Composite absorbent and sanitary products using the absorbent

Abstract

This invention provides a composite absorbent that can be compressed in thickness while inhibiting the leakage of bodily fluids and can exert high absorption performance. Composite absorbent (4) is a sanitary product used to absorb bodily fluids. Composite absorbent comprises pulp fibers, a polymer absorbent with a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer. The initial absorption rate is pulp fibers > polymer absorbent > superabsorbent polymer.

Description

Technical Field

[0001] The present invention relates to a composite absorbent and a sanitary product using the same. Prior Art

[0002] Absorbents used in sanitary products such as disposable diapers and sanitary napkins are known to contain pulp fibers and superabsorbent polymers. The inclusion of superabsorbent polymers allows for maintaining absorbency while reducing the amount of pulp fibers. This allows for a thinner absorbent and, consequently, sanitary products, resulting in a more comfortable fit.

[0003] Patent Document 1, for example, discloses water-absorbent resin particles as a superabsorbent polymer for sanitary products. According to Patent Document 1, the water-absorbent resin particles comprise a cross-linked polymer containing at least one of acrylic acid and its salts as monomer units. The particles have an absorption rate of 1 to 15 seconds for physiological saline solution, a median particle size of 100 to 600 μm, and a residual volatile component content of 0.44% to 1.5% by mass. The residual volatile component is at least one selected from the group consisting of chain aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons. [Prior Art Literature] [Patent Document]

[0004] [Patent Document 1] Japanese Patent No. 6872503 Summary of the Invention

[0005] [Problems to be solved by the invention]

[0006] Absorbents composed of pulp fibers and superabsorbent polymers absorb fluids first, because the superabsorbent polymers, which have a higher water-retention capacity, have a slower absorption rate. Consequently, the faster-absorbing pulp fibers absorb body fluids first, followed by the superabsorbent polymers. However, if the rate of fluid transfer from the pulp fibers to the superabsorbent polymers is too slow, the pulp fibers may not be able to fully absorb large amounts of fluid when excreted. Alternatively, fluid transfer from the pulp fibers to the superabsorbent polymers may not be rapid enough. This inevitably leads to fluid leakage from the absorbent, potentially preventing the superabsorbent polymers from fully utilizing their water-retention capacity and, consequently, the absorbent's full absorption performance.

[0007] Patent Document 1 describes a method for improving the absorption rate of water-absorbent resin particles compared to conventional superabsorbent polymers. However, the present inventors' research has shown that the absorption rate is not sufficiently fast, specifically, the rate of transfer from pulp fibers to the water-absorbent resin particles is not sufficient. Consequently, even when large amounts of bodily fluid are excreted, leakage from the absorbent is undeniable, and there is a risk that the water-retention capacity of the superabsorbent polymer, and therefore the absorbent's absorption performance, will not be fully utilized.

[0008] The object of the present invention is to provide a composite absorbent body which can suppress thickness while inhibiting leakage of body fluids and can exert high absorption performance, and a sanitary product using the same. [Methods used to solve the problem]

[0009] One aspect of the present invention is a composite absorbent for use in sanitary products for absorbing body fluids, comprising pulp fibers, a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer. The order of initial absorption rate is the pulp fibers > the polymer absorbent > the superabsorbent polymer.

[0010] Another aspect of the present invention is a sanitary product comprising a surface sheet, a back sheet, and the composite absorbent body located between the surface sheet and the back sheet. [Effects of the Invention]

[0011] According to the present invention, a composite absorbent body capable of suppressing thickness while inhibiting body fluid leakage and exhibiting high absorption performance and a sanitary product using the same can be provided. Simple diagram description

[0012] FIG1 is a schematic top view of a disposable diaper 1 in an embodiment in an unfolded state, viewed from the skin-facing side in the thickness direction. FIG. 2 is a diagram illustrating a manufacturing process of absorbent A, which is an example of a polymer absorbent according to an embodiment. [Figure 3] is a SEM photograph of absorbent A at a magnification of 50 times. [Figure 4] is a SEM photograph of absorbent A at a magnification of 100 times. Figure 5 is a SEM photograph of absorbent A at a magnification of 500 times. FIG6 is a SEM photograph of absorbent A at a magnification of 1500 times. FIG7 is a graph showing the relationship between liquid migration speed and migration time. [Fig. 8] is a graph showing the relationship between absorption rate and absorbent body thickness. FIG9 is a schematic diagram showing a measuring device used in the non-pressurized DW method. Implementation Method

[0013] This embodiment relates to the following aspects. [Aspect 1] A composite absorbent for use in sanitary products for absorbing body fluids, comprising pulp fibers, a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, and a superabsorbent polymer. The order of initial absorption speed is pulp fibers > polymer absorbent > superabsorbent polymer.

[0014] In this composite absorbent, the initial absorption rates are pulp fibers > polymer absorbent > superabsorbent polymer. Therefore, body fluids absorbed by the pulp fibers are temporarily received (absorbed) by the polymer absorbent, and then subsequently received (absorbed) by the superabsorbent polymer. Consequently, body fluids initially absorbed by the pulp fibers (with a faster absorption rate) are subsequently transferred (absorbed) to the polymer absorbent (with a higher absorption rate), thereby preventing the pulp fibers from fully absorbing the body fluids. Furthermore, since body fluids absorbed by the polymer absorbent are subsequently transferred (absorbed) to the superabsorbent polymer (with a slower absorption rate but higher absorption capacity), insufficient transfer of body fluids to the superabsorbent polymer is prevented. This reduces the thickness of the composite absorbent while suppressing leakage of body fluids from the composite absorbent, fully utilizing the water-retention capacity of the superabsorbent polymer and, consequently, the absorbent's absorption performance.

[0015] [Aspect 2] The composite absorbent of aspect 1, wherein the absorption rate of the polymer absorbent obtained by the Voltex method is less than 5 seconds. In this composite absorbent, body fluid temporarily absorbed by the pulp fibers is rapidly transferred to the polymer absorbent within a short period of time (within 5 seconds). This prevents excessive accumulation of body fluid in the pulp fibers, which in turn slows the absorption rate and prevents the pulp fibers from fully absorbing the body fluid. Consequently, body fluid absorbed by the faster-absorbing pulp fibers is quickly transferred to the polymer absorbent. The fluid transferred by the polymer absorbent is then further transferred to the highly absorbent superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0016] [Aspect 3] A composite absorbent as in aspect 1 or 2, wherein the liquid migration rate from the pulp fibers is greater than that of the polymer absorbent and the superabsorbent polymer. In this composite absorbent, body fluid temporarily absorbed by the pulp fibers migrates to the faster-absorbing polymeric absorbent faster than to the slower-absorbing superabsorbent polymer. This prevents excessive accumulation of body fluid in the pulp fibers, slowing absorption, or insufficient absorption by the pulp fibers. Consequently, body fluid absorbed by the pulp fibers is continuously and rapidly transferred to the superabsorbent, and body fluid transferred to the superabsorbent is further transferred to the superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0017] [Aspect 4] A composite absorbent as in any one of aspects 1 to 3, wherein the amount of liquid migration toward the aforementioned superabsorbent polymer is greater than the aforementioned polymer absorbent and the aforementioned pulp fiber. In this composite absorbent, a greater amount of body fluid can migrate to and be absorbed by the polymer absorbent than by pulp fibers. Furthermore, a greater amount of body fluid that migrates to the polymer absorbent can migrate to the superabsorbent polymer than does pulp fibers. Therefore, after the body fluid migrates, the water absorption capacity of the polymer absorbent is restored. This allows body fluid absorbed by the pulp fibers to be continuously and rapidly transferred to the polymer absorbent, and body fluid transferred to the polymer absorbent can then be transferred to the superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption capacity.

[0018] [Aspect 5] The composite absorbent of any one of aspects 1 to 4, wherein (the weight per unit area of ​​the pulp fibers) / (the weight per unit area of ​​the polymer absorbent) is greater than 1, and / or (Weight per unit area of ​​the aforementioned super absorbent polymer) / (Weight per unit area of ​​the aforementioned polymer absorbent) is greater than 1. In this composite absorbent, because the pulp fibers have a greater weight per unit area than the polymer absorbent, bodily fluids are initially more readily absorbed by the faster-absorbing pulp fibers. Subsequently, bodily fluids absorbed by the pulp fibers are readily transferred to the polymer absorbent. Consequently, when the superabsorbent polymer has a greater weight per unit area than the polymer absorbent, the polymer absorbent can readily contact the superabsorbent polymer, and bodily fluids absorbed by the polymer absorbent can readily transfer to the superabsorbent polymer. This allows bodily fluids to be rapidly absorbed by the pulp fibers, transferred from the pulp fibers to the polymer absorbent, and then transferred from the polymer absorbent to the superabsorbent polymer. This prevents leakage of bodily fluids from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0019] [Aspect 6] The composite absorbent according to any one of aspects 1 to 5, wherein the water absorption capacity obtained by the demand wettability method is greater than that of the polymer absorbent and the superabsorbent polymer. In this composite absorbent, the polymer absorbent absorbs free water that may form in the gaps between the nonwoven fabric and the polymer absorbent, or in the gaps between the polymer absorbents themselves, as absorbed body fluid diffuses. In other words, the polymer absorbent absorbs free water without leaking out. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0020] [Aspect 7] The composite absorbent according to any one of aspects 1 to 6, wherein the amount of liquid discharged is greater than the amount of the polymer absorbent and the amount of the super absorbent polymer. The drainage rate of the absorbed liquid is the same as that of the aforementioned high molecular absorbent>the aforementioned super absorbent polymer. In this composite absorbent, bodily fluid temporarily absorbed by the polymer absorbent is readily transferred to the superabsorbent polymer. Consequently, bodily fluid that has migrated from the pulp fibers can be rapidly transferred from the polymer absorbent to the superabsorbent polymer. Consequently, bodily fluid absorbed by the pulp fibers is continuously and rapidly transferred to the polymer absorbent, and bodily fluid transferred by the polymer absorbent is further transferred to the superabsorbent polymer. This prevents leakage of bodily fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0021] [Aspect 8] The composite absorbent according to any one of aspects 1 to 7, wherein the water absorption per unit mass of the polymer absorbent is 30 g / g or more. In this composite absorbent, the polymer absorbent has a significantly higher water absorption capacity per unit mass (over 30 g / g) than, for example, pulp fiber alone (approximately 20 g / g). Therefore, bodily fluids absorbed by the pulp fibers are rapidly and generously absorbed by the polymer absorbent. This prevents leakage of bodily fluids from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0022] [Aspect 9] As in any one of aspects 1 to 8, the composite absorbent, wherein the water absorption viscosity is such that the aforementioned polymer absorbent is greater than the aforementioned super absorbent polymer. The polymer absorbent contained in this composite absorbent has a higher viscosity when absorbing body fluids than the superabsorbent polymer. Therefore, when the composite absorbent absorbs body fluids, the viscosity of the polymer absorbent increases, inhibiting the movement of the polymer absorbent, as well as surrounding superabsorbent polymer and absorbent materials such as pulp fibers within the composite absorbent, thereby preventing fluidization. This allows the composite absorbent to deform with the wearer's body movements without causing gaps in the absorbent material due to localized distribution within the composite absorbent. This prevents leakage of body fluids from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0023] [Aspect 10] The composite absorbent body of any one of aspects 1 to 9, wherein the thickness of the composite absorbent body is 3 mm or less, and the repeated absorption rate of the composite absorbent body is 20 seconds or less. Since the composite absorbent has a thickness of less than 3 mm and a repeated absorption rate of less than 20 seconds, it can quickly absorb multiple or large amounts of body fluids, fully utilizing the absorption performance of the composite absorbent. At the same time, the composite absorbent has a good wearing feel when used as a sanitary product.

