder 8; and a weight 10. Then the measurement part 5 is formed by mounting the filter paper 7 and the supporting cylinder 8, namely a wire net 9, in this order on the glass filter 6 and further mounting the weight 10 inside the supporting cylinder 8, namely on the wire net 9. The supporting cylinder 8 is formed in an internal diameter of 60 mm. The wire net 9 is made of stainless steel and formed in a mesh size of 400 mesh (38 µm). An arrangement is made such that a predetermined amount of water-absorbent resin can uniformly be spread on the wire net 9. In addition, the weight 10 is adjusted in weight such that a load of 50 g/cm2 (about 4.83 kPa) can uniformly be applied to the water-absorbent resin.
Then, the absorption capacity (g/g) under the load in 60 minutes from the absorption initiation was calculated from the above-mentioned W4 (g) in accordance with the following equation: Absorption capacity g / g under load = weight W 4 g / weight g of water - absorbent resin
First, predetermined preparatory operations were made, in which, for example, a predetermined amount of synthetic urine 11 (comprising: 0.2 weight % of sodium sulfate, 0.2 weight % of potassium chloride, 0.05 weight % of magnesium chloride 6 hydrate, 0.025 weight % of calcium chloride dihydrate, 0.085 weight % of ammonium dihydrogen phosphate, 0.015 weight % of diammonium hydrogen phosphate, and 99.425 weight % of deionized water, and liquid temperature: 25 ± 2 °C) was placed into a vessel 2, and an air-inhaling pipe 3 was inserted into the vessel 2. Next, a filter paper 7 was mounted on a glass filter 6. In parallel with this mounting operation, 0.055 ± 0.005 g of water-absorbent resin was uniformly spread inside a supporting cylinder 8, namely, on a wire net 9, and a weight 10 is then put on this water-absorbent resin. Thereafter, the total weight before measurement W5 (g) of the supporting cylinder 8 fixed by the wire net 9, the water-absorbent resin, and the weight 10 was measured. Incidentally, as to the water-absorbent resin for measuring the estimate of uniform surface-treatment, water-absorbent resins having particle diameters of 600 to 300 µm and 300 to 150 µm respectively obtained by beforehand classification were used as measurement samples.
Then, the single-layer absorption capacity (g/g) under the load in 10 or 60 minutes from the absorption initiation was calculated from the above-mentioned W5 (g) and W6 (g) in accordance with the following equation. Single - layer absorption capacity g / g under load = total weight after measurement W 6 g - total weight before measurement W 5 g / weight g of water - absorbent resin
Accordingly, the following four values of single-layer absorption capacities (g/g) under a load were calculated: the single-layer absorption capacity (10 min.) of particles having particle diameters of 600 to 300 µm under a load; the single-layer absorption capacity (60 min.) of particles having particle diameters of 600 to 300 µm under a load; the single-layer absorption capacity (10 min.) of particles having particle diameters of 300 to 150 µm under a load; and the single-layer absorption capacity (60 min.) of particles having particle diameters of 300 to 150 µ under a load.
The time variation of single-layer absorption capacity of particles having particle diameters of 600 to 300 µm under a load was calculated in accordance with the following equation. The variation of single - layer absorption capacity of particles having particle diameters of 600 to 300 μm under a load = single - layer absorption capacity 10 min . of particles having particle diameters of 600 to 300 μm under a load / single - layer absorption capacity 60 min . of particles having particle diameters of 600 to 300 μm under a load .
The time variation of single-layer absorption capacity of particles having particle diameters of 300 to 150 µm under a load was calculated in accordance with the following equation. Time variation of the single - layer absorption capacity of particles having particle diameters of 300 to 150 μm under a load = single - layer absorption capacity 10 min . of particles having particle diameters of 300 to 150 μm under a load / single - layer absorption capacity 60 min . of particles having particle diameters of 300 to 150 μm under a load .
