Classifications

• • 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
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F13/00—Bandages or dressings; Absorbent pads
  • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
  • A61F13/53—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the absorbing medium
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F13/00—Bandages or dressings; Absorbent pads
  • A61F13/15—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators
  • A61F13/45—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the shape
  • A61F13/49—Absorbent pads, e.g. sanitary towels, swabs or tampons for external or internal application to the body; Supporting or fastening means therefor; Tampon applicators characterised by the shape specially adapted to be worn around the waist, e.g. diapers, nappies
• • 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
• • 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
  • B01J20/261—Synthetic macromolecular compounds obtained by reactions only involving carbon to carbon unsaturated bonds
• • 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
• • 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
• • 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
  • B01J20/28047—Gels
• • 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
  • B01J2220/00—Aspects relating to sorbent materials
  • B01J2220/50—Aspects relating to the use of sorbent or filter aid materials
  • B01J2220/68—Superabsorbents

Definitions

• the present invention relates to a particulate water-absorbing agent, an absorbent body containing the particulate water-absorbing agent, and a sanitary product containing the absorbent body.
• a water-absorbent resin (SAP/Super Absorbent Polymer) is a water-swellable, water-insoluble polymer gelling agent.
• Particulate water-absorbent agents that contain water-absorbent resin as the main component are used in absorbent articles for various applications, such as sanitary products such as paper diapers, sanitary napkins, and adult incontinence products, soil water-retaining agents for agricultural and horticultural use, and industrial water-stopping agents.
• Many monomers and hydrophilic polymers have been proposed as raw materials for such water-absorbent resins. From the viewpoints of performance and cost, polyacrylic acid (salt)-based water-absorbent resins that use acrylic acid and/or its salt as a monomer are most commonly used as the water-absorbent resin.
• particulate water absorbents are primarily used in disposable diapers, many functions (physical properties) are required of the particulate water absorbent.
• One of these functions is the ability to have excellent liquid retention and reduce liquid return, even when pressure is applied from the outside while the particulate water absorbent is in a swollen state.
• Absorbent articles such as disposable diapers and other sanitary products, are not replaced every time liquid to be absorbed, such as urine, is discharged, but rather liquid is normally discharged into the absorbent article multiple times.
• the particulate water absorbing agent that has absorbed liquid becomes swollen. Therefore, a user may use an absorbent article having a particulate water absorbing agent in a swollen state.
• the particulate water absorbing agent is required to have excellent liquid retention and a function of reducing liquid return, regardless of the wearer's daily movements, especially in situations where pressure is applied to the particulate water absorbing agent from the outside, such as when the weight of the wearer is applied to the absorbent article.
• a state where the weight of the wearer is applied to the absorbent article include a state where the wearer is lying on his/her back and a state where the wearer is sitting.
• Patent Document 1 proposes a particulate water absorbent in which the water absorption capacity under pressure at a pressure condition of 2.06 kPa: AAP (2.06 kPa), the water absorption capacity without pressure: CRC, and the water absorption capacity under pressure after swelling: RCAP (2.06 kPa) have a specific relationship.
• RCAP (2.06 kPa) represents the weight change of the particulate water absorbent before and after an operation of immersing the particulate water absorbent in a 0.9 wt % sodium chloride aqueous solution for 1 hour to form a swollen gel, and then leaving it for 1 minute under a load of 2.06 kPa, i.e., the water absorption capacity.
• the particulate water absorbing agent contained in the sanitary product needs to absorb a large amount of liquid such as urine without pressure in a time shorter than the immersion time (1 hour) in the measurement of the RCAP (2.06 kPa). Furthermore, when the sanitary product is actually used, it is considered that the swollen particulate water absorbing agent is maintained without pressure or a pressure higher than 2.06 kPa is applied to it in accordance with the movements of the user.
• the RCAP (2.06 kPa) is a parameter corresponding to the conditions during actual use of the sanitary product. Therefore, there is room for improvement in the sanitary product containing the particulate water-absorbing agent described in Patent Document 1 in terms of reducing the return of absorbed liquid during actual use.
• the present invention was made in consideration of the above-mentioned problems, and its objective is to provide a particulate water-absorbing agent that can be used to manufacture sanitary products that can further reduce the return of absorbed liquid during actual use.
• the inventors have found two new parameters that correspond to the conditions of practical use of the sanitary product, and have discovered that a particulate water absorbing agent with these parameters falling within a specific range can solve the above problem, leading to the invention.
• the parameters are a parameter that corresponds to the water absorption capacity of a swollen gel obtained by swelling the particulate water absorbing agent in a short time when held under no pressure, and a parameter that corresponds to the water absorption capacity of the swollen gel when held under high pressure.
• one embodiment of the present invention relates to a particulate water absorbing agent mainly composed of a surface-crosslinked polyacrylic acid (salt)-based water absorbent resin, which satisfies the following formula (A) and formula (B): SRC(NP)>50.0g/g (A) SRC (4.83kPa)>41.5g/g (B)
• SRC(NP) is measured by a method including the following steps (a) to (c):
• test liquid 0.9% aqueous sodium chloride solution
• step (b) Separate the swollen gel obtained in step (a) from the test liquid.
• the SRC (4.83 kPa) is measured by carrying out a method including steps (c') to (e') described below in place of step (c) in the method including steps (a) to (c).
• step (c') A load of 4.83 kPa is applied to the swollen gel separated in step (b) for one minute.
• step (d') The exudate exuded from the swollen gel in step (c') is removed.
• the particulate water-absorbing agent according to one embodiment of the present invention has the effect of being usable in the manufacture of sanitary products that can further reduce the return of absorbed liquid during actual use.
• Water-absorbent resin refers to a crosslinked polymer having "swellability” and “insolubility” that absorbs liquid, swells, and becomes an insoluble gel, and satisfies the following physical properties: That is, the "water-swellable” crosslinked polymer has a CRC of 5 g/g or more as specified in ERT441.2-02, and the "water-insoluble” crosslinked polymer has an Ext of 50 wt% or less as specified in ERT470.2-02.
• the water-absorbent resin can be designed appropriately according to its application, and is not particularly limited, but is preferably a hydrophilic cross-linked polymer obtained by cross-linking an unsaturated monomer having a carboxyl group.
• it is not limited to a form in which the total amount (100% by weight) is a polymer, and may be a water-absorbent resin composition containing additives, etc., within the range that satisfies the above physical properties (CRC, Ext).
• the water-absorbent resin in one embodiment of the present invention is not limited to a final product, but may refer to an intermediate in the manufacturing process of the water-absorbent resin (for example, a hydrous gel-like cross-linked polymer after polymerization and a dried polymer after drying, as well as water-absorbent resin powder before surface cross-linking, etc.). In this specification, all of these are collectively referred to as "water-absorbent resin".
• the shape of the water-absorbent resin may be sheet-like, fibrous, film-like, particulate, gel-like, etc., but the water-absorbent resin in one embodiment of the present invention is mainly in particulate (powder) form.
• the water absorbing agent contains water absorbent resin as a main component.
• the particulate water absorbing agent means a particulate (also called powder) water absorbing agent (containing water absorbent resin particles as a main component), and is referred to as a particulate water absorbing agent whether it is a single particulate water absorbing agent or a plurality of particulate water absorbing agents.
• "Particulate” means having a particle form, and a particle means a small solid or liquid granular body having a measurable size (JIS Industrial Terminology Dictionary, 4th Edition, p. 2002). In this specification, the particulate water absorbing agent may be simply referred to as a water absorbing agent.
• the aqueous liquid is not limited to water, but may also be urine, blood, sweat, feces, waste liquid, moisture, steam, ice, a mixture of water and an organic solvent and/or an inorganic solvent, rainwater, groundwater, etc., and is not particularly limited as long as it contains water.
• Preferred examples of the aqueous liquid include urine, menstrual blood, sweat, and other body fluids.
• the particulate water absorbent according to one embodiment of the present invention is suitable for use as a sanitary material for absorbing aqueous liquids.
• the particulate water absorbent is mainly composed of a surface-crosslinked polyacrylic acid (salt)-based water absorbent resin (particles) (hereinafter also simply referred to as polyacrylic acid (salt)-based water absorbent resin).
• the surface-crosslinked polyacrylic acid (salt)-based water absorbent resin is preferably contained in the particulate water absorbent in an amount of 60 to 100% by weight, 70 to 100% by weight, 80 to 100% by weight, or 90 to 100% by weight.
• the particulate water absorbent optionally contains one or more materials selected from the group consisting of other water absorbent resin particles, water, and additives.
• the additives are inorganic colloid particles, water-insoluble inorganic particles, water-soluble polyvalent metal cation-containing compounds, and the like.
• the suitable water content of the particulate water absorbent is 0.2 to 30% by weight. In other words, a water absorbent resin composition in which these components are integrated also falls within the category of the particulate water absorbent.
• the upper limit of the content of the polyacrylic acid (salt)-based water-absorbing resin in the water-absorbing agent is about 99% by weight, particularly about 95%, 90%, or 85% by weight, and preferably further contains water and/or additives described below (inorganic colloid particles, water-insoluble inorganic particles, water-soluble polyvalent metal cation-containing compounds).
• the particulate water absorbent according to one embodiment of the present invention may contain a polyacrylic acid (salt)-based water absorbent resin as a main component, and may also contain other water absorbent resins.
• the other water absorbent resins include polysulfonic acid (salt)-based water absorbent resins, maleic anhydride (salt)-based water absorbent resins, polyacrylamide-based water absorbent resins, polyvinyl alcohol-based water absorbent resins, polyethylene oxide-based water absorbent resins, polyaspartic acid (salt)-based water absorbent resins, polyglutamic acid (salt)-based water absorbent resins, polyalginic acid (salt)-based water absorbent resins, starch-based water absorbent resins, and cellulose-based resins.
• the other water absorbent resins may be one type or two or more types.
• polyacrylic acid (salt) refers to polyacrylic acid and/or its salt.
• polyacrylic acid (salt)-based water-absorbing resin refers to a polyacrylic acid (salt) cross-linked polymer that contains, as a main component, a structural unit derived from acrylic acid and/or its salt (hereinafter referred to as "acrylic acid (salt)”) as a repeating unit and has an internal cross-linked structure.
• the polyacrylic acid (salt)-based water-absorbing resin is preferably surface-cross-linked.
• the polyacrylic acid (salt)-based water-absorbing resin is preferably in particulate form (also called powder form) among the particulate water-absorbing agents.
• the “main component” refers to the amount (content) of acrylic acid (salt) used relative to the total monomers (excluding the internal crosslinking agent) used in the polymerization, which is usually 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably substantially 100 mol%.
• EDANA European Disposables and Nonwovens Associations
• ERT is an abbreviation for EDANA Recommended Test Methods, a European standard (almost global standard) for measuring the properties of water-absorbent resins.
• the physical properties of the water-absorbent resin are measured in accordance with the original ERT (revised in 2002/publicly known document).
• CRC is an abbreviation for Centrifuge Retention Capacity, and means the water absorption capacity without load of a particulate water-absorbing agent or a water-absorbing resin (sometimes referred to as “water absorption capacity”).
• particulate water absorbent or water absorbent resin is placed in a nonwoven bag, which is then immersed in a large excess of 0.9% by weight sodium chloride aqueous solution for 30 minutes to allow free swelling, and then the water is removed using a centrifuge (250 G). This refers to the water absorption capacity (unit: g/g).
• PSD is an abbreviation for Particle Size Distribution, and means the particle size distribution of a particulate water-absorbing agent or water-absorbing resin measured by sieve classification.
• the weight-average particle diameter (D50) and the logarithmic standard deviation ( ⁇ ) of particle size distribution are measured in the same manner as described in U.S. Patent No. 7,638,570, "(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation ( ⁇ ) of Particle Diameter Distribution.”
• liter may be abbreviated as “l” or “L” and “weight percent” as “wt%.” Furthermore, when measuring trace components, amounts below the detection limit are expressed as N.D. (Non Detected).
• a particulate water absorbing agent according to one embodiment of the present invention is a particulate water absorbing agent mainly composed of a surface-crosslinked polyacrylic acid (salt)-based water absorbent resin, and satisfies the following formula (A) and formula (B).
• the SRC(NP) is measured by a method including the following steps (a) to (c):
• test liquid 0.9% aqueous sodium chloride solution
• step (b) Separate the swollen gel obtained in step (a) from the test liquid.
• the SRC (4.83 kPa) is measured by carrying out a method including steps (c') to (e') described below in place of step (c) in the method including steps (a) to (c).
