Composite absorbents and polymeric absorbents

Abstract

To provide an absorber that is capable of instantly absorbing a large volume of 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 polymer absorbent (4) having hydrophilic continuous skeletons and continuous pores; and a highly absorbent polymer (5). When absorbing liquid, the liquid is taken into the continuous skeletons and then continuous pores.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a composite absorbent and a polymeric absorbent. [Background technology]

[0002] 2. Description of the Related Art Known absorbents used to absorb liquids such as aqueous solutions include those containing porous materials such as sponge materials and superabsorbent polymers (so-called "SAPs") having high absorption capacities. Such absorbents containing porous materials or SAPs are used in various fields, including disposable paper diapers, anti-condensation sheets, civil engineering and construction materials such as simple soil, base materials for pharmaceuticals, and materials for absorbing leaked liquids, as disclosed in Patent Documents 1 to 5, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3231320 [Patent Document 2] JP 2017-36638 A [Patent Document 3] JP 2017-205225 A [Patent Document 4] Japanese Patent Application Publication No. 63-75016 [Patent Document 5] Japanese Patent Application Publication No. 8-38893 Summary of the Invention [Problem to be solved by the invention]

[0004] The absorbent materials used in such conventional absorbents have the following characteristics. For example, a polymer foam material (i.e., a porous material) consisting of a hydrophilic flexible structure of interconnected open cells as disclosed in Patent Document 1 absorbs liquid by taking it into a plurality of pores having a predetermined space, and can instantly absorb liquid by utilizing capillary action. However, since the space that can absorb liquid is limited to the predetermined space formed by the plurality of pores, it is difficult to absorb a large amount of liquid. On the other hand, superabsorbent polymers (SAPs) as disclosed in Patent Documents 2 to 5 absorb liquid while expanding the space (i.e., expanding) by the volume of the absorbed liquid, and therefore can retain a large amount of liquid (i.e., have a high liquid retention capacity), but have a slow liquid absorption speed, making it difficult to instantly absorb liquid. In addition, it is possible to use these absorbent materials simultaneously to compensate for the shortcomings of each absorbent material. However, for example, when a large amount of liquid to be absorbed is supplied, the amount that can be absorbed by the porous material (absorption limit) may be exceeded in the initial stage of absorption. Furthermore, any liquid that is not absorbed by the porous material will not be immediately absorbed by SAP, so there is a risk that high absorption performance will not be achieved.

[0005] The present invention has been made in view of the above problems, and has an object to provide an absorbent body having high absorption performance capable of instantly absorbing a large amount of liquid. [Means for solving the problem]

[0006] One aspect of the present invention (Aspect 1) is a composite absorbent for absorbing liquid, comprising: The composite absorbent body includes a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer; The polymer absorbent is a composite absorbent characterized in that, when absorbing a liquid, the polymer absorbent incorporates the liquid into the continuous framework and then into the continuous pores.

[0007] In the composite absorbent of this embodiment, when the polymer absorbent having a hydrophilic continuous skeleton and continuous pores absorbs a liquid such as an aqueous solution, the hydrophilic continuous skeleton instantaneously takes up the liquid due to osmotic pressure and expands, thereby expanding the volume of the continuous pores and enabling the liquid to be further absorbed into the enlarged continuous pores, thereby enabling the composite absorbent to instantaneously absorb a large amount of liquid and then transfer the absorbed liquid to a superabsorbent polymer (SAP) with high liquid retention capacity where it can be steadily retained within the SAP. This allows the composite absorbent body of this embodiment to exhibit high absorption performance as an absorbent body.

[0008] In another aspect (Aspect 2) of the present invention, in the composite absorbent of Aspect 1 above, the polymer absorbent is characterized in that, at the time of liquid retention limit absorption, the volume of the expanded polymer absorbent is larger than the volume of the absorbed liquid.

[0009] The composite absorbent of this embodiment can exhibit higher absorption performance as an absorbent since the polymer absorbent can incorporate a larger amount of liquid into the open pores.

[0010] In still another aspect (aspect 3) of the present invention, in the composite absorbent of aspect 1 or 2 above, the polymer absorbent is characterized in that the liquid absorption capacity of the continuous pores is greater than the liquid absorption capacity of the continuous skeleton.

[0011] The composite absorbent of this embodiment can exhibit even higher absorption performance as an absorbent since the polymer absorbent can take in a larger amount of liquid into the open pores.

[0012] In yet another aspect (Aspect 4) of the present invention, in the composite absorbent of any of Aspects 1 to 3 above, the polymer absorbent is characterized in that the mass ratio of the liquid absorption capacity of the continuous pores to the liquid absorption capacity of the continuous skeleton is 60:40 to 95:5.

[0013] In the composite absorbent of this embodiment, the mass ratio of the liquid absorption amount of the continuous pores of the polymer absorbent to the liquid absorption amount of the continuous skeleton is within the above-mentioned specific range, so that when the polymer absorbent absorbs liquid, the liquid can be more reliably absorbed into the continuous skeleton and then into the continuous pores.

[0014] In still another aspect (Aspect 5) of the present invention, in the composite absorbent of any of Aspects 1 to 4 above, the polymer absorbent is characterized in that the absorption rate from immediately after the start of absorption until the liquid retention limit is reached is relatively high, and the absorption rate after the liquid retention limit is relatively low.

[0015] In the composite absorbent of this embodiment, in the initial stage of liquid absorption from immediately after the start of liquid absorption until the liquid retention limit is reached, the absorption speed of the polymer absorbent is relatively high and the liquid can be instantaneously taken up into the continuous skeleton, whereas in the later stage of liquid absorption after the liquid retention limit, the absorption speed of the polymer absorbent is relatively low and the liquid can be steadily taken up into the continuous pores enlarged by the expansion of the continuous skeleton, so that the absorbent can more reliably exhibit its high absorption performance as an absorbent.

[0016] In still another aspect (aspect 6) of the present invention, in the composite absorbent of any one of aspects 1 to 5 above, the polymer absorbent is a monolithic absorbent.

[0017] In the composite absorbent of this embodiment, the polymer absorbent is a monolithic absorbent, so that it can quickly absorb liquid and can more reliably transfer the liquid temporarily held in the polymer absorbent to the SAP.

[0018] In yet another aspect (Aspect 7) of the present invention, in the composite absorbent of any of Aspects 1 to 6 above, the polymer absorbent is a hydrolysate of a crosslinked polymer of a (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.

[0019] In the composite absorbent of this embodiment, since the polymer absorbent has the above-mentioned specific configuration, when absorbing liquid, the hydrophilic continuous skeleton is easily elongated (i.e., easily expanded) and the continuous pores are easily expanded, so that a larger amount of liquid can be taken up into the continuous pores more quickly, and the absorbent can exhibit even better absorption performance.

[0020] Yet another embodiment (embodiment 8) of the present invention is a polymeric absorbent used together with a superabsorbent polymer, It has a hydrophilic continuous skeleton and continuous pores, This polymer absorbent is characterized in that, when absorbing a liquid, the liquid is incorporated into the continuous framework and then into the continuous pores.