The variation between particles of the single-layer absorption capacity (10 min.) under a load was calculated in accordance with the following equation. Variation between particles of the single - layer absorption capacity 10 min . under a load = single - layer absorption capacity 10 min . of particles having particle diameters of 300 to 150 μm under a load / single - layer absorption capacity 10 min . of particles having particle diameters of 600 to 300 μm under a load .
The variation between particles of the single-layer absorption capacity (60 min.) under a load was calculated in accordance with the following equation. Variation between particles of the single - layer absorption capacity 60 min . under a load = single - layer absorption capacity 60 min . of particles having particle diameters of 300 to 150 μm under a load / single - layer absorption capacity 60 min . of particles having particle diameters of 600 to 300 μm under a load .
Furthermore, the index of uniform surface-treatment was calculated from the four values of the variations as calculated in the above way in accordance with the following equation. Index of uniform surface - treatment = time variation of the single - layer absorption capacity of particles having particle diameters of 600 to 300 μm under a load × time variation of single - layer absorption capacity of particles having particle diameters of 300 to 150 μm under a load × variation between particles of the single - layer absorption capacity 10 min . under a load × variation between particles of the single - layer absorption capacity 60 min . under a load .
The resultant hydrogel polymer was dried in a hot air dryer adjusted at a temperature of 170 °C for 60 minutes. The resultant dried product was pulverized with a roller mill, and then classified with a mesh of 850 µm to remove particles larger than 850 µm, thus obtaining a water-absorbent resin (A1).
The above water-absorbent resin (A1) was kept at about 60 °C and supplied into a continuous high-speed-stirring blender (a turbulizer made by Hosokawa Micron Co., Ltd.) equipped with two hydraulic hollow cone spray nozzles (C1, 1/4M-K-040, made by H. Ikeuchi & Co., Ltd.; their spray patterns were circular and hollow cone shapes) with a feeding speed of 100 kg/hr, and an aqueous surface-crosslinking agent solution prepared with a blending ratio of glycerin : water : isopropyl alcohol = 1 : 4 : 1 as a liquid material (B1) was blended therewith by spraying so that the amount of the aqueous solution as added would be adjusted to 3 weight % relative to the weight of the water-absorbent resin (A1). After the resultant mixture was heat-treated at a water-absorbent resin temperature (material temperature) of 190 °C for one hour, the entirety was passed through a sieve having a mesh opening of 850 µm, thus obtaining a surface-treated water-absorbent resin (1).
The hydraulic hollow cone spray nozzles (C1, 1/4M-K-040) were used.
Therefore, the spray angle of the aqueous surface-treating agent solution from the hydraulic hollow cone spray nozzles was 70 °, and the dispersing area of a spray-dispersing state projected onto a sectional area perpendicular to the stirring shaft direction of the blending apparatus accounted for about 89 % by the nozzles.
The spray angle was 110 ° by use of the hydraulic flat spray nozzles (C2, 1/4M-V-115-05) when the dispersing area of a spray-dispersing state was projected onto a sectional area perpendicular to the stirring shaft direction of the blending apparatus. The dispersing area of a spray-dispersing state projected onto a sectional area perpendicular to the shaft direction of the blending apparatus accounted for about 97 % by the nozzles.
The hydraulic hollow cone spray nozzle (C3, 1/4M-K-100) was used. Therefore, the spray angle of the aqueous surface-treating agent solution from the hydraulic hollow cone spray nozzle was 70 °, and the dispersing area of a spray-dispersing state projected onto a sectional area perpendicular to the shaft direction of the blending apparatus accounted for about 77 %.
A comparative surface-treated water-absorbent resin (1) was obtained in the same way as of Example 1 except that the blender was changed into a continuous high-speed-stirring blender equipped with two straight pipe nozzles (C1') having an internal diameter of 6 mm instead of the hydraulic hollow cone spray nozzles made by H. Ikeuchi & Co., Ltd..
The aqueous surface-crosslinking agent solution (B1) was supplied in a form of liquid drop from the straight pipe nozzles (C1') as used. Therefore, the spray angle and the dispersing area of a spray-dispersing state projected onto a sectional area of the blending apparatus could not be measured.
