JP2023066295A - Stretchable sheet - Google Patents

Abstract

To provide a stretchable sheet having a large ratio of a contraction stress after a certain period of time to an initial contraction stress.SOLUTION: In a stretchable sheet 10, a plurality of elastic filaments 13 arrayed in such a way as to extend in one direction are bonded to extendable nonwoven fabrics 11 and 12. A high elongation area and a low elongation area extending in a direction orthogonal to a stretching direction of the stretchable sheet 10 are arranged alternately along the stretching direction. The elastic filaments 13 are fused to the nonwoven fabrics 11 and 12 substantially in a non-stretched state. The stress retention rate is 50% or more. Each of the elastic filaments 13 includes a thermoplastic elastomer and oil.SELECTED DRAWING: Figure 1

Description

The present invention relates to stretch sheets.

As a conventional technique related to stretch sheets made by combining elastic fibers and nonwoven fabrics, the present applicant previously disclosed that a large number of elastic filaments arranged so as to extend in one direction without proposed a stretch sheet bonded to a stretchable nonwoven fabric over the entire length thereof (see Patent Document 1). Since the elastic filaments of this stretchable sheet are arranged so as to extend in one direction, it has the advantage that it can be stretched in the direction in which the elastic filaments extend without causing width shrinkage. In addition, this stretch sheet has a high strength, and has the advantage that when the stretch sheet is stretched, the elastic filaments and the nonwoven fabric are less likely to separate.

When the stretchable sheet is used as an outer layer sheet in an absorbent article such as a disposable diaper, the absorbent article fits well on the wearer's body due to the good stretchability of the stretchable sheet. , leakage of excrement and the like are effectively prevented.

Japanese Patent Application Laid-Open No. 2008-179128

By the way, it is known that when an elastic fiber is stretched and kept in that state for a long time, a phenomenon occurs in which the stress is reduced due to stress relaxation. In particular, when the elastic sheet described above is used as the outer covering of a disposable diaper, the body temperature of the wearer heats the elastic fibers, which facilitates stress relaxation. Therefore, when an absorbent article having a stretchable sheet having elastic fibers is put on by a wearer, even if it exhibits an appropriate fit in the initial state of wearing, the fit deteriorates as the wearer wears it for a long period of time. Items slip off easily. If the shrinkage stress of the stretchable sheet is increased to prevent the absorbent article from slipping down, an excessive force is required to put the absorbent article on the wearer, making it difficult to put on the absorbent article.
Therefore, the present invention relates to a stretch sheet that is easy to put on and has excellent resistance to slipping down when used in an absorbent article.

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

According to the present invention, a stretch sheet having a large ratio of shrinkage stress after a certain period of time to initial shrinkage stress is provided.

FIG. 1 is a partially broken perspective view showing one embodiment of the stretch sheet of the present invention. 2(a) and 2(b) are vertical cross-sectional views of the elastic sheet shown in FIG. 1 in a natural state and 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 manufacturing the stretch sheet shown in FIG.

The present invention will be described below based on its preferred embodiments.
TECHNICAL FIELD The present invention relates to a stretch sheet comprising elastic filaments and a nonwoven fabric. In this specification, elasticity and stretchability are stretchable and when the force is released from a state of being stretched 100% with respect to the original length (becomes 200% of the original length) In addition, it is the property of returning to a length of 125% or less of the original length.

The stretch sheet of the present invention can have, for example, one nonwoven fabric and a plurality of elastic filaments arranged on one surface of the nonwoven fabric. Alternatively, the stretch sheet of the present invention can have two nonwoven fabrics and a plurality of elastic filaments disposed between the two nonwoven fabrics. Each elastic filament is bonded with a nonwoven. If the elastic filaments are arranged between two nonwovens, each elastic filament is bonded to at least one nonwoven, or to both nonwovens. Also, when the elastic filaments are arranged between two nonwoven fabrics, the two nonwoven fabrics may be of the same type or of different types. In this specification, nonwoven fabrics of the same kind mean nonwoven fabrics having the same manufacturing process, the same 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, and the like. If at least one of these is different, it is said to be a heterogeneous nonwoven fabric.

