The present invention relates to a stretchable absorbent core. The stretchable absorbent core of the invention is suitably used as a constituent core for absorbent articles such as sanitary napkins and disposable diapers.
Absorbent articles having stretchable absorbent core are known in the art. Patent Document 1, for example, discloses a stretchable sheet-like absorbent core that has a conjugate sheet consisting of an elastic sheet 11 and a nonwoven fabric 12 bonded to the elastic sheet 11. The nonwoven fabric 12 of the conjugate sheet is joined to the elastic sheet 11 continuously in a first direction, but joined in a discontinuous manner in a second direction orthogonal to the first direction such that the nonwoven fabric 12 has some allowance with respect to the elastic sheet 11. Joining the sheets in this way forms channels extending in the first direction and parallel to one another. Rod-like absorbers 15 are respectively placed in those channels. Extending this sheet-like absorbent core stretches and flattens out the channels formed by the nonwoven fabric 12. The shapes of the channels thus deform depending on the stretch state of the sheet-like absorbent core, which causes variation in the distance between the nonwoven fabric 12 and each of the absorbers 15. This means that the absorbency of the sheet-like absorbent core varies depending on the degree of stretch thereof. That is, stretch of the sheet-like absorbent core due to a wearer's movement etc. causes variation in its absorbency.
Patent Document 2 discloses a resilient body including two thin layers 1 and 6, and material bodies 4 disposed between the two thin layers 1 and 6 according to a given pattern, at least one of the two layers being woven by elastic threads for providing stretchability. The two thin layers 1 and 6 are attached mutually spaced from one another in their stretched state. Similar to the sheet-like absorbent core disclosed in Patent Document 1, the material bodies 4 in the resilient body deform depending on the degree of stretch of the resilient body, which results in that stretch of the sheet-like absorbent core due to a wearer's movement etc. causes variation in its absorbency.
Aside from the techniques disclosed in Patent Documents 1 and 2, Patent Document 3 discloses an absorbent core of an absorbent article that consists of a laminate of a nonwoven fabric layer and a fibrous web layer. The laminate includes first network regions that are thin and have high density, and second network regions that are thick and have a lower density than the first network regions. The surface of the fibrous web layer is bulky and has projections and depressions. The first network regions are arranged in the form of bands intersecting one another, whereas the second network regions are provided as partitioned layers surrounded by the first network regions. This laminate absorbent core, however, has no stretchability, and thus will not easily conform to a wearer's movement, leading to poor adaptability to the body.
Patent Document 1: Japanese Patent Laid Open JP-A-6