JP7293479B1 - ABSORBENT FOR ABSORBENT ARTICLE, AND ABSORBENT ARTICLE - Google Patents

Abstract

[PROBLEMS] To provide an absorbent body for an absorbent article that can provide an absorbent article that satisfactorily suppresses liquid return during use of the absorbent article even if the absorbent article contains hardwood pulp fibers. SOLUTION: The absorbent body for absorbent articles includes a hardwood pulp fiber-containing absorbent body containing pulp fibers containing softwood pulp fibers and hardwood pulp fibers, and a superabsorbent polymer. In the total pulp fibers of the hardwood pulp-containing absorbent, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is 40% or more on a mass basis, and the pulp fibers having a fiber width of 10 µm or more and less than 35 µm. The proportion is 90% or more on a mass basis. [Selection drawing] Fig. 3

Description

TECHNICAL FIELD The present invention relates to an absorbent core for absorbent articles and absorbent articles.

In absorbent articles such as disposable diapers, sanitary napkins, incontinence pads, and panty liners (panty liners), the absorber ( (also called an absorbent core, etc.). Absorbents generally include pulp fibers and superabsorbent polymers. As wood pulp, which is a raw material for pulp fibers, softwood-derived pulp has been used in many cases, but in recent years, use of hardwood-derived pulp has also been investigated (for example, Patent Document 1).

JP 2020-014646 A

Hardwood-derived pulp is relatively inexpensive compared to softwood-derived pulp, and is advantageous in terms of cost. However, hardwood-derived pulp fibers (hardwood pulp fibers) have at least a shorter fiber length than softwood-derived pulp fibers (softwood pulp fibers). Therefore, when the ratio of hardwood pulp fibers in the absorbent body is high, there is a tendency that the absorbent capacity and absorption speed are reduced. , a phenomenon in which the absorbed liquid seeps out to the skin side again) may occur. Such liquid return may cause a rash. Therefore, there is a demand for an absorbent structure in which liquid return is suppressed even if hardwood pulp fibers are contained.

Therefore, one aspect of the present invention is to provide an absorbent body for an absorbent article that can provide an absorbent article that satisfactorily suppresses liquid return during use of the absorbent article even if it contains hardwood pulp fibers. Make it an issue.

An absorbent body for an absorbent article according to the first aspect of the present invention includes a hardwood pulp fiber-containing absorbent body containing pulp fibers containing softwood pulp fibers and hardwood pulp fibers, and a superabsorbent polymer. In the absorber containing broad-leaved tree pulp fibers, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is 40% or more on a mass basis, and the fiber width is 10 μm or more and 35 μm. ≥ 90% by mass of pulp fibers with less than

According to the first aspect, the pulp fibers contained in the absorbent body include softwood-derived pulp fibers (softwood pulp fibers) and hardwood-derived pulp fibers (hardwood pulp fibers). As described above, hardwood pulp fibers have a shorter fiber length and a smaller fiber width (or fiber diameter) than softwood pulp fibers. tends to decrease. However, according to this aspect, by combining the softwood pulp fibers and the hardwood pulp fibers, it is possible to secure the absorption capacity and absorption speed of the absorber and also to have the liquid retention ability of the fibers due to capillary action. It is possible to improve the effect of suppressing liquid backflow (also referred to as liquid backflow) of an absorbent article constructed using the body and the absorbent body. Furthermore, the present inventors have found that by keeping the ratio of pulp fibers having a predetermined fiber length within a predetermined range and keeping the ratio of pulp fibers having a predetermined fiber width within a predetermined range, the above-described effect of suppressing liquid return can be further enhanced. I have found that it can be improved.

In addition, since hardwood pulp fibers have a short fiber length, etc., a pulp sheet containing hardwood pulp fibers tends to be inferior in defibration (or pulverization). It tends to be difficult to loosen when (grinding) into fluff pulp. On the other hand, according to this aspect, softwood pulp fibers and hardwood pulp fibers are combined, and the ratio of pulp fibers with a predetermined fiber length is within a predetermined range, and the ratio of pulp fibers with a predetermined fiber width is within a predetermined range. The configuration of the present embodiment, in which the fiber is contained in the fiber, also improves defibration properties.

Furthermore, since hardwood pulp fibers generally have a short fiber length, the workability in the process of producing an absorbent body from a pulp sheet containing hardwood pulp fibers tends to decrease. Paper dust) is likely to fly, and pulp fibers are likely to accumulate on the apparatus. On the other hand, according to this aspect, the softwood pulp fiber and the hardwood pulp fiber are combined, and the ratio of the pulp fiber with a predetermined fiber length is within a predetermined range, and the ratio of the pulp fiber with a predetermined fiber width is within a predetermined range. Workability in the absorbent body manufacturing process can also be improved by the configuration of this embodiment in which the absorbent body is housed in the absorbent body.

In the second aspect of the present invention, the mass ratio of the hardwood pulp fibers to the softwood pulp fibers in the hardwood pulp fiber-containing absorbent body is 25/75 or more and 38/62 or less.

According to the second aspect, it is possible to promote one or more of the above-described improvement in reversion suppression effect, improvement in fibrillation property, and improvement in workability.

In a third aspect of the present invention, the content of acacia wood in the raw material wood for the hardwood pulp fiber is 5% by mass or more and 95% by mass or less.

According to the third aspect, it is possible to promote one or more of the above-described improvement in reversion suppression effect, improvement in fibrillation property, and improvement in workability.

In a fourth aspect of the present invention, the average fiber length when the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm are measured at intervals of 0.02 mm is 0.5 mm or more and 0.8 mm or less, and the standard The deviation σ is 0.58 mm or less, the average fiber width is 15 μm or more and 30 μm or less when the pulp fibers having a fiber width of 10 μm or more and less than 35 μm are measured at intervals of 1 μm, and the standard deviation σ is 2.9 μm or less. .

According to the fourth aspect, it is possible to promote one or more effects of the above-described improvement in reversion suppression effect, improvement in fibrillation property, and improvement in workability.

In a fifth aspect of the present invention, the hardwood pulp fiber has a skin side facing the wearer's skin when the absorbent article is worn, and a non-skin side opposite to the skin side. A contained absorbent is included on the skin side.

According to the fifth aspect, as described above, the absorbent body portion having a high liquid backflow suppressing effect is arranged on the side that comes into direct contact with the skin. can be suppressed.

A sixth aspect of the present invention is composed of two or more separate layers, and the skin-side layer located on the skin side is composed of the hardwood pulp fiber-containing absorbent body.

According to the sixth aspect, since it is composed of two or more separate layers, i.e., separately stacked absorbent layers, the configuration of each layer can be changed, and the absorbent body as a whole can have various configurations. becomes feasible. At least the skin-side layer is made of the hardwood pulp fiber-containing absorbent, so that the layer having a high liquid reversion suppressing effect can be arranged on the side that comes into direct contact with the skin, thereby effectively suppressing rashes and the like in the absorbent article. can.

A seventh aspect of the present invention is an absorbent article comprising the absorbent core for absorbent articles according to any one of the first to sixth aspects.

According to the seventh aspect, it is possible to provide an absorbent article that exhibits the same effects as those obtained by any one of the first to sixth aspects.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to provide an absorbent body for an absorbent article that can provide an absorbent article that satisfactorily suppresses backflow of liquid during use of the absorbent article even if it contains hardwood pulp fibers.

1 is a plan view of one form of an absorbent article including an absorbent body according to this form, viewed from the skin side. FIG. FIG. 2 is a schematic diagram of a cross section taken along the line II of FIG. 1; It is an enlarged view of only an absorber. It is a figure which put together the features, such as an absorber, by the kind of pulp fiber. 1 is a cross-sectional view of an absorbent body including multiple absorbent layers; FIG. FIG. 4 is a cross-sectional view of an absorbent body including multiple absorbent layers, according to another example. It is a schematic diagram of the manufacturing apparatus of the absorber by this form. It is the schematic of another manufacturing apparatus of the absorber by this form. FIG. 4 is a plan view of another form of an absorbent article including an absorbent body according to the present form, viewed from the skin side. FIG. 8 is a schematic diagram of a cross section taken along the line II-II of FIG. 7;

<Absorbent article>
One aspect of the present invention relates to an absorbent body for absorbent articles. An absorbent core for absorbent articles is a member that is placed inside an absorbent article and performs functions such as absorbing, retaining, and diffusing liquid. Absorbent articles in which the absorbent according to this embodiment is used are not particularly limited, but the absorbent according to this embodiment may be disposable diapers (including tape type, pants type, and pad type), sanitary napkins, incontinence pads, panties, etc. It can be suitably used in liners, interlabial pads, sheets for pets and the like. Among these, it can be suitably used in sanitary goods used facing the bodily fluid outlet, particularly disposable diapers, sanitary napkins, incontinence pads and the like.

