Composite absorbent and sanitary article

Abstract

Provided is a composite absorbent for sanitary products that can suppress a decrease in water absorption amount compared to pore volume and has excellent absorption performance. A composite absorbent for sanitary products (4) for absorbing body fluids includes a high-molecular absorbent having a continuous skeleton and continuous pores. In the high-molecular absorbent, the ratio of the pore volume of pores having a pore radius of 1 μm or more is 90% or more of the pore volume of all pores.

Description

Technical Field

[0001] This invention relates to composite absorbents and sanitary products having the same. Background Technology

[0002] For absorbent articles such as disposable diapers and sanitary napkins, porous materials such as sponge materials are known to be used as absorbent bodies. For example, Patent Document 1 discloses an absorbent article comprising a polymer foam material formed from a hydrophilic flexible structure of interconnected continuous air bubbles.

[0003] Existing technical documents

[0004] Patent documents

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

[0006] The problem the invention aims to solve

[0007] According to the research of the inventors of the present invention, for porous materials such as the polymer foam material of Patent Document 1, there are many pores with relatively small pore radii. However, for porous structures, there is a tendency for moisture to be easily introduced into pores with relatively large pore radii. Therefore, when using a porous material with many small-diameter pores as described above, moisture does not enter the small-diameter pores during water absorption, and the water absorption may be reduced compared to the pore volume.

[0008] The present invention was made in view of this problem, and its object is to provide a composite absorbent for sanitary products that can suppress the decrease in water absorption compared with the pore volume and have excellent absorption performance, as well as sanitary products having the same.

[0009] Solution for solving the problem

[0010] One aspect (Aspect 1) of the present invention is a composite absorbent, characterized in that it is a composite absorbent for use in sanitary products for absorbing bodily fluids, the composite absorbent comprising: a polymeric absorbent having a hydrophilic continuous framework and continuous pores, wherein in the aforementioned polymeric absorbent, the ratio of the pore volume based on pores with a pore radius of 1 μm or more is 90% or more of the total pore volume.

[0011] In this composite absorbent, the proportion of pore volume based on pores with a radius of 1 μm or larger in the polymer absorbent is over 90% of the total pore volume. Therefore, during water absorption, water has difficulty entering pores with a radius less than 1 μm. Even if it cannot enter, water can still enter pores with a radius of 1 μm or larger, ensuring sufficient water absorption. This suppresses the decrease in water absorption compared to the pore volume, resulting in excellent absorption performance.

[0012] Furthermore, another aspect (mean 2) of the present invention is characterized in that, in the composite absorbent of the above-mentioned mean 1, in the aforementioned polymer absorbent, the ratio of the pore volume based on the pores with a pore radius of 0.005 μm or less is less than 10% of the total pore volume.

[0013] The composite absorbent of this method has a very small pore volume ratio for pores with a pore radius of less than 0.005 μm, which are difficult to absorb water, and a large pore volume ratio for pores with a pore radius of more than 1 μm, which are capable of absorbing water. Therefore, the pores of the polymer absorbent can be effectively utilized for water absorption, ensuring sufficient water absorption.

[0014] The present invention is further characterized in that, in the composite absorber of the above-mentioned method 1 or 2, the pore radius of the polymer absorbent at the maximum value of the pore volume is 500 μm or less.

[0015] The composite absorbent of this method has a pore radius of less than 500 μm when the pore volume is at its maximum value. This can prevent the continuous skeleton structure of the polymer absorbent from being destroyed (crushed) during water absorption, making it easy to obtain excellent absorption rate and stably ensuring sufficient water absorption (when the pore radius is greater than 500 μm when the pore volume is at its maximum value, the continuous skeleton structure may not be maintained during water absorption and may be crushed).

[0016] The further embodiment of the present invention (e.g., embodiment 4) is characterized in that, in the composite absorbent of any one of embodiments 1 to 3, the pore distribution variation coefficient of the aforementioned polymer absorbent with a pore radius of 1 μm or more is 1.4 or less.

[0017] The composite absorbent of this method exhibits a small deviation in pore radius relative to the average pore radius due to a pore distribution variation coefficient of less than 1.4. This results in a sharp peak in the pore distribution near the average pore radius. Therefore, the polymeric absorbent can absorb moisture approximately uniformly across all directions and surfaces. This allows for efficient utilization of the polymeric absorbent's pores for water absorption, ensuring sufficient absorbency.

[0018] The further embodiment of the present invention (e.g., embodiment 5) is characterized in that, in the composite absorbent of any one of embodiments 1 to 3, the variation coefficient of the pore distribution of the aforementioned polymer absorbent with a pore radius of 1 μm or more exceeds 1.4.

[0019] In this composite absorbent, the coefficient of variation of the pore distribution exceeds 1.4, resulting in a large deviation of the pore radius relative to the average pore radius. This leads to a broadening of the peaks exhibited by the pore distribution near the average pore radius. In other words, the polymeric absorbent contains both small and large pores. Therefore, capillary forces are more effective in small pores, leading to faster water absorption, while the absorption volume is more easily increased in large pores. Thus, through the synergistic effect of both, the polymeric absorbent can instantly absorb a large amount of water into the interior of the pores.

[0020] The invention is further characterized in another aspect (mean 6) of the present invention, in the composite absorbent described in the above-mentioned means 5, in the aforementioned polymer absorbent, for the pore radius corresponding to the maximum value of the pore volume in the curve showing 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 greater number of pores with larger pore radii compared to pores with smaller pore radii. The greater number of pores with larger pore radii makes it easier to increase the water absorption volume, allowing a larger amount of water to be absorbed into the interior of the pores.

[0022] The invention is further characterized in another aspect (mean 7) of the present invention, in the composite absorbent described in the above-mentioned means 5, in the aforementioned polymer absorbent, for the pore radius corresponding to the maximum value of the pore volume in the curve showing the pore distribution, the portion of the pore radius smaller than the portion of the larger pore radius is wider.

[0023] For the composite absorbent of this method, the polymeric absorbent has the aforementioned structure, namely, a greater number of pores with smaller pore radii compared to pores with larger pore radii. Because of the greater number of pores with smaller pore radii, capillary forces are more easily activated, thereby accelerating water absorption and allowing for the instantaneous absorption of water into the interior of the pores.

[0024] The present invention is further characterized in that, in any of the composite absorbents described in any of the embodiments 1 to 3, in the aforementioned polymeric absorbent, there are at least two maximum values ​​of the pore volume in the curve showing the pore distribution.

[0025] For the composite absorbent of this method, the polymeric absorbent has the above-described structure, namely, it contains pores with a specified small pore radius and its vicinity, and pores with a specified large pore radius and its vicinity. Therefore, for pores with relatively small pore radii, capillary forces are more easily activated, thereby increasing the water absorption rate; for pores with relatively large pore radii, the water absorption volume is more easily increased. Thus, through the synergistic effect of both, the polymeric absorbent can instantly absorb a large amount of water into the interior of the pores.

[0026] The invention is further characterized in another aspect (mean 9) of the present invention, in the composite absorbent described in the above-mentioned means 8, in the aforementioned polymeric absorbent, for the two maxima of the pore volume in the curve showing the pore distribution, the maxima of the relatively smaller pore radius is larger than the maxima of the relatively larger pore radius.

[0027] For the composite absorbent of this method, the polymeric absorbent has the above-mentioned structure, namely, it contains more pores with smaller pore radii compared to pores with larger pore radii. With more pores with smaller pore radii, capillary forces are more easily activated, thus increasing the water absorption rate and allowing for the instantaneous absorption of water into the interior of the pores.

