Patent Description:
In absorbent articles, for example, disposable diapers, in order to improve fit to the body surface, it is common to impart elasticity to appropriate positions such as around the legs and around the waist. Conventionally, as a technique for imparting elasticity, a technique of fixing an elongated elastic member such as a rubber thread in a state of being stretched in the longitudinal direction has been widely adopted, but when it is desired to impart elasticity with a certain width, a manner is adopted in which rubber threads are fixed along the width direction in a state of being arranged side by side at intervals.

On the other hand, as a material which imparts elasticity by pressing on a surface in place of a plurality of rubber threads disposed in parallel and which is selected also from consideration on texture, a stretchable sheet having a structure of nonwoven web/elastomer film/nonwoven web is proposed. (Refer to, for example, Patent Literature <NUM>).

Patent Literature <NUM> discloses an un-apertured embodiment in which apertures are not formed in the whole of a first outer layer, a second outer layer, and an elastic film (elastomer) as well as an apertured embodiment in which apertures are formed through the whole of the first outer layer, the second outer layer, and the elastic film.

In the un-apertured embodiment, when the stretchable sheet is used as a sheet constituting, for example, the back side of a disposable diaper, there is a problem such as stuffiness because there is no air permeability.

On the other hand, in the apertured embodiment disclosed in Patent Literature <NUM>, between the first outer layer and the second outer layer, an elastic film is supplied continuously; the elastic film is stretchable in a machine direction (MD) and has a melting point higher than the melting points of the first outer layer and the second outer layer or having no melting point; and the first outer layer and the second outer layer are directly bonded at predetermined sites by welding. Then, by applying a stretching force in a cross direction (CD), through holes that penetrate throughout the first outer layer, the elastic film, and the second outer layer are formed in the bond sites to ensure air permeability.

In any case, if an elastic film (elastomer) is stretched in the MD, so-called neck-in occurs by which the width of the elastic film is decreased. As a result of this neck-in, in order to obtain a laminated sheet having a desired width, it is necessary to prepare an elastic film having a width wider than each width of the first outer layer and the second outer layer, which leads to high cost of the material.

In addition, with respect to the CD of the actually laminated sheet, a stretching stress differs between the center in the width direction and the both side portions in the width direction due to the neck-in of the elastic film, and when the laminated stretchable sheet is applied to a product, for example, a disposable diaper, there may be a problem that uniform stretching stress cannot be obtained.

On the other hand, Patent Literature <NUM> discloses a method in which a plurality of stretch rolls is provided, and stretching is performed in the process of passing over the stretch rolls. In this method, "necking" is considered, and this method is intended to suppress "necking" (neck-in) by shortening the distance between the stretch rolls, but it does not seem to indicate sufficient effects.

<CIT> relates to a tape-type disposable diaper having a tape made of a stretchable sheet, and a method for manufacturing the same, wherein the method comprises a supply step of interposing an extendable and contractible elastic film in an elongated state; and a supplying step of supplying the elastic film in an extended state between the first sheet layer and the second sheet layer, applying a thermal melting energy to the elastic film from a plurality of hot melting portions spaced apart by a heat melting device from the outside of the first sheet layer and the second sheet layer to melt the elastic film. According to an embodiment, the heat melting device comprises an ultrasonic horn for bonding, an anvil roll having projections, an opposed roll facing the anvil roll, and a drive roll for nipping the elastic film between the drive roll and the opposed roll. According to a drawing, the elastic film is nipped between the anvil roll and the opposed roll, and the holding angle with which the elastic film passes along the opposed roll and the holding angle with which the elastic film and the second sheet layer passes along the anvil roll are both not less <NUM>°.

<CIT> describes a method for manufacturing a stretchable sheet.

<CIT> relates to an absorbent article provided with a stretchable sheet, wherein a method for manufacturing the stretchable sheet is described.

<CIT> is concerned with an elastic film stretching structure in which an elastic film is layered between a first sheet layer and a second sheet layer, including a region having a non-stretching region and a stretching region being bonded via through-holes penetrating through the elastic film by numerous sheet bonding sections, and a method for preparing the same.

<CIT> relates to a pants-type disposable diaper comprising an elastic area formed by a first sheet layer made from nonwoven cloth and a second sheet layer made from nonwoven cloth, having laminated therebetween an elastic film, the first sheet layer and second sheet layer are joined via through holes formed in the elastic film at a large number of sheet joining sections. A method for preparing the same is also described.