First, a pad-type disposable diaper will be taken as an example to explain how the absorber is used. FIG. 1 shows an expanded view of an absorbent article (a pad-type disposable diaper) 1 viewed from the side facing the skin (skin side) when worn. FIG. 2 schematically shows a cross section taken along line II of FIG. The members of the absorbent article (pad type diaper) 1 are joined at predetermined locations or regions by adhesive, fusion, or mechanical means. 1 and 2 show only main members of the absorbent article (pad type disposable diaper) 1. As shown in FIG. In addition, in FIG. 2, illustration of joining between members is omitted in order to facilitate understanding of the positional relationship of the members.

As shown in FIGS. 1 and 2, the absorbent article 1 has a skin side that faces the skin of the side wearer when worn, and a non-skin side that is opposite to the skin side. The side facing the front side (abdominal side) of the wearer's body when worn is called the front side, and the side facing the rear side (back side) of the wearer's body is called the rear side. Therefore, the front-rear direction D1 of the absorbent article 1 is a direction extending from the front side to the back side or from the back side to the front side when the absorbent article 1 is unfolded (not folded). The width direction D2 is a direction perpendicular to the front-rear direction D1 when the absorbent article 1 is spread out. The absorbent article 1 as a whole has an elongated shape in plan view with the front-rear direction D1 as the longitudinal direction, and as shown in FIG. may

As shown in FIGS. 1 and 2, an absorbent article (pad type diaper) 1 comprises a liquid-permeable topsheet 3 arranged on the skin side and a liquid-impermeable back arranged on the non-skin side. Between the sheets 2 and 23, an absorber (absorbent article absorber) 4 is sandwiched. When wearing the absorbent article 1, the top sheet 3 side is placed against the skin, and the back sheet 2 side is fixed to an outer (outer diaper), underwear, or the like. The backsheet 2 has a shape and size such that the absorbent body 4 fits within the backsheet 2 .

As the back sheet 2, in addition to a polyethylene film or the like, a moisture-permeable sheet can be used without impairing water impermeability from the viewpoint of preventing stuffiness. The water-impermeable/moisture-permeable sheet is a microporous sheet obtained by, for example, forming a sheet by melt-kneading an inorganic filler in an olefin resin such as polyethylene or polypropylene, and then stretching the sheet in a uniaxial or biaxial direction. can be used. The outer surface of the back sheet 2 can also be covered with an exterior sheet such as a nonwoven fabric.

The top sheet 3 may cover the entire absorbent core 4, or may not partially cover the end portions of the absorbent core 4 in the width direction D2 as shown in FIG. When the top sheet 3 does not cover the entire absorbent body 4, the uncovered portions of the absorbent body 4 are covered with other sheets (the side sheets 7 and 7 in the case of the form of FIG. 1), Thereby, the absorber 4 is prevented from being exposed to the outside. As the top sheet 3, a perforated or non-perforated nonwoven fabric, a perforated plastic sheet, or the like can be used. As material fibers constituting the non-woven fabric, synthetic fibers such as olefin-based, polyester-based, and amide-based fibers such as polyethylene and polypropylene, regenerated fibers such as rayon and cupra, and natural fibers such as cotton can be used.

On both sides of the absorbent article 1 in the width direction D2, a pair of side sheets 7, 7 may be arranged on the side of the top sheet 3 along the front-rear direction D1. As the side sheet 7, a plastic sheet, a meltblown nonwoven fabric, or the like can be used, but a nonwoven fabric that has been water-repellent treated with silicone or the like is preferably used from the viewpoint of a good feel to the skin.

In regions where the back sheet 2 and the top sheet 3 are directly overlapped on both ends of the absorbent body 4 in the front-rear direction D1, they may be joined. In addition, the side sheets 7, 7 may be joined to the back sheet 2 or the top sheet 3 at both ends in the front-rear direction D1 of the absorbent article 1, and are joined to the back sheet 2 at both sides in the width direction D2. May be joined. The members are joined by hot melt adhesive, heat sealing, ultrasonic sealing, or the like.

Although not shown, an elastic member formed in the shape of a thread, a string, a belt, or the like is fixed to the inner end portion of each side seat 7 in the width direction D2 in a stretched state along the front-rear direction D1. good. Accordingly, when the absorbent article is used, the inner ends of the side sheets 7 in the width direction D2 contract in the front-rear direction D1 to form the gathers G standing on the skin side. The elastic member may be made of styrene-based rubber, olefin-based rubber, urethane-based rubber, ester-based rubber, or the like.

Depending on the intended use of the absorbent article 1, additional sheets may be provided in addition to the members shown in FIGS. For example, a nonwoven fabric, a mesh film, or the like may be interposed as an intermediate sheet between the top sheet 3 and the absorbent body 4 to promote the prevention of backflow of bodily fluids. can do.

<Absorber>
The absorbent body 4 (also called an absorbent core, an absorbent core, etc.) is a member mainly responsible for absorbing and retaining bodily fluids, and is arranged inside the absorbent article without being exposed to the outside as described above. It is. The planar shape of the absorbent body 4 in the absorbent article 1 is not particularly limited. (FIG. 1).

As shown in FIGS. 1 and 2 , the absorbent body 4 may be wrapped with an enveloping sheet (also called a core wrap sheet or the like) 5 . The enveloping sheet 5 is a liquid-permeable sheet, and specifically may be unprocessed or processed paper such as crepe paper, non-woven fabric, or the like. The enveloping sheet 5 may be uncolored (white) or colored. In this specification, the entire absorbent body 4 wrapped in the enveloping sheet 5 may be referred to as an absorbent body, in which case the member inside the enveloping sheet 5 is referred to as an absorbent body. By wrapping the absorbent body 4 with the wrapping sheet 5, the absorbent body 4 can be prevented from being twisted or cracked during use, and the shape can be maintained. Moreover, when superabsorbent polymer particles and other components other than pulp are contained, it is possible to prevent such components from spilling out of the absorbent body.

FIG. 3 shows a cross section of only the absorbent body 4 taken out from the absorbent article 1. As shown in FIG. The absorbent body 4 according to this embodiment includes pulp fibers 41 and a superabsorbent polymer (SAP) 45 . As shown in FIG. 3, the superabsorbent polymer 45 is in the form of particles, and such particles are held between the pulp fibers 41, 41, . . . in the absorbent body.

Superabsorbent polymers (SAP) include polyacrylate-based, polysulfonate-based, and maleic anhydride-based absorbent polymers. The average particle size (at the time of drying) of the superabsorbent polymer is preferably 150 μm or more and 400 μm or less. The absorber feeds the fluff pulp obtained by defibrating the pulp sheet into the duct, mixes the superabsorbent polymer particles at that time, stacks it in the stacking type of the stacking drum, and scuffs as necessary. It can be molded by making the surface uniform with a roll or the like (also explained later). The absorbent core taken out of the stacking mold can also be compressed in the thickness direction by compression means.

The absorber 4 may optionally contain substances other than pulp fibers and superabsorbent polymers, such as fillers, pigments, sizing agents, coagulants, oil-resistant agents, aluminum sulfate, retention improvers, and drainage improvers. , dry paper strength agents, wet paper strength agents, coloring pigments, water resistance agents, and other additives may be added.

<Pulp fiber>
Pulp is a collection of fibers (pulp fibers) extracted from wood, grass, or other plants by mechanical and/or chemical treatments. As raw materials for pulp, in addition to coniferous trees and broadleaf trees, bamboo, rice, waste, pampas grass, hemp, sugar cane, etc. can be used. In addition, artificial cellulose such as rayon and acetate can also be used.

The pulp fibers contained in the absorbent body according to one embodiment of the present invention contain softwood-derived pulp fibers (softwood pulp fibers) and hardwood-derived pulp fibers (hardwood pulp fibers). Further, the softwood pulp fiber is softwood bleached kraft pulp (NBKP) produced by the kraft method, and the hardwood pulp fiber is preferably hardwood bleached kraft pulp (LBKP) produced by the kraft method. In this specification, an absorbent body containing pulp fibers containing both softwood pulp fibers and hardwood pulp fibers is referred to as "hardwood pulp fiber-containing absorbent body".

The ratio of softwood pulp fibers and hardwood pulp fibers in the total pulp fibers is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and still more preferably 98% by mass or more. Point. It is also preferred that all pulp fibers consist essentially of softwood pulp fibers and hardwood pulp fibers.

In the present specification, unless otherwise specified, the amount of pulp fibers or materials that will become pulp fibers refers to the amount of internal addition in the bone dry state, that is, the mass ratio in the bone dry state.

