Composite absorber and hygiene product

Abstract

To provide an absorber excellent in absorption performance, capable of absorbing body fluid efficiently.SOLUTION: A composite absorber (4) which is a composite absorber for a sanitary article for absorbing body fluid, includes a particulate polymer absorbent having hydrophilic continuous skeleton and continuous pores. The polymer absorbent has a particle size of 300 μm or more.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a composite absorber and a sanitary product having the same.

Background Art

[0002] In sanitary products such as disposable diapers and sanitary napkins, those containing a porous material such as a sponge material as an absorber are known. For example, Patent Document 1 discloses an absorbent article containing a polymer foam material composed of a hydrophilic flexible structure of interconnected open cells.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Such a porous material may be used in a particulate form so as to absorb body fluids more efficiently. However, when the particle size becomes small, the pore structure of the porous material may collapse, and the absorption performance of body fluids may deteriorate.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide an absorber that can efficiently absorb body fluids and has excellent absorption performance.

Means for Solving the Problems

[0006] One aspect (Aspect 1) of the present invention is a composite absorber for a sanitary product for absorbing body fluids, including a particulate polymer absorbent having a hydrophilic continuous skeleton and continuous pores, wherein the polymer absorbent has a particle size of 300 μm or more.

[0007] In the composite absorber of Embodiment 1, since the particulate polymer absorbent capable of taking in body fluid into continuous pores by capillary action has a particle diameter of 300 μm or more, it is easy to maintain the pore structure including the continuous skeleton and continuous pores, so that body fluid can be efficiently absorbed and excellent absorption performance can be exhibited.

[0008] Further, in another embodiment (Embodiment 2) of the present invention, in the composite absorber of Embodiment 1, the volume increase rate of the polymer absorbent at the time of saturated liquid absorption with respect to the volume before liquid absorption is 233% to 567%.

[0009] In the composite absorber of Embodiment 2, since the volume increase rate of the polymer absorbent at the time of liquid absorption is 233% to 567%, body fluid can be absorbed more efficiently and further excellent absorption performance can be exhibited.

[0010] In still another embodiment (Embodiment 3) of the present invention, in the composite absorber of Embodiment 1 or 2, the porosity per unit volume of the polymer absorbent is 85% or more.

[0011] In the composite absorber of Embodiment 3, since the porosity per unit volume of the polymer absorbent is 85% or more, more body fluid can be absorbed and further excellent absorption performance can be exhibited.

[0012] In still another embodiment (Embodiment 4) of the present invention, in the composite absorber of any one of Embodiments 1 to 3, the average diameter of the continuous pores is 1 μm to 1000 μm.

[0013] In the composite absorber of Embodiment 4, since the average diameter of the continuous pores of the polymer absorbent is 1 μm to 1000 μm, the space (pores) for the polymer absorbent to take in body fluid is not easily collapsed, and it can have a higher absorption rate, and excellent absorption performance can be stably exhibited.

[0014] In yet another aspect (Aspect 5) of the present invention, in the composite absorber according to any one of the above Aspects 1 to 4, the polymer absorbent is a monolithic absorbent.

[0015] Since the polymer absorbent of the composite absorber of this Aspect 5 is a monolithic absorbent, it can quickly absorb body fluids and can more steadily transfer the temporarily held body fluids to the SAP.

[0016] In yet another aspect (Aspect 6) of the present invention, in the composite absorber according to any one of the above Aspects 1 to 5, the polymer absorbent is a hydrolyzate of a cross-linked polymer of (meth)acrylic acid ester and a compound containing two or more vinyl groups in one molecule, and is characterized by containing at least one -COONa group.

[0017] Since the polymer absorbent of the composite absorber of this Aspect 6 has the above specific configuration, when absorbing body fluids, the hydrophilic continuous skeleton is easy to extend and the continuous pores are also easy to expand. Therefore, more body fluids can be taken into the continuous pores more quickly, and the composite absorber can exhibit better absorption performance as an absorber.

[0018] Moreover, yet another aspect (Aspect 7) of the present invention is a sanitary product characterized by having the composite absorber according to any one of the above Aspects 1 to 6.

[0019] Since the sanitary product of this Aspect 7 has the composite absorber according to any one of the above Aspects 1 to 6, it can efficiently absorb body fluids as a sanitary product and can exhibit excellent absorption performance.

Advantages of the Invention

[0020] According to the present invention, it is possible to efficiently absorb body fluids and provide an absorber having excellent absorption performance.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a preferred embodiment of the composite absorber of the present invention will be described in detail using the light incontinence pad 1, which is an example of a sanitary product to which the composite absorber is applied. In this specification, unless otherwise specified, "viewing an object (for example, a light incontinence pad, a composite absorber, etc.) placed on a horizontal plane in a deployed state from the upper side in the vertical direction (the surface sheet side when the object is a sanitary product) in the thickness direction of the object" is simply referred to as "plan view".

[0023] In this specification, the "longitudinal direction" refers to "the longer direction of the length of a vertically long object (for example, a light incontinence pad in a deployed state, a composite absorber, etc.) in plan view", the "width direction" refers to "the shorter direction of the length of a vertically long object in plan view", and the "thickness direction" refers to "the direction perpendicular to an object placed on a horizontal plane in a deployed state". These longitudinal direction, width direction, and thickness direction are in a mutually orthogonal relationship.

[0024] In addition, in this specification, unless otherwise specified, in the thickness direction of the light incontinence pad 1, "the relatively proximal side with respect to the wearer's skin surface when the light incontinence pad 1 is worn" is referred to as the "skin-facing surface side", and "the relatively distal side with respect to the wearer's skin surface when the light incontinence pad 1 is worn" is referred to as the "non-skin-facing surface side".

[0025] [Light incontinence pad] FIG. 1 is a schematic plan view of the light incontinence pad 1 in a deployed state to which the composite absorber 4 according to an embodiment of the present invention is applied. As shown in FIG. 1, the light incontinence pad 1 has a longitudinal outer shape in a plan view, having a longitudinal direction L and a width direction W, and two longitudinal edges protruding in an arc shape toward the outer side in the longitudinal direction. Note that the outer shape of the light incontinence pad 1 is not limited to such a mode, and any shape (for example, an oval shape, a rectangular shape, an hourglass shape, etc.) according to various uses and usage modes can be adopted as long as it is a longitudinal shape.

[0026] The light incontinence pad 1 basically includes, in the thickness direction, a liquid-permeable surface sheet 2 forming the surface on the skin-facing surface side of the light incontinence pad 1, a back sheet 3 forming the surface on the non-skin-facing surface side of the light incontinence pad 1, and a composite absorber 4 located between these sheets. In addition, the light incontinence pad 1 further includes an adhesive portion (not shown) disposed on the surface on the non-skin-facing surface side of the back sheet 3 for adhesively fixing the light incontinence pad 1 to the inner surface of clothing such as the wearer's underwear.

[0027] Note that the light incontinence pad 1 is not limited to such a configuration. For example, a pair of side sheets for forming a leakage-preventing wall, which are located at both ends in the width direction W of the light incontinence pad 1 at a position closer to the skin-facing surface side than the surface sheet 2 and are arranged to extend in the longitudinal direction L, and a plurality of elastic members arranged along the longitudinal direction L in each of the pair of side sheets may be provided.

