Expandable sheets and absorbent articles

Abstract

To provide a stretchable sheet that achieves both elasticity and flexibility. [Solution] The expandable sheet 1 comprises a first sheet 2, a second sheet 3, and a plurality of elastic members 4 arranged to be expandable and contractible between the two sheets 2 and 3. The plurality of elastic members 4 are arranged to extend in one direction X without intersecting each other. The first sheet 2 and the second sheet 3 are intermittently fused together at a plurality of fusion joints 10. The plurality of elastic members 4 and the first sheet 2 are joined together by a predetermined joining means. The plurality of elastic members 4 and the second sheet 3 are fused together only at positions that overlap with the fusion joints 10 in a plan view of the expandable sheet 1.

Description

Technical Field

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[0003]

[0001] The present invention relates to a stretchable sheet and an absorbent article provided with the same.

Background Art

[0002] From the viewpoint of fitting an absorbent article such as a diaper to the body, a stretchable sheet member formed by joining an elastic member such as a thread rubber between two sheets is used as the sheet member constituting the exterior body of the absorbent article. As such a sheet member, for example, in Patent Document 1, there is proposed an exterior body having an outer layer sheet disposed on the side far from the wearer's skin and including a stretchable non-woven fabric having stretchability, and an inner layer sheet disposed relatively closer to the wearer's skin and including a non-stretchable non-woven fabric of a color different from that of the stretchable non-woven fabric, and in which a filamentous elastic filament is arranged on the outer layer sheet.

[0003] Further, in Patent Document 2, there are provided two sheets and a plurality of elongated elastic members disposed at intervals in the vertical direction in an extended state between the two sheets, and in a state where the extended state is released, folds having a plurality of ridges extending in the vertical direction are formed on each of the inner side and the outer side, and at the waist edge portion, the space serving as a valley between the ridges does not communicate from the uppermost to the lowermost of the plurality of elastic members, and at the lower waist portion, the space serving as a valley between the ridges communicates from the uppermost to the lowermost of the plurality of elastic members. An exterior body is proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The exterior bodies described in Patent Documents 1 and 2 are expandable and contractible along the direction of extension of the elastic member or elastic filament. However, there was a demand for greater flexibility while maintaining expandability. Therefore, the object of the present invention is to provide an expandable sheet that achieves both elasticity and flexibility. [Means for solving the problem]

[0006] The present invention comprises a first sheet, a second sheet, and a plurality of elastic members stretchably arranged between the two sheets. The present invention provides an expandable sheet in which the aforementioned plurality of elastic members are arranged so as to extend in one direction without intersecting each other. In one embodiment, it is preferable that the first sheet and the second sheet are intermittently fused together at a plurality of fusion points. In one embodiment, it is preferable that the plurality of elastic members and the first sheet are joined by a predetermined joining means. In one embodiment, it is preferable that the plurality of elastic members and the second sheet are fused together only at positions that overlap with the fused portion in a plan view of the stretchable sheet. [Effects of the Invention]

[0007] According to the present invention, an expandable sheet is provided that achieves both elasticity and flexibility. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing the cross-section of the expandable sheet of the present invention when it is cut along a direction perpendicular to the extending direction of the elastic member. [Figure 2] Figure 2 is a schematic, enlarged plan view showing the second sheet side when the expandable sheet of the present invention is fully extended. [Figure 3] Figure 3 is a plan view enlarged showing a modified arrangement pattern of the fused portions when the expandable sheet of the present invention is fully extended. [Figure 4]Figure 4 is a cross-sectional view showing the stretchable sheet of the present invention in its natural state, when cut along the extending direction of the elastic member. [Figure 5] Figure 5 is a perspective view showing the method for manufacturing the stretchable sheet of the present invention. [Modes for carrying out the invention]

[0009] The stretchable sheet of the present invention will be described below with reference to the drawings, based on a preferred embodiment thereof. Figures 1 and 2 show a stretchable sheet 1 according to a preferred embodiment of the present invention.

[0010] As shown in Figures 1 and 2, the stretchable sheet 1 comprises a first sheet 2, a second sheet 3, and a plurality of elastic members 4 stretchably arranged between the two sheets. The first sheet 2 and the second sheet 3 are composed of various types of fiber sheets, for example. Nonwoven fabrics are typical examples of fiber sheets. Examples of nonwoven fabrics include air-through nonwoven fabrics, spunbond nonwoven fabrics, meltblown nonwoven fabrics, spunlace nonwoven fabrics, and laminated nonwoven fabrics formed by laminating these nonwoven fabrics. The first sheet 2 and the second sheet 3 may be of the same type or of different types. Here, "same type of sheet" means sheets that have the same manufacturing process, thickness, and basis weight, and, if the sheet is composed of fibers, the same type, diameter, and length of the constituent fibers. If at least one of these differs, they are considered different types of sheets.

[0011] The elastic members 4 are substantially continuous along the entire length of the stretchable sheet 1. In this embodiment, the elastic members 4 are elastic filaments containing an elastic resin. The elastic members 4 are arranged to extend in one direction without intersecting each other. However, it is permissible for the elastic members 4 to intersect unintentionally due to unavoidable fluctuations in the manufacturing conditions of the stretchable sheet 1. The elastic members 4 may extend in a straight line or in a meandering manner, as long as they do not intersect each other. Details of the elastic members 4 will be described later. As shown in Figure 2, the expandable sheet 1 has an extension direction X of the elastic member 4 and a direction Y perpendicular to direction X.

