Patent Application
20240180759
The present invention relates to an absorbent body and an absorbent article and more particularly to an absorbent body suitably used for sanitary supplies such as disposable diapers, sanitary napkins, and incontinence pads, an absorbent article employing the absorbent body.
In recent years, water-absorbent resins have been widely used in the field of sanitary supplies such as disposable diapers, sanitary napkins, and incontinence pads.
As such a water-absorbent resin, a crosslinked product of a polymer of water-soluble ethylenically unsaturated monomers, specifically a crosslinked product of a partially neutralized acrylic acid polymer, is considered to be a preferable water-absorbent resin because it has a better water-absorbing capacity, and acrylic acid as a raw material thereof is easily industrially available, which has many advantages such as an ability to be produced at a low cost with a uniform quality and little likelihood of being putrefied or deteriorated (see, for example, Patent Document 1).
On the other hand, an absorbent article such as a disposable diaper, a sanitary napkin, and an incontinence pad mainly includes an absorbent body that absorbs and holds body fluids such as urine and menstrual blood excreted from the body and is disposed in a central portion, a liquid-permeable surface sheet (top sheet) disposed on a side in contact with the body, and a liquid-impermeable underside sheet (back sheet) disposed on a side opposite to the side in contact with the body. The absorbent body is usually composed of hydrophilic fibers such as pulp and a water-absorbent resin.
In such an absorbent article, the water-absorbent resin contained in the absorbent body is required to have a high water retention. By increasing the water retention of the water-absorbent resin, it is possible to ameliorate a phenomenon in which backflow of the liquid once absorbed in the absorbent body occurs (that is, it is a phenomenon in which the liquid returns from the absorbent body, and when the absorbent body is touched with a hand, uncomfortable wetting is felt). However, in the case where the absorbent surface of the absorbent article is inclined at the time of use of the absorbent article, the repeatedly excreted liquid is not sufficiently absorbed, and there may be a problem that the liquid leaks out of the absorbent article although the water retention of the water-absorbent resin is high.
Under such circumstances, a main object of the present invention is to provide an absorbent body that shows suppressed backflow and leakage of liquid absorbed.
The present inventor has conducted intensive studies in order to solve the above problems. As a result, the present inventor has found that when the absorbent body contains a water-absorbent resin having a physiological saline retention of 45 g/g or more and a 5-minute non-pressurized demand wettability (DW) of 45 ml/g or more and when the weight per unit area of the water-absorbent resin in the absorbent body is set to the range of 50 g/m2 or more and 350 g/m2 or less, backflow and leakage of liquid in the absorbent body can be suitably suppressed. The present invention has been completed through further intensive studies based on such findings.
That is, the present invention provides an invention having the following configurations.
Item 1. An absorbent body including a water-absorbent resin,
Item 2. The absorbent body according to item 1, in which the water-absorbent resin satisfies a relationship represented by Formula (1) below.
0.85≤5-minute non-pressurized DW/water retention ≤5.0 (1)
Item 3. The absorbent body according to item 1 or 2, in which the water-absorbent resin has a median particle diameter of 200 μm or more and 700 μm or less.
Item 4. The absorbent body according to any one of items 1 to 3, further including a hydrophilic fiber.
Item 5. The absorbent body according to item 4, in which the hydrophilic fiber is at least one selected from the group consisting of finely pulverized wood pulp, cotton, a cotton linter, rayon, cellulose acetate, a polyamide, a polyester, and a polyolefin.
Item 6. An absorbent article including the absorbent body according to any one of items 1 to 5.
Item 7. The absorbent article according to item 6, further including a laminate including the absorbent body containing the water-absorbent resin and core wrap disposed on upper and lower sides of the absorbent body to sandwich the absorbent body, a liquid-permeable sheet disposed on an upper surface of the laminate, and a liquid-impermeable sheet disposed on a surface of the laminate on a side opposite to a side of the liquid-permeable sheet.
Item 8. The absorbent article according to item 7, in which the liquid-permeable sheet has a weight per unit area of 5 g to 200 g/m2.
Item 9. The absorbent article according to item 7 or 8, in which the liquid-permeable sheet is at least one selected from the group consisting of a thermally bonded non-woven fabric, an air through non-woven fabric, a spunbonded non-woven fabric, and a spunbonded/meltblown/spunbonded (SMS) non-woven fabric.
The present invention can provide an absorbent body that shows suppressed backflow and leakage of liquid absorbed. Furthermore, the present invention can also provide an absorbent body and an absorbent article including the water-absorbent resin.
In the present specification, the term “comprising” includes “consisting essentially of” and “consisting of”. In addition, in the present specification, “(meth)acrylic” means “acrylic or methacrylic”, and “(meth)acrylate” means “acrylate or methacrylate”.
In addition, in the present specification, numerical values joined by “to” means a numerical range including numerical values before and after “to” as a lower limit value and an upper limit value. When a plurality of lower limit values and a plurality of upper limit values are described separately, an arbitrary lower limit value and an arbitrary upper limit value can be selected and connected by “to”.
An absorbent body of the present invention contains a water-absorbent resin having a physiological saline retention of 45 g/g or more and a 5-minute non-pressurized DW of 45 ml/g or more, and the weight per unit area of the water-absorbent resin in the absorbent body is in the range of 50 g/m2 or more and 350 g/m2 or less. As for the absorbent body of the present invention having such a characteristic, backflow and leakage of liquid absorbed are suppressed.
The absorbent article of the present invention includes the absorbent body of the present invention. The absorbent article of the present invention includes, in addition to the absorbent body, core wrap that retains the shape of the absorbent body; a liquid-permeable sheet disposed on the outermost side on the side into which liquid to be absorbed permeates; a liquid-impermeable sheet disposed on the outermost side opposite to the side into which the liquid to be absorbed permeates. Examples of the absorbent article include diapers (such as disposable diapers), potty training pants, incontinence pads, sanitary supplies (such as sanitary napkins and tampons), sweat absorbing pads, puppy pads, members for portable toilets, and animal excrement treatment materials. The absorbent article may be disposable. Hereinafter, the absorbent body and the absorbent article of the present invention will be described in detail.
The absorbent body 10 of the present invention includes a water-absorbent resin 10a according to the present embodiment and a fiber layer 10b containing hydrophilic fibers, which is preferably used. Note that the absorbent body 10 may or may not include hydrophilic fibers. The water-absorbent resin 10a is, for example, supported and dispersed in the fiber layer 10b. Examples of the configuration of the absorbent body 10 include a sheet-like structure in which the water-absorbent resin is fixed on a non-woven fabric or between a plurality of non-woven fabrics, a mixed dispersion obtained by mixing the water-absorbent resin and hydrophilic fibers so as to have a uniform composition, a sandwich structure in which the water-absorbent resin is sandwiched between layered hydrophilic fibers, and a structure in which the water-absorbent resin and hydrophilic fibers are wrapped with tissue.
The planar shape of the absorbent body 10 is appropriately determined according to the use or the shape of the absorbent article, examples thereof include a substantially rectangular shape, an elliptical shape, an hourglass shape, and a battledore shape, and there may be a notch or the like in the absorbent body for improving a fit. Furthermore, the internal structure of the absorbent body 10 is also appropriately determined according to the purpose. For example, in addition to a constitution including a single absorbent body, a plurality of absorbent bodies (divided on a plane, divided in the vertical direction, or the like) may be combined, or a quantitative distribution gradient (uniform distribution, quantitative distribution according to liquid input unit, or the like) of the water-absorbent resin and other components may be provided inside the absorbent body. In the absorbent body 10, embossing may be performed in the absorbent body 10 in order to provide a liquid flow path.
The weight of the water-absorbent resin per unit area in the absorbent body 10 of the present invention is 50 g/m2 or more and 350 g/m2 or less. From the viewpoint of more suitably exerting the effect of the present invention, the weight per unit area is preferably 100 g/m2 or more, more preferably 150 g/m2 or more, still more preferably 200 g/m2 or more, and is preferably 300 g/m2 or less, more preferably 250 g/m2 or less, still more preferably 200 g/m2 or less. The absorbent body of the present invention has effects of suppressing backflow and leakage of the absorbed liquid, but a suitable weight per unit area may also be different depending on the application in which each effect is exerted. For example, the weight per unit area is preferably 50 g/m2 or more and 200 g/m2 or less for light incontinence and is preferably 200 g/m2 or more and 350 g/m2 or less for heavy incontinence.
The content of the water-absorbent resin in the absorbent body of the present invention is preferably 5 to 100 mass %, more preferably 10 to 95 mass %, still more preferably 20 to 90 mass %, still more preferably 30 to 80 mass %.
