Patent Application
20130066290
The present invention relates to bodily fluid absorbent structures and methods for manufacturing the same and, more specifically, to bodily fluid absorbent structures which are capable of absorbing and containing a relatively large amount of bodily fluids and applicable to wearing articles such as urine absorbent pads, pantiliners, sanitary pads, sanitary napkins and disposable diapers, and to methods for manufacturing such bodily fluid absorbent structures.
Conventionally, bodily fluid absorbent structures including a liquid-absorbent core adapted to absorb and to contain bodily fluids and a core wrapping sheet formed of tissue paper adapted to wrap a liquid-absorbent core and to facilitate the diffusion of bodily fluids are known. For example, JP H8-196559 A (PTL 1) discloses the bodily fluid absorbent structure including the liquid-absorbent core including a mixture of superabsorbent polymer particles and fluff pulp, the fiber assembly layer lying on the upper surface of the core, and the core wrapping sheet adapted to wrap them.
{PTL 1}: JP H8-196559 A
In the bodily fluid absorbent structure disclosed in PTL 1, the liquid-absorbent core, the fiber assembly layer and the liquid-absorbent core wrapping sheet are bonded together with hot melt adhesives intermittently applied to the respective surfaces along which these constituents are put in contact with each other. This bodily fluid absorbent structure includes the fiber assembly layer lying on the upper surface of the liquid-absorbent core and, as a result, the bodily fluid absorbent structure is capable of absorbing and containing a relatively large amount of bodily fluids.
However, it is difficult to overlap the opposite lateral portions of the core wrapping sheet during the process of manufacturing due to the convex shape of the bodily fluid absorbent structure and, in consequence, the region in which the opposite lateral portions of the core wrapping sheet overlap each other might partially be curled up, and then the hot melt adhesives applied thereto might adhere to the manufacturing apparatus, thereby high-speed production might be interrupted.
To deal with such problem, it may be contemplated to secure the core wrapping sheet as a whole to the liquid-absorbent core by press working. However, in this case, there is a likelihood that a securing effect of entirely compressed region might be released when the liquid-absorbent core absorbs bodily fluids and expand and eventually the core wrapping sheet might be separated from the liquid-absorbent core. If the compression area is enlarged and/or the pressure for the compression is increased to avoid the above-mentioned situation, a stiffness of the bodily fluid absorbent structure as a whole will be unacceptably increased and the desired flexibility will be deteriorated, and thereby deteriorate a feeling to wear the article.
An object of the present invention is to provide a bodily fluid absorbent structure adapted to be stably secured in a state in which a liquid-absorbent core is wrapped with a core wrapping sheet and ensuring a high workability for a process of manufacturing the bodily fluid absorbent structure used for wearing articles, and the method for manufacturing the same.
A first aspect of this invention relates to a bodily fluid absorbent structure having a longitudinal axis and a transverse axis being orthogonal to the longitudinal axis, which includes a liquid-absorbent core containing at least water-absorbent fibers and a core wrapping sheet adapted to wrap the liquid-absorbent core entirely.
The first aspect of this invention further includes the following features:
the bodily fluid absorbent structure has first and second end regions spaced apart from and opposite to each other in a direction of the longitudinal axis and a middle region extending in the direction of the longitudinal direction between the first and second end regions;
on the side of the first surface, the core wrapping sheet and the liquid-absorbent core are bonded to each other by the intermediary of a bond region defined by a hot melt adhesive intermittently applied to substantially entire opposite surfaces of the core wrapping sheet and the liquid-absorbent core; and
on the side of the second surface, lateral portions of the core wrapping sheet are overlapped each other, and the core wrapping sheet and the liquid-absorbent core are secured to each other in compressed end portions formed in the first and second end regions and a compressed middle portions formed in lateral portions of the middle region except a central zone as viewed in the direction of the transverse axis.
A second aspect of this invention relates to a method for manufacturing the bodily fluid absorbent structure, which method includes the steps of:
conveying a continuous web as material of the core wrapping sheet in a machine direction and coating the continuous web at given locations with adhesive;
placing the liquid-absorbent cores in respective regions coated with the adhesive;
overwrapping lateral portions of the continuous web extending in the machine direction each other and thereafter press working the continuous web to form the compressed end portions extending in a direction crossing the machine direction; and,
after the compressed end portions have been formed, press working the continuous web to form the compressed middle portions extending in the machine direction between the compressed end portions.