[0012] As shown in Figures 1 and 2, the first sheet 2 and the second sheet 3 are intermittently fused together by a plurality of fusion portions 10. As shown in Figure 2, in a plan view, the fusion portions 10 have a dot-like shape, and the plurality of fusion portions 10 are arranged along one direction α. ​​Here, the state in which the plurality of fusion portions 10 are intermittently arranged on a single straight line is also called a "sequence of dots 11," and in this embodiment, the plurality of fusion portions 10 are arranged to form multiple sequences of dots 11 extending along one direction α. ​​In this embodiment, one direction α (the direction in which the sequence of dots 11 extends) coincides with the extension direction X of the elastic member 4. Each row of points 11 is arranged at intervals along a direction β that is perpendicular to the aforementioned direction α. ​​In this embodiment, direction β coincides with direction Y, and each row of points 11 is arranged at approximately equal intervals in direction Y. Thus, the fusion portion 10 in this embodiment is located at the intersection of the grid extending in directions X and Y, respectively. By arranging the fused portions 10 in this manner, the total area of ​​the fused portions 10 can be reduced compared to the case where the fused portions between the elastic member 4 and the first sheet 2 and the second sheet 3 are arranged continuously along the entire length of the elastic member 4. Consequently, the flexibility of the stretchable sheet 1 can be improved compared to the case where the fused portions between the elastic member 4 and the first sheet 2 and the second sheet 3 are arranged continuously along the entire length of the elastic member 4.

[0013] As shown in Figure 2, one or more elastic members 4 are placed between adjacent rows of points 11. By arranging the fused portions 10 in this way, the total area of ​​the fused portions 10 can be made smaller than when one or more fused portions 10 are placed for each elastic member 4 to fix the elastic member 4, and as a result, the flexibility of the stretchable sheet 1 can be increased compared to the latter case. From the viewpoint of making this effect more pronounced, it is preferable that one or more elastic members 4 are placed between adjacent rows of points 11, and more preferably that two or more elastic members 4 are placed. Thus, it is preferable that the number of rows of points 11 is less than the number of elastic members 4.

[0014] As shown in FIG. 2, in plan view, the maximum length d1 of the fusion part 10 along the extending direction X of the elastic member 4 and the maximum length d2 of the fusion part 10 along the direction Y orthogonal to the direction X are each preferably less than 3 mm independently, more preferably 2 mm or less, and even more preferably 1 mm or less. By setting d1 and d2 to be less than 3 mm independently, the joining strength of the first sheet and the second sheet can be ensured with a small-area fusion part 10, and the flexibility of the stretchable sheet 1 can be enhanced. The maximum lengths d1 and d2 are the arithmetic mean values of the measured values in 10 randomly selected fusion parts 10.

[0015] As shown in FIG. 2, when paying attention to any one dot sequence 11, among the fusion parts 10 constituting the dot sequence 11, the interval L1 between adjacent fusion parts 10 and the interval L2 between adjacent dot sequences 11 (in the embodiment shown in FIG. 2, it is equal to the interval between adjacent fusion parts 10 along the direction Y) are each preferably 3 mm or more independently, more preferably 3.5 mm or more, and even more preferably 4 mm or more. By setting L1 and L2 to be 3 mm or more independently, the area of the portion where the first sheet 2 and the second sheet 3 are not fused can be made sufficiently larger than the case where the fusion parts of the elastic member 4 with the first sheet 2 and the second sheet 3 are continuously arranged over the entire length of the elastic member 4. Due to this, the flexibility of the stretchable sheet 1 can be enhanced more than the case where the fusion parts of the elastic member 4 with the first sheet 2 and the second sheet 3 are continuously arranged over the entire length of the elastic member 4. Also, from the viewpoint of ensuring the joining strength of the first sheet 2 and the second sheet 3, the intervals L1 and L2 are each preferably 10 mm or less independently, more preferably 8 mm or less, and even more preferably 6 mm or less. As shown in Fig. 2, the interval L1 is the distance between the centers of adjacent fusion parts 10, and is the arithmetic mean value of the measured values in a set of 10 randomly selected fusion parts. Also, the interval L2 is the interval between adjacent point sequences 11, where the "point sequence 11" here means a straight line connecting the centers of the fusion parts 10. The interval L2 is the arithmetic mean value of the measured values of the intervals of 10 randomly selected adjacent pairs of point sequences 11.

[0016] Preferably, the interval L1 is larger than the interval L2. Thereby, in the natural state of the stretchable sheet 1, it is possible to facilitate the formation of the fold structure 30 described later. From this viewpoint, the ratio L1 / L2 of the interval L1 to the interval L2 is preferably 1.1 or more, more preferably 1.3 or more, and still more preferably 1.4 or more.

[0017] Figs. 3(a) to (f) show modified examples of the shape and arrangement pattern of the fusion parts 10. The shape of the fusion part 10 in plan view is elliptical in Figs. 3(a) and 3(b), circular in Fig. 3(c), square or rhomboid in Fig. 3(d), cross-shaped in Fig. 3(e), and square in Fig. 3(f). In any of the embodiments of Figs. 3(a) to (f), a plurality of fusion parts 10 are arranged so as to form a plurality of point sequences 11 extending along one direction α. In these embodiments, one direction α (the direction in which the point sequence 11 extends) coincides with the extending direction X of the elastic member 4. Also, each point sequence 11 is arranged at intervals along a direction β orthogonal to the one direction α. In the present embodiment, the direction β coincides with the direction Y, and each point sequence 11 is arranged at substantially equal intervals in the direction Y. However, the directions α and β do not necessarily coincide with the directions X and Y.