[0028] The invention is further characterized in another aspect (mean 10) of the present invention, in the composite absorbent described in the above-mentioned means 8, in the aforementioned polymeric absorbent, for the two maxima of the pore volume in the curve showing the pore distribution, the maxima of the relatively smaller pore radius is smaller than the maxima of the relatively larger pore radius.

[0029] For the composite absorbent of this method, the polymeric absorbent has the above-mentioned structure, namely, it contains more pores with larger pore radii compared to pores with small pore radii. With more pores with larger pore radii, the water absorption volume is more easily increased, allowing a larger amount of water to be absorbed into the interior of the pores.

[0030] The present invention is further characterized in that, in any of the composite absorbents described in any of the embodiments 1 to 10, the total pore volume in the aforementioned polymeric absorbent is 0.9 mL / g or more.

[0031] For the composite absorbent of this method, the total micropore volume in the polymer absorbent is above 0.9 mL / g, thus ensuring sufficient micropore volume and adequate water absorption. Furthermore, the spaces (pores) in the porous body used to introduce the target fluid (body fluid) are less likely to be damaged during absorption, preventing a decrease in water absorption capacity and rate.

[0032] A further embodiment of the present invention (embodiment 12) is characterized in that, in the composite absorbent described in any one of embodiments 1 to 11, the bulk density of the aforementioned polymeric absorbent is 0.07 to 0.6 g / cm³. 3 .

[0033] For the composite absorbent of this method, the bulk density in the polymer absorbent is 0.07–0.6 g / cm³. 3 Therefore, the water absorption rate (DW) can be above 6 mL / 30 sec. That is, the water absorption rate is faster, allowing the polymer absorbent to instantly absorb water into the interior of the pores.

[0034] The present invention is further characterized in that, in any of the composite absorbents described in any of the embodiments 1 to 12, the aforementioned polymeric absorbent is a monolithic absorbent.

[0035] The composite absorbent of this method can quickly absorb moisture because the polymer absorbent is a monolithic columnar absorbent.

[0036] The further embodiment of the present invention (e.g., embodiment 14) is characterized in that, in the composite absorbent of any one of embodiments 1 to 13, the aforementioned polymer absorbent is a hydrolysate of a cross-linked polymer of (meth)acrylate and a compound containing two or more vinyl groups, and contains at least one -COONa group.

[0037] The composite absorbent of this method has the above-mentioned specific structure through the polymer absorbent. When absorbing body fluid, the hydrophilic continuous skeleton is easy to elongate and the continuous pores are easy to expand. Therefore, more body fluid can be introduced into the continuous pores more quickly, and the absorbent can exert a further excellent absorption performance.

[0038] In addition, another aspect (mean 15) of the present invention is a hygiene product characterized by having a composite absorbent as described in any one of means 1 to 14 above.

[0039] The sanitary products of this method, having a composite absorbent of any one of the above methods 1 to 14, can exhibit excellent absorbency as sanitary products.

[0040] The effects of the invention

[0041] According to the present invention, a composite absorbent with excellent absorbency performance that can suppress the decrease in water absorption compared with the pore volume, and sanitary products having the same, can be provided. Attached Figure Description

[0042] Figure 1This is a schematic top view of the light incontinence pad 1 as seen from the side opposite the skin in the thickness direction.

[0043] Figure 2 The diagram illustrates the manufacturing process of absorbent A, an example of a polymeric absorbent.

[0044] Figure 3 This is a SEM image of absorbent A at 50x magnification.

[0045] Figure 4 This is a SEM image of absorbent A at 100x magnification.

[0046] Figure 5 This is a SEM image of absorbent A at 500x magnification.

[0047] Figure 6 This is a SEM image of absorbent A at 1000x magnification.

[0048] Figure 7 SEM image of absorbent A at 1500x magnification

[0049] Figure 8 This is a graph showing the relationship between the pore radius and the cumulative pore volume of absorbent A.

[0050] Figure 9 This is a graph showing the relationship between the pore radius and the differential pore volume of absorbent A.

[0051] Figure 10 A graph showing the relationship between the bulk density and absorption performance (DW) of absorbent A.

[0052] Figure 11 This is a schematic diagram illustrating the measuring apparatus used in the pressureless DW method. Detailed Implementation

[0053] The preferred embodiment of the composite absorbent of the present invention will be described in detail below using a light incontinence pad 1 as an example of a sanitary product to which the composite absorbent is applied.

[0054] It should be noted that, unless otherwise specified, in this instruction manual, "the view of an object placed horizontally in its unfolded state from the vertical top side (the surface side when the object is a sanitary product) in the thickness direction of the object (e.g., incontinence pads, composite absorbents, etc.)" will be referred to only as "top view".

[0055] It should be noted that in this specification, "length direction" refers to "the direction of the longer length of an object in a top view (such as a light incontinence pad, composite absorbent, etc. in an unfolded state)," "width direction" refers to "the direction of the shorter length of an object in a top view," and "thickness direction" refers to "the direction perpendicular to an object placed on a horizontal surface in an unfolded state." These length, width, and thickness directions are all orthogonal to each other.

[0056] In addition, unless otherwise specified in this instruction manual, in the thickness direction of the incontinence pad 1, the side "proximal to the wearer's skin when wearing the incontinence pad 1" is referred to as the "skin-opposing side", and the side "far from the wearer's skin when wearing the incontinence pad 1" is referred to as the "non-skin-opposing side".

[0057] [Minor Incontinence Pad]

[0058] Figure 1 A schematic top view of the light incontinence pad 1 in its unfolded state, according to an embodiment of the present invention, of the composite absorbent 4.

[0059] like Figure 1 As shown, when viewed from above, the incontinence pad 1 has a longitudinally elongated shape with a length direction L and a width direction W, and two longitudinally elongated end edges protruding outward in an arc shape along the length direction. It should be noted that the shape of the incontinence pad 1 is not limited to this type. If it is longitudinally elongated, it can adopt any shape (e.g., oblong, rectangular, hourglass, etc.) depending on various uses and methods of use.

[0060] The incontinence pad 1 has a liquid-permeable surface sheet 2 forming the skin-facing side of the incontinence pad 1 in the thickness direction, a back sheet 3 forming the non-skin-facing side of the incontinence pad 1, and a composite absorbent body 4 located between these sheets as its basic components.

[0061] In addition, the incontinence pad 1 also has a surface disposed on the non-skin-facing side of the back panel 3, and an adhesive part (not shown) for adhering and fixing the incontinence pad 1 to the inner surface of the wearer's underwear or other clothing.

[0062] It should be noted that the incontinence pad 1 is not limited to this configuration. For example, it may have a pair of side sheets for forming a leak-proof wall, which are arranged at both ends of the incontinence pad 1 in the width direction W and extend in the length direction L, compared with the surface sheet 2 on the skin-opposing side; and multiple elastic members arranged in the length direction L of the pair of side sheets respectively.

[0063] Furthermore, in the light incontinence pad 1, the composite absorbent 4 is located between the surface sheet 2 and the back sheet 3 and is formed by a water-absorbing component capable of absorbing bodily fluids such as urine and menstrual blood that are excreted by the wearer and pass through the surface sheet 2. The composite absorbent 4 includes a polymeric absorbent having a hydrophilic continuous skeleton and continuous pores. In this embodiment, it also includes a superabsorbent polymer (SAP).

[0064] Furthermore, this polymeric absorbent exhibits a unique water absorption behavior when absorbing moisture, which involves introducing moisture into the continuous skeleton and then into the continuous pores.