[0024] [Aspect 11] The composite absorbent of any one of aspects 1 to 10, wherein the polymer absorbent is a hydrolyzate of a cross-linked polymer of (meth)acrylate and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group. In this composite absorbent, the polymer absorbent has the aforementioned structure, allowing it to quickly receive (absorb) body fluids absorbed by the pulp fibers. This fluid is then quickly received (absorbed) by the superabsorbent polymer. This composite absorbent suppresses leakage of body fluids and exhibits high absorption performance.

[0025] [Aspect 12] A sanitary product comprises a surface sheet, a back sheet, and a composite absorbent body as described in any one of aspects 1 to 11 located between the surface sheet and the back sheet. Since the sanitary product has the composite absorbent body, it can maintain or improve the absorption performance of the sanitary product and reduce the thickness of the sanitary product to make it feel good to wear.

[0026] Hereinafter, a preferred embodiment of the composite absorbent body of the present invention will be described using a disposable diaper 1 (pants-type diaper) as an example of a sanitary product to which the composite absorbent body is applicable.

[0027] In this specification, unless otherwise specified, "viewing an object (e.g., a disposable diaper, composite absorbent, etc.) in its unfolded state on a horizontal surface from the vertically upper side (the surface sheet side in the case of sanitary products) in the thickness direction of the object" is simply referred to as "top view." Furthermore, "longitudinal direction" refers to "the direction in which the length of a longitudinally long object (e.g., a disposable diaper, composite absorbent, etc.) in its unfolded state is longer when viewed from above." "Width direction" refers to "the direction in which the length of a longitudinally long object in its unfolded state is shorter when viewed from above." "Thickness direction" refers to "the direction perpendicular to the object in its unfolded state on a horizontal surface." These longitudinal, width, and thickness directions are orthogonal to each other. Furthermore, in the thickness direction of the disposable diaper 1, "the side of the disposable diaper 1 that is relatively closer to the wearer's skin when worn" is referred to as the "skin-facing side," and "the side of the disposable diaper 1 that is relatively farther from the wearer's skin when worn" is referred to as the "non-skin-facing side."

[0028] [Disposable diapers] Figure 1 is a schematic top view of a disposable diaper 1 in an unfolded state, including a composite absorbent body 4 according to an embodiment. The disposable diaper 1 of this embodiment has a longitudinal direction L, a width direction W, and a thickness direction T, which are mutually orthogonal when viewed from above. The disposable diaper 1 comprises a cover sheet 9 and an absorbent body 10, which form a ventral region FW, a dorsal region RW, and a crotch region CA. One end of the absorbent body 10 in the longitudinal direction L is laminated to the skin-facing surface of the ventral region FW, while the other end is laminated to the skin-facing 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 of the ventral region FW in the width direction W and the two end portions RWa, RWa of the dorsal region RW in the width direction W overlap in the thickness direction T and are joined along the longitudinal direction L to form the disposable diaper 1. In this case, the disposable diaper 1 defines a waist opening for the wearer's waist to pass through, defined by the outer end FWe of the ventral region FW in the longitudinal direction L and the outer end RWe of the dorsal region RW in the longitudinal direction L. Furthermore, the disposable diaper 1 defines a pair of leg openings for the wearer's feet to pass through, defined by the side portions Ce, Ce on either side of the crotch region CA in the width direction W. The cover sheet 9 has a roughly hourglass shape when viewed from above, and the absorbent body 10 has a roughly rectangular shape extending along the longitudinal direction L when viewed from above. The outer shape of the disposable diaper 1 is not particularly limited and can adopt any conventional shape depending on the intended use and usage.

[0029] The cover sheet 9 is, for example, composed of two layers, with a plurality of elastic members 111a, 111b, 113a, 113b, and 107 disposed between the two layers. The plurality of elastic members 111a and 111b are located in the ventral region FW. The plurality of elastic members 111a are disposed inwardly in the longitudinal direction L of the ventral region FW, and on both sides of the absorbent body 10 in the width direction W. Meanwhile, the plurality of elastic members 111b are disposed outwardly in the longitudinal direction L of the ventral region FW. Similarly, the plurality of elastic members 113a and 113b are located in the dorsal region RW. The plurality of elastic members 113a are disposed inwardly in the longitudinal direction L of the dorsal region RW, and on both sides of the absorbent body 10 in the width direction W. Meanwhile, the plurality of elastic members 113b are disposed outwardly in the longitudinal direction L of the dorsal region RW. The plurality of elastic members 107 are arranged on both sides of the region from the ventral region FW to the dorsal region RW in the width direction W. The plurality of elastic members 111a, 111b; 113a, 113b; 107 are exemplified by yarn rubber. The cover sheet 95 is made of, for example, a nonwoven fabric or a resin film.

[0030] The absorbent body 10 has as its basic structure a liquid-permeable surface sheet 2 forming the surface of the absorbent body 10 facing the skin in the thickness direction, a back sheet 3 forming the surface of the absorbent body 10 facing the non-skin side, and a composite absorbent body 4 arranged between these sheets.

[0031] The absorbent body 10 of this embodiment further includes a pair of side sheets 5 located at opposite ends of the side sheet 5 in the width direction W and extending along the longitudinal direction L. Each side sheet 5 has a leakage barrier 6 and a fixing region 7. The fixing regions 7 are located at the front and rear ends of the side sheet 5 in the longitudinal direction L. The leakage barrier 6 is fixed to the skin-facing surface of the absorbent body 10 (the top sheet 2). The leakage barrier 6 is located between the fixing regions 7 on the front and rear sides of the side sheet 5 in the longitudinal direction L. The outer edges of the leakage barrier 6 in the width direction W are fixed to the skin-facing surface of the absorbent body 10 (the top sheet 2), while the inner edges are not fixed. In this case, the leakage barrier 6 and fixing region 7 are formed by, for example, the inner portions of the side sheet 5 in the width direction W, with the outer portions of the side sheet 5 in the width direction W being fixed to the absorbent body 10 (the top sheet 2). Each leakage preventing wall 6 includes one or more elastic members 8 extending along the longitudinal direction L at the inner end portion in the width direction W. The elastic member 8 is exemplified by yarn rubber.

[0032] The absorbent body 10 may further include a pair of linear high-density portions (not shown) extending in the longitudinal direction L or the width direction W and spaced apart in the width direction W or the longitudinal direction L. However, "along a specific direction" includes not only parallel to that direction but also deviations of ±30° from that direction. The high-density portions can be formed, for example, by embossing the topsheet 2 and the composite absorbent body 4 in the thickness direction.

[0033] Furthermore, the disposable diaper 1 (and the absorbent body 10) is not limited to these structures, and may have other structures as long as it includes the structure of the composite absorbent body 4 described below.

[0034] In the absorbent body 10 of the disposable diaper 1, the composite absorbent body 4 is located between the topsheet 2 and the backsheet 3 and is formed from a water-absorbing member that absorbs body fluids such as urine and menstrual blood excreted from the wearer and that pass through the topsheet 2. The composite absorbent body 4 comprises a hydrophilic continuous skeleton and a polymer absorbent with continuous pores as the water-absorbing member.

[0035] Polymer absorbents exhibit a unique water-absorbing behavior: when absorbing fluid, the water is drawn into the continuous matrix and then into the continuous pores. Therefore, when the polymer absorbent absorbs body fluids such as urine or menstrual blood, the hydrophilic continuous matrix instantly absorbs the fluid and expands due to osmotic pressure, expanding the volume of the continuous pores and allowing the fluid to be drawn into the expanded continuous pores. Therefore, the polymer absorbent can instantly absorb large amounts of body fluid. In this embodiment, the absorbed body fluid is then transferred to the highly water-retaining superabsorbent polymer and stably retained within the superabsorbent polymer.

[0036] In the disposable diaper 1, the composite absorbent body 4, as an absorbent component, contains pulp fibers and superabsorbent polymers, in addition to a hydrophilic continuous matrix and a polymeric absorbent with continuous pores. Therefore, the initial absorption rates of these absorbent components follow the order: pulp fibers > polymeric absorbent > superabsorbent polymer. In other words, pulp fibers have the fastest initial absorption rate, polymeric absorbents have the second fastest, and superabsorbent polymers have the slowest initial absorption rate.

[0037] Thus, in the composite absorbent body 4, the initial absorption rates are in the order of pulp fibers > polymer absorbent > superabsorbent polymer. Therefore, body fluid absorbed by the pulp fibers is temporarily received (absorbed) by the polymer absorbent, and then subsequently received (absorbed) by the superabsorbent polymer. This prevents incomplete absorption of body fluid by the pulp fibers because body fluid absorbed by the faster-absorbing pulp fibers is sequentially transferred (absorbed) to the faster-absorbing polymer absorbent, thereby preventing the pulp fibers from completely absorbing the body fluid. Furthermore, since body fluid absorbed by the polymer absorbent is sequentially transferred (absorbed) to the superabsorbent polymer, which has a slower absorption rate but higher absorption capacity, it also prevents the body fluid from being transferred to the superabsorbent polymer quickly enough. Thus, the use of superabsorbent polymer reduces the thickness of the composite absorbent body and prevents leakage of body fluid from the composite absorbent body, fully utilizing the water-retention capacity of the superabsorbent polymer and, consequently, the absorbent body's absorption performance. Furthermore, the excreted body fluid is first mostly absorbed by the pulp fibers, but a portion is absorbed by the high molecular absorbent and then moves to the superabsorbent polymer.

[0038] Therefore, the disposable diaper 1 (absorbent body 10) having such a composite absorbent body 4 can also use a superabsorbent polymer to press the thickness while suppressing the leakage of body fluids, and can exert the excellent absorption performance of the disposable diaper (absorbent body).

[0039] Hereinafter, various components of sanitary products to which the composite absorbent body of the present invention is applicable will be further described using the disposable diaper 1 described above.