<CIT> describes a pants-type disposable diaper formed as a stretchable region formed as a stretchable elastic film structure in which a first sheet layer and a second sheet layer are bonded directly or indirectly with a plurality of sheet bonding sections aligned in a state in which an elastic film is laminated between the first and the second sheet layer sheet layer and the elastic film is stretched in the width direction. A method for preparing the same is also described.

Therefore, the main object of the present invention is to provide a method for manufacturing a stretchable sheet capable of suppressing neck-in.

The present invention that have solved the above problem will be described below.

A method for manufacturing a stretchable sheet of the present invention includes:.

In the stretchable sheet obtained according to one embodiment of the present invention, no holes penetrating the first sheet layer and the second sheet layer are formed. It is different from the stretchable sheet illustrated in <FIG> or <FIG> of <CIT> in this respect.

On the other hand, it is possible to form a through hole at least at a boundary portion between the elastic film and the bonded portion in the MD by supplying the elastic film in a stretched state in the MD to a bonding position. The reason why this through hole is formed will be described in detail later.

The heat melting apparatus has an anvil roll and an ultrasonic horn and is a unit for melting at least a part of at least one of the first sheet, the second sheet layer, and the elastic film by energy to be applied.

It is considered that, as the elastic film stretches, unevenness of a group of the protrusions on the anvil roll suppresses, as the resistance, the neck-in which is intended to cause due to the moving force toward the center in the width direction of the elastic film.

In the present invention, a counter roll is disposed apart from an anvil roll, and a nip roll that nips an elastic film is disposed corresponding to the counter roll.

The elastic film passes through the nip position between the counter roll and the nip roll and passes along the counter roll and the anvil roll, and by making the circumferential speed of the anvil roll faster than the circumferential speed of the counter roll, the elastic film is stretched.

That is, since the elastic film is nipped between the counter roll and the nip roll, by setting the circumferential speed of the anvil roll faster than the circumferential speed of the nip roll, the elastic film is substantially started to stretch (elongate) from the nip position.

Furthermore, since the elastic film passes along the anvil roll after passing along the counter roll, the resistance between the elastic film and the roll surface of the counter roll and the surface of the anvil roll suppresses the neck-in.

Moreover, owing to nipping, the resistance force between the elastic film and at least the surface of the counter roll further increases, which is considered to contribute to suppressing the neck-in.

It is desirable that the elastic film be not stretched on the upstream side of the nip position, and even if it is stretched, a stretch rate be equal to or less than <NUM>% of the required stretch rate.

Therefore, according to a preferred embodiment of the present invention, stretching is started from the nip position. Alternatively, stretching of more than <NUM>% of the required stretch rate is started from the nip position.

It is desirable that the distance between the nip position and the bonding position be less than <NUM>. Particularly <NUM> to <NUM> is desirable.

When the elastic film starts to separate from the anvil roll at a distance of <NUM> or less on the downstream side of the bonding position after passing the bonding position, it is desirable that a distance between the nip position and the position where the elastic film starts to separate from the anvil roll be less than <NUM>.

The anvil roll is desirably a crown roll rather than a flat roll. If the anvil roll is a crown roll, the resistance force of the elastic film to a crown roll surface is strengthened, which is considered to contribute to suppressing neck-in.

For example, the bonded portions are disposed in a staggered shape.

In one embodiment of the present invention, when the anvil roll is viewed in an unfolded state, it is desirable that an area rate of the total area occupied by the group of the protrusions included in the unit area be different at least according to the roll length direction.

On the other hand, it is possible to form a through hole at least at a boundary portion between the elastic film and the bonded portion in the MD by supplying the elastic film in a stretched state in the MD to the bonding position.

For the bonded portion of the present invention, for example, the following bonding modes can be raised.

Among these modes, particularly in the mode (<NUM>) and the mode (<NUM>), difference in strength of the elastic film arises between a bonded portion and a non-bonded portion. Therefore, after releasing the stretched state of the stretchable sheet holding stretchability once to contract the stretchable sheet to make a product; or after bonding the stretchable sheet holding stretchability to another member and releasing the stretched state once to make a product, when the stretchable sheet is stretched in the stretchable direction mechanically or manually, breakage occurs at a boundary portion between the bonded portion and the non-bonded portion.

With the through hole formed, there is an advantage that air permeability is secured. The through hole does not need to be formed at every bonded portion, and air permeability is shown even if the through holes are formed at not all but some bonded portions. When the elastic film is stretchable only in the MD, the through hole has a shape extending in the MD from the edge of the bonded portion. When the elastic film is stretchable both in the machine direction (MD) and in a direction orthogonal thereto (for example, CD), the through hole has a shape extending in both directions from the edge of the bonded portion, and may have an annular shape around the bonded portion.