Examples of the hydrophilic fibers include at least one selected from the group consisting of finely pulverized wood pulp, cotton, cotton linters, rayon, cellulose acetate, polyamides, polyesters, and polyolefins. More specific examples include cellulose fibers such as cotton-like pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood, artificial cellulose fibers such as rayon and acetate, and fibers made of synthetic resins such as hydrophilized polyamide, polyester, and polyolefin. The average fiber length of the hydrophilic fibers is usually 0.1 to 10 mm or may be 0.5 to 5 mm.
For example, the core wrap 20 is disposed so as to cover the outer periphery of the absorbent body 10. The absorbent body 10 is disposed in the core wrap 20. Examples of the core wrap 20 include tissue and non-woven fabrics. The core wrap 20 has, for example, a main surface having a size equivalent to that of the absorbent body 10.
In order to enhance the form retention before and during use of the absorbent body, an adhesive binder may be blended. Examples of the adhesive binder include heat-sealable synthetic fibers, hot melt adhesives, and adhesive emulsions.
Examples of the heat-sealable synthetic fibers include an entirely meltable binder such as polyethylene (PE), polypropylene (PP), and an ethylene-propylene copolymer, and a not entirely meltable binder having a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above-described not entirely meltable binder, only the PE portion is thermally fused. Examples of the hot melt adhesive include a blend of a base polymer such as an ethylene-vinyl acetate copolymer, a styrene-isoprene-styrene block copolymer, a styrene-butadiene-styrene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, a styrene-ethylene-propylene-styrene block copolymer, or amorphous PP with a tackifier, a plasticizer, an antioxidant, or the like.
Examples of the adhesive emulsion include a polymer of at least one or more types of monomers selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate. These adhesive binders may be used singly or in combination of two or more.
The absorbent body according to the present invention may further contain additives such as an inorganic powder (such as amorphous silica), a deodorant, a pigment, a dye, an antibacterial agent, a perfume, and a pressure-sensitive adhesive. These additives can impart various functions to the absorbent body. When the water-absorbent resin contains inorganic particles, the absorbent body may contain an inorganic powder separately from the inorganic particles in the water-absorbent resin. Examples of the inorganic powder include silicon dioxide, zeolite, kaolin, and clay.
The liquid-permeable sheet 30 is disposed at the outermost portion on the side into which the liquid to be absorbed permeates. The liquid-permeable sheet 30 is disposed on the core wrap 20 in contact with the core wrap 20. The liquid-impermeable sheet 40 is disposed on the outermost side opposite to the liquid-permeable sheet 30 in the absorbent article 100. The liquid-impermeable sheet 40 is disposed on the lower side of the core wrap 20 in contact with the core wrap 20. The liquid-permeable sheet 30 and the liquid-impermeable sheet 40 have, for example, main surfaces greater than the main surface of the absorbent body 10, and the outer edge portions of the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 extend around the absorbent body 10 and the core wrap 20.
The size relationship among the absorbent body 10, the core wrap 20, the liquid-permeable sheet 30, and the liquid-impermeable sheet 40 is appropriately adjusted according to the use of the absorbent article or the like without particular limitation. The absorbent body 10 illustrated in
The liquid-permeable sheet 30 may be a sheet formed of a resin or fibers commonly used in the art. From the viewpoint of liquid permeability, flexibility, and strength when used for the absorbent article, the liquid-permeable sheet 30 may contain, for example, a synthetic resin such as a polyolefin such as PE and PP, a polyester such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN), a polyamide such as nylon, and rayon, regenerated fibers such as cuprammonium rayon, acetate, or synthetic fibers containing these synthetic resins, or may be natural fibers containing cotton, silk, hemp, or pulp (cellulose). From the viewpoint of, for example, increasing the strength of the liquid-permeable sheet 30, the liquid-permeable sheet 30 may contain synthetic fibers. The synthetic fibers may in particular be polyolefin fibers, polyester fibers, or combinations thereof. These materials may be used singly or in combination of two or more materials.
The liquid-permeable sheet 30 may be a non-woven fabric, a porous sheet, or a combination thereof. The non-woven fabric is a sheet in which fibers are entangled without being woven. The non-woven fabric may be a non-woven fabric (staple non-woven fabric) constituted of short fibers (that is, staples) or a non-woven fabric (filament non-woven fabric) constituted of long fibers (that is, filaments). The staples may generally have a fiber length of several hundred millimeters or less although it is not limited thereto.
The liquid-permeable sheet 30 may be a thermally bonded non-woven fabric, an air through non-woven fabric, a resin-bonded non-woven fabric, a spunbonded non-woven fabric, a meltblown non-woven fabric, an air-laid non-woven fabric, a spunlace non-woven fabric, a point-bonded non-woven fabric, or a laminate of two or more kinds of non-woven fabrics selected from these. These non-woven fabrics can be formed of, for example, the above-mentioned synthetic fibers or natural fibers. The laminate of two or more kinds of non-woven fabrics may be, for example, an SMS non-woven fabric, which is a composite non-woven fabric including a spunbonded non-woven fabric, a meltblown non-woven fabric, and a spunbonded non-woven fabric laminated in this order. The liquid-permeable sheet 30 may be a thermally bonded non-woven fabric, an air through non-woven fabric, a spunbonded non-woven fabric, or an SMS non-woven fabric in the viewpoint of suppressing leakage of liquid.
The non-woven fabric used as the liquid-permeable sheet 30 desirably has an appropriate hydrophilic property from the viewpoint of liquid absorption performance of the absorbent article. From this viewpoint, the liquid-permeable sheet 30 may be a non-woven fabric having a hydrophilicity of 5 to 200 as measured in accordance with the measurement method of Paper Pulp Test Method No. 68 (2000) by Japan Technical Association of the Pulp and Paper Industry. The hydrophilicity of the non-woven fabric may be 10 to 150. For details of the Paper Pulp Test Method No. 68, for example, WO 2011/086843 A can be referred to.
The non-woven fabric having a hydrophilic property as described above may be formed of, for example, fibers exhibiting appropriate hydrophilicity such as rayon fibers or may be formed of fibers obtained by hydrophilizing hydrophobic chemical fibers such as polyolefin fibers and polyester fibers. Examples of a method for obtaining a non-woven fabric containing hydrophilized hydrophobic chemical fibers include a method for obtaining a non-woven fabric by a spunbond method using a mixture of a hydrophilizing agent with hydrophobic chemical fibers, a method of entraining a hydrophilizing agent when a spunbonded non-woven fabric is produced with hydrophobic chemical fibers, and a method of impregnating a spunbonded non-woven fabric obtained using hydrophobic chemical fibers with a hydrophilizing agent. As the hydrophilizing agent, an anionic surfactant such as an aliphatic sulfonic acid salt and a higher alcohol sulfuric acid ester salt, a cationic surfactant such as a quaternary ammonium salt, a nonionic surfactant such as a polyethylene glycol fatty acid ester, a polyglycerol fatty acid ester, and a sorbitan fatty acid ester, a silicone-based surfactant such as a polyoxyalkylene-modified silicone, a stain release agent made of a polyester-based resin, a polyamide-based resin, an acryl-based resin, or a urethane-based resin, or the like is used.
The liquid-permeable sheet 30 may be a non-woven fabric that is moderately bulky and has a large weight per unit area from the viewpoint of being able to impart good liquid permeability, flexibility, strength, and cushioning property to the absorbent article and from the viewpoint of increasing the liquid permeation speed of the absorbent article. The weight per unit area of the non-woven fabric used for the liquid-permeable sheet 30 may be 5 to 200 g/m2, 8 to 150 g/m2, or 10 to 100 g/m2. The thickness of the non-woven fabric used for the liquid-permeable sheet 30 may be 20 to 1,400 μm, 50 to 1,200 μm, or 80 to 1,000 μm.
The liquid-permeable sheet 30 may be formed of two or more sheets, or its surface may be embossed or perforated, in order to improve the liquid diffusibility. The embossing and the perforating can be performed by a known method. In addition, the liquid-permeable sheet 30 may contain a skin lotion, a moisturizing agent, an antioxidizing agent, an anti-inflammatory agent, a pH adjusting agent, and the like in order to reduce irritation to the skin. The shape of the liquid-permeable sheet 30 depends on the shapes of the absorbent body and the absorbent article but may be a shape that covers the absorbent body 10 so as not to cause liquid leakage.
The liquid-impermeable sheet 40 is disposed on the outermost side opposite to the liquid-permeable sheet 30 in the absorbent article 100. The liquid-impermeable sheet 40 is disposed on the lower side of the core wrap 20 in contact with the core wrap 20. The liquid-impermeable sheet 40 has, for example, a main surface greater than the main surface of the absorbent body 10, and the outer edge portions of the liquid-impermeable sheet 40 extend around the absorbent body 10 and the core wrap 20. The liquid-impermeable sheet 40 prevents the liquid absorbed by the absorbent body 10 from leaking from the liquid-impermeable sheet 40 side to the outside.
