JP3249047U - Stretchable Sheet - Google Patents

Abstract

The present invention provides a stretch sheet that has a large ratio of shrinkage stress after a certain period of time to the initial shrinkage stress.
[Solution] The stretch sheet 10 has a plurality of elastic filaments 13 arranged to extend in one direction bonded to extensible nonwoven fabrics 11, 12. High elongation regions and low elongation regions extending in a direction perpendicular to the stretch direction of the stretch sheet 10 are alternately arranged along said stretch direction. The elastic filaments 13 are fused to the nonwoven fabrics 11, 12 in a substantially unstretched state. The stress retention rate is 50% or more. The elastic filaments 13 contain a thermoplastic elastomer and oil.
[Selected Figure] Figure 1

Description

This invention relates to a stretchable sheet.

As a conventional technique for a stretch sheet made by combining elastic fibers and nonwoven fabric, the present applicant previously proposed a stretch sheet in which a large number of elastic filaments arranged to extend in one direction without crossing each other are bonded to a stretchable nonwoven fabric over their entire length in a substantially unstretched state (see Patent Document 1). This stretch sheet has the advantage that, because the elastic filaments are arranged to extend in one direction, it can be stretched in the direction in which the elastic filaments extend without shrinking in width. In addition, this stretch sheet has the advantage that it is strong, and when the stretch sheet is stretched, peeling of the elastic filaments and the nonwoven fabric is unlikely to occur.

When the stretch sheet is used as an outer layer sheet in an absorbent article such as a disposable diaper, the excellent stretchability of the stretch sheet allows the absorbent article to fit well to the wearer's body, effectively preventing leakage of excrement, etc.

JP 2008-179128 A

It is known that when elastic fibers are stretched and maintained in a stretched state for a long time, a phenomenon occurs in which stress is reduced due to stress relaxation. In particular, when the above-mentioned stretch sheet is used as an outer body of a disposable diaper, the elastic fibers are heated by the body temperature of the wearer, and stress relaxation is likely to be promoted. Therefore, when an absorbent article including a stretch sheet having elastic fibers is put on a wearer, even if the absorbent article shows a suitable fit in the initial state of wearing, the fit decreases after a long period of wearing, and the absorbent article is likely to slip off. If the contraction stress of the stretch sheet is increased to prevent the absorbent article from slipping off, excessive force is required when the absorbent article is put on by the wearer, making it difficult to put on.
Therefore, the present invention relates to a stretch sheet that, when used in an absorbent article, is easy to put on and does not easily slip down.

The present invention provides a stretch sheet in which a plurality of elastic filaments arranged to extend in one direction are bonded to an extensible nonwoven fabric.
It is preferable that high elongation regions and low elongation regions extending in a direction perpendicular to the stretch direction of the stretch sheet are alternately arranged along the stretch direction.
The elastic filaments are preferably fused to the nonwoven fabric in a substantially unstretched state.
The stretch sheet preferably has a stress retention rate of 50% or more.

This invention provides a stretch sheet that has a large ratio of shrinkage stress after a certain period of time to the initial shrinkage stress.

FIG. 1 is a partially cutaway perspective view showing one embodiment of the stretch sheet of the present invention. 2(a) and 2(b) are longitudinal cross-sectional views of the stretch sheet shown in FIG. 1 in a natural state and in a stretched state, respectively, along the direction in which the elastic filaments extend. FIG. 3 is a schematic diagram showing an apparatus suitably used for producing the stretch sheet shown in FIG.

The present invention will be described below based on its preferred embodiments.
The present invention relates to a stretch sheet comprising elastic filaments and 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 in which the sheet is stretched 100% of its original length (i.e., 200% of its original length).

The stretch sheet of the present invention may have, for example, one nonwoven fabric and a plurality of elastic filaments arranged on one side of the nonwoven fabric. Alternatively, the stretch 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 an elastic filament is arranged between two nonwoven fabrics, each elastic filament is bonded to at least one of the nonwoven fabrics or to both of the nonwoven fabrics. When an elastic filament is arranged between two nonwoven fabrics, the two nonwoven fabrics may be of the same type or different types. In this specification, the term "same type of nonwoven fabric" refers to nonwoven fabrics that are all the same in terms of the manufacturing process of the nonwoven fabric, the type of constituent fibers of the nonwoven fabric, the fiber diameter and length of the constituent fibers, the thickness and basis weight of the nonwoven fabric, etc. When at least one of these is different, the nonwoven fabrics are said to be of different types.