The resultant comparative surface-treated water-absorbent resin (1) had particles which were agglomerated rigidly, and could not be crashed, and weren't passed through a sieve having a mesh opening of 850 µm. Therefore, the properties of the resultant comparative surface-treated water-absorbent resin (1) were listed in Table 1. However, the value of the particle size distribution as measured includes particles not passing through a sieve having a mesh opening of 850 µm. The absorption capacity without load and absorption capacity under a load were measured by removing the particles not passing through a sieve having a mesh opening of 850 µm.
A comparative surface-treated water-absorbent resin (2) was obtained in the same way as of Example 1 except that the blender was changed into a continuous high-speed-stirring blender equipped with an air-atomizing nozzle (C2', its spray setup number was SU1, and its spray pattern was a circular and full cone shape; made by Spraying Systems Co., Japan).
The air-atomizing nozzle (C2', its spray setup number was SU1, made by Spraying Systems Co., Japan) was used. Therefore, the spray angle of the aqueous surface-treating agent solution from the air-atomizing nozzle was 18 °, and the dispersing area of a spray-dispersing state projected onto a sectional area perpendicular to the shaft direction of the blending apparatus accounted for about 20 %.
The resultant comparative surface-treated water-absorbent resin (2) had particles which were agglomerated rigidly, and could not be crashed, and weren't passed through a sieve having a mesh opening of 850 µm. Therefore, the properties of the resultant comparative surface-treated water-absorbent resin (2) were listed in Table 1. However, the value of the particle size distribution as measured includes particles not passing through a sieve having a mesh opening of 850 µm. The absorption capacity without load and absorption capacity under a load were measured by removing the particles not passing through a sieve having a mesh opening of 850 µm.
The granulation was carried out in order to decrease the amount of the surface-treated water-absorbent resin (1) as passed through a sieve having a mesh opening of 150 µm. That is to say, the water-absorbent resin (1) as a water-absorbent resin (A2) before modifying was supplied into a continuous bigh-speed-stirring blender (a turbulizer made by Hosokawa Micron Co., Ltd.) equipped with two hydraulic hollow cone spray nozzles (C1, 1/4M-K-040, made by H. Ikeuchi & Co., Ltd.; their spray patterns were circular and hollow cone shapes) with a feeding speed of 100 kg/hr, and water as a liquid material (B4) was blended therewith so that the amount of the water as added would be adjusted to 5 weight % relative to the weight of the water-absorbent resin (A2). Then, the resultant mixture was left still at 80 °C for 1 hour to cure, and the entirety was passed through a sieve having a mesh opening of 850 µm, thus obtaining a modified (granulated) water-absorbent resin (4).
The hydraulic hollow cone spray nozzles (C1, 1/4M-K-040) were used. Therefore, the spray angle of the water (B4) was 70 °, and the dispersing area of a spray-dispersing state projected onto a sectional area of the blending apparatus accounted for about 89 % by the nozzles.
The hydraulic flat spray nozzles (C2, 1/4M-V-115-05) were used. Therefore, the spray angle was 110°, and the dispersing area of a spray-dispersing state projected onto a sectional area of the blending apparatus accounted for about 97 % by the nozzles.
The hydraulic hollow cone spray nozzle (C3, 1/4M-K-100) was used. Therefore, the spray angle of the water (B4) was 70 °, and the dispersing area of a spray-dispersing state projected onto a sectional area of the blending apparatus accounted for about 77 %.
A comparative modified (granulated) water-absorbent resin (3) was obtained in the same way as of Example 4 except that the blender was changed into a continuous high-speed-stirring blender equipped with two hydraulic flat spray nozzles (C3', 1/4M-V-040-05, made by H. Ikeuchi & Co., Ltd.; their spray patterns were double-convex-lens and elliptic cone shapes). Incidentally, the hydraulic flat spray nozzles (C3', 1/4M-V-040-05) were attached to the blender very carefully so that the spray angle would be the largest when the dispersing area of a spray-dispersing state was projected onto a sectional area perpendicular to the stirring shaft direction of the continuous high-speed-stirring blending apparatus.