[0040] (Surface sheet) As shown in Figure 1, the topsheet 2 has a longitudinally elongated shape, extending from one end edge to the other end edge of the absorbent body 10 in the longitudinal direction L, and from near one end edge to near the other end edge in the width direction W of the absorbent body 10, when viewed from above. The topsheet 2 is positioned on the skin-facing side of the absorbent body 10 in the thickness direction and forms the contact surface that contacts the wearer's skin, i.e., the skin-facing surface of the absorbent body 10. The topsheet 2 is formed from a liquid-permeable sheet-like member.

[0041] 1, the topsheet 2 has slightly larger dimensions in both the length direction L and the width direction W than the composite absorbent body 4 disposed on the non-skin facing side of the topsheet 2. Therefore, the topsheet 2 is joined to the backsheet 3 on the non-skin facing side at the peripheral edge.

[0042] In the present invention, the outer shape, various dimensions, and unit weight of the surface sheet are not particularly limited as long as they can be used as the surface sheet of sanitary products. Any outer shape, various dimensions, and unit weight can be used according to the required liquid permeability, skin feel, softness, strength, etc.

[0043] (Back sheet) The back sheet 3 has a longitudinally elongated shape, extending from one end edge of the absorbent body 10 in the longitudinal direction L to the other end edge, and from one end edge to the other end edge in the width direction W of the absorbent body 10, when viewed from above. The back sheet 3 is positioned on the non-skin-facing side of the absorbent body 10 in the thickness direction, constituting the non-skin-facing surface of the absorbent body 10. The back sheet 3 is formed from a liquid-impermeable sheet-like member to prevent body fluids such as urine and menstrual blood that have passed through the composite absorbent body 4 from leaking out of the absorbent body 10.

[0044] In the present invention, the outer shape, various dimensions, and unit area weight of the back sheet are not particularly limited as long as they can be used as the back sheet of sanitary products. Any outer shape, various dimensions, and unit area weight corresponding to the required leak-proof performance, breathability, strength, etc. can be adopted.

[0045] (Composite absorber) As shown in FIG1 , the composite absorbent body 4 has a longitudinally approximately rectangular shape in a plan view, centered at the center of the longitudinal direction L and the width direction W of the absorbent body 10, extending from near one side end edge of each of the longitudinal direction L and the width direction W to near the other side end edge.

[0046] Specifically, the composite absorbent body 4 has a substantially rectangular shape extending in the longitudinal direction L, similar to the absorbent body 10, when viewed from above. However, the outer shape of the composite absorbent body 4 is not particularly limited and can adopt any conventional shape corresponding to various uses or usage patterns.

[0047] The composite absorbent body 4 is positioned between the topsheet 2 and backsheet 3 in the thickness direction of the disposable diaper 1. It absorbs and retains body fluids such as urine and menstrual blood that have passed through the topsheet 2. It is composed of a specific absorbent member. The absorbent member includes absorbent materials such as polymer absorbents, pulp fibers, and superabsorbent polymers, as described below, and a sheet-like material that retains these absorbent materials. In other words, the composite absorbent body 4 is an absorbent member composed of an absorbent material that absorbs and retains body fluids and a sheet material that retains these absorbent materials.

[0048] In the absorbent body 10, the composite absorbent body 4 is bonded to each of the topsheet 2 and the backsheet 3 by an optional adhesive such as a heat-sealing adhesive.

[0049] The composite absorbent 4 comprises a polymer absorbent having a hydrophilic continuous skeleton and continuous pores, exhibiting unique water-absorbing behavior, as described above, and further comprising pulp fibers and a superabsorbent polymer. When the polymer absorbent is in the form of particles, its average particle size (when dry) is, for example, several hundred μm (200-500 μm). The polymer absorbent may be in sheet form. Polymer absorbents will be described later. Superabsorbent polymers are called SAPs (superabsorbent polymers). Their types are not particularly limited, and materials known in the art can be used. Examples of superabsorbent polymers include polyacrylates, polysulfonates, and maleic anhydride salts. When the superabsorbent polymer is in the form of particles, its average particle size (when dry) is, for example, several hundred μm (200-500 μm). The superabsorbent polymer may be in sheet form. The type of pulp fibers is not particularly limited, and materials known in the art can be used. Examples of pulp fibers include cellulose fibers. Examples of cellulosic fibers include wood pulp, cross-linked pulp, non-wood pulp, regenerated cellulose, and semi-synthetic cellulose. Examples of pulp fiber sizes include an average fiber length of several tens of micrometers (20-40 μm) and an average fiber length of several millimeters (2-5 mm). The composite absorbent can be enclosed in a core bag formed of a liquid-permeable sheet.

[0050] The absorbent materials of the polymer absorbent, pulp fibers, and superabsorbent polymer are generally uniformly arranged throughout the composite absorbent body 4 when viewed from above, except for manufacturing errors. However, the present invention is not limited to this example; other arrangements may be employed in which at least one of the absorbent materials is generally non-uniform and intentionally distributed in a specific manner. For example, the polymer absorbent may be arranged between one and the other of a pair of high-density portions in the width direction W at a higher basis weight than in other areas, or between one and the other of a pair of high-density portions in the longitudinal direction L at a higher basis weight than in other areas. Alternatively, the polymer absorbent may be arranged outside each of the pair of high-density portions in the width direction W at a higher basis weight than in other areas, or outside each of the pair of high-density portions in the longitudinal direction L at a higher basis weight than in other areas. To ensure that bodily fluids absorbed by the pulp fibers are transferred to the superabsorbent polymer, the polymer absorbent is preferably in contact with the superabsorbent polymer.

[0051] In the present invention, the external shape, various dimensions, unit area weight, etc. of the composite absorbent are not particularly limited as long as they do not hinder the effects of the present invention. Any external shape, various dimensions, unit area weight, etc. corresponding to the required water absorbency, softness, strength, etc. can be adopted.

[0052] The following is a more detailed description of the polymer absorbent used in the composite absorbent of the present invention.

[0053] [Polymer absorbent] There are no specific restrictions on polymer absorbents, as long as they possess a hydrophilic continuous backbone and continuous pores, exhibit water absorption behavior whereby water is drawn into the continuous backbone and then into the continuous pores, and the initial absorption rate follows the order of pulp fiber > polymer absorbent > superabsorbent polymer. Examples of such polymer absorbents include hydrolyzates of cross-linked polymers containing at least two (meth)acrylate monomers, and polymer compounds having at least one hydrophilic group in their functional groups. More specifically, hydrolyzates of cross-linked polymers of (meth)acrylate and a compound containing at least two vinyl groups per molecule, and polymer compounds having at least one -COONa group. Such polymer absorbents are organic porous materials containing at least one -COONa group per molecule, and may also contain -COOH groups. The -COONa groups are substantially uniformly distributed throughout the backbone of the porous material.

[0054] When a polymer absorbent has the above structure, as described below, its hydrophilic continuous backbone readily expands (i.e., easily swells) and its continuous pores easily enlarge when absorbing body fluids such as urine or menstrual blood. This allows for faster absorption of more body fluids into the continuous pores, demonstrating its superior absorbency as an absorbent material. Furthermore, the polymer absorbent quickly and temporarily receives (absorbs) body fluids absorbed by the pulp fibers, and then the superabsorbent polymer receives (absorbs) the body fluids absorbed by the polymer absorbent.

[0055] In this specification, the term "(meth)acrylate" refers to acrylate or methacrylate.

[0056] For example, a polymer absorbent can be formed from a hydrolyzed product of a cross-linked polymer of (meth)acrylate and divinylbenzene. In this polymer absorbent, an organic polymer containing at least -COONa groups forms a continuous hydrophilic backbone, with interconnected pores (continuous pores) formed between the backbones, serving as absorption sites for the target fluid (e.g., body fluids such as urine or menstrual blood). Because the hydrolysis converts the -COOR groups (i.e., carboxylate groups) of the cross-linked polymer into -COONa or -COOH groups (see Figure 2), the polymer absorbent can contain -COOR groups.

[0057] The presence of -COOH groups and -COONa groups in the organic polymer forming the hydrophilic continuous backbone can be confirmed by infrared spectrophotometry and quantitative analysis of weakly acidic ion exchange groups.

[0058] Figure 2 illustrates the production process of absorbent A, an example of a polymer absorbent. The top diagram of Figure 2 shows the polymerized raw materials, the middle diagram shows a macroblock A of a cross-linked polymer of (meth)acrylate and divinylbenzene, and the bottom diagram shows absorbent A obtained by hydrolyzing and drying the macroblock A in the middle diagram.

[0059] The polymer absorbent will be described below using absorbent A formed from a hydrolyzate of a cross-linked polymer of (meth)acrylate and divinylbenzene, which is an example of the polymer absorbent.

[0060] Furthermore, the polymer absorbent is not limited to this type of absorbent A. The polymer absorbent may be, for example, a hydrolyzate of a cross-linked polymer of a (meth)acrylate and a compound having two or more vinyl groups per molecule. Alternatively, the polymer absorbent may be, for example, a hydrolyzate of a cross-linked polymer of two or more monomers containing at least one (meth)acrylate. However, if the polymer absorbent is in a bulk form, it can rapidly absorb body fluids and more reliably transfer body fluids temporarily retained by the polymer absorbent to the superabsorbent polymer.

[0061] In the following description, "bulk A" refers to an organic porous material composed of a cross-linked polymer of (meth)acrylate and divinylbenzene before hydrolysis, sometimes referred to as a "bulk-shaped organic porous material." Furthermore, "absorbent A" refers to the hydrolyzate of the cross-linked polymer of (meth)acrylate and divinylbenzene (bulk A) after hydrolysis and drying. In the following description, absorbent A refers to the dry state.

[0062] First, the structure of absorbent A is described. Absorbent A has a hydrophilic continuous backbone and continuous pores as described above. As shown in Figure 2, absorbent A, an organic polymer with a hydrophilic continuous backbone, is obtained by cross-linking (meth)acrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, followed by further hydrolysis of the resulting cross-linked polymer (macroblock A).

[0063] The organic polymer forming the hydrophilic continuous backbone comprises a polymerized residue of a vinyl group (hereinafter referred to as "constituent unit X") and a cross-linked polymerized residue of divinylbenzene (hereinafter referred to as "constituent unit Y") as constituent units. Furthermore, the polymerized residue of the vinyl group (constituent unit X) in the organic polymer forming the hydrophilic continuous backbone comprises a -COONa group generated by hydrolysis of a carboxylate ester group, or a combination of a -COOH group and a -COONa group. Furthermore, when the polymerizable monomer is a (meth)acrylate, the polymerized residue of the vinyl group (constituent unit X) comprises a -COONa group, a -COOH group, and an ester group.