It is preferable to employ fusion bonding as a mode of joining the elastic filaments and the nonwoven fabric. By joining the two by fusion bonding, the stretch sheet can be made flexible and highly stretchable. If, for example, an adhesive is used to join the two, the stretch sheet tends to feel hard due to the solidification of the adhesive. In addition, the adhesive tends to inhibit the expansion and contraction of the elastic filaments.

The stretchable sheet is stretchable in the same direction as the direction in which the elastic filaments extend. The stretchability of the stretch sheet is developed due to the elasticity of the elastic filaments. When the stretchable sheet is stretched in the same direction as the direction in which the elastic filaments extend, the elastic filaments 1 and the nonwoven fabric are stretched. When the stretching of the stretchable sheet is released, the elastic filaments contract, and the nonwoven fabric returns to its original state before being stretched along with the shrinkage.

An elastic filament has a filamentous form with thickness and length. The length of the elastic filaments is very large relative to the thickness, for example the length of the elastic filaments can be 500 times or more, in particular 1000 times or more, the thickness.

Each elastic filament preferably exists substantially continuously over the entire length of the stretch sheet. The elastic filaments contain elastic resin. Each elastic filament is arranged so as to extend in one direction. Each elastic filament may extend linearly or meanderingly. Each elastic filament is preferably arranged so as to extend in one direction without intersecting each other. However, crossing of the elastic filaments is not prevented. For example, unintentional crossing of elastic filaments due to unavoidable variations in stretch sheet manufacturing conditions is acceptable.

The direction in which the elastic filaments extend may coincide with the machine direction during manufacture of the nonwoven fabric, or may be perpendicular to the machine direction during manufacture of the nonwoven fabric. When the stretch sheet is manufactured according to the preferred manufacturing method described later, the direction in which the elastic filaments extend coincides with the flow direction during manufacture of the nonwoven fabric.

The basis weight of the elastic filaments 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, from the viewpoint of stretchability, texture, thickness and cost. The thickness of the elastic filaments, the number of arranged filaments, the arrangement intervals, etc. may be appropriately set according to the basis weight of the elastic filaments. 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 aligned in one direction as shown in FIG. 1 to be described later, the pitch of adjacent elastic filaments (the distance between the centers of adjacent elastic filaments) is 0.5. It can be set to 1 mm or more and 5 mm or less, particularly 0.3 mm or more and 1.8 mm or less.

Preferably, the elastic filaments are bonded to the nonwoven in a substantially non-stretched state. When the elastic filaments are joined to the nonwoven fabric in an unstretched state, there is an advantage that relaxation (creep) due to stretching does not occur and stretchability is less likely to decrease. Furthermore, for example, when an elastic filament is stretched twice and bonded to a non-woven fabric, if it shrinks to 1.3 times the initial size, it can only be stretched to 1.54 times from this state, but in the non-stretched state. When the elastic filament and the nonwoven fabric are joined by , the initial origin when the elastic sheet is stretched is different, so it is possible to stretch it to the stretchable length of the nonwoven fabric or the maximum elongation of the elastic filament. There are advantages.

The nonwoven fabric to which the elastic filaments are joined is extensible. Specifically, the nonwoven fabric can be stretched in the same direction as the direction in which the elastic filaments extend. Extensible means (a) when the constituent fibers of the nonwoven fabric themselves are elongated, and (b) even if the constituent fibers themselves are not elongated, the fibers bonded at the intersection point are separated or the fibers are bonded together. It includes the case where the three-dimensional structure formed by a plurality of fibers is structurally changed, the constituent fibers are torn, or the slackness of the fibers is stretched, so that the nonwoven fabric as a whole is elongated.