Examples of the liquid-impermeable sheet 40 include a sheet made of a synthetic resin such as PE, PP, and polyvinyl chloride, a sheet made of a non-woven fabric such as an SMS nonwoven fabric obtained by sandwiching a water-resistant meltblown non-woven fabric with high-strength spunbonded non-woven fabrics, and a sheet made of a composite material of these synthetic resins and a non-woven fabric (such as a spunbonded non-woven fabric and a spunlace non-woven fabric). The liquid-impermeable sheet 40 may have air permeability from the viewpoint of reducing stuffiness when being worn and reducing discomfort given to the wearer. As the liquid-impermeable sheet 40, a sheet made of a synthetic resin mainly containing a low density polyethylene (LDPE) resin can be used. From the viewpoint of securing flexibility so as not to impair the wear comfort of the absorbent article, the liquid-impermeable sheet 40 may be, for example, a sheet made of a synthetic resin having a weight per unit area of 10 to 50 g/m2. In addition, in order to impart air permeability to the liquid-impermeable sheet 40, for example, a filler can be blended in the resin sheet, or embossing can be performed on the liquid-impermeable sheet 40. As the filler, calcium carbonate or the like is used.
The absorbent article 100 can be produced, for example, by a method including disposing the absorbent body 10 in the core wrap 20 and disposing them between the liquid-permeable sheet 30 and the liquid-impermeable sheet 40. The laminate in which the liquid-impermeable sheet 40, the core wrap 20, the absorbent body 10, the core wrap 20, and the liquid-permeable sheet 30 are laminated in this order is pressurized as necessary.
The members constituting the absorbent article 100 may be bonded together. For example, by bonding the absorbent body 10 and the liquid-permeable sheet 30, the liquid is more smoothly guided to the absorbent body, and an absorbent article better in leakage prevention is easily obtained. When the absorbent body 10 is covered with or sandwiched between the core wrap 20, it is preferable that at least the core wrap 20 and the liquid-permeable sheet 30 be bonded to each other, and it is more preferable that the core wrap 20 and the absorbent body 10 be bonded to each other. Examples of the bonding method include known methods such as a method using an adhesive, heat sealing, and ultrasonic sealing. Examples thereof include a method of applying a hot melt adhesive to the liquid-permeable sheet 30 at predetermined intervals in the width direction thereof in a longitudinal stripe shape, a spiral shape, or the like, and a method of using a water-soluble adhesive selected from starch, carboxymethylcellulose, polyvinyl alcohol, polyvinylpyrrolidone, and other water-soluble polymers. In addition, when the absorbent body 10 contains heat-sealable synthetic fibers, a method by heat sealing thereof may be adopted.
The shape of the absorbent article 100 is appropriately determined according to the application, and examples thereof include a substantially rectangular shape, an elliptical shape, an hourglass shape, a battledore shape, and the like when the absorbent article is a bladder control pad or a sanitary napkin.
In the absorbent article 100, members may be appropriately present according to the application and function in addition to the liquid-permeable sheet, the absorbent body, the liquid-impermeable sheet, and the core wrap described above. Examples thereof include a liquid acquisition diffusion sheet, an outer cover non-woven fabric, and a leg gather.
Although not shown in
Typically the liquid acquisition diffusion sheet with a shorter width than the absorbent body 10 is positioned in the central portion but may be positioned over the entire width. The length of the liquid acquisition diffusion sheet in the front-back direction may be substantially equal to the entire length of the absorbent article, may be substantially equal to the entire length of the absorbent body 10, or may be a length in a range determined in consideration of a portion to which the liquid is input.
The outer cover non-woven fabric may be disposed on the side of the liquid-impermeable sheet 40 facing the absorbent body. The outer cover non-woven fabric can be bonded to the liquid-impermeable sheet 40 using, for example, an adhesive. The outer cover non-woven fabric may be formed of one or more layers and may be a soft material. The outer cover non-woven fabric may be imparted with a flexible tactile sensation, may have a pattern printed thereon, or may have a plurality of joining portions, embossing, or a three-dimensional form in order to appeal to consumers' willingness to purchase, or according to other reasons.
The absorbent article 100 of the present invention may include leg gathers provided with an elastic member having stretchability, disposed outside both end portions of the absorbent body 10 in the width direction, and disposed substantially parallel to the longitudinal direction of the absorbent body 10. The length of the leg gathers is set to a length about equal to or longer than the girth of the wearer's legs. The extension rate of the leg gather is appropriately set from the viewpoint of preventing leakage of the discharged liquid and reducing a feeling of pressure at the time of wearing for a long time.
(Front/Back Gathers) The absorbent article 100 of the present invention may include front/back gathers that are arranged in the vicinity of both end portions in the longitudinal direction of the absorbent article and include an elastic member that expands and contracts in the width direction.
The absorbent article 100 includes front/back gathers that can rise above side edges in the width direction of the absorbent body 10. That is, on each of both sides in the longitudinal direction of the absorbent article, a sheet member of front/back gathers having a gather elastic member is disposed to form the front/back gathers.
The member for the front/back gathers is usually made of a liquid-impermeable or water-repellent material, preferably a moisture-permeable material. Examples thereof include a liquid-impermeable or water-repellent porous sheet, a liquid-impermeable or water-repellent non-woven fabric, and a laminate of the porous sheet and the non-woven fabric. Examples of the non-woven fabric include a thermally bonded non-woven fabric, a spunbonded non-woven fabric, a meltblown non-woven fabric, a spunlace nonwoven fabric, and an SMS non-woven fabric. The weight per unit area of the member may be 5 to 100 g/m2, 8 to 70 g/m2, or 10 to 40 g/m2.
The absorbent body of the present invention is an absorbent body containing a water-absorbent resin. In the absorbent body of the present invention, the water-absorbent resin has a physiological saline retention of 45 g/g or more and a 5-minute non-pressurized DW of 45 ml/g or more.
From the viewpoint of more suitably exerting the effect of the present invention, the physiological saline retention of the water-absorbent resin is preferably 46 g/g or more, more preferably 47 g/g or more, still more preferably 48 g/g or more, still more preferably 50 g/g or more. The physiological saline retention is preferably 70 g/g or less, more preferably 60 g/g or less, still more preferably 55 g/g or less, still more preferably 52 g/g or less. A method for measuring the physiological saline retention is as follows.
A cotton bag (No. 60 count cotton broadcloth, 100 mm in width×200 mm in length) in which 2.0 g of the water-absorbent resin has been weighed out is placed in a 500-mL beaker. Into the cotton bag containing the water-absorbent resin, 500 g of a 0.9-mass % aqueous sodium chloride solution (physiological saline) is poured at once so as not to form lumps, the upper portion of the cotton bag is tied with a rubber band, and the cotton bag is left to stand for 30 minutes to allow the water-absorbent resin to swell. The cotton bag after 30 minutes is dehydrated for 1 minute using a dehydrator set so that the centrifugal force is 167 G, and the mass Wa (g) of the cotton bag containing the swollen gel after dehydration is measured. The same operation is performed without adding the water-absorbent resin, the empty mass Wb (g) of the cotton bag in a wet state is measured, and the physiological saline retention is calculated from the following equation.
Physiological saline retention (g/g)=[Wa−Wb]/2.0
From the viewpoint of more suitably exerting the effect of the present invention, the 5-minute non-pressurized DW of the water-absorbent resin is preferably 48 l/g or more, more preferably 53 ml/g or more, still more preferably 56 ml/g or more, still more preferably 60 ml/g or more. The 5-minute non-pressurized DW is preferably 90 ml/g or less, more preferably 80 ml/g or less, still more preferably 75 ml/g or less, still more preferably 70 ml/g or less. A more specific measurement method is as described in the EXAMPLES section.
The non-pressurized DW of particles of the water-absorbent resin is measured using a measuring device shown in the schematic diagram of
First, the cock 22 and the cock 24 of the burette unit 1 are closed, and 0.9-mass % saline 50 adjusted to 25° C. is put into the burette tube 21 from the opening of the upper portion of the burette tube 21. The concentration of the saline of 0.9 mass % is a concentration based on the mass of the saline. After the opening of the burette tube 21 was tightly sealed with the rubber stopper 23, the cock 22 and the cock 24 were opened. The inside of the conduit 5 is filled with the 0.9-mass % saline 50 so that air bubbles do not enter. The height of the measurement stage 13 is adjusted such that the height of the surface of the 0.9-mass % saline reaching the inside of the through hole 13a becomes equal to the height of the upper surface of the measurement stage 13. After the adjustment, the height of the surface of the 0.9-mass % saline 50 in the burette tube 21 is read using the graduations on the burette tube 21, and the position is set as a 0 point (reading at 0 seconds).