[0064] In absorbent A, the ratio of cross-linked polymerized residues of divinylbenzene (constituent units Y) in the organic polymer forming a hydrophilic continuous skeleton is, for example, 0.1 to 30 mol%, preferably 0.1 to 20 mol%, relative to the total constituent units. For example, in absorbent A using butyl methacrylate as a polymerization monomer and divinylbenzene as a cross-linking monomer, the ratio of cross-linked polymerized residues of divinylbenzene (constituent units Y) in the organic polymer forming a hydrophilic continuous skeleton is, for example, approximately 3%, preferably 0.1 to 10 mol%, and more preferably 0.3 to 8 mol%, relative to the total constituent units. Furthermore, when the ratio of cross-linked polymerized residues of divinylbenzene in the organic polymer forming a hydrophilic continuous skeleton is 0.1 mol% or greater, the strength of absorbent A is unlikely to decrease. When the ratio of cross-linked polymerized residues of divinylbenzene is 30 mol% or less, the amount of absorption of an absorbent object is unlikely to decrease.

[0065] Furthermore, in the absorbent A, the organic polymer forming the hydrophilic continuous skeleton may be composed only of the structural units X and Y, or may contain structural units other than the structural units X and Y, that is, may contain polymerized residues of monomers other than (meth)acrylate and divinylbenzene.

[0066] Examples of constituent units other than the constituent unit X and the constituent unit Y include polymerized residues of monomers such as styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, glycidyl (meth)acrylate, isobutylene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate.

[0067] The ratio of the structural units other than the structural units X and Y in the organic polymer forming the hydrophilic continuous skeleton relative to the total structural units is, for example, 0 to 50 mol%, preferably 0 to 30 mol%.

[0068] Furthermore, the hydrophilic continuous skeleton of absorbent A preferably has a thickness of 0.1 to 100 μm. When the hydrophilic continuous skeleton of absorbent A is 0.1 μm or thicker, the spaces (pores) within the porous body that absorb the target fluid (body fluid) are less likely to collapse during absorption, thus minimizing the absorption capacity. On the other hand, when the hydrophilic continuous skeleton is 100 μm or thinner, excellent absorption rates are easily achieved.

[0069] Furthermore, because the pore structure of the hydrophilic continuous skeleton of absorbent A is an interconnected cell structure, the thickness of the continuous skeleton is measured using a cross-section of the skeleton as seen on a test piece for electron microscopy. Since the continuous skeleton is formed by the spaces between water (water droplets) removed by dehydration and drying after hydrolysis, it is often polygonal in shape. Therefore, the thickness of the continuous skeleton is the average diameter (μm) of the circle circumscribing the polygonal cross-section. In rare cases where a polygon contains small holes, the thickness is measured using the circumscribing circle surrounding the small holes.

[0070] Furthermore, the average continuous pore diameter of the absorbent A is preferably 1 to 1000 μm. When the average continuous pore diameter of the absorbent A is 1 μm or greater, the spaces (pores) within the porous body that absorb the target fluid (body fluid) are less likely to collapse during absorption, thus minimizing the absorption rate. On the other hand, when the average continuous pore diameter is 1000 μm or less, an excellent absorption rate is easily achieved.

[0071] The average diameter (μm) of the continuous pores of absorbent A can be measured by mercury intrusion porosimetry, using the maximum value of the pore distribution curve obtained by this method. Samples used for measuring the average diameter of the continuous pores, regardless of the ionic form of absorbent A, must be dried in a vacuum dryer set at 50°C for at least 18 hours. The ultimate pressure is 0 Torr.

[0072] Figure 3 is a 50x magnification SEM photograph of absorbent A, Figure 4 is a 100x magnification SEM photograph of absorbent A, Figure 5 is a 500x magnification SEM photograph of absorbent A, and Figure 6 is a 1500x magnification SEM photograph of absorbent A. The absorbent A shown in Figures 3-6 is an example of an absorbent using butyl methacrylate as a polymerizing monomer and divinylbenzene as a crosslinking monomer. Each absorbent has a 2 mm square cubic structure.

[0073] The absorbent A shown in Figures 3-6 has numerous bubble-like macropores, and furthermore, these bubble-like macropores have overlapping portions. The absorbent A has a continuous bubble structure in which these overlapping portions of macropores form a common opening (mesopore), forming a continuous bubble structure (continuous macropore structure).

[0074] The overlapping portions of these macropores form common openings (mesopores) with an average diameter in the dry state of 1 to 1000 μm, preferably 10 to 200 μm, and particularly preferably 20 to 100 μm, with the majority of these openings forming an open-pore structure. When the average diameter of the mesopores in the dry state is 1 μm or greater, the absorption rate of the target liquid is improved. On the other hand, when the average diameter of the mesopores in the dry state is 1000 μm or less, the absorbent A is less likely to become brittle. In addition, the number of overlapping large holes in one large hole is about 1 to 12, and most of the time it is about 3 to 10.

[0075] Furthermore, since the absorbent A has such a continuous bubble structure, macropore groups or mesopore groups can be uniformly formed, and compared with the particle aggregation type porous body described in Japanese Patent Application Laid-Open No. 8-252579, etc., it has the advantage of significantly increasing the pore volume and specific surface area.

[0076] The total pore volume of the pores (vacancies) of absorbent A is preferably 0.5-50 mL / g, more preferably 2-30 mL / g. By ensuring a total pore volume of 0.5 mL / g or greater, absorbent A can maintain sufficient pore volume, thereby ensuring sufficient water absorption. Furthermore, the spaces (vacancies) within the porous body that absorb the target fluid (body fluid) are less likely to collapse during absorption, and the amount and rate of water absorption are less likely to decrease. Furthermore, when the total pore volume of absorbent A is 50 mL / g or less, the strength of absorbent A is less likely to decrease.

[0077] The total pore volume can be measured by mercury intrusion porosimetry. Samples used for total pore volume measurement, regardless of the ionic form of absorbent A, must be dried in a vacuum dryer set at 50°C for at least 18 hours. The ultimate pressure is 0 Torr.

[0078] The following description focuses on the state of absorbent A when in contact with a liquid such as bodily fluid (hereinafter referred to as "bodily fluid"). However, the same applies to the composite absorbent body 4 containing absorbent A when in contact with the bodily fluid. Furthermore, since the mass of absorbed bodily fluid is generally proportional to the volume of the bodily fluid, the mass of the bodily fluid will sometimes be referred to simply as the "volume of the bodily fluid" in the following description.

[0079] First, the continuous pores of absorbent A shown in Figures 3-6 are formed by interconnected pores (pores), and the presence of these pores is visually discernible. When body fluids such as urine or menstrual blood come into contact with absorbent A, which possesses these pores, the hydrophilic continuous skeleton first instantly absorbs a portion of the fluid due to osmotic pressure and then expands (i.e., swells). This expansion of the continuous skeleton occurs in nearly all directions. Thus, absorbent A, which has grown in size by absorbing a certain amount of body fluid, can then absorb a specific amount of body fluid into the expanded continuous pores through capillary action. When absorbing water (body fluid), these absorbents A exhibit a unique water absorption behavior: the water is drawn into the hydrophilic continuous skeleton and then into the continuous pores, where it is absorbed.

[0080] Here, bodily fluid absorbed within the hydrophilic continuous matrix of absorbent A is difficult to release from the continuous matrix (i.e., difficult to dehydrate). On the other hand, bodily fluid absorbed within the continuous pores dehydrates easily. Therefore, in the composite absorbent, bodily fluid absorbed within the continuous pores dehydrates and is transferred to the highly water-retaining superabsorbent polymer, where it is stably retained. Furthermore, the amount of bodily fluid absorbed within the continuous matrix of absorbent A and the amount of bodily fluid absorbed within the continuous pores represent the total amount of fluid absorbed by absorbent A. The amount of bodily fluid that dehydrates from absorbent A by centrifugation (150g / 90 seconds) (dehydrated amount) becomes the amount of bodily fluid absorbed within the continuous pores, while the remaining amount of bodily fluid (the amount of bodily fluid that did not dehydrate from absorbent A during centrifugation) becomes the amount of bodily fluid absorbed within the continuous matrix.

[0081] Furthermore, compared to the body fluid absorbed within the hydrophilic continuous matrix, more body fluid is retained within the pores of absorbent A. Because absorbent A absorbs body fluid primarily through capillary action, retaining the fluid within the pores, a higher porosity (the ratio of the void volume of the pores to the volume of absorbent A)—the ratio of the void volume of the pores (total pore volume)—allows for greater absorption of body fluid. This porosity is preferably 85% or greater.

[0082] For example, the porosity of absorbent A shown in Figures 3-6 above is calculated as follows. First, the specific surface area of ​​absorbent A, as determined by mercury intrusion porosimetry, is 400 m² / g, and its pore volume is 15.5 mL / g. This pore volume of 15.5 mL / g means that the pore volume of 1 gram of absorbent A is 15.5 mL. Assuming the specific gravity of absorbent A is 1 g / mL, the volume occupied by the pores in 1 gram of absorbent A, i.e., the pore volume, is 15.5 mL, and the volume of 1 gram of absorbent A is 1 mL. Therefore, the total volume (volume) of 1 gram of absorbent A is 15.5 + 1 (mL). Since the ratio of the pore volume is the porosity, the porosity of absorbent A is 15.5 / (15.5 + 1) × 100, which is approximately 94%.

[0083] This absorbent A, or polymer absorbent, possessing a hydrophilic continuous matrix and continuous pores, is suitable for use in composite absorbents such as the composite absorbent 4 of the absorbent body 10 of the disposable diaper 1 described above, for absorbing body fluids such as urine and menstrual blood. Furthermore, as described above, this polymer absorbent exhibits a unique water-absorbing behavior: when absorbing water (directly or through pulp fibers), the water is drawn into the hydrophilic continuous matrix and then into the continuous pores. Consequently, the polymer absorbent can instantly absorb a large amount of body fluid surrounding it (in the pulp fibers), then transfer the absorbed fluid (primarily absorbed in the continuous pores) to the highly water-retaining superabsorbent polymer, where it is stably retained. Consequently, composite absorbents employing this polymer absorbent exhibit high absorbency.

[0084] In this embodiment, the polymer absorbent comprising absorbent A preferably has an absorption rate of 5 seconds or less as determined by the Voltex method. Therefore, once body fluid is absorbed by the pulp fibers in the composite absorbent 4, it can be rapidly transferred to the polymer absorbent in a short period of time (5 seconds or less). This prevents excessive accumulation of body fluid in the pulp fibers, slowing their absorption rate, or insufficient absorption of body fluid by the pulp fibers. Consequently, body fluid absorbed by the faster-absorbing pulp fibers can be quickly transferred to the polymer absorbent. The fluid transferred by the polymer absorbent can then be transferred to the highly absorbent superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption capacity.