Here, the combination of softwood pulp fibers and hardwood pulp fibers according to the present embodiment will be briefly described with reference to FIG. FIG. 4 summarizes the features of (I) a form consisting of softwood pulp fibers, (II) a form consisting of hardwood pulp fibers, and (III) a form consisting of softwood pulp fibers and hardwood pulp fibers.

As shown in FIG. 1, (I) in the case of the form made of softwood pulp fibers, the fiber length and fiber width of the pulp fibers are relatively large, and the variation in fiber length and fiber width is also relatively large. The distance is large and the resulting absorbent body is bulky. Therefore, the absorption capacity (water absorption) of pulp fibers is large, and the absorption speed of the absorbent body or absorbent article is relatively high. However, since the distance between pulp fibers is large, the liquid retention capacity of the fibers due to capillary action is relatively low, and the super absorbent polymer (SAP) tends to fall off in the direction of gravity. Since the retention property is slightly inferior, the liquid retention capacity of the superabsorbent polymer is also small. As a result, the liquid retention capacity of the absorbent body or absorbent article is reduced. Therefore, the effect of suppressing liquid return (liquid backflow) of the absorbent article is rather low.

In addition, in the form of (II) hardwood pulp fibers, the fiber length and fiber width of the pulp fibers are relatively small, and the variation in the fiber length and fiber width is relatively small, so the distance between the pulp fibers is small. The fiber density in the absorbent is also high. Therefore, the absorption capacity (water absorption) of the pulp fibers is small, and the absorption speed as an absorbent body or absorbent article is slow. However, since the distance between pulp fibers is small, the liquid holding capacity of the fibers due to capillarity is high. Due to the small distance between pulp fibers, it may be difficult to retain the superabsorbent polymer between the fibers, but the retention of the superabsorbent polymer is generally good, and the liquid retention capacity of the superabsorbent polymer is I) higher than the form. As a result, the liquid retention capacity of the absorbent body or absorbent article is higher than that of the form (I), and the effect of suppressing the liquid backflow (liquid backflow) of the absorbent article is obtained to some extent. However, due to the decrease in absorption capacity and absorption speed, the effect of suppressing liquid backflow is rather low with respect to the amount of liquid normally absorbed by the absorbent article.

(III) In the form of softwood pulp fibers and hardwood pulp fibers, fibers having a relatively long fiber length and a large fiber width as described above are combined with fibers having a relatively short fiber length and a small fiber width. As a result, the fiber density is between (I) and (II). Therefore, the absorption capacity of the fibers can be secured to some extent, the absorption speed of the absorbent body or absorbent article can be maintained, and the liquid retention capacity of the fibers due to capillary action can be secured. In addition, the distance between the fibers becomes appropriate for retaining the superabsorbent polymer, and the ability of the superabsorbent polymer to retain liquid can be further enhanced compared to (I) and (II). As a result, liquid retention ability can be obtained while maintaining the absorption capacity and absorption speed of the absorbent body or absorbent article. In this way, in the form (III), both the absorption capacity and absorption rate and the liquid retention capacity can be secured, thereby improving the effect of suppressing liquid backflow, thereby preventing skin rashes due to use of the absorbent article. In particular, it contributes to prevention of skin rash when the absorbent article is used for a long time.

In addition, as shown in FIG. 4, the fibrillation property, that is, the ease of fibrillation or loosening when producing flap pulp from a pulp sheet (a raw material for an absorber formed by compressing pulp fibers into a sheet) is , The fiber length is long and the fiber width is large and the bulky (I) is high in the form of softwood pulp fibers, and the density is high in the form of short fiber length and small fiber width (II) low in the form of hardwood pulp fibers. . (III) In the form of softwood pulp fibers and hardwood pulp fibers, a certain degree of good defibration property can be ensured.

In addition, in (III), by containing the softwood pulp fibers, the bulkiness of the absorbent body can be secured to some extent, and the obtained absorbent article can also have a good texture. In addition, by including softwood pulp fibers, workability (that is, the effect of suppressing the scattering of powdery materials and the adhesion of fibers to equipment) when producing fluff pulp from pulp sheets is ensured. Good workability contributes to overall high productivity in manufacturing absorbent articles.

In the absorber according to one aspect of the present invention, in the total pulp fibers of the absorber containing hardwood pulp fibers, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is 40% or more on a mass basis, and the fiber width is 10 μm. The ratio of pulp fibers having a diameter of 35 μm or more is 90% or more on a mass basis. In addition, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is preferably 42.6% or more, more preferably 43% or more, and still more preferably 43.2% or more and 43.7% or more. , 45 or more. In addition, the proportion of pulp fibers having a fiber width of 10 μm or more and less than 35 μm is preferably 90.6% or more, more preferably 91.0% or more, and still more preferably 91.2% or more and 91.4% or more. you can In this way, the absorber contains a specific pulp fiber length and a specific pulp fiber width in specific ranges, respectively, thereby further improving the advantages of the form (III) described with reference to FIG. can be made into In particular, it is possible to further improve the effect of suppressing the liquid return of the absorbent body or absorbent article, and to ensure good defibration and workability when producing fluff pulp from the pulp sheet.

The upper limit of the ratio of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm in the total pulp fibers of the hardwood pulp fiber-containing absorber is not particularly limited, but the pulp is a natural material. Therefore, it can be 80% by mass or less, 60% by mass or less, or 55% by mass or less. Similarly, the upper limit of the ratio of pulp fibers having a fiber width of 10 μm or more and less than 35 μm is not particularly limited, but it can be 98% by mass or less, 95% by mass or less, or 94% by mass or less.

The fiber length and fiber width of the pulp fiber are measured using a measuring machine "VALMET FS5" according to JIS-P8226: 2011 (ISO16065-2: 2007) "Pulp - Fiber length measurement method by optical automatic analysis method". can be measured by

Furthermore, in the hardwood pulp fiber-containing absorber, the average fiber length when measuring pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm at intervals of 0.02 mm (with a classification width of 0.02 mm) is 0.5 mm. 0.8 mm or less, preferably 0.6 mm or more and 0.7 mm or less. As a result, the bulkiness of the pulp sheet can be improved, and the disentanglement property at the time of fluff pulp production can be improved. , can ensure the absorption speed.

In addition, in the hardwood pulp fiber-containing absorber, when pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm are measured at intervals of 0.02 mm (with a classification width of 0.02 mm), the standard deviation σ is 0.58 mm. Below, it is preferably 0.56 mm or less, more preferably 0.54 mm or less, and still more preferably 0.50 mm or less. When the standard deviation is within the above range, it is possible to improve the absorption capacity and absorption rate of the absorbent body and to improve the effect of suppressing liquid return.

Furthermore, the average fiber width of pulp fibers having a fiber width of 10 μm or more and less than 35 μm measured at intervals of 1 μm (with a classification width of 1 μm) may be 15 μm or more and 30 μm or less, preferably 18 μm or more and 27 μm or less. By setting the average fiber width in the above range, it is possible to maintain the gaps between the fibers appropriately, prevent a decrease in the absorption rate, and prevent the contact area between the pulp fibers from becoming too large. Excessive increase in bonding strength can be prevented. Thereby, the disentanglement property at the time of manufacture can be made suitable. If the defibration property of the pulp sheet is excessively low, excessive defibration occurs (excessive defibration work is performed) during production of fluff pulp, and fine fibers are generated, resulting in a decrease in the absorption speed of the absorber. there is a risk of

When pulp fibers having a fiber width of 10 μm or more and less than 35 μm are measured at intervals of 1 μm (with a classification width of 1 μm), the standard deviation σ is 2.9 μm or less, preferably 2.8 μm or less, more preferably 2.75 μm or less. Preferably, it may be 2.6 μm or less and 2.59 μm or less. By setting the standard deviation within the above range, it is possible to improve the absorption speed and the effect of suppressing liquid return.

As described above, in the present embodiment, it is preferable to reduce variations in the distribution of the fiber length in the specific range and the distribution of the fiber width in the specific range. An absorbent body for an absorbent article containing such pulp fibers exhibits a good effect of suppressing liquid backflow while ensuring absorption capacity and absorption speed, despite the fact that hardwood pulp fibers are blended. Therefore, the absorbent article having the absorbent body according to the present embodiment can satisfactorily reduce rashes.

Pine trees represented by radiata pine and various cedars are suitably used as raw material wood for the softwood pulp fibers contained in the pulp fibers.

As hardwood pulp fibers, acacia wood, eucalyptus wood, and the like are preferably used. Acacia wood shrinks less when dried, is strong against impacts, and is strong and hard. The pulp obtained from acacia wood inherits its original properties, and is a useful raw material pulp with high water absorption and drying properties. is. Eucalyptus wood belongs to the genus Eucalyptus, and Eucalyptus globulus, Eucalyptus grandis, Eucalyptus europhylla, Eucalyptus nitens, Eucalyptus regnans, etc. have been widely used as raw material pulp materials for paper production for a long time. has a fiber lumen that is hard to collapse and is rigid, and by blending this pulp fiber, it is possible to increase the bulk and reduce the density of the absorbent body. As hardwood pulp fibers, acacia wood is preferable because it is bulkier than eucalyptus wood because it has a larger fiber width, and even when combined with softwood pulp fibers, there is little reduction in absorption amount and absorption rate.