As described above, since the elastic film of the present invention generally uses an elastomer, it is stretchable in the MD and the orthogonal direction (CD).

Besides a shape which does not have a directionality such as a circle, the bonded portion has a shape which has a length in the orthogonal direction (width direction: CD) being longer than the length in the MD.

To implement the method according to the present invention, the melting point of the elastic film is preferably about <NUM> to <NUM>, and the melting points of the first sheet layer and the second sheet layer are preferably about <NUM> to <NUM>, particularly preferably <NUM> to <NUM>. The difference between the melting points of the first sheet layer and the second sheet layer and the melting point of the elastic film <NUM> that is a lower melting point is preferably about <NUM> to <NUM>.

As a preferred specific example, the melting point of the elastic film is <NUM> to <NUM>, the melting point of the first sheet layer is higher than <NUM> and not higher than <NUM>, more preferably <NUM> to <NUM>, and the second sheet layer has a melting point of higher than <NUM> and not higher than <NUM>, more preferably <NUM> to <NUM>.

When the anvil roll is viewed in an unfolded state, it is desirable that the area rate of the total area occupied by the group of the protrusions included in the unit area be different at least according to the roll length direction.

The protrusions correspond to the bonded portions. As a preferred example of the bonded portion, the area of the bonded portion is <NUM><NUM> to <NUM><NUM>. Further, the area rate of the bonded portions is desirably <NUM>% to <NUM>%.

The area rate of the bonded portions in a stretchable region is <NUM>% to <NUM>%.

Here, "area rate" refers to a rate of a target portion to a unit area and expresses the rate as a percentage by dividing a total area of the target portions (for example, the bonded portions, the openings of the through holes) in a target region (for example, the stretchable region) by an area of the target region. In particular, the "area rate of the bonded portions" means an area rate in a state where the stretchable region is stretched to the elastic limit in the stretchable direction.

It is preferable that the area of the opening of the through hole in a state of natural length of the stretchable sheet is more than <NUM> time and not more than <NUM> times the area of the bonded portion.

The area of the opening of the through hole refers to a value while a stretchable structure is in a state of natural length and refers to the minimum value in the case where the area of the opening of the through hole is not uniform in the thickness direction such as a case where the area on the front surface of the elastic film is different from the area on the back surface of the elastic film.

By selecting the size, shape, separation distance, arrangement pattern in the roll length direction and roll circumferential direction, etc. of protrusions of the anvil roll to be described later, the area rate of the bonded portions described herein can be selected.

"Stretching stress" to be described later indicates "a stress (N/<NUM>) in stretching to <NUM>% of the elastic limit" measured by a tensile test at the initial chuck interval (distance between the gauge marks) of <NUM>, and the speed of testing of <NUM>/min according to <NPL>-". When a test piece with a width of <NUM> cannot be cut out, a test piece is formed with a maximum possible width and the measured value is converted into a value at a width of <NUM>. Even if a sufficiently large test piece cannot be prepared from a target region with a small area, small test pieces can also be used for comparison of the stretching stress at least.

Further, in the embodiment to be described later, when a plurality of different stretching stresses are present in the region, how to collect a test piece for verifying the difference in the stretching stresses becomes a problem. In this case, in order to compare the stretching stresses, apart from obtaining the absolute value of the stretching stress, test pieces are taken from each site of the stretchable sheet, and for the respective test pieces, it is also possible to compare the stresses when the stretchable sheet is stretched from a natural length (<NUM>%) to <NUM>% length.

As described above, the present invention provides a method for manufacturing a stretchable sheet capable of suppressing neck-in and reducing material costs.

The stretchable sheet of the present invention can be used, for example, for absorbent articles that absorb and retain body fluids, such as disposable diapers, sanitary napkins, absorbent pads and the like.

As illustrated in <FIG>, in the stretchable sheet, an elastic film <NUM> stretchable in the front-back direction is stacked between a first sheet layer <NUM> made of, for example, a nonwoven fabric having no elasticity and a second sheet layer <NUM> having no elasticity such as a nonwoven fabric, and the first sheet layer <NUM> and the second sheet layer <NUM> are bonded to each other directly or via the elastic film <NUM> with a large number of bonded portions <NUM> spaced apart from each other.

Here, the expression "no elasticity" does not mean that the first sheet layer <NUM> and the second sheet layer <NUM> do not stretch at all. Instead, it means that the elastic film is not substantially stretchable compared with the elastic film.

