Composite absorbent and high molecular absorbent

Abstract

Provided is a composite absorbent for sanitary products, which has excellent absorbency and inhibits a decrease in the amount of liquid absorbed relative to the pore volume. A composite absorbent for sanitary products (4) for absorbing liquid includes a high-molecular absorbent having a continuous skeleton and continuous pores. In the high-molecular absorbent, the proportion of the pore volume of pores having a pore radius of 1 μm or more is 90% or more of the total pore volume.

Description

Technical Field

[0001] This invention relates to composite absorbers and polymeric absorbents. Background Technology

[0002] Absorbents for absorbing liquids such as aqueous solutions include porous materials such as sponge materials. For example, Patent Document 1 discloses an absorbent article containing a polymer foam material comprising a hydrophilic flexible structure of interconnected continuous air bubbles.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Patent No. 3231320 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] According to the inventors' research in this case, porous materials such as the polymer foam material in Patent Document 1 have a large number of pores with smaller pore radii. However, in porous structures, liquid components tend to easily enter pores with larger pore radii. Therefore, in porous materials with many small-diameter pores as described above, there is a concern that during liquid absorption, the liquid component will not enter the small-diameter pores, resulting in a decrease in the amount of liquid absorbed relative to the pore volume.

[0008] The present invention was made in view of this problem, and aims to provide a composite absorbent and a polymer absorbent that can suppress the decrease in liquid absorption volume relative to the pore volume and have excellent absorption performance.

[0009] Technical solutions for solving the problem

[0010] One aspect of the present invention (Aspect 1) is a composite absorbent for use in sanitary products for absorbing liquids, comprising a continuous hydrophilic skeleton and a polymer absorbent with continuous pores, wherein the proportion of the pore volume of pores with a pore radius of 1 μm or more in the polymer absorbent is 90% or more of the total pore volume.

[0011] For the composite absorbent of this method, the proportion of pore volume with a pore radius of 1 μm or larger in the polymer absorbent is more than 90% of the total pore volume. Therefore, during liquid absorption, liquid has difficulty entering pores with pore radii smaller than 1 μm. Even if it cannot enter, liquid can still enter pores with a pore radius of 1 μm or larger, ensuring sufficient liquid absorption. Thus, the situation where the liquid absorption volume decreases relative to the pore volume can be suppressed, resulting in excellent absorption performance.

[0012] Furthermore, in another aspect (aspect 2) of the present invention, in the composite absorbent of aspect 1 described above, the proportion of the pore volume of pores with a pore radius of 0.005 μm or less in the polymer absorbent is less than 10% of the total pore volume.

[0013] For the composite absorber of this method, the proportion of pore volume of pores with a pore radius of less than 0.005 μm, which are very small and difficult to absorb liquid, is very small, while the proportion of pore volume of pores with a pore radius of more than 1 μm, which are large and capable of absorbing liquid, is large. Therefore, the pores of the polymer absorbent can be effectively used for liquid absorption, ensuring sufficient liquid absorption.

[0014] In another embodiment of the present invention (Amendment 3), in the composite absorber of Embodiment 1 or 2 above, the maximum pore volume in the polymer absorbent corresponds to a pore radius of 500 μm or less.

[0015] For the composite absorbent of this method, by setting the pore radius corresponding to the maximum pore volume to below 500 μm, the structural damage (collapse) of the continuous skeleton of the polymer absorbent can be suppressed during liquid absorption, making it easier to obtain excellent absorption rate and stably ensuring sufficient liquid absorption (when the pore radius is above 500 μm at the maximum pore volume, the continuous skeleton structure cannot be maintained during liquid absorption, and there is a concern about collapse).

[0016] In another embodiment of the present invention (Amendment 4), in the composite absorber of any one of Embodiments 1 to 3 above, the coefficient of variation of the pore distribution in the polymer absorbent with a pore radius of 1 μm or more is 1.4 or less.

[0017] For the composite absorber of this method, since the variation coefficient of the pore distribution is less than 1.4, the deviation of the pore radius from the average pore radius is small, and the peak value of the pore distribution becomes sharp near the average pore radius. Therefore, the polymeric absorbent can absorb liquid approximately uniformly from all directions / all surfaces. Thus, the pores of the polymeric absorbent can be effectively used for liquid absorption, ensuring sufficient liquid absorption.

[0018] In another embodiment of the present invention (Amendment 5), in the composite absorbent of any one of Embodiments 1 to 3 above, in the polymer absorbent, the variation coefficient of the pore distribution in the pores with a pore radius of 1 μm or more exceeds 1.4.

[0019] For the composite absorbent of this method, since the coefficient of variation of the pore distribution exceeds 1.4, the deviation of the pore radius from the average pore radius is large, and the peak value of the pore distribution becomes wider near the average pore radius. That is, in the polymeric absorbent, there are both small and large pores. Therefore, in pores with small pore radii, capillary forces are more likely to occur, thus the liquid absorption rate tends to be faster; in pores with large pore radii, the liquid absorption volume tends to be larger. Thus, through the synergistic effect of these two factors, the polymeric absorbent can instantaneously absorb a large amount of liquid inside the pores.

[0020] In another aspect of the invention (aspect 6), in the composite absorbent described in aspect 5 above, in the polymer absorbent, for the pore radius corresponding to the maximum value of the pore volume in the curve representing the pore distribution, the portion on the side with the larger pore radius is wider than the portion on the side with the smaller pore radius.

[0021] For the composite absorbent of this method, the polymeric absorbent has the aforementioned structure, namely, a structure in which there are more pores with large pore diameters than pores with small pore radii. Because there are more pores with large pore radii, the liquid absorption volume can be increased, allowing for the absorption of a larger amount of liquid within the pores.

[0022] In another aspect of the invention (aspect 7), in the composite absorbent described in aspect 5 above, in the polymer absorbent, for the pore radius corresponding to the maximum value of the pore volume in the curve representing the pore distribution, the portion on the side with the smaller pore radius is wider than the portion on the side with the larger pore radius.

[0023] For the composite absorbent of this method, the polymeric absorbent has the aforementioned structure, namely, a structure in which there are more pores with small pore diameters than pores with large pore radii. Because there are more pores with small pore radii, capillary forces are more easily exerted, thus the liquid absorption rate is faster, and liquid can be absorbed more instantaneously inside the pores.

[0024] In another embodiment of the invention (e.g., embodiment 8), in the composite absorbent of any one of embodiments 1 to 3, there are at least two maxima of pore volume in the curve representing the pore distribution of the polymer absorbent.

[0025] In this composite absorbent, the polymeric absorbent possesses the aforementioned structure: pores with a given small pore radius and its vicinity, and pores with a given large pore radius and its vicinity. Therefore, in pores with relatively small pore radii, capillary forces readily exert their influence, resulting in faster liquid absorption; in pores with relatively large pore radii, the liquid absorption volume readily increases. Thus, through the synergistic effect of these two factors, the polymeric absorbent can instantaneously absorb a large amount of liquid within the pores.

[0026] In another aspect of the invention (aspect 9), in the composite absorbent described in aspect 8 above, in the polymer absorbent, the maximum value of the relatively smaller pore radius is larger than the maximum value of the relatively larger pore radius among the two maxima of the pore volume in the curve representing the pore distribution.

[0027] In this composite absorbent, the polymeric absorbent exhibits the aforementioned structure, meaning that there are more pores with smaller pore radii than with larger pore radii. Because there are more pores with smaller pore radii, capillary forces are more easily activated, the liquid absorption rate is faster, and liquid can be absorbed more instantaneously within the pores.

[0028] In another aspect of the invention (aspect 10), in the composite absorbent described in aspect 8 above, in the polymer absorbent, the maximum value of the relatively smaller pore radius is smaller than the maximum value of the relatively larger pore radius among the two maxima of the pore volume in the curve representing the pore distribution.

[0029] In this type of composite absorbent, the polymeric absorbent has the aforementioned structure, meaning that there are more pores with larger pore diameters than pores with smaller pore radii. Because there are more pores with larger pore radii, the liquid absorption volume can be increased, allowing for the absorption of a larger amount of liquid within the pores.

[0030] In another embodiment of the present invention (e.g., embodiment 11), in the composite absorbent described in any one of embodiments 1 to 10, the total pore volume of the polymer absorbent is 0.9 mL / g or more.

[0031] In this composite absorbent, the total pore volume of the polymer absorbent is 0.9 mL / g or more, thus ensuring sufficient pore volume and consequently, sufficient liquid absorption. Furthermore, the spaces (pores) used to absorb the target liquid as a porous body are less likely to collapse during absorption, preventing a decrease in absorption volume and rate.