The nylon mesh sheet 15 (100 mm×100 mm, 250 mesh, thickness of about 50 μm) is laid in the vicinity of the through hole 13a on the measurement stage 13, and a cylinder having an inner diameter of 30 mm and a height of 20 mm is placed at the center thereof. In the cylinder, 1.00 g of a water-absorbent resin 10a is uniformly spread. Thereafter, the cylinder is carefully removed to obtain a sample in which the water-absorbent resin 10a is circularly dispersed on the central portion of the nylon mesh sheet 15. Next, the nylon mesh sheet 15 on which the water-absorbent resin 10a is placed is moved quickly to such an extent that the water-absorbent resin 10a is not scattered so that the center of the nylon mesh sheet 15 is located at the position of the through hole 13a, and measurement is started. A point of time when air bubbles are first introduced from the air introduction tube 25 into the burette tube 21 is defined as the start of water absorption (0 seconds).
A decrease amount (that is, the amount of the 0.9-mass % saline absorbed by the water-absorbent resin 10a) of the 0.9-mass % saline 50 in the burette tube 21 was sequentially read in increments of 0.1 mL, and the decrement We (g) of the 0.9-mass % saline 50 after 5 minutes from the start of water absorption by the water-absorbent resin 10a was read. From the decrement Wc, the five-minute non-pressurized DW is obtained by the following equation. The non-pressurized DW is a water absorption amount per 1.00 g of the water-absorbent resin 10a.
Non-pressurized DW value(mL/g)=Wc/1.00
From the viewpoint of more suitably exerting the effect of the present invention, the water-absorbent resin contained in the absorbent body of the present invention preferably satisfies the relationship of Formula (1) below.
0.85≤5-minute non-pressurized DW/water retention≤5.0 (1)
The relationship of Formula (1) may be 0.85≤5-minute non-pressurized DW/water retention ≤5.0, 0.90≤5-minute non-pressurized DW/water retention ≤4.0, 1.00≤5-minute non-pressurized DW/water retention ≤3.0, or 1.10≤5-minute non-pressurized DW/water retention ≤2.0.
As for the water-absorbent resin, the number of times of input of the liquid until occurrence of leakage measured by the following leakage test is preferably three or more. The number of times of input is, for example, eight times or less. The absorption amount of the liquid until the occurrence of leakage is preferably 160 g or more, more preferably 180 g or more. The absorption amount of the liquid until the occurrence of leakage is, for example, 700 g or less, 600 g or less, or 550 g or less.
As illustrated in the schematic diagram of
When the test liquid that has not been absorbed by the absorbent article 100 leaks from the lower portion of the supporting plate 40, the leaked test liquid is collected in a metal tray 44 disposed below the supporting plate 40. The mass (g) of the collected test liquid is measured with a balance 43, and the value is recorded as the leakage amount. The absorption amount until leakage occurs is calculated by subtracting the leakage amount from the total input amount of the test liquid. As this numerical value is larger, leakage of liquid is judged to be less likely to occur when the absorbent article is worn.
The test liquid is prepared by blending and dissolving an inorganic salt in ion-exchanged water so that the inorganic salt is present as described below and further blending a small amount of Brilliant Blue FCF.
As for the water-absorbent resin, the backflow amount measured by the following backflow test is preferably 35 g or less, more preferably 20 g or less.
A measuring instrument including a cylinder for inputting liquid having an opening with an inner diameter of 3 cm is placed on a central portion of an absorbent article arranged on a horizontal stage. Next, 150 mL of the test liquid adjusted to 25±1° C. is input into the cylinder at once (supplied from the vertical direction). After 5 minutes from the start of input of the test liquid, filter paper of 10 cm square having a mass (We (g), about 80 g) measured in advance is placed near the input position of the test liquid on the absorbent article, and a weight having a mass of 5 kg and a bottom surface of 10 cm×10 cm is placed on the filter paper. After applying the load for five minutes, the mass of the filter paper (Wf (g)) is measured, and the increased mass is taken as the liquid backflow amount (g). It can be said that the smaller the liquid backflow amount is, the more preferable the absorbent article is.
Liquid backflow amount (g)=Wf−We
Examples of the water-absorbent resin include a crosslinked product of a polymer of water-soluble ethylenically unsaturated monomers, a crosslinked product of a hydrolysis product of a graft copolymer of starch and an acrylic acid salt, a crosslinked product of a copolymer of vinyl alcohol and an acrylic acid salt, a crosslinked product of a maleic anhydride grafted polyvinyl alcohol, a crosslinked isobutylene-maleic anhydride copolymer, and a saponified product of a vinyl acetate-acrylate ester copolymer. Among them, a crosslinked product of a polymer of water-soluble ethylenically unsaturated monomers is suitably used from the viewpoint of being able to absorb a large amount of water and retain the absorbed water in the molecule even when some load is applied, and specific examples thereof include a crosslinked product of a polymer of a partially neutralized polyacrylic acid.
The water-absorbent resin used in the present invention may have various shapes. Examples of the shape of the water-absorbent resin include a granular shape, a substantially spherical shape, an indefinite crushed shape, a plate shape, a fibrous shape, a flake shape, and a shape in which these pieces of the resin are aggregated. The water-absorbent resin preferably has a granular shape, a substantially spherical shape, an indefinite crushed shape, a fibrous shape, a shape in which these pieces of the resin are aggregated, or the like.
The water-absorbent resin may be in a form in which fine particles (primary particles) are aggregated (secondary particles) in addition to a form in which particles of the water-absorbent resin are single particles. Examples of the shape of the primary particles include a substantially spherical shape, an indefinite crushed shape, and a plate shape. Examples of the primary particles produced by reversed phase suspension polymerization include substantially spherical single particles having a smooth surface shape such as a perfect spherical shape and an ellipsoidal shape. The primary particles having such a shape and having a smooth surface shape thus have high flowability as a powder, and aggregated particles are easily densely packed and thus are less likely to be broken even when subjected to impact, so that a water-absorbent resin having high particle strength is provided.
The median particle diameter of the water-absorbent resin is preferably 200 μm or more, 250 μm or more, 280 μm or more, 300 μm or more, or 320 μm or more from the viewpoint of more suitably exerting the effect of the present invention. From the same viewpoint, the median particle diameter is preferably 700 μm or less, 600 μm or less, 550 μm or less, 500 μm or less, 450 μm or less, or 400 μm or less. That is, the median particle diameter is preferably 200 the 700 μm, preferably 200 to 600 μm, more preferably 250 to 500 μm, still more preferably 300 to 450 μm, still more preferably 320 to 400 μm. With such a particle diameter, it is possible to suitably maintain the absorption performance of the absorbent body and to obtain comfortable feeling of use of the absorbent article.
The median particle diameter of the water-absorbent resin can be measured using a JIS standard sieve. Specifically, the median particle diameter is a value measured by the method described in the EXAMPLES section.
As a polymerization method of the water-soluble ethylenically unsaturated monomers, an aqueous solution polymerization method, an emulsion polymerization method, a reversed phase suspension polymerization method, and the like, which are representative polymerization methods, are used. In the aqueous solution polymerization method, polymerization is performed by heating a water-soluble ethylenically unsaturated aqueous monomer solution while stirring the aqueous solution as necessary. In the reversed phase suspension polymerization method, polymerization is performed by heating water-soluble ethylenically unsaturated monomers in a hydrocarbon dispersion medium under stirring. The reversed phase suspension polymerization method is preferably used from the viewpoint of enabling precise control of the polymerization reaction and control over a wide particle diameter range.
A specific embodiment of a method for producing a water-absorbent resin will be described below using a reversed phase suspension polymerization method as an example.
Specific examples of the method for producing a water-absorbent resin include a method for producing a water-absorbent resin by performing reversed phase suspension polymerization of water-soluble ethylenically unsaturated monomers in a hydrocarbon dispersion medium, the method including a step of performing polymerization in the presence of a radical polymerization initiator and a step of post-crosslinking a hydrogel-like product obtained by the polymerization in the presence of a post-crosslinking agent. In the method for producing a water-absorbent resin, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomers as necessary to form a hydrogel-like product having an internal crosslinked structure.
In order to set the physiological saline retention to 45 g/g or more and to set the 5-minute non-pressurized DW to 45 ml/g or more for the water-absorbent resin, for example, in the step of post-crosslinking in the presence of a post-crosslinking agent, it is preferable to adjust the amount of water in the hydrogel-like product at the time of post-crosslinking and the amount of the post-crosslinking agent to be added as described later. When the amount of water in the hydrogel-like product at the time of post-crosslinking is increased to a higher level than usual and the amount of the post-crosslinking agent added is decreased to a lower level than usual, the crosslink density can be decreased while increasing the crosslinking thickness of the surface portion of the hydrogel-like product, and the obtained water-absorbent resin can have a physiological saline retention of 45 g/g or more and a 5-minute non-pressurized DW of 45 ml/g or more. Further, in the present invention, by using the water-absorbent resin at a specific weight per unit area of 50 g/m2 or more and 350 g/m2 or less, both suppression of backflow and suppression of leakage of the liquid absorbed by the absorbent body are suitably achieved.
