CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage application of International Application PCT/JP2017/002520, filed Jan. 25, 2017, which international application was published on Aug. 3, 2017, as International Publication WO 2017/131023 in the Japanese language. The International Application claims priority of Japanese Patent Application No. 2016-016058, filed Jan. 29, 2016. The international application and Japanese application are both incorporated herein by reference, in entirety.

TECHNICAL FIELD

The present invention relates to a stretchable structure of an absorbent article and a method of manufacturing a stretchable structure of an absorbent article.

BACKGROUND ART

In general, a stretchable structure is provided in an absorbent article to improve fitting property of each part. For example, in a disposable diaper of an underpants-type or a tape-type, it has been widely practiced to provide the stretchable structure in a lower torso portion along the circumferential direction thereof or to provide the stretchable structure in a leg portion along the circumferential direction thereof. Further, it is widely practiced to provide the stretchable structure in the front-back direction called a “three-dimensional gather” and a “plane gather” over an absorbent article including a sanitary napkin as well as a disposable diaper of an underpants-type and a tape-type (for example, refer to Patent Literatures 1 to 5).

A representative example of such a stretchable structure of an absorbent article includes a first sheet layer, a second sheet layer opposed to one surface of the first sheet layer, and a plurality of elongated elastically stretchable members provided along a stretchable direction with intervals from each other between the first sheet layer and the second sheet layer. The first sheet layer and the second sheet layer play a role of forming a planar stretchable region and also covering and concealing the elastically stretchable members. The elastically stretchable members incorporated between the first sheet layer and the second sheet layer play a role of creating elastically stretchable force. At least both ends of the elastically stretchable members are fixed to the first sheet layer and the second sheet layer in a stretched state in the stretchable direction. By this fixing, the elastically stretchable members and the first sheet layer and the second sheet layer are combined as one unit, and the first sheet layer and the second sheet layer contract due to contraction force of the elastically stretchable members to form pleats or wrinkles. After this contracted state, when the first sheet layer and the second sheet layer are stretched against the contraction force of the elastically stretchable members, the pleats and wrinkles are spread. Normally, at the limit of elastically stretching, the sheet layer is spread without pleats and wrinkles; as the elastically stretchable members are contracted, the sheet layer is gathered to form pleats; and in the natural length state, the sheet is gathered to form closest pleats. At the present time, in most cases, a hot melt adhesive is selected as a means for fixing the elastically stretchable members to the first sheet layer and the second sheet layer.

In addition, the first sheet layer and the second sheet layer are intermittently or continuously bonded to each other in at least one of the stretchable direction and the direction orthogonal to the stretchable direction. This is because when there is almost no bonding between the first sheet layer and the second sheet layer, one sheet layer largely lifts or shifts from the other sheet layer, such that the appearance and the wearing feeling deteriorate. The bonding mode of the first sheet layer and the second sheet layer is classified into a combined mode (refer to Patent Literatures 1 to 3) and an independent mode (refer to Patent Literatures 4 and 5). In the combined mode, the first sheet layer and the second sheet layer are bonded with a hot melt adhesive at least at passing positions of elastically stretchable members, which functions also to fix the elastically stretchable members to the first sheet layer and the second sheet layer. In the independent mode, the first sheet layer and the second sheet layer are bonded by welding such as ultrasonic welding at positions other than the passing positions of elastically stretchable members independently of fixing the elastically stretchable members to the first sheet layer and the second sheet layer.

On the other hand, in manufacturing a product, the stretchable structure of an absorbent article is at the limit of elastically stretching and in using the product, the stretchable structure is in a certain level of stretched state. Therefore, at least in these states, the contraction force of the elastically stretchable members acts in a shearing direction with respect to the fixed portions of the elastically stretchable members with the first sheet layer and the second sheet layer. At this time, if the holding power in adhesion of the end portions of the elastically stretchable members is insufficient, there is a possibility that fixing of the elastically stretchable members may be released due to the shearing force continuously applied during manufacturing or using. Particularly, when one end of the elastically stretchable member is released, the portion where the fixing is released contracts and is drawn to the opposite side (hereinafter also simply referred to as “pull-in”) and loses elasticity. For this reason, as a hot melt adhesive for adhering the elastically stretchable members and the sheet layer, a hot melt adhesive having high holding power (hardly causing cohesive failure) is used.