The spray angle was 40 ° by use of the hydraulic flat spray nozzles (C3', 1/4M-V-040-05) when the dispersing area of a spray-dispersing state was projected onto a sectional area perpendicular to the stirring shaft direction of the blending apparatus. The dispersing area of a spray-dispersing state projected onto a sectional area perpendicular to the shaft direction of the blending apparatus accounted for about 67 % by the nozzles.
The resultant comparative modified (granulated) water-absorbent resin (3) had particles which were agglomerated rigidly, and could not be crashed, and weren't passed through a sieve having a mesh opening of 850 µm. Therefore, the properties of the resultant comparative water-absorbent resin (3) were listed in Table 2. However, the value of the particle size distribution as measured includes particles not passing through a sieve having a mesh opening of 850 µm.
When the hydraulic flat spray nozzles (C2, 1/4M-V-115-05) were used, they were attached carefully so that the spray angle would be the smallest in the above way. Therefore, the spray angle was 10° when the dispersing area of a spray-dispersing state was projected onto a sectional area perpendicular to the stirring shaft direction of the blending apparatus. The dispersing area of a spray-dispersing state projected onto a sectional area of the blending apparatus accounted for about 23 % by the nozzles.
The resultant comparative modified (granulated) water-absorbent resin (4) had particles which were agglomerated rigidly, and could not be crashed, and weren't passed through a sieve having a mesh opening of 850 µm. Therefore, the properties of the resultant comparative water-absorbent resin (4) were listed in Table 2. However, the value of the particle size distribution as measured includes particles not passing through a sieve having a sieve opening of 850 µm. Table 1
Absorption capacity without a load (g/g) 34.3 35.1 35.3 34.9 34.7
Absorption capacity under a load (g/g) 27.7 27.5 27.0 23.2 24.9
Particle size distribution Not smaller than 850 µm 0.0 0.0 0.0 0.9 0.8
850 to 500 µm 29.7 29.4 29.1 30.0 29.1
500 to 300 µm 45.0 44.7 45.7 43.5 44.5
300 to 150 µm 19.3 19,7 18.9 18.5 18.2
Smaller than 150 µm 6.0 6.2 6.3 7.1 7.4
Example 4 Example 5 Example 6 Comparative Example 3 Comparative Example 4
Particle size distribution Not smaller than 850 µm 0.0 0.0 0.0 1.2 1.8
850 to 500 µm 33.3 32.9 32.2 32.0 31.5
500 to 300 µm 46.4 46.1 45.5 45.3 45.5
300 to 150 µm 16.4 17.7 17.8 16.3 15.7
Smaller than 150 µm 3.9 3.3 4.5 5.2 5.5
From Table 1, the resultant surface-crosslinked water-absorbent resin obtained by blending according to the present invention process displayed a higher absorption capacity under a load, and was not observed to produce very hard agglomerated materials such that could not be passed through a sieve having a mesh opening of 850 µm in comparison with those obtained by a blending process using the straight pipe nozzles. In addition, it would be understood that: the growth of piled materials due to adding the liquid material excessively was not observed in the blending apparatus, and the water-absorbent resin was uniformly blended with the aqueous surface-crosslinking agent solution as the liquid material.
From Table 2, the ratio of particles smaller than 150 µm was decreased, and the production of very hard agglomerated materials such that could not be passed through a sieve having a mesh opening of 850 µm was not observed, because the blending process according to the present invention was applied. It would be understood that the present process was effective for blending much aqueous solution for the purpose of decreasing dusts of water-absorbent resins as caused.
