Composite absorbent material and sanitary products using the same

Abstract

To provide a composite absorber that can suppress leakage of body fluid while suppressing the thickness and can exert high absorption performance.SOLUTION: A composite absorber (4) is used for sanitary article for absorbing body fluid. The composite absorber includes: a pulp fiber; a polymer absorber including a hydrophilic continuous skeleton and a continuous vacancy; and a high-water absorption polymer. A speed of initial absorption rate represents as: pulp fiber>polymer absorber>high-water absorption polymer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a composite absorbent body and a sanitary product using the same. [Background technology]

[0002] Absorbents used in sanitary products such as disposable diapers and sanitary napkins are known to contain pulp fibers and superabsorbent polymers. By containing a superabsorbent polymer, the amount of pulp fibers is reduced while maintaining the absorption performance, making the absorbent and therefore the sanitary product thinner, and improving the wearing comfort of the sanitary product.

[0003] As a highly water-absorbent polymer used in sanitary products, for example, water-absorbent resin particles are disclosed in Patent Document 1. According to Patent Document 1, the water-absorbent resin particles contain a crosslinked polymer containing at least one of acrylic acid and a salt thereof as a monomer unit, have a physiological saline absorption rate of 1 to 15 seconds, a median particle diameter of 100 to 600 μm, and a residual volatile component amount of 0.44% by mass or more and 1.5% by mass or less, and the residual volatile component is at least one selected from the group consisting of chain aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6872503 Summary of the Invention [Problem to be solved by the invention]

[0005] In an absorbent body containing pulp fibers and a superabsorbent polymer, the pulp fibers, which have a high absorption rate, first absorb body fluids because the superabsorbent polymer, which has a high water retention capacity, has a slow absorption rate, and then the superabsorbent polymer absorbs the body fluid absorbed by the pulp fibers. However, if the transfer rate of body fluids from the pulp fibers to the superabsorbent polymer is too slow, when a large amount of body fluid is excreted, the pulp fibers may not be able to absorb it all, and the transfer of body fluids from the pulp fibers to the superabsorbent polymer may not be able to keep up. In that case, leakage of body fluids from the absorbent body cannot be prevented, and the water retention capacity of the superabsorbent polymer, and therefore the absorption performance of the absorbent body, may not be fully exhibited.

[0006] According to the description in Patent Document 1, the water-absorbent resin particles have an improved absorption rate compared to general superabsorbent polymers. However, according to the inventor's study, the absorption rate is not sufficiently fast, and therefore the migration rate from the pulp fibers to the water-absorbent resin particles is not sufficient. Therefore, when a large amount of body fluid is excreted, leakage of body fluid from the absorbent body cannot be denied, and there is a risk that the water retention capacity of the superabsorbent polymer, and therefore the absorption performance of the absorbent body, cannot be fully exhibited.

[0007] An object of the present invention is to provide a composite absorbent body that can suppress leakage of body fluids while keeping the thickness small and exhibit high absorption performance, and a sanitary product using the same. [Means for solving the problem]

[0008] One aspect of the present invention is a composite absorbent for sanitary products to absorb body fluids, the composite absorbent comprising pulp fibers, a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer, wherein the initial absorption rate is in the order of pulp fibers > polymer absorbent > superabsorbent polymer.

[0009] Another aspect of the present invention is a sanitary article comprising a top sheet, a back sheet, and the above-described composite absorbent body positioned between the top sheet and the back sheet. Effect of the Invention

[0010] According to the present invention, it is possible to provide a composite absorbent body that can suppress leakage of bodily fluids while keeping the thickness small and can exhibit high absorption performance, and a sanitary product using the same. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic plan view of a disposable diaper 1 according to an embodiment in an unfolded state, as viewed in a thickness direction from the skin-facing surface side. [Diagram 2] FIG. 2 is a diagram illustrating a manufacturing process of absorbent A, which is an example of a polymer absorbent according to an embodiment. [Diagram 3] This is an SEM photograph of absorbent A at a magnification of 50 times. [Figure 4] This is an SEM photograph of absorbent A at a magnification of 100 times. [Diagram 5] This is an SEM photograph of absorbent A at a magnification of 500 times. [Figure 6] This is an SEM photograph of absorbent A at a magnification of 1500 times. [Figure 7] 1 is a graph showing the relationship between liquid transfer rate and transfer time. [Figure 8] 1 is a graph showing the relationship between absorption rate and absorbent body thickness. [Figure 9] FIG. 1 is a schematic diagram showing a measurement device used in a pressureless DW method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present embodiment relates to the following aspects. [Aspect 1] A composite absorbent for sanitary products for absorbing body fluids, comprising pulp fibers, a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer, wherein the initial absorption rate is in the order of pulp fibers>polymer absorbent>superabsorbent polymer.

[0013] In this composite absorbent, the order of the initial absorption speed is pulp fiber>polymer absorbent>superabsorbent polymer. Therefore, the polymer absorbent first receives (absorbs) the body fluid absorbed by the pulp fiber, and then the superabsorbent polymer receives (absorbs) the body fluid absorbed by the polymer absorbent. In this way, the body fluid absorbed by the pulp fiber, which has a high absorption speed, is first transferred (absorbed) sequentially to the polymer absorbent, which has a relatively high absorption speed, so that it is possible to prevent the pulp fiber from being unable to absorb all the body fluid. Furthermore, the body fluid absorbed by the polymer absorbent is transferred (absorbed) sequentially to the superabsorbent polymer, which has a slow absorption speed but high absorption performance, so that it is possible to prevent the body fluid from being transferred to the superabsorbent polymer too late. As a result, it is possible to prevent leakage of body fluid from the composite absorbent while suppressing the thickness, and it is possible to fully demonstrate the water retention capacity of the superabsorbent polymer and, in turn, the absorption performance of the absorbent.

[0014] [Aspect 2] 2. The composite absorbent according to claim 1, wherein the polymer absorbent has an absorption speed of 5 seconds or less as measured by the Vortex method. In this composite absorbent, body fluids once absorbed by the pulp fibers can be transferred quickly to the polymer absorbent in a short time (within 5 seconds). This prevents the pulp fibers from accumulating too much body fluid, slowing down the absorption rate of the pulp fibers, or preventing the pulp fibers from absorbing all of the body fluid. This allows the pulp fibers, which have a fast absorption rate, to quickly transfer the body fluid absorbed to the polymer absorbent, which in turn transfers the body fluid to the highly absorbent polymer, which has high absorption performance. This prevents leakage of body fluids from the composite absorbent, allowing the composite absorbent to fully exhibit its absorption performance.

[0015] [Aspect 3] 3. The composite absorbent of claim 1 or 2, wherein a liquid transfer rate from the pulp fibers is such that the polymer absorbent is greater than the superabsorbent polymer. In this composite absorbent, the body fluid absorbed by the pulp fibers can be transferred quickly to the polymer absorbent, which has a fast absorption rate, first, faster than the transfer to the superabsorbent polymer, which has a slow absorption rate. This prevents the pulp fibers from accumulating too much body fluid, slowing down the absorption rate of the pulp fibers, or preventing the pulp fibers from absorbing all the body fluid. This allows the body fluid absorbed by the pulp fibers to be continuously and quickly transferred to the polymer absorbent, and the polymer absorbent can further transfer the body fluid transferred to the superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent, and allows the composite absorbent to fully exhibit its absorption performance.

[0016] [Aspect 4] Aspect 4. The composite absorbent body according to any one of aspects 1 to 3, wherein an amount of liquid transferred to the superabsorbent polymer is such that the polymer absorbent is greater than the amount of the pulp fiber. In this composite absorbent, more body fluid can be transferred to and absorbed by the polymer absorbent than by the pulp fibers, and the body fluid transferred to the polymer absorbent can be transferred to the superabsorbent polymer in a larger amount than by the pulp fibers. Therefore, the absorbency of the polymer absorbent can be restored after the transfer of body fluid. This allows the body fluid absorbed by the pulp fibers to be continuously and quickly transferred to the polymer absorbent, and the body fluid transferred to the polymer absorbent can be further transferred to the superabsorbent polymer. Therefore, leakage of body fluid from the composite absorbent can be suppressed, and the absorption performance of the composite absorbent can be fully exhibited.

[0017] [Aspect 5] A composite absorbent body according to any one of claims 1 to 4, wherein (the basis weight of the pulp fibers) / (the basis weight of the polymer absorbent) is greater than 1, and / or (the basis weight of the superabsorbent polymer) / (the basis weight of the polymer absorbent) is greater than 1. In this composite absorbent, since the basis weight of the pulp fibers is greater than that of the polymer absorbent, the pulp fibers, which have a high absorption rate, can easily absorb body fluids in the initial stage, and the body fluids absorbed by the pulp fibers can be easily transferred to the polymer absorbent after that. When the basis weight of the superabsorbent polymer is greater than that of the polymer absorbent, the polymer absorbent can easily come into contact with the superabsorbent polymer, and the body fluids absorbed by the polymer absorbent can be easily transferred to the superabsorbent polymer. This allows the pulp fibers to quickly absorb body fluids, the pulp fibers to quickly transfer the body fluids to the polymer absorbent, and the polymer absorbent to quickly transfer the body fluids to the superabsorbent polymer. This makes it possible to suppress leakage of body fluids from the composite absorbent, and to fully demonstrate the absorption performance of the composite absorbent.

[0018] [Aspect 6] A composite absorbent body according to any one of aspects 1 to 5, wherein the water absorption amount according to a non-pressure demand wettability method is such that the polymer absorbent is greater than the highly water-absorbent polymer. In this composite absorbent, the polymer absorbent can draw in free water that may occur in gaps between the nonwoven fabric and the polymer absorbent, and in gaps between the polymer absorbents, when absorbed body fluids diffuse. In other words, the polymer absorbent can absorb free water without leaking. This makes it possible to suppress leakage of body fluids from the composite absorbent, and allows the composite absorbent to fully exhibit its absorption performance.

[0019] [Aspect 7] A composite absorbent body according to any one of aspects 1 to 6, wherein the discharge amount of absorbed liquid is such that the polymer absorbent>the highly absorbent polymer, and the discharge rate of absorbed liquid is such that the polymer absorbent>the highly absorbent polymer. In this composite absorbent, the polymer absorbent can easily transfer the body fluid that it has absorbed to the superabsorbent polymer, so the body fluid transferred from the pulp fibers can be quickly transferred from the polymer absorbent to the superabsorbent polymer. This allows the body fluid absorbed by the pulp fibers to be quickly transferred to the polymer absorbent, and the body fluid transferred to the polymer absorbent can be further transferred to the superabsorbent polymer. This makes it possible to prevent leakage of body fluid from the composite absorbent, and to fully demonstrate the absorption performance of the composite absorbent.

[0020] [Aspect 8] Aspect 8. The composite absorbent of any one of aspects 1 to 7, wherein the polymer absorbent has a water absorption per unit mass of 30 g / g or more. In this composite absorbent, the water absorption capacity per unit mass of the polymer absorbent is sufficiently large (30 g / g or more) compared to the water absorption capacity per unit mass of pulp fiber alone (approximately 20 g / g), so the polymer absorbent can quickly and with a sufficient capacity absorb the body fluid absorbed by the pulp fiber. This makes it possible to prevent leakage of body fluid from the composite absorbent, and allows the composite absorbent to fully exhibit its absorption performance.