In this embodiment, the mass ratio of hardwood pulp fibers to softwood pulp fibers in the hardwood pulp fiber-containing absorber is not limited, but is preferably 25/75 or more and 38/62 or less, more preferably 25/75. 38/62 or more, more preferably 26/74 or more and 36/64 or less, or 28/72 or more and 35/65 or less. When the mass ratio is less than 25/75, even if the average fiber length and average fiber width of all pulp fibers are within a predetermined range, the fibers of the absorbent article obtained from the fluff pulp pulp sheet There is a risk that unevenness will easily occur in the voids and that the product will easily revert and cause a rash. On the other hand, if the mass ratio exceeds 38/62, even if the fiber width of the bleached hardwood kraft pulp is within the predetermined range, the fluff pulp pulp sheet may become dense and the water absorption rate may decrease.

In addition, the content of acacia wood in the raw material wood of the hardwood pulp fiber, that is, the content ratio of the acacia wood-derived pulp fiber in the hardwood pulp fiber in the hardwood pulp fiber-containing absorber is preferably 5% by mass or more and 95% by mass or less. , more preferably 5% by mass or more and less than 95% by mass, more preferably 20% by mass or more and 93% by mass or less, 20% by mass or more and 90% by mass or less, 25% by mass or more and 85% by mass or less, 50% by mass or more and 80% by mass may be: Even hardwood pulp fibers, which have a shorter fiber length than softwood pulp fibers and tend to be tightly packed with each other, may be used in any direction (for example, the length direction, width direction, and direction of the resulting absorbent article). / Or in any direction of the thickness direction), even if it is oriented, the gaps between the fibers can be uniformly secured, so that the defibration property when producing fluff pulp from the fluff pulp pulp sheet, the absorption amount and It can be compatible with absorption speed. If the content of acacia wood is outside the above range, for example, if the proportion of rigid eucalyptus wood is high, the number of voids derived from rigidity increases, but the fiber width is lower than that of acacia wood, so the fiber can be oriented in any direction. It is easy to cause variations in the gaps depending on whether the Therefore, not only is the fibrillating property at the time of production of fluff pulp low, but also the absorption rate tends to be uneven, and as a result, there is a possibility that the absorption rate tends to decrease.

The kappa number of the hardwood bleached kraft pulp is preferably 0.3 or less. If the kappa number exceeds the upper limit, the lignin in the fiber cannot be sufficiently removed, and the water absorbency of the pulp fiber becomes low, which may easily cause a rash. The kappa number is measured according to JIS-P8211 (2011).

In addition to the bleached softwood kraft pulp and the bleached hardwood kraft pulp, other pulps such as soda pulp, sulfite pulp, chemithermomechanical pulp, chemrefiner mechanical pulp, thermochemimechanical pulp, and the like may be used. However, if the lignin in the fibers is not sufficiently removed, the absorption amount and absorption rate of the pulp fibers tend to decrease, so bleached pulp from which lignin has been sufficiently removed is preferable. When the other pulp is contained, the content of the other pulp is preferably 10% by mass or less with respect to the entire pulp raw material.

Further, the pulp fibers contained in the absorbent body according to the present embodiment may contain regenerated pulp fibers (recycled pulp fibers) regardless of the type of pulp fibers. For example, the pulp fibers may contain recycled softwood pulp fibers, recycled hardwood pulp fibers. By using recycled pulp fibers, it is possible to promote the reuse of materials and promote efforts to realize a sustainable society in this field.

When recycled pulp fibers are used, the amount of ash in the pulp fibers used in the absorber, for example in fluff pulp, is preferably as low as possible.

In addition, when recycled pulp fibers are used, when pulp derived from the same raw material is compared before and after recycling, the brightness of recycled pulp is lower than that of virgin pulp (unrecycled pulp or unrecycled pulp). They may be the same, but they are preferably the same.

Furthermore, when pulp fibers derived from the same raw material are compared before and after recycling, the absorption capacity (water absorption capacity) of the recycled pulp fibers used may be approximately the same as that of virgin pulp.

If necessary, other additives can be internally added to the pulp sheet for fluff pulp, which is the raw material of the absorber. Additives include, for example, fillers, pigments, sizing agents, coagulants, oil resistance agents, aluminum sulfate, retention aids, drainage improvers, dry paper strength agents, wet paper strength agents, coloring pigments, and water resistance agents. etc., can be used singly or in combination. Therefore, the obtained absorbent may also contain the above additives.

<Arrangement of Hardwood Pulp Fiber-Containing Absorbent in Absorber>
The absorber according to this embodiment (FIGS. 1 to 3) as a whole contains the hardwood pulp fiber-containing absorber (softwood pulp fiber and hardwood pulp fiber, and fibers of a specific fiber length are specified (absorbent body containing fibers in a specific range and fibers with a specific fiber width in a specific range), or the hardwood pulp fiber-containing absorbent body as described above is partially included in the absorbent body 4 in the absorbent article 1 You may do so. The distribution of such hardwood pulp fiber-containing absorbent bodies can be arranged according to the type of absorbent article or the purpose of use. For example, the hardwood pulp fiber-containing absorber may be locally arranged in a cross-sectional view, locally arranged in a plan view, or both. In the former case, different functions can be imparted to the absorbent body 4 in the thickness direction, and in the latter case, different functions can be imparted to the absorbent body 4 in the plane direction.

When the hardwood pulp fiber-containing absorbent body is locally arranged in a cross-sectional view, for example, one layer of the absorbent body is divided into two in the thickness direction, and the absorbent body portion on the skin side is the hardwood pulp fiber-containing absorbent body, It is possible to prevent the non-skin-side absorbent body from becoming the hardwood pulp fiber-containing absorbent body. With such a configuration, the absorption amount and absorption rate can be ensured and the effect of suppressing liquid backflow can be exhibited on the skin side of the absorbent body 4, so the absorbent article obtained using this absorbent body can be used for a long time. It is possible to prevent rashes and the like even when used.

The absorbent body 4 may be composed of a single layer or multiple layers. In this specification, the absorbent layer is a layer obtained through a stacking process using a stacking type of a predetermined stacking drum and, if necessary, a compression process in the thickness direction. Therefore, for example, as shown in FIG. 5, the absorbent body 4 may be composed of two layers, a skin-side layer 4a and a non-skin-side layer 4b. In this case, the skin-side layer 4a may be an absorbent body containing hardwood pulp fibers, and the skin-side layer 4a may be an absorbent body containing hardwood pulp fibers. In that case, it is preferable from the viewpoint of suppressing/preventing rash and the like for the same reason as described in the description of the single-layer structure.

In addition, the sizes of the layers included in the absorbent body 4 may be the same or different. Moreover, the thicknesses of the layers included in the absorber 4 may be the same or different. For example, as shown in FIG. 6, the skin-side layer 4a and the non-skin-side layer 4b included in the absorbent body 4 may have different widths and thicknesses. In the example shown in FIG. 6, the width and thickness of the skin-side layer 4a are smaller than those of the non-skin-side layer 4b. The sizes of the multiple layers included in the absorbent body can be set according to the form and intended use of the absorbent article. Note that the number of layers is not limited to two, and may be three or more.

When the absorbent body 4 has two layers, the ratio of the super absorbent polymer in the non-skin side layer 4b and the ratio of the super absorbent polymer in the skin side layer 4a may be different. When the ratio of the superabsorbent polymer in the non-skin side layer 4b is made larger than the ratio of the superabsorbent polymer in the skin side layer 4a, the non-skin side 4b has a liquid absorption function and retention by the superabsorbent polymer. The function is improved, and the backflow of the liquid to the skin side layer 4a, and thus the backflow of the liquid to the user's skin, can be further prevented.

The thickness of the absorbent body 4 (when the absorbent body is composed of multiple layers, the total thickness of the multiple layers) may be 0.5 mm or more and 20 mm or less, preferably 1 mm or more and 15 mm or less. For example, in the case of a disposable diaper such as the absorbent article 1, the thickness of the absorbent body 4 may be 1 mm or more and 30 mm or less, preferably 1.5 mm or more and 15 mm or less. The thickness of the absorber 4 may be uniform, or may have relatively thick or relatively thin regions. Further, grooves or through slits may be formed in the absorber.

