Patent Application
20240336047
The claimed invention relates to a stretchable laminate that can be utilized for parts of disposable wearable articles such as disposable diapers and disposable pants.
A stretchable composite sheet, that is, a stretchable laminate, is formed by extruding into a film and cooling an elastic resin material having a thermoplastic resin as its main component, then laminating a base sheet on at least one side of the film, and intermittently heat fusing the film and the base sheet. See, for example, WO2020/090753.
When forming such a stretchable composite sheet, the resin material, which is in a molten state just after the film is extruded, shrinks in its width direction perpendicular to the extrusion direction due to necking, and after cooling, the thickness of the film at both side edge portions in the width direction ends up becoming thick, with the result that the elongation stress (a mechanical property) of the stretchable composite sheet becomes different in the width direction.
In order to obtain a stretchable composite sheet with uniform elongation stress, it may be conceivable to cut off all the parts of the composite sheet in the regions where the thickness of the film is thick. However, such a process increases material waste.
It is an object of the claimed invention to obtain a stretchable composite sheet, that is, a stretchable laminate, with which material waste can be reduced and which has smaller variations in elongation stress.
A laminate of the claimed invention is a laminate W comprising a thermoplastic elastomer film F having greater stretchability in a stretch direction Ds than in a width direction Dw orthogonal to the stretch direction Ds and nonwoven fabric sheet S1, S2 that are laminated to each other,
The pair of nonwoven fabric sheets and the elastomer film F are heat fused to each other at the bonded portions 8. The elastomer film F around the bonded portions 8 breaks during the heat fusion or breaks during re-elongation such as during wearing, so that holes appear in an elongated state of the elastomer film F. The holes greatly extend in the stretch direction Ds with a small tensile force because the elastomer film is missing in them.
The magnitude of this extension becomes greater the longer the length of the holes in the width direction Dw is. The lengths of the holes in the width direction Dw approximate the lengths of the bonded portions 8. Consequently, the greater the sum of the lengths of the bonded portions 8 in the width direction Dw is, the greater the laminate stretches in the stretch direction Ds with a small tensile force.
Furthermore, since it is also not necessary to cut off all the portions of the laminate in the regions where the thickness of the film is thick, there is also no significant increase in material waste.
It will be noted that from the standpoint of improving the appearance of the product for example, part of the side edge portion of the laminate may be cut off.
In the claimed invention, “side edge portion” means a region that is near an edge of the laminate and in which the sum of the lengths of the bonded portions in the width direction Dw is greater than the sum of the lengths of other bonded portions in the width direction, and “non-side edge portion” means a portion other than the side edge portion.
Preferably, a length L of each of the bonded portions 8 in the width direction Dw is longer than that of the bonded portions 8 in the stretch direction Ds.
The length of the bonded portions in the stretch direction may be made longer than their length in the width direction, but in this case, the effect of reducing variations in elongation stress in the width direction is reduced. In contrast, by making the length of the bonded portions in the width direction longer than their length in the stretch direction, the effect of reducing variations in elongation stress in the width direction is easy to obtain.
Preferably, lengths L1, L2 in the width direction Dw in the side edge portion AE are set longer than a length L3 in the width direction Dw in the non-side edge portion Ac.
In this case, the lengths in the width direction in the side edge portion become longer, and it becomes easy to further reduce variations in the elongation stress in the width direction.
The degree of necking is greater closer to the edge of the laminate, and the elastomer film is often thicker closer to the edge.
For that reason, for example, at least two rows of first bonded portions 81 and second bonded portions 82 intermittently arranged in the stretch direction Ds may be provided in the side edge portion AE,
In this case, preferably a length L1 of the first bonded portions 81 in the width direction Dw is longer than a length L2 of the second bonded portions 82 in the width direction Dw.
In this way, because the first bonded portions that are in positions closest to the edge of the laminate have a longer length in the width direction compared with the second bonded portions in the adjacent row, variations in the elongation stress of the thick elastomer film can be further reduced closer to the edge.
Even more preferably, a plurality of third bonded portions 83 are provided in the non-side edge portion Ac, and the length L2 of the second bonded portions 82 in the width direction Dw is longer than a length L3 of the third bonded portions 83 in the width direction Dw.
