JP7680836B2 - Composite absorbents and polymeric absorbents - Google Patents

Description

The present invention relates to a composite absorbent and a polymer absorbent.

Absorptive bodies containing superabsorbent polymers (so-called "SAP") with high absorption capacity are known as absorbents used to absorb liquids such as aqueous solutions. As disclosed in, for example, Patent Documents 1 to 4, absorbents containing such superabsorbent polymers are used in a variety of fields, including disposable paper diapers, civil engineering and construction materials such as condensation prevention sheets and simple soil, base materials for pharmaceuticals, and materials for absorbing leaked liquids.

JP 2017-36638 A JP 2017-205225 A Japanese Unexamined Patent Publication No. 63-75016 Japanese Patent Application Publication No. 8-38893

Although such superabsorbent polymers (SAPs) can retain a large amount of liquid (i.e., have a high liquid retention capacity), they have a slow absorption rate, and therefore, in conventional absorbents such as disposable paper diapers, they are used in combination with pulp to temporarily absorb and retain liquid. In such conventional absorbents, the liquid is quickly absorbed by the pulp in the absorbent and temporarily retained within the pulp, and then transferred to the SAP with a high liquid retention capacity and retained within the SAP.
However, in such conventional absorbents, the liquid retention capacity of the pulp is low, and if the amount of liquid that can be retained is exceeded in the early stages of absorption, the liquid will diffuse and become difficult to absorb and retain by the SAP, which could result in low liquid absorption efficiency.

The present invention was made in consideration of these problems, and aims to provide an absorbent with high absorption efficiency.

One aspect of the present invention (Aspect 1) is a composite absorbent for absorbing liquid, comprising:
The present invention relates to a polymeric absorbent material having a hydrophilic continuous skeleton and continuous pores,
The polymer absorbent is a composite absorbent characterized in that the initial liquid absorption amount 5 seconds after a load of 40 g/ ^cm2 is applied is 5 g/g or more, and the liquid absorption amount after 20 seconds or more is 110% or more of the initial liquid absorption amount.

In the composite absorbent of this embodiment, the polymer absorbent, which can absorb liquids such as aqueous solutions into its continuous pores by capillary action, has the above-mentioned specific initial liquid absorption amount and liquid absorption amount after 20 seconds or more have elapsed, so that the composite absorbent has a large liquid absorption amount in the initial stage of absorption, can temporarily retain liquid, and can continue to absorb liquid even after a predetermined time has elapsed.
This allows the composite absorbent body of this embodiment to exhibit high absorption efficiency as an absorbent body.

In another aspect (Aspect 2) of the present invention, the composite absorbent of Aspect 1 above is characterized in that the composite absorbent further contains a superabsorbent polymer.

Since the composite absorbent of this embodiment contains a superabsorbent polymer (SAP) along with the above-mentioned polymer absorbent, the liquid is quickly absorbed by the polymer absorbent in the composite absorbent, temporarily retained, and then handed over to the SAP, which has a high liquid retention capacity, and retained within the SAP.
This allows the composite absorbent body of this embodiment to exhibit higher absorption efficiency.

In yet another aspect (aspect 3) of the present invention, the composite absorbent of aspect 2 above is characterized in that the amount of liquid transfer from the polymer absorbent to the superabsorbent polymer is 5.0 g/g or more.

In the composite absorbent of this embodiment, the amount of liquid transfer from the polymer absorbent to the SAP is 5.0 g/g or more, so that the liquid temporarily held by the polymer absorbent can be more reliably transferred to the SAP.
This allows the composite absorbent body of this embodiment to more reliably exhibit high absorption efficiency.

In yet another aspect (aspect 4) of the present invention, in the composite absorbent of aspect 2 or 3 above, the polymer absorbent is characterized in that the liquid discharge rate of the absorbed liquid component is 65% or more.

In this embodiment of the composite absorbent, the polymer absorbent has a liquid discharge rate of 65% or more, and the polymer absorbent easily releases the liquid components it has absorbed, so the liquid temporarily held by the polymer absorbent can be more easily transferred to the SAP.

In yet another aspect (aspect 5) of the present invention, in the composite absorbent of any of aspects 1 to 4 above, the polymer absorbent is a monolithic absorbent.

The composite absorbent of this embodiment is capable of absorbing liquid quickly because the polymer absorbent is a monolithic absorbent, and the temporarily held liquid can be transferred more reliably to the SAP.

In yet another aspect (aspect 6) of the present invention, in the composite absorbent of any of aspects 1 to 5 above, the polymer absorbent is a hydrolyzate 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.

In the composite absorbent of this embodiment, since the polymer absorbent has the above-mentioned specific configuration, when liquid is absorbed, the hydrophilic continuous skeleton is easily extended and the continuous pores are easily expanded, so that more liquid can be taken in by the continuous pores more quickly, and the absorbent can exhibit even better absorption efficiency.