Examples of the water-soluble ethylenically unsaturated monomers include (meth)acrylic acid (in the present specification, “acrylic” and “methacrylic” are collectively referred to as “(meth)acrylic”. The same applies hereinafter) and salts thereof; 2-(meth)acrylamido-2-methylpropane sulfonic acid and salts thereof; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl (meth)acrylate, N-methylol(meth)acrylamide, and polyethylene glycol mono(meth)acrylate; and amino group-containing unsaturated monomers such as N,N-diethylaminoethyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate, and diethylaminopropyl(meth)acrylamide and quaternized products thereof. Among these water-soluble ethylenically unsaturated monomers, (meth)acrylic acid or a salt thereof, (meth)acrylamide, and N,N-dimethylacrylamide are preferable, and (meth)acrylic acid and a salt thereof are more preferable from the viewpoint of industrial availability and the like. These water-soluble ethylenically unsaturated monomers may be used singly or in combination of two or more kinds thereof.
Among them, acrylic acid and salts thereof are widely used as raw materials of water-absorbent resins, and these acrylic acid and/or a salt thereof may be copolymerized with another one of the above water-soluble ethylenically unsaturated monomers. In this case, acrylic acid and/or a salt thereof is preferably used as main water-soluble ethylenically unsaturated monomers in an amount of 70 to 100 mol % with respect to the total amount of water-soluble ethylenically unsaturated monomers.
The water-soluble ethylenically unsaturated monomers are preferably dispersed in a hydrocarbon dispersion medium in a state of an aqueous solution and subjected to reversed phase suspension polymerization. When the water-soluble ethylenically unsaturated monomers are in an aqueous solution, the dispersion efficiency in the hydrocarbon dispersion medium can be increased. The concentration of the water-soluble ethylenically unsaturated monomers in this aqueous solution is preferably in the range of 20 mass % to a saturated concentration. The concentration of the water-soluble ethylenically unsaturated monomers is more preferably 55 mass % or less, still more preferably 50 mass % or less, still more preferably 45 mass % or less. On the other hand, the concentration of the water-soluble ethylenically unsaturated monomers is more preferably 25 mass % or more, still more preferably 28 mass % or more, still more preferably 30 mass % or more.
When the water-soluble ethylenically unsaturated monomers have acid groups such as (meth)acrylic acid and 2-(meth)acrylamido-2-methylpropane sulfonic acid, a compound in which the acid group has been neutralized in advance with an alkaline neutralizing agent as necessary may be used. Examples of such an alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide, and potassium carbonate; and ammonia. In addition, these alkaline neutralizing agents may be used in the form of an aqueous solution in order to simplify the neutralization operation. The above alkaline neutralizing agents may be used singly or in combination of two or more kinds thereof.
The neutralization degree of the water-soluble ethylenically unsaturated monomers with the alkaline neutralizing agent is preferably 10 to 100 mol %, more preferably 30 to 90 mol %, still more preferably 40 to 85 mol %, still more preferably 50 to 80 mol %, as the neutralization degree with respect to all the acid groups of the water-soluble ethylenically unsaturated monomers.
Examples of the radical polymerization initiator added in the polymerization step include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, and hydrogen peroxide, and azo compounds such as 2,2′-azobis(2-amidinopropane) dihydrochloride, 2,2′-azobis[2-(N-phenylamidino)propane]dihydrochloride, 2,2′-azobis[2-(N-allylamidino)propane]dihydrochloride, and 2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane dihydrochloride, 2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and 4,4′-azobis(4-cyanovaleric acid). Among these radical polymerization initiators, potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2′-azobis(2-amidinopropane) dihydrochloride are preferable from the viewpoint of easy availability and easy handling. These radical polymerization initiators may be used singly or in combination of two or more. The radical polymerization initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid.
The amount of the radical polymerization initiator used is, for example, 0.00005 to 0.01 mol with respect to 1 mol of the water-soluble ethylenically unsaturated monomers. By satisfying such a use amount, occurrence of a rapid polymerization reaction can be avoided, and the polymerization reaction can be completed in an appropriate time.
Examples of the internal crosslinking agent include those capable of crosslinking a polymer of water-soluble ethylenically unsaturated monomers to be used, such as unsaturated polyesters obtained by reacting polyols such as diols and triols such as (poly)ethylene glycol[“(poly)” means with or without a “poly” prefix. The same applies hereinafter], (poly)propylene glycol, 1,4-butanediol, trimethylolpropane, and (poly)glycerol with an unsaturated acid such as (meth)acrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylic acid esters or tri(meth)acrylic acid esters obtained by reacting a polyepoxide with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanate such as tolylene diisocyanate and hexamethylene diisocyanate with hydroxyethyl (meth)acrylate; compounds having two or more polymerizable unsaturated groups, such as allylated starch, allylated cellulose, diallyl phthalate, N,N′,N″-triallyl isocyanurate, and divinylbenzene; polyglycidyl compounds such as diglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether and triglycidyl compounds; epihalohydrin compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; and oxetane compounds such as 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol. Among these internal crosslinking agents, an unsaturated polyester or a polyglycidyl compound is preferably used, a diglycidyl ether compound is more preferably used, and (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether are preferably used. These internal crosslinking agents may be used singly or in combination of two or more.
The amount of the internal crosslinking agent used is preferably 0.000001 to 0.02 mol, more preferably 0.00001 to 0.01 mol, still more preferably 0.00001 to 0.005 mol, still more preferably 0.00005 to 0.002 mol, with respect to 1 mol of the water-soluble ethylenically unsaturated monomers.
Examples of the hydrocarbon dispersion medium include aliphatic hydrocarbons having six to eight carbon atoms such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons such as benzene, toluene, and xylene. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly preferably used because they are industrially easily available, have stable quality, and are inexpensive. These hydrocarbon dispersion media may be used singly or in combination of two or more. As an example of a mixture of the hydrocarbon dispersion media, a suitable result can be obtained by using a commercially available product such as Exxsol Heptane (manufactured by Exxon Mobil Corporation: containing 75 to 85 mass % of heptane and an isomer hydrocarbon thereof).
The amount of the hydrocarbon dispersion medium used is preferably 100 to 1,500 parts by mass, more preferably 200 to 1,400 parts by mass, with respect to 100 parts by mass of the first-step water-soluble ethylenically unsaturated monomers from the viewpoint of uniformly dispersing the water-soluble ethylenically unsaturated monomers and facilitating the control of the polymerization temperature. As will be described later, the reversed phase suspension polymerization is performed in one step (single step) or multiple steps of two or more steps, and the above-described first-step polymerization means the first-step polymerization reaction in the single-step polymerization or the multi-step polymerization (the same applies hereinafter).
In the reversed phase suspension polymerization, a dispersion stabilizer can also be used in order to improve the dispersion stability of the water-soluble ethylenically unsaturated monomers in the hydrocarbon dispersion medium. As the dispersion stabilizer, a surfactant can be used.
Examples of the surfactant used include a sucrose fatty acid ester, a polyglycerol fatty acid ester, a sorbitan fatty acid ester, a polyoxyethylene sorbitan fatty acid ester, a polyoxyethylene glycerol fatty acid ester, a sorbitol fatty acid ester, a polyoxyethylene sorbitol fatty acid ester, a polyoxyethylene alkyl ether, a polyoxyethylene alkyl phenyl ether, a polyoxyethylene castor oil, a polyoxyethylene hydrogenated castor oil, an alkylallyl formaldehyde condensed polyoxyethylene ether, a polyoxyethylene polyoxypropylene block copolymer, a polyoxyethylene polyoxypropyl alkyl ether, a polyethylene glycol fatty acid ester, an alkyl glucoside, an N-alkyl gluconamide, a polyoxyethylene fatty acid amide, a polyoxyethylene alkylamine, a phosphoric acid ester of a polyoxyethylene alkyl ether, and a phosphoric acid ester of a polyoxyethylene alkyl allyl ether. Among these surfactants, it is particularly preferable to use a sorbitan fatty acid ester, a polyglycerol fatty acid ester, or a sucrose fatty acid ester from the viewpoint of dispersion stability of the monomers. These surfactants may be used singly or in combination of two or more.
The amount of the surfactant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, with respect to 100 parts by mass of the first-step water-soluble ethylenically unsaturated monomers.
As the dispersion stabilizer used in the reversed phase suspension polymerization, a polymeric dispersant may be used together with the surfactant described above.