[0065] In the composite absorbent 4, when the aforementioned polymeric absorbent with a hydrophilic continuous framework and continuous pores absorbs bodily fluids such as urine and menstrual blood, the hydrophilic continuous framework expands instantly by introducing bodily fluids through osmotic pressure, thereby increasing the volume of the continuous pores. This allows bodily fluids to be introduced into the expanded continuous pores, thus enabling the instantaneous absorption of large amounts of bodily fluids. In this embodiment, the absorbed bodily fluids can then be transported to a high-water-retention SAP and firmly retained within the SAP.

[0066] Therefore, composite absorber 4 can perform high absorption performance as an absorber.

[0067] Therefore, the incontinence pad 1, which also possesses this composite absorbent 4, can also perform excellent absorption as an incontinence pad.

[0068] The following describes in detail the various constituent components of sanitary products to which the composite absorbent of the present invention is applicable, using the above-described light incontinence pad 1.

[0069] (Surface sheet)

[0070] In the aforementioned mild incontinence pad 1, such as Figure 1 As shown, the surface sheet 2 has a longitudinally elongated shape, extending from one end edge in the length direction L of the incontinence pad 1 to the other end edge, and from near one end edge in the width direction W of the incontinence pad 1 to near the other end edge, when viewed from above. The surface sheet 2 is a liquid-permeable sheet-like member formed by being positioned in the thickness direction of the incontinence pad 1 on the skin-facing side, creating a contact surface that can abut against the wearer's skin, i.e., the skin-facing side surface of the incontinence pad 1.

[0071] In addition, such as Figure 1 As shown, the surface sheet 2 has a slightly larger size in the length direction L and width direction W compared to the composite absorber 4 disposed on the non-skin-facing side of the surface sheet 2, and is joined to the back sheet 3 located on the non-skin-facing side in the periphery.

[0072] In this invention, there are no particular restrictions on the shape, size, weight, etc. of the surface sheet, as long as it can be used as a surface sheet for hygiene products. Any shape, size, weight, etc. can be adopted that corresponds to the desired liquid permeability, skin feel, softness, strength, etc.

[0073] (Back panel)

[0074] In the aforementioned incontinence pad 1, the back panel 3 has an elongated shape, extending from one end edge in the length direction L of the incontinence pad 1 to the other end edge, and from one end edge in the width direction W of the incontinence pad 1 to the other end edge, when viewed from above. The back panel 3 is a non-permeable sheet member disposed in the thickness direction of the incontinence pad 1 on the non-skin-facing side, forming the non-skin-facing surface of the incontinence pad 1, and preventing leakage of bodily fluids such as urine and menstrual blood through the composite absorbent 4 to the outside of the incontinence pad 1.

[0075] In this invention, there are no particular restrictions on the shape, size, weight, etc. of the back sheet, as long as it can be used as the back sheet of a sanitary product. Any shape, size, weight, etc. can be adopted that corresponds to the desired leak-proof performance, breathability, strength, etc.

[0076] (Complex absorber)

[0077] In the aforementioned mild incontinence pad 1, such as Figure 1 As shown, the composite absorbent 4 has the following longitudinal shape when viewed from above: it extends in a wide region along the length direction L from near one end edge to near the other end edge, with the center portion of the light incontinence pad 1 in the length direction L as the center, and also extends in a wide region along the width direction W from near one end edge to near the other end edge, and the two ends in the length direction protrude outward in an arc shape.

[0078] More specifically, when viewed from above, the composite absorber 4 has a tapered portion in the middle of its length direction that is relatively smaller in the width direction compared to other parts, and further includes a minimum width portion in which the composite absorber 4 has the minimum width in the tapered portion, and a maximum width portion in which the composite absorber 4 has the maximum width on the outer side of the tapered portion in the length direction.

[0079] The composite absorbent 4 is formed by a defined absorbent component disposed between the surface sheet 2 and the back sheet 3 in the thickness direction of the light incontinence pad 1, capable of absorbing and retaining bodily fluids such as urine and menstrual blood that permeate through the surface sheet 2. This absorbent component is composed of absorbent materials such as polymeric absorbents, hydrophilic fibers, and highly absorbent polymers (described later), and a sheet such as thin paper for retaining it. In other words, the composite absorbent refers to an absorbent component composed of absorbent materials capable of absorbing and retaining bodily fluids, and a sheet for retaining them.

[0080] It should be noted that in the light incontinence pad 1, the composite absorbent 4 is bonded to the surface sheet 2 and the back sheet 3 using any adhesive such as a hot melt adhesive.

[0081] Furthermore, the composite absorbent 4 comprises a polymeric absorbent exhibiting the aforementioned unique water-absorbing behavior, possessing a hydrophilic continuous skeleton and continuous pores as described above. In this embodiment, it also comprises a highly absorbent polymer. As described below, the highly absorbent polymer is a powder or granular material formed from highly absorbent polymers such as sodium acrylate copolymers, which is known in the art and is referred to as SAP (Super Absorbent Polymer).

[0082] It should be noted that the composite absorbent 4, as a water-absorbing material, may contain only the aforementioned polymeric absorbent, may contain only a polymeric absorbent and a highly absorbent polymer, or may contain, in addition to these, water-absorbing materials known in the field. Examples of such water-absorbing materials include, for example, hydrophilic fibers; more specifically, examples include pulp fibers (e.g., crushed pulp), cotton, rayon, cellulose fibers such as acetate, etc.

[0083] It should be noted that the composite absorbent 4 can have a structure in which any absorbent material such as a polymer absorbent or a highly absorbent polymer is covered by a coating sheet such as hydrophilic paper.

[0084] In this invention, the shape, size, and weight of the composite absorbent are not particularly limited as long as they do not hinder the effect of the invention. Any shape, size, and weight corresponding to the desired absorbency, softness, strength, etc., can be adopted.

[0085] The polymeric absorbent used in the composite absorbent of the present invention will be described in more detail below.

[0086] [Polymer absorbent]

[0087] In this invention, the polymeric absorbent is not particularly limited if it possesses a hydrophilic continuous framework and continuous pores, and exhibits a unique water-absorbing behavior of introducing water into the continuous framework and then into the continuous pores during water absorption. Examples of such polymeric absorbents include hydrolysates of cross-linked polymers containing at least two monomers of (meth)acrylate, and examples of polymeric compounds having at least one hydrophilic group in their functional groups. More specifically, examples of hydrolysates are hydrolysates of cross-linked polymers containing (meth)acrylate and compounds containing two or more vinyl groups per molecule, and examples of polymeric compounds having at least a -COONa group. The aforementioned polymeric absorbent is an organic porous body having at least one -COONa group per molecule, and may further have -COOH groups. The -COONa groups are distributed substantially uniformly in the framework of the porous body.

[0088] If 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, then as described later, when absorbing bodily fluids such as urine and menstrual blood, the hydrophilic continuous skeleton is easy to elongate (i.e., easy to expand), and the continuous pores are also easy to enlarge. Therefore, more bodily fluids can be introduced into the continuous pores more quickly, and it can play a further excellent absorption role as an absorbent.

[0089] It should be noted that in this specification, (meth)acrylate refers to acrylate or methacrylate.

[0090] In the polymeric absorbent formed by the hydrolysis of this crosslinked polymer of (meth)acrylate and divinylbenzene, a hydrophilic continuous skeleton is formed by an organic polymer having at least -COONa groups, and there are connecting pores (continuous pores) between the skeletons that serve as absorption sites for the target fluid (i.e., urine, menstrual blood, etc.).

[0091] It should be noted that hydrolysis treatment causes the -COOR groups (i.e., carboxylic acid ester groups) of the cross-linked polymer to form -COONa groups or -COOH groups (see reference). Figure 2 Therefore, polymeric absorbents can have -COOR groups.

[0092] 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.