[0021] When the polymer absorbent of this embodiment absorbs a liquid such as an aqueous solution, the hydrophilic continuous skeleton instantly takes up the liquid due to osmotic pressure and expands, thereby expanding the volume of the continuous pores, and the polymer absorbent can further take up the liquid into the expanded continuous pores, thereby enabling the polymer absorbent to instantly absorb a large amount of liquid, and furthermore, the absorbed liquid can be transferred to a superabsorbent polymer (SAP) with high liquid retention capacity and steadily retained within the SAP. Therefore, when the polymer absorbent of this embodiment is used together with SAP in an absorbent body, the absorbent body can exhibit high absorption performance. Effect of the Invention

[0022] According to the present invention, it is possible to provide an absorbent body having high absorption performance that can instantly absorb a large amount of liquid. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is an exploded perspective view of a composite absorbent body 1 according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an exploded perspective view of a composite absorbent body 1' according to another embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram illustrating a manufacturing process of absorbent A, which is an example of a polymer absorbent. [Figure 4] FIG. 4 is an SEM photograph of absorbent A at a magnification of 50 times. [Diagram 5] FIG. 5 is a SEM photograph of absorbent A at a magnification of 100 times. [Figure 6] FIG. 6 is an SEM photograph of absorbent A at a magnification of 500 times. [Figure 7] FIG. 7 is a SEM photograph of absorbent A at a magnification of 1000 times. [Figure 8] FIG. 8 is an SEM photograph of absorbent A at a magnification of 1500 times. [Figure 9] FIG. 9 is a set of cross-sectional photographs taken with a scanning electron microscope, showing the state of absorbent A before and after it absorbed liquid. [Figure 10] FIG. 10 is a set of CT images showing the absorption state of absorbent A for each amount of distilled water dispensed. [Figure 11] FIG. 11 shows CT images showing the absorption state of two types of SAP at different drip amounts of distilled water. [Figure 12] FIG. 12 is a set of CT images showing the absorption state of Infinity particles for each drop amount of distilled water. [Figure 13] FIG. 13 is a graph showing the relationship between the liquid absorption capacity and the amount of volume change of absorbent A, which is an example of the polymer absorbent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] A preferred embodiment of the present invention will be described in detail below using a composite absorbent body 1 as one embodiment. In this specification, unless otherwise specified, "planar view" simply means "viewing an object (e.g., a composite absorbent body) placed on a horizontal surface in an unfolded state in the thickness direction of the object from above in the vertical direction."

[0025] [Composite absorber] FIG. 1 is an exploded perspective view of a composite absorbent body 1 according to one embodiment of the present invention. The composite absorbent 1 shown in FIG. 1 has a generally rectangular outer shape in a plan view, and basically comprises a first retention sheet 2 forming one surface of the composite absorbent 1 in the thickness direction, a second retention sheet 3 forming the other surface of the composite absorbent 1, and a liquid-absorbent member located between these sheets and consisting of a mixture of a polymer absorbent 4 and a superabsorbent polymer 5 (SAP).

[0026] The liquid-absorbent member in the composite absorbent body 1 is configured to absorb and retain liquid that has permeated through the first retaining sheet 2, using a polymer absorbent 4 and a highly absorbent polymer 5 that are located between the first retaining sheet 2 and the second retaining sheet 3 and have a hydrophilic continuous skeleton and continuous pores. Furthermore, the above-mentioned polymer absorbent 4 exhibits a unique liquid absorption behavior in that, when absorbing a liquid, the liquid is incorporated into the continuous skeleton and then into the continuous pores.

[0027] When the polymer absorbent 4 having the above-mentioned hydrophilic continuous skeleton and continuous pores absorbs a liquid such as an aqueous solution, the hydrophilic continuous skeleton instantly takes up the liquid by osmotic pressure and expands, thereby expanding the volume of the continuous pores, and the polymer absorbent 4 can further take up the liquid in the expanded continuous pores, thereby enabling the polymer absorbent 4 to instantly absorb a large amount of liquid, and furthermore, the absorbed liquid can be transferred to the SAP having a high liquid retention capacity and steadily retained in the SAP. Therefore, the composite absorbent body 1 containing such an absorbent polymer 4 can exhibit high absorption performance as an absorbent body.

[0028] In the present invention, the absorbent member is not limited to the form of the composite absorbent 1 in the above-mentioned embodiment, and the absorbent member may or may not contain other absorbent materials as long as it contains at least a polymer absorbent exhibiting the above-mentioned specific absorbent behavior and SAP.

[0029] Furthermore, in the present invention, the configuration of the composite absorbent is not limited to the form of the composite absorbent 1 of the above-mentioned embodiment, and the composite absorbent may have, for example, a hydrophilic fiber sheet 6 located between the first retention sheet 2 and the liquid-absorbent member (i.e., the polymer absorbent 4 and the highly absorbent polymer 5), as in a composite absorbent 1' of another embodiment of the present invention shown in Figure 2.

[0030] In the present invention, the outer shape, various dimensions, basis weight, etc. of the composite absorbent body are not particularly limited as long as they do not impair the effects of the present invention, and any outer shape (e.g., circular, elliptical, polygonal, hourglass, design shape, etc.), various dimensions, basis weight, etc. can be adopted according to various applications and usage modes, etc.

[0031] Various constituent members of the composite absorbent body of the present invention will be described in further detail below, taking as an example the composite absorbent body 1 of the embodiment shown in FIG.

[0032] (Retaining sheet) 1, a first retention sheet 2 forming one surface of the composite absorbent body 1 has a substantially rectangular outer shape in a plan view similar to the outer shape of the composite absorbent body 1. The first retention sheet 2 is formed of a liquid-permeable sheet-like member that allows liquid supplied to the composite absorbent body 1 to pass therethrough and be absorbed and retained in the liquid-absorbent member on the inside.

[0033] The first retaining sheet 2 has an overall size that is slightly larger than the absorbent member located on the inside (i.e., compared to the area in which absorbent materials such as polymer absorbent 4 are located), and is joined at its peripheral portion to the second retaining sheet 3 located on the other side of the composite absorbent 1 in the thickness direction by any adhesive or heat sealing means, etc.

[0034] On the other hand, the second retention sheet 3 forming the other surface of the composite absorbent body 1 has a substantially rectangular outer shape in a plan view similar to the outer shape of the composite absorbent body 1. The second retention sheet 3 is made of a liquid-impermeable sheet-like member that prevents liquid that has not been absorbed and retained in the inner liquid-absorbent member and liquid that has seeped out from the liquid-absorbent member from leaking out to the outside of the composite absorbent body 1.

[0035] In the present invention, the sheet-like members usable as the first and second retaining sheets are not limited to those in the above-mentioned embodiments, and the composite absorbent of the present invention may be any one of the first and second retaining sheets formed from a liquid-permeable sheet-like member. That is, the composite absorbent of the present invention may be any one of the first and second retaining sheets formed from a liquid-impermeable sheet-like member.

[0036] 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 impair the effects of the present invention, and any liquid-permeable sheet-like member can be used according to various applications, usage modes, etc. Examples of such liquid-permeable sheet-like members include hydrophilic nonwoven fabrics such as air-through nonwoven fabrics, spunbond nonwoven fabrics, and point-bond nonwoven fabrics, woven fabrics, knitted fabrics, and porous resin films.