[0028] In the light incontinence pad 1, the composite absorber 4 is located between the surface sheet 2 and the back sheet 3, and is formed of a water-absorbent member capable of absorbing body fluids such as urine discharged from the wearer and passing through the surface sheet 2. Such a composite absorber 4 contains a particulate polymer absorbent having a particle diameter of 300 μm or more and having a hydrophilic continuous skeleton and continuous pores.

[0029] Such a polymer absorbent can take in body fluids into the continuous pores by capillary action, and further, because it has a specific particle diameter of 300 μm or more, it is easy to maintain the pore structure having the continuous skeleton and continuous pores, so that body fluids can be efficiently absorbed and excellent absorption performance can be exhibited. Thereby, the composite absorber 4 containing such a polymer absorbent can exhibit excellent absorption performance as an absorber.

[0030] Therefore, the light incontinence pad 1 provided with such a composite absorber 4 can also efficiently absorb body fluids as a light incontinence pad and exhibit excellent absorption performance. The particle diameter of the polymer absorbent will be described later.

[0031] Hereinafter, various constituent members of the sanitary product to which the composite absorber of the present invention is applied will be described in more detail using the above-described light incontinence pad 1.

[0032] (Surface sheet) In the above-described light incontinence pad 1, as shown in FIG. 1, the surface sheet 2 extends in a longitudinal outer shape that extends from one end edge to the other end edge in the longitudinal direction L of the light incontinence pad 1 and extends from near one end edge to near the other end edge in the width direction W of the light incontinence pad 1 in a plan view. Such a surface sheet 2 is disposed at a position on the skin-facing surface side in the thickness direction of the light incontinence pad 1 and is constituted by a liquid-permeable sheet-like member that forms a contact surface that can contact the skin of the wearer, that is, the surface on the skin-facing surface side of the light incontinence pad 1.

[0033] Further, as shown in FIG. 1, the surface sheet 2 has a size slightly larger than that of the composite absorber 4 disposed on the non-skin facing surface side of the surface sheet 2 in the longitudinal direction L and the width direction W, and is joined to the back sheet 3 located on the non-skin facing surface side at the peripheral portion.

[0034] In the present invention, the outer shape, various dimensions, basis weight, etc. of the surface sheet are not particularly limited as long as they can be used as the surface sheet of a sanitary product, and any outer shape, various dimensions, basis weight, etc. corresponding to desired liquid permeability, touch feeling, flexibility, strength, etc. can be adopted.

[0035] (Back sheet) In the above-mentioned light incontinence pad 1, the back sheet 3 extends from one end edge to the other end edge in the longitudinal direction L of the light incontinence pad 1 and from one end edge to the other end edge in the width direction W of the light incontinence pad 1 in a plan view, and has a vertically long outer shape. Such a back sheet 3 is disposed at a position on the non-skin facing surface side in the thickness direction of the light incontinence pad 1, forms the non-skin facing surface of the light incontinence pad 1, and is composed of a liquid-impermeable sheet member that prevents body fluids such as urine that have passed through the composite absorber 4 from leaking to the outside of the light incontinence pad 1.

[0036] In the present invention, the outer shape, various dimensions, basis weight, etc. of the back sheet are not particularly limited as long as they can be used as the back sheet of a sanitary product, and any outer shape, various dimensions, basis weight, etc. corresponding to desired leakage prevention performance, breathability, strength, etc. can be adopted.

[0037] (Composite absorber) In the above-mentioned light incontinence pad 1, as shown in FIG. 1, the composite absorber 4 extends in a wide area in the longitudinal direction L from near one end edge to near the other end edge in the longitudinal direction L around the central portions of the longitudinal direction L and the width direction W of the light incontinence pad 1 in a plan view, and also extends in a wide area in the width direction W from near one end edge to near the other end edge in the width direction W, and further has a vertically long outer shape in which two longitudinal end edges protrude in an arc shape toward the outer side in the longitudinal direction.

[0038] More specifically, the composite absorber 4 has a constricted portion in the central part in the longitudinal direction in plan view, with a relatively smaller widthwise length compared to other parts. Further, in this constricted portion, there is a minimum width portion having the minimum width of the composite absorber 4, and a maximum width portion having the maximum width of the composite absorber 4 on the outer side in the longitudinal direction of the constricted portion.

[0039] The composite absorber 4 is disposed between the surface sheet 2 and the back sheet 3 in the thickness direction of the light incontinence pad 1, and is formed of a predetermined water-absorbing member capable of absorbing and holding body fluids such as urine that has passed through the surface sheet 2. Such a water-absorbing member is composed of a water-absorbing material such as a polymer absorbent, a hydrophilic fiber, and a superabsorbent polymer described later, and a sheet such as a tissue that holds it. That is, the composite absorber means a water-absorbing member composed of a water-absorbing material capable of absorbing and holding body fluids and a sheet that holds it.

[0040] In the light incontinence pad 1, the composite absorber 4 is joined to each of the surface sheet 2 and the back sheet 3 by an arbitrary adhesive such as a hot melt adhesive.

[0041] And the composite absorber 4 contains a polymer absorbent having a specific particle diameter, which has a hydrophilic continuous skeleton and continuous pores as described above. This polymer absorbent will be described later.

[0042] Note that the composite absorber 4 may contain only the above-described polymer absorbent as the water-absorbing material, or may further contain a water-absorbing material known in the art in addition to the above-described polymer absorbent. Examples of such water-absorbing materials include hydrophilic fibers and superabsorbent polymers. More specifically, pulp fibers (e.g., pulverized pulp, etc.), cotton, rayon, acetate and other cellulose-based fibers; particulate matter composed of superabsorbent polymers (SAP) such as sodium acrylate copolymer; mixtures of these arbitrarily combined, etc. can be mentioned.

[0043] Incidentally, the composite absorber 4 has a configuration in which such a polymer absorbent or a water-absorbing material is covered with a wrap sheet such as a hydrophilic tissue.

[0044] In the present invention, the outer shape, various dimensions, basis weight, etc. of the composite absorber are not particularly limited as long as the effects of the present invention are not impaired, and any outer shape, various dimensions, basis weight, etc. corresponding to desired water absorption, flexibility, strength, etc. can be adopted.

[0045] Hereinafter, the polymer absorbent used in the composite absorber of the present invention will be described in more detail.

[0046] [Polymer absorbent] The polymer absorbent is a particulate polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and is not particularly limited as long as it has a specific particle diameter of 300 μm or more. For example, it is a hydrolyzate of a crosslinked polymer of two or more monomers containing at least (meth)acrylate ester, and examples thereof include a polymer compound having at least one hydrophilic group in the functional group. More specifically, it is a hydrolyzate of a crosslinked polymer of (meth)acrylate ester and a compound containing two or more vinyl groups in one molecule, and examples thereof include a polymer compound having at least -COONa group. Such a polymer absorbent is an organic porous body having at least one -COONa group in one molecule, and may further have a -COOH group. In the skeleton of the porous body, -COONa groups are distributed substantially uniformly.

