WO2011025013A1 - 吸水性樹脂の製造方法 - Google Patents
吸水性樹脂の製造方法 Download PDFInfo
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- WO2011025013A1 WO2011025013A1 PCT/JP2010/064746 JP2010064746W WO2011025013A1 WO 2011025013 A1 WO2011025013 A1 WO 2011025013A1 JP 2010064746 W JP2010064746 W JP 2010064746W WO 2011025013 A1 WO2011025013 A1 WO 2011025013A1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/12—Powdering or granulating
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
- C08J3/245—Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2300/00—Characterised by the use of unspecified polymers
- C08J2300/14—Water soluble or water swellable polymers, e.g. aqueous gels
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
- C08J2333/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
Definitions
- the present invention relates to a method for producing a water absorbent resin. More specifically, the present invention relates to an improvement in the drying step of a hydrogel for efficiently producing a water absorbent resin having excellent physical properties.
- Water absorbent resin (Super Absorbent Polymer: SAP) is a water-swellable and water-insoluble polymer gelling agent, such as absorbent articles such as paper diapers and sanitary napkins, agricultural and horticultural water retention agents, industrial waterstop materials, etc. Mainly used for single use. Many monomers and hydrophilic polymers have been proposed as raw materials for such water-absorbing resins.
- a polyacrylic acid (salt) water-absorbing resin using acrylic acid and / or a salt thereof hereinafter also referred to as “acrylic acid (salt)” as a monomer is industrial because of its high water absorption performance. Are most manufactured.
- the water-absorbing resin is generally produced by finely granulating a water-containing gel (water-containing gel-like polymer) obtained by polymerizing monomers in an aqueous solution, if necessary, at the time of polymerization or after polymerization, and then drying the gel. .
- a water-containing gel water-containing gel-like polymer
- Patent Documents 1 to 5 As a method for drying the hydrogel, a method using a belt dryer (Patent Documents 1 to 5), a method of drying a thin film with a drum dryer or the like (Patent Document 6), a method of azeotropic dehydration in an organic solvent (Patent Document 7). ), A method of drying in a fluidized bed (Patent Document 8), a method of vibrating fluidized drying (Patent Document 9), and a method of stirring and drying with a rotor (Patent Document 10).
- Patent Documents 11 and 12 As a drying condition of the hydrogel, a method of controlling the dew point and temperature for improving physical properties (for example, reduction of residual monomers, improvement of water absorption ratio, reduction of water-soluble components) (Patent Documents 11 and 12). A method of coarsely pulverizing and stirring and drying in the middle of drying (Patent Document 13) has been proposed.
- an undried product (undried gel) may be generated in the drying step of the hydrogel. If such an undried product is present, an excessive load is applied to the pulverizer in the pulverization step after the drying step. Therefore, a method for removing the undried material (Patent Documents 14 to 16) is also known.
- a method for prescribing the fluidity of the hydrogel (Patent Document 17), a method using a hydrogel leveling device in the dryer (Patent Documents 18 and 19), and a specific dryer
- a drying method (Patent Document 20) using a quantitative supply device for supplying an amount of water-containing gel
- a method of adding an additive such as a surfactant or inorganic fine particles to the hydrogel to improve the drying efficiency (Patent Documents 22 to 26) is also known.
- Patent Document 27 A drying method (Patent Document 27) suitable for a hydrogel having a low neutralization rate has also been proposed. Further, when pulverizing a hydrogel having a solid content of 50 to 70% by weight with a screw extruder, 0.1 to 30 parts by weight of water is supplied to 100 parts by weight of the hydrous gel and then dried. In addition, a technique of drying with a ventilation belt (Patent Document 28) is also proposed.
- Patent Document 27 discloses drying of hydrous gel with low neutralization
- Patent Document 28 discloses refinement and drying of high-concentration hydrous gel, respectively, but these techniques still have sufficient problems. It could not be solved.
- an object of the present invention is to provide a method for producing a water-absorbing resin that can efficiently obtain a water-absorbing resin having excellent physical properties.
- the present inventors conducted extensive research. As a result, in the drying process of the hydrogel having a high solid content, it was found that the above problem can be solved by changing the thickness of the hydrogel loaded on the aeration belt using a continuous aeration belt dryer. It came to complete.
- the method for producing a water-absorbent resin (first method) of the present invention comprises a polymerization step of obtaining an aqueous gel by subjecting an aqueous monomer solution to a polymerization reaction, and a drying step of drying the aqueous gel.
- the drying process is performed using a continuous ventilating belt dryer, and the solid content of the hydrogel used in the drying process is 35% by weight or more.
- the thickness change rate (1) represented by the following formula 1 of the hydrated gel loaded on the ventilation belt in the continuous ventilation belt type dryer is 1.05 to 5.
- the method for producing a water-absorbent resin of the present invention comprises a step of obtaining a water-containing gel by subjecting an aqueous monomer solution to a polymerization reaction, and a step of drying the water-containing gel.
- a method for producing a resin wherein drying in the drying step is performed using a continuous aeration belt dryer, and the solid content of the hydrous gel provided in the drying step is 35% by weight or more,
- the water-containing gel is loaded on a continuous ventilation belt type dryer using a non-constant speed traverse feeder or vibration feeder.
- a water absorbent resin having excellent physical properties can be obtained efficiently.
- the present embodiment is a method for producing a water-absorbent resin comprising: a polymerization step of subjecting an aqueous monomer solution to a polymerization reaction to obtain a hydrogel; and a drying step of drying the hydrogel;
- the present invention also relates to a method for producing a water-absorbent resin having a thickness change rate (1) represented by the following formula 1 of the hydrous gel of 1.05 to 5.
- the “water-absorbing resin” means a water-swellable and water-insoluble polymer gelling agent having the following physical properties.
- the water absorption capacity (CRC) of the water absorbent resin is essentially 5 g / g or more, preferably 10 to 100 g / g, and more preferably 20 to 80 g / g.
- the soluble content of the water-absorbing resin (Extractables) is essentially 0 to 50% by weight or less, preferably 0 to 30% by weight, more preferably 0 to 20% by weight, still more preferably 0 ⁇ 10% by weight.
- the water-absorbing resin in the present specification is not limited to the case of being composed only of a polymer having water-absorbing performance, and may contain other components other than the polymer as long as various performances can be maintained. .
- the content of polyacrylic acid (salt) in the water-absorbing resin containing polyacrylic acid (salt) as a polymer is preferably 70 to 99.9% by weight, more preferably based on the total weight of the water-absorbing resin. Is 80 to 99.7% by weight, more preferably 90 to 99.5% by weight.
- water is preferable from the viewpoint of improving the water absorption speed and impact resistance, If necessary, the additives described below can also be used.
- polyacrylic acid (salt) is obtained by (co) polymerizing a monomer which optionally contains a graft component and has acrylic acid (salt) as a main component as a monomer.
- Co polymer means. Specifically, the proportion of acrylic acid (salt) contained in the monomer constituting the polyacrylic acid (salt) (excluding the crosslinking agent) is essentially 50 to It is 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, still more preferably substantially 100 mol%.
- the salt as a (co) polymer essentially includes a water-soluble salt, preferably a monovalent salt, more preferably an alkali metal salt or an ammonium salt, still more preferably an alkali metal salt, particularly preferably. Contains sodium salt.
- initial coloring means unavoidable coloring in the manufacturing process of a water absorbing resin.
- the initial coloration is determined by using the measurement method described in International Publication No. 2009/005114 pamphlet for the water-absorbent resin immediately after production (measured within 1 hour after production in the examples) (for example, L / a / b value, YI value, WB value, etc.).
- coloring with time means coloring (usually yellowing or browning) that occurs when an unused (unswelled) water-absorbing resin is stored for a long period of time. .
- the coloring over time occurs, for example, when an unused diaper is stored in a warehouse or the like for a long period of time, and can reduce the commercial value of the diaper. Since coloration is not observed after storage for several months to several years in storage at room temperature, the coloration over time is usually carried out by an accelerated test under high temperature and high humidity conditions described in International Publication No. 2009/005114. Verified using.
- EDANA European Disposables and Nonwovens Associations.
- ERT is an abbreviation for European standard water-absorbent resin measurement method (ERT / EDANA Recommended Test Method), which is now almost the world standard. In this specification, unless otherwise specified, the physical properties of the water-absorbent resin are measured with reference to the original ERT (known document; revised in 2002).
- CRC is an abbreviation for centrifuge retention capacity, and means the water absorption capacity without pressure (hereinafter also referred to as “water absorption capacity”). Specifically, after absorbing 0.200 g of the water-absorbing resin in the non-woven bag in a 0.9% by weight aqueous sodium chloride solution for 30 minutes, the water absorption capacity after draining 250 G with a centrifuge (unit: [g / g ]).
- AAP is an abbreviation for water absorption under pressure (Absorbency against Pressure). Specifically, it is defined by the water absorption capacity (unit: [g / g]) after 0.900 g of a water absorbent resin is swollen in a 0.9 wt% sodium chloride aqueous solution under a load for 1 hour. In this specification, APP was measured when the load condition was 21 g / cm 2 (0.3 psi) or 50 g / cm 2 (0.7 psi).
- Soluble content means the amount of water-soluble component contained in the water-absorbent resin. Specifically, 1 g of a water-absorbing resin is added to 200 g of a 0.9 wt% sodium chloride aqueous solution, and after stirring for 16 hours, the amount of dissolved polymer is measured by pH titration (unit: wt%).
- FSC (ERT440.2-02) “FSC” is an abbreviation for Free Swell Capacity. Specifically, after absorbing 0.200 g of the water-absorbing resin in the nonwoven fabric in a 0.9 wt% sodium chloride aqueous solution for 30 minutes, the water absorption ratio (unit: [g / g] measured without draining with a centrifuge ]).
- the “remaining monomer amount” means the amount of monomer (monomer) remaining in the water absorbent resin. Specifically, 1.0 g of a water-absorbing resin is added to 200 cm 3 of a 0.9 wt% sodium chloride aqueous solution, stirred for 1 hour at 500 rpm, and then the amount of monomer eluted in the aqueous solution is measured by high performance liquid chromatography. (Unit: ppm).
- Liquid permeability means the flow of liquid flowing between swollen gel particles under load or no load.
- Typical measurement methods include SFC (Saline Flow Conductivity) and GBP (Gel Bed Permeability).
- SFC has a permeability of 0.69% physiological saline to 0.9 g of water-absorbent resin under a load condition of 21 g / cm 2 (0.3 psi), and is obtained by the method described in US Pat. No. 5,669,894. Desired.
- the GBP under load or free swelling is determined by the method described in International Publication No. 2005/016393 pamphlet.
- the monomer aqueous solution essentially contains a monomer and may contain other additives as necessary.
- each component contained in the monomer aqueous solution will be described in detail.
- the monomer in the present embodiment is not particularly limited as long as it is a monomer containing a polymerizable unsaturated bond (unsaturated monomer), but it is difficult to color the water-absorbent resin and from the viewpoint of physical properties Therefore, it is preferable that acrylic acid and / or a neutralized product thereof (that is, acrylic acid (salt)) be a main component.
- the content of protoanemonin and / or furfural as impurities is reduced from the viewpoint of difficulty in coloring in the water-absorbent resin (color stability effect) and reduction of residual monomer. It is preferable to use a small amount of acrylic acid as a raw material.
- the content of protoanemonin and / or furfural in acrylic acid is preferably 0 to 10 ppm by weight, more preferably 0 to 5 ppm by weight, and still more preferably 0 to 1 ppm by weight. It is as follows.
- the amount of aldehyde and / or maleic acid other than furfural contained in acrylic acid is smaller.
- the content of aldehyde other than furfural and / or maleic acid in acrylic acid is preferably 0 to 5 ppm by weight, more preferably 0 to 3 ppm by weight, and still more preferably 0 to 1 ppm by weight, particularly preferably 0 ppm by weight (below the detection limit).
- aldehydes other than furfural include benzaldehyde, acrolein, and acetaldehyde.
- the amount of dimer (dimer) contained in acrylic acid is smaller.
- the content of the dimer in acrylic acid is preferably 0 to 500 ppm by weight, more preferably 0 to 200 ppm by weight, and still more preferably 0 to 100 ppm by weight.
- the acrylic acid used in the present embodiment is not particularly limited, but for example, acrylic acid obtained by gas phase oxidation of propylene or propane as a raw material may be used, or glycerin obtained from natural fats and oils. Acrylic acid derived from non-fossil raw materials by oxidation such as may be used. Furthermore, acrylic acid may be obtained by directly oxidizing these raw material compounds, or acrylic acid may be obtained by oxidizing this via an acrolein as an intermediate.
