WO2016052537A1 - 吸水性樹脂粉末及び吸水性樹脂粉末の弾性率の測定方法 - Google Patents
吸水性樹脂粉末及び吸水性樹脂粉末の弾性率の測定方法 Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
- B01J20/26—Synthetic macromolecular compounds
- B01J20/265—Synthetic macromolecular compounds modified or post-treated polymers
- B01J20/267—Cross-linked polymers
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/22—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons containing macromolecular materials
- A61L15/24—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/42—Use of materials characterised by their function or physical properties
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/42—Use of materials characterised by their function or physical properties
- A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
- B01J20/28002—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their physical properties
- B01J20/28004—Sorbent size or size distribution, e.g. particle size
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
- B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
- B01J20/28016—Particle form
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B7/00—Mixing; Kneading
- B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices
- B29B7/34—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices
- B29B7/38—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary
- B29B7/40—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft
- B29B7/42—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft with screw or helix
- B29B7/428—Parts or accessories, e.g. casings, feeding or discharging means
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B7/00—Mixing; Kneading
- B29B7/30—Mixing; Kneading continuous, with mechanical mixing or kneading devices
- B29B7/34—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices
- B29B7/38—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary
- B29B7/40—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft
- B29B7/42—Mixing; Kneading continuous, with mechanical mixing or kneading devices with movable mixing or kneading devices rotary with single shaft with screw or helix
- B29B7/428—Parts or accessories, e.g. casings, feeding or discharging means
- B29B7/429—Screws
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/02—Making granules by dividing preformed material
- B29B9/06—Making granules by dividing preformed material in the form of filamentary material, e.g. combined with extrusion
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/12—Making granules characterised by structure or composition
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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
- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
- C08J3/075—Macromolecular 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
- 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
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L33/00—Compositions 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; Compositions of derivatives of such polymers
- C08L33/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/44—Resins; rubber; leather
- G01N33/442—Resins, plastics
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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 water-absorbing resin powder, and more particularly to a water-absorbing resin powder exhibiting very excellent diffusion absorption characteristics.
- the present invention also relates to a method for measuring the elastic modulus of a water absorbent resin powder.
- Water-absorbing resin (SAP / Super Absorbent Polymer) is a water-swellable, water-insoluble polymer gelling agent, absorbent articles such as paper diapers and sanitary napkins, as well as water retaining agents for agriculture and horticulture, industrial use As water material etc., it is frequently used mainly for disposable use.
- water-absorbing resins in particular, a polyacrylic acid (salt) water-absorbing resin using acrylic acid and its salt as a monomer, or a combination thereof, is industrially used from the viewpoint that its water-absorbing performance is high. Most often used.
- water-absorbent resins With the improvement in performance of paper diapers, which are the main use of water-absorbent resins, many functions (physical properties) are required for water-absorbent resins.
- specific examples of physical properties of the water-absorbing resin are not limited to high water absorption capacity, but include gel strength, water-soluble content, water absorption speed, water absorption capacity under pressure, liquid permeability, particle size distribution, urine resistance, Examples include antibacterial properties, impact resistance (damage resistance), powder flowability, deodorization, coloration resistance (whiteness), and low dust.
- liquid permeability is considered to become one of the more important physical properties as the amount of water-absorbent resin used in paper diapers increases (for example, 50% by weight or more).
- the water absorption speed is considered to be an important basic physical property of the water absorbent resin. For this reason, techniques for improving the liquid permeability of the water-absorbent resin, preferably both the liquid permeability and the water absorption speed have been studied.
- Patent Document 1 discusses a method for producing a polyacrylic acid (salt) water-absorbent resin powder having improved both liquid permeability and water absorption speed. Specifically, Patent Document 1 discusses controlling the gel pulverization process, the drying process, and the surface treatment process in the production process of the polyacrylic acid (salt) -based water absorbent resin powder.
- Patent Document 2 includes the generation of bubbles in the aqueous acrylic acid monomer solution by reducing the solubility of dissolved gas in the aqueous monomer solution in the presence of a surfactant and / or dispersant.
- a method including a step of containing bubbles to be generated is disclosed, and an object of the present invention is to provide a white water-absorbent resin powder having both high liquid permeability (for example, SFC) and water absorption speed (for example, FSR). .
- Patent Document 3 discloses a method including a step of polymerizing an aqueous acrylic acid monomer solution in which a gas is dissolved and / or dispersed by a predetermined method in the absence of a surfactant or in the presence of 300 ppm or less.
- the purpose of the present invention is to produce a water-absorbing resin having a high water absorption rate with high efficiency without impairing the liquid-absorbing characteristics of sanitary goods and the like, without excessively lowering the bulk specific gravity.
- Patent Document 4 discloses that a polymerization mixture or a crosslinked hydrogel for forming a crosslinked hydrogel is mixed with a chlorine or bromine-containing oxidizing agent and heat-treated (heated), whereby an absorption capacity and centrifugal absorption under pressure are applied.
- a method for producing water-absorbing resin particles having an excellent capacity is disclosed.
- Patent Document 5 a compound obtained by neutralizing acrylic acid or methacrylic acid and a crosslinking agent having two or more polymerizable unsaturated groups are copolymerized. Add 0.0001 mol% to 0.1 mol% with respect to the total amount of monomers, and then add the radical polymerization initiator in a total amount of 0.01 mol% to 5 mol% with respect to the total amount of monomers one or more times.
- a method for polymerizing is disclosed, and a hydrogel capable of rapidly absorbing and retaining a large amount of water can be produced inexpensively and easily, and a hydrogel having a low content of unreacted monomers can be produced. Yes.
- the present inventors have intensively studied and found that the physical properties of the water-absorbent resin are dramatically improved by controlling the shape of the water-absorbent resin powder particles more precisely. It was.
- the present invention includes the following inventions.
- a water-absorbent resin powder comprising a polyacrylic acid (salt) -based water-absorbent resin as a main component, surface-crosslinked, and satisfying the following (1) to (3): (1) The proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is 90% by weight or more; (2) Water absorption time by vortex method is 42 seconds or less; (3) The elastic modulus index (600-500) is 5500 or more.
- the present inventor has found a method capable of accurately obtaining the elastic modulus, and has completed the present invention. That is, the present invention includes the following inventions.
- a load-loading process in which the load is applied while increasing the load on an ongoing basis including a measurement step of measuring storage elastic modulus under a constant load
- a method for measuring an elastic modulus of a water-absorbent resin powder characterized in that at least a part of a bottom surface of the housing part and / or a part of the plate-like body in contact with the swelling gel is made of aluminum.
- the water-absorbent resin powder according to the present invention exhibits very excellent diffusion absorption characteristics, it can provide sanitary goods such as paper diapers, sanitary napkins and medical blood-collecting agents having more excellent physical properties. There is an effect. Furthermore, the elastic modulus measurement method of the water-absorbent resin powder according to the present invention is a member in which the water-absorbent resin powder having a relatively uniform particle size is the object of measurement, and at least a part of the portion in contact with the swollen gel is made of aluminum. Since the swollen gel is sandwiched and a load is applied to the swollen gel by a predetermined method, the elastic modulus can be accurately measured.
- FIG. 3 is a schematic view showing a state in which the member shown in FIG. 2 is placed on a tray and a weight is placed on an upper lid provided with an insertion hole in the diffusion absorption time measurement apparatus. It is the upper side figure and side view of the upper cover of a diffusion absorption time measuring apparatus, and the upper side figure and side view of a tray. It is a schematic diagram which shows a mode that the particle
- FIG. 8 is a cross-sectional view of a screw and a barrel cut along a line X-X ′ in FIG.
- FIG. 9 is a view in which a screw is cut along a plane Y-Y ′ in FIG. 8 and a barrel is developed in a planar shape.
- FIG. 10 is an enlarged view of one reversing prevention member by cutting the barrel along the Z-Z ′ plane of FIG. 9, and is a schematic cross-sectional view showing two flight portions.
- FIG. 3 is a graph plotting diffusion and absorption times for the water absorbent resin powders (1) to (4) obtained in Examples and the comparative water absorbent resin powders (1) to (5) obtained in Comparative Examples.
- the present invention is not limited to the following embodiments, and various modifications can be made within the scope shown in the claims, and technical means disclosed in different embodiments can be appropriately combined. The obtained embodiment is also included in the technical scope of the present invention.
- Water absorbent resin The “water-absorbing resin” in the present invention means a water-swellable water-insoluble polymer gelling agent.
- water swellability means that the CRC defined by ERT441.2-02 is 5 g / g or more, and “water-insoluble” is defined by ERT470.2-02. Ext is 0 to 50% by weight.
- the water-absorbent resin can be appropriately designed according to its use and is not particularly limited, but may be a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group. preferable.
- the total amount (100% by weight) is not limited to a polymer form, and may be a composition containing a surface-crosslinked one, an additive, or the like within a range that maintains the above performance.
- the “water-absorbing resin” is a resin in which the hydrophilic crosslinked polymer is powdered.
- the water-absorbing resin before surface treatment or surface crosslinking is referred to as “water-absorbing resin particles”.
- the water absorbent resin after surface treatment or surface crosslinking is referred to as “water absorbent resin powder”.
- the water-absorbing resin is different in shape obtained in each step (the shape includes, for example, a sheet shape, a fiber shape, a film shape, a gel shape, etc.), the water-absorbing resin composition containing an additive or the like Even a product is collectively referred to as “water-absorbing resin” in the present specification.
- the “resin in which the hydrophilic cross-linked polymer is powdered” may be a resin in which the hydrophilic cross-linked polymer is pulverized to form a powder, for example, water absorption produced by a reverse phase suspension polymerization method.
- the hydrophilic crosslinked polymer may be powdered without being pulverized.
- Polyacrylic acid (salt) “Polyacrylic acid (salt)” “Polyacrylic acid (salt)” in the present invention includes a graft component as necessary, and as a repeating unit, acrylic acid and its salt (in this specification, both are collectively referred to as “acrylic acid (salt)”. Or a combination thereof as a main component.
- the “polyacrylic acid (salt)” in the present invention is essentially 50 mol% to 100 mol of acrylic acid (salt) among the total monomers (excluding the internal crosslinking agent) used in the polymerization. %, Preferably 70 mol% to 100 mol%, more preferably 90 mol% to 100 mol%, still more preferably substantially 100 mol%.
- polyacrylic acid (salt) when polyacrylic acid (salt) is used as the polymer, it always contains a water-soluble salt, and the main component of the water-soluble salt (neutralized salt) is preferably a monovalent salt, more preferably An alkali metal salt or an ammonium salt, more preferably an alkali metal salt, and particularly preferably a sodium salt.
- EDANA European Disposables and Nonwovens Associations
- ERT a method for measuring water-absorbent resin (EDANA Recommended Test Methods) which is a European standard (almost world standard). Abbreviation. In the present invention, unless otherwise specified, measurement is performed in accordance with the ERT original (known document: revised in 2002).
- CRC is an abbreviation for Centrifugation Retention Capacity (centrifuge retention capacity) and means a water absorption capacity under no pressure (referred to herein as “water absorption capacity”).
- water absorption capacity means that 0.200 g of the water-absorbent resin in the non-woven bag was freely swollen for 30 minutes in a large excess of 0.9 wt% sodium chloride aqueous solution and drained using a centrifuge. It refers to the water absorption capacity (unit: g / g) of the subsequent water absorbent resin.
- AAP is an abbreviation for Absorption against Pressure, and means the water absorption capacity under pressure. Specifically, “AAP” means that 0.9 g of a water-absorbing resin is swollen with a large excess of 0.9 wt% sodium chloride aqueous solution for 1 hour under a load of 2.06 kPa (0.3 psi). Of water absorption (unit: g / g). In this specification, it is expressed as AAP0.3. In ERT442.2-02, “Absorption Under Pressure” is written, which is substantially the same as AAP. Moreover, in this invention, it evaluates by the value computed using the weight of the water absorbing resin which performed moisture content correction
- Ext is an abbreviation for Extractables, which means the water-soluble component (water-soluble component amount) of the water-absorbent resin. Specifically, “Ext” refers to the amount of dissolved polymer (unit: wt%) after adding 1.0 g of the water-absorbing resin to 200 ml of 0.9 wt% sodium chloride aqueous solution and stirring at 500 rpm for 16 hours. The amount of dissolved polymer is measured by pH titration.
- PSD is an abbreviation for Particle Size Distribution, and means a particle size distribution of a water-absorbent resin measured by sieving classification.
- the weight average particle diameter (D50) and the logarithmic standard deviation ( ⁇ ) of the particle size distribution are described in US Pat. No. 7,638,570 “(3) Mass-Average Particle Diameter (D50) and Logical Standard Deviation ( ⁇ ) of”. It measures by the method similar to "Particle Diameter Distribution.”
- “Moisture Content” means the water content of the water-absorbent resin.
- “Moisture Content” is a value (unit:% by weight) calculated from a loss on drying when 1 g of the water-absorbent resin is dried at 105 ° C. for 3 hours. In the present invention, the drying temperature is changed to 180 ° C., the measurement is performed 5 times per sample, and the average value is adopted. The water content of the hydrogel crosslinked polymer is measured by changing the sample to 2 g, the drying temperature to 180 ° C., and the drying time to 16 hours. Further, the value calculated by ⁇ 100-water content (% by weight) ⁇ is “resin solid content” in the present invention, and can be applied to both the water-absorbent resin and the water-containing gel-like crosslinked polymer.
- SFC is an abbreviation for “Saline Flow Conductivity”, and the permeability (unit: ⁇ 10) of a 0.69 wt% sodium chloride aqueous solution to a water absorbent resin at a load of 2.07 kPa. ⁇ 7 ⁇ cm 3 ⁇ s ⁇ g ⁇ 1 ). The larger the SFC value, the higher the water-absorbent resin has liquid permeability. It is measured according to the SFC test method described in US Pat. No. 5,849,405.
- Water absorption time by vortex method is a water absorption time determined according to “Water absorption rate test method of high water absorption resin” described in JIS K7224, and 2 g of water absorption resin is 50 g. This is the time (unit: seconds) required to absorb physiological saline (specifically, 0.9 wt% sodium chloride aqueous solution).
- the “water absorption time by the vortex method” may be expressed as “water absorption time” or “Vortex”.
- the “elastic modulus index” in the present invention is a value (unit: Pa / m 2 ) obtained by correcting the elastic modulus measured by the following method with the theoretical surface area and CRC of the swollen gel particles, and absorbs water. It is a value that serves as an index when evaluating the performance of the functional resin.
- the “swelled gel particles” refers to gel particles obtained by swelling a water-absorbing resin with a swelling liquid (particularly pure water).
- “elastic modulus index” may be abbreviated as “EMI” from “Elastic Modulus Index” in English. The specific measurement method and calculation method of EMI will be described in Examples.
- “Diffusion absorption time” means that when the 0.9 wt% sodium chloride aqueous solution is added to the water absorbent resin a plurality of times, the water absorbent resin absorbs the entire amount of the sodium chloride aqueous solution. This is the total time taken (unit: seconds).
- X to Y indicating a range means “X or more and Y or less”.
- T (ton) which is a unit of weight means “Metric ton”, and unless otherwise noted, “ppm” means “ppm by weight”.
- Weight” and “mass”, “wt%” and “mass%”, “part by weight” and “part by mass” are treated as synonyms.
- ⁇ acid (salt) means “ ⁇ acid and / or salt thereof”
- (meth) acryl means “acryl and / or methacryl”.
- main component means that 51% or more of the whole is occupied.
- the water-absorbent resin powder according to the present invention comprises a polyacrylic acid (salt) -based water-absorbent resin as a main component and is surface-crosslinked, and the following (1) to (3) A water-absorbent resin powder that satisfies: (1) The proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is 90% by weight or more; (2) Water absorption time by vortex method is 42 seconds or less; (3) The elastic modulus index (600-500) is 5500 or more.
- the water-absorbent resin powder according to the present invention will be described focusing on the above requirements (1) to (3).
- the following (2-1) to (2-1) are satisfied after satisfying the above physical properties (1) to (3). It is preferable to satisfy any one or more physical properties selected from the physical properties described in (2-8).
- particle size refers to the particle size distribution of the water-absorbent resin powder defined by JIS standard sieve (JIS Z8801-1 (2000)).
- JIS standard sieve JIS Z8801-1 (2000).
- the “water-absorbing resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m” in (1) above passes through a JIS standard sieve having an opening of 850 ⁇ m, but does not pass through a JIS standard sieve having an opening of 150 ⁇ m. I mean.
- the proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is essentially 90% by weight or more, preferably 95% by weight or more. Preferably it is 97 weight% or more, More preferably, it is 98 weight% or more (an upper limit is 100 weight%).
- the proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 710 ⁇ m is preferably 90% by weight or more, more preferably 95% by weight or more, and still more preferably 97% by weight or more. Particularly preferred is 98% by weight or more (the upper limit is 100% by weight).
- it is preferably 0 to 5% by weight, more preferably 0 to 3% by weight, still more preferably 0 to 1% by weight.
- % To 5% by weight, more preferably 0% to 3% by weight, still more preferably 0% to 1% by weight.
- the lower limit of the ratio of these particles is preferably as small as possible in any case, and is preferably 0% by weight, preferably 0.1%. What is necessary is just weight% or more.
- content (particle size distribution) for every particle size of the water-absorbent resin powder according to the present invention is as follows. That is, (A) The proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 300 ⁇ m is preferably 5% by weight to 50% by weight, more preferably 10% by weight to 40% by weight, and still more preferably 15% by weight to 35% by weight. %, The proportion of the water absorbent resin powder having a particle size of 300 ⁇ m or more and less than 425 ⁇ m is preferably 10% by weight to 60% by weight, more preferably 15% by weight to 35% by weight, and still more preferably 20% by weight.
- the proportion of the water-absorbing resin powder having a particle size of (c) of 425 ⁇ m or more and less than 500 ⁇ m to ⁇ 40 wt% is preferably 5 wt% to 50 wt%, more preferably 10 wt% to 40 wt%, still more preferably
- the proportion of (d) the water-absorbent resin powder having a particle size of 500 ⁇ m or more and less than 600 ⁇ m to 15 wt% to 35 wt% is preferably 5 wt% to 50 wt%, and more
- the proportion of the water-absorbing resin powder having a particle size of 600 ⁇ m or more and less than 850 ⁇ m or a particle size of 600 ⁇ m or more and less than 710 ⁇ m is preferably 10 wt% to 40 wt%, more preferably 15 wt% to 35 wt%.
- the ratios (a) to (e) can be selected from any combination within the range satisfying the above-described particle size (150 ⁇ m or more and less than 850 ⁇ m or 150 ⁇ m or more and less than 710 ⁇ m).
- the weight of the water-absorbent resin powder according to the present invention is 100% by weight, in the water-absorbent resin powder according to the present invention, the total proportion of the water-absorbent resin powders having the particle sizes shown in (a) to (e) above is It is preferably 90% to 100% by weight, more preferably 95% to 100% by weight, and still more preferably 97% to 100% by weight.
- the water-absorbent resin powder according to the present invention has a weight average particle diameter (D50) of preferably 300 ⁇ m to 500 ⁇ m, more preferably 320 ⁇ m to 480 ⁇ m, and still more preferably 340 ⁇ m to 460 ⁇ m from the viewpoint of improving physical properties.
- D50 weight average particle diameter
- the water-absorbent resin powder according to the present invention preferably has a logarithmic standard deviation ( ⁇ ) of particle size distribution of 0.25 to 0.45, more preferably 0.27 to 0.43, from the viewpoint of improving physical properties. It is preferably 0.29 to 0.41.
- the above ranges can be appropriately combined with respect to the above-described weight average particle diameter (D50) and logarithmic standard deviation ( ⁇ ) of the particle size distribution.
- D50 weight average particle diameter
- ⁇ logarithmic standard deviation
- the water absorbent resin powder according to the present invention is essentially 42 seconds or less, preferably 40 seconds or less, more preferably 35 seconds or less from the viewpoint of water absorption time by the vortex method. More preferably, it is 30 seconds or less, and particularly preferably 25 seconds or less.
- the lower limit value is not particularly limited as long as it exceeds 0 seconds, but it is preferably 5 seconds or more, more preferably 10 seconds or more as a general lower limit value.
- the preferable range of the elastic modulus index of the water absorbent resin powder according to the present invention varies depending on the particle size of the water absorbent resin powder. This is because, in the measurement of the elastic modulus used for calculating the elastic modulus index, in order to accurately obtain the elastic modulus, it is necessary to make the particle size of the water absorbent resin powder to be measured within a specific range. Hereinafter, a preferable range of the elastic modulus index will be described for each particle size.
- the elastic modulus index of a water absorbent resin powder having a particle size of 500 ⁇ m or more and less than 600 ⁇ m is expressed as “EMI (600-500)”.
- the water-absorbent resin powder according to the present invention has an essential requirement that the modulus of elasticity index (600-500) is 5500 or more, and if the requirement is satisfied,
- the elastic modulus index in any desired range described in (2-3-1) to (2-3-5) described later can be appropriately combined.
- a water-absorbent resin powder satisfying an elastic modulus index (600-500) of 5500 or more, an elastic modulus index (500-425) of 4500 or more, and an elastic modulus index (425-300) of 3500 or more; -500) is a water-absorbent resin powder satisfying 6000 or more and an elastic modulus index (500-425) of 4500 or more; an elastic modulus index (600-500) of 6500 or more, an elastic modulus index (500-425) of 5000 or more, A water-absorbing resin powder satisfying an elastic modulus index (425-300) of 4500 or more and an elastic modulus index (710-600) of 5000 or more.
- the elastic modulus index (600-500) of the water absorbent resin powder according to the present invention is essentially 5500 or more, preferably 6000 or more, more preferably 6500 or more, and further preferably 7000 or more.
- the diffusion absorption time becomes shorter as the elastic modulus index increases. That is, the larger the value of the elastic modulus index, the more preferable it is because a water-absorbing resin powder having more excellent diffusion absorption characteristics can be obtained.