[0047] When the polymer absorbent is a hydrolyzate of such a crosslinked polymer of (meth)acrylate ester and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group, the hydrophilic continuous skeleton is likely to elongate when absorbing body fluids such as urine, and the continuous pores are also likely to expand. Therefore, more body fluids can be taken into the continuous pores more quickly, and the absorber can exhibit more excellent absorption performance.

[0048] In this specification, the (meth)acrylic acid ester refers to an acrylic acid ester or a methacrylic acid ester.

[0049] In such a polymer absorbent formed by the hydrolyzate of a crosslinked polymer of such a (meth)acrylic acid ester and divinylbenzene, a hydrophilic continuous skeleton is formed by an organic polymer having at least -COONa groups, and there are continuous pores (continuous voids) serving as absorption sites for the liquid to be absorbed (i.e., body fluids such as urine) between the skeletons. Note that since the hydrolysis treatment is to convert the -COOR group (i.e., carboxylic acid ester group) of the crosslinked polymer into a -COONa group or a -COOH group (see Figure 2), the polymer absorbent may have a -COOR group.

[0050] The presence of -COOH groups and -COONa groups in the organic polymer forming the hydrophilic continuous skeleton can be confirmed by analysis using infrared spectrophotometry and the method for quantifying weakly acidic ion exchange groups.

[0051] Here, Figure 2 is a diagram for explaining the manufacturing process of absorbent A which is an example of a polymer absorbent. In this Figure 2, the upper diagram shows the constituent raw materials of the polymerization, the middle diagram shows monolith A which is a crosslinked polymer of a (meth)acrylic acid ester and divinylbenzene, and the lower diagram shows absorbent A obtained by subjecting the monolith A in the middle diagram to hydrolysis and drying treatments.

[0052] Hereinafter, an explanation will be given using absorbent A formed by the hydrolyzate of a crosslinked polymer of a (meth)acrylic acid ester and divinylbenzene, which is an example of a polymer absorbent.

[0053] Note that the polymer absorbent is not limited to such absorbent A, and may be, for example, the hydrolyzate of a crosslinked polymer of a (meth)acrylic acid ester and a compound having two or more vinyl groups in one molecule, or the hydrolyzate of a crosslinked polymer of two or more types of monomers containing at least a (meth)acrylic acid ester.

[0054] In the following description, "monolith A" is an organic porous body composed of a cross-linked polymer of (meth)acrylic acid ester and divinylbenzene before hydrolysis treatment, and may be referred to as "monolithic organic porous body". Also, "absorbent A" is a hydrolyzate of a cross-linked polymer (monolith A) of (meth)acrylic acid ester and divinylbenzene after hydrolysis treatment and drying treatment. In the following description, absorbent A refers to the dry state.

[0055] First, the structure of absorbent A will be described. As described above, absorbent A has a hydrophilic continuous skeleton and continuous pores. Absorbent A, which is an organic polymer having a hydrophilic continuous skeleton, is obtained by cross-linking polymerization of (meth)acrylic acid ester as a polymerization monomer and divinylbenzene as a cross-linking monomer, and further hydrolyzing the obtained cross-linked polymer (monolith A) as shown in Fig. 2.

[0056] The organic polymer forming the hydrophilic continuous skeleton has, as constituent units, a polymerization residue of an ethylene group (hereinafter referred to as "constituent unit X") and a cross-linked polymerization residue of divinylbenzene (hereinafter referred to as "constituent unit Y"). Furthermore, the polymerization residue of the ethylene group (constituent unit X) in the organic polymer forming the hydrophilic continuous skeleton has a -COONa group generated by hydrolysis of a carboxylic acid ester group, or both a -COOH group and a -COONa group. When the polymerization monomer is (meth)acrylic acid ester, the polymerization residue of the ethylene group (constituent unit X) has a -COONa group, a -COOH group and an ester group.

[0057] In absorbent A, the proportion of the crosslinked polymerization residue (structural unit Y) of divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is, for example, 0.1 to 30 mol% with respect to all the structural units, preferably 0.1 to 20 mol%. For example, in absorbent A using butyl methacrylate as the polymerization monomer and divinylbenzene as the crosslinking monomer, the proportion of the crosslinked polymerization residue (structural unit Y) of divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is, for example, about 3% with respect to all the structural units, preferably 0.1 to 10 mol%, and more preferably 0.3 to 8 mol%. In addition, when the proportion of the crosslinked polymerization residue of divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is 0.1 mol% or more, the strength of absorbent A is less likely to decrease. Also, when the proportion of the crosslinked polymerization residue of divinylbenzene is 30 mol% or less, the absorption amount of the liquid to be absorbed is less likely to decrease.

[0058] In absorbent A, the organic polymer forming the hydrophilic continuous skeleton may consist only of structural unit X and structural unit Y, or may have, in addition to structural unit X and structural unit Y, structural units other than structural unit X and structural unit Y, that is, polymerization residues of monomers other than (meth)acrylate and divinylbenzene.

[0059] Examples of the structural units other than structural unit X and structural unit Y include polymerization residues of monomers such as styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, glycidyl (meth)acrylate, isobutene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate.

[0060] In addition, the proportion of the structural units other than structural unit X and structural unit Y in the organic polymer forming the hydrophilic continuous skeleton is, for example, 0 to 50 mol% with respect to all the structural units, preferably 0 to 30 mol%.

[0061] Further, the absorbent A preferably has a hydrophilic continuous skeleton thickness of 0.1 to 100 μm. When the thickness of the hydrophilic continuous skeleton of the absorbent A is 0.1 μm or more, the space (pores) for taking in the liquid to be absorbed (body fluid) in the porous body is less likely to collapse during absorption, and the absorption amount is less likely to decrease. On the other hand, when the thickness of the hydrophilic continuous skeleton is 100 μm or less, an excellent absorption rate is easily obtained.

[0062] Since the pore structure of the hydrophilic continuous skeleton of the absorbent A is a continuous bubble structure, for the measurement of the thickness of the continuous skeleton, the cross-section of the skeleton appearing on the test piece for electron microscope measurement is taken as the evaluation location of the thickness. Since the continuous skeleton is formed by the interval between the water (water droplets) removed by dehydration and drying after hydrolysis, it is often polygonal in shape. Therefore, the thickness of the continuous skeleton is taken as the average value of the diameters (μm) of the circles circumscribing the polygonal cross-section. Also, although there may be cases where small holes are open in the polygon rarely, in that case, the circumscribed circle of the cross-section of the polygon surrounding the small hole is measured.

[0063] Furthermore, the absorbent A preferably has an average diameter of continuous pores of 1 μm to 1000 μm. When the average diameter of the continuous pores of the absorbent A is 1 μm or more, the space (pores) for taking in the liquid to be absorbed (body fluid) in the porous body is less likely to collapse during absorption, and the absorption rate is less likely to decrease. On the other hand, when the average diameter of the continuous pores is 1000 μm or less, an excellent absorption rate is easily obtained. Thereby, the composite absorber containing such an absorbent A can have a higher absorption rate and can stably exhibit excellent absorption performance.