Yet another aspect (aspect 7) of the present invention is a polymeric absorbent having a hydrophilic continuous skeleton and continuous pores,
The polymer absorbent is characterized in that the initial liquid absorption amount 5 seconds after a load of 40 g/ ^cm2 is applied is 5 g/g or more, and the liquid absorption amount after 20 seconds or more is 110% or more of the initial liquid absorption amount.

The polymer absorbent of this embodiment has the above-mentioned specific initial liquid absorption amount and liquid absorption amount after 20 seconds or more have elapsed, and therefore has a large liquid absorption amount in the initial stage of absorption, can temporarily retain liquid, and can absorb liquid even after a predetermined time has elapsed.
Therefore, when the polymer absorbent of this embodiment is used in an absorbent body, the absorbent body can exhibit high absorption efficiency.

The present invention provides an absorbent with high absorption efficiency.

FIG. 1 is an exploded perspective view of a composite absorbent body 1 according to one embodiment of the present invention. FIG. 2 is an exploded perspective view of a composite absorbent body 1' according to another embodiment of the present invention. FIG. 3 is a diagram illustrating a manufacturing process of absorbent A, which is an example of a polymer absorbent. FIG. 4 is a SEM photograph of absorbent A at a magnification of 50 times. FIG. 5 is a SEM photograph of absorbent A at a magnification of 100 times. FIG. 6 is a SEM photograph of absorbent A at a magnification of 500 times. FIG. 7 is a SEM photograph of absorbent A at a magnification of 1000 times. FIG. 8 is a SEM photograph of absorbent A at a magnification of 1500 times.

Hereinafter, preferred embodiments of the present invention will be described in detail using a composite absorbent body 1 as one embodiment.
In this specification, unless otherwise specified, "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" is simply referred to as "planar view."

[Composite absorbent body]
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 Figure 1 has a roughly rectangular outer shape in a plan view, and basically comprises a first retention sheet 2 that forms one surface of the composite absorbent 1 in the thickness direction, a second retention sheet 3 that forms the other surface of the composite absorbent 1, and a liquid-absorbent member that is located between these sheets and is made of a mixture of a polymer absorbent 4 and a superabsorbent polymer (SAP) 5.

The liquid-absorbent member in the composite absorbent 1 is configured to absorb and retain liquid that has permeated through the first retention sheet 2, using a polymer absorbent 4 and a highly absorbent polymer 5 having a hydrophilic continuous skeleton and continuous pores, which are located between the first retention sheet 2 and the second retention sheet 3.
Furthermore, the above-mentioned polymer absorbent 4 has a unique liquid absorption property in which the initial liquid absorption amount 5 seconds after a load of 40 g/ ^cm2 is applied is 5 g/g or more, and the liquid absorption amount after 20 seconds or more is 110% or more of the initial liquid absorption amount.

The polymer absorbent 4 can take up liquid into its continuous pores by capillary action, and further has the above-mentioned specific initial liquid absorption amount and liquid absorption amount after 20 seconds or more have passed, so that the liquid absorption amount in 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 passed.
Therefore, the composite absorbent 1 containing such a polymer absorbent 4 can exhibit high absorption efficiency as an absorbent.

Here, the load of 40 g/ ^cm2 is a load assuming a general pressure (e.g., body pressure) applied to a composite absorbent, and the liquid absorption amount after 20 seconds or more means the liquid absorption amount (mass; g/g) at any timing after 20 seconds (e.g., after 20 seconds, after 60 seconds, after 300 seconds, after 3600 seconds, etc.) from the application of the load under a specified temperature condition. The method for measuring the liquid absorption amount of the polymer absorbent under the specified load will be described later.

Furthermore, the above-mentioned amount of liquid absorption after 20 seconds or more is 110% or more of the initial amount of liquid absorption means that when the initial amount of liquid absorption after 5 seconds has elapsed is taken as 100%, the amount of liquid absorption is 110% or more.

In the present invention, the absorbent member is not limited to the composite absorbent 1 of the above embodiment, and the absorbent member may or may not contain other absorbent materials as long as it contains at least the polymer absorbent having the above-mentioned specific absorbency.

In addition, in the present invention, the configuration of the composite absorbent is not limited to the composite absorbent 1 of the above embodiment, and the composite absorbent may have 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 the composite absorbent 1' of another embodiment of the present invention shown in FIG. 2.

In the present invention, the outer shape, various dimensions, basis weight, etc. of the composite absorbent are not particularly limited as long as they do not impede 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.

The various components of the composite absorbent body of the present invention will be described in more detail below using the composite absorbent body 1 of the embodiment shown in Figure 1.