An aqueous monomer solution was prepared by mixing 3,683 parts by weight of aqueous sodium acrylate solution of 37 weight %, 562 parts by weight of acrylic acid, 4.26 parts by weight of polyethylene glycol diacrylate (average unit of ethylene oxide: 8), and 1,244 parts by weight of deionized water. In a monomer degassing vessel, nitrogen was blown into 1 liter of this aqueous monomer solution with a feeding rate of 0.8 liter/minute for 30 minutes in order to remove the dissolved oxygen in the aqueous solution. Next, 4.5 parts by weight of an aqueous sodium perfulfate solution of 5 weight %, 4.0 part by weight of an aqueous L-ascorbic acid solution of 0.5 weight %, and 4.4 parts by weight of 2,2'-azobis-(2-amidinopropane)dihydrochloride solution were mixed with the aqueous monomer solution from a polymerization initiator vessel respectively. While 3.2 parts by weight of an aqueous hydrogen peroxide solution of 3.5 weight % was supplied, the aqueous monomer solution mixed with the polymerization initiator was supplied onto a belt to carry out a stationary polymerization continuously.
The full length of the belt was 3.5 m, and the interval from a portion for supplying the aqueous monomer solution to 1 m toward the driving direction was equipped with a cooling apparatus for cooling the surface of the belt, and the residual portion was equipped with a heat-treating apparatus for heating the surface of the belt. The aqueous monomer solution supplied onto the belt formed a viscous gel material after about one minute, and the temperature was reached to the maximum after 7 minutes. The maximum temperature was 80 °C. Continuously, the polymerized gel was matured in a heating zone of 60 °C, thus obtaining a transparent hydrogel. This hydrogel was crushed with a meat chopper, and dried in a hot-blow dryer for 65 minutes at 160 °C. The resultant dried product was crushed, thus obtaining a water-absorbent resin (A3) having an average particle diameter of 350 µm, wherein particles having particle diameters of smaller than 150 µm was 5 weight % of the water-absorbent resin. Its absorption capacity and extractable content were 52 times (52 g/g) and 12 % respectively.
(Example 7) (not according to the invention)
A mixed composition comprising 0.5 part of 1,3-propanediol, 0.5 part of propylene glycol, 3.0 parts of water, and 0.5 part of ethanol was blended into 100 parts of the water-absorbent resin (A3) as obtained in Referential Example 1 with a turbulizer. The mixture as obtained was heat-treated for one hour in a paddle-type dryer, wherein the internal wall (heat medium) temperature of the paddle-type dryer was 185 °C, and the atmosphere of the space portion in the dryer was adjusted to have a dew point of 40 °C and a temperature of 97 °C, thus obtaining a water-absorbent resin (absorbing agent) (7). The results were listed in Table 3.
(Example 8) (not according to the invention)
A water-absorbent resin (absorbing agent) (8) was obtained in the same way as of Example 7 except that the atmosphere of the space portion in the paddle-type dryer was adjusted to have a dew point of 50 °C and a temperature of 119 °C. The results were listed in Table 3.
(Example 9) (not according to the invention)
A mixed composition comprising 0.5 part of 1,3-propanediol, 0.5 part of propylene glycol, 3.0 parts of water, and 0.5 part of ethanol was blended into 100 parts of the water-absorbent resin (A3) as obtained in Referential Example 1 with a turbulizer. The mixture as obtained was heat-treated for one hour in a double-arm type kneader, wherein the internal wall (heat medium) temperature of the double-arm type kneader was 185 °C, and the atmosphere of the space portion in the dryer was adjusted to have a dew point of 60 °C and a temperature of 145 °C, thus obtaining a water-absorbent (absorbing agent) (9). The results were listed in Table 3.
A comparative water-absorbent resin (comparative absorbing agent) (5) was obtained in the same way as of Example 7 except that the atmosphere of the space portion in the paddle-type dryer was adjusted to have a dew point of 25 °C and a temperature of 88 °C. The results were listed in Table 3.