[0064] The average diameter (μm) of the continuous pores of the absorbent A can be measured by the mercury intrusion method, and the maximum value of the pore size distribution curve obtained by such mercury intrusion method is adopted. For the sample for measuring the average diameter of the continuous pores, regardless of the ionic form of the absorbent A, a sample dried in a vacuum dryer set at a temperature of 50 °C for 18 hours or more is used. Note that the final pressure reached is 0 Torr. Also, naturally, the average diameter of the continuous pores of this absorbent A is smaller than the particle diameter of the absorbent A.

[0065] Here, Fig. 3 is an SEM photograph of the absorbent A at a magnification of 50 times, Fig. 4 is an SEM photograph of the absorbent A at a magnification of 100 times, Fig. 5 is an SEM photograph of the absorbent A at a magnification of 500 times, Fig. 6 is an SEM photograph of the absorbent A at a magnification of 1000 times, and furthermore, Fig. 7 is an SEM photograph of the absorbent A at a magnification of 1500 times. The absorbent A shown in Figs. 3 to 7 is an example of an absorbent using butyl methacrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, and SEM photographs are taken using those having a structure of a 2 mm square cube.

[0066] The absorbent A shown in Figs. 3 to 7 has a large number of bubble-like macropores, and furthermore, has portions where these bubble-like macropores overlap. The absorbent A has a continuous bubble structure in which the overlapping portions of these macropores become a common opening (mesopore), that is, it is a continuous bubble structure (continuous macropore structure).

[0067] The overlapping portion of these macropores becomes a common opening (mesopore) having an average diameter in the dry state of 1 to 1000 μm, preferably 10 to 200 μm, particularly preferably 20 to 100 μm, and most of it has an open pore structure. When the average diameter of the mesopores in the dry state is 1 μm or more, the absorption rate of the liquid to be absorbed becomes better. On the other hand, when the average diameter of the mesopores in the dry state is 1000 μm or less, the absorbent A is less likely to become brittle. Note that such an overlap of macropores is about 1 to 12 per macropore, and many are about 3 to 10.

[0068] In addition, since the absorbent A has such a continuous bubble structure, macropore groups and mesopore groups can be uniformly formed, and there is an advantage that the pore volume and specific surface area can be significantly increased compared to the particle-aggregated porous bodies described in, for example, Japanese Patent Laid-Open No. 8-252579.

[0069] Note that the total pore volume of the pores (voids) of the absorbent A is preferably 0.5 to 50 mL / g, more preferably 2 to 30 mL / g. When the total pore volume of the absorbent A is 0.5 mL / g or more, the space (pores) for taking in the liquid to be absorbed (body fluid) of the porous body is less likely to collapse during absorption, and the absorption amount and absorption rate are less likely to decrease. On the other hand, when the total pore volume of the absorbent A is 50 mL / g or less, the strength of the absorbent A is less likely to decrease.

[0070] Note that the total pore volume can be measured by the mercury intrusion method. As the sample for measuring the total pore volume, regardless of the ionic form of the absorbent A, a sample dried in a vacuum dryer set at a temperature of 50°C for 18 hours or more is used. Note that the final pressure reached is set to 0 Torr.

[0071] Hereinafter, the state when the absorbent A comes into contact with a liquid such as body fluid (hereinafter simply referred to as "body fluid") will be described, but the same applies to the case when the composite absorber 4 containing the absorbent A comes into contact with the body fluid. In addition, since the mass of the absorbed body fluid is substantially proportional to the amount of body fluid, in the following description, the mass of the body fluid may sometimes be simply referred to as the "amount of body fluid".

[0072] First, the continuous pores of the absorbent A shown in FIGS. 3 to 7 are pores in which a plurality of pores (voids) communicate with each other, and it can be visually confirmed with the naked eye that a large number of pores are provided even from the appearance. When body fluid comes into contact with the absorbent A having such a large number of pores, a certain amount of body fluid enters into these numerous pores by capillary action and is absorbed by the absorbent A. At this time, among the body fluid absorbed by the absorbent A, a part of the body fluid is absorbed into the hydrophilic continuous skeleton by osmotic pressure, and the continuous skeleton elongates. On the other hand, among the body fluid absorbed by the absorbent A, the body fluid that is not absorbed into the hydrophilic continuous skeleton is absorbed while being retained in the pores.

[0073] In this way, the absorbent A has the property that the hydrophilic continuous skeleton elongates when absorbing body fluid. The elongation of this continuous skeleton occurs almost omnidirectionally. Furthermore, as the outer shape of the absorbent A becomes larger due to the elongation of such a continuous skeleton, the size of each pore also becomes larger. When the size of the pore becomes larger in this way, the volume inside the pore becomes larger, so the amount of body fluid that can be retained in the pore also increases. That is, the absorbent A that has become larger by absorbing a certain amount of body fluid can absorb a further predetermined amount of body fluid into the enlarged pores by capillary action. Furthermore, since the absorbent A absorbs body fluid by capillary action, it can absorb body fluid quickly.

[0074] Also, more body fluid remains in the pores than in the hydrophilic continuous skeleton among the body fluid absorbed by the absorbent A. Since most of the absorption of body fluid by the absorbent A is carried out by retaining the body fluid in the pores by capillary action, the higher the porosity (the volume of the voids of the pores with respect to the unit volume of the absorbent A), which is the ratio of the volume of the voids of the pores (total pore volume), the more body fluid can be absorbed.

[0075] The porosity per unit volume of this polymer absorbent is preferably 85% or more, more preferably 90% or more. When the porosity per unit volume of the polymer absorbent is 85% or more, more body fluid can be absorbed, and more excellent absorption performance can be exhibited.

[0076] For example, when determining the porosity of absorbent A shown in FIGS. 3 to 7 above, it is as follows. First, the specific surface area of absorbent A obtained by the mercury intrusion method is 400 m 2 / g, and the pore volume is 15.5 mL / g. This pore volume of 15.5 mL / g means that the volume of pores in 1 g of absorbent A is 15.5 mL. Here, assuming that the specific gravity of absorbent A is 1 g / mL, the volume occupied by pores in 1 g of absorbent A, that is, the pore volume, is 15.5 mL, and the volume of 1 g of absorbent A is 1 mL. Then, the total volume (volume) of 1 g of absorbent A is 15.5 + 1 (mL). Since the ratio of the pore volume among them is the porosity, the porosity of absorbent A is 15.5 / (15.5 + 1)×100 ≒ 94%.

[0077] And in the present invention, absorbent A having such a hydrophilic continuous skeleton and continuous pores, that is, the polymer absorbent, is in a particulate form having a specific particle diameter of 300 μm or more, and is applied to a composite absorbent for absorbing body fluids such as urine like the composite absorbent 4 of the above-mentioned light incontinence pad 1.

[0078] Such a polymer absorbent can take in body fluid into the continuous pores by capillary action, and further, because it has a specific particle diameter of 300 μm or more, it is easy to maintain the pore structure having the above-mentioned continuous skeleton and continuous pores, so that body fluid can be efficiently absorbed and excellent absorption performance can be exhibited. Thereby, the composite absorbent of the present invention containing such a polymer absorbent can efficiently absorb body fluid as an absorbent and exhibit excellent absorption performance.