- the value of the elastic modulus index is preferably as large as possible, and the upper limit is not particularly limited, but because of physical limitations, In general, it is preferable to satisfy 15000 or less, more preferably 11000 or less, and still more preferably 7500 or less.
- the preferable range of the said elasticity modulus index changes according to the particle size of the water absorbent resin powder which is a measuring object.
- the water absorption time by the vortex method satisfies the requirement of 42 seconds or less, it is considered that the larger the value of the elastic modulus index, the shorter the diffusion absorption time. Therefore, only the preferable range of the elastic modulus index is described for each particle size below.
- the elastic modulus index (500-425) of the water-absorbent resin powder according to the present invention is preferably 4500 or more, more preferably 5000 or more, still more preferably 5500 or more, particularly preferably 6000 or more, and most preferably 6500 or more.
- the upper limit value of the elastic modulus index is not particularly limited, but is generally preferably 14500 or less, more preferably 10500 or less, and even more preferably 7000 or less because of physical limitations.
- the elastic modulus index (425-300) of the water-absorbent resin powder according to the present invention is preferably 3500 or more, more preferably 4000 or more, still more preferably 4500 or more, still more preferably 5000 or more, particularly preferably 5500 or more, most preferably Preferably it is 6000 or more.
- the upper limit value of the elastic modulus index is not particularly limited, but is generally preferably 14,000 or less, more preferably 10,000 or less, and even more preferably 6500 or less because of physical limitations.
- the elastic modulus index (710-600) of the water-absorbent resin powder according to the present invention is preferably 5500 or more, more preferably 6000 or more, further preferably 6500 or more, particularly preferably 7000 or more, and most preferably 7500 or more.
- the upper limit value of the elastic modulus index is not particularly limited, but is generally preferably 15500 or less, more preferably 11500 or less, and even more preferably 8000 or less because of physical limitations.
- the elastic modulus index (300-150) of the water absorbent resin powder according to the present invention is preferably 3500 or more, more preferably 4000 or more.
- the upper limit value of the elastic modulus index is not particularly limited, but is generally preferably 13500 or less, more preferably 9500 or less, and further preferably 4500 or less because of physical limitations.
- the water absorbent resin powder according to the present invention preferably has an internal cell ratio of 0% to 3.7%, more preferably 1.3% to 3.3%, and still more preferably 1. 7% to 3.0%. It is conventionally known that a water-absorbing resin powder having a high water absorption rate is produced by known foam polymerization. On the other hand, the water-absorbent resin powder according to the present invention has a lower internal cell ratio than the water-absorbent resin powder produced by the known foam polymerization (internal cell ratio is about 4%), but also has a high water absorption rate. As described above, it is rich in elasticity and exhibits excellent diffusion absorption characteristics. In addition, the measuring method of an internal bubble rate is later mentioned in an Example.
- the water-absorbent resin powder according to the present invention preferably has a surface tension of 69 mN / m or more, more preferably 70 mN / m or more, and still more preferably 71 mN / m or more.
- the upper limit of the surface tension is preferably 74 mN / m or less, more preferably 73 mN / m or less, from the viewpoint of general measurement accuracy. It is preferable to make the surface tension within the above range since the amount of return can be remarkably suppressed when the water-absorbent resin powder is used as an absorbent body for absorbent articles such as paper diapers.
- the measuring method of surface tension is demonstrated in an Example.
- the water absorbent resin powder according to the present invention has a CRC (centrifuge retention capacity) of preferably 25 g / g to 50 g / g, more preferably 26 g / g to 45 g / g, and still more preferably 26 g / g to 33 g / g. It is.
- the CRC is preferably 25 g / g or more from the viewpoint of sufficient liquid absorption capacity, and preferably 50 g / g or less from the viewpoint of maintaining diffusibility.
- CRC can be appropriately controlled by the amount of the crosslinking agent during polymerization and the subsequent surface crosslinking (secondary crosslinking).
- the water absorbent resin powder according to the present invention is in a state where the crosslink density in the vicinity of the surface is increased, that is, in a state where the surface is crosslinked. Therefore, the water-absorbent resin powder preferably has an AAP (water absorption capacity under pressure) of 8 g / g to 29 g / g, more preferably 10 g / g to 27 g / g, still more preferably 12 g / g to 25 g / g, and / Or SFC (saline flow conductivity) is preferably 5 ⁇ 10 ⁇ 7 ⁇ s ⁇ cm 3 ⁇ g ⁇ 1 or more, more preferably 10 ⁇ 10 ⁇ 7 ⁇ s ⁇ cm 3 ⁇ g ⁇ 1 or more, Preferably, it satisfies 20 ⁇ 10 ⁇ 7 ⁇ s ⁇ cm 3 ⁇ g ⁇ 1 or more. That is, when the AAP and / or SFC satisfies
- the diffusion absorption time of the water absorbent resin powder according to the present invention is preferably 100 seconds or less, more preferably 95 seconds or less, still more preferably 90 seconds or less, and particularly preferably 85 seconds or less. . Since the diffusion absorption time is more preferable as it is shorter, the lower limit value is not particularly limited, but it is preferably more than 5 seconds, more preferably 10 seconds or more, still more preferably 20 seconds or more, and particularly preferably 40 seconds or more. .
- a water absorption resin powder is used in an absorbent article such as a paper diaper, This is preferable because it has excellent liquid uptake that is not possible in the past and can reduce liquid leakage.
- the above-mentioned “elastic modulus index” is a value obtained by correcting the elastic modulus with the theoretical surface area and CRC of the swollen gel particles, and the performance of the water absorbent resin powder. It is a value that is an index of.
- the “swelled gel particles” are swollen gel particles obtained by swelling a water absorbent resin powder with a swelling liquid.
- the elastic modulus index may be abbreviated as “EMI”.
- water absorption time a water-absorbent resin powder which is rich in elasticity and excellent in water absorption time by the vortex method (hereinafter sometimes simply referred to as “water absorption time”) exhibits excellent diffusion absorption characteristics.
- the elastic modulus changes depending on the water absorption magnification. For example, it has been found that improving the water absorption ratio decreases the polymer concentration of the water absorbent resin powder and decreases the elastic modulus. Therefore, it has been found that the elasticity is preferably expressed based on an index considering the influence of the water absorption magnification of the water absorbent resin powder.
- the elastic modulus can be measured by a rheometer described later. At that time, the swollen gel particles are sandwiched between the surface of the rheometer dish and the surface of the parallel plate, and a load is applied. At this time, if there is a particle size distribution in the water-absorbent resin powder, the surface of the parallel plate first comes into contact with the swollen gel particles having a large particle size, so that a phenomenon in which particles having a small particle size are not sandwiched occurs. Therefore, the measurement of the elastic modulus is required to be performed after the particle size of the water-absorbent resin powder is made uniform to some extent by, for example, classification.
- a product of water-absorbent resin powder usually has a particle size distribution. Moreover, since the water absorbent resin powder having a small particle size has a large surface area, the elastic modulus is larger than that of the water absorbent resin powder having a larger particle size. However, for example, particles called so-called fine powder having a particle size of less than 150 ⁇ m have poor water absorption performance and are not suitable for actual use.
- a water-absorbent resin powder rich in elasticity and having a short water absorption time exhibits excellent diffusion absorption characteristics.
- the elastic modulus and the water-absorbent resin powder There is a problem that it does not necessarily correlate with the performance.
- the present inventor derived an elastic modulus index that is a value obtained by correcting the elastic modulus with the water absorption ratio of the water absorbent resin powder and the theoretical surface area of the swollen gel particles. Then, the elasticity index can accurately represent the elasticity of the water-absorbent resin powder, taking into account the influence of the water absorption ratio of the water-absorbent resin powder and the theoretical surface area of the swollen gel particles on the value of the elastic modulus. The value was correlated with the performance of the conductive resin powder.
- Elastic modulus index can be calculated based on the following equation (3). A specific calculation method will be described in detail in the example section.
- the elastic modulus index is an important index that is an index of the performance of the water-absorbent resin powder, but since the elastic modulus value of the water-absorbent resin powder is corrected, the above elastic modulus can be accurately obtained. If not, the elastic modulus index cannot be calculated accurately.
- the present inventors have studied and established a method for measuring an elastic modulus that can accurately measure the elastic modulus.
- the measuring method of the elastic modulus of the water-absorbent resin powder according to the present invention classifies the water-absorbent resin powder (A) using two or more sieves having different openings to obtain the water-absorbent resin powder (B).
- a load-loading process in which the load is applied while increasing the load on an ongoing basis including a measurement step of measuring storage elastic modulus under a constant load, At least a part of the bottom surface of the accommodating portion and / or the plate-like body in contact with the swelling gel is made of aluminum.
- FIG. 1 is an external view showing an example of an apparatus used for measuring the elastic modulus of a water absorbent resin powder.
- 300 is a rheometer which is the above device
- 40 is a dish (accommodating portion) for accommodating a swollen water absorbent resin powder (hereinafter abbreviated as swollen gel)
- 41 is a swollen gel
- 42 is a parallel plate (plate).
- the parallel plate (plate-like body) 42 is configured to be fitted into a dish (accommodating portion) 40.
- FIG. 1A is an external perspective view of each member of the rheometer 300
- FIG. 1B is a state in which a parallel plate (plate-like body) 42 is fitted in a dish (accommodating portion) 40
- FIG. 2 is a longitudinal sectional view of a rheometer 300.
- the rheometer 300, the dish 40 and the parallel plate 42 are installed strictly horizontally.
- the elastic modulus is measured accurately by using a device such as a rheometer 300, sandwiching the swelling gel 41 between the dish (container) 40 and the parallel plate (plate-like body) 42, and applying vibration. It is preferable to perform a correct measurement.
- the rotation angle at the time of rotation is controlled by a strain (unit:%) as a set value of a normal apparatus.
- the strain amount is, for example, preferably 0.005% to 2%, more preferably 0.01% to 1%, and still more preferably 0.02% to 0.5%.
- the rotating shaft 43 is provided on the parallel plate (plate-like body) 42, but the present invention is not necessarily limited thereto.
- the rotating shaft 43 may be provided in the dish (accommodating portion) 40 and may be provided perpendicular to the parallel plate (plate-like body) 42 and the dish (accommodating portion) 40. At this time, the parallel plate (plate-like body) 42 is fixed without rotating.
- the particle to be measured is a mixture of particles having greatly different particle sizes, the particles having a small particle size cannot be sandwiched, and there is a possibility that accurate measurement cannot be performed because the particles are not measured. is there. For this reason, it is preferable to measure the water-absorbent resin powder with a limited particle size range.
- the water-absorbent resin powder (A) is obtained using two or more sieves having different openings. Is classified to obtain a water absorbent resin powder (B).
- the water absorbent resin powder (A) refers to a water absorbent resin powder before classification
- the water absorbent resin powder (B) is a water absorbent resin powder obtained by classification and used.
- the water absorbent resin powder that has not passed through the sieve having the smallest openings are two or more sieves having different openings.
- the two or more sieves having different openings are preferably sieves selected from sieves having an opening of 710 ⁇ m to 150 ⁇ m.
- a JIS standard sieve JIS Z8801-1 (2000)
- JIS standard sieves having openings of 710 ⁇ m, 600 ⁇ m, 500 ⁇ m, 425 ⁇ m, 300 ⁇ m, 150 ⁇ m, etc. can be used.
- the water-absorbent resin powder (A) is classified using the sieve having a mesh size of 710 ⁇ m, and then the water-absorbent resin powder that has passed through the sieve is used. Further, the particles are classified using a JIS standard sieve having an opening of 600 ⁇ m, and the particles remaining on the sieve are collected to obtain a water absorbent resin powder having a particle size of 600 ⁇ m or more and less than 710 ⁇ m (the above “water absorbent resin powder (B)”). Applicable).
- the above is an example using two sieves having different openings, but is not limited to this, and appropriately obtaining water absorbent resin powder having a desired particle size using three or more sieves having different openings. Can do.
- the water absorbent resin powder (B) preferably has a difference of 200 ⁇ m or less between the sieve opening that can pass and the sieve opening that cannot pass. Thereby, since the range of a particle size is limited to 200 ⁇ m or less, it is possible to obtain a measurement object with a more uniform particle size, which is preferable for accurate measurement of elastic modulus.
- the water-absorbent resin powder (B) in which the difference between the sieve opening that can pass and the sieve opening that cannot pass is 200 ⁇ m or less, for example, using two of the JIS standard sieves having a difference of 200 ⁇ m or less. It can be obtained by classifying the water absorbent resin powder (A).
- the water-absorbent resin powder (B) with a limited particle size range obtained as described above is swollen with a swelling liquid and subjected to a swelling step to obtain a swollen gel.
- a swelling liquid a liquid having an ionic strength of 0 to 2.1 is preferably used.
- pure water, deionized water, distilled water, or the like can be used.
- the swelling liquid in the elastic modulus measuring method As the swelling liquid in the elastic modulus measuring method according to the present invention, pure water (the ionic strength is substantially 0, and the standard for pure water preferably satisfies Grade 3 of ISO 3696, and more preferably satisfies Grade 2). Is used.
- the ionic strength is the swelling ratio suitable for elastic modulus measurement. From this viewpoint, it is preferably 0 to 1.0, more preferably 0 to 0.1.
- CRCdw refers to the above-described swelling liquid instead of 0.9 wt% sodium chloride aqueous solution in the above-mentioned CRC (water absorption capacity under no pressure), and the amount of water absorbent resin powder used at the time of measurement from 0.2 g
- the water absorption capacity under no pressure is calculated in accordance with the formula (4) described later by performing the same operation as the CRC measurement except that the free swelling time is changed to 0.05 g and the free swelling time is set to 16 hours.
- the CRCdw may be referred to as “centrifuge retention capacity (absorption capacity) in pure water swelling”.
- the swelling gel 41 when the swelling gel 41 is sandwiched between the dish (container) 40 and the parallel plate (plate-like body) 42 using an apparatus such as the rheometer 300, the swelling gel 41 is evenly sandwiched and swollen. In order to load the gel evenly, the volume of the swollen gel 41 is preferably substantially constant.
- the weight when the water absorbent resin powder (B) swells into a swollen gel can be predicted.
- the swelling gel 41 whose volume is substantially constant can be obtained by weighing the water-absorbent resin powder (B) calculated from the weight and subjecting it to the swelling step.
- the water-absorbent resin powder (B) having a weight obtained by dividing the desired weight of the swollen gel 41 by the CRCdw is weighed, mixed with a swelling liquid in a conventionally known plastic container, and swollen.
- the weighing is preferably performed with as high accuracy as possible. For example, it is preferable to carry out with an accuracy of ⁇ 0.0005 g or more.
- the capacity of the dish (accommodating part) of the rheometer 300 is preferably 100% or less, more preferably 70% or less, still more preferably 50. % Or less.
- the swelling time is preferably 30 minutes or longer and 48 hours or shorter, more preferably 12 hours or longer and 36 hours or shorter, and even more preferably 16 hours or longer and 24 hours or shorter in order to obtain a gel in an equilibrium swelling state.
- the swollen gel obtained by the swelling step is housed in a dish (accommodating portion) 40 of the rheometer 300 (swelling gel 41 shown in FIG. 1).
- the dish (container) 40 has a horizontal bottom surface.
- the swollen gel 41 accommodated in the dish (accommodating portion) 40 is preferably in a state of being immersed in a swelling liquid. This is because a load (pressure) can be more evenly applied to the swollen gel 41, and drying of the swollen gel 41 during measurement can be prevented.
- the degree of immersion it is preferable that the swelling gel 41 is not exposed from the surface of the swelling liquid.
- the weight of the swollen gel 41 per bottom area of the dish (container) 40 is preferably 5.0 mg / mm 2 or less, more preferably 3.0 mg / mm 2 in order to reduce measurement errors when measuring the elastic modulus. Hereinafter, it is more preferably 1.5 mg / mm 2 or less.
- the swollen gel 41 is sandwiched between a bottom surface of a dish (container) 40 that is in contact with the swollen gel 41 and a parallel plate (plate-like body) 42 parallel to the bottom surface.
- a dish (container) 40 that is in contact with the swollen gel 41
- a parallel plate (plate-like body) 42 parallel to the bottom surface.
- the difference between the inner diameter of the dish (accommodating portion) 40 having the horizontal bottom surface and the outer diameter of the parallel plate (plate-like body) 42 is that the parallel plate (plate-like body) 42 is fitted into the dish (accommodating portion) 40.
- it is preferably 3 mm or less, more preferably 2 mm or less, and still more preferably 1 mm or less.
- the above “horizontal bottom surface” means that the bottom surface of the dish (accommodating portion) 40 does not have substantially unevenness.
- At least a part of the bottom surface of the dish (accommodating portion) 40 or the portion of the parallel plate (plate-like body) 42 that contacts the swelling gel 41 is made of aluminum.
- the bottom surface of the dish (accommodating part) 40 or the part of the parallel plate (plate-like body) 42 that contacts the swelling gel 41 is made of stainless steel, the swelling gel 41 and the dish (accommodating part) 40 Since the adhesion between the bottom surface and the parallel plate (plate-like body) 42 is insufficient and slipping occurs, the elastic modulus cannot be measured accurately.
- the “at least part” 50% or more of the bottom surface of the dish (accommodating portion) 40 or the surface parallel to the bottom surface of the parallel plate (plate-like body) 42 is in contact with the swelling gel 41.
- the order is 60% or more, 70% or more, 80% or more, 90% or more, and 100% is most preferably made of aluminum.
- stainless steel or brass can be used.
- At least a part of the portion in contact with the swelling gel 41 is made of aluminum.
- at least a part of the portion in contact with the swollen gel 41 is made of aluminum, so that the above-described effect can be obtained more reliably.
- the swollen gel 41 is subjected to a load loading process in which a load is applied while increasing the load discontinuously up to a target load of at least 2.4 kPa or more perpendicular to the swollen gel 41.
- the load is applied to the parallel plate (plate-like body) 42 in the direction of the dish (housing portion) 40, and the parallel plate (plate-like body) 42 and the dish (housing portion). It can be performed by pushing down while maintaining parallel to the bottom surface of 40. If a condition is set in the rheometer 300, a load can be automatically applied according to the condition until the target load is reached.
- “Up to the target load while increasing the load discontinuously” means that the target load is applied per unit area of the surface of the parallel plate (plate-like body) 42 that contacts the swelling gel 41. It means increasing the load stepwise. That is, instead of gradually increasing the load continuously, a certain load is applied in a certain time zone, and a certain constant load is further increased in the next time zone after that time has elapsed. It means increasing the load, such as loading. For example, the load is increased by applying a load of 1 kPa for 10 seconds and increasing the load, and then applying a load of 2 kPa for the next 10 seconds.
- the target load is the final load applied to the swollen gel.
- the “target load of at least 2.4 kPa” may be a case where the load is 2.4 kPa, increasing the load discontinuously until reaching 2.4 kPa, or 2.4 kPa. It may be a case where a load exceeding the load is set as a target load and the load is increased while being discontinuously increased until the target load is reached.
- the target load is less than 2.4 kPa, the pressure necessary for measuring the elastic modulus cannot be applied to the swollen gel 41, which is not preferable.
- the upper limit value of the target load is preferably 30 kPa or less, more preferably 26 kPa or less, and even more preferably 22 kPa or less so that the pressure on the swollen gel 41 is not excessive. is there.
- the rate of increase in load when discontinuously increasing the load is not particularly limited, but it takes an extra measurement time, and is preferably 0.1 kPa / s or more, more preferably 0.3 kPa / s or more, and more Preferably, it is increased at 0.5 kPa / s or more.
- the load loading process includes a measurement process for measuring the storage elastic modulus under a constant load.
- the load is applied while increasing the load discontinuously up to a target load of at least 2.4 kPa or more.
- “Measuring the storage elastic modulus under a constant load” means measuring the storage elastic modulus in a time zone in which a constant load is applied in the process of increasing the load discontinuously. That is, in order to increase the load discontinuously, as described above, a constant load is applied in a certain time zone, and in the next time zone after the time zone has passed, the constant time is increased from the immediately preceding time zone. The operation of loading the load is repeated, but the storage elastic modulus in each time zone is measured.
- the measurement interval of the storage elastic modulus is not particularly limited. However, since there is a possibility that an error may increase, the measurement is preferably performed every 20 seconds, more preferably every 10 seconds, and even more preferably every 5 seconds. .
- the elastic modulus can be obtained by obtaining an arithmetic average value of values measured in a time zone when a target load is applied among measured storage elastic moduli.
- the measurement value used for obtaining the arithmetic mean value is not particularly limited, but it is preferably as many as possible. Also, since the value becomes more stable in the latter half of the measured time zone, several points from the end of the measured time zone (preferably 1 to 10 points, more preferably 3 to 5 points, 5 points in the embodiment). The arithmetic average value of the measured values may be obtained.
- the elastic modulus index can be obtained by correcting the value of the elastic modulus thus obtained with the CRC of the water-absorbent resin powder and the theoretical surface area of the swollen gel particles as shown in the above formula (3).
- the method for measuring the elastic modulus of the water-absorbent resin powder according to the present invention limits the particle size range of the water-absorbent resin powder to be measured, and the gel is made of a member having high adhesion to the swollen gel.
- the elastic modulus can be accurately measured because the load is applied while increasing the load discontinuously up to a predetermined target load.
- the water-absorbent resin powder according to the present invention is rich in elasticity, has a high water absorption rate, and as a result exhibits excellent diffusion absorption characteristics. This is considered to be because the shape of the particles is more strictly controlled and the particles having a flat shape are excluded.
- Embodiment 1 The method for producing a water-absorbent resin powder according to the present embodiment includes a water-absorbent resin powder having a polyacrylic acid (salt) -based water-absorbent resin as a main component and a surface-crosslinked water-absorbent resin powder having an opening of 150 ⁇ m or more and 850 ⁇ m or less.
- Classifying using a seed sieve obtaining a water absorbent resin powder (i) remaining on the sieve (a) having the smallest mesh among the sieves used; Classifying the water-absorbent resin powder (i) using a sieve (b) having a rectangular aperture to obtain a water-absorbent resin powder (ii) remaining on the sieve (b),
- the length of the long side of the rectangular aperture is larger than that of the sieve (a), and the aperture of the sieve (c) is a sieve that defines the upper limit of the particle size of the water absorbent resin powder (i). It is a method in which the length is not less than the length of the side, and preferably the length of the short side of the rectangular mesh is 2/3 or less (more preferably 1/2 or less) of the length of the long side.
