Composite absorber and polymer absorbent

Abstract

To provide an absorber that is capable of efficiently absorbing liquid and has high absorption performance.SOLUTION: A composite absorber (1) according to the present invention is for absorbing liquid, the composite absorber (1) comprising: a particulate polymer absorbent (4) having hydrophilic continuous skeletons and continuous pores. The polymer absorbent (4) has a particle size of 300 μm or more.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a composite absorber and a polymer absorbent.

Background Art

[0002] Absorbers containing porous materials such as sponge materials are known as absorbers used for absorbing liquids such as aqueous solutions. Such absorbers containing porous materials are applied to various fields such as disposable paper diapers, medical composite absorbent members, dew condensation prevention sheets, civil engineering and construction materials such as simple soils, base materials for pharmaceuticals, and materials for absorbing leaked liquids, as disclosed in Patent Documents 1 and 2, for example.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Such porous materials may be used in a particulate form so as to more efficiently absorb liquids such as aqueous solutions. However, when the particle diameter becomes small, the pore structure of the porous material may collapse, and the liquid absorption performance 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 liquids and has excellent absorption performance.

Means for Solving the Problems

[0006] One aspect (Aspect 1) of the present invention is a composite absorber for absorbing a liquid, It contains a particulate polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and is a composite absorber characterized in that the polymer absorbent has a particle diameter of 300 μm or more.

[0007] In the composite absorber of this embodiment, since the particulate polymer absorbent capable of taking in a liquid such as an aqueous solution into the continuous pores by capillary action has a particle diameter of 300 μm or more, it is easy to maintain the pore structure having the continuous skeleton and continuous pores, so that the liquid can be efficiently absorbed and excellent absorption performance can be exhibited.

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

[0009] In the composite absorber of this embodiment, since the volume increase rate of the polymer absorbent during liquid absorption is 233% to 567%, the liquid can be absorbed more efficiently, and even more 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 this embodiment, since the porosity per unit volume of the polymer absorbent is 85% or more, more liquid can be absorbed, and even more 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 this embodiment, 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 liquid is difficult to collapse, and it can have a higher absorption rate, and excellent absorption performance can be stably exhibited.

[0014] In still another embodiment (Embodiment 5) of the present invention, in the composite absorber according to any one of the above Embodiments 1 to 4, the polymer absorbent is characterized in that it is a monolithic absorbent.

[0015] In the composite absorber of this embodiment, since the polymer absorbent is a monolithic absorbent, it can quickly absorb liquid and can more steadily transfer the temporarily held liquid to the SAP.

[0016] In still another embodiment (Embodiment 6) of the present invention, in the composite absorber according to any one of the above Embodiments 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 in that it contains at least one -COONa group.

[0017] In the composite absorber of this embodiment, since the polymer absorbent has the above specific configuration, when absorbing liquid, the hydrophilic continuous skeleton is easy to stretch and the continuous pores are also easy to expand. Therefore, more liquid can be taken into the continuous pores more quickly, and the absorber can exhibit more excellent absorption performance.

[0018] Still another embodiment (Embodiment 7) of the present invention is a particulate polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and is characterized in that it has a particle diameter of 300 μm or more.

[0019] The polymer absorbent of this embodiment has a particle diameter of 300 μm or more, so it is easy to maintain the pore structure having the above continuous skeleton and continuous pores, and thus can efficiently absorb liquid and exhibit excellent absorption performance. Therefore, when the high molecular absorbent of the present embodiment is used for the absorber, the absorber can exhibit excellent absorption performance.

Advantages of the Invention

[0020] According to the present invention, a liquid can be efficiently absorbed, and an absorber excellent in absorption performance can be provided.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail using a composite absorber 1 which is one embodiment. In this specification, unless otherwise specified, "looking at an object (for example, a composite absorber, etc.) placed on a horizontal plane in a developed state from the upper side in the vertical direction in the thickness direction of the object" is simply referred to as "plan view".

[0023] [Composite Absorber] FIG. 1 is an exploded perspective view of a composite absorber 1 according to an embodiment of the present invention. The composite absorber 1 shown in FIG. 1 has a substantially rectangular outer shape in plan view. In the thickness direction, it basically includes a first holding sheet 2 forming one surface of the composite absorber 1, a second holding sheet 3 forming the other surface of the composite absorber 1, and a liquid-absorbing member made of a polymer absorbent 4 located between these sheets.

[0024] The liquid-absorbing member in the composite absorber 1 is located between the first holding sheet 2 and the second holding sheet 3 and is configured to absorb and hold the liquid that has passed through the first holding sheet 2. Such a liquid-absorbing member includes a particulate polymer absorbent 4 having a particle diameter of 300 μm or more and having a hydrophilic continuous skeleton and continuous pores.

[0025] The polymer absorbent 4 can take in liquid into the continuous pores by capillary action. Further, since 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 the liquid can be efficiently absorbed and excellent absorption performance can be exhibited. Therefore, the composite absorber 1 containing such a polymer absorbent 4 can exhibit excellent absorption performance as an absorber.

[0026] In the present invention, the liquid-absorbing member is not limited to the form of the composite absorber 1 of the above-described embodiment. As long as the liquid-absorbing member contains at least a polymer absorbent having the above specific particle diameter, it may or may not contain other liquid-absorbing materials. For example, in the composite absorber 1' of another embodiment of the present invention shown in FIG. 2, the liquid-absorbing member located between the first holding sheet 2 and the second holding sheet 3 is composed of a mixture of a particulate polymer absorbent 4 having a particle diameter of 300 μm or more and having a hydrophilic continuous skeleton and continuous pores and a superabsorbent polymer 5 (SAP).

[0027] In the present invention, the configuration of the composite absorber is not limited to the aspect of the composite absorber 1 of the above-described embodiment. For example, the composite absorber may have a hydrophilic fiber sheet 6 positioned between the first holding sheet 2 and the liquid-absorbing member (i.e., the polymer absorbent 4 and the superabsorbent polymer 5), as in the composite absorber 1' of another embodiment of the present invention shown in FIG. 2.