[0079] Incidentally, the particle size of the polymer absorbent is preferably 2000 μm or less, more preferably 400 μm to 1500 μm, from the viewpoints of absorption efficiency and wearing comfort (foreign body sensation). In particular, when the particle size of the polymer absorbent is 400 μm or more, the number of pores present inside the particles of the polymer absorbent can be ensured to be a certain amount or more, and more absorption target liquid (body fluid) can be stably taken in, that is, excellent water absorption can be stably exhibited.

[0080] Also, the particle size of the polymer absorbent can be measured by the sieve method, which means the average particle size of the particles classified by a sieve tester.

[0081] Here, a plurality of types of polymer absorbents with different particle sizes classified using a sieve tester were prepared, and the water absorption amounts of the polymer absorbents with different particle sizes were measured according to the following measurement method. The measurement results of this water absorption amount are shown in Table 1 below.

[0082] <Measurement Method of Water Absorption Amount of Polymer Absorbent> (1) Enclose 1 g of the sample for measurement (polymer absorbent) in a mesh bag (manufactured by NBC Mesh Tech Co., Ltd., N-NО255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) cut into a 10 cm square. Incidentally, the mass (g) of the mesh bag is measured in advance. Also, this measurement method is carried out under the conditions of a temperature of 25 °C and a humidity of 60%. Furthermore, when the sample for measurement (polymer absorbent) is recovered from a hygiene product and used, it can be obtained according to the <Recovery Method of Sample for Measurement (Polymer Absorbent)> described later. (2) Immerse the mesh bag containing the sample in physiological saline (0.9% sodium chloride aqueous solution) for 1 hour. (3) Measure the mass (g) after hanging the mesh bag for 5 minutes to drain the water. (4) Calculate the water absorption amount (g) of the sample by subtracting the mass of the sample (= 1 g) and the total mass of the mesh bag from the mass of the mesh bag after water drainage measured in (3) above, and further divide this water absorption amount by the mass of the sample (= 1 g) to obtain the water absorption amount per unit mass (g / g) of the sample (polymer absorbent).

[0083] In addition, when the sample (polymer absorbent) for the above measurement is recovered and used from a hygiene product, it can be obtained as follows.

[0084] <Recovery Method of Sample (Polymer Absorbent) for Measurement> (1) Peel off the surface sheet etc. from the hygiene product to expose the composite absorber. (2) Drop the measurement object (polymer absorbent) from the exposed composite absorber, and remove things other than the measurement object (in particle form) (for example, pulp, synthetic resin fibers, etc.) using tweezers or the like. (3) Using a microscope or a simple magnifying glass as the magnifying observation means, observe at a magnification at which the difference from SAP can be recognized or at a magnification at which the pores of the porous body can be visually recognized, and recover the measurement object using tweezers or the like. The magnification of the simple magnifying glass is not particularly limited as long as it is a magnification at which the pores of the porous body can be visually recognized, and for example, magnifications of 25 times to 50 times can be mentioned. (4) The measurement object recovered in this way is used as the sample for measurement in various measurement methods.

[0085]

Table 1

[0086] As shown in Table 1, the polymer absorbent having a hydrophilic continuous skeleton and continuous pores shows excellent water absorption even in a polymer absorbent with a small particle diameter of 300 μm, and furthermore, it can be seen that in a polymer absorbent having a particle diameter of 400 μm or more (more specifically, 430 μm or more), a stable and high water absorption is shown.

[0087] Also, as described above, when body fluid enters the continuous pores due to capillary action in the continuous skeleton of the polymer absorbent, a part of the entered body fluid is absorbed by osmotic pressure and the polymer absorbent expands. And due to such expansion, more body fluid can be taken into the enlarged pores. That is, the polymer absorbent can further absorb body fluid while expanding (increasing in volume) (in other words, it can expand and further increase the water absorption amount and the liquid retention amount). Therefore, even if the size and amount of the polymer absorbent before body fluid absorption (before expansion) are small, it can efficiently absorb more body fluid. Particularly in the present invention, from the viewpoint of such body fluid absorption efficiency, it is preferable that the polymer absorbent has a volume increase rate of 233% to 567% with respect to the pre-absorption volume at the time of saturated liquid absorption. When the volume increase rate of the polymer absorbent at the time of liquid absorption is within such a range, body fluid can be absorbed more efficiently, and more excellent absorption performance can be exhibited. In addition, the volume increase rate of the polymer absorbent with respect to the pre-absorption volume at the time of saturated liquid absorption can be measured as follows.

[0088] <Method for Measuring the Volume Increase Rate of the Pre-absorption Volume with Respect to the Volume at the Time of Saturated Liquid Absorption> (1) Place the sample for measurement (polymer absorbent) in an acrylic cylinder (inner diameter: 26 mm, outer diameter: 38 mm, height: 80 mm, mass: 57 g) with a nylon mesh material ((manufactured by NBC Mesh Tech Co., Ltd., N-NО255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) attached to the bottom surface, and measure the height (mm) from the bottom surface of the cylinder to the upper surface of the sample in the cylinder. When the upper surface of the sample in the cylinder is not flat, measure the height to the highest part (top). Also, this measurement method is carried out under the conditions of a temperature of 25°C and a humidity of 60%. Further, when the sample for measurement (polymer absorbent) is recovered from a hygiene product and used, it can be obtained according to the aforementioned <Method for Recovering the Sample for Measurement (Polymer Absorbent)>. (2) Calculate the volume of the sample in the cylinder, that is, the pre-absorption volume (mm 3 ) from the measured height of the sample in the cylinder and the bottom area in the cylinder (taking the pi as 3.14). (3) Next, put 60 mL of physiological saline (0.9% sodium chloride aqueous solution) into a petri dish (inner diameter: 97 mm, mass: 58 g), place the cylinder containing the sample of (1) above into this petri dish, immerse the bottom surface of the cylinder in the physiological saline, and let the physiological saline be absorbed by the sample inside the cylinder. (4) As the sample inside the cylinder absorbs the physiological saline, the height (volume) of the sample inside the cylinder changes. Continuously observe the change in the height of the sample inside the cylinder, and when this height no longer changes (i.e., when the liquid absorption reaches saturation), measure the height of the sample inside this cylinder (i.e., the height at the time of saturated liquid absorption; mm). When the upper surface of the sample inside the cylinder is not flat at the time of saturated liquid absorption, measure the height up to the highest part (top). (5) From the measured height of the sample inside the cylinder at the time of saturated liquid absorption and the bottom area inside the cylinder (taking the pi as 3.14), calculate the volume of the sample inside the cylinder at the time of saturated liquid absorption, that is, the saturated liquid absorption volume (mm 3 ). (6) Divide the saturated liquid absorption volume calculated in (5) above by the volume before liquid absorption calculated in (2) above and multiply by 100 to obtain the volume increase rate (%) of the saturated liquid absorption volume of the sample (polymer absorbent) with respect to the volume before liquid absorption.