It is preferable to use fusion bonding as a bonding method between the elastic filaments and the nonwoven fabric. Bonding the two by fusion makes it possible to make the stretch sheet flexible and highly stretchable. If, for example, an adhesive is used to bond the two, the stretch sheet tends to feel hard due to the solidification of the adhesive. In addition, the adhesive tends to inhibit the stretching of the elastic filaments.

The stretch sheet is capable of stretching in the same direction as the elastic filaments extend. The stretchability of the stretch sheet is manifested by the elasticity of the elastic filaments. When the stretch sheet is stretched in the same direction as the elastic filaments extend, the elastic filaments 1 and the nonwoven fabric extend. When the stretch sheet is released from the stretching state, the elastic filaments contract, and as they contract, the nonwoven fabric returns to its pre-stretch state.

Elastic filaments have a thread-like form having a thickness and a length. The length of an elastic filament is extremely large compared to its thickness, for example, the length of an elastic filament can be 500 times or more, particularly 1000 times or more, compared to its thickness.

Each elastic filament is preferably present substantially continuously over the entire length of the stretch 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 may extend in a serpentine manner. Each elastic filament is preferably arranged to extend in one direction without crossing each other. However, crossing of elastic filaments is not prevented. For example, unintentional crossing of elastic filaments due to unavoidable fluctuations in the manufacturing conditions of the stretch sheet is permitted.

The direction in which the elastic filaments extend may be the same as the flow direction of the nonwoven fabric during production, or may be perpendicular to the flow direction of the nonwoven fabric during production. When a stretch sheet is produced according to the preferred production method described below, the direction in which the elastic filaments extend will be the same as the flow direction of the nonwoven fabric during production.

From the viewpoints of elasticity, texture, thickness, and cost, the basis weight of the elastic filament is preferably 4 g/m ² or more and 30 g/m ² or less, particularly 6 g/m ² or more and 15 g/m ² or less. The thickness, number of arranged filaments, and arrangement interval, etc. of the elastic filament may be appropriately set according to the basis weight of the elastic filament. For example, the diameter of the elastic filament can be set to 30 μm or more and 200 μm or less, particularly 50 μm or more and 130 μm or less. When the elastic filaments are arranged in a state where they are drawn in one direction as shown in FIG. 1 described later, the pitch of adjacent elastic filaments (the distance between the centers of adjacent elastic filaments) can be set to 0.1 mm or more and 5 mm or less, particularly 0.3 mm or more and 1.8 mm or less.

It is preferable that the elastic filament is bonded to the nonwoven fabric in a substantially unstretched state. When the elastic filament is bonded to the nonwoven fabric in an unstretched state, there is an advantage that relaxation (creep) due to stretching does not occur, and the elasticity is less likely to decrease. Furthermore, for example, when the elastic filament is stretched twice and bonded to the nonwoven fabric, if it shrinks to the initial 1.3 times, it can only be stretched to 1.54 times from this state. However, when the elastic filament is bonded to the nonwoven fabric in an unstretched state, there is an advantage that it can be stretched to the stretchable length of the nonwoven fabric or to the maximum elongation of the elastic filament, since the initial origin when the stretch sheet is stretched is different.

The nonwoven fabric to which the elastic filaments are bonded is stretchable. More specifically, the nonwoven fabric is stretchable in the same direction as the elastic filaments extend. Stretchable includes (a) the case where the constituent fibers of the nonwoven fabric themselves stretch, and (b) the case where the constituent fibers themselves do not stretch, but the nonwoven fabric as a whole stretches by separating fibers that were bonded at intersections, structurally changing the three-dimensional structure formed by multiple fibers due to bonding between fibers, tearing of constituent fibers, or stretching of slack fibers.

The nonwoven fabric may be already stretchable in the state of the original roll before being joined to the elastic filament. Alternatively, the nonwoven fabric may not be stretchable in the state of the original roll before being joined to the elastic filament, but may be processed so as to become stretchable after being joined to the elastic filament. Specific methods for making the nonwoven fabric stretchable include heat treatment, stretching between rolls, stretching by bite using grooves or gears, and tensile stretching using a tenter. Considering the preferred manufacturing method of the stretch sheet described later, it is preferable that the nonwoven fabric is not stretchable in the state of the original roll, since this improves the transportability of the nonwoven fabric when the elastic filament is fused to the nonwoven fabric.