[0032] In another embodiment of the invention (e.g., embodiment 12), in the composite absorbent described in any one of embodiments 1 to 11, the bulk density of the polymer absorbent is 0.07 to 0.6 g / cm³. 3 .

[0033] In this type of composite absorbent, the bulk density of the polymeric absorbent is 0.07–0.6 g / cm³. 3 Therefore, the absorption rate (DW) can be set to 6 mL / 30 sec or higher. That is, the absorption rate is faster, so the polymer absorbent can absorb liquid more instantly inside the pores.

[0034] In another embodiment of the present invention (e.g., embodiment 13), in the composite absorbent described in any one of embodiments 1 to 12 above, the polymer absorbent is a monolithic absorbent.

[0035] In this type of composite absorbent, the polymer absorbent is a monolithic absorbent, thus enabling it to rapidly absorb liquids.

[0036] In another embodiment of the invention (e.g., embodiment 14), in the composite absorbent of any one of embodiments 1 to 13 above, the polymer absorbent is a hydrolysate of a crosslinked polymer of (meth)acrylate and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group.

[0037] For the composite absorbent of this method, the polymer absorbent has the above-mentioned specific structure, so that when absorbing liquid, the hydrophilic continuous skeleton is easy to elongate and the continuous pores are easy to widen. Therefore, more liquid can be drawn into the continuous pores more quickly, and the absorbent can perform better absorption performance.

[0038] In addition, another aspect of the present invention (aspect 15) is a polymeric absorbent having a hydrophilic continuous framework and continuous pores, wherein the proportion of the pore volume of pores with a pore radius of 1 μm or more is 90% or more of the total pore volume.

[0039] For the polymeric absorbent of this method, the proportion of pore volume with a pore radius of 1 μm or larger is more than 90% of the total pore volume. Therefore, during liquid absorption, even if the liquid does not enter pores with smaller pore radii (less than 1 μm), sufficient liquid absorption can be ensured. This prevents the liquid absorption from decreasing relative to the pore volume, resulting in excellent absorption performance.

[0040] Invention Effects

[0041] According to the present invention, a composite absorbent that can suppress the decrease in liquid absorption volume relative to the pore volume and has excellent absorption performance, and a sanitary product having the composite absorbent, can be provided. Attached Figure Description

[0042] Figure 1 This is an exploded perspective view of the composite absorber 1 as an embodiment of the present invention.

[0043] Figure 2 This is an exploded perspective view of the composite absorber 1' as another embodiment of the present invention.

[0044] Figure 3 This diagram illustrates the manufacturing process of an example of a polymeric absorbent, namely absorbent A.

[0045] Figure 4 This is a SEM image of absorbent A at 50x magnification.

[0046] Figure 5 This is a SEM image of absorbent A at 100x magnification.

[0047] Figure 6 This is a SEM image of absorbent A at 500x magnification.

[0048] Figure 7 This is a SEM image of absorbent A at 1000x magnification.

[0049] Figure 8 This is a SEM image of absorbent A at 1500x magnification.

[0050] Figure 9 A graph showing the relationship between the pore radius and the cumulative pore volume of absorbent A.

[0051] Figure 10 A graph showing the relationship between the pore radius and differential pore volume of absorbent A.

[0052] Figure 11 A graph showing the relationship between bulk density and absorption capacity (DW) in absorbent A.

[0053] Figure 12 This is a schematic diagram illustrating the measuring apparatus used in the pressureless DW method. Detailed Implementation

[0054] Hereinafter, a preferred embodiment of the present invention will be described in detail using composite absorber 1 as one embodiment.

[0055] In addition, unless otherwise stated, in this specification, "an object (e.g., a composite absorber, etc.) placed on a horizontal surface in an unfolded state as viewed from the upper vertical side in the thickness direction of the object" is simply referred to as "top view".

[0056] [Complex Absorber]

[0057] Figure 1 This is an exploded perspective view of the composite absorber 1 as one embodiment of the present invention.

[0058] Figure 1 The composite absorbent 1 shown has a generally rectangular shape when viewed from above, and includes, in the thickness direction: a first retaining sheet forming one side of the surface of the composite absorbent 1; a second retaining sheet 3 forming the other side of the composite absorbent 1; and a liquid-absorbing member located between these sheets and containing a polymer absorbent 4.

[0059] Furthermore, the liquid-absorbing component in the composite absorbent 1 is configured such that a polymer absorbent 4 with a hydrophilic continuous skeleton and continuous pores located between the first retaining sheet 2 and the second retaining sheet 3 can absorb and retain liquid that permeates through the first retaining sheet 2.

[0060] Furthermore, the aforementioned polymeric absorbent 4 exhibits the following unique liquid absorption behavior: when absorbing liquid, it draws the liquid into the continuous skeleton and then into the continuous pores.

[0061] When the aforementioned polymer absorbent 4 absorbs liquids such as aqueous solutions, its hydrophilic continuous skeleton expands by instantly absorbing the liquid through osmotic pressure, thereby enlarging the volume of the continuous pores. This allows the liquid to be drawn into the enlarged continuous pores, thus enabling the instantaneous absorption of a large amount of liquid. The absorbed liquid is then transferred to the SAP with high water retention capacity and can be accurately maintained within the SAP.

[0062] Therefore, the composite absorber 1 containing this polymer absorbent 4 can perform high absorption performance as an absorber.

[0063] Furthermore, in this invention, the liquid-absorbing component is not limited to the composite absorbent 1 described in the above embodiments. The liquid-absorbing component may or may not contain other liquid-absorbing materials, as long as it contains at least a polymeric absorbent exhibiting the aforementioned unique liquid-absorbing behavior. For example, such as... Figure 2 As shown in another embodiment of the present invention, the liquid-absorbing member located between the first retaining sheet 2 and the second retaining sheet 3 can be composed of a mixture of a polymeric absorbent 4 and a superabsorbent polymer 5 (SAP).

[0064] Furthermore, in this invention, the structure of the composite absorber is not limited to the composite absorber 1 described in the above embodiment; for example, the composite absorber may be as follows: Figure 2 As shown in another embodiment of the invention, the composite absorbent 1' can have a hydrophilic fiber sheet 6 located between the first retaining sheet 2 and the liquid-absorbing member (i.e., the polymer absorbent 4 and the superabsorbent polymer 5).

[0065] In this invention, the shape, size, weight, etc. of the composite absorbent are not particularly limited as long as they do not hinder the effect of this invention. Any shape (e.g., round, oblong, polygonal, hourglass, or other designed shapes), size, weight, etc., corresponding to various uses and methods of use can be adopted.

[0066] In the following, examples are used Figure 1 The composite absorber 1 of the illustrated embodiment will be described in more detail to illustrate the various components of the composite absorber of the present invention.

[0067] (Keep the sheet)

[0068] exist Figure 1 In the composite absorbent 1 shown, the first retaining sheet 2 forming one side surface of the composite absorbent 1 has a generally rectangular shape that is the same as the shape of the composite absorbent 1 when viewed from above. The first retaining sheet 2 is formed of a liquid-permeable sheet member that allows liquid supplied to the composite absorbent 1 to pass through and be absorbed and retained by the liquid-absorbing member on the inside.

[0069] Compared to the absorbent member disposed on the inner side (i.e., compared to the area where absorbent materials such as polymer absorbent 4 are disposed), the first retaining sheet 2 has a slightly larger overall size, and at the periphery, it is joined to the second retaining sheet 3 located on the other side of the thickness direction of the composite absorbent 1 by any adhesive or thermal fusion unit.

[0070] On the other hand, the second retaining sheet 3 forming the other side of the surface of the composite absorbent 1 has a generally rectangular shape that is the same as the shape of the composite absorbent 1 when viewed from above. The second retaining sheet 3 is formed of a liquid-impermeable sheet member that prevents liquid that is not absorbed and retained by the inner absorbent member, or liquid that seeps out from the absorbent member, from leaking to the outside of the composite absorbent 1.

[0071] In this invention, the sheet-like members that can be used as the first retaining sheet and the second retaining sheet are not limited to the sheet-like members of the above embodiments. For the composite absorbent of this invention, it is sufficient that at least one of the first retaining sheet and the second retaining sheet is formed of a liquid-permeable sheet-like member. That is, for the composite absorbent of this invention, at least one of the first retaining sheet and the second retaining sheet can be formed of a liquid-impermeable sheet-like member.