[0021] [Aspect 9] A composite absorbent body according to any one of the first to eighth aspects, wherein the magnitude of water absorption viscosity is such that the polymeric absorbent is greater than the highly water-absorbent polymer. The polymer absorbent contained in the composite absorbent has a higher water absorption viscosity when absorbing body fluids than the superabsorbent polymer. Therefore, when the composite absorbent absorbs body fluids, the viscosity of the polymer absorbent increases, suppressing the movement, i.e., fluidization, of the polymer absorbent and the absorbent materials present around it, such as the superabsorbent polymer and pulp fibers, in the composite absorbent. This allows the composite absorbent to deform in accordance with the wearer's body movements without causing gaps due to uneven distribution of the absorbent material in the composite absorbent, thereby suppressing leakage of body fluids from the composite absorbent and allowing the composite absorbent to fully exhibit its absorption performance.

[0022] [Aspect 10] The composite absorbent body according to any one of aspects 1 to 9, wherein the thickness of the composite absorbent body is 3 mm or less, and the repeated absorption speed of the composite absorbent body is 20 seconds or less. This composite absorbent has a thickness of 3 mm or less while increasing the repeated absorption speed to 20 seconds or less, so that it can quickly absorb multiple or large amounts of bodily fluids, fully demonstrating the absorption performance of the composite absorbent, while also providing a comfortable fit when used in sanitary products.

[0023] [Aspect 11] The composite absorbent according to any one of claims 1 to 10, wherein the polymer absorbent is a hydrolysate of a crosslinked polymer of a (meth)acrylic acid ester and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group. In the present composite absorbent, since the polymer absorbent has the above-mentioned configuration, the polymer absorbent can quickly receive (absorb) the body fluid absorbed by the pulp fibers, and then the superabsorbent polymer can quickly receive (absorb) the body fluid absorbed by the polymer absorbent. As a result, the composite absorbent can suppress leakage of body fluids and exhibit high absorption performance.

[0024] [Aspect 12] 12. A sanitary article comprising a top sheet, a back sheet, and the composite absorbent body according to any one of aspects 1 to 11 located between the top sheet and the back sheet. Since the present sanitary product is equipped with the above-mentioned composite absorbent, it is possible to maintain or improve the absorption performance of the sanitary product while reducing the thickness of the sanitary product to provide a comfortable fit.

[0025] A preferred embodiment of the composite absorbent body of the present invention will be described below using a disposable diaper 1 (pants-type diaper) as an example of a sanitary product to which the composite absorbent body can be applied.

[0026] In this specification, unless otherwise specified, "viewing an object (e.g., a disposable diaper, a composite absorbent, etc.) placed on a horizontal surface in an unfolded state in the thickness direction of the object from the vertical upper side (the top sheet side if the object is a sanitary product)" is simply referred to as "planar view". In addition, "longitudinal direction" refers to "the longer direction of the length of a vertically elongated object (e.g., a disposable diaper, a composite absorbent, etc. in an unfolded state) in a planar view". "Width direction" refers to "the shorter direction of the length of a vertically elongated object in a planar view". "Thickness direction" refers to "the perpendicular direction to an object placed on a horizontal surface in an unfolded state". These longitudinal direction, width direction and thickness direction are mutually orthogonal. In addition, in the thickness direction of the disposable diaper 1, "the side proximal to the wearer's skin surface when the disposable diaper 1 is worn" is referred to as "skin-facing side", and "the side distal to the wearer's skin surface when the disposable diaper 1 is worn" is referred to as "non-skin-facing side".

[0027] [Disposable diapers] FIG. 1 is a schematic plan view of a disposable diaper 1 in an unfolded state to which a composite absorbent body 4 according to an embodiment is applied. The disposable diaper 1 of this embodiment has a longitudinal direction L, a width direction W, and a thickness direction T that are perpendicular to each other in a plan view. The disposable diaper 1 includes a cover sheet 9 constituting a ventral region FW, a dorsal region RW, and a crotch region CA, and an absorbent body 10. One end of the absorbent body 10 in the longitudinal direction L is laminated on the skin-side surface of the ventral region FW, and the other end is laminated on the skin-side surface of the dorsal region RW. The crotch region CA supports the absorbent body 10 from the non-skin side. The two end portions FWa, FWa in the width direction W of the ventral region FW and the two end portions RWa, RWa in the width direction W of the dorsal region RW overlap in the thickness direction T and are joined along the longitudinal direction L to form the disposable diaper 1. In this case, in the disposable diaper 1, the outer end FWe in the longitudinal direction L of the ventral region FW and the outer end RWe in the longitudinal direction L of the dorsal region RW define a waist opening through which the wearer's waist passes. In the disposable diaper 1, the side portions Ce, Ce on both sides in the width direction W of the crotch region CA define a pair of leg openings through which the wearer's legs pass. The cover sheet 9 has a substantially hourglass shape in a plan view, and the absorbent body 10 has a substantially rectangular shape extending in the longitudinal direction L in a plan view. The outer shape of the disposable diaper 1 is not particularly limited, and any known shape may be adopted according to various applications, usage modes, etc.

[0028] The cover sheet 9 is composed of, for example, two-layered sheets, and a plurality of elastic members 111a, 111b; 113a, 113b; 107 are arranged between the two layers of sheets. The plurality of elastic members 111a, 111b are located in the ventral region FW. The plurality of elastic members 111a are arranged on the inside of the longitudinal direction L in the ventral region FW and on both sides of the width direction W with the absorbent body 10 in between. On the other hand, the plurality of elastic members 111b are arranged on the outside of the longitudinal direction L in the ventral region FW. Similarly, the plurality of elastic members 113a, 113b are located in the dorsal region RW. The plurality of elastic members 113a are arranged on the inside of the longitudinal direction L in the dorsal region RW and on both sides of the width direction W with the absorbent body 10 in between. On the other hand, the plurality of elastic members 113b are arranged on the outside of the longitudinal direction L in the dorsal region RW. The plurality of elastic members 107 are arranged on both sides of the width direction W in the region from the ventral region FW to the dorsal region RW. The elastic members 111a, 111b, 113a, 113b, and 107 are exemplified by rubber threads. The cover sheet 95 is made of, for example, a nonwoven fabric or a resin film.

[0029] The absorbent body 10 basically comprises, in the thickness direction, a liquid-permeable top sheet 2 which forms the surface of the absorbent body 10 facing the skin, a back sheet 3 which forms the surface of the absorbent body 10 not facing the skin, and a composite absorbent 4 which is located between these sheets.

[0030] The absorbent body 10 of this embodiment further includes a pair of side sheets 5 located at both ends in the width direction W at a position closer to the skin-facing side than the top sheet 2 and extending in the longitudinal direction L. Each side sheet 5 has a leakage barrier wall 6 and a fixing region 7. The fixing region 7 is located at the front and rear ends of the side sheet 5 in the longitudinal direction L, and fixes the leakage barrier wall 6 to the skin-facing surface of (the top sheet 2 of) the absorbent body 10. The leakage barrier wall 6 is located between the fixing regions 7 on the front and rear sides in the longitudinal direction L of the side sheet 5, and has an outer edge in the width direction W fixed to the skin-facing surface of (the top sheet 2 of) the absorbent body 10, and an inner edge in the width direction W not fixed. In this case, the leakage barrier wall 6 and the fixing region 7 are formed, for example, in the inner part of the side sheet 5 in the width direction W, and the outer part of the side sheet 5 in the width direction W is fixed to (the top sheet 2 of) the absorbent body 10. Each leak-preventing wall 6 includes one or more elastic members 8 extending along the longitudinal direction L at an inner end in the width direction W. The elastic members 8 are exemplified by rubber threads.

[0031] The absorbent body 10 may further include a pair of linear high density parts (not shown) extending along the longitudinal direction L or the width direction W and arranged at an interval in the width direction W or the longitudinal direction L. However, "along a predetermined direction" includes not only parallel to the direction but also shifted by ±30° from the direction. The high density parts are formed, for example, by embossing the topsheet 2 and the composite absorbent body 4 in the thickness direction.

[0032] The disposable diaper 1 (and the absorbent body 10) is not limited to the above configuration, and may have other configurations as long as it includes the configuration of the composite absorbent body 4 described below.

[0033] In the absorbent body 10 of the disposable diaper 1, the composite absorbent 4 is located between the top sheet 2 and the back sheet 3, and is formed of a water-absorbent member capable of absorbing bodily fluids such as urine and menstrual blood discharged from the wearer and permeating the top sheet 2. The composite absorbent 4 contains, as the water-absorbent member, a polymeric absorbent having a hydrophilic continuous skeleton and continuous pores.

[0034] When absorbing water, the polymer absorbent exhibits a unique water absorption behavior in which the water is first absorbed into the continuous skeleton and then into the continuous pores. Therefore, when the polymer absorbent absorbs body fluids such as urine or menstrual blood, the hydrophilic continuous skeleton instantly absorbs the body fluid due to osmotic pressure and expands, thereby expanding the volume of the continuous pores, and the body fluid can be further absorbed into the expanded continuous pores. Therefore, the polymer absorbent can instantly absorb a large amount of body fluid. In this embodiment, the absorbed body fluid can be further transferred to a highly water-retaining superabsorbent polymer and steadily retained in the superabsorbent polymer.

[0035] In the disposable diaper 1, the composite absorbent 4 contains, as absorbent members, pulp fibers and a superabsorbent polymer in addition to a polymer absorbent having a hydrophilic continuous skeleton and continuous pores. The initial absorption speeds of these absorbent members are pulp fibers>polymer absorbent>superabsorbent polymer. In other words, the initial absorption speed of the pulp fibers is the fastest, the initial absorption speed of the polymer absorbent is next fastest, and the initial absorption speed of the superabsorbent polymer is the slowest.

[0036] In this way, in the composite absorbent 4, the order of the initial absorption speed is pulp fiber>polymer absorbent>superabsorbent polymer. Therefore, the polymer absorbent first receives (absorbs) the body fluid absorbed by the pulp fiber, and then the superabsorbent polymer receives (absorbs) the body fluid absorbed by the polymer absorbent. In this way, the body fluid absorbed by the pulp fiber, which has a high absorption speed, is first transferred (absorbed) sequentially to the polymer absorbent, which has a relatively high absorption speed, so that it is possible to prevent the pulp fiber from being unable to absorb all the body fluid. Furthermore, the body fluid absorbed by the polymer absorbent is transferred (absorbed) sequentially to the superabsorbent polymer, which has a slow absorption speed but high absorption performance, so that it is possible to prevent the transfer of body fluid to the superabsorbent polymer from keeping up. As a result, it is possible to prevent leakage of body fluid from the composite absorbent while suppressing the thickness by using the superabsorbent polymer, and it is possible to fully exhibit the water retention capacity of the superabsorbent polymer and, in turn, the absorption performance of the absorbent. Most of the excreted body fluid is first absorbed by the pulp fibers, but a portion is absorbed by the polymer absorbent and then transferred to the highly water-absorbent polymer.