Regarding bonding, for example, as illustrated in <FIG> indicating a first bonding example, which is not according to the present invention, between an anvil roll <NUM> having protrusions 60a formed in a predetermined pattern on the outer surface and an ultrasonic horn <NUM>, the first sheet layer <NUM>, the elastic film <NUM>, and the second sheet layer <NUM> are supplied, ultrasonic melting energy is applied by the ultrasonic horn <NUM>, and, for example, mainly the elastic film <NUM> is melted, to bond the first sheet layer <NUM> and the second sheet layer <NUM>.

A counter roll <NUM> is disposed so as to face the anvil roll <NUM>. Further, a nip roll <NUM> for nipping the elastic film <NUM> is provided on the counter roll <NUM>. The anvil roll <NUM> is driven such that the circumferential speed of the anvil roll <NUM> becomes faster than the circumferential speed of the counter roll <NUM> and the nip roll <NUM>.

In this structure of the apparatus, after the elastic film <NUM> passes through a nip position at which the elastic film <NUM> is nipped by the counter roll <NUM> and the nip roll <NUM>, the elastic film <NUM> passes along the outer periphery of the counter roll <NUM> and then passes along the anvil roll <NUM>.

At that time, the elastic film <NUM> is stretched by setting the circumferential speed of the anvil roll <NUM> to be driven to be faster than the circumferential speed of the counter roll <NUM> and the nip roll <NUM>, and bonding is performed by the ultrasonic horn <NUM> and the group of the protrusions 60a of the anvil roll <NUM>.

At this time, by selecting the speed difference that makes the circumferential speed of the anvil roll <NUM> faster than the circumferential speed of the nip roll <NUM>, the stretch rate in the manufacturing process of the elastic film <NUM> (when the length in a natural state is taken as <NUM>%) can be set.

In the example of <FIG>, although the anvil roll <NUM> and the counter roll <NUM> do not nip the elastic film <NUM>, they are disposed close to each other. Then, the elastic film <NUM> passes along the counter roll <NUM> with the holding angle θ of more than <NUM>° and less than <NUM>° with respect to the counter roll <NUM>. From the nip position with the nip roll <NUM>, the holding angle α is approximately <NUM>°.

The elastic film <NUM> and the second sheet layer <NUM> pass along the anvil roll <NUM> with a holding angle β of about <NUM>°.

The arrangement of the anvil roll <NUM>, the counter roll <NUM>, and the nip roll <NUM> is to be selected appropriate. For example, as illustrated in <FIG> indicating a second bonding example, which is according to the invention, the anvil roll <NUM> and the counter roll <NUM> are disposed slightly apart without nipping the elastic film <NUM>. In the example of <FIG>, the elastic film <NUM> is not in contact with the counter roll <NUM> until reaching a position of the nip roll <NUM>.

As a result, the elastic film <NUM> passes along the counter roll <NUM> with the holding angle α of less than <NUM>° with respect to the counter roll <NUM>.

The elastic film <NUM> and the second sheet layer <NUM> pass along the anvil roll <NUM> with the holding angle β of less than <NUM>°.

A distance from a position where the elastic film <NUM> is separated from the counter roll <NUM> to a position where the elastic film starts to be held by the anvil roll <NUM> is <NUM> or less, preferably <NUM> or less, particularly preferably <NUM> or less for suppressing neck-in.

In the example of <FIG> indicating a third bonding example, which is not according to the invention, although the anvil roll <NUM> and the counter roll <NUM> do not nip the elastic film <NUM>, they are disposed close to each other. Then, the nip roll <NUM> is disposed to the counter roll <NUM>, and the elastic film <NUM> passes along the counter roll <NUM> with the holding angle α of more than <NUM>° and less than <NUM>°.

In the first bonding example to the third bonding example described above, stretching (elongation) of the elastic film <NUM> is started from the nip position between the counter roll <NUM> and the nip roll <NUM>. However, in the fourth bonding example <NUM>, which is not according to the invention, the elastic film <NUM> is nipped between the pre-roll <NUM> and the pre-nip roll <NUM>, and the elastic film <NUM> is nipped between the counter roll <NUM> and the nip roll <NUM>, such that the circumferential speed of the pre-roll <NUM> and the pre-nip roll <NUM>, the circumferential speed of the counter roll <NUM> and the nip roll <NUM>, and the circumferential speed of the anvil roll <NUM> are gradually increased, whereby it is possible to stretch (elongate) two stages.

It is possible to stretch (elongate) three stages by adding the same structure.

<FIG> shows a result of examining the relationship between the distance from the nip position to the bonding position and the neck-in ratio.