[0028] 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 (e.g., circular shape, oval shape, polygonal shape, hourglass shape, design shape, etc.), various dimensions, basis weight, etc. according to various applications and usage modes can be adopted.

[0029] Hereinafter, various constituent members of the composite absorber of the present invention will be described in more detail using the composite absorber 1 of the embodiment shown in FIG. 1.

[0030] (Holding Sheet) In the composite absorber 1 shown in FIG. 1, the first holding sheet 2 forming one surface of the composite absorber 1 has a substantially rectangular outer shape similar to the outer shape of the composite absorber 1 in plan view. Such a first holding sheet 2 is formed of a liquid-permeable sheet-like member that can permeate the liquid supplied to the composite absorber 1 and be absorbed and held by the inner liquid-absorbing member.

[0031] The first holding sheet 2 has a slightly larger size overall compared to the liquid-absorbing member disposed inside (i.e., compared to the arrangement region of the polymer absorbent 4), and is joined to the second holding sheet 3 located on the other side in the thickness direction of the composite absorber 1 at the peripheral edge by any adhesive or heat-sealing means, etc.

[0032] On the other hand, the second holding sheet 3 that forms the surface on the other side of the composite absorber 1 has a substantially rectangular outer shape similar to the outer shape of the composite absorber 1 in plan view. Such a second holding sheet 3 is formed of a liquid-impermeable sheet-like member that prevents liquid that has not been absorbed and held by the inner liquid-absorbing member or liquid that has exuded from the liquid-absorbing member from leaking to the outside of the composite absorber 1.

[0033] In the present invention, each sheet-like member that can be used as the first holding sheet and the second holding sheet is not limited to those in the above-described embodiment. As long as at least one of the first holding sheet and the second holding sheet of the composite absorber of the present invention is formed of a liquid-permeable sheet-like member. That is, in the composite absorber of the present invention, either one of the first holding sheet and the second holding sheet may be formed of a liquid-impermeable sheet-like member.

[0034] When a liquid-permeable sheet-like member is used as the holding sheet, the liquid-permeable sheet-like member is not particularly limited as long as it does not inhibit the effects of the present invention, and any liquid-permeable sheet-like member corresponding to various applications and usage modes can be adopted. Examples of such liquid-permeable sheet-like members include air-through nonwoven fabrics, spunbond nonwoven fabrics, point-bond nonwoven fabrics, and other nonwoven fabrics, woven fabrics, knitted fabrics, porous resin films, etc. having hydrophilicity.

[0035] Furthermore, when a hydrophilic nonwoven fabric, woven fabric, knitted fabric, etc. (hereinafter collectively referred to as "fiber sheet") is used as the liquid-permeable sheet-like member, these fiber sheets may have a single-layer structure or a multi-layer structure of two or more layers. The type of constituent fibers of such a fiber sheet is not particularly limited, and examples include hydrophilic fibers such as cellulose-based fibers and thermoplastic resin fibers subjected to hydrophilic treatment. These fibers may be used alone or in combination of two or more types of fibers. Furthermore, examples of the cellulosic fibers that can be used for the constituent fibers of the fiber sheet include natural cellulosic fibers (such as plant fibers like cotton), regenerated cellulosic fibers, purified cellulosic fibers, semi-synthetic cellulosic fibers, and the like. Examples of the thermoplastic resin fibers that can be used for the constituent fibers of the fiber sheet include fibers made of known thermoplastic resins such as olefin resins like polyethylene (PE) and polypropylene (PP), polyester resins like polyethylene terephthalate (PET), and polyamide resins like 6-nylon. These resins may be used alone or in combination of two or more kinds.

[0036] Also, when using a liquid-impermeable sheet-like member as the holding sheet, the liquid-impermeable sheet-like member is not particularly limited as long as it does not inhibit the effects of the present invention, and any liquid-impermeable sheet-like member corresponding to various uses and usage modes can be adopted. Examples of such liquid-impermeable sheet-like members include hydrophobic nonwoven fabrics formed by any hydrophobic thermoplastic resin fibers (such as polyolefin fibers like PE and PP, polyester fibers like PET, and various composite fibers such as core-sheath type); porous or non-porous resin films formed by hydrophobic thermoplastic resins such as PE and PP; laminates obtained by laminating a nonwoven fabric to the resin film; laminated nonwovens such as SMS nonwovens, and the like.

[0037] In the present invention, the outer shape, various dimensions, basis weight, etc. of the holding sheet are not particularly limited as long as they do not inhibit the effects of the present invention, and any outer shape (such as circular shape, oval shape, polygonal shape, hourglass shape, design shape, etc.), various dimensions, basis weight, etc. corresponding to various uses and usage modes can be adopted.

[0038] (Liquid-absorbing member) In the composite absorber 1 shown in FIG. 1, the liquid-absorbing member is configured to be able to absorb and hold the liquid that has passed through the first holding sheet 2 by the polymer absorbent 4 having the specific particle diameter and having a hydrophilic continuous skeleton and continuous pores, which is located between the first holding sheet 2 and the second holding sheet 3 as described above.

[0039] In the composite absorber 1, the polymer absorbent 4 of the liquid-absorbing member is joined to each of the above-described first holding sheet 2 and second holding sheet 3 by an arbitrary adhesive such as a hot-melt adhesive. However, in the composite absorber of the present invention, the polymer absorbent may not be joined to the holding sheet.

[0040] And, as described above, the liquid-absorbing member includes, as an essential constituent, a polymer absorbent having a hydrophilic continuous skeleton and continuous pores and having the above-specified particle diameter. This polymer absorbent will be described later.