In addition, the basis weight of the pulp in the absorbent body 4 (when the absorbent body is composed of multiple layers, the basis weight of the entire multiple layers) is 100 g/m ² or more and 300 g, although it depends on the use of the absorbent article in which the absorbent body is arranged. /m ² or less, preferably 120 g/m ² or more and 250 g/m ² or less. For example, in the case of a disposable diaper such as the absorbent article 1, the basis weight of pulp may be 100 g/m ² or more and 300 g/m ² or less, preferably 120 g/m ² or more and 200 g/m ² or less. The basis weight of the pulp absorbent body may be uniform as a whole, or regions with relatively high or relatively low basis weight may be formed.

The basis weight of the superabsorbent polymer in the absorbent body (in the case where the absorbent body consists of multiple layers, the basis weight of the entire multiple layers) is 50 g/m ² or more and 350 g/m ² or less, preferably 100 g/m ² or more and 300 g/m ^{2 .} may be: For example, in the case of a disposable diaper such as the absorbent article 1, the superabsorbent polymer has a basis weight of 50 g/m ² or more and 300 g/m ² or less, preferably 100 g/m ² or more and 250 g/m ² or less. .

<Production of absorbent material (pulp sheet)>
The manufacture of a fluff pulp pulp sheet, which is a raw material for the absorbent body according to the present embodiment, will also be described below. The method for producing the pulp sheet is not particularly limited, but for example, a cooking step of cooking raw wood to make unbleached pulp, a delignification step of performing delignification, a bleaching step of bleaching to make bleached pulp, and a bleached pulp A beating step of beating to obtain a desired freeness, a step of preparing a pulp slurry, and a step of making paper from the pulp slurry. In addition, a dehydration washing step can be appropriately provided between the above steps.

(Cooking process)
In the cooking step, raw material wood is cooked to obtain unbleached pulp. White liquor and raw wood chips (hardwood and/or softwood) are placed in the digester and cooked, and the resulting (unwashed) pulp slurry mixed with black liquor is removed from the bottom of the continuous digester. The cooking method can be arbitrarily selected from commercially available kraft improvement methods such as MCC, EMCC, ITC, Lo-Solids, KobudoMari, Compact method, etc. The digester may be either a continuous digester or a batch method. Also, the cooking conditions (cooking temperature, H factor obtained by multiplying the degree of influence of the cooking temperature and cooking time and combined into one factor, the content of active alkali or effective alkali, etc.) are not particularly limited.

In the cooking of hardwood pulp fibers, the lower limit of the sulfidity of white liquor for cooking pulp is preferably 25%, more preferably 28%. If the sulfidity is less than 25%, the pulp fibers are likely to be damaged, the resulting fluff pulp will be dense, and there is a risk that the absorption rate of the absorbent will decrease. On the other hand, the upper limit of the sulfidity is preferably 32%, more preferably 30%. If the sulfidity exceeds the above upper limit, the pulp fibers are hard to be damaged and remain rigid, and the voids of the obtained absorbent body become uneven, and the backflow amount increases, which may cause a rash. The above sulfidity is calculated as the ratio of sodium sulfide to the sum of sodium sulfide and caustic soda according to the following formula:
Sulfidity (%) = ( _Na2S /(NaOH+ _Na2S )) x 100

(Delignification process)
In the delignification step, the unbleached pulp is delignified. Alkaline chemicals and oxygen are added to unbleached pulp, and lignin is decomposed at high temperature and pressure, and lignin is eluted into the alkaline chemicals. The delignification process may be of low consistency (pulp density: 3% to 8%), medium consistency (pulp density: 8% to 15%), or high consistency (pulp density: 20% to 30%).

(Washing process)
In the washing process, the unbleached pulp is washed by a combination of displacement, dilution or dewatering. The washing method is not particularly limited, and washing can be performed using a known washing machine. For example, a displacement cleaning method, a dilution/dehydration method, a press cleaning method, or a cleaning method combining these methods is used. Diffusion washers, pressurized diffusion washers, belt-type washers, and the like are used as displacement wash-type washers. A vacuum filter washer, a pressure filter washer, and the like are used as the dilution/dehydration type washer. As the press cleaning method, a screw type press cleaning machine, a disc type press cleaning machine, a roll type press cleaning machine, or the like is used.

In the present embodiment, it is preferable to remove lignin and reduce the kappa number, so it is preferable to use a press washing machine that easily removes lignin. The pulp concentration after washing by the press washing method is preferably 30% or more, more preferably 32% or more, and even more preferably 35% or more. In the dehydration by the press washing method, the moisture inside the fibers can also be squeezed out and removed, so compared to other washing methods, it is easy to sufficiently remove the lignin released inside the pulp fibers.

(Bleaching process)
In the bleaching step, the delignified unbleached pulp is bleached to obtain bleached pulp. The bleaching method is not particularly limited, and can be bleached by a known bleaching method. For example, acid treatment, ozone bleaching, chlorine dioxide bleaching, hydrogen peroxide bleaching, alkali extraction with these, alkali extraction with oxygen added, alkali extraction with oxygen and hydrogen peroxide added, etc., can be performed singly or in combination. can do.

In the bleaching step, it is preferable to use ozone bleaching, which can adjust the water absorbency of pulp fibers by damaging the pulp fibers. The method of ozone bleaching is not particularly limited, and can be carried out at any of high concentration (30 to 40%), medium concentration (8 to 15%), and low concentration (1 to 3%). Concentration methods are preferred. A known device can be used as the ozone generator. The generated ozone may be mixed with the pulp as it is, or dissolved in water and then mixed with the pulp.

In ozone bleaching, a lower pH promotes delignification and less damage to fibers, so it is preferable to adjust the pH according to the required quality of the fluff pulp pulp sheet. The pH in the ozone bleaching of the pulp sheet for fluff pulp is preferably 6 or less, more preferably 4 or less, and still more preferably 2-3. When the pH of the pulp sheet for fluff pulp in ozone bleaching is within the above range, the water absorption speed required for the pulp sheet for fluff pulp can be improved.

(Preparation process)
In the preparing step, a pulp slurry is prepared. Further, if necessary, in the preparation step, the bleached pulp is beaten to a desired freeness. After that, other additives are added as necessary to prepare a stock.

When hardwood pulp fibers are obtained, the Canadian Standard Freeness (CSF) of unbeaten hardwood bleached kraft pulp is preferably adjusted to 520 ml or more and 580 ml or less. If the freeness of the unbeaten pulp of the bleached hardwood kraft pulp is less than 520 ml, the dewatering property deteriorates during pulp sheet production. Not only is the bonding between the fibers stronger, but also the bulkiness of the pulp sheet is lowered, which may reduce the fibrillation property during production. On the other hand, if the Canadian standard freeness of the unbeaten pulp exceeds 580 ml, the voids between fibers in the pulp sheet become too large, and the absorbent obtained by defibrating the pulp sheet tends to have uneven fibrillation. may become

(Papermaking process)
Next, using these raw material slurries, paper is made by a paper machine in a neutral range so that the pH is 6 or more and 8 or less. In the papermaking process, the raw material pulp is made into paper using a papermaking machine that makes paper from the pulp raw material jetted onto the running wire. The paper machine is not particularly limited, and a known paper machine such as a fourdrinier paper machine, a cylinder paper machine, a hybrid former, a gap former, or the like can be used. be. The pulp sheet for fluff pulp can be produced by combining a single layer or a plurality of layers, but a single layer is preferable because the density in the layer can be easily made uniform.

<Physical properties of absorbent material (pulp sheet)>
The physical properties of the pulp sheet for fluff pulp, which is the raw material of the absorber, will also be described below.

(Krem water absorption)
The Kremm water absorbency is obtained by immersing the lower end of the paper vertically in water and measuring the height of water absorbed by capillary action, and is measured in accordance with JIS-P8141 (2004). Kremm water absorbency is an index for evaluating the absorption performance over a relatively long period of time after water contacts the sample, but in absorbent articles, absorbability in a shorter time is important, Measure as follows. After preparing a sample using the pulp sheet for fluff pulp, in the water absorption test at room temperature, the height [mm] for 1 minute after the start of measurement and the water absorption rate [mm / min for 1 minute to 2 minutes after the start of measurement] ] is measured. The height 1 minute after the start of measurement is used as a measure of the water absorption of the fluff pulp pulp sheet, and the water absorption rate between 1 and 2 minutes after the start of measurement is used as a measure of the water absorption rate of the fluff pulp pulp sheet. These water absorption amount and water absorption rate are indicators of the short-term absorption capacity and absorption rate of the absorbent article.