A comparative water-absorbent resin (comparative absorbing agent) (6) was obtained in the same way as of Example 7 except that the atmosphere of the space portion in the paddle-type dryer was adjusted to have a dew point of 100 °C and a temperature of 142 °C. The results were listed in Table 3. Table 3
Atmosphere Absorption capacity (g/g) Absorption capacity under a load (g/g)
Dew point (°C) Temperature (°C)
Example 7 Water-absorbent resin (absorbing agent) (7) 40 97 35 32
Example 8 Water-absorbent resin (absorbing agent) (8) 50 119 33 35
Example 9 Water-absorbent resin (absorbing agent) (9) 60 145 35 30
Comparative Example 5 Comparative witer-absorbent resin (comparative absorbing agent) (5) 25 88 40 14
Comparative Example 6 Comparative water-absorbent resin (comparative absorbing agent) (6) 100 142 37 13
The resultant hydrogel polymer was dried in a hot air dryer adjusted at a temperature of 170 °C for 60 minutes. The resultant dried product was pulverized with a roller mill, and then classified with a mesh of 850 µm to remove particles larger than 850 µm, thus obtaining a water-absorbent resin (A4). The resultant water-absorbent resin (A4) had a particle size distribution such that the average particle diameter was 350 µm and the ratio of particles having particle diameters of smaller than 150 µm was 7 weight %, and exhibited an absorption capacity of 45 times (45 g/g).
The above water-absorbent resin (A4) was supplied into a continuous high-speed-stirring blender (a turbulizer made by Hosokawa Micron Co., Ltd.) equipped with a hydraulic hollow cone spray nozzle (C1, 1/4M-K-040, made by H. Ikeuchi & Co., Ltd.; its spray pattern was a circular and hollow cone shape) with a feeding speed of 100 kg/hr, and an aqueous surface-crosslinking agent solution prepared with a blending ratio of 1,4-butandiol: propylene glycol: water = 1 : 1 : 6 as a liquid material (B10) was blended therewith so that the amount of the aqueous solution as added would be adjusted to 4 weight % relative to the weight of the water-absorbent resin (A4). After the resultant mixture was heat-treated for 50 minutes in a paddle-type dryer of 190 °C (water-absorbent resin temperature (material temperature)), wherein the atmosphere of the upper space inside of the paddle-type dryer had a dew point of 50 °C and a temperature of 160 °C, the entirety was passed through a sieve having a mesh opening of 850 µm, thus obtaining a surface-treated water-absorbent resin (10).
The hydraulic hollow cone spray nozzle (C1, 1/4M-K-040; its spray pattern was a circular and hollow cone shape) was used. Therefore, the spray angle of the aqueous surface-treating agent solution from the hydraulic hollow cone spray nozzle was 70 °, and the dispersing area of a spray-dispersing state projected onto a sectional area perpendicular to the stirring shaft direction of the blending apparatus accounted for about 77 %.
All the procedures were carried out in the same way as of Example 10 except that the aqueous surface-crosslinking agent solution was replaced with an aqueous surface-crosslinking agent solution (B11) prepared with a blending ratio of 1,3-dioxolane-2-one: water: ethanol = 1: 1: 1 as the liquid material, and was blended so that the amount of the aqueous solution as added would be adjusted to 7.5 weight % relative to the weight of the water-absorbent resin (A4).
All the procedures were carried out in the same way as of Example 10 except that the mixture resultant from the water-absorbent resin (A4) and the liquid material (B10) was heat-treated treated for 50 minutes in a paddle-type dryer of 190 °C (water-absorbent resin temperature (material temperature)), wherein the atmosphere of the upper space inside of the paddle-type dryer had a dew point of 40 °C and a temperature of 80 °C.
As is shown in Table 4, the properties of Example 12 were inferior to that of Example 10. Incidentally, Example 12 is an example for the production process, but is not for the water-absorbent resin. Table 4
Single-layer absorption capacity under a load (g/g) 600 to 300 µm 10 min. 31.8 29.2 32.0
60 min. 37.9 37.2 39.6
300 to 150 µm 10 min. 32.2 30.3 29.8
Time variation of single-layer absorption capacity under a load 600 to 300 µm 0.84 0.78 0.81
300 to 150 µm 0.94 0.94 0.88
Variation between particles of single-layer absorption capacity under a load 10 min. 1.01 1.03 0.93
60 min. 0.91 0.87 0.87
The foregoing description of the preferred embodiments according to the present invention is provided for the purpose of illustration only, and not for the purpose of limiting the invention as defined by the appended claims.