In this case, variations in elongation stress between the side edge portion and the non-side edge portion can be further reduced.
Preferably, arrangement pitch P1, P2 of the bonded portions 8 in the stretch direction Ds in the side edge portion AE is set smaller than an arrangement pitch P3 of the bonded portions 8 in the stretch direction Ds in the non-side edge portion Ac.
By setting the pitches of the bonded portions in this way, the sum of said lengths in the side edge portions can be set greater than the sum of said lengths in the non-side edge portion.
Preferably, an arrangement pitch P1 of the first bonded portions 81 in the stretch direction Ds is smaller than an arrangement pitch P2 of the second bonded portions 82 in the stretch direction Ds.
In this way, because the first bonded portions that are in positions closest to the edge of the laminate have a small arrangement pitch compared with the second bonded portions in the row next to them, variations in the elongation stress of the thick elastomer film can be reduced closer to the edge.
Preferably, an arrangement pitch P2 of the second bonded portions 82 in the stretch direction Ds is smaller than an arrangement pitch P3 of the third bonded portions 83 in the stretch direction Ds in one row in the non-side edge portion Ac.
In this case, variations in elongation stress between the side edge portion and the non-side edge portion can be further reduced.
Preferably, a first area ratio α1 of the area of the bonded portions 8 in at least one side edge portion AE in the width direction Dw to the unit area of the laminate in that side edge portion AE is greater than a second area ratio α2 of the area of the bonded portions 8 in a non-side edge portion Ac in the width direction Dw to the unit area of the laminate W in that non-side edge portion Ac.
Here, the bonded portions in the claimed invention will be described.
At each of the bonded portions, the elastomer film and the sheets are heat fused to each other, and because of this, a state in which the film and the sheets are laminated is maintained. The bonded portions at which the two are heat fused to each other are in a relaxed state in which pre-stress that occurred during manufacture is removed. Consequently, the bonded portions mitigate the ease with which the laminate shrinks.
Furthermore, at the bonded portions, some of the resin component of the elastomer film penetrates between the fibers of the nonwoven fabric sheets, and the mechanically effective thickness of the film becomes smaller. For that reason, resistance to stretching is small at the bonded portions compared with their surrounding portions. Consequently, it is easy for the laminate to stretch when it is pulled in the stretch direction.
Since the bonded portions have the property of mitigating the ease with which the laminate shrinks and making it easier for the laminate to stretch as described above, in a no-load state, the bonded portions can be said to be in a “relaxed state.”
Here, the first area ratio α1 of the bonded portions in the side edge portion is greater than the second area ratio α2 in the non-side edge portion. In other words, the area ratio of the bonded portions is large in the side edge portion compared with in the non-side edge portion. Because the area ratio of the bonded portions is large in this way, even if the side edge portion is thick due to necking compared with the non-side edge portion, the bonded portions in the “relaxed state” can lower the resistance of the side edge portion and bring it closer to the resistance of the non-side edge portion. Consequently, variations in elongation stress become smaller in the width direction of the laminate.
Preferably, each bonded portion 8 of a plurality of bonded portions 8 at which the nonwoven fabric sheets S1, S2 and the elastomer film F are heat fused to each other includes a fused region α at which the sheets S1, S2 and the elastomer film F are heat fused to each other, and
In this case, as mentioned above, holes 8H defined by boundary lines 80 spread wide when the laminate stretches in the stretch direction Ds. For that reason, the side edge portion having the bonded portions 8 that are long in the width direction Dw easily stretches in spite of the elastomer film F being thick.
In the laminate, a thickness Th1 of the elastomer film F in the at least one side edge portion AE may be greater than a thickness Th3 of the elastomer film F in the non-side edge portion Ac.
Preferably, at each of the bonded portions 8, some of a resin configuring the elastomer film F penetrates between plural fibers configuring the nonwoven fabric sheets S1, S2.
In this case, the thickness of the elastomer film F in the bonded portions 8 is thinner than the thickness of the elastomer film F in non-bonded portions 9 around the bonded portions 8.