[0093] Here, Figure 2 This diagram illustrates the manufacturing process of absorbent A, an example of a polymeric absorbent. Figure 2In the diagram, the top figure shows the constituent raw materials of the polymerization, the middle figure shows the monolithic column A, which is a crosslinked polymer of (meth)acrylate and divinylbenzene, and the bottom figure shows the absorbent A obtained by hydrolyzing and drying the monolithic column A in the middle figure.

[0094] The following description uses absorbent A, formed from the hydrolysate of a crosslinked polymer of (meth)acrylate and divinylbenzene, as an example of a polymer absorbent.

[0095] It should be noted that the polymer absorbent is not limited to absorbent A, but can also 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 containing at least two monomers of (meth)acrylate, etc.

[0096] However, if the polymeric absorbent is a monolithic columnar absorbent, it can not only absorb body fluids quickly, but also has the advantage of delivering the body fluids temporarily held in the polymeric absorbent more firmly to the SAP.

[0097] It should be noted that in the following description, "monolithic column A" refers to an organic porous body formed by a cross-linked polymer of (meth)acrylate and divinylbenzene before hydrolysis treatment, sometimes referred to as "monolithic columnar organic porous body".

[0098] Additionally, "Absorbent A" is a hydrolysate of a cross-linked polymer (monolithic column A) of (meth)acrylate and divinylbenzene that has undergone hydrolysis and drying treatment. It should be noted that in the following description, Absorbent A refers to the absorbent in its dried state.

[0099] First, the structure of absorbent A will be explained.

[0100] As described above, absorbent A has a hydrophilic continuous backbone and continuous pores. Absorbent A is an organic polymer with a hydrophilic continuous backbone, such as... Figure 2 As shown, the cross-linked polymer (monolithic column A) is obtained by cross-linking (meth)acrylate as a polymerizing monomer and divinylbenzene as a cross-linking monomer, and then further hydrolyzing the resulting cross-linked polymer.

[0101] Organic polymers that form a hydrophilic continuous backbone, as structural units, have vinyl polymeric residues (hereinafter referred to as "structural unit X") and divinylbenzene crosslinked polymeric residues (hereinafter referred to as "structural unit Y").

[0102] Furthermore, the vinyl polymeric residues (structural unit X) in the organic polymer forming the hydrophilic continuous backbone have two types of groups: -COONa group, or -COOH group and -COONa group, generated by the hydrolysis of the carboxylic acid ester group. It should be noted that when the polymeric monomer is (meth)acrylate, the vinyl polymeric residues (structural unit X) have -COONa group, -COOH group and ester group.

[0103] In absorbent A, the ratio of cross-linked polymeric residues (structural unit Y) of divinylbenzene in the organic polymer forming a hydrophilic continuous backbone is, for example, 0.1 to 30 mol%, preferably 0.1 to 20 mol%, relative to all structural units. For example, in absorbent A where butyl methacrylate is used as the polymeric monomer and divinylbenzene is used as the cross-linking monomer, the ratio of cross-linked polymeric residues (structural unit Y) of divinylbenzene in the organic polymer forming a hydrophilic continuous backbone is, for example, about 3%, preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%, relative to all structural units.

[0104] It should be noted that if the ratio 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 is not easily reduced. In addition, if the ratio of cross-linked polymer residues of divinylbenzene is 30 mol% or less, the absorption amount of the target liquid is not easily reduced.

[0105] In addition, the organic polymer forming the hydrophilic continuous backbone in absorbent A may contain only structural units X and Y, or may contain polymer residues of monomers other than structural units X and Y, namely (meth)acrylate and divinylbenzene.

[0106] As structural units other than structural units X and Y, examples include polymer residues of monomers such as styrene, α-methylstyrene, vinyltoluene, vinyl benzyl chloride, glycidyl methacrylate, isobutylene, 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.

[0107] It should be noted that the ratio of structural units other than structural units X and Y in the organic polymer forming the hydrophilic continuous backbone is, for example, 0 to 50 mol%, preferably 0 to 30 mol%, relative to all structural units.

[0108] Furthermore, absorbent A preferably has a hydrophilic continuous framework with a thickness of 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) in the porous body used to introduce the target fluid (body fluid) are less likely to be damaged during absorption, and the absorption capacity is less likely to decrease. On the other hand, if the thickness of the hydrophilic continuous framework is 100 μm or less, an excellent absorption rate is easily obtained. The thickness of the continuous framework can be obtained, for example, from SEM images of absorbent A.

[0109] It should be noted that the hydrophilic continuous framework of absorbent A has a continuous bubble structure, therefore the thickness of the continuous framework is measured at the cross-section of the framework appearing on the test piece used for electron microscopy. Since the continuous framework is formed by the spacing of water (droplets) removed through dehydration / drying after hydrolysis, it is mostly polygonal in shape. Therefore, the thickness of the continuous framework is set as the average value of the diameter (μm) of the circumcircle of the polygonal cross-section. In rare cases, small holes are formed within the polygon; in such cases, the circumcircle of the polygonal cross-section surrounding the small hole is measured.

[0110] Furthermore, absorbent A preferably has an average diameter of continuous pores of 1 to 1000 μm. If the average diameter of continuous pores in absorbent A is 1 μm or more, the spaces (pores) in the porous body used to introduce the target fluid (body fluid) are less likely to be damaged during absorption, and the absorption rate is less likely to decrease. On the other hand, if the average diameter of continuous pores is 1000 μm or less, an excellent absorption rate is easily obtained.

[0111] It should be noted that the average diameter (μm) of the continuous pores in absorbent A can be determined using mercury intrusion porosimetry, employing the maximum value of the pore distribution curve obtained using this method. For the sample used to determine the average diameter of the continuous pores, regardless of the ionic form of absorbent A, the sample is prepared by drying in a vacuum desiccator at a temperature set to 50°C for at least 18 hours. It should be noted that the ultimate limiting pressure is set to 0 Torr.

[0112] Here, Figure 3 This is a SEM image of absorbent A at 50x magnification. Figure 4 This is a SEM image of absorbent A at 100x magnification. Figure 5 This is a SEM image of absorbent A at 500x magnification. Figure 6 A SEM image of absorbent A at 1000x magnification, and then... Figure 7 This is a SEM image of absorbent A at 1500x magnification.

[0113] These Figures 3-7The absorbent A shown is an example of an absorbent in which butyl methacrylate is used as a polymer monomer and divinylbenzene is used as a crosslinking monomer, and each has a cubic structure of 2 mm square.

[0114] Figures 3-7 The absorbent A shown has numerous bubble-like macropores, and these bubble-like macropores overlap with each other. The overlapping portions of these macropores in absorbent A form a continuous bubble structure with common openings (mesopores), that is, a continuous bubble structure (continuous macroporous structure).

[0115] The overlapping portions of these macropores form common openings (mesopores) with an average diameter of 1–1000 μm, preferably 10–200 μm, and particularly preferably 20–100 μm in the dry state, and most of them form 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 target liquid is better. On the other hand, if the average diameter of the mesopores in the dry state is 1000 μm or less, the absorbent A is less likely to become brittle.

[0116] It should be noted that the overlap of these large holes is about 1 to 12 for a single large hole, and mostly about 3 to 10.

[0117] Furthermore, since absorbent A has this continuous bubble structure, it has the advantage of being able to uniformly form macropore groups and mesopore groups, and compared with the particle-aggregated porous bodies described in Japanese Patent Application Publication No. 8-252579, it can significantly increase the pore volume and specific surface area.

[0118] 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 a total micropore volume of 0.5 mL / g or more, sufficient micropore volume can be guaranteed in the absorbent A, thus ensuring sufficient water absorption. Furthermore, the spaces (cavities) in the porous body used to introduce the target fluid (body fluid) are less likely to be damaged during absorption, preventing a decrease in absorption capacity and 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.