The nonwoven fabric may already be extensible in the raw state before being joined with the elastic filaments. Alternatively, the nonwoven fabric is not extensible in the original state before being joined to the elastic filaments, but is made extensible by being processed so as to be extensible after being joined to the elastic filaments. good too. Specific methods for making the nonwoven fabric stretchable include heat treatment, stretching between rolls, bite stretching by tooth grooves or gears, tensile stretching by a tenter, and the like. Considering the suitable manufacturing method of the elastic sheet described later, it is preferable that the nonwoven fabric is not stretchable in its raw state, in order to improve the transportability of the nonwoven fabric when the elastic filaments are fused to the nonwoven fabric.

In addition to being extensible as described above, the nonwoven is preferably substantially inelastic. For this purpose, the nonwoven preferably comprises non-elastic fibers and no elastic fibres. Inelastic, as used herein, refers to properties that do not meet the definition of elasticity set forth above.

Examples of non-elastic fibers constituting the non-woven fabric include fibers made of polyethylene (PE), polypropylene (PP), polyester (PET or PBT), polyamide, and the like. The fibers constituting the nonwoven fabric may be short fibers or long fibers, and may be hydrophilic or water-repellent. In addition, core-sheath type or side-by-side type conjugate fibers, split fibers, modified cross-section fibers, crimped fibers, heat-shrinkable fibers, and the like can also be used. These fibers can be used singly or in combination of two or more. The nonwoven can be a continuous filament or staple fiber nonwoven.
The basis weight of the nonwoven fabric is preferably 3 g/m ² or more and 100 g/m ² or less, more preferably 5 g/m ² or more and 30 g/m ^{2 or} less, from the viewpoint of texture, thickness, design properties, and the like.

One embodiment of the elastic sheet is shown in FIG. 2(a) and 2(b) show cross-sectional views in the thickness direction of the stretch sheet shown in FIG. 2(a) and 2(b) are cross-sectional views along the direction in which the elastic filaments extend in the stretch sheet.
The stretch sheet 10 of the embodiment shown in FIG. 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 so as to extend in one direction without intersecting each other.

FIG. 2(a) is a cross-sectional view of the stretch sheet 10 in a natural state (relaxed state), and FIG. 2(b) is a cross-sectional view of the stretch sheet 10 in a stretched state. In the natural state, the elastic sheet 10 has a wavy shape in which peaks 14' projecting upward from the sheet 10 and valleys 14'' projecting downward from the sheet 10 are alternately arranged. 14' and the valley portion 14'' are connected via the ridgeline portion 15'. When the stretch sheet 10 is viewed from above, the peaks 14 ′, the ridges 15 ′, and the 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 elastic sheet 10 has low basis weight regions 14 and high basis weight regions 15 alternately arranged along the direction in which the elastic filaments 13 extend. Each of the regions 14 and 15 extends in a strip shape in the direction in which the elastic filaments 13 extend, that is, in the direction orthogonal to the stretching direction of the stretchable sheet 10 . The low grammage areas 14 and the high grammage areas 15 are alternately arranged at regular intervals.

As is clear from the comparison between FIG. 2(a) and FIG. 2(b), the portions that are mainly stretched when the stretchable sheet 10 is stretched are the top portions 14′ and the valley portions 14″ in FIG. 2(a). , is the low basis weight region 14 in Fig. 2(b).In other words, the ridge line portion 15' in Fig. 2(a) (that is, the high basis weight region 15 in Fig. 2(b)) stretches the elastic sheet 10. Thus, in the stretch sheet 10, high-stretch regions and low-stretch regions extending in a direction orthogonal to the stretch direction are alternately arranged along the stretch direction. The high elongation regions are peaks 14' and valleys 14'' in FIG. 2(a) and low basis weight regions 14 in FIG. 2(b). The low elongation region is the ridgeline portion 15' in FIG. 2(a) and the high basis weight region 15 in FIG. 2(b). In order to form the high stretch region and the low stretch region in the stretch sheet 10, the stretch sheet 10 may be manufactured, for example, by the method described later.