[0037] Therefore, a disposable diaper 1 (absorbent body 10) equipped with such a composite absorbent 4 can also suppress leakage of bodily fluids while keeping its thickness down by using a highly absorbent polymer, and can exhibit excellent absorption performance as a disposable diaper (absorbent body).

[0038] Hereinafter, various components of sanitary goods to which the composite absorbent body of the present invention is applied will be further described using the above-mentioned disposable diaper 1.

[0039] (Surface sheet) 1, the top sheet 2 has a vertically elongated outer shape in plan view, extending from one edge to the other edge in the longitudinal direction L of the absorbent main body 10 and extending from the vicinity of one edge to the vicinity of the other edge in the width direction W of the absorbent main body 10. The top sheet 2 is disposed at a position on the skin-facing side in the thickness direction of the absorbent main body 10 and constitutes a contact surface that can come into contact with the wearer's skin, i.e., the surface of the skin-facing side of the absorbent main body 10. The top sheet 2 is formed of a liquid-permeable sheet-like member.

[0040] 1, the topsheet 2 is slightly larger in size in the longitudinal direction L and width direction W than the composite absorbent 4 arranged on the non-skin facing side of the topsheet 2. The topsheet 2 is joined at its periphery to the backsheet 3 located on the non-skin facing side.

[0041] In the present invention, the outer shape, various dimensions, basis weight, etc. of the top sheet are not particularly limited as long as they can be used as a top sheet for sanitary products, and any outer shape, various dimensions, basis weight, etc. can be adopted depending on the desired liquid permeability, feel to the skin, flexibility, strength, etc.

[0042] (Back sheet) The back sheet 3 has a vertically elongated outer shape in a plan view, extending from one side edge to the other side edge in the longitudinal direction L of the absorbent main body 10 and from one side edge to the other side edge in the width direction W of the absorbent main body 10. The back sheet 3 is disposed at a position on the non-skin facing side in the thickness direction of the absorbent main body 10 and constitutes the non-skin facing surface of the absorbent main body 10. The back sheet 3 is formed of a liquid-impermeable sheet-like member and prevents body fluids such as urine and menstrual blood that have permeated the composite absorbent body 4 from leaking out of the absorbent main body 10.

[0043] In the present invention, the outer shape, various dimensions, basis weight, etc. of the back sheet are not particularly limited as long as they can be used as a back sheet of a sanitary product, and any outer shape, various dimensions, basis weight, etc. can be adopted according to the desired leak prevention performance, breathability, strength, etc.

[0044] (Composite absorber) As shown in Figure 1, when viewed in a plane, the composite absorbent body 4 has an elongated, approximately rectangular outer shape that extends over a wide area from near one end edge to near the other end edge in each of the longitudinal direction L and width direction W, centered on the central portion in the longitudinal direction L and width direction W of the absorbent main body 10.

[0045] Specifically, the composite absorbent body 4 has, in a plan view, a generally rectangular shape extending in the longitudinal direction L, which is generally the same as that of the absorbent main body 10. However, the outer shape of the composite absorbent body 4 is not particularly limited, and any known shape may be adopted according to various applications, modes of use, and the like.

[0046] The composite absorbent 4 is disposed between the top sheet 2 and the back sheet 3 in the thickness direction of the disposable diaper 1, and is formed from a predetermined absorbent member capable of absorbing and retaining body fluids such as urine and menstrual blood that have permeated through the top sheet 2. The absorbent member includes absorbent materials such as polymer absorbents, pulp fibers, and highly absorbent polymers, which will be described later, and a tissue-like sheet that retains the absorbent materials. In other words, the composite absorbent 4 refers to a absorbent member that is composed of absorbent materials capable of absorbing and retaining body fluids, and a sheet that retains the absorbent materials.

[0047] In the absorbent body 10, the composite absorbent body 4 is bonded to each of the top sheet 2 and the back sheet 3 by any adhesive such as a hot melt adhesive.

[0048] The composite absorbent 4 includes a polymer absorbent having a hydrophilic continuous skeleton and continuous pores and exhibiting a unique water absorption behavior as described above, and further includes pulp fibers and a superabsorbent polymer. When the polymer absorbent is a particle, the size (when dry) may be, for example, an average particle size of several hundred μm (200 to 500 μm). The polymer absorbent may be in a sheet form. The polymer absorbent will be described later. The superabsorbent polymer is called SAP (Super Absorbent Polymer), and there is no particular limit to the type, and materials known in the art may be used. For example, the superabsorbent polymer may be a polyacrylate-based, polysulfonate-based, or maleic anhydride-based water-absorbing polymer. When the superabsorbent polymer is a particle, the size (when dry) may be, for example, an average particle size of several hundred μm (200 to 500 μm). The superabsorbent polymer may be in a sheet form. There is no particular limit to the type of pulp fiber, and materials known in the art may be used. For example, the pulp fiber may be a cellulose-based fiber. Examples of cellulosic fibers include wood pulp, crosslinked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. The size of the pulp fibers is, for example, an average value of the major axis of the fibers of several tens of μm (20 to 40 μm) and an average value of the fiber length of several mm (2 to 5 mm). The composite absorbent may be enclosed in a core wrap formed of a liquid-permeable sheet.

[0049] The absorbent materials, which are the polymer absorbent, pulp fiber, and superabsorbent polymer, are generally uniformly arranged throughout the composite absorbent 4 in plan view, except for manufacturing errors. However, the present invention is not limited to this example, and at least one of the absorbent materials may have another arrangement in which it is not generally uniform but has a predetermined distribution intentionally. For example, the polymer absorbent may be arranged between one and the other of a pair of high-density parts in the width direction W with a higher basis weight than other areas, or between one and the other of a pair of high-density parts in the longitudinal direction L with a higher basis weight than other areas. Alternatively, the polymer absorbent may be arranged on the outside of each of the pair of high-density parts in the width direction W with a higher basis weight than other areas, or on the outside of each of the pair of high-density parts in the longitudinal direction L with a higher basis weight than other areas. It is preferable that the polymer absorbent be in contact with the superabsorbent polymer in order to reliably transfer the body fluid absorbed by the pulp fiber to the superabsorbent polymer.

[0050] In the present invention, the outer shape, various dimensions, basis weight, etc. of the composite absorbent body are not particularly limited as long as they do not impair the effects of the present invention, and any outer shape, various dimensions, basis weight, etc. can be adopted according to the desired water absorbency, flexibility, strength, etc.

[0051] The polymer absorbent used in the composite absorbent of the present invention will be described in more detail below.

[0052] [Polymer absorbent] The polymer absorbent has a hydrophilic continuous skeleton and continuous pores, and when absorbing moisture, it exhibits a water absorption behavior in which the moisture is absorbed into the continuous skeleton and then into the continuous pores, and the initial absorption speed is not particularly limited as long as it is pulp fiber>polymer absorbent>highly water-absorbent polymer. Such a polymer absorbent is, for example, a hydrolyzate of a crosslinked polymer of two or more monomers including at least (meth)acrylic acid ester, and a polymer compound having at least one hydrophilic group in the functional group. More specifically, a polymer compound is a hydrolyzate of a crosslinked polymer of a compound containing a (meth)acrylic acid ester and two or more vinyl groups in one molecule, and has at least a -COONa group. Such a polymer absorbent is an organic porous body having at least one -COONa group in one molecule, and may further have a -COOH group. The -COONa group is distributed approximately uniformly in the skeleton of the porous body.

[0053] When the polymer absorbent has the above-mentioned structure, as described below, the continuous hydrophilic skeleton is more likely to extend (i.e., expand) when absorbing body fluids such as urine or menstrual blood, and the continuous pores are more likely to expand. Therefore, a larger amount of body fluid can be more quickly incorporated into the continuous pores, and the absorbent material can exhibit excellent absorption performance. In addition, the body fluid absorbed by the pulp fibers can be quickly received (absorbed) by the polymer absorbent, and then the body fluid absorbed by the polymer absorbent can be received (absorbed) by the highly water-absorbent polymer.

[0054] In this specification, the (meth)acrylic acid ester refers to an acrylic acid ester or a methacrylic acid ester.

[0055] The polymer absorbent is formed, for example, by a hydrolyzate of a crosslinked polymer of (meth)acrylic acid ester and divinylbenzene. In such a polymer absorbent, a hydrophilic continuous skeleton is formed by an organic polymer having at least -COONa groups, and continuous holes (continuous pores) that serve as absorption sites for the liquid to be absorbed (e.g., body fluids such as urine and menstrual blood) are formed between the skeletons. Note that the hydrolysis treatment converts the -COOR groups (i.e., carboxylate ester groups) of the crosslinked polymer into -COONa groups or -COOH groups (see Figure 2), so the polymer absorbent may have -COOR groups.

[0056] The presence of -COOH and -COONa groups in the organic polymer forming the hydrophilic continuous backbone can be confirmed by analysis using infrared spectroscopy and a quantitative method for weakly acidic ion exchange groups.

[0057] Here, Fig. 2 is a diagram for explaining the manufacturing process of absorbent A, which is an example of a polymer absorbent. In this Fig. 2, the upper diagram shows the constituent raw materials for polymerization, the middle diagram shows monolith A, which is a crosslinked polymer of (meth)acrylic acid ester and divinylbenzene, and the lower diagram shows absorbent A obtained by subjecting monolith A in the middle diagram to hydrolysis and drying treatment.

[0058] The polymer absorbent will be described below using absorbent A, which is an example of the polymer absorbent and is formed from a hydrolysate of a crosslinked polymer of a (meth)acrylic acid ester and divinylbenzene.

[0059] The polymer absorbent is not limited to such absorbent A. The polymer absorbent may be, for example, a hydrolysate of a cross-linked polymer of a (meth)acrylic acid ester and a compound having two or more vinyl groups in one molecule. Alternatively, the polymer absorbent may be, for example, a hydrolysate of a cross-linked polymer of two or more monomers including at least a (meth)acrylic acid ester. However, if the polymer absorbent is a monolithic absorbent, it has the advantage that it can quickly absorb body fluids and can more steadily transfer the body fluids temporarily held in the polymer absorbent to the highly water-absorbent polymer.

[0060] In the following description, "monolith A" refers to an organic porous body made of a crosslinked polymer of (meth)acrylic acid ester and divinylbenzene before hydrolysis treatment, and may be referred to as a "monolithic organic porous body." Furthermore, "absorbent A" refers to a hydrolyzate of a crosslinked polymer of (meth)acrylic acid ester and divinylbenzene (monolith A) after hydrolysis treatment and drying treatment. In the following description, absorbent A refers to the one in a dry state.

[0061] First, the structure of absorbent A will be described. As described above, absorbent A has a hydrophilic continuous skeleton and continuous pores. As shown in Figure 2, absorbent A, which is an organic polymer having a hydrophilic continuous skeleton, is obtained by cross-linking polymerizing (meth)acrylic acid ester, which is a polymerization monomer, and divinylbenzene, which is a cross-linking monomer, and further hydrolyzing the obtained cross-linked polymer (monolith A).

[0062] The organic polymer forming the hydrophilic continuous skeleton has, as structural units, a polymerized residue of an ethylene group (hereinafter referred to as "structural unit X") and a cross-linked polymerized residue of divinylbenzene (hereinafter referred to as "structural unit Y"). Furthermore, the polymerized residue of the ethylene group (structural unit X) in the organic polymer forming the hydrophilic continuous skeleton has a -COONa group generated by hydrolysis of a carboxylate group, or both a -COOH group and a -COONa group. When the polymerization monomer is a (meth)acrylic acid ester, the polymerized residue of the ethylene group (structural unit X) has a -COONa group, a -COOH group, and an ester group.