According to <FIG>, the neck-in ratio does not increase in direct proportion to the distance between the stretching rollers, but the neck-in ratio suddenly increases when the distance between the stretching rollers is reached to <NUM> or more. Therefore, in the example illustrated in <FIG>, it is desirable that the distance from the nip position for the elastic film <NUM> between the counter roll <NUM> and the nip roll <NUM> to the bonding position of the anvil roll <NUM> be <NUM> or less. In particular, <NUM> or less is desirable.

Further, with respect to the counter roll <NUM>, the holding angle α from the nip position for the elastic film <NUM> to the position where the elastic film <NUM> is separated is desirably <NUM>° to <NUM>° (more desirably <NUM>° to <NUM>°) to suppress neck-in. It is desirable for the neck-in suppression that the holding angle β of the anvil roll <NUM> is <NUM>° to <NUM>° (more desirably <NUM>° to <NUM>°). According to the present invention, both the holding angle α and the holding angle β is less than <NUM>°.

As can be inferred from the result of <FIG>, when stepwise stretching (elongation) is performed as in the example of <FIG>, in comparison with one stage stretching (elongation) as in the first bonding example to the third bonding example, the separation distance from the nip position to the bonding position becomes longer, which is not preferable. One stage stretching (elongation) as in the first bonding example to the third bonding example is desirable, and it is desirable that the elastic film does not stretch on the upstream side of the nip position.

It is preferable that the anvil roll <NUM> is a crown roll as illustrated in <FIG>. The length of the anvil roll <NUM> is preferably about <NUM>.

The amount of crown can be selected appropriately, but if necessary, the amount of crown can be adjusted by cooling the end of the roll.

On the other hand, the protrusions 60a of the anvil roll <NUM> can be formed so as to be denser toward the center of the roll length. In such arrangement, the central portion is most thermally expanded, and the crown is easily applied.

On the other hand, it is preferable to use die steel for the material of the anvil roll <NUM>, and the optimal hardness is HRC <NUM> to <NUM>.

<FIG> schematically illustrates a section of the stretchable sheet after bonding in a stretched state (however, a through hole is not yet formed). When the stretched state of the stretchable sheet in the MD (the right-left direction in <FIG>) is released, as illustrated in <FIG> (schematic view), the stretchable sheet contracts due to the contracting force of the elastic film <NUM> and can be stretched by applying an external force. Therefore, if the stretchable sheet is applied for example to a disposable diaper, when the stretchable direction of the stretchable sheet is made to coincide with the front-back direction of the disposable diaper, the disposable diaper can be stretched in the front-back direction. When the stretchable direction is made to coincide with the width direction of the disposable diaper, the disposable diaper can be stretched in the circumferential direction of the lower torso part or the circumferential direction of the waist portion.

The stretchable sheet can be manufactured in the product production line, and the stretchable sheet obtained after cutting the web into a desired area after manufacturing the stretchable sheet web, can be applied to a predetermined site of a product.

In a conventional disposable diaper, it is common to fix a plurality of rubber threads in parallel on a sheet, but this causes inferior quality due to deterioration of a hot melt adhesive for fixing the rubber threads to the sheet, and it is difficult to keep stable productivity at the time of production. These problems can be solved by the above-described stretchable sheet.

In addition, as can be seen from the contracted state of <FIG>, since, on the outer surface of the stretchable sheet, fine wrinkles or fine pleats are regularly generated, and texture of the sheet to the wearer's skin is improved.

On the other hand, in the above example, the first sheet layer <NUM> and the second sheet layer <NUM> are bonded by melting the elastic film <NUM>. In this case, there are (<NUM>) a mode in which the first sheet layer <NUM> or the second sheet layer <NUM> is bonded on the surface of the elastic film <NUM>, (<NUM>) a mode in which the surface portion of the elastic film <NUM> melts and it intrudes into fibers of each of the first sheet layer <NUM> and the second sheet <NUM> for bonding the sheet layers <NUM>, <NUM>, and (<NUM>) a mode in which almost all of the elastic film <NUM> melts, and it intrudes into fibers of each of the first sheet layer <NUM> and the second sheet layer <NUM> for bonding the sheet layers <NUM>, <NUM>. In the present invention, the bonding modes of the layers are not limited to these examples.

In the mode (<NUM>) among these modes, it can be evaluated that the first sheet layer <NUM> and the second sheet layer <NUM> are bonded directly, that is, while the elastic film is not remained.

In the above modes (<NUM>) to (<NUM>), the melting point of the elastic film <NUM> is lower than the melting points of the first sheet layer <NUM> and the second sheet layer <NUM>. However, when the melting point of the elastic film <NUM> may be higher than the melting point of the first sheet layer <NUM> and/or the second sheet layer <NUM>. In this case, the surface portion of the first sheet layer <NUM> and/or the second sheet layer <NUM> on the elastic film <NUM> side is activated or melted to be bonded to the elastic film <NUM>.