(Retaining sheet)
1, a first retention sheet 2 forming one surface of the composite absorbent body 1 has, in a plan view, a substantially rectangular outer shape 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 inner liquid-absorbent member.

The first retaining sheet 2 is slightly larger overall than the liquid-absorbent member located on the inside (i.e., compared to the area where the polymer absorbent 4, etc. are located), and is joined at its periphery to the second retaining sheet 3 located on the other side in the thickness direction of the composite absorbent 1 by any adhesive or heat-sealing means, etc.

On the other hand, the second retention sheet 3 that forms the other surface of the composite absorbent 1 has an approximately rectangular outer shape in a plan view similar to the outer shape of the composite absorbent 1. This second retention sheet 3 is formed from a liquid-impermeable sheet-like member that prevents liquid that is not absorbed and retained in the inner liquid-absorbent member and liquid that seeps out from the liquid-absorbent member from leaking out of the composite absorbent 1.

In the present invention, the sheet-like members that can be used as the first and second holding sheets are not limited to those in the above-mentioned embodiments, and the composite absorbent of the present invention may be such that at least one of the first and second holding sheets is formed from a liquid-permeable sheet-like member. In other words, the composite absorbent of the present invention may be such that either one of the first and second holding sheets is formed from a liquid-impermeable sheet-like member.

When a liquid-permeable sheet-like member is used as the retaining 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 depending on various applications and usage modes. Examples of such liquid-permeable sheet-like members include hydrophilic air-through nonwoven fabrics, spunbond nonwoven fabrics, point-bond nonwoven fabrics, and other nonwoven fabrics, woven fabrics, knitted fabrics, and porous resin films.

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.
Furthermore, 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-based resins such as polyethylene (PE) and polypropylene (PP), polyester-based resins such as polyethylene terephthalate (PET), and polyamide-based resins such as 6-nylon. These resins may be used alone or in combination of two or more types.

In addition, when a liquid-impermeable sheet-like member is used as the retaining 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. Examples of such liquid-impermeable sheet-like members include hydrophobic nonwoven fabrics formed from any hydrophobic thermoplastic resin fibers (e.g., polyolefin fibers such as PE and PP, polyester fibers such as PET, various composite fibers such as core-sheath type, etc.); perforated or non-perforated resin films formed from hydrophobic thermoplastic resins such as PE and PP; laminates in which nonwoven fabrics are bonded to the resin films; laminated nonwoven fabrics such as SMS nonwoven fabrics, etc.

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 impede the effects of the present invention, and any external 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.

(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 located between the first retaining sheet 2 and the second retaining sheet 3 as described above.

In the composite absorbent 1, the polymer absorbent 4 and the highly absorbent polymer 5 of the liquid-absorbent member are bonded to the first retaining sheet 2 and the second retaining sheet 3 described above, respectively, with any adhesive such as a hot melt adhesive, but in the composite absorbent of the present invention, the polymer absorbent does not need to be bonded to the retaining sheet.

As described above, the liquid-absorbent member contains, as an essential component, a polymer absorbent that has a hydrophilic continuous skeleton and continuous pores and has the above-mentioned unique liquid-absorbency. This polymer absorbent will be described later.

In the present invention, the liquid-absorbent member located between the first holding sheet and the second holding sheet may or may not contain other liquid-absorbent materials, so long as it contains at least the polymer absorbent having the above-mentioned specific liquid-absorbency. That is, the liquid-absorbent member may contain only the above-mentioned polymer absorbent as the liquid-absorbent material, or may further contain a liquid-absorbent material known in the art in addition to the above-mentioned polymer absorbent. Examples of such liquid-absorbent materials include hydrophilic fibers and superabsorbent polymers, and more specifically, cellulose-based fibers such as pulp fibers (e.g., ground pulp), cotton, rayon, and acetate; granules made of superabsorbent polymers (SAP) such as sodium acrylate copolymer; and mixtures of any combination of these.
For example, in the embodiment of the composite absorbent 1 shown in Figure 1, the liquid-absorbent member located between the first retention sheet 2 and the second retention sheet 3 contains a superabsorbent polymer 5 in addition to a polymer absorbent 4 that has a hydrophilic continuous skeleton and continuous pores and has the above-mentioned unique liquid-absorbency.

In the present invention, the outer shape (planar shape of the arrangement area), various dimensions, basis weight, etc. of the liquid-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 according to various applications, usage modes, etc.

(hydrophilic fiber sheet)
In addition, in the present invention, the composite absorbent may have 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), for example, as in another embodiment of the composite absorbent 1' shown in Figure 2.

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.

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, semi-synthetic cellulose fibers, etc. Furthermore, 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-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.

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 impair the effects of the present invention, and any outer shape, various dimensions, basis weight, etc. can be adopted according to various applications and usage modes, etc.