Examples of the polymeric dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymers, maleic anhydride-modified EPDM (ethylene-propylene-diene terpolymers), maleic anhydride-modified polybutadiene, maleic anhydride-ethylene copolymers, maleic anhydride-propylene copolymers, maleic anhydride-ethylene-propylene copolymers, maleic anhydride-butadiene copolymers, polyethylene, polypropylene, ethylene-propylene copolymers, oxidized polyethylene, oxidized polypropylene, oxidized ethylene-propylene copolymers, ethylene-acrylic acid copolymers, ethyl cellulose, and ethyl hydroxyethyl cellulose. Among these polymeric dispersants, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene-propylene copolymers, maleic anhydride-ethylene copolymers, maleic anhydride-propylene copolymers, maleic anhydride-ethylene-propylene copolymers, polyethylene, polypropylene, ethylene-propylene copolymers, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymers are particularly preferably used from the viewpoint of dispersion stability of the monomers. These polymeric dispersants may be used singly or in combination of two or more.
The amount of the polymeric dispersant used is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, with respect to 100 parts by mass of the first-step water-soluble ethylenically unsaturated monomers.
In the method for producing a water-absorbent resin, if desired, other components may be added to an aqueous solution containing the water-soluble ethylenically unsaturated monomers to perform reversed phase suspension polymerization. As other components, various additives such as a thickener and a chain transfer agent can be added.
As an example, reversed phase suspension polymerization can be performed with a thickener added to an aqueous solution containing the water-soluble ethylenically unsaturated monomers. Adding a thickener as described above to adjust the viscosity of the aqueous solution enables control of the median particle diameter obtained by the reversed phase suspension polymerization.
As the thickener, for example, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, (partially) neutralized polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, or the like can be used. When the stirring rate during polymerization is constant, the primary particles and/or the secondary particles of the resulting particles tend to be larger as the viscosity of the aqueous solution of the water-soluble ethylenically unsaturated monomers is higher.
In performing the reversed phase suspension polymerization, for example, a aqueous monomer solution containing the water-soluble ethylenically unsaturated monomers is dispersed in a hydrocarbon dispersion medium in the presence of a dispersion stabilizer. At this time, as long as it is before the polymerization reaction is started, the addition timing of the dispersion stabilizer (surfactant or polymeric dispersant) may be either before or after the addition of the aqueous monomer solution.
Among them, from the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the resulting water-absorbent resin, it is preferable to perform polymerization after dispersing the surfactant in the hydrocarbon dispersion medium in which the polymeric dispersant has been dispersed and in which the aqueous monomer solution has then been dispersed.
Such reversed phase suspension polymerization can be performed in one step or multiple steps of two or more steps. In addition, from the viewpoint of enhancing productivity, it is preferable to employ two or three steps.
When the reversed phase suspension polymerization is performed in two or more steps, the first-step reversed phase suspension polymerization is performed, then the water-soluble ethylenically unsaturated monomers are added to and mixed with the reaction mixture obtained in the first-step polymerization reaction, and the second-step or subsequent reversed phase suspension polymerization may be performed in the same manner as the first-step polymerization. In the reversed phase suspension polymerization in each of the second and subsequent steps, in addition to the water-soluble ethylenically unsaturated monomers, a radical polymerization initiator is preferably added within the range of the molar ratio of each component to the water-soluble ethylenically unsaturated monomers described above based on the amount of the water-soluble ethylenically unsaturated monomers added in the reversed phase suspension polymerization in each of the second and subsequent steps to perform reversed phase suspension polymerization. In the second and subsequent polymerization, an internal crosslinking agent may be added to the water-soluble ethylenically unsaturated monomers as necessary.
The reaction temperature of the polymerization reaction is preferably 20 to 110° C., more preferably 40 to 90° C., from the viewpoint of enhancing the economic efficiency by rapidly progressing the polymerization and shortening the polymerization time and easily removing the heat of polymerization to smoothly perform the reaction.
Next, the water-absorbent resin is obtained by adding a post-crosslinking agent to a hydrogel-like product having an internally crosslinked structure obtained by polymerizing the water-soluble ethylenically unsaturated monomers, and crosslinking the hydrogel-like product (post-crosslinking reaction). This post-crosslinking reaction is preferably performed in the presence of a post-crosslinking agent after polymerization of the water-soluble ethylenically unsaturated monomers. As described above, by subjecting the hydrogel-like product having an internally crosslinked structure to a post-crosslinking reaction after polymerization, it is possible to appropriately increase the crosslinking density in the vicinity of the surface of the water-absorbent resin to provide a water-absorbent resin better in various performances such as the non-pressurized DW.
As described above, in order to set the physiological saline retention to 45 g/g or more and to set the 5-minute non-pressurized DW to 45 ml/g or more for the water-absorbent resin, for example, in the step of post-crosslinking in the presence of a post-crosslinking agent, it is preferable to adjust the amount of water in the hydrogel-like product at the time of post-crosslinking and the amount of the post-crosslinking agent to be added as described later. When the amount of water in the hydrogel-like product at the time of post-crosslinking is increased to a higher level than usual and the amount of the post-crosslinking agent added is also decreased to a lower level than usual, the crosslink density can be decreased while increasing the crosslinking thickness of the surface portion of the hydrogel-like product, and a water-absorbent resin having a physiological saline retention of 45 g/g or more even with a similar absorption capacity and a 5-minute non-pressurized DW of 45 ml/g or more can be obtained. Further, in the present invention, by using the water-absorbent resin at a specific weight per unit area of 50 g/m2 or more and 350 g/m2 or less, both suppression of backflow and suppression of leakage of the liquid absorbed by the absorbent body are suitably achieved.
From the viewpoint of setting the physiological saline retention to 45 g/g or more and the 5-minute non-pressurized DW to 45 ml/g or more for the water-absorbent resin, as for the amount of water in the hydrogel-like product at the time of post-crosslinking, addition is preferably performed in the presence of water in the range of 5 to 140 parts by mass, more preferably in the presence of water in the range of 15 to 100 parts by mass, still more preferably in the presence of water in the range of 20 to 50 parts by mass, still more preferably in the presence of water in the range of 22 to 28 parts by mass, with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomers. From the same viewpoint, the added amount of the post-crosslinking agent on the surface of the hydrogel-like product is preferably 0.00001 to 0.01 mol, more preferably 0.00002 to 0.001 mol, still more preferably 0.00005 to 0.0005 mol, on the basis of a total of 1 mol of the water-soluble ethylenically unsaturated monomers used for polymerization.
Examples of the post-crosslinking agent include compounds having two or more reactive functional groups. Examples include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerol, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; oxetane compounds such as 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, and 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. Among these post-crosslinking agents, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferable. These post-crosslinking agents may be used singly or in combination of two or more.
The amount of the post-crosslinking agent used is preferably 0.00001 to 0.01 mol, more preferably 0.00002 to 0.001 mol, still more preferably 0.00005 to 0.0005 mol, with respect to a total of 1 mol of the water-soluble ethylenically unsaturated monomers used for the polymerization.
As a method for adding the post-crosslinking agent, the post-crosslinking agent may be added as it is or in the form of an aqueous solution or may be added in the form of a solution containing a hydrophilic organic solvent as a solvent as necessary. Examples of the hydrophilic organic solvent include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amides such as N,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents may be used singly or in combination of two or more or may be used in the form of a mixed solvent with water.
The addition timing of the post-crosslinking agent is after almost all the polymerization reaction of the water-soluble ethylenically unsaturated monomers is completed, and the post-crosslinking agent is preferably added in the presence of water in the range of 5 to 140 parts by mass, more preferably in the presence of water in the range of 15 to 100 parts by mass, still more preferably in the presence of water in the range of 20 to 50 parts by mass, still more preferably in the presence of water in the range of 22 to 28 parts by mass, with respect to 100 parts by mass of the water-soluble ethylenically unsaturated monomers. The amount of water means the total amount of water contained in the reaction system and water used as necessary when the post-crosslinking agent is added.
The reaction temperature in the post-crosslinking reaction is preferably 50 to 250° C., more preferably 60 to 180° C., still more preferably 60 to 140° C., still more preferably 70 to 120° C. The reaction time of the post-crosslinking reaction is preferably 1 to 300 minutes, more preferably 5 to 200 minutes.
The method may include a drying step of removing water, a hydrocarbon dispersion medium, and the like by distillation by externally applying energy such as heat after performing the reversed phase suspension polymerization described above. When dehydration is performed from the hydrogel after the reversed phase suspension polymerization, the system in which the hydrogel is dispersed in the hydrocarbon dispersion medium is heated, so that water and the hydrocarbon dispersion medium are temporarily distilled off to the outside of the system by azeotropic distillation. At this time, when only the distilled hydrocarbon dispersion medium is returned into the system, continuous azeotropic distillation becomes possible. In that case, since the temperature in the system during drying is maintained at an azeotropic temperature with the hydrocarbon dispersion medium or lower, that case is preferable from the viewpoint that the resin is hardly deteriorated. Subsequently, water and the hydrocarbon dispersion medium are distilled off to obtain the water-absorbent resin. Various performances of the water-absorbent resin to be obtained can be controlled by controlling the treatment conditions in the drying step after the polymerization to adjust the amount of water to be removed.