- the length of the side of the sieve (c) is preferably 710 ⁇ m or less, and the rectangular mesh preferably has a long side of 710 ⁇ m or more and a short side of 350 ⁇ m or less.
- the “water-absorbing resin powder mainly composed of polyacrylic acid (salt) -based water-absorbing resin and surface-crosslinked” is as described above.
- the sieve having a mesh size of 150 ⁇ m or more and 850 ⁇ m or less is a sieve having a square mesh with one side of 150 ⁇ m or more and 850 ⁇ m or less, and is preferably a JIS standard sieve.
- JIS standard sieves having openings of 850 ⁇ m, 710 ⁇ m, 600 ⁇ m, 500 ⁇ m, 425 ⁇ m, 300 ⁇ m, 150 ⁇ m, etc. can be used. What is necessary is just to use at least 2 sorts of sieves with 150 to 850 micrometers of mesh openings.
- the sieve (a) is placed on the sieve (a) having the smallest opening among the used sieves.
- the water-absorbent resin powder (i) having a particle size equal to or larger than the mesh size remains.
- the water-absorbent resin powder (i) contains many spherical or near-shaped particles, but may also contain flat-shaped particles (flaky particles).
- the flat shaped particles are preferably removed because they deteriorate the elasticity of the water-absorbent resin powder and deteriorate the absorption characteristics of the water-absorbent resin powder.
- the water absorbent resin powder (i) is classified using a sieve (b) having a rectangular opening for the purpose of removing flat particles, and the water absorbent resin remaining on the sieve (b) Powder (ii) is obtained.
- a sieve (b) the sieve provided with the conventionally well-known ton cap wire mesh can be used, for example.
- FIG. 5 is a schematic diagram showing a state in which flat particles are removed using rectangular openings.
- FIG. 5 (a) shows that spherical particles cannot pass through a rectangular aperture
- FIG. 5 (b) shows a flat particle having a rectangular aperture with a length a shown in the figure. If it is shorter than the long side, it indicates that it can pass through the mesh.
- the length of the long side of the rectangular mesh is a sieve that defines an upper limit of the particle size of the water-absorbent resin powder (i) and has a larger mesh size than the sieve (a) of the at least two types of sieves. It is more than the length of the side of the opening of a certain sieve (c).
- the sieve (c) corresponds to a sieve having an opening having a size one higher than the sieve having the smallest opening among at least two kinds of sieves having an opening of 150 ⁇ m or more and 850 ⁇ m or less.
- the JIS standard sieve with the smallest openings of 500 ⁇ m is used.
- the sieve (a) corresponds to the sieve (a).
- the water absorbent resin powder (i) having a particle size of 500 ⁇ m or more and less than 710 ⁇ m remains on the sieve (a), and the upper limit value of the particle size of the water absorbent resin powder (i) is defined.
- What is present is a JIS standard sieve having a mesh size of 710 ⁇ m and having a mesh size one size higher than that of the sieve (a), and therefore the sieve corresponds to the sieve (c).
- the length of the long side of the opening of the rectangle is equal to or longer than the length of the opening of the sieve (c), and preferably the length of the short side of the opening of the rectangular is the length of the long side.
- Particles that pass through the sieve (c) but cannot pass through the sieve (b) in the water-absorbent resin powder (i) by being 2/3 or less (more preferably 1/2 or less) ( The water absorbent resin powder (ii)) will remain on the sieve (b). Since the water-absorbent resin powder (ii) is a particle larger than the rectangular aperture, it can be said to be a particle having a low flatness. On the other hand, since the particles passing through the sieve (b) are particles smaller than the rectangular openings, the particles have high flatness.
- the water absorbent resin powder that has passed through the sieve (a) may be mixed with the water absorbent resin powder remaining on the sieve (b).
- the sieve (a) is, for example, a JIS standard sieve having an opening of 150 ⁇ m
- the water absorbent resin powder that has passed through the sieve (a) corresponds to a so-called fine powder having poor performance as a water absorbent resin. Therefore, it is not always necessary to mix with the water absorbent resin powder remaining on the sieve (b).
- the above steps may be repeated multiple times. For example, the following steps can be taken.
- a JIS standard sieve having an opening of 850 ⁇ m (corresponding to the above sieve (c)) and a JIS standard sieve having an opening of 710 ⁇ m (corresponding to the above sieve (a)).
- a step of obtaining a water-absorbing resin powder (i) having a particle size of 710 ⁇ m or more and less than 850 ⁇ m is performed, and the length of the long side is 850 ⁇ m or more and the length of the short side is 2/3 or less (more preferably 1/2).
- the flat-shaped particles are removed using a sieve (b) that is the following) to obtain a water absorbent resin powder (ii); (II) particles having a particle size of less than 710 ⁇ m that have passed through the JIS standard sieve having an aperture of 710 ⁇ m, Classification is performed using a JIS standard sieve having a mesh size of 500 ⁇ m (corresponding to the above sieve (a)) to obtain a water absorbent resin powder (i ′) having a particle size of 500 ⁇ m or more and less than 710 ⁇ m, and the length of the long side is 710 ⁇ m or more. And the length of the short side is 710 m 2/3 or less (more preferably 1/2 or less) to remove particles of further flat shape using a sieve (b) is to obtain a water-absorbent resin powder (ii ').
- an operation of further removing the flat particles contained in the particles that have passed through the sieve corresponding to the sieve (a) may be performed.
- the length of the long side of the sieve (b) is only required to remove the flat particles contained in the water absorbent resin powder (i), so the upper limit of the particle size of the water absorbent resin powder (i).
- What is necessary is just to be the length of the side of the opening of the sieve (c) which is a sieve that defines
- the length of the short side of the sieve (b) is not more than 2/3 of the length of the long side from the viewpoint of leaving particles that are close to a sphere or a cube and removing only flatter particles. Is preferable, and it is more preferable that it is 1/2 or less.
- Example 1 the manufacturing method according to Embodiment 1, it is possible to manufacture a water-absorbent resin powder from which particles having a flat shape have been significantly removed, and as shown in Example 1 described later, The water-absorbent resin powder according to the present invention having high elasticity and high water absorption speed can be obtained.
- the water absorbent resin powder (1) from which the flat particles (flaky particles) contained in the comparative water absorbent resin powder (1) were removed was obtained, and the water absorbent resin powder (1) was obtained.
- Embodiment 2 The manufacturing method of the water absorbent resin powder according to Embodiment 2 is the following method. That is, the water absorption according to the present invention comprising a polymerization step of an acrylic acid (salt) monomer aqueous solution, a gel grinding step of a hydrogel crosslinked polymer during or after polymerization, and a drying step after gel grinding.
- the water absorption according to the present invention comprising a polymerization step of an acrylic acid (salt) monomer aqueous solution, a gel grinding step of a hydrogel crosslinked polymer during or after polymerization, and a drying step after gel grinding.
- a method for producing a conductive resin powder In the gel pulverization step, a hydrogel crosslinked polymer having a resin solid content of 10 wt% to 80 wt% is pulverized using the following gel pulverizer (A):
- a gel crusher used for producing a water-absorbent resin powder comprising a screw, a supply port, an extrusion port, a perforated plate, and a barrel,
- the barrel includes a back-preventing member on its inner surface, YH is the height of the anti-reverse member obtained when the barrel is cut perpendicularly to the extrusion direction of the gel of the water-absorbent resin, and the extension direction of the anti-reverse member on the upper surface of the anti-reverse member
- the barrel satisfies the following (a) and (b):
- the screw is provided with a rotation shaft serving as a center of rotation and a flight
- the present inventors have crushed the hydrogel so as to knead it by using a gel crushing device having a specific device shape in the gel crushing step which is one of the manufacturing steps of the water absorbent resin.
- the inventors have found that the water-absorbent resin powder according to the present invention can be easily obtained, and found that the liquid permeability of the obtained water-absorbent resin powder, preferably both the liquid permeability and the water absorption speed can be improved.
- the gel crusher used in this embodiment subdivides the hydrated gel-like crosslinked polymer during polymerization or after polymerization to obtain a desired shape of hydrated gel-like crosslinked polymer (in this specification, “particulate hydrated gel”). It is an apparatus used for obtaining the above.
- FIG. 6 is a schematic cross-sectional view showing the overall configuration of the gel crusher 100 used in the present embodiment.
- the gel crusher 100 is an apparatus used for obtaining a particulate hydrogel having a desired shape, and corresponds to the gel crusher (A).
- the gel pulverization apparatus 100 is an apparatus used in a gel pulverization process performed between a polymerization process and a drying process, in particular, in the production of a water absorbent resin.
- the gel crusher 100 includes a screw 11, a porous plate 12, a barrel 13, a supply port 14, a hopper 15, an extrusion port 16, a rotary blade 17, a ring 18, a reverse prevention member 19, a table 20, and a motor. 21 etc.
- a screw 11 is provided inside a cylindrical barrel 13.
- One end of the barrel 13 is provided with an extrusion port 16 for extruding a hydrogel and pulverizing the gel, and a perforated plate 12 is installed in front of the extrusion port 16.
- a table 20 whereby a screw type extruder can be stably installed.
- a supply port 14 for supplying a hydrogel, and a hopper 15 is provided to facilitate the supply of the hydrogel.
- the gel crusher 100 is preferably maintained in durability even when used for 8000 hours or more per year. Therefore, it is preferable that the connection part of each member is attached so that it may not come off easily even if power is applied.
- FIG. 7 is a schematic cross-sectional view showing the vicinity of the extrusion port 16 of the gel crusher 100.
- the screw 11 mainly includes a rotating shaft 22 and a flight part 23.
- the flight part 23 is mounted in a spiral shape around the rotation shaft 22.
- the number of turns of the flight part 23 around the rotating shaft 22 refers to the number of windings from the end of the rotating shaft 22 to the other end.
- the number of turns of the flight part is not particularly limited, but is preferably 3 or more, and particularly preferably 4 or more.
- the flight part 23 may be a single helix, a double helix, or a triple helix, and the number of the flight parts 23 mounted on the rotating shaft 22 is not particularly limited.
- the flight part 23 wound around the rotating shaft 22 is wound around the rotating shaft 22 in a direction opposite to the direction in which the rotating shaft 22 rotates. That is, in FIG. 6, when the gel crusher according to the present invention is viewed from the motor 21 toward the extrusion port 16, and the rotation of the rotary shaft 22 is a right rotation, the flight unit 23 is It is wound around the rotation shaft 22 by left rotation.
- the shape or size of the barrel 13 is not particularly limited as long as it has a cylindrical inner surface corresponding to the shape of the screw 11.
- the barrel 13 is provided with a reverse prevention member 19.
- the reversion preventing member 19 is not particularly limited as long as it is a structure that can prevent the water-containing gel from reversing, and the inner wall of the barrel 13 is a spiral or concentric belt-like protrusion, or a line parallel to the screw 11. , Granular, spherical, or angular protrusions.
- the formation of the reversal prevention member 19 on the inner wall of the barrel 13 has an effect of preventing the water-containing gel from reversing.
- the phrase “the reversal prevention member 19 is parallel to the screw 11” only needs to be substantially parallel to the screw 11. That is, the angle formed by the surface of the screw 11 side of the reversal prevention member 19 and the surface of the flight part 23 of the screw 11 on the barrel 13 side from the inlet to the outlet of the gel crusher is preferably 0 ° to 10 °. Within the range, more preferably within the range of 0 ° to 5 °, still more preferably 0 °.
- the reversal prevention member 19 When the reversal prevention member 19 is spirally formed inside the barrel 13, it is formed on the barrel 13 in the same direction as the rotation shaft 22 rotates. That is, in FIG. 6, when the direction from the motor 21 to the extrusion port 16 is viewed, and the rotation of the rotary shaft 22 is a right rotation, the reverse return preventing member 19 is formed on the barrel by a right rotation.
- the barrel multiplier is preferably 1 to 16, more preferably 1 to 8, still more preferably 1 to 7, and most preferably 1 to 4.
- the barrel multiplier in the present invention is larger than 16, the gel is clogged in the gap between the barrels, and the gel may be retained, thereby deteriorating the gel.
- the “projection” in the shape of the reversing prevention member 19 is not limited to a convex shape, and is a concave shape when a groove is formed in the barrel 13 in construction (a convex shape around the concave shape forming the concave shape). ).
- FIG. 8 is a cross-sectional view of the screw 11 and the barrel 13 cut along the X-X ′ plane of FIG. 7 and cut in a direction perpendicular to the extrusion direction of the hydrogel.
- the maximum inner diameter at which the reversing prevention member 19 inside the barrel 13 does not contact the screw 11 is N (also referred to as “inner diameter N” in the present specification), and the area of the surface where the inner diameter is N.
- A also referred to as “cross-sectional area A” in the present specification
- B also referred to as “cross-sectional area B” in the present specification).
- the diameter of the rotating shaft 22 is preferably in the range of 25 mm to 400 mm, more preferably 40 mm to 300 mm.
- the “screw cross-sectional area ratio” refers to the ratio of the cross-sectional area B to the cross-sectional area A and is expressed as “B / A”.
- the range of the screw cross-sectional area ratio B / A is preferably 0.540 to 0.630.
- the water absorption capacity of the water absorbent resin under pressure is preferably improved.
- the gap between the reversing prevention member 19 inside the barrel 13 and the flight part 23 is denoted by ⁇ (also referred to as “clearance ⁇ ” in the present specification).
- the clearance ⁇ is preferably 0.5 mm to 7 mm, more preferably 1 mm to 5 mm, and still more preferably 1 mm to 3 mm.
- clearance sigma
- pulverization becomes large.
- the clearance ⁇ is larger than 7 mm, sufficient shearing is not performed, and there is a possibility that a water absorbent resin having the intended performance cannot be obtained.
- FIG. 9 is a view in which the screw is cut along the Y-Y ′ plane of FIG. 8 and the barrel is developed in a planar shape.
- the W-W ′ plane in FIG. 9 is a plane perpendicular to the Y-Y ′ plane in FIG. 8.
- the back-preventing member 19 is spirally formed inside the barrel 13, the back-preventing member 19 is formed at an angle ⁇ with respect to the WW ′ plane, as shown in FIG. It is preferable.
- ⁇ is referred to as “barrel installation angle”.
- the barrel installation angle ⁇ in the present invention is preferably 10 ° to 90 °, more preferably 20 ° to 60 °, and still more preferably 30 ° to 45 °. If ⁇ is less than 10 °, the gel's anti-reverse effect is too strong, so that sufficient shearing force may not be applied to the gel. If it is greater than 90 °, the anti-reverse effect may not be exhibited.
- FIG. 10 is an enlarged view of one reversion preventing member 19 by cutting the barrel along the Z-Z ′ plane of FIG. 9, and is a schematic cross-sectional view showing two flight portions 23.
- “barrel mountain height YH” refers to the distance from the inner surface of the barrel 13 to the upper surface of the protruding back prevention member 19.
- the barrel peak height YH is preferably 4 mm to 40 mm, more preferably 7 mm to 30 mm, although the optimum height varies depending on the inner diameter N.
- the value (YH / N) of the barrel height YH with respect to the inner diameter N is preferably 0.05 to 0.2. It is preferable that the YH / N is 0.05 to 0.2 because the water-absorbing resin is sufficiently kneaded.
- the “barrel peak width YF” refers to a width in a direction perpendicular to the extending direction of the reverse-turning prevention member 19 on the surface of the reverse-turning prevention member 19 that is closest to the screw 11.
- the barrel crest width YF is preferably 4 mm to 40 mm, more preferably 8 mm to 30 mm, although the optimum width varies depending on the inner diameter N.
- the value (YF / N) of the barrel crest width YF with respect to the inner diameter N is preferably 0.05 to 0.2.
- the YF / N of 0.05 to 0.2 is preferable because the water-absorbent resin can be sufficiently kneaded.
- the width in the direction perpendicular to the extending direction of the flight part 23 on the upper surface of the flight part 23 not in contact with the rotating shaft 22 is defined as F (also referred to as “flight width F” in this specification).
- the value of the flight width (F / N) with respect to the inner diameter N is preferably 0.07 to 0.13.
- the F / N is in the above range, it is preferable that an area kneaded between the screw and the barrel protrusion can be appropriately taken, and sufficient shearing is applied to the gel, so that the desired performance can be easily obtained. Moreover, when the value of F / N is within the above range, the water absorption capacity of the water absorbent resin under pressure is preferably improved.
- FIG. 11 is a schematic cross-sectional view illustrating the inner diameter N of the barrel, the flight width F of the screw, and the pitch length P.
- the value (P / N) of the pitch length P for one turn of flight from the end of the screw on the outlet side of the gel grinder with respect to the inner diameter N is preferably 0.15 to 0.68, more preferably 0.20. To 0.50, more preferably 0.25 to 0.40.
- any pitch length satisfies the above range
- any pitch length from the first to the second volume satisfies the above range. It is more preferable that the pitch length of the first roll satisfies the above range.
- the above-mentioned YH / N, YF / N, B / A and F / N are respectively It is preferable that the above requirements (a) to (d) are satisfied.
- a gel crusher that satisfies the requirements, it is possible to easily produce the water-absorbent resin powder according to the present invention that is rich in elasticity, has a high water absorption rate, and is excellent in diffusion absorption characteristics.
- the material of the screw 11 and the barrel 13 is not particularly limited, but is preferably stainless steel, and more preferably austenitic stainless steel from the viewpoint of corrosion resistance. Specifically, SUS304 is preferable.
- FIG. 12 shows an example of a barrel that can be used in the gel crusher used in this embodiment. 12 is a view of the barrel viewed from the extrusion port 16 in FIG. 6 in the direction of the motor 21, and the barrel no. B88-874.
- the perforated plate 12 is a member provided at the outlet portion where the hydrogel in the barrel 13 is extruded in the gel crusher used in the present embodiment.
- the thickness, pore diameter, or open area ratio of the porous plate 12 can be selected as appropriate depending on the amount of treatment per unit time of the gel crushing device or the shape of the hydrogel, but is not particularly limited.
- (Also referred to as “die thickness”) is preferably 3.5 mm to 40 mm, more preferably 8 mm to 30 mm, and still more preferably 10 mm to 25 mm.
- the hole diameter of the perforated plate (also referred to as “die hole diameter” in the present specification) is preferably 3.2 mm to 30 mm, more preferably 7.5 mm to 25 mm.
- the aperture ratio of the perforated plate (also referred to as “die aperture ratio” in this specification) is preferably 20% to 80%, more preferably 30% to 55%.
- the simple average value of the pore diameters of the perforated plates is used as the pore size of the perforated plate in the gel crusher.
- the shape of the hole is preferably a circle, but is not particularly limited, and in the case of a shape other than a circle (for example, a quadrangle, an ellipse, a slit, etc.) mm).
- the die thickness is thinner than 3.5 mm
- the die hole diameter is larger than 30 mm
- the die opening rate is larger than 80%
- the water-containing gel may be excessively sheared / compressed, and the physical properties of the water-absorbent resin may be deteriorated.
- the material (metal) of the porous plate 12 is preferably a material (metal) different from the material of the screw 11 and the barrel 13.
- the material of the perforated plate 12 is the same as that of the screw 11 and the barrel 13, there is a risk of damage to the apparatus due to seizure or the like.
- the material of the porous plate 12 is preferably a metal whose hardness can be increased by quenching (heat treatment).
- the barrel 13 is preferably austenitic stainless steel.
- the gel crusher used in the present embodiment may include a bearing portion.
- the “bearing portion” refers to a member provided between a die plate and a rotating shaft.
- the material of the portion where the rotating shaft 22 and the bearing portion contact is preferably different from the material of the rotating shaft and the bearing portion, and more preferably a metal of a different material.
- the material of the rotating shaft 22 and the bearing portion is the same as that of the portion where the rotating shaft 22 and the bearing portion are in contact with each other, there is a risk of damage to the device due to seizure or the like, and mixing of metal powder into the product.
- the rotational speed of the rotating shaft 22 and the outer peripheral speed of the flight part 23 The rotational speed of the rotary shaft 22 cannot be generally specified because the outer peripheral speed of the rotary blade changes depending on the inner diameter of the barrel 13, but the rotational speed of the rotary shaft 22 is preferably 60 rpm to 500 rpm, more preferably 80 rpm to 400 rpm, More preferably, it is 100 rpm to 200 rpm. When the rotation speed of the rotating shaft 22 is less than 60 rpm, there is a possibility that the shear / compression force necessary for gel crushing cannot be obtained.
- the temperature at the time of use of the gel crusher 100 used in the present embodiment is preferably 40 ° C. to 120 ° C., more preferably 60 ° C. to 100 ° C. in order to prevent adhesion of the hydrogel.
- the gel crusher 100 used by this embodiment has a heating apparatus, a heat retention apparatus, etc.
- the temperature of the hydrogel before gel pulverization supplied to the gel pulverizer used in this embodiment is preferably 40 ° C. to 120 ° C. from the viewpoint of particle size control and physical properties. ° C, more preferably 60 ° C to 120 ° C, still more preferably 60 ° C to 110 ° C, particularly preferably 65 ° C to 110 ° C.
- the gel temperature When the gel temperature is less than 40 ° C., the hardness and elasticity are increased due to the characteristics of the hydrous gel, which may make it difficult to control the particle shape or particle size distribution during gel pulverization. Moreover, when the said gel temperature exceeds 120 degreeC, the softness of a water-containing gel increases and there exists a possibility that control of a particle shape or a particle size distribution may become difficult.
- the gel temperature can be appropriately controlled by the polymerization temperature or the post-polymerization heating, heat retention or cooling.
- the processing amount per unit time of the gel crusher used in the present embodiment is a value depending on the inner diameter N, and a suitable range varies.
- T unit; g / hr
- N 3 unit: mm 3
- the throughput per unit time of the gel crusher used in the embodiment can be represented by a throughput inner diameter ratio (T / N 3 ) (unit: g / hr / mm 3 ).