• step (c') A load of 4.83 kPa is applied to the swollen gel separated in step (b) for one minute.
• step (d') The exudate exuded from the swollen gel in step (c') is removed.
• the SRC (NP) is a parameter that represents the amount of liquid retained in the particulate water absorbing agent when the particulate water absorbing agent is allowed to absorb liquid in a short time, swell, and then held under no pressure. Note that "SRC (NP)” is an abbreviation for Short-time Retention Capacity (No Pressure).
• the SRC (4.83 kPa) is a parameter that represents the amount of liquid retained in the particulate water absorbing agent when the particulate water absorbing agent is allowed to absorb liquid in a short time, swell, and then held under high pressure.
• the particulate water absorbing agent of the present invention satisfies the above formula (A) and formula (B). Therefore, the particulate water absorbing agent of the present invention can absorb a large amount of liquid in a short time, and is excellent in the amount of liquid retained both when held in a swollen state without pressure and when held under high pressure.
• absorbing a large amount of liquid in a short time and being excellent in the amount of liquid retained both when held in a swollen state without pressure and when held under high pressure are characteristics necessary for further reducing the liquid return during actual use of the sanitary product. This point is as described in the above-mentioned "Problem to be solved by the invention" section. Therefore, the particulate water absorbing agent of the present invention can be used in the manufacture of sanitary products that can further reduce the return of absorbed liquid during actual use.
• the particulate water absorbing agent W 0 [g] is contacted with a 0.9% sodium chloride aqueous solution (hereinafter referred to as the "test liquid") adjusted to 23 ⁇ 1°C for 10 minutes without applying a load.
• the particulate water absorbing agent is generally limited in its water absorbing ability when a load is applied. Therefore, the above-mentioned "contact for 10 minutes without applying a load” means that the particulate water absorbing agent is contacted with a large excess of the test liquid without limiting its water absorbing ability by a load, and the particulate water absorbing agent is kept in a state in which it can sufficiently absorb the test liquid for 10 minutes to allow it to freely swell.
• the above-mentioned "contact” means that the particulate water absorbing agent is contacted with the test liquid and made to be in a state in which it can absorb the test liquid.
• the particulate water absorbing agent and the test liquid may be contacted via a member through which liquid can pass, such as a nonwoven fabric and a wire mesh. Therefore, in the step (a), the amount of the test liquid used and the conditions such as the shape and size of the measuring device are appropriately adjusted so that the test liquid used is not insufficient during the 10 minutes, and the free swelling of the particulate water absorbing agent is not hindered.
• the container for carrying out the step (a) is not particularly limited, and may be, for example, a cylinder equipped with a piston.
• the bottom surface of the cylinder is preferably fitted with a wire mesh that is impermeable to the particulate water absorbent and swollen gel described below, and that allows the test liquid and exudate described below to flow in or to be discharged.
• a cylinder and piston used in the Gel Bed Permeability test described in U.S. Patent Publication No. 8,269,060 may be used.
• the specific method for carrying out the step (a) is not particularly limited.
• the method may include the steps (a1) to (a3) shown below.
• step (a2) Following the step (a1), a step of weighing out about 0.9 g of a sample of the particulate water absorbing agent to be measured and uniformly scattering it on the bottom surface of the cylinder, where the accurate weight of the sample is measured in advance and designated as W 0 [g].
• step (a3) Following step (a2), the cylinder is placed in a large excess of 0.9% aqueous sodium chloride solution as a test liquid, and the uniformly dispersed sample is brought into contact with the test liquid for 10 minutes to obtain a swollen gel.
• the sample absorbs the test liquid and swells without being subjected to a load, resulting in a swollen gel.
• the shape and size of the measuring device are not limited. From the viewpoint of improving the accuracy of the measurement of the SRC (NP) and the SRC (4.83 kPa), the device used for the measurement is preferably a circular cylinder with a bottom area of 19 to 40 cm 2.
• the basis weight of the particulate water absorbing agent used for the measurement is preferably 250 to 350 g/m 2.
• the amount of the particulate water absorbing agent used is preferably 0.9 g.
• the swollen gel obtained in the step (a) is separated from the test liquid. That is, this means that the contact between the particulate water absorbing agent and the test liquid performed in the step (a) is terminated, and the test liquid (hereinafter, also referred to as "excess water") that is not absorbed by the hydrogel particles and exists between the hydrogel particles of the swollen gel obtained in the step (a) is removed.
• the method for removing the excess water is not particularly limited.
• the swollen gel obtained in the step (a) is pulled out from the large excess of the test liquid, placed on a sieve and left to stand, and the liquid is drained.
• the time for draining the liquid is preferably about 1 minute.
• the liquid is drained until the excess liquid is removed from the hydrogel particles.
• the "state where excess water is removed” means a state where no water drops fall from the measuring device for 5 seconds.
• the surrounding environment be room temperature (20-25°C) and normal pressure (1 atmosphere) to match the environment in which sanitary products such as diapers are used.
• the step (b) in order to make the thickness of the swollen gel uniform, it is preferable to lift the swollen gel from the test liquid with a piston or the like placed on the swollen gel. Furthermore, it is preferable to drain the liquid from the swollen gel while the piston or the like is still placed on the swollen gel.
• the load applied by the piston is preferably 0.22 to 0.28 kPa, more preferably 0.24 to 0.26 kPa, and particularly preferably 0.25 kPa, from the viewpoint of making the thickness of the swollen gel uniform without applying an excessive load to the swollen gel.
• the weight of the swollen gel separated in the step (b), i.e., the swollen gel separated from the test liquid is measured.
• the method for measuring the weight of the swollen gel is not particularly limited, and the weight can be measured using a commercially available weighing scale.
• the steps (a) to (c) can be performed in a state in which the particulate water absorbing agent and the swollen gel are placed in a container composed of a cylinder, a piston, or the like. In that case, the weight of the container is measured in advance, and the total weight of the container and the swollen gel is measured, and the weight of the swollen gel can be calculated by subtracting the weight of the container from the total weight.
• the test liquid adheres to the container as water droplets the water droplets are removed using, for example, Kimwipes, before measuring the weight.
• the value of the SRC(NP) is calculated based on the following formula (1) using the weight W0 [g] of the particulate water absorbing agent before swelling obtained in the step (a) and the weight W1 [g] of the swollen gel obtained in the step (c).
• SRC (NP) [g/g] W 1 /W 0 (1)
• a load of 4.83 kPa is applied to the swollen gel separated in the step (b), i.e., the swollen gel separated from the test liquid, for 1 minute.
• the surrounding environment when applying the load to the swollen gel is preferably room temperature (20 to 25°C) and normal pressure (1 atm) in order to match the usage environment of sanitary products such as diapers, as in the step (b).
• the load can be applied, for example, by placing a piston on the swollen gel uniformly spread on the bottom surface of a cylinder, and placing a weight capable of applying a load of 4.83 kPa to the swollen gel on the piston.
• a part of the liquid absorbed by the swollen gel in the step (b) exudes from the swollen gel.
• the exuded liquid is referred to as "exudate".
• the exudate seeped out from the swollen gel obtained in the step (c') is removed. That is, the exudate seeped out from the swollen gel after a load of 4.83 kPa is applied for 1 minute is removed.
• the method for removing the exudate is not particularly limited, and examples include a method of performing the following steps (i) and (ii).
• the weight of the swollen gel obtained in the step (d'), i.e., the weight of the swollen gel after the exudate has been removed, is measured.
• the method for measuring the weight of the swollen gel is not particularly limited, and the weight can be measured using a commercially available weighing scale.
• the steps (a), (b) and (c') to (e') can be performed in a state in which the particulate water absorbing agent and the swollen gel are placed in a container composed of a cylinder, a piston, a weight, etc.
• the weight of the container is measured in advance, the total weight of the container and the swollen gel is measured, and the weight of the swollen gel can be calculated by subtracting the weight of the container from the total weight.
• the test liquid and the exudate are attached to the container as water droplets, the water droplets remaining in the container are removed using, for example, Kimwipes, etc., before measuring the weight.
• the value of the SRC (4.83 kPa) is calculated based on the following formula (2) using the weight W0 [g] of the particulate water absorbing agent before swelling obtained in the step (a) and the weight W2 [g] of the swollen gel obtained in the step (e').
• the "liquid return” that is usually used as a physical property evaluation of a water-absorbent resin is an evaluation of an absorbent sheet (absorbent body) in which an absorbent layer containing a water-absorbent resin (water-absorbing agent) and pulp or the like is laminated with a nonwoven fabric or the like, and is not an evaluation of the water-absorbent resin (water-absorbing agent) itself.
• the "liquid return” is also sometimes called the amount of return or Re-Wet.
• SRC (NP) The method for measuring the SRC(NP) is not particularly limited as long as it includes the above-mentioned steps (a) to (e).
• the SRC(NP) is measured, for example, by the method described in the Examples of the present application. It is possible.
• the lower limit of the SRC(NP) is a value exceeding 50.0 g/g, preferably exceeding 54.0 g/g, more preferably exceeding 56.0 g/g, even more preferably exceeding 58.0 g/g, and particularly preferably 59.0 g/g or more.
• the upper limit of the SRC(NP) is not particularly limited, and is usually 70.0 g/g or less.
• the particulate water absorbing agent of the present invention, having the SRC(NP) exceeding the preferred lower limit can absorb a larger amount of liquid in a short time, and can sufficiently retain the large amount of liquid when retained in a swollen state without pressure. As a result, the sanitary product containing the particulate water absorbing agent of the present invention can further reduce the return of absorbed liquid during actual use.
• SRC (4.83kPa) The method for measuring the SRC (4.83 kPa) is not particularly limited as long as it includes the above-mentioned steps (a), (b), and (c') to (e'). can be measured, for example, by the method described in the Examples of the present application.
• the lower limit of the SRC (4.83 kPa) is a value exceeding 41.5 g/g, preferably a value exceeding 42.0 g/g, more preferably a value exceeding 42.5 g/g, and particularly preferably 43.0 g/g.
• the upper limit of the SRC (4.83 kPa) is not particularly limited and is usually 50.0 g/g or less. Since the particulate water absorbing agent of the present invention has an SRC (4.83 kPa) exceeding the preferred lower limit, the agent can absorb a larger amount of liquid in a short time, and can sufficiently retain the large amount of liquid when held under a high pressure of 4.83 kPa in a swollen state. As a result, the sanitary product containing the particulate water absorbing agent of the present invention can further reduce the return of absorbed liquid during actual use.
• CRC centrifuge holding capacity
• particulate water absorbent or water absorbent resin is placed in a nonwoven bag, which is then immersed in a large excess of 0.9% by weight sodium chloride aqueous solution for 30 minutes to allow free swelling, and then the water is removed using a centrifuge (250 G). This refers to the water absorption capacity (unit: g/g).
• the lower limit of the CRC (centrifuge retention capacity) of the particulate water absorbing agent of the present invention is preferably 35 g/g or more, more preferably 36 g/g or more, even more preferably 38 g/g or more, even more preferably 39 g/g or more, particularly preferably 40 g/g or more, and even particularly preferably 41 g/g or more.
• the upper limit of the CRC (centrifuge retention capacity) of the particulate water absorbing agent of the present invention is preferably 70 g/g or less, more preferably 60 g/g or less. If the CRC exceeds 70 g/g, gel blocking is likely to occur when the particulate water absorbing agent swells. Therefore, by having a CRC in an appropriate range, the particulate water absorbing agent becomes suitable for use in disposable diapers and the like with a high water absorption rate.
• the CRC can be controlled by the type and/or amount of the internal cross-linking agent.
• the water absorption speed (Vortex method) of the particulate water absorbing agent of the present invention is preferably 40 seconds or less, more preferably 38 seconds or less, even more preferably 35 seconds or less, particularly preferably 33 seconds or less, and even more particularly preferably 31 seconds or less.
• the surface tension is the work (free energy) required to increase the surface area of a solid and/or liquid, expressed per unit area.
• the surface tension of the aqueous solution is measured by the following procedure. 50 ml of saline solution and a thoroughly washed 25 mm long fluororesin rotor are placed in the container. The surface tension of the saline solution is then measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). The surface tension is measured and confirmed to be 71 to 75 [mN/m]. Next, 0.5 ml of the particulate water absorbing agent is added to the beaker containing the physiological saline solution adjusted to 20° C. after the surface tension measurement.
• the surface tension of the particulate water absorbing agent of the present invention is preferably 66 [mN/m] or more, more preferably 68 [mN/m] or more, even more preferably 70 [mN/m] or more, even more preferably 71 [mN/m] or more, and particularly preferably 72 [mN/m] or more.