According to one embodiment of this invention, a mass of the water-absorbent fibers constituting the liquid-absorbent core is higher in the middle region than the remaining regions and, as a result, the liquid-absorbent core has a convex shape.
According to another embodiment of this invention, a compressed area ratio of a compression pattern defining the compressed end portions is in a range of 30 to 50% of a total area of the first and second end regions and a compressed area ratio of a compression pattern defining the compressed middle portions is in a range of 5 to 25% of the total area of the middle region.
According to even another embodiment of this invention, a liquid-pervious topsheet is laid on one of the side of the first surface and the second surface and hinge lines are formed so as to be convex from the topsheet toward the liquid-absorbent core.
According to still another embodiment of this invention, a range in which lateral portions of the core wrapping sheet are overlapped each other in one of lateral portions of the middle region.
In the bodily fluid absorbent structure according to one or more embodiments of this invention, on the side of the first surface, the core wrapping sheet is bonded to the liquid-absorbent core with a hot melt adhesive and, on the side of the second surface, the core wrapping sheet is secured to the liquid-absorbent core by the intermediary of the compressed end portions and the compressed middle portions. In this way, the core wrapping sheet may be stably secured to the liquid-absorbent core which is kept in entirely wrapped by the core wrapping sheet and therefore the core wrapping sheet might be separated from the liquid-absorbent core. According to the manufacturing method according to this invention, the second surface side on which the lateral portions of the core wrapping sheet are overlapped each other is not coated with adhesive and consequently the hot melt adhesive should not run off from the overlapping portions of the lateral portions and cling to part of the manufacturing apparatus.
As specific embodiments of the wearing article using a bodily fluid absorbent structure 15, this invention will be described hereunder on the basis of a urine absorbent pad 10.
Referring to
The topsheet 13 may be formed, for example, of a liquid-pervious fibrous nonwoven fabric, a porous plastic film or a laminate sheet thereof and the backsheet 14 may be formed, for example, of a liquid-impervious but moisture-pervious plastic film, a liquid-impervious fibrous nonwoven fabric or a laminate sheet thereof. The cushion sheet 20 may be formed, for example, of a breathable and liquid-pervious fibrous nonwoven fabric to improve cushioning properties desired for the wearer's skin, to ensure bodily fluids to be absorbed and contained at a central region of the urine absorbing pad 10 without leaving bodily fluids diffuse and, in addition, to separate the topsheet 13 and the bodily fluid absorbent structure 15 from each other and thereby to prevent bodily fluids from freely flowing back toward the topsheet 13. Though not illustrated, it is possible to use thermoplastic sheet members as material of the topsheet 13 and the cushion sheet 20 and to compress these sheet members under heating so that these sheet members maybe integrally heat-sealed. According to the illustrated embodiments, respective sheet members overlapping each other are bonded to each other by known adhesive means such as hot melt adhesives.
Referring to
The liquid-absorbent core 24 is molded into a predetermined shape and has a rigidity higher than those of the sheet members such as the topsheet 13, the backsheet 14 and the core wrapping sheet 23. In other words, the liquid-absorbent core 24 is a semirigid panel formed from a mixture of superabsorbent polymer particles and water-absorbent fibers such as fluff pulp and optionally thermoplastic short fibers. While a mixture proportions of the superabsorbent polymer particles and the water-absorbent fibers may be appropriately varied depending on the absorption rate and the absorptive capacity required for the liquid-absorbent core 24, the mixture proportion of the superabsorbent polymer particles in the liquid-absorbent core 24 as a whole is preferably in a range of 35 to 65%. This is because, if the mixture proportion thereof is less than 35%, a preventive function against rewetting phenomenon might be reduced and, if the mixture proportion exceeds 65%, the bodily fluid absorption rate might unacceptably decrease.