[0037] Furthermore, when hydrophilic nonwoven fabrics, woven fabrics, knitted fabrics, etc. (hereinafter collectively referred to as "fiber sheets") are 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 fiber constituting such a fiber sheet is not particularly limited, and examples thereof include hydrophilic fibers such as cellulosic fibers and thermoplastic resin fibers that have been subjected to a hydrophilization treatment. These fibers may be used alone or in combination of two or more types of fibers. Examples of cellulose-based fibers that can be used as constituent fibers of the fiber sheet include natural cellulose fibers (e.g., plant fibers such as cotton), regenerated cellulose fibers, refined cellulose fibers, and semi-synthetic cellulose fibers. Examples of thermoplastic resin fibers that can be used as constituent fibers of the fiber sheet include fibers made of known thermoplastic resins such as olefin resins such as polyethylene (PE) and polypropylene (PP), polyester resins such as polyethylene terephthalate (PET), and polyamide resins such as 6-nylon. These resins may be used alone or in combination of two or more types.

[0038] In addition, when a liquid-impermeable sheet-like member is used as the holding sheet, the liquid-impermeable sheet-like member is not particularly limited as long as it does not impair the effects of the present invention, and any liquid-impermeable sheet-like member can be adopted according to various applications and usage modes, etc. Examples of such liquid-impermeable sheet-like members include hydrophobic nonwoven fabrics formed from any hydrophobic thermoplastic resin fibers (for example, polyolefin fibers such as PE and PP, polyester fibers such as PET, various composite fibers such as core-sheath type, etc.); porous or nonporous resin films formed from hydrophobic thermoplastic resins such as PE and PP; laminates in which a nonwoven fabric is bonded to the resin film; laminated nonwoven fabrics such as SMS nonwoven fabrics, etc.

[0039] In the present invention, the external shape, various dimensions, basis weight, etc. of the retaining sheet are not particularly limited as long as they do not impair the effects of the present invention, and any external shape (e.g., circular, oval, polygonal, hourglass, design shape, etc.), various dimensions, basis weight, etc. can be adopted according to various applications and usage modes, etc.

[0040] (Liquid-absorbent member) In the composite absorbent 1 shown in Figure 1, the liquid-absorbent member is configured to absorb and retain liquid that has permeated through the first retaining sheet 2 by using a polymer absorbent 4 having a hydrophilic continuous skeleton and continuous pores and a superabsorbent polymer 5, which are located between the first retaining sheet 2 and the second retaining sheet 3 as described above.

[0041] In the composite absorbent 1, the polymer absorbent 4 and the highly absorbent polymer 5 of the liquid-absorbent member are bonded to each of the above-mentioned first retaining sheet 2 and second retaining sheet 3 by any adhesive such as a hot melt adhesive, but in the composite absorbent of the present invention, the polymer absorbent does not have to be bonded to the retaining sheet.

[0042] In the present invention, the liquid-absorbent member contains, as essential components, a polymer absorbent having a hydrophilic continuous skeleton and continuous pores and exhibiting the above-mentioned specific liquid-absorbing behavior, and a superabsorbent polymer. The polymer absorbent will be described later, and the superabsorbent polymer is a powder or granular material made of a highly absorbent polymer such as a sodium acrylate copolymer known in the art, and is called SAP (Super Absorbent Polymer).

[0043] In the present invention, the liquid-absorbent member located between the first and second holding sheets may contain only the above-mentioned polymer absorbent and superabsorbent polymer as the liquid-absorbent material, or may further contain a liquid-absorbent material known in the art in addition to these. Examples of such liquid-absorbent materials include hydrophilic fibers, and more specifically, pulp fibers (e.g., ground pulp, etc.), and cellulosic fibers such as cotton, rayon, and acetate.

[0044] In the present invention, the outer shape (planar shape of the area where the absorbent material is arranged), various dimensions, basis weight, etc. of the absorbent member are not particularly limited as long as they do not impair the effects of the present invention, and any outer shape, various dimensions, basis weight, etc. can be adopted depending on the desired absorbency, flexibility, strength, etc.

[0045] (hydrophilic fiber sheet) In the present invention, the composite absorbent may have a hydrophilic fiber sheet 6 between the first retention sheet 2 and the liquid-absorbent member (i.e., the polymer absorbent 4 and the highly absorbent polymer 5), for example, as in another embodiment of the composite absorbent 1' shown in Figure 2.

[0046] In the present invention, the hydrophilic fiber sheet that can be used in the composite absorbent is not particularly limited as long as it does not impair the effects of the present invention, and any hydrophilic fiber sheet can be used depending on various applications and usage modes. Examples of such hydrophilic fiber sheets include nonwoven fabrics, woven fabrics, knitted fabrics, etc. that have hydrophilicity. The hydrophilic fiber sheet may have a single-layer structure or a multi-layer structure of two or more layers.

[0047] The type of the constituent fiber of such a hydrophilic fiber sheet is not particularly limited, and examples thereof include hydrophilic fibers such as cellulosic fibers and thermoplastic resin fibers that have been subjected to a hydrophilic treatment. These fibers may be used alone or in combination of two or more types of fibers. Furthermore, examples of cellulose-based fibers that can be used as constituent fibers of the hydrophilic fiber sheet include natural cellulose fibers (e.g., plant fibers such as cotton), regenerated cellulose fibers, refined cellulose fibers, and semi-synthetic cellulose fibers. Examples of thermoplastic resin fibers that can be used as constituent fibers of the hydrophilic fiber sheet include fibers made of known thermoplastic resins such as olefin resins such as PE and PP, polyester resins such as PET, and polyamide resins such as 6-nylon. These resins may be used alone or in combination of two or more types.

[0048] In the present invention, the outer shape, various dimensions, basis weight, etc. of the hydrophilic fibrous sheet are not particularly limited as long as they do not impair the effects of the present invention, and any outer shape, various dimensions, basis weight, etc. can be adopted according to various applications, usage modes, etc.

[0049] The polymer absorbent used in the composite absorbent of the present invention will be described in more detail below.

[0050] [Polymer absorbent] In the present invention, the polymer absorbent is not particularly limited as long as it has a hydrophilic continuous skeleton and continuous pores, and exhibits a unique liquid absorption behavior in which the liquid is absorbed in the continuous skeleton and then in the continuous pores when absorbing a liquid. Examples of such polymer absorbents include a polymer compound that is a hydrolyzate of a crosslinked polymer of two or more monomers including at least a (meth)acrylic acid ester and has at least one hydrophilic group in the functional group. More specifically, examples of such polymer absorbents include a polymer compound that is a hydrolyzate of a crosslinked polymer of a compound containing a (meth)acrylic acid ester and two or more vinyl groups in one molecule and has at least a -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. The -COONa group is distributed approximately uniformly in the skeleton of the porous body.

[0051] If the polymer absorbent is a hydrolyzate of a crosslinked polymer of such a (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, as described below, when absorbing a liquid such as an aqueous solution, the hydrophilic continuous skeleton is easily extended (i.e., it is easily expanded), and the continuous pores are easily expanded, so that more liquid can be taken in the continuous pores more quickly. Therefore, a composite absorbent containing such a polymer absorbent can exhibit even better absorption performance as an absorbent.