One of the characteristics of the stretch sheet of the present invention is that, in addition to having the structure described above, the ratio of the shrinkage stress after a certain period of time to the initial shrinkage stress is large. In the following description, for convenience, the ratio of shrinkage stress after 2 hours to initial shrinkage stress is also referred to as "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 better, but if the stress retention rate is as high as about 50%, the desired object of the present invention can be achieved.
A method for measuring the stress retention rate will be described in Examples described later.

As a result of intensive studies by the present inventors for the purpose 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 filaments used in the stretch sheet. High-molecular-weight elastic resins have the advantage that stress relaxation is less likely to occur than low-molecular-weight elastic resins. Therefore, it is possible to increase the stress retention rate by using a high-molecular-weight elastic resin. From this point of view, it is preferable to use a resin having a weight-average molecular weight of 70,000 or more as the elastic resin constituting the elastic filaments. The weight-average molecular weight of the elastic resin is more preferably 80,000 or more, even more preferably 100,000 or more. The higher the molecular weight of the elastic resin, the better from the viewpoint of suppression of stress relaxation. From this point of view, the weight average molecular weight of the elastic resin is preferably 70,000 or more and 150,000 or less, more preferably 80,000 or more and 130,000 or less, and even more preferably 90,000 or more and 110,000 or less.

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

Examples of elastic resins constituting the elastic filaments include synthetic rubbers such as natural rubber, EVA rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber and neoprene rubber, polyurethanes and thermoplastic elastomers. These elastic resins can be used singly or in combination of two or more.

In particular, it is preferable to use a thermoplastic elastomer as the elastic resin because it is easy to develop desired elasticity. Thermoplastic elastomers can be melt-spun using an extruder in the same manner as ordinary thermoplastic resins, and the elastic filaments thus obtained are easy to fuse, making them suitable for the manufacturing method described below. be.

Examples of thermoplastic elastomers include SBS (styrene-butadiene-styrene), SIS (styrene-isoprene-styrene), SEBS (styrene-ethylene-butadiene-styrene), and SEPS (styrene-ethylene-propylene-styrene). Olefin-based elastomers such as styrene-based elastomers, ethylene-based α-olefin elastomers, and propylene-based elastomers obtained by copolymerizing ethylene/butene/octene, etc., polyester-based elastomers, and polyurethane-based elastomers can be mentioned. Core-sheath type or side-by-side type composite fibers made of these elastomers can also be used.

In particular, as the thermoplastic elastomer, an A1-B-A2 type triblock copolymer consisting of polymer blocks A1 and A2 mainly composed of vinyl aromatic polymer and polymer block B mainly composed of polyolefin is used. is preferable from the point of suppressing stress relaxation and the melt moldability of elastic filaments.

The weight average molecular weight of the triblock copolymer as a whole is preferably 70,000 or more and 150,000 or less, more preferably 80,000 or more and 130,000 or less, and 90,000 or more and 110,000 or less. More preferred. When the weight average molecular weight of the triblock copolymer is within this range, the stress relaxation of the elastic filaments containing the triblock copolymer is suppressed, so that the elastic sheet of the present invention maintains the stress. It is possible to increase the rate easily.

For the same reason as described above, the total weight average molecular weight of the polymer blocks A1 and A2 in the triblock copolymer is preferably 20,000 or more and 70,000 or less, and preferably 25,000 or more and 60,000 or less. more preferably 27,000 or more and 50,000 or less.

The polymer block A1 is mainly composed of a vinyl aromatic polymer. Vinyl aromatics constituting the vinyl aromatic polymer include, for example, styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, p-tert-butoxy Styrene, dimethylaminomethylstyrene, dimethylaminoethylstyrene, vinyltoluene, 1-vinylnaphthalene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-(phenylbutyl) Styrene and the like can be mentioned. The vinyl aromatic polymer may be composed of one of these vinyl aromatics, or may be composed of two or more. Of these vinyl aromatics, styrene is preferred from the viewpoint of ease of polymerization and versatility.

The content of the vinyl aromatic polymer in the 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 the polymer block A1. is.