[0041] In the present invention, the liquid-absorbing member located between the first holding sheet and the second holding sheet may contain other liquid-absorbing materials as long as it contains at least a polymer absorbent having the above-specified particle diameter. That is, the liquid-absorbing member may contain only the above-described polymer absorbent as the liquid-absorbing material, or may further contain a liquid-absorbing material known in the art in addition to the above-described polymer absorbent. Examples of such liquid-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 obtained by arbitrarily combining these, and the like. For example, in the composite absorber 1' of another embodiment of the present invention shown in FIG. 2, the liquid-absorbing member located between the first holding sheet 2 and the second holding sheet 3 includes a superabsorbent polymer 5 in addition to the particulate polymer absorbent 4 having a hydrophilic continuous skeleton and continuous pores and having the above-specified particle diameter.

[0042] In the present invention, the outer shape (planar shape of the arrangement region), various dimensions, basis weight, etc. of the liquid-absorbing member 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 various applications and usage modes can be adopted.

[0043] (Hydrophilic fiber sheet) In the present invention, the composite absorber may have a hydrophilic fiber sheet 6 positioned between, for example, a first holding sheet 2 and a liquid-absorbing member (i.e., a polymer absorbent 4 and a superabsorbent polymer 5), as in the composite absorber 1' of another embodiment shown in FIG. 2.

[0044] In the present invention, the hydrophilic fiber sheet that can be used for the composite absorber is not particularly limited as long as it does not inhibit the effects of the present invention, and any hydrophilic fiber sheet according to various applications, usage modes, etc. can be adopted. Examples of such hydrophilic fiber sheets include non-woven fabrics, woven fabrics, and knitted fabrics having hydrophilicity. Note that the hydrophilic fiber sheet may have a single-layer structure or a multi-layer structure of two or more layers.

[0045] The type of constituent fibers of such a hydrophilic fiber sheet is also not particularly limited, and examples include hydrophilic fibers such as cellulose-based fibers and thermoplastic resin fibers subjected to hydrophilic treatment. These fibers may be used alone or in combination of two or more types of fibers. Furthermore, examples of the cellulose-based fibers that can be used for the constituent fibers of the hydrophilic fiber sheet include natural cellulose fibers (e.g., plant fibers such as cotton), regenerated cellulose fibers, purified cellulose fibers, semi-synthetic cellulose fibers, etc. Also, examples of the thermoplastic resin fibers that can be used for the constituent fibers of the hydrophilic fiber sheet include fibers made of known thermoplastic resins such as olefin-based resins such as PE and PP, polyester-based resins such as PET, and polyamide-based resins such as 6-nylon. These resins may be used alone or in combination of two or more types of resins.

[0046] In the present invention, the outer shape, various dimensions, basis weight, etc. of the hydrophilic fiber sheet are not particularly limited as long as they do not inhibit the effects of the present invention, and any outer shape, various dimensions, basis weight, etc. according to various applications, usage modes, etc. can be adopted.

[0047] Hereinafter, the polymer absorbent used in the composite absorber of the present invention will be described in more detail.

[0048] [Polymer Absorbent] The high molecular absorbent is a particulate high molecular 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 cross-linked polymer of two or more monomers containing at least (meth)acrylic acid ester, and examples of the high molecular compound having at least one or more hydrophilic groups in the functional group can be given. More specifically, it 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 examples of the high molecular compound having at least -COONa group can be given. Such a high molecular absorbent is an organic porous body having at least one or more -COONa groups in one molecule, and may further have a -COOH group. In the skeleton of the porous body, -COONa groups are distributed substantially uniformly.

[0049] When the high molecular absorbent is a hydrolyzate of such a cross-linked polymer of (meth)acrylic acid ester and a compound containing two or more vinyl groups in one molecule and contains at least one or more -COONa groups, the hydrophilic continuous skeleton is likely to elongate when absorbing a liquid, and the continuous pores are also likely to expand. Therefore, more liquid can be taken into the continuous pores more quickly, and the absorbent can exhibit better absorption performance as an absorber.

[0050] In this specification, (meth)acrylic acid ester means acrylic acid ester or methacrylic acid ester.

[0051] In the high molecular absorbent formed by the hydrolyzate of such a cross-linked polymer of (meth)acrylic acid ester and divinylbenzene, a hydrophilic continuous skeleton is formed by an organic polymer having at least -COONa group, and there are continuous pores (continuous holes) serving as absorption fields for the liquid to be absorbed between the skeletons. Note that since the hydrolysis treatment is to convert the -COOR group (that is, carboxylic acid ester group) of the cross-linked polymer into -COONa group or -COOH group (see FIG. 3), the high molecular absorbent may have a -COOR group.

[0052] 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 a method for quantifying weakly acidic ion exchange groups.

[0053] Here, FIG. 3 is a diagram for explaining the manufacturing process of absorbent A, which is an example of a polymer absorbent. In this FIG. 3, the upper diagram shows the constituent raw materials for polymerization, the middle diagram shows monolith A, which is a crosslinked polymer of (meth)acrylate and divinylbenzene, and the lower diagram shows absorbent A obtained by subjecting the monolith A in the middle diagram to hydrolysis and drying treatments.

[0054] Hereinafter, an explanation will be given using absorbent A formed by hydrolysis of a crosslinked polymer of (meth)acrylate and divinylbenzene, which is an example of a polymer absorbent.

[0055] Note that the polymer absorbent is not limited to such absorbent A, and may be a hydrolyzate of a crosslinked polymer of (meth)acrylate and a compound having two or more vinyl groups in one molecule, or a hydrolyzate of a crosslinked polymer of two or more monomers including at least (meth)acrylate. However, when the polymer absorbent is a monolithic absorbent, there are advantages that it can quickly absorb a liquid and can more steadily transfer the liquid temporarily held in the polymer absorbent to the SAP.

[0056] Note that in the following description, "monolith A" is an organic porous body composed of a crosslinked polymer of (meth)acrylate and divinylbenzene before hydrolysis treatment, and may be referred to as a "monolithic organic porous body". Also, "absorbent A" is a hydrolyzate of a crosslinked polymer (monolith A) of (meth)acrylate and divinylbenzene after hydrolysis treatment and drying treatment. Note that in the following description, absorbent A refers to the dry state.