In the drying step, the drying treatment by distillation may be performed under normal pressure or under reduced pressure. From the viewpoint of enhancing the drying efficiency, the drying may be performed under a flow of nitrogen or the like. The drying temperature when the drying treatment is performed under normal pressure is preferably 70 to 250° C., more preferably 80 to 180° C., still more preferably 80 to 140° C., still more preferably 90 to 130° C. When the drying treatment is performed under reduced pressure, the drying temperature is preferably 40 to 160° C., more preferably 50 to 110° C.
When the post-crosslinking step with the post-crosslinking agent is performed after the polymerization of the monomers is performed by reversed phase suspension polymerization, the drying step by distillation described above is performed after the completion of the post-crosslinking step. Alternatively, the post-crosslinking step and the drying step may be performed simultaneously.
The water-absorbent resin may contain an additive according to the purpose. Examples of such an additive include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, radical chain inhibitors, antioxidants, and antibacterial agents. For example, by adding 0.05 to 5 parts by mass of amorphous silica as an inorganic powder to 100 parts by mass of the water-absorbent resin, the flowability of the water-absorbent resin can be further improved.
Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. However, the present invention is not limited to the examples.
The water-absorbent resins obtained in the examples and comparative examples were evaluated through the following various tests. Unless otherwise specified, the measurement was performed under an environment of a temperature of 25±2° C. and a humidity of 50±10%. Hereinafter, each evaluation test method will be described.
A cotton bag (No. 60 count cotton broadcloth, 100 mm in width×200 mm in length) in which 2.0 g of the water-absorbent resin had been weighed out was placed in a 500-mL beaker. Into the cotton bag containing the water-absorbent resin, 500 g of a 0.9-mass % aqueous sodium chloride solution (physiological saline) was poured at once so as not to form lumps, the upper portion of the cotton bag was tied with a rubber band, and the cotton bag was left to stand for 30 minutes to allow the water-absorbent resin to swell. The cotton bag after 30 minutes was dehydrated for 1 minute using a dehydrator (manufactured by KOKUSAN Co. Ltd., product No. H-122) set so that the centrifugal force was 167 G, and the mass Wa (g) of the cotton bag containing the swollen gel after dehydration was measured. The same operation was performed without adding the water-absorbent resin, the empty mass Wb (g) of the cotton bag in a wet state was measured, and the physiological saline retention was calculated from the following equation.
Physiological saline retention (g/g)=[Wa−Wb]/2.0
The non-pressurized DW of particles of the water-absorbent resin was measured using a measuring device shown in
First, the cock 22 and the cock 24 of the burette unit 1 were closed, and the 0.9-mass % saline 50 adjusted to 25° C. was put into the burette tube 21 from the opening of the upper portion of the burette tube 21. The concentration of the saline of 0.9 mass % is a concentration based on the mass of the saline. After the opening of the burette tube 21 was tightly sealed with the rubber stopper 23, the cock 22 and the cock 24 were opened. The inside of the conduit 5 was filled with the 0.9-mass % saline 50 so that air bubbles did not enter. The height of the measurement stage 13 was adjusted such that the height of the surface of the 0.9-mass % saline reaching the inside of the through hole 13a became equal to the height of the upper surface of the measurement stage 13. After the adjustment, the height of the surface of the 0.9-mass % saline 50 in the burette tube 21 was read using the graduations on the burette tube 21, and the position was set as a 0 point (reading at 0 seconds).
The nylon mesh sheet 15 (100 mm×100 mm, 250 mesh, thickness of about 50 μm) was laid in the vicinity of the through hole 13a on the measurement stage 13, and a cylinder having an inner diameter of 30 mm and a height of 20 mm was placed at the center thereof. In the cylinder, 1.00 g of a water-absorbent resin 10a was uniformly spread. Thereafter, the cylinder was carefully removed to obtain a sample in which the water-absorbent resin 10a was circularly dispersed on the central portion of the nylon mesh sheet 15. Next, the nylon mesh sheet 15 on which the water-absorbent resin 10a was placed was moved quickly to such an extent that the water-absorbent resin 10a was not scattered so that the center of the nylon mesh sheet 15 was located at the position of the through hole 13a, and measurement was started. A point of time when air bubbles were first introduced from the air introduction tube 25 into the burette tube 21 was defined as the start of water absorption (0 seconds).
A decrease amount (that is, the amount of the 0.9-mass % saline absorbed by the water-absorbent resin 10a) of the 0.9-mass % saline 50 in the burette tube 21 was sequentially read in increments of 0.1 mL, and the decrement We (g) of the 0.9-mass % saline 50 after 5 minutes from the start of water absorption by the water-absorbent resin 10a was read. From the decrement Wc, the five-minute non-pressurized DW was obtained by the following equation. The non-pressurized DW is a water absorption amount per 1.00 g of the water-absorbent resin 10a.
Non-pressurized DW value (mL/g)=Wc/1.00
Using an automated sonic sieving particle size analyzer (Robot Sifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.), sieves with aperture sizes of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 250 μm, and 150 μm conforming to JIS standards, and a pan, 10 g of the particulate water-absorbent resin was sieved. The mass of the particles remaining on each sieve was calculated as a mass percentage with respect to the total amount. The mass percentages of the particles remaining on the respective sieves were integrated in the descending order of particle diameters, and the relationship between the aperture size of the sieve and the integrated value of the mass percentage of the particles remaining on the sieve was plotted on log-probability paper. The plots on the probability paper were connected by a straight line to determine the particle diameter corresponding to an integrated mass percentage of 50 mass %, and the determined value was defined as the median particle diameter.
A test liquid was prepared by blending and dissolving an inorganic salt in ion-exchanged water so that the inorganic salt was present as described below and further blending a small amount of Brilliant Blue FCF.
A measuring instrument including a cylinder for inputting liquid having an opening with an inner diameter of 3 cm was placed on a central portion of the absorbent article arranged on a horizontal stage. Next, 150 mL of the test liquid adjusted to 25±1° C. was input into the cylinder at once (supplied from the vertical direction). After 5 minutes from the start of input of the test liquid, filter paper of 10 cm square having a mass (We (g), about 80 g) measured in advance was placed near the input position of the test liquid on the absorbent article, and a weight having a mass of 5 kg and a bottom surface of 10 cm×10 cm was placed on the filter paper. After applying the load for five minutes, the mass of the filter paper (Wf (g)) was measured, and the increased mass was taken as the liquid backflow amount (g). It can be said that the smaller the liquid backflow amount is, the more preferable the absorbent article is.
Liquid backflow amount (g)=Wf−We
When the test liquid that had not been absorbed by the absorbent article 100 leaked from the lower portion of the supporting plate 40, the leaked test liquid was collected in the metal tray 44 disposed below the supporting plate 40. The mass (g) of the collected test liquid was measured with the balance 43, and the value was recorded as the leakage amount. The absorption amount until leakage occurred was calculated by subtracting the leakage amount from the total input amount of the test liquid. As this numerical value is larger, leakage of liquid is judged to be less likely to occur when the absorbent article is worn. The density of the test liquid was supposed to be 1.0 g/mL.
A 2-L round-bottomed cylindrical separable flask having an inner diameter of 11 cm and equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirring blade with double 4-winged inclined paddles having a blade diameter of 5 cm as a stirrer was prepared. To this flask, 293 g of n-heptane as the hydrocarbon dispersion medium was charged, 0.736 g of a maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, Inc., Hi-WAX 1105A) as the polymeric dispersant was added, the temperature was raised to 80° C. with stirring at a rotation speed of the stirrer of 300 rpm to dissolve the dispersant, and then the dispersant solution formed was cooled to 50° C.
On the other hand, 92.0 g (1.03 mol) of a 80.5-mass % aqueous acrylic acid solution as the ethylenically unsaturated monomers was put in a beaker having an internal volume of 300 ml, 147.5 g of a 20.9-mass % aqueous sodium hydroxide solution was added dropwise with cooling from the outside to perform neutralization of 75 mol %, and then 0.092 g of hydroxyethyl cellulose (Sumitomo Seika Chemicals Company, Limited, HEC AW-15F) as the thickener, 0.0736 g (0.272 mmol) of potassium persulfate as the radical polymerization agent, and 0.00276 g (0.016 mmol) of ethylene glycol diglycidyl ether as the internal crosslinking agent were added thereto and dissolved, thereby preparing a first-step aqueous monomer solution.
The prepared first-step aqueous monomer solution was added to the dispersant solution in the separable flask and stirred for 10 minutes to obtain a suspension. Next, a surfactant solution obtained by heating and dissolving 0.736 g of sucrose stearate (HLB: 3, Mitsubishi-Chemical Foods Corporation, RYOTO Sugar Ester S-370) as the surfactant in 6.62 g of n-heptane was added to the suspension, and the inside of the system was sufficiently purged with nitrogen while stirring at a rotation speed of a stirrer of 550 rpm. Thereafter, the flask was immersed in a water bath at 70° C. to raise the temperature, and polymerization was performed for 60 minutes to provide a first-step polymerization slurry.