- the upper limit of the processing amount inner diameter ratio (T / N 3 ) is preferably 2.0 or less, more preferably 1.5 or less, and still more preferably 1.0 or less.
- the upper limit of the processing amount inner diameter ratio (T / N 3 ) is a processing amount larger than 2.0, sufficient shear cannot be applied to the hydrated gel, and the target performance may not be obtained.
- the lower limit of the inner diameter ratio (T / N 3 ) is preferably 0.05 or more, more preferably 0.10 or more, and further preferably 0.15 or more.
- the processing amount inner diameter ratio (T / N 3 ) is a processing amount smaller than 0.05, the processing amount is too small, so that the hydrogel stays in the gel crushing device, and excessive shearing or gel deterioration occurs. May cause.
- the gel can be crushed by adding water to the hydrous gel.
- the “water” added in the present invention may include any form of solid, liquid, and gas. From the viewpoint of handleability, a liquid or gas form or a mixed form of liquid and gas is preferable.
- the method of adding water or the timing of adding water is not particularly limited, but it is sufficient that water is supplied into the apparatus while the hydrogel is staying in the gel crushing apparatus 100. Further, a hydrogel to which water has been added in advance may be charged into the gel crusher 100. Furthermore, the addition of water may be performed by adding “water” alone, other additives (for example, a surfactant, a neutralizing base, a crosslinking agent, an inorganic salt, etc.) or a solvent other than water. You may add together. When water and other additives or solvents other than water are added together, the water content is preferably 90% to 100% by weight, more preferably 99% to 100% by weight, and still more preferably substantially 100% by weight. %.
- the amount of water supplied in the above water addition is preferably 0 to 4 parts by weight, more preferably 0 to 2 parts by weight, with respect to 100 parts by weight of the hydrogel.
- the supply amount of water exceeds 4 parts by weight, there is a risk that problems such as generation of undried material occur during drying.
- the temperature at the time of supply is preferably 10 ° C. to 100 ° C., more preferably 40 ° C. to 100 ° C.
- the temperature at the time of supply is preferably 100 ° C. to 220 ° C., more preferably 100 ° C. to 160 ° C., and further preferably 100 ° C. to 130 ° C.
- the preparation method is not particularly limited.
- a method using water vapor generated by heating of a boiler, a gas generated from a water surface by vibrating water with ultrasonic waves The method of using the water of this is mentioned.
- steam having a pressure higher than atmospheric pressure is preferable, and steam generated in a boiler is more preferable.
- water-containing gel As described above, it is preferable to add water to the water-containing gel and pulverize the gel. However, in addition to water, other additives or neutralizers may be added to the water-containing gel and kneaded to crushed the gel. The water-absorbing resin to be produced may be modified.
- an aqueous solution containing a basic substance may be neutralized at the time of gel pulverization, or a water absorbent resin fine powder (0. 1% to 30% by weight (based on resin solids)) may be added for fine powder recycling.
- a polymerization initiator, a reducing agent, and a chelating agent are added at 0.001% to 3% by weight (based on resin solids) and mixed during gel grinding to reduce residual monomer, improve coloring, and provide durability. May be.
- GGE Gel grinding energy
- GGE2 Gel grinding energy (2)
- the gel grinding energy (GGE) for gel grinding of the hydrogel is preferably 100 J / g or less, more preferably 60 J / g or less, and even more preferably 50 J / g or less as the upper limit. Moreover, as a lower limit, Preferably it is 15 J / g or more, More preferably, it is 18 J / g or more, More preferably, it is 20 J / g or more.
- the gel grinding energy (GGE) for grinding the hydrogel is preferably 15 J / g to 100 J / g, more preferably 18 J / g to 60 J / g, and still more preferably 20 J / g to 50 J / g.
- GGE gel grinding energy
- the gel pulverization energy (GGE) is defined including the energy during idling of the gel pulverizer.
- the gel crushing energy 2 (GGE2 / Gel Grinding Energy) is preferably controlled within a certain range.
- the gel grinding energy (2) (GGE (2)) for gel grinding of the hydrogel is preferably 40 J / g or less, more preferably 32 J / g or less, and even more preferably 25 J as the upper limit. / G or less.
- it is 7 J / g or more, More preferably, it is 8 J / g or more, More preferably, it is 10 J / g or more, Most preferably, it is 12 J / g or more.
- the gel grinding energy (2) (GGE (2)) for gel grinding of the hydrogel is preferably 7 J / g to 40 J / g, more preferably 8 J / g to 32 J / g, Preferably, it is 10 J / g to 25 J / g.
- GGE (2) gel grinding energy (2)
- gel crushing when gel crushing is performed in a plurality of devices, such as the use of the gel crushing device 100 used in the present embodiment after kneader polymerization, or the use of a plurality of gel crushing devices, the energy consumed in each device.
- the total is defined as gel grinding energy (2) (GGE (2)).
- the water-absorbent resin according to the present invention which is rich in elasticity and has a high water absorption rate, and as a result exhibits excellent diffusion absorption characteristics.
- a powder can be obtained. This is because the pulverization of the gel is optimized by the above apparatus, so that particles having a nearly spherical shape are obtained, and the number of flat particles that deteriorate the elasticity and the performance of the water absorbent resin can be reduced. it is conceivable that.
- the water absorbent resin powder according to the present invention can be obtained.
- the method for producing the water absorbent resin powder is not limited thereto. It is not something that can be done.
- the water-absorbent resin powder obtained in the present invention is usually polymerized in an aqueous solution state using a monomer containing acrylic acid (salt) as a main component as a raw material.
- a monomer containing acrylic acid (salt) as a main component is also referred to as “acrylic acid (salt) -based monomer aqueous solution”.
- the monomer (monomer) concentration in the aqueous monomer solution is preferably 10% by weight to 80% by weight, more preferably 20% by weight to 80% by weight, still more preferably 30% by weight to 70% by weight, particularly preferably. Is 40% to 60% by weight.
- the acid groups of the polymer is preferably neutralized from the viewpoint of water absorption performance or residual monomer.
- the salt of the neutralized portion is not particularly limited, but from the viewpoint of water absorption performance, monovalent salts selected from alkali metal salts, ammonium salts, or amine salts are preferable, alkali metal salts are more preferable, and sodium salts Alkali metal salts selected from lithium salts or potassium salts are more preferred, and sodium salts are particularly preferred.
- the basic substance used for neutralization is not particularly limited, but alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, or lithium hydroxide, sodium carbonate (hydrogen), potassium carbonate (hydrogen), etc.
- alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, or lithium hydroxide, sodium carbonate (hydrogen), potassium carbonate (hydrogen), etc.
- Monovalent basic substances such as carbonic acid (hydrogen) salts are preferred, and sodium hydroxide is particularly preferred.
- the neutralization can be carried out in each form / state before, during or after polymerization.
- a hydrogel obtained by polymerizing unneutralized or low-neutralized acrylic acid (for example, 0 mol% to 30 mol%) can be neutralized, particularly neutralized simultaneously with gel pulverization.
- it is preferable to neutralize acrylic acid before polymerization That is, it is preferable to use neutralized acrylic acid (partially neutralized salt of acrylic acid) as a monomer.
- the neutralization rate in the neutralization is not particularly limited, but is preferably 10 mol% to 100 mol%, more preferably 30 mol% to 95 mol%, still more preferably 45 mol% as the final water absorbent resin. It is ⁇ 90 mol%, particularly preferably 60 mol% to 80 mol%.
- the neutralization temperature is not particularly limited, but is preferably 10 ° C to 100 ° C, more preferably 30 ° C to 90 ° C.
- the conditions disclosed in EP 574260 are preferably applied to the present invention.
- water-soluble resins or water-absorbent resins such as starch, cellulose, polyvinyl alcohol (PVA), polyacrylic acid (salt), and polyethyleneimine; carbonates, azo
- various foaming agents such as compounds and bubble generating agents
- surfactants such as monomer aqueous solution, hydrous gel, dry polymer or water absorbent resin Can be added.
- the amount of these optional components added is preferably 0% by weight to 50% by weight, more preferably 0% by weight to 20% by weight, and still more preferably, with respect to the monomer. It is 0 to 10% by weight, particularly preferably 0 to 3% by weight.
- the above foaming agent, surfactant or additive it is preferably 0% by weight to 5% by weight, more preferably 0% by weight to 1% by weight.
- a graft polymer or a water-absorbing resin composition can be obtained by adding the above aqueous resin or water-absorbing resin.
- These starch-acrylic acid polymer, PVA-acrylic acid polymer and the like are also polyacrylic acid in the present invention. Treat as a (salt) water-absorbing resin.
- a chelating agent for the purpose of improving the color stability (color stability when stored for a long time under high temperature and high humidity) or urine resistance (preventing gel deterioration) of the water absorbent resin powder obtained in the present invention, a chelating agent, An ⁇ -hydroxycarboxylic acid compound and an inorganic reducing agent can be used, and it is particularly preferable to use a chelating agent.
- the amount of these used is preferably 10 ppm to 5,000 ppm, more preferably 10 ppm to 1,000 ppm, still more preferably 50 ppm to 1,000 ppm, and particularly preferably 100 ppm to 1,000 ppm with respect to the water absorbent resin.
- the chelating agent a compound disclosed in US Pat. No. 6,599,989 or International Publication No. 2008/090961 is applied in the present invention. Among them, it is preferable to use an aminocarboxylic acid metal chelating agent or a polyvalent phosphoric acid compound as the chelating agent.
- acrylic acid (salt) when acrylic acid (salt) is used as a main component, a hydrophilic or hydrophobic unsaturated monomer other than acrylic acid (salt) (referred to as “other monomer” in the present specification). ) May be used in combination.
- Examples of such other monomers include, but are not particularly limited to, for example, methacrylic acid, (anhydrous) maleic acid, 2- (meth) acrylamide-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 (meta ) Acrylate, polyethylene glycol (meth) acrylate, stearyl acrylate, and salts thereof.
- the amount used is appropriately determined within a range that does not impair the water absorption performance of the resulting water absorbent resin powder, and is not particularly limited. It is 0 mol% to 50 mol%, more preferably 0 mol% to 30 mol%, still more preferably 0 mol% to 10 mol%.
- Internal crosslinking agent In the present invention, it is preferable to use a crosslinking agent (referred to as “internal crosslinking agent” in the present specification) from the viewpoint of the water absorption performance of the water-absorbent resin powder obtained.
- the internal cross-linking agent is not particularly limited, and examples thereof include a polymerizable cross-linking agent with acrylic acid, a reactive cross-linking agent with a carboxyl group, or a cross-linking agent having both of them.
- polymerizable crosslinking agent examples include N, N′-methylenebisacrylamide, (poly) ethylene glycol di (meth) acrylate, (polyoxyethylene) trimethylolpropane tri (meth) acrylate, and poly (meth) allyloxy.
- examples thereof include compounds having at least two double bonds having polymerizability in the molecule, such as alkanes.
- the reactive cross-linking agent examples include polyglycidyl ethers such as ethylene glycol diglycidyl ether; covalent cross-linking agents such as polyhydric alcohols such as propanediol, glycerin and sorbitol, and polyvalent metal compounds such as aluminum salts.
- polyglycidyl ethers such as ethylene glycol diglycidyl ether
- covalent cross-linking agents such as polyhydric alcohols such as propanediol, glycerin and sorbitol
- polyvalent metal compounds such as aluminum salts.
- a polymerizable crosslinking agent with acrylic acid is more preferable, and an acrylate-based, allyl-based, and acrylamide-based polymerizable crosslinking agent is particularly preferable.
- These internal cross-linking agents may be used alone or in combination of two or more.
- the mixing ratio is preferably 10: 1 to 1:10.
- the amount of the internal cross-linking agent used is preferably 0.001 mol% to 5 mol%, more preferably 0.002 mol% to 2 mol%, with respect to the monomer excluding the crosslinker, from the viewpoint of physical properties. More preferably, it is 0.04 mol% to 1 mol%, particularly preferably 0.06 mol% to 0.5 mol%, and most preferably 0.07 mol% to 0.2 mol%. Furthermore, in a particularly preferred form of the present invention, the polymerizable crosslinking agent is preferably 0.01 mol% to 1 mol%, more preferably 0.04 mol% to 0.5 mol%, and still more preferably 0.06 mol%. Use ⁇ 0.1 mol%.
- the polymerization initiator used in the present invention is appropriately selected depending on the polymerization form and is not particularly limited, and examples thereof include a photodegradable polymerization initiator, a thermal decomposition polymerization initiator, and a redox polymerization initiator.
- photodegradable polymerization initiator examples include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds.
- thermal decomposition polymerization initiator examples include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide; 2 Azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride and 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride.
- persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate
- peroxides such as hydrogen peroxide, t-butyl peroxide, and methyl ethyl ketone peroxide
- 2 Azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride and 2,2′-azobis [2- (2-imidazolin-2-yl) propane]
- redox polymerization initiator examples include a system in which a reducing compound such as L-ascorbic acid or sodium bisulfite is used in combination with the persulfate or peroxide.
- the amount of the polymerization initiator used is preferably 0.0001 mol% to 1 mol%, more preferably 0.0005 mol% to 0.5 mol%, based on the monomer.
- the usage-amount of the said polymerization initiator exceeds 1 mol%, there exists a possibility that the color tone of a water absorbing resin may deteriorate.
- the amount of the polymerization initiator used is less than 0.0001 mol%, there is a concern about an increase in residual monomers, which is not preferable.
- the polymerization method may be to obtain a particulate hydrous gel by spray droplet polymerization or reverse phase suspension polymerization. From the viewpoint of (SFC) and water absorption rate (FSR), ease of polymerization control, and the like, aqueous solution polymerization is employed.
- the aqueous solution polymerization may be tank type (silo type) non-stir polymerization, but is preferably kneader polymerization or belt polymerization, more preferably continuous aqueous solution polymerization, further preferably high concentration continuous aqueous solution polymerization, particularly preferably high concentration / high temperature. Initiated continuous aqueous polymerization is employed.
- Stir polymerization means that a water-containing gel (particularly a water-containing gel having a polymerization rate of 10 mol% or more, more preferably 50 mol% or more) is polymerized while stirring, particularly stirring and fragmenting. Before and after the stirring-free polymerization, the monomer aqueous solution (with a polymerization rate of 0 mol% to less than 10 mol%) may be appropriately stirred.
- continuous aqueous solution polymerization examples include continuous kneader polymerization described in U.S. Pat. Nos. 6,987,171 and 6,710,141, U.S. Pat. Nos. 4,893,999, 6,241,928, U.S. Patent Application Publication No. 2005/215734, and the like. Continuous belt polymerization. By these aqueous solution polymerization, a water-absorbent resin powder can be produced with high productivity.
- the monomer concentration (solid content) is preferably 35% by weight or more, more preferably 40% by weight or more, and further preferably 45% by weight or more (the upper limit is a saturated concentration).
- the polymerization initiation temperature is preferably 30 ° C. or higher, more preferably 35 ° C. or higher, still more preferably 40 ° C. or higher, and particularly preferably 50 ° C. or higher (the upper limit is the boiling point).
- High concentration, high temperature starting continuous aqueous solution polymerization is a combination of these polymerizations.
- the high concentration / high temperature starting continuous aqueous solution polymerization is disclosed in US Pat. Nos. 6,906,159 and 7,091,253. This polymerization method is preferable because a water-absorbing resin powder having a high whiteness can be obtained and production on an industrial scale is easy.
- the polymerization method in the production method according to the present invention is preferably applied to a production apparatus on a huge scale with a large production amount per line.
- the production amount is preferably 0.5 t / hr or more, more preferably 1 t / hr or more, still more preferably 5 t / hr or more, and particularly preferably 10 t / hr or more.
- the polymerization can be carried out in an air atmosphere, but from the viewpoint of preventing coloring, it can be carried out in an inert gas atmosphere (for example, oxygen concentration of 1% by volume or less) such as water vapor, nitrogen or argon. preferable. Furthermore, it is preferable to perform polymerization after replacing (degassing) the dissolved oxygen in the monomer or the monomer-containing solution with an inert gas (for example, less than 1 mg / L of oxygen). Even if such deaeration is performed, the stability of the monomer is excellent, gelation before polymerization does not occur, and a water-absorbent resin powder having higher physical properties and higher whiteness can be provided.
- an inert gas atmosphere for example, oxygen concentration of 1% by volume or less
- an inert gas for example, less than 1 mg / L of oxygen
- the amount of the inert gas used is preferably 0.005% to 0.2% by weight, more preferably 0.01% to 0.1% by weight, and still more preferably 0.015%, based on the total amount of monomers. % By weight to 0.5% by weight. Moreover, as an inert gas used, nitrogen is preferable.
- a surfactant and / or a dispersant may be used as necessary.
- the surfactant and / or the dispersion liquid it is possible to stably suspend the bubbles in the water absorbent resin during polymerization.
- the water absorbing resin powder which has a desired physical property can be obtained by adjusting suitably the kind or quantity of surfactant and / or a dispersing agent.
- the surfactant is preferably a non-polymer surfactant and the dispersant is preferably a polymer dispersant.
- the surfactant and / or the dispersant is added at a stage before polymerization or before the temperature of the monomer aqueous solution at the time of polymerization reaches 50 ° C. or more.
- the amount of surfactant and / or dispersant used can be appropriately determined according to the type.
- the amount of the surfactant and / or dispersant used is such that the surface tension of the water-absorbent resin powder obtained is preferably 69 mN / m or more, more preferably 70 mN / m or more, and even more preferably 71 mN / m or more. decide.
- Suitable types and amounts of surfactants are as described in [2-8] above.
- (5-2) Gel Grinding Step This step is a step of obtaining a particulate hydrogel crosslinked polymer by fragmenting the hydrogel crosslinked polymer during or after the polymerization described above.
- this process is called “gel grinding” to distinguish it from “pulverization” in the following (5-4) grinding process / classification process.
- the method described in the first embodiment does not control the shape of the particles in the gel pulverization process, it is not necessary to use the gel pulverization apparatus described in the second embodiment in this process.
- a conventionally known pulverizer such as a meat chopper may be used in this step.
- the gel pulverization apparatus used in the gel pulverization step is the gel pulverization apparatus described in the second embodiment, and the configuration, temperature, and operating conditions of the gel pulverization apparatus are as follows. This is as described in Form 2.
- This step is a step of drying the particulate hydrogel obtained in the gel pulverization step to obtain a dry polymer.
- a drying method preferably applied in the present invention will be described. explain.
- drying method in the drying process of the present invention heat drying, hot air drying, vacuum drying, infrared drying, microwave drying, drum dryer drying, azeotropic dehydration drying with a hydrophobic organic solvent, high humidity using high temperature steam
- hot air drying is preferable, and in particular, hot air drying with a dew point of 40 ° C. to 100 ° C., more preferably 50 ° C. to 90 ° C. is preferably used.
- a ventilation dryer is preferable, and a ventilation belt type hot air dryer is more preferably used.
- the direction of the hot air used in the dryer is perpendicular to the hydrous gel layer laminated on the vent belt (for example, combined use in the vertical direction, Or, an upward direction or a downward direction) is essential.
- the ventilation belt type dryer is not used or when hot air in the vertical direction is not used, uniform drying cannot be performed, and physical properties such as liquid permeability may be deteriorated.
- the “vertical direction” refers to the upper and lower sides (from the top to the bottom of the gel layer, or the gel layer) with respect to the gel layer (particulate hydrogel having a thickness of 10 mm to 300 mm laminated on a punching metal or metal net). It refers to the state of ventilation from the bottom to the top), and is not limited to the strict vertical direction as long as it is vented in the vertical direction.
- hot air in an oblique direction may be used.
- the vertical direction is preferably within 30 °, more preferably within 20 °, still more preferably within 10 °, particularly preferably within 5 °, most preferably. 0 ° hot air is used.
- the drying temperature in the drying step of the present invention is preferably 100 ° C. to 300 ° C., more preferably 150 ° C. to 250 ° C., still more preferably 160 ° C. to 220 ° C., particularly preferably. Is 170 ° C. to 200 ° C.
- both shortening of the drying time and reduction of coloring of the obtained dry polymer can be achieved.
- the liquid permeability of the obtained water absorbent resin powder preferably both the liquid permeability and the water absorption rate tend to be improved.
- a drying temperature exceeds 300 degreeC, there exists a possibility that a polymer chain may be affected and a physical property may fall.
- the drying temperature is less than 100 ° C., there is no change in the water absorption rate, and an undried product is generated, and clogging occurs during the subsequent pulverization step.
- the drying time in the drying step in the present invention depends on the surface area of the particulate water-containing gel, the type of the dryer, etc., and is appropriately set so as to achieve the desired moisture content. However, it is preferably 1 minute to 10 hours, more preferably 5 minutes to 2 hours, still more preferably 10 minutes to 1 hour, particularly preferably 15 minutes to 45 minutes.
- the time until the particulate hydrogel discharged from the gel grinding step (5-2) is introduced into the drying step that is, the particulate hydrogel moves from the outlet of the gel grinding device to the dryer inlet.
- the time is preferably shorter from the viewpoint of coloring with the water-absorbent resin powder, specifically, preferably within 2 hours, more preferably within 1 hour, further preferably within 30 minutes, particularly preferably within 10 minutes, Most preferably, it is within 2 minutes.
- the air velocity of the hot air in the above-described ventilation dryer is preferably in the vertical direction (vertical direction), preferably 0.8 m / s. Is 2.5 m / s, more preferably 1.0 m / s to 2.0 m / s.
- the said wind speed is less than 0.8 m / s, drying time is delayed and there exists a possibility that the liquid permeability and water absorption speed of the water absorbent resin powder obtained may be inferior.
- the said wind speed exceeds 2.5 m / s, there exists a possibility that a particulate water-containing gel may rise during a drying period, and the stable drying may be difficult.
- the above wind speed may be controlled within a range that does not impair the effects of the present invention.
- it is preferably controlled within a range of preferably 70% or more, more preferably 90% or more, and still more preferably 95% or more of the drying time. That's fine.