Further, in addition to melting a part of the elastic film <NUM>, the first sheet layer <NUM> and/or the second sheet layer <NUM> may also be melted and bonded.

The first sheet layer <NUM> and/or the second sheet layer <NUM> may be a nonwoven fabric, and the fiber may have a core/sheath structure. In this case, for example, only the sheath component of the fiber melts and can contribute to bonding.

In the stretchable sheet of the present invention, the shape, size and arrangement of the bonded portions may be uniform, and also the rate of the total area occupied by the bonded portions included in the unit area of the region to the unit area, that is, the area rate of the bonded portions can be selected.

<FIG> is a plan view of an example in which an arrangement pattern of bonded portions (approximate to an arrangement pattern of a group of protrusions when an anvil roll is viewed in an unfolded state) is illustrated.

As in <FIG>, as the area rate of the bonded portions in a state where the stretchable sheet is stretched to the elastic limit in the stretchable direction, the area rate of the total area occupied by the bonded portions <NUM>, <NUM>. included in the unit area S is indicated by percentage. In this case, it is desirable to set the unit area S to such a size that ten or more bonded portions are included (comparison of stretching stresses is difficult with a small number of bonded portions). In the example of <FIG>, thirteen bonded portions are included. In addition to a square shape, the outer shape that defines the unit area S may be another shape such as a rectangle or a circle.

An example of the bonded portion <NUM> is a circular shape illustrated in <FIG>. It is obvious that the bonded portion <NUM> has a shape such as an ellipse or a rectangle. Lm in <FIG> is an arrangement interval length in the MD, Lc is an arrangement interval length in the orthogonal direction (cross direction: CD) orthogonal to the MD, Pm is a pitch length in the MD, and Pc is a pitch length of the orthogonal direction (CD).

<FIG> illustrate embodiments in each of which the area rate of the bonded portions varies depending on the regions in the stretchable sheet.

<FIG> illustrates the relationship of the stretching stress between the regions A and B, which is set to be A > B by setting the relationship of the area rate of the bonded portions between the regions A and B to A < B.

For example, when the region A in which the pitch length Pm and the pitch length Pc are long is compared with the regions B in each of which the pitch length Pm and the pitch length Pc are short, the stretch rate is larger in the region A in which the pitch lengths Pm and Pc are long (that is, the area rate of the bonded portions is low) than in the regions B in each of which the pitch lengths Pm and Pc are short (that is, the area rate of the bonded portions is high). As a result, relationship of the stretching stress is set to A > B.

In the embodiment of <FIG>, since the stretching stress in the lateral direction of <FIG> varies depending on the regions, the region A having a large stretching stress is made to correspond to the central section in the width direction of an absorbent article. Then, the regions B in each of which the stretching stress is small (that is, the stretchability is small) are made to correspond to both laterally external side sections with respect to the region A corresponding to the central section.

In the case of <FIG>, the regions B having small stretching stress are disposed on the front side and back side with respect to the region A at the middle in the front-back direction of a central part of the stretching sheet. In this example, the front and back regions B, B can correspond to, for example, the end portions in the front-back direction of a disposable diaper, and since the stretching stress is small at these end portions in the front-back direction, the shape stability is improved such that a wearer can easily wear the disposable diaper.

In the present invention, the difference in the area rate of the bonded portions can be obtained not only by varying the density of the bonded portions in an arrangement pattern but also by changing the area of each bonded portion.

In order to make this easier to understand, <FIG> illustrates an example in which a large number of small bonded portions are disposed in the region C and the area occupied by the small bonded portions in the region C is the same as the area occupied by the bonded portions in the region D. By setting the relationship of the area of the bonded portions among the regions A, C and D to A < C = D, the relationship of the stretching stress is set to A > C = D.

Physical properties such as thickness, material, strain/stress characteristic, melting point and the like of the elastic film can be appropriately selected. By selecting the relationship among this elastic film, the ultrasonic melting energy applied to the elastic film, and the stretch rate of the elastic film at the time of manufacturing the stretchable sheet, as illustrated in <FIG>, the through hole <NUM> can be formed around each of the bonded portions <NUM>. When the first sheet layer <NUM> and the second sheet layer <NUM> are formed using, for example, nonwoven fabrics as the materials, since the nonwoven fabrics exhibit air permeability, air permeability is exhibited on the front surface and back surface of the stretchable sheet due to the formed through holes <NUM>. Therefore, when the stretchable sheet is used as, for example, an external sheet or an outer sheet of a disposable diaper, the air permeability of the disposable diaper is improved.