[0119] It should be noted that the total pore volume can be determined using mercury porosimetry. For the sample used in the determination of total pore volume, regardless of the ionic form of absorbent A, the sample is dried in a vacuum desiccator at a temperature set to 50°C for at least 18 hours. The ultimate limiting pressure is set to 0 Torr. Using this mercury porosimetry, 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. From this, the total pore volume (mL / g), average pore radius (μm), maximum pore radius (μm), pore volume (mL / g) and percentage (%) of pores above (or below) a specified pore radius, and the coefficient of variation of pore volume, etc., can be calculated. It should be noted that the maximum pore radius (μm) refers to the pore radius of the pore that shows the maximum pore volume. In addition, the pore volume (mL / g) of each pore radius is calculated using the log differential pore volume (mL / g) in the log differential pore volume distribution.

[0120] Here, for the pores (voids) of absorbent A, the ratio 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 of the total pore volume. Since the ratio of the pore volume of pores with a pore radius of 1 μm or more is 90% or more, during water absorption, water is less likely to enter pores with a pore radius of less than 1 μm, and even if it does not enter, sufficient water absorption can be ensured. Therefore, the decrease in water absorption compared to the pore volume can be suppressed, and excellent absorption performance can be obtained.

[0121] For the pores of absorbent A, the ratio of the pore volume based on pores with a pore radius of 0.005 μm or less is preferably less than 10% of the total pore volume (total pore volume), and more preferably less than 10% of the total pore volume (total pore volume). For absorbent A, the ratio of the pore volume based on pores with a pore radius of 0.005 μm or less (which are very small and difficult to absorb water) is very small, while the ratio of the pore volume based on pores with a pore radius of 1 μm or more (which are large and capable of absorbing water) is large (over 90%). Therefore, the pores of absorbent A can be effectively utilized for water absorption, ensuring sufficient water absorption.

[0122] Furthermore, regarding the pores of absorbent A, the pore radius of the pores at which the maximum pore volume is shown 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. Setting the pore radius to 500 μm or less when the pore volume is at its maximum prevents the continuous framework structure of absorbent A from being damaged (crushed) during water absorption, easily achieving excellent absorption rates and consistently ensuring sufficient water absorption. If the pore radius is 500 μm or more when the pore volume is at its maximum, the continuous framework structure may not be maintained during water absorption, potentially leading to crushing.

[0123] Furthermore, for the micropores of absorbent A, the variation coefficient of the micropore distribution (micropore volume) for micropores with a micropore radius of 1 μm or greater can be 1.4 or less. When the variation coefficient of the micropore distribution is 1.4 or less, the deviation of the micropore radius relative to the average micropore radius is small, and the peaks shown by the micropore distribution near the average micropore radius become sharp. Therefore, absorbent A can absorb moisture approximately uniformly from all directions / the entire surface. Thus, the micropores of the polymer absorbent can be effectively utilized for water absorption, ensuring sufficient water absorption.

[0124] On the other hand, for the pores of absorbent A, the coefficient of variation of the pore distribution (pore volume) for pores with a pore radius of 1 μm or more can exceed 1.4. In this case, because 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 shown by this pore distribution becomes broader near the average pore radius. That is, absorbent A contains both small and large pores. Therefore, for pores with small pore radii, capillary forces are more likely to function, thus increasing the water absorption rate; for pores with large pore radii, the water absorption volume is more likely to increase. Therefore, through the synergistic effect of both, absorbent A can instantly absorb a large amount of water into the interior of the pores.

[0125] Here, regarding the pores of absorbent A, when considering the peak width shown in the pore distribution curve, the portion of the pore radius corresponding to the maximum pore volume in the curve showing the pore distribution can be wider on the larger side compared to the smaller side. In this case, absorbent A has a configuration with more pores with larger pore radii than pores with smaller pore radii. Therefore, with more pores with larger pore radii, the water absorption volume is more easily increased, allowing a larger amount of water to be absorbed into the interior of the pores.

[0126] On the other hand, regarding the pores of absorbent A, even if the pore distribution shows a peak width, the portion of the pore radius corresponding to the maximum pore volume in the curve showing the pore distribution can be wider on the smaller side compared to the larger pore radius side. In this case, absorbent A has a configuration with more pores with smaller pore radii than pores with larger pore radii. Because there are more pores with smaller pore radii, capillary forces are more easily activated, thereby increasing the water absorption rate and allowing for faster, more instantaneous absorption of water into the interior of the pores.

[0127] Furthermore, for the pores of absorbent A, there can be at least two maxima in the pore volume shown in the curve illustrating the pore distribution. In this case, for absorbent A, there are pores with a defined small pore radius and its vicinity, and pores with a defined large pore radius and its vicinity. Therefore, for pores with relatively small pore radii, capillary forces are more readily applied, thus increasing the water absorption rate; for pores with relatively large pore radii, the water absorption volume is more readily increased. Thus, through the synergistic effect of both, the polymeric absorbent can instantly absorb a large amount of water into the interior of the pores.

[0128] Here, regarding the pores of absorbent A, if there are two maxima of pore volume, the maxima of the relatively smaller pore radius can be larger than the maxima of the relatively larger pore radius in the curve showing the pore distribution. In this case, absorbent A has more pores with smaller pore radii compared to those with larger pore radii. With more pores with smaller pore radii, capillary forces are more easily activated, thus increasing the water absorption rate and allowing for faster, more instantaneous absorption of water into the pores.

[0129] On the other hand, even if there are two maxima in the pore volume of absorbent A, for the two maxima of pore volume shown in the curve illustrating the pore distribution, the maxima of the relatively smaller pore radius can be smaller than the maxima of the relatively larger pore radius. In this case, for absorbent A, there are more pores with larger pore radii compared to those with smaller pore radii. With more pores with larger pore radii, the water absorption volume is more easily increased, allowing a larger amount of water to be absorbed into the interior of the pores.

[0130] Furthermore, for the fine pores of absorbent A, the bulk density is preferably 0.07–0.6 g / cm³. 3 More preferably 0.1–0.4 g / cm³ 3 Further optimization is needed, with a concentration of 0.15–0.35 g / cm³. 3At this point, as described later, the water 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, the water absorption rate is faster, so the polymer absorbent can further absorb water into the interior of the pores instantly.

[0131] <Method for determining water absorption rate (DW)>

[0132] The water absorption rate of the absorbent was determined using the Demand Wettability (DW) method without pressure. Figure 11 This is a schematic diagram illustrating the measuring apparatus used in the unpressurized Demand-Wettability (DW) method. As this measuring apparatus, a Demand-Wettability (DW) device (manufactured by Taiyo Create 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, valves 15 and 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.

[0133] The measurement procedure is as follows.

[0134] (1) With the two valves 15 and 16 of the DW device 11 closed, add the test solution 20 to above the 0 point (the uppermost mark of the burette 12 (0ml line)), install the rubber stopper 13 on the upper part of the burette 12 and seal it.

[0135] (2) After placing filter paper at the liquid outlet 18 of the measuring platform 17, open the two valves 15 and 16. While the filter paper absorbs the liquid coming out of the liquid outlet 18, make the liquid level align with the 0 point. After adjustment, close valves 15 and 16.

[0136] (3) A 100% wood pulp thin paper (weight per unit area of ​​15 ± 1 gsm, pressure measured using a nonwoven fabric thickness gauge of 3 g / cm) was placed on the measuring table 17 with the liquid outlet 18 as the center. 2 The thickness at that time was 0.1 ± 0.02 mm.