[0018] In Figure 3(a), the major axes of multiple fusion sections 10, which are elliptical in plan view, coincide with each other, whereas in Figure 3(b), multiple types of fusion sections 10 with different major axis directions are scattered. Specifically, the fusion section 10 consists of a first group of fusion sections 10A inclined in a first direction with respect to the direction in which the sequence of points extends, and a second group of fusion sections 10B inclined in a direction different from the first direction. The sequence of points 11 consists of a first sequence of points 11a made up of the first group of fusion sections 10A and a second sequence of points 11b made up of the second group of fusion sections 10B, with the first sequence of points 11a and the second sequence of points 11b being arranged alternately along direction β (direction Y).

[0019] In Figures 3(a), 3(b), 3(e), and 3(f), the fused portions 10 are arranged in a sequence of points along not only direction α (direction X) but also direction β (direction Y). In contrast, in Figures 3(c) and 3(d), the fused portions 10 are arranged in a sequence of points 12 extending along a direction intersecting direction Y. By arranging the fused portions 10 to form a sequence of points 12 extending along a direction intersecting direction Y, multiple fused portions 10 that cause a decrease in the elasticity of the elastic member 4 are eliminated along direction Y. This improves the fit when wearing an absorbent article incorporating the stretchable sheet 1, and also makes it easier for the wearer to feel the flexibility of the absorbent article.

[0020] The shape of the fused portion 10 shown in Figures 3(a) and 3(b) is advantageous for increasing the flexibility of the pleated structure 30, which will be described later. This is because the fused portion 10 shown in Figures 3(a) and 3(b) has a shape that is short in direction X and long in direction Y. Having such a shape allows for a large gap between adjacent fused portions 10 in direction X, while reducing the gap between adjacent fused portions 10 in direction Y. Reducing the gap between adjacent fused portions 10 in direction Y makes it easier for the pleated structure 30, which will be described later, to form in the natural state of the expandable sheet 1. In addition, increasing the gap between adjacent fused portions 10 in direction X increases the flexibility of the pleated structure 30.

[0021] The shape of the fused portion 10 shown in Figures 3(c) to 3(e) is advantageous for increasing the flexibility of the expandable sheet 1. This is because the joint strength of the first sheet 2 and the second sheet 3 can be ensured without excessively increasing the area of ​​the fused portion 10.

[0022] The fused portion 10 shown in Figure 3(e) has a shape in which the four corners of the square-shaped fused portion 10 shown in Figure 3(f) have been removed, resulting in a smaller area in plan view. Therefore, the shape of the fused portion 10 shown in Figure 3(e) is elongated in both directions X and Y, yet the area of ​​the fused portion 10 in plan view can be reduced, thereby increasing the flexibility of the expandable sheet 1.

[0023] As described above, modified examples of the shape and arrangement pattern of the fused portion 10 have been explained using Figures 3(a) to (f), but the shape and arrangement pattern of the fused portion 10 are not limited to these. For example, the fused portion 10 may have the elliptical shape shown in Figure 3(a), and may be arranged in an arrangement pattern that forms a sequence of points 12 extending along a direction intersecting direction Y, as shown in Figure 3(c).

[0024] Returning to the embodiments shown in Figures 1 and 2, as shown in Figure 1, the multiple elastic members 4 arranged on the stretchable sheet 1 and the first sheet 2 are joined at the joint 5 by a predetermined joining means. The joining means between the elastic members 4 and the first sheet 2 may include, but is not limited to, fusion bonding or adhesive bonding. Fusion bonding includes both a state in which the elastic member 4 and the first sheet 2 are joined by melting each other, and a state in which one of them melts and the other bites into it to join them. In particular, from the viewpoint of improving the flexibility of the stretchable sheet 1, it is preferable that the elastic member 4 and the first sheet 2 are fused together. In this case, the stretchable sheet 1 as a whole does not contain any adhesive.

[0025] When focusing on one elastic member 4, the joint 5 between the elastic member 4 and the first sheet 2 is arranged continuously along the entire length of the elastic member 4. By joining the elastic member 4 and the first sheet 2 in this way, the joint between the elastic member 4 and the first sheet 2 can be reliably established, and the expandable sheet 1 can be reliably expanded and contracted. Alternatively, when focusing on one elastic member 4, the joint portion 5 between the elastic member 4 and the first sheet 2 may be intermittently arranged in the extending direction X of the elastic member 4. By joining the elastic member 4 and the first sheet 2 in this way, the area of ​​the joint portion 5 can be reduced compared to when the joint portion 5 is continuously arranged along the entire length of the elastic member 4, and as a result, the flexibility of the expandable sheet 1 can be improved compared to when the joint portion 5 is continuously arranged along the entire length of the elastic member 4.