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

[Polymer absorbent]
The polymer absorbent is not particularly limited as long as it is a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and has a unique liquid absorption property in which the initial liquid absorption amount 5 seconds after a load of 40 g/ ^cm2 is applied is 5 g/g or more, and the liquid absorption amount after 20 seconds or more is 110% or more of the initial liquid absorption amount. For example, 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 can be mentioned. More specifically, 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 can be mentioned. Such a polymer absorbent is an organic porous body having at least one or more -COONa groups in one molecule, and may further have a -COOH group. The -COONa groups are distributed approximately uniformly in the skeleton of the porous body.

If the polymer absorbent is a hydrolysate 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 -COONa group, as described below, the continuous hydrophilic skeleton is more likely to extend when absorbing liquid, and the continuous pores are also more likely to expand, so that more liquid can be taken up into the continuous pores more quickly, and the absorbent can exhibit even better absorption efficiency.

In this specification, (meth)acrylic acid ester refers to acrylic acid ester or methacrylic acid ester.

In the polymer absorbent formed by the hydrolysis product of a crosslinked polymer of such a (meth)acrylic acid ester and divinylbenzene, a hydrophilic continuous skeleton is formed by an organic polymer having at least a -COONa group, and the skeleton has communicating holes (continuous pores) that serve as absorption fields for the liquid to be absorbed.
In addition, since the hydrolysis treatment converts the -COOR group (i.e., the carboxylate group) of the crosslinked polymer into a -COONa group or a -COOH group (see FIG. 3), the polymer absorbent may have a -COOR group.

The presence of -COOH groups and -COONa groups in organic polymers that form a continuous hydrophilic skeleton can be confirmed by analysis using infrared spectroscopy and a method for quantifying weakly acidic ion exchange groups.

Here, Figure 3 is a diagram explaining the manufacturing process of absorbent A, which is an example of a polymer absorbent. In this Figure 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.

The following description will use absorbent A, which is an example of a polymer absorbent and is formed from a hydrolyzate of a cross-linked polymer of (meth)acrylic acid ester and divinylbenzene.

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, when 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.

In the following description, "Monolith A" refers to an organic porous material consisting of a crosslinked polymer of a (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.

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

The organic polymer forming the 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 an ethylene group (structural unit X) in the organic polymer forming the hydrophilic continuous skeleton has a -COONa group, or both a -COOH group and a -COONa group, which are generated by hydrolysis of a carboxylate group. When the polymerization monomer is a (meth)acrylic acid ester, the polymerized residue of an ethylene group (structural unit X) has a -COONa group, a -COOH group, and an ester group.

In the absorbent A, the ratio of the crosslinked polymerized 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 %, relative to 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 polymerized 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 %, relative to the total structural units.
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 the 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.

In absorbent A, the organic polymer forming the hydrophilic continuous skeleton may consist only of structural units X and Y, or may contain, in addition to structural units X and Y, structural units other than structural units X and Y, i.e., polymerized residues of monomers other than (meth)acrylic acid esters and divinylbenzene.

Examples of constituent units other than the constituent unit X and the constituent 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.

In addition, the ratio of structural units other than structural unit X and 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 the total structural units.

In addition, it is preferable that the thickness of the hydrophilic continuous skeleton of absorbent A is 0.1 to 100 μm. If the thickness of the hydrophilic continuous skeleton of 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, if the thickness of the hydrophilic continuous skeleton is 100 μm or less, an excellent absorption speed is more likely to be obtained.

The pore structure of the hydrophilic continuous skeleton of absorbent A is an open-cell structure, so the thickness of the continuous skeleton is measured at the cross-section of the skeleton that appears on the test piece for electron microscope measurement. The continuous skeleton is often polygonal in shape, as it is formed by the spaces between water (water droplets) that are removed in the dehydration and drying process after hydrolysis. Therefore, the thickness of the continuous skeleton is the average value of the diameters (μm) of circles circumscribing the polygonal cross-section. In rare cases, small holes may be present within the polygon, in which case the circumscribing circle of the polygonal cross-section surrounding the small holes is measured.

Furthermore, it is preferable that the average diameter of the interconnected pores of absorbent A is 1 to 1000 μm. When the average diameter of the interconnected pores of 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 the interconnected pores is 1000 μm or less, an excellent absorption rate is more likely to be obtained.

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 this 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.

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 absorbent A shown in these Figs. 4 to 8 is an example of an absorbent having butyl methacrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, and each has a cubic structure of 2 mm square.

The absorbent A shown in Figures 4 to 8 has numerous bubble-like macropores, and further has portions where these bubble-like macropores overlap. The 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 (continuous macropore structure).

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, most of which 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.

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

The total pore volume of the pores (voids) of absorbent A is preferably 0.5 to 50 mL/g, and more preferably 2 to 30 mL/g. If the total pore volume of 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, if the total pore volume of absorbent A is 50 mL/g or less, the strength of absorbent A is less likely to decrease.