[0089] Also, in the present invention, the polymer absorbent preferably has a specific water absorption property that the initial water absorption amount after 5 seconds from applying a load of 40 g / cm 2 is 5 g / g or more, and the water absorption amount after 20 seconds or more has passed is 110% or more of the initial water absorption amount. When the polymer absorbent has such a specific initial absorption amount and the absorption amount after 20 seconds or more has passed, the absorption amount in the initial stage of absorption is large, and it can temporarily hold body fluid, and it can also absorb body fluid even after a predetermined time has passed, so it can exhibit higher absorption performance.

[0090] Here, the above 40 g / cm 2The load is a load assuming general body pressure, and the water absorption amount after 20 seconds or more has elapsed means the water absorption amount (mass; g / g) at any timing after 20 seconds from when the above load is applied under predetermined temperature conditions (for example, any timing such as after 20 seconds, after 60 seconds, after 300 seconds, after 3600 seconds, etc.). The initial water absorption amount and the water absorption amount after a predetermined time of the polymer absorbent can be measured as follows.

[0091] <Method for Measuring Water Absorption Amount of Polymer Absorbent under Specific Load> (1) Put 25 g of physiological saline (0.9% sodium chloride aqueous solution) into a petri dish with a pedestal (inner diameter: 85 mm, depth: 20 mm, pedestal arrangement: two pedestals are arranged in parallel at a 24 - mm interval at the center of the bottom surface (inner surface side), pedestal width: 2 mm, pedestal height: 2 mm, pedestal length: 25 mm). This measurement method is carried out under the conditions of a temperature of 25°C and a humidity of 60%. (2) Put 0.16 g of the sample for measurement (polymer absorbent) into a plastic cylinder (inner diameter: 26 mm, outer diameter: 32 mm, height: 33 mm) with a nylon mesh material ((manufactured by NBC Mesh Tech Co., Ltd., N - NО255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) attached to the bottom surface, and spread it evenly. When the sample for measurement (polymer absorbent) is recovered from a hygiene product and used, it can be obtained according to the aforementioned <Method for Recovering Sample for Measurement (Polymer Absorbent)>. (3) Place a cylindrical plastic piston (diameter: 25 mm, mass: 5 g) on the sample in the cylinder, and further place a weight of a predetermined mass (200 g; load 40 g / cm 2 for use) on the plastic piston, and measure the mass (g) of the cylinder. (4) Place the cylinder containing the sample, the plastic piston, and the weight on the pedestal at the center of the petri dish, immerse the bottom surface of the cylinder in the physiological saline, and let the physiological saline be absorbed by the sample in the cylinder. After a predetermined time has elapsed (for example, after 5 seconds, 20 seconds, 60 seconds, 300 seconds, 3600 seconds, etc.), the cylinder is pulled up, tilted at 45°, drained for 1 minute, and then the mass (g) of the cylinder is measured. (6) The water absorption amount (g) of the sample is calculated by subtracting the mass of the cylinder before water absorption measured in (3) above from the mass of the cylinder after water absorption measured in (5) above, and further, the water absorption amount per unit mass (g / g) of the sample (polymer absorbent) is obtained by dividing this water absorption amount by the mass of the sample (= 0.16 g). Note that when the predetermined time (i.e., the water absorption time) in (5) above is 5 seconds, the water absorption amount (g / g) is the "initial water absorption amount after 5 seconds from applying a load of 40 g / cm 2 and when the water absorption time is 20 seconds or more, the water absorption amount (g / g) is the "water absorption amount after 20 seconds or more have elapsed".

[0092] In the present invention, it is preferable that the composite absorber further contains a conventional superabsorbent polymer (SAP) in addition to the above-described polymer absorbent. When the composite absorber contains SAP together with the polymer absorbent, body fluids such as urine are quickly absorbed by the polymer absorbent in the composite absorber and temporarily held, and then the body fluids are transferred to SAP having a high water retention ability and can be held in the SAP. Therefore, as an absorber, higher absorption performance can be exhibited.

[0093] Furthermore, when the composite absorber contains such a polymer absorbent and SAP, it is preferable that the liquid transfer amount from the polymer absorbent to SAP is 5.0 g / g or more. When the liquid transfer amount from the polymer absorbent to SAP is 5.0 g / g or more, the body fluids temporarily held by the polymer absorbent can be more reliably transferred to SAP. Therefore, as an absorber, high absorption efficiency can be more reliably exhibited. Note that the liquid transfer amount from the polymer absorbent to SAP is more preferably 23.0 g / g or more, still more preferably 27.0 g / g or more, and particularly preferably 33.0 g / g or more. The liquid transfer amount from this polymer absorbent to SAP can be measured as follows.

[0094] <Method for Measuring the Amount of Liquid Transfer from a Polymer Absorbent to SAP> (1) Place 0.3 g of the sample for measurement (polymer absorbent) into a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) with a nylon mesh material ((manufactured by NBC Mesh Tech Co., Ltd., N-NО255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) attached to the bottom surface, and level it evenly. Then measure the mass (g) of the cylinder. This measurement method is carried out under the conditions of a temperature of 25 °C and a humidity of 60%. Also, when the sample for measurement (polymer absorbent) is recovered from a hygiene product and used, it can be obtained according to the aforementioned <Method for Recovering the Sample for Measurement (Polymer Absorbent)>. (2) Place a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) into a petri dish (inner diameter: 85 mm, depth: 20 mm). After evenly pouring 0.3 g of superabsorbent polymer (SAP) into the cylinder, remove the cylinder and measure the mass (g) of the petri dish. (3) Pour 60 mL of physiological saline (0.9% sodium chloride aqueous solution) into a petri dish with a pedestal (inner diameter: 85 mm, depth: 20 mm, pedestal arrangement: two pedestals are arranged in parallel at a 24 mm interval at the center of the bottom surface (inner side), pedestal width: 2 mm, pedestal height: 2 mm, pedestal length: 25 mm). (4) Place the cylinder containing the sample for measurement (polymer absorbent) on the pedestal at the center of the petri dish with a pedestal, immerse the bottom surface of the cylinder in the physiological saline, and let the physiological saline absorb into the sample in the cylinder for 3 minutes. (5) After 3 minutes of water absorption, lift up the cylinder, tilt the cylinder at 45° and drain for 1 minute, and then measure the mass (g) of the cylinder. (6) Calculate the water absorption amount (g) of the sample by subtracting the mass (g) of the cylinder after water absorption measured in (5) above from the mass (g) of the cylinder before water absorption measured in (1) above. Further, divide this water absorption amount by the mass of the sample (=0.3 g) to obtain the water absorption amount per unit mass of the sample (g / g). (7) Then, place the cylinder after draining water in step (5) above on a petri dish containing SAP, and bring the sample in the cylinder into contact with the SAP in the petri dish through the bottom surface (mesh material) of the cylinder. (8) Three minutes after bringing the sample into contact with the SAP, remove the cylinder and measure the mass (g) of the petri dish. (9) Calculate the water absorption amount (g) of the SAP by subtracting the mass (g) of the petri dish measured in step (8) above from the mass (g) of the petri dish measured in step (2) above, and further divide this water absorption amount by the mass of the sample (= 0.3 g) to obtain the water absorption amount of the SAP per unit mass of the sample (g / g), that is, the liquid transfer amount to the SAP per unit mass of the sample (g / g).