The polymer block A1 may contain a conjugated diene compound polymer in addition to the vinyl aromatic polymer. Conjugated diene compounds constituting the conjugated diene compound polymer include, for example, 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, 3-butyl-1,3-octadiene and the like. The conjugated diene compound polymer may be composed of one of these conjugated diene compounds, or may be composed of two or more.

The content of the conjugated diene compound polymer in the 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 the polymer block A1. is.

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 polymer block as the polymer block A1 can be used. The description for the polymer block A1 applies appropriately to the points that are not particularly described for the polymer block A2.
In the A1-B-A2 type triblock copolymer, polymer block A1 and polymer block A2 may have the same structure or different structures.

In particular, both polymer blocks A1 and A2 are preferably polystyrene. That is, it is preferable that the elastic filament of the present invention contain only polystyrene as the polymer block A1 and only polystyrene as the polymer block A2.

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

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

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 kind of these olefins, or may be composed of two or more kinds. Among these olefins, ethylene and propylene are preferred from the viewpoint of weather resistance and stretchability.

The content of the polyolefin in the 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 the polymer block B.

The polymer block B may contain, in addition to the polyolefin, other polymers polymerizable with the polyolefin, which are derived from other polymerizable monomers. Other polymerizable monomers include, for example, styrene. The other polymer polymerizable with the polyolefin that constitutes the polymer block B may be composed of one kind of these other polymerizable monomers, or may be composed of two or more kinds.

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

Specific examples of the polymer block B include polyisoprene, polybutadiene, poly(ethylene-propylene), poly(ethylene-butylene) and the like. Among these, poly(ethylene-propylene) is preferable from the viewpoint of weather resistance and stretchability.

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

Specific examples of the A1-B-A2 type triblock copolymer include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and hydrogenated products of SBS. Styrene-ethylene-butylene-styrene block copolymer (SEBS), hydrogenated SIS styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS) and the like. Among these, SEBS, SEPS, and SEEPS are preferable from the viewpoint of obtaining elastic filaments having excellent thermal stability and weather resistance.

The elastic resin constituting the elastic filaments may contain only the A1-B-A2 type triblock copolymer described above, and if necessary, the A1-B-A2 In addition to the type triblock copolymer, other one or more resins may be included. 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. % by mass or less, more preferably 95% by mass or more and 100% by mass or less. From the viewpoint of maximizing melt moldability and stretchability, the elastic resin preferably contains only the A1-B-A2 type triblock copolymer.

In addition, the elastic resin constituting the elastic filament may contain one type of A1-B-A2 type triblock copolymer, and two or more types of A1-B-A2 type triblock copolymers having different structures It may be configured including a copolymer.

As described above, in the elastic sheet of the present invention, it is preferable that the elastic resin in the elastic filaments constituting the elastic sheet has a high molecular weight. However, if the molecular weight of the elastic resin is excessively high, the melt moldability of the elastic resin tends to deteriorate. Therefore, as a result of investigations by the present inventors, it was found that it is advantageous to blend oil into the elastic filament for the purpose of obtaining good melt moldability even when a high-molecular-weight elastic resin is used. As the oil, it is preferable to use one that does not easily reduce the cohesive force derived from the hard segments in the elastic resin. In addition, if an oil with a high plasticizing action is used, it tends to act on the hard segments in the elastic resin and reduce the elasticity of the elastic resin. In other words, it can be said that it is preferable to use an oil that has a low plasticizing effect on the elastic resin. From the above point of view, it is preferable to use an oil having a high kinematic viscosity. From this point of view, the kinematic viscosity measured according to JIS K2283 is 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 still more preferably 200 mm ² /s or more. It is preferable to use oil with a velocity of 400 mm ² /s or less.

From the above point of view, it is advantageous to use paraffinic oil as the oil. In particular, it is preferable to use a paraffinic oil whose kinematic viscosity satisfies the above range.
As the paraffinic oil, various aliphatic hydrocarbons called liquid paraffin, liquid paraffin, mineral oil, white mineral oil, etc. can be used without particular limitation.