- the said wind speed is represented by the average flow velocity of the hot air which passes a perpendicular
- the hot air used in the ventilating belt dryer contains at least water vapor and has a dew point of preferably 30 ° C. to 100 ° C., more preferably 30 ° C. to 80 ° C. Residual monomer can be reduced by controlling the dew point of hot air or, more preferably, the gel particle size within the above range, and further the reduction of the bulk specific gravity of the dried polymer can be prevented.
- the dew point is a value when the moisture content of the particulate hydrogel is at least 10% by weight, preferably at least 20% by weight.
- the dew point is high in the initial stage of drying; Specifically, it is preferable that hot air having a dew point of 10 ° C. to 50 ° C., more preferably 15 ° C. to 40 ° C. higher than that near the dryer outlet is brought into contact with the particulate hydrous gel near the dryer inlet.
- the particulate hydrogel obtained in the gel pulverization step is dried in the main drying step to obtain a dry polymer, and is obtained from its loss on drying (1 g of powder or particles is heated at 180 ° C. for 3 hours).
- the resin solid content is preferably more than 80% by weight, more preferably 85% by weight to 99% by weight, still more preferably 90% by weight to 98% by weight, and particularly preferably 92% by weight to 97% by weight.
- the surface temperature of the particulate hydrogel obtained in the gel pulverization step immediately before being charged into the dryer is preferably 40 ° C to 110 ° C, more preferably 60 ° C to 110 ° C, and further The temperature is preferably 60 ° C to 100 ° C, particularly preferably 70 ° C to 100 ° C.
- the temperature is less than 40 ° C., a balloon-like dried product is generated at the time of drying, and a lot of fine powder is generated at the time of pulverization, which may cause a decrease in physical properties of the water absorbent resin.
- the surface temperature of the particulate hydrogel before drying exceeds 110 ° C., the water-absorbent resin may be deteriorated (for example, increased in water-soluble content) or colored after drying.
- Pulverization step and classification step This step is a step of pulverizing and classifying the dried polymer obtained in the drying step to obtain water-absorbing resin particles.
- the (5-2) gel pulverization step is different from the resin solid content at the time of pulverization, particularly in that the object to be pulverized has undergone a drying step (preferably dried to the resin solid content).
- the water-absorbent resin particles obtained after the pulverization step may be referred to as a pulverized product.
- the water absorbent resin powder according to the present invention needs to be surface-crosslinked as described in the following (5-5). Therefore, it is preferable to control to a specific particle size in order to improve physical properties in the surface crosslinking step.
- the particle size control can be appropriately performed not only in the main pulverization step and the classification step, but also in a polymerization step, a fine powder recovery step, a granulation step, and the like.
- the particle size is defined by a standard sieve (JIS Z8801-1 (2000)) as described above.
- the pulverizer that can be used in the pulverization process is not particularly limited.
- vibration mill, roll granulator, knuckle type pulverizer, roll mill, high-speed rotary pulverizer (pin mill, hammer mill, screw mill), cylindrical mixer, etc. can be mentioned.
- classification operation is performed so as to have the following particle size.
- the classification operation is preferably performed before the surface crosslinking step ( The first classification step) and the classification operation (second classification step) may be performed after the surface crosslinking.
- the classification operation is not particularly limited, but classification is performed as follows in sieving using a sieve. That is, when the particle size distribution of the water-absorbent resin particles is set to 150 ⁇ m to 850 ⁇ m, for example, first, the pulverized product is sieved with a sieve having an opening of 850 ⁇ m, and the pulverized product that has passed through the sieve has an opening of 150 ⁇ m or 150 ⁇ m. Further sieving with an excess sieve (eg 200 ⁇ m). The pulverized product remaining on the sieve having an opening of 150 ⁇ m or the like becomes water absorbent resin particles having a desired particle size distribution. In addition to sieving classification, various classifiers such as airflow classification can also be used.
- the water absorbent resin powder according to the present invention can satisfy the condition that the proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is 90% by weight or more.
- the water absorbent resin powder according to the present invention has a polyacrylic acid (salt) -based water absorbent resin as a main component and is surface crosslinked.
- the surface treatment step for performing surface crosslinking includes a surface crosslinking step performed using a known surface crosslinking agent and a surface crosslinking method, and further includes other addition steps as necessary.
- Examples of the surface cross-linking agent that can be used in the present invention include various organic or inorganic cross-linking agents, and organic surface cross-linking agents are preferable.
- a surface cross-linking agent a polyhydric alcohol compound, an epoxy compound, a polyvalent amine compound or a condensate thereof with a haloepoxy compound, an oxazoline compound, a (mono, di, or poly) oxazolidinone compound, an alkylene carbonate compound
- a dehydration-reactive crosslinking agent composed of a polyhydric alcohol compound, an alkylene carbonate compound, or an oxazolidinone compound, which requires a reaction at a high temperature, can be used.
- the amount of the surface cross-linking agent to be used is suitably determined from about 0.001 to 10 parts by weight, more preferably about 0.01 to 5 parts by weight, with respect to 100 parts by weight of the water-absorbent resin particles.
- Water is preferably used in accordance with the surface cross-linking agent.
- the amount of water used is preferably in the range of 0.5 to 20 parts by weight, more preferably in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the water-absorbent resin particles.
- the inorganic surface cross-linking agent and the organic surface cross-linking agent are used in combination, it is preferably in the range of 0.001 to 10 parts by weight, more preferably 0.01 parts by weight with respect to 100 parts by weight of the water-absorbent resin particles. Used in the range of 5 parts by weight to 5 parts by weight.
- a hydrophilic organic solvent may be used, and the amount used is preferably in the range of 0 to 10 parts by weight, more preferably 0 parts by weight, relative to 100 parts by weight of the water-absorbent resin particles.
- the range is from 5 parts by weight.
- the crosslinking agent solution is mixed with the water-absorbent resin particles, the range does not hinder the effect of the present invention, for example, preferably 0 to 10 parts by weight, more preferably 0 to 5 parts by weight, and still more preferably.
- Is 0 to 1 part by weight, and a water-insoluble fine particle powder or a surfactant may coexist.
- the surfactant used or the amount of use thereof is exemplified in US Pat. No. 7,473,739.
- a vertical or horizontal high-speed rotary stirring mixer is preferably used.
- the rotational speed of the mixer is preferably 100 rpm to 10,000 rpm, more preferably 300 rpm to 2,000 rpm.
- the residence time of the water absorbent resin in the apparatus is preferably within 180 seconds, more preferably from 0.1 second to 60 seconds, and even more preferably from 1 second to 30 seconds.
- a surface cross-linking method using a radical polymerization initiator (US Pat. No. 4,783,510, International Publication No. 2006/062258) or water absorption instead of surface cross-linking using the above-described surface cross-linking agent.
- a surface crosslinking method in which a monomer is polymerized on the surface of the conductive resin (US Application Publication Nos. 2005/048221, 2009/0239966, and International Publication No. 2009/048160) may be used.
- the radical polymerization initiator preferably used is a persulfate, and preferable monomers used as necessary include acrylic acid (salt) or other cross-linking agents described above,
- the preferred solvent used is water.
- Non-binding surface cross-linking agent In this invention, you may further include the addition process which adds any one or more of a polyvalent metal salt, a cationic polymer, or an inorganic fine particle simultaneously or separately with the surface crosslinking process mentioned above. That is, in addition to the organic surface cross-linking agent, an inorganic surface cross-linking agent may be used or used in combination to improve liquid permeability and water absorption rate. The inorganic surface crosslinking agent can be used simultaneously with or separately from the organic surface crosslinking agent.
- examples of the inorganic surface cross-linking agent to be used include divalent or higher, preferably trivalent or tetravalent polyvalent metal salts (organic salts or inorganic salts) or hydroxides.
- examples of the polyvalent metal that can be used include aluminum and zirconium, and examples thereof include aluminum lactate and aluminum sulfate. An aqueous solution containing aluminum sulfate is preferred.
- a cationic polymer particularly a weight average molecular weight of about 5,000 to 1,000,000 may be used simultaneously or separately to improve liquid permeability.
- the cationic polymer used is preferably, for example, a vinylamine polymer or the like.
- inorganic fine particles may be added.
- silicon dioxide or the like is preferable, and exemplified in US Pat. No. 7,638,570.
- the water-absorbent resin powder according to the present invention it is preferable to include a step of adding any one or more of the polyvalent metal, the cationic polymer, and the inorganic fine particles.
- These additives are preferably used simultaneously or separately with the above-described covalently-bonded surface cross-linking agent, and can further solve the problem of the present invention (improvement of liquid diffusion absorption characteristics).
- a surfactant having reactivity or polymerizability with the water absorbent resin powder or its monomer for example, unsaturated polymerizable group (especially ⁇ , ⁇ -unsaturated).
- a surfactant having a saturated double bond), a reactive group (hydroxyl group or amino group), or a hydrophilic surfactant having a high solubility in water for example, HLB is 1 to 18, particularly preferably 8 to 15).
- HLB is 1 to 18, particularly preferably 8 to 15.
- a nonionic surfactant is preferably selected, more preferably a nonionic surfactant having a polyoxyethylene chain in the molecule, and still more preferably a polyoxyethylene sorbitan fatty acid ester.
- the amount of these surfactants to be used depends on the type of surfactant to be used or the target physical properties (especially the water absorption speed and surface tension), but is typically preferable to the amount of monomers used. Is more than 0 and less than or equal to 2% by weight, more preferably more than 0 and less than or equal to 0.03% by weight, even more preferably more than 0 and less than 0.015% by weight, particularly preferably more than 0 and less than 0.01% by weight, most preferably Is more than 0 and 0.008% by weight or less.
- the amount of the surfactant used can be applied to the water-absorbing resin powder after polymerization, and if necessary, as a final product obtained after coating with the surfactant described in “[2-6] Surface cross-linking”. It is applicable also to this water-absorbent resin powder.
- water absorbent resin powder The use of the water absorbent resin powder according to the present invention is not particularly limited, but it is preferably used for absorbent articles such as paper diapers, sanitary napkins, incontinence pads, and the like. Excellent performance when used in high-concentration diapers (paper diapers that use a large amount of water-absorbent resin per paper diaper).
- the “absorber” includes at least the water-absorbent resin powder according to the present invention, and optionally contains other absorbent materials (fibrous materials such as pulp fibers).
- the said absorber contains the water absorbing resin powder manufactured by the manufacturing method mentioned above, and the said absorber is used for an absorbent article.
- the content of the water absorbent resin in the absorbent body is preferably 30% by weight.
- core concentration that is, the content of the water absorbent resin powder with respect to the total amount of the water absorbent resin powder and the fibrous material
- core concentration is preferably 30% by weight.
- core concentration that is, the content of the water absorbent resin powder with respect to the total amount of the water absorbent resin powder and the fibrous material.
- the water-absorbent resin powder according to the present invention when used at the above-mentioned concentration, it has excellent diffusion absorption ability of absorption liquid such as urine due to high diffusion absorption characteristics, so that liquid distribution is efficiently performed and absorption of the entire absorbent article As the amount improves, quick liquid absorption can be realized. Furthermore, an absorbent article using an excellent absorbent body can be provided.
- the said absorber for absorbent articles, such as a paper diaper, a sanitary napkin, an incontinence pad, a medical pad
- the liquid-permeable top sheet arrange
- a liquid impervious backsheet disposed adjacent to the wearer's garment away from the wearer's body
- an absorbent body disposed between the topsheet and the backsheet It is used in the configuration consisting of
- the absorber may be two or more layers, and may be used together with a pulp layer or the like.
- the present invention will be described according to examples, but the present invention is not construed as being limited to the examples.
- the physical properties described in the claims or examples of the present invention are the EDANA method and the following measuring methods under conditions of room temperature (20 ° C. to 25 ° C.) and humidity of 50 RH% unless otherwise specified. Sought according to.
- the electrical equipment presented in the examples and comparative examples used a power supply of 200 V or 100 V and 60 Hz.
- “liter” may be described as “L”
- wt%” may be described as “wt%”.
- the physical property affected by the moisture content is evaluated by a value obtained by correcting the measured value with the moisture content.
- the moisture content correction value can be obtained by dividing the actually measured value by (1-water content / 100).
- the moisture content correction value was expressed as a value for 100 parts by weight of the solid content of the water absorbent resin powder.
- the water-absorbent resin powder incorporated in absorbent articles such as paper diapers distributed in the market normally absorbs moisture, so the CRC, particle size, etc. are the correct values inherent in the water-absorbent resin powder. Absent. Therefore, when the moisture content exceeds 10% by weight (especially 20% by weight), for example, after drying under reduced pressure at 60 ° C. ⁇ 16 hours ⁇ 10 mmHg to reduce the moisture content to 10% by weight or less, the physical properties Can be measured.
- Particle size distribution Particle size distribution
- D50 weight average particle size
- ⁇ logarithmic standard deviation
- the particle size distribution (PSD) of the water-absorbent resin powder according to the present invention was measured according to the EDANA method (ERT420.2-02).
- the weight average particle diameter (D50) and the logarithmic standard deviation ( ⁇ ) of the particle size distribution are described in US Pat. No. 7,638,570, “(3) Mass-Average Particle Diameter (D50) and Logical Standard Deviation ( ⁇ ) of”. Measurement was performed according to “Particle Diameter Distribution”.
- EMI Modulus of elasticity
- the water absorbent resin powder obtained by sieving using the above sieve having an opening of 600 ⁇ m in the upper stage and the above sieve having an opening of 500 ⁇ m in the lower stage has a particle diameter of 500 ⁇ m or more and less than 600 ⁇ m.
- the elastic modulus index measured using a water-absorbing resin powder having a particle size (particle size) of 500 ⁇ m or more and less than 600 ⁇ m is an elastic modulus index (600-500).
- the said Formula (9) is a type
- the weight of the gel particles after swelling may not be exactly 2.00 g due to errors in measurement, and weight correction is performed in that case.
- CRCdw in Formula (9) is CRC (centrifuge retention capacity) when swollen with pure water.
- the CRCdw used in the following (6) CRC measurement uses pure water instead of 0.9 wt% sodium chloride aqueous solution, the sample amount is changed from 0.2 g to 0.05 g, and the immersion time is 30 minutes. It is calculated
- the swollen gel 41 obtained in the above procedure 2 is put into the dish 40 (inner diameter: 51 mm, depth: 10 mm / aluminum) of the rheometer 300 together with the swollen liquid (pure water). Evenly arranged within 40.
- the dish 40 is fixed to the rheometer 300, and the rheometer 300 and the dish 40 are installed so as to be strictly horizontal.
- a parallel plate 42 (diameter: 50 mm / aluminum) in which the rotating shaft 43 is vertically installed is fitted into the dish 40, and then the rotating shaft 43 is rotated in the direction of the arrow in FIG. A vibration was given.
- the storage elastic modulus was measured under the following measurement conditions.
- Measurement mode Vibration (dynamic) measurement Strain: 0.02% (error ⁇ 2%)
- Angular frequency 10 rad / s (error ⁇ 2%)
- Measurement interval 5 seconds
- Number of measurement points 20 Point x 7 load condition
- the dish 40 and the parallel plate 42 used in the above measurement use a new one each time, or wash thoroughly after use and polish the dried one (cloth made by Trusco Nakayama Co., Ltd., substrate: cotton, polished) Agent: Polished with A abrasive (particle size: # 15000), containing wax, and then washed again.
- the amount of distortion and the angular frequency were appropriately selected under the conditions where the measured value was stable within the above range.
- the arithmetic average value of the measured values of a total of 5 points obtained in a measurement time of 600 seconds to 700 seconds is the elastic modulus G ′ ( Unit: Pa).
- the elastic modulus index (EMI) was calculated based on the following formulas (3) and (10) to (17) using the above elastic modulus and the following CRC and CRCdw values.
- the elastic modulus index (EMI) is a value obtained by correcting the elastic modulus G ′ by the theoretical surface area and CRC of the swollen gel, and serves as an index for judging the performance of the water absorbent resin powder.
- the elastic modulus index is abbreviated as EMI.
- CRC is a value measured for the water-absorbent resin powder before performing the procedure 1 in the measurement of the elastic modulus.
- the “swelling gel” is obtained by the procedure 2 in the measurement of the elastic modulus.
- the internal cell ratio of the water-absorbent resin powder was calculated according to the following formula (5).
- the diameter of the internal bubbles (closed cells) present in the water absorbent resin powder is usually 1 ⁇ m to 300 ⁇ m, but at the time of pulverization, the water absorbent resin powder is preferentially pulverized from a portion close to the closed cells. Therefore, when the water absorbent resin powder is pulverized until the particle diameter is less than 45 ⁇ m, the obtained water absorbent resin powder contains almost no closed cells. Therefore, the dry density of the water-absorbent resin powder pulverized to less than 45 ⁇ m was evaluated as a true density in the present invention.
- the surface tension of the physiological saline is measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). Measured. In this measurement, the surface tension value must be in the range of 71 mN / m to 75 mN / m.
- the CRC of the water-absorbent resin powder according to the present invention was measured according to the EDANA method (ERT441.2-02). That is, 0.200 g of water-absorbent resin powder was weighed, uniformly placed in a non-woven bag (60 ⁇ 60 mm) and heat-sealed, and then 0.9 mL of a 0.9 wt% sodium chloride aqueous solution adjusted to 25 ⁇ 3 ° C. Soaked in. After 30 minutes, the bag was pulled up and drained using a centrifuge (centrifuge manufactured by Kokusan Co., Ltd., type: H-122) at 250 G for 3 minutes.
- a centrifuge centrifuge manufactured by Kokusan Co., Ltd., type: H-122
- the CRCdw of the water absorbent resin powder according to the present invention is as follows: 0.9 wt% sodium chloride aqueous solution in pure water, water absorbent resin powder amount from 0.200 g to 0.05 g, and free swelling time from 30 minutes to 16 hours. The calculation was performed according to the equation (4) by performing the same operation as the CRC except that each was changed.
- AAP of the water-absorbent resin powder according to the present invention was measured according to the EDANA method (ERT442.2-02).
- (11) Diffusion Absorption Time The diffusion absorption time of the water absorbent resin powder according to the present invention was measured by the following procedure. In addition, the diffusion absorption time measuring apparatus 200 shown in FIG. 2 was used for the measurement. The measurement apparatus will be described.
- the diffusion absorption time measuring device 200 shown in FIG. 2 is a measuring device manufactured to simulate the performance of absorbent articles such as paper diapers.
- 30 is a tray
- 31 is a water-absorbing resin powder spraying part
- 32 is a water-absorbing resin powder
- 33 is a top sheet
- 34 is a wire mesh
- 35 is a slot
- 36 is an upper lid
- 37 is a weight. ing.
- the material of the tray 30 and the upper lid 36 is not particularly limited, but preferably an acrylic resin, polypropylene, Teflon (registered trademark) resin, or the like can be used.
- the spraying unit 31 uses an appropriate amount of water-absorbing resin powder 32 and performs uniform absorption, so that the center of the tray 30 has an area that is about 1 ⁇ 2 of the area of the bottom surface of the recess of the tray 30. It is preferable to make it.
- the water-absorbent resin powder 32 is preferably in such an amount that it can be sprayed evenly on the sprayed portion 31 with as little gap as possible. In order to perform uniform absorption, it is preferable to apply an antistatic agent to the tray 30 or blow a breath so that static electricity is not generated before spraying.
- the top sheet 33 is a sheet containing a non-woven fabric and paper that are arranged on the most wearer side in an absorbent article such as a paper diaper, and uses a conventionally known one, for example, one recovered from the absorbent article. can do.
- a product obtained from Unicharm Co., Ltd., trade name Mummy Pokotape type, L size (purchased in Japan in June 2014, package bottom number: 4040888043) is used. However, it is not limited to this.
- the top sheet 33 can completely cover the spraying portion 31 and does not exceed the size of the concave portion of the tray 30. Furthermore, it is preferable that the distance from the inner wall of the tray 30 is the same in the horizontal direction and the vertical direction. In FIG. 2, the long side direction of the tray 30 is a horizontal direction, and the short side direction of the tray 30 is a vertical direction.
- the wire mesh 34 is used for diffusing the 0.9 wt% sodium chloride aqueous solution introduced from the introduction port 35 while allowing it to permeate.
- the material of the wire mesh 34 is not particularly limited, but is preferably made of stainless steel.
- the size (opening) of the holes of the wire mesh 34 is preferably 600 ⁇ m to 2000 ⁇ m, more preferably 1000 ⁇ m to 1500 ⁇ m.
- a JIS wire mesh made of stainless steel, 14 mesh, a mesh size of 1.21 mm, and a wire diameter of 0.6 mm is used as the wire mesh 34.
- the weight 37 may be anything as long as a load can be applied evenly to the water-absorbent resin powder 32, and the material, the number, and the like are not particularly limited.
- the load is preferably 35 g / cm 2 to 500 g / cm 2 with respect to the spray area of the water absorbent resin powder 32 (the area of the spray part 31).
- the four weights 37 are placed at the four corners of the upper lid 36, but the embodiment is not limited to this mode as long as a load can be applied evenly.
- two rectangular parallelepiped weights whose long sides are the same as the short sides of the upper lid 36 may be placed on the upper lid 36 along the short sides of the upper lid 36.
- the inlet 35 is preferably installed at the center of the upper lid 36 as shown in FIG. 2 in order to perform uniform absorption.
- the upper lid 36 is preferably slightly smaller than the inner dimension of the tray 30 in order to fit into the concave portion of the tray 30.
- FIG. 4 is a top view (FIG. 4A) and a side view (FIG. 4B) of the upper lid 36 provided with the insertion hole 35, and a top view of the tray 30 (FIG. 4C). And a side view ((d) of FIG. 4).
- a represents the inner diameter of the insertion hole 35
- b and c represent the horizontal and vertical dimensions of the upper lid 36
- d represents the height of the cylindrical portion of the insertion hole 35.
- E corresponds to the thickness of the upper lid 36.
- FIG. 4 shows the positional relationship of the water absorbent resin powder spraying portion 31 in the tray 30.
- FIG. 4D is the side view.