[0052] In this specification, the (meth)acrylic acid ester refers to an acrylic acid ester or a methacrylic acid ester.

[0053] In such a polymer absorbent formed by the hydrolysis product of a cross-linked polymer of a (meth)acrylic acid ester and divinylbenzene, a hydrophilic continuous skeleton is formed by an organic polymer having at least -COONa groups, and the skeleton has interconnected pores (interconnected pores) that serve as liquid absorption fields. In addition, since the hydrolysis treatment converts the -COOR groups (that is, carboxylate groups) of the crosslinked polymer into -COONa groups or -COOH groups (see FIG. 3), the polymer absorbent may have -COOR groups.

[0054] The presence of --COOH groups and --COONa groups in the organic polymer forming the hydrophilic continuous skeleton can be confirmed by analysis using infrared spectroscopy and a method for quantifying weakly acidic ion-exchange groups.

[0055] 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)acrylic acid ester and divinylbenzene, and the lower diagram shows absorbent A obtained by subjecting monolith A in the middle diagram to hydrolysis and drying treatment.

[0056] Hereinafter, an explanation will be given using absorbent A, which is an example of a polymer absorbent and is formed from a hydrolysate of a crosslinked polymer of a (meth)acrylic acid ester and divinylbenzene.

[0057] The polymer absorbent is not limited to the absorbent A, but may be a hydrolysate of a cross-linked polymer of a (meth)acrylic acid ester and a compound having two or more vinyl groups in one molecule, or a hydrolysate of a cross-linked polymer of two or more monomers including at least a (meth)acrylic acid ester. However, if the polymer absorbent is a monolithic absorbent, it has the advantage that it can absorb liquid quickly and that the liquid temporarily held in the polymer absorbent can be transferred to the SAP more reliably.

[0058] In the following description, "Monolith A" refers to an organic porous material consisting of a crosslinked polymer of (meth)acrylic acid ester and divinylbenzene before hydrolysis treatment, and may be referred to as a "monolithic organic porous material." In addition, "absorbent A" is a hydrolyzate of a crosslinked polymer (monolith A) of (meth)acrylic acid ester and divinylbenzene after hydrolysis and drying. In the following description, absorbent A refers to the absorbent in a dry state.

[0059] First, the structure of absorbent A will be described. As described above, absorbent A has a hydrophilic continuous skeleton and continuous pores. As shown in Fig. 3, absorbent A, which is an organic polymer having a hydrophilic continuous skeleton, is obtained by cross-linking 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).

[0060] The organic polymer that forms a hydrophilic continuous skeleton has, as structural units, a polymerized residue of an ethylene group (hereinafter referred to as "structural unit X") and a cross-linked polymerized residue of divinylbenzene (hereinafter referred to as "structural unit Y"). Furthermore, the polymerized residue of the ethylene group (structural unit X) in the organic polymer forming the hydrophilic continuous skeleton has a -COONa group generated by hydrolysis of the carboxylate group, or both a -COOH group and a -COONa group. When the polymerized monomer is a (meth)acrylic acid ester, the polymerized residue of the ethylene group (structural unit X) has a -COONa group, a -COOH group, and an ester group.

[0061] In the absorbent A, the ratio of the crosslinked polymer residue of divinylbenzene (structural unit Y) in the organic polymer forming the hydrophilic continuous skeleton is, for example, 0.1 to 30 mol %, preferably 0.1 to 20 mol %, based on the total structural units. For example, in the absorbent A in which butyl methacrylate is used as the polymerization monomer and divinylbenzene is used as the crosslinked monomer, the ratio of the crosslinked polymer residue of divinylbenzene (structural unit Y) in the organic polymer forming the hydrophilic continuous skeleton is, for example, about 3 mol %, preferably 0.1 to 10 mol %, more preferably 0.3 to 8 mol %, based on the total structural units. Furthermore, when the ratio of cross-linked polymerized residues 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 ratio of cross-linked polymerized residues of divinylbenzene is 30 mol % or less, the absorption amount of the liquid to be absorbed is less likely to decrease.

[0062] In addition, in the absorbent A, the organic polymer forming the hydrophilic continuous skeleton may be composed only of the structural unit X and the structural unit Y, or may have, in addition to the structural unit X and the structural unit Y, a structural unit other than the structural unit X and the structural unit Y, that is, a polymerized residue of a monomer other than a (meth)acrylic acid ester and divinylbenzene.

[0063] Examples of structural units other than the structural unit X and the structural unit Y include polymerized 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, and trimethylolpropane tri(meth)acrylate.

[0064] The proportion of structural units other than the structural unit X and the structural unit Y in the organic polymer that forms the hydrophilic continuous skeleton is, for example, 0 to 50 mol %, and preferably 0 to 30 mol %, relative to all structural units.

[0065] The thickness of the hydrophilic continuous skeleton of the absorbent A is preferably 0.1 to 100 μm. When the thickness of the hydrophilic continuous skeleton of the absorbent A is 0.1 μm or more, the spaces (pores) for absorbing liquid in the porous body are less likely to collapse during absorption, and the amount of absorbed liquid 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 speed is easily obtained.

[0066] In addition, since the pore structure of the hydrophilic continuous skeleton of absorbent A is an open-cell structure, the thickness of the continuous skeleton is measured by evaluating the cross section of the skeleton that appears on the test piece for electron microscope measurement. The continuous skeleton is often polygonal in shape because it is formed by the gaps between water (water droplets) removed by the dehydration and drying process after hydrolysis. Therefore, the thickness of the continuous skeleton is the average value of the diameter (μm) of the circle circumscribing the polygonal cross section. In rare cases, there may be small holes in the polygon, in which case the circumscribing circle of the polygonal cross section surrounding the small holes is measured.

[0067] Furthermore, the absorbent A preferably has an average diameter of interconnected pores of 1 to 1000 μm. When the average diameter of interconnected pores in the absorbent A is 1 μm or more, the spaces (pores) for absorbing liquid in the porous body are less likely to collapse during absorption, and the absorption rate is less likely to decrease. On the other hand, when the average diameter of interconnected pores is 1000 μm or less, an excellent absorption rate is more likely to be obtained.

[0068] The average diameter (μm) of the interconnected pores of absorbent A can be measured by mercury intrusion porosimetry, and the maximum value of the pore distribution curve obtained by the mercury intrusion porosimetry is used. Regardless of the ionic form of absorbent A, samples for measuring the average diameter of interconnected pores are those dried for 18 hours or more in a reduced pressure dryer set at a temperature of 50°C. The final pressure reached is 0 Torr.

[0069] Here, FIG. 4 is an SEM photograph of absorbent A at a magnification of 50 times, FIG. 5 is an SEM photograph of absorbent A at a magnification of 100 times, FIG. 6 is an SEM photograph of absorbent A at a magnification of 500 times, FIG. 7 is an SEM photograph of absorbent A at a magnification of 1000 times, and further, FIG. 8 is an SEM photograph of absorbent A at a magnification of 1500 times. The absorbents A shown in these Figs. 4 to 8 are examples of absorbents that use butyl methacrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, and each has a cubic structure with a side length of 2 mm.