[0072] Furthermore, when using a sheet material as a liquid-permeable sheet member, the liquid-permeable sheet member is not particularly limited as long as it does not hinder the effects of the present invention, and any liquid-permeable sheet member corresponding to various uses and methods of application can be used. Examples of such liquid-permeable sheet members include nonwoven fabrics, woven fabrics, knitted fabrics, porous resin films, etc., which are hydrophilic and breathable, spunbond nonwoven fabrics, dot-bonded nonwoven fabrics, etc.

[0073] Furthermore, when using hydrophilic nonwoven fabrics, woven fabrics, knitted fabrics, etc. (hereinafter collectively referred to as "fiber sheets") as liquid-permeable sheet components, these fiber sheets can have a single-layer structure or a multi-layer structure with two or more layers. The type of structural fiber in the fiber sheets is not particularly limited; examples include cellulose-based fibers and hydrophilic fibers such as thermoplastic resin fibers that have undergone hydrophilic treatment. These fibers can be used alone or in combination of two or more fibers.

[0074] Cellulose-based fibers, which can be used as structural fibers in fiber sheets, include, for example, natural cellulose fibers (e.g., plant fibers such as cotton), regenerated cellulose fibers, refined cellulose fibers, and semi-synthetic cellulose fibers. Furthermore, thermoplastic resin fibers, which can also be used as structural fibers in fiber sheets, include, for example, fibers made from known thermoplastic resins such as olefin resins like polyethylene (PE) and polypropylene (PP), polyester resins like polyethylene terephthalate (PET), and polyamide resins like 6-nylon. These resins can be used alone or in combination of two or more resins.

[0075] Furthermore, when using a liquid-impermeable sheet member as the retaining sheet, the liquid-impermeable sheet member is not particularly limited as long as it does not hinder the effect of the present invention, and any liquid-impermeable sheet member corresponding to various uses and methods of use can be adopted. Examples of such liquid-impermeable sheet 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.), porous or non-porous resin films formed from hydrophobic thermoplastic resins such as PE and PP, laminates formed by bonding nonwoven fabrics to resin films, and laminated nonwoven fabrics such as SMS nonwoven fabrics.

[0076] In this invention, the shape, size, weight, etc. of the sheet are not particularly limited as long as they do not hinder the effect of this invention. Any shape (e.g., round, oblong, polygonal, hourglass, or other designed shapes), size, weight, etc., corresponding to various uses and methods of use can be adopted.

[0077] (Absorbent component)

[0078] exist Figure 1 In the composite absorbent 1 shown, as described above, the liquid-absorbing component is configured to absorb and retain liquid that permeates through the first retaining sheet 2 via a continuous hydrophilic skeleton and a continuous porous polymer absorbent 4 located between the first retaining sheet 2 and the second retaining sheet 3.

[0079] In addition, in the composite absorbent 1, the polymer absorbent 4 of the liquid-absorbing component is bonded to each of the first retaining sheet 2 and the second retaining sheet 3 by any adhesive such as a hot-melt adhesive. However, in the composite absorbent of the present invention, the polymer absorbent may not be bonded to the retaining sheet.

[0080] Furthermore, as described above, in this invention, the liquid-absorbing component comprises a continuous hydrophilic framework and a continuous porous polymeric absorbent exhibiting the aforementioned unique liquid-absorbing behavior. The polymeric absorbent will be described later.

[0081] In this invention, the absorbent member located between the first retaining sheet and the second retaining sheet may or may not include other absorbent materials, provided that it is an absorbent member that includes at least the aforementioned polymeric absorbent. That is, even if the absorbent member is an absorbent member that only includes the aforementioned polymeric absorbent as an absorbent material, it may also be an absorbent member that includes absorbent materials known in the art in addition to the aforementioned polymeric absorbent. Examples of such absorbent materials include, for example, hydrophilic fibers, superabsorbent polymers, and more specifically, pulp fibers (e.g., pulverized pulp), cotton, rayon, cellulose fibers such as acetate, granules composed of superabsorbent polymers (SAP) such as sodium acrylate copolymers, and mixtures thereof.

[0082] For example, in Figure 2 In the composite absorbent 1' of another embodiment of the present invention shown, in addition to the particulate polymer absorbent 4 having a hydrophilic continuous skeleton and continuous pores and having the specific particle size described above, the liquid-absorbing member located between the first retaining sheet 2 and the second retaining sheet 3 also includes a highly absorbent polymer 5.

[0083] Furthermore, in this invention, the shape (top view of the area where the absorbent material is disposed), various sizes, weight, etc. of the absorbent member are not particularly limited as long as they do not hinder the effect of this invention. Any shape, various sizes, weight, etc., corresponding to the desired absorbency, softness, strength, etc., can be adopted.

[0084] (Hydrophilic fiber sheet)

[0085] In this invention, for example, such as Figure 2 As shown in the other embodiment of the composite absorbent 1', the composite absorbent may also have a hydrophilic fiber sheet 6 between the first retaining sheet 2 and the liquid-absorbing member (i.e., the polymer absorbent 4 and the superabsorbent polymer 5).

[0086] In this invention, the hydrophilic fiber sheet that can be used in the composite absorbent is not particularly limited as long as it does not hinder the effect of this invention, and any hydrophilic fiber sheet that corresponds to various uses and methods of application can be used. Examples of such hydrophilic fiber sheets include hydrophilic nonwoven fabrics, woven fabrics, and knitted fabrics. In addition, the hydrophilic fiber sheet can have a single-layer structure or a multi-layer structure with two or more layers.

[0087] The types of structural fibers used in the hydrophilic fiber sheets are not particularly limited; examples include cellulose fibers and thermoplastic resin fibers that have undergone hydrophilic treatment. These fibers can be used alone or in combination of two or more fibers.

[0088] Furthermore, cellulose-based fibers, which can be used as structural fibers for hydrophilic fiber sheets, include, for example, natural cellulose fibers (e.g., plant fibers such as cotton), regenerated cellulose fibers, refined cellulose fibers, and semi-synthetic cellulose fibers. Additionally, thermoplastic resin fibers, which can be used as fiber structures for hydrophilic fiber sheets, include, for example, fibers composed of known thermoplastic resins such as olefin resins like PE and PP, polyester resins like PET, and polyamide resins like 6-nylon. These resins can be used alone or in combination of two or more resins.

[0089] In this invention, the shape, size, and weight of the hydrophilic fiber sheet are not particularly limited as long as they do not hinder the effect of the invention. Any shape, size, and weight corresponding to various uses and methods of use can be adopted.

[0090] The polymeric absorbent used in the composite absorber of the present invention will be described in more detail below.

[0091] [Polymer absorbent]

[0092] In this invention, the polymeric absorbent is not particularly limited as long as it possesses a hydrophilic continuous framework and continuous pores, and exhibits the following characteristic liquid absorption behavior: when absorbing liquid, the liquid is first drawn into the continuous framework, and then into the continuous pores. Examples of such polymeric absorbents include hydrolysates of cross-linked polymers containing at least two or more monomers of (meth)acrylate, and examples of polymeric compounds having at least one hydrophilic group among their functional groups. More specifically, examples of hydrolysates are hydrolysates of cross-linked polymers of (meth)acrylate and compounds comprising two or more vinyl groups in one molecule, and examples of polymeric compounds having at least a -COONa group. The polymeric absorbent in question is an organic porous body having at least one -COONa group in one molecule, and may also have a -COOH group. The -COONa groups are distributed substantially uniformly in the framework of the porous body.

[0093] If the polymeric absorbent is a hydrolysate of a cross-linked polymer of such (meth)acrylate and a compound containing two or more vinyl groups in one molecule, and is a polymeric absorbent containing at least one -COONa group, then, as described later, when absorbing liquids such as aqueous solutions, the hydrophilic continuous skeleton becomes more easily elongated (i.e., more easily expanded), and the continuous pores also easily widen, thus enabling more liquid to be absorbed into the continuous pores more quickly. Therefore, composite absorbents including such polymeric absorbents can exhibit superior absorption performance as absorbents.

[0094] In addition, in this specification, (meth)acrylate refers to acrylate or methacrylate.

[0095] In the polymeric absorbent formed from the hydrolysate of this crosslinked polymer of (meth)acrylate and divinylbenzene, a hydrophilic continuous skeleton is formed by an organic polymer having at least -COONa groups, with interconnecting pores (continuous pores) between the skeletons that serve as absorption sites for liquids.

[0096] Furthermore, the hydrolysis process converts the -COOR groups (i.e., carboxylic acid ester groups) of the crosslinked polymer into -COONa groups or -COOH groups (see reference). Figure 2 Therefore, polymeric absorbents can have -COOR groups.

[0097] The presence of -COOH and -COONa groups in organic polymers that form a hydrophilic continuous backbone can be confirmed by analysis using infrared spectrophotometry and quantitative methods for weakly acidic ion-exchange groups.