Although the reason why such a ventilation through hole <NUM> is formed is not necessarily clear, since the elastic film <NUM> is melted with the ultrasonic melting energy and the bonded portions <NUM> are thinned by pressing from the protrusions 60a of the anvil roll <NUM>, it is considered that, at this time, while the elastic film <NUM> is also thinned, the peripheral portion of the bonded portion <NUM> reaches the breaking strength, breakage is started by the stretching stress acting on the stretched elastic film <NUM>, the elastic film <NUM> contracts to an equilibrium point, and the through hole <NUM> opens.

<FIG> schematically illustrates an example of the through hole <NUM> formed for the bonded portion <NUM> which is formed in the case of the circular protrusion 60a. Substantially crescent shaped through holes <NUM> are formed on both sides in the MD (stretchable direction) of the bonded portion <NUM>.

The bonded portion can be elongated in the direction (CD) orthogonal to the stretchable direction (MD). In this case, for example, as illustrated in <FIG>, semicircular through holes <NUM> each having a large opening can be formed, which is a preferable means when it is desired to increase the air permeability.

On the other hand, it is not indispensable for the through hole <NUM> to be formed in all the bonded portions. If it is required to reliably form the through hole <NUM> or to make a large opening, the method indicated in <FIG> can be adopted.

That is, as illustrated in <FIG>, the stretchable sheet provided with the bonded portions <NUM> is passed between a pair of the rolls <NUM> having projections or protrusions 64a, each protrusion 64a of one roll <NUM> is inserted between each pair of adjacent protrusions 64a of the other roll <NUM>, and a deforming force is applied to the stretchable sheet to form the through hole <NUM>.

Meanwhile, the shapes of the individual bonded portions <NUM> and the through holes <NUM> in the natural length state can be arbitrary shapes such as polygonal shapes (including linear and rounded) such as a perfect circle, an elliptical shape, and a rectangular shape, a star shape, a cloud shape, and the like. The size of each bonded portion <NUM> may be determined appropriately, but if it is too large, the hardness of the bonded portion <NUM> exerts an influence on the texture, and if it is too small, a bonded area becomes too small and materials are insufficiently adhered. Therefore, in the usual case, the area of each bonded portion <NUM> is preferably about <NUM> to <NUM><NUM>. The area of an opening of each through hole <NUM> may be equal to or more than that of the bonded portion because the bonded portion is formed through the through hole <NUM>, and it is preferable to set to about <NUM> to <NUM> times the area of the bonded portion.

Further, for the bonded portions of the present invention, a main elastic region may be directly transferred to a non-elastic region, but it is also possible to provide a transition elastic region between the main elastic region and the non-elastic region.

In general, the area and the area rate of the individual bonded portions <NUM> in each region are preferably set as follows.

Although the planar arrangement of the bonded portions <NUM> and the through holes <NUM> can be appropriately determined, it is preferable to adopt a planar arrangement in which they are regularly repeated, such as an oblique lattice shape as illustrated in <FIG>, a hexagonal lattice shape (also referred to as a staggered shape) as illustrated in <FIG>, a square lattice shape as illustrated in <FIG>, a rectangular lattice shape as illustrated in <FIG>, and a parallelotope lattice shape as illustrated in <FIG> (two groups are provided such that a large number of parallel oblique row groups cross each other in the drawing) (including those inclined at an angle of less than <NUM>° with respect to the stretchable direction). Additionally, it is also possible to adopt a planar arrangement in which a group of the bonded portions <NUM> (each group may be regularly or irregularly arranged, and may be a pattern, a letter shape etc.) can be regularly repeated. The arrangement pattern of the bonded portions <NUM> and the through holes <NUM> may be the same in the main elastic region, the transition elastic region, and the non-stretchable region, or may be different.