• the surface tension satisfies the above conditions, the amount of return in the sanitary products such as diapers can be further reduced.
• An upper limit of the surface tension of 75 [mN/m] is usually sufficient.
• the particle shape of the water absorbent resin (powder) is preferably irregularly pulverized.
• the irregularly pulverized particle means a particle in a pulverized state that does not have a uniform shape.
• the irregularly pulverized particle is preferable for the following reasons (i) to (iii).
• Irregularly pulverized particles have a large surface area and a large contact area with liquid, and therefore have an excellent absorption rate.
• irregularly pulverized particles are not uniform in shape, gaps are easily formed between the particles, and the resulting gaps between the particles have the ability to retain liquid, which increases the amount of absorption.
• irregularly shaped particles do not have a fixed shape, they are highly compatible with hydrophilic fibers such as pulp, and have high liquid diffusion properties due to the gaps between the particles.
• the particulate water absorbing agent according to one embodiment of the present invention is preferably a pulverized product obtained in aqueous solution polymerization.
• the irregularly pulverized particles are obtained by pulverizing a gel or a dried product (preferably a dried product) of a crosslinked polymer obtained through aqueous solution polymerization.
• a pulverization step typically, spherical particles or granulated products of spherical particles obtained by reversed-phase suspension polymerization and droplet polymerization such as spraying and polymerizing a polymerization monomer are not irregularly pulverized.
• the particulate water absorbing agent When the shape of the particulate water absorbing agent is irregularly pulverized, the particulate water absorbing agent is superior in one or more physical properties selected from the group consisting of water absorption speed, SRC (NP) and SRC (4.83 kPa) compared to particulate water absorbing agents with high average circularity (e.g., spherical ones).
• the average circularity of the particulate water absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.
• the particulate water absorbing agent according to one embodiment of the present invention further contains at least one kind selected from the group consisting of inorganic colloid particles, water-insoluble inorganic particles, and water-soluble polyvalent metal cation-containing compound.
• the particulate water absorbing agent of the present invention contains any one of inorganic colloid particles, water-insoluble inorganic particles, and water-soluble polyvalent metal cation-containing compounds, it has excellent handleability in a humid environment. Therefore, by using such a particulate water absorbing agent, problems such as the occurrence of aggregation and clogging in the transfer piping of the manufacturing plant and the inability to mix uniformly with hydrophilic fibers can be made less likely to occur when manufacturing a thin absorbent for sanitary products. Therefore, using such a particulate water absorbing agent is preferable because it can suppress the deterioration of the performance of the sanitary product when manufacturing the thin absorbent containing the particulate water absorbing agent of the present invention.
• the particulate water absorbent contains inorganic colloidal particles, which can further improve the performance of the particulate water absorbent.
• the inorganic colloidal particles refer to inorganic particles dispersed in a dispersion medium in a colloidal solution. Specific examples of the inorganic colloidal particles include colloidal silica in which silicon dioxide particles are dispersed in water, and alumina sol in which aluminum oxide is dispersed in water.
• the content of the inorganic colloidal particles is preferably 0.001 to 5 parts by weight, and more preferably 0.01 to 1 part by weight, in terms of solid content, relative to 100 parts by weight of the polyacrylic acid (salt)-based water absorbent resin in the particulate water absorbent of the present invention.
• the particulate water absorbing agent contains water-insoluble inorganic particles, which can further improve the performance of the particulate water absorbing agent.
• the water-insoluble inorganic particles are not particularly limited. Specific examples of the water-insoluble inorganic particles include silicon dioxide (silica), aluminum hydroxide, zinc oxide, talc, zeolite, hydrotalcite, and tricalcium phosphate.
• the content of the water-insoluble inorganic particles is preferably 0.01% by weight or more and less than 10% by weight, and more preferably 0.1 to 5% by weight, relative to 100% by weight of the polyacrylic acid (salt)-based water-absorbent resin.
• the performance of the particulate water absorbent can be improved.
• the water-soluble polyvalent metal cation-containing compound refers to a compound that contains a divalent or higher, preferably a trivalent or higher metal cation, and is water-soluble. There are no particular limitations on the water-soluble polyvalent metal cation compound. Specific examples of the water-soluble polyvalent metal cation compound include aluminum chloride, potassium zirconium carbonate, zirconium sulfate, aluminum sulfate, potassium aluminum sulfate, and sodium aluminum sulfate.
• water-soluble refers to the property of being soluble (or easily soluble) in water at room temperature (20-25°C) and under normal pressure (1 atm), for example, the amount of dissolution in 100 ml of water at room temperature and normal pressure is 1 g or more.
• water-insoluble refers to the property of being insoluble (or poorly soluble) in water at room temperature (20-25°C) and under normal pressure (1 atm), for example, the amount of dissolution in 100 ml of water at room temperature and normal pressure is less than 1 g.
• the water-insoluble property is preferably such that the amount of dissolution in 100 ml of water at room temperature and normal pressure is less than 0.1 g.
• the content of the water-soluble polyvalent metal cation-containing compound is preferably 0.001 to 5 parts by weight, more preferably 0.01 to 2 parts by weight, and even more preferably 0.01 to 1 part by weight, converted into the amount of polyvalent metal cations relative to 100 parts by weight of the polyacrylic acid (salt)-based water absorbent resin. By having the content within these ranges, the performance of the particulate water absorbent can be improved.
• the particulate water absorbing agent of the present invention preferably further contains at least one chelating agent for the purpose of preventing coloration and deterioration.
• the chelating agent may be at least one chelating agent selected from the group consisting of organic phosphorus chelating agents and aminocarboxylic acid chelating agents.
• the particulate water absorbing agent that has absorbed urine deteriorates over time due to trace amounts of metal ions and L-ascorbic acid contained in the urine, and therefore the liquid retention capacity decreases, and there is a risk that the liquid once absorbed will be discharged again from the sanitary article.
• a chelating agent in the particulate water absorbing agent it is possible to suppress liquid returning over time when the particulate water absorbing agent is used in a sanitary article.
• the content of the chelating agent is preferably 0 to 3 parts by weight, more preferably 0.005 to 1 part by weight, and even more preferably 0.01 to 0.5 parts by weight, relative to 100 parts by weight of the polyacrylic acid (salt)-based water-absorbing resin.
• chelating agent for example, the compounds disclosed in “[2] Chelating Agents” of WO 2011/040530 and the amounts of use thereof may be applied to one embodiment of the present invention.
• This step is a step of preparing an aqueous solution containing acrylic acid (salt) as a monomer as a main component (hereinafter referred to as "monomer aqueous solution").
• monomer aqueous solution an aqueous solution containing acrylic acid (salt) as a monomer as a main component
• a monomer slurry liquid can also be used within a range in which the water absorption performance of the obtained water absorbent resin is not deteriorated, for the sake of convenience, the monomer aqueous solution will be described in this section.
• the “main component” means that the amount (content) of acrylic acid (salt) used is usually 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more (upper limit 100 mol%), based on the total amount of monomers (excluding internal crosslinking agents) used in the polymerization reaction of the water absorbent resin.
• acrylic acid In one embodiment of the present invention, from the viewpoint of the physical properties and productivity of the resulting particulate water absorbing agent, acrylic acid and/or a salt thereof (hereinafter referred to as "acrylic acid (salt)”) is used as a monomer.
• the "acrylic acid” may be a known acrylic acid.
• the "acrylic acid” may contain, as a polymerization inhibitor, preferably methoxyphenols, more preferably p-methoxyphenol, preferably at 200 ppm or less, more preferably 10 to 160 ppm, and even more preferably 20 to 100 ppm.
• the content of the polymerization inhibitor is preferable from the viewpoint of the polymerizability of the acrylic acid and/or the color tone of the particulate water absorbent.
• impurities in acrylic acid the compounds described in U.S. Patent Application Publication No. 2008/0161512 are also applicable to one embodiment of the present invention.
• the "acrylic acid salt” is obtained by neutralizing the acrylic acid with the following basic composition.
• the acrylic acid salt may be a commercially available acrylic acid salt (e.g., sodium acrylate), or may be one obtained by neutralizing acrylic acid in a manufacturing plant for a particulate water absorbent.
• base composition refers to a composition containing a basic compound, such as a commercially available aqueous sodium hydroxide solution.
• the basic compound examples include carbonates or hydrogen carbonates of alkali metals, hydroxides of alkali metals, ammonia, organic amines, and the like.
• the basic compound is strongly basic. That is, the basic compound is preferably a hydroxide of an alkali metal such as sodium hydroxide, potassium hydroxide, or lithium hydroxide, and more preferably sodium hydroxide.
• neutralization As the neutralization in one embodiment of the present invention, either neutralization of acrylic acid (before polymerization) or neutralization of a hydrogel-like crosslinked polymer obtained by crosslinking and polymerizing acrylic acid (after polymerization) (hereinafter referred to as "post-neutralization”) can be selected or used in combination.
• these neutralizations may be either continuous or batchwise, and are not particularly limited, but continuous neutralization is preferred from the viewpoint of production efficiency, etc.
• the neutralization rate is preferably 10 to 90 mol%, more preferably 40 to 85 mol%, even more preferably 50 to 80 mol%, and particularly preferably 60 to 75 mol%, based on the acid groups of the monomer. If the neutralization rate is less than 10 mol%, the water absorption capacity may decrease significantly. On the other hand, if the neutralization rate exceeds 90 mol%, a water-absorbent resin with a high water absorption capacity under pressure may not be obtained.
• the above neutralization rate is the same in the case of post-neutralization.
• the above neutralization rate is also applied to the neutralization rate of the particulate water absorbent as a final product.
• a "neutralization rate of 75 mol%” means a mixture of 25 mol% acrylic acid and 75 mol% acrylic acid salt. The mixture is also sometimes called a partially neutralized product of acrylic acid.
• the "other monomer” refers to a monomer other than the acrylic acid (salt), and the particulate water absorbing agent can be produced by using the other monomer together with the acrylic acid (salt).
• the other monomer may be a water-soluble or hydrophobic unsaturated monomer.
• the compounds described in U.S. Patent Application Publication No. 2005/0215734 (excluding acrylic acid) are also applicable to one embodiment of the present invention.
• Internal Crosslinking Agent As the internal crosslinking agent used in one embodiment of the present invention, the compounds described in U.S. Pat. No. 6,241,928 are also applied to one embodiment of the present invention. Among these, one or more compounds are selected in consideration of reactivity. Although a crosslinked polymer may be obtained without using an internal crosslinking agent depending on the polymerization form and/or the type of polymerization initiator described later, it is preferable to use at least one internal crosslinking agent.
• the amount of the internal crosslinking agent used is preferably 0.0001 to 10 mol%, more preferably 0.001 to 1 mol%, even more preferably 0.001 to 0.5 mol%, even more preferably 0.005 to 0.1 mol%, and particularly preferably 0.005 to 0.05 mol% relative to the total monomer.
• the mol% relative to the total monomer refers to the percentage of the number of moles of the internal crosslinking agent relative to the total number of moles of the monomers contained in the aqueous monomer solution.
• a method is preferably applied in which a predetermined amount of an internal crosslinking agent is added to an aqueous monomer solution in advance, and a crosslinking reaction occurs simultaneously with polymerization.
• a method of post-crosslinking by adding an internal crosslinking agent during and/or after polymerization; a radical crosslinking method using a radical polymerization initiator; a radiation crosslinking method using active energy rays such as electron beams and ultraviolet rays, etc. can also be used. These methods can also be used in combination.
• hydrophilic polymers such as starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), and crosslinked polyacrylic acid (salt).
• the hydrophilic polymer can be added to the monomer aqueous solution in an amount of preferably 50% by weight or less, more preferably 20% by weight or less, even more preferably 10% by weight or less, and particularly preferably 5% by weight or less (the lower limit is 0% by weight).
• foaming agents such as carbonates, azo compounds, and bubbles, surfactants, chelating agents, ⁇ -hydroxycarboxylic acids (salts), and chain transfer agents can be added to the monomer aqueous solution in an amount of preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0.5% by weight or less.
• the lower limit of the amount of the substance to be added is 0% by weight.
• the chelating agent include diethylenetriaminepentaacetic acid (salt), triethylenetetraminehexaacetic acid (salt), hydroxyethylidene diphosphonic acid (salt), and ethylenediaminetetramethylenephosphonic acid (salt).
• the ⁇ -hydroxycarboxylic acid (salt) the compounds exemplified in the additive addition step (3-7) described below can be added in the same manner.