[0098] Here, Figure 3 This diagram illustrates the manufacturing process of absorbent A, an example of a polymeric absorbent. Figure 3 The top diagram shows the raw materials for polymerization, the middle diagram shows the cross-linked polymer of (meth)acrylate and divinylbenzene, i.e., material A, and the bottom diagram shows the absorbent A obtained by hydrolyzing and drying material A from the middle diagram.

[0099] The following is an example of a polymeric absorbent, namely absorbent A, which is formed from the hydrolysate of a crosslinked polymer of (meth)acrylate and divinylbenzene.

[0100] In addition, as a polymeric absorbent, it is not limited to absorbent A, but can be a hydrolysate of a cross-linked polymer of (meth)acrylate and a compound having two or more vinyl groups in one molecule, or a hydrolysate of a cross-linked polymer of at least two or more monomers including (meth)acrylate, etc.

[0101] However, if the polymeric absorbent is a monolithic absorbent, it has the advantage of being able to quickly absorb liquids and more accurately transfer liquids temporarily held in the polymeric absorbent to the SAP.

[0102] Additionally, in the following description, “monolithic material A” refers to an organic porous body composed of a cross-linked polymer of (meth)acrylate and divinylbenzene before hydrolysis treatment, sometimes referred to as “monolithic organic porous body”.

[0103] Furthermore, "Absorbent A" is a hydrolysate of a cross-linked polymer (material A) of (meth)acrylate and divinylbenzene that has undergone hydrolysis and drying treatment. Additionally, in the following description, Absorbent A refers to the absorbent in its dried state.

[0104] First, the structure of absorbent A will be explained.

[0105] As described above, absorbent A has a hydrophilic continuous framework and continuous pores. For example... Figure 3 As shown, the organic polymer with a hydrophilic continuous skeleton, namely absorbent A, is obtained by cross-linking the polymer monomer (meth)acrylate and the cross-linking monomer (divinylbenzene), and then hydrolyzing the resulting cross-linked polymer (material A).

[0106] Organic polymers that form a hydrophilic continuous backbone have ethylene polymeric residues (hereinafter referred to as "constituent unit X") and divinylbenzene crosslinking polymeric residues (hereinafter referred to as "constituent unit Y") as constituent units.

[0107] Furthermore, the ethylidene polymer residues (constituent unit X) in the organic polymer forming a hydrophilic continuous backbone have two groups: a -COONa group generated by the hydrolysis of a carboxylic acid ester group, or a -COOH group and a -COONa group. Additionally, when the polymerizing monomer is a (meth)acrylate, the ethylidene polymer residues (constituent unit X) have a -COONa group, a -COOH group, and an ester group.

[0108] In absorbent A, the proportion of divinylbenzene crosslinking polymer residues (constituent unit Y) in the organic polymer forming a hydrophilic continuous backbone is, for example, 0.1 to 30 mol% relative to the total constituent units, preferably 0.1 to 20 mol%. For example, in absorbent A using butyl methacrylate as a polymerizing monomer and divinylbenzene as a crosslinking monomer, the proportion of divinylbenzene crosslinking polymer residues (constituent unit Y) in the organic polymer forming a hydrophilic continuous backbone is, for example, about 3% relative to the total constituent units, preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%.

[0109] Furthermore, if the proportion of cross-linked polymer residues of divinylbenzene in the organic polymer forming the hydrophilic continuous backbone is 0.1 mol% or more, the strength of absorbent A becomes difficult to reduce. In addition, if the proportion of cross-linked polymer residues of divinylbenzene is 30 mol% or less, the amount of liquid absorbed by the target liquid becomes difficult to reduce.

[0110] Furthermore, in absorbent A, the organic polymer forming the hydrophilic continuous backbone can be an organic polymer consisting only of constituent units X and Y, or, in addition to constituent units X and Y, it can also have polymer residues of monomers other than (meth)acrylate and divinylbenzene.

[0111] Examples of constituent units other than constituent unit X and constituent unit Y include polymer residues of monomers such as styrene, α-methylstyrene, vinyltoluene, vinyl benzyl chloride, glycidyl acrylate, isobutylene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, methacrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate.

[0112] In addition, the proportion of constituent units other than constituent unit X and constituent unit Y in the organic polymer that forms a hydrophilic continuous backbone is, for example, 0 to 50 mol% relative to the total constituent units, preferably 0 to 30 mol%.

[0113] Furthermore, the thickness of the hydrophilic continuous framework of absorbent A is preferably 0.1 to 100 μm. If the thickness of the hydrophilic continuous framework of absorbent A is 0.1 μm or more, the spaces (pores) used to absorb liquid from the porous body become less prone to collapse during absorption, and the liquid absorption rate becomes less likely to decrease. On the other hand, if the thickness of the hydrophilic continuous framework is 100 μm or less, it becomes easier to obtain an excellent absorption rate.

[0114] Furthermore, since the hydrophilic continuous skeleton of absorbent A has a continuous bubble structure, the skeleton cross-section appearing in the test piece measured by electron microscopy is used as the evaluation area for thickness measurement. Because the continuous skeleton is formed by the spacing of water (droplets) removed during the dehydration and drying process after hydrolysis, it is often polygonal in shape. Therefore, the thickness of the continuous skeleton is set as the average value of the diameter (μm) of the circle circumscribed around the polygonal cross-section. In addition, there are very few cases where small holes are formed within the polygon; in these cases, the circumscribed circle of the polygonal cross-section surrounding the small hole is measured.

[0115] Furthermore, the average diameter of the continuous pores in absorbent A is preferably 1 to 1000 μm. If the average diameter of the continuous pores in absorbent A is 1 μm or more, the space (pores) used to absorb liquid from the porous body becomes less prone to collapse during absorption, and the absorption rate becomes less likely to decrease. On the other hand, if the average diameter of the continuous pores is 1000 μm or less, it becomes easier to obtain an excellent absorption rate.

[0116] Furthermore, the average diameter (μm) of the continuous pores in absorbent A can be measured by mercury infiltration, using the maximum value of the pore distribution curve obtained by the mercury infiltration method. For the sample used to measure the average diameter of the continuous pores, regardless of the ionic type of absorbent A, the sample is obtained by drying in a vacuum desiccator at a temperature set to 50°C for at least 18 hours. Additionally, the final pressure is set to 0 Torr.

[0117] Here, Figure 4 This is a SEM image of absorbent A at 50x magnification. Figure 5 This is a SEM image of absorbent A at 100x magnification. Figure 6 This is a SEM image of absorbent A at 500x magnification. Figure 7 This is a SEM image of absorbent A at 1000x magnification. Figure 8 This is a SEM image of absorbent A at 1500x magnification.

[0118] These Figures 4-8 The absorbent A shown is an example of an absorbent that uses butyl methacrylate as a polymerizing monomer and divinylbenzene as a crosslinking monomer, and has a cubic structure of 2 mm square.

[0119] Figures 4-8 The absorbent A shown has a large number of bubble-like macropores, and these bubble-like macropores also have overlapping portions. The absorbent A has a continuous bubble structure, which is the opening (mesopore) shared by the overlapping portions of these macropores, and thus becomes a continuous bubble structure (continuous macropore structure).

[0120] The overlapping portions of these macropores form a common opening (mesopore) with an average diameter of 1–1000 μm in the dry state, preferably 10–200 μm, and particularly preferably 20–100 μm; this majority of the opening constitutes an open-pore structure. If the average diameter of the mesopores in the dry state is 1 μm or more, the absorption rate of the liquid to be absorbed becomes better. On the other hand, if the average diameter of the mesopores in the dry state is 1000 μm or less, the absorbent A becomes less prone to embrittlement.

[0121] In addition, the number of overlapping large holes in a single large hole is about 1 to 12, with most being about 3 to 10.

[0122] Furthermore, absorbent A, by having this continuous bubble structure, can uniformly form macropore groups and mesopore groups, and compared with the particulate aggregated porous material described in Japanese Patent Application Publication No. 8-252579, it has the advantage of significantly increasing the micropore volume and specific surface area.

[0123] The absorbent A has continuous pores consisting of multiple interconnected micropores (cavities). The total micropore volume of the absorbent A is preferably 0.5–50 mL / g, more preferably 0.9–40 mL / g, and even more preferably 2–30 mL / g. By ensuring the total micropore volume of the absorbent A is 0.5 mL / g or more, sufficient micropore volume is ensured, thus ensuring sufficient liquid absorption. Furthermore, the spaces (cavities) used to absorb liquid from the porous body are less likely to collapse during absorption, preventing a decrease in liquid absorption volume and absorption rate. On the other hand, when the total micropore volume of the absorbent A is 50 mL / g or less, the strength of the absorbent A is less likely to decrease.