[0070] 4 to 8 has a large number of cellular macropores and further has portions where these cellular macropores overlap. Absorbent A has an open cell structure in which the overlapping portions of the macropores form common openings (mesopores), i.e., it has an open cell structure (open macropore structure).

[0071] The overlapping portions of the macropores form common openings (mesopores) having an average diameter in a dry state of 1 to 1000 μm, preferably 10 to 200 μm, and particularly preferably 20 to 100 μm, and most of them have an open pore structure. When the average diameter of the mesopores in a dry state is 1 μm or more, the absorption rate of the liquid to be absorbed is improved. On the other hand, when the average diameter of the mesopores in a dry state is 1000 μm or less, the absorbent A is less likely to become embrittled. The number of overlapping macropores in each macropore is about 1 to 12, and in most cases, about 3 to 10.

[0072] In addition, since absorbent A has such an open cell structure, macropores and mesopores can be uniformly formed, and there is an advantage in that the pore volume and specific surface area can be significantly increased compared to the particle agglomeration type porous bodies as described in JP-A-8-252579 and the like.

[0073] 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 spaces (voids) for absorbing liquid in the porous body are less likely to collapse during absorption, and the amount of absorbed liquid and the 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.

[0074] The total pore volume can be measured by mercury intrusion porosimetry. The sample for measuring the total pore volume is dried for 18 hours or more in a vacuum dryer set at a temperature of 50°C, regardless of the ion form of absorbent A. The final pressure is 0 Torr.

[0075] Below, we will explain what happens when the absorbent A comes into contact with a liquid, but the same applies to the case where a liquid comes into contact with a liquid-absorbent member or a composite absorbent containing the absorbent A. In addition, since the mass of absorbed liquid is approximately proportional to the amount of liquid, in the following explanation, the mass of liquid may be simply referred to as the "amount of liquid."

[0076] First, the continuous pores of the absorbent A shown in Figures 4 to 8 are pores in which a plurality of pores (voids) are interconnected, and the presence of a large number of voids can be visually confirmed by the naked eye from the outside. When liquid comes into contact with absorbent A having such a large number of voids, first, the hydrophilic continuous skeleton instantly absorbs a portion of the liquid due to osmotic pressure and elongates (i.e., expands). This elongation of the continuous skeleton occurs in almost all directions. Here, Fig. 9 is a cross-sectional photograph taken with a scanning electron microscope (SEM) showing the state of absorbent A before and after absorbing liquid. In this Fig. 9, the SEM photograph (a) on the left side is absorbent A before absorbing liquid, and the SEM photograph (b) on the right side is absorbent A after absorbing liquid. As shown in Figure 9, the size of each pore of absorbent A increases as the external shape of absorbent A increases due to the extension of the continuous skeleton during liquid absorption. When the size of the pores increases in this way, the volume of the pores increases, and the amount of liquid that can be retained in the pores also increases. In other words, absorbent A, which has increased in size by absorbing a certain amount of liquid in this way, is able to absorb a further predetermined amount of liquid into the enlarged pores due to capillary action. In this way, absorbent A exhibits a unique liquid absorption behavior in which, when absorbing a liquid, the liquid is incorporated into the hydrophilic continuous framework and then absorbed by the continuous pores.

[0077] In addition, the liquid absorbed into the hydrophilic continuous skeleton of absorbent A is not easily released from the continuous skeleton (i.e., it is not easily synergized), whereas the liquid absorbed into the continuous pores is easily released. Therefore, within the composite absorbent, the liquid absorbed into the continuous pores synergizes and is transferred to the superabsorbent polymer (SAP) with high liquid retention capacity, and is steadily retained within the SAP. Here, the amount of liquid absorbed into the continuous skeleton of absorbent A and the amount of liquid absorbed into the continuous pores are determined as follows: out of the total amount of liquid absorbed by absorbent A, the amount of liquid released from absorbent A during centrifugation (150G / 90 seconds) (amount of liquid released) is the amount of liquid absorbed into the continuous pores, and the remaining amount of liquid (i.e., the amount of liquid that did not release liquid from absorbent A during centrifugation) is the amount of liquid absorbed into the continuous skeleton.

[0078] Furthermore, of the liquid absorbed by absorbent A, more remains in the pores than in the hydrophilic continuous skeleton. Most of the liquid absorbed by absorbent A is achieved by retaining the liquid in the pores through capillary action, so the greater the porosity (the volume of the pores relative to the volume of absorbent A), which is the ratio of the volume of the voids in the pores (total pore volume), the more liquid can be absorbed. It is preferable that this porosity is 85% or more.

[0079] For example, when the porosity of the absorbent A shown in the above-mentioned Figs. 4 to 8 is calculated, it is as follows. First, the specific surface area of ​​absorbent A obtained by mercury porosimetry 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 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, i.e., the pore volume, is 15.5 mL, and the volume of 1 g of absorbent A is 1 mL. In this case, the total volume (volume) of 1 g of absorbent A is 15.5 + 1 (mL), and the ratio of the pore volume to that is the porosity, so the porosity of absorbent A is 15.5 / (15.5 + 1) × 100 ≒ 94%.

[0080] In the present invention, the absorbent A having such a hydrophilic continuous skeleton and continuous pores, that is, a polymeric absorbent, is applied to the composite absorbent in the form of, for example, particles or a sheet. Furthermore, as described above, this polymer absorbent exhibits a unique liquid absorption behavior in which, when absorbing liquid, the liquid is first incorporated into the hydrophilic continuous skeleton and then into the continuous pores, so that it can instantly absorb a large amount of liquid and can transfer the absorbed liquid (mainly the liquid absorbed into the continuous pores) to the SAP with high liquid retention capacity and steadily retain it within the SAP. Therefore, a composite absorbent using such a polymer absorbent can exhibit high absorption performance as an absorbent.

[0081] Here, a polymer absorbent as an example of the present invention, two types of superabsorbent polymers (SAP(A) and SAP(B)) as comparative examples, and an Infinity particle as a comparative example were prepared, and the absorption state when a predetermined amount of distilled water was dropped on each was observed by photographing it using a 3D micro X-ray CT device (CosmoScan FX (manufactured by Rigaku Corporation)). In this photographing, a sample of the polymer absorbent or the like was fixed to the bed of the device with double-sided tape, and distilled water was added from above. The photographing conditions were tube voltage: 90 kV, tube current: 88 μA, irradiation time: 2 minutes, resolution: 20 μm, matrix: 512 x 512 x 512. These observation results are shown in Figures 10 to 12. Fig. 10 is a CT image showing the absorption state of absorbent A for each drop amount of distilled water, Fig. 11 is a CT image showing the absorption state of two types of SAP for each drop amount of distilled water, and Fig. 12 is a CT image showing the absorption state of Infinity particles for each drop amount of distilled water. In Figs. 10 to 12, the white parts of each CT image correspond to the parts absorbing liquid, and each drop amount of distilled water is shown by the amount of liquid absorbed (mass) per unit mass of the absorbent such as a polymer absorbent, i.e., the liquid absorption ratio (g / g). The Infinity particles mentioned above are absorbents manufactured by P&G, and have a structure (foam structure) similar to that of polymer absorbents. However, unlike polymer absorbents, they do not have the ability to absorb liquid and expand.