[0085] The polymer absorbent containing absorbent A preferably has an absorption rate of 3 seconds or less, and even more preferably 2 seconds or less, as determined by the Voltex method. Furthermore, this absorption rate is preferably greater than the absorption rate of pulp fibers in seconds, preferably greater than 1 second. Bodily fluids absorbed by pulp fibers can be transferred to the polymer absorbent more quickly and efficiently.

[0086] However, since the absorption rate obtained by the Voltex method measures the time it takes for an object to absorb a specific solution, a shorter absorption time indicates a faster absorption rate. The absorption rate (absorption time) obtained by the Voltex method is measured using the following method (refer to JIS-K7224).

[0087] <Method for measuring (initial) absorption rate by the Voltex method> (1) Place a 30 × 8 mm rotor in a 100 ml beaker and add 50 g of a 0.9 wt% NaCl aqueous solution adjusted to a temperature of 25°C ± 1°C. (2) Using a magnetic stirrer (MITAMURA RIKEN KOGYO INC. MAGMIX stirrer (AC100W)), adjust the rotor speed to 600 ± 30 rpm and stir the NaCl aqueous solution. (3) Place 2.00 g of absorbent A into the stirring container and start measuring the time at the same time. (4) The absorption time (absorption rate) is then measured as the time it takes for the surface of the solution to become flat. The flattening of the surface of the solution is determined by observing the disappearance of the brightness reflected from the surface of the vortex liquid at the point where the tilt of the vortex approaches the plane of the solution. This measurement method is carried out under conditions of a temperature of 25°C and a humidity of 60%.

[0088] In this embodiment, the liquid transfer rate from the pulp fibers is preferably such that the polymer absorbent is greater than the superabsorbent polymer. Therefore, in the composite absorbent body 4, body fluid temporarily absorbed by the pulp fibers migrates first to the faster-absorbing polymer absorbent, rather than to the slower-absorbing superabsorbent polymer. This prevents excessive accumulation of body fluid in the pulp fibers, slowing the absorption rate of the pulp fibers, or insufficient absorption of body fluid by the pulp fibers. Consequently, body fluid absorbed by the pulp fibers is continuously and rapidly transferred to the polymer absorbent, and the body fluid transferred by the polymer absorbent is then transferred to the superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent body, allowing the composite absorbent body to fully utilize its absorption performance.

[0089] The liquid transfer rate (30 seconds) of the polymer absorbent from the pulp fibers is preferably 60% or greater. This further satisfies the requirement of polymer absorbent > super absorbent polymer. In the composite absorbent body 4, body fluid temporarily absorbed by the pulp fibers can migrate more quickly to the polymer absorbent (with a faster absorption rate) than to the super absorbent polymer (with a slower absorption rate).

[0090] However, the amount and rate of liquid transfer from material A to material B are measured using the following method. However, if material A is pulp fiber and material B is a polymer absorbent or superabsorbent polymer, the rate of liquid transfer from the polymer absorbent or superabsorbent polymer to the pulp fiber can be measured. If material A is a polymer absorbent or pulp fiber and material B is a superabsorbent polymer, the rate of liquid transfer from the superabsorbent polymer to the polymer absorbent or pulp fiber can be measured.

[0091] <Method for Determining the Amount and Rate of Liquid Transfer from Material A to Material B> (1) Place 0.3 g of the test sample (Material A) 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, 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. Mix the mixture evenly and measure the mass (g) of the cylinder. This test method is carried out at 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) in a petri dish (inner diameter: 85 mm, depth: 20 mm). After vibrating 0.3 g of material B evenly into the cylinder, remove the cylinder and measure the mass of the petri dish (g). (3) Add 60 mL of normal saline (0.9% sodium chloride aqueous solution) to a culture dish with a base (inner diameter: 85 mm, depth: 20 mm, base configuration: two bases are arranged in parallel at a 24 mm interval in the center of the bottom surface (inner side), base width: 2 mm, base height: 2 mm, base length: 25 mm). (4) Place the cylinder containing the test sample (Material A) on the base in the center of the culture dish with a base, immerse the bottom of the cylinder in physiological saline, and allow the sample in the cylinder to absorb the physiological saline for 3 minutes. (5) After absorbing water for 3 minutes, pull up the cylinder, tilt it at 45 degrees and let it drain for 1 minute, then measure the mass of the cylinder (g). (6) The amount of water absorbed by the sample (material A) (g) was calculated by subtracting the mass of the cylinder (g) after water absorption measured in (5) from the mass of the cylinder before water absorption (g). The amount of water absorbed was then divided 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) Next, the cylinder that has been drained in step (5) is placed on a culture dish containing material B, and the sample (material A) in the cylinder is brought into contact with material B in the culture dish through the bottom surface of the cylinder (mesh material). (8) After a specific time (e.g., 30 seconds, 10 seconds) has passed since the sample (Material A) and Material B came into contact, the cylinder was removed and the mass (g) of the culture dish was measured. (9) Calculate the amount of water absorbed by Material B (g) by subtracting the mass of the Petri dish (g) measured in (2) from the mass of the Petri dish (g) measured in (8), and then divide the amount of water absorbed by the mass of the sample (= 0.3g). This yields the amount of water absorbed by Material B per unit mass of the sample after a specific time (e.g., 30 seconds, 10 seconds) (g / g), i.e., the amount of liquid transferred to Material B per unit mass of the sample (Material A) after a specific time (g / g). (10) The water absorption per unit mass (g / g) of material B after a specific time (e.g., 30 seconds, 10 seconds) obtained in (9) above is divided by the water absorption per unit mass (g / g) of the sample (material A) obtained in (6) above, and then multiplied by 100 to obtain the liquid migration rate per unit mass after a specific time (e.g., 30 seconds, 10 seconds).

[0092] In this embodiment, the amount of fluid transferred to the superabsorbent polymer is preferably in the order of polymer absorbent > pulp fibers. Therefore, in the composite absorbent 4, more body fluid transfers to and absorbs the polymer absorbent than to the pulp fibers, and more body fluid transferred to the polymer absorbent is transferred to the superabsorbent polymer than to the pulp fibers. Consequently, the absorbent performance of the polymer absorbent is restored after the fluid transfer. This allows body fluid absorbed by the pulp fibers to be continuously and rapidly transferred to the polymer absorbent, and body fluid transferred to the polymer absorbent is further transferred to the superabsorbent polymer. Consequently, leakage of body fluid from the composite absorbent is suppressed, allowing the composite absorbent to fully utilize its absorption performance.

[0093] In this embodiment, the liquid transfer rate (30 seconds) from the polymer absorbent to the superabsorbent polymer is preferably 6.0 g / g or greater, more preferably 8.0 g / g or greater. This further satisfies the polymer absorbent > pulp fiber requirement, allowing more body fluid transferred to the polymer absorbent than to the pulp fibers. Therefore, when the liquid transfer rate from the polymer absorbent to the superabsorbent polymer is 6.0 g / g or greater, body fluid temporarily retained by the polymer absorbent is more reliably transferred to the superabsorbent polymer, allowing the absorbent composite absorbent to fully and reliably exhibit its absorption performance.

[0094] In this embodiment, the weight per unit area of ​​the pulp fibers, polymer absorbent, and superabsorbent polymer in the composite absorbent body 4 is preferably such that (weight per unit area of ​​the pulp fibers) / (weight per unit area of ​​the polymer absorbent) is greater than 1. By making the weight per unit area of ​​the pulp fibers greater than the weight per unit area of ​​the polymer absorbent, bodily fluids are initially more readily absorbed by the pulp fibers, which have a faster absorption rate. Subsequently, bodily fluids absorbed by the pulp fibers are readily transferred to the polymer absorbent.

[0095] Furthermore, the weight per unit area of ​​the pulp fibers, high molecular weight absorbent, and super absorbent polymer in the composite absorbent body 4 is preferably such that (weight per unit area of ​​super absorbent polymer) / (weight per unit area of ​​high molecular weight absorbent) is greater than 1. By making the weight per unit area of ​​the super absorbent polymer greater than the weight per unit area of ​​the high molecular weight absorbent, the high molecular weight absorbent and the super absorbent polymer can be more easily brought into contact, allowing body fluids absorbed by the high molecular weight absorbent to be easily transferred to the super absorbent polymer.

[0096] Therefore, by satisfying at least one (preferably both) of the two relationships related to the basis weight described above, the pulp fibers can rapidly absorb body fluids, rapidly transfer body fluids from the pulp fibers to the polymer absorbent, and rapidly transfer body fluids from the polymer absorbent to the superabsorbent polymer. This prevents leakage of body fluids from the composite absorbent, allowing the composite absorbent to fully demonstrate its absorbent properties.

[0097] Based on the above viewpoint, (weight per unit area of ​​pulp fiber) / (weight per unit area of ​​polymer absorbent) is more preferably greater than 1 and less than 10, and even more preferably greater than 1 and less than 5. Furthermore, based on the above viewpoint, (weight per unit area of ​​superabsorbent polymer) / (weight per unit area of ​​polymer absorbent) is even more preferably greater than 1 and less than 10, and even more preferably greater than 1 and less than 5.

[0098] The basis weights of the pulp fibers, the polymer absorbent, and the superabsorbent polymer can be appropriately selected based on the desired absorbent properties of the composite absorbent 4. For example, the basis weight of the pulp fibers is 50-500 g / m³, the basis weight of the polymer absorbent is 1-100 g / m³, and the basis weight of the superabsorbent polymer is 50-500 g / m³.

[0099] In this embodiment, the water absorption capacity of the composite absorbent 4, as measured by the Demand Wettability method, is preferably such that the polymer absorbent is greater than the superabsorbent polymer. Therefore, in the composite absorbent 4, since the polymer absorbent absorbs free water more readily than the superabsorbent polymer, the polymer absorbent can absorb free water that may form in the gaps between the nonwoven fabric and the polymer absorbent, or in the gaps between the polymer absorbents themselves, as absorbed body fluid diffuses. In other words, the polymer absorbent can absorb free water without leaking out. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption performance.

[0100] In this embodiment, the water absorption capacity (30 seconds) of the polymer absorbent as measured by the non-pressurized DW method is preferably 8.0 g / g or greater, more preferably 12 g / g or greater. Thus, the polymer absorbent absorbs free water more readily than superabsorbent polymers. However, the water absorption capacity measured by the non-pressurized DW method is measured by the following method.

[0101] <Determination of water absorption by the non-pressurized DW method> Figure 9 is a schematic diagram of the measuring apparatus used in the non-pressurized DW method. A DW apparatus (Demand Wettability Apparatus, manufactured by Taiyo Create Co., Ltd.) 11 is used as this measuring apparatus. As shown, DW apparatus 11 comprises 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 the tip) 14, a stopcock 15, a stopcock 16, a measuring platform 17, a liquid discharge port (3 mm inner diameter) 18, a cylinder 19, and a test solution 20. A tube (7 mm inner diameter) is installed from the burette 12 to the measuring platform 17. A 0.9% sodium chloride aqueous solution is used as the test solution. Measurements are conducted at a temperature of 25°C and a humidity of 60%.