In addition to being extensible as described above, the nonwoven fabric is preferably substantially inelastic. To this end, the nonwoven fabric preferably comprises inelastic fibers and does not contain elastic fibers. In this specification, inelastic refers to a property that does not meet the definition of elasticity given above.

Examples of inelastic fibers constituting the nonwoven fabric include fibers made of polyethylene (PE), polypropylene (PP), polyester (PET or PBT), polyamide, etc. The fibers constituting the nonwoven fabric may be short or long fibers, and may be hydrophilic or water-repellent. In addition, core-sheath or side-by-side composite fibers, split fibers, modified cross-section fibers, crimped fibers, heat-shrinkable fibers, etc. may also be used. These fibers may be used alone or in combination of two or more. The nonwoven fabric may be a continuous filament or short fiber nonwoven fabric.
From the viewpoints of texture, thickness, design, and the like, the nonwoven fabric has a basis weight of preferably 3 g/m ² or more and 100 g/m ² or less, and more preferably 5 g/m ² or more and 30 g/m ² or less.

An embodiment of a stretch sheet is shown in Fig. 1. Also, Figs. 2(a) and (b) show cross-sectional views in the thickness direction of the stretch sheet shown in Fig. 1. Figs. 2(a) and (b) are cross-sectional views along the extension direction of elastic filaments in the stretch sheet.
The stretch sheet 10 of the embodiment shown in Fig. 1 is composed 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. The elastic filaments 13 are arranged so as to extend in one direction without crossing each other.

2(a) is a cross-sectional view of the stretch sheet 10 in its natural state (relaxed state), and FIG. 2(b) is a cross-sectional view of the stretch sheet 10 in its stretched state. In its natural state, the stretch sheet 10 has a wave-like shape in which peaks 14' protruding upward from the sheet 10 and valleys 14" protruding downward from the sheet 10 are arranged alternately. The peaks 14' and valleys 14" are connected via ridges 15'. When the stretch sheet 10 is viewed in a plane, the peaks 14', ridges 15', and valleys 14" extend in a direction perpendicular to the stretch direction of the stretch sheet 10.

On the other hand, in the stretched state, the stretch sheet 10 has low basis weight regions 14 and high basis weight regions 15 arranged alternately along the extension direction of the elastic filaments 13. Each region 14, 15 extends in a strip shape in the extension direction of the elastic filaments 13, i.e., in a direction perpendicular to the stretch direction of the stretch sheet 10. The low basis weight regions 14 and high basis weight regions 15 are arranged alternately at a constant interval.

2(a) and 2(b), the areas which primarily stretch when the stretch sheet 10 is stretched are the peaks 14' and valleys 14" in FIG. 2(a) and the low basis weight regions 14 in FIG. 2(b). In other words, the ridges 15' in FIG. 2(a) (i.e. the high basis weight regions 15 in FIG. 2(b)) do not stretch to a large extent when the stretch sheet 10 is stretched. Thus, in the stretch sheet 10, high and low elongation regions which extend in a direction perpendicular to the stretch direction are alternately arranged along the stretch direction. The high elongation regions are the peaks 14' and valleys 14" in FIG. 2(a) and the low basis weight regions 14 in FIG. 2(b). The low elongation regions are the ridges 15' in FIG. 2(a) and the high basis weight regions 15 in FIG. 2(b). To form high elongation regions and low elongation regions in the stretch sheet 10, the stretch sheet 10 may be manufactured, for example, by the method described below.

In addition to having the above-mentioned structure, the stretch sheet of the present invention is characterized in that the ratio of the shrinkage stress after a certain time to the initial shrinkage stress is large. In the following description, for convenience, the ratio of the shrinkage stress after 2 hours to the initial shrinkage stress is also referred to as the "stress retention rate". The stretch sheet of the present invention can achieve a high stress retention rate of preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. The closer the stress retention rate is to 100%, the more preferable, but if the stress retention rate is high, such as about 50%, the intended purpose of the present invention will be achieved.
The method for measuring the stress retention rate will be described in the examples described later.