[0082] As shown in FIG. 10, in the absorbent A of the present invention, as the amount of distilled water dropped (absorption capacity) increases, the hydrophilic continuous skeleton absorbs liquid and expands, causing the outer shape of the absorbent A to become larger. H After the absorption capacity reaches 10 g / g (i.e., 25% liquid absorption), the liquid absorption in the interconnected pores progresses and it becomes possible to absorb more liquid. A After reaching an absorption capacity of 60 g / g, it becomes difficult to absorb liquid, and at an absorption capacity of 90 g / g, the liquid begins to overflow, as shown in FIG.

[0083] On the other hand, in the SAPs of the comparative examples, as shown in FIG. 11, with an increase in the amount of distilled water dropped (liquid absorption ratio), both types of SAP absorbed the liquid while diffusing it uniformly within the SAP, and did not show a stepwise liquid absorption behavior as in absorbent A of the invention example. Furthermore, in the Infinity particle body of the comparative example, as shown in Figure 12, as the amount of distilled water dripped increases, liquid absorption progresses from the upper side of the Infinity particle body, and this Infinity particle body also does not show a gradual liquid absorption behavior like absorbent A of the present invention example.

[0084] As described above, absorbent A of the present invention exhibits the above-mentioned unique liquid absorption behavior not found in conventional SAP or Infinity particles, and is capable of instantly absorbing a large amount of liquid and furthermore, of transferring the absorbed liquid to the SAP with high liquid retention capacity, demonstrating excellent absorption performance.

[0085] In the present invention, the polymer absorbent has a liquid retention limit L HDuring liquid absorption, the volume of the expanded polymer absorbent is preferably larger than the volume of the absorbed liquid. Since such a polymer absorbent can absorb a larger amount of liquid into the interconnected pores, a composite absorbent containing such a polymer absorbent can exhibit higher absorption performance as an absorbent. The characteristics of such a polymer absorbent can be realized, for example, by appropriately adjusting the total pore volume of the interconnected pores and the porosity of the polymer absorbent. Here, the liquid retention limit L H The volume of the polymer absorbent expanded when absorbing liquid, and the liquid retention limit L H The volume of liquid taken up by the polymer absorbent during liquid absorption can be measured as follows.

[0086] <Liquid retention limit L H How to measure the volume of a polymer absorbent that expands when absorbing liquid> (1) 1 g of the sample (polymer absorbent) for measurement is placed in a mesh bag (NBC Meshtec Co., Ltd., N-No. 255HD 115) cut to a size of 10 cm square. The mass (g) of the mesh bag is measured in advance. (2) The mesh bag containing the sample is immersed in a 0.9% sodium chloride solution for one hour. (3) Hang the mesh bag for 5 minutes and drain, then measure its mass (g). (4) After draining the water, the mesh bag is centrifuged at 150 G for 90 seconds, and the mass (g) of the mesh bag after centrifugation is measured. (5) The liquid retention capacity (g) of the sample is calculated by subtracting the mass of the sample (=1g) and the total mass of the mesh bag from the mass of the mesh bag after centrifugation, and then this liquid retention capacity is divided by the mass of the sample (=1g) to obtain the liquid retention capacity (g / g) per unit mass of the sample (polymer absorbent). This liquid retention capacity per unit mass is the liquid retention limit L H (g / g). (6) Separately, take out 30 particles of the measurement sample (polymer absorbent), measure their mass, and further divide the mass by the number of particles (30 particles) to calculate the average mass (g) per sample particle. (7) From the 30 samples, one sample that best matches the average mass value is selected, and that sample is fixed to the bed of a 3D micro X-ray CT device (CosmoScan FX, Rigaku Corporation) with double-sided tape. (8) From above the fixed sample, measure the liquid retention limit L obtained in (5) above. H Add an amount (g) of distilled water equivalent to the amount of water added, and soak the single grain of sample in distilled water. (9) A sample containing distilled water was observed using the 3D micro X-ray CT device (tube voltage: 90 kV, tube current: 88 μA, exposure time: 2 min, resolution: 20 μm, matrix: 512 x 512 x 512), and the liquid retention limit L was calculated from the obtained CT image. H The volume (cm) of a single sample expanded at 3 ) is calculated.

[0087] In addition, the liquid retention limit L H The volume of liquid absorbed by the polymer absorbent during absorption is 1g = 1cm of distilled water. 3 As the above liquid retention limit L H Amount (g) of volume (cm 3 ) is calculated.

[0088] In addition, when the measurement sample (polymer absorbent) is recovered from the composite absorbent product, it can be obtained according to the following <Method for recovering the measurement sample (polymer absorbent)>.

[0089] <How to collect the measurement sample (polymer absorbent)> (1) Peel off the retaining sheet or the like from the composite absorbent product to expose the liquid-absorbent member. (2) The object to be measured (polymer absorbent) is dropped from the exposed liquid-absorbent member, and anything other than the (particulate) object to be measured (e.g., pulp, synthetic resin fibers, etc.) is removed using tweezers or the like. (3) A microscope or a simple magnifying glass is used as a magnifying observation means, and the measurement object is collected using tweezers or the like while observing at a magnification at which the difference from SAP can be recognized or at which the pores of the porous body can be visually recognized. The magnification of the simple magnifying glass is not particularly limited as long as the pores of the porous body can be visually recognized, and may be, for example, 25 to 50 times. (4) The objects to be measured thus collected are used as samples for measurement in various measurement methods.

[0090] Furthermore, it is preferable that the polymer absorbent has a liquid absorption capacity of the continuous pores that is greater than that of the continuous skeleton. Since such a polymer absorbent can incorporate a larger amount of liquid into the continuous pores, a composite absorbent containing such a polymer absorbent can exhibit even higher absorption performance as an absorbent. Note that such properties of the polymer absorbent can be realized, for example, by appropriately adjusting the total pore volume of the above-mentioned continuous pores or the porosity of the polymer absorbent. Here, the liquid absorption amount of the continuous pores and the liquid absorption amount of the continuous skeleton of the polymer absorbent can be measured as follows.

[0091] <Method for measuring the amount of liquid absorption of the continuous pores and the continuous skeleton of a polymer absorbent> (1) 1 g of the sample (polymer absorbent) for measurement is placed in a mesh bag (NBC Meshtec Co., Ltd., N-No. 255HD 115) cut to a size of 10 cm square. The mass (g) of the mesh bag is measured in advance. (2) The mesh bag containing the sample is immersed in a 0.9% sodium chloride solution for one hour. (3) Hang the mesh bag for 5 minutes and drain, then measure its mass (g). (4) The amount of liquid absorbed by the sample (g) is calculated by subtracting the total mass of the sample (=1g) and the mesh bag from the mass of the mesh bag after draining measured in (3) above, and then this amount of liquid absorbed is divided by the mass of the sample (=1g) to obtain the amount of liquid absorbed per unit mass of the sample (polymer absorbent) (g / g). This amount of liquid absorbed per unit mass is called the liquid absorption limit L A (g / g). (5) Furthermore, the mesh bag after draining in (3) above is centrifuged at 150 G for 90 seconds, and the mass (g) of the mesh bag after the centrifugation is measured. (6) The liquid retention amount (g) of the sample is calculated by subtracting the mass of the sample (=1g) and the total mass of the mesh bag from the mass of the mesh bag after centrifugation measured in (5) above, and then this liquid retention amount is divided by the mass of the sample (=1g) to obtain the liquid retention amount (g / g) per unit mass of the sample (polymer absorbent). This liquid retention amount per unit mass is the liquid retention limit L H (g / g), and this liquid retention limit L H is defined as the "liquid absorption amount of the continuous skeleton." (7) And the liquid absorption limit L obtained in (4) above A Liquid retention limit L H The amount (g / g) obtained by subtracting this is the "liquid absorption amount of the interconnected pores."