Because the film is thin in this way, resistance to stretching in each of the bonded portions becomes smaller, and consequently it becomes easy to reduce variations in the elongation stress of the elastomer film.
For example, the laminate may configure at least part of a waist portion of a disposable wearable article, and the at least one side edge portion AE may be an upper edge portion or a lower edge portion of the waist portion.
In this case, a situation where elongation stress becomes greater in the upper edge portion and/or the lower edge portion of the waist portion can be avoided and fit improves.
The features described and/or illustrated in association with one of the above aspects or the following embodiments can be used in the same or similar form in one or more other aspects or other embodiments and/or in combination with, or instead of, features of other aspects or embodiments.
The claimed invention will become more clearly understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are merely for the purposes of illustration and explanation and should not be utilized to define the scope of the claimed invention. The scope of the claimed invention shall be defined only by the claims. In the accompanying drawings, like parts numbers in multiple views refer to the same or corresponding parts.
It will be noted that some KATAKANA notations in the present specification are accompanied by English words in parentheses to make their meanings clearer.
An embodiment of the claimed invention will be described below in accordance with the drawings.
The stretchable laminate can be used for a variety of purposes. Below, a case where the laminate is applied to a disposable diaper (an example of a wearable article) will be exemplified and described. The diaper includes a waist portion that covers the waist of the wearer and a crotch portion that covers the crotch of the wearer. The laminate is used for the waist portion.
A detailed structure in a case where the stretchable laminate is used in a disposable diaper is, for example, disclosed in US 2013/0110073 A1 (WO 2012/017817 A1), and the entire disclosure thereof is incorporated herein.
A laminate W shown in
The pair of nonwoven fabric sheets S1, S2 and the film F are laminated by being heat fused to each other at numerous bonded portions 8 (hereinafter called bonded portions 8 when, for example, collectively referring to bonded portions 81, 82, 83) shown in
The bonded portions 8 may be formed by the vibrational energy of an ultrasonic horn or may be formed by being heated with a heating roll.
An example of the wearable article will be described before detailed description of the laminate.
As shown in this drawing, the wearable article 10 includes an absorbent body 20 and a waist portion 30. The absorbent body 20 is long in a longitudinal direction orthogonal to the waist direction. The wearable article may be the pants type of
The absorbent body 20 is provided with an absorbent core not shown in the drawings. The absorbent core absorbs bodily fluids. The absorbent core is sandwiched between a topsheet and a backsheet. The sheets and the absorbent core are laminated to each other.
The topsheet comprises a thin nonwoven fabric permeable to liquid and covers the skin side of the absorbent core. A cuff not shown in the drawings may be provided on the topsheet.
The backsheet covers the non-skin side of the absorbent core and comprises a resin sheet impermeable to liquid. The waist portion 30 is adhered to end portions in the longitudinal direction of the absorbent body 20.
The waist portion 30 is formed of the stretchable laminate W, extends in the waist direction of the wearer, and is configured to cover the waist of the wearer. The absorbent body 20 is configured to cover the crotch of the wearer.
Oblong first and second bonded portions 81, 82 are provided in a plurality of columns and a plurality of rows (two rows) in an upper edge portion 32 of the waist portion 30. Oblong third bonded portions 83 are provided in a plurality of columns and a plurality of rows (in a matrix) in a lower portion 31 of the waist portion 30. Each bonded portion 8 is intermittently arranged in the waist direction and intermittently arranged in the longitudinal direction.
Next, details about the structure of the laminate W will be described.
In the laminate W shown in
The laminate W shown in
A thickness Th1 of the elastomer film F in the side edge portions AE on both sides is greater than a thickness Th3 of the elastomer film F in the non-side edge portion Ac.
In
As indicated by halftone dots in
The elastomer film F that is substantially thin in this way reduces the elongation stress of the laminate W.
As shown in
Here, a sum Σ1 of first lengths and a sum Σ2 of second lengths are set as follows.
Sum of first lengths Σ1: The sum of lengths of each of the bonded portions 8 in the width direction Dw in at least one side edge portion AE in the width direction Dw per unit area of the laminate in that side edge portion AE.