- f and g indicate that the water absorbent resin powder spraying portion 31 is located 100.5 mm inside from each inner wall in the vertical direction, and h indicates the water absorbent resin powder spraying portion 31.
- the horizontal dimension (200 mm) is shown.
- i indicates the inner dimension (401 mm) of the tray 30, j indicates the inner dimension of the tray 30 and the vertical dimension (151 mm) of the water absorbent resin powder spraying portion 31, and k and l indicate the inner dimensions of the tray 30, respectively.
- the difference (5 mm) between the outer dimensions “m” indicates a lateral outer dimension (411 mm) of the tray 30, and “n” indicates a height (35 mm) of the tray 30.
- a top sheet 33 was placed on the sprayed water absorbent resin powder 32.
- the top sheet 33 was arranged such that the distance from the inner wall of the tray 30 was the same in the horizontal direction and the vertical direction.
- the said top sheet 33 used the thing taken out from Unicharm Co., Ltd. brand name Mummy Pokotape type, L size (June 2014 purchase in Japan, number on the bottom of a package: 4040888043).
- the removed top sheet had a size of 14 cm long ⁇ 39 cm wide and a weight of 3.3 g to 3.6 g.
- the pulp etc. in the paper diaper adhered with the adhesive, it was used after fully removing.
- a wire mesh 34 (size; width 398 mm ⁇ length 148 mm / JIS wire mesh, stainless steel, 14 mesh, mesh opening 1.21 mm, wire diameter 0.6 mm) was placed.
- an acrylic resin top cover 36 having a cylindrical inlet 35 with an inner diameter of 70 mm at the center (size: width 400 mm ⁇ length 150 mm, thickness: 20 mm, height of the cylinder portion: 70 mm) was placed.
- a stainless steel weight 37 was placed on the upper lid 36 so that the water absorbent resin powder 32 was evenly loaded.
- the weights of the weight 37 and the like were adjusted so that the total weight of the wire mesh 34, the acrylic resin upper lid 36 and the weight 37 was 5672 g (the load was 9.45 g / weight relative to the area of the wire mesh 34). cm 2 , 18.78 g / cm 2 for the sprayed area of the water absorbent resin powder 32).
- aqueous sodium chloride aqueous solution 60 g was charged from the charging port 35 provided on the upper lid 36 in 5 seconds. The introduced liquid diffused on the wire mesh 34 while passing through the wire mesh 34, and was then absorbed by the water absorbent resin powder 32.
- the aqueous sodium chloride solution may be colored with Blue No. 1 (0.04 g added to 1000 g of aqueous solution).
- the time (first time) until the entire amount of the liquid retained between the meshes of the wire mesh 34 was absorbed by the water absorbent resin powder was measured.
- the swollen gel may protrude from the outer edge portion of the wire mesh 34, and in this case, it may be difficult to determine the absorption of the liquid. Therefore, the measurement of the time was performed by excluding the portion of the outer edge of the wire mesh 34 of about 1 cm.
- the total of the first to fourth times obtained by the above operation was taken as the diffusion absorption time of the present invention.
- a continuous manufacturing apparatus composed of processes was prepared.
- the production capacity of the continuous production apparatus is about 3500 kg / hr, and the above steps may be one series or two series or more, respectively. In the case of two or more series, the production capacity is indicated by the total amount of each series.
- polyacrylic acid (salt) -based water absorbent resin powder was produced continuously.
- a monomer aqueous solution (1) comprising 52 parts by weight of a methylenephosphonic acid) 5 sodium aqueous solution and 134 parts by weight of deionized water was prepared.
- the monomer aqueous solution (1) adjusted to 40 ° C. is continuously supplied to the continuous production apparatus by a metering pump, and then 97.1 parts by weight of a 48 wt% sodium hydroxide aqueous solution is continuously added to the line. Mixing. At this time, the temperature of the aqueous monomer solution (1) rose to 85 ° C. due to heat of neutralization.
- a continuous polymerization machine having a planar polymerization belt with weirs at both ends has a thickness of about 7.5 mm.
- the monomer aqueous solution (1) was continuously supplied.
- polymerization (polymerization time 3 minutes) was continuously carried out to obtain a strip-like hydrogel (1).
- the band-shaped hydrogel (1) was continuously cut at equal intervals so that the cut length was about 300 mm in the width direction with respect to the traveling direction of the polymerization belt.
- the hydrogel (1) having a cutting length of about 300 mm was supplied to a screw extruder and gel pulverized (gel pulverization step).
- a meat chopper having a diameter of 340 mm, a hole diameter of 22 mm, a hole number of 105, a hole plate ratio of 52%, a thickness of 20 mm and a screw shaft diameter of 152 mm was used.
- the hydrous gel (1) was supplied at 132800 g / min, and at the same time, hot water at 70 ° C. was supplied at 855.8 g / min and water vapor at 3333 g / min.
- the gel grinding energy (GGE) at this time was 27.8 J / g, and the gel grinding energy (2) (GGE (2)) was 15.5 J / g.
- the current value of the meat chopper during gel pulverization was 104.7 A on average.
- the temperature of the hydrogel (1) before gel pulverization was 90 ° C., and the temperature of the comparative pulverized gel after gel pulverization, that is, the comparative particulate hydrogel (1) was lowered to 85 ° C.
- the comparative particulate water-containing gel (1) was sprayed on the ventilation belt within 1 minute after the completion of the gel grinding (the temperature of the comparative particulate water-containing gel (1) at this time was 80 ° C.), and 30 ° C. at 185 ° C. Drying was performed for a minute (drying step), and 246 parts by weight of the comparative dry polymer (1) (total discharge amount in the drying step) was obtained.
- the moving speed of the ventilation belt was 1 m / min, and the average wind speed of hot air was 1.0 m / s in the direction perpendicular to the traveling direction of the ventilation belt.
- the wind speed of the hot air was measured with a constant temperature thermal anemometer Anemomaster 6162 manufactured by Nippon Kanomax Co., Ltd.
- the total amount of the comparative dry polymer (1) of about 60 ° C. obtained in the above drying step was continuously supplied to a three-stage roll mill and pulverized (pulverization step), and then further passed through a JIS standard sieve having openings of 710 ⁇ m and 175 ⁇ m. By classifying, comparatively water-absorbent resin particles (1) of irregularly crushed shape were obtained.
- Comparative water-absorbent resin particles (1) have a weight average particle diameter (D50) of 340 ⁇ m, a logarithmic standard deviation of particle size distribution ( ⁇ ) of 0.32, a CRC of 32.0 g / g, a water-soluble content of 6.9% by weight, 150 ⁇ m passing particles (the ratio of particles passing through a sieve having an opening of 150 ⁇ m) was 0.7% by weight.
- the comparative water absorbent resin particles (1) for 100 parts by weight of the comparative water absorbent resin particles (1), 0.3 parts by weight of 1,4-butanediol, 0.6 parts by weight of propylene glycol and 3.0 parts by weight of deionized water ( Covalent bond) Surface crosslinker solution (1) is uniformly mixed, and the CRC of the comparative water absorbent resin powder (1) obtained is about 26.6 g / g to 27.4 g / g for about 40 minutes at 208 ° C. It heat-processed so that it might become inside.
- the comparative water absorbent resin powder (1) obtained by the above operation was classified with a JIS standard sieve having openings of 710 ⁇ m and 500 ⁇ m to obtain particles having a particle size of 500 ⁇ m or more and less than 710 ⁇ m.
- the ratio of flaky particles (particles with a thickness of approximately 300 ⁇ m or less) contained in particles having a particle size of 500 ⁇ m or more and less than 710 ⁇ m is observed with an electron microscope (electron microscope; observed using 3D measurement function of VE-9800 manufactured by Keyence Corporation) ), It was 16% (32 out of 200 particles were flaky particles).
- Example 1 The comparative water absorbent resin powder (1) obtained in Comparative Example 1 was classified with a JIS standard sieve having openings of 710 ⁇ m and 500 ⁇ m to obtain particles having a particle size of 500 ⁇ m or more and less than 710 ⁇ m and particles having a particle size of less than 500 ⁇ m. Among them, particles having a particle size of 500 ⁇ m or more and less than 710 ⁇ m were classified with a sieve covered with a toncap wire net having a rectangular mesh (long: 728 ⁇ m, short: 335 ⁇ m), and flaky particles were removed.
- the ratio of the weight of the removed flaky particles to the weight of the particles having a particle size of 500 ⁇ m or more and less than 710 ⁇ m subjected to the sieve was 17.1% by weight. Further, when the particles were observed with an electron microscope, no flaky particles were found.
- the water absorbent resin powder (1) had an internal cell ratio of 2.1%, a surface tension of 72 mN / m, and AAP0.3 of 28.3 g / g.
- Table 3 shows the water absorption time and diffusion absorption time of the water absorbent resin powder (1) by CRC, EMI, vortex method.
- Table 5 shows the measurement results of the elastic modulus of the water absorbent resin powder (1).
- Comparative Example 2 In Comparative Example 1, the same operation as in Comparative Example 1 was performed except that the amount of polyethylene glycol diacrylate (average n number; 9) was changed to 1.05 parts by weight, and the strip-shaped hydrogel (2) and A cut hydrous gel (2) was obtained.
- the cut hydrous gel (2) obtained by the above operation was mounted with a perforated plate having a diameter of 100 mm, a die hole diameter of 9.5 mm, and a die thickness of 10 mm.
- S86-445 see Table 1 for screw shape
- B88-874 see Table 2 for the barrel shape
- the hydrated gel (2) was cut at 360 g / min (60 g of gel was 10% with the rotational speed of the screw rotating shaft being 172 rpm). The gel was crushed.
- a comparative particulate hydrous gel (2) was obtained.
- Comparative Example 1 drying step, pulverizing step, classification with JIS standard sieves having openings of 710 ⁇ m and 175 ⁇ m
- Comparative water-absorbent resin particles (2) were obtained.
- the surface cross-linking agent solution (2) was uniformly mixed and heat-treated at 208 ° C. for about 40 minutes. Thereafter, cooling is performed, from 1.17 parts by weight of 27.5% by weight aluminum sulfate aqueous solution (8% by weight in terms of aluminum oxide), 0.196 parts by weight of 60% by weight sodium lactate aqueous solution and 0.029 parts by weight of propylene glycol. The resulting (ion binding) surface cross-linking agent solution (2) was mixed uniformly.
- a comparative water absorbent resin powder (2) was crushed (size-regulating step) until it passed through a JIS standard sieve having a mesh size of 710 ⁇ m to obtain a comparative water absorbent resin powder (2).
- Table 3 shows the water absorption time and diffusion absorption time by CRC, EMI, vortex method of the comparative water absorbent resin powder (2).
- Table 6 shows the elastic modulus measurement results of the comparative water absorbent resin powder (2).
- AAP0.3 of the obtained comparative water absorbent resin powder (2) was 28.1 g / g.
- Example 2 In Comparative Example 2, the screw was S86-4610 (see Table 1 for screw shape), barrel no. A water-absorbent resin particle (2) and a water-absorbent resin powder (2) were obtained in the same manner as in Comparative Example 2, except that each was changed to B88-178 (see Table 2 for the barrel shape).
- the water absorbing resin powder (2) had an internal cell ratio of 1.9% and a surface tension of 72 mN / m.
- Table 3 shows the water absorption time and diffusion absorption time by CRC, EMI, vortex method of the water absorbent resin powder (2).
- Table 7 shows the elastic modulus measurement results of the water absorbent resin powder (2).
- Example 3 In Comparative Example 1, the same operation as in Comparative Example 1 was performed except that the amount of polyethylene glycol diacrylate (average n number; 9) was changed to 0.84 parts by weight, and the strip-shaped hydrogel (3) and A cut hydrous gel (3) was obtained.
- the amount of polyethylene glycol diacrylate average n number; 9 was changed to 0.84 parts by weight, and the strip-shaped hydrogel (3) and A cut hydrous gel (3) was obtained.
- the water-absorbent resin particles were subjected to the same operation as in Example 2 except that the die hole diameter of the porous plate used at the time of gel pulverization was changed to 8.0 mm. (3) and water absorbent resin powder (3) were obtained.
- Table 3 shows the water absorption time and diffusion absorption time of the water absorbent resin powder (3) by CRC, EMI, and vortex method.
- Table 8 shows the elastic modulus measurement results of the water absorbent resin powder (3).
- AAP0.3 of the obtained water absorbent resin powder (3) was 28.3 g / g.
- Example 4 In the said comparative example 1, except having changed the usage-amount of polyethyleneglycol diacrylate (average n number; 9) into 0.70 weight part, operation similar to the comparative example 1 was performed, and a strip
- the cut water-containing gel (4) obtained by the above operation was subjected to the same operation as in Example 2 to obtain water absorbent resin particles (4) and water absorbent resin powder (4).
- Table 3 shows the water absorption time and diffusion absorption time of the water absorbent resin powder (4) by CRC, EMI, vortex method.
- Table 9 shows the elastic modulus measurement results of the water absorbent resin powder (4).
- AAP0.3 of the obtained water absorbent resin powder (4) was 32.0 g / g.
- Comparative water-absorbent water-absorbent resin powder (amorphous crushed particles) taken from paper diapers purchased in Belgium in June 2013 (Procter & Gamble Co., Ltd .: trade name “Papers Easy Up Pants”, size 4 Maxi) Resin powder (3) was obtained.
- Table 3 shows the water absorption time and diffusion absorption time of the comparative water absorbent resin powder (3) by CRC, EMI, vortex method.
- Table 10 shows the elastic modulus measurement results of the comparative water absorbent resin powder (3).
- Comparative Example 4 Water absorbent resin powder (spherical granulated particles) taken from paper diapers purchased in Indonesia in October 2011 (product name “Mamy Poko Pants”, L size) manufactured by Unicharm Co., Ltd., comparative water absorbent resin powder (4).
- the comparative water absorbent resin powder (4) had an internal cell ratio of 0.9% and a surface tension of 60 mN / m.
- Table 3 shows the water absorption time and diffusion absorption time of the comparative water absorbent resin powder (4) by CRC, EMI, vortex method.
- Table 11 shows the measurement results of the elastic modulus of the comparative water absorbent resin powder (4).
- Example 5 A water absorbent resin powder (amorphous crushed particles) taken from a paper diaper purchased in Turkey in April 2013 (made by Kimberly Clark: trade name “HUGGIES”, size 4 Maxi) is compared with a comparative water absorbent resin powder (5). did.
- the comparative water absorbent resin powder (5) had an internal cell ratio of 3.8% and a surface tension of 63 mN / m.
- Table 3 shows the water absorption time and diffusion absorption time of the comparative water absorbent resin powder (5) by CRC, EMI, vortex method.
- Table 12 shows the measurement results of the elastic modulus of the comparative water absorbent resin powder (5).
- FIG. 13 shows diffusion absorption times shown in Table 3 for the water absorbent resin powders (1) to (4) obtained in the examples and the comparative water absorbent resin powders (1) to (5) obtained in the comparative examples.
- FIG. The horizontal axis represents the water absorption time (unit: seconds) by the vortex method, and the vertical axis represents the elastic modulus index (EMI).
- the EMI is the same as the procedure 1.
- a water absorbent resin powder having a particle size of 600 ⁇ m to 500 ⁇ m obtained by sieving using a JIS standard sieve having an opening of 600 ⁇ m in the upper stage and a JIS standard sieve having an opening of 500 ⁇ m in the lower stage It is the value.
- the value shown in the figure is the diffusion absorption time (unit: second) and corresponds to the value shown in Table 3. Further, in the figure, black circles represent the results of the example, black triangles represent the results of the comparative example, for example, “real 1” represents the result of example 1, and “ratio 1” represents the result of comparative example 1.
- the proportion of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is 90% by weight or more. From FIG. 13, the water-absorbing resin powders (1) to (4) having a water absorption time by a vortex method of 42 seconds or less and a particle size of 500 ⁇ m or more and less than 600 ⁇ m and an elastic modulus index of 5500 or more are In both cases, the diffusion absorption time shows an excellent value of less than 100 seconds.
- the water-absorbent resin powder (1) obtained in Example 1 was obtained by removing flaky particles from the comparative water-absorbent resin powder (1) using a ton cap wire net having a rectangular mesh, and further having a thickness of 500 ⁇ m. The following particles are remixed.
- Comparative water-absorbent resin powder (1) contains 16% of flaky particles as shown in Comparative Example 1.
- the water absorbent resin powder (1) since the flaky particles are removed by the ton cap wire mesh, the shape of the particles is aligned to be nearly spherical. Therefore, the water-absorbent resin powder (1) has a higher EMI value than the comparative water-absorbent resin powder (1), the water absorption time is short (that is, the water absorption speed is excellent), and the diffusion absorption time is an excellent value of 86 seconds. It is thought that it showed.
- Water-absorbent resin powders (2) to (4) are water-absorbent resin powders obtained by gel pulverization using a gel pulverizer (A) equipped with the same screw and barrel, and are different from Comparative Example 2. It is a water-absorbent resin powder obtained using a screw and a barrel under conditions.
- the shape of the particles is aligned to a nearly spherical shape, and as a result, a water-absorbent resin with excellent diffusion absorption time It is thought that a powder was obtained. If only the water absorption time is seen, the comparative water absorbent resin powders (1), (4) and (5) may show values superior to the water absorbent resin powders obtained in the examples. All comparative water-absorbent resin powders have an EMI of less than 5,500.
- the ratio of the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is 90% by weight or more
- the water absorption time is 42 seconds or less
- the elastic modulus index of the water absorbent resin powder having a particle size of 500 ⁇ m or more and less than 600 ⁇ m is When it is 5500 or more, it can be seen that a water absorbent resin powder having an excellent diffusion absorption time of less than 100 seconds can be obtained.
- the elastic modulus index of the water absorbent resin powder having a particle size of 425 ⁇ m or more and less than 500 ⁇ m is more preferably 4500 or more, and the elastic modulus index of the water absorbent resin powder having a particle size of 300 ⁇ m or more and less than 425 ⁇ m. It can be seen that it is even more preferable that is 3500 or more.
- the water absorbent resin powder having a particle size of 150 ⁇ m or more and less than 850 ⁇ m is 90% by weight or more, the water absorption time is 42 seconds or less, and the particle size is 500 ⁇ m or more and 600 ⁇ m.
- the elastic modulus index of the water-absorbent resin powder is less than 5500, the diffusion absorption time is less than 100 seconds, and it can be seen that very excellent diffusion absorption characteristics are exhibited.
- the water absorbent resin powder according to the present invention and the water absorbent resin powder produced by the production method according to the present invention are useful for sanitary goods such as paper diapers, sanitary napkins, and blood collecting agents for medical use.
- pet urine absorbent, mobile toilet urine gelling agent and freshness maintaining agent such as fruits and vegetables, meat and seafood drip absorbent, cold insulation, disposable warmer, battery gelling agent, water retention agent for plants and soil, etc. It can also be used in various applications such as anti-condensation agents, water-stopping agents and packing agents, and artificial snow.