As a result of intensive research by the inventor with the aim of increasing the stress retention rate of the stretch sheet, it was found that it is effective to use a high molecular weight elastic resin as the constituent resin of the elastic filament used in the stretch sheet. A high molecular weight elastic resin has the advantage that stress relaxation is less likely to occur than a low molecular weight elastic resin. Therefore, it is possible to increase the stress retention rate by using a high molecular weight elastic resin. From this viewpoint, it is preferable to use an elastic resin that constitutes the elastic filament with a weight average molecular weight of 70,000 or more. It is more preferable that the weight average molecular weight of the elastic resin is 80,000 or more, and even more preferable that it is 100,000 or more. The higher the molecular weight of the elastic resin, the more preferable it is from the viewpoint of suppressing stress relaxation, but if the weight average molecular weight is about 150,000, the intended purpose of the present invention is achieved. From this viewpoint, it is preferable that the weight average molecular weight of the elastic resin is 70,000 to 150,000, more preferably 80,000 to 130,000, and even more preferably 90,000 to 110,000.

The method for measuring the weight average molecular weight of the elastic resin is as follows.
The weight average molecular weight is measured by gel permeation chromatography (GPC). A TSKgel G-2000H column is used. The column temperature is set to 40°C. Tetrahydrofuran (THF) is used as the mobile phase. The flow rate is set to 1.0 mL/min. The sample concentration is set to 10 mg/5 mL-THF. The injection amount is set to 500 μL. The measured values are values converted into polystyrene values. The analytical sample is prepared by dissolving 10 mg of sample in 5 mL of THF at room temperature for 10 minutes and filtering the solution through a sintered filter with a pore size of 0.45 μm.

Examples of elastic resins that make up the 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 alone or in combination of two or more.

In particular, it is preferable to use a thermoplastic elastomer as the elastic resin, since it is easy to achieve the desired elasticity. Furthermore, like ordinary thermoplastic resins, thermoplastic elastomers can be melt spun using an extruder, and the elastic filaments thus obtained are easy to fuse, making them suitable for the manufacturing method described below.

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. Core-sheath or side-by-side composite fibers made of these elastomers can also be used.

In particular, it is preferable to use an A1-B-A2 type triblock copolymer, which is composed of polymer blocks A1 and A2 mainly made of vinyl aromatic polymers and polymer block B mainly made of polyolefin, as the thermoplastic elastomer, in terms of suppressing stress relaxation and melt moldability of the elastic filaments.

The triblock copolymer preferably has an overall weight-average molecular weight of 70,000 to 150,000, more preferably 80,000 to 130,000, and even more preferably 90,000 to 110,000. When the weight-average molecular weight of the triblock copolymer is within this range, the stress relaxation of the elastic filament containing the triblock copolymer is suppressed, and the stretch sheet of the present invention can easily increase its stress retention rate.

For the same reasons as above, the triblock copolymer preferably has a total weight average molecular weight of polymer blocks A1 and A2 of 20,000 or more and 70,000 or less, more preferably 25,000 or more and 60,000 or less, and even more preferably 27,000 or more and 50,000 or less.

The polymer block A1 is mainly composed of a vinyl aromatic polymer. Examples of vinyl aromatics constituting this vinyl aromatic polymer include styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, p-tert-butoxystyrene, dimethylaminomethylstyrene, dimethylaminoethylstyrene, vinyltoluene, 1-vinylnaphthalene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, and 4-(phenylbutyl)styrene. The vinyl aromatic polymer may be composed of one or more of these vinyl aromatics. Of these vinyl aromatics, styrene is preferred in terms of ease of polymerization and versatility.

The content of the vinyl aromatic polymer in polymer block A1 is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, based on the total structural units of polymer block A1.

The polymer block A1 may be composed of a conjugated diene compound polymer in addition to the vinyl aromatic polymer. Examples of the conjugated diene compound constituting this conjugated diene compound polymer include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, phenylbutadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. The conjugated diene compound polymer may be composed of one type of these conjugated diene compounds, or may be composed of two or more types.

The content of the conjugated diene compound polymer in polymer block A1 is preferably 0% by mass or more and 10% by mass or less, more preferably 0% by mass or more and 5% by mass or less, based on the total structural units of polymer block A1.

The weight average molecular weight of polymer block A1 is preferably 7,000 to 35,000, more preferably 10,000 to 20,000.

As the polymer block A2, the same one as the polymer block A1 described above can be used. Where no particular description is given of the polymer block A2, the description of the polymer block A1 is appropriately applied.
In the A1-B-A2 type triblock copolymer, the polymer block A1 and the polymer block A2 may have the same structure or different structures.