[0124] Furthermore, the total pore volume can be measured using the mercury infiltration method. Regardless of the ionicity of absorbent A, the sample used for measuring the total pore volume is a substance dried in a vacuum desiccator at a temperature set to 50°C for at least 18 hours. The final pressure is set to 0 Torr. Using this mercury infiltration method, the cumulative pore volume distribution (relationship between pore radius and cumulative pore volume), the log differential pore volume distribution (relationship between pore radius and log differential pore volume), etc., can be obtained. The total pore volume (mL / g), average pore radius (μm), maximum pore radius (μm), pore volume (mL / g) of pores above (or below) a given pore radius, percentage (%), and coefficient of variation of pore volume, etc., can be calculated. Additionally, the maximum pore diameter (μm) refers to the pore radius of the pore that represents the maximum pore volume. Furthermore, the pore volume (mL / g) at each pore radius is calculated using the log differential pore volume (mL / g) from the log differential pore volume distribution.

[0125] Here, in the pores (voids) of absorbent A, the proportion of the pore volume of pores with a pore radius of 1 μm or more is 90% or more, preferably 93% or more, and more preferably 95% or more. By ensuring that the proportion of the pore volume of pores with a pore radius of 1 μm or more is 90% or more, during liquid absorption, liquid components are less likely to enter pores with smaller pore radii (less than 1 μm). Even if they cannot enter, sufficient liquid absorption is ensured. Therefore, the decrease in liquid absorption relative to the pore volume can be suppressed, resulting in excellent absorption performance.

[0126] In the pores of absorbent A, it is preferable that the proportion of the pore volume of pores with a pore radius of 0.005 μm or less is less than 10% of the total pore volume (total pore volume), more preferably, the proportion of the pore volume of pores with a pore radius of 0.05 μm or less is less than 10% of the total pore volume (total pore volume). In absorbent A, the proportion of the pore volume of pores with a pore radius of 0.005 μm or less, which are very small and difficult to absorb liquid, is very small, while the proportion of the pore volume of pores with a pore radius of 1 μm or more, which are large and capable of absorbing liquid, is large (90% or more). Therefore, the pores of absorbent A can be effectively used for liquid absorption, ensuring a sufficient liquid absorption volume.

[0127] Furthermore, in the pores of absorbent A, the pore radius in the pores representing the maximum pore volume is preferably (0.5 μm or more) and 500 μm or less, more preferably 300 μm or less, and even more preferably 150 μm or less. By setting the pore radius corresponding to the maximum pore volume to 500 μm or less, the structural disruption (collapse) of the continuous framework of absorbent A can be suppressed during liquid absorption, making it easier to obtain excellent absorption rates and stably ensuring sufficient liquid absorption. When the pore radius corresponding to the maximum pore volume is 500 μm or more, the structure of the continuous framework cannot be maintained during liquid absorption, raising concerns about collapse.

[0128] Furthermore, in the pores of absorbent A, the coefficient of variation of the pore distribution (pore volume) in pores with a pore radius of 1 μm or more can be 1.4 or less. When the coefficient of variation of the pore distribution is 1.4 or less, the deviation of the pore radius from the average pore radius is small, and the peak value of the pore distribution becomes sharp near the average pore radius. Therefore, absorbent A can absorb liquid approximately uniformly from all directions / all surfaces. Thus, the pores of the polymer absorbent can be effectively used for liquid absorption, ensuring sufficient liquid absorption.

[0129] On the other hand, in the pores of absorbent A, the coefficient of variation of the pore distribution (pore volume) in pores with a pore radius of 1 μm or more can exceed 1.4. In this case, since the coefficient of variation of the pore distribution exceeds 1.4, the deviation of the pore radius from the average pore radius is large, and the peak value of the pore distribution becomes wider near the average pore radius. That is, absorbent A contains both small and large pores. Therefore, in pores with small pore radii, capillary forces are more likely to function, thus increasing the liquid absorption rate; in pores with large pore radii, the liquid absorption volume is more likely to increase. Therefore, through the synergistic effect of both, absorbent A can instantly absorb a large amount of liquid inside the pores.

[0130] Here, in the pores of absorbent A, when the peak shown in the pore distribution broadens, the portion on the side with the larger pore radius corresponding to the maximum value of the pore volume in the curve representing the pore distribution can be wider than the portion on the side with the smaller pore radius. In this case, absorbent A has a structure in which there are more pores with larger pore diameters than pores with smaller pore radii. Therefore, since there are more pores with larger pore radii, the liquid absorption volume can easily become larger, and a larger amount of liquid can be absorbed inside the pores.

[0131] On the other hand, even when the peak shown in the pore distribution of absorbent A broadens, the portion on the side with the smaller pore radius can still be wider than the portion on the side with the larger pore radius, for the pore radius corresponding to the maximum value of the pore volume in the curve representing the pore distribution. In this case, absorbent A has a structure in which there are more pores with smaller pore diameters than pores with larger pore radii. Because there are more pores with smaller pore radii, capillary forces are more easily exerted, thus the liquid absorption rate is more easily increased, and liquid can be absorbed more instantaneously inside the pores.

[0132] Furthermore, within the pores of absorbent A, at least two maxima of pore volume can exist in the curve representing the pore distribution. In this case, absorbent A contains pores with a given small pore radius and its vicinity, and pores with a given large pore radius and its vicinity. Therefore, in pores with relatively small pore radii, capillary forces are more readily applied, resulting in faster liquid absorption; conversely, in pores with relatively large pore radii, the liquid absorption volume is more readily increased. Thus, through the synergistic effect of both, the polymeric absorbent can instantaneously absorb a large amount of liquid within the pores.

[0133] Here, in the case where there are two maxima of pore volume in the pores of absorbent A, the maxima of the smaller pore radius can be larger than the maxima of the larger pore radius in the curve representing the pore distribution. In this case, there are more pores with smaller pore radii than pores with larger pore radii in absorbent A. Because there are more pores with smaller pore radii, capillary forces are more easily exerted, thus the liquid absorption rate is faster, and liquid can be absorbed more instantaneously inside the pores.

[0134] On the other hand, even when there are two maximum pore volumes in the pores of absorbent A, the maximum value of the smaller pore radius is smaller than the maximum value of the larger pore radius among the two maximum pore volume values ​​in the curve representing the pore distribution. In this case, absorbent A has more pores with larger pore diameters than pores with smaller pore radii. Because there are more pores with larger pore radii, the liquid absorption volume is more easily increased, and a larger amount of liquid component can be absorbed inside the pores.

[0135] Furthermore, the bulk density within the fine pores of absorbent A is preferably 0.07–0.6 g / cm³. 3 More preferably, it is 0.1–0.4 g / cm³. 3 More preferably, it is 0.15–0.35 g / cm³. 3 In this case, as described later, the absorption rate (DW) can be set to 6 mL / 30 sec. or higher, more preferably 10 mL / 30 sec. or higher, and even more preferably 12 mL / 30 sec. or higher. That is, because the absorption rate is faster, the polymeric absorbent can absorb liquid more instantly inside the pores.

[0136] <Method for measuring aspiration rate (DW)>

[0137] The absorption rate of the absorbent was measured using the Demand Wettability (DW) method without pressure. Figure 12 This is a schematic diagram showing the measuring apparatus used in the unpressurized Demand-Wettability (DW) method. As this measuring apparatus, a Demand-Wettability (DW) device (manufactured by Taiyo Creation Co., Ltd.) 11 is used. As shown, the DW device 11 includes a burette 12 (50 ml graduation capacity, 86 cm length, 1.05 cm inner diameter), a rubber stopper 13, an air inlet capillary tube (3 mm inner diameter at the tip) 14, a stopcock 15, a stopcock 16, a measuring stage 17, a liquid outlet (3 mm inner diameter) 18, a cylinder 19, and a test solution 20. A conduit (7 mm inner diameter) is installed from the burette 12 to the measuring stage 17. A 0.9% sodium chloride aqueous solution is used as the test solution. The measurement is performed in a constant temperature and humidity (RH) atmosphere at 25°C and 50% humidity.

[0138] The measurement steps are as follows.

[0139] (1) With the two stopcocks 15 and 16 of the DW device 11 closed, add the test solution 20 to above the 0 point (the top of the scale of the burette 12 (0ml line)), place the rubber stopper 13 on the top of the burette 12 and seal it.