• the substance may be added not only to the aqueous monomer solution, but also during the polymerization process, or these forms may be used in combination.
• a graft polymer or water-absorbent resin composition for example, starch-acrylic acid polymer, PVA-acrylic acid polymer, etc.
• these polymers and water-absorbent resin compositions also fall within the scope of the present invention.
• the concentration of the monomer component in the aqueous monomer solution is not particularly limited, and is preferably 10 to 80% by weight, more preferably 20 to 75% by weight, and further preferably 30 to 70% by weight, from the viewpoint of the physical properties of the water absorbent resin.
• a solvent other than water can be used in combination as necessary.
• the type of solvent is not particularly limited.
• the "monomer component concentration” is the value calculated by the following formula (3), and the weight of the aqueous monomer solution does not include the weight of the graft component, the water-absorbent resin, or the hydrophobic solvent in the reversed-phase suspension polymerization.
• This step is a step of polymerizing the acrylic acid (salt)-based monomer aqueous solution obtained in the monomer aqueous solution preparation step to obtain a hydrous gel crosslinked polymer (hereinafter referred to as "hydrous gel").
• the polymerization initiator used in one embodiment of the present invention is not particularly limited since it is appropriately selected depending on the polymerization form, etc.
• a thermally decomposable polymerization initiator, a photodecomposable polymerization initiator, or a redox-based polymerization initiator in combination with a reducing agent that promotes the decomposition of these polymerization initiators can be mentioned.
• one or more of the polymerization initiators disclosed in U.S. Pat. No. 7,265,190 are used.
• a peroxide or an azo compound preferably a peroxide, and even more preferably a persulfate is used.
• the amount of the polymerization initiator used is preferably 0.001 to 1 mol %, more preferably 0.001 to 0.5 mol %, based on the monomer.
• the amount of the reducing agent used is preferably 0.0001 to 0.02 mol %, based on the monomer.
• the polymerization reaction may be carried out by irradiating the material with active energy rays such as radiation, electron beams, and ultraviolet rays, and these active energy rays may be used in combination with the polymerization initiator.
• active energy rays such as radiation, electron beams, and ultraviolet rays
• the polymerization form applied to the present invention is not particularly limited, but from the viewpoint of water absorption characteristics, ease of polymerization control, etc., preferably includes spray droplet polymerization, aqueous solution polymerization, and reversed phase suspension polymerization, more preferably aqueous solution polymerization, reversed phase suspension polymerization, and even more preferably aqueous solution polymerization.
• continuous aqueous solution polymerization is particularly preferred.
• the continuous aqueous solution polymerization either continuous belt polymerization or continuous kneader polymerization can be applied.
• continuous belt polymerization is disclosed in U.S. Pat. Nos. 4,893,999, 6,241,928, and U.S. Patent Application Publication No. 2005/215734
• continuous kneader polymerization is disclosed in U.S. Pat. Nos. 6,987,151 and 6,710,141.
• Preferred forms of the continuous aqueous solution polymerization include “high-temperature initiated polymerization” and “high-concentration polymerization.”
• “High-temperature initiated polymerization” refers to a form in which polymerization is initiated at a temperature of the aqueous monomer solution of preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and particularly preferably 50°C or higher (upper limit is the boiling point).
• “High-concentration polymerization” refers to a form in which polymerization is performed at a monomer concentration of preferably 30% by weight or higher, more preferably 35% by weight or higher, even more preferably 40% by weight or higher, and particularly preferably 45% by weight or higher (upper limit is the saturation concentration).
• the polymerization can be carried out in an air atmosphere, but from the viewpoint of the color tone of the resulting water-absorbent resin, the polymerization can be carried out in an inert gas atmosphere such as nitrogen or argon.
• an inert gas atmosphere such as nitrogen or argon.
• foaming polymerization can be used in which bubbles (especially the inert gases mentioned above) are dispersed in the aqueous monomer solution to carry out polymerization.
• This step is a step in which the hydrogel obtained in the polymerization step is crushed by a gel crusher such as a screw extruder such as a kneader or a meat chopper, or a cutter mill, to obtain a particulate hydrogel (hereinafter referred to as a "particulate hydrogel").
• a gel crusher such as a screw extruder such as a kneader or a meat chopper, or a cutter mill
• the polymerization step and the gel crushing step are carried out simultaneously.
• gas phase polymerization, reverse phase suspension polymerization, or the like is used in the polymerization step and the particulate hydrogel is obtained directly in the polymerization process, the gel crushing step may not be carried out.
• the SRC (NP) and SRC (4.83 kPa) of the particulate water absorbent produced can be controlled by controlling the gel crushing means (kneader, etc.) and the gel crushing energy (GGE), which is one of the gel crushing conditions described below.
• GGE gel crushing energy
• the contents disclosed in International Publication No. 2011/126079 as the gel crushing conditions and form other than the gel crushing energy (GGE) are preferably applied to one embodiment of the present invention.
• This step is a step of drying the particulate hydrogel obtained in the polymerization step and/or gel crushing step to a desired resin solid content to obtain a dry polymer.
• the resin solid content is determined from the loss on drying (weight change when 1 g of the water-absorbent resin is heated at 180°C for 3 hours), and is preferably 80% by weight or more, more preferably 85 to 99% by weight, even more preferably 90 to 98% by weight, and particularly preferably 92 to 97% by weight.
• the method for drying the particulate hydrogel is not particularly limited, and examples thereof include heat drying, hot air drying, reduced pressure drying, fluidized bed drying, infrared drying, microwave drying, drum dryer drying, drying by azeotropic dehydration with a hydrophobic organic solvent, and high humidity drying using high-temperature water vapor.
• hot air drying is preferred, and band drying in which hot air drying is performed on a ventilated belt is more preferred.
• the drying temperature (hot air temperature) in the hot air drying is preferably 120 to 250°C, more preferably 150 to 200°C, from the viewpoint of the color tone of the water-absorbent resin and drying efficiency.
• the drying conditions other than the drying temperature such as the hot air speed and drying time, may be appropriately set according to the water content, total weight, and target resin solid content of the particulate hydrogel to be dried.
• band drying the various conditions described in WO 2006/100300, WO 2011/025012, WO 2011/025013, WO 2011/111657, etc. are appropriately applied.
• Pulverization step, classification step This step is a step of pulverizing the dried polymer obtained in the drying step (pulverization step), and adjusting the particle size to a predetermined range (classification step) to obtain a water absorbent resin powder (a powdered water absorbent resin before surface crosslinking is conveniently referred to as a "water absorbent resin powder").
• the equipment used in the grinding step includes, for example, high-speed rotary grinders such as roll mills, hammer mills, screw mills, and pin mills, vibration mills, knuckle-type grinders, and cylindrical mixers. These may be used in combination as necessary.
• high-speed rotary grinders such as roll mills, hammer mills, screw mills, and pin mills, vibration mills, knuckle-type grinders, and cylindrical mixers. These may be used in combination as necessary.
• the method of adjusting the particle size in the classification process in one embodiment of the present invention is not particularly limited, and examples thereof include sieve classification using a JIS standard sieve (JIS Z8801-1 (2000)), air flow classification, etc.
• the particle size adjustment of the water absorbent resin is not limited to the pulverization process and classification process, and can be appropriately performed in the polymerization process (particularly reverse phase suspension polymerization and spray droplet polymerization) and other processes (for example, a granulation process and a fine powder recovery process).
• the weight average particle diameter (D50) of the water absorbent resin powder (water absorbent resin powder before the surface cross-linking step, so-called base polymer) obtained in the above step is preferably 200 to 600 ⁇ m, more preferably 200 to 550 ⁇ m, even more preferably 250 to 500 ⁇ m, and particularly preferably 300 to 500 ⁇ m.
• the ratio of particles having a particle diameter of less than 150 ⁇ m in the water absorbent resin powder is preferably 10% by weight or less, more preferably 5% by weight or less, even more preferably 3% by weight or less, and particularly preferably 1% by weight or less.
• the ratio of particles having a particle diameter of 850 ⁇ m or more in the water absorbent resin powder is preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 1% by weight or less.
• the lower limit value of the ratio of these particles the lower the better in any case, and 0% by weight is desirable, but about 0.1% by weight may be sufficient.
• the logarithmic standard deviation ( ⁇ ) of the particle size distribution is preferably 0.20 to 0.50, more preferably 0.25 to 0.40, and even more preferably 0.27 to 0.35.
• the water absorbent resin powder in one embodiment of the present invention satisfies the above particle size distribution. Note that these particle sizes are measured using standard sieves in accordance with the measurement method disclosed in U.S. Patent No. 7,638,570 or EDANA ERT420.2-02.
• the above-mentioned particle size is applied not only to the water-absorbent resin after surface cross-linking (hereinafter, for convenience, may be referred to as "water-absorbent resin particles"), but also to the particulate water-absorbing agent as a final product. Therefore, in the water-absorbent resin particles, it is preferable to perform a surface cross-linking treatment (surface cross-linking step) so as to maintain the particle size in the above-mentioned range, and it is more preferable to adjust the particle size by providing a sizing step after the surface cross-linking step.
• a surface cross-linking treatment surface cross-linking step
• This step is a step for providing a portion with a higher cross-linking density on a surface layer (a portion several tens of ⁇ m from the surface of a water absorbent resin powder) of a water absorbent resin powder obtained through the above-mentioned steps, and is composed of a mixing step, a heat treatment step, and a cooling step (optional).
• surface cross-linked water-absorbent resin (water-absorbent resin particles) is obtained by radical cross-linking on the surface of the water-absorbent resin powder, surface polymerization, cross-linking reaction with a surface cross-linking agent, etc.
• the surface crosslinking agent used in one embodiment of the present invention is not particularly limited, and may be an organic or inorganic surface crosslinking agent. Among them, from the viewpoint of the physical properties of the water-absorbent resin and the handling of the surface crosslinking agent, an organic surface crosslinking agent that reacts with a carboxyl group is preferred. For example, one or more surface crosslinking agents disclosed in U.S. Patent No. 7,183,456 may be mentioned.
• polyhydric alcohol compounds epoxy compounds, haloepoxy compounds, polyamine compounds or their condensates with haloepoxy compounds, oxazoline compounds, oxazolidinone compounds, polyvalent metal salts, alkylene carbonate compounds, cyclic urea compounds, etc. may be mentioned.
• organic surface crosslinking agent examples include polyalcohol compounds such as (di-, tri-, tetra-, poly)ethylene glycol, (di-, poly)propylene glycol, 1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, (poly)glycerin, 2-butene-1,4-diol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, trimethylolpropane, di- or triethanolamine, pentaerythritol, and sorbitol; ) Epoxy compounds such as ethylene glycol diglycidyl ether, (di, poly)glycerol polyglycidyl ether, and glycidol; oxazoline compounds such as 2-oxazolidone, N-hydroxyethyl-2-oxazolidone
• the polyhydric alcohol is preferably a polyhydric alcohol having 2 to 8 carbon atoms, more preferably a polyhydric alcohol having 3 to 6 carbon atoms, and even more preferably a polyhydric alcohol having 3 or 4 carbon atoms.
• diols are particularly preferred as the polyhydric alcohol. Examples of the diols include ethylene glycol, propylene glycol, 1,3-propanediol, and 1,4-butanediol.
• the polyhydric alcohol is preferably one or more polyhydric alcohols selected from propylene glycol (1,2-propanediol), 1,3-propanediol, and 1,4-butanediol.
• the epoxy compound is preferably a polyglycidyl compound, and ethylene glycol diglycidyl ether is preferably used.
• a polyvalent cationic polymer such as a polyamine polymer and/or a water-soluble polyvalent metal cation-containing compound may be used in combination as an ion-bonding surface crosslinking agent.
• the water-soluble polyvalent metal cation-containing compound is as described above.
• These polyvalent cationic polymers and/or water-soluble polyvalent metal cation-containing compounds may be added to a surface crosslinking agent solution described later and mixed with the water absorbent resin powder, or may be added to the water absorbent resin powder separately from the surface crosslinking agent solution and mixed.
• the amount of the surface cross-linking agent used is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight, relative to 100 parts by weight of the water absorbent resin powder.
• the surface cross-linking agent is preferably added as an aqueous solution, and in this case, the amount of water used is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, relative to 100 parts by weight of the water absorbent resin powder.
• the amount used is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, relative to 100 parts by weight of the water absorbent resin powder.
• This step is a step of mixing a water absorbent resin powder with the surface crosslinking agent.