[0063] In the absorbent A, the ratio of the cross-linked polymer residue of divinylbenzene (structural unit Y) in the organic polymer forming the hydrophilic continuous skeleton is, for example, 0.1 to 30 mol %, preferably 0.1 to 20 mol %, based on the total structural units. For example, in the absorbent A in which butyl methacrylate is used as the polymerization monomer and divinylbenzene is used as the cross-linking monomer, the ratio of the cross-linked polymer residue of divinylbenzene (structural unit Y) in the organic polymer forming the hydrophilic continuous skeleton is, for example, about 3% based on the total structural units, preferably 0.1 to 10 mol %, more preferably 0.3 to 8 mol %. If the ratio of the cross-linked polymer residue of divinylbenzene in the organic polymer forming the hydrophilic continuous skeleton is 0.1 mol % or more, the strength of the absorbent A is unlikely to decrease, and if the ratio of the cross-linked polymer residue of divinylbenzene is 30 mol % or less, the absorption amount of the liquid to be absorbed is unlikely to decrease.

[0064] In addition, in the absorbent A, the organic polymer forming the hydrophilic continuous skeleton may be composed only of the structural unit X and the structural unit Y, or may have, in addition to the structural unit X and the structural unit Y, a structural unit other than the structural unit X and the structural unit Y, that is, a polymerized residue of a monomer other than a (meth)acrylic acid ester and divinylbenzene.

[0065] Examples of structural units other than the structural unit X and the structural unit Y include polymerized residues of monomers such as styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, glycidyl (meth)acrylate, isobutene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate.

[0066] The proportion of structural units other than the structural unit X and the structural unit Y in the organic polymer that forms the hydrophilic continuous skeleton is, for example, 0 to 50 mol %, and preferably 0 to 30 mol %, relative to all structural units.

[0067] In addition, the thickness of the hydrophilic continuous skeleton of the absorbent A is preferably 0.1 to 100 μm. When the thickness of the hydrophilic continuous skeleton of the absorbent A is 0.1 μm or more, the spaces (pores) for taking in the liquid to be absorbed (body fluid) in the porous body are less likely to collapse during absorption, and the absorption amount is less likely to decrease. On the other hand, when the thickness of the hydrophilic continuous skeleton is 100 μm or less, an excellent absorption speed is easily obtained.

[0068] In addition, since the pore structure of the hydrophilic continuous skeleton of absorbent A is an open-cell structure, the thickness of the continuous skeleton is measured by evaluating the cross section of the skeleton that appears on the test piece for electron microscope measurement. The continuous skeleton is often polygonal in shape because it is formed by the gaps between water (water droplets) removed by the dehydration and drying process after hydrolysis. Therefore, the thickness of the continuous skeleton is the average value of the diameter (μm) of the circle circumscribing the polygonal cross section. In rare cases, there may be small holes in the polygon, in which case the circumscribing circle of the polygonal cross section surrounding the small holes is measured.

[0069] Furthermore, the absorbent A preferably has an average diameter of interconnected pores of 1 to 1000 μm. When the average diameter of interconnected pores in the absorbent A is 1 μm or more, the spaces (pores) for taking in the liquid to be absorbed (body fluid) in the porous body are less likely to collapse during absorption, and the absorption rate is less likely to decrease. On the other hand, when the average diameter of interconnected pores is 1000 μm or less, an excellent absorption rate is easily obtained.

[0070] The average diameter (μm) of the interconnected pores of absorbent A can be measured by mercury intrusion porosimetry, and the maximum value of the pore distribution curve obtained by the mercury intrusion porosimetry is used. Regardless of the ionic form of absorbent A, samples for measuring the average diameter of interconnected pores are those dried for 18 hours or more in a reduced pressure dryer set at a temperature of 50°C. The final pressure reached is 0 Torr.

[0071] Fig. 3 is an SEM photograph of absorbent A at a magnification of 50 times, Fig. 4 is an SEM photograph of absorbent A at a magnification of 100 times, Fig. 5 is an SEM photograph of absorbent A at a magnification of 500 times, and Fig. 6 is an SEM photograph of absorbent A at a magnification of 1500 times. The absorbent A shown in Figs. 3 to 6 is an example of an absorbent that uses butyl methacrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, and each has a cubic structure with a side of 2 mm.

[0072] 3 to 6 has a large number of cellular macropores and further has portions where these cellular macropores overlap. Absorbent A has an open cell structure in which the overlapping portions of the macropores form common openings (mesopores), i.e., it has an open cell structure (open macropore structure).

[0073] The overlapping portions of the macropores form common openings (mesopores) having an average diameter in a dry state of 1 to 1000 μm, preferably 10 to 200 μm, and particularly preferably 20 to 100 μm, and most of them have an open pore structure. When the average diameter of the mesopores in a dry state is 1 μm or more, the absorption rate of the liquid to be absorbed is improved. On the other hand, when the average diameter of the mesopores in a dry state is 1000 μm or less, the absorbent A is less likely to become embrittled. The number of overlapping macropores in each macropore is about 1 to 12, and in most cases, about 3 to 10.

[0074] In addition, since absorbent A has such an open cell structure, macropores and mesopores can be uniformly formed, and there is an advantage in that the pore volume and specific surface area can be significantly increased compared to the particle agglomeration type porous bodies as described in JP-A-8-252579 and the like.

[0075] The total pore volume of the pores (voids) of the absorbent A is preferably 0.5 to 50 mL / g, more preferably 2 to 30 mL / g. When the total pore volume of the absorbent A is 0.5 mL / g or more, a sufficient pore volume can be ensured in the absorbent A, and therefore a sufficient amount of water absorption can be ensured. In addition, the spaces (voids) for taking in the liquid to be absorbed (body fluid) of the porous body can be made less likely to collapse during absorption, and the amount and speed of water absorption can be made less likely to decrease. On the other hand, when the total pore volume of the absorbent A is 50 mL / g or less, the strength of the absorbent A can be made less likely to decrease.

[0076] The total pore volume can be measured by mercury intrusion porosimetry. The sample for measuring the total pore volume is dried for 18 hours or more in a vacuum dryer set at a temperature of 50°C, regardless of the ion form of absorbent A. The final pressure is 0 Torr.

[0077] Hereinafter, the state when the absorbent A comes into contact with a liquid such as a body fluid (hereinafter simply referred to as "body fluid") will be described, but the same applies to the state when the body fluid comes into contact with a composite absorbent 4 containing the absorbent A. Furthermore, since the mass of absorbed body fluid is approximately proportional to the amount of body fluid, in the following description, the mass of body fluid may be simply referred to as the "amount of body fluid".

[0078] First, the continuous pores of the absorbent A shown in Figs. 3 to 6 are pores in which a plurality of pores (voids) are interconnected, and it is possible to visually confirm with the naked eye that a large number of voids are provided from the outside. When body fluids such as urine or menstrual blood come into contact with the absorbent A having such a large number of pores, the hydrophilic continuous skeleton first instantly absorbs a portion of the body fluid due to osmotic pressure and expands (i.e., expands). This expansion of the continuous skeleton occurs in almost all directions. The absorbent A thus absorbs a certain amount of body fluid and becomes enlarged, and is then able to absorb a further predetermined amount of body fluid into the expanded continuous pores due to capillary action. In this way, the absorbent A exhibits a unique water absorption behavior in which, when absorbing water (body fluid), the water is absorbed into the hydrophilic continuous skeleton and then absorbed by the continuous pores.

[0079] Here, 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 easily synergized). On the other hand, the body fluid absorbed into the continuous pores is easily synergized. Therefore, in the composite absorbent, the body fluid absorbed into the continuous pores is synergized and transferred to the highly water-retaining superabsorbent polymer, and is steadily retained in the superabsorbent polymer. The amount of body fluid absorbed into the continuous skeleton of absorbent A and the amount of body fluid absorbed into the continuous pores are calculated by dividing the total amount of fluid absorbed by absorbent A by the amount of body fluid that is synergized from absorbent A by centrifugation (150G / 90 seconds) and absorbed into the continuous pores, and the remaining amount of body fluid (the amount of body fluid that is not synergized from absorbent A by centrifugation) is the amount of body fluid absorbed into the continuous skeleton.

[0080] Furthermore, more of the body fluid absorbed by absorbent A remains in the pores than in the hydrophilic continuous skeleton. Most of the body fluid is absorbed by absorbent A by retaining the body fluid in the pores through capillary action, so the greater the porosity (the volume of the pores relative to the volume of absorbent A), which is the ratio of the volume of the voids in the pores (total pore volume), the more body fluid can be absorbed. It is preferable that this porosity is 85% or more.

[0081] For example, the porosity of the absorbent A shown in the above-mentioned Figs. 3 to 6 can be calculated as follows. First, the specific surface area of ​​the absorbent A obtained by mercury porosimetry is 400 m 2 / g, and the 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. If we assume that the specific gravity of absorbent A is 1g / mL, the volume that the pores occupy in 1g of absorbent A, i.e., the pore volume, is 15.5mL, and the volume of 1g of absorbent A is 1mL. Then, the total volume (volume) of 1g of absorbent A is 15.5+1(mL), and the ratio of the pore volume to that is the porosity, so the porosity of absorbent A is 15.5 / (15.5+1)×100 ≒ 94%.

[0082] The absorbent A having such a hydrophilic continuous skeleton and continuous pores, i.e., a polymer absorbent, is applied in the form of particles, a sheet, or the like to a composite absorbent for absorbing body fluids such as urine and menstrual blood, such as the composite absorbent 4 of the absorbent body 10 of the disposable diaper 1 described above. As described above, this polymer absorbent exhibits a unique water absorption behavior in which, when absorbing moisture (directly or via pulp fibers), the moisture is absorbed into the hydrophilic continuous skeleton and then into the continuous pores. Therefore, this polymer absorbent can instantly absorb a large amount of surrounding body fluids (in the pulp fibers), and further, the absorbed body fluids (mainly the body fluids absorbed into the continuous pores) can be transferred to a highly water-retaining superabsorbent polymer and steadily retained within the superabsorbent polymer. Therefore, a composite absorbent to which such a polymer absorbent is applied can exhibit high absorption performance as an absorbent.

[0083] In this embodiment, the absorption speed of the polymer absorbent containing absorbent A by the Vortex method is preferably 5 seconds or less. In this way, in the composite absorbent 4, the body fluid once absorbed by the pulp fibers can be quickly transferred to the polymer absorbent in a short time (5 seconds or less). Therefore, it is possible to prevent the pulp fibers from accumulating too much body fluid, slowing down the absorption speed of the pulp fibers, or preventing the pulp fibers from absorbing all the body fluid. As a result, the pulp fibers, which have a high absorption speed, can quickly transfer the absorbed body fluid to the polymer absorbent, and the polymer absorbent can then further transfer the transferred body fluid to the highly absorbent polymer, which has high absorption performance. Therefore, it is possible to prevent leakage of body fluid from the composite absorbent, and to fully exhibit the absorption performance of the composite absorbent.