The lower limit of the water absorption height of the fluff pulp pulp sheet at a basis weight of 200 g/m ² one minute after the start of measurement is preferably 25 mm, more preferably 27 mm, and even more preferably 29 mm. If the water absorption height is less than 25 mm at 1 minute after the start of the measurement, fluff pulp and absorbent articles produced from the fluff pulp pulp sheet may cause skin rashes due to the low water absorption. On the other hand, the upper limit of the water absorption height at 1 minute after the start of the measurement is preferably 40 mm. If the water absorption height at 1 minute after the start of the measurement exceeds 40 mm, the water absorption is too high, the water absorption rate is reduced for 1 minute to 2 minutes after the start of measurement, and the fluff pulp produced from the pulp sheet for fluff pulp. And in the case of absorbent articles, the amount of water-absorbing liquid that flows back may increase, causing skin rashes. When the water absorption height at 1 minute after the start of the measurement is within the above range, the pulp sheet for fluff pulp can obtain fluff pulp with good water absorption.

The lower limit of the water absorption rate for 1 to 2 minutes after the start of measurement when the basis weight of the fluff pulp pulp sheet is 200 g/m ² is preferably 5 mm/min, more preferably 7 mm/min, and even more preferably 9 mm/min. When the water absorption rate is less than 5 mm/min for 1 to 2 minutes after the start of the measurement, the fluff pulp and absorbent articles produced from the fluff pulp pulp sheet have a low water absorption rate, so the amount of water-absorbing liquid returned may increase and skin rash may occur. When the water absorption rate is within the above range for 1 to 2 minutes after the start of the measurement, the fluff pulp pulp sheet can obtain fluff pulp having a good water absorption rate. In the fluff pulp pulp sheet, the water absorption height at 1 minute after the start of the measurement and the water absorption speed at 1 to 2 minutes after the start of the measurement are both within the above ranges, so that the fluff pulp is excellent in the water absorption amount and the water absorption speed. can be manufactured, and an absorbent article can be obtained that has little reversion and can suppress rashes. Here, even if the basis weight of the pulp sheet for fluff pulp exceeds 200 g / m ² , the sample is subjected to a standard disintegration machine in accordance with JIS-P8220 (2012) "Pulp - Defiberization method". , JIS-P8222 (1998) "Pulp-Method for preparing handsheet for testing-Method using ^a standard handsheet".

(density)
The density of the pulp sheet for flap pulp is measured according to JIS-P8118 (2014) "Paper and paperboard-Testing methods for thickness, density and specific volume". The lower limit of the density of the pulp sheet for fluff pulp is preferably 0.50 g/cm ³ , more preferably 0.52 g/cm ³ , and still more preferably 0.55 g/cm ³ . The upper limit of the density of the pulp sheet for fluff pulp is preferably 0.65 g/cm ³ , more preferably 0.62 g/cm ³ , and still more preferably 0.60/cm ³ . When the density of the pulp sheet for fluff pulp is within the above range, it is possible to improve defibration properties during the manufacturing process, and to obtain fluff pulp in which it is easy to ensure even and uniform voids between fibers. Therefore, the water absorption amount and water absorption speed required for fluff pulp can be improved. The density can be measured under an atmosphere of 23±1° C. and 50±2% RH as described in JIS-P8111 (1998) “Paper, paperboard and pulp—standard conditions for humidity control and testing”. .

(Ratio burst strength)
The specific burst strength of a pulp sheet for flap pulp is a value obtained by dividing the burst strength of paper measured in kilopascals (kPa) by the basis weight, measured in accordance with JIS-P8131 (2009). The lower limit of the specific burst strength is preferably 1.0 kPa·m ² /g, more preferably 1.1 kPa·m ² /g, and even more preferably 1.2 kPa·m ² /g. If the specific bursting strength of the fluff pulp pulp sheet is less than the above lower limit, the fibers are likely to be cut due to excessive defibration, so the fluff pulp becomes dense, the water absorption rate decreases, and rashes may easily occur. . On the other hand, the upper limit of the specific bursting strength of the pulp sheet for fluff pulp is preferably 1.7 kPa·m ² /g, more preferably 1.6 kPa·m ² /g, and more preferably 1.5 kPa·m ² /g. More preferred. If the above-mentioned specific bursting strength of the fluff pulp pulp sheet exceeds the above-mentioned upper limit, the defibration property during the manufacturing process is poor, and the resulting fluff pulp has many voids, which makes it easy for the water-absorbing liquid to return and causes rashes. It may occur more easily. When the fluff pulp pulp sheet has a specific bursting degree within the above range, the fluff pulp pulp sheet obtained by mixing the hardwood bleached kraft pulp and the softwood bleached kraft pulp can be improved in defibration during production. In the case of fluff pulp, it becomes easy to ensure even and uniform voids between fibers, so that the water absorption rate of fluff pulp can be improved. In addition, the relative burst rate measurement is performed under an atmosphere of 23 ± 1 ° C. and 50 ± 2% RH, as described in JIS-P8111 (1998) "Paper, paperboard and pulp - standard conditions for humidity conditioning and testing". can be measured by

<Method for manufacturing absorber>
Furthermore, manufacturing of the absorbent body for absorbent articles according to the present embodiment will be described. The absorbent body 4 (FIG. 3, etc.) according to this embodiment can be manufactured by a known method. FIG. 7 shows a schematic diagram of the absorbent body manufacturing apparatus 100 . As shown in FIG. 7, upstream of the absorbent body manufacturing apparatus 100, there is provided a pulp supply section 61 that mainly supplies fiber materials containing pulp. The pulp supply unit 61 may include a defibrator, to which pulp sheets are supplied.

The pulp sheet may have been produced as described above. Such a pulp sheet is defibrated into fibers by mechanical treatment to obtain fluff pulp. The supplied fluff pulp pulp sheet may be in the form of either a veil or a roll, but a roll is preferable because productivity can be easily improved.

Moreover, the device used for the mechanical treatment for defibrating the pulp sheet is not particularly limited. A known defibrator that is used in the production of absorbent articles such as disposable diapers can be used, and a defibrator that utilizes frictional force or shear force as a mechanical treatment can be preferably used. The method of the defibrator includes, for example, a hammer-type defibrator, an impact-type defibrator, a roll-type defibrator, and a jet-type defibrator.

Fluff pulp obtained by defibration is supplied into the duct 62 . A polymer particle introduction part 63 for supplying superabsorbent polymer particles may be provided in the middle of the duct 62 . Therefore, the pulp (fluff pulp) and superabsorbent polymer particles are mixed in the duct 62 , and the absorbent material obtained by mixing is supplied to the fiber stacking drum 65 .

A plurality of absorber molds 50 are arranged on the outer peripheral surface of the fiber stacking drum 65 so as to be spaced apart in the circumferential direction. By rotating the fiber stacking drum 65, the absorbent molds 50, 50, . . . can sequentially receive the absorbent material. The bottom surface of the absorber mold 50 is composed of a perforated plate or a mesh plate, and the absorber material can be accumulated on the bottom surface of the absorber mold 50 by sucking gas through the openings. In addition, the absorbent body 4 can be supplied to a conveying means 66 such as a belt conveyor by discharging the gas through the openings. A negative pressure chamber and a positive pressure chamber are provided inside the fiber stacking drum 65, and each chamber enables gas suction and discharge, respectively.

A scuffing roll (or brush) 64 may be provided at a downstream position within the duct 62 . The scuffing rolls 64 can scrape off excess absorbent material that has been piled up to make the surface of the absorbent material accumulated in the absorbent mold 50 uniform. Also, the absorbent body 4 supplied to the conveying means 66 can be compressed in the thickness direction by the compressing means 67 . The compressing means 67 may be a pair of rolls as shown in FIG. 7 or a pair of pressing members approaching from both sides of the absorbent body 4 . The compression means 67 enhances the shape retention of the absorbent body 4 .

Further downstream, the absorbent body 4 can be wrapped by an enveloping sheet 5 . The step of wrapping the absorbent body 4 with the wrapping sheet 5 can also be performed by a known method.

FIG. 8 shows a manufacturing apparatus 200 for the absorbent body 4 (FIGS. 5 and 6, etc.) in which the absorbent body 4 is composed of two layers. The manufacturing apparatus 200 includes single-layer manufacturing units 101 and 102 that respectively manufacture the layers included in the absorbent body 4, the skin-side layer 4a and the non-skin-side layer 4b in the illustrated example. Both of the single-layer manufacturing units 101 and 102 have the same configuration as the manufacturing apparatus 100 (FIG. 7) for manufacturing a single-layer absorbent body. The absorbent layers 4a and 4b manufactured by the single layer manufacturing departments 101 and 102 can be wrapped in the wrapping sheet 5 after being stacked in the thickness direction.

<Another form of absorbent article>
FIG. 9 shows a plan view of another form of absorbent article (sanitary napkin) 11 viewed from the side (skin side) facing the skin when worn. FIG. 10 schematically shows the II-II section of FIG. The members of the absorbent article (sanitary napkin) 11 are joined at predetermined locations or regions by adhesive, fusion, or mechanical means. 9 and 10 show only main members of the absorbent article (sanitary napkin) 11. FIG. In addition, in FIG. 7, in order to make it easier to understand the positional relationship of the members, illustration of joining between members is omitted.