[0140] (2) After placing the filter paper on the liquid outlet 18 of the measuring platform 17, open the two stopcocks 15 and 16, use the filter paper to draw up the liquid coming out of the liquid outlet 18, and align the liquid level with the 0 point. After adjustment, close the stopcocks 15 and 16.

[0141] (3) Place a 100% wood pulp paper towel on the measuring table 17, centering it on the liquid outlet 18 (visually estimated at 15±1 gsm, measured pressure of 3 g / cm using a nonwoven fabric thickness gauge). 2 The thickness at that time was 0.1±0.02mm.

[0142] (4) Place the 30mm diameter cylinder 19 in the center of the paper towel, and place the test object (polymer absorbent) inside with the liquid outlet 18 as the center. The test object is placed in the cylinder 19 and is constrained by the cylinder 19.

[0143] (5) Open the stopcocks 15 and 16. The test object begins to absorb the test liquid 20. The time when the first bubble introduced from the air into the capillary tube 14 reaches the water surface of the test liquid 20 in the burette 12 (the time when the water surface of the test liquid 20 in the burette 12 drops) is taken as the measurement start time.

[0144] (6) Continue to read the decrease in test solution 20 in burette 12 (the amount of test solution 20 absorbed by the test object) M (ml).

[0145] (7) The amount of the test object absorbed after a given time (30 seconds in this embodiment) from the start of absorption is calculated by the absorption amount (ml / g) of the DW method = M (ml) / (weight (g) of the test object (polymer absorbent)).

[0146] The following description describes the situation when absorbent A is in contact with the liquid; however, the same applies to the situation when the liquid-absorbing component or composite absorbent 4, which includes absorbent A, is in contact with the liquid. Furthermore, since the mass of the absorbed liquid is approximately proportional to the liquid volume, the mass of the liquid will sometimes be referred to simply as "liquid volume" in the following description.

[0147] first, Figures 4-8 The absorbent A shown has a continuous network of interconnected pores, which are visually apparent to the naked eye. When a liquid comes into contact with absorbent A, which has a large number of pores, the hydrophilic continuous framework initially absorbs a portion of the liquid instantaneously through osmotic pressure, causing it to elongate (i.e., expand). This elongation of the continuous framework occurs almost omnidirectionally. Absorbent A, which expands by absorbing a constant amount of liquid, can further absorb a given amount of liquid into the enlarged continuous pores through capillary action. Thus, absorbent A exhibits the following unique liquid absorption behavior: when absorbing liquid, it first draws the liquid into the hydrophilic continuous framework and then into the continuous pores for absorption.

[0148] In addition, the liquid absorbed within the hydrophilic continuous skeleton of absorbent A is difficult to release from the continuous skeleton (i.e., difficult to leave the liquid), while the liquid absorbed within the continuous pores is easy to release. Therefore, within the composite absorbent, the liquid absorbed within the continuous pores leaves the liquid and is transferred to the highly absorbent polymer (SAP) with high liquid retention capacity, and is precisely retained within the SAP.

[0149] Here, regarding the amount of liquid absorbed within the continuous framework and the amount of liquid absorbed within the continuous pores of absorbent A, of the total amount of liquid absorbed by absorbent A, the amount of liquid released from absorbent A through centrifugation (150G / 90 seconds) (liquid separation) becomes the amount of liquid absorbed within the continuous pores, while the remaining amount of liquid (i.e., the amount of liquid that did not separate from absorbent A through centrifugation) becomes the amount of liquid absorbed within the continuous framework.

[0150] Furthermore, for the liquid absorbed by absorbent A, more liquid is retained within the pores than within the hydrophilic continuous framework. Since most of the liquid absorption based on absorbent A occurs through capillary action, retaining the liquid within the pores, a higher porosity (the volume of pores relative to the volume of absorbent A) results in greater liquid absorption. Preferably, this porosity is 85% or higher.

[0151] For example, to find the above Figures 4-8 The porosity of absorbent A shown is as described below.

[0152] First, the specific surface area of ​​absorbent A obtained by mercury impregnation is 400 m². 2 / g, the pore volume is 15.5mL / g. This pore volume of 15.5mL / g means that the pore volume of 1g of absorbent A is 15.5mL.

[0153] Assuming the specific gravity of absorbent A is 1 g / mL, then the volume occupied by the micropores in 1 g of absorbent A, i.e., the micropore volume, is 15.5 mL, and the volume of 1 g of absorbent A is 1 mL.

[0154] Thus, the total volume of 1g of absorbent A is 15.5+1 (mL), and the ratio of the pore volume is the porosity. Therefore, the porosity of absorbent A is 15.5 / (15.5+1)×100≈94%.

[0155] Furthermore, in this invention, absorbent A, i.e., polymeric absorbent, which possesses such a hydrophilic continuous skeleton and continuous pores, is suitable for composite absorbents in the form of granules, flakes, etc.

[0156] Furthermore, as described above, this polymeric absorbent exhibits the following unique liquid absorption behavior: when absorbing liquid, it draws the liquid into the hydrophilic continuous framework and then into the continuous pores, thus enabling it to absorb a large amount of liquid instantaneously. The absorbed liquid (mainly the liquid absorbed by the continuous pores) is then transferred to the highly water-retaining SAP and precisely held within the SAP. Therefore, composite absorbers using this polymeric absorbent can perform high absorption performance as absorbers.

[0157] The liquid absorption capacity of the polymer absorbent can be measured according to the following <Method for Measuring the Liquid Absorption Capacity of Polymer Absorbents>.

[0158] <Methods for measuring the liquid absorption capacity of polymeric absorbents>

[0159] (1) Seal 1g of the sample (polymer absorbent) for measurement into a mesh bag cut to 10cm square (manufactured by NBCMeshtec Co., Ltd., N-NO255HD 115 (specifications: width: 115cm, 255 mesh / 2.54cm, opening: 57μm, wire diameter: 43μm, thickness: 75μm)). The mass (g) of the mesh bag is measured beforehand. Furthermore, this measurement method is performed at a temperature of 25°C and a humidity of 60%. Moreover, when the sample (polymer absorbent) for measurement is recovered and used from a hygiene product, it can be obtained according to the <Method for Recovering the Sample (Polymer Absorbent) for Measurement> described later.

[0160] (2) Immerse the mesh bag containing the sample in a 0.9% sodium chloride aqueous solution for 1 hour.

[0161] (3) The mass (g) of the net bag after it has been suspended for 5 minutes and drained is measured.

[0162] (4) The liquid absorption 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 filtered mesh bag measured in (3) above. Then, the liquid absorption amount per unit mass of the sample (polymer absorbent) is obtained by dividing the liquid absorption amount by the mass of the sample (=1g).

[0163] In addition, when recovering and using the sample (polymer absorbent) for measurement from the product of the composite absorbent, it can be obtained according to the following <Method for recovering the sample (polymer absorbent) for measurement>.

[0164] <Methods for recovering the sample (polymer absorbent) used in the measurement>

[0165] (1) Peel the product holding sheet from the composite absorbent and expose the liquid-absorbing component.

[0166] (2) Drip the object to be measured (polymer absorbent) from the exposed absorbent component and remove the substance other than the (particulate) object to be measured (e.g., pulp, synthetic resin fiber, etc.) using tweezers or the like.

[0167] (3) Use a microscope or a simple magnifying glass as the magnification observation unit, and observe at a magnification that can identify the difference from SAP or that can visualize the pores of the porous material. At the same time, use tweezers or other means to retrieve the object being measured. In addition, the magnification of the simple magnifying glass is not particularly limited as long as it can visualize the pores of the porous material. For example, magnifications of 25x to 50x can be used.

[0168] (4) The objects recovered in this way are used as samples for measurement in various measurement methods.

[0169] The following will use absorbent A as an example to illustrate in detail the manufacturing method of this polymeric absorbent.

[0170] [Manufacturing method of polymeric absorbent]

[0171] like Figure 3 As shown, the absorbent A described above can be obtained through a cross-linking polymerization process and a hydrolysis process. These processes will be explained below.

[0172] (Cross-linking polymerization process)

[0173] First, the oil-soluble monomers, crosslinking monomers, surfactants, water, and polymerization initiators used for crosslinking polymerization are mixed as needed to obtain a water-in-oil emulsion. This water-in-oil emulsion is an emulsion in which the oil phase is a continuous phase and water droplets are dispersed within it.

[0174] Moreover, in the above-mentioned absorbent A, such as Figure 3 As shown in the figure above, butyl methacrylate (a meth)acrylate is used as an oil-soluble monomer, divinylbenzene is used as a crosslinking monomer, sorbitol monooleate is used as a surfactant, and isobutyronitrile is used as a polymerization initiator to crosslink and polymerize it to obtain integral material A.