[0026] As shown in Figures 1 and 2, the fused portion 10 can be classified into a first fused portion 10a that overlaps with the elastic member 4 in a plan view, and a second fused portion 10b that does not overlap with the elastic member 4 in a plan view. The elastic member 4 and the second sheet are fused only at the position where they overlap with the fused portion 10 (more specifically, the first fused portion 10a) in a plan view of the expandable sheet 1. The elastic member 4 is not fused to the second sheet at any other position than where it overlaps with the first fused portion 10a in a plan view. In other words, the expandable sheet 1 has an elastic member 4a that is fused to the second sheet 3 at the position where it overlaps with the first fused portion 10a in a plan view, and an elastic member 4b that is not fused to the second sheet 3. Since the elastic member 4b that is not fused to the second sheet 3 is more likely to exhibit elasticity, the stretchable sheet 1 having such elastic member 4b has high elasticity.

[0027] From the viewpoint of further enhancing the elasticity of the stretchable sheet 1, the ratio of elastic members 4b that are not fused to the second sheet 3 to the total number of elastic members 4 is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. Furthermore, the ratio is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

[0028] In the expandable sheet 1, it is preferable that there is no other sheet between the first sheet 2 and the second sheet 3. By adopting this configuration, the number of sheet members can be minimized, and combined with the small total area of ​​the fused portion 10 between the first sheet 2 and the second sheet 3, the flexibility of the expandable sheet 1 can be improved.

[0029] Figure 4 shows a cross-sectional view of the expandable sheet 1 in its natural state, along the extension direction X of the elastic member 4. The natural state refers to the state in which no external forces other than gravity act on the expandable sheet 1. Note that the joint 5 between the elastic member 4 and the first sheet 2 is omitted in Figure 4. When the joint 5 between the elastic member 4 and the first sheet 2 is arranged continuously along the entire length of the elastic member 4, as shown in Figure 4, in its natural state, the second sheet 3 has a pleated structure 30 consisting of a plurality of recessed portions 32 extending in a direction perpendicular to the extending direction X of the elastic member 4 (direction Y in Figure 2), and hollow convex portions 33 located between the recessed portions 32, with the fused portion 10 included at the bottom portion 31. The reason for this is that in its natural state, the elastic member 4 contracts, and the joining of the elastic member 4 and the second sheet 3 is intermittent along the extending direction X of the elastic member 4, so that the second sheet 3 separates from the elastic member 4 in places where the elastic member 4 and the second sheet 3 are not joined. The pleated structure 30 is formed on the second sheet 3 side of the expandable sheet 1. On the other hand, no pleat structure 30 is formed on the first sheet 2 side of the expandable sheet 1, and the outer surface of the first sheet 2 is flat. This is because the joint portion 5 between the elastic member 4 and the first sheet 2 is arranged continuously along the entire length of the elastic member 4. From the viewpoint of ensuring that no pleat structure 30 is formed on the first sheet 2 side, it is preferable that the first sheet 2 is stretchable. Details of the stretchability of the first sheet 2 will be described later.

[0030] The fold structure 30 is formed on the second sheet 3 side of the stretchable sheet 1, improving the cushioning and flexibility of the stretchable sheet 1. In addition, the flat outer surface of the first sheet 2 allows the stretchable sheet 1 to be made thinner. In an absorbent article equipped with the stretchable sheet 1 as an outer sheet, arranging the stretchable sheet 1 so that the first sheet 2 becomes the outer surface of the absorbent article makes it easier for the wearer to put on clothes over the absorbent article. This is because the outer surface of the absorbent article is made up of a flat sheet (first sheet 2), so clothes are less likely to get caught on the absorbent article, and clothes can be put on without having to spread them out wide. In addition, the fold structure 30, which is formed facing the wearer's skin, acts as a cushion and fits the wearer's body, so that the absorbent article does not shift position due to being dragged by clothes. In particular, arranging the stretchable sheet 1 so that the recessed portion 32 and the convex portion 33 extend in the longitudinal direction of the absorbent article makes it even easier to put on clothes and improves the fit of the absorbent article to the body.

[0031] When the stretchable sheet 1 is manufactured by the manufacturing method described later, the first sheet 2 has a low basis weight portion (not shown) and a high basis weight portion (not shown) in which there is more forming material for the first sheet 2 than in the low basis weight portion. These low basis weight portion and high basis weight portion extend along direction Y and are arranged alternately along the extending direction X of the elastic member 4. The low basis weight portion and high basis weight portion are formed in the first sheet 2 by the stretchability imparting process described later. As a result of this stretchability imparting process, the first sheet 2 has stretchability that allows it to stretch along the extending direction of the elastic member 4. "Having stretchability" includes (a) cases in which the constituent fibers of the first sheet 2 themselves stretch, and (b) cases in which, even if the constituent fibers themselves do not stretch, the first sheet 2 as a whole stretches due to the separation of fibers that were bonded at intersections, structural changes in the three-dimensional structure formed by multiple fibers due to bonding between fibers, etc., the tearing of constituent fibers, or the stretching of fiber slack. The first sheet 2 in this embodiment has the configuration of (b) above. However, this does not prevent the first sheet 2 from also having the configuration of (a) above.

[0032] Next, the details of the elastic member 4 will be described. The elastic member 4 may be a filamentous synthetic rubber yarn or natural rubber. Alternatively, it may be obtained by dry spinning (melt spinning) or wet spinning. Of these, considering the preferred manufacturing method described later, it is preferable that the elastic member 4 is obtained directly by melt spinning without being wound or stored beforehand.