The total pore volume can be measured by mercury intrusion porosimetry. The sample used to measure 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 ionic form of absorbent A. The final pressure reached is 0 Torr.

Below, we will explain what happens when absorbent A comes into contact with liquid, but the same applies when liquid comes into contact with a liquid-absorbent member or composite absorbent containing absorbent A.

First, the continuous pores of absorbent A shown in Figures 4 to 8 are pores in which multiple pores (voids) are interconnected, and the presence of a large number of voids can be seen with the naked eye from the outside. When liquid comes into contact with absorbent A, which has such a large number of voids, a certain amount of liquid enters the large number of voids due to capillary action and is absorbed into absorbent A. At this time, a portion of the liquid absorbed into absorbent A is absorbed into the hydrophilic continuous skeleton by osmotic pressure, and the continuous skeleton is extended. Meanwhile, the liquid absorbed into absorbent A that is not absorbed into the hydrophilic continuous skeleton is absorbed while remaining within the pores.

Thus, absorbent A has the property that the hydrophilic continuous skeleton extends when it absorbs liquid. This extension of the continuous skeleton occurs in almost all directions. Furthermore, as the external shape of absorbent A increases due to this extension of the continuous skeleton, the size of each pore also increases. When the size of the pores increases in this way, the volume within the pores increases, and the amount of liquid that can be retained within the pores also increases. In other words, absorbent A, which has become larger by absorbing a certain amount of liquid, can absorb a further predetermined amount of liquid into the enlarged pores due to capillary action.
Furthermore, since the absorbent A absorbs liquid by capillary action, it can quickly absorb liquid.

More of the liquid absorbed by absorbent A remains in the pores than in the hydrophilic continuous skeleton. Most of the liquid absorbed by absorbent A is retained in the pores by 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.

For example, the porosity of the absorbent A shown in the above-mentioned FIGS.
First, the specific surface area of absorbent A obtained by mercury intrusion 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%.

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 has a unique liquid absorption property in which the initial liquid absorption amount 5 seconds after a load of 40 g/ ^cm2 is applied is 5 g/g or more, and the liquid absorption amount after 20 seconds or more is 110% or more of the initial liquid absorption amount.

Such a polymer absorbent can absorb liquid into its continuous pores by capillary action, and further has the above-mentioned specific initial liquid absorption amount and liquid absorption amount after 20 seconds or more have passed, so that the amount of liquid absorption in the initial stage of absorption is large, and the polymer absorbent can temporarily retain liquid and can continue to absorb liquid even after a predetermined time has passed.
As a result, the composite absorbent of the present invention containing such a polymer absorbent can exhibit high absorption efficiency as an absorbent.
The initial liquid absorption amount of the polymer absorbent and the liquid absorption amount after a predetermined time have elapsed can be measured as follows.

<Method for measuring liquid absorption amount under specific load>
(1) 25 g of 0.9% sodium chloride solution is placed in a petri dish with a pedestal (inner diameter: 85 mm, depth: 20 mm, pedestal arrangement: two pedestals arranged parallel to each other with an interval of 24 mm in the center of the bottom (inner side), pedestal width: 2 mm, pedestal height: 2 mm, pedestal length: 25 mm). This measurement method is performed under conditions of a temperature of 25°C and a humidity of 60%.
(2) 0.16 g of a measurement sample (polymer absorbent) is placed in a plastic cylinder (inner diameter: 26 mm, outer diameter: 32 mm, height: 33 mm) with a nylon mesh material (NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh/2.54 cm, opening: 57 μm, line diameter: 43 μm, thickness: 75 μm)) attached to the bottom, and the measurement sample (polymer absorbent) is spread evenly. When the measurement sample (polymer absorbent) is recovered from the composite absorbent product and used, it can be obtained according to the <Method of recovering measurement sample (polymer absorbent)> described later.
(3) A cylindrical plastic piston (diameter: 25 mm, mass: 5 g) is placed on the sample in the cylinder, and a weight of a specified mass (200 g; for a load of 40 g/ ^cm2 ) is then placed 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 base in the center of the petri dish, and immerse the bottom of the cylinder in the above-mentioned aqueous sodium chloride solution to allow the sample in the cylinder to absorb the aqueous sodium chloride solution.
(5) After a predetermined time has elapsed (for example, after 5 seconds, 20 seconds, 60 seconds, 300 seconds, 3600 seconds, etc.), the cylinder is pulled out, tilted 45° and drained for 1 minute, and the mass (g) of the cylinder is measured.
(6) The amount of liquid absorbed by the sample (g) is calculated by subtracting the mass of the cylinder before liquid absorption measured in (3) above from the mass of the cylinder after liquid absorption measured in (5) above, and the amount of liquid absorbed by the sample (= 0.16 g) is further divided by the mass of the sample to obtain the amount of liquid absorbed per unit mass of the sample (polymer absorbent) (g/g).
The amount of absorption (g/g) when the specified time (i.e., the absorption time) in (5) above is 5 seconds is the "initial amount of absorption 5 seconds after application of a load of 40 g/ ^cm2 ," and the amount of absorption (g/g) when the absorption time is 20 seconds or longer is the "amount of absorption after 20 seconds or longer."