The ratio of the oil contained in the elastic filament is preferably 25% by mass or more and 60% by mass or less based on the mass of the elastic filament, from the viewpoint of the balance between suppression of stress relaxation of the elastic resin and melt moldability. From the viewpoint of making this advantage more remarkable, the proportion of oil contained in the elastic filament is more preferably 30% by mass or more and 55% by mass or less based on the mass of the elastic filament, and more preferably 30% by mass or more and 50% by mass. % or less.

Since the elastic filament contains the above-described elastic resin and the above-described oil, it is difficult for stress relaxation to occur, and melt moldability is improved. When the meltability of the elastic filament is represented by a melt flow rate (MFR), the melt flow rate measured under a load of 2.16 kg at 230°C according to JIS K7210 is preferably 3 g/10 min or more and 100 g/10 min or less, more preferably. is 5 g/10 min or more and 50 g/10 min or less, more preferably 10 g/10 min or more and 30 g/10 min or less.
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 manufacturing the stretch sheet of the present invention will be described with reference to FIG. 3, taking as an example the method for manufacturing the stretch sheet 10 shown in FIGS.
In this manufacturing method, as shown in FIG. 3, a plurality of molten elastic filaments 13 spun from a spinning nozzle 16 are drawn at a predetermined speed and stretched, and before solidification of the elastic filaments 13, the elastic filaments are drawn. The elastic filaments 13 are fused to the non-woven fabrics 11 and 12 so that the filaments 13 are arranged in one direction without intersecting each other, and then the composite 19 with the fused elastic filaments 13 is stretched along the direction in which the elastic filaments 13 extend. The composite 19 is provided with stretchability by undergoing elasticity development treatment.

A spinning nozzle 16 is provided on a spinning head 17 . A spinning head 17 is connected to the extruder. The elastic resin melted and kneaded by the extruder (this elastic resin is blended with the oil described above as necessary) 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 distance between adjacent spinning nozzles 16 corresponds to the distance between elastic filaments 13 in the target stretchable sheet 10 . The spinning nozzle 16 is generally circular and its diameter affects the diameter of the elastic filament 13 and the draw ratio. From this point of view, the diameter of the spinning nozzle 16 is preferably 0.1 mm or more and 2 mm or less, particularly 0.2 mm or more and 0.6 mm or less. For the purpose of increasing the bonding strength with the nonwoven fabrics 11 and 12, the purpose of increasing the spinnability of the elastic filaments 13, and the purpose of improving the stretchability of the stretchable sheet 10, the elastic filaments 13 are formed in a composite form (side-by-side, core-sheath, sea-island structure). ).

The spun elastic filaments 13 in a molten state join the first nonwoven fabric 11 and the second nonwoven fabric 12 which are fed out from the original fabric at the same speed, are sandwiched between the nonwoven fabrics 11 and 12, and are spun at a predetermined speed. to be taken over. The take-up speed of the elastic filaments 13 matches the delivery speed of both nonwoven fabrics 11 and 12 .

The elastic filaments 13 join the first and second nonwoven fabrics 11, 12 before their solidification, ie in a fusible state. As a result, the elastic filaments 13 are fused to the first and second nonwoven fabrics 11 and 12 while being sandwiched between them. That is, the elastic filaments 13 are drawn and stretched while the elastic filaments before solidification are fused to the non-woven fabrics 11 and 12 being conveyed. No external heat is applied to the first and second nonwoven fabrics 11 and 12 when the elastic filaments 13 are fused. That is, the elastic filaments 13 and the two non-woven fabrics 11 and 12 are fused only by the heat of fusion caused by the elastic filaments 13 that are fused. As a result, among the constituent fibers of both non-woven fabrics 11 and 12, only the fibers existing around the elastic filament 13 are fused with the elastic filament, and the fibers existing further apart are not fused. As a result, the heat applied to both nonwoven fabrics 11 and 12 is kept to a minimum, so that the original good texture of the nonwoven fabrics themselves is maintained. Thereby, the stretch sheet 10 to be obtained has a good texture.