Sum of second lengths Σ2: The sum of lengths of each of the bonded portions 8 in the width direction Dw in the non-side edge portion Ac in the width direction Dw per unit area of the laminate W in that non-side edge portion Ac.
The sum Σ1 of the first lengths defined as described above is greater than the sum Σ2 of the second lengths. In order to set the sums of the lengths to such a relationship, in the present example the length L and arrangement pitches P of the bonded portions 8 are set as follows.
When for example collectively referring to the bonded portions, to the lengths, and to the arrangement pitches, for the sake of convenience subscript numbers are not added.
It will be noted that the bonded portions 8 may, for example, each be rhombic, elliptical, or hourglass-shaped. Furthermore, the shape of each of the bonded portions 8 may be a mixture of two or more shapes.
In
In order to obtain the aforementioned relationship between the sums of the lengths, in the present example the lengths and arrangement pitches of the first, second, and third bonded portions 8 are set as follows.
For example, the lengths of the bonded portions 8 in the width direction Dw are set as follows.
In
The arrangement pitches of the bonded portions 8 in the width direction Dw are set as follows.
In
It will be noted that it is desirable that the bonded portions 8 be arrayed in a staggered fashion so that they are not too close to each other.
It will be noted that the lengths L1, L2, L3 of each of the first, second, and third bonded portions does not need to be the same. For example, the length L1 of the first bonded portions may vary.
Furthermore, each of the arrangement pitches P1, P2, or P3 may likewise also vary.
As shown in
The pair of nonwoven fabric sheets S1, S2 and the elastomer film F are heat fused to each other at the bonded portions 8 shaded in gray. The elastomer film F around the bonded portions 8 breaks during the heat fusion or breaks during re-elongation such as during wearing, so that holes 8H indicated by dashed lines appear in an elongated state of the elastomer film F in
Here, a first area ratio α1 and a second area ratio α2 are defined as follows.
First area ratio α1: Area ratio of the area of the bonded portions 8 in at least one side edge portion AE in the width direction Dw to the unit area of the laminate in that side edge portion AE.
Second area ratio α2: Area ratio of the area of the bonded portions 8 in the non-side edge portion Ac to the unit area of the laminate W in that non-side edge portion Ac.
The first area ratio α1 defined as described above is greater than the second area ratio α2.
Next, an example of a method of obtaining the waist portion from the laminate W and forming the wearable article will be briefly described.
As shown in
Nip rolls not shown in the drawings sandwich the elastomer film F having the pair of side edge portions AE extending in the transport direction between the two sheets (continuous nonwoven fabric) S1, S2, and bond the first sheet S1, the second sheet S2, and the elastomer film F so that they lie on top of each other to form the laminate W.
That is, the sheets S1, S2 and the elastomer film F are welded and bonded to each other at the numerous first to third bonded portions 81, 82, 83 disposed intermittently in the stretch direction Ds of
As shown in
Thereafter, as the pair of waist continuous bodies are transported in the transport direction generally parallel to each other, the absorbent body 20 is disposed (laid) so that the absorbent body 20 straddles the pair of waist continuous bodies and overlaps in part each waist continuous body, whereby a continuous laminate W1 is formed.
Thereafter, as shown in
Side seals are formed in end portions in the transport direction of the portions that become the front and rear waist portions 30, whereby the pair of waist continuous bodies are welded and bonded to each other. It will be noted that this welding and bonding may be welding by the ultrasonic energy of an ultrasonic horn or may be heat sealing.
Thereafter, the continuous laminate W1 is cut out into sizes (units) of individual wearable articles 10 along imaginary cutting lines indicated by the long dashed double-short dashed line. That is, in order to successively form the individual wearable articles 10, the continuous laminate W1 is successively cut between the absorbent main bodies 20 adjacent to each other in the transport direction. Because of this cutting, individual pants-type wearable articles 10 shown in
In this way, the laminate configures at least part of the waist portion 30 of the disposable wearable article, and each side edge portion AE becomes the upper edge portion 32 of the waist portion.
Next, an example of a method and apparatus for manufacturing the laminate W will be described.