The absorbent article 11 shown in FIGS. 9 and 10 also includes a liquid-permeable top sheet 3 arranged on the skin side and a liquid-impermeable back sheet 2 arranged on the non-skin side. An absorbent body 4 is sandwiched between the sheets 2 and 23. - 特許庁When wearing the absorbent article 11, the top sheet 3 side is made to face the skin, and the back sheet 2 side is fixed to underwear such as shorts. The backsheet 2 has a shape and size such that the absorbent body 4 fits within the backsheet 2 . These points are the same as the absorbent article 1 shown in FIGS. Also, the materials of the top sheet 3 and the back sheet 2 are the same as those of the absorbent article 1 .

The absorbent article (sanitary napkin) 11 is also similar to the absorbent article 1 (FIGS. 1 and 2) in that the side sheets 7, 7 are provided on both sides in the width direction D2. And, as shown in FIG. 2, the side sheets 7, 7 may extend laterally and be joined to the back sheet 2, which similarly extends laterally, to form wings.

The material of the absorbent body 4 in the absorbent article (sanitary napkin) 11 may also be the same as that of the absorbent body 4 in the absorbent article (pad-type disposable diaper) 1 . In the absorbent article (sanitary napkin) 11, the absorbent body 4 may have a thickness of 0.3 mm or more and 30 mm or less, preferably 1.0 mm or more and 15 mm or less. The absorber 4 may have grooves formed by pressing (pressed grooves or embossments). The compressed grooves formed in the absorbent body 4 are grooves (core emboss) formed by compressing the absorbent body 4 itself (the absorbent body or the portion consisting of the absorbent body and the wrapping sheet) from the skin side. Alternatively, grooves (fit embossing) formed by pressing a laminate including at least the absorbent body 4 and the top sheet 3 from the skin side may be used. FIG. 9 shows an example of the fit emboss EB. In addition, black in the fit emboss EB is a high-pressed portion that is pressed with a higher pressure, and white is a low-pressed portion that is pressed with a lower pressure than the high-pressed portion.

In this embodiment, the pulp in the absorbent body 4 contains recycled pulp, and contains more fibers with a short fiber length and/or a small fiber width. Therefore, even if the compressed grooves are formed deeply, that is, even if the density of the grooves is increased by pressing with a high pressure, excessive hardening of the compressed grooves and the peripheral portions of the grooves can be avoided.

The basis weight of the pulp in the absorbent body 4 (the basis weight of the entire multiple layers when the absorbent body is composed of multiple layers) is 150 g/m ² or more and 500 g/m ² or less, preferably 250 g/m ² or more and 400 g/m ² or less. It's okay. The basis weight of the pulp absorbent body may be uniform as a whole, or regions with relatively high or relatively low basis weight may be formed. In addition, the superabsorbent polymer weight in the absorbent body 4 (when the absorbent body consists of multiple layers, the weight of the entire multiple layers) is 70 g/m ² or more and 470 g/m ² or less, preferably 140 g/m ² or more and 240 g. /m ² or less.

<Preparation of sheet for fluff pulp>
Using the materials shown in Table 1, fluff pulp sheets of Examples 1 to 19 and Comparative Examples 1 to 5 were produced according to the following procedure. Comparative Example 1 is a reproduction of an existing 100% softwood pulp sheet for fluff pulp.

(Cooking process)
(1) Hardwood Acacia and eucalyptus are mixed so that the mass ratio is as shown in Table 1, white liquor having a predetermined sulfidity is added, and the mixture is rotated at a liquor ratio of 6.0 (L / kg) and a maximum temperature of 170 ° C. Digestion was carried out by a type autoclave to obtain hardwood unbleached kraft pulp having a kappa number of about 16.
(2) Conifer A white liquor having a predetermined degree of sulfidity is added to cedar, and the liquor ratio is 6.0 (L/kg), and the maximum temperature is 170°C. Got kraft pulp.

(Washing process)
After diluting the unbleached pulp to about 2% pulp consistency, the Buchner funnel was filled with a No. 2 Filter paper (manufactured by ADVANTEC) was laid and dewatered to a pulp concentration of about 12%. After that, the unbleached pulp was sandwiched between square filter papers (manufactured by ADVANTEC), pressure was applied with a press, and dewatered to a pulp concentration of 33%. This washing step was performed twice.

(Bleaching process)
(1) Hardwood Unbleached kraft pulp was ozone bleached with ozone gas of 8.1% concentration at 45° C. for about 2 minutes. For ozone bleaching, ozone gas from a laboratory ozone generator of PSA Ozonizer SGA-01A-PSA4 manufactured by Sumitomo Precision Products Co., Ltd. was used. Further, the ozone-bleached pulp was bleached with chlorine dioxide at 70° C. with a chlorine dioxide addition rate of 1.5% and a pulp concentration of 10% by mass to obtain broadleaf tree bleached kraft pulp. Between each bleaching step, after diluting the pulp to a concentration of about 2%, a Buchner funnel with No. 2 Filter paper (manufactured by ADVANTEC) was laid, and a dilution washing step of dehydrating to a pulp concentration of about 12% was performed twice.
(2) Softwood Unbleached kraft pulp was bleached with chlorine dioxide at a chlorine dioxide addition rate of 1.5% and a pulp concentration of 10% by mass at 70°C for 30 minutes. Subsequently, alkaline hydrogen peroxide bleaching was carried out at 1% alkali addition rate, 0.3% hydrogen peroxide addition rate, pulp concentration 10% by mass, and 70° C. for 120 minutes. Subsequently, alkali treatment was performed at 70° C. for 120 minutes with a sodium hydroxide addition rate of 0.2% and a pulp concentration of 10 mass %. Subsequently, chlorine dioxide bleaching was carried out at a chlorine dioxide addition rate of 0.3% and a pulp concentration of 10% by mass at 70° C. for 150 minutes to obtain softwood bleached kraft pulp. Between each bleaching step, after diluting the pulp to a concentration of about 2%, a Buchner funnel with No. 2 Filter paper (manufactured by ADVANTEC) was laid, and a dilution washing step of dehydrating to a pulp concentration of about 12% was performed twice.

(Papermaking process)
The resulting hardwood kraft pulp and softwood kraft pulp were diluted to a concentration of about 2% without being beaten, and adjusted to the blend ratio shown in Table 2. Using the adjusted pulp slurry, a semi-automatic sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) was used to prepare a hand-made sheet (fluff pulp pulp sheet) having a basis weight of 800 g/m ² .

<Production of absorbent article>
Using the pulp sheet for fluff pulp of each example, an absorbent body for an absorbent article was produced in an apparatus as shown in FIG. The amount of superabsorbent polymer added to the flap pulp was 9.3 grams to 7.7 grams of fluff pulp. A disposable diaper (tape type, L size) was produced using the obtained absorbent body.

<Measurement of fiber length and fiber width of pulp fiber>
The fiber length and fiber width of the hardwood unbleached kraft pulp of each example after the cooking and washing steps were measured. The fiber length and fiber width are measured using a fiber length measuring machine "VALMET FS5" manufactured by Valmet Co., Ltd., according to JIS-P8226: 2011 (ISO16065-2: 2007) "Pulp - fiber length measurement method by optical automatic analysis method". Measured according to The fiber analyzer "VALMET FS5" is a device that can measure the length and width of pulp fibers by image analysis when diluted pulp fibers pass through the measuring cell inside the fiber analyzer. From the measured values obtained, the mass-based ratio of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm and the mass-based ratio of pulp fibers having a fiber width of 10 μm or more and less than 35 μm were calculated. . In addition, the average fiber length and standard deviation σ when the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm are measured at intervals of 0.02 mm (with a classification width of 0.02 mm), and the fiber width is 10 μm or more and 35 μm. The average fiber width and standard deviation σ were calculated when pulp fibers of less than 1 μm were measured at intervals of 1 μm (with a classification width of 1 μm). The above average values (average fiber length and average fiber width) are arithmetic averages. Moreover, the above standard deviation is a value calculated from n=10000 or more measured based on a fiber analyzer. Table 1 shows the calculation results.

<Evaluation>
Evaluation was performed as described above. Evaluation results are shown in Table 2.

(density)
The density of the pulp sheet for fluff pulp of each example was measured according to "Paper and paperboard-Testing methods for thickness, density and specific volume" described in JIS-P8118 (2014).

(Calculation of specific burst strength)
The specific bursting strength of the pulp sheet for fluff pulp of each example is the value obtained by dividing the bursting strength [kPa] measured according to JIS-P8131 (2009) by the basis weight [kPa ^m /g]. asked.