[0057] First, the structure of absorbent A will be described. Absorbent A has a hydrophilic continuous skeleton and continuous pores as described above. Absorbent A, which is an organic polymer having a hydrophilic continuous skeleton, as shown in Figure 3, is obtained by cross-linking and polymerizing (meth)acrylic acid ester, which is a polymerization monomer, and divinylbenzene, which is a cross-linking monomer, and further hydrolyzing the obtained cross-linked polymer (monolith A).

[0058] 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-linking 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.

[0059] In absorbent A, the proportion of the cross-linking polymerization residue of divinylbenzene (constituent unit Y) in the organic polymer forming the hydrophilic continuous skeleton is, for example, 0.1 to 30 mol% with respect to all constituent units, preferably 0.1 to 20 mol%. For example, in absorbent A using butyl methacrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, the proportion of the cross-linking polymerization residue of divinylbenzene (constituent unit Y) in the organic polymer forming the hydrophilic continuous skeleton is, for example, about 3% with respect to all constituent units, preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%. In addition, when the proportion of the cross-linking 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, and when the proportion of the cross-linking polymerization residue of divinylbenzene is 30 mol% or less, the liquid absorption amount of the liquid to be absorbed is less likely to decrease.

[0060] In absorbent A, the organic polymer forming the hydrophilic continuous skeleton may consist only of structural unit X and structural unit Y, or in addition to structural unit X and structural unit Y, it may have structural units other than structural unit X and structural unit Y, that is, polymerization residues of monomers other than (meth)acrylate and divinylbenzene.

[0061] 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, etc.

[0062] 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%.

[0063] Also, absorbent A preferably has a hydrophilic continuous skeleton thickness of 0.1 to 100 μm. When the thickness of the hydrophilic continuous skeleton of absorbent A is 0.1 μm or more, the space (pores) for taking in liquid in the porous body is less likely to collapse during absorption, and the liquid absorption amount is less likely to decrease. On the other hand, when the thickness of the hydrophilic continuous skeleton is 100 μm or less, it is easier to obtain an excellent absorption rate.

[0064] Since the pore structure of the hydrophilic continuous skeleton of absorbent A is a continuous bubble structure, the thickness of the continuous skeleton is measured by taking the cross-section of the skeleton appearing on the test piece for electron microscopy measurement as the evaluation location for the thickness. Since the continuous skeleton is formed by the intervals between the waters (water droplets) removed by the dehydration and drying treatment 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 are rare cases where small holes are open in the polygon, in such cases, the circumscribed circle of the cross-section of the polygon surrounding the small hole is measured.

[0065] Furthermore, for absorbent A, it is preferable that the average diameter of the continuous pores is 1 to 1000 μm. When the average diameter of the continuous pores of absorbent A is 1 μm or more, the space (pores) for taking in liquid 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, it is easier to obtain an excellent absorption rate. Thereby, a composite absorber containing such absorbent A can have a higher absorption rate and can stably exhibit excellent absorption performance.

[0066] The average diameter (μm) of the continuous pores of absorbent A can be measured by the mercury intrusion method, and the maximum value of the pore size distribution curve obtained by such a mercury intrusion method is adopted. For the sample for measuring the average diameter of the continuous pores, regardless of the ionic form of absorbent A, a sample dried in a vacuum dryer set at a temperature of 50°C for 18 hours or more is used as the sample. The final pressure reached is set to 0 Torr. Also, naturally, the average diameter of the continuous pores of this absorbent A is a value smaller than the particle diameter of absorbent A.

[0067] Here, Figure 4 is an SEM photograph of absorbent A at a magnification of 50 times, Figure 5 is an SEM photograph of absorbent A at a magnification of 100 times, Figure 6 is an SEM photograph of absorbent A at a magnification of 500 times, Figure 7 is an SEM photograph of absorbent A at a magnification of 1000 times, and furthermore, Figure 8 is an SEM photograph of absorbent A at a magnification of 1500 times. The absorbent A shown in FIGS. 4 to 8 is an example of an absorbent that uses butyl methacrylate as a polymerization monomer and divinylbenzene as a crosslinking monomer, and SEM photographs were taken using those having a structure of a cube with 2 mm sides respectively.

[0068] The absorbent A shown in FIGS. 4 to 8 has a large number of bubble-like macropores, and further 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 common openings (mesopores), that is, it has become a continuous bubble structure (continuous macropore structure).

[0069] The overlapping portions of these macropores become common openings (mesopores) with 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 them have 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 one macropore, and many are about 3 to 10.

[0070] In addition, since the absorbent A has such a continuous bubble structure, macropore groups and mesopore groups can be formed uniformly, and there is an advantage that the pore volume and specific surface area can be significantly increased compared to particulate-aggregated porous bodies described in, for example, JP-A-8-252579.

[0071] 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 (voids) for taking in the liquid in the porous body is less likely to collapse during absorption, and the liquid 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.

[0072] Note that the total pore volume can be measured by mercury intrusion porosimetry. As the sample for measuring the total pore volume, use the one dried in a vacuum dryer set at a temperature of 50°C for 18 hours or more regardless of the ionic form of absorbent A. Note that the final pressure reached is 0 Torr.

[0073] Hereinafter, the state when the absorbent A comes into contact with the liquid will be described, but the same applies when the liquid comes into contact with the liquid-absorbing member or composite absorber containing the absorbent A.

[0074] First, the continuous pores provided in the absorbent A shown in FIGS. 4 to 8 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 the liquid comes into contact with the absorbent A having such a large number of pores, a certain amount of the liquid enters into the large number of pores by capillary action and is absorbed by the absorbent A. At this time, a part of the liquid absorbed by the absorbent A is absorbed into the hydrophilic continuous skeleton by osmotic pressure, and the continuous skeleton extends. On the other hand, the liquid that has not been absorbed into the hydrophilic continuous skeleton among the liquid absorbed by the absorbent A is absorbed while being retained in the pores.