- Examples of basic substances used for neutralizing acrylic acid when preparing acrylates include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide, and carbonic acid (hydrogen). Examples thereof include monovalent bases such as sodium and carbonate (hydrogen) salts such as potassium carbonate (hydrogen), among which sodium hydroxide is preferably used.
- acrylic acid (salt) When acrylic acid (salt) is used as a monomer, the acrylic acid (salt) may be composed of only acrylic acid, or acrylic acid and acrylic acid partially neutralized with acrylic acid.
- the form of a mixture with a salt may be sufficient, and the form which consists only of acrylates from which all of acrylic acid was neutralized may be sufficient.
- AAP water absorption capacity under pressure
- SFC physiological saline flow conductivity
- at least a part of acrylic acid is neutralized (including acrylate) Is preferred.
- the ratio of acrylate to the total amount of acrylic acid (salt) is preferably 10 to 100 mol%, more preferably 30 to 95 mol%, and further preferably 50 to 90 mol%.
- the mol% is particularly preferably 60 to 80 mol%.
- the neutralization of acrylic acid can be performed in the state of acrylic acid or an aqueous acrylic acid solution.
- the temperature at the time of neutralization is not particularly limited and is appropriately determined at 10 to 100 ° C. and 30 to 90 ° C.
- the method as described in an international publication 2006/109842 pamphlet and the US Patent 6388000 can be employ
- an acid group of a polymer obtained in a polymerization step described later may be neutralized.
- the neutralization rate of the acid group in the polymer is preferably 10 to 100 mol%, more preferably 30 to 95 mol%, still more preferably 50 to 90 mol%, and particularly preferably. Is 60 to 80 mol%.
- a hydrophilic or hydrophobic monomer other than acrylic acid (salt) may be used as the monomer.
- other monomers include methacrylic acid, (anhydrous) maleic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, (meth) acryloxyalkanesulfonic acid, N-vinyl-2-pyrrolidone, N-vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) Examples thereof include acrylate, stearyl acrylate, and salts thereof.
- the monomer concentration (solid content concentration) in the aqueous monomer solution is usually 10 to 90% by weight, preferably 20 to 80% by weight, more preferably 30 to 70% by weight, and still more preferably. 40 to 60% by weight.
- the polymerization concentration exceeds the saturation concentration, and the monomer aqueous solution may be a slurry (aqueous dispersion).
- the concentration is preferably set to the saturation concentration or less so as not to precipitate.
- the monomer aqueous solution of this form further contains an internal crosslinking agent from a viewpoint of improving the water absorption characteristic of water absorbing resin.
- the crosslinking agent is not particularly limited, but is a polymerizable crosslinking agent having two or more polymerizable unsaturated groups per molecule, or a reactive functional group capable of reacting with a carboxyl group to form a covalent bond or an ionic bond.
- a reactive crosslinking agent having two or more groups per molecule or a crosslinking agent having both a polymerizable unsaturated group and a reactive functional group may be used.
- the polymerizable crosslinking agent N, N′-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (polyoxyethylene) trimethylolpropane tri (meth) acrylate, poly (meth) Examples include allyloxyalkanes.
- polyglycidyl ether for example, ethylene glycol diglycidyl ether
- a polyvalent metal including a covalent crosslinking agent such as polyhydric alcohol (for example, propanediol, glycerin, sorbitol), aluminum, and the like
- covalent crosslinking agent such as polyhydric alcohol (for example, propanediol, glycerin, sorbitol), aluminum, and the like
- examples thereof include ion-bonding cross-linking agents such as compounds.
- these crosslinking agents from the viewpoint of improving the water absorption characteristics of the water absorbent resin, the above-mentioned acrylate-based, allyl-based, or acrylamide-based polymerizable crosslinking agents are preferably used.
- the addition amount of the cross-linking agent is preferably 0.001 to 5 mol%, more preferably 0.001%, based on the physical properties of the water-absorbent resin, with respect to the total amount of the above monomers (excluding the cross-linking agent). 005 to 2 mol%, more preferably 0.01 to 1 mol%, particularly preferably 0.03 to 0.5 mol%.
- the monomer aqueous solution of this embodiment preferably further contains a polymerization inhibitor from the viewpoint of polymerization stability.
- the polymerization inhibitor include methoxyphenols. Among them, p-methoxyphenol is preferably used.
- the addition amount of the polymerization inhibitor is preferably from 1 to 250 ppm, more preferably from 5 to 200 ppm, still more preferably from 10 to 160 ppm, still more preferably from 20 to 100 ppm, based on the monomer.
- the addition amount of the polymerization inhibitor exceeds 250 ppm, problems of polymerization rate and coloring (particularly initial coloring) occur, and when the addition amount of the polymerization inhibitor is less than 1 ppm, the polymerization stability is poor, which is not preferable. .
- the monomer aqueous solution of this embodiment may further contain iron.
- the iron is present in the form of ions in an aqueous monomer solution.
- the iron content is usually from 0 to 10 ppm by weight, preferably from 0 to 5 ppm by weight, more preferably from 0 to less than 5 ppm by weight, in terms of Fe 2 O 3 relative to the monomer. More preferably 0.001 to 5 ppm by weight, particularly preferably 0.001 to 4 ppm by weight, and most preferably 0.005 to 3 ppm by weight.
- a method for controlling the iron content a method disclosed in International Publication No. 2006/109842 can be employed.
- Fe 2 O 3 conversion means the amount of Fe in a compound containing iron (for example, Fe 2 O 3 and its iron salt, iron hydroxide, iron complex, etc.) or the amount of Fe alone, Fe 2 It is expressed as the amount of iron compound represented by O 3 (molecular weight 159.7), and the iron amount as Fe content is 55.85 ⁇ 2 / 159.7 (Fe in Fe 2 O 3 ). Can be calculated uniquely.
- the iron content in the monomer aqueous solution can be measured by, for example, an ICP emission spectroscopic analysis method described in JIS K1200-6.
- the ICP emission spectroscopic analyzer is commercially available from HORIBA, Ltd., ULTIMA, etc.
- the monomer aqueous solution may contain a water-soluble resin or a water-absorbing resin such as starch, cellulose, polyvinyl alcohol, polyacrylic acid (salt), and polyethyleneimine in addition to the above-described components.
- a water-soluble resin or a water-absorbing resin such as starch, cellulose, polyvinyl alcohol, polyacrylic acid (salt), and polyethyleneimine in addition to the above-described components.
- These water-soluble resins or water-absorbing resins are, for example, 0 to 50% by weight, preferably 0 to 20% by weight, more preferably 0 to 10% by weight, still more preferably 0 to 3%, based on the total amount of monomers. It can be added in a percentage by weight.
- a graft polymer eg, starch acrylic acid graft polymer
- a water-absorbing resin composition obtained by using other components is also collectively referred to as a polyacrylic acid (salt) -based water-absorbing resin.
- various foaming agents carbonates, azo compounds, bubbles, etc.
- surfactants or various other additives are added, for example, 0 to 5% by weight, preferably 0 to 1% by weight to absorb water.
- Various physical properties of the functional resin may be improved.
- Examples of the various additives include chelating agents, hydroxycarboxylic acids, and reducing inorganic salts. Among these, it is preferable to use a chelating agent.
- a chelating agent, hydroxycarboxylic acid, or reducing inorganic salt is used, it is preferably 10 to 5000 ppm by weight, more preferably 10 to 1000 ppm by weight, and even more preferably 50 to 1000 ppm by weight with respect to the water absorbent resin. Particularly preferably, it is added so as to be 100 to 1000 ppm by weight.
- chelating agents By using these chelating agents, hydroxycarboxylic acids, and reducing inorganic salts, it is possible to achieve difficulty in coloring with time in the water-absorbent resin and improvement in urine resistance (preventing gel degradation).
- Specific examples of the chelating agent, hydroxycarboxylic acid, and reducing inorganic salt include International Publication No. 2009/005114, European Patent Application Publication No. 2057228, and European Patent Application Publication No. 1848758.
- the compounds described can be preferably used.
- the components (b) to (e) other than the monomer may be added to the aqueous monomer solution as described above, but may be added at any stage in the method for producing the water absorbent resin of the present embodiment. May be.
- it can be added to a reaction solution during the polymerization reaction, a hydrogel after the polymerization reaction, a dried product obtained by drying the hydrogel, or a powder obtained by pulverizing the dried product.
- aqueous solution polymerization or reverse phase suspension polymerization can be usually employed from the viewpoint of performance of the water-absorbing resin and ease of control of the polymerization reaction.
- aqueous solution polymerization is preferable, and continuous aqueous solution polymerization is more preferable.
- a continuous aqueous solution for producing a water-absorbing resin in a single line on a huge scale of 0.5 t / hr or more, more preferably 1 t / hr or more, further preferably 5 t / hr or more, particularly preferably 10 t / hr or more.
- Polymerization can be employed.
- Specific continuous aqueous solution polymerization includes continuous kneader polymerization (for example, US Pat. Nos. 6,987,151 and 6,701,141), continuous belt polymerization (for example, US Pat. Nos. 4,893,999, 6,241,928) and US Patent Application Publication No. 2005-215734).
- the starting temperature of continuous aqueous solution polymerization is preferably high.
- the temperature of the aqueous monomer solution is preferably controlled to 30 ° C. or higher, more preferably 35 ° C. or higher, further preferably 40 ° C. or higher, particularly preferably 50 ° C. or higher (however, the upper limit is the boiling point).
- the monomer concentration is high.
- the concentration of the monomer in the reaction solution is preferably controlled to 35% by weight or more, more preferably 40% by weight or more, and further preferably 45% by weight or more (however, the upper limit is a saturated concentration). It is preferable.
- the polymerization reaction can be carried out in an air atmosphere, but it is preferably carried out in an inert gas atmosphere such as nitrogen or argon (for example, an oxygen concentration of 1% by volume or less) from the viewpoint of reducing coloring of the water-absorbent resin.
- the monomer or the aqueous monomer solution is preferably used in the polymerization reaction after the dissolved oxygen is sufficiently substituted with an inert gas (for example, the oxygen concentration is less than 1 ppm).
- an inert gas for example, the oxygen concentration is less than 1 ppm.
- the polymerization initiator used in the polymerization process of this embodiment is appropriately selected depending on the form of polymerization.
- the polymerization initiator include radical polymerization initiators such as a photodegradable polymerization initiator, a thermal decomposition polymerization initiator, and a redox polymerization initiator.
- Examples of the photodegradable polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds.
- Examples of the thermal decomposition type polymerization initiator include persulfates (sodium persulfate, potassium persulfate, ammonium persulfate), peroxides (hydrogen peroxide, t-butyl peroxide, methyl ethyl ketone peroxide), azo compounds ( 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, and the like.
- Persulfates, peroxides, and azo compounds can also be used as photopolymerization initiators.
- redox polymerization initiator examples include a system in which the persulfate or peroxide is combined with a reducing compound such as L-ascorbic acid or sodium bisulfite. Moreover, it is also mentioned as a preferable aspect to use together the said photodegradable initiator and the said thermal decomposition type polymerization initiator.
- the amount of the polymerization initiator used is preferably 0.0001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the total amount of monomers.
- the usage-amount of a polymerization initiator is 1 mol% or less, coloring of a water absorbing resin can be suppressed.
- a residual monomer can be reduced as the usage-amount of a polymerization initiator is 0.0001 mol% or more.
- the coloring is performed without adversely affecting the polymerization reaction and various physical properties of the water absorbent resin. Can be reduced.
- hydrogel The hydrogel polymer obtained in the above polymerization step (hereinafter also simply referred to as "hydrogel”) may be subjected to the drying step as it is, after the polymerization step, and Prior to the drying step, if necessary, it is finely divided into particles using a pulverizer (kneader, meat chopper, etc.).
- a pulverizer kneader, meat chopper, etc.
- polymerization process is reverse phase suspension polymerization, since a water-containing gel is refined
- the temperature of the water-containing gel at the time of fine granulation is controlled by heat retention or heating so that it is preferably in the range of 40 to 95 ° C, more preferably 50 to 80 ° C, from the viewpoint of the physical properties of the water-absorbent resin.
- the solid content of the hydrogel is preferably 10 to 70% by weight, more preferably 15 to 65% by weight, and still more preferably 30 to 55% by weight from the viewpoint of physical properties.
- the weight average particle diameter (specified by sieve classification) of the finely divided hydrogel is preferably 0.5 to 4 mm, more preferably 0.3 to 3 mm. More preferably, it is 0.5 to 2 mm.
- the particles having a particle size of 5 mm or more in the particulate hydrogel are preferably 0 to 10% by weight, more preferably 0 to 5% by weight, based on the total amount of the particulate hydrogel.
- at least a part, preferably 1 to 50% by weight of the particulate hydrous gel is preferably smaller than the pores of the ventilation belt described later.