[0137] (4) A cylinder 19 with a diameter of 30 mm is placed in the center of the thin paper, and the test object (polymer absorbent) is placed in it with the liquid outlet 18 as the center. The test object is added into the cylinder 19 and is confined by the cylinder 19.

[0138] (5) Open valves 15 and 16, and the test object begins to absorb the test liquid 20. The moment 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 moment when the water surface of the test liquid 20 in the burette 12 decreases) is set as the measurement start time.

[0139] (6) Continuously read the decrease in test solution 20 in burette 12 (the amount of test solution 20 absorbed by the test object) M (ml).

[0140] (7) The amount of the test object absorbed after a specified time (30 seconds in this embodiment) from the start of liquid absorption is calculated by the absorption amount (ml / g) obtained by the DW method = M (ml) / (weight (g) of the test object (polymer absorbent)).

[0141] The following describes the appearance of absorbent A in contact with bodily fluids (hereinafter referred to as "bodily fluids"). The same applies to the contact between the composite absorbent 4 containing absorbent A and bodily fluids. Furthermore, the mass of the absorbed bodily fluid is approximately proportional to the volume of the bodily fluid; therefore, in the following description, the mass of the bodily fluid will sometimes be referred to simply as the "volume of the bodily fluid."

[0142] first, Figures 3-7 The absorbent A shown has a continuous porous structure consisting of multiple interconnected pores, which can be visually confirmed by the presence of numerous pores. When bodily fluids such as urine or menstrual blood come into contact with this porous absorbent A, the hydrophilic continuous framework initially expands (i.e., swells) by instantaneously introducing a portion of the fluid through osmotic pressure. This expansion of the continuous framework occurs in almost all directions. The absorbent A, having absorbed a certain amount of fluid and increased in size, can further absorb a specified amount of fluid into the enlarged continuous pores through capillary action. Thus, absorbent A exhibits a unique water-absorbing behavior when absorbing water (bodily fluids): introducing water into the hydrophilic continuous framework and then introducing and absorbing it into the continuous pores.

[0143] It should be noted that the body fluid absorbed into the hydrophilic continuous skeleton of absorbent A is not easily released from the continuous skeleton (i.e., it is not easy to release water), while the body fluid absorbed into the continuous pores is easy to release water. Therefore, in the composite absorbent, the body fluid absorbed into the continuous pores releases water and is transported to the superabsorbent polymer (SAP) with high water retention capacity, and is firmly retained in the SAP.

[0144] Here, regarding the amount of body fluid absorbed into the continuous skeleton of absorbent A and the amount of body fluid absorbed into the continuous pores, of the total amount of body fluid absorbed by absorbent A, the amount of body fluid released by absorbent A through centrifugation (150G / 90 seconds) is the amount of body fluid absorbed into the continuous pores, and the other amount of body fluid (i.e., the amount of body fluid that was not released by absorbent A through centrifugation) is the amount of body fluid absorbed into the continuous skeleton.

[0145] Furthermore, compared to body fluid absorbed into the hydrophilic continuous framework, more body fluid remains within the pores when absorbed by absorbent A. Since most of the body fluid absorption achieved using absorbent A occurs through capillary action, retaining the body fluid within the pores, a higher porosity (the volume of pores relative to the volume of absorbent A) allows for the absorption of more body fluid. It should be noted that this porosity is preferably 85% or higher.

[0146] For example, if the above is obtained... Figures 3-7 The porosity of absorbent A shown is as follows.

[0147] Firstly, absorbent A, obtained using the mercury intrusion porosimetry method, has a specific surface area of ​​400 m². 2 / g, pore volume is 15.5mL / g. This pore volume of 15.5mL / g means that the volume of the pores in 1g of absorbent A is 15.5mL.

[0148] If the specific gravity of absorbent A is assumed to be 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.

[0149] Therefore, the total volume of 1g of absorbent A is 15.5+1 (mL), and the ratio of the pore volume is the porosity. Thus, the porosity of absorbent A is 15.5 / (15.5+1)×100≒94%.

[0150] The absorbent A, i.e., the polymer absorbent, which has this hydrophilic continuous skeleton and continuous pores, is used in composite absorbent bodies such as the composite absorbent body 4 of the aforementioned incontinence pad 1 for absorbing bodily fluids such as urine and menstrual blood, for example in the form of granules or flakes.

[0151] Furthermore, as described above, this polymeric absorbent exhibits a unique water-absorbing behavior when absorbing moisture: it introduces water into a hydrophilic continuous framework and then into continuous pores. Therefore, it can instantly absorb large amounts of body fluid, and then transport this absorbed body fluid (mainly the fluid absorbed into the continuous pores) to the high-water-retention SAP (Superabsorbent Polymer), where it is firmly retained. Thus, composite absorbents using this polymeric absorbent can exhibit high absorption performance.

[0152] The water absorption capacity of polymeric absorbents can be determined according to the following <Method for Determining the Water Absorption Capacity of Polymeric Absorbents>.

[0153] <Method for Determining the Water Absorption Capacity of Polymer Absorbents>

[0154] (1) Seal 1g of the test sample (polymer absorbent) into a mesh bag cut into 10cm squares (manufactured by NBCMeshtec Inc., N-NO255HD 115 (standard width: 115cm, 255 meshes / 2.54cm, opening: 57μm, wire diameter: 43μm, thickness: 75μm)). It should be noted that the mass (g) of the mesh bag is measured beforehand. Furthermore, this test method is performed at a temperature of 25°C and a humidity of 60%. If the test sample (polymer absorbent) is recycled from a sanitary product, it can be obtained according to the <Recycling Method of Test Sample (Polymer Absorbent)> described later.

[0155] (2) Immerse the mesh bag containing the sample in physiological saline (0.9% sodium chloride aqueous solution) for 1 hour.

[0156] (3) Determine the mass (g) of the mesh bag after it has been suspended for 5 minutes to drain water.

[0157] (4) Subtract the mass of the sample (=1g) and the total mass of the mesh bag from the mass of the mesh bag after water control determined in (3) above, and calculate the water absorption (g) of the sample. Then divide the water absorption by the mass of the sample (=1g) to obtain the water absorption per unit mass of the sample (polymer absorbent) (g / g).

[0158] It should be noted that when the test sample (polymer absorbent) is recycled from the sanitary product, it can be obtained according to the following <Recycling Method of Test Sample (Polymer Absorbent)>.

[0159] <Method for recovering the sample (polymer absorbent) used in the determination>

[0160] (1) Peel off the surface sheet or other parts of the sanitary product to expose the absorbent.

[0161] (2) Allow the analyte (polymer absorbent) to fall from the exposed absorber, and use tweezers or the like to remove the (particulate) analyte other substances (such as pulp, synthetic resin fibers, etc.).

[0162] (3) As a means of magnified observation, a microscope or a simple magnifying glass is used to observe the sample at a magnification that allows for the recognition of the difference from SAP or to visually confirm the pores of the porous body. At the same time, tweezers or similar tools are used to retrieve the sample. It should be noted that the magnification of the simple magnifying glass is not particularly limited if it is a magnification that allows for visual confirmation of the pores of the porous body. For example, magnifications of 25x to 50x can be listed.

[0163] (4) The analytes recovered in this way are used as test samples in various test methods.

[0164] The manufacturing method of this polymeric absorbent will be described in detail below, using absorbent A as an example.

[0165] [Manufacturing method of polymeric absorbent]

[0166] The above-mentioned absorbent A can be as follows: Figure 2 As shown, it is obtained through a cross-linking polymerization process and a hydrolysis process. These processes are explained below.

