Expandable sheet for absorbent articles and method for manufacturing the same, and raw material nonwoven fabric

Abstract

To provide: a stretchable sheet which exhibits a good appearance and satisfies both of high stretchability and high air permeability; and a production method thereof.SOLUTION: Provided is a production method of a stretchable sheet for absorbent article, comprising: a step of contacting elastic filaments in a fusible state with a nonwoven cloth to form a laminate formed by fusion of the elastic filaments to the nonwoven cloth; and stretching the laminate to provide the same with a treatment for stretchability manifestation. As the nonwoven fabric, there is used one having maximum strength of 40 N / 50 mm or less under a condition of a strain rate of 3.3 s-1. In the treatment step for stretchability manifestation, the laminate is stretched at a strain rate of 30 s-1 to 200 s-1.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a stretchable sheet and a method for manufacturing the same.

Background Art

[0002] As a conventional technique related to a stretchable sheet formed by laminating elastic fibers and a non-woven fabric, the applicant has previously proposed a stretchable sheet in which a large number of elastic filaments arranged so as to extend in one direction without crossing each other are joined to a stretchable non-woven fabric in a substantially non-extended state over their entire lengths (see Patent Document 1). This stretchable sheet is manufactured by subjecting a composite body in which elastic filaments are fused to a non-woven fabric to a stretching process to impart stretchability to the composite body.

Prior Art Documents

Patent Documents

[0003] <00000�0>

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The stretchable sheet manufactured by the method described in Patent Document 1 maintains air permeability, has excellent stretchability, and has practically sufficient strength. By the way, a higher air permeability is required for this type of stretchable sheet. However, if the stretching ratio in the stretching process is set high or the processing speed is increased in order to improve the air permeability of the stretchable sheet described in the same document, the elastic filaments are likely to be cut. The occurrence of cutting in the elastic filaments contributes to a decrease in the stretchability of the stretchable sheet and a decrease in the quality of the appearance. <XXXXX091>Therefore, an object of the present invention is to provide a stretchable sheet and a method for manufacturing the same that can solve the drawbacks of the conventional techniques described above.

Means for Solving the Problems

[0005] The present invention includes a step of bringing a fusible elastic filament into contact with a nonwoven fabric to form a laminate in which the elastic filament is fused to the nonwoven fabric, and a step of stretching the laminate to perform an elastic expression treatment, and is a method for manufacturing a stretch sheet for absorbent articles, wherein, as the nonwoven fabric, one having a maximum strength of 40 N / 50 mm or less under the condition of a strain rate of 3.3 s , , ,

[0007] , -1 , 2 , , is used, and in the elastic expression treatment step, the laminate is stretched at a strain rate of 30 s -1 or more and 200 s -1 or less, thereby providing a method for manufacturing a stretch sheet for absorbent articles.

[0006] Further, the present invention includes a step of bringing a fusible elastic filament into contact with a nonwoven fabric to form a laminate in which the elastic filament is fused to the nonwoven fabric, and a step of stretching the laminate to perform an elastic expression treatment, and is a method for manufacturing a stretch sheet for absorbent articles, wherein, as the nonwoven fabric, one having a strength at 5% elongation of less than 12 N / 50 mm is used, and in the elastic expression treatment step, the laminate is stretched at a strain rate of 30 s -1 or more and 200 s -1 or less, thereby providing a method for manufacturing a stretch sheet for absorbent articles. <​​​​​​​​​A high-elongation region and a low-elongation region extending in a direction orthogonal to the stretching direction of the stretch sheet are alternately arranged along the stretching direction, and the width W of the low-elongation region along the stretching direction at 2.2-fold elongation L with respect to the width W of the high-elongation region along the stretching direction H of the ratio W H / W L is 10 or less, and a stretch sheet for absorbent articles is provided.

Advantages of the Invention

[0008] According to the present invention, there are provided a stretch sheet having a good appearance and having high stretchability and high air permeability, and a method for manufacturing the same.

Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a partially broken perspective view showing an embodiment of the stretch sheet of the present invention. [Figure 2] FIGS. 2(a) and 2(b) are longitudinal sectional views in a natural state and an extended state along the direction in which the elastic filament extends in the stretch sheet shown in FIG. 1, respectively. [Figure 3] FIG. 3 is a schematic view showing an apparatus suitably used for manufacturing the stretch sheet of the present invention. [Figure 4] FIG. 4 is an explanatory view showing a method for calculating the strain rate in the manufacture of the stretch sheet of the present invention.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described based on its preferred embodiments. The present invention relates to a stretch sheet for absorbent articles. In the present specification, absorbent articles widely include articles used for absorbing and holding body fluids excreted from the human body. For example, diapers, incontinence pads used for absorbing and holding urine and feces, menstrual pads used for absorbing and holding menstrual blood, breast pads used for absorbing and holding breast milk, etc. are included, but are not limited thereto.