[0175] Specifically, in absorbent A, such as Figure 3 As shown in the figure above, firstly, 9.2 g of tert-butyl methacrylate as an oil-soluble monomer, 0.28 g of divinylbenzene as a crosslinking monomer, 1.0 g of sorbitan monooleate (hereinafter referred to as "SMO") as a surfactant, and 0.4 g of 2,2'-azobis(isobutyronitrile) as a polymerization initiator are mixed and dissolved uniformly.

[0176] Next, the mixture of tert-butyl methacrylate / divinylbenzene / SMO / 2,2'-azobis(isobutyronitrile) was added to 180g of pure water and stirred under reduced pressure using a vacuum stirrer (manufactured by EME Corporation) as a planetary stirrer to obtain a water-in-oil emulsion.

[0177] The emulsion was then rapidly transferred to a reaction vessel and sealed, and polymerized at 60°C for 24 hours under static conditions. After polymerization, the contents were removed, extracted with methanol, and dried under reduced pressure to obtain solid A with a continuous macroporous structure. Furthermore, SEM observation of the internal structure of solid A revealed a continuous bubble structure with a continuous framework thickness of 5.4 μm. Additionally, the average diameter of the continuous pores, measured by mercury infiltration, was 36.2 μm, and the total micropore volume was 15.5 mL / g.

[0178] Furthermore, the content of divinylbenzene relative to all monomers is preferably 0.3 to 10 mol%, more preferably 0.3 to 5 mol%. Additionally, 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%. Furthermore, 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%.

[0179] The amount of surfactant added can be set according to the type of oil-soluble monomer and the desired size of emulsion particles (macropores), preferably in the range of about 2 to 70% relative to the total amount of oil-soluble monomer and surfactant.

[0180] In addition, in order to control the shape and size of the bubbles in the bulk material 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 can coexist in the polymerization system.

[0181] Furthermore, the mixing method for forming a water-in-oil emulsion is not particularly limited. For example, any mixing method can be used, such as mixing all components together at once, or mixing the components after the oil-soluble monomer, surfactant, and oil-soluble polymerization initiator (i.e., the oil-soluble component) and water and water-soluble polymerization initiator (i.e., the water-soluble component) have been dissolved uniformly separately.

[0182] Furthermore, the mixing device used to form the emulsion is not particularly limited. Any device such as a conventional mixer, homogenizer, or high-pressure homogenizer can be used depending on the desired emulsion particle diameter. In addition, the material to be processed can be placed in a mixing container and mixed by rotating around its own axis while the mixing container is tilted, which is called a planetary mixing device.

[0183] Furthermore, there are no particular restrictions on mixing conditions; the stirring speed and stirring time can be set arbitrarily according to the desired emulsion particle diameter. Additionally, the planetary stirring device described above can uniformly generate water droplets in the W / O emulsion, and the average diameter of these droplets can be set arbitrarily within a wide range.

[0184] The polymerization conditions for water-in-oil emulsions can be varied depending on the type of monomer and initiator. For example, when using azobisisobutyronitrile, benzoyl peroxide, or potassium persulfate as polymerization initiators, polymerization can be carried out in a sealed container under an inert atmosphere at a temperature of 30–100°C for 1–48 hours. When using hydrogen peroxide-ferrous chloride or sodium persulfate-sodium acid sulfite as polymerization initiators, polymerization can be carried out in a sealed container under an inert atmosphere at a temperature of 0–30°C for 1–48 hours.

[0185] In addition, after polymerization, the contents are removed and subjected to Soxhlet extraction with solvents such as isopropanol to remove unreacted monomers and residual surfactants, thereby obtaining... Figure 3 The solid material A shown in the diagram.

[0186] (Hydrolysis process)

[0187] Next, the process of hydrolyzing compound A (crosslinked polymer) to obtain absorbent A (hydrolysis process) will be described.

[0188] First, the bulk material A is impregnated in dichloroethane with added zinc bromide and stirred at 40°C for 24 hours. It is then sequentially contacted with methanol, 4% hydrochloric acid, 4% sodium hydroxide aqueous solution, and water for hydrolysis. After drying, a block-shaped absorbent A is obtained. Next, the block-shaped absorbent A is pulverized into a given size to obtain granular absorbent A. Furthermore, the absorbent A is not limited to granular form; for example, it can be formed into flakes during or after drying.

[0189] Furthermore, the method of hydrolyzing whole material A is not particularly limited, and various methods can be used. For example, methods can be used to contact strong bases such as sodium hydroxide with aromatic solvents such as toluene and xylene, halogen solvents such as chloroform and dichloroethane, ether solvents such as tetrahydrofuran and isopropyl ether, amine 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. Alternatively, methods can be used to contact protic acids such as hydrochloric acid, sulfuric acid, nitric acid, trifluoroacetic acid, methanesulfonic acid, and p-toluenesulfonic acid, or Lewis acids such as zinc bromide, aluminum chloride, aluminum bromide, titanium chloride (IV), cerium chloride / sodium iodide, and magnesium iodide.

[0190] Furthermore, among the polymer raw materials for the organic polymer that forms the hydrophilic continuous skeleton of absorbent A, there are no particular limitations on (meth)acrylates, but C1 to C10 (i.e., 1 to 10 carbon atoms) alkyl esters of (meth)acrylates are preferred, and C4 (i.e., 4 carbon atoms) alkyl esters of (meth)acrylates are particularly preferred.

[0191] In addition, examples of C4 alkyl esters of (meth)acrylic acid include tert-butyl (meth)acrylic acid, n-butyl (meth)acrylic acid, and isobutyl (meth)acrylic acid.

[0192] Furthermore, the monomers used for crosslinking polymerization can be only (meth)acrylate and divinylbenzene, or they can contain other monomers besides (meth)acrylate and divinylbenzene.

[0193] In the latter case, there are no particular restrictions on other monomers, but examples include styrene, α-methylstyrene, vinyltoluene, vinyl benzyl chloride, glycidyl methacrylate, 2-ethylhexyl methacrylate, isobutylene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, methacrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc.

[0194] In addition, the proportion of monomers other than (meth)acrylate and divinylbenzene in all monomers used for crosslinking polymerization is preferably 0 to 80 mol%, more preferably 0 to 50 mol%.

[0195] Furthermore, the surfactant is not limited to the aforementioned sorbitol monooleate; any substance capable of forming a water-in-oil (W / O) emulsion when mixed with monomers for crosslinking polymerization and water is acceptable. Examples of such surfactants include nonionic surfactants such as sorbitol monolaurate, sorbitol monopalmitate, sorbitol monostearate, sorbitol trioleate, polyoxyethylene nonylphenyl ether, polyoxyethylene stearyl ether, and polyoxyethylene sorbitol monooleate; anionic surfactants such as potassium oleate, sodium dodecylbenzenesulfonate, and sodium dioctyl sulfosuccinate; cationic surfactants such as distearate dimethyl ammonium chloride; and amphoteric surfactants such as lauryl dimethyl betaine. These surfactants can be used individually or in combination of two or more.

[0196] Furthermore, the polymerization initiator is preferably a compound that generates free radicals through heat and light irradiation. Moreover, the polymerization initiator can be water-soluble or oil-soluble, and examples include azobis(4-methoxy-2,4-dimethylpentanonitrile), azobisisobutyronitrile, azobisdimethylpentanonitrile, azodicyclohexanenitrile, azodicyclohexanenitrile, azobis(2-methylpropanediamine) dihydrochloride, benzoyl peroxide, potassium persulfate, ammonium persulfate, hydrogen peroxide-ferrous chloride, sodium persulfate-sodium acid sulfite, tetramethylthiuram disulfide, etc. However, depending on the circumstances, there are also systems where polymerization occurs solely through heating and light irradiation without the addition of a polymerization initiator; therefore, the addition of a polymerization initiator is not required in such systems.

[0197] Example

[0198] The present invention is illustrated below with examples, but the present invention is not limited to these examples.

[0199] (A)Sample

[0200] (a) Regarding the distribution of fine pores

[0201] The polymeric absorbent of the present invention, manufactured using the above-described manufacturing method, was used as samples in Examples 1-5, and Infinity particles were prepared as samples in Comparative Examples 1-2. However, for the samples in Examples 1-5, the surfactant / monomer ratio (wt%) and stirring time (minutes) during the formation of the water-in-oil emulsion in the manufacturing method were varied. Furthermore, Infinity particles refer to absorbents manufactured by P&G, which, although having a structure similar to polymeric absorbents (foamed structure), do not possess the function of absorbing liquid and swelling, unlike polymeric absorbents.