[0167] (Cross-linking polymerization process)

[0168] First, oil-soluble monomers for crosslinking polymerization, crosslinking monomers, surfactants, water, and a polymerization initiator as needed are mixed to obtain a water-in-oil droplet emulsion. This water-in-oil droplet emulsion is an emulsion in which the oil phase forms a continuous phase and water droplets are dispersed therein.

[0169] Next, regarding the absorbent A mentioned above, such as Figure 2 As shown in the figure above, butyl methacrylate, an oil-soluble monomer, is used as a (meth)acrylate; divinylbenzene is used as a crosslinking monomer; sorbitol monooleate is used as a surfactant; and isobutyronitrile is used as a polymerization initiator to carry out crosslinking polymerization to obtain the monolithic column A.

[0170] Specifically, for absorbent A, such as Figure 2 As shown in the figure above, first mix 9.2g of tert-butyl methacrylate as an oil-soluble monomer, 0.28g of divinylbenzene as a crosslinking monomer, 1.0g of sorbitan monooleate (hereinafter referred to as "SMO") as a surfactant, and 0.4g of 2,2'-azobis(isobutyronitrile) as a polymerization initiator and dissolve them evenly.

[0171] 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 stirring degassing mixer (manufactured by EME, Inc.) as a planetary stirring device to obtain a water-in-oil droplet emulsion.

[0172] The emulsion was then rapidly transferred to a reaction vessel and sealed, and polymerized at 60°C for 24 hours. After polymerization, the contents were removed, extracted with methanol, and dried under reduced pressure to obtain a monolithic column A with a continuous macroporous structure. It should be noted that SEM observation of the internal structure of monolithic column A revealed a continuous bubble structure with a continuous framework thickness of 5.4 μm. Furthermore, mercury porosimetry determined the average diameter of the continuous pores to be 36.2 μm and the total micropore volume to be 15.5 mL / g.

[0173] It should be noted that the content of divinylbenzene relative to all monomers is preferably 0.3 to 10 mol%, more preferably 0.3 to 5 mol%. Furthermore, 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%. It should be noted that 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%.

[0174] The amount of surfactant added can be set according to the type of oil-soluble monomer and the desired size of emulsion particles (macropores), and is preferably in the range of about 2% to 70% relative to the total amount of oil-soluble monomer and surfactant.

[0175] It should be noted that, in order to control the shape and size of the bubbles in column 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 can coexist in the polymerization system.

[0176] Furthermore, there are no particular restrictions on the mixing method when forming water-in-oil droplet emulsions. For example, any mixing method can be used, such as mixing all components together at once, or dissolving the oil-soluble components (which are oil-soluble monomers, surfactants, and oil-soluble polymerization initiators) and the water-soluble components (which are water-soluble polymerization initiators) uniformly separately and then mixing the components.

[0177] Furthermore, there are no particular limitations on the mixing device used to form the emulsion. Any device such as a conventional mixer, homogenizer, or high-pressure homogenizer can be used depending on the desired emulsion particle size. Alternatively, a so-called planetary mixing device can be used, in which the material to be treated is added to a mixing container, and the mixing container rotates on its own axis while being tilted, thereby stirring and mixing the material to be treated.

[0178] 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 size. It should be noted that when using the aforementioned planetary stirring device, water droplets in the W / O emulsion can be generated uniformly, and their average diameter can be set arbitrarily within a wide range.

[0179] The polymerization conditions for water-in-oil droplet emulsions can vary 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.

[0180] It should be noted that after polymerization, the contents are removed and subjected to Soxhlet extraction using solvents such as isopropanol. This removes unreacted monomers and residual surfactants, yielding the desired product. Figure 2 The overall column A is shown in the middle figure.

[0181] (Hydrolysis process)

[0182] Next, the process of hydrolyzing the monolithic column A (crosslinked polymer) to obtain absorbent A (hydrolysis process) will be described.

[0183] First, the monolithic column A is immersed in dichloroethane containing zinc bromide and stirred at 40°C for 24 hours. It is then hydrolyzed by sequential contact with methanol, 4% hydrochloric acid, 4% sodium hydroxide aqueous solution, and water, followed by drying to obtain a block-shaped absorbent A. Next, the block-shaped absorbent A is pulverized into a specified size to obtain granular absorbent A. It should be noted that the form of absorbent A is not limited to granules; for example, it can be formed into flakes during or after drying.

[0184] Furthermore, there are no particular restrictions on the method of hydrolyzing the monolithic column A; various methods can be used. Examples include contacting 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, 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; or contacting hydrohalic 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.

[0185] In addition, among the polymer raw materials of 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., carbon number 1 to 10) alkyl esters of (meth)acrylates are preferred, and C4 (i.e., carbon number 4) alkyl esters of (meth)acrylates are particularly preferred.

[0186] It should be noted that, as C4 alkyl esters of (meth)acrylic acid, examples include tert-butyl (meth)acrylic acid, n-butyl (meth)acrylic acid, and isobutyl (meth)acrylic acid.

[0187] In addition, the monomers used in crosslinking polymerization can be only (meth)acrylate and divinylbenzene, or they can contain other monomers besides (meth)acrylate and divinylbenzene.

[0188] In the latter case, other monomers are not particularly limited, and 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.

[0189] It should be noted that the ratio of monomers other than (meth)acrylate and divinylbenzene in the total monomers used in the crosslinking polymerization is preferably 0 to 80 mol%, more preferably 0 to 50 mol%.

[0190] Furthermore, the surfactant is not limited to the aforementioned sorbitol monooleate; any surfactant that can form a water-in-oil (W / O) emulsion when the monomer for crosslinking polymerization is mixed with 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 alone or in combination of two or more.

[0191] Furthermore, polymerization initiators are suitably compounds that generate free radicals through heat and light irradiation. Moreover, polymerization initiators can be water-soluble or oil-soluble, and examples include azobis(4-methoxy-2,4-dimethylpentanonitrile), azobisisobutyronitrile, azobisdimethylpentanonitrile, azobiscyclohexanenitrile, azobiscyclohexaneformitrile, 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 need, there are also systems where polymerization occurs even without the addition of a polymerization initiator, only through heating and light irradiation; therefore, when using such systems, it is not necessary to add a polymerization initiator.

[0192] Example

[0193] The following embodiments illustrate the present invention, but the present invention is not limited to these embodiments.

[0194] (A) Sample

[0195] (a) For pore distribution

[0196] The polymeric absorbent of the present invention, manufactured using the above-described manufacturing method, was prepared as samples for Examples 1-5, and Infinity particles were prepared as samples for Comparative Examples 1-2. For the samples of Examples 1-5, the surfactant / monomer ratio (wt%) and stirring time (minutes) during the formation of the water-in-oil droplet emulsion were varied. Furthermore, Infinity particles refer to absorbents manufactured by P&G Corporation, which have a structure similar to polymeric absorbents (foamed structure), but unlike polymeric absorbents, they do not have the function of absorbing water and swelling.

[0197] (b) The relationship between bulk density and water absorption rate

[0198] For the samples in the above embodiments, samples with various bulk densities were prepared by changing the conditions of ethanol impregnation and drying. Specifically, after the dried polymer absorber was fully impregnated in a 40% ethanol aqueous solution, the supernatant was repeatedly removed and ethanol was added to adjust the ethanol aqueous solution to a specified concentration. After full impregnation, the wet polymer absorber was filtered and dried under reduced pressure at 50°C overnight to obtain polymer absorbers with different bulk densities.

[0199] (B) Evaluation

[0200] (a) For pore distribution

[0201] Using mercury porosimetry, for each sample, the cumulative pore volume distribution (the relationship between pore radius and cumulative pore volume), the log differential pore volume distribution (the 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 ratio of pore volume above (below) the specified pore radius, and the pore volume variation coefficient are calculated.