[0084] The absorption speed of the polymer absorbent including absorbent A by the Vortex method is preferably 3 seconds or less, and more preferably 2 seconds or less. The absorption speed is preferably equal to or greater than the absorption speed of the pulp fiber, and more preferably equal to or greater than 1 second. The body fluid absorbed by the pulp fiber can be transferred to the polymer absorbent more quickly in a shorter period of time.

[0085] However, since the absorption rate by the Voltex method is measured as the absorption time for the object to absorb a predetermined solution, the shorter the absorption time, the faster the absorption rate. The absorption rate (absorption time) by the Voltex method is measured by the following method (refer to JIS-K7224).

[0086] <Measurement Method for (Initial) Absorption Rate by Voltex Method> (1) Place a rotor with a size of 30×8 mm in a 100 ml beaker, and add 50 g of an aqueous NaCl solution with a concentration of 0.9 wt% adjusted to a liquid temperature of 25 °C ± 1 °C. (2) Use a magnetic stirrer (MITAMURA RIKEN KOGYO INC. MAGMIX STIRRER (AC100W)) to adjust the rotation speed of the rotor to 600 ± 30 rpm and stir the aqueous NaCl solution. (3) Add 2.00 g of absorbent A to the stirring container, and start measuring the time simultaneously with the addition. (4) Then, measure the time when the solution surface in the solution becomes flat as the absorption time (absorption rate). The time when the solution surface becomes flat is defined as the point where the inclination of the vigorously rotating liquid vortex approaches a plane, and it is judged by observing the disappearance of the light reflected on the liquid surface of the vortex. Note that this measurement method is carried out under the conditions of a temperature of 25 °C and a humidity of 60%.

[0087] In this embodiment, the liquid transfer rate from the pulp fiber is preferably a polymer absorbent > superabsorbent polymer. Thus, in the composite absorbent 4, the body fluid once absorbed by the pulp fiber can be quickly transferred to the polymer absorbent with a high absorption rate rather than to the superabsorbent polymer with a slow absorption rate. Therefore, it is possible to suppress the situation where the pulp fiber accumulates too much body fluid, resulting in a slow absorption rate of the pulp fiber or the pulp fiber being unable to absorb all the body fluid. Thereby, continuously, the body fluid absorbed by the pulp fiber can be quickly transferred to the polymer absorbent, and the body fluid transferred to the polymer absorbent can be further transferred to the superabsorbent polymer. Therefore, leakage of body fluid from the composite absorbent can be suppressed, and the absorption performance of the composite absorbent can be fully exerted.

[0088] The liquid transfer rate (30 seconds) of the polymer absorbent from the pulp fiber is preferably 60% or more. This satisfies the relationship of polymer absorbent > superabsorbent polymer, and in the composite absorbent 4, the body liquid once absorbed by the pulp fiber can be transferred quickly to the polymer absorbent with a fast absorption rate, faster than the transfer to the superabsorbent polymer with a slow absorption rate.

[0089] The amount and rate of liquid transfer from material A to material B are measured by the following method. If material A is pulp fiber and material B is a polymer absorbent or a highly absorbent polymer, the liquid transfer rate from the pulp fiber of the polymer absorbent or highly absorbent polymer can be measured. If material A is a polymer absorbent or pulp fiber and material B is a highly absorbent polymer, the liquid transfer rate from the polymer absorbent or pulp fiber of the highly absorbent polymer can be measured.

[0090] <Method for measuring the amount and rate of liquid transfer from material A to material B> (1) 0.3 g of the sample to be measured (material A) is placed in a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) with a nylon mesh material (NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) attached to the bottom, and 0.3 g of the sample to be measured (material A) is spread evenly and the mass (g) of the cylinder is measured. This measurement method is performed under conditions of a temperature of 25°C and a humidity of 60%. (2) Place a plastic cylinder (inner diameter: 60 mm, outer diameter: 70 mm, height: 52 mm, mass: 64 g) into a petri dish (inner diameter: 85 mm, depth: 20 mm) and sprinkle 0.3 g of material B evenly into the cylinder. Then remove the cylinder and measure the mass (g) of the petri dish. (3) Place 60 mL of saline (0.9% sodium chloride solution) into a petri dish with a pedestal (inner diameter: 85 mm, depth: 20 mm, pedestal arrangement: two pedestals arranged parallel to each other with an interval of 24 mm in the center of the bottom (inner surface), pedestal width: 2 mm, pedestal height: 2 mm, pedestal length: 25 mm). (4) Place the cylinder containing the sample to be measured (material A) on the base in the center of a pedestal-equipped petri dish, immerse the bottom of the cylinder in saline, and allow the sample in the cylinder to absorb the saline for 3 minutes. (5) After absorbing water for 3 minutes, the cylinder is pulled out, tilted 45° and allowed to drain for 1 minute, and then the mass (g) of the cylinder is measured. (6) Calculate the amount of water absorbed by the sample (material A) (g) by subtracting the mass (g) of the cylinder after water absorption measured in (5) above from the mass (g) of the cylinder before water absorption measured in (1) above. Further, divide this amount of water absorption by the mass of the sample (=0.3 g) to obtain the amount of water absorbed per unit mass of the sample (material A) (g / g). (7) Then, the cylinder after draining in (5) above is placed on top of the petri dish containing material B, and the sample (material A) in the cylinder and material B in the petri dish are brought into contact with each other via the bottom surface of the cylinder (mesh material). (8) After a predetermined time (e.g. 30 seconds, 10 seconds) has elapsed since the sample (material A) and material B were brought into contact with each other, the cylinder was removed and the mass (g) of the dish was measured. (9) The mass (g) of the petri dish measured in (8) above is subtracted by the mass (g) of the petri dish measured in (2) above to calculate the amount of water absorption (g) of material B, and this amount of water absorption is then divided by the mass of the sample (=0.3 g). This gives the amount of water absorption (g / g) of material B per unit mass of the sample after a certain time (e.g. 30 seconds, 10 seconds) has elapsed, i.e., the amount of liquid transferred (g / g) to material B per unit mass of the sample (material A) after the certain time has elapsed. (10) The liquid transfer rate per unit mass after a predetermined time (e.g., 30 seconds, 10 seconds) is obtained by dividing the water absorption per unit mass (g / g) of material B after a predetermined time (e.g., 30 seconds, 10 seconds) determined in (9) above by the water absorption per unit mass (g / g) of the sample (material A) determined in (6) above, and multiplying the result by 100.

[0091] In this embodiment, the amount of liquid transferred to the superabsorbent polymer is preferably polymer absorbent>pulp fiber. In this way, in the composite absorbent 4, more body fluid is transferred to and absorbed by the polymer absorbent than by the pulp fiber, and the body fluid transferred to the polymer absorbent can be transferred to the superabsorbent polymer in a larger amount than by the pulp fiber. Therefore, the water absorption performance of the polymer absorbent can be restored after the transfer of body fluid. As a result, the body fluid absorbed by the pulp fiber can be continuously and quickly transferred to the polymer absorbent, and the body fluid transferred to the polymer absorbent can be further transferred to the superabsorbent polymer. Therefore, leakage of body fluid from the composite absorbent can be suppressed, and the absorption performance of the composite absorbent can be fully exhibited.

[0092] In this embodiment, the amount of liquid transferred from the polymer absorbent to the superabsorbent polymer (30 seconds) is preferably 6.0 g / g or more, and more preferably 8.0 g / g or more. This satisfies the ratio of polymer absorbent > pulp fiber, and the body fluid transferred to the polymer absorbent can be transferred to the superabsorbent polymer in a larger amount than the pulp fiber. When the amount of liquid transferred from the polymer absorbent to the superabsorbent polymer is 6.0 g / g or more, the body fluid temporarily held by the polymer absorbent can be more reliably transferred to the superabsorbent polymer, so that the absorption performance of the composite absorbent can be fully and reliably exhibited.

[0093] In this embodiment, the relationship regarding basis weight between the pulp fibers, the absorbent polymer, and the superabsorbent polymer in the composite absorbent 4 is preferably (basis weight of pulp fibers) / (basis weight of absorbent polymer) greater than 1. When the basis weight of the pulp fibers is greater than the basis weight of the absorbent polymer, the pulp fibers, which have a fast absorption rate, can easily absorb body fluids in the early stages, and thereafter, the body fluid absorbed by the pulp fibers can be easily transferred to the absorbent polymer.

[0094] Furthermore, the relationship regarding basis weight between the pulp fibers, the polymer absorbent, and the superabsorbent polymer in the composite absorbent 4 is preferably such that (basis weight of superabsorbent polymer) / (basis weight of polymer absorbent) is greater than 1. When the basis weight of the superabsorbent polymer is greater than the basis weight of the polymer absorbent, the polymer absorbent can easily come into contact with the superabsorbent polymer, and the polymer absorbent can easily transfer absorbed body fluid to the superabsorbent polymer.

[0095] Therefore, by satisfying at least one of the two relationships regarding the above basis weight (preferably both), the body fluid can be rapidly absorbed by the pulp fibers, rapidly transferred from the pulp fibers to the polymer absorbent, and rapidly transferred from the polymer absorbent to the highly water-absorbent polymer, thereby preventing leakage of body fluid from the composite absorbent and allowing the composite absorbent to fully exhibit its absorption performance.

[0096] From the above viewpoints, the ratio (basis weight of pulp fiber) / (basis weight of polymer absorbent) is preferably greater than 1 and less than 10, and more preferably greater than 1 and less than 5. In addition, the ratio (basis weight of superabsorbent polymer) / (basis weight of polymer absorbent) is preferably greater than 1 and less than 10, and more preferably greater than 1 and less than 5, from the above viewpoints.

[0097] Here, the basis weight of the pulp fiber, the basis weight of the polymer absorbent, and the basis weight of the highly water-absorbent polymer can be appropriately selected according to the absorption performance required for the composite absorbent body 4. For example, the basis weight of the pulp fiber is 50 to 500 g / m 3 The basis weight of the polymer absorbent is 1 to 100 g / m 3 The basis weight of the highly absorbent polymer is 50 to 500 g / m 3 Examples include:

[0098] In this embodiment, it is preferable that the water absorption amount of the composite absorbent 4 measured by the unpressurized Demand Wettability (DW) method is such that the polymer absorbent is greater than the superabsorbent polymer. In this manner, in the composite absorbent 4, the polymer absorbent is more likely to absorb free water than the superabsorbent polymer, and therefore the polymer absorbent can draw in free water that may occur when absorbed body fluid diffuses, in gaps between the nonwoven fabric and the polymer absorbent, and in gaps between the polymer absorbents. In other words, the polymer absorbent can absorb free water without leaking it. This makes it possible to suppress leakage of body fluid from the composite absorbent, and to fully exhibit the absorption performance of the composite absorbent.

[0099] In this embodiment, the water absorption amount (30 seconds) of the polymer absorbent by the non-pressure DW method is preferably 8.0 g / g or more, more preferably 12 g / g or more. This allows the polymer absorbent to absorb free water more easily than the highly water-absorbent polymer. However, the water absorption amount by the non-pressure DW method is measured by the following method.