The pre-elastomer M discharged from the discharge outlet TO becomes wrapped on the outer peripheral surface of a first cooling roll T1 and temporarily cooled, and is transported toward the outer peripheral surface of a second cooling roll T2 below the first cooling roll T1. Because of this, the pre-elastomer M generally solidifies and has elasticity (stretchability) as the elastomer film (an example of a thermoplastic film) F.
The pre-elastomer M headed toward the second cooling roll T2 is secondarily cooled by the outer peripheral surface of the second cooling roll T2. Because of this, the pre-elastomer M completely solidifies into the elastomer film (elastic film) F.
The secondarily cooled elastomer film F becomes sandwiched between the second cooling roll T2 and a nip roll Nr and then heads to a bonding roll Ar. The bonding roll Ar has a greater circumferential velocity (transport velocity) than the second cooling roll T2, and for that reason the elastomer film F is stretched in the transport direction between the nip roll Nr and the bonding roll Ar.
In this way, the molten resin becomes the elastomer film (thermoplastic film) F via the state of the pre-elastomer (film raw material) M. Here, the point in time at which the molten resin as a substance transitions to the pre-elastomer M and/or transitions from the pre-elastomer M to the elastomer film F varies depending on the glass transition temperature, the thickness of the resin, and the room temperature, and is not certain.
For example, although the molten resin turns into the pre-elastomer M just after exiting the discharge port TO and may appear at first glance to be solid, it may have properties close to those of a liquid without elasticity.
Furthermore, although the pre-elastomer M changes to the elastomer film F at the position where it is pulled downstream from the nip roll Nr, it may turn into the elastomer film F after coming into contact with the second cooling roll T2 upstream of the nip roll Nr or turn into the elastomer film F after coming into contact with the first cooling roll T1.
Film pass line 3 is a transport path for the film in a state in which the film is at least in part the pre-elastomer (film raw material) M.
Meanwhile, the first and second sheets S1, S2 comprising nonwoven fabric are supplied to the bonding roll Ar. The sheets S1, S2 are each supplied to the bonding roll Ar along a first pass line 1 or a second pass line 1A for the sheet.
The elastomer film F is introduced to the bonding roll Ar in a state in which it is sandwiched between the pair of sheets S1, S2. On the bonding roll Ar, the pair of sheets S1, S2 and the elastomer film F are bonded and laminated to each other by an ultrasonic horn H, whereby the laminate W is formed.
It will be noted that the laminate W may be formed by being heat welded with a heating roll rather than by ultrasonic bonding by the ultrasonic horn H.
The production of the laminate W is continuously performed, but production may be temporarily stopped for size changes and the like. In this case, formation of the film pass line shown in
Next, the manufacturing apparatus will be described.
The cooling rolls T1, T2 of
To newly form the film pass line 3 (
After the process of forming the film pass line 3 of
This bonding is executed as a result of the elastomer film F, whose temperature has increased by being heated by ultrasonic energy, heat fusing to the nonwoven fabrics sheets. At the same time, the bonding is performed in a state in which tensile force acts on the film and the sheets due to the difference in velocity between the circumferential velocity Vs of the second cooling roll T2 and the circumferential velocity V of the bonding roll Ar. For that reason, the elastomer film F that has softened due to its temperature increasing is stretched in the stretch direction Ds in
While preferred embodiments have been described above with reference to the drawings, a variety of obvious changes and modifications will readily occur to those skilled in the art upon reading the present specification.
For example, just the lower edge portion of the waist portion may have the structure of the side edge portion. Furthermore, the upper and lower edge portions of the waist portion may have the structure of the side edge portion without slitting the laminate in two. Furthermore, the bonded portions may be circular or square for example.
Consequently, such changes and modifications are to be interpreted as being within the scope of the claimed invention as defined by the claims.
The claimed invention can be applied to the manufacture of a laminate for wearable articles such as disposable diapers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-212033 | Dec 2021 | JP | national |
This application is the U.S. National Phase of International Application PCT/JP2022/045638 filed Dec. 12, 2022, the priority benefit of which is claimed and the contents of which are incorporated herein by reference. This application also claims the priority benefit of Japanese Patent Application 2021-212033 filed Dec. 27, 2021, the contents of which are incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/045638 | 12/12/2022 | WO |