[0092] In addition, the polymer absorbent preferably has a mass ratio of the liquid absorption amount of the continuous pores to the liquid absorption amount of the continuous skeleton of 60:40 to 95:5. When the mass ratio of the liquid absorption amount of the continuous pores to the liquid absorption amount of the continuous skeleton of the polymer absorbent is within such a specific range, when the polymer absorbent absorbs a liquid, the liquid can be more reliably absorbed into the continuous skeleton and then into the continuous pores. In addition, such properties of the polymer absorbent can also be realized by appropriately adjusting, for example, the total pore volume of the above-mentioned continuous pores or the porosity of the polymer absorbent.

[0093] In addition, it is preferable that the polymer absorbent has a relatively high absorption rate from immediately after the start of absorption until the liquid retention limit is reached, and a relatively low absorption rate after the liquid retention limit. Here, FIG. 13 is a graph showing the relationship between the liquid absorption capacity and the amount of volume change of absorbent A, which is an example of the polymer absorbent of the present invention. As shown in FIG. 13, after the start of liquid absorption, the amount of volume change of the absorbent A increases rapidly with an increase in the liquid absorption capacity (i.e., the liquid absorption rate R 1 The liquid absorption capacity of absorbent A is the liquid retention limit L H After reaching 10 g / g, the volume change rate increases slowly (i.e., the liquid absorption rate R 2 is small). In this way, the absorbent A reaches the liquid retention limit L immediately after the start of absorption. HIn the initial stage of liquid absorption, the absorption rate is relatively high, so liquid can be instantly absorbed into the continuous skeleton. H In the later stage of liquid absorption, the absorption rate is relatively slow, so liquid can be steadily taken into the open pores expanded by the expansion of the open skeleton. This allows absorbent A to more reliably demonstrate its high absorption performance as an absorbent.

[0094] The volume change of the polymer absorbent is the above-mentioned <Liquid Retention Limit L H The volume of the polymer absorbent swelled at each absorption capacity is measured in accordance with the method for measuring the volume of the polymer absorbent swelled when absorbing liquid, and the volume is divided by the volume of the polymer absorbent before absorbing liquid, and multiplied by 100 to obtain the volume.

[0095] Hereinafter, the method for producing such a polymer absorbent will be described in detail using the above-mentioned absorbent A as an example.

[0096] [Method of manufacturing polymer absorbent] The above-mentioned absorbent A can be obtained through a cross-linking polymerization step and a hydrolysis step, as shown in Fig. 3. Each of these steps will be described below.

[0097] (Crosslinking polymerization process) First, an oil-soluble monomer for crosslinking polymerization, a crosslinkable monomer, a surfactant, water, and optionally a polymerization initiator are mixed to obtain a water-in-oil emulsion, which is an emulsion in which the oil phase is the continuous phase and water droplets are dispersed within it.

[0098] In the above-mentioned absorbent A, as shown in the upper diagram of Figure 3, butyl methacrylate, which is a (meth)acrylic acid ester, is used as the oil-soluble monomer, divinylbenzene is used as the cross-linking monomer, sorbitan monooleate is used as the surfactant, and isobutyronitrile is used as the polymerization initiator to cause cross-linking polymerization to obtain monolith A.

[0099] Specifically, for absorbent A, as shown in the upper diagram of Figure 3, first, 9.2 g of t-butyl methacrylate as an oil-soluble monomer, 0.28 g of divinylbenzene as a cross-linking monomer, 1.0 g of sorbitan monooleate (hereinafter abbreviated as "SMO") as a surfactant, and 0.4 g of 2,2'-azobis(isobutyronitrile) as a polymerization initiator are mixed and dissolved uniformly. 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 planetary stirring device, a vacuum stirring and degassing mixer (manufactured by EME), to obtain a water-in-oil emulsion.

[0100] Furthermore, this emulsion is quickly transferred to a reaction vessel, sealed, and polymerized at 60°C for 24 hours under stationary conditions. After the polymerization is completed, the contents are removed, extracted with methanol, and then dried under reduced pressure to obtain Monolith A, which has a continuous macropore structure. The internal structure of Monolith A was observed by SEM, and it was found that Monolith A had a continuous cell structure and the thickness of the continuous skeleton was 5.4 μm. 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.

[0101] The content of divinylbenzene in the total monomers is preferably 0.3 to 10 mol%, more preferably 0.3 to 5 mol%. 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-mentioned 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%.

[0102] The amount of surfactant added can be set depending on the type of oil-soluble monomer and the desired size of emulsion particles (macropores), and is preferably in the range of about 2 to 70% of the total amount of the oil-soluble monomer and surfactant.

[0103] In order to control the shape and size of the bubbles in 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 be coexisted in the polymerization system.

[0104] In addition, the mixing method for forming the water-in-oil emulsion is not particularly limited, and any mixing method can be used, such as a method of mixing all the components at once, or a method of separately and uniformly dissolving oil-soluble components such as the oil-soluble monomer, surfactant, and oil-soluble polymerization initiator, and water-soluble components such as water and the water-soluble polymerization initiator, and then mixing the respective components.

[0105] Furthermore, the mixing device for forming the emulsion is not particularly limited, and any device such as a normal mixer, homogenizer, or high-pressure homogenizer can be used depending on the desired emulsion particle size. Furthermore, a so-called planetary mixing device can also be used in which the material to be treated is placed in a mixing container and rotated while revolving around the revolution axis while tilting the mixing container, thereby stirring and mixing the material to be treated.

[0106] In addition, there are no particular limitations on the mixing conditions, and the stirring rotation speed, stirring time, etc. can be set as desired according to the desired emulsion particle size. Note that, with the above planetary stirring device, water droplets in the W / O emulsion can be uniformly generated, and the average diameter can be set as desired within a wide range.

[0107] The polymerization conditions for the water-in-oil emulsion can be various, depending on the type of monomer and initiator, etc. For example, when azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, etc. are used as the polymerization initiator, the polymerization can be carried out by heating in a sealed container under an inert atmosphere at a temperature of 30 to 100°C for 1 to 48 hours, and when hydrogen peroxide-ferrous chloride, sodium persulfate-acidic sodium sulfite, etc. are used as the polymerization initiator, the polymerization can be carried out in a sealed container under an inert atmosphere at a temperature of 0 to 30°C for 1 to 48 hours.