The core wrapping sheet 23 may be formed of tissue paper, a hydrophilic fibrous nonwoven fabric, a hydrophilized hydrophobic fibrous nonwoven fabric, a porous plastic film or a laminate sheet including these nonwoven fabric and/or film. The core wrapping sheet 23 functions not only to improve diffusion of bodily fluids but also to ensure shape retention of the liquid-absorbent core 24 and, at the same time, to prevent the superabsorbent polymer particles from falling off. Furthermore, the core wrapping sheet 23 serves as carrier sheet in a process of manufacturing the bodily fluid absorbent structure 15 as will be described later.
As the superabsorbent polymer particles, it is possible to use water-insoluble polymeric hydrogels, for example, graft polymer of starch, modified cellulose or self-cross-linking type acrylic metal salts known as the absorbent material of absorbent articles such as sanitary napkins and disposable diapers, at a mass per unit area in a range of 100 to 600 g/m2.
As an optional extra, thermoplastic branched staple fibers (split yarns or split fibers) of 15% or less by mass may be blended into the liquid-absorbent core 24 to ensure that these staple fibers intertwine with the fluff pulp fibers as well as the superabsorbent polymer particles to improve the shape retention of the liquid-absorbent core 24 and capillary action channels are formed between the staple fibers and the fluff pulp fibers to improve the bodily fluid-absorption capacity.
Referring again to
Referring to
The bodily fluid absorbent structure 15 has a convex shape in which a mass of the water-absorbent fibers constituting the liquid-absorbent core 24 is higher in the middle region 33 than in the remaining regions. More specifically, the mass of the water-absorbent fibers constituting the liquid-absorbent core 24 is in a range of 400 to 700 g/m2 in the middle region 33 and in a range of 200 to 400 g/m2 in the remaining regions, i.e., in the first and second end regions 31, 32 and the intermediate regions 34, respectively. The bodily fluid absorbent structure 15 having such a convex shape ensures high cushioning properties and makes it possible for the middle region 33 to absorb and contain relatively large amount of bodily fluids in a rapid manner. In this regard, as will be described later in detail, the mass of the water-absorbent fibers in the first and second end regions 31, 32 may be set to be lower than that in the intermediate regions 33, for example, to a range of 100 to 300 g/m2 in order that the first and second end regions 31, 32 may be subject to compression working in a correspondingly easy manner.
Referring to
The side of the second surface 22 of the bodily fluid absorbent structure 15 is subjected to pressurizing compression working in the first and second end regions 31, 32 and the lateral portions of the middle region 33 to form compressed end portions 42, 43 and compressed middle portions 44, respectively. In the compressed end portions 42, 43 as well as in the compressed middle portions 44, the core wrapping sheet 23 and the liquid-absorbent core 24 are secured to each other and, in these portions 42, 43, 44, the liquid-absorbent core 24 is in a sufficiently compressed state to ensure that the liquid-absorbent core 24 should not lose its initial shape even when the liquid-absorbent core 24 absorbs bodily fluids. The opposite end sections 42, 43 formed on the first and second end regions 31, 32, respectively, ensure to prevent part of the liquid-absorbent core 24, particularly the superabsorbent polymer particles from leaking out of the first and second end regions 31, 32 in the direction of the longitudinal axis P. In addition, since the compressed middle portions 44 are formed on both sides of the middle region 33 and not along a central zone 46 of the middle region 33 as viewed in the direction of the transverse axis Q, the central zone 46 of the middle region 33 is more bulky and correspondingly more flexible and cushiony than the remaining regions.
More specifically, the compressed end portions 42, 43 are formed in a lattice pattern at an area ratio in a range of 30 to 50% of the first and second end regions 31, 32, as a whole. The compressed middle portions 44 are formed at an area ratio in a range of 5 to 25% of the middle region 33 as a whole by the press working at a pressure higher than that at which the compressed end portions 42, 43 are formed and arranged in a zigzag compression pattern defined by a plurality of dots 47. While both the compressed end portions 42, 43 and the compressed middle portions 43 may be formed so as to have various shapes and sizes other than those as have been described above, when the compressed middle portions 44 are formed in the dot-like compression pattern as in the illustrated embodiment, the respective dots 47 preferably have a diameter in a range of about 0.5 to about 5.0 mm and a distance between each pair of the adjacent dots 47 is preferably in a range of about 2.0 to about 10.0 mm in order to prevent the compressed regions from being excessively hardened. The respective dots 47 are locally independent compressed regions which are tapered downward in a thickness direction of the liquid-absorbent core 24.