(Fibrillation evaluation)
Based on the above specific bursting strength, the defibration property of the pulp sheet for fluff pulp of each example was evaluated. The evaluation criteria were the following five stages. When the evaluations are A, B, C and D, the defibration property of the pulp sheet for fluff pulp is good, and among these, the defibration property in the case of A is excellent. Also, although D is slightly inferior, it is at a practically acceptable level.
A: The specific burst strength is 1.2 kPa·m ² /g or more and 1.5 kPa·m ² /g or less.
B: The specific burst strength is 1.6 kPa·m ² /g or 1.1 kPa·m ² /g.
C: The specific burst strength is 1.7 kPa·m ² /g or 1.0 kPa·m ² /g.
D: The specific burst strength is 1.8 kPa·m ² /g or 0.9 kPa·m ² /g.
E: The specific burst strength is 1.9 kPa·m ² /g or more or 0.8 kPa·m ² /g or less.

(Measurement of Klemm water absorption)
The Klemm water absorbency of the pulp sheet for fluff pulp of each example was measured according to "Paper and paperboard-Water absorption test method-Klemm method" described in JIS-P8141 (2004). More specifically, for each fluff pulp pulp sheet having a basis weight of 200 g / m ² , the height [mm] of 1 minute after the start of measurement is measured, and the height [mm] of 1 minute and 2 minutes after the start of measurement Based on the above, the water absorption rate [mm/min] for 1 to 2 minutes after the start of measurement was calculated.

(Water absorption evaluation)
Based on the value of the height 1 minute after the start of the measurement, the water absorption amount (absorption performance) of the flap pulp sheet was evaluated according to the following criteria.
A: The height of 1 minute after the start of measurement of Klemm's water absorbency is 29 mm or more and 40 mm or less.
B: The height of 1 minute after the start of measurement of Klemm's water absorbency is 27 mm or more and less than 29 mm.
C: The height of 1 minute after the start of measurement of Klemm's water absorbency is 25 mm or more and less than 27 mm.
D: The height 1 minute after the start of measurement of the Klemm water absorbency is less than 25 mm.

(Water absorption rate evaluation)
The water absorption rate of the flap pulp sheet was evaluated according to the following criteria based on the value of the water absorption rate between 1 and 2 minutes after the start of the measurement.
A: The water absorption rate is 9 mm/min or more for 1 to 2 minutes after the start of measurement of Klemm's water absorbency.
B: The water absorption rate is 7 mm/min or more and less than 9 m/min for 1 to 2 minutes after the start of measurement of the Klemm water absorbency.
C: The water absorption rate is 5 mm/min or more and less than 7 mm/min for 1 minute to 2 minutes after the start of measurement of the Klemm water absorbency.
D: The water absorption rate is more than 3 mm/less than 5 mm/ for 1 minute to 2 minutes after the start of measurement of Klemm water absorbency.
E: The water absorption rate is 3 mm/min or less for 1 to 2 minutes after the start of measurement of Klemm's water absorbency.

(Evaluation of workability during production of fluff pulp)
The workability at the time of producing fluff pulp was measured by cutting a fluff pulp pulp sheet of each example having a basis weight of 200 g/m ² into 2 cm × 2 cm pieces and pulverizing them with a commercially available mixer (manufactured by Tescom, mixer TM856). It was evaluated by examining the degree of paper dust generation. It should be noted that the amount of accumulated paper dust generated during pulverization increases from E to A. Evaluation was carried out according to the following five stages. When the evaluations are A, B, C and D, workability is good.
A: Paper dust floats when the pulp sheet is pulverized, and there is a slight accumulation of pulp on the walls of the mixer.
B: Paper dust flutters when the pulp sheet is pulverized, and there is some accumulation of pulp on the walls of the mixer.
C: Paper dust flutters during pulverization of the pulp sheet, and a small amount of pulp deposits on the walls of the mixer.
D: Paper dust floats when the pulp sheet is pulverized, and some pulp deposits on the walls of the mixer, but this is within the range of no problem.
E: Paper dust flutters when the pulp sheet is pulverized, and a large amount of pulp accumulates on the walls of the mixer.

(Skin rash suppression evaluation of absorbent articles)
A total of 220 monitors were asked to use 10 disposable diapers of Examples 1 to 19 and Comparative Examples 1 to 5, respectively. That is, evaluation was conducted by 10 monitors for one example of the disposable diaper. Then, the number of sheets on which rash occurred was evaluated as a percentage. Evaluation was carried out according to the following five stages. The evaluations of A, B, C and D mean that the effect of suppressing skin rashes is better than that of Comparative Example 1 having the same composition as the existing product.
A: Better than Comparative Example 1 in rash occurrence rate.
B: Slightly superior to Comparative Example 1 in rash occurrence rate.
C: Slightly superior to Comparative Example 1 in rash occurrence rate.
D: Slightly superior to Comparative Example 1 in rash occurrence rate, practically usable.
E: The rash occurrence rate is equivalent to that of Comparative Example 1, and is at the same level as the existing product.
The effect of suppressing rashes is related to the effect of suppressing backflow of the absorbent body and the absorption capacity of the absorbent body.

From Tables 1 and 2, hardwood pulp fibers and softwood pulp fibers are contained, the proportion of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm in all pulp fibers is 42.6% or more, and the fiber width is 10 μm or more and 35 μm Examples 1 to 19, in which the percentage of pulp fibers having a viscosity of less than 90.6% or more, showed particularly good results in terms of fibrillation, workability in producing fluff pulp, and the effect of suppressing rashes in absorbent articles. Got.

On the other hand, Comparative Example 1, which contained only softwood pulp fibers, was inferior to Examples in terms of fibrillation properties and rash-suppressing effects in absorbent articles. Comparative Example 2, which contained only hardwood pulp fibers, was inferior in fibrillation properties, workability during production of fluff pulp, and rash-suppressing effects in absorbent articles.

Among the above examples, Example 7 in which the blending amount of acacia material in chips for making hardwood pulp is outside the range of 5% by mass or more and less than 95% by mass, and hardwood pulp fiber relative to softwood pulp fiber In Example 17, in which the mass ratio was outside the range of 25/75 or more and less than 38/62, the fibrillating property, workability, and the effect of suppressing reversion in the absorbent article were slightly inferior.

Although the present invention has been described above based on specific embodiments, the present invention is not limited to these embodiments. In addition, the above-described forms are capable of various changes, modifications, substitutions, additions, deletions, combinations, etc. within the scope described in the claims, and these also belong to the technical scope of the present invention.

Reference Signs List 1, 11 Absorbent article 2 Back sheet 3 Top sheet 4 Absorber 4a Skin-side layer 4b Non-skin-side layer 5 Enveloping sheet 7 Side sheet 50 Absorbent type 100, 200 Absorber production apparatus 101, 102 Single layer production department 61 Pulp Supply part 62 Duct 63 Super absorbent polymer particle introducing part 64 Scuffing roll 65 Stacking drum 66 Conveying means 67 Compressing means D1 Front-back direction D2 Width direction

Claims (6)

An absorbent body for absorbent articles, comprising a hardwood pulp fiber-containing absorbent body containing pulp fibers containing softwood pulp fibers and hardwood pulp fibers, and a superabsorbent polymer,
The mass ratio of the hardwood pulp fibers to the softwood pulp fibers in the hardwood pulp fiber-containing absorbent body is 25/75 or more and 38/62 or less,
Pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm in the total pulp fibers of the hardwood pulp fiber-containing absorber are 40% or more and 55% or less on a mass basis, and a fiber width of 10 μm or more and less than 35 μm. is 90% or more and 93.1% or less on a mass basis. 2. The absorbent body for absorbent articles according to claim 1, wherein the content of the acacia wood in the raw material wood of the hardwood pulp fiber is 5% by mass or more and 95% by mass or less. When the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm are measured at intervals of 0.02 mm, the average fiber length is 0.5 mm or more and 0.8 mm or less, and the standard deviation σ is 0.58 mm or less. ,
2. The absorbent article according to claim 1, wherein the pulp fibers having a fiber width of 10 μm or more and less than 35 μm have an average fiber width of 15 μm or more and 30 μm or less and a standard deviation σ of 2.9 μm or less when measured at intervals of 1 μm. Absorber for. Having a skin side facing the wearer's skin when the absorbent article is worn, and a non-skin side opposite to the skin side,
2. The absorbent body for absorbent articles according to claim 1, wherein said hardwood pulp fiber-containing absorbent body is included on said skin side. Consists of two or more separate layers,
5. The absorbent body for absorbent articles according to claim 4 , wherein the skin-side layer positioned on the skin side comprises the hardwood pulp fiber-containing absorbent body. An absorbent article comprising the absorbent body for absorbent articles according to any one of claims 1 to 5 .

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