• a method of mixing the surface crosslinking agent is not particularly limited, and includes a method of preparing a surface crosslinking agent solution in advance, and preferably spraying or dropping the liquid onto the water absorbent resin powder, more preferably spraying and mixing.
• the device used for the mixing is not particularly limited, but is preferably a high-speed stirring mixer, more preferably a high-speed stirring continuous mixer.
• This step is a step in which heat is applied to the mixture discharged from the mixing step to cause a crosslinking reaction on the surface of the water absorbent resin powder.
• the device for carrying out the crosslinking reaction is not particularly limited, and a paddle dryer is preferred.
• the reaction temperature in the crosslinking reaction is set appropriately depending on the type of surface crosslinking agent used, and is preferably 50 to 300°C, more preferably 80 to 200°C.
• This step is an optional step which is performed as necessary after the heat treatment step.
• the cooling device is not particularly limited, but is preferably a device with the same specifications as the device used in the heat treatment step, and more preferably a paddle dryer. This is because the device can be used as a cooling device by changing the heat medium to a refrigerant.
• the water-absorbent resin particles obtained in the heat treatment step are forcibly cooled, as necessary, in the cooling step, preferably to 40 to 80°C, more preferably to 50 to 70°C.
• This step is a step of adding additives such as polyvalent metal salts, cationic polymers, chelating agents, inorganic reducing agents, hydroxycarboxylic acid compounds, water-insoluble inorganic particles, inorganic colloidal particles, water-soluble polyvalent metal cation-containing compounds, surfactants, non-polymeric water-soluble compounds, etc. to the water absorbent resin particles obtained in the surface crosslinking step.
• additives can also be mixed with the water absorbent resin powder simultaneously with the surface crosslinking agent (aqueous solution).
• a polyvalent metal salt and/or a cationic polymer may be added to the water absorbent resin particles obtained in the surface cross-linking step.
• polyvalent metal salt and/or cationic polymer that can be used in one embodiment of the present invention include the compounds disclosed in “[7] Polyvalent metal salt and/or cationic polymer” of WO 2011/040530 and the amounts of the compounds used.
• a chelating agent may be added to the water absorbing resin particles obtained in the surface cross-linking step.
• the compounds and the amounts used thereof disclosed in “[2] Chelating Agents” of WO 2011/040530 are applicable to one embodiment of the present invention.
• an inorganic reducing agent may be added to the water absorbing resin particles obtained in the surface cross-linking step.
• the compounds and the amounts used thereof disclosed in “[3] Inorganic reducing agents” of WO 2011/040530 are applicable to one embodiment of the present invention.
• an ⁇ -hydroxycarboxylic acid may be added to the water absorbent resin particles obtained in the surface cross-linking step.
• the " ⁇ -hydroxycarboxylic acid compound” refers to a carboxylic acid having a hydroxyl group in the molecule or a salt thereof, and is a hydroxycarboxylic acid having a hydroxyl group at the ⁇ -position.
• ⁇ -hydroxycarboxylic acid compound for example, the compounds and the amounts used thereof disclosed in “[6] ⁇ -hydroxycarboxylic acid compounds” of WO 2011/040530 are applicable to one embodiment of the present invention, with malic acid (salt) and lactic acid (salt) being particularly preferred.
• water-insoluble inorganic particles may be added to the water-absorbent resin particles obtained in the surface cross-linking step.
• examples of the water-insoluble inorganic particles added to the water-absorbent resin particles obtained in the surface cross-linking step include the water-insoluble inorganic particles described in the section (2-6) above.
• inorganic colloid particles may be added to the water absorbent resin particles obtained in the surface cross-linking step.
• examples of the inorganic colloid particles added to the water absorbent resin particles obtained in the surface cross-linking step include the inorganic colloid particles described in the section (2-6) above.
• a water-soluble polyvalent metal cation-containing compound may be added to the water-absorbent resin particles obtained in the surface cross-linking step.
• the water-soluble polyvalent metal cation-containing compound include the water-soluble polyvalent metal cation-containing compounds described in the section (2-6) above.
• a surfactant may be added to the water absorbent resin particles obtained in the surface cross-linking step.
• surfactant examples include those disclosed in International Publication No. 97/017397 or U.S. Patent No. 6,107,358, i.e., nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc.
• Non-polymer water-soluble compound From the viewpoint of reducing dust of the water absorbent resin, a non-polymeric water-soluble compound may be added to the water absorbent resin particles obtained in the surface cross-linking step.
• the compounds and the amounts used thereof disclosed in the section "Non-polymeric water-soluble compounds" of WO 2014/034667 are applicable to one embodiment of the present invention.
• additives other than the additives described above can be added to the water-absorbent resin particles obtained in the surface cross-linking step in order to impart various functions to the water-absorbent resin.
• additives include compounds having phosphorus atoms, oxidizing agents, organic reducing agents, organic powders such as metal soaps, deodorants, antibacterial agents, pulp, and thermoplastic fibers.
• the amount of the additive used is not particularly limited, as it is appropriately determined depending on the application.
• the amount used (addition amount) is preferably 3 parts by weight or less, and more preferably 1 part by weight or less, per 100 parts by weight of the water-absorbent resin.
• the additive can also be added in a process separate from the above process.
• a granulation step, a sizing step, a fine powder removal step, a fine powder reuse step, etc. can be provided as necessary.
• one or more steps such as a transport step, a storage step, a packaging step, and a storage step may be further included.
• the "sizing step” includes a fine powder removal step subsequent to the surface crosslinking step, and a step of classifying and pulverizing the water absorbent resin when the water absorbent resin aggregates and exceeds a desired size.
• the "fine powder reuse step” includes a step of adding the fine powder as it is as in the present invention, and a step of making the fine powder into a large hydrous gel and adding it to any step of the water absorbent resin production process.
• the control method may be, for example, carrying out the gel crushing described in the above section "(3-3) Gel Crushing Step” under specific conditions.
• the gel crushing may be carried out by controlling the gel crushing energy (GGE) to preferably 15 to 40 J/g, more preferably 20 to 40 J/g, even more preferably 20 to 35 J/g, and particularly preferably 25 to 35 J/g.
• GGE gel crushing energy
• the gel crushing can be carried out while applying appropriate shear force and compression force to the hydrogel.
• the particle shape and particle size distribution of the hydrogel can be controlled, and the SRC (NP) and SRC (4.83 kPa) of the produced particulate water absorbent can be controlled within the above-mentioned preferred ranges.
• gel grinding energy in one embodiment of the present invention refers to the unit energy required by the gel grinding device when grinding the hydrous gel, i.e., the mechanical energy per unit mass of the hydrous gel. The energy for heating and cooling the jacket, and the energy of the water and steam input are not included in the gel grinding energy. Note that “gel grinding energy” is abbreviated to "GGE” from the English term “Gel Grinding Energy.”
• the "power factor” and “motor efficiency” are values specific to the device that change depending on the operating conditions of the gel grinding device, and take values of 0 to 1. These values can be obtained by contacting the device manufacturer, etc.
• GGE can be calculated by changing " ⁇ 3" to "1" in the above formula (6).
• the unit of voltage is [V]
• the unit of current is [A]
• the unit of mass of hydrous gel is [g/s].
• the "power factor” and “motor efficiency” of the GGE are values used when gel is being crushed.
• the power factor and motor efficiency values during idle operation are approximately defined as in formula (6) above, since the current value during idle operation is small.
• the "mass of hydrous gel fed into the gel crusher per second" [g/s] refers to the value converted to [g/s], for example, when the hydrous gel is continuously fed by a fixed quantity feeder.
• the hydrous gel may contain recycled granulated gel, as described below.
• the mechanical energy applied to the hydrogel is important. Therefore, it is preferable to calculate the gel crushing energy by using the current value obtained by subtracting the current value when the gel crushing device is running without electricity from the current value when the gel is crushed as the "current" value in the above formula (6).
• the total current value during running without electricity becomes large, so it is preferable to calculate GGE by using the current value obtained by subtracting the current value when the gel is crushed without electricity from the current value when the gel is crushed as the "current” value in the above formula (6).
• the hydrous gel is crushed by applying a high GGE of 15 J/g or more in the gel crushing step
• the CRC of the water-absorbent resin particles obtained by carrying out the drying step and the crushing and classification step described above after the gel crushing step is preferably 50 to 70 g/g, more preferably 50 to 65 g/g, even more preferably 51 to 63 g/g, and particularly preferably 52 to 62 g/g.
• the reasons are as follows.
• the hydrogel obtained in the polymerization step must be a low-crosslinked gel with a relatively low crosslinking density. It is difficult to crush such a low-crosslinked gel by applying a high GGE of 15 J/g or more. Therefore, it is difficult to apply appropriate shear force and compression force to the low-crosslinked gel in order to control the SRC (NP) and SRC (4.83 kPa) to the preferred ranges described above.
• Methods for reducing the dischargeability of the hydrous gel include installing a weir at the crusher outlet, reducing the size of the crusher outlet, and adjusting the perforated plate installed at the crusher outlet. This makes it easier to apply energy to the low-crosslinked gel, even if the hydrous gel supplied to the crusher is a low-crosslinked gel, and allows appropriate shear and compression forces to be applied to the low-crosslinked gel. As a result, the SRC (NP) and SRC (4.83 kPa) were improved.
• GGE gel grinding energy
• the control method can include, for example, a method of making the water-absorbent resin particles into a foamed shape, and a method of polymerizing the water-absorbent resin particles by lowering the monomer concentration in the aqueous monomer solution in the polymerization step.
• a method of making the water-absorbent resin particles into a foamed shape By making the water-absorbent resin particles into a foamed shape, the surface area of the water-absorbent resin particles can be increased, and the liquid retention of the particulate water absorbent can be improved.
• the performance of the particulate water absorbent can be improved.
• the SRC (NP) and SRC (4.83 kPa) of the produced particulate water absorbent can be controlled to the above-mentioned preferred ranges.
• the particulate water absorbing agent of the present invention is used for purposes of absorbing water, and is widely used as an absorbent.
• the particulate water absorbing agent of the present invention can also be used in absorbent articles including the absorbent.
• the particulate water absorbing agent of the present invention is reduced in liquid return under pressure, and is therefore suitably used as sanitary articles for absorbing bodily fluids such as urine and blood used by humans, among other absorbent articles.
• a preferred embodiment of the present invention is an absorbent body containing the particulate water absorbing agent of the above-mentioned form.
• Another preferred embodiment of the present invention is a sanitary article containing the absorbent body. Since the absorbent body contains the particulate water absorbing agent of the present invention, the sanitary product containing the absorbent body can further reduce the return of absorbed liquid during actual use.
• the absorbent body may be an absorbent material formed from a particulate water absorbing agent and a fiber base material (e.g., hydrophilic fiber) as main components.
• the content (core concentration) of the particulate water absorbing agent relative to the total weight of the particulate water absorbing agent and hydrophilic fiber in the absorbent body is preferably 10 to 100% by weight, more preferably 15 to 90% by weight, particularly preferably 20 to 80% by weight, and most preferably 25 to 80% by weight.
• the higher the core concentration in the absorbent body the more the water absorption performance of the absorbent body and the sanitary product containing the absorbent body is affected by the water absorption performance of the particulate water absorbing agent contained in the absorbent body and the sanitary product.
• the particulate water absorbing agent contained in the absorbent body and the sanitary product is the particulate water absorbing agent used in the manufacture of the absorbent body and the sanitary product.
• Such an absorbent body is formed, for example, by blending or sandwiching a fiber base material such as hydrophilic fiber and a particulate water absorbing agent.
• fiber substrates that can be used include hydrophilic fibers such as ground wood pulp, cotton linters, crosslinked cellulose fibers, rayon, cotton, wool, acetate, vinylon, etc. These fiber substrates are preferably air-laid.
• the absorbent may also be a (pulpless) absorbent sheet in which an absorbent resin is fixed between two sheets (e.g., nonwoven fabric).
• the absorbent article is one comprising the absorbent body, a liquid-permeable top sheet, and a liquid-impermeable back sheet.
• the absorbent article is prepared by producing an absorbent body (absorbent core) and sandwiching the absorbent core between a liquid-permeable top sheet and a liquid-impermeable back sheet. Thereafter, an elastic member, a diffusion layer, an adhesive tape, etc. are provided as necessary to obtain an absorbent article such as a paper diaper for adults or a sanitary napkin.
• the absorbent core is compression molded to have a density of 0.06 to 0.50 [g/cm 3 ] and a basis weight of 0.01 to 0.20 [g/cm 2 ].
• One embodiment of the present invention may include the inventions shown in [1] to [8] below.