In particular, it is preferable that both the polymer blocks A1 and A2 are polystyrene. In other words, it is preferable that the elastic filament of the present invention is configured so that the polymer block A1 contains only polystyrene and the polymer block A2 contains only polystyrene.

The total content of polymer blocks A1 and A2 in the A1-B-A2 triblock copolymer is preferably 15% by mass or more and 40% by mass or less, more preferably 18% by mass or more and 35% by mass or less, based on the total structural units of the A1-B-A2 triblock copolymer.

As described above, when both polymer blocks A1 and A2 are polystyrene, the ratio of polymer block A1 to polymer block A2 in the A1-B-A2 triblock copolymer is preferably (A1/A2)=0.8 to 1.2 by mass, more preferably (A1/A2)=0.9 to 1.1 by mass.

The polymer block B is mainly composed of polyolefin. Examples of olefins constituting this polyolefin include isoprene, butadiene, ethylene, propylene, and butylene. The olefin constituting the polymer block B may be composed of one of these olefins, or may be composed of two or more of these olefins. Of these olefins, ethylene and propylene are preferred from the standpoint of weather resistance and elasticity characteristics.

The content of the polyolefin in polymer block B is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, based on the total structural units of polymer block B.

The polymer block B may be composed of, in addition to the polyolefin, other polymers that are derived from other polymerizable monomers and can be polymerized with the polyolefin. Examples of such other polymerizable monomers include styrene. The other polymers that can be polymerized with the polyolefin constituting the polymer block B may be composed of one type of these other polymerizable monomers, or may be composed of two or more types.

The content of the other polymer in polymer block B is preferably 0% by mass or more and 10% by mass or less, and more preferably 0% by mass or more and 5% by mass or less, based on the total structural units of polymer block B.

Specific examples of polymer block B include polyisoprene, polybutadiene, poly(ethylene-propylene), poly(ethylene-butylene), etc. Among these, poly(ethylene-propylene) is preferred from the viewpoints of weather resistance and elasticity properties.

The content of polymer block B in the A1-B-A2 triblock copolymer is preferably 60% by mass or more and 85% by mass or less, and more preferably 65% by mass or more and 82% by mass or less, based on the total structural units of the A1-B-A2 triblock copolymer.

Specific examples of A1-B-A2 type triblock copolymers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene-styrene block copolymer (SEBS) which is a hydrogenated product of SBS, and styrene-ethylene-propylene-styrene block copolymer (SEPS) and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) which are hydrogenated products of SIS. Among these, SEBS, SEPS, and SEEPS are preferred because they can provide elastic filaments with excellent thermal stability and weather resistance.

The elastic resin constituting the elastic filament may be composed of only the above-mentioned A1-B-A2 type triblock copolymer, or may be composed of one or more other resins in addition to the A1-B-A2 type triblock copolymer as necessary within the scope of the present invention. When the elastic resin contains the A1-B-A2 type triblock copolymer and other resins, the content of the A1-B-A2 type triblock copolymer in the elastic resin is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less. From the viewpoint of maximally improving the melt moldability and stretchability, it is preferable that the elastic resin is composed of only the A1-B-A2 type triblock copolymer.

The elastic resin constituting the elastic filament may be composed of one type of A1-B-A2 type triblock copolymer, or may be composed of two or more types of A1-B-A2 type triblock copolymers having different structures.

As mentioned above, in the stretch sheet of the present invention, it is preferable that the elastic resin in the elastic filament constituting the sheet is of high molecular weight. However, if the molecular weight of the elastic resin is excessively high, the melt moldability of the elastic resin tends to decrease. Therefore, the inventor's research has revealed that it is advantageous to blend oil with the elastic filament in order to obtain good melt moldability even when a high molecular weight elastic resin is used. It is preferable to use an oil that does not easily reduce the cohesive force derived from the hard segment in the elastic resin. In addition, if an oil with a high plasticizing effect is used, it tends to act on the hard segment in the elastic resin and reduce the elasticity of the elastic resin. In other words, it is preferable to use an oil that has a low plasticizing effect on the elastic resin. From the above viewpoint, it is preferable to use an oil with a high kinetic viscosity. From this viewpoint, it is preferable to use oil having a kinetic viscosity measured in accordance with JIS K2283 of preferably 3 mm ² /s or more and 600 mm ² /s or less, more preferably 30 mm ² /s or more and 500 mm ² /s or less, and even more preferably 200 mm ² /s or more and 400 mm ² /s or less.