[0095] Furthermore, when the composite absorber contains the above-mentioned polymer absorbent and SAP, it is preferable that the polymer absorbent has a liquid discharge rate of the absorbed water of 70% or more. When the liquid discharge rate of the polymer absorbent is 70% or more, since the polymer absorbent easily releases the absorbed water, the body fluid temporarily held by the polymer absorbent can be more easily transferred to the SAP. In addition, it is particularly preferable that the liquid discharge rate of the polymer absorbent is 75% or more. The liquid discharge rate of this polymer absorbent can be measured as follows.

[0096] <Method for Measuring the Liquid Discharge Rate of the Polymer Absorbent> (1) Enclose 1 g of the sample for measurement (polymer absorbent) in a mesh bag cut into a 10 cm square ((manufactured by NBC Mesh Tech Co., Ltd., N - NО255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm))). The mass (g) of the mesh bag should be measured in advance. In addition, this measurement method is carried out under the conditions of a temperature of 25°C and a humidity of 60%. Furthermore, when the sample for measurement (polymer absorbent) is recovered from a hygiene product and used, it can be obtained according to the aforementioned <Method for Recovering the Sample for Measurement (Polymer Absorbent)>. (2) Immerse the mesh bag containing the sample in physiological saline (0.9% sodium chloride aqueous solution) for 1 hour. (3) Measure the mass (g) of the mesh bag after hanging it for 5 minutes to drain the water. (4) Calculate the water absorption amount (g) of the sample by subtracting the mass of the sample (= 1 g) and the total mass of the mesh bag from the mass of the mesh bag after draining measured in (3) above, and further divide this water absorption amount by the mass of the sample (= 1 g) to obtain the water absorption amount per unit mass (g / g) of the sample (polymer absorbent). (5) Further, subject the mesh bag after draining in (3) above to centrifugation at 150 G for 90 seconds, and measure the mass (g) of the mesh bag after the centrifugation. (6) Subtract the mass of the sample (= 1 g) and the total mass of the mesh bag from the mass of the mesh bag after centrifugation measured in (5) above Subtract the mass (g) of the paste from the water absorption (g) of the sample measured in (4) above. to calculate the liquid discharge amount (g) of the sample, and further divide this liquid discharge amount by the mass of the sample (= 1 g) to obtain the liquid discharge amount per unit mass (g / g) of the sample (polymer absorbent). (7) Divide the liquid discharge amount per unit mass obtained in (6) above by the water absorption amount per unit mass obtained in (4) above and multiply by 100 to obtain the liquid discharge amount with respect to the water absorption amount of the sample (polymer absorbent), that is, the liquid discharge rate (%).

[0097] Hereinafter, such a method for producing a polymer absorbent will be described in detail using the above absorbent A as an example.

[0098] [Method for Producing Polymer Absorbent] As shown in FIG. 2, the above absorbent A can be obtained through a crosslinking polymerization step and a hydrolysis step. Hereinafter, each of these steps will be described.

[0099] (Crosslinking Polymerization Step) First, mix an oil-soluble monomer for crosslinking polymerization, a crosslinkable monomer, a surfactant, water, and, if necessary, a polymerization initiator to obtain an oil-in-water droplet type emulsion. This oil-in-water droplet type emulsion is an emulsion in which the oil phase is the continuous phase and water droplets are dispersed therein.

[0100] In the above absorbent A, as shown in the upper figure of Fig. 2, butyl methacrylate, which is a (meth)acrylate ester, is used as the oil-soluble monomer, divinylbenzene is used as the crosslinkable monomer, sorbitan monooleate is used as the surfactant, and isobutyronitrile is used as the polymerization initiator for crosslinking polymerization to obtain monolith A.

[0101] Specifically, in absorbent A, as shown in the upper figure of Fig. 2, first, 9.2 g of t-butyl methacrylate as the oil-soluble monomer, 0.28 g of divinylbenzene as the crosslinkable monomer, 1.0 g of sorbitan monooleate (hereinafter abbreviated as "SMO") as the surfactant, and 0.4 g of 2,2'-azobis(isobutyronitrile) as the polymerization initiator are mixed and uniformly dissolved. Next, the mixture of t-butyl methacrylate / divinylbenzene / SMO / 2,2'-azobis(isobutyronitrile) is added to 180 g of pure water, and stirred under reduced pressure using a vacuum stirring and degassing mixer (manufactured by EMI Co., Ltd.), which is a planetary stirring device, to obtain a water-in-oil emulsion.

[0102] Furthermore, this emulsion is quickly transferred to a reaction vessel and sealed, and polymerized under static conditions at 60 °C for 24 hours. After the polymerization is completed, the content is taken out, extracted with methanol, and then dried under reduced pressure to obtain monolith A having a continuous macroporous structure. As a result of observing the internal structure of monolith A by SEM, monolith A has a continuous bubble structure, and the thickness of the continuous skeleton is 5.4 μm. Also, the average diameter of the continuous pores measured by the mercury intrusion method is 36.2 μm, and the total pore volume is 15.5 mL / g.

[0103] In addition, the content of divinylbenzene with respect to all monomers is preferably 0.3 to 10 mol%, more preferably 0.3 to 5 mol%. Further, the ratio of divinylbenzene to the total of butyl methacrylate and divinylbenzene is preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%. In the above absorbent A, the ratio of butyl methacrylate to the total of butyl methacrylate and divinylbenzene is 97.0 mol%, and the ratio of divinylbenzene is 3.0 mol%.

[0104] The addition amount of the surfactant can be set according to the type of the oil-soluble monomer and the size of the desired emulsion particles (macropores), and is preferably in the range of about 2 to 70% with respect to the total amount of the oil-soluble monomer and the surfactant.

[0105] In addition, in order to control the bubble shape, size, etc. of the monolith A, alcohols such as methanol and stearyl alcohol; carboxylic acids such as stearic acid; hydrocarbons such as octane, dodecane, and toluene; cyclic ethers such as tetrahydrofuran and dioxane may coexist in the polymerization system.

[0106] Moreover, the mixing method when forming the water-in-oil emulsion is not particularly limited, and for example, a method of mixing all components at once, a method of separately and uniformly dissolving the oil-soluble components such as the oil-soluble monomer, the surfactant, and the oil-soluble polymerization initiator, and the water-soluble components such as water and the water-soluble polymerization initiator, and then mixing the respective components, etc. Any mixing method can be adopted.

[0107] Furthermore, the mixing device for forming the emulsion is not particularly limited, and any device such as a normal mixer, a homogenizer, a high-pressure homogenizer, etc. can be adopted according to the desired emulsion particle size. Further, the object to be treated is put into a mixing container, and the object to be treated is stirred and mixed by rotating it around the revolution axis while revolving around the revolution axis with the mixing container tilted. A so-called planetary stirring device can also be used.

[0108] Also, the mixing conditions are not particularly limited, and the stirring speed, stirring time, etc. can be arbitrarily set according to the desired emulsion particle size. In the above planetary stirring device, water droplets in the W / O emulsion can be uniformly generated, and their average diameter can be arbitrarily set within a wide range.