[0075] In this way, the absorbent A has the property that the hydrophilic continuous skeleton extends when absorbing the liquid. The extension of this continuous skeleton occurs almost omnidirectionally. Furthermore, as the outer shape of the absorbent A increases due to the extension of such a continuous skeleton, the size of each pore also increases. When the size of the pores increases in this way, the volume inside the pores increases, so the amount of liquid that can be retained in the pores also increases. That is, the absorbent A that has absorbed a certain amount of liquid and has become larger can absorb a further predetermined amount of liquid into the enlarged pores by capillary action. Furthermore, since the absorbent A absorbs the liquid by capillary action, the liquid can be absorbed quickly.

[0076] In addition, for the liquid absorbed by the absorbent A, more of the liquid remains in the pores than the liquid absorbed within the hydrophilic continuous skeleton. Since most of the absorption of the liquid by the absorbent A is achieved by retaining the liquid in the pores through capillary action, the larger the porosity (the volume of the pore voids relative to the unit volume of the absorbent A), which is the ratio of the volume of the pore voids (total pore volume), the more liquid can be absorbed.

[0077] The porosity per unit volume of this polymer absorbent is preferably 85% or more, and more preferably 90% or more. When the porosity per unit volume of the polymer absorbent is 85% or more, more liquid can be absorbed, and more excellent absorption performance can be exhibited.

[0078] For example, when determining the porosity of the absorbent A shown in FIGS. 4 to 8 described above, the following results are obtained. First, the specific surface area of the 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 the pores in 1 g of the absorbent A is 15.5 mL. Here, assuming that the specific gravity of the absorbent A is 1 g / mL, the volume occupied by the pores in 1 g of the absorbent A, that is, the pore volume, is 15.5 mL, and the volume of 1 g of the absorbent A is 1 mL. Then, the total volume (volume) of 1 g of the absorbent A is 15.5 + 1 (mL). Since the ratio of the pore volume among them is the porosity, the porosity of the absorbent A is 15.5 / (15.5 + 1)×100 ≒ 94%.

[0079] In the present invention, the absorbent A having such a hydrophilic continuous skeleton and continuous pores, that is, the polymer absorbent, is applied to the composite absorber in a particulate form having a specific particle size of 300 μm or more.

[0080] Such a polymer absorbent can take in liquids such as aqueous solutions into continuous pores by capillary action, and further, because it has a specific particle size of 300 μm or more, it is easy to maintain the pore structure including the continuous skeleton and continuous pores, so that the liquid can be efficiently absorbed and excellent absorption performance can be exhibited. Accordingly, the composite absorbent of the present invention containing such a polymer absorbent can efficiently absorb a liquid as an absorbent and can exhibit excellent absorption performance.

[0081] In addition, 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, wearing feeling (foreign body feeling), etc. In particular, when the particle size of the polymer absorbent is 400 μm or more, the number of pores existing inside the particles of the polymer absorbent can be ensured to be a certain amount or more, and more liquid can be stably taken in, that is, excellent liquid absorption properties can be stably exhibited.

[0082] Also, the particle size of the polymer absorbent can be measured by a sieve method and means the average particle size of the particles classified by a sieve tester.

[0083] Here, a plurality of types of polymer absorbents having different particle sizes classified using a sieve tester were prepared, and the liquid absorption amounts of the polymer absorbents having different particle sizes were measured according to the following measurement method. The measurement results of this liquid absorption amount are shown in Table 1 below.

[0084] <Measurement Method of Liquid Absorption Amount of Polymer Absorbent> (1) Weigh 1 g of the sample for measurement (polymer absorbent), and enclose it in a mesh bag (manufactured by NBC Mesh Tech Co., Ltd., N-NО255HD 115 (standard size: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) cut into a 10 cm square. Note that the mass (g) of the mesh bag should be 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 the product of the composite absorber and used, it can be obtained according to the <Method for Recovering the Sample for Measurement (Polymer Absorbent)> described below. (2) Immerse the mesh bag containing the sample in a 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 liquid absorption amount (g) of the sample by subtracting the total mass of the sample (=1 g) and the mesh bag from the mass of the mesh bag after draining measured in (3) above, and further divide this liquid absorption amount by the mass of the sample (=1 g) to obtain the liquid absorption amount per unit mass (g / g) of the sample (polymer absorbent).

[0085] Note that when the above-mentioned sample for measurement (polymer absorbent) is recovered from the product of the composite absorber and used, it can be obtained as follows.

[0086] <Method for Recovering the Sample for Measurement (Polymer Absorbent)> (1) Peel off the holding sheet etc. from the product of the composite absorber to expose the liquid-absorbing member. (2) Drop all the liquid-absorbing materials including the measurement object (polymer absorbent) from the exposed liquid-absorbing member, and remove the liquid-absorbing materials 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 that can recognize the difference from SAP or a magnification that can visually recognize the pores of the porous body, and recover the measurement object using tweezers or the like. Note that the magnification of the simple magnifying glass is not particularly limited as long as it can visually recognize the pores of the porous body, and for example, magnifications of 25 times to 50 times can be mentioned. (4) The measurement object recovered in this way is used as a sample for measurement in various measurement methods.

[0087]

Table 1

[0088] As shown in Table 1, the polymer absorbent having a hydrophilic continuous skeleton and continuous pores exhibits excellent liquid absorption capacity even in a polymer absorbent with a small particle diameter of 300 μm. 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 liquid absorption capacity is exhibited.