- the particle diameter of particulate water-containing gel is calculated
- the weight average particle diameter of the particulate hydrogel is also determined in the same manner as the weight average particle diameter (D50) described later.
- the measurement is performed using the wet classification method described in paragraph [0091] of JP-A No. 2000-63527.
- the manufacturing method of the water-absorbent resin of this form has the characteristics in the drying process of hydrous gel. That is, when the present inventors dry a hydrogel having a high solid content (essentially 35% by weight or more, preferably 40% by weight or more, more preferably 45% by weight or more) using a continuous ventilation belt type dryer. The inventors have found that the above problem can be solved by changing the thickness of the hydrogel with respect to the width direction of the ventilation belt, and have completed the present invention. Hereinafter, this drying process will be described in detail.
- the solid content of the hydrogel subjected to this drying step is essentially 35% by weight or more, preferably 40% by weight or more, more preferably 45% by weight or more, More preferably, it is 50 weight% or more, Most preferably, it is 55 weight% or more.
- the upper limit of the solid content is not particularly limited, but is preferably 80% by weight or less, more preferably 75% by weight or less, and further preferably 70% by weight or less. When the solid content is lower than 35% by weight, productivity may be lowered. Moreover, when solid content is too high, physical properties, such as a water absorption magnification, may fall.
- the solid content can be adjusted by adjusting the monomer concentration at the time of polymerization and the evaporation amount of water at the time of polymerization. Furthermore, if necessary, the solid content may be controlled by adding a fine powder obtained in the pulverization step / classification step described later or a mixture obtained by adding water to the fine powder during or after the polymerization.
- a continuous ventilation belt type dryer is used for drying the hydrogel.
- the continuous ventilation belt type dryer may be composed of a single belt or may have a plurality of belts.
- the continuous ventilation belt type dryer may be a single device or may be formed as a multi-stage device combined with devices of other processes.
- the length of the ventilation belt in the ventilation belt dryer is not particularly limited, but is preferably 5 to 100 m, more preferably 10 to 70 m, and even more preferably 20 to 60 m.
- the width of the ventilation belt is not particularly limited, but is preferably 0.5 to 10 m, and more preferably 1 to 5 m.
- the ratio of the length to the width of the ventilation belt is preferably 3 to 500 times, more preferably 5 to 100 times.
- the ventilation belt is preferably made of a wire mesh (for example, openings of 1000 to 45 ⁇ m) or punching metal, and more preferably made of punching metal.
- a wire mesh for example, openings of 1000 to 45 ⁇ m
- punching metal for example, a round shape, an ellipse shape, a square shape, a hexagon shape, a long round shape, a long angle shape, a rhombus shape, a cross shape, these combinations etc. are mentioned.
- the arrangement of the holes is not particularly limited, and may be a staggered shape or a parallel shape.
- the hole may be formed in a planar manner, or may be formed in a three-dimensional manner such as a louver (bay window), but is preferably a planarly formed hole.
- the pitch direction may be any of vertical, horizontal, and diagonal with respect to the traveling direction of the belt, or a combination thereof.
- the ventilation belt may be subjected to a predetermined surface treatment such as electropolishing or Teflon treatment.
- the material when using the punching metal as the ventilation belt is preferably stainless steel, and the thickness is usually appropriately determined from 0.3 to 10 mm, preferably from 1 to 5 mm.
- the surface roughness (Rz) (JIS B 0601-2001) of the belt surface is usually 800 nm or less, preferably 500 nm or less, more preferably 300 nm or less, still more preferably 200 nm or less, particularly preferably. It is 185 nm or less, and most preferably 170 nm or less.
- the lower limit of the surface roughness (Rz) is not particularly limited, but about 10 nm, further about 20 nm is sufficient.
- the surface roughness (Ra) (JIS B 0601-2001) is preferably 250 nm or less, more preferably 200 nm or less. These surface roughnesses can be measured in accordance with JIS B 0651-2001 with a stylus type surface roughness measuring device.
- the moving speed of the ventilation belt in the continuous ventilation belt type dryer is the belt width, belt length, although it can be appropriately adjusted according to the drying time and production amount of the water-absorbent resin, it is preferably 0.3 to 5 m / min from the viewpoint of the load and durability of the belt driving device, and more preferably 0. It is 5 to 2.5 m / min, more preferably 0.5 to 2 m / min, and particularly preferably 0.7 to 1.5 m / min.
- the drying process of this embodiment it is preferable to perform drying by changing the drying conditions (temperature, dew point, air volume) in multiple stages.
- the drying chamber is 5 or more, further 6 or more, especially 8 or more.
- a ventilation belt type dryer having the above.
- the upper limit is usually about 20 rooms from the viewpoint of scale and the like.
- the venting belt opening rate is defined by the ratio (percentage) of the hole area to the entire area (including the hole area) of the ventilation belt.
- the hole area ratio is determined by the area, number, arrangement (pitch), etc. of the holes, but even if there are no holes in a certain area of the ventilation belt (for example, the ridge portion of the ventilation belt)
- the total area of the ventilation belt including the area that is not used.
- the open area ratio is preferably 20 to 50%, more preferably 20 to 45%, and further preferably 25 to 40%. When the open area ratio is within the above range, the physical properties and drying efficiency of the water absorbent resin can be improved.
- the area of the hole of the ventilation belt is preferably larger than the cross-sectional area of one grain of the hydrogel subjected to drying, The area is more preferably 100 times, more preferably 4 to 50 times.
- the maximum hole opening distance (the longest distance between any two points on the periphery of the hole) is preferably larger than the weight average particle diameter of the hydrogel, and 2 to 100 from the weight average particle diameter.
- the ratio is more preferably double, and further preferably 4 to 50 times.
- the average area per hole is preferably 5 to 500 mm 2 , more preferably 10 to 100 mm 2 , and further preferably 15 to 50 mm 2 .
- the average area per hole is larger than 5 mm 2 , the drying efficiency is excellent.
- the average area of the pores is smaller than 500 mm 2 , the dried hydrogel is difficult to fall from the pores, and thus the yield can be prevented from decreasing.
- both the drying efficiency and the physical properties of the water-absorbent resin can be improved by setting the aperture ratio of the ventilation belt, the maximum aperture distance of the apertures, and the average area of the apertures to the above ranges. . More specifically, it is possible to prevent the undried product from remaining or the dried product from escaping, and to suppress the decrease in water absorption properties and coloring of the water absorbent resin.
- the water-containing gel for example, 1 to 2 mm
- a wire mesh for example, an opening of 300 ⁇ m.
- a ventilation belt having larger holes than the conventional one. Is preferably used.
- area occupancy rate means the ratio (percentage) of the area occupied by the hydrated gel loaded on the ventilation belt before drying to the area of the ventilation belt. ). Specifically, it is defined by the area of the ventilation belt from the point where the loading of the hydrogel to the ventilation belt is completed to the point where it has advanced in the direction of travel for 1 minute, preferably 0.5 minutes, and most preferably 0.1 minutes.
- area occupation rate of the below-mentioned Example is the value measured in the area from the point where loading of the hydrogel was completed on the ventilation belt to the point advanced for 0.1 minutes in the advancing direction. The area is appropriately determined depending on the speed of the ventilation belt.
- the area is 1 m, preferably 0.5 m from the point where the loading of the hydrogel is completed on the ventilation belt. Most preferably, the area is up to 0.1 m.
- the area occupation ratio is represented by B / A ⁇ 100 [%].
- the point where the loading of the hydrogel on the ventilation belt is completed refers to the end point of the loading in the traveling direction when looking at the loading in the width direction of the belt.
- the hydrogel is drawn by drawing an arc or a wave in the width direction.
- it can be defined by the most advanced portion in the traveling direction of the hydrated gel.
- the area occupation ratio is preferably 85 to 100%, more preferably 87 to 100%, further preferably 87 to 99%, and more preferably 90 to 98%. More preferred is 93 to 97%.
- the area occupancy is out of the above range, the physical properties of the water absorbent resin may be lowered, or the drying efficiency may be lowered.
- the area occupation ratio is less than 100%, it means that the hydrogel is not loaded on at least a part of the ventilation belt.
- the portion where the hydrated gel is not loaded may be any portion on the ventilation belt, but it is preferable that a certain region where the hydrated gel is not loaded is provided at both ends of the ventilation belt.
- the width occupancy is preferably 85 to 100%, more preferably 87 to 100%, and more preferably 87 to 99%. More preferably, it is 90 to 98%, more preferably 93 to 97%.
- the “width occupancy ratio” means the ratio (percentage) of the width of the moisture-containing gel before drying loaded on the ventilation belt to the ventilation belt with respect to the section of the ventilation belt. Specifically, it is defined by the occupancy rate of the hydrogel in the width direction of the ventilation belt at the point where the loading of the hydrogel on the ventilation belt is completed.
- the area occupancy and the width occupancy can be substituted for each other because they are substantially in the same range if averaged over the long term.
- the area occupied ratio or width occupied ratio is evaluated by the average value in the period.
- the area occupancy rate or the width occupancy rate is outside the above range in a part of the period or the change.
- the area occupancy is preferably included in the above range throughout the entire period on the ventilation belt.
- the section in which the area occupancy ratio or the width occupancy ratio is included in the above range throughout one cycle or continuous drying period is preferably 60% or more, and 75% with respect to the entire ventilation belt. More preferably, it is more preferably 90% or more, and particularly preferably 100%. That is, it is preferable that the average area and / or width occupancy rate in one cycle or continuous drying period satisfy the above range.
- the water-containing gel is dried by changing the thickness of the water-containing gel laminated on the ventilation belt.
- the thickness change rate (1) represented by the following formula 1 is defined within a predetermined range.
- the “thickness in the width direction” means a cross section when cut in a direction perpendicular to the advancing direction of the continuously operating ventilation belt at the loading completion point of the hydrogel (for example, FIG. 1a, FIG. 1b). This means the thickness of the gel, and can be measured using, for example, a laser distance meter or a laser displacement meter.
- the “thickness of the hydrogel” does not mean the thickness of one hydrogel but means the thickness of the aggregate formed by loading the hydrogel particles.
- Maximum thickness in the width direction means the maximum value when the thickness is measured continuously in the width direction or every 10 cm from the center of the ventilation belt (for example, in the case of a ventilation belt with a width of 2 m, at a maximum of 21 locations). To do.
- the “average thickness in the width direction” means an average value when the thickness is measured continuously in the width direction or every 10 cm from the center of the ventilation belt (for example, in the case of a ventilation belt with a width of 2 m, at a maximum of 21 locations). Means.
- the thickness change rate (1) is 1.05 to 5.00.
- the lower limit of the thickness change rate (1) is preferably 1.10 or more, more preferably 1.15 or more, still more preferably 1.20 or more, particularly preferably 1.25 or more, Most preferably, it is 1.30 or more.
- the upper limit is preferably 2.00 or less, more preferably 1.80 or less, still more preferably 1.60 or less, and particularly preferably 1.50 or less.
- the numerical range of the thickness change rate (1) is preferably 1.10 to 3.00, more preferably 1.15 to 2.00, still more preferably 1.20 to 1.80, Particularly preferred is 1.25 to 1.60, and most preferred is 1.30 to 1.50.
- the thickness change rate (2) in the width direction of the ventilation belt is set to 1.05 to 3.00.
- the thickness change rate (2) is defined by the following formula 2.
- both ends of the ventilation belt means a portion having a width of 1/3 of the entire width of the ventilation belt from both ends of the ventilation belt.
- Maximum thickness at both ends means a maximum value when measured at a position where the heights at both ends (left and right 3) are maximum. Of the two ends, the maximum value may be at either end.
- the “central portion of the ventilation belt” means a portion other than the both end portions.
- the “maximum thickness at the center” means the maximum value when measured at the position where the height of the center (center 1/3) is maximum.
- the thickness change rate (2) is preferably 1.05 to 3.00.
- the lower limit of the thickness change rate (2) is preferably 1.10 or more, more preferably 1.15 or more, still more preferably 1.20 or more, particularly preferably 1.25 or more, Most preferably, it is 1.30 or more.
- the upper limit is preferably 2.00 or less, more preferably 1.80 or less, still more preferably 1.60 or less, and particularly preferably 1.50 or less.
- the numerical range of the thickness change rate (2) is preferably 1.10 to 3.00, more preferably 1.15 to 2.00, still more preferably 1.20 to 1.80, and particularly preferably. Is from 1.25 to 1.60, most preferably from 1.30 to 1.50.
- the thickness change of the hydrogel changes symmetrically from the middle point in the width direction of the ventilation belt toward both ends. More preferably, the “maximum thickness at both ends” is present in at least one of two portions having a width of 1/6 with respect to the entire width of the ventilation belt from both ends of the ventilation belt.
- the physical properties of the water absorbent resin can be improved or the amount of undried product can be reduced by making the thickness of the hydrogel uniform. It is said.