[0033] The elastic member 4 is preferably obtained by stretching molten resin extruded from a nozzle along a spinning wire. Stretching causes the polymer constituting the elastic member 4 to be molecularly oriented in the longitudinal direction of the elastic member 4, thereby reducing hysteresis loss. Furthermore, stretching allows for the production of a thinner elastic member 4. From this viewpoint, the elastic member 4 is preferably stretched to a length of 1.1 to 400 times, and particularly to 4 to 100 times.

[0034] In particular, it is preferable that the elastic member 4 is formed by stretching an elastic resin in a molten or softened state. This makes it possible to obtain a sufficiently fine filament, which improves the texture for reasons described later. Also, because the elastic resin is stretched in a molten or softened state, after being bonded to the first sheet 2 and the second sheet 3, the elastic member 4 does not exhibit a force that tries to shrink when it reaches room temperature, and the elastic member 4 is in the same state as if it had been bonded to the first sheet 2 and the second sheet 3 in an unstretched state. Specific stretching operations in this embodiment include (a) melt-spinning the resin that will be the raw material for the elastic member 4 to obtain an unstretched yarn, and then reheating the unstretched elastic member yarn and stretching it at a state above the softening temperature (glass transition temperature Tg of the hard segment), and (b) directly stretching the molten fibers obtained by melt-spinning the resin that will be the raw material for the elastic member 4. When the stretchable sheet 1 is manufactured according to the preferred manufacturing method described later, the elastic member 4 is obtained by directly stretching the molten fibers obtained by melt-spinning.

[0035] The elastic member 4 obtained by stretching after spinning preferably has a diameter of 10 μm to 200 μm, and more preferably 20 μm to 130 μm. This range was determined considering the texture of the stretchable sheet 1 and the productivity of the elastic member 4. In detail, if the diameter of the elastic member 4 is too large, when the stretchable sheet 1 is touched, the step caused by the elastic member 4 becomes more easily perceived. This step negatively affects the texture of the stretchable sheet 1. From this viewpoint, the smaller the diameter of the elastic member 4, the more easily only the texture of the first and second sheets is perceived, which is preferable. Furthermore, a thinner elastic member 4 is preferable in order to reduce the light transmittance of the first and second sheets, thereby providing the ability to conceal the color of bodily fluids.

[0036] Next, a preferred manufacturing method for the stretchable sheet 1 of this embodiment will be described with reference to Figure 5. Note that this manufacturing method is merely one preferred example of a manufacturing method for the stretchable sheet 1, and there is no prejudice to manufacturing the stretchable sheet 1 by other methods. This manufacturing method comprises the steps of: bringing a plurality of molten or softened elastic members 4 spun from a plurality of spinning nozzles 16 into contact with one side of a first raw material sheet 2a before the elastic members 4 solidify, thereby obtaining a composite sheet 2b in which the elastic members 4 are fused to the first raw material sheet 2a; an elasticity imparting step to impart elasticity to the composite sheet 2b; and a fusion step to laminate and fuse a second raw material sheet 3a onto the side of the elastic composite sheet 2b on which the elastic members 4 are arranged.

[0037] The spinning nozzle 16 is provided on the spinning head 17. The spinning head 17 is connected to an extruder. Resin can also be supplied to the spinning head 17 via a gear pump. The elastic resin, melted and kneaded by the extruder, is supplied to the spinning head 17. The spinning head 17 has a number of spinning nozzles 16 arranged in a straight line. The spinning nozzles 16 are arranged along the width direction (a direction perpendicular to the conveying direction) of the first raw material sheet 2a. The spacing between adjacent spinning nozzles 16 corresponds to the spacing of the elastic members 4 in the target stretchable sheet 1. The spinning nozzles 16 are usually circular, and their diameter affects the diameter and stretch ratio of the elastic members 4. From this viewpoint, the diameter of the spinning nozzles 16 is preferably 0.1 mm or more and 2 mm or less, and particularly preferably 0.2 mm or more and 0.6 mm or less. For the purpose of increasing the bonding strength with the first sheet 2, improving the spinnability of the elastic member 4, and improving the stretchability of the stretchable sheet 1, the elastic member 4 can also be made into a composite form (side-by-side, core-sheath, sea-island structure). Specifically, it is preferable to combine a PP-based elastomer resin and a styrene-based elastomer resin.

[0038] The elastic member 4 merges with the first raw material sheet 2a before solidification, i.e., while it is in a fusion-ready state. As a result, the elastic member 4 fuses to one side of the first raw material sheet 2a. In other words, the elastic member 4 is taken up and stretched while fusing to the first raw material sheet 2a as it is being transported. No external heat is applied to the first raw material sheet 2a during the fusion of the elastic member 4. That is, the elastic member 4 and the first raw material sheet 2a fuse only due to the heat of fusion generated by the fusion-ready elastic member 4. As a result, of the constituent fibers of the first raw material sheet 2a, only the fibers surrounding the elastic member 4 fuse to the elastic member 4, while fibers located further away do not fuse. Consequently, the heat applied to the first raw material sheet 2a is kept to a minimum, and the good texture inherent in the first raw material sheet 2a itself is maintained. This results in a good texture for the resulting stretchable sheet 1.

[0039] While the spun elastic member 4 is being joined with the first raw material sheet 2a, the elastic member 4 is stretched and its molecules are oriented in the stretching direction. Its diameter also decreases. This molecular orientation results in an elastic member 4 with a small stretch / rebound ratio (hysteresis) at 50% elongation. From the viewpoint of sufficiently stretching the elastic member 4 and preventing the elastic member 4 from breaking, the temperature of the spun elastic member 4 may be adjusted by blowing air (hot air, cold air) at a predetermined temperature onto the elastic member 4.