When using the above-mentioned measurement sample (polymer absorbent) recovered from a composite absorbent product, it can be obtained as follows.

<Method of collecting the measurement sample (polymer absorbent)>
(1) The retaining sheet or the like is peeled off from the composite absorbent product to expose the liquid-absorbent member.
(2) All absorbent materials including the object to be measured (polymer absorbent) are dropped from the exposed absorbent member, and the absorbent materials other than the (particulate) object to be measured (e.g., pulp, synthetic resin fiber, etc.) are removed using tweezers or the like.
(3) A microscope or a simple loupe 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 loupe is not particularly limited as long as the pores of the porous body can be visually recognized, and examples of the magnification include 25 to 50 times.
(4) The measurement objects thus collected are used as samples for measurement in various measurement methods.

Here, a polymer absorbent as an example of the present invention, pulp fiber (fluff pulp) as a comparative example, Infinity particles as a comparative example, and a superabsorbent polymer (SAP) as a comparative example were prepared, and the initial liquid absorption amount and the liquid absorption amount after a predetermined time were measured under a specific load (i.e., under a load of 40 g/ ^cm2 ) and under no load (i.e., under a load of ⁰ g/cm2). The measurement results of the liquid absorption amount are shown in Table 1 below.
The above-mentioned Infinity particles are an absorbent 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.

As shown in Table 1, the polymer absorbent, like the pulp fiber and Infinity particle body, has a larger amount of liquid absorbed in the initial stage of absorption than SAP, both under a specific load and without a load. Furthermore, while the pulp fiber and Infinity particle body both reach saturation in terms of the amount of liquid absorbed after 20 seconds or more have passed, the polymer absorbent continues to absorb more liquid even after such a certain time has passed, demonstrating that it has a unique and excellent liquid absorption property not found in conventional pulp fiber, Infinity particle body, SAP, etc.

In addition, in the present invention, it is preferable that the composite absorbent further contains a conventional superabsorbent polymer (SAP) in addition to the polymer absorbent, as in the embodiment shown in Figure 1 above. When the composite absorbent contains SAP together with the polymer absorbent, the liquid is quickly absorbed and temporarily held by the polymer absorbent in the composite absorbent, and then the liquid is transferred to the SAP, which has a high liquid retention capacity, and held within the SAP, so that the absorbent can exhibit higher absorption efficiency.

Furthermore, when the composite absorbent contains such a polymer absorbent and SAP, the amount of liquid transfer from the polymer absorbent to the SAP is preferably 5.0 g/g or more. If the amount of liquid transfer from the polymer absorbent to the SAP is 5.0 g/g or more, the liquid temporarily held by the polymer absorbent can be more reliably transferred to the SAP, so that the absorbent can more reliably exhibit high absorption efficiency. The amount of liquid transfer from the polymer absorbent to the SAP is more preferably 23.0 g/g or more, even more preferably 27.0 g/g or more, and particularly preferably 33.0 g/g or more.
The amount of liquid migration from the polymer absorbent to the SAP can be measured as follows.