- the drying efficiency the amount of undried material, the yield of the dried product, etc.
- the properties of the water-absorbent resin CRC, soluble content, residual monomer, coloring, AAP, SFC, etc.
- the hydrated gel can be dried more uniformly, thereby suppressing the formation of undried material, improving physical properties, and reducing coloring.
- the thickness of the ventilation belt in the traveling direction may be constant, but may be changed periodically or aperiodically.
- the pattern (shape) and period are not particularly limited.
- the thickness change rates (1) and (2) in the width direction are defined by the average value. Therefore, in a certain section, the thickness change rates (1) and (2) may be out of the above range microscopically.
- the section in which the thickness change rates (1) and (2) are included in the above range is preferably 60% or more, more preferably 75%, more preferably 90% with respect to the entire ventilation belt. More preferably, it is more preferably 100%.
- the average value of the thickness of the hydrogel loaded on the ventilation belt is usually 1 to 30 cm, preferably 2 to 20 cm, more preferably 5 to 15 cm, and further preferably 7 to 13 cm. Further, the thickness of the hydrogel loaded on the ventilation belt is usually 0 to 30 cm, preferably 5 to 20 cm, more preferably 8 to 15 cm, and further preferably 9 to 11 cm. What is necessary is just to give a change in thickness within.
- the drying efficiency and various physical properties of the water-absorbent resin can be improved. In particular, the bulk specific gravity of the water-absorbent resin is controlled to be high. be able to.
- the specific method for controlling the area occupation ratio or the thickness of the hydrogel on the ventilation belt is not particularly limited, and examples thereof include the following (1) to (4). These methods may be used in combination as appropriate.
- a method of adjusting the feed amount of the hydrogel with respect to the width direction of the ventilation belt (2) A method of smoothing the gel supplied on the ventilation belt using a control plate or a roller having a certain shape in the width direction (eg, wave shape, comb shape, jagged shape); (3) A method of supplying a hydrogel from a plurality of locations in the width direction (each supply amount may be changed) on the ventilation belt; (4) A method of supplying the hydrogel on the ventilation belt in a plurality of times.
- a traverse feeder or a vibration feeder (Oscillating Feeder) is used as a hydrated gel supply device, and the servo motor and inverter motor of the device are controlled in sequence. That is, it is preferable to operate the traverse feeder or the vibration feeder (Oscillating Feeder) at a non-uniform speed, and in this case, the peripheral speed is increased from the center toward both ends, preferably 1.1 times or more. The peripheral speed is preferably increased by 1.3 to 20 times.
- the thickness of the hydrogel can be controlled to be constant within the above range, and the problem of the present invention is further solved.
- the gap between the supply device and the ventilation belt surface is preferably 20 to 80 cm, particularly 30 to 50 cm, and is preferably supplied from the supply device to the ventilation belt by free fall. .
- the traverse feeder and the vibration feeder preferably digitally (continuous on-off or periodic change of speed)
- the area occupancy rate or the thickness change rate can be controlled within a predetermined range.
- Patent Documents 1 to 3 do not describe control using an Oscillating Feeder.
- Patent Document 2 Pamphlet of International Publication No. 2008/087114
- Patent Document 28 US Patent Application Publication No. 2004/0234607 disclose a traverse feeder and a vibration feeder, their peripheral speed and speed change are disclosed. Is not disclosed or suggested.
- the present invention provides a method for producing a water-absorbent resin, in which a water-containing gel is sprayed on a ventilation belt using a traverse feeder or a vibration feeder that preferably operates at a non-constant peripheral speed and dried.
- the method for producing a water-absorbent resin of the present invention comprises a polymerization step in which an aqueous monomer solution is subjected to a polymerization reaction to obtain a hydrous gel, and a drying step in which the hydrous gel is dried.
- the drying process is performed using a continuous ventilating belt dryer, and the solid content of the hydrogel used in the drying process is 35% by weight or more.
- the water-absorbing resin is loaded on a continuous ventilating belt dryer using a non-constant speed traverse feeder (also referred to as neck swing feeder) or a vibration feeder (also referred to as vibration conveyor belt), particularly a traverse feeder.
- a manufacturing method is provided.
- the “traverse feeder” refers to a feeder (for example, FIG. 3) in which the position of the feeder itself is variable, particularly periodically variable, and further circularly moves in a plane direction.
- the vibration feeder is illustrated as 200 in FIGS. 2 and 3. Although it is illustrated also in the said patent document 2 (international publication 2008/087114 pamphlet) and patent document 28 (US Patent application publication 2004/0234607 specification), it is not limited to these.
- the hydrogel is loaded on a continuous ventilation belt type dryer using a non-constant speed traverse feeder, particularly a traverse belt feeder, and the peripheral speed (m / sec) of the traverse feeder. Is higher at both ends than at the center.
- non-constant speed refers to a state in which the speed of the traverse feeder that changes direction is accelerated or decelerated.
- the traverse feeder changes its direction at a constant period or angle ⁇ (see FIG. 3), but accelerates or decelerates the speed at both ends other than analog or digital.
- the both end portions are defined, for example, at a position where the angle from the central portion is 45 ° or 10 ° narrower than the maximum neck swing angle ⁇ of the traverse feeder.
- the rotational speed of the conveyor belt (the feed speed of the hydrogel) is appropriately determined, but is preferably 0.1 (m / s) or more, preferably 0.1 to 10 (m / s). s) is more preferable, and 0.4 to 8 (m / s) is further preferable.
- the rotation speed of the conveyor belt may be constant speed or non-constant speed as long as it is within the above range, and is preferably constant speed.
- the peripheral speed and angle ( ⁇ ) of the traverse feeder are also determined as appropriate.
- the thickness change rate and the occupation ratio are controlled, and the solid content, punching metal, drying conditions, polymerization conditions and the like described above or below are also controlled.
- the bulk specific gravity of the hydrated hydrogel loaded on the ventilation belt is preferably less than 0.7 g / cm 3 , and 0.6 g / cm More preferably, it is less than 3 , more preferably less than 0.55 g / cm 3 , and the lower limit is preferably 0.35 g / cm 3 or more.
- a method for controlling the bulk specific gravity there is a method in which the hydrogel is dropped from a predetermined height and dispersed on the ventilation belt. At this time, if the gel after spraying is smoothed with a roller or the like as in Patent Document 18, it is difficult to control the density.
- the bulk specific gravity can be obtained by calculating from the weight of the hydrogel loaded on the ventilation belt and the volume of the particulate hydrogel loaded by scanning with a laser distance meter or a laser displacement sensor.
- the drying temperature in the continuous aeration belt dryer is preferably 110 to 230 ° C, more preferably 150 to 230 ° C, and further preferably 160 to 200 ° C. By setting the drying temperature to 110 to 230 ° C., it is possible to reduce both the drying time and the coloring of the water absorbent resin.
- the drying temperature is defined by the ambient temperature.
- the wind speed of the hot air is preferably 3.0 m / second or less.
- drying time can be appropriately adjusted by those skilled in the art depending on the surface area of the hydrogel, the moisture content, and the type of dryer. Usually, the drying time is 10 to 120 minutes, preferably 20 to 60 minutes.
- (J) Dew point In the drying step, water-containing air or inert gas is brought into contact with the hydrogel.
- the dew point of the steam mixed gas is preferably high at the inlet of the dryer and low at the outlet of the dryer.
- the dew point of the steam mixed gas is preferably 50 to 100 ° C., more preferably 50 to 70 ° C. Residual monomer can be reduced by controlling in this range.
- hot air having a high dew point of preferably 10 to 50 ° C., more preferably 15 to 40 ° C. is preferably contacted with the hydrogel from the viewpoints of residual monomer, water absorption characteristics and coloring. By controlling within this range, it is possible to reduce residual monomers, improve water absorption characteristics, and suppress coloring. By controlling the dew point as described above, it is possible to prevent a decrease in the bulk specific gravity of the water absorbent resin.
- the drying step after completion of the polymerization step the following (A) or (B), more preferably (A) and (B) are preferably performed. That is, it is preferable that the polymerization step or the granulation step and the drying step are directly connected and the hydrogel is immediately put into the drying step without staying and storing.
- the water-containing gel is dried by heating to a solid content of 70% by weight or more, preferably 75% or more, more preferably 80% or more, preferably within 10 minutes. More preferably, after completion of the polymerization step, the hydrogel is dried by heating to a solid content of 65% by weight or more, preferably 70% by weight or more within 5 minutes.
- the solid content of the hydrogel is increased by 10% or more, preferably 20% or more, more preferably 30% or more. More preferably, within 5 minutes after the completion of the polymerization step, the solid content of the hydrated gel is heat-dried to 65% by weight or more, preferably 70% by weight or more.
- the drying step immediately after the polymerization step it is possible to achieve a reduction in coloring of the water-absorbent resin, an improvement in water absorption capacity, or a soluble content.
- Patent Document 17 or Patent Document 19 the water-containing gel after polymerization is stored before drying, or the water-containing gel is subjected to a predetermined treatment, and the solid content is increased in a short time after the polymerization step. Is not disclosed.
- the hydrogel taken out from the polymerization apparatus is continuously charged into a dryer, and the residence time thereof is within 1 minute, preferably within 0.5 minute, further 0 Within 2 minutes. Furthermore, the upper limit of the solid content after the drying step in 5 to 10 minutes is preferably 90% by weight or less, more preferably 85% by weight or less.
- the temperature of the hydrogel crosslinked polymer from polymerization to the start of drying is preferably controlled to 50 to 80 ° C., more preferably 60 to 70 ° C.
- the hydrogel having a solid content of 93% by weight or more by drying is further heated and dried for 5 minutes or more.
- the water-absorbing magnification (CRC) is improved by further heating and drying the almost dried water-containing gel.
- the obtained dried product may be pulverized as necessary to adjust the particle size.
- a pulverized product amorphous crushed water-absorbent resin powder obtained by pulverizing the dried product obtained in the drying step is obtained.
- the pulverization method is not particularly limited.
- a conventionally known pulverizer such as a roll mill, a hammer mill, a roll granulator, a joke crusher, a gyle crusher, a cone crusher, a roll crusher, or a cutter mill is used.
- a pulverization method is mentioned. Among these, it is preferable to use a roll mill or a roll granulator in multiple stages from the viewpoint of particle size control.
- various classifiers such as sieve classification and airflow classification can be used.
- the particle size (specified by JIS Z8801-1 (2000)) can be appropriately adjusted by the above-described polymerization step (particularly reversed-phase suspension polymerization), pulverization, classification, granulation, fine powder recovery, and the like.
- the weight average particle diameter (D50) of the pulverized product obtained in the pulverization step is preferably 200 to 600 ⁇ m, more preferably 200 to 550 ⁇ m, still more preferably 250 to 500 ⁇ m, and particularly preferably 350 to 500 ⁇ m. 450 ⁇ m. Further, the smaller the number of particles less than 150 ⁇ m, the better.
- the content of particles less than 150 ⁇ m is preferably 0 to 5% by weight, more preferably 0 to 3% by weight, and 0 to 1% by weight. More preferably. Further, the smaller the particles of 850 ⁇ m or more, the better.
- the content of particles exceeding 850 ⁇ m is preferably 0 to 5% by weight, more preferably 0 to 3% by weight, and 0 to 1% by weight. More preferably.
- the logarithmic standard deviation ( ⁇ ) of the particle size distribution is preferably 0.20 to 0.40, more preferably 0.27 to 0.37, and further preferably 0.25 to 0.35. preferable. These physical property values are measured by a method described in, for example, International Publication No. 2004/69915 pamphlet or EDANA-ERT420.2-02 using a standard sieve.
- the proportion of particles of 150 to 850 ⁇ m is preferably 95% by weight or more, more preferably 98% by weight or more (upper limit 100% by weight) with respect to the whole. It is preferable to surface-crosslink the dried product or powder having this ratio.
- the particle size before the surface crosslinking is preferably applied to the final product after the surface crosslinking.
- the ratio of the particles of 850 to 150 ⁇ m is controlled to be preferably 95% or more, more preferably 98% or more (however, the upper limit is 100%).
- the production method of this embodiment preferably further includes a step of surface cross-linking the water-absorbent resin powder obtained in the above step (drying step, pulverizing step or classification step). By performing the surface cross-linking step, a water-absorbing resin that is less colored and whiter can be obtained.
- the surface crosslinking method is not particularly limited, and examples thereof include a method of crosslinking the surface of the water absorbent resin powder using a surface crosslinking agent.
- surface cross-linking by high temperature heating is suitable.
- organic or inorganic surface cross-linking agents can be exemplified, but organic surface cross-linking agents are preferably used.
- the organic surface crosslinking agent may be used in combination with an ion binding surface crosslinking agent.