• the SRC(NP) is measured by a method including the following steps (a) to (c):
• test liquid 0.9% aqueous sodium chloride solution
• step (b) Separate the swollen gel obtained in step (a) from the test liquid.
• the SRC (4.83 kPa) is measured by carrying out a method including steps (c') to (e') described below in place of step (c) in the method including steps (a) to (c).
• step (c') A load of 4.83 kPa is applied to the swollen gel separated in step (b) for one minute.
• step (d') The exudate exuded from the swollen gel in step (c') is removed.
• CRC centrifuge retention capacity
• the particulate water absorbent according to any one of [1] to [7], further comprising at least one selected from the group consisting of inorganic colloid particles, water-insoluble inorganic particles, and water-soluble polyvalent metal cation-containing compounds.
• a hygiene product comprising the absorbent body described in [9].
• the electrical equipment used in the Examples, Comparative Examples, and Reference Examples used a power supply of 200V or 100V unless otherwise noted.
• the total weight of the cylinder and the piston used for measuring SRC (NP) was measured, and the value was designated as W a [g].
• W a the total weight of the cylinder and the piston used for measuring SRC
• about 0.9 g of a sample of the particulate water absorbing agent to be measured was weighed out and uniformly spread on the bottom surface of the cylinder.
• the exact weight of the sample was designated as W 0 [g].
• the cylinder was placed in a large excess of a 0.9% aqueous sodium chloride solution adjusted to 23 ⁇ 1° C. as a test liquid. In this way, the uniformly spread sample was brought into contact with the test liquid for 10 minutes, and the sample was made to absorb the test liquid and swell without applying a load, thereby obtaining a swollen gel.
• a piston (approximately 72 g) was placed on top of the swollen gel in the cylinder, and the cylinder was lifted out of the test liquid.
• the cylinder lifted out of the test liquid was placed on a JIS standard sieve with a mesh size of 2000 ⁇ m.
• the solution present in the cylinder that was not held by the swollen gel i.e., the excess liquid, was drained off from the bottom of the cylinder. In other words, the excess liquid that was not held by the swollen gel was removed.
• the cylinder was left on the JIS standard sieve for 1 minute to remove excess water from the swollen gel particles. That is, at the start of the draining, i.e., 1 minute after the cylinder was placed on the JIS standard sieve, no water droplets fell from the measuring device for 5 seconds. Thereafter, the weights of the cylinder, the swollen gel, and the piston were measured. At this time, if water droplets were attached to the bottom and/or side of the cylinder, the water droplets were removed using Kimwipe (S-200 manufactured by Nippon Paper Crecia) or the like before the weight measurement. The weight of the obtained cylinder, the swollen gel, and the piston was defined as W b [g].
• the SRC (NP) of the particulate water absorbent constituting the sample was calculated based on the following formula (1').
• (W b [g] - W a [g]) in the formula (1') described below is the weight of the swollen gel after being allowed to stand in the above-mentioned step (b): W 1 [g].
• the total weight of the cylinder, the piston, and the weight used in measuring the SRC (4.83 kPa) was measured, and the value was designated as W c [g].
• W c the total weight of the cylinder, the piston, and the weight used in measuring the SRC (4.83 kPa) was measured, and the value was designated as W c [g].
• about 0.9 g of a sample of the particulate water absorbing agent to be measured was weighed out and uniformly spread on the bottom surface of the cylinder.
• the exact weight of the sample was designated as W 0 [g].
• the cylinder was placed in a large excess of a 0.9% aqueous sodium chloride solution adjusted to 23 ⁇ 1° C. as a test liquid. In this way, the uniformly spread sample was brought into contact with the test liquid for 10 minutes, and the sample was made to absorb the test liquid and swell without applying a load, thereby obtaining a swollen gel.
• a piston (approximately 72 g) was placed on top of the swollen gel in the cylinder, and the cylinder was lifted out of the test liquid.
• the cylinder lifted out of the test liquid was placed on a JIS standard sieve with a mesh size of 2000 ⁇ m.
• the solution present in the cylinder that was not held by the swollen gel i.e., the excess liquid, was drained off from the bottom of the cylinder. In other words, the excess liquid that was not held by the swollen gel was removed.
• the cylinder was left on the JIS standard sieve for 1 minute to remove excess water from the swollen gel particles. That is, at the start of the draining, i.e., 1 minute after the cylinder was placed on the JIS standard sieve, no water droplets fell from the measuring device for 5 seconds. Then, the weight (about 1316 g) was additionally placed on the piston. At this time, the load applied to the swollen gel was 4.83 kPa. The above operation caused the solution that had been held between the swollen gels before pressure to seep out.
• the exudate stopped seeping out and reached a steady state, so the remainder of the exudate that had accumulated on the top of the piston was quickly removed using a dropper.
• the weights of the cylinder, the piston, the weight, and the swollen gel were measured.
• the water droplets were attached to the bottom and/or side of the cylinder, the water droplets were removed using Kimwipes (S-200 manufactured by Nippon Paper Crecia) or the like before measuring the weight.
• the weight of the cylinder, the piston, the weight, and the swollen gel obtained is W d [g].
• W 0 , W c , and W d the SRC (4.83 kPa) of the particulate water absorbent constituting the sample was calculated based on the following formula (2').
• Particle size distribution Particle size distribution, weight average particle diameter (D50), logarithmic standard deviation of particle size distribution ( ⁇ )
• the particle size distribution (particle size distribution, weight average particle diameter (D50), logarithmic standard deviation ( ⁇ ) of particle size distribution) of the particulate water-absorbing agent or water-absorbing resin was measured in accordance with “(3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation ( ⁇ ) of Particle Diameter Distribution” described in columns 27 and 28 of U.S. Pat. No. 7,638,570.
• the end point was measured as the water absorption rate (seconds) in accordance with the standard described in JIS K 7224-1996 "Explanation of the water absorption rate test method for superabsorbent resins" and the time until the water absorbing agent absorbed the physiological saline and the test liquid covered the stirrer tip.
• the particulate water absorbing agent was added to a beaker containing the physiological saline solution after the surface tension measurement, which had been adjusted to 20°C, and the solution was stirred for 4 minutes at 500 rpm. After 4 minutes, the stirring was stopped, and the particulate water absorbing agent containing water was allowed to settle, after which the surface tension of the supernatant liquid was measured by carrying out the same operation as that for measuring the surface tension of the physiological saline solution alone.
• a plate method using a platinum plate was adopted, and the plate was thoroughly washed with deionized water before each measurement, and heated and washed with a gas burner before use.
• absorbent material A 3g of particulate water absorbing agent was uniformly scattered on the upper surface, and the other of the absorbent cotton sheets weighing 2.8g was placed on top to form a sand structure. Furthermore, a load of 10kg was applied to the entire frame and held for 1 minute to form an absorbent body. After this, the load and the frame were removed, and both ends of the absorbent paper were folded back along the longitudinal direction of the absorbent body so as to wrap the absorbent body. The obtained absorbent material was placed in a nonwoven bag (10 cm x 22 cm) made using Heatlon paper, and the periphery was heat sealed to prepare absorbent material A.
• an acrylic plate was placed on a portion of the upper surface of the absorbent A having an area of 8 cm x 16 cm where the particulate water absorbing agent was present, and a weight with a total weight of 6405 g together with the acrylic plate was placed on top of the acrylic plate, and the liquid was drained for 1 minute.
• the pressure applied by the acrylic plate and the weight to the portion of the absorbent A on which the acrylic plate was placed was 50 g/ cm2 .
• the weight of absorbent body A after the liquid was drained was measured, and the difference between this weight and the weight of absorbent body A before immersion, which was previously measured, was calculated as the “absorption amount by absorbent body.” The calculated values are shown in Table 2.
• the frame was removed, and an air-through nonwoven fabric cut to a size of 100 mm x 200 mm was placed on the particulate water absorbing agent, and the outer periphery of the air-through nonwoven fabric was attached to the vinyl tape to form an absorbent B.
• the sodium chloride aqueous solution was poured using a liquid pouring device having a cylinder with an inner diameter of 20 mm and a length of 80 mm at the center of a flat plate of 80 mm x 160 mm with a circular hole with an inner diameter of 20 mm at the center. The inside of the cylinder was connected to the circular hole.
• the liquid pouring device was installed on the 8 cm x 16 cm part of the upper surface of absorbent B where the particulate water absorbing agent was present, i.e., on the central part, and the sodium chloride aqueous solution was poured into the center of absorbent B through the cylinder and the circular hole using a funnel with a flow rate of 7 mL/sec. 10 minutes after the start of pouring the sodium chloride aqueous solution, 30 sheets of 80 mm x 80 mm filter paper whose weight had been measured in advance were placed in the central part, and the entire filter paper was pressed with a 3200 g weight for 1 minute. At that time, liquid oozed out from absorbent B and was absorbed by the filter paper.
• the filter paper used was a filter paper manufactured by ADVANTEC, model No. 2, 100 mm x 100 mm cut to 80 mm x 80 mm.
• the difference between the weight of the filter paper before use and the weight of the filter paper after absorbing the liquid was calculated as the "amount of liquid returning from the absorbent". The calculated values are shown in Table 2.
• aqueous monomer solution (1) consisting of 300 parts by weight of acrylic acid, 123.6 parts by weight of a 48% by weight aqueous sodium hydroxide solution, 0.44 parts by weight of polyethylene glycol diacrylate (average n number: 9) (hereinafter referred to as “PEGDA-9”), 1.18 parts by weight of a 31% by weight aqueous ethylenediaminetetramethylenephosphonic acid solution, and 331.8 parts by weight of deionized water was prepared.
• PEGDA-9 polyethylene glycol diacrylate
• the monomer aqueous solution (1) whose temperature had been adjusted to 41°C, was continuously supplied by a metering pump to a continuous polymerization machine having a flat polymerization belt with weirs on both ends of the belt, and polymerization was carried out.
• 127.0 parts by weight of a 48% by weight aqueous sodium hydroxide solution was continuously mixed with the monomer aqueous solution (1) by a line mixer. After mixing, the liquid temperature of the mixture of the monomer aqueous solution (1) and the 48% by weight aqueous sodium hydroxide solution rose to 80°C due to the heat of neutralization.
• the obtained monomer aqueous solution (1) was continuously mixed with 10.6 parts by weight of a 5 wt% aqueous sodium persulfate solution using a line mixer to obtain a mixed solution.
• the mixed solution was continuously supplied to the continuous polymerization machine so that the liquid depth on the polymerization belt was 10 mm.
• a polymerization reaction occurred on the polymerization belt, and a belt-shaped hydrogel (1) was obtained.
• the polymerization time was 3 minutes.
• the obtained belt-shaped hydrogel (1) was continuously cut at equal intervals in the width direction relative to the traveling direction of the polymerization belt so that the cut length was 300 mm, to obtain a hydrogel (1).
• the hydrous gel (1) was fed to a screw extruder, and gel pulverization of the hydrous gel (1) was carried out.
• the screw extruder was a meat chopper with a screw shaft having an outer diameter of 86 mm and a perforated plate with a diameter of 100 mm, a hole diameter of 4.0 mm, 207 holes, and a thickness of 10 mm at the tip.
• the screw shaft rotation speed of the meat chopper set to 130 rpm
• the hydrous gel (1) was fed to the meat chopper at 4640 [g/min] and steam at 83 [g/min], respectively, at the same time.
• gel pulverization was carried out on the hydrous gel (1).
• a pulverized gel after gel pulverization i.e., a particulate hydrous gel (1).
• the gel pulverization energy (GGE) in the gel pulverization was 29.3 [J/g].
• the particulate hydrogel (1) was spread on a 50-mesh wire screen and dried with hot air at 180°C for 30 minutes to obtain dried product A (1).
• the dried product A (1) was pulverized using a roll mill (WML type roll pulverizer/Inoguchi Giken Co., Ltd.) to obtain pulverized product (1).
• the pulverized product (1) was then sieved using JIS sieves with mesh sizes of 850 ⁇ m, 600 ⁇ m, 500 ⁇ m, 300 ⁇ m, 150 ⁇ m, and 45 ⁇ m.
• irregularly pulverized water-absorbent resin particles (1) were obtained.
• the physical properties of the water-absorbent resin particles (1) were measured by the above-mentioned method.
• the water-absorbent resin particles (1) had a mass average particle diameter (D50) of 358 ⁇ m, a logarithmic standard deviation of the particle size distribution ( ⁇ ) of 0.36, and a centrifuge retention capacity (CRC) of 53.4 (g/g).