[0089] Also, as described above, when the liquid enters the continuous pores due to capillary action in the continuous skeleton of the polymer absorbent, a part of the entered liquid is absorbed by osmotic pressure and the continuous skeleton expands. And the liquid can be further taken into the pores enlarged by this expansion. That is, the polymer absorbent can further absorb the liquid while expanding (increasing in volume) (in other words, it can expand and further increase the liquid absorption capacity and liquid retention capacity). Therefore, even if the size and amount of the polymer absorbent before liquid absorption (before expansion) are small, it can efficiently absorb more liquid. Particularly in the present invention, from the viewpoint of such liquid absorption efficiency, it is preferable that the volume increase rate of the polymer absorbent with respect to the volume before liquid absorption at the time of saturated liquid absorption is 233% to 567%. When the volume increase rate of the polymer absorbent at the time of liquid absorption is within such a range, the liquid can be absorbed more efficiently, and more excellent absorption performance can be exhibited. Note that the volume increase rate of the polymer absorbent with respect to the volume before liquid absorption at the time of saturated liquid absorption can be measured as follows.

[0090] <Measurement method of volume increase rate of volume before liquid absorption with respect to volume at saturated liquid absorption> (1) Place a measurement sample (polymer absorbent) into 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. Measure the height (mm) from the bottom surface of the cylinder to the upper surface of the sample inside the cylinder. If the upper surface of the sample inside 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%. Furthermore, when the measurement sample (polymer absorbent) is recovered from the product of the composite absorbent and used, it can be obtained according to the aforementioned <Recovery method of the measurement sample (polymer absorbent)>. (2) Calculate the volume of the sample inside the cylinder, that is, the pre-absorption volume (mm 3 ) from the measured height of the sample inside the cylinder and the bottom area inside the cylinder (assuming the pi is 3.14). (3) Next, put 60 mL of 0.9% sodium chloride aqueous solution into a petri dish (inner diameter: 97 mm, mass: 58 g), place the cylinder containing the sample in (1) above into this petri dish, immerse the bottom surface of the cylinder in the sodium chloride aqueous solution, and let the sodium chloride aqueous solution be absorbed by the sample inside the cylinder. (4) As the sample inside the cylinder absorbs the sodium chloride aqueous solution, 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 (that is, when it has absorbed liquid until saturation), measure the height of the sample inside the cylinder (that is, the height at the time of saturated liquid absorption; mm). If the upper surface of the sample inside the cylinder at the time of saturated liquid absorption is not flat, measure the height to the highest part (top). (5) 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 ) from the measured height of the sample inside the cylinder at the time of saturated liquid absorption and the bottom area inside the cylinder (assuming the pi is 3.14). (6) Divide the saturated liquid absorption volume calculated in (5) above by the pre-absorption volume 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 pre-absorption volume.

[0091] Also, in the present invention, the polymer absorbent has an initial liquid absorption amount of 5 g / g or more 5 seconds after applying a load of 40 g / cm 2 and preferably has a specific liquid absorption property such that the liquid absorption amount 20 seconds or more after the application of the load is 110% or more of the initial liquid absorption amount. When the polymer absorbent has such a specific initial liquid absorption amount and a liquid absorption amount 20 seconds or more after the application of the load, the liquid absorption amount at the initial stage of absorption is large, and the liquid can be temporarily retained, and the liquid can be absorbed even after a predetermined time has elapsed. Therefore, higher absorption performance can be exhibited.

[0092] Here, the load of 40 g / cm 2 is a load assumed to be a general pressure (for example, body pressure, etc.) applied to the composite absorbent, and the liquid absorption amount 20 seconds or more after the application of the load means the liquid absorption amount (mass; g / g) at any timing (for example, 20 seconds after the application of the load, 60 seconds after the application of the load, 300 seconds after the application of the load, 3600 seconds after the application of the load, etc.) after 20 seconds have elapsed after applying the load under predetermined temperature conditions. Incidentally, the initial liquid absorption amount and the liquid absorption amount after a predetermined time of the polymer absorbent can be measured as follows.

[0093] <Method for Measuring Liquid Absorption Amount of Polymer Absorbent under Specific Load> (1) Put 25 g of a 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) Place 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-NO255HD 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 the product of the composite absorber and used, it can be obtained according to the <Recovery method of the sample for measurement (polymer absorbent)> described above. (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 used) on the plastic piston to measure the mass (g) of the cylinder. (4) Place the cylinder containing the sample, plastic piston, and weight on the pedestal at the center of the petri dish, immerse the bottom surface of the cylinder in the sodium chloride aqueous solution, and allow the sodium chloride aqueous solution to be absorbed by the sample in the cylinder. (5) After a predetermined time has elapsed (for example, after 5 seconds, 20 seconds, 60 seconds, 300 seconds, 3600 seconds, etc.), lift the cylinder, tilt the cylinder at 45° and drain for 1 minute, and then measure the mass (g) of the cylinder. (6) Calculate the liquid absorption amount (g) of the sample by subtracting the mass of the cylinder before liquid absorption measured in (3) from the mass of the cylinder after liquid absorption measured in (5) above, and further divide this liquid absorption amount by the mass of the sample (= 0.16 g) to obtain the liquid absorption amount per unit mass (g / g) of the sample (polymer absorbent). Note that the liquid absorption amount (g / g) when the predetermined time in (5) above (i.e., the liquid absorption time) is 5 seconds is the "initial liquid absorption amount after 5 seconds from applying a load of 40 g / cm 2 and the liquid absorption amount (g / g) when the liquid absorption time is 20 seconds or more is the "liquid absorption amount after 20 seconds or more have elapsed".

[0094] In the present invention, it is preferable that the composite absorber further contains a conventional superabsorbent polymer (SAP) in addition to the polymer absorbent as in the embodiment shown in FIG. 2 described above. When the composite absorber contains SAP together with the polymer absorbent, after the liquid is quickly absorbed by the polymer absorbent in the composite absorber and temporarily retained, the liquid can be transferred to the SAP with high liquid retention capacity and retained in the SAP. Therefore, as an absorber, higher absorption efficiency can be exhibited.