From the above viewpoints, it is advantageous to use paraffin-based oil as the oil, and it is particularly preferable to use paraffin-based oil whose kinetic viscosity falls within the above-mentioned range.
As the paraffin-based oil, various aliphatic hydrocarbons called liquid paraffin, mineral oil, white mineral oil, etc. can be used without any particular limitation.

From the viewpoint of the balance between suppressing stress relaxation of the elastic resin and melt moldability, it is preferable that the proportion of oil contained in the elastic filament is 25% by mass or more and 60% by mass or less based on the mass of the elastic filament. From the viewpoint of making this advantage more prominent, it is more preferable that the proportion of oil contained in the elastic filament is 30% by mass or more and 55% by mass or less based on the mass of the elastic filament, and even more preferable that it is 30% by mass or more and 50% by mass or less.

The elastic filament contains the above-mentioned elastic resin and the above-mentioned oil, so that stress relaxation is unlikely to occur and the melt moldability is good. When the meltability of the elastic filament is expressed by melt flow rate (MFR), the melt flow rate measured in accordance with JIS K7210 at 230° C. under a load of 2.16 kg is preferably 3 g/10 min to 100 g/10 min, more preferably 5 g/10 min to 50 g/10 min, and even more preferably 10 g/10 min to 30 g/10 min.
The die used in measuring the melt flow rate has a height of 8 mm and an inner diameter of 2.095 mm.

Next, a preferred method for producing the stretch sheet of the present invention will be described with reference to FIG. 3, taking as an example a method for producing the stretch sheet 10 shown in FIG. 2(a) and FIG. 2(b).
In this manufacturing method, as shown in Figure 3, multiple molten elastic filaments 13 spun from a spinning nozzle 16 are taken up and stretched at a predetermined speed, and before the elastic filaments 13 solidify, the elastic filaments 13 are fused to the nonwoven fabrics 11, 12 so that the elastic filaments 13 are arranged in one direction without crossing each other, and then the composite 19 to which the elastic filaments 13 are fused is subjected to an elasticity development treatment along the extension direction of the elastic filaments 13 to impart elasticity to the composite 19.

The spinning nozzle 16 is provided in the spinning head 17. The spinning head 17 is connected to an extruder. The elastic resin (which is mixed with the above-mentioned oil as necessary) melted and kneaded by the extruder is supplied to the spinning head 17. A large number of spinning nozzles 16 are arranged in a straight line in the spinning head 17. The spinning nozzles 16 are arranged along the width direction of the first and second nonwoven fabrics 11 and 12. The spacing between adjacent spinning nozzles 16 corresponds to the spacing between the elastic filaments 13 in the target stretch sheet 10. The spinning nozzle 16 is usually circular, and its diameter affects the diameter and stretch ratio of the elastic filaments 13. From this viewpoint, it is preferable that the diameter of the spinning nozzle 16 is 0.1 mm or more and 2 mm or less, particularly 0.2 mm or more and 0.6 mm or less. The elastic filaments 13 can be in a composite form (side-by-side, core-sheath, or sea-island structure) for the purposes of increasing the bonding strength with the nonwoven fabrics 11 and 12, increasing the spinnability of the elastic filaments 13, and improving the stretch properties of the stretch sheet 10.

The spun elastic filament 13 in a molten state merges with the first nonwoven fabric 11 and the second nonwoven fabric 12, which are each unwound at the same speed from the original rolls, and is sandwiched between the two nonwoven fabrics 11, 12 and taken up at a predetermined speed. The take-up speed of the elastic filament 13 is the same as the unwound speed of the two nonwoven fabrics 11, 12.

The elastic filament 13 joins the first and second nonwoven fabrics 11, 12 before solidification, i.e., in a fusible 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 the unsolidified elastic filament to the nonwoven fabrics 11, 12 being transported. When fusing the elastic filament 13, no heat is applied from the outside to the first and second nonwoven fabrics 11, 12. In other words, the elastic filament 13 fuses to both nonwoven fabrics 11, 12 only by the melting heat caused by the fusible elastic filament 13. As a result, of the constituent fibers of both nonwoven fabrics 11, 12, only the fibers present around the elastic filament 13 fuse to the elastic filament, and the fibers present at a position further away do not fuse. As a result, the heat applied to both nonwoven fabrics 11 and 12 is kept to a minimum, so the inherent good texture of the nonwoven fabrics themselves is maintained. This results in a good texture for the resulting stretch sheet 10.