[0040] The stretching of the elastic member 4 may be performed not only by stretching the raw material resin in its molten state (melt stretching), but also by stretching it in its softened state during the cooling process (softened stretching). The molten state is the state in which the resin flows when an external force is applied. The melting temperature of the resin is measured as the peak temperature of Tanδ, which is measured by viscoelastic measurement (for example, by applying rotational vibration strain to the resin sandwiched between circular parallel plates). To prevent thread breakage in the case of elastic resin, it is desirable to ensure a long stretching section. Similarly, to prevent thread breakage, the melting temperature of the elastic resin is preferably between 130°C and 300°C. Furthermore, from the viewpoint of heat resistance of the elastic resin, the melting temperature is preferably 220°C or lower. The molding temperature (die temperature) of the elastic member 4 is preferably +50°C or higher of the melting temperature of the raw material resin to increase the fluidity of the resin and improve moldability, and preferably +110°C or lower for heat resistance. The softening temperature is measured as the Tg temperature in the viscoelastic properties of the measurement sample of the sheet-shaped elastic resin. The range from the softening temperature to the melting temperature is called the softened state. The state at a temperature lower than the softening temperature is called the solidified state. From the viewpoint of the growth of elastic resin crystals during storage of the expandable sheet 1 and the deterioration of the expandable properties of the expandable sheet 1 due to body temperature, the softening temperature is preferably 60°C or higher, and more preferably 80°C to 180°C.

[0041] When joining the elastic member 4 to the first raw material sheet 2a, the temperature of the elastic member 4 is preferably 100°C or higher to ensure fiber fusion. More preferably 120°C or higher, and even more preferably 140°C or higher. Furthermore, from the viewpoint of maintaining the shape of the elastic member 4 and obtaining an expandable sheet 1 with good stretchability, the temperature of the elastic member 4 is preferably 180°C or lower. More preferably 160°C or lower. As a result, the optimal filament temperature is in the range of 120°C to 160°C, and even more preferably 140°C to 160°C. The temperature at the time of joining can be measured by observing the joining state using a film made of modified polyethylene or modified polypropylene, which has a different melting point from the elastic resin constituting the elastic member 4, as the sheet substrate to be joined to the elastic member 4. At this time, if the elastic member 4 and the sheet substrate are fused, the joining temperature is above the melting point of the sheet substrate.

[0042] When the elastic member 4 and the first raw material sheet 2a are joined, the elastic member 4 is substantially in a non-stretched state (a state in which it does not shrink when the external force is removed). In the joined state, it is preferable that at least a portion of the fibers constituting the first raw material sheet 2a are fused to the elastic member 4, or more preferably that both the elastic member 4 and at least a portion of the fibers constituting the first raw material sheet 2a are fused. This is because sufficient bonding strength can be obtained. The stretchability of the resulting stretchable sheet 1 is affected by the density of the bonding points between the elastic member 4 and the first raw material sheet 2a. Furthermore, the stretchability can be adjusted by the bonding temperature, bonding pressure, and the separation of the bonding points due to the elasticity-developing treatment of the first raw material sheet 2a described later. By fusing the constituent fibers of the first raw material sheet 2a to the elastic member 4, the bonding strength of each bonding point is increased. Lowering the density of bonding points is preferable because it reduces the inhibition of stretching by the first raw material sheet 2a and allows for the acquisition of a stretchable sheet 1 with sufficient bonding strength.

[0043] When the elastic members 4 are joined to the first raw material sheet 2a, they are arranged in one direction without intersecting each other. Then, with the elastic members 4 joined to the first raw material sheet 2a and in contact with the first raw material sheet 2a, the two are clamped together by a pair of nip rolls 18a and 18b. The clamping conditions affect the texture of the resulting stretchable sheet 1. If the clamping force is too high, the elastic members 4 tend to get stuck in the first raw material sheet 2a, which can easily lead to a decrease in the texture of the resulting stretchable sheet 1. From this perspective, the clamping force applied by the nip rolls 18a and 18b should be sufficient to ensure contact between the elastic members 4 and the first raw material sheet 2a, and excessively high clamping force is not required.

[0044] Another condition for pressing with the nip rolls 18a and 18b is the temperature of the nip rolls 18a and 18b. As a result of our investigations, we found that a stretchable sheet 1 with a good texture is obtained by pressing with the nip rolls 18a and 18b without heating them (i.e., letting it happen naturally) or while cooling them, rather than pressing with the nip rolls 18a and 18b heated. When cooling the nip rolls 18a and 18b, it is preferable to use a refrigerant such as cooling water and adjust the temperature so that the surface temperature of the nip rolls 18a and 18b is between 10°C and 50°C.

[0045] In this way, a composite sheet 2b is obtained in which the elastic member 4 is fused to one side of the first raw material sheet 2a. Next, the composite sheet 2b is subjected to an elasticity-enhancing process along the direction in which the elastic member 4 extends, thereby imparting elasticity to the composite sheet 2b. Through this process, the first raw material sheet 2a, which does not inherently possess stretchability, is given stretchability.