Abstract
Description
(1)粒度が150μm以上850μm未満である吸水性樹脂粉末の割合が90重量%以上;
(2)ボルテックス法による吸水時間が42秒以下;
(3)弾性率指数(600-500)が5500以上である。
上記吸水性樹脂粉末(B)を膨潤液によって膨潤させ、膨潤ゲルとする膨潤工程と、
上記膨潤ゲルを、水平な底面を有する収容部に入れる収容工程と、
上記膨潤ゲルと接する収容部の底面と、該底面と平行である板状体と、で上記膨潤ゲルを挟持し、上記膨潤ゲルに対し垂直に、少なくとも2.4kPa以上の目的荷重まで、非連続的に荷重を増加させながら荷重を負荷する荷重負荷工程と、
上記荷重負荷工程において、一定荷重下で貯蔵弾性率を測定する測定工程と、を含み、
上記収容部の底面及び/又は上記板状体の、上記膨潤ゲルと接する部分の少なくとも一部分はアルミニウム製であることを特徴とする吸水性樹脂粉末の弾性率の測定方法。
(1-1)「吸水性樹脂」
本発明における「吸水性樹脂」とは、水膨潤性水不溶性の高分子ゲル化剤を意味する。ここで、「水膨潤性」とは、ERT441.2-02にて規定されるCRCが5g/g以上であることをいい、「水不溶性」とは、ERT470.2-02にて規定されるExtが0重量%~50重量%であることをいう。
本発明における「ポリアクリル酸(塩)」とは、グラフト成分を必要に応じて含んでおり、繰り返し単位として、アクリル酸、その塩(本明細書中では両者をまとめて「アクリル酸(塩)」と称する)、又はその組み合わせを主成分とする重合体を意味する。
「EDANA」とは、欧州不織布工業会(European Disposables and Nonwovens Associations)の略称であり、「ERT」とは、欧州標準(ほぼ世界標準)である吸水性樹脂の測定方法(EDANA Recommended Test Methods)の略称である。なお、本発明においては、特に断りのない限り、ERT原本(公知文献:2002年改定)に準拠して測定を行う。
「CRC」は、Centrifuge Retention Capacity(遠心分離機保持容量)の略称であり、無加圧下での吸水倍率(本明細書中にて「吸水倍率」と称する)を意味する。具体的に「CRC」とは、不織布袋中の0.200gの吸水性樹脂を、大過剰の0.9重量%塩化ナトリウム水溶液に対して30分間自由膨潤させ、遠心分離機を用いて水切りした後の吸水性樹脂の吸水倍率(単位;g/g)をいう。また、本発明においては、含水率補正を行った吸水性樹脂の重量を用いて算出した値で評価する。
「AAP」は、Absorption Against Pressureの略称であり、加圧下での吸水倍率を意味する。具体的に「AAP」とは、吸水性樹脂0.9gを大過剰の0.9重量%塩化ナトリウム水溶液に対して、1時間、2.06kPa(0.3psi)の荷重下で膨潤させた後の吸水倍率(単位;g/g)をいう。また、本明細書においてはAAP0.3と表記する。なお、ERT442.2-02には、Absorption Under Pressureと表記されているが、実質的にAAPと同一内容である。また、本発明においては、含水率補正を行った吸水性樹脂の重量を用いて算出した値で評価する。
「Ext」は、Extractablesの略称であり、吸水性樹脂の水可溶分(水可溶成分量)を意味する。具体的に「Ext」とは、吸水性樹脂1.0gを0.9重量%塩化ナトリウム水溶液200mlに添加し、500rpmで16時間攪拌した後の溶解ポリマー量(単位;重量%)をいう。なお、溶解ポリマー量は、pH滴定で測定する。
「PSD」は、Particle Size Distributionの略称であり、篩分級により測定される、吸水性樹脂の粒度分布を意味する。なお、重量平均粒子径(D50)及び粒度分布の対数標準偏差(σζ)は、米国特許第7638570号に記載された「(3)Mass-Average Particle Diameter(D50) and Logarithmic Standard Deviation(σζ) of Particle Diameter Distribution」と同様の方法で測定する。
「Moisture Content」は、吸水性樹脂の含水率を意味する。具体的に「Moisture Content」とは、吸水性樹脂1gを105℃で3時間にわたって乾燥させたときの乾燥減量から算出した値(単位;重量%)である。なお、本発明では乾燥温度を180℃に変更し、測定は1サンプルにつき5回行い、その平均値を採用する。また、含水ゲル状架橋重合体の含水率は、試料を2g、乾燥温度を180℃、乾燥時間を16時間にそれぞれ変更して測定を行う。更に、{100-含水率(重量%)}で算出される値を、本発明では「樹脂固形分」とし、吸水性樹脂及び含水ゲル状架橋重合体の双方に適用することができる。
本発明における「SFC」とは、Saline Flow Conductivity(食塩水流れ誘導性)の略称であり、荷重2.07kPaにおける吸水性樹脂に対する0.69重量%塩化ナトリウム水溶液の通液性(単位;×10-7・cm3・s・g-1)を意味する。SFCの値が大きいほど、吸水性樹脂は、高い液透過性を有することとなる。米国特許第5849405号明細書に記載されたSFC試験方法に準じて測定される。
本発明における「ボルテックス法による吸水時間」とは、JIS K7224に記載された「高吸水性樹脂の吸水速度試験法」に準じて求められる吸水時間のことであり、2gの吸水性樹脂が50gの生理食塩水(具体的には0.9重量%の塩化ナトリウム水溶液)を吸水するのに要する時間(単位;秒)のことである。なお、本明細書では「ボルテックス法による吸水時間」を、「吸水時間」又は「Vortex」と表記する場合もある。
本発明における「弾性率指数」とは、下記に示した方法で測定された弾性率を、膨潤ゲル粒子の理論表面積及びCRCで補正した値(単位;Pa/m2)のことであり、吸水性樹脂の性能を評価する際の指標となる値である。なお、上記「膨潤ゲル粒子」とは、吸水性樹脂を膨潤液(特に純水)で膨潤させたゲル粒子のことをいう。また、本明細書では、「弾性率指数」は英語表記の「Elastic Modulus Index」から「EMI」と略記することもある。EMIの具体的な測定方法、算出方法は実施例にて説明する。
本発明における「拡散吸収時間」とは、吸水性樹脂に対して、0.9重量%の塩化ナトリウム水溶液を複数回投入した際、該吸水性樹脂が該塩化ナトリウム水溶液の全量を吸収するのに要した時間をすべて合計した時間(単位;秒)のことをいう。
本明細書において、範囲を示す「X~Y」は、「X以上、Y以下」を意味する。重量の単位である「t(トン)」は、「Metric ton(メトリック トン)」を意味し、更に、特に注釈のない限り、「ppm」は「重量ppm」を意味する。「重量」と「質量」、「重量%」と「質量%」、「重量部」と「質量部」は同義語として扱う。更に、「~酸(塩)」は「~酸及び/又はその塩」を意味し、「(メタ)アクリル」は「アクリル及び/又はメタクリル」を意味する。また、「主成分」は、全体の51%以上を占めていることを意味する。
本発明に係る吸水性樹脂粉末は、ポリアクリル酸(塩)系吸水性樹脂を主成分とし、表面架橋されていると共に、以下の(1)~(3)を満たす吸水性樹脂粉末である:
(1)粒度が150μm以上850μm未満である吸水性樹脂粉末の割合が90重量%以上;
(2)ボルテックス法による吸水時間が42秒以下;
(3)弾性率指数(600-500)が5500以上である。
本発明において、「粒度」とは、JIS標準篩(JIS Z8801-1(2000))で規定される、吸水性樹脂粉末の粒子径分布のことをいう。なお、上記(1)の「粒度が150μm以上850μm未満である吸水性樹脂粉末」とは、目開き850μmのJIS標準篩を通過するが、目開き150μmのJIS標準篩は通過しない吸水性樹脂粉末のことをいう。
(a)粒度が150μm以上300μm未満である吸水性樹脂粉末の割合としては、好ましくは5重量%~50重量%、より好ましくは10重量%~40重量%、更に好ましくは15重量%~35重量%に、(b)粒度が300μm以上425μm未満である吸水性樹脂粉末の割合としては、好ましくは10重量%~60重量%、より好ましくは15重量%~35重量%、更に好ましくは20重量%~40重量%に、(c)粒度が425μm以上500μm未満である吸水性樹脂粉末の割合としては、好ましくは5重量%~50重量%、より好ましくは10重量%~40重量%、更に好ましくは15重量%~35重量%に、(d)粒度が500μm以上600μm未満である吸水性樹脂粉末の割合としては、好ましくは5重量%~50重量%、より好ましくは10重量%~40重量%、更に好ましくは15重量%~35重量%に、(e)粒度が600μm以上850μm未満又は粒度が600μm以上710μm未満である吸水性樹脂粉末の割合としては、好ましくは0.1重量%~50重量%、より好ましくは0.5重量%~40重量%、更に好ましくは1重量%~30重量%である。なお、上記(a)~(e)の割合は、上述した粒度(150μm以上850μm未満又は150μm以上710μm未満)を満たす範囲内で、任意の組み合わせを選択することができる。本発明に係る吸水性樹脂粉末の重量を100重量%とした場合、本発明に係る吸水性樹脂粉末において、上記(a)~(e)にそれぞれ示す粒度の吸水性樹脂粉末の割合の合計は、好ましくは90重量%~100重量%、より好ましくは95重量%~100重量%、更に好ましくは97重量%~100重量%である。
本発明に係る吸水性樹脂粉末は、ボルテックス法による吸水時間が吸水性の観点から、必須に42秒以下、好ましくは40秒以下、より好ましくは35秒以下、更に好ましくは30秒以下、特に好ましくは25秒以下である。なお、下限値は0秒超であれば特に限定されるものではないが、一般的な下限値として好ましくは5秒以上、より好ましくは10秒以上である。
本発明に係る吸水性樹脂粉末の弾性率指数は、吸水性樹脂粉末の粒度ごとに好ましい範囲が異なる。これは、弾性率指数の算出に用いられる弾性率の測定において、該弾性率を正確に求めるには、測定対象である吸水性樹脂粉末の粒度を特定範囲に揃える必要があることに起因する。以下、粒度ごとに弾性率指数の好ましい範囲について述べる。なお、粒度が500μm以上600μm未満である吸水性樹脂粉末の弾性率指数を「EMI(600-500)」と表記する。
本発明に係る吸水性樹脂粉末の弾性率指数(600-500)は、必須に5500以上、好ましくは6000以上、より好ましくは6500以上、更に好ましくは7000以上である。実施例で示したように、ボルテックス法による吸水時間が42秒以下という要件を満たす場合、弾性率指数が大きくなるほど、拡散吸収時間は短時間となる。つまり、該弾性率指数の値が大きいほど、拡散吸収特性がより優れた吸水性樹脂粉末が得られるため、好ましい。
本発明に係る吸水性樹脂粉末の弾性率指数(500-425)は、好ましくは4500以上、より好ましくは5000以上、更に好ましくは5500以上、特に好ましくは6000以上、最も好ましくは6500以上である。上記弾性率指数の上限値は特に限定されないが、物理的な限界のため、一般的には好ましくは14500以下、より好ましくは10500以下、更に好ましくは7000以下を満たせばよい。
本発明に係る吸水性樹脂粉末の弾性率指数(425-300)は、好ましくは3500以上、より好ましくは4000以上、更に好ましくは4500以上、更により好ましくは5000以上、特に好ましくは5500以上、最も好ましくは6000以上である。上記弾性率指数の上限値は特に限定されないが、物理的な限界のため、一般的には好ましくは14000以下、より好ましくは10000以下、更に好ましくは6500以下を満たせばよい。
本発明に係る吸水性樹脂粉末の弾性率指数(710-600)は、好ましくは5500以上、より好ましくは6000以上、更に好ましくは6500以上、特に好ましくは7000以上、最も好ましくは7500以上である。上記弾性率指数の上限値は特に限定されないが、物理的な限界のため、一般的には好ましくは15500以下、より好ましくは11500以下、更に好ましくは8000以下を満たせばよい。
本発明に係る吸水性樹脂粉末の弾性率指数(300-150)は、好ましくは3500以上、より好ましくは4000以上である。上記弾性率指数の上限値は特に限定されないが、物理的な限界のため、一般的には好ましくは13500以下、より好ましくは9500以下、更に好ましくは4500以下を満たせばよい。
本発明に係る吸水性樹脂粉末は、内部気泡率が好ましくは0%~3.7%、より好ましくは1.3%~3.3%、更に好ましくは1.7%~3.0%である。公知の発泡重合によって、吸水速度が速い吸水性樹脂粉末が製造されることは従来から知られている。一方、本発明に係る吸水性樹脂粉末は、上記公知の発泡重合によって製造された吸水性樹脂粉末(内部気泡率が約4%)よりも内部気泡率が低いものの、吸水速度が速いだけでなく、上述のように弾性に富み、優れた拡散吸収特性を示す。なお、内部気泡率の測定方法は実施例にて後述する。
本発明に係る吸水性樹脂粉末は、表面張力が好ましくは69mN/m以上、より好ましくは70mN/m以上、更に好ましくは71mN/m以上である。また、表面張力の上限値は、一般的な測定精度の観点から、好ましくは74mN/m以下、より好ましくは73mN/m以下であればよい。上記表面張力を上記範囲内とすることで、上記吸水性樹脂粉末を紙オムツ等の吸収性物品の吸収体に使用した際、戻り量を著しく抑制することができるため、好ましい。なお、表面張力の測定方法は、実施例にて説明する。
本発明に係る吸水性樹脂粉末は、CRC(遠心分離機保持容量)が好ましくは25g/g~50g/g、より好ましくは26g/g~45g/g、更に好ましくは26g/g~33g/gである。該CRCは、十分な液の吸収能力の観点から25g/g以上とすることが好ましく、拡散性を維持する観点から50g/g以下とすることが好ましい。なお、CRCは、重合時の架橋剤量及びその後の表面架橋(2次架橋)によって適宜制御できる。
本発明に係る吸水性樹脂粉末は、表面近傍の架橋密度が高くなった状態、即ち、表面架橋されている状態である。そのため、当該吸水性樹脂粉末は、AAP(加圧下吸水倍率)が好ましくは8g/g~29g/g、より好ましくは10g/g~27g/g、更に好ましくは12g/g~25g/g、及び/又は、SFC(食塩水流れ誘導性)が好ましくは5×10-7・s・cm3・g-1以上、より好ましくは10×10-7・s・cm3・g-1以上、更に好ましくは20×10-7・s・cm3・g-1以上を満たすことが好ましい。つまり、上記AAP及び/又はSFCが上記範囲を満たしている場合、その吸水性樹脂粉末は表面架橋されているといえる。
本発明に係る吸水性樹脂粉末の拡散吸収時間は、好ましくは100秒以下、より好ましくは95秒以下、更に好ましくは90秒以下、特に好ましくは85秒以下である。該拡散吸収時間は短時間ほどより好ましいため、下限値は特に限定されないが、好ましくは5秒超、より好ましくは10秒以上、更に好ましくは20秒以上、特に好ましくは40秒以上を満たせばよい。
上述した「弾性率指数」とは、弾性率を粒子の膨潤ゲル粒子の理論表面積とCRCとで補正した値であり、吸水性樹脂粉末の性能の指標となる値である。なお、「膨潤ゲル粒子」とは、吸水性樹脂粉末を膨潤液によって膨潤させて得られた膨潤ゲルの粒子である。また、本明細書では、弾性率指数を「EMI」と略記する場合もある。
上記吸水性樹脂粉末(B)を膨潤液によって膨潤させ、膨潤ゲルとする膨潤工程と、
上記膨潤ゲルを、水平な底面を有する収容部に入れる収容工程と、
上記膨潤ゲルと接する収容部の底面と、該底面と平行である板状体と、で上記膨潤ゲルを挟持し、上記膨潤ゲルに対し垂直に、少なくとも2.4kPa以上の目的荷重まで、非連続的に荷重を増加させながら荷重を負荷する荷重負荷工程と、
上記荷重負荷工程において、一定荷重下で貯蔵弾性率を測定する測定工程と、を含み、
上記収容部の底面及び/又は上記板状体の、上記膨潤ゲルと接する部分の少なくとも一部分はアルミニウム製である。
本発明に係る吸水性樹脂粉末は、上述のように、弾性に富み、吸水速度が速く、その結果優れた拡散吸収特性を示す。これは、粒子の形状がより厳密に制御され、扁平な形状の粒子が排除されているためであると考えられる。
本実施の形態にかかる吸水性樹脂粉末の製造方法は、ポリアクリル酸(塩)系吸水性樹脂を主成分とし、表面架橋されている吸水性樹脂粉末を、目開き150μm以上850μm以下の少なくとも2種の篩を用いて分級し、用いた篩のうち最も目開きの小さい篩(a)上に残存した吸水性樹脂粉末(i)を得る工程と、
長方形の目開きを有する篩(b)を用いて吸水性樹脂粉末(i)を分級し、篩(b)上に残存する吸水性樹脂粉末(ii)を得る工程と、を含み、
上記長方形の目開きの長辺の長さは、上記篩(a)より目開きが大きく、吸水性樹脂粉末(i)の粒度の上限値を規定する篩である篩(c)の目開きの辺の長さ以上であり、好ましくは上記長方形の目開きの短辺の長さが上記長辺の長さの2/3以下(より好ましくは1/2以下)であるという方法である。
実施の形態2に係る吸水性樹脂粉末の製造方法は、以下の方法である。すなわち、アクリル酸(塩)系単量体水溶液の重合工程と、重合中又は重合後の含水ゲル状架橋重合体のゲル粉砕工程と、ゲル粉砕後の乾燥工程とを含む、本発明にかかる吸水性樹脂粉末を製造する方法であって、
上記ゲル粉砕工程において、以下のゲル粉砕装置(A)を用いて、樹脂固形分が10重量%~80重量%の含水ゲル状架橋重合体を粉砕することを特徴とする方法:
(A)スクリュー、供給口、押出口、多孔板、及びバレルを備えた、吸水性樹脂粉末を製造するために使用するゲル粉砕装置であって、
上記バレルが、その内面に逆戻り防止部材を備えており、
上記バレルを吸水性樹脂のゲルの押出方向に対して垂直に切断したときに得られる、上記逆戻り防止部材の高さをYH、上記逆戻り防止部材の上面の、当該逆戻り防止部材の延伸方向に対して垂直方向の幅をYF、上記逆戻り防止部材を含まない上記バレルの内部の直径をNとしたとき、当該バレルが、下記(a)及び(b)を満たしており、
上記スクリューが、回転の中心となる回転軸及び上記回転軸に螺旋状に設けられたフライトを備えており、
上記スクリューを吸水性樹脂のゲルの押出方向に対して垂直に切断したときに得られる上記回転軸の断面積をB、上記フライトの回転部の断面積をA、上記フライトの延伸方向に対して垂直方向の幅をFとしたとき、当該スクリューが、下記(c)及び(d)を満たす;
(a)0.05≦YH/N≦0.2
(b)0.05≦YF/N≦0.2
(c)0.540≦B/A≦0.630
(d)0.07<F/N≦0.13。
図6は、本実施形態で用いるゲル粉砕装置100の全体構成を示す概略の断面図である。ゲル粉砕装置100は、所望の形状の粒子状含水ゲルを得るために用いる装置であり、上記ゲル粉砕装置(A)に該当する。上記ゲル粉砕装置100は、特に、吸水性樹脂の製造において、重合工程と乾燥工程との間に行われるゲル粉砕工程にて用いられる装置である。
図7は、ゲル粉砕装置100の押出口16付近を示す概略の断面図である。スクリュー11は主に、回転軸22及びフライト部23から構成されている。フライト部23は、回転軸22を中心として螺旋状に搭載されている。回転軸22に対するフライト部23の巻き数は、回転軸22の端部からもう一方の端部までに巻かれている数をいう。フライト部の巻き数は特に限定されないが、好ましくは3巻以上であり、特に好ましくは4巻以上である。また、フライト部23は、一重螺旋であっても、二重螺旋であっても、三重螺旋であってもよく、回転軸22に搭載されているフライト部23の数は特に限定されない。
多孔板12とは、本実施形態で用いられるゲル粉砕装置において、バレル13中の含水ゲルが押出される出口部分に備えられている部材である。上記多孔板12の厚さ、孔径又は開孔率は、ゲル粉砕装置の単位時間当りの処理量又は含水ゲルの形状等によって適宜選択でき、特に限定されないが、多孔板の厚さ(本明細書中において「ダイス厚さ」ともいう)は好ましくは3.5mm~40mm、より好ましくは8mm~30mm、更に好ましくは10mm~25mmである。また、多孔板の孔径(本明細書中において「ダイス孔径」ともいう)は、好ましくは3.2mm~30mm、より好ましくは7.5mm~25mmである。更に、多孔板の開孔率(本明細書中において「ダイス開孔率」ともいう)は、好ましくは20%~80%、より好ましくは30%~55%である。
本実施形態で用いるゲル粉砕装置は、軸受け部を備えていてもよい。本明細書中「軸受け部」とは、ダイスのプレートと回転軸との間に備えられる部材をいう。回転軸22及び軸受け部が接触する部分の材質は、回転軸及び軸受け部の材質と異なることが好ましく、異なる材質の金属であることがより好ましい。回転軸22及び軸受け部と、回転軸22及び軸受け部が接触する部分との材質が同じ場合、焼き付き等による装置の破損や、金属粉の製品への混入のおそれがある。
回転軸22の回転数は、バレル13の内径によって回転羽根の外周速度が変わるため、一概に規定できないが、上記回転軸22の回転数は、好ましくは60rpm~500rpm、より好ましくは80rpm~400rpm、更に好ましくは100rpm~200rpmである。上記回転軸22の回転数が60rpm未満の場合、ゲル粉砕に必要なせん断・圧縮力が得られないおそれがある。また、上記回転軸22の回転数が500rpmを超える場合、含水ゲルに与えるせん断・圧縮力が過剰となり、得られる吸水性樹脂の物性の低下を招いたり、本実施形態に係るゲル粉砕装置に掛かる負荷が大きくなり破損したりするおそれがある。
本実施形態で用いるゲル粉砕装置100の使用時の温度は、含水ゲルの付着等を防ぐために、好ましくは40℃~120℃、より好ましくは60℃~100℃である。また、本実施形態で用いるゲル粉砕装置100は、加熱装置や保温装置などを有することが好ましい。
本実施形態で用いるゲル粉砕装置に供給されるゲル粉砕前の含水ゲルの温度(本明細書中にて「ゲル温度」ともいう)は、粒度制御や物性の観点から、好ましくは40℃~120℃、より好ましくは60℃~120℃、更に好ましくは60℃~110℃、特に好ましくは65℃~110℃である。
本実施形態で用いるゲル粉砕装置の単位時間当たりの処理量は、上記内径Nに依存する値であり、好適な範囲が変化する。本実施形態で用いるゲル粉砕装置の1時間当たりの含水ゲルの処理量をT(単位;g/hr)、上記内径Nを3乗した値をN3(単位;mm3)とするとき、本実施形態で用いるゲル粉砕装置の単位時間当たりの処理量は、処理量内径比(T/N3)(単位;g/hr/mm3)にて表わすことができる。
本実施形態で用いるゲル粉砕装置100において、含水ゲルに水を添加してゲル粉砕することができる。本発明において添加する「水」とは、固体、液体、気体の何れの形態を含むものであってもよい。取扱い性の観点から、液体や気体の形態、或いは液体及び気体の混合形態が好ましい。
上述したように、含水ゲルに水を添加してゲル粉砕することが好ましいが、水以外に他の添加剤又は中和剤等を含水ゲルに添加・混練してゲル粉砕することもでき、得られる吸水性樹脂を改質してもよい。
本発明に係る吸水性樹脂粉末の製造方法では、ゲル粉砕エネルギー(GGE/Gel Grinding Energey)が一定範囲に制御されることが好ましい。
(5-1)重合工程