[0202] (b) The relationship between bulk density and liquid absorption rate

[0203] Regarding the samples in the above embodiments, samples with various bulk densities were prepared by changing the ethanol impregnation and drying conditions. Specifically, the dried polymer absorber was thoroughly impregnated in a 40% ethanol aqueous solution, and the supernatant was repeatedly removed and ethanol was added to adjust the ethanol aqueous solution to a given concentration. After thorough impregnation, the wet polymer absorber was filtered and dried under reduced pressure at 50°C overnight to obtain polymer absorbers with different bulk densities.

[0204] (B) Evaluation

[0205] (a) Regarding the distribution of fine pores

[0206] Using the mercury indentation method, for each sample, the cumulative pore volume distribution (relationship between pore radius and cumulative pore volume) and the log differential pore volume distribution (relationship between pore radius and log differential pore volume) are determined. The total pore volume (mL / g), average pore radius (μm), maximum pore radius (μm), the proportion of pore volume above (below) a given pore radius, and the pore volume variation coefficient are also calculated.

[0207] (b) Relationship between bulk density and liquid absorption rate

[0208] The relationship between the bulk density and the absorption rate (DW) of each sample was investigated by measuring the absorption rate (DW).

[0209] (C) Evaluation Results

[0210] (a) Regarding the distribution of fine pores

[0211] The measurement results are shown in Figure 9 as well as Figure 10 The summarized results are shown in Table 1. Figure 9 The diagram shows the cumulative pore volume distribution, i.e., the relationship between pore radius (horizontal axis) and cumulative pore volume (vertical axis). Figure 10 The diagram shows the distribution of the log differential pore volume, i.e., the relationship between the pore radius (horizontal axis) and the log differential pore volume (vertical axis). Additionally, in... Figure 9 as well as Figure 10 In the examples, Example 1 is a dashed line (thick line), Example 2 is a single-dot dashed line (thin line), Example 3 is a dashed line (thin line), Example 4 is a dashed line, Example 5 is a solid line (thin line), Comparative Example 1 is a solid line (thick line), and Comparative Example 2 is a single-dot dashed line (thick line).

[0212] [Table 1]

[0213]

[0214] *Pore radius greater than 1μm

[0215] In the samples of Examples 1 to 5, the following situation can be confirmed.

[0216] The proportion of pore volume of pores with a radius of 1 μm or more is 90% or more of the total pore volume. The proportion of pore volume of pores with a radius of 0.005 μm or less is less than 10% of the total pore volume. The pore radius corresponding to the maximum pore volume is 500 μm or less. There are cases where the variation coefficient of pore distribution in pores with a radius of 1 μm or more is 1.4 or less (Example 3). There are cases where the variation coefficient of pore distribution in pores with a radius of 1 μm or more exceeds 1.4 (Examples 4 and 5). For the pore radius corresponding to the maximum value of pore volume in the curve representing pore distribution, there are cases where the portion on the side with the larger pore radius is wider than the portion on the side with the smaller pore radius (Example 5). For the pore radius corresponding to the maximum value of pore volume in the curve representing pore distribution, there are cases where the portion on the side with the smaller pore radius is wider than the portion on the side with the larger pore radius (Example 4). There are cases where at least two maxima of pore volume exist in the curve representing pore distribution (Examples 1 and 2). Regarding the two maxima of pore volume in the curve representing pore distribution, there is a case where the maximum value of the relatively smaller pore radius is larger than the maximum value of the relatively larger pore radius (Example 2). Regarding the two maxima of pore volume in the curve representing pore distribution, there is a case where the maximum value of the relatively smaller pore radius is smaller than the maximum value of the relatively larger pore radius (Example 1). The total pore volume is 0.9 mL / g or more. On the other hand, in Comparative Examples 1 and 2, the proportion of pore volume of pores with a pore radius of at least 1 μm or more is less than 90% of the total pore volume.

[0217] (b) Relationship between bulk density and liquid absorption rate

[0218] The measurement results are shown in Figure 11 . Figure 11 This is a graph showing the relationship between the obtained bulk density (horizontal axis) and the liquid absorption rate (vertical axis). As shown in the figure, the bulk density was set to 0.07–0.6 g / cm³. 3 It was confirmed that the drawdown rate (DW) could be set to 6 mL / 30 sec or higher. Furthermore, the bulk density was set to 0.1–0.4 g / cm³. 3 It was confirmed that the water absorption rate (DW) could be set to 10 mL / 30 sec or higher. Furthermore, the bulk density was set to 0.15–0.35 g / cm³. 3 It was confirmed that the aspiration rate (DW) performance could be set to 12 mL / 30 sec or higher.

[0219] Furthermore, the composite absorbent of the present invention is not particularly limited, but can be applied to composite absorbents in various fields such as condensation prevention sheets, civil / building materials such as simple soil, substrates such as pharmaceuticals, and absorbent materials for leaking liquids. Therefore, the liquid to be absorbed by the composite absorbent is not particularly limited, and examples include water, aqueous solutions (e.g., seawater), acids (e.g., hydrochloric acid), alkalis (e.g., sodium hydroxide), and 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.). In addition, these liquids can be mixtures of two or more liquids.

[0220] Furthermore, the present invention is not limited to the embodiments described above, and can be combined, substituted, or modified as appropriate without departing from the purpose and spirit of the present invention. Additionally, in this specification, ordinal numbers such as "first" and "second" are used to distinguish the items attached to those ordinal numbers and do not imply the order, priority, or importance of the items.

[0221] Label Explanation

[0222] 1. Composite absorber

[0223] 2. First, maintain the sheet material

[0224] 3. Second retaining sheet

[0225] 4. Polymer absorbent

[0226] 5. Superabsorbent Polymer (SAP)

[0227] 6. Hydrophilic fiber sheets.

Claims

1. A composite absorber for absorbing liquid, characterized in that, The composite absorbent comprises a polymeric absorbent having a hydrophilic continuous framework and continuous pores. In the aforementioned polymeric absorbent, the proportion of pore volume with a pore radius of 1 μm or more is more than 90% of the total pore volume. In the polymer absorbent, in pores with a pore radius of 1 μm or more, the coefficient of variation of the pore distribution, which reflects the deviation of the pore radius from the average value of the pore radius, exceeds 1.

4.

2. The composite absorber according to claim 1, characterized in that, In the polymer absorbent, the proportion of the pore volume of pores with a pore radius of less than 0.005 μm is less than 10% of the total pore volume.

3. The composite absorber according to claim 1 or 2, characterized in that, In the polymer absorbent, the maximum pore volume corresponds to a pore radius of less than 500 μm.

4. The composite absorber according to claim 1, characterized in that, In the polymer absorbent, the portion on the side with a larger pore radius is wider than the portion on the side with a smaller pore radius, relative to the pore radius corresponding to the maximum value of the pore volume in the curve representing the pore distribution.

5. The composite absorber according to claim 1, characterized in that, In the polymer absorbent, the portion on the side with a smaller pore radius is wider than the portion on the side with a larger pore radius, relative to the pore radius corresponding to the maximum value of the pore volume in the curve representing the pore distribution.

6. The composite absorber according to claim 1 or 2, characterized in that, In the polymeric absorbent, there are at least two maxima of pore volume in the curve representing the pore distribution.

7. The composite absorber according to claim 6, characterized in that, In the polymer absorbent, the maximum value of the pore volume in the curve representing the pore distribution is larger for the relatively smaller pore radius than for the relatively larger pore radius.

8. The composite absorber according to claim 6, characterized in that, In the polymer absorbent, the maximum value of the pore volume in the curve representing the pore distribution is smaller for the relatively smaller pore radius than for the relatively larger pore radius.

9. The composite absorber according to claim 1 or 2, characterized in that, In the polymer absorbent, the total micropore volume is 0.9 mL / g or more.

10. The composite absorber according to claim 1 or 2, characterized in that, The bulk density of the polymeric absorbent is 0.07–0.6 g / cm³. 3 .

11. The composite absorber according to claim 1 or 2, characterized in that, The polymeric absorbent is a monolithic absorbent.

12. The composite absorber according to claim 1 or 2, characterized in that, The polymeric absorbent is a hydrolysate of a cross-linked polymer of (meth)acrylate and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group.

13. A polymeric absorbent, characterized in that, The polymeric absorbent has a hydrophilic continuous framework and continuous pores. The proportion of micropore volume with a pore radius of 1 μm or more is more than 90% of the total micropore volume. In the polymer absorbent, in pores with a pore radius of 1 μm or more, the coefficient of variation of the pore distribution, which reflects the deviation of the pore radius from the average value of the pore radius, exceeds 1.4.

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