[0011] The stretchable sheet of the present invention can be applied to various parts of absorbent articles where elasticity is required. For example, the stretchable sheet of the present invention can be applied to the outer casing that constitutes the outer surface of an absorbent article, the leak-proof cuffs placed on both sides of the absorbent article, the waist gathers that constitute the waist opening area of ​​an absorbent article, and the leg gathers that constitute the leg opening area of ​​an absorbent article. Absorbent articles to which the stretchable sheet of the present invention is applied to these parts will have a good fit to the wearer's body due to the elasticity of the stretchable sheet, and will be less prone to stuffiness when worn due to the breathability of the stretchable sheet.

[0012] The stretchable sheet of the present invention comprises an elastic filament and a nonwoven fabric. In this specification, elasticity and stretchability refer to the property of being able to be stretched and returning to a length of 125% or less of the original length when the force is released from a state where it is stretched to 100% of its original length (becoming 200% of its original length).

[0013] The stretchable sheet of the present invention may, for example, have one nonwoven fabric and a plurality of elastic filaments arranged on one surface of the nonwoven fabric. Alternatively, the stretchable sheet of the present invention may have two nonwoven fabrics and a plurality of elastic filaments arranged between the two nonwoven fabrics. Each elastic filament is bonded to the nonwoven fabric. When the elastic filament is arranged between two nonwoven fabrics, each elastic filament is bonded to at least one of the nonwoven fabrics, or to both nonwoven fabrics. Furthermore, when the elastic filament is arranged between two nonwoven fabrics, the two nonwoven fabrics may be of the same type or of different types. In this specification, "same type of nonwoven fabric" means nonwoven fabrics in which the manufacturing process, the type of constituent fibers, the fiber diameter and length of the constituent fibers, the thickness and basis weight of the nonwoven fabric, etc., are all the same. If at least one of these is different, they are said to be different types of nonwoven fabrics.

[0014] Fusion bonding is preferred as the method of joining the elastic filament and the nonwoven fabric. By joining the two by fusion bonding, the stretchable sheet can be made flexible and highly stretchable. If, for example, an adhesive is used to join the two, the stretchable sheet tends to feel stiff due to the solidification of the adhesive. In addition, the stretching and contracting of the elastic filament tends to be inhibited by the adhesive.

[0015] The stretchable sheet is designed to stretch in the same direction as the elastic filaments. The stretchability of the stretchable sheet is due to the elasticity of the elastic filaments. When the stretchable sheet is stretched in the same direction as the elastic filaments, the elastic filaments and nonwoven fabric stretch. When the stretching of the stretchable sheet is released, the elastic filaments contract, and the nonwoven fabric returns to its pre-stretch state as it contracts.

[0016] An elastic filament has a thread-like form with thickness and length. The length of an elastic filament is extremely large relative to its thickness; for example, the length of an elastic filament can be 500 times or more, and especially 1000 times or more, relative to its thickness.

[0017] Preferably, each elastic filament is substantially continuous along the entire length of the stretchable sheet. The elastic filaments contain an elastic resin. Each elastic filament is arranged to extend in one direction. Each elastic filament may extend linearly or meander. Preferably, each elastic filament is arranged to extend in one direction without intersecting each other. However, intersecting elastic filaments are not prevented. For example, unintentional intersecting of elastic filaments due to unavoidable fluctuations in the manufacturing conditions of the stretchable sheet is permissible.

[0018] The direction in which the elastic filaments extend may coincide with the machine direction during the manufacturing of the nonwoven fabric, or it may be perpendicular to the machine direction during the manufacturing of the nonwoven fabric. When a stretchable sheet is manufactured according to a preferred manufacturing method described later, the direction in which the elastic filaments extend coincides with the machine direction during the manufacturing of the nonwoven fabric.

[0019] The basis weight of the elastic filament is 4 g / m², considering its stretchability, texture, thickness, and cost. 2 More than 30g / m 2 Below, especially 6g / m 2 More than 15g / m 2 The following is preferable. The thickness, number, and spacing of the elastic filaments can be appropriately set according to the basis weight of the elastic filaments. For example, the diameter of the elastic filaments can be set to 30 μm or more and 200 μm or less, and particularly to 50 μm or more and 130 μm or less. When the elastic filaments are arranged in a state aligned in one direction, as shown in Figure 1 described later, the pitch of adjacent elastic filaments (distance between the centers of adjacent elastic filaments) can be set to 0.1 mm or more and 5 mm or less, and particularly to 0.3 mm or more and 1.8 mm or less.

[0020] It is preferable that the elastic filament is bonded to the nonwoven fabric in a substantially unstretched state. Bonding the elastic filament to the nonwoven fabric in an unstretched state has the advantage that relaxation (creep) due to stretching does not occur, and the elasticity is less likely to decrease. Furthermore, for example, if the elastic filament is stretched to twice its original length and bonded to the nonwoven fabric, and it is assumed that it will shrink to 1.3 times its initial length, it can only be stretched to 1.54 times from this state. However, if the elastic filament and nonwoven fabric are bonded in an unstretched state, the initial origin when the stretchable sheet is stretched is different, which has the advantage that it can be stretched to the stretchable length of the nonwoven fabric or to the maximum elongation of the elastic filament.

[0021] Examples of elastic resins that constitute elastic filaments include natural rubber, EVA rubber, synthetic rubbers such as styrene-butadiene rubber, butadiene rubber, isoprene rubber, and neoprene rubber, polyurethane, and thermoplastic elastomers. These elastic resins can be used individually or in combination of two or more.