[0100] <Method for measuring water absorption using the non-pressure DW method> FIG. 9 is a schematic diagram showing a measuring device used in the non-pressurized DW method. A DW device (Demand Wetability device, manufactured by Taiyo Create Co., Ltd.) 11 is used as such a measuring device. As shown in the figure, the DW device 11 includes a burette 12 (50 ml graduated capacity, 86 cm long, 1.05 cm inner diameter), a rubber stopper 13, an air inlet capillary (3 mm inner diameter at tip) 14, a cock 15, a cock 16, a measuring stand 17, a liquid outlet (3 mm inner diameter) 18, a cylinder 19, and a test liquid 20. A conduit (7 mm inner diameter) is attached from the burette 12 to the measuring stand 17. A 0.9% sodium chloride aqueous solution is used as the test liquid. The measurement is performed under conditions of a temperature of 25° C. and a humidity of 60%.

[0101] The measurement procedure is as follows. (1) With both cocks 15, 16 of the DW apparatus 11 closed, pour the test liquid 20 above the 0 point (the top of the burette 12 scale (0 ml line)) and place the rubber stopper 13 on the top of the burette 12 to seal it. (2) After placing filter paper on the liquid outlet 18 of the measuring table 17, open both cocks 15 and 16 and adjust the liquid level to the zero point while using the filter paper to suck up the liquid coming out of the liquid outlet 18. After adjustment, close the cocks 15 and 16. (3) A nylon mesh (manufactured by NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) cut to a 10 cm square is placed on the measuring table 17 so that the liquid outlet 18 is in the center. (4) Place a cylinder 19 with a diameter of 30 mm on the center of the mesh, and place the sample evenly inside it, centered on the liquid outlet 18. Remove the cylinder 19. (5) Open the taps 15 and 16, and the measurement start time is the time when the sample begins to absorb the test liquid 20 and the first bubble introduced from the air inlet capillary 14 reaches the surface of the test liquid 20 in the burette 12 (the time when the surface of the test liquid 20 in the burette 12 drops). (6) Continuously read the amount of test liquid 20 in the burette 12 (the amount of test liquid 20 absorbed by the test object) M (ml). (7) The amount of absorbed sample after a predetermined measurement time has elapsed (e.g., 30 seconds) from the start of absorption is calculated using the DW method: Absorption amount (ml / g) = M (ml) / (weight of sample (g)). Since the specific gravity of the test liquid is 1, the measured absorption amount can also be expressed in units of (g / g).

[0102] In this embodiment, it is preferable that the discharge amount of absorbed liquid is polymer absorbent>super absorbent polymer, and the discharge rate of absorbed liquid is polymer absorbent>super absorbent polymer. In this way, in the composite absorbent 4, the polymer absorbent can easily transfer the body fluid once absorbed to the super absorbent polymer, so that the body fluid transferred from the pulp fiber can be quickly transferred from the polymer absorbent to the super absorbent polymer. As a result, the body fluid absorbed by the pulp fiber can be quickly transferred to the polymer absorbent, and the body fluid transferred to the polymer absorbent can be further transferred to the super absorbent polymer. Therefore, leakage of body fluid from the composite absorbent can be suppressed, and the absorption performance of the composite absorbent can be fully exhibited.

[0103] Furthermore, it is preferable that the polymer absorbent has a discharge amount of absorbed water of 25 g / g or more and a discharge rate of 65% or more. It is more preferable that the polymer absorbent has a discharge amount of 35 g / g or more and a discharge rate of 70% or more. In this way, in the composite absorbent 4, since the polymer absorbent has excellent water release properties (water release), it is possible to hold a large amount of body fluid at one time and to release a large amount of the absorbed and held body fluid. Therefore, a large amount of body fluid can be transferred from the polymer absorbent to the superabsorbent polymer, and the water retention ability of the superabsorbent polymer can be fully utilized. However, the discharge amount and discharge rate of the polymer absorbent are measured by the following method.

[0104] <Method of measuring liquid discharge amount and liquid discharge rate> (1) 1 g of the sample to be measured is cut into a 10 cm square mesh bag (NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) and enclosed. The mass (g) of the mesh bag is measured in advance. This measurement method is performed under conditions of a temperature of 25°C and a humidity of 60%. (2) The mesh bag containing the sample is immersed in saline (0.9% sodium chloride solution) for one hour. (3) Hang the mesh bag for 5 minutes and drain, then measure its mass (g). (4) Calculate the amount of water absorbed by the sample (g) by subtracting the total mass of the sample (= 1 g) and the mesh bag from the mass of the mesh bag after draining, measured in (3) above. Then, divide this amount of water absorbed by the mass of the sample (= 1 g) to obtain the amount of water absorbed per unit mass of the sample (g / g). (5) Furthermore, the mesh bag after draining in (3) above is centrifuged at 150 G for 90 seconds, and the mass (g) of the mesh bag after the centrifugation is measured. (6) From the mass of the mesh bag after centrifugation measured in (5) above, calculate the mass of the sample (=1 g) and the total mass of the mesh bag. The weight (g) is subtracted from the amount of water absorbed (g) of the sample measured in (4) above.The liquid discharge amount (g) of the sample is calculated by the above formula, and then this liquid discharge amount is divided by the mass of the sample (=1 g) to obtain the liquid discharge amount per unit mass of the sample (polymer absorbent) (g / g). (7) The liquid discharge amount per unit mass obtained in (6) above is divided by the water absorption amount per unit mass obtained in (4) above, and the result is multiplied by 100 to obtain the liquid discharge amount relative to the water absorption amount of the sample (polymer absorbent), i.e., the liquid discharge rate (%). The repeated discharge amount (g / g) and discharge rate after water absorption and water release are repeated two or three times means the discharge amount (g / g) and discharge rate (%) after the above steps (2) to (6) are repeated two or three times.

[0105] In this embodiment, the water absorption amount per unit mass of the polymer absorbent is preferably 30 g / g or more, more preferably 40 g / g or more, and even more preferably 50 g / g or more. In this way, in the composite absorbent 4, the water absorption amount per unit mass of the polymer absorbent is sufficiently large (30 g / g or more) compared to the water absorption amount per unit mass of pulp fiber alone (about 20 g / g), for example, so that the polymer absorbent can quickly and with a margin absorb the body fluid absorbed by the pulp fiber. This makes it possible to suppress leakage of body fluid from the composite absorbent, and to fully exhibit the absorption performance of the composite absorbent. However, the water absorption amount per unit mass is measured by the following method.

[0106] <Method for measuring water absorption per unit mass> (1) 1 g of the measurement sample is cut into a 10 cm square mesh bag (NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 mesh / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) and enclosed. The mass (g) of the mesh bag is measured in advance. When the measurement sample (polymer absorbent) is to be recovered from a sanitary product and used, it can be obtained according to the above-mentioned <Recovery method of measurement sample (polymer absorbent)>. (2) The mesh bag containing the sample is immersed in saline (0.9% sodium chloride solution) for one hour. (3) Hang the mesh bag for 5 minutes and drain, then measure its mass (g). (4) Calculate the amount of water absorbed by the sample (g) by subtracting the total mass of the sample (= 1 g) and the mesh bag from the mass of the mesh bag after draining, measured in (3) above. Then, divide this amount of water absorbed by the mass of the sample (= 1 g) to obtain the amount of water absorbed per unit mass of the sample (g / g). The above measurement methods are carried out under conditions of a temperature of 25°C and a humidity of 60%.

[0107] In this embodiment, the magnitude of the water absorption viscosity is preferably the polymer absorbent > the superabsorbent polymer. Thus, in the composite absorbent 4, the polymer absorbent has a higher water absorption viscosity when absorbing body fluid than the superabsorbent polymer. Therefore, when the composite absorbent absorbs body fluid, the viscosity of the polymer absorbent increases, suppressing the movement, i.e., fluidization, of the polymer absorbent and the absorbent materials present around it, such as the superabsorbent polymer and pulp fiber, in the composite absorbent. This allows the composite absorbent to deform in accordance with the wearer's body movements without causing gaps due to uneven distribution of the absorbent material in the composite absorbent, and therefore suppresses leakage of body fluids from the composite absorbent, allowing the composite absorbent to fully exhibit its absorption performance.

[0108] Furthermore, the water absorption viscosity of the polymer absorbent is more preferably 80 Pa·s, and more preferably 90 Pa·s. Since the water absorption viscosity during body fluid absorption is high, when the composite absorbent absorbs body fluid, the viscosity of the polymer absorbent increases, which can further suppress the movement of the absorbent material containing the polymer absorbent within the composite absorbent, i.e., fluidization. The water absorption viscosity is measured by the following method.

[0109] <Method for measuring water absorption viscosity> (1) Place 100 ml of saline and a rotor (30 mm x 10 mm) in a 100 ml HARIO beaker (inner diameter 50 mm) and rotate at 600 rpm. (2) Weigh out 1.5 g of the sample and place it in the beaker in (1) above. Wait until the liquid level solidifies and stops (if the liquid does not solidify, stop the rotor after 1 minute has elapsed). (3) Leave it for 5 minutes. (4) The viscosity is measured using a viscometer (Toki Sangyo Co., Ltd., TVB-10 type viscometer, rotor used: M4, rotation speed: 3 rpm). The above measurement methods are carried out under conditions of a temperature of 25°C and a humidity of 60%.

[0110] In this embodiment, it is preferable that the thickness of the composite absorbent is 3 mm or less, and the repeated absorption speed of the composite absorbent is 20 seconds or less. In this way, the composite absorbent 4 has a thickness of 3 mm or less and a repeated absorption speed of 20 seconds or less, so that the composite absorbent can quickly absorb multiple or large amounts of body fluids, and can fully exhibit the absorption performance of the composite absorbent while providing a good wearing comfort when the composite absorbent is applied to a sanitary product. However, the thickness and repeated absorption speed of the composite absorbent are measured by the following methods.

[0111] <Method for measuring thickness of composite absorbent material> (1) 15cm 2 A thickness gauge with a gauge head of 3g / cm (model FS-60DS, manufactured by Daiei Chemical Industry Co., Ltd.) was used. 2 The thickness of the composite absorbent body is measured under the measurement load condition. The thickness is measured at three points on one sample, and the average value of the three thicknesses is regarded as the thickness of the composite absorbent body.

[0112] <Method for measuring the repeated absorption rate of composite absorbents> (1) Prepare a sample. Pulp fiber, polymer absorbent, and superabsorbent polymer are weighed out on an electronic balance to the desired mass (mass that will give the desired basis weight), and mixed uniformly to obtain a mixture. Then, a tissue (14 g / m2) coated with hot melt adhesive is used. 3 ) is used to clamp the mixture from above and below, and a circular sample with a radius of 45 mm is then cut out. (2) Place the sample in a glass petri dish with a radius of 46 mm and a height of 20 mm. (3) 30 ml of artificial urine is dropped onto the sample using a glass burette at 8 ml / s, and the speed (in seconds) at which the liquid disappears from the surface of the sample is measured. The artificial urine is prepared by dissolving 200 g of urea, 80 g of sodium chloride, 8 g of magnesium sulfate, 3 g of calcium chloride, and approximately 1 g of dye: Blue No. 1 in 10 L of ion-exchanged water. (4) After 5 minutes, place a filter paper (manufactured by ADVANTEC, radius 45 cm, No. 2, mass 30 g) on ​​the dropped portion of the sample, and then place a load of 2 kg on top of that. (5) After 3 minutes, remove the load and filter paper, and measure the mass of the filter paper. (6) Repeat steps (3) to (5) above. (7) The rate (seconds) of the first and second absorptions (3) above is added together to form the repeated absorption rate (seconds). The above measurement methods are carried out under conditions of a temperature of 25°C and a humidity of 60%.