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

[0203] The relationship between the bulk density and the water absorption rate (DW) of each sample was investigated by measuring the water absorption rate (DW).

[0204] (C) Evaluation Results

[0205] (a) For pore distribution

[0206] The measurement results are as follows Figure 8 and Figure 9 The contents summarized from these are shown in Table 1. Among them, Figure 8 This represents the cumulative pore volume distribution, i.e., the relationship between pore radius (horizontal axis) and cumulative pore volume (vertical axis). Figure 9 This represents the logarithmic differential pore volume distribution, i.e., the relationship between the pore radius (horizontal axis) and the logarithmic differential pore volume (vertical axis). It should be noted that... Figure 8 and Figure 9 In the examples, Example 1 is a dashed line (thick line), Example 2 is a dotted line (thin line), Example 3 is a dashed line (thin line), Example 4 is a dotted line, Example 5 is a solid line (thin line), Comparative Example 1 is a solid line (thick line), and Comparative Example 2 is a dotted line (thick line).

[0207] [Table 1]

[0208]

[0209] *Pore radius greater than 1μm

[0210] For the samples of Examples 1 to 5, the following can be confirmed.

[0211] The ratio of pore volume based on pores with a radius of 1 μm or more is 90% or more of the total pore volume. The ratio of pore volume based on pores with a radius of 0.005 μm or less is less than 10% of the total pore volume. The pore radius at which the maximum pore volume is reached is 500 μm or less. The coefficient of variation of the pore distribution for pores with a radius of 1 μm or more is sometimes 1.4 or less (Example 3). For pores with a radius of 1 μm or more, the coefficient of variation of the pore distribution sometimes exceeds 1.4 (Examples 4 and 5). For the pore radius corresponding to the maximum pore volume in the curve showing the pore distribution, the portion on the larger side of the pore radius is sometimes wider than the portion on the smaller side of the pore radius (Example 5). For the pore radius corresponding to the maximum pore volume in the curve showing the pore distribution, the portion on the smaller side of the pore radius is sometimes wider than the portion on the larger side of the pore radius (Example 4). In the curves showing the pore volume distribution, there are sometimes at least two maxima of pore volume (Examples 1 and 2). For the two maxima of pore volume in the curves showing the pore volume distribution, the maxima of the relatively smaller pore radius is sometimes larger than the maxima of the relatively larger pore radius (Example 2). For the two maxima of pore volume in the curves showing the pore volume distribution, the maxima of the relatively smaller pore radius is sometimes smaller than the maxima 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 ratio of pore volume based on pores with a pore radius of 1 μm or more is less than 90% of the total pore volume.

[0212] (b) The relationship between bulk density and water absorption rate

[0213] The measurement results are as follows Figure 10 As shown. Figure 10 This is a graph showing the relationship between the obtained bulk density (horizontal axis) and water absorption rate (vertical axis). As shown in the figure, it can be confirmed that by setting the bulk density to 0.07–0.6 g / cm³... 3 This allows for a water absorption rate (DW) of 6 mL / 30 sec or higher. Furthermore, it can be confirmed that setting the bulk density to 0.1–0.4 g / cm³ is sufficient. 3 This allows for a water absorption rate (DW) of 10 mL / 30 sec or higher. Furthermore, it can be confirmed that setting the bulk density to 0.15–0.35 g / cm³ is sufficient. 3 It can achieve a water absorption rate (DW) of 12 mL / 30 sec or higher.

[0214] It should be noted that, in addition to the light incontinence pad described in the above embodiments, the composite absorbent of the present invention can also be applied to various hygiene products such as shorts-type disposable diapers, band-type disposable diapers, sanitary napkins, absorbent linings, absorbent pads (e.g., pressure ulcer pads, maternity pads, etc.), absorbent sheets, breast pads, disposable diapers for pets, absorbent pads for pets, pet waste disposal sheets, wet wipes, wet wipes, cosmetic wipes, and masks. Therefore, the bodily fluids that the composite absorbent is intended to absorb are liquids excreted by the wearer of the hygiene products, such as urine, sweat, feces, menstrual blood, vaginal discharge, breast milk, blood, and exudate.

[0215] Furthermore, the present invention is not limited to the above-described embodiments, and can be appropriately combined, substituted, or modified without departing from the purpose and spirit of the present invention.

[0216] Explanation of reference numerals in the attached figures

[0217] 1. Light incontinence pad

[0218] 2 Surface sheet

[0219] 3. Back side

[0220] 4. Complex Absorber

Claims

1. A composite absorbent body, characterized by, A composite absorbent for a sanitary product for absorbing body fluids, The composite absorbent includes a high-molecular absorbent having a continuous skeleton and continuous pores with hydrophilicity, In the high-molecular absorbent, the ratio of the pore volume of the pores having a pore radius of 1 μm or more is 90% or more of the total pore volume, The high-molecular absorbent is a hydrolysis product of a crosslinked polymer of (meth)acrylate and divinylbenzene which is a compound having two or more vinyl groups in one molecule, The ratio of the crosslinked polymer residue of divinylbenzene in the organic polymer forming the continuous skeleton with hydrophilicity is 0.1 to 30 mol% with respect to the total structural units.

2. The composite absorbent according to claim 1, wherein, In the high-molecular absorbent, the ratio of the pore volume of the pores having a pore radius of 0.005 μm or less is less than 10% of the total pore volume.

3. The composite absorbent according to claim 1 or 2, characterized in that, In the high-molecular absorbent, the pore radius at the maximum value of the pore volume is 500 μm or less.

4. The composite absorbent according to claim 1 or 2, characterized in that, In the high-molecular absorbent, the pore distribution coefficient of the pores having a pore radius of 1 μm or more is 1.4 or less.

5. The composite absorbent according to claim 1 or 2, wherein In the high-molecular absorbent, the pore distribution coefficient of the pores having a pore radius of 1 μm or more exceeds 1.

4.

6. The composite absorbent according to claim 5, wherein, In the high-molecular absorbent, for the pore radius corresponding to the maximum value of the pore volume in the curve showing the pore distribution, the large-pore-radius side is wider than the small-pore-radius side.

7. The composite absorbent body according to claim 5, wherein In the high-molecular absorbent, for the pore radius corresponding to the maximum value of the pore volume in the curve showing the pore distribution, the small-pore-radius side is wider than the large-pore-radius side.

8. The composite absorbent according to claim 1 or 2, wherein, In the high-molecular absorbent, there are at least two maximum values of the pore volume in the curve showing the pore distribution.

9. The composite absorbent according to claim 8, wherein, In the high-molecular absorbent, for the two maximum values of the pore volume in the curve showing the pore distribution, the maximum value of the relatively small pore radius is larger than the maximum value of the relatively large pore radius.

10. The composite absorbent body according to claim 8, wherein In the high-molecular absorbent, for the two maximum values of the pore volume in the curve showing the pore distribution, the maximum value of the relatively small pore radius is smaller than the maximum value of the relatively large pore radius.

11. The composite absorbent according to claim 1 or 2, wherein In the high-molecular absorbent, the total pore volume is 0.9 mL / g or more.

12. The composite absorbent according to claim 1 or 2, wherein, In the high molecular absorbent, the bulk density is 0.07-0.6 g / cm 3 .

13. The composite absorbent according to claim 1 or 2, wherein The high-molecular absorbent is a monolithic columnar absorbent.

14. The composite absorbent according to claim 1 or 2, wherein, The high-molecular absorbent contains at least one -COONa group.

15. A sanitary article, characterized in that It has the composite absorbent described in any one of claims 1 to 14.

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