[0102] The measurement procedure is as follows. (1) With the two screw taps 15 and 16 of the DW device 11 closed, place the test solution 20 above the 0 point (the top of the scale on the burette 12 (0 ml line)) and tighten the rubber stopper 13 on the top of the burette 12 to seal it. (2) Place the filter paper behind the drain port 18 of the measuring table 17. Open the two screws 15 and 16. While absorbing the liquid from the drain port 18 with the filter paper, align the liquid level with the zero point. After adjustment, close the screws 15 and 16. (3) A nylon mesh (made by NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) cut into 10 cm squares is placed on the measuring table 17 so that the discharge port 18 is at the center. (4) Place a cylinder 19 with a diameter of 30 mm in the center of the mesh and evenly distribute the sample around the drain port 18. Remove the cylinder 19. (5) Open the cocks 15 and 16, and the sample begins to absorb the test liquid 20. The time when the first bubble introduced from the air into the capillary tube 14 reaches the water surface of the test liquid 20 in the burette 12 (the time when the water surface of the test liquid 20 in the burette 12 drops) is set as the start time of measurement. (6) The amount of test solution 20 reduced in the burette 12 (the amount of test solution 20 absorbed by the test object) M (ml) is continuously read. (7) The amount of sample absorbed after a specific measurement time (e.g., 30 seconds) from the start of liquid absorption can be calculated using the DW method: absorption (ml / g) = M (ml) / (sample weight (g)). Since the specific gravity of the test solution is 1, the absorption value is expressed in (g / g).

[0103] In this embodiment, the preferred drainage ratio of absorbed fluid is the ratio of polymer absorbent to superabsorbent polymer, and the drainage rate of absorbed fluid is the ratio of polymer absorbent to superabsorbent polymer. In this composite absorbent 4, since body fluid temporarily absorbed by the polymer absorbent is easily transferred to the superabsorbent polymer, body fluid that migrates from the pulp fibers can be rapidly transferred from the polymer absorbent to the superabsorbent polymer. This allows body fluid absorbed by the pulp fibers to be continuously and rapidly transferred to the polymer absorbent, and body fluid that has transferred to the polymer absorbent can then be transferred to the superabsorbent polymer. This prevents leakage of body fluid from the composite absorbent, allowing the composite absorbent to fully utilize its absorption properties.

[0104] Furthermore, the polymer absorbent preferably has a discharge capacity of 25 g / g or more of absorbed water and a discharge rate of 65% or more. More preferably, the polymer absorbent has a discharge capacity of 35 g / g or more, and an even more preferably a discharge rate of 70% or more. Thus, by providing the polymer absorbent with excellent water-releasing properties (water separation), the composite absorbent 4 not only retains a large amount of body fluid at once but also releases a large amount of absorbed / retained body fluid. Consequently, since a large amount of body fluid can be transferred from the polymer absorbent to the superabsorbent polymer, the water-retention capacity of the superabsorbent polymer can be fully utilized. The discharge capacity and discharge rate of the polymer absorbent are measured using the following method.

[0105] <Method for measuring discharge volume and discharge rate> (1) Seal 1 g of the sample to be measured in a mesh bag (made by NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) cut into 10 cm squares. Measure the mass (g) of the mesh bag in advance. This measurement method is carried out under conditions of a temperature of 25°C and a humidity of 60%. (2) Soak the mesh bag containing the sample in physiological saline (0.9% sodium chloride aqueous solution) for 1 hour. (3) Hang the mesh bag for 5 minutes and drain it, then measure its mass (g). (4) Calculate the water absorption (g) of the sample by subtracting the mass of the sample (=1g) and the total mass of the mesh bag from the mass of the drained mesh bag measured in (3) above. Then divide the water absorption by the mass of the sample (=1g) to obtain the water absorption per unit mass of the sample (g / g). (5) In addition, the drained mesh bag in (3) was centrifuged at 150G for 90 seconds, and the mass (g) of the mesh bag after the centrifugation was measured. (6) Calculate the sample discharge volume (g) by subtracting the sample mass (=1 g) and the total mass of the mesh bag from the mass of the mesh bag after centrifugation measured in (5) above. Then, divide the discharge volume by the sample mass (=1 g) to obtain the discharge volume per unit mass of the sample (g / g). (7) By dividing the drainage volume per unit mass obtained in (6) above by the water absorption volume per unit mass obtained in (4) above and then multiplying by 100, the drainage volume of the sample (polymer absorbent) relative to the water absorption volume, that is, the drainage rate (%), is obtained. In addition, the repeated drainage volume (g / g) / drainage rate after water absorption and dehydration are repeated 2 or 3 times means the drainage volume (g / g) / drainage rate (%) after the above steps (2) to (6) are repeated 2 or 3 times.

[0106] In this embodiment, the water absorption per unit mass of the polymer absorbent is preferably 30 g / g or greater, more preferably 40 g / g or greater, and even more preferably 50 g / g or greater. Thus, in the composite absorbent 4, the water absorption per unit mass of the polymer absorbent is significantly greater (approximately 30 g / g) compared to the water absorption per unit mass of pulp fibers alone (approximately 20 g / g). Therefore, bodily fluids absorbed by the pulp fibers are rapidly and readily absorbed by the polymer absorbent. This prevents leakage of bodily fluids from the composite absorbent, allowing the composite absorbent to fully utilize its absorption performance. The water absorption per unit mass is measured by the following method.

[0107] <Determination method of water absorption per unit mass> (1) Seal 1 g of the test sample in a mesh bag (made by NBC Meshtec Co., Ltd., N-NO255HD 115 (standard width: 115 cm, 255 meshes / 2.54 cm, opening: 57 μm, wire diameter: 43 μm, thickness: 75 μm)) cut into 10 cm squares. Measure the mass (g) of the mesh bag in advance. When the test sample (polymer absorbent) is recovered from sanitary products for use, it can be obtained according to the aforementioned <Method for Recovering the Test Sample (Polymer Absorbent)>. (2) Immerse the mesh bag containing the sample in physiological saline (0.9% sodium chloride aqueous solution) for 1 hour. (3) Hang the mesh bag for 5 minutes and drain it, then measure its mass (g). (4) Calculate the water absorption of the sample (g) by subtracting the mass of the sample (=1g) and the total mass of the mesh bag from the mass of the mesh bag after draining measured in (3) above. Then divide the water absorption by the mass of the sample (=1g) to obtain the water absorption per unit mass of the sample (g / g). The above measurement method was carried out at a temperature of 25°C and a humidity of 60%.

[0108] In this embodiment, the water absorption viscosity is preferably such that the polymer absorbent is greater than the superabsorbent polymer. Thus, in the composite absorbent body 4, the water absorption viscosity of the polymer absorbent is higher than that of the superabsorbent polymer during body fluid absorption. Therefore, when the composite absorbent body absorbs body fluid, the increased viscosity of the polymer absorbent suppresses the movement of the polymer absorbent, the surrounding superabsorbent polymer, and other absorbent materials, such as pulp fibers, within the composite absorbent body, thereby preventing fluidization. This allows the composite absorbent body to follow the wearer's body movements, preventing deformation of the composite absorbent body due to localized distribution of absorbent material within the composite absorbent body and the creation of gaps. This prevents leakage of body fluid from the composite absorbent body, allowing the composite absorbent body to fully utilize its absorption properties.

[0109] Furthermore, the water absorption viscosity of the polymer absorbent is more preferably 80 Pa·s, and even more preferably 90 Pa·s. Since the water absorption viscosity is relatively high during body fluid absorption, the increased viscosity of the polymer absorbent during body fluid absorption in the composite absorbent further inhibits the migration of the absorbent material containing the polymer absorbent within the composite absorbent, thereby further suppressing fluidization. However, the water absorption viscosity is measured by the following method.

[0110] <Determination method of water absorption viscosity> (1) Place 100 ml of physiological saline and a rotor (30 mm × 10 mm) in a 100 ml beaker (inner diameter 50 mm) manufactured by HARIO and rotate at 600 rpm. (2) Measure 1.5 g of the sample and place it in the beaker of (1) above. Wait until the liquid surface becomes hard and still (if it has not solidified, stop the rotor after 1 minute). (3) Let it stand for 5 minutes. (4) The viscosity was measured using a viscometer (TVB-10 viscometer manufactured by Toki Industry Co., Ltd., using rotor M4 and a rotation speed of 3 rpm). The above measurement method was carried out at a temperature of 25°C and a humidity of 60%.

[0111] In this embodiment, the composite absorbent body has a thickness of 3 mm or less, and its reabsorption rate is preferably 20 seconds or less. Because the composite absorbent body 4 has a thickness of 3 mm or less and a reabsorption rate of 20 seconds or less, it can quickly absorb multiple or large amounts of body fluids, fully utilizing its absorbent properties. Furthermore, when used in sanitary products, the composite absorbent body provides a comfortable wear feel. The thickness and reabsorption rate of the composite absorbent body are measured using the following methods.

[0112] <Method for measuring the thickness of composite absorbent body> (1) Using a thickness gauge with a 15 cm² measuring cell (model FS-60DS manufactured by Daiei Chemical Seiki Co., Ltd.), measure the thickness of the composite absorbent at a load of 3 g / cm². Measure the thickness at three locations on each sample, and the average of the three measurements is defined as the thickness of the composite absorbent.

[0113] <Method for determining the repeated absorption rate of composite absorbents> (1) Prepare the sample. Use an electronic balance to weigh the pulp fiber, high molecular absorbent, and superabsorbent polymer to the desired mass (the mass required to achieve the desired weight per unit area) and mix them evenly to form a mixture. Then, clamp the mixture from top to bottom with thin paper (14 g / m3) coated with hot-melt adhesive and cut it into a circle with a radius of 45 mm to prepare the sample. (2) Place the sample in a glass culture dish with a radius of 46 mm and a height of 20 mm. (3) Using a glass burette, drip 30 ml of artificial urine onto the sample at 8 ml / s, and measure the speed (in seconds) at which the liquid disappears from the sample surface. 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 the pigment, Blue No. 1, in 10 L of ion-exchange water. (4) After 5 minutes, filter paper (manufactured by ADVANTEC, radius 45 cm, No. 2, mass 30 g) was placed on the dripping portion of the sample, and a 2 kg load was placed on top of it. (5) After 3 minutes, remove the load and filter paper and measure the mass of the filter paper. (6) Carry out the above steps (3) to (5) again. (7) Add the speed (seconds) of the first and second times in (3) above to obtain the repeated absorption speed (seconds). The above measurement method was carried out under the conditions of temperature 25°C and humidity 60%.