- organic surface crosslinking agent examples include mono-, di-, tri-, or tetra-propylene glycol, 1,3-propanediol, glycerin, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol.
- Polyhydric alcohol compounds such as 1,6-hexanediol and sorbitol; epoxy compounds such as ethylene glycol diglycidyl ether and glycidol; polyvalent amine compounds or condensates thereof with haloepoxy compounds, oxazoline compounds; (mono, di, or Poly) oxazolidinone compounds; alkylene carbonate compounds such as ethylene carbonate; oxetane compounds; cyclic urea compounds such as 2-imidazolidinone, and the like, U.S. Pat. Calligraphy It can be exemplified compounds exemplified.
- a dehydrating esterification reactive surface cross-linking agent made of a polyhydric alcohol compound, an alkylene carbonate compound, or an oxazolidinone compound, which requires a reaction at a high temperature, can be particularly preferably used.
- the said organic surface crosslinking agent may be used independently and may use 2 or more types together.
- examples of the inorganic surface cross-linking agent include divalent or higher, preferably trivalent or tetravalent polyvalent metal salts (organic salts or inorganic salts) or hydroxides.
- examples of the polyvalent metal include aluminum and zirconium, and examples of the polyvalent metal salt include aluminum lactate and aluminum sulfate.
- the amount of the surface cross-linking agent used is preferably 0.001 to 10 parts by weight and more preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin powder.
- water is preferably used.
- the amount of water used is not particularly limited, but is preferably 0.5 to 20 parts by weight, more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the water absorbent resin powder. .
- a hydrophilic organic solvent may be used in addition to the above water.
- the amount of the hydrophilic organic solvent to be used is not particularly limited, but is preferably 0 to 10 parts by weight, more preferably 0 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin powder.
- hydrophilic organic solvent examples include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, and t-butyl alcohol; ketones such as acetone and methyl ethyl ketone; dioxane, alkoxy (poly ) Ethers such as ethylene glycol and tetrahydrofuran; Amides such as ⁇ -caprolactam and N, N-dimethylformamide; Sulphoxides such as dimethyl sulfoxide; Ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, glycerin, 2-butene- , 4-diol, 1,3-butanediol, 1,4-butanediol,
- a water-insoluble fine particle powder or a surfactant may be allowed to coexist within a range not impeding the effects of the present invention.
- the amount of the water-insoluble fine particle powder or surfactant used is preferably 0 to 10 parts by weight, more preferably 0 to 5 parts by weight, with respect to 100 parts by weight of the water absorbent resin powder. More preferably, it is ⁇ 1 part by weight.
- the type of surfactant and the amount used are described in US Pat. No. 7,473,739.
- the mixed liquid of the water-absorbent resin powder and the surface cross-linking agent solution is subjected to heat treatment, and then subjected to cooling treatment as necessary.
- the heating temperature is preferably 70 to 300 ° C, more preferably 120 to 250 ° C, and further preferably 150 to 250 ° C.
- the heating time is preferably 1 minute to 2 hours.
- the heat treatment can be performed with a normal dryer or a heating furnace.
- a water-absorbing resin having high whiteness can be provided even when high-temperature heating or drying using hot air, which has been a cause of significant coloring, is employed.
- the water absorption capacity under pressure (AAP) described later is set to a preferable range of 20 g / g or more by the surface crosslinking step. Can be increased.
- a polyvalent metal salt surface treatment step an evaporation monomer recycling step, a granulation step, a fine powder removal step, a fine powder recycling step, and the like may be provided as necessary.
- the above-mentioned additives may be used for the monomer or a polymer thereof (water-containing gel) in order to reduce coloring over time (improve the stability effect), prevent gel degradation, and the like.
- the surface treatment step of the polyvalent metal salt is highly liquid-permeable under pressure (SFC described in US Pat. No. 5,669,894, GBP described in International Publication No. 2004/96303, and International Publication No. 2005/016393) This can be done when seeking For example, the methods described in US Pat. No. 6,605,673 and US Pat. No. 6,620,899 can be applied.
- the fine powder recycling step refers to the fine powder removed in the classification step or the like (for example, containing particles of less than 150 ⁇ m as a main component; particularly preferably including particles of less than 150 ⁇ m in an amount of 70% by weight or more), or after removing water.
- a fine powder recycling step refers to the fine powder removed in the classification step or the like (for example, containing particles of less than 150 ⁇ m as a main component; particularly preferably including particles of less than 150 ⁇ m in an amount of 70% by weight or more), or after removing water.
- Preferable fine powder recycling methods include, for example, the methods described in US Patent Application Publication No. 2006/247351 and US Patent No. 6228930.
- the drying of the water-containing gel to which the fine powder is added becomes uneven, or the fine powder is recycled to the polymerization process.
- the residual monomer increased, physical properties such as a reduction in water absorption decreased, while the water absorbent resin manufacturing method of the present embodiment, even when performing a fine powder recycling step, Decrease in physical properties and coloring of the resin can be effectively suppressed.
- the method for producing the water-absorbent resin of the present embodiment includes at least one of the following physical properties (a) to (f), preferably two or more including AAP, more preferably AAP. It is suitable for producing a water-absorbing resin satisfying three or more including A water-absorbent resin satisfying these physical properties is preferably applied to sanitary materials, particularly paper diapers. If the water absorbent resin does not satisfy these physical properties, sufficient performance may not be exhibited in a high-concentration paper diaper having a water absorbent resin concentration of 40% by weight or more.
- the water-absorbing resin obtained by the production method of the present embodiment has little initial coloring.
- the L value (Lightness) is preferably 85 or more, more preferably 87 or more, still more preferably 89 or more; and the b value is ⁇ 5 to 10 More preferably, it is -5 to 9, more preferably -4 to 8, particularly preferably -1 to 7, and the a value is preferably -2 to 2, more preferably -1 to 1. More preferably, it is ⁇ 0.5 to 1, particularly preferably 0 to 1.
- YI is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less.
- WB is preferably 70 or more, more preferably 75 or more, and even more preferably 77 or more.
- the water-absorbent resin obtained by the production method of the present embodiment is less colored with time and exhibits sufficient whiteness even in a model test for long-term storage under high temperature and high humidity.
- the water absorbent resin obtained by the production method of the present embodiment preferably has a water absorption capacity (AAP) with respect to a 0.9 wt% sodium chloride aqueous solution under a pressure of 0.3 psi, more preferably under a pressure of 0.7 psi. It may be 10 [g / g] or more, more preferably 20 [g / g] or more, further preferably 22 [g / g] or more, and particularly preferably 24 [g / g] or more.
- AAP is preferably as high as possible, but the upper limit is 40 [g / g] or less in consideration of balance with other physical properties. When the AAP is in the above range, it is possible to prevent leakage in a paper diaper.
- the water-absorbent resin obtained by the production method of this embodiment preferably has a 0.69% sodium chloride aqueous solution flow conductivity (SFC), which is one index of liquid permeability under pressure, preferably 1 [cm 3 ⁇ s ⁇ 10 ⁇ 7 / g] or more, more preferably 10 [cm 3 ⁇ s ⁇ 10 ⁇ 7 / g] or more, and still more preferably 50 [cm 3 ⁇ s ⁇ 10 ⁇ 7 / g] or more, It is particularly preferably 70 [cm 3 ⁇ s ⁇ 10 ⁇ 7 / g] or more, and most preferably 100 [cm 3 ⁇ s ⁇ 10 ⁇ 7 / g] or more.
- SFC sodium chloride aqueous solution flow conductivity
- the water-absorbing resin obtained by the production method of this embodiment preferably has a water absorption capacity (CRC) under no pressure of 10 [g / g] or more, more preferably 20 [g / g] or more, and still more preferably. It is 25 [g / g] or more, and particularly preferably 30 [g / g] or more. The higher the CRC, the better.
- the upper limit value is not particularly limited, but considering the balance with other physical properties, it is preferably 100 [g / g] or less, more preferably 50 [g / g] or less. Preferably it is 45 [g / g] or less, Most preferably, it is 40 [g / g] or less.
- the water-absorbent resin obtained by the production method of this embodiment preferably has a soluble content of 0 to 35% by weight or less, more preferably 25% by weight or less, still more preferably 15% by weight or less, and particularly preferably. May be up to 10% by weight.
- the water-absorbent resin obtained by the production method of the present embodiment preferably has a residual monomer (residual monomer) amount of 0 to 400 ppm by weight, more preferably 0 to 300 ppm by weight, More preferably, it may be 0 to 200 ppm by weight.
- the water-absorbent resin obtained by the production method of the present embodiment preferably has a solid content of 85 to 99.9% by weight, more preferably 90 to 99.9% by weight, More preferably, it is 99.9% by weight.
- solid content is controlled in the said range, the fall of the physical property of water absorbing resin can be prevented.
- the water-absorbing resin is a polyacrylic acid (salt) -based water-absorbing resin, and the effect is more exhibited when at least one of the following (a) to (c) is satisfied. .
- water-absorbent resin obtained by the production method of the present embodiment is not particularly limited. It can be used for solidification applications, civil engineering and architecture applications. Among these applications, particularly excellent performance is exhibited when used in absorbent articles that use a water-absorbent resin at a high concentration.
- the content (core concentration) of the water absorbent resin contained in the absorbent body in the absorbent article is usually 30 to 100% by weight, preferably 40%. -100% by weight, more preferably 50-100% by weight, still more preferably 60-100% by weight, particularly preferably 70-100% by weight, and most preferably 75-95% by weight.
- the water-absorbent resin obtained by the production method of the present embodiment is excellent in liquid permeability (liquid permeability under pressure), even when the water-absorbent resin is contained in the absorbent in a high concentration, the absorbed urine, etc. Body fluid diffuses quickly. This effect is particularly remarkable when used in the upper layer portion of the absorber. Therefore, liquid distribution can be performed efficiently in an absorbent article such as a paper diaper, and the absorption amount of the entire water absorbent article can be improved.
- the water-absorbent resin obtained by the production method of the present embodiment is difficult to be colored, the white state of the absorber can be maintained and a clean appearance can be maintained for a long time.
- the absorbent body is preferably compression-molded so as to have a density of 0.06 to 0.50 g / cc and a basis weight of 0.01 g / cm 2 to 0.20 g / cm 2 . Furthermore, when the thickness of the absorber is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 10 mm or less, the absorbent body can be suitably used in a thin absorbent article such as a disposable diaper.
- the amount of the hydrated gel was set to about 2 to 4 g, and the measurement was carried out in the same manner as in the case of the water-absorbent resin except that it was left to dry in an oven for 24 hours.
- the GEX value was calculated according to the description of US Patent Application Publication No. 2006/0167198.
- the GEX value is defined by the following formula 4 or 5 when the water absorption capacity (CRC) under no pressure is represented by y [g / g] and the soluble content is represented by x (% by weight).
- the soluble content is small with respect to CRC, and it is preferable that the soluble content is large, but the GEX value is an index for performing this evaluation. It shows that the performance of a water absorbing resin is so high that the said GEX value is large.
- Example 1 75 mol% neutralized acrylic acid partial sodium salt aqueous solution (monomer concentration 38 wt%) containing 0.07 mol% (based on monomer) of polyethylene glycol diacrylate as an internal cross-linking agent was prepared as an aqueous monomer solution.
- the monomer aqueous solution was continuously fed to the container using a metering pump. At this time, nitrogen gas was continuously blown in the middle of the transport pipe so that the oxygen concentration in the monomer aqueous solution was 0.5 ppm or less.
- 0.14 g of sodium persulfate and 0.005 g of L-ascorbic acid per mole of the monomer were continuously mixed by line mixing. And this mixture was supplied to the flat steel belt which has a weir in both ends so that it might become thickness of about 30 mm, and continuous stationary aqueous solution polymerization was performed for 30 minutes, and the water-containing gel was obtained.
- the obtained hydrogel was subdivided with a meat chopper having a pore diameter of 7 mm to obtain a particulate hydrogel (A) having a weight average particle diameter of 1.3 mm and a solid content of 39% by weight.
- the particulate hydrogel (A) (hydrogel temperature 60 ° C., solid content 39% by weight) is controlled by using a traverse feeder in a continuous aeration belt dryer and controlling the traverse feeder sequence (high speed at both ends). It was continuously loaded on a continuously moving ventilation belt (punching metal). The particulate hydrogel on the ventilation belt was continuously dried for about 38 minutes.
- the thickness / area occupancy of the particulate hydrous gel, the dryer, and the drying conditions are as follows.
- the hot air temperature in the drying chamber was set to 170 ° C.
- the linear velocity of the hot air was set to 1.0 m / second.
- the dew point is adjusted by mixing steam with hot air, the dew point of the drying chamber (first chamber) at the dryer inlet is 80 ° C, and the dew point of the drying chamber (sixth chamber) near the dryer outlet is 20 ° C. It was adjusted.