[0095] Furthermore, when the composite absorber contains such a polymer absorbent and SAP, the liquid transfer amount from the polymer absorbent to the SAP is preferably 5.0 g / g or more. When the liquid transfer amount from the polymer absorbent to the SAP is 5.0 g / g or more, the liquid temporarily retained by the polymer absorbent can be more reliably transferred to the SAP. Therefore, as an absorber, high absorption efficiency can be more reliably exhibited. Note that the liquid transfer amount from the polymer absorbent to the 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 the SAP can be measured as follows.

[0096] <Method for Measuring Liquid Transfer Amount from 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%. When the sample for measurement (polymer absorbent) is recovered from the composite absorber product and used, it can be obtained according to the aforementioned <Method for Recovering Sample for Measurement (Polymer Absorbent)>. (2) Place a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) in a petri dish (inner diameter: 85 mm, depth: 20 mm). After evenly sprinkling 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 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 above sodium chloride aqueous solution, and allow the sodium chloride aqueous solution to absorb into the sample in the cylinder for 3 minutes. (5) After 3 minutes of liquid absorption, lift the cylinder, tilt the cylinder at 45° and drain for 1 minute, then measure the mass (g) of the cylinder. (6) Calculate the liquid absorption amount (g) of the sample by subtracting the mass (g) of the cylinder after liquid absorption measured in (5) above from the mass (g) of the cylinder before liquid absorption measured in (1) above. Further, divide this liquid absorption amount by the mass of the sample (= 0.3 g) to obtain the liquid absorption amount per unit mass of the sample (g / g). (7) Then, place the cylinder drained in (5) above on the 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 SAP, remove the cylinder and measure the mass (g) of the petri dish. (9) Calculate the liquid absorption amount (g) of SAP by subtracting the mass (g) of the petri dish measured in (8) above from the mass (g) of the petri dish measured in (2) above. Further, divide this liquid absorption amount by the mass of the sample (= 0.3 g) to obtain the liquid absorption amount of SAP per unit mass of the sample (g / g), that is, the liquid transfer amount to SAP per unit mass of the sample (g / g).

[0097] Furthermore, when the composite absorber contains the polymer absorbent and SAP as described above, the polymer absorbent preferably has a liquid discharge rate of the absorbed liquid component of 70% or more. When the liquid discharge rate of the polymer absorbent is 70% or more, since the liquid component absorbed by the polymer absorbent is easily released, the liquid temporarily held by the polymer absorbent can be more easily transferred to the SAP. In addition, the liquid discharge rate of the polymer absorbent is particularly preferably 75% or more. The liquid discharge rate of this polymer absorbent can be measured as follows.

[0098] <Measurement Method of Liquid Discharge Rate 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-NO255HD 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. The mass (g) of the mesh bag should be measured in advance. 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 the composite absorber product and used, it can be obtained according to the aforementioned <Recovery Method of Sample for Measurement (Polymer Absorbent)>. (2) Immerse the mesh bag containing the sample in a 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 liquid absorption amount (g) of the sample by subtracting the total mass of the sample (=1 g) and the mesh bag from the mass of the mesh bag after draining measured in (3) above, and further divide this liquid absorption amount by the mass of the sample (=1 g) to obtain the liquid absorption amount per unit mass (g / g) of the sample (polymer absorbent). (5) Furthermore, subject the mesh bag drained in (3) above to a centrifugal treatment at 150G for 90 seconds, and measure the mass (g) of the mesh bag after the centrifugal treatment. (6) Subtract the total mass of the sample (=1 g) and the mesh bag from the mass of the mesh bag after the centrifugal treatment measured in (5) above. Subtract the mass (g) of the fibers from the liquid absorption amount (g) of the sample calculated in the above (4).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 liquid absorption amount per unit mass obtained in (4) above and multiply by 100 to obtain the liquid discharge amount relative to the liquid absorption amount of the sample (polymer absorbent), that is, the liquid discharge rate (%).

[0099] Hereinafter, such a method for producing a polymer absorbent will be described in detail using the above-mentioned absorbent A as an example.

[0100] [Method for Producing Polymer Absorbent] As shown in FIG. 3, the above-mentioned absorbent A can be obtained through a crosslinking polymerization step and a hydrolysis step. Hereinafter, each of these steps will be described.

[0101] (Crosslinking Polymerization Step) First, an oil-soluble monomer for crosslinking polymerization, a crosslinkable monomer, a surfactant, water, and, if necessary, a polymerization initiator are mixed to obtain a water-in-oil emulsion. This water-in-oil emulsion is an emulsion in which the oil phase is the continuous phase and water droplets are dispersed therein.

[0102] In the above-mentioned absorbent A, as shown in the upper figure of FIG. 3, 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.

[0103] Specifically, in absorbent A, as shown in the upper figure of FIG. 3, 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 dissolved uniformly. Next, a 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 defoaming mixer (manufactured by EMI), which is a planetary stirring device, to obtain a water-in-oil type emulsion.

[0104] 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 had a continuous bubble structure, and the thickness of the continuous skeleton was 5.4 μm. Also, the average diameter of the continuous pores measured by mercury intrusion porosimetry was 36.2 μm, and the total pore volume was 15.5 mL / g.

[0105] Note that the content of divinylbenzene with respect to all monomers is preferably 0.3 to 10 mol%, more preferably 0.3 to 5 mol%. Also, 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%.

[0106] The addition amount of the surfactant can be set according to the type of oil-soluble monomer and the size of the desired emulsion particles (macropores), and it is preferably in the range of about 2 to 70% with respect to the total amount of the oil-soluble monomer and the surfactant.

[0107] Note that in order to control the bubble shape, size, etc. of 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, etc. may coexist in the polymerization system.

[0108] Moreover, the mixing method for forming the water-in-oil emulsion is not particularly limited. For example, methods such as mixing all components at once, or a method where the oil-soluble components, which are the oil-soluble monomer, surfactant, and oil-soluble polymerization initiator, and the water-soluble components, which are water or the water-soluble polymerization initiator, are separately and uniformly dissolved and then the respective components are mixed, can be adopted.