When the elastic filaments 13 and the nonwoven fabrics 11 and 12 are joined, the elastic filaments 13 are substantially in a non-stretched state (a state in which they do not shrink when the external force is removed). In the bonded state of the two, the fibers forming the nonwoven fabrics 11 and 12 and the elastic filaments 13 are at least partially fused. In the above state, it is preferable that both nonwoven fabrics 11 and 12 are fused together while sandwiching the elastic filaments 13 .

Thus, a composite 19 in which the elastic filaments 13 are sandwiched between the two nonwoven fabrics 11 and 12 is obtained. When nonwoven fabrics 11 and 12 that are inherently extensible are used, this composite 19 becomes the stretch sheet 10 itself. On the other hand, when non-woven fabrics 11 and 12 that do not inherently have extensibility are used, the composite 19 containing the non-woven fabrics 11 and 12 is treated to exhibit elasticity along the direction in which the elastic filaments 13 extend, An operation is performed to impart stretchability to the composite 19 . In this manufacturing method, this operation is performed by using an elasticity development processing device 22 having a pair of tooth groove rolls 20 and 21 each having teeth and tooth bottoms alternately formed in the circumferential direction, and the composite 19 is transported in the conveying direction. That is, the elastic filament 13 is subjected to elastic development treatment along the extending direction.

The elasticity developing device 22 has a known elevating mechanism (not shown) for vertically displacing the pivots of one or both of the tooth gap rolls 20, 21, and the gap between the tooth gap rolls 20, 21 can be adjusted. It has become. In this manufacturing method, the teeth of one tooth space roll 20 are loosely inserted between the teeth of the other tooth space roll 21, and the teeth of the other tooth space roll 21 are inserted into the teeth of one tooth space roll. The grooved rolls 20 are combined so as to be loosely inserted between the teeth of the grooved rolls 20, and the composite 19 is inserted between the tooth grooved rolls 20 and 21 in that state and subjected to elasticity development treatment.

The target stretchable sheet 10 is obtained by subjecting the composite 19 to elasticity development treatment by a pair of tooth groove rolls 20 and 21 . After passing through the tooth groove rolls 20 and 21, the obtained stretchable sheet 10 is quickly released from the stretched state in the conveying direction by its own shrinkage restoring force. As a result, the stretchable sheet 10 restores its length in the conveying direction. As a result, in the stretched state, the high stretch regions and the low stretch regions are alternately arranged in the direction in which the elastic filaments 13 extend.

The stretch sheet of the present invention thus obtained is suitably used, for example, as an outer covering for disposable diapers. Disposable diapers provided with the elastic sheet of the present invention, such as pants-type disposable diapers, are easy to spread the waist when worn, and are difficult to slip off even when worn for a long period of time. .
In addition to the above applications, the elastic sheet of the present invention can be used for various applications such as medical disposable clothing, cleaning sheets, eye patches, masks, and bandages, taking advantage of its good texture, elasticity, and breathability. can also be used. In particular, it is preferably used as a constituent material for absorbent articles such as sanitary napkins and disposable diapers. The constituent materials include, for example, a liquid-permeable sheet (including a top sheet, a sublayer sheet, etc.) positioned closer to the skin than the absorbent body, a sheet constituting the outer surface of a disposable diaper, a waist portion, a waist portion, A sheet or the like for imparting elastic stretchability to the leg-surrounding part or the like can be mentioned. It can also be used as a sheet forming wings of a napkin. Moreover, even if it is a part other than that, it can be used for a part etc. to which elasticity is desired to be imparted. The basis weight and thickness of the stretchable sheet can be appropriately adjusted according to its specific use. For example, when used as a constituent material of an absorbent article, it is desirable that the basis weight is about 20 g/m ² or more and 60 g/m ² or less, and the thickness is about 0.5 mm or more and 1.5 mm or less.