- the linear velocity was 1.0 [m / sec]
- the wind direction of the first chamber was upward from the bottom surface
- the wind direction of the sixth chamber was downward from the top of the dryer to the bottom surface.
- Ventilation belt The material of the ventilation belt was SUS304, the hole area ratio was 33%, and the average area of the holes was 16 mm 2 .
- the particulate hydrogel (A) loaded on the ventilation belt by the traverse feeder had a thickness change rate (1) of 1.41 and a thickness change rate (2) of 1.33.
- the average thickness of the hydrogel was 10.5 cm, and the area occupancy (and width occupancy) was 95%.
- the thickness of the particulate hydrogel loaded on the ventilation belt was measured using a laser displacement sensor.
- the water-containing gel was sampled and the solid content was measured. As a result, the solid content after 5 minutes was 67% by weight, and the solid content after 10 minutes was 72% by weight. . Furthermore, in the sixth chamber, the dried water-containing gel having a solid content of 93% by weight was dried on the belt for about 8 minutes, and the solid content of the dried product was 94% by weight.
- ⁇ Crushing step and classification step> After the drying, the whole amount of the dried product is pulverized by continuously supplying it to a three-stage roll mill (roll gap is 1.0 mm / 0.55 mm / 0.42 mm from above), and then a sieve having a metal sieve mesh with an opening of 850 ⁇ m
- the water-absorbent resin (1) was obtained by classifying with a separator. After the pulverization, there was no deposit derived from undried material on the surface of the roll mill. Table 1 shows the analysis results of the water absorbent resin (1a).
- ⁇ Surface cross-linking step> The obtained water-absorbing resin (1) was continuously fed to a high-speed continuous mixer at a rate of 1500 kg / hr using a quantitative feeder. Then, a surface treating agent solution composed of a mixed solution of 0.3 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol and 2.7 parts by weight of pure water is sprayed on 100 parts by weight of the water absorbent resin. Sprayed and mixed.
- the obtained mixture was continuously heat-treated at 198 ° C. for 40 minutes using a paddle dryer, and then 0.5 parts by weight of aluminum sulfate and 1 part by weight of water were added to 100 parts by weight of the obtained powder.
- the solution was forcibly cooled to 60 ° C. using a paddle dryer while spraying 0.05 parts by weight of propylene glycol.
- the 850 ⁇ m passing material was classified by a sieving device. At this time, the coarse powder remaining on the sieve screen having an opening of 850 ⁇ m was pulverized again and then mixed with the 850 ⁇ m passing material. As a result, the surface was cross-linked and all passed through 850 ⁇ m to obtain a water absorbent resin (1b).
- Table 2 The analysis results of the water absorbent resin (1b) are shown in Table 2.
- Example 2 In the polymerization step of Example 1, the monomer concentration of the aqueous monomer solution was 45% by weight, the amount of sodium persulfate used was 0.1 g per mole of monomer, and L-ascorbic acid was not used. Except for the above, the same operation was performed to obtain a particulate hydrous gel (B).
- the particulate hydrogel (B) had a weight average particle diameter of 1.2 mm and a solid content of 46% by weight.
- the thickness change rate (1) of the particulate hydrogel (B) loaded on the ventilation belt by a traverse feeder controlled at non-constant speed (high speed at both ends) is 1.38.
- the thickness change rate (2) was 1.45, the average thickness was 10.3 cm, and the area occupancy (and width occupancy) was 96%.
- the solid content after 5 minutes from the start of drying was 70% by weight, and the solid content after 10 minutes was 85% by weight. Furthermore, the solid content of the dried product obtained by drying the hydrogel having a solid content of 95% by weight dried in the sixth chamber on the belt for about 8 minutes was 96.0% by weight.
- Example 2 After drying, the same pulverization step and classification step as in Example 1 were performed to obtain a water absorbent resin (2a). After the pulverization, there was no deposit derived from the undried material on the surface of the roll mill. Table 1 shows the analysis results of the water absorbent resin (2a).
- Example 2 Furthermore, the same surface cross-linking step as in Example 1 was performed on the water-absorbent resin (2a) to obtain a surface-crosslinked water-absorbent resin (2b). Table 2 shows the analysis results of the water absorbent resin (2b).
- Example 1 In the drying process of Example 1, the dew point of the first chamber of the dryer was adjusted to 55 ° C, and the dew point of the sixth chamber was adjusted to 60 ° C. A ventilation belt having an aperture ratio of 52% and an average area of holes of 8 mm 2 was used. The particulate hydrous gel (A) loaded on the ventilation belt by the traverse feeder has a thickness change rate (1) of 5.51, a thickness change rate (2) of 3.80, an average thickness value of 14.6 cm, and an area. The occupation ratio (and width occupation ratio) was 84%. Except this, it dried by the same operation as Example 1.
- the solid content after 5 minutes from the start of drying was 55% by weight, and the solid content after 10 minutes was 67% by weight. Furthermore, the solid content of the dried product obtained by drying the hydrogel having a solid content of 88% by weight dried in the sixth chamber on the belt for about 8 minutes was 90% by weight.
- Example 1 After drying, the same pulverization step and classification step as in Example 1 were performed to obtain a comparative water absorbent resin (1a). In addition, after pulverization, deposits derived from undried material were present on the surface of the roll mill. The analysis results of the comparative water absorbent resin (1a) are shown in Table 1.
- the solid content after 4 minutes from the start of drying was 61% by weight, and the solid content after 10 minutes was 67% by weight. Furthermore, the solid content of the dried product obtained by drying the hydrogel having a solid content of 89% by weight dried in the sixth chamber on the belt for about 8 minutes was 92% by weight.
- Example 2 After drying, the same pulverization step and classification step as in Example 1 were performed to obtain a comparative water absorbent resin (2a).
- the analysis results of the comparative water absorbent resin (2a) are shown in Table 1.
- an additive is conventionally used.
- Activator and manufacturing equipment can be manufactured in a stable and mass-produced manner with high physical properties and low cost by a simple technique of changing the thickness of the hydrous gel in the width direction of the ventilation belt. .
- Screw extruder also known as meat chopper
- particulate hydrous gel 110 particulate hydrous gel
- Traverse Feeder also known as Nipple Feeder