[0109] Furthermore, the mixing device for forming the emulsion is not particularly limited, and any device such as a normal mixer, homogenizer, high-pressure homogenizer, etc. can be adopted according to the desired emulsion particle size. Additionally, a so-called planetary stirring device that stirs and mixes the object to be treated by placing the object to be treated in a mixing container and rotating it around the revolution axis while revolving in a tilted state of the mixing container can also be used.

[0110] Also, the mixing conditions are not particularly limited, and the stirring rotation speed, stirring time, etc. can be arbitrarily set according to the desired emulsion particle size. In the above-mentioned 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.

[0111] The polymerization conditions of 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, heating polymerization can be carried out at a temperature of 30 - 100°C for 1 - 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, polymerization can be carried out at a temperature of 0 - 30°C for 1 - 48 hours in a sealed container under an inert atmosphere.

[0112] 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 3 can be obtained.

[0113] (Hydrolysis Step) Subsequently, the process of hydrolyzing the monolith A (crosslinked polymer) to obtain the absorbent A (hydrolysis step) will be described.

[0114] 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. After that, it is dried to obtain a block-shaped absorbent A. Further, this block-shaped absorbent A is pulverized into a predetermined size (that is, a particle diameter of 300 μm or more) to obtain a particulate absorbent A. Note that the particulate form of this absorbent A may be formed (granulated) into particles during drying or after drying.

[0115] Also, the method for hydrolyzing the monolith A is not particularly limited, and various methods can be adopted. For example, aromatic solvents such as toluene and xylene, halogen 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 a solvent, and contacting with a strong base such as sodium hydroxide, or a method of contacting with a Bronsted acid such as 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. can be mentioned.

[0116] 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 (that is, 1 to 10 carbon atoms) of (meth)acrylic acid is preferable, and an alkyl ester of C4 (that is, 4 carbon atoms) of (meth)acrylic acid is particularly preferable. Examples of the C4 alkyl ester of (meth)acrylic acid include t-butyl (meth)acrylate, n-butyl (meth)acrylate, and iso-butyl (meth)acrylate.

[0117] The monomer used for crosslinking polymerization may be only (meth)acrylic acid ester and divinylbenzene, or may contain other monomers in addition to (meth)acrylic acid 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, isobutylene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and the like. The proportion of other monomers other than (meth)acrylic acid ester and divinylbenzene in all the monomers used for crosslinking polymerization is preferably 0 to 80 mol%, more preferably 0 to 50 mol%.

[0118] In addition, the surfactant is not limited to the above-mentioned sorbitan monooleate, and any surfactant can be used as long as it can form a water-in-oil (W / O) emulsion when the monomer for crosslinking polymerization 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.

[0119] In addition, a compound that generates radicals by heat and light irradiation is preferably used as the polymerization initiator. 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 bisulfite, and tetramethylthiuram disulfide. However, in some cases, polymerization may proceed only by heating or only by light irradiation without adding a polymerization initiator, so the addition of a polymerization initiator is unnecessary in such systems.

[0120] The composite absorber of the present invention is not particularly limited, and can be applied to composite absorbers in various fields such as civil engineering and construction materials such as dew prevention sheets and simple soils, base materials for pharmaceuticals, and materials for absorbing leaked liquids. Therefore, the liquid to be absorbed by the composite absorber is also not particularly limited, and examples include water and aqueous solutions (such as seawater), acids (such as hydrochloric acid), bases (such as sodium hydroxide), and organic solvents (such as alcohols such as methanol and ethanol, ketones such as acetone, ethers such as tetrahydrofuran (THF) and 1,4-dioxane, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), etc.). These liquids may be mixtures of two or more liquids.

[0121] In addition, the present invention is not limited to the above-described embodiments, etc., and appropriate combinations, substitutions, changes, etc. are possible within the scope not departing from the object and gist of the present invention. In this specification, ordinal numbers such as "first" and "second" are for distinguishing the matters to which the ordinal numbers are attached, and do not mean the order, priority, importance, etc. of each matter.

Explanation of Reference Numerals

[0122] 1 Composite absorber 2 First holding sheet 3 Second holding sheet 4 Polymer absorbent 5 Superabsorbent polymer (SAP) 6 Hydrophilic fiber sheet

Claims

1. A composite absorber for absorbing liquids, for use in civil engineering materials, building materials, or materials for absorbing leaked liquids consisting of organic solvents (provided that the use is not for disposable pants-type diapers, tape-type disposable diapers, sanitary napkins, absorption pads, disposable diapers for pets, or absorption pads for pets). It contains a particulate polymer absorbent having a hydrophilic continuous skeleton and continuous pores. The polymer absorbent is a hydrolyzate of a cross-linked polymer of (meth)acrylic acid ester and divinylbenzene, which is a compound containing two or more vinyl groups in one molecule, and contains at least one or more -COONa groups. The proportion of the cross-linked polymerization residue of divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is 0.1 to 30 mol% based on all constitutional units. The composite absorber is characterized in that the polymer absorbent has a particle size of 300 μm or more.

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. A particulate polymer absorbent having a hydrophilic continuous skeleton and continuous pores, for use in civil engineering materials, building materials, or materials for absorbing leaked liquids consisting of organic solvents (provided that the use is not for disposable pants-type diapers, tape-type disposable diapers, sanitary napkins, absorption pads, disposable diapers for pets, or absorption pads for pets). The polymer absorbent is a hydrolyzate of a cross-linked polymer of (meth)acrylic acid ester and divinylbenzene, which is a compound containing two or more vinyl groups in one molecule, and contains at least one or more -COONa groups. The proportion of the cross-linked polymerization residue of divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is 0.1 to 30 mol% based on all constitutional units. A polymer absorbent characterized by having a particle diameter of 300 µm or more.

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