However, as in the above-described combined mode, in the case where fixing of the elastically stretchable members to the first sheet layer and the second sheet layer and bonding of the first sheet layer and the second sheet layer are performed via a single hot melt adhesive, both of the fixing and the bonding must be performed with the hot melt adhesive having high holding power, and since the hot melt adhesive having high holding power is hard, flexibility is impaired at a portion only for bonding the first sheet layer and the second sheet layer.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2004-229857 A

Patent Literature 2: JP 2013-132331 A

Patent Literature 3: JP 2009-148447 A

Patent Literature 4: JP 2008-295930 A

Patent Literature 5: JP 2009-297096 A

SUMMARY OF INVENTION

Technical Problem

In view of the above, the main object of the present invention is to achieve compatibility between flexibility and fixability of elastically stretchable members when both of fixing of the elastically stretchable members to the first sheet layer and the second sheet layer and the first sheet layer and the second sheet layer are bonded via a hot melt adhesive.

Solution to Problem

The present invention which solves the above problem is as follows.

<Invention According to Claim1>

A stretchable structure of an absorbent article, comprising:

a first sheet layer made of a nonwoven fabric; a second sheet layer made of a nonwoven fabric and opposed to one side of the first sheet layer; and a plurality of elongated elastically stretchable members provided along a stretchable direction at intervals from each other between the first sheet layer and the second sheet layer,

wherein the elastically stretchable member is fixed to at least one of the first sheet layer and the second sheet layer via a first hot melt adhesive at each pair of adhesion sites provided at an interval in the stretchable direction,

the first sheet layer and the second sheet layer are bonded via a second hot melt adhesive in a range at least in the stretchable direction corresponding to a space between the pair of the adhesion sites, and

holding power of the first hot melt adhesive is higher than holding power of the second hot melt adhesive.

(Function and Effect)

The present invention is characterized in that the function of fixing elastically stretchable members to at least one of a first sheet layer and a second sheet layer and the function of bonding the first sheet layer and the second sheet layer are shared to a first hot melt adhesive and a second hot melt adhesive, and the hot melt adhesives having different holding power are used (material welding is not used for both the functions). Hot melt adhesives each with high holding power are excellent in fixability but hard. On the other hand, hot melt adhesives each with low holding power are inferior in fixability but flexible. Therefore, as in the present invention, if the holding power of the first hot melt adhesive is higher than the holding power of the second hot melt adhesive, the elastically stretchable members are firmly fixed at both end portions of the stretchable range, and the first sheet layer and the second sheet layer can be bonded more flexibly in a range in the stretchable direction corresponding to a space between the both end portions. In this case, although the fixed portions by the first hot melt adhesive have hard texture, the influence is limited locally. Further, since the elastically stretchable members are firmly fixed at both end portions of the stretchable range, the second hot melt adhesive in the range in the stretchable direction corresponding to the space between the both end portions has very little necessity to play a role of fixing function of the elastically stretchable members, and it is only necessary for the second hot melt adhesive to bond the first sheet layer and the second sheet layer. Therefore, the adhesive having low holding power can be used without any problem, which actually brings advantage that the main stretchable region becomes further flexible.

<Invention According to Claim2>

The stretchable structure of an absorbent article according to claim1, wherein the melt viscosity of the first hot melt adhesive is higher than the melt viscosity of the second hot melt adhesive.

(Function and Effect)

In general, since a hot melt adhesive having high melt viscosity has high holding power, as described in this claim, it is desirable that the melt viscosity of the first hot melt adhesive is higher than the melt viscosity of the second hot melt adhesive.

<Invention According to Claim3>

The stretchable structure of an absorbent article according to claim1or2, wherein the loop tack adhesive strength of the second hot melt adhesive is higher than the loop tack adhesive strength of the first hot melt adhesive.

(Function and Effect)

Since the hot melt adhesive having high loop tack adhesive strength is suitable for adhering nonwoven fabrics to each other, as described in this claim, it is desirable that the loop tack adhesive strength of the second hot melt adhesive is higher than the loop tack adhesive strength of the first hot melt adhesive.

<Invention According to Claim4>

The stretchable structure of an absorbent article according to any one of claims1to3, wherein the first hot melt adhesive has a peel strength of 100 cN/25 mm or more in both longitudinal and lateral directions, and the second hot melt adhesive has a peel strength of 100 cN/25 mm or more in both longitudinal and lateral directions.