- 300 ventilation dryer 310 continuous ventilation belt
- 320 drying vat ⁇ Neck angle.
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Abstract
Description
以下、本明細書で使用される用語について説明する。
本明細書において、「吸水性樹脂」とは、以下の物性を有する水膨潤性かつ水不溶性の高分子ゲル化剤を意味する。吸水性樹脂の吸水倍率(CRC)は、必須に5g/g以上であり、好ましくは10~100g/gであり、より好ましくは20~80g/gである。また、吸水性樹脂の可溶分(Extractables)は、必須に0~50重量%以下であり、好ましくは0~30重量%であり、より好ましくは0~20重量%であり、さらに好ましくは0~10重量%である。
本明細書において、「ポリアクリル酸(塩)」とは、任意にグラフト成分を含み、単量体としてアクリル酸(塩)を主成分とする単量体を(共)重合することにより得られる(共)重合体を意味する。具体的には、ポリアクリル酸(塩)を構成する単量体(ただし、架橋剤を除く)に含まれるアクリル酸(塩)の割合は、単量体の全量に対して、必須に50~100モル%であり、好ましくは70~100モル%であり、より好ましくは90~100モル%であり、さらに好ましくは実質100モル%である。(共)重合体としての塩は、必須に水溶性塩を含み、好ましくは一価塩を含み、より好ましくはアルカリ金属塩またはアンモニウム塩を含み、さらに好ましくはアルカリ金属塩を含み、特に好ましくはナトリウム塩を含む。
本明細書において、「初期着色」とは、吸水性樹脂の製造工程における不可避的な着色を意味する。当該初期着色は、製造直後(実施例では製造後1時間以内に測定)の吸水性樹脂に対して、国際公開第2009/005114号パンフレットに記載される測定方法を用いることにより求められる(例えば、L/a/b値、YI値、WB値など)。
本明細書において、「経時着色」とは、未使用(未膨潤)状態の吸水性樹脂を長期間保管等する際に起こる着色(通常、黄変ないし茶変)を意味する。当該経時着色は、例えば、未使用のおむつを倉庫等で長期間保管する場合などに起こり、おむつの商品価値の低下となりうる。室温での保管では数ヶ月ないし数年経過しないと着色が認められないため、通常、当該経時着色は国際公開第2009/005114号パンフレットに記載される、高温・高湿条件下での促進試験を用いて検証される。
「EDANA」とは、欧州不織布工業会(European Disposables and Nonwovens Associations)の略称である。また、「ERT」とは、欧州標準の吸水性樹脂の測定法(ERT/EDANA Recomeded Test Method)の略称であり、現在これがほぼ世界基準となっている。本明細書においては特に断りのない限り、ERT原本(公知文献;2002年改定)を参照して、吸水性樹脂の物性を測定する。
「CRC」は、遠心分離機保持容量(Centrifuge Retention Capacity)の略称であり、無加圧下吸水倍率(以下、「吸水倍率」とも称する)を意味する。具体的には、0.9重量%塩化ナトリウム水溶液に不織布袋中の吸水性樹脂0.200gを30分間浸漬した後、遠心分離機で250Gの水切りした後の吸水倍率(単位;[g/g])で規定される。
「AAP」は、加圧下吸水倍率(Absorbency Against Pressure)の略称である。具体的には、0.9重量%塩化ナトリウム水溶液に吸水性樹脂0.900gを荷重下で1時間膨潤させた後の吸水倍率(単位;[g/g])で規定される。本明細書では、荷重条件が21g/cm2(0.3psi)または50g/cm2(0.7psi)である場合のAPPを測定した。
「可溶分」とは、吸水性樹脂中に含まれる水に可溶な成分の量を意味する。具体的には、0.9重量%塩化ナトリウム水溶液200gに吸水性樹脂1gを投入し、16時間攪拌した後、溶解したポリマー量をpH滴定で測定することにより求められる(単位;重量%)。
「FSC」は、自由膨潤倍率(Free Swell Capacity)の略称である。具体的には、0.9重量%塩化ナトリウム水溶液に不織布中の吸水性樹脂0.200gを30分間浸漬した後、遠心分離機による水切りを行わないで測定した吸水倍率(単位;[g/g])で規定される。
「残存モノマー量」とは、吸水性樹脂中に残存しているモノマー(単量体)量を意味する。具体的には、0.9重量%塩化ナトリウム水溶液200cm3に吸水性樹脂を1.0g投入し、500rpmで1時間攪拌した後、当該水溶液に溶出したモノマー量を高速液体クロマトグラフィーで測定することにより求められる(単位;ppm)。
粒度分布は、篩分級により求められる。
「通液性」とは、荷重下または無荷重下において膨潤ゲル粒子間を流れる液体の流れ具合を意味する。代表的な測定法に、SFC(Saline Flow Conductivity)と、GBP(Gel Bed Permeability)とがある。SFCは、21g/cm2(0.3psi)の荷重条件における、吸水性樹脂0.9gに対する0.69%生理食塩水の通液性であり、米国特許第5669894号明細書に記載の方法により求められる。荷重下または自由膨潤のGBPは、国際公開第2005/016393号パンフレットに記載の方法により求められる。
上記以外の吸水性樹脂等の物性は、以下のERT原本(2002年改定)の測定方法により求められる。
含水率(Moisture Content)(ERT430.2-2)
流下速度(Flow Rate)(ERT450.2-02)
嵩比重(Density)(ERT460.2-02)
呼吸域粉塵(Respirable Particles)(ERT480.2-02)
粉塵(Dust)(ERT490.2-02)。
(1)重合工程
本形態の吸水性樹脂の製造方法では、まず、単量体水溶液を重合反応に供して含水ゲルを得る、重合工程が行われる。
単量体水溶液は、単量体を必須に含み、必要によりその他の添加剤を含みうる。以下、単量体水溶液に含まれる各成分について詳細に説明する。
本形態における単量体は重合性不飽和結合を含む単量体(不飽和単量体)であれば特に制限はないが、吸水性樹脂の着色し難さや物性の観点から、アクリル酸および/またはその中和物(すなわちアクリル酸(塩))を主成分とすることが好ましい。
本形態の単量体水溶液は、吸水性樹脂の吸水特性を向上させる観点から、内部架橋剤をさらに含むことが好ましい。
本形態の単量体水溶液は、重合安定性の面から、重合禁止剤をさらに含むことが好ましい。重合禁止剤としては、例えば、メトキシフェノール類が挙げられ、なかでもp-メトキシフェノールを使用することが好ましい。重合禁止剤の添加量は、単量体に対して、好ましくは1~250ppmであり、より好ましくは5~200ppmであり、さらに好ましくは10~160ppmであり、さらに好ましくは20~100ppmである。上記重合禁止剤の添加量が250ppmを超える場合、重合速度や着色(特に初期着色)の問題が生じ、また、重合禁止剤の添加量が1ppm未満の場合、重合安定性に劣るため、好ましくない。
本形態の単量体水溶液は、さらに鉄を含みうる。当該鉄は、単量体水溶液中でイオンの形態で存在する。鉄の含有量は単量体に対してFe2O3換算値として、通常0~10重量ppmであり、好ましくは0~5重量ppmであり、より好ましくは0を超えて5重量ppm未満であり、さらに好ましくは0.001~5重量ppmであり、特に好ましくは0.001~4重量ppmであり、最も好ましくは0.005~3重量ppmである。鉄の含有量の制御手法としては、国際公開第2006/109842号パンフレットに開示される手法が採用されうる。
単量体水溶液は、上述の成分以外にも、澱粉、セルロース、ポリビニルアルコール、ポリアクリル酸(塩)、ポリエチレンイミンなどの水溶性樹脂または吸水性樹脂を含みうる。これらの水溶性樹脂または吸水性樹脂は、単量体の全量に対して、例えば0~50重量%、好ましくは0~20重量%、より好ましくは0~10重量%、さらに好ましくは0~3重量%の割合で添加されうる。なお、その他成分を使用して得られたグラフト重合体(例;澱粉アクリル酸グラフト重合体)ないし吸水性樹脂組成物も、本発明ではポリアクリル酸(塩)系吸水性樹脂と総称する。また、各種の発泡剤(炭酸塩、アゾ化合物、気泡など)、界面活性剤、またはこれら以外の各種添加剤等を、例えば0~5重量%、好ましくは0~1重量%添加して、吸水性樹脂の諸物性を改善してもよい。
本形態の重合工程における重合反応は、吸水性樹脂の性能や重合反応の制御の容易さの観点から、通常、水溶液重合または逆相懸濁重合など採用されうる。このうち、水溶液重合が好ましく、連続水溶液重合がより好ましい。
上記重合工程で得られた含水ゲル状重合体(以下、単に「含水ゲル」とも称する)は、そのまま乾燥工程に供されてもよいが、重合工程の後で、且つ乾燥工程の前に、必要により粉砕機(ニーダー、ミートチョッパーなど)を用いて細粒化され粒子状にされる。なお、重合工程における重合反応が逆相懸濁重合である場合は、重合時に溶媒中での分散によって含水ゲルが細粒化されるため、細粒化工程を要しない場合がある。
本形態の吸水性樹脂の製造方法は、含水ゲルの乾燥工程に特徴を有する。すなわち、本発明者らは高固形分(必須に35重量%以上、好ましくは40重量%以上、さらに好ましくは45重量%以上)の含水ゲルを連続通気ベルト式乾燥機を用いて乾燥する際に通気ベルトの幅方向に対して、含水ゲルの厚みを変化させることで上記課題が解決できること見出し、本発明を完成させるに至った。以下、本乾燥工程について詳細に説明する。
本乾燥工程に供される含水ゲルの固形分は、必須に35重量%以上であり、好ましくは40重量%以上であり、より好ましくは45重量%以上であり、さらに好ましくは50重量%以上であり、特に好ましくは55重量%以上である。固形分の上限値は特に制限されないが、好ましくは80重量%以下であり、より好ましくは75重量%以下であり、さらに好ましくは70重量%以下である。固形分が35重量%よりも低いと、生産性が低くなることがある。また固形分が過度に高いと、吸水倍率などの物性が低下することがある。固形分の調整は、重合時の単量体の濃度や重合時の水等の蒸発量を調節することにより行うことができる。さらに、必要により、重合中や重合後に、後述の粉砕工程・分級工程で得られた微粉末や、当該微粉末に水を添加したものを添加して固形分を制御してもよい。
本形態においては、含水ゲルの乾燥に連続通気ベルト式乾燥機が用いられる。連続通気ベルト式乾燥機は、単一のベルトからなるものであってもよく、複数のベルトを有するものであってもよい。また、連続通気ベルト式乾燥機は、単独の装置であってもよいし、その他の工程の装置と組み合わせた多段階装置として形成されていてもよい。
連続通気ベルト式乾燥機における通気ベルトの移動速度は、ベルト幅やベルト長、吸水性樹脂の乾燥時間や生産量に応じて適宜調整することができるが、ベルト駆動装置の負荷や耐久性等の観点から、好ましくは0.3~5m/分であり、より好ましくは0.5~2.5m/分であり、さらに好ましくは0.5~2m/分であり、特に好ましくは0.7~1.5m/分である。
本形態において、通気ベルトの開孔率とは、通気ベルトの全面積(孔の面積も含む)に対する、孔の面積の割合(百分率)で規定される。開孔率は孔の面積、数、配置(ピッチ)などにより決定されるが、仮に通気ベルトの一定領域(例えば通気ベルトの淵部分)に孔を有しない場合であっても、当該孔を有しない領域も含めて通気ベルトの全面積とする。該開孔率は、20~50%であることが好ましく、20~45%であることがより好ましく、25~40%であることがさらに好ましい。開孔率が上記範囲内であると、吸水性樹脂の物性および乾燥効率等を向上させることができる。
また、本形態においては、通気ベルトの孔の面積が、乾燥に供される含水ゲルの一粒の断面積より大きいことが好ましく、当該断面積の2~100倍の面積であることがより好ましく、4~50倍の面積であることがさらに好ましい。
本明細書において「面積占有率」とは、通気ベルトの面積に対する、通気ベルト上に積載された乾燥前の含水ゲルが通気ベルトに占める面積の割合(百分率)を意味する。具体的には、通気ベルト上に含水ゲルの積載が完了した地点から進行方向に1分間、好ましくは0.5分間、最も好ましくは0.1分間進んだ地点までの通気ベルトの面積で規定される。なお、後述の実施例の面積占有率は、通気ベルト上に含水ゲルの積載が完了した地点から進行方向に0.1分間進んだ地点までの面積において測定した値である。当該面積は、通気ベルトの速度によって適宜決定されるが、例えば、通気ベルト速度が1[m/min]の場合、通気ベルト上に含水ゲルの積載が完了した地点から1m、好ましくは0.5m、最も好ましくは0.1mまでの面積となる。当該通気ベルトの面積を(A)とし、この面積に積載される含水ゲルの占有面積を(B)とした場合に、面積占有率は、B/A×100[%]で表される。
本形態の乾燥工程では、通気ベルト上に積層される含水ゲルの厚みに変化を持たせて、含水ゲルを乾燥する。具体的には、下記式1で表される厚み変化率(1)を所定の範囲に規定する。
(2)幅方向に一定の形状(例;波状、櫛状、ギザギザ状)を有する制御板やローラーを用いて通気ベルト上に供給されたゲルをならす方法;
(3)通気ベルト上に、幅方向の複数箇所(それぞれ供給量を変化させてもよい)から含水ゲルを供給する方法;
(4)通気ベルト上に、複数回に分けて含水ゲル供給する方法。
本形態の乾燥工程において、通気ベルトに積載される、未乾燥状態の含水ゲルの嵩比重は0.7g/cm3未満であることが好ましく、0.6g/cm3未満であることがより好ましく、0.55g/cm3未満であることがさらに好ましく、その下限値としては0.35g/cm3以上であることが好ましい。嵩比重の制御方法としては含水ゲルを所定の高さから落下させて、通気ベルトに散布するする方法が挙げられる。なお、その際に、前記特許文献18のように散布後のゲルをローラーなどで平滑化させると密度の制御が困難である。当該嵩比重は、通気ベルト上に積載された含水ゲルの重量と、レーザー式距離計やレーザー式変位センサーの走査による粒子状含水ゲルの積載物の体積とから算出することにより求めることができる。
連続通気ベルト式乾燥機における乾燥温度は110~230℃とすることが好ましく、150~230℃とすることがより好ましく、160℃~200℃とすることがさらに好ましい。乾燥温度を110~230℃とすることにより、乾燥時間の短縮と、吸水性樹脂の着色低減の両立が可能となる。なお、乾燥温度は、雰囲気温度により規定される。
乾燥時間は、含水ゲルの表面積、含水率、および乾燥機の種類よって当業者が適宜調製することができる。通常、乾燥時間は10~120分間であり、好ましくは20~60分間である。
乾燥工程においては、含水ゲルに、水蒸気を含む空気または不活性気体を接触させる。当該水蒸気混合気体の露点は、乾燥機入口において高く、乾燥機出口において低いことが好ましい水蒸気混合気体の露点は50~100℃であることが好ましく、50~70℃であることがより好ましい。この範囲に制御することで残存モノマーを低減させることができる。さらに、乾燥工程において、残存モノマー、吸水特性や着色の観点から、好ましくは10~50℃、より好ましくは15~40℃露点が高い熱風を含水ゲルに接触させることが好ましい。この範囲に制御することによって、残存モノマーの低減、吸水特性の向上、着色の抑制が可能となる。以上のように露点を制御することで、吸水性樹脂の嵩比重の低下をも防止できる。
上記特許文献17または特許文献19では重合後の含水ゲルを乾燥前に貯蔵したり、含水ゲルに対して所定の処理を行ったりしており、重合工程後の短時間において固形分を上昇させる技術は開示されていない。