本工程は、アクリル酸(塩)を主成分とする水溶液を重合して、含水ゲル状架橋重合体(本明細書中において「含水ゲル」と称することがある)を得る工程である。
本発明にて得られる吸水性樹脂粉末は、アクリル酸(塩)を主成分として含む単量体を原料として使用し、通常、水溶液状態にて重合される。本明細書中にて、アクリル酸(塩)を主成分として含む単量体の水溶液を、「アクリル酸(塩)系単量体水溶液」とも称する。単量体水溶液中の単量体(モノマー)濃度としては、好ましくは10重量%~80重量%、より好ましくは20重量%~80重量%、更に好ましくは30重量%~70重量%、特に好ましくは40重量%~60重量%である。
本発明において、得られる吸水性樹脂粉末の吸水性能の観点から、架橋剤(本明細書中において「内部架橋剤」と称する)を使用することが好ましい。該内部架橋剤としては特に限定されないが、例えば、アクリル酸との重合性架橋剤、カルボキシル基との反応性架橋剤、又はこれらを併せ持った架橋剤等が挙げられる。
本発明において使用される重合開始剤は、重合形態によって適宜選択され、特に限定されないが、例えば、光分解型重合開始剤、熱分解型重合開始剤、レドックス系重合開始剤等が挙げられる。
本発明に係る吸水性樹脂粉末の製造方法において、その重合方法は、噴霧液滴重合又は逆相懸濁重合により粒子状含水ゲルを得てもよいが、得られる吸水性樹脂粉末の通液性(SFC)及び吸水速度(FSR)、並びに重合制御の容易性等の観点から、水溶液重合が採用される。
本発明における重合工程においては、必要に応じて界面活性剤及び/又は分散剤を用いてもよい。界面活性剤及び/又は分散液を用いることで、重合中の吸水性樹脂中に気泡を安定的に懸濁させることができる。また、界面活性剤及び/又は分散剤の種類又は量を適宜調節することにより、所望の物性を有する吸水性樹脂粉末を得ることができる。界面活性剤は非高分子界面活性剤であり、分散剤は高分子分散剤であることが好ましい。また、界面活性剤及び/又は分散剤は、重合前又は重合時のモノマー水溶液の温度が50℃以上となるよりも前の段階で添加されていることが好ましい。
本工程は、上述した重合中又は重合後の含水ゲル状架橋重合体を細分化して、粒子状の含水ゲル状架橋重合体を得る工程である。なお、下記(5-4)粉砕工程・分級工程の「粉砕」と区別して、本工程は「ゲル粉砕」という。
本工程は、上記ゲル粉砕工程にて得られた粒子状含水ゲルを乾燥し、乾燥重合体を得る工程であり、以下、本発明にて好ましく適用される乾燥方法について説明する。
本発明における乾燥工程(好ましくは、上記通気ベルト型乾燥機)での乾燥温度は、好ましくは100℃~300℃、より好ましくは150℃~250℃、更に好ましくは160℃~220℃、特に好ましくは170℃~200℃である。
本発明における乾燥工程(好ましくは、上記通気ベルト型乾燥機)での乾燥時間は、粒子状含水ゲルの表面積及び乾燥機の種類等に依存し、目的とする含水率となるように適宜設定すればよいが、好ましくは1分間~10時間、より好ましくは5分間~2時間、更に好ましくは10分間~1時間、特に好ましくは15分間~45分間である。
本発明における乾燥工程において、本発明の課題をより解決するために、上記通気乾燥機、特にベルト型乾燥機での熱風の風速は、垂直方向(上下方向)に、好ましくは0.8m/s~2.5m/s、より好ましくは1.0m/s~2.0m/sである。上記風速を上記範囲とすることで、得られる乾燥重合体の含水率を所望の範囲に制御できるだけでなく、吸水速度が向上する。上記風速が0.8m/s未満の場合、乾燥時間が遅延し、得られる吸水性樹脂粉末の通液性及び吸水速度が劣るおそれがある。また、上記風速が2.5m/sを超える場合、乾燥期間中に粒子状含水ゲルが舞い上がり安定した乾燥が困難というおそれがある。
本発明における乾燥工程において、上記通気ベルト型乾燥機で用いられる熱風は、少なくとも水蒸気を含有し、かつ露点が好ましくは30℃~100℃、より好ましくは30℃~80℃である。熱風の露点又は更に好ましくはゲル粒径を上記範囲に制御することで残存モノマーを低減することができ、更に、乾燥重合体の嵩比重の低下を防止することができる。なお、上記露点は、粒子状含水ゲルの含水率が少なくとも10重量%以上、好ましくは20重量%以上の時点での値とする。
上記ゲル粉砕工程にて得られた粒子状含水ゲルの、乾燥機に投入される直前の粒子状含水ゲルの表面温度は、好ましくは40℃~110℃、より好ましくは60℃~110℃、更に好ましくは60℃~100℃、特に好ましくは70℃~100℃である。40℃に満たない場合、乾燥時に風船状乾燥物が生じ、粉砕時に微粉が多く発生し、吸水性樹脂の物性の低下を招くおそれがある。乾燥前の粒子状含水ゲルの表面温度が110℃を超える場合、乾燥後の吸水性樹脂の劣化(例えば、水可溶分の増加等)又は着色が生じるおそれがある。
本工程は、上記乾燥工程にて得られた乾燥重合体を、粉砕・分級して、吸水性樹脂粒子を得る工程である。なお、上記(5-2)ゲル粉砕工程とは、粉砕時の樹脂固形分、特に粉砕対象物が乾燥工程を経ている点(好ましくは、上記樹脂固形分まで乾燥)で異なる。また、粉砕工程後に得られる吸水性樹脂粒子を粉砕物と称することもある。
本発明に係る吸水性樹脂粉末は、ポリアクリル酸(塩)系吸水性樹脂を主成分とし、表面架橋されている。表面架橋を行うための表面処理工程は、公知の表面架橋剤及び表面架橋方法を用いて行う表面架橋工程を含み、更に必要に応じてその他の添加工程を含む。
本発明にて用いることのできる表面架橋剤としては、種々の有機又は無機架橋剤を例示することができるが、有機表面架橋剤が好ましい。物性面において、好ましくは、表面架橋剤として、多価アルコール化合物、エポキシ化合物、多価アミン化合物又はそのハロエポキシ化合物との縮合物、オキサゾリン化合物、(モノ、ジ、又はポリ)オキサゾリジノン化合物、アルキレンカーボネート化合物であり、特に高温での反応が必要な、多価アルコール化合物、アルキレンカーボネート化合物、オキサゾリジノン化合物からなる脱水反応性架橋剤を使用することができる。
表面架橋剤の混合には、縦型又は横型の高速回転攪拌型の混合機が好適に使用される。該混合機の回転数は好ましくは100rpm~10,000rpm、より好ましくは300rpm~2,000rpmである。また、装置内における吸水性樹脂の滞留時間は好ましくは180秒以内、より好ましくは0.1秒~60秒、更に好ましくは1秒~30秒である。
本発明において用いられる表面架橋方法として、上記の表面架橋剤を用いる表面架橋に代わって、ラジカル重合開始剤を用いる表面架橋方法(米国特許第4783510号、国際公開第2006/062258号)、又は吸水性樹脂の表面で単量体を重合する表面架橋方法(米国出願公開第2005/048221号、同第2009/0239966号、国際公開第2009/048160号)を用いてもよい。
本発明では、上述した表面架橋工程と同時又は別途に、多価金属塩、カチオン性ポリマー又は無機微粒子の何れか一つ以上を添加する添加工程を更に含んでもよい。即ち、上記有機表面架橋剤以外に無機表面架橋剤を使用又は併用して通液性・吸水速度等を向上させてもよい。上記無機表面架橋剤は、上記有機表面架橋剤と同時又は別途に使用できる。
本発明に係る吸水性樹脂粉末の用途は特に限定されないが、好ましくは紙オムツ、生理用ナプキン、失禁パット等の吸収性物品に使用される。高濃度オムツ(紙オムツ1枚当りの吸水性樹脂使用量が多い紙オムツ)に使用した場合に、優れた性能を発揮する。
以下、本発明に係る吸水性樹脂粉末について、その物性の測定方法を説明する。なお、測定対象が吸水性樹脂粉末以外である場合、例えば、吸水性樹脂粒子である場合には、物性測定の説明中の「吸水性樹脂粉末」を「吸水性樹脂粒子」に読み替えて適用する。
本発明に係る吸水性樹脂粉末の粒度分布(PSD)は、EDANA法(ERT420.2-02)に準拠して測定した。また、重量平均粒子径(D50)及び粒度分布の対数標準偏差(σζ)は、米国特許第7638570号に記載された「(3)Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution」に準拠して測定した。
本発明に係る吸水性樹脂粉末のボルテックス法による吸水時間は、以下の手順により測定した。
本発明に係る吸水性樹脂粉末の弾性率指数(EMI)は、以下の手順により測定した。
先ず、以下に記載する方法によって、粒子径(粒度)別に分けられた吸水性樹脂粉末の弾性率を測定した。
目開きが710μm、600μm、500μm、425μm、300μm、150μmである6つのJIS標準篩(THE IIDA TESTING SIEVE:径8cm)を用いて、吸水性樹脂粉末10gを分級した。該分級は、振動分級機(IIDA SIEVE SHAKER、TYPE:ES-65型(回転数:60Hz 230rpm、衝撃数:60Hz 130rpm)、SER.No.0501)で、5分間篩い分けることで実施した。
上記手順1で得られた粒度別に分級された吸水性樹脂粉末について、下記式(9)に従って算出して得られた量(添加量)を、容量10mlのプラスチック製容器に入れ、純水8.0gを加えて16時間浸漬させて膨潤させた。
上記手順2で得られた膨潤した吸水性樹脂粉末(以下、「膨潤ゲル」と称する)について、レオメーター(アントンパール社製、MCR301)(図1参照)を用いて、該膨潤ゲルの弾性率を測定した。以下、図1を用いて、測定方法を詳細に説明する。
測定モード:振動(動的)測定
歪み(strain):0.02%(誤差±2%)
角周波数:10rad/s(誤差±2%)
測定開始時:上部パラレルプレート42が膨潤ゲル41に接触した時点
垂直荷重:10N~40N/非連続的に荷重
測定時間が100秒経過するごとに5Nずつ増加させる
測定間隔:5秒
測定点数:20点×7荷重条件
測定時間:700秒(=5秒×20点×7荷重条件)
上記測定を、手順1で得られた各粒度の吸水性樹脂粉末に対して行った。なお、上記測定で使用するディッシュ40及びパラレルプレート42は、毎回新品を使用するか、又は、使用後十分に洗浄し、乾燥したものを磨きクロス(トラスコ中山株式会社製、基材:綿、研磨剤:A砥材(粒度:#15000)、ワックス入り)で磨いてから再度洗浄したものを使用した。また、歪み量や角周波数は、上記範囲内で測定値が安定する条件を適宜選択した。
上記弾性率、下記CRC及びCRCdwの値を用いて、下記式(3)、式(10)~式(17)に基づいて、弾性率指数(EMI)を算出した。該弾性率指数(EMI)は、弾性率G’を膨潤ゲルの理論表面積及びCRCで補正した値であり、吸水性樹脂粉末の性能を判断する指標となる値である。以下、弾性率指数をEMIと略記する。
本発明に係る吸水性樹脂粉末の内部気泡率は、以下の手順により測定した。
吸水性樹脂粉末の水分を除去した後、樹脂内部に存在する気泡(内部気泡)を考慮した見かけ密度を乾式密度計で測定(所定重量の吸水性樹脂粉末についてその体積を乾式測定)した。
吸水性樹脂粉末内部に存在する内部気泡(独立気泡)の径は、通常1μm~300μmであるが、粉砕時には、吸水性樹脂粉末は、独立気泡に近い部分から優先的に粉砕される。そこで、粒子径が45μm未満となるまで吸水性樹脂粉末を粉砕すると、得られた吸水性樹脂粉末には独立気泡がほとんど含まれない。従って、45μm未満まで粉砕された吸水性樹脂粉末の乾式密度を本発明では真密度として評価した。
本発明に係る吸水性樹脂粉末の表面張力は、以下の手順により測定した。
本発明に係る吸水性樹脂粉末のCRCは、EDANA法(ERT441.2-02)に準拠して測定した。即ち、吸水性樹脂粉末0.200gを秤量し、不織布製の袋(60×60mm)に均一に入れてヒートシールした後、25±3℃に調温した0.9重量%の塩化ナトリウム水溶液1000mL中に浸漬させた。30分経過後、上記袋を引き上げ、遠心分離機(株式会社コクサン社製遠心機、形式;H-122)を用いて、250G、3分間の条件で水切りを行った。
本発明に係る吸水性樹脂粉末のAAPは、EDANA法(ERT442.2-02)に準拠して測定した。
本発明に係る吸水性樹脂粉末のExtは、EDANA法(ERT470.2-02)に準拠して測定した。
本発明に係る吸水性樹脂粉末の含水率は、EDANA法(ERT430.2-02)に準拠して測定した。なお、本発明においては、試料量を1.0g、乾燥温度を180℃にそれぞれ変更した。また、(100-含水率)で算出される値を樹脂固形分(単位;重量%)として規定する。
本発明に係る吸水性樹脂粉末のSFCは、米国特許第5669894号に記載された測定方法に準拠して測定した。
本発明に係る吸水性樹脂粉末の拡散吸収時間は、以下の手順によって測定した。なお、測定には、図2に示した拡散吸収時間測定装置200を用いた。当該測定装置について説明する。
図2に示した拡散吸収時間測定装置200は、紙オムツ等の吸収性物品の性能を模擬的に評価するために作製された測定装置である。なお、図中、30はトレー、31は吸水性樹脂粉末の散布部、32は吸水性樹脂粉末、33はトップシート、34は金網、35は投入口、36は上蓋、37は錘をそれぞれ表している。
先ず、吸水性樹脂粉末32を12g、トレー30(内寸;横401mm×縦151mm×高さ30mm/外寸;横411mm×縦161mm×高さ35mm/アクリル樹脂製)内に設けられた散布部31(大きさ;横200mm×縦151mm/トレー30の縦方向の内壁から100.5mm内側)に均等に散布した(坪量;397g/m2)。なお、散布前には静電気が発生しないように、静電防止剤をトレー30に塗布した。
WO2011/126079号公報の製造例1及び実施例1を参考にして以下の操作を行った。
上記比較例1で得られた比較吸水性樹脂粉末(1)について、目開き710μm及び500μmのJIS標準篩で分級し、粒度が500μm以上710μm未満の粒子及び粒度が500μm未満の粒子を得た。このうち、粒度が500μm以上710μm未満の粒子について、長方形の目開きを有するトンキャップ金網(長目:728μm、短目:335μm)を張った篩で分級し、薄片状粒子を取り除いた。上記篩に供した粒度が500μm以上710μm未満の粒子の重量に対する、取り除いた薄片状粒子の重量の割合は17.1重量%であった。また、当該粒子を電子顕微鏡により観察したところ、薄片状粒子は見当たらなかった。
上記比較例1において、ポリエチレングリコールジアクリレート(平均n数;9)の使用量を1.05重量部に変更した以外は比較例1と同様の操作を行って、帯状の含水ゲル(2)及び切断含水ゲル(2)を得た。
上記比較例2において、スクリューをNo.S86-4610(スクリュー形状は表1を参照)、バレルをNo.B88-178(バレル形状は表2を参照)にそれぞれ変更した以外は、比較例2と同様の操作を行って、吸水性樹脂粒子(2)及び吸水性樹脂粉末(2)を得た。吸水性樹脂粉末(2)の内部気泡率は1.9%、表面張力は72mN/mであった。吸水性樹脂粉末(2)のCRC、EMI、ボルテックス法による吸水時間、拡散吸収時間を表3に示す。また、吸水性樹脂粉末(2)の弾性率測定結果を表7に示す。
上記比較例1において、ポリエチレングリコールジアクリレート(平均n数;9)の使用量を0.84重量部に変更した以外は比較例1と同様の操作を行って、帯状の含水ゲル(3)及び切断含水ゲル(3)を得た。
上記比較例1において、ポリエチレングリコールジアクリレート(平均n数;9)の使用量を0.70重量部に変更した以外は比較例1と同様の操作を行って、帯状の含水ゲル(4)及び切断含水ゲル(4)を得た。
2013年6月にベルギーで購入した紙オムツ(プロクター・アンド・ギャンブル社製:商品名「Pampers Easy Up Pants」、サイズ4Maxi)から取り出した吸水性樹脂粉末(不定形破砕状粒子)を比較吸水性樹脂粉末(3)とした。比較吸水性樹脂粉末(3)のCRC、EMI、ボルテックス法による吸水時間、拡散吸収時間を表3に示す。また、比較吸水性樹脂粉末(3)の弾性率測定結果を表10に示す。
2011年10月にインドネシアで購入した紙オムツ(ユニチャーム社製:商品名「Mamy Poko Pants」、Lサイズ)から取り出した吸水性樹脂粉末(球の造粒体状粒子)を比較吸水性樹脂粉末(4)とした。比較吸水性樹脂粉末(4)の内部気泡率は0.9%、表面張力は60mN/mであった。比較吸水性樹脂粉末(4)のCRC、EMI、ボルテックス法による吸水時間、拡散吸収時間を表3に示す。また、比較吸水性樹脂粉末(4)の弾性率測定結果を表11に示す。
2013年4月にトルコで購入した紙オムツ(キンバリークラーク社製:商品名「HUGGIES」、サイズ4Maxi)から取り出した吸水性樹脂粉末(不定形破砕状粒子)を比較吸水性樹脂粉末(5)とした。比較吸水性樹脂粉末(5)の内部気泡率は3.8%、表面張力は63mN/mであった。比較吸水性樹脂粉末(5)のCRC、EMI、ボルテックス法による吸水時間、拡散吸収時間を表3に示す。また、比較吸水性樹脂粉末(5)の弾性率測定結果を表12に示す。
41 膨潤ゲル
42 パラレルプレート(板状体)
43 回転軸
300 レオメーター
30 トレー
31 散布部
32 吸水性樹脂粉末
33 トップシート
34 金網
35 投入口
36 上蓋
37 錘
200 拡散吸収時間測定装置
11 スクリュー
12 多孔板
13 バレル
14 供給口
15 ホッパー
16 押出口
17 回転刃
18 リング
19 逆戻り防止部材
20 台
21 モーター
22 回転軸
23 フライト部
100 ゲル粉砕装置
Claims (20)
- ポリアクリル酸(塩)系吸水性樹脂を主成分とし、表面架橋されていると共に、以下の(1)~(3)を満たすことを特徴とする吸水性樹脂粉末:
(1)粒度が150μm以上850μm未満である吸水性樹脂粉末の割合が90重量%以上;
(2)ボルテックス法による吸水時間が42秒以下;
(3)弾性率指数(600-500)が5500以上である。 - 更に、以下の(4)を満たすことを特徴とする請求項1に記載の吸水性樹脂粉末:
(4)弾性率指数(500-425)が4500以上。 - 更に、以下の(5)を満たすことを特徴とする請求項2に記載の吸水性樹脂粉末:
(5)弾性率指数(425-300)が3500以上。 - (a)粒度が150μm以上300μm未満である吸水性樹脂粉末の割合が5重量%~50重量%、
(b)粒度が300μm以上425μm未満である吸水性樹脂粉末の割合が10重量%~60重量%、
(c)粒度が425μm以上500μm未満である吸水性樹脂粉末の割合が5重量%~50重量%、
(d)粒度が500μm以上600μm未満である吸水性樹脂粉末の割合が5重量%~50重量%、
(e)粒度が600μm以上850μm未満である吸水性樹脂粉末の割合が0.1重量%~50重量%
であり、上記(a)~(e)にそれぞれ示す粒度の吸水性樹脂粉末の割合の合計が90重量%~100重量%である、請求項1~3の何れか1項に記載の吸水性樹脂粉末。 - 内部気泡率が0%~3.7%であることを特徴とする請求項1から4の何れか1項に記載の吸水性樹脂粉末。
- 表面張力が69mN/m以上であることを特徴とする請求項1から5の何れか1項に記載の吸水性樹脂粉末。
- ERT441.2-02に規定されるCRCが25g/g~50g/gであることを特徴とする請求項1から6の何れか1項に記載の吸水性樹脂粉末。
- 重量平均粒子径(D50)が300μm~500μmであり、粒度分布の対数標準偏差(σζ)が0.25~0.45であることを特徴とする請求項1から7の何れか1項に記載の吸水性樹脂粉末。
- 請求項1から8の何れか1項に記載の吸水性樹脂粉末を含有する吸収体。
- 請求項1から8の何れか1項に記載の吸水性樹脂粉末を含有する吸収性物品。
- 目開きの異なる2つ以上の篩を用いて吸水性樹脂粉末(A)を分級し、吸水性樹脂粉末(B)を得る分級工程と、
上記吸水性樹脂粉末(B)を膨潤液によって膨潤させ、膨潤ゲルとする膨潤工程と、
上記膨潤ゲルを、水平な底面を有する収容部に入れる収容工程と、
上記膨潤ゲルと接する収容部の底面と、該底面と平行である板状体と、で上記膨潤ゲルを挟持し、上記膨潤ゲルに対し垂直に、少なくとも2.4kPa以上の目的荷重まで、非連続的に荷重を増加させながら荷重を負荷する荷重負荷工程と、
上記荷重負荷工程において、一定荷重下で貯蔵弾性率を測定する測定工程と、を含み、
上記収容部の底面及び/又は上記板状体の、上記膨潤ゲルと接する部分の少なくとも一部分はアルミニウム製であることを特徴とする吸水性樹脂粉末の弾性率の測定方法。 - 上記目開きの異なる2つ以上の篩が、目開き710μm~150μmの篩から選択されることを特徴とする請求項11に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記吸水性樹脂粉末(B)が通過できる篩の目開きと通過できない篩の目開きとの差が200μm以下であることを特徴とする請求項11又は12に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記目的荷重が、30kPa以下であることを特徴とする請求項11~13の何れか1項に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記膨潤ゲルの、上記収容部の底面積あたりの重量が、5.0mg/mm2以下であることを特徴とする請求項11~14の何れか1項に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記膨潤液のイオン強度が0~2.1であることを特徴とする請求項11~15の何れか1項に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記膨潤工程の膨潤時間が30分以上であることを特徴とする請求項11~16の何れか1項に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記収容部の内径と上記板状体の外径との差が3mm以下であることを特徴とする請求項11~17の何れか1項に記載の吸水性樹脂粉末の弾性率の測定方法。
- 上記収容部に収容された上記膨潤ゲルが、上記膨潤液に浸漬された状態であることを特徴とする請求項11~18の何れか1項に記載の吸水性樹脂粉末の弾性率の測定方法。
- 請求項1から8の何れか1項に記載の吸水性樹脂粉末を含有する吸収体の、吸収性物品への使用。
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JPWO2016052537A1 (ja) | 2017-07-06 |
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EP3202823A4 (en) | 2018-10-10 |
CN106715543B (zh) | 2020-10-30 |
CN106715543A (zh) | 2017-05-24 |
JP6441374B2 (ja) | 2018-12-19 |
US10300458B2 (en) | 2019-05-28 |
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US20170216817A1 (en) | 2017-08-03 |
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