(Function and Effect)

It is desirable that the peel strength of the first hot melt adhesive and the peel strength of the second hot melt adhesive are within the range described in this claim.

<Invention According to Claim5>

The stretchable structure of an absorbent article according to any one of claims1to4,

wherein sheet bonded portions, at which the first sheet layer and the second sheet layer are bonded via the second hot melt adhesive, are disposed in a striped pattern that is intermittent in the longitudinal direction of the elastically stretchable members and continuous in a direction intersecting the elastically stretchable members, and

the width of each sheet bonded portion in the stretchable direction is 0.5 to 4 mm, and the interval between adjacent two sheet bonded portions is 4 to 8 mm

(Function and Effect)

When the sheet bonded portions by the second hot melt adhesive are disposed in such a pattern (bonding mode being continuous in the direction intersecting the elastically stretchable members), in a natural length state or in a certain level of contracted state, the first sheet layer and the second sheet layer contract as the elastically stretchable members contract, and the portions located between the sheet bonded portions of the first sheet layer and the second sheet layer are raised in opposite directions to each other to form pleats, and the pleats extended straightly and also have sufficient height but rarely fall.

More specifically, the width in the stretchable direction of each sheet bonded portion affects the interval between adjacent pleats. If the pleats are formed to be thin, and the width is larger than 4 mm, the space between adjacent pleats becomes too wide, and individual pleats become independent in appearance. In addition, when the pleats are deformed to collapse and spread or to fall due to the compressive force in the thickness direction, the effect of mutual support of the adjacent pleats is reduced. As a result, resistance with respect to the deformation and restoration after the deformation are also weaken, and the fullness becomes insufficient.

In addition, even in a case where the width of the sheet bonded portion in the stretchable direction is set to 0.5 to 4 mm, if the interval between adjacent sheet bonded portions is set to less than 4 mm or more than 8 mm, the following situation will be caused. That is, the interval between the adjacent sheet bonded portions affects the height and width of pleats, and if the interval between adjacent sheet bonded portions is about 2 mm, the pleats have poor continuity in the orthogonal direction as with the case of continuously bonding in the stretchable direction (it has no meaning to provide sheet bonded portions intermittently in the stretchable direction). If the interval is 3 mm, the pleats extended straightly in the direction orthogonal to the stretchable direction, but the effect of mutual support of the adjacent pleats cannot be expected, which results in insufficient fullness. In addition, when the interval between the sheet bonded portions exceeds 8 mm, the pleats are collapsed irregularly due to the compression during wrapping, and the product appearance deteriorates. On the other hand, when the width of the sheet bonded portion in the stretchable direction is 0.5 to 4 mm, and at the same time, the interval between the sheet bonded portions is 4 to 8 mm, sufficient fullness can be finally obtained, and against the compression during wrapping, the pleats are unlikely to be collapsed irregularly.

In the case of having sheet bonded portions of such a pattern, from the viewpoint of flexibility, it is desirable that the application width of second hot melt adhesive is narrow, and the holding power of the second hot melt adhesive is low. In that case, it is difficult to firmly fix the elastically stretchable members to at least one of the first sheet layer and the second sheet layer only with the second hot melt adhesive. Therefore, the present invention is particularly suitable to the embodiment described in this claim.

In this claim, continuous application of the second hot melt adhesive includes the mode that the second hot melt adhesive is continuously applied in the direction intersecting the stretchable direction at both of the first sheet layer-side and the second sheet layer-side of the elastically stretchable members at portions where the sheet bonded portions and the elastically stretchable members are intersecting each other, and also includes the mode that due to the elastically stretchable members being interposed, the adhesive is continuously applied in the direction intersecting the stretchable direction on one of the first sheet layer-side and the second sheet layer-side of the elastically stretchable members and discontinuously applied in the direction intersecting the stretchable direction on the other of the first sheet layer-side and the second sheet layer-side of the elastically stretchable members.

<Invention According to Claim6>

The stretchable structure of an absorbent article according to claim5, wherein the first hot melt adhesive is disposed intermittently in a direction orthogonal to the elastically stretchable members at positions overlapping with the elastically stretchable members.