[0046] The process of imparting elasticity can utilize an elasticity-generating processing unit 22 equipped with a pair of tooth-groove rolls 20a, 20b in which teeth and tooth roots extending axially are alternately formed along the circumferential direction. The elasticity-generating processing unit 22 comprises a pair of tooth-groove rolls 20a, 20b and a pair of nip rolls 19a, 19b, 21a, 21b positioned upstream and downstream of the tooth-groove rolls 20a, 20b in the conveying direction of the composite sheet 2b. The degree of stretching of the composite sheet 2b can be adjusted by appropriately adjusting the conveying speed of the pair of nip rolls 19a, 19b upstream of the pair of tooth-groove rolls 20a, 20b and the pair of nip rolls 21a, 21b downstream.

[0047] The elasticity-generating processing unit 22 has a known lifting mechanism (not shown) that displaces one or both pivot points of a pair of grooved rolls 20a and 20b vertically, and the distance between the two grooved rolls 20a and 20b is adjustable. For example, the pair of grooved rolls 20a and 20b are combined such that the teeth of one are loosely inserted between the teeth of the other, and the teeth of the other are loosely inserted between the teeth of the first. A composite sheet 2b is inserted between the two grooved rolls 20a and 20b in this state to form a low-weight portion and a high-weight portion, thereby providing elasticity. The pair of grooved rolls 20a and 20b may both be driven by a drive source (co-rotating rolls), or only one may be driven by a drive source (independent-rotating rolls). As for the tooth profiles of the grooved rolls 20a and 20b, general involute tooth profiles and cycloidal tooth profiles are used, and those with narrower tooth widths are particularly preferred.

[0048] In this process, the constituent fibers of the first raw material sheet 2a, i.e., the first sheet 2, undergo plastic deformation and elongation, causing the fibers to become thinner and the first sheet 2 to become bulkier, resulting in improved texture and flexibility. For the above process of imparting elasticity, the elasticity-developing treatment described in paragraphs

[0066] to

[0069] of Japanese Patent Application Publication No. 2008-179128 can be appropriately utilized.

[0049] Next, a fusion process is performed to laminate and fuse the second raw material sheet 3a onto the side of the composite sheet 2b on which the elastic member 4, which has been given elasticity by the elasticity imparting process, is located, thereby obtaining an expandable sheet 1. In this process, the second raw material sheet 3a is fed out from the feeding unit 24 and laminated onto the composite sheet 2b, and then the composite sheet 2b and the second raw material sheet 3a are joined at the sheet joining unit 27.

[0050] The sheet joining section 27 comprises an anvil roll 26 and an ultrasonic joining device 25. The anvil roll 26 is driven by a drive source (not shown) and rotates in the direction indicated by the arrow R in Figure 5. The anvil roll 26 has a plurality of protrusions 26a on its circumferential surface. The protrusions 26a are arranged regularly and intermittently at least in the circumferential direction of the anvil roll 26, in other words, along the rotational direction R. The ultrasonic bonding device 25 is equipped with an ultrasonic horn 25a. The ultrasonic bonding device 25 is installed so that the tip of the ultrasonic horn 25a, i.e., the surface to which ultrasonic vibration is applied, faces the circumferential surface of the anvil roll 26. Furthermore, the ultrasonic bonding device 25 is installed so that the tip of the ultrasonic horn 25a can move toward and away from the circumferential surface of the anvil roll 26.

[0051] In the sheet joining section 27, the superimposed composite sheet 2b and the second raw material sheet 3a are passed between a rotating anvil roll 26 and an ultrasonic horn 25a positioned opposite the circumferential surface of the anvil roll 26, and the two sheets 2b and 3a are joined together by ultrasonic vibrations from the ultrasonic horn 25a. In detail, the two overlapping sheets 2b and 3a are conveyed as the anvil roll 26 rotates, reaching a position where they face the ultrasonic horn 25a, and the two sheets 2b and 3a are joined (fused) together by the ultrasonic vibrations generated by the ultrasonic horn 25a. Since the joining of the two sheets 2b and 3a occurs when the ultrasonic horn 25a faces the convex portion 26a of the anvil roll 26, the formation pattern of the fused portion 10 in the expandable sheet 1 formed by the joining of the two sheets 2b and 3a matches the arrangement pattern of the convex portion 26a provided on the circumferential surface of the anvil roll 26. At this time, by adjusting the arrangement pattern of the convex portion 26a, a first fused portion 10a that overlaps with the elastic member 4 in a plan view, and a second fused portion 10b that does not overlap with the elastic member 4 can be formed in the expandable sheet 1.

[0052] The stretchable sheet obtained in this way is suitably used as an outer sheet for absorbent articles. The absorbent article using the stretchable sheet of the present invention generally has a longitudinal shape having a longitudinal direction corresponding to the direction extending from the wearer's ventral side through the crotch area to the dorsal side, and a width direction perpendicular thereto. The absorbent article has a crotch area that is positioned in the wearer's crotch area, and ventral and dorsal portions that extend in front of and behind it. The crotch area has an excretory area facing portion that is positioned opposite the wearer's excretory area when the absorbent article is worn, and this excretory area facing portion is usually located in or near the center of the longitudinal direction of the absorbent article.