• the physical properties of the water-absorbent resin particles (2) were measured by the above-mentioned method.
• the water-absorbent resin particles (2) had a mass average particle diameter (D50) of 337 ⁇ m, a logarithmic standard deviation ( ⁇ ) of the particle size distribution of 0.34, and a centrifuge retention capacity (CRC) of 56.1 (g/g).
• the physical properties of the water-absorbent resin particles (3) were measured by the above-mentioned method.
• the water-absorbent resin particles (3) had a mass average particle diameter (D50) of 346 ⁇ m, a logarithmic standard deviation ( ⁇ ) of the particle size distribution of 0.35, and a centrifuge retention capacity (CRC) of 51.1 (g/g).
• the water absorbent resin particles (4) had a mass average particle diameter (D50) of 341 ⁇ m, a logarithmic standard deviation ( ⁇ ) of the particle size distribution of 0.34, and a centrifuge retention capacity (CRC) of 53.7 (g/g).
• the water absorbent resin particles (5) had a mass average particle diameter (D50) of 353 ⁇ m, a logarithmic standard deviation ( ⁇ ) of the particle size distribution of 0.36, and a centrifuge retention capacity (CRC) of 56.3 (g/g).
• the water absorbent resin particles (6) had a mass average particle diameter (D50) of 338 ⁇ m, a logarithmic standard deviation ( ⁇ ) of the particle size distribution of 0.34, and a centrifuge retention capacity (CRC) of 50.9 (g/g).
• the gel crushing energy (GGE) in the gel crushing of Production Example 9 was 29.0 [J/g].
• the physical properties of the water-absorbent resin particles (9) were measured by the above-mentioned method.
• the water-absorbent resin particles (9) had a mass average particle diameter (D50) of 350 ⁇ m, a logarithmic standard deviation of the particle size distribution ( ⁇ ) of 0.37, and a centrifuge retention capacity (CRC) of 53.1 (g/g).
• the gel crushing energy (GGE) in the gel crushing of Production Example 10 was 28.1 [J/g].
• the physical properties of the water-absorbent resin particles (10) were measured by the above-mentioned method.
• the water-absorbent resin particles (10) had a mass average particle diameter (D50) of 342 ⁇ m, a logarithmic standard deviation ( ⁇ ) of the particle size distribution of 0.36, and a centrifuge retention capacity (CRC) of 54.0 (g/g).
• Example 1 The water absorbent resin particles (1) obtained in Production Example 1 were uniformly mixed with a surface crosslinking agent solution, and the resulting mixture was then heat-treated at 190° C. for 30 minutes to obtain a water absorbent resin (1).
• the surface crosslinking agent solution was a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water relative to 100 parts by weight of the water absorbent resin particles (1).
• the aqueous solution of EDTMP.5Na was an aqueous solution consisting of 1 part by weight of water and 0.01 part by weight of sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP.5Na) when the weight of the water-absorbent resin (1) was taken as 100 parts by weight.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of cationic colloidal silica aqueous solution per 100 parts by weight of water absorbent resin (1) was uniformly mixed with the water absorbent resin (1) mixed with the EDTMP.5Na aqueous solution.
• the cationic colloidal silica aqueous solution is a product name: Klebosol 30CAL25 30% aqueous solution, manufactured by AZ Electronic Materials, Inc./aluminum cation-containing silicon dioxide microparticles.
• the resulting mixture was dried at 60°C for 1 hour, and then passed through a JIS standard sieve with a mesh size of 850 ⁇ m to obtain a particulate water absorbent (1).
• the physical properties of the particulate water absorbent (1) were measured using the method described above. The results are shown in Table 2 below.
• Example 2 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (2).
• a surface crosslinking agent solution a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.31 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water was used relative to 100 parts by weight of the water absorbent resin particles (2).
• EDTMP.5Na aqueous solution an aqueous solution consisting of 1 part by weight of water, 0.03 parts by weight of EDTMP.5Na, and 0.05 parts by weight of sodium hydrogen sulfite was used.
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• a solution consisting of 1.0 part by weight of water and 1.5 parts by weight of an aqueous alumina sol solution was used.
• the physical properties of the particulate water absorbing agent (2) were measured using the method described above. The results are shown in Table 2 below.
• the alumina sol aqueous solution used was Aluminasol 520-A (a 20.5% aqueous solution of aluminum oxide, manufactured by Nissan Chemical Industries, Ltd.).
• Example 3 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (3).
• the surface cross-linking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol, and 3.2 parts by weight of deionized water, relative to 100 parts by weight of the water absorbent resin particles (1), was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (1) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes, instead of at 190° C. for 30 minutes. - The shaking time of the paint shaker was changed from 30 minutes to 10 minutes.
• an aqueous polyethylene glycol solution consisting of 1 part by weight of water and 0.03 part by weight of polyethylene glycol (average molecular weight 400) was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution the mixture of the aqueous polyethylene glycol solution and the water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m. After passing through a JIS standard sieve, 0.3 parts by weight of silicon dioxide (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) was further mixed uniformly.
• Example 4 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (4).
• a surface crosslinking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, 2.7 parts by weight of deionized water, and 0.5 parts by weight of aluminum sulfate 14-18 hydrate with respect to 100 parts by weight of the water absorbent resin particles (1) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (1) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes, instead of at 190° C. for 30 minutes.
• the shaking time of the paint shaker was changed from 30 minutes to 10 minutes.
• an aqueous polyethylene glycol solution consisting of 1 part by weight of water, 0.12 parts by weight of polyethylene glycol (average molecular weight 600), and 0.03 parts by weight of sodium sulfite was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• the mixture of the aqueous polyethylene glycol solution and the water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m.
• Example 5 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (5).
• a surface crosslinking agent solution a solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water, relative to 100 parts by weight of the water absorbent resin particles (1), was used.
• EDTMP.5Na aqueous solution an aqueous polyethylene glycol solution consisting of 1 part by weight of water and 0.1 part by weight of polyethylene glycol (average molecular weight 400) was used.
• an aqueous aluminum sulfate solution consisting of 1.5 parts by weight of water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate was used.
• Example 6 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (6).
• the water-absorbent resin particles (1) instead of the water-absorbent resin particles (1), the water-absorbent resin particles (2) prepared in Production Example 2 were used.
• the EDTMP.5Na aqueous solution an aqueous solution of diethylenetriaminepentaacetic acid.3Na (DTPA.3Na) consisting of 2.0 parts by weight of water, 0.02 parts by weight of DTPA.3Na, and 0.1 parts by weight of sodium sulfite was used.
• DTPA.3Na diethylenetriaminepentaacetic acid.3Na
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• the mixture of the DTPA.3Na aqueous solution and the water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m. After passing through a JIS standard sieve, 0.3 parts by weight of hydrotalcite (product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.) was further mixed uniformly.
• Example 7 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (7).
• the water-absorbent resin particles (2) prepared in Production Example 2 were used.
• the surface cross-linking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, and 2.7 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin particles (2) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (2) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes instead of at 190° C. for 30 minutes.
• the shaking time of the paint shaker was changed from 30 minutes to 10 minutes.
• an aqueous sodium hydrogen sulfite solution consisting of 0.5 parts by weight of water and 0.03 parts by weight of sodium hydrogen sulfite was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution a solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous alumina sol solution was used.
• the physical properties of the particulate water absorbent (7) were measured using the method described above. The results are shown in Table 2 below.
• the alumina sol aqueous solution used was Aluminasol 520-A (a 20.5% aqueous solution of aluminum oxide, manufactured by Nissan Chemical Industries, Ltd.).
• Example 8 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (8).
• the water-absorbent resin particles (2) prepared in Production Example 2 were used.
• As a surface crosslinking agent solution a solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.31 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water was used with respect to 100 parts by weight of the water absorbent resin particles (2).
• the shaking time of the paint shaker was changed from 30 minutes to 10 minutes.
• a mixture of an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution and a water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m.
• Example 9 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (9). Instead of the water-absorbent resin particles (1), the water-absorbent resin particles (2) prepared in Production Example 2 were used. Instead of the EDTMP.5Na aqueous solution, an aqueous solution of diethylenetriaminepentaacetic acid.3Na (DTPA.3Na) consisting of 1.5 parts by weight of water and 0.01 parts by weight of DTPA.3Na was used.
• DTPA.3Na diethylenetriaminepentaacetic acid.3Na
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• an aqueous aluminum sulfate solution consisting of 1.5 parts by weight of water, 1.0 part by weight of propylene glycol, and 0.5 parts by weight of aluminum sulfate 14-18 hydrate was used.
• Example 10 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (10). Instead of the water-absorbent resin particles (1), the water-absorbent resin particles (2) prepared in Production Example 2 were used. Instead of the EDTMP.5Na aqueous solution, a mixed solution consisting of 2.0 parts by weight of water, 0.01 parts by weight of trisodium diethylenetriaminepentaacetate (DTPA.3Na), 0.05 parts by weight of sodium sulfite, and 0.03 parts by weight of polyethylene glycol (average molecular weight 600) was used.
• DTPA.3Na trisodium diethylenetriaminepentaacetate
• sodium sulfite 0.05 parts by weight of sodium sulfite
• polyethylene glycol average molecular weight 600
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous solution of cationic colloidal silica
• a mixture of the mixed solution and a water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m.
• 0.3 parts by weight of silicon dioxide product name: Reolosil QS-20, manufactured by Tokuyama Corporation
• Example 11 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (11).
• the water-absorbent resin particles (3) prepared in Production Example 3 were used.
• a surface crosslinking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 2.45 parts by weight of propylene glycol, 3.55 parts by weight of deionized water, and 0.5 parts by weight of aluminum sulfate 14-18 hydrate with respect to 100 parts by weight of the water absorbent resin particles (3) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (3) and the surface cross-linking agent was heat-treated at 100° C.
• DTPA.3Na diethylenetriaminepentaacetic acid.trisodium
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• the mixture of the DTPA.3Na aqueous solution and the water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m.
• Example 12 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (12).
• the water-absorbent resin particles (3) prepared in Production Example 3 were used.
• As a surface crosslinking agent solution a solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propanediol, 0.5 parts by weight of propylene glycol, and 2 parts by weight of deionized water, relative to 100 parts by weight of the water absorbent resin particles (3), was used.
• EDTMP.5Na aqueous solution
• a mixed solution consisting of 1.5 parts by weight of water, 0.05 parts by weight of polyethylene glycol (average molecular weight 600), 0.05 parts by weight of the sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP.5Na), and 0.1 parts by weight of sodium sulfite was used.
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• a solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous alumina sol solution was used.
• Example 13 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (13).
• the water-absorbent resin particles (3) prepared in Production Example 3 were used.
• the surface cross-linking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol, and 3.2 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin particles (3) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (3) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes, instead of at 190° C. for 30 minutes.
• an aqueous solution of diethylenetriaminepentaacetic acid.trisodium (DTPA.3Na) consisting of 1 part by weight of water and 0.02 part by weight of DTPA.3Na was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution an aqueous solution consisting of 1.0 part by weight of water and 1.5 parts by weight of an aqueous cationic colloidal silica solution was used.
• Comparative Example 1 A comparative particulate water absorbing agent (1) was produced in the same manner as in Example 1, except that the water absorbing resin particles (4) prepared in Production Example 4 were used instead of the water absorbing resin particles (1).
• the physical properties of the comparative particulate water absorbing agent (1) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 2 A comparative particulate water absorbing agent (2) was produced in the same manner as in Example 3, except that the water absorbing resin particles (4) prepared in Production Example 4 were used instead of the water absorbing resin particles (1).
• the physical properties of the comparative particulate water absorbing agent (2) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 3 A comparative particulate water absorbing agent (3) was produced in the same manner as in Example 5, except that the water absorbing resin particles (4) prepared in Production Example 4 were used instead of the water absorbing resin particles (1).
• the physical properties of the comparative particulate water absorbing agent (3) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 4 A comparative particulate water absorbing agent (4) was produced in the same manner as in Example 6, except that the water absorbing resin particles (5) prepared in Production Example 5 were used instead of the water absorbing resin particles (2).
• the physical properties of the comparative particulate water absorbing agent (4) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 5 A comparative particulate water absorbing agent (5) was produced in the same manner as in Example 9, except that the water absorbing resin particles (2) were replaced with the water absorbing resin particles (5) prepared in Production Example 5. The physical properties of the comparative particulate water absorbing agent (5) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 6 A comparative particulate water absorbing agent (6) was produced in the same manner as in Example 12, except that the water absorbing resin particles (6) prepared in Production Example 6 were used instead of the water absorbing resin particles (3).