Next, 128.8 g (1.43 mol) of a 80.5-mass % aqueous acrylic acid solution as the ethylenically unsaturated monomers was placed in another beaker having an internal volume of 500 ml, and 160.7 g of a 27-mass % aqueous sodium hydroxide solution was added dropwise thereto with cooling from the outside to perform neutralization of 75 mol %. Thereafter, 0.090 g (0.334 mmol) of potassium persulfate as the radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as the internal crosslinking agent were added and dissolved, thereby preparing a second-step aqueous monomer solution.
The inside of the system in the separable flask was cooled to 25° C. with stirring at a rotation speed of the stirrer of 1,000 rpm. Then, the whole amount of the second-step aqueous monomer solution was added to the first-step polymerization slurry in the separable flask, and the inside of the system was purged with nitrogen for 30 minutes. Thereafter, the flask was immersed in a water bath at 70° C. again to raise the temperature, and a polymerization reaction was performed for 60 minutes.
To the reaction solution containing the hydrogel-like polymer after the second-step polymerization, 0.265 g of a 45-mass % aqueous pentasodium diethylenetriaminepentaacetate solution was added under stirring. Thereafter, the flask was immersed in an oil bath set at 125° C., and 263.7 g of water was removed to the outside of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Thereafter, 4.42 g (0.507 mmol) of a 2-mass % aqueous ethylene glycol diglycidyl ether solution as the post-crosslinking agent was added to the flask, and the mixture was held at 83° C. for 2 hours.
Thereafter, n-heptane was evaporated at 125° C. and dried to obtain polymer particles (dry product). The polymer particles were passed through a sieve with an aperture size of 850 μm, and 0.5 mass % of amorphous silica (Oriental Silicas Corporation, Tokusil NP—S, hydrophilic) with respect to the mass of the polymer particles was mixed with the polymer particles to provide 237.9 g of water-absorbent resin particles containing amorphous silica. The median particle diameter of the water-absorbent resin particles was 343 μm. The value calculated from Formula (1) was 1.36.
Except that the amount of water to be removed to the outside of the system by azeotropic distillation was changed to 266.4 g, and the amount of the aqueous ethylene glycol diglycidyl ether solution as the post-crosslinking agent was changed to 4.42 g (0.507 mmol), 224.6 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1. The median particle diameter of the water-absorbent resin particles was 341 μm. The value calculated from Formula (1) was 1.22.
Except that the amount of water to be removed to the outside of the system by azeotropic distillation was changed to 249.3 g, and the amount of the aqueous ethylene glycol diglycidyl ether solution as the post-crosslinking agent was changed to 5.52 g (0.634 mmol), 228.0 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1. The median particle diameter of the water-absorbent resin particles was 374 μm. The value calculated from Formula (1) was 1.68.
Except that the amount of water to be removed to the outside of the system by azeotropic distillation was changed to 286.4 g, and the amount of the aqueous ethylene glycol diglycidyl ether solution as the post-crosslinking agent was changed to 13.25 g (1.521 mmol), 227.6 g of water-absorbent resin particles were obtained in the same manner as in Production Example 1. The median particle diameter of the water-absorbent resin particles was 385 μm. The value calculated from Formula (1) was 0.84.
A sheet-shaped absorbent body having a size of 12 cm×32 cm was produced by uniformly mixing 3.8 g of the water-absorbent resin particles obtained in Production Example 1 and 3.8 g of pulverized pulp by air papermaking using an air flow type mixer (Padformer manufactured by O-tec Co., Ltd.). The absorbent body was disposed on tissue paper (core wrap) having a basis weight of 16 g/m2, and tissue paper (core wrap) was laminated on the absorbent body in this order. A load of 196 kPa was applied to the laminate for 30 seconds. Further, an air through non-woven fabric having the same size as the absorbent body and a basis weight of 17 g/m2 was disposed on the upper surface of the absorbent body, and a polyethylene liquid-impermeable sheet having the same size and a basis weight of 40 g/m2 was disposed on the lower surface of the absorbent body to produce a test absorbent article. In the absorbent article, the basis weight of the water-absorbent resin particles was 100 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 100 g/m2. The mass of the absorbent article was 11 g.
An absorbent article of Example 2 was produced in the same manner as in Example 1 except that the amount of the water-absorbent resin particles was changed to 5.8 g, and the amount of the pulverized pulp was changed to 5.8 g. In the absorbent article, the basis weight of the water-absorbent resin particles was 150 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 150 g/m2. The mass of the absorbent article was 15 g.
An absorbent article of Example 3 was produced in the same manner as in Example 1 except that the amount of the water-absorbent resin particles was changed to 9.6 g, and the amount of the pulverized pulp was changed to 9.6 g. In the absorbent article, the basis weight of the water-absorbent resin particles was 250 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 250 g/m2. The mass of the absorbent article was 22 g.
An absorbent article of Example 4 was produced in the same manner as in Example 1 except that the amount of the water-absorbent resin particles was changed to 13.4 g, and the amount of the pulverized pulp was changed to 13.4 g. In the absorbent article, the basis weight of the water-absorbent resin particles was 350 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 350 g/m2. The mass of the absorbent article was 30 g.
An absorbent article of Example 5 was produced in the same manner as in Example 2 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 2. The mass of the absorbent article was 15 g.
An absorbent article of Example 6 was produced in the same manner as in Example 3 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 2. The mass of the absorbent article was 23 g.
An absorbent article of Example 7 was produced in the same manner as in Example 4 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 2. The mass of the absorbent article was 29 g.
An absorbent article of Comparative Example 1 was produced in the same manner as in Example 1 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. The mass of the absorbent article was 11 g.
An absorbent article of Comparative Example 2 was produced in the same manner as in Example 2 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. The mass of the absorbent article was 15 g.
An absorbent article of Comparative Example 3 was produced in the same manner as in Example 3 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. The mass of the absorbent article was 23 g.
An absorbent article of Comparative Example 4 was produced in the same manner as in Example 4 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. The mass of the absorbent article was 29 g.
An absorbent article of Comparative Example 5 was produced in the same manner as in Example 2 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 4. The mass of the absorbent article was 15 g.
An absorbent article of Comparative Example 6 was produced in the same manner as in Example 3 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 4. The mass of the absorbent article was 23 g.
An absorbent article of Comparative Example 7 was produced in the same manner as in Example 4 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 4. The mass of the absorbent article was 30 g.
The absorbent articles of the examples showed small liquid backflow amounts with any weight per unit area of the water-absorbent resin and large absorption amounts until occurrence of leakage in the leakage test, and it can therefore be seen that both backflow and leakage of the absorbent bodies were suppressed.
An absorbent article of Example 8 was produced in the same manner as in Example 1 except that the amount of the water-absorbent resin particles was changed to 7.7 g, the amount of the pulverized pulp was changed to 15.4 g, and the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 2. In the absorbent article, the basis weight of the water-absorbent resin particles was 200 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 400 g/m2. The mass of the absorbent article was 27 g.
An absorbent article of Example 9 was produced in the same manner as in Example 1 except that the amount of the water-absorbent resin particles was changed to 7.7 g, the amount of the pulverized pulp was changed to 7.7 g, and the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 2. In the absorbent article, the basis weight of the water-absorbent resin particles was 200 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 200 g/m2. The mass of the absorbent article was 19 g.
An absorbent article of Example 10 was produced in the same manner as in Example 1 except that the amount of the water-absorbent resin particles was changed to 7.7 g, the amount of the pulverized pulp was changed to 3.3 g, and the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 2. In the absorbent article, the basis weight of the water-absorbent resin particles was 200 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 85 g/m2. The mass of the absorbent article was 15 g.
An absorbent article of Comparative Example 8 was produced in the same manner as in Example 8 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. In the absorbent article, the basis weight of the water-absorbent resin particles was 200 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 400 g/m2. The mass of the absorbent article was 26 g.
An absorbent article of Comparative Example 9 was produced in the same manner as in Example 9 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. In the absorbent article, the basis weight of the water-absorbent resin particles was 200 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 200 g/m2. The mass of the absorbent article was 19 g.
An absorbent article of Comparative Example 10 was produced in the same manner as in Example 10 except that the water-absorbent resin particles were replaced with the water-absorbent resin particles obtained in Production Example 3. In the absorbent article, the basis weight of the water-absorbent resin particles was 200 g/m2, and the basis weight of the pulverized pulp (hydrophilic fibers) was 85 g/m2. The mass of the absorbent article was 14 g.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-057724 | Mar 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/013236 | 3/22/2022 | WO |