When the elastic filament 13 is joined to the nonwoven fabrics 11 and 12, the elastic filament 13 is in a substantially unstretched state (a state in which it does not shrink when external force is removed). In the joined state, the fibers constituting the nonwoven fabrics 11 and 12 and the elastic filament 13 are at least partially fused to each other. In this state, it is preferable that the nonwoven fabrics 11 and 12 are fused to each other while sandwiching the elastic filament 13.

In this way, a composite 19 is obtained in which the elastic filament 13 is sandwiched between two sheets of nonwoven fabric 11, 12. When nonwoven fabrics 11, 12 that are inherently stretchable are used, the composite 19 becomes the stretch sheet 10 itself. On the other hand, when nonwoven fabrics 11, 12 that are inherently non-stretchable are used, the composite 19 including the nonwoven fabrics 11, 12 is subjected to an elasticity development process along the extension direction of the elastic filament 13 to impart elasticity to the composite 19. In this manufacturing method, this process is performed by using an elasticity development processing device 22 equipped with a pair of grooved rolls 20, 21, each of which has teeth and tooth bases formed alternately in the circumferential direction, and subjecting the composite 19 to an elasticity development process along its conveying direction, i.e., the extension direction of the elastic filament 13.

The elasticity development processing device 22 has a known lifting mechanism (not shown) that displaces the pivot points of one or both of the tooth groove rolls 20, 21 up and down, making it possible to adjust the distance between the tooth groove rolls 20, 21. In this manufacturing method, the tooth groove rolls 20, 21 are assembled so that the teeth of one tooth groove roll 20 are loosely inserted between the teeth of the other tooth groove roll 21, and the teeth of the other tooth groove roll 21 are loosely inserted between the teeth of one tooth groove roll 20, and the composite 19 is inserted between the tooth groove rolls 20, 21 in this state and subjected to elasticity development processing.

The composite 19 is subjected to an elasticity development process by a pair of grooved rolls 20, 21 to obtain the desired stretch sheet 10. After passing through the grooved rolls 20, 21, the stretch sheet 10 is quickly released from its stretched state in the conveying direction due to its own shrinkage restoring force. As a result, the length of the stretch sheet 10 is largely restored in the conveying direction. As a result, in the stretched state, high stretch regions and low stretch regions are arranged alternately in the extension direction of the elastic filaments 13.

The stretch sheet of the present invention thus obtained can be suitably used, for example, as the outer casing of a disposable diaper. Disposable diapers equipped with the stretch sheet of the present invention, such as pants-type disposable diapers, are easy to put on because the waist part can be easily expanded, and they are less likely to slip down even when worn for long periods of time.
In addition to the above uses, the stretch sheet of the present invention can also be used for various uses such as medical disposable clothing, cleaning sheets, eye patches, masks, bandages, etc., taking advantage of its good texture, stretchability, breathability, etc. In particular, it is preferably used as a constituent material of absorbent articles such as sanitary napkins and disposable diapers. Examples of the constituent material include liquid-permeable sheets (including top sheets, sublayer sheets, etc.) located on the skin side of the absorbent body, sheets constituting the outer surface of disposable diapers, and sheets for imparting elastic stretchability to the waist, waist, leg circumference, etc. In addition, it can be used as a sheet forming the wings of a napkin. It can also be used in other parts, such as parts where stretchability is desired. The basis weight and thickness of the stretch sheet can be appropriately adjusted according to the specific use. For example, when used as a constituent material of absorbent articles, it is desirable to set the basis weight to about 20 g/m ² or more and 60 g/m ² or less, and the thickness to about 0.5 mm or more and 1.5 mm or less.

The stretchability of the stretch sheet can be appropriately set depending on the specific application of the stretch sheet. When the stretch sheet is used, for example, as an outer body of a disposable diaper, the initial stress A measured in the measurement of the stress retention rate explained in the examples below is preferably 10 cN/50 mm or more and 500 cN/50 mm or less, more preferably 20 cN/50 mm or more and 250 cN/50 mm or less, and even more preferably 30 cN/50 mm or more and 100 cN/50 mm or less.

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 such examples. Unless otherwise specified, "%" means "% by mass."