[0109] The polymerization conditions for the water-in-oil emulsion can adopt various conditions according to the types of monomers and initiators, etc. For example, when using azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, etc. as the polymerization initiator, it can be heated and polymerized at a temperature of 30 to 100 °C for 1 to 48 hours in a sealed container under an inert atmosphere. When using hydrogen peroxide-ferrous chloride, sodium persulfate-sodium acid sulfite, etc. as the polymerization initiator, it can be polymerized at a temperature of 0 to 30 °C for 1 to 48 hours in a sealed container under an inert atmosphere.

[0110] After the polymerization is completed, the content is taken out and Soxhlet extraction is performed with a solvent such as isopropanol to remove unreacted monomers and residual surfactants, and the monolith A shown in the middle figure of Figure 2 can be obtained.

[0111] (Hydrolysis step) Subsequently, the step of hydrolyzing the monolith A (crosslinked polymer) to obtain the absorbent A (hydrolysis step) will be described.

[0112] First, the monolith A is immersed in dichloroethane added with zinc bromide and stirred at 40 °C for 24 hours, and then contacted with methanol, 4% hydrochloric acid, 4% sodium hydroxide aqueous solution, and water in this order for hydrolysis, and then dried to obtain a block-shaped absorbent A. Further, this block-shaped absorbent A is pulverized to a predetermined size (that is, a particle size of 300 μm or more) to obtain a particulate absorbent A. The particulate form of this absorbent A may be formed (granulated) into particles during or after drying.

[0113] Moreover, the method for hydrolyzing the monolith A is not particularly limited, and various methods can be adopted. For example, using aromatic solvents such as toluene and xylene, halogenated solvents such as chloroform and dichloroethane, ether solvents such as tetrahydrofuran and isopropyl ether, amide solvents such as dimethylformamide and dimethylacetamide, alcohol solvents such as methanol and ethanol, carboxylic acid solvents such as acetic acid and propionic acid, or water as the solvent, contacting with a strong base such as sodium hydroxide, or contacting with a Bronsted acid such as hydrohalic acid like hydrochloric acid, sulfuric acid, nitric acid, trifluoroacetic acid, methanesulfonic acid, p-toluenesulfonic acid, or a Lewis acid such as zinc bromide, aluminum chloride, aluminum bromide, titanium(IV) chloride, cerium chloride / sodium iodide, magnesium iodide, etc.

[0114] Among the polymerization raw materials of the organic polymer that forms the hydrophilic continuous skeleton of the absorbent A, the (meth)acrylate ester is not particularly limited, but an alkyl ester of C1 - C10 (i.e., having 1 - 10 carbon atoms) of (meth)acrylic acid is preferred, and an alkyl ester of C4 (i.e., having 4 carbon atoms) of (meth)acrylic acid is particularly preferred. Examples of the C4 alkyl ester of (meth)acrylic acid include t-butyl (meth)acrylate, n-butyl (meth)acrylate, and iso-butyl (meth)acrylate.

[0115] Also, the monomer used for crosslinking polymerization may be only (meth)acrylate ester and divinylbenzene, or in addition to (meth)acrylate ester and divinylbenzene, it may contain other monomers other than (meth)acrylate ester and divinylbenzene. In the latter case, the other monomers are not particularly limited, and examples thereof include styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, glycidyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobutene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and the like. In addition, the proportion of monomers other than (meth)acrylate esters and divinylbenzene in all the monomers used for crosslinking polymerization is preferably 0 to 80 mol%, more preferably 0 to 50 mol%.

[0116] Further, the surfactant is not limited to the above-mentioned sorbitan monooleate, and any surfactant may be used as long as it can form an oil-in-water (W / O) emulsion when the crosslinking polymerization monomer and water are mixed. Examples of such surfactants include nonionic surfactants such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene nonylphenyl ether, polyoxyethylene stearyl ether, and polyoxyethylene sorbitan monooleate; anionic surfactants such as potassium oleate, sodium dodecylbenzenesulfonate, and sodium dioctyl sulfosuccinate; cationic surfactants such as distearyldimethylammonium chloride; and amphoteric surfactants such as lauryldimethylbetaine. These surfactants may be used alone or in combination of two or more.

[0117] In addition, as the polymerization initiator, a compound that generates radicals by heat and light irradiation is preferably used. Furthermore, the polymerization initiator may be water-soluble or oil-soluble. Examples thereof include azobis(4-methoxy-2,4-dimethylvaleronitrile), azobisisobutyronitrile, azobisdimethylvaleronitrile, azobiscyclohexanenitrile, azobiscyclohexanecarbonitrile, azobis(2-methylpropionamidine) dihydrochloride, benzoyl peroxide, potassium persulfate, ammonium persulfate, hydrogen peroxide-ferrous chloride, sodium persulfate-sodium acid sulfite, and tetramethylthiuram disulfide. However, in some cases, there are systems in which polymerization proceeds only by heating or only by light irradiation without adding a polymerization initiator. In such systems, the addition of a polymerization initiator is unnecessary.

[0118] In addition to the light incontinence pad of the above-described embodiment, the composite absorber of the present invention can be applied to various sanitary products such as panty-type disposable diapers, tape-type disposable diapers, sanitary napkins, absorption liners, absorption pads (for example, pressure ulcer pads, maternity pads, etc.), absorption sheets, breast pads, disposable diapers for pets, absorption pads for pets, excrement treatment sheets for pets, wet sheets, wet tissues, cosmetic wiping sheets, and masks. Therefore, the body fluid that is the liquid to be absorbed by the composite absorber is a liquid discharged from the wearer of the sanitary product, and examples thereof include urine, sweat, feces, menstrual blood, lochia, breast milk, blood, and exudate.

[0119] In addition, the present invention is not limited to the above-described embodiments and the like, and appropriate combinations, substitutions, changes, etc. are possible within the range not departing from the object and gist of the present invention.

Explanation of Reference Numerals

[0120] 1 Light incontinence pad 2 Surface sheet 3 Back sheet 4 Composite absorber

Claims

1. A composite absorber for sanitary products for absorbing body fluids, comprising a particulate polymer absorbent having a hydrophilic continuous backbone and continuous pores, wherein the polymer absorbent has a particle diameter of 300 μm or more, a water absorption capacity of 54.5 g / g or more, and a liquid discharge rate of 70% or more. A composite absorber characterized by that.

2. The composite absorber according to claim 1, characterized in that the volume increase rate of the polymer absorbent at the time of saturated liquid absorption with respect to the volume before liquid absorption is 233% to 567%.

3. The composite absorber according to claim 1 or 2, characterized in that the porosity per unit volume of the polymer absorbent is 85% or more.

4. The composite absorber according to any one of claims 1 to 3, characterized in that the average diameter of the continuous pores is 1 μm to 1000 μm.

5. The composite absorber according to any one of claims 1 to 4, characterized in that the polymer absorbent is a monolithic absorbent.

6. The polymer absorbent is a hydrolyzate of a cross-linked polymer of (meth)acrylate and a compound containing two or more vinyl groups in one molecule, and contains at least one —COONa group. The composite absorber according to any one of claims 1 to 5, characterized by that.

7. A sanitary product characterized by having the composite absorber according to any one of claims 1 to 6.

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