[0113] In this embodiment, as described above, the disposable diaper 1 (the absorbent main body 10 thereof), i.e., the sanitary product, comprises a top sheet 2, a back sheet 3, and the above-mentioned composite absorbent body 4 located between the top sheet 2 and the back sheet 3. In other words, since the disposable diaper 1 (sanitary product) comprises the above-mentioned composite absorbent body 4, it is possible to simultaneously maintain or improve the absorption performance of the disposable diaper 1 (sanitary product) and reduce the thickness of the disposable diaper 1 (sanitary product) to improve the wearing comfort.

[0114] Hereinafter, the method for producing such a polymer absorbent will be described in detail using the above-mentioned absorbent A as an example.

[0115] [Method of manufacturing polymer absorbent] The above-mentioned absorbent A can be obtained through a cross-linking polymerization step and a hydrolysis step, as shown in Fig. 2. Each of these steps will be described below.

[0116] (Crosslinking polymerization process) First, an oil-soluble monomer for crosslinking polymerization, a crosslinkable monomer, a surfactant, water, and optionally a polymerization initiator are mixed to obtain a water-in-oil emulsion, which is an emulsion in which the oil phase is the continuous phase and water droplets are dispersed within it.

[0117] In the above-mentioned absorbent A, as shown in the upper diagram of Figure 2, butyl methacrylate, which is a (meth)acrylic acid ester, is used as the oil-soluble monomer, divinylbenzene is used as the cross-linking monomer, sorbitan monooleate is used as the surfactant, and isobutyronitrile is used as the polymerization initiator to cause cross-linking polymerization to obtain monolith A.

[0118] Specifically, for absorbent A, as shown in the upper diagram of Figure 2, first, 9.2 g of t-butyl methacrylate as an oil-soluble monomer, 0.28 g of divinylbenzene as a cross-linking monomer, 1.0 g of sorbitan monooleate (hereinafter abbreviated as "SMO") as a surfactant, and 0.4 g of 2,2'-azobis(isobutyronitrile) as a polymerization initiator are mixed and dissolved uniformly.

[0119] Next, the mixture of t-butyl methacrylate / divinylbenzene / SMO / 2,2'-azobis(isobutyronitrile) is added to 180 g of pure water and stirred under reduced pressure using a planetary stirring device, a vacuum stirring and degassing mixer (manufactured by EME), to obtain a water-in-oil emulsion.

[0120] Furthermore, this emulsion is quickly transferred to a reaction vessel, sealed, and polymerized at 60°C for 24 hours under stationary conditions. After the polymerization is completed, the contents are removed, extracted with methanol, and then dried under reduced pressure to obtain Monolith A, which has a continuous macropore structure. The internal structure of Monolith A was observed by SEM, and it was found that Monolith A had a continuous cell structure and the thickness of the continuous skeleton was 5.4 μm. The average diameter of the continuous pores measured by mercury intrusion porosimetry was 36.2 μm, and the total pore volume was 15.5 mL / g.

[0121] The content of divinylbenzene in the total monomers is preferably 0.3 to 10 mol%, more preferably 0.3 to 5 mol%. The ratio of divinylbenzene to the total of butyl methacrylate and divinylbenzene is preferably 0.1 to 10 mol%, more preferably 0.3 to 8 mol%. In the above-mentioned absorbent A, the ratio of butyl methacrylate to the total of butyl methacrylate and divinylbenzene is 97.0 mol%, and the ratio of divinylbenzene is 3.0 mol%.

[0122] The amount of surfactant added can be set depending on the type of oil-soluble monomer and the desired size of emulsion particles (macropores), and is preferably in the range of about 2 to 70% of the total amount of the oil-soluble monomer and surfactant.

[0123] In order to control the shape and size of the bubbles in Monolith A, alcohols such as methanol and stearyl alcohol; carboxylic acids such as stearic acid; hydrocarbons such as octane, dodecane, and toluene; cyclic ethers such as tetrahydrofuran and dioxane, etc. may be allowed to coexist in the polymerization system.

[0124] In addition, the mixing method for forming the water-in-oil emulsion is not particularly limited, and any mixing method can be used, such as a method of mixing all the components at once, or a method of separately and uniformly dissolving oil-soluble components such as the oil-soluble monomer, surfactant, and oil-soluble polymerization initiator, and water-soluble components such as water and the water-soluble polymerization initiator, and then mixing the respective components.

[0125] Furthermore, the mixing device for forming the emulsion is not particularly limited, and any device such as a normal mixer, homogenizer, or high-pressure homogenizer can be used depending on the desired emulsion particle size. Furthermore, a so-called planetary mixing device can also be used in which the material to be treated is placed in a mixing container and rotated while revolving around the revolution axis while tilting the mixing container, thereby stirring and mixing the material to be treated.

[0126] In addition, there are no particular limitations on the mixing conditions, and the stirring rotation speed, stirring time, etc. can be set as desired according to the desired emulsion particle size. Note that, with the above planetary stirring device, water droplets in the W / O emulsion can be uniformly generated, and the average diameter can be set as desired within a wide range.

[0127] The polymerization conditions for the water-in-oil emulsion can be various, depending on the type of monomer and initiator, etc. For example, when azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, etc. are used as the polymerization initiator, the polymerization can be carried out by heating in a sealed container under an inert atmosphere at a temperature of 30 to 100°C for 1 to 48 hours, and when hydrogen peroxide-ferrous chloride, sodium persulfate-acidic sodium sulfite, etc. are used as the polymerization initiator, the polymerization can be carried out in a sealed container under an inert atmosphere at a temperature of 0 to 30°C for 1 to 48 hours.

[0128] After the polymerization is completed, the contents are taken out and subjected to Soxhlet extraction with a solvent such as isopropanol to remove unreacted monomers and residual surfactants, thereby obtaining monolith A shown in the center diagram of Figure 2.

[0129] (Hydrolysis process) Next, the step of hydrolyzing the monolith A (crosslinked polymer) to obtain the absorbent A (hydrolysis step) will be described.

[0130] First, monolith A is immersed in dichloroethane containing zinc bromide and stirred at 40° C. for 24 hours, then contacted with methanol, 4% hydrochloric acid, 4% aqueous sodium hydroxide solution, and water in that order to carry out hydrolysis, and then dried to obtain a block-shaped absorbent A. Furthermore, this block-shaped absorbent A is crushed to a predetermined size to obtain a particulate absorbent A. Note that the form of this absorbent A is not limited to particulate, and for example, it may be formed into a sheet during or after drying.

[0131] In addition, the method of hydrolysis of monolith A is not particularly limited, and various methods can be adopted. For example, aromatic solvents such as toluene and xylene, halogen-based solvents such as chloroform and dichloroethane, ether-based solvents such as tetrahydrofuran and isopropyl ether, amide-based solvents such as dimethylformamide and dimethylacetamide, alcohol-based solvents such as methanol and ethanol, carboxylic acid-based solvents such as acetic acid and propionic acid, or water as a solvent are contacted with a strong base such as sodium hydroxide, or a hydrohalic acid such as hydrochloric acid, a Bronsted acid such as sulfuric acid, nitric acid, trifluoroacetic acid, methanesulfonic acid, and p-toluenesulfonic acid, or a Lewis acid such as zinc bromide, aluminum chloride, aluminum bromide, titanium (IV) chloride, cerium chloride / sodium iodide, and magnesium iodide.

[0132] Furthermore, among the polymerization raw materials of the organic polymer that forms the hydrophilic continuous skeleton of the absorbent A, the (meth)acrylic acid ester is not particularly limited, but is preferably a C1 to C10 (i.e., carbon number 1 to 10) alkyl ester of (meth)acrylic acid, and more preferably a C4 (i.e., carbon number 4) alkyl ester of (meth)acrylic acid. Examples of C4 alkyl esters of (meth)acrylic acid include t-butyl (meth)acrylic acid ester, n-butyl (meth)acrylic acid ester, and iso-butyl (meth)acrylic acid ester.

[0133] The monomers used in the crosslinking polymerization may be only (meth)acrylic acid esters and divinylbenzene, or may contain, in addition to (meth)acrylic acid esters and divinylbenzene, other monomers other than (meth)acrylic acid esters and divinylbenzene. In the latter case, the other monomers are not particularly limited, but examples thereof include styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, glycidyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobutene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. The proportion of monomers other than (meth)acrylic acid ester and divinylbenzene in all monomers used in the crosslinking polymerization is preferably from 0 to 80 mol %, more preferably from 0 to 50 mol %.

[0134] The surfactant is not limited to the above-mentioned sorbitan monooleate, and may be any surfactant capable of forming a water-in-oil type (W / O) emulsion when the monomer for crosslinking polymerization is mixed with water. Examples of such surfactants include nonionic surfactants such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene nonylphenyl ether, polyoxyethylene stearyl ether, and polyoxyethylene sorbitan monooleate, anionic surfactants such as potassium oleate, sodium dodecylbenzenesulfonate, and dioctyl sodium sulfosuccinate, cationic surfactants such as distearyl dimethyl ammonium chloride, and amphoteric surfactants such as lauryl dimethyl betaine. These surfactants may be used alone or in combination of two or more.

[0135] In addition, the polymerization initiator is preferably a compound that generates radicals by heat and light irradiation. Furthermore, the polymerization initiator may be water-soluble or oil-soluble, and examples thereof include azobis(4-methoxy-2,4-dimethylvaleronitrile), azobisisobutyronitrile, azobisdimethylvaleronitrile, azobiscyclohexanenitrile, azobiscyclohexanecarbonitrile, azobis(2-methylpropionamidine)dihydrochloride, benzoyl peroxide, potassium persulfate, ammonium persulfate, hydrogen peroxide-ferrous chloride, sodium persulfate-acidic sodium sulfite, and tetramethylthiuram disulfide. However, in some cases, there are systems in which polymerization proceeds only by heating or light irradiation without the addition of a polymerization initiator, and in such systems, the addition of a polymerization initiator is not necessary.

[0136] When it is desired to obtain (change) the desired absorption performance or pore distribution in a polymer absorbent, the pore size, pore distribution, and thus the absorption performance can be adjusted mainly by the amount of surfactant added in the cross-linking polymerization process (e.g., surfactant / monomer ratio) and the mixing conditions (e.g., stirring speed, stirring time).