The elastic film <NUM> is not particularly limited, and a resin film having elasticity can be used without particular limitation. A blend of one or two or more thermoplastic elastomers such as styrene elastomers, olefin elastomers, polyester elastomers, polyamide elastomers and polyurethane elastomers, which is processed into a film shape by extrusion molding such as T-die method or inflation method can be used. As the elastic film <NUM>, besides a non-porous film, it is also possible to use a film having a large number of holes or slits for ventilation. In particular, it is preferable that in the elastic film <NUM>, the tensile strength in the stretchable direction is <NUM> to <NUM> N/<NUM>, the tensile strength in the direction orthogonal to the stretchable direction is <NUM> to <NUM> N/<NUM>, the tensile elongation in the stretchable direction is <NUM> to <NUM>%, and the tensile elongation in the direction orthogonal to the stretchable direction is <NUM> to <NUM>%. Now that the tensile strength and the tensile elongation (tensile elongation at break) refer to values obtained by measuring at an initial chuck interval of <NUM> and a speed of testing of <NUM>/min according to JIS K7127: <NUM> "Plastics-Determination of tensile properties-" except that the test piece is formed into a rectangular shape having a width of <NUM> × a length of <NUM> using a tensile tester (for example, AUTOGRAPHAGS-G100N manufactured by SHIMADZU Corporation). The thickness of the elastic film <NUM> is not particularly limited, but it is preferably about <NUM> to <NUM>. Although the basis weight of the elastic film <NUM> is not particularly limited, it is preferably about <NUM> to <NUM>/m<NUM>, and particularly preferably about <NUM> to <NUM>/m<NUM>.

The following terms in the specification have the following meanings unless otherwise specified in the specification.

"Stretch rate" represents a value relative to the natural length (<NUM>%).

"Basis weight" is measured as follows. After the sample or test piece is preliminarily dried, it is allowed to stand in a test room or apparatus under normal conditions (the test location is at a temperature of <NUM> ± <NUM> and with a relative humidity of <NUM>% or less) until the constant mass. The preliminary drying is to make the sample or test piece be constant mass in an environment at a temperature not exceeding <NUM> within a relative humidity of <NUM> to <NUM>%. The fibers of an official moisture regain of <NUM>% does not need preliminary drying. A cut sample of dimensions of <NUM> × <NUM> (± <NUM>) is cut using a cutting template (<NUM> × <NUM>, ± <NUM>) from a test piece in the constant mass. The sample is weighed, and the weight is multiplied by <NUM> into the weight per one square meter. The resulting value is defined as the basis weight.

In the absence of description about environmental conditions in a test room or apparatus under normal conditions (the test location is at a temperature of <NUM> ± <NUM> and a relative humidity of <NUM>% or less).

The stretchable sheet of the present invention can be used for all absorbent articles having a stretchable structure such as underpants-type disposable diapers, various types of disposable diapers such as tape type and pad type, sanitary napkins and the like.

Claim 1:
A method for manufacturing a stretchable sheet, comprising:
a supplying step in which a stretchable elastic film (<NUM>) is interposed in a stretched state between a first sheet layer (<NUM>) having no elasticity and a second sheet layer (<NUM>) having no elasticity; and
a bonding step in which, in a state where the elastic film (<NUM>) is interposed in a stretched state between the first sheet layer (<NUM>) and the second sheet layer (<NUM>) in the supplying step, the first sheet layer (<NUM>) and the second sheet layer (<NUM>) are bonded directly or via an elastic film (<NUM>) at a plurality of bonded portions (<NUM>) by applying heat melt energy to a region of the plurality of bonded portions (<NUM>) spaced apart from each other by a heat melting apparatus from the outside of the first sheet layer (<NUM>) and the second sheet layer (<NUM>) to melt the elastic film (<NUM>),
wherein the heat melting apparatus has an anvil roll (<NUM>) and an ultrasonic horn (<NUM>), the anvil roll (<NUM>) has a plurality of protrusions (60a) spaced apart from each other in a roll length direction and an outer circumference direction on an outer surface of the anvil roll (<NUM>),
a counter roll (<NUM>) is disposed apart from the anvil roll (<NUM>),
the elastic film (<NUM>) is not nipped between the anvil roll (<NUM>) and the counter roll (<NUM>),
a nip roll (<NUM>) that nips the elastic film (<NUM>) is disposed corresponding to the counter roll (<NUM>),
the elastic film (<NUM>) passes through a nip position between the counter roll (<NUM>) and the nip roll (<NUM>) to pass along the counter roll (<NUM>) and then along the anvil roll (<NUM>),
the elastic film (<NUM>) is stretched by making a circumferential speed of the anvil roll (<NUM>) faster than a circumferential speed of the counter roll (<NUM>), and
bonding is performed by the ultrasonic horn (<NUM>) and a group of the protrusions (60a) of the anvil roll (<NUM>),
wherein the elastic film (<NUM>) passes along the counter roll (<NUM>) with a holding angle α of less than <NUM>° with respect to the counter roll (<NUM>), and the elastic film (<NUM>) and the second sheet layer (<NUM>) pass along the anvil roll (<NUM>) with a holding angle β of less than <NUM>°, and
a distance from a position where the elastic film (<NUM>) is separated from the counter roll (<NUM>) to a position where the elastic film (<NUM>) starts to be held by the anvil roll (<NUM>) is <NUM> or less.