<Method for measuring the amount of liquid migration from polymer absorbent to SAP>
(1) 0.3 g of a sample for measurement (polymer absorbent) is placed in a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) with a nylon mesh material (NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh/2.54 cm, opening: 57 μm, line diameter: 43 μm, thickness: 75 μm)) attached to the bottom surface, and the mass (g) of the cylinder is measured. This measurement method is performed under conditions of a temperature of 25° C. and a humidity of 60%. When the sample for measurement (polymer absorbent) is recovered from a composite absorbent product and used, it can be obtained according to the above-mentioned <Method for recovering a sample for measurement (polymer absorbent)>.
(2) Place a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) into a petri dish (inner diameter: 85 mm, depth: 20 mm) and sprinkle 0.3 g of superabsorbent polymer (SAP) evenly into the cylinder. Then, remove the cylinder and measure the mass (g) of the petri dish.
(3) 60 mL of 0.9% sodium chloride aqueous solution is placed in a petri dish with a pedestal (inner diameter: 85 mm, depth: 20 mm, pedestal arrangement: two pedestals arranged parallel to each other with an interval of 24 mm in the center of the bottom (inner surface), pedestal width: 2 mm, pedestal height: 2 mm, pedestal length: 25 mm).
(4) Place a cylinder containing a measurement sample (polymer absorbent) on the central base of a pedestal-equipped petri dish, immerse the bottom of the cylinder in the above-mentioned sodium chloride aqueous solution, and allow the sample in the cylinder to absorb the sodium chloride aqueous solution for 3 minutes.
(5) After absorbing the liquid for 3 minutes, the cylinder is pulled out, tilted at a 45° angle, and drained for 1 minute, and then the mass (g) of the cylinder is measured.
(6) The mass (g) of the cylinder after absorbing the liquid, measured in (5) above, is subtracted from the mass (g) of the cylinder before absorbing the liquid, measured in (1) above, to calculate the amount of liquid absorbed by the sample (g). This amount of liquid absorbed is then divided by the mass of the sample (=0.3 g) to obtain the amount of liquid absorbed per unit mass of the sample (g/g).
(7) Then, the cylinder after draining in (5) above is placed on top of the petri dish containing the SAP, and the sample in the cylinder and the SAP in the petri dish are brought into contact with each other via the bottom surface (mesh material) of the cylinder.
(8) Three minutes after the sample and the SAP have been in contact with each other, the cylinder is removed and the mass (g) of the dish is measured.
(9) The mass (g) of the petri dish measured in (8) above is subtracted by the mass (g) of the petri dish measured in (2) above to calculate the amount of liquid absorbed by the SAP (g). This amount of liquid absorbed is then divided by the mass of the sample (=0.3 g) to obtain the amount of liquid absorbed by the SAP per unit mass of the sample (g/g), i.e., the amount of liquid transferred to the SAP per unit mass of the sample (g/g).

Furthermore, when the composite absorbent contains the above-mentioned polymer absorbent and SAP, the polymer absorbent preferably has a liquid discharge rate of 65% or more for the absorbed liquid component. If the liquid discharge rate of the polymer absorbent is 65% or more, the polymer absorbent is more likely to release the absorbed liquid component, so that the liquid temporarily held by the polymer absorbent can be more easily transferred to the SAP. The liquid discharge rate of the polymer absorbent is more preferably 70% or more, and particularly preferably 75% or more.
The liquid discharge rate of the polymer absorbent can be measured as follows.

<Method for measuring the liquid discharge rate of polymer absorbent>
(1) 1 g of a measurement sample (polymer absorbent) is cut into a 10 cm square mesh bag (NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh/2.54 cm, opening: 57 μm, line diameter: 43 μm, thickness: 75 μm)) and enclosed. The mass (g) of the mesh bag is measured in advance. This measurement method is performed under conditions of a temperature of 25° C. and a humidity of 60%. Furthermore, when the measurement sample (polymer absorbent) is recovered from a composite absorbent product and used, it can be obtained according to the above-mentioned <Recovery method of measurement sample (polymer absorbent)>.
(2) The mesh bag containing the sample is immersed in a 0.9% sodium chloride solution for one hour.
(3) The mesh bag is hung for 5 minutes and the water is drained, after which the mass (g) is measured.
(4) The amount of liquid absorbed by the sample (g) is calculated 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 the amount of liquid absorbed by the sample (= 1 g) is then divided by the mass of the sample (= 1 g) to obtain the amount of liquid absorbed per unit mass of the sample (polymer absorbent) (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 mass (g) obtained by subtracting the mass of the sample (= 1 g) and the total mass of the mesh bag from the mass of the mesh bag after centrifugation measured in (5) above is subtracted from the liquid absorption amount (g) of the sample calculated in (4) above to calculate the liquid discharge amount (g) of the sample, and the liquid discharge amount (g) per unit mass of the sample (polymer absorbent) is obtained by dividing this liquid discharge amount by the mass (= 1 g) of the sample.
(7) The liquid discharge amount per unit mass obtained in (6) above is divided by the liquid absorption amount per unit mass obtained in (4) above, and the result is multiplied by 100 to obtain the liquid discharge amount relative to the liquid absorption amount of the sample (polymer absorbent), i.e., the liquid discharge rate (%).

The manufacturing method for such a polymer absorbent will be explained in detail below, using the above-mentioned absorbent A as an example.

[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.

(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.

As shown in the upper diagram of Figure 3, the above-mentioned absorbent A uses butyl methacrylate, which is a (meth)acrylic acid ester, as the oil-soluble monomer, divinylbenzene as the cross-linking monomer, sorbitan monooleate as the surfactant, and isobutyronitrile as the polymerization initiator to cross-link and polymerize the materials to obtain monolith A.

Specifically, for absorbent A, as shown in the upper diagram of FIG. 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 Corporation) to obtain a water-in-oil emulsion.