[0137] [Method of manufacturing a composite absorbent containing a polymer absorbent] The composite absorbent body is not particularly limited and may be manufactured by a known method. For example, the composite absorbent body is manufactured by using a fiber stacking device including a material supplying device and a rotating drum. The rotating drum has a suction means on the inner surface thereof, and includes a fiber stacking support disposed on the outer peripheral surface of the rotating drum so as to be rotatable together with the rotating drum. The fiber stacking support has a stacking recess for stacking pulp fibers, a polymer absorbent, and a highly absorbent polymer. The material supplying device supplies pulp fibers, a polymer absorbent, and a highly absorbent polymer, the basis weights of which (mixing ratios) are adjusted, in a mixed state to the fiber stacking support. In the manufacturing method, the pulp fibers, the polymer absorbent, and the highly absorbent polymer, which are supplied in a mixed state by the material supplying device, are stacked in the stacking recess of the fiber stacking support by the suction means to form a fiber stack. Then, the fiber stack is transferred from the fiber stacking support to a sheet member having an adhesive applied to its surface, and the composite absorbent body is manufactured by wrapping the fiber stack in the sheet member. Alternatively, stacks of pulp fibers and highly absorbent polymer may be prepared by the above-mentioned method, and a polymer absorbent may be separately sprayed onto the stacks before wrapping them in the sheet member. EXAMPLES

[0138] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0139] (A) Sample The properties of the polymer absorbent as an example manufactured by the above manufacturing method, the superabsorbent polymer of Patent Document 1 as a comparative example (manufactured by Sumitomo Seika Chemicals Co., Ltd., hereinafter referred to as "high-speed SAP"), and a normal superabsorbent polymer as another comparative example (AQUAKEEP SA60S, manufactured by Sumitomo Seika Chemicals Co., Ltd., hereinafter referred to as "normal SAP") were compared. In addition, as necessary, a comparison was also made with the properties of normal pulp fiber (ground wood pulp product) as another comparative example.

[0140] (B) Evaluation All or part of the above samples were evaluated for the following items: absorption speed (Voltex method), liquid migration rate from pulp fiber, liquid migration amount to superabsorbent polymer, water absorption amount (unpressurized DW method), liquid discharge amount / liquid discharge rate, water absorption viscosity, thickness of the composite absorbent body, and repeated absorption speed.

[0141] (C) Result (1) Absorption speed The initial absorption speed was measured using the above-mentioned Vortex method for measuring (initial) absorption speed. The results were 1.7 seconds for the polymer absorbent, 1.0 seconds for the pulp fiber, 5.4 seconds for the high-speed SAP, and 46.8 seconds for the regular SAP. In other words, the initial absorption speed was pulp fiber > polymer absorbent > superabsorbent polymer (high-speed SAP, regular SAP). Also, the absorption speed of the polymer absorbent using the Vortex method was less than 5 seconds.

[0142] (2) Liquid migration rate from pulp fibers The liquid transfer rate per unit mass from the pulp fiber was measured by the above-mentioned method for measuring the amount of liquid transfer from material A to material B and the liquid transfer rate. However, material A is pulp fiber, and material B is a polymer absorbent, a high-speed SAP, and a normal SAP. The results are shown in Figure 7. Figure 7 is a graph showing the relationship between the liquid transfer rate and the transfer time. The vertical axis shows the liquid transfer rate (%), and the horizontal axis shows the transfer time (seconds). The thick solid line and the circle show the polymer absorbent, the thin solid line and the triangle show the high-speed SAP, and the dashed line and the diamond show the normal SAP. The liquid transfer rate (%) was 61% for the polymer absorbent, 40% for the high-speed SAP, and 7% for the normal SAP at a transfer time of 10 seconds, and 63% for the polymer absorbent, 57% for the high-speed SAP, and 18% for the normal SAP at a transfer time of 30 seconds. Therefore, when the transfer time was within 30 seconds, the polymer absorbent was greater than the superabsorbent polymer (high-speed SAP, normal SAP). As can be seen from the graph, regardless of the transfer time, the polymer absorbent was superior to the superabsorbent polymer (normal SAP). Also, the liquid transfer rate of the polymer absorbent (30 seconds) was 60% or more.

[0143] (3) Amount of liquid transferred to the superabsorbent polymer The amount of liquid transferred per unit mass to the superabsorbent polymer was measured by the above-mentioned method for measuring the amount of liquid transferred from material A to material B and the liquid transfer rate (value (9)). However, material A is a polymer absorbent, high-speed SAP, and pulp fiber, and material B is normal SAP. In this case, the amount of liquid transferred from material A to material B, which absorbed physiological saline under the same conditions, is shown. As a result, the amount of water absorbed per unit mass (g / g) was 82.3g / g for the polymer absorbent, 60.3g / g for the high-speed SAP, and 23.3g / g for the pulp fiber. And, the amount of liquid transferred (g / g) was 9.9g / g for the polymer absorbent, 5.6g / g for the high-speed SAP, and 3.8g for the pulp fiber at a transfer time of 30 seconds. Therefore, the amount of liquid transferred to the superabsorbent polymer was polymer absorbent>high-speed SAP>pulp fiber. And, the amount of liquid transferred to the polymer absorbent (30 seconds) was 6g / g or more.

[0144] (4) Water absorption (non-pressure DW method) The water absorption (non-pressure DW method) was measured by the method for measuring water absorption by the non-pressure DW method described above. As a result, the water absorption was 14.5g / g for the polymer absorbent, 8.9g / g for the pulp fiber, 7.9g / g for the high-speed SAP, and 6.7g / g for the normal SAP at a measurement time of 30 seconds. Therefore, the water absorption (non-pressure DW method) was polymer absorbent > superabsorbent polymer (high-speed SAP, normal SAP). In addition, the water absorption (non-pressure DW method) of the polymer absorbent was 8.0 seconds or more.

[0145] (5) Water absorption viscosity The water absorption viscosity was measured using the method for measuring water absorption viscosity described above. As a result, the water absorption viscosity was 96 Pa·s for the polymer absorbent, 23 Pa·s for the high-speed SAP, and 72 Pa·s for the normal SAP. Therefore, the water absorption viscosity was higher for the polymer absorbent than for the highly water-absorbent polymer. The water absorption viscosity of the polymer absorbent was 80 Pa·s.

[0146] The above results are shown in Table 1. [Table 1]

[0147] (6) Liquid discharge amount / liquid discharge rate The discharge amount and discharge rate of the absorbed liquid were measured by the above-mentioned method for measuring the discharge amount and discharge rate. As a result, the discharge amount was 39-42g / g for the polymer absorbent, 24g / g for the high-speed SAP, and 20-22g / g for the normal SAP. The discharge rate was 75-76% for the polymer absorbent, 44-46% for the high-speed SAP, and 34-36% for the normal SAP. Therefore, the discharge amount was polymer absorbent > highly absorbent polymer, and the discharge rate was polymer absorbent > highly absorbent polymer. The discharge amount of the polymer absorbent was 25g / g or more, and the discharge rate was 65% or more. When the number of absorption / separation times was 2 or 3, the discharge rate was 44-46% in each measurement, but the final discharge rate was 45% in all cases, so it is listed as 45% in the table.

[0148] The above results are shown in Table 2. [Table 2]

[0149] (7) Thickness and repeated absorption rate of the composite absorbent The thickness and repeated absorption speed of the composite absorbent body were measured by the above-mentioned method for measuring the thickness of the composite absorbent body and the method for measuring the repeated absorption speed of the composite absorbent body, respectively. The configuration of the absorbent body to be evaluated is shown in Table 3 below. The absorbent body configuration was pulp fiber / normal SAP / polymer absorbent as an example (composite absorbent body), and pulp fiber / normal SAP as a comparative example (normal absorbent body). For both materials, the basis weight of the normal SAP was the same, and in the composite absorbent body, the basis weight of the polymer absorbent was also the same, and the thickness was changed by the basis weight of the pulp fiber. The results are shown in Table 3 and Figure 8.

[0150] FIG. 8 is a graph showing the relationship between thickness and repeated absorption speed. The vertical axis shows the absorption speed (seconds) of each absorbent body, and the horizontal axis shows the thickness (mm) of each absorbent body. The thick solid line and circles show composite absorbents made of pulp fiber / normal SAP / polymer absorbent, and the thin solid line and triangles show normal absorbents made of pulp fiber / normal SAP. It was found that with the composite absorbent body, by including a polymer absorbent, the repeated absorption speed can be made 20 seconds or less even if the thickness is reduced to 3 mm or less. On the other hand, it was found that with normal absorbents, the repeated absorption speed cannot be made 20 seconds or less if the thickness is reduced to 3 mm or less.

[0151] [Table 3]

[0152] In addition to the pants-type disposable diaper of the above-mentioned embodiment, the composite absorbent of the present invention can be applied to various sanitary products, such as tape-type disposable diapers, sanitary napkins, absorbent liners, absorbent pads (e.g., incontinence pads, bedsore pads, and postpartum pads), absorbent sheets, breast milk pads, disposable diapers for pets, absorbent pads for pets, pet waste disposal sheets, wet sheets, wet tissues, cosmetic wipes, masks, etc. Therefore, the body fluids to be absorbed by the composite absorbent are liquids discharged from the wearer of the sanitary product, such as urine, sweat, feces, menstrual blood, vaginal discharge, breast milk, blood, and exudates.

[0153] The present invention is not limited to the above-described embodiments, and appropriate combinations, substitutions, modifications, and the like are possible without departing from the scope and spirit of the present invention. [Explanation of symbols]

[0154] 1. Disposable diapers 2 Surface sheet 3 Back sheet 4. Composite absorber

Claims

1. 1. A composite absorbent body for sanitary products for absorbing body fluids, comprising: The present invention relates to a method for producing a water-absorbent material comprising: a pulp fiber; a polymer absorbent having a hydrophilic continuous skeleton and continuous pores; and a highly water-absorbent polymer. The initial absorption rate is in the order of the pulp fiber>the polymer absorbent>the highly absorbent polymer, The liquid transfer rate from the pulp fibers is greater than that of the polymer absorbent and greater than that of the superabsorbent polymer; The amount of liquid transferred to the superabsorbent polymer is greater than that of the pulp fiber. Composite absorber.

2. The absorption speed of the polymer absorbent by the Vortex method is 5 seconds or less; 2. The composite absorbent body of claim 1.

3. (Basis weight of the pulp fibers) / (Basis weight of the polymeric absorbent) is greater than 1; and / or (Basis weight of the superabsorbent polymer) / (Basis weight of the polymer absorbent) is greater than 1; 3. The composite absorbent body according to claim 1.

4. The water absorption amount measured by the non-pressure Demand Wetability method is greater than that of the polymer absorbent.

4. The composite absorbent body according to claim 1.

5. The amount of absorbed liquid discharged from the polymer absorbent is greater than the amount of the highly water-absorbent polymer, The discharge rate of the absorbed liquid is such that the polymer absorbent is greater than the highly water-absorbent polymer.

5. The composite absorbent body according to claim 1.

6. The water absorption amount per unit mass of the polymer absorbent is 30 g / g or more; 6. The composite absorbent body according to claim 1.

7. The magnitude of the water absorption viscosity is the polymer absorbent>the highly water-absorbent polymer; 7. The composite absorbent body according to claim 1.

8. The thickness of the composite absorbent is 3 mm or less, The repeated absorption speed of the composite absorbent is 20 seconds or less.

8. The composite absorbent body according to claim 1.

9. The polymer absorbent is a hydrolyzate of a crosslinked polymer of a (meth)acrylic acid ester and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group.

9. The composite absorbent body according to claim 1.

10. A sanitary article comprising a top sheet, a back sheet, and the composite absorbent body according to any one of claims 1 to 9 located between the top sheet and the back sheet.

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