[0108] After the polymerization is completed, the contents are taken out and subjected to Soxhlet extraction with a solvent such as isopropanol to remove unreacted monomers and residual surfactants, thereby obtaining monolith A shown in the center diagram of Figure 3.

[0109] (Hydrolysis process) Next, the step of hydrolyzing the monolith A (crosslinked polymer) to obtain the absorbent A (hydrolysis step) will be described.

[0110] First, monolith A is immersed in dichloroethane containing zinc bromide and stirred at 40° C. for 24 hours, then contacted with methanol, 4% hydrochloric acid, 4% aqueous sodium hydroxide solution, and water in that order to carry out hydrolysis, and then dried to obtain a block-shaped absorbent A. Furthermore, this block-shaped absorbent A is crushed to a predetermined size to obtain a particulate absorbent A. The form of this absorbent A is not limited to particulate, and for example, it may be formed into a sheet during or after drying.

[0111] In addition, the method of hydrolysis of monolith A is not particularly limited, and various methods can be adopted. For example, aromatic solvents such as toluene and xylene, halogen-based solvents such as chloroform and dichloroethane, ether-based solvents such as tetrahydrofuran and isopropyl ether, amide-based solvents such as dimethylformamide and dimethylacetamide, alcohol-based solvents such as methanol and ethanol, carboxylic acid-based solvents such as acetic acid and propionic acid, or water as a solvent are contacted with a strong base such as sodium hydroxide, or a hydrohalic acid such as hydrochloric acid, a Bronsted acid such as sulfuric acid, nitric acid, trifluoroacetic acid, methanesulfonic acid, and p-toluenesulfonic acid, or a Lewis acid such as zinc bromide, aluminum chloride, aluminum bromide, titanium (IV) chloride, cerium chloride / sodium iodide, and magnesium iodide.

[0112] Furthermore, among the polymerization raw materials of the organic polymer that forms the hydrophilic continuous skeleton of the absorbent A, the (meth)acrylic acid ester is not particularly limited, but is preferably a C1 to C10 (i.e., carbon number 1 to 10) alkyl ester of (meth)acrylic acid, and more preferably a C4 (i.e., carbon number 4) alkyl ester of (meth)acrylic acid. Examples of C4 alkyl esters of (meth)acrylic acid include t-butyl (meth)acrylic acid ester, n-butyl (meth)acrylic acid ester, and iso-butyl (meth)acrylic acid ester.

[0113] Furthermore, the monomers used in the crosslinking polymerization may be only (meth)acrylic acid esters and divinylbenzene, or may contain, in addition to (meth)acrylic acid esters and divinylbenzene, other monomers other than (meth)acrylic acid esters and divinylbenzene. In the latter case, the other monomers are not particularly limited, but 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, and trimethylolpropane tri(meth)acrylate. The proportion of monomers other than (meth)acrylic acid ester and divinylbenzene in all monomers used in the crosslinking polymerization is preferably from 0 to 80 mol %, more preferably from 0 to 50 mol %.

[0114] The surfactant is not limited to the above-mentioned sorbitan monooleate, and may be any surfactant capable of forming a water-in-oil type (W / O) emulsion when the monomer for crosslinking polymerization is mixed with water. 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 dioctyl sodium sulfosuccinate, cationic surfactants such as distearyl dimethyl ammonium chloride, and amphoteric surfactants such as lauryl dimethyl betaine. These surfactants may be used alone or in combination of two or more.

[0115] In addition, the polymerization initiator is preferably a compound that generates radicals by heat and light irradiation. Furthermore, the polymerization initiator may be water-soluble or oil-soluble, and 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-acidic sodium sulfite, and tetramethylthiuram disulfide. However, in some cases, there are systems in which polymerization proceeds only by heating or light irradiation without the addition of a polymerization initiator, and in such systems, the addition of a polymerization initiator is not necessary.

[0116] The composite absorbent of the present invention is not particularly limited, but can be applied to various fields of composite absorbents such as dew condensation prevention sheets, simple soil, and other civil engineering and construction materials, base materials for medicines, and materials for absorbing leaked liquids. Therefore, the liquid to be absorbed by the composite absorbent is not particularly limited, and examples thereof include water and aqueous solutions (e.g., seawater, etc.), acids (e.g., hydrochloric acid, etc.), bases (e.g., sodium hydroxide, etc.), organic solvents (e.g., 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.

[0117] Furthermore, the present invention is not limited to the above-described embodiments, and appropriate combinations, substitutions, modifications, etc. are possible within the scope of the object and intent of the present invention. Note that in this specification, ordinal numbers such as "first" and "second" are used to distinguish the items to which the ordinal numbers are attached, and do not indicate the order, priority, importance, etc. of each item. [Explanation of symbols]

[0118] 1 Composite absorber 2. First retaining sheet 3 Second Retaining Sheet 4. Polymer absorbents 5. Superabsorbent polymer (SAP) 6 Hydrophilic fiber sheet

Claims

1. A composite absorbent for absorbing liquids for civil engineering materials, building materials, or materials for absorbing leaked liquids consisting of organic solvents (excluding cases where the use is for absorbent articles such as pants-type disposable diapers, tape-type disposable diapers, sanitary napkins, absorbent pads, disposable diapers for pets, and absorbent pads for pets), The composite absorbent body includes a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer; The polymer absorbent is a hydrolyzate of a crosslinked polymer of a (meth)acrylic acid ester and divinylbenzene, which is a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group; a ratio of crosslinked polymer residues of the divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is 0.1 to 30 mol % based on all constitutional units, The composite absorbent body as described above is characterized in that, when absorbing a liquid, the polymer absorbent incorporates the liquid into the continuous skeleton and then into the continuous pores.

2. 2. The composite absorbent according to claim 1, wherein the volume of the expanded polymer absorbent is larger than the volume of the liquid absorbed at the liquid retention limit.

3. 3. The composite absorbent according to claim 1, wherein the polymer absorbent has a liquid absorption capacity of the continuous pores greater than a liquid absorption capacity of the continuous skeleton.

4. The composite absorbent according to any one of claims 1 to 3, characterized in that the mass ratio of the liquid absorption amount of the continuous pores to the liquid absorption amount of the continuous skeleton of the polymer absorbent is 60:40 to 95:

5.

5. The composite absorbent according to any one of claims 1 to 4, characterized in that the polymer absorbent has a relatively high absorption rate from immediately after the start of absorption until it reaches a liquid retention limit, and an absorption rate after the liquid retention limit is relatively low.

6. The composite absorbent according to any one of claims 1 to 5, wherein the polymer absorbent is a monolithic absorbent.

7. A polymer absorbent used together with a superabsorbent polymer for civil engineering materials, building materials, or materials for absorbing leaked liquids consisting of organic solvents (excluding cases where the use is for absorbent articles such as pants-type disposable diapers, tape-type disposable diapers, sanitary napkins, absorbent pads, disposable diapers for pets, and absorbent pads for pets), It has a hydrophilic continuous skeleton and continuous pores, The polymer absorbent is a hydrolyzate of a crosslinked polymer of a (meth)acrylic acid ester and divinylbenzene, which is a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group; a ratio of crosslinked polymer residues of the 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 in that, when absorbing a liquid, the liquid is incorporated into the continuous framework and then into the continuous pores.

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