A production process for a water-absorbent resin, comprising the steps of:
blending a liquid material and a water-absorbent resin; and heating the resultant mixture in order to produce a modified water-absorbent resin,
wherein said blending step comprises spray-blending a water-absorbent resin (A) and a liquid material (B) with a blending apparatus equipped with a spray nozzle (C),
characterized in that the liquid material (B) is sprayed from the spray nozzle (C) in a spray pattern which has a circular and hollow cone shape, wherein the area of the cone shaped spray pattern of the liquid material (B) as seen projected onto the sectional area which is perpendicular to the axis direction of the blending apparatus and includes the spraying point of the spray nozzle (C) accounts for not less than 70 % of the sectional area perpendicular to the axis direction of the blending apparatus,
and the modification by adding the liquid material includes at least one selected from among the following surface-crosslinking, granulation, and addition of additives.
characterized in that the liquid material (B) is sprayed from the spray nozzle (C) in a spray pattern which has a double-convex-lens and elliptic cone shape, wherein
the area of the cone shaped spray pattern of the liquid material (B) as seen projected onto the sectional area which is perpendicular to the axis direction of the blending apparatus and includes the spraying point of the spray nozzle (C) accounts for not less than 70 % of the sectional area perpendicular to the axis direction of the blending apparatus,
A production process according to claim 1 or 2, wherein the blending step is carried out using a continuous stirring blending apparatus.
A production process according to any one of claims 1 to 3, wherein the heating step is a heat-treating step which is carried out under an atmosphere having a dew point of not higher than 60 °C and a temperature of not lower than 90 °C.
A production process according to any one of claims 1 to 4, wherein the blending apparatus equipped with the spray nozzle (C) is a continuous blending apparatus comprising an agitation shaft having a plurality of paddles.
A production process according to any one of claims 1 to 5, wherein the blending apparatus is equipped with a plurality of spray nozzles (C).
A production process according to any one of claims 1 to 6, wherein the liquid material (B) is an aqueous solution of a surface-crosslinking agent which forms a covalent bond by reacting with a functional group of the water-absorbent resin (A), and
which further comprises the step of heat-treating the mixture resultant from the blending step at a water-absorbent resin temperature of 80 to 250 °C.
A production process according to claim 7, wherein the liquid material (B) is an aqueous solution including at least one selected from the group consisting of polyhydric alcohols, polyglycidyl compounds, 1,3-dioxolan-2-on, poly(2-oxazolidinone), bis(2-oxazolidinone), and mono(2-oxazolidinone).
A production process according to claim 8, wherein the liquid material (B) is an aqueous surface-crosslinking agent solution including a polyhydric alcohol.
EP20010121378 2000-09-20 2001-09-06 Production process for a water-absorbent resin Active EP1191051B1 (en)
EP10009389.7A EP2272898B1 (en) 2000-09-20 2001-09-06 Water-absorbent polymer particles and production process therefor
EP10009389.7A Division EP2272898B1 (en) 2000-09-20 2001-09-06 Water-absorbent polymer particles and production process therefor
EP10009389.7 Division-Into 2010-09-09
EP1191051A2 EP1191051A2 (en) 2002-03-27
EP1191051A3 EP1191051A3 (en) 2002-09-25
EP1191051B1 true EP1191051B1 (en) 2010-11-03
EP20010121378 Active EP1191051B1 (en) 2000-09-20 2001-09-06 Production process for a water-absorbent resin
EP10009389.7A Active EP2272898B1 (en) 2000-09-20 2001-09-06 Water-absorbent polymer particles and production process therefor
JP3349768B2 (en) 1992-06-10 2002-11-25 株式会社日本触媒 Production method and compositions of the acrylate-based polymer
JP3659507B2 (en) 1993-09-13 2005-06-15 月島機械株式会社 Purification method of acrylic acid
JP4256484B2 (en) 1996-10-15 2009-04-22 株式会社日本触媒 Method for producing a water absorbing agent, absorbent article and the water-absorbing agent
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