[0053] Absorbent articles generally comprise a surface sheet located on the side facing the wearer's skin, a back sheet located on the side not facing the skin, and an absorbent material interposed between the two sheets. Furthermore, an outer covering is provided on the outer surface of the back sheet to form the shape of the absorbent article. The surface sheet can be a liquid-permeable sheet, such as a nonwoven fabric or a perforated film. The surface sheet may have an uneven surface on its skin-facing side. For example, multiple convex areas can be formed in a scattered pattern on the skin-facing side of the surface sheet. Alternatively, alternating ridges and grooves extending in one direction can be formed on the skin-facing side of the surface sheet. For such purposes, the surface sheet can also be formed using two or more nonwoven fabrics.

[0054] On the other hand, as the backing sheet, for example, a liquid-impermeable film or a spunbond-meltblown-spunbond laminated nonwoven fabric can be used. A liquid-impermeable film may be provided with multiple micropores to give the film water vapor permeability.

[0055] In addition to the surface sheet, back sheet, absorbent material, and outer casing described above, depending on the specific application of the absorbent article, leak-proof cuffs extending along the longitudinal direction may be provided on both sides along the longitudinal direction on the skin-facing side. Leak-proof cuffs generally have a base end and a free end. The leak-proof cuff has its base end on the skin-facing side of the absorbent article and stands upright from the skin-facing side. The leak-proof cuff is made of a material that is liquid-resistant or water-repellent and breathable. An elastic member made of elastic thread or the like may be provided in an extended state at or near the free end of the leak-proof cuff. When the absorbent article is worn, this elastic member contracts, causing the leak-proof cuff to stand upright toward the wearer's body, effectively preventing liquid discharged onto the surface sheet from leaking outward in the width direction of the absorbent article along the surface sheet.

[0056] The absorbent article may further have an adhesive layer on the non-skin-facing surface. The adhesive layer is used to secure the absorbent article to underwear or another absorbent article when it is worn.

[0057] Absorbent articles having the above configuration include, but are not limited to, unfoldable disposable diapers, pant-type disposable diapers, sanitary napkins, and incontinence pads.

[0058] In the absorbent article described above, the stretchable sheet 1 of the present invention is used as the outer covering. In this case, it is preferable that the stretchable sheet 1 is positioned so that the second sheet 3 faces the wearer's skin. This is because the second sheet 3 side does not have a joint 5 and has a pleated structure 30, making it highly flexible, and positioning the second sheet on the skin side improves the wearing comfort of the absorbent article. [Explanation of Symbols]

[0059] 1. Stretchable sheet 2. Sheet 1 3. Second seat 4 Elastic members 5 Joint 10 Fusion part

Claims

1. It comprises a first sheet, a second sheet, and a plurality of elastic members arranged to be expandable and contractible between the two sheets. The aforementioned plurality of elastic members are arranged so as to extend in one direction without intersecting each other, in an expandable sheet, The first sheet and the second sheet are intermittently fused together at multiple fusion points. The plurality of elastic members and the first sheet are joined together by a predetermined joining means. An expandable sheet in which the plurality of elastic members and the second sheet are fused together only at positions that overlap with the fused portions in a plan view of the expandable sheet.

2. In a plan view of the stretchable sheet, the multiple fused portions are arranged to form multiple rows of points extending in one direction. The aforementioned sequence of points is arranged at intervals along a direction perpendicular to the aforementioned one direction, The expandable sheet according to claim 1, wherein one or more of the elastic members are arranged between adjacent rows of points.

3. The stretchable sheet according to claim 1, wherein there is no other sheet between the first sheet and the second sheet.

4. The stretchable sheet according to claim 1, wherein, in a plan view, the maximum length of the fused portion along the extending direction of the elastic member and the maximum length of the fused portion along the direction perpendicular to that direction are each independently less than 3 mm.

5. In a plan view of the stretchable sheet, the multiple fused portions are arranged to form multiple rows of points extending in one direction. The aforementioned sequence of points is arranged at intervals along a direction perpendicular to the aforementioned one direction, The spacing between adjacent points is 3 mm or more. The stretchable sheet according to claim 1, wherein, when focusing on any one of the aforementioned sequences of points, the distance between adjacent fused portions among the fused portions constituting the sequence of points is 3 mm or more.

6. In a plan view of the stretchable sheet, the multiple fused portions are arranged to form multiple rows of points extending in one direction. The aforementioned sequence of points is arranged at intervals along a direction perpendicular to the aforementioned one direction, The stretchable sheet according to claim 1, wherein the number of the dot sequences is less than the number of the elastic members.

7. The expandable sheet according to claim 1, wherein, with respect to one of the elastic members, the joints between the elastic member and the first sheet are arranged intermittently.

8. Focusing on one of the aforementioned elastic members, the joint between the elastic member and the first sheet is continuously arranged along the entire length of the elastic member, as described in claim 1, for the stretchable sheet.

9. In a plan view of the stretchable sheet, the multiple fused portions are arranged to form multiple rows of points extending in one direction. The aforementioned sequence of points is arranged at intervals along a direction perpendicular to the aforementioned one direction, The stretchable sheet according to claim 1, wherein in the natural state of the stretchable sheet, the second sheet has a pleated structure consisting of a plurality of recessed portions extending in a direction perpendicular to the one direction, with the fused portion included at the bottom, and hollow convex portions located between the recessed portions.

10. The stretchable sheet according to claim 1, wherein the outer surface of the first sheet is flat in its natural state.

11. The stretchable sheet according to claim 1, which does not contain an adhesive.

12. The exterior sheet is made of the expandable sheet described in any one of claims 1 to 11. An absorbent item in which the second sheet is positioned to face the wearer's skin.

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