As illustrated in
Referring to
On the side of the first surface 21, the core wrapping sheet 23 as a whole and the liquid-absorbent core 24 are almost evenly bonded to each other by the intermediary of the bond region 49, and thereby it is possible to inhibit a possible distortion of the bodily fluid absorbent structure 15, and also when it is desired to form the hinge lines 18 from above the topsheet 13, such hinge lines 18 may be relatively easily formed in a given shape.
While the first surface 21 of the bodily fluid absorbent structure 15 lies on the side of the upper surface 11 of the urine absorbent pad 10 and the second surface 22 lies on the side of the lower surface 12 of the urine absorbent pad 10 in this embodiment, an alternative arrangement is also possible in which the first surface 21 lies on the side of the lower surface 12 of the urine absorbent pad 10 and the second surface 22 lies on the side of the upper surface 11.
As the hot melt adhesive used to form the bond region 49, various types of hot melt adhesive widely used in the relevant technical field such as SIS-based hot melt adhesives, SBS-based hot melt adhesives and SEBS-based hot melt adhesives may be used without limitation and may be applied selectively in various patterns such as a solid pattern using a coater, a controlled seam pattern, a spiral pattern and a summit pattern. In this regard, when the first surface 21 lies on the side of the upper surface 11 of the urine absorbent pad 10, the hot melt adhesive is preferably applied in the intermittent pattern such as a spiral pattern in consideration of the bodily fluid absorbent performance as well as the bond strength. When the first surface 21 lies on the side of the lower surface 12, the hot melt adhesive is preferably applied in the solid pattern using a coater in order to ensure a desired bond strength.
Referring to
The continuous web 60 of which the lateral portions 65, 66 are kept in an overlapped state is conveyed in the machine direction MD to a first press working station 70 defined by a rotary roll formed on its peripheral surface with a plurality of protrusions 70a, at which given regions of the continuous web 60 are press worked to form the compressed end portions 42, 43 extending in the cross direction CD. The respective end sections' compressed regions 42, 43 are spaced apart from each other in the machine direction MD by a given dimension and formation of these compressed end portions 42, 43 ensures it to prevent the lateral portions 65, 66 of the continuous web 60 from being distorted in the course of being conveyed and, at the same time, to prevent each of the liquid-absorbent cores 24 having been transferred onto given sections (corresponding to the bodily fluid absorbent structures 15) from partially moving to the adjacent sections. Then, the continuous web 60 enters a second press working station 71 defined by a rotary roll formed on its peripheral surface with a plurality of dot-like deboss patterns and, in this second press working station 71, the continuous web 60 is press worked on both sides of the overlapping lateral portions 65, 66 to form the compressed middle portions 44. After the compressed middle portions 44 have been formed, the continuous web 60 is cut at given regions to form the individual bodily fluid absorbent structures 15.
In this process, on the side of the continuous web 60 on which the lateral portions 65, 66 are overlapped each other, the continuous web 60 and the liquid-absorbent cores 24 are secured to each other not with hot melt adhesive but by the intermediary of the compressed end portions 42 and the compressed middle portions 44. Consequently, hot melt adhesive should not run off from the overlapping portions of the lateral portions 65, 66 and cling to a part of the manufacturing apparatus.
According to this embodiment, on the side of the second surface 22 of the bodily fluid absorbent structure 15, the lateral portions 36, 37 of the core wrapping sheet 23 overlap each other not in the central zone 46 but in one lateral region in the direction of the transverse axis Q of the bodily fluid absorbent structure 15 and one of the compressed middle portions 44 is formed in the overlapping portion 40 of the lateral portions 36, 37. The compressed middle portions 44 formed in the overlapping portion 40 ensures it to prevent the superabsorbent polymer particles from falling off.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-116782 | May 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/061443 | 5/18/2011 | WO | 00 | 11/19/2012 |