The emulsion is then quickly transferred to a reaction vessel, sealed, and polymerized at 60°C for 24 hours under static conditions. After polymerization is complete, the contents are removed, extracted with methanol, and dried under reduced pressure to obtain Monolith A, which has a continuous macropore structure. When the internal structure of Monolith A was observed using an SEM, it was found that Monolith A had a continuous cell structure, with a continuous skeleton thickness of 5.4 μm. The average diameter of the continuous pores, measured using mercury intrusion porosimetry, was 36.2 μm, and the total pore volume was 15.5 mL/g.

The content of divinylbenzene relative to the total monomers is preferably 0.3 to 10 mol%, and 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%, and 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%.

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

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; and cyclic ethers such as tetrahydrofuran and dioxane may be allowed to coexist in the polymerization system.

The mixing method for forming the water-in-oil emulsion is not particularly limited, and any mixing method can be used, such as mixing all the components at once, or dissolving the oil-soluble components (oil-soluble monomer, surfactant, and oil-soluble polymerization initiator) separately and the water-soluble components (water and water-soluble polymerization initiator) uniformly, and then mixing the respective components.

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 mixing and stirring the material to be treated.

There are also no particular limitations on the mixing conditions, and the stirring speed, stirring time, etc. can be set as desired depending on the desired emulsion particle size. The planetary stirring device described above can generate water droplets uniformly in the W/O emulsion, and the average diameter can be set as desired within a wide range.

Polymerization conditions for water-in-oil emulsions can vary depending on the type of monomer and initiator. For example, when azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, etc. are used as the polymerization initiator, 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. When hydrogen peroxide-ferrous chloride, sodium persulfate-acidic sodium sulfite, etc. are used as the polymerization initiator, 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.

After the polymerization is complete, the contents are removed and Soxhlet extraction is performed with a solvent such as isopropanol to remove unreacted monomers and residual surfactants, yielding monolith A, as shown in the center of Figure 3.

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

First, monolith A is immersed in dichloroethane containing added 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 for hydrolysis, and then dried to obtain a block of absorbent A. This block of absorbent A is then crushed to a predetermined size to obtain particulate absorbent A. Note that the form of absorbent A is not limited to particulate, and it may be formed into a sheet during or after drying, for example.

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 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 are contacted with a strong base such as sodium hydroxide, or with a hydrohalic acid such as hydrochloric acid, a Brønsted 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.

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 the C4 alkyl ester of (meth)acrylic acid include t-butyl (meth)acrylic acid, n-butyl (meth)acrylic acid, and iso-butyl (meth)acrylic acid.

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 0 to 80 mol %, more preferably 0 to 50 mol %.

The surfactant is not limited to the above-mentioned sorbitan monooleate, and may be any surfactant capable of forming a water-in-oil (W/O) emulsion when the crosslinking polymerization monomer 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.

The polymerization initiator is preferably a compound that generates radicals by heat and light irradiation. 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.

The composite absorbent of the present invention can be applied to a variety of fields, including, but not limited to, civil engineering and construction materials such as condensation prevention sheets and simple soil, base materials for medicines, and materials for absorbing leaked liquids. Therefore, the liquid to be absorbed by the composite absorbent is also not particularly limited, and examples thereof 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.

The present invention is not limited to the above-described embodiments, and suitable combinations, substitutions, modifications, etc. are possible within the scope of the purpose 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.

1 Composite absorbent 2 First retention sheet 3 Second retention sheet 4 Polymer absorbent 5 Superabsorbent polymer (SAP)
6 Hydrophilic fiber sheet

Claims (6)

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 present invention relates to a polymeric absorbent material having 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 to all constitutional units is 0.1 to 30 mol %;
The (meth)acrylic acid ester contains a C4 alkyl ester of (meth)acrylic acid,
The polymer absorbent has an initial liquid absorption amount of 8 g/g or more 5 seconds after a load of 40 g/ ^cm2 is applied, and an absorption amount after 20 seconds or more is 137.5% or more of the initial liquid absorption amount. The composite absorbent body according to claim 1, characterized in that the composite absorbent body further contains a superabsorbent polymer. The composite absorbent according to claim 2, characterized in that the amount of liquid transferred from the polymer absorbent to the superabsorbent polymer is 5.0 g/g or more. The composite absorbent according to claim 2 or 3, characterized in that the polymer absorbent has a liquid discharge rate of 65% or more of the absorbed liquid component. The composite absorbent according to any one of claims 1 to 4, characterized in that the polymer absorbent is a monolithic absorbent. A 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 (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 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 to all constitutional units is 0.1 to 30 mol %;
The (meth)acrylic acid ester contains a C4 alkyl ester of (meth)acrylic acid,
A polymer absorbent characterized in that the initial liquid absorption amount 5 seconds after a load of 40 g/ ^cm2 is applied is 8 g/g or more, and the liquid absorption amount after 20 seconds or more is 137.5% or more of the initial liquid absorption amount.

Images