The stretchability of the stretch sheet can be appropriately set according to the specific use of the stretch sheet. For example, when the stretch sheet is used as an exterior body of a disposable diaper, the initial stress A measured in the measurement of the stress retention rate described in the examples described later is preferably 10 cN/50 mm or more and 500 cN/50 mm or less, and 20 cN. /50 mm or more and 250 cN/50 mm or less, and more preferably 30 cN/50 mm or more and 100 cN/50 mm or less.

EXAMPLES The present invention will be described in more detail below with reference to examples. However, the scope of the invention is not limited to such examples. "%" means "% by mass" unless otherwise specified.

[Example 1]
(1) Preparation of Elastic Filaments Elastic filaments containing a thermoplastic elastomer and oil shown in Table 1 below were prepared. The percentage of oil contained in the elastic filaments is as shown in the same table. The MFR of the elastic filament is also shown in the same table.

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

(3) Manufacture of stretch sheet The stretch sheet having the structure shown in Fig. 1 and Figs. 2(a) and 2(b) was manufactured using the apparatus shown in Fig. 3 .
The elasticity development treatment was performed using an elasticity development treatment device 22 having a pair of tooth groove rolls 20 and 21 in which teeth and tooth bottoms were alternately formed in the axial direction. As a result, a stretchable sheet 10 having a basis weight of 46 g/m ² and stretchable in the direction in which the elastic filaments 13 extend was obtained.

[Examples 2 to 4]
The oil shown in Table 1 below was used as the oil mixed with the elastic filament. Also, the ratio of the oil contained in the elastic filaments was as shown in Table 1. A stretch sheet was obtained in the same manner as in Example 1 except for these.

[Comparative Examples 1 to 3]
As the thermoplastic elastomer constituting the elastic filaments, those shown in Table 1 below were used. Also, no oil was added to the elastic filaments. A stretch sheet was obtained in the same manner as in Example 1 except for these. In Comparative Example 3, the melt fluidity of the elastic resin was poor, and the elastic filaments could not be melt-spun.

〔evaluation〕
The stress retention rate of the stretch sheets obtained in 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 of the stretch sheet 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 distance between chucks of 100 mm so that the direction of expansion and contraction was the direction of tension.
At an ambient temperature of 40° C., the test piece was pulled at a speed of 300 mm/min, and when the chuck-to-chuck distance reached 200 mm, the pulling was stopped and the state was maintained for 2 hours, during which the stress was measured over time.
The stress retention rate (%) is defined as B/A×100, where A is the initial stress when the chuck-to-chuck distance reaches 200 mm, and B is the stress after 2 hours.

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

REFERENCE SIGNS LIST 10 elastic sheet 11 first nonwoven fabric 12 second nonwoven fabric 13 elastic filament 14 high basis weight region 14' crest 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,
High elongation regions and low elongation regions extending in a direction orthogonal to the stretching direction of the stretch sheet are alternately arranged along the stretching direction,
said elastic filaments being fused to said nonwoven fabric in a substantially non-stretched state;
A stretch 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,
A high stretch region and a low stretch region are arranged alternately along the stretch direction in a direction orthogonal to the stretch direction of the stretch sheet,
said elastic filaments being fused to said nonwoven fabric in a substantially non-stretched state;
A stretch sheet, wherein the elastic filaments comprise a thermoplastic elastomer and oil. 3. The stretch sheet according to claim 2, wherein the proportion of said oil is 25% by mass or more and 60% by mass or less based on the mass of said elastic filaments. The stretch sheet according to claim 2 or 3, wherein the oil is paraffinic oil. The thermoplastic elastomer is an A1-B-A2 type triblock copolymer consisting of polymer blocks A1 and A2 mainly composed of vinyl aromatic polymer and polymer block B mainly composed of polyolefin, is 70,000 or more and 150,000 or less, and the total weight average molecular weight of the polymer blocks A1 and A2 is 27,000 or more and 70,000 or less, Elastic sheet as described. The elastic filament according to any one of claims 1 to 5, wherein the melt flow rate measured under a load of 2.16 kg at 230°C is 3 g/10 min or more and 100 g/10 min or less according to JIS K7210. stretch sheet.

Images