上記乾燥工程の後、得られた乾燥物を必要により粉砕して粒度を調整してもよい。粉砕工程により、上記乾燥工程で得られた乾燥物が粉砕された粉砕物(不定形破砕状の吸水性樹脂粉末)が得られる。後述の表面架橋工程を行う場合は、吸水性樹脂の物性向上のため、粒度を特定の範囲内に制御することが好ましい。
本形態の製造方法においては、上記工程(乾燥工程、粉砕工程または分級工程)で得られた吸水性樹脂粉末を表面架橋する工程をさらに含むことが好ましい。当該表面架橋工程を行うことによって、着色が少なく、より白色である吸水性樹脂を得ることができる。
上述工程以外にも、必要により、多価金属塩の表面処理工程、蒸発モノマーのリサイクル工程、造粒工程、微粉除去工程、微粉リサイクル工程などを設けてもよい。さらに、経時着色の低減(安定性効果の向上)やゲル劣化防止等のために、上述の添加剤を単量体またはその重合体(含水ゲル)に使用してもよい。
本形態の吸水性樹脂の製造方法は、下記(a)~(f)の物性のうち、少なくとも1つ、好ましくはAAPを含めた2つ以上、より好ましくはAAPを含めた3つ以上を満たす吸水性樹脂を製造する場合に好適である。これらの物性を満たす吸水性樹脂は、衛生材料、特に紙おむつに好ましく適用される。吸水性樹脂がこれらの物性を満たさない場合、吸水性樹脂濃度が40重量%以上の高濃度紙おむつにおいて十分な性能を発揮しないことがある。
本形態の製造方法で得られる吸水性樹脂は、初期着色が少ない。具体的には、ハンターLab表面色系において、L値(Lightness)が好ましくは85以上であり、より好ましくは87以上であり、さらに好ましくは89以上であり;b値が-5から10であり、より好ましくは-5~9であり、さらに好ましくは-4~8であり、特に好ましくは-1~7であり;a値が好ましくは-2~2であり、より好ましくは-1~1であり、さらに好ましくは-0.5~1であり、特に好ましくは0~1である。YIは好ましくは10以下であり、より好ましくは8以下であり、さらに好ましくは6以下である。WBは好ましくは70以上であり、より好ましくは75以上であり、さらに好ましくは77以上である。さらに、本形態の製造方法で得られる吸水性樹脂は、経時着色も少なく、高温高湿下における長期保存のモデル試験でも十分な白色度を示す。
本形態の製造方法で得られる吸水性樹脂は、0.3psiの加圧下、さらに好ましくは0.7psiの加圧下での0.9重量%の塩化ナトリウム水溶液に対する吸水倍率(AAP)が、好ましくは10[g/g]以上、よりに好ましくは20[g/g]以上、さらに好ましくは22[g/g]以上、特に好ましくは24[g/g]以上でありうる。AAPは高いほど好ましいが、他の物性とのバランスを考慮すると上限は40[g/g]以下である。AAPが上記範囲であると、紙おむつでのモレを防止することができる。
本形態の製造方法で得られる吸水性樹脂は、加圧下での通液性の一つの指標である0.69%塩化ナトリウム水溶液流れ誘導性(SFC)が、好ましくは1[cm3・s・10-7/g]以上であり、より好ましくは10[cm3・s・10-7/g]以上であり、さらに好ましくは50[cm3・s・10-7/g]以上であり、特に好ましくは70[cm3・s・10-7/g]以上であり、最も好ましくは100[cm3・s・10-7/g]以上でありうる。SFCが上記範囲であると、紙おむつでのモレを防止することができる。
本形態の製造方法で得られる吸水性樹脂は、無加圧下吸水倍率(CRC)が好ましくは10[g/g]以上であり、より好ましくは20[g/g]以上であり、さらに好ましくは25[g/g]以上であり、特に好ましくは30[g/g]以上でありうる。CRCは高いほど好ましく、上限値は特に限定されないが、他の物性とのバランスを考慮すると、好ましくは100[g/g]以下であり、より好ましくは50[g/g]以下であり、さらに好ましくは45[g/g]以下であり、特に好ましくは40[g/g]以下である。
本形態の製造方法で得られる吸水性樹脂は、可溶分が好ましくは0~35重量%以下であり、より好ましくは25重量%以下であり、さらに好ましくは15重量%以下であり、特に好ましくは10重量%以下でありうる。
本形態の製造方法で得られる吸水性樹脂は、残存モノマー(残存単量体)量が好ましくは0~400重量ppmであり、より好ましくは0~300重量ppmであり、さらに好ましくは0~200重量ppmでありうる。
本形態の製造方法で得られる吸水性樹脂は、固形分が85~99.9重量%であることが好ましく、90~99.9重量%であることがより好ましく、95~99.9重量%であることがさらに好ましい。固形分が上記範囲内に制御されると、吸水性樹脂の物性の低下を防ぐことができる。
本形態の製造方法で得られる吸水性樹脂の用途は、特に限定されにないが、好ましくは紙おむつ、生理ナプキン、失禁パット等の吸収物品や、農園芸用途、廃液固化用途、土木建築用途等に使用されうる。これらの用途のうち、高濃度で吸水性樹脂を使用する吸収物品に使用した場合に、特に優れた性能が発揮される。
国際公開第2009/005114号パンフレット記載された方法により測定した。
予め正確に秤量した吸水性樹脂を、底面の直径が約50mmのアルミカップに量り取り、吸水性樹脂およびアルミカップの総重量W1[g]を測定した。吸水性樹脂の使用量の目安は約1gである。その後、雰囲気温度180℃のオーブン中に3時間静置して乾燥した。3時間後、オーブンから取り出した吸水性樹脂、およびアルミカップをデシケーター中で十分に室温まで冷却した後、乾燥後の吸水性樹脂およびアルミカップの総重量W2[g]を求め、下記式3に従って固形分[重量%]を求めた。
米国特許第5669894号明細書に記載された方法により測定した。
米国特許出願公開第2006/0167198号明細書の記載に従い、GEX値を算出した。GEX値は、無加圧下吸水倍率(CRC)をy[g/g]、可溶分をx(重量%)で表す時下記式4または5で定義される。
ERT/EDANAまたは米国特許出願公開第2006/204755号に記載の方法に従って、0.9%塩化ナトリウム水溶液での無加圧下吸水倍率(CRC)、粒度分布、pH、可溶分、残存アクリル酸量を測定した。
<重合工程>
内部架橋剤としてポリエチレングリコールジアクリレート(平均分子量400)を0.07モル%(対 単量体)含む、75モル%が中和されたアクリル酸部分ナトリウム塩水溶液(単量体濃度38重量%)を単量体水溶液として準備した。容器に当該単量体水溶液を、定量ポンプを用いて、連続的にフィードした。この際、輸送管の途中で窒素ガスを連続的に吹き込み、単量体水溶液中の酸素濃度を0.5ppm以下とした。当該単量体水溶液に、単量体1モル当たり過硫酸ナトリウム0.14gおよびL-アスコルビン酸0.005gをラインミキシングで連続混合した。そして、この混合物を、両端に堰を有する平面スチールベルトに厚み約30mmとなるように供給して、連続的な静置水溶液重合を30分間行い、含水ゲルを得た。
得られた含水ゲルを孔径7mmのミートチョッパーで細分化することにより、重量平均粒子径が1.3mm、固形分39重量%である粒子状含水ゲル(A)を得た。
粒子状含水ゲル(A)(含水ゲル温度60℃、固形分39重量%)を、連続通気ベルト式乾燥機にトラバースフィーダーを用いて、トラバースフィーダーのシーケンスを制御(両端部を高速)することで、連続可動している通気ベルト(パンチングメタル)上に連続的に積載した。そして、通気ベルト上の粒子状含水ゲルを約38分間連続乾燥した。粒子状含水ゲルの厚み・面積占有率、乾燥機、および乾燥条件等は以下の通りである。
合計6室の互いに独立して熱風条件を調整できる乾燥室を有し、この乾燥室を通気ベルトが通過する連続通気ベルト式乾燥機を使用した。なお、通気ベルトのベルト長は17mであり、ベルト幅は1.2mであり、連続通気ベルトの移動速度は0.25m/分であった。
乾燥室の熱風温度は170℃、熱風の線速は1.0m/秒に設定した。また、熱風に水蒸気を混合することにより露点を調整し、乾燥機入口の乾燥室(第一室)の露点を80℃、乾燥機出口付近の乾燥室(第六室)の露点を20℃に調整した。なお、線速は1.0[m/秒]において、第一室の風向きは底面から上向き、第六室の風向きは乾燥機上部から底面への下向きとした。
通気ベルトの材質はSUS304であり、開孔率は33%であり、孔の平均面積は16mm2であった。
トラバースフィーダーにより通気ベルト上に積載された粒子状含水ゲル(A)は、厚み変化率(1)が1.41であり、厚み変化率(2)が1.33であった。また、含水ゲルの厚みの平均値は10.5cmであり、面積占有率(および幅占有率)は95%であった。なお、通気ベルト上に積載された粒子状含水ゲルの厚みの測定は、レーザー式変位センサーを用いて行った。
前記乾燥後、乾燥物の全量を3段ロールミル(ロールギャップが上から1.0mm/0.55mm/0.42mm)に連続供給することで粉砕した後、目開き850μmの金属篩網を有する篩い分け装置で分級し吸水性樹脂(1)を得た。なお、粉砕後、ロールミルの表面には未乾燥物由来の付着物はなかった。吸水性樹脂(1a)の分析結果を表1に示す。
得られた吸水性樹脂(1)を、定量供給機を用いて、高速連続混合機に1500kg/hrの割合で連続供給した。そして、吸水性樹脂100重量部に対して、1、4-ブタンジオール0.3重量部、プロピレングリコール0.5重量部、純水2.7重量部の混合液からなる表面処理剤溶液をスプレーで噴霧し混合した。
実施例1の重合工程において、単量体水溶液の単量体濃度を45重量%、過硫酸ナトリウムの使用量を単量体1モル当たり0.1gとし、L-アスコルビン酸を使用しなかったこと以外は、同様の操作を行い、粒子状含水ゲル(B)を得た。粒子状含水ゲル(B)の重量平均粒子径は1.2mm、固形分は46重量%であった。
実施例1の乾燥工程において、乾燥機の第一室の露点を55℃、第六室の露点を60℃に調整した。通気ベルトは開孔率が52%であり、孔の平均面積が8mm2であるものを使用した。トラバースフィーダーにより通気ベルト上に積載された粒子状含水ゲル(A)の厚み変化率(1)を5.51、厚み変化率(2)を3.80、厚みの平均値を14.6cm、面積占有率(および幅占有率)を84%とした。これ以外は実施例1と同じ操作で乾燥を行った。
比較例1の乾燥工程において、トラバースフィーダーにより通気ベルト上に積載された粒子状含水ゲル(A)の厚み変化率(1)を1.02、厚み変化率(2)を1.01、厚みの平均値を8.6cm、面積占有率(および幅占有率)を82%とした以外は、比較例1と同様の操作で乾燥を行った。
110 粒子状含水ゲル、
200 トラバースフィーダー(別称;首ふりフィーダー)、
300 通気乾燥機、
310 連続通気ベルト、
320 乾燥用バット、
θ 首ふり角度。
Claims (21)
- 単量体水溶液を重合反応に供して含水ゲルを得る工程と、
前記含水ゲルを乾燥させる乾燥工程と、を含む吸水性樹脂の製造方法であって、
前記乾燥工程における乾燥が、連続通気ベルト式乾燥機を用いて行われるものであり、
前記乾燥工程に供される含水ゲルの固形分が35重量%以上であり、
前記含水ゲルを非等速のトラバースフィーダーまたは振動フィーダーにて連続通気ベルト式乾燥機に積載することを特徴とする、吸水性樹脂の製造方法。 - 前記通気ベルトがパンチングメタルである、請求項1~3のいずれか1項に記載の製造方法。
- 前記通気ベルトの開孔率が20~50%である、請求項1~4いずれか1項に記載の製造方法。
- 前記通気ベルトの長さが5~100mであり、前記通気ベルトの幅が1~10mであり、前記通気ベルトに積載された前記含水ゲルの厚みが1~30cmである、請求項1~5のいずれか1項に記載の製造方法。
- 前記乾燥工程後の分級工程によって分離される微粉末または当該微粉末の水添加物を、前記重合工程または前記乾燥工程にリサイクルする、請求項1~6のいずれか1項に記載の製造方法。
- 前記重合工程の後で、且つ前記乾燥工程の前に、含水ゲルを細粒化する細粒化工程をさらに含む、請求項1~7のいずれか1項に記載の製造方法。
- 前記乾燥工程において、前記重合工程後10分以内に、前記含水ゲルの固形分を70重量%以上とする、請求項1~8のいずれか1項に記載の製造方法。
- 前記乾燥工程において、前記重合工程後5分以内に、前記含水ゲルの固形分を65重量%以上とする、請求項1~9のいずれか1項に記載の製造方法。
- 前記乾燥工程における乾燥が、前記含水ゲルを、温度150~230℃、風速3m/秒以下の熱風に曝すことにより行われるものである、請求項1~10のいずれか1項に記載の製造方法。
- 前記単量体水溶液がメトキシフェノール類を含む、請求項1~11のいずれか1項に記載の製造方法。
- 前記連続通気ベルト式乾燥機が、5室以上の乾燥室を有する連続通気ベルト式乾燥機である、請求項1~12のいずれか1項に記載の製造方法。
- 前記乾燥工程において、乾燥に供する含水ゲルの固形分が45~80重量%である、請求項1~13のいずれか1項に記載の製造方法。
- 前記乾燥工程において、乾燥によって固形分93重量%以上となった含水ゲルをさらに5分以上加熱乾燥する、請求項1~14のいずれか1項に記載の製造方法。
- 乾燥工程において、乾燥工程前半よりも乾燥工程後半の露点を低く制御する請求項1~15のいずれか1項に記載の製造方法。
- 前記単量体がアクリル酸(塩)を含む、請求項1~16のいずれか1項に記載の製造方法。
- 前記乾燥工程後に、粉砕工程、分級工程および表面架橋工程をさらに含む、請求項1~17のいずれか1項に記載の製造方法。
- 前記吸水性樹脂がポリアクリル酸(塩)系吸水性樹脂であり、下記(a)~(c)の少なくとも1つを満たすことを特徴とする請求項1~18のいずれか1項に記載の吸水性樹脂の製造方法;
(a)無加圧下吸水倍率(CRC)が20~100g/gである;
(b)加圧下吸水倍率(AAP0.3psiまたはAAP0.7psi)が10g/g以上40g/g以下である;
(c)生理食塩水流れ誘導性(SFC)が10(10-7・cm3・s・g-1)以上である。 - 前記含水ゲルを非等速のトラバースフィーダーを用いて連続通気ベルト式乾燥機に積載し、かつ、トラバースフィーダーの周速(m/s)が通気ベルトの中央部より両端部で高速度となっている、請求項1~19のいずれか1項に記載の製造方法。
- 前記トラバースフィーダーの、通気ベルト両端部における周速が中央部での周速の1.1~100倍の高速である、請求項1~20のいずれか1項に記載の製造方法。
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EP2471847A4 (en) | 2013-10-30 |
JP5616347B2 (ja) | 2014-10-29 |
JPWO2011025012A1 (ja) | 2013-01-31 |
EP2471848B1 (en) | 2014-08-06 |
EP2471847A1 (en) | 2012-07-04 |
US8809475B2 (en) | 2014-08-19 |
CN102482435B (zh) | 2014-04-30 |
EP2471847B1 (en) | 2014-08-27 |
US20120157644A1 (en) | 2012-06-21 |
EP2471848A1 (en) | 2012-07-04 |
US8802800B2 (en) | 2014-08-12 |
EP2471847B2 (en) | 2018-01-03 |
WO2011025012A1 (ja) | 2011-03-03 |
JPWO2011025013A1 (ja) | 2013-01-31 |
US20120157648A1 (en) | 2012-06-21 |
EP2471848A4 (en) | 2013-10-30 |
JP5616346B2 (ja) | 2014-10-29 |
EP2471848B2 (en) | 2017-11-29 |
CN102482435A (zh) | 2012-05-30 |
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