[0114] In this embodiment, as described above, the disposable diaper 1 (absorbent body 10), i.e., a sanitary product, comprises a topsheet 2, a backsheet 3, and the composite absorbent body 4 positioned between the topsheet 2 and the backsheet 3. Specifically, since the disposable diaper 1 (sanitary product) comprises the composite absorbent body 4, the absorbent performance of the disposable diaper 1 (sanitary product) can be maintained or improved while also being thin and providing a comfortable wearing feel.

[0115] Hereinafter, the manufacturing method of such polymer absorbents will be described in detail using the absorbent A mentioned above as an example.

[0116] [Method for producing polymer absorbent] As shown in Figure 2, the absorbent A can be obtained through a cross-linking polymerization step and a hydrolysis step. Each of these steps is described below.

[0117] (Cross-linking polymerization step) First, an oil-soluble monomer for crosslinking polymerization, a crosslinking monomer, a surfactant, water, and, if necessary, a polymerization initiator are mixed to form a water-in-oil droplet emulsion. This water-in-oil droplet emulsion has an oil phase as the continuous phase and water droplets dispersed within it.

[0118] Next, as shown in the upper diagram of FIG. 2 , cross-linking polymerization was carried out in the absorbent A using butyl methacrylate of (meth)acrylate as an oil-soluble monomer, divinylbenzene as a cross-linking monomer, sorbitan monooleate as a surfactant, and isobutyronitrile as a polymerization initiator to obtain a bulk A.

[0119] Specifically, as shown in the upper diagram of FIG2 , 9.2 g of tert-butyl methacrylate (oil-soluble monomer), 0.28 g of divinylbenzene (cross-linking monomer), 1.0 g of sorbitan monooleate (hereinafter referred to as "SMO") (surfactant), and 0.4 g of 2,2'-azobis(isobutyronitrile) (polymerization initiator) were first mixed and uniformly dissolved in absorbent A.

[0120] Next, a mixture of tert-butyl methacrylate / divinylbenzene / SMO / 2,2'-azobis(isobutyronitrile) was added to 180 g of pure water and stirred under reduced pressure using a planetary agitator vacuum defoaming mixer (manufactured by EME) to obtain a water-in-oil droplet emulsion.

[0121] The emulsion was then quickly transferred to a sealed reaction vessel and allowed to polymerize at 60°C for 24 hours. After polymerization, the contents were removed, extracted with methanol, and dried under reduced pressure to yield macroblocks A with a continuous macroporous structure. SEM observation of the internal structure of macroblock A revealed a continuous pore structure with a continuous skeleton thickness of 5.4 μm. Mercury intrusion porosimetry revealed an average diameter of 36.2 μm for the continuous pores, and a total pore volume of 15.5 mL / g.

[0122] The content of divinylbenzene relative to the total monomers is preferably 0.3-10 mol%, more preferably 0.3-5 mol%. Furthermore, the ratio of divinylbenzene to the total of butyl methacrylate and divinylbenzene is preferably 0.1-10 mol%, more preferably 0.3-8 mol%. Furthermore, in the 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%.

[0123] The amount of surfactant added can be set according to the type of oil-soluble monomer and the desired emulsion particle (macroporous) size, and is preferably in the range of about 2-70% relative to the total amount of oil-soluble monomer and surfactant.

[0124] Furthermore, in order to control the shape and size of the bubbles in the bulk A, alcohols such as methanol and stearyl alcohol; carboxylic acids such as stearic acid; hydrocarbons such as octane, dodecane, and toluene; and cyclic ethers such as tetrahydrofuran and dioxane can coexist in the polymerization system.

[0125] The mixing method for forming the water-in-oil droplet emulsion is not particularly limited, and any mixing method may be employed, such as a method of mixing all the components at once; a method of uniformly dissolving the oil-soluble monomer, the surfactant, and the oil-soluble component of the oil-soluble polymerization initiator, and water or the water-soluble component of the water-soluble polymerization initiator, and then mixing the components.

[0126] Furthermore, the mixing device used to form the emulsion is not particularly limited; depending on the desired emulsion particle size, any device such as a conventional mixer, homogenizer, or high-pressure homogenizer may be used. Furthermore, a so-called planetary mixer may be used, in which the material to be processed is placed in a mixing container and the container is tilted so that it rotates around its axis while stirring and mixing the material to be processed.

[0127] Furthermore, there are no particular restrictions on mixing conditions; the stirring speed and stirring time can be arbitrarily set according to the desired emulsion particle size. Furthermore, the planetary stirring device described above can uniformly generate water droplets in the W / O emulsion, and the average diameter of the droplets can be arbitrarily set within a wide range.

[0128] The polymerization conditions for water-in-oil droplet emulsions vary depending on the type of monomer or initiator. For example, when using azobisisobutyronitrile, benzoyl peroxide, or potassium persulfate as polymerization initiators, heating in a sealed container under an inert atmosphere at 30-100°C for 1-48 hours is sufficient. When using hydrogen peroxide-ferrous chloride or sodium persulfate-sodium bisulfite as polymerization initiators, heating in a sealed container under an inert atmosphere at 0-30°C for 1-48 hours is sufficient.

[0129] After the polymerization is completed, the contents are taken out and subjected to Soxhlet extraction with a solvent such as isopropyl alcohol to remove unreacted monomers and residual surfactants, thereby obtaining a bulk A as shown in the middle figure of FIG2 .

[0130] (Hydrolysis Step) Next, the step of hydrolyzing the bulk A (cross-linked polymer) to obtain the absorbent A (hydrolysis step) is described.

[0131] First, bulk A is immersed in dichloroethane containing zinc bromide and stirred at 40°C for 24 hours. It is then sequentially exposed to methanol, 4% hydrochloric acid, 4% aqueous sodium hydroxide solution, and water for hydrolysis, followed by drying to obtain bulk absorbent A. The bulk absorbent A is then pulverized to a specific size to obtain granular absorbent A. The form of the absorbent A is not limited to granular form; for example, it can be formed into a sheet during or after drying.

[0132] The method for hydrolyzing bulk A is not particularly limited, and various methods can be employed. For example, methods include contacting the solvent with a strong base such as sodium hydroxide using an aromatic solvent such as toluene or xylene, a halogenated solvent such as chloroform or dichloroethane, an ether solvent such as tetrahydrofuran or isopropyl ether, an amide solvent such as dimethylformamide or dimethylacetamide, an alcohol solvent such as methanol or ethanol, a carboxylic acid solvent such as acetic acid or propionic acid, or water; or contacting the solvent with a halogenated hydroacid such as hydrochloric acid, sulfuric acid, nitric acid, trifluoroacetic acid, methanesulfonic acid, or p-toluenesulfonic acid, or a Lewis acid such as zinc bromide, aluminum chloride, aluminum bromide, titanium (IV) chloride, potassium chloride / sodium iodide, or magnesium iodide.

[0133] In the raw material for the organic polymer forming the hydrophilic continuous backbone of absorbent A, the (meth)acrylate is not particularly limited, but is preferably a C1-C10 (i.e., carbon number 1-10) alkyl (meth)acrylate, and particularly preferably a C4 (i.e., carbon number 4) alkyl (meth)acrylate. Examples of C4 alkyl (meth)acrylates include tert-butyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate.

[0134] Furthermore, the monomers used for cross-linking polymerization may be only (meth)acrylate and divinylbenzene, or may contain other monomers besides (meth)acrylate and divinylbenzene. In the latter case, other monomers are not particularly limited, but examples thereof include styrene, α-methylstyrene, vinyltoluene, vinylbenzyl chloride, glycidyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobutylene, butadiene, isoprene, chloroprene, vinyl chloride, vinyl bromide, vinylidene chloride, tetrafluoroethylene, (meth)acrylonitrile, vinyl acetate, ethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. In all monomers used for cross-linking polymerization, the ratio of monomers other than (meth)acrylate and divinylbenzene is preferably 0-80 mol%, more preferably 0-50 mol%.

[0135] Furthermore, the surfactant is not limited to the aforementioned sorbitan monooleate; any surfactant capable of forming a water-in-oil (W / O) emulsion when the cross-linked polymerizable monomer is mixed with water can be used. 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 distearyldimethylammonium chloride; and amphoteric surfactants such as lauryldimethylbetaine. These surfactants may be used alone or in combination of two or more.

[0136] Furthermore, compounds that generate free radicals upon heat or light irradiation are preferably used as polymerization initiators. Furthermore, polymerization initiators may be either water-soluble or oil-soluble, and examples include azobis(4-methoxy-2,4-dimethylvaleronitrile), azobisisobutyronitrile, azobisdimethylvaleronitrile, azobiscyclohexanecarbonitrile, azobiscyclohexanecarbonitrile, azobis(2-methylpropionamidine) dihydrochloride, benzoyl peroxide, potassium persulfate, ammonium persulfate, hydrogen peroxide-ferrous chloride, sodium persulfate-sodium bisulfite, and tetramethylthiuram disulfide. However, depending on the situation, some systems can proceed without the addition of a polymerization initiator, simply by heating or light irradiation. Therefore, in these systems, the addition of a polymerization initiator is unnecessary.

[0137] To achieve (or modify) the desired absorption performance and pore size distribution in polymer absorbents, the absorption performance can be adjusted primarily by adjusting the pore size and pore size distribution by adjusting the amount of surfactant added (e.g., surfactant / monomer ratio) and mixing conditions (e.g., stirring speed and stirring time) during the cross-linking polymerization step.

[0138] [Method for producing a composite absorbent containing a polymer absorbent] The composite absorbent body can be manufactured without particular limitation using conventional methods, for example, using a fiber accumulation device equipped with a material feeder and a rotating drum. The rotating drum has a suction mechanism on its inner side, including a fiber accumulation support body provided on the outer peripheral surface of the rotating drum and capable of rotating together with the rotating drum. The fiber accumulation support body has a stacking depression for stacking pulp fibers, high molecular absorbents, and super absorbent polymers. The material feeder supplies pulp fibers, high molecular absorbents, and super absorbent polymers with adjusted unit area weight (blending ratio) in a mixed state to the fiber accumulation support body. The manufacturing method is to stack the pulp fibers, high molecular absorbents, and super absorbent polymers supplied in a mixed state by the material feeder in the stacking depression of the fiber accumulation support body by means of a suction mechanism to form a fiber accumulation body. Then, the fiber accumulation body is transferred from the fiber accumulation support body to a sheet member coated with an adhesive, and the sheet member is used to wrap the fiber accumulation body to manufacture the composite absorbent body. Alternatively, the above method can be used to prepare a fiber mass of pulp fibers and super absorbent polymers, and before wrapping with a sheet, a high molecular absorbent can be spread on the fiber mass and then wrapped. [Example]

[0139] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0140] (A) Sample The properties of the polymer absorbent produced using the above-described production method as an example were compared with the superabsorbent of Patent Document 1 (manufactured by Sumitomo Seika Chemicals Co., Ltd., hereinafter referred to as "High-SAP") as a comparative example, and a conventional superabsorbent (Aquakeep SA60S manufactured by Sumitomo Seika Chemicals Co., Ltd., hereinafter referred to as "Conventional SAP") as another comparative example. Furthermore, as needed, the properties of the conventional pulp fiber (comminuted wood pulp) as another comparative example were also compared.