[0022] In particular, using a thermoplastic elastomer as the elastic resin is preferable because it easily exhibits the desired elasticity. Furthermore, thermoplastic elastomers can be melt-spun using an extruder, just like ordinary thermoplastic resins, and the elastic filaments obtained in this way are easily fused, making them suitable for the manufacturing method described later.

[0023] Examples of thermoplastic elastomers include styrene-based elastomers such as SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene), SEBS (styrene-ethylene-butadiene-styrene), and SEPS (styrene-ethylene-propylene-styrene); olefin-based elastomers such as ethylene-based α-olefin elastomers and propylene-based elastomers copolymerized with ethylene-butene-octene, etc.; polyester-based elastomers; and polyurethane-based elastomers.

[0024] The nonwoven fabric to which the elastic filaments are joined is stretchable. More specifically, the nonwoven fabric is stretchable in the same direction as the stretching of the elastic filaments. Stretchability includes (a) cases where the constituent fibers of the nonwoven fabric themselves stretch, and (b) cases where, even if the constituent fibers themselves do not stretch, the nonwoven fabric as a whole stretches due to the separation of fibers that were joined at intersections, structural changes in the three-dimensional structure formed by multiple fibers due to bonding between fibers, etc., or due to the tearing of constituent fibers or the stretching of loose fibers.

[0025] Nonwoven fabrics may be stretchable in their raw state before being bonded with elastic filaments. Alternatively, nonwoven fabrics may not be stretchable in their raw state before being bonded with elastic filaments, but may become stretchable after being processed to do so. Specific methods for making nonwoven fabrics stretchable include heat treatment, stretching between rolls, stretching by gripping with teeth or gears, and tensile stretching with a tenter. Considering the preferred manufacturing method for stretchable sheets described later, it is preferable that nonwoven fabrics are not stretchable in their raw state, as this improves the transportability of the nonwoven fabric when the elastic filaments are fused to it.

[0026] In addition to being stretchable as described above, nonwoven fabrics are preferably substantially inelastic. For this purpose, it is preferable that the nonwoven fabric contains inelastic fibers and not elastic fibers. In this specification, inelastic means a property that does not conform to the definition of elasticity described above.

[0027] Non-elastic fibers that make up nonwoven fabrics include polyethylene (PE), polypropylene (PP), polyester (PET and PBT), polyamide, and the like. The fibers that make up the nonwoven fabric may be short fibers or long fibers, and may be hydrophilic or hydrophobic. In addition, core-sheath type or side-by-side composite fibers, split fibers, irregular cross-section fibers, crimped fibers, heat-shrinkable fibers, etc., can also be used. These fibers can be used individually or in combination of two or more types. The nonwoven fabric may be a continuous filament or short fiber nonwoven fabric. The basis weight of the nonwoven fabric is 3 g / m², considering factors such as texture, thickness, and design. 2 More than 100g / m 2 The following, in particular, 5g / m 2 More than 30g / m 2 The following is preferable:

[0028] Figure 1 shows one embodiment of a stretchable sheet. Figures 2(a) and (b) show cross-sectional views in the thickness direction of the stretchable sheet shown in Figure 1. Figures 2(a) and (b) are cross-sectional views along the direction in which the elastic filaments in the stretchable sheet extend. The stretchable sheet 10 of the embodiment shown in Figure 1 is composed of a total of two nonwoven fabrics, a first nonwoven fabric 11 and a second nonwoven fabric 12, and a plurality of elastic filaments 13 sandwiched between the two nonwoven fabrics. Each elastic filament 13 is arranged to extend in one direction without intersecting each other.

[0029] Figure 2(a) is a cross-sectional view of the expandable sheet 10 in its natural state (relaxed state), and Figure 2(b) is a cross-sectional view of the expandable sheet 10 in its stretched state. In its natural state, the expandable sheet 10 has a corrugated shape with alternating peaks 14' and valleys 14''. The peaks 14' and valleys 14'' are connected via ridges 15'. When the expandable sheet 10 is viewed from above, the peaks 14', ridges 15', and valleys 14'' extend in directions perpendicular to the expansion and contraction direction of the expandable sheet 10.

[0030] On the other hand, in the stretched state, the stretchable sheet 10 has alternating low-density regions 14 and high-density regions 15 arranged along the direction in which the elastic filaments 13 extend. Each region 14 and 15 extends in a strip-like shape in a direction perpendicular to the direction in which the elastic filaments 13 extend, that is, the stretching direction of the stretchable sheet 10. The low-density regions 14 and high-density regions 15 are arranged alternately at a constant period. The low-density regions 14 are arranged alternately with those protruding to the upper side of the stretchable sheet 10 and those protruding to the lower side of the stretchable sheet 10. The low-density regions 14 protruding to the upper side of the stretchable sheet 10 originate from the apex 14' of the stretchable sheet 10 in its natural state as shown in Figure 2(a). On the other hand, the low-density regions 14 protruding to the lower side of the stretchable sheet 10 originate from the valley 14'' of the stretchable sheet 10 in its natural state as shown in Figure 2(a). The high-density regions 15 originate from the ridge 15' of the stretchable sheet 10 in its natural state as shown in Figure 2(a).

[0031] As is clear from the comparison between Figure 2(a) and Figure 2(b), the parts that primarily stretch when the stretchable sheet 10 is stretched are the peak 14' and valley 14'' in Figure 2(a), and the low-density region 14 in Figure 2(b). In other words, the ridge 15' in Figure 2(a) (i.e., the high-density region 15 in Figure 2(b)) does not stretch significantly even when the stretchable sheet 10 is stretched. Thus, the stretchable sheet 10 has high-stretch regions and low-stretch regions that extend in a direction perpendicular to the stretching direction, which are alternately arranged along the stretching direction. The high-stretch regions are the peak 14' and valley 14'' in Figure 2(a), and the low-density region 14 in Figure 2(b). The low-stretch regions are the ridge 15' in Figure 2(a), and the high-density region 15 in Figure 2(b). To form high-elongation and low-elongation regions in the stretchable sheet 10, the stretchable sheet 10 can be manufactured, for example, by the method described later.

[0032] As described above, the high-elongation region in the stretchable sheet 10 is the low-density region 14, and the low-elongation region is the high-density region 15. Therefore, when the stretchable sheet 10 is stretched, the air permeability of the high-elongation region, which is the low-density region 14, is higher than that of the low-elongation region, which is the high-density region 15. Increasing the stretching speed is also an effective way to further improve air permeability. When the stretching speed is high, the nonwoven fabric is subjected to a large amount of stretch locally, resulting in higher air permeability. Conversely, when the stretching speed is low, the nonwoven fabric is stretched as a whole, and the amount of stretch in local areas becomes smaller. In other words, the width W of the high-elongation region H and width W of the low-elongation region L The ratio of widths decreases as the stretching speed increases. From this perspective, the width W of the low-stretch region along the stretching direction when the stretchable sheet 10 is stretched 2.2 times is considered. L The width W of the highly elongated region along the direction of expansion and contraction. H W is the ratio of H / W L Setting the value of 10 or less is preferable from the viewpoint of achieving both breathability and elasticity of the stretchable sheet 10. From the viewpoint of making this advantage even more pronounced, W H / W LThe value of is more preferably 6.5 or less, and even more preferably 6.3 or less. Also, W H / W L From the viewpoint of providing sufficient elasticity to the stretchable sheet 10, the value of is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. Width W of the low-elongation region L and the width W of the high-elongation region H The measurement method will be explained in the examples described later.

[0033] In this specification, the low-elongation region is the region in which, when an expandable sheet is stretched 50% along its stretching direction, the rate of change in strain before and after stretching is less than 10%. The high-elongation region is the region in which the rate of change in strain is 10% or more.

[0034] Width W of the low-elongation region L and the width W of the high-elongation region H By appropriately selecting the material, the breathability of the stretchable sheet 10 is increased. Specifically, the breathability value measured in accordance with JIS P8117 is 900 cc / cm². 2 It is preferable that it be 1000 cc / cm³ or more. 2 It is even more preferable that it be 1100 cc / (cm³) or more. 2 It is even more preferable that it be 2000 sec or longer.

[0035] Next, a preferred method for manufacturing the expandable sheet of the present invention will be explained using the manufacturing method of the expandable sheet 10 shown in Figures 2(a) and 2(b) as an example, with reference to Figure 3. In this manufacturing method, as shown in Figure 3, a plurality of fused elastic filaments 13 spun from a spinning nozzle 16 are taken up at a predetermined speed and stretched. Before the elastic filaments 13 solidify, the elastic filaments 13 are brought into contact with the two raw material nonwoven fabrics 11' and 12' so that the elastic filaments 13 do not intersect with each other and are arranged in one direction, thereby forming a laminate 19 in which the elastic filaments 13 are fused to the two raw material nonwoven fabrics 11' and 12'. Next, the laminate 19 is subjected to an elasticity-developing treatment that stretches it along the direction in which the elastic filaments 13 extend, thereby imparting elasticity to the laminate 19.

[0036] The spinning nozzle 16 is provided on the spinning head 17. The spinning head 17 is connected to an extruder. 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 of the first and second raw nonwoven fabrics 11', 12'. The spacing between adjacent spinning nozzles 16 corresponds to the spacing of the elastic filaments 13 in the target stretchable sheet 10. The spinning nozzles 16 are usually circular, and their diameter affects the diameter and stretch ratio of the elastic filaments 13. 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 two raw nonwoven fabrics 11' and 12', improving the spinnability of the elastic filament 13, and improving the stretchability of the stretchable sheet 10, the elastic filament 13 can also be made into a composite form (side-by-side, core-sheath, sea-island structure).

[0037] The molten elastic filament 13 that is spun merges with the first nonwoven fabric roll 11' and the second nonwoven fabric roll 12', which are fed out from the raw material roll at the same speed, and is sandwiched between the two nonwoven fabric rolls 11' and 12' and taken up at a predetermined speed. The take-up speed of the elastic filament 13 matches the feeding speed of the two nonwoven fabric rolls 11' and 12'. The first nonwoven fabric roll 11' and the second nonwoven fabric roll 12' are stretched by the elasticity-developing processing device 22, which will be described later, to become the first nonwoven fabric 11 and the second nonwoven fabric 12 in the target stretchable sheet 10. The transport direction of the first nonwoven fabric roll 11' and the second nonwoven fabric roll 12' matches the machine direction during the manufacturing of these two nonwoven fabric rolls 11' and 12'.

[0038] The elastic filament 13 merges with the first and second nonwoven fabrics 11', 12' before solidification, i.e., while in a fusion-ready state. As a result, the elastic filament 13 fuses to the first and second nonwoven fabrics 11', 12' while being sandwiched between them. In other words, the elastic filament 13 is taken up and stretched while fusing to the two nonwoven fabrics 11', 12' as they are being transported. No external heat is applied to the first and second nonwoven fabrics 11', 12' during the fusion of the elastic filament 13. That is, the elastic filament 13 fuses to the two nonwoven fabrics 11', 12' solely by the heat of melt generated by the fusion-ready elastic filament 13. As a result, among the constituent fibers of the two raw nonwoven fabrics 11' and 12', only the fibers located around the elastic filament 13 fuse with the elastic filament, while fibers located further away do not fuse. Consequently, the heat applied to the two raw nonwoven fabrics 11' and 12' is kept to a minimum, thus maintaining the inherent good texture of the nonwoven fabric itself. This results in a good texture for the resulting stretchable sheet 10.

[0039] When the elastic filament 13 is joined to the two nonwoven fabrics 11' and 12', the elastic filament 13 is substantially in an unstretched state (a state in which it does not shrink when the external force is removed). In the joined state, the fibers constituting the two nonwoven fabrics 11' and 12' and the elastic filament 13 are fused together at least in part. In the above state, it is preferable that the two nonwoven fabrics 11' and 12' are fused together while sandwiching the elastic filament 13.

[0040] In this way, a laminate 19 is obtained in which elastic filaments 13 are sandwiched between two nonwoven fabrics 11' and 12'. If nonwoven fabrics 11' and 12' are inherently stretchable, this laminate 19 becomes the stretchable sheet 10 itself. On the other hand, if nonwoven fabrics 11' and 12' are not inherently stretchable, the laminate 19 containing the nonwoven fabrics 11' and 12' is subjected to an elasticity-developing treatment along the direction in which the elastic filaments 13 extend, thereby imparting elasticity to the laminate 19. In this manufacturing method, this operation is performed using an elasticity-developing processing device 22 equipped with a pair of tooth groove rolls 20 and 21, each with teeth and tooth roots alternately formed in the circumferential direction, to perform the elasticity-developing treatment on the laminate 19 along its transport direction, i.e., the direction in which the elastic filaments 13 extend.

[0041] The elasticity-developing processing device 22 has a known lifting mechanism (not shown) that displaces the pivot points of one or both of the grooved rolls 20 and 21 vertically, and the distance between the grooved rolls 20 and 21 is adjustable. In this manufacturing method, the grooved rolls 20 and 21 are combined such that the teeth of one grooved roll 20 are loosely inserted between the teeth of the other grooved roll 21, and the teeth of the other grooved roll 21 are loosely inserted between the teeth of one grooved roll 20, and the laminate 19 is inserted between the two grooved rolls 20 and 21 in this state and subjected to elasticity-developing processing.

[0042] The laminate 19 is subjected to elasticity-developing treatment by a pair of grooved rolls 20 and 21 to obtain the desired expandable sheet 10. After passing through the grooved rolls 20 and 21, the expandedable sheet 10 is quickly released from its stretched state in the transport direction by its own shrinkage recovery force. As a result, the expandable sheet 10 largely returns to its original length in the transport direction. Consequently, in the stretched state, high-elongation regions and low-elongation regions are arranged alternately in the direction in which the elastic filaments 13 extend.

[0043] As a result of various studies on elasticity development treatment, the inventors found that, depending on the conditions of the elasticity development treatment, the elastic filaments 13 may be unintentionally cut while the laminate 19 is being stretched. Cutting of the elastic filaments 13 is an event that should be avoided as much as possible, as it can impair the elasticity and appearance of the target stretchable sheet 10. As a result of studies conducted by the inventors to avoid this inconvenience, it was found that controlling the strain rate of the laminate 19 during the elasticity development treatment process is effective in successfully stretching the laminate 19 without unintentional cutting of the elastic filaments 13. The strain rate is the value obtained by dividing the amount of deformation per unit time by the original length, and its unit is s. -1 Therefore, as a result of the inventor's investigation, in the elasticity development process, the strain rate of the laminate 19 is set to 200 s -1 The following settings are preferable because they effectively suppress unintended cutting of the elastic filaments 13. From this perspective, the strain rate of the laminate 19 is set to 180s. -1 It is even more preferable to set it as follows: 150s -1 It is even more preferable to set it as follows. A smaller strain rate is desirable from the viewpoint of preventing breakage of the elastic filaments 13, but on the other hand, in order to further improve breathability, it is necessary to increase the strain rate and apply a large localized stretch to the nonwoven fabric. In order to apply a large localized stretch to the nonwoven fabric, 30s -1 The strain rate needs to be set as described above. From this perspective, the strain rate of the laminate 19 in the elastic development process is 30s. -1 More than 200s -1 The following is preferable: 50s -1 Above 180s -1It is even more preferable that the following apply: 80s -1 More than 150s -1 The following is even more preferable.

[0044] The calculation of the strain rate in the elastic development process using a pair of grooved rolls 20 and 21 is performed by the method described in paragraph

[0051] and Figure 3 of Japanese Patent Publication No. 2016-151076. Specifically, L is the arc length from the point where the nonwoven fabric and the roll protrusion begin to come into contact to the point where the nonwoven fabric intersects with a virtual straight line connecting the centers of the two rolls. The deformation time T is obtained by dividing the arc length L by the peripheral speed Vc of the roll. Next, with the grooved rolls 20 and 21 meshed, as shown in Figure 4, the maximum stretch ratio of the nonwoven fabric between the top land surface edge 20D of the protrusion 20A and the top land surface edge 21D of the opposite protrusion 21A is defined as the maximum stretch ratio. The maximum stretch ratio is calculated assuming no slippage of the nonwoven fabric, and assuming that the protrusion 21A is at the center L of the recess 20B. C Assuming the position is as shown, the distance between the top land edge 20D of the convex portion 20A and the top land edge 21D of the convex portion 21A is calculated by dividing the distance by the original nonwoven fabric length. The strain rate is calculated as deformation rate / T = Vc / Vi * maximum stretch ratio (times) / T, where Vi is the feed rate of the nonwoven fabric. In Figure 4, each edge 20D, 20E, 21D, and 21E are edges in the tooth width direction, and their positions are indicated by black circles for clarity.

[0045] The inventors further investigated the phenomenon of elastic filament breakage when the laminate 19 is subjected to elasticity-developing treatment. They found that the stress applied to the two-layer nonwoven fabrics 11',12' during the stretching of the laminate 19 is transmitted to the elastic filament 13 via the fusion points between the elastic filament 13 and the two-layer nonwoven fabrics 11',12'. Therefore, by reducing the stress applied to the two-layer nonwoven fabrics 11',12' during the stretching of the laminate 19, the stress transmitted to the elastic filament 13 can be reduced. From this viewpoint, it is advantageous to use two-layer nonwoven fabrics 11',12' with a low maximum strength before fracture. From this viewpoint, it is preferable to use two-layer nonwoven fabrics 11',12' with a maximum strength of 40 N / 50 mm or less, more preferably 35 N / 50 mm or less, and even more preferably 30 N / 50 mm or less. The lower the maximum strength value, the more effective it is in preventing the elastic filament 13 from cutting. However, if the maximum strength is as low as 5N / 50mm, the cutting of the elastic filament 13 can be effectively prevented. From this viewpoint, it is preferable to use nonwoven fabrics 11' and 12' with a maximum strength of 5N / 50mm or more and 40N / 50mm or less, more preferably 10N / 50mm or more and 35N / 50mm or less, and even more preferably 15N / 50mm or more and 30N / 50mm or less. The aforementioned maximum intensity is achieved at a strain rate of 3.3 s. -1 The measurements were taken under these conditions. The reason for measuring the maximum strength at this strain rate is that the inventors have found that the elastic filament 13 is more likely to break when the strain rate is high. The maximum strength is measured on a rectangular test specimen with a length of 50 mm along the stretch direction of the stretchable sheet 10 and a length of 50 mm perpendicular to that direction. The distance between the chucks of the tensile testing machine is set to 5 mm, and the strain rate is 3.3 s. -1 Set it to [this setting] and take the measurement.

[0046] In order to effectively prevent the elastic filaments 13 from being cut when the laminate 19 is subjected to elasticity-developing treatment, as described above, it is advantageous to use nonwoven fabrics 11' and 12' with low maximum strength before breakage. In other words, it is advantageous to use nonwoven fabrics 11' and 12' with high elongation. From this viewpoint, it is preferable to use nonwoven fabrics 11' and 12' with a maximum elongation in the machine direction of 100% or more, more preferably 120% or more, and even more preferably 130% or more. The higher the value of the maximum elongation, the more effective it is in preventing the nonwoven fabric from cutting, but if the maximum elongation is as high as 250%, the cutting of the nonwoven fabric can be effectively prevented. From this perspective, it is preferable to use nonwoven fabrics 11' and 12' with a maximum elongation of 100% or more and 250% or less, more preferable to use those with a maximum elongation of 120% or more and 250% or less, and even more preferable to use those with a maximum elongation of 130% or more and 250% or less. The aforementioned maximum elongation is achieved at a strain rate of 0.03 s. -1 The measurements were taken under the following conditions. Maximum elongation is measured on a rectangular test specimen with a length of 200 mm along the expansion direction of the stretchable sheet 10 and a length of 50 mm perpendicular to that direction. The chuck distance of the tensile testing machine is set to 150 mm, and the strain rate is 0.03 s. -1 Set it to [this setting] and take the measurement.

[0047] In order to effectively prevent the elastic filaments 13 from being cut when the laminate 19 is subjected to elasticity-developing treatment, the inventors' research has shown that it is also effective to use nonwoven fabrics 11' and 12' with low initial tensile strength. From this viewpoint, it is preferable to use nonwoven fabrics 11' and 12' with a strength of less than 12 N / 50 mm at 5% elongation, more preferably 11 N / 50 mm or less, and even more preferably 10 N / 50 mm or less. The lower the strength value at 5% elongation, the more effective it is in preventing the elastic filaments 13 from being cut, but a strength of around 3 N / 50 mm is sufficient to effectively prevent the elastic filaments 13 from being cut. From this perspective, it is preferable to use nonwoven fabrics 11' and 12' with a strength of 3N / 50mm or more and less than 12N / 50mm at 5% elongation, more preferably 3N / 50mm or more and 11N / 50mm or less, and even more preferably 3N / 50mm or more and 10N / 50mm or less. The strength at 5% elongation is calculated at a strain rate of 0.03 s. -1 The measurements were taken under the following conditions. The strength at 5% elongation was measured on a rectangular test specimen with a length of 200 mm along the direction of elongation of the stretchable sheet 10 and a length of 50 mm perpendicular to that direction. The distance between the chucks of the tensile testing machine was set to 150 mm, and the strain rate was 0.03 s. -1 Set it to [this setting] and take the measurement.

[0048] As described above, in order to effectively prevent the elastic filaments 13 from being cut when the laminate 19 is subjected to elasticity-developing treatment, it is advantageous to use nonwoven fabrics 11' and 12' made of highly extensible fibers as the base nonwoven fabrics. For example, nonwoven fabrics made of undrawn fibers or fibers with a low draw ratio can be used. There are no particular restrictions on the type of nonwoven fabric, and those manufactured by known methods can be used. For example, air-through nonwoven fabrics, spunbond nonwoven fabrics, spunlace nonwoven fabrics, meltblown nonwoven fabrics, needle-punched nonwoven fabrics, etc. can be used.

[0049] The stretchable sheet obtained in this manner exhibits suppressed breakage of elastic filaments during the elasticity development treatment, resulting in fewer breakage points of the elastic filaments in the stretchable sheet. Specifically, in the non-stretched state of the stretchable sheet, i.e., the natural state in which no external force is applied to the stretchable sheet, the number of breakage points of the elastic filaments is preferably 2.0 points / cm. 2 More preferably, 1.0 location / cm 2 Further preferably, 0.8 locations / cm 2 The number is as small as follows:

[0050] As described above, the stretchable sheet of the present invention exhibits good elasticity due to the small number of breaks in the elastic filaments. Specifically, the stretchable sheet of the present invention exhibits a high elongation rate, preferably 120% or more, more preferably 130% or more, and even more preferably 150% or more, while also showing high recovery strength when returned to its original state from the stretched state. This elongation rate is the value at a load of 3N / 50mm. The specific measurement method is as follows: The measurement is performed on a rectangular test piece with a length of 200mm along the stretching direction of the stretchable sheet 10 and a length of 50mm perpendicular to that direction. The distance between the chucks of the tensile testing machine is set to 150mm, and the strain rate is 0.03s. -1 Set the value to 3N / 50mm. The elongation when the strength of the test specimen is 3N / 50mm is defined as the elongation rate. [Examples]

[0051] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0052] [Example 1] (1) Preparation of elastic filaments SEPS was used as the elastic filament.

[0053] (2) Preparation of raw material nonwoven fabric Basis weight: 18 g / m² 2Two sheets of spunbond nonwoven fabric made of polypropylene fibers were prepared. The specifications of the raw nonwoven fabric are shown in Table 1 below.

[0054] (3) Manufacturing of stretchable sheets Using the apparatus shown in Figure 3, stretchable sheets with the structures shown in Figures 1, 2(a), and 2(b) were manufactured. The diameter of the elastic filament 13 was 120 μm. The elasticity-developing treatment was performed using an elasticity-developing treatment apparatus 22 equipped with a pair of tooth groove rolls 20, 21 in which teeth and tooth roots are alternately formed in the axial direction. By adjusting the amount of pressure applied by the upper and lower tooth groove rolls, the laminate 19 was subjected to elasticity-developing treatment in the direction of the elongation of the elastic filaments 13 at a stretching ratio of 6.6 times. The strain rate at this time is shown in Table 1. As a result, an expandable sheet 10 that expands and contracts in the direction of the elongation of the elastic filaments 13 was obtained.

[0055] [Examples 2 and 3] The nonwoven fabrics shown in Table 1 were used as the raw material. A stretchable sheet was obtained in the same manner as in Example 1, except for the use of these materials.

[0056] [Comparative Example 1] The nonwoven fabrics shown in Table 1 were used as the raw material. The strain rate was also set as shown in the same table. Except for these factors, the stretchable sheet was obtained in the same manner as in Example 1.

[0057] [Comparative Example 2] In Comparative Example 1, the strain rate was as shown in Table 1. Otherwise, the stretchable sheet was obtained in the same manner as in Comparative Example 1.