Example 1
(1) Preparation of Elastic Filament Elastic filaments containing the thermoplastic elastomer and oil shown in Table 1 were prepared. The ratio of oil contained in the elastic filament is as shown in the same table. The MFR of the elastic filament is also as shown in the same table.

(2) Preparation of Nonwoven Fabric Two sheets of spunbond nonwoven fabric having a basis weight of 18 g/ ^m2 were prepared. The fibers were made of polypropylene.

(3) Production of Stretch Sheet Stretch sheets having the structures shown in FIG. 1, FIG. 2(a) and FIG. 2(b) were produced using the apparatus shown in FIG.
The elasticity development treatment was carried out using an elasticity development treatment device 22 equipped with a pair of grooved rolls 20, 21 in which teeth and tooth bottoms were alternately formed in the axial direction. As a result, a stretch sheet 10 having a basis weight of 46 g/ ^m2 and stretching in the direction in which the elastic filaments 13 extend was obtained.

[Examples 2 to 4]
The oils used in the elastic filaments were those shown in Table 1 below. The ratio of the oil contained in the elastic filaments was also shown in Table 1. A stretch sheet was obtained in the same manner as in Example 1, except for the above.

Comparative Examples 1 to 3
The thermoplastic elastomers used to compose the elastic filaments were those shown in Table 1 below. In addition, no oil was blended into the elastic filaments. Except for these, a stretch sheet was obtained in the same manner as in Example 1. In Comparative Example 3, the elastic resin had poor melt fluidity, and the elastic filaments could not be melt-spun.

〔evaluation〕
The stress retention rate of the stretch sheets obtained in the examples and comparative examples was measured by the following method. The results are shown in Table 1 below.

[Measurement of stress retention rate]
A test piece was obtained by cutting the stretch sheet so that the length in the stretch direction was 150 mm and the length in the direction perpendicular to the stretch direction was 50 mm.
This test piece was attached to a tensile tester with a chuck distance of 100 mm so that the stretching direction was the tensile direction.
At an ambient temperature of 40° C., the test piece was pulled at a speed of 300 mm/min. When the chuck distance reached 200 mm, the pulling was stopped and this state was maintained for 2 hours, during which the stress was measured over time.
When the initial stress when the chuck distance reaches 200 mm is defined as A and the stress after 2 hours is defined as B, the stress retention rate (%) is defined as B/A×100.

As is clear from the results shown in Table 1, the stretch sheets obtained in the examples show a higher stress retention rate than the stretch sheets obtained in the comparative examples.

10 Stretch sheet 11 First nonwoven fabric 12 Second nonwoven fabric 13 Elastic filament 14 High basis weight region 14' Peak 14" Valley 15 Low basis weight region 15' Ridge

Claims (6)

A stretch sheet in which a plurality of elastic filaments arranged to extend in one direction are bonded to an extensible nonwoven fabric,
The high elongation regions and the low elongation regions extending in a direction perpendicular to the stretch direction of the stretch sheet are alternately arranged along the stretch direction,
the elastic filaments are fused to the nonwoven fabric in a substantially unstretched state;
A stretchable sheet having a stress retention rate of 50% or more. A stretch sheet in which a plurality of elastic filaments arranged to extend in one direction are bonded to an extensible nonwoven fabric,
The stretch sheet has high elongation regions and low elongation regions arranged alternately in a direction perpendicular to the stretch direction, and the high elongation regions and low elongation regions are arranged alternately in the stretch direction,
the elastic filaments are fused to the nonwoven fabric in a substantially unstretched state;
The elastic filaments comprise a thermoplastic elastomer and an oil. The stretch sheet according to claim 2, wherein the proportion of the oil is 25% by mass or more and 60% by mass or less based on the mass of the elastic filaments. The stretch sheet according to claim 2 or 3, wherein the oil is a paraffin-based oil. The stretch sheet according to any one of claims 2 to 4, wherein the thermoplastic elastomer is an A1-B-A2 type triblock copolymer consisting of polymer blocks A1 and A2 mainly made of vinyl aromatic polymer and polymer block B mainly made of polyolefin, the weight average molecular weight of the whole is 70,000 or more and 150,000 or less, and the sum of the weight average molecular weights of the polymer blocks A1 and A2 is 27,000 or more and 70,000 or less. The elastic filament has a melt flow rate of 3 g/10 min or more and 100 g/10 min or less, measured at 230° C. under a load of 2.16 kg in accordance with JIS K7210. The stretch sheet according to any one of claims 1 to 5.