[0141] (B) Evaluation All or a portion of the above samples were evaluated for the following parameters: absorption rate (Voltex method), liquid transfer rate from pulp fibers, liquid transfer rate to superabsorbent polymer, water absorption (unpressurized water method), liquid drainage / drainage rate, water absorption viscosity, composite absorbent thickness, and repeated absorption rate.

[0142] (C) Results (1) Absorption rate The initial absorption rate was measured using the Voltex method described above. The results showed that the polymer absorbent had an initial absorption rate of 1.7 seconds, pulp fiber had an initial absorption rate of 1.0 seconds, high-speed SAP had an initial absorption rate of 5.4 seconds, and standard SAP had an initial absorption rate of 46.8 seconds. In other words, the initial absorption rate ranked pulp fiber > polymer absorbent > superabsorbent polymer (high-speed SAP, standard SAP). Furthermore, the absorption rate of the polymer absorbent using the Voltex method was less than 5 seconds.

[0143] (2) Liquid migration rate from pulp fibers The liquid transfer rate per unit mass from pulp fiber was measured using the aforementioned method for measuring the amount of liquid transferred and the liquid transfer rate from material A to material B. However, material A was pulp fiber, and material B was a polymer absorbent, a high-speed SAP, and a conventional SAP. The results are shown in Figure 7. Figure 7 is a graph showing the relationship between liquid transfer rate and transfer time. The vertical axis represents the liquid transfer rate (%), and the horizontal axis represents the transfer time (seconds). The thick solid line and circles represent the polymer absorbent, the thin solid line and triangles represent the high-speed SAP, and the dashed line and diamonds represent the conventional SAP. The liquid transfer rate (%) within a transfer time of 10 seconds was 61% for the polymer absorbent, 40% for the high-speed SAP, and 7% for the conventional SAP. Within a transfer time of 30 seconds, the polymer absorbent was 63%, the high-speed SAP was 57%, and the conventional SAP was 18%. Therefore, within a transfer time of 30 seconds or less, the polymer absorbent was greater than the superabsorbent (high-speed SAP, conventional SAP). As can be seen from the graph, regardless of migration time, the polymer absorbent surpasses the superabsorbent polymer (typically SAP). Furthermore, the polymer absorbent's liquid migration rate (30 seconds) is over 60%.

[0144] (3) Liquid migration to super absorbent polymer The amount of liquid transferred per unit mass to the superabsorbent polymer was determined by the above-mentioned method for measuring the amount of liquid transferred and the liquid transfer rate from material A to material B (values ​​of (9)). However, material A is a polymer absorbent, a high-speed SAP, and pulp fiber, and material B is a normal SAP. In this case, the amount of liquid transferred from material A absorbing physiological saline to material B under the same conditions is shown. As a result, the amount of water absorbed per unit mass (g / g) was 82.3 g / g for the polymer absorbent, 60.3 g / g for the high-speed SAP, and 23.3 g / g for the pulp fiber. Therefore, the amount of liquid transferred (g / g) within a transfer time of 30 seconds was 9.9 g / g for the polymer absorbent, 5.6 g / g for the high-speed SAP, and 3.8 g for the pulp fiber. Therefore, the order of the amount of liquid transferred to the superabsorbent polymer is polymer absorbent > high-speed SAP > pulp fiber. Furthermore, the liquid transfer capacity (30 seconds) of the polymer absorbent is 6 g / g or more.

[0145] (4) Water absorption (non-pressurized DW method) Water absorption (non-pressurized DW method) was measured using the non-pressurized DW method described above. The results showed that within 30 seconds, the water absorption for the polymer absorbent was 14.5 g / g, for pulp fiber it was 8.9 g / g, for high-speed SAP it was 7.9 g / g, and for conventional SAP it was 6.7 g / g. Therefore, the water absorption (non-pressurized DW method) for the polymer absorbent was greater than that for the superabsorbent polymer (high-speed SAP and conventional SAP). Furthermore, the water absorption (non-pressurized DW method) for the polymer absorbent was greater than that for the superabsorbent polymer (high-speed SAP and conventional SAP).

[0146] (5) Water absorption viscosity The water absorption viscosity was measured using the aforementioned method. The results showed that the water absorption viscosity of the polymer absorbent was 96 Pa·s, that of the high-speed SAP was 23 Pa·s, and that of the standard SAP was 72 Pa·s. Therefore, the water absorption viscosity of the polymer absorbent was greater than that of the superabsorbent polymer. Furthermore, the water absorption viscosity of the polymer absorbent was 80 Pa·s.

[0147] The above results are shown in Table 1.

[0148] (6) Liquid discharge volume / discharge rate The amount of absorbed liquid discharged / the rate of discharge were measured using the aforementioned methods for measuring discharge amount and rate. The results showed that the discharge amount for the polymer absorbent was 39-42 g / g, the high-speed SAP was 24 g / g, and the standard SAP was 20-22 g / g. Furthermore, the discharge rates for the polymer absorbent were 75-76%, the high-speed SAP was 44-46%, and the standard SAP was 34-36%. Therefore, the discharge amount for the polymer absorbent was greater than that for the superabsorbent polymer, and the discharge rate for the polymer absorbent was greater than that for the superabsorbent polymer. Furthermore, the discharge amount for the polymer absorbent was greater than 25 g / g, and the discharge rate was greater than 65%. Furthermore, when the absorption / desorption cycles were repeated two or three times, the discharge rate was measured at 44-46% each time, but the final discharge rate was always 45%, so it is recorded as 45% in the table.

[0149] The above results are shown in Table 2.

[0150] (7) Thickness and repeated absorption rate of composite absorbent The thickness and reabsorption rate of the composite absorbent were measured using the aforementioned methods for measuring the thickness of composite absorbents and the reabsorption rate of composite absorbents, respectively. The composition of the evaluated absorbents is shown in Table 3 below. The absorbent configuration used was a pulp fiber / conventional SAP / polymer absorbent configuration for the Example (composite absorbent), and a pulp fiber / conventional SAP configuration for the Comparative Example (conventional absorbent). The basis weight of the conventional SAP was kept constant for both materials, while the basis weight of the polymer absorbent was also kept constant for the composite absorbent. The thickness was varied by adjusting the basis weight of the pulp fiber. The results are shown in Table 3 and Figure 8.

[0151] Figure 8 is a graph showing the relationship between thickness and repeated absorption rate. The vertical axis represents the absorption rate (seconds) of each absorbent, and the horizontal axis represents the thickness (mm) of each absorbent. The thick solid line and circles represent composite absorbents composed of pulp fiber / conventional SAP / polymer absorbent, while the thin solid line and triangles represent conventional absorbents composed of pulp fiber / conventional SAP. It is found that the inclusion of a polymer absorbent in composite absorbents allows repeated absorption rates to be below 20 seconds, even with thicknesses as thin as 3 mm or less. On the other hand, conventional absorbents cannot achieve repeated absorption rates below 20 seconds when the thickness is less than 3 mm.

[0152]

[0153] Furthermore, the composite absorbent body of the present invention is applicable not only to the pants-type disposable diapers of the above-mentioned embodiment, but also to various sanitary products such as belt-type disposable diapers, sanitary napkins, absorbent pads, absorbent pads (such as incontinence pads, bedsore pads, and postpartum pads), absorbent sheets, breast milk pads, pet disposable diapers, pet absorbent pads, pet excrement disposal sheets, wet sheets, wet tissues, cosmetic wipes, and masks. Therefore, the body fluids absorbed by the composite absorbent body are fluids discharged from the wearer of the sanitary product, such as urine, sweat, feces, menstrual blood, vaginal secretions, breast milk, blood, and exudate.

[0154] The present invention is not limited to the above-described embodiments, and appropriate combinations, substitutions, and changes may be made without departing from the purpose and spirit of the present invention.

[0155] 1: Disposable diapers 2: Surface sheet 3: Back sheet 4: Composite absorber

Claims

1. A composite absorbent for use in sanitary products for absorbing bodily fluids, comprising pulp fibers, a polymeric 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 > polymeric absorbent > superabsorbent polymer, the liquid migration rate from the pulp fibers is in the order of polymeric absorbent > superabsorbent polymer, and the liquid migration amount from the superabsorbent polymer is in the order of polymeric absorbent > pulp fibers.

2. The composite absorbent as claimed in claim 1, wherein the absorption rate of the aforementioned polymeric absorbent obtained by the Voltex method is less than 5 seconds.

3. The composite absorbent as claimed in claim 1, wherein (weight per unit area of ​​the aforementioned pulp fiber) / (weight per unit area of ​​the aforementioned polymeric absorbent) is greater than 1, and / or (weight per unit area of ​​the aforementioned superabsorbent polymer) / (weight per unit area of ​​the aforementioned polymeric absorbent) is greater than 1.

4. The composite absorbent as claimed in claim 1, wherein the water absorption capacity obtained by the demand wettability method without pressure is greater than that of the aforementioned polymeric absorbent than that of the aforementioned superabsorbent polymer.

5. The composite absorbent as claimed in claim 1, wherein the amount of absorbed liquid discharged is greater than that of the aforementioned polymeric absorbent > the aforementioned superabsorbent polymer, and the discharge rate of the absorbed liquid is greater than that of the aforementioned polymeric absorbent > the aforementioned superabsorbent polymer.

6. The composite absorbent as claimed in claim 1, wherein the water absorption capacity per unit mass of the aforementioned polymer absorbent is 30 g / g or more.

7. The composite absorbent as claimed in claim 1, wherein the water absorption viscosity is greater than that of the aforementioned polymeric absorbent than the aforementioned superabsorbent polymer.

8. The composite absorber as claimed in claim 1, wherein the thickness of the composite absorber is 3 mm or less, and the reabsorption rate of the composite absorber is 20 seconds or less.

9. The composite absorbent of claim 1, wherein the aforementioned polymeric absorbent is a hydrolysate of a cross-linked polymer of (meth)acrylate and a compound containing two or more vinyl groups in one molecule, and contains at least one -COONa group.

10. A sanitary product comprising a surface sheet, a back sheet, and a composite absorbent as claimed in any one of claims 1 to 9 located between the surface sheet and the back sheet.

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