[0058] 〔evaluation〕 For the stretchable sheets obtained in the examples and comparative examples, the cutting points of the elastic filaments and the width W of the high-elongation region were measured. H and width W of the low-elongation region L The following measurements were taken. Furthermore, the air permeability was measured using the method described above. The results are shown in Table 1.

[0059] [Cutting point of the elastic filament] With the stretchable sheet stretched to 2.2 times its original length, the elastic filaments were observed using a magnifying glass across an area measuring 5 cm wide by 15 cm long, and the number of breaks in the elastic filaments was counted. The total number of breaks was divided by the measured area (5 × 15 cm²) to calculate the value.

[0060] [Width W of the high-elongation region] H and width W of the low-elongation region L ] A stretchable sheet was stretched 2.2 times in its stretching direction, and photographs were taken at a magnification of 30x. Ten locations were arbitrarily selected in both the high-stretch and low-stretch regions, and the width along the stretching direction was measured. The arithmetic mean of the 10 measurement results was used to determine the width W of the high-stretch region. H and width W of the low-elongation region L That's what I decided.

[0061] [Table 1]

[0062] As is clear from the results shown in Table 1, the stretchable sheets obtained in each example exhibit less elastic filament breakage and higher stretchability compared to the stretchable sheet obtained in the comparative example. Furthermore, the stretchable sheets obtained in the examples exhibit superior breathability compared to the stretchable sheet obtained in the comparative example. [Explanation of symbols]

[0063] 10 Stretchable Sheets 11. First nonwoven fabric 11' First raw material nonwoven fabric 12. Second nonwoven fabric 12' Second raw material nonwoven fabric 13 Elastic filaments 14 Low density region 14' top 14” Tanibe 15 High density area 15' Ridge section

Claims

1. A step of bringing a spunbond nonwoven fabric made of polypropylene fibers into contact with a fusionable elastic filament to form a laminate in which the elastic filament is fused to the spunbond nonwoven fabric in a substantially unstretched state in a molten state before solidification, as spun from a spinning nozzle; A method for manufacturing an expandable sheet for absorbent articles, comprising the steps of stretching the laminate and subjecting it to an elasticity-developing treatment, As the spunbond nonwoven fabric mentioned above, Distortion speed: 3.3s －１ The maximum strength under these conditions is 40 N / 50 mm or less. Under the condition of a strain rate of 0.03 s⁻¹, the maximum elongation in the mechanical direction is between 100% and 250%. Under the condition of a strain rate of 0.03 s⁻¹, use materials with a strength of less than 12 N / 50 mm at 5% elongation. As the elastic filament, one having a diameter of 30 μm or more and 200 μm or less, and containing a thermoplastic elastomer, is used. In the aforementioned elasticity development process, 30s －１ More than 200s －１ A method for manufacturing an expandable sheet for absorbent articles, wherein the laminate is stretched at the following strain rate.

2. The manufacturing method according to claim 1, wherein the spunbond nonwoven fabric has a maximum elongation in the machine direction of 120% or more and 250% or less.

3. In the aforementioned elasticity development process, 80s －１ The above 180s －１ The manufacturing method according to claim 1 or 2, wherein the laminate is stretched at the following strain rate.

4. An expandable sheet for absorbent articles, wherein multiple elastic filaments, arranged so as not to intersect each other and extending in one direction, are fused to a stretchable nonwoven fabric in a molten state before solidification, spun from a spinning nozzle, over their entire length in a substantially unstretched state, The elastic filament has a diameter of 30 μm or more and 200 μm or less, and contains a thermoplastic elastomer. The aforementioned nonwoven fabric is a spunbond nonwoven fabric made of polypropylene fibers. The aforementioned spunbond nonwoven fabric is Under the condition of a strain rate of 0.03 s⁻¹, the maximum elongation in the mechanical direction is between 100% and 250%. The strength at 5% elongation under the condition of a strain rate of 0.03 s⁻¹ is less than 12 N / 50 mm. The aforementioned expandable sheet has an elongation rate of 120% or more under a load of 3N / 50mm. In the aforementioned stretchable sheet, the number of cut points of the elastic filament is 2.0 points / cm in the non-stretched state of the stretchable sheet. ２ The following: A high elongation region and a low elongation region extending in a direction orthogonal to the elongation direction of the stretch sheet are alternately arranged along the elongation direction, and the width W of the low elongation region along the elongation direction at 2.2 times elongation Ｌ with respect to the width W of the high elongation region along the elongation direction Ｈ of the ratio W Ｈ / W Ｌ is 10 or less, a stretch sheet for absorbent articles.

5. Distortion speed: 3.3s －１ A nonwoven fabric made of polypropylene fibers, wherein the maximum strength under the following conditions is 40 N / 50 mm or less, the maximum elongation in the mechanical direction under the strain rate of 0.03 s⁻¹ is 100% or more and 250% or less, and the strength at 5% elongation under the strain rate of 0.03 s⁻¹ is less than 12 N / 50 mm, A base nonwoven fabric used to produce a stretchable sheet, wherein elastic filaments having a diameter of 30 μm or more and 200 μm or less, and containing a thermoplastic elastomer, are fused to the spunbond nonwoven fabric in a substantially unstretched state while in a molten state before solidification, as spun from a spinning nozzle.

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