• the physical properties of the comparative particulate water absorbing agent (6) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 7 The same operation as in Example 7 of WO 2017/170605 was performed to produce a comparative particulate water absorbing agent (7).
• the physical properties of the comparative particulate water absorbing agent (7) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 8 The same operation as in Example 12-1 of WO 2017/170605 was performed to produce a comparative particulate water absorbing agent (8).
• the physical properties of the comparative particulate water absorbing agent (8) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Comparative Example 9 The same operation as in Example 1-13 of WO 2021/201177 was performed to produce a comparative particulate water absorbing agent (9).
• the physical properties of the comparative particulate water absorbing agent (9) were measured using the above-mentioned method. The results are shown in Table 2 below.
• Example 14 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (14). Instead of the water-absorbent resin particles (1), the water-absorbent resin particles (9) prepared in Production Example 9 were used.
• a surface crosslinking agent solution a solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, and 2.7 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin particles (9) was used.
• the mixture obtained by uniformly mixing the water-absorbing resin particles (9) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes instead of at 190° C. for 30 minutes.
• an aqueous solution of diethylenetriaminepentaacetic acid.trisodium (DTPA.3Na) consisting of 1.5 parts by weight of water and 0.02 parts by weight of DTPA.3Na was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous alumina sol solution was used.
• the physical properties of the particulate water absorbing agent (14) were measured using the method described above. The results are shown in Table 2 below.
• the alumina sol aqueous solution used was Aluminasol 520-A (a 20.5% aqueous solution of aluminum oxide, manufactured by Nissan Chemical Industries, Ltd.).
• Example 15 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (15).
• the water-absorbent resin particles (1) instead of the water-absorbent resin particles (1), the water-absorbent resin particles (9) prepared in Production Example 9 were used.
• a surface crosslinking agent solution a solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.26 parts by weight of 1,3-propanediol, 0.5 parts by weight of propylene glycol and 2 parts by weight of deionized water was used with respect to 100 parts by weight of the water absorbent resin particles (9).
• EDTMP.5Na aqueous solution
• a mixed solution consisting of 0.5 parts by weight of water, 0.05 parts by weight of polyethylene glycol (average molecular weight 400), 0.03 parts by weight of the sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP.5Na), and 0.05 parts by weight of sodium sulfite was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution an aqueous solution consisting of 1.5 parts by weight of water, 1.0 part by weight of propylene glycol, and 0.5 parts by weight of aluminum sulfate 14-18 hydrate was used.
• Example 16 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (16).
• the water-absorbent resin particles (1) instead of the water-absorbent resin particles (1), the water-absorbent resin particles (9) prepared in Production Example 9 were used.
• As a surface crosslinking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol, and 3.2 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin particles (9) was used.
• the mixture obtained by uniformly mixing the water-absorbing resin particles (9) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes instead of at 190° C. for 30 minutes.
• the shaking time of the paint shaker was changed from 30 minutes to 10 minutes.
• an aqueous solution consisting of 1.5 parts by weight of water, 0.07 parts by weight of the sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP.5Na), and 0.1 parts by weight of sodium sulfite was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution, a mixture of the aqueous solution and a water absorbent resin was dried at 60° C.
• hydrotalcite product name: DHT-6, manufactured by Kyowa Chemical Industry Co., Ltd.
• Example 17 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (17).
• the water-absorbent resin particles (1) instead of the water-absorbent resin particles (1), the water-absorbent resin particles (10) prepared in Production Example 10 were used.
• As a surface crosslinking agent solution a solution containing 0.025 parts by weight of ethylene glycol diglycidyl ether, 1.3 parts by weight of propylene glycol, and 3.2 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin particles (10) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (10) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes, instead of at 190° C.
• aqueous solution a mixed solution consisting of 1.5 parts by weight of water, 0.03 parts by weight of polyethylene glycol (average molecular weight 600), and 0.05 parts by weight of diethylenetriaminepentaacetic acid.trisodium (DTPA.3Na) was used.
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution an aqueous solution consisting of 1.0 part by weight of water and 1.5 parts by weight of an aqueous cationic colloidal silica solution was used.
• Example 18 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (18).
• the water-absorbent resin particles (1) instead of the water-absorbent resin particles (1), the water-absorbent resin particles (10) prepared in Production Example 10 were used.
• As a surface crosslinking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, and 2.7 parts by weight of deionized water with respect to 100 parts by weight of the water absorbent resin particles (10) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (10) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes, instead of at 190° C.
• EDTMP.5Na aqueous solution a mixed solution consisting of 2 parts by weight of water, 0.25 parts by weight of polyethylene glycol (average molecular weight 400), and 0.1 parts by weight of diethylenetriaminepentaacetic acid.trisodium (DTPA.3Na) was used.
• an aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• an aqueous aluminum sulfate solution consisting of 1.5 parts by weight of water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate was used.
• Example 19 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (19).
• the water-absorbent resin particles (1) instead of the water-absorbent resin particles (1), the water-absorbent resin particles (10) prepared in Production Example 10 were used.
• As a surface crosslinking agent solution a solution containing 0.02 parts by weight of ethylene glycol diglycidyl ether, 1.8 parts by weight of propylene glycol, 2.7 parts by weight of deionized water, and 0.5 parts by weight of aluminum sulfate 14-18 hydrate with respect to 100 parts by weight of the water absorbent resin particles (10) was used.
• the mixture obtained by uniformly mixing the water-absorbent resin particles (10) and the surface cross-linking agent was heat-treated at 100° C. for 40 minutes, instead of at 190° C. for 30 minutes.
• a mixed solution consisting of 2 parts by weight of water, 0.2 parts by weight of polyethylene glycol (average molecular weight 600), 0.07 parts by weight of diethylenetriaminepentaacetic acid.trisodium (DTPA.3Na), and 0.1 parts by weight of sodium sulfite was used.
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous solution of cationic colloidal silica
• a mixture of the mixed solution and a water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m.
• Example 20 The same procedure as in Example 1 was carried out except for the following points, to obtain a particulate water absorbing agent (20). Instead of the water-absorbent resin particles (1), the water-absorbent resin particles (10) prepared in Production Example 10 were used. Instead of the EDTMP.5Na aqueous solution, an aqueous solution consisting of 1 part by weight of water, 0.07 part by weight of the sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP.5Na), and 0.03 part by weight of sodium hydrogen sulfite was used.
• EDTMP.5Na an aqueous solution consisting of 1 part by weight of water, 0.07 part by weight of the sodium salt of ethylenediaminetetramethylenephosphonic acid (EDTMP.5Na), and 0.03 part by weight of sodium hydrogen sulfite was used.
• aqueous solution consisting of 1.0 part by weight of water, 1.0 part by weight of propylene glycol, and 1.5 parts by weight of an aqueous cationic colloidal silica solution
• a mixture of the aqueous solution and a water absorbent resin was dried at 60° C. for 1 hour, and then passed through a JIS standard sieve having an opening of 850 ⁇ m.
• 0.3 parts by weight of silicon dioxide product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.
• the water absorbent resin particles (6) obtained in Production Example 6 were uniformly mixed with a surface crosslinking agent solution, and the resulting mixture was then heat-treated at 190° C. for 30 minutes to obtain a water absorbent resin (1).
• the surface crosslinking agent solution was a solution consisting of 0.025 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of ethylene carbonate, 0.5 parts by weight of propylene glycol, and 2.0 parts by weight of deionized water relative to 100 parts by weight of the water absorbent resin particles (1).
• the obtained mixture was dried at 60°C for 1 hour, and then passed through a JIS standard sieve with a mesh size of 850 ⁇ m to obtain a comparative particulate water absorbent (10).
• the physical properties of the comparative particulate water absorbent (10) were measured using the method described above. The results are shown in Table 2 below.
• Comparative Example 11 An aluminum sulfate aqueous solution was uniformly mixed with the comparative particulate water absorbing agent (10) obtained in Comparative Example 10.
• the aluminum sulfate aqueous solution was an aqueous solution containing 1.5 parts by weight of water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate, where the weight of the comparative particulate water absorbing agent (10) was taken as 100 parts by weight.
• the obtained mixture was dried at 60°C for 1 hour, and then passed through a JIS standard sieve with a mesh size of 850 ⁇ m to obtain a comparative particulate water absorbing agent (11).
• the physical properties of the comparative particulate water absorbing agent (11) were measured using the method described above. The results are shown in Table 2 below.
• Comparative Example 12 The comparative particulate water absorbing agent (10) obtained in Comparative Example 10 was uniformly mixed with an aqueous solution consisting of 1 part by weight of water, 0.01 part by weight of trisodium diethylenetriaminepentaacetate (DTPA.3Na), and 0.004 part by weight of polyoxyethylenesorbitan monostearate (product name: Rheodol Tw-S120V, manufactured by Kao Corporation).
• DTPA.3Na trisodium diethylenetriaminepentaacetate
• polyoxyethylenesorbitan monostearate product name: Rheodol Tw-S120V, manufactured by Kao Corporation.
• the aluminum sulfate aqueous solution was an aqueous solution consisting of 1.5 parts by weight of water and 0.5 parts by weight of aluminum sulfate 14-18 hydrate, assuming that the weight of the comparative particulate water absorbing agent (10) was 100 parts by weight.
• the obtained mixture was dried at 60°C for 1 hour, and then passed through a JIS standard sieve with a mesh size of 850 ⁇ m to obtain a comparative particulate water absorbing agent (12).
• the physical properties of the comparative particulate water absorbing agent (12) were measured using the method described above. The results are shown in Table 2 below.
• the particulate water absorbing agents (1) to (20) produced in Examples 1 to 20 have SRC (NP) exceeding 50.0 g/g and SRC (4.83 kPa) exceeding 41.5 g/g. Therefore, the particulate water absorbing agents (1) to (20) correspond to the particulate water absorbing agents of the present invention. In addition, the particulate water absorbing agents (1) to (20) are also excellent in water absorption speed (Vortex).
• the comparative particulate water absorbing agents (1) to (12) produced in Comparative Examples 1 to 12 have SRC (NP) of 50.0 g/g or less and/or SRC (4.83 kPa) of 41.5 or less, and do not correspond to the particulate water absorbing agent of the present invention.
• the water absorbent using the particulate water absorbents (1) to (20) has a larger absorption amount in the absorbent and a smaller amount of liquid returning in the absorbent, compared to the comparative particulate water absorbents (1) to (12).
• the amount of liquid returning in the absorbent is very small for the particulate water absorbents (1) to (20) compared to the comparative particulate water absorbent (9) with a low SRC (4.83 kPa) and the comparative particulate water absorbent (12) with a low STR.
• the particulate water absorbents (1) to (20) can absorb a large amount of 0.9% sodium chloride aqueous solution in a short time because of their high SRC (NP), and that even when held under high pressure after absorbing liquid, they have excellent liquid retention and reduced liquid returning because of their high SRC (4.83 kPa).
• the particulate water absorbent of the present invention has a function of absorbing a large amount of urine in a short time, and also has a function of retaining liquid even when strong external pressure is applied due to the user's movements after absorbing the water.
• the above function is particularly necessary for a particulate water absorbent used in sanitary products such as diapers for adults who urinate a large amount at a time.
• the particulate water absorbent has an effect of being used in the manufacture of sanitary products that have excellent liquid retention properties during actual use and can further reduce the return of absorbed liquid during actual use.
• the particulate water absorbing agent according to one embodiment of the present invention can be widely used in the field of sanitary products such as diapers.

Landscapes

• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Health & Medical Sciences (AREA)
• Epidemiology (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Heart & Thoracic Surgery (AREA)
• Vascular Medicine (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Dispersion Chemistry (AREA)
• Absorbent Articles And Supports Therefor (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Related Child Applications (1)

Publications (1)

Family

ID=92906554

Family Applications (1)

Country Status (6)

Cited By (1)

Citations (23)

• 2024
  • 2024-03-26 JP JP2025510889A patent/JPWO2024204126A1/ja active Pending
  • 2024-03-26 EP EP24780240.8A patent/EP4691627A1/en active Pending
  • 2024-03-26 WO PCT/JP2024/011819 patent/WO2024204126A1/ja not_active Ceased
  • 2024-03-26 KR KR1020257035427A patent/KR20250165404A/ko active Pending
  • 2024-03-26 CN CN202480022250.7A patent/CN120981284A/zh active Pending
• 2025
  • 2025-09-25 US US19/339,556 patent/US20260021472A1/en active Pending

Patent Citations (25)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events