(Function and Effect)

Since the fixing portions of the elastically stretchable members by the first hot melt adhesive are hard, it is preferable to intermittently apply the first hot melt adhesive, rather than to continuously apply it, in a direction orthogonal to the elastically stretchable members so as not to impair the flexibility.

<Invention According to Claim7>

The stretchable structure of an absorbent article according to any one of claims1to4, wherein

the absorbent article is an underpants-type disposable diaper, in which an outer member disposed in a front body and a back body and an inner member attached to the outer member and including an absorber are provided, both side edges of the outer member of the front body and both side edges of the outer member of the back body are bonded to each other, a range in a front-back direction corresponding to the bonded side edges is an annular lower torso portion, and a waist opening and a pair of right and left leg openings are formed, and

the stretchable structure is provided in a region including at least both sides in the width direction of the inner member in the outer member such that the elastically stretchable members are along the width direction.

(Function and Effect)

As described above, the stretchable structure according to the present invention is suitable for the region including at least both sides in the width direction of the inner member in the outer member of the underpants-type disposable diaper.

<Invention According to Claim8>

A method of manufacturing a stretchable structure of an absorbent article, comprising:

a step of sandwiching a plurality of elongated elastically stretchable members provided along a stretchable direction at intervals from each other between a first sheet layer made of a nonwoven fabric and a second sheet layer made of a nonwoven fabric and opposed to one side of the first sheet layer;

a step of fixing the elastically stretchable member to at least one of the first sheet layer and the second sheet layer via a first hot melt adhesive at each pair of adhesion sites provided at an interval in the stretchable direction; and

a step of bonding the first sheet layer and the second sheet layer to each other in a range at least in the stretchable direction corresponding to a space between the pair of the adhesion sites via a second hot melt adhesive having lower holding power than the first hot melt adhesive.

(Function and Effect)

The same functions and effects as those obtained in the invention according to claim1is obtained.

<Invention According to Claim9>

The method of manufacturing a stretchable structure of an absorbent article according to claim8, wherein the melt viscosity of the first hot melt adhesive is higher than the melt viscosity of the second hot melt adhesive.

(Function and Effect)

The same functions and effects as those obtained in the invention according to claim2is obtained.

<Invention According to Claim10>

The method of manufacturing a stretchable structure of an absorbent article according to claim8or9, wherein the loop tack adhesive strength of the second hot melt adhesive is higher than the loop tack adhesive strength of the first hot melt adhesive.

(Function and Effect)

The same functions and effects as those obtained in the invention according to claim3is obtained.

<Invention According to Claim11>

The method of manufacturing a stretchable structure of an absorbent article according to any one of claims8to10, comprising:

a step of applying the second hot melt adhesive, wherein at least one of the first sheet layer and the second sheet layer is brought into contact with an engraved roll such that a circumferential direction of the engraved roll is the stretchable direction, and the second hot melt adhesive, which is held in a striped pattern that is intermittent in the circumferential direction and continuous in the axial direction on the outer peripheral surface of the engraved roll, is transferred on the at least one of the first sheet layer and the second sheet layer; and

a step of performing pressure bonding, wherein the elastically stretchable members are sandwiched between the first sheet layer and the second sheet layer, on at least one of which the second hot melt adhesive is transferred,

wherein in the step of applying the second hot melt adhesive, the application width in the circumferential direction of the second hot melt adhesive is set to 0.5 to 4 mm, and the interval between adjacent applications in the circumferential direction of the second hot melt adhesive is set to 4 to 8 mm on the outer peripheral surface of the engraved roll.

(Function and Effect)

The same functions and effects as those obtained in the invention according to claim5is obtained.

<Invention According to Claim12>

The method of manufacturing a stretchable structure of an absorbent article according to claim11, comprising:

a step of applying the first hot melt adhesive on the elastically stretchable members,

wherein in the step of performing pressure bonding, the elastically stretchable members applied with the first hot melt adhesive are sandwiched between the first sheet layer and the second sheet layer, on at least one of which the second hot melt adhesive is transferred.

(Function and Effect)

The same functions and effects as those obtained in the invention according to claim6is obtained.

Advantageous Effects of Invention

As described above, according to the present invention, when both the fixing of the elastically stretchable members to the first sheet layer and the second sheet layer and the bonding of the first sheet layer and the second sheet layer are performed via the hot melt adhesives, an advantage of sufficient flexibility and reliable fixability of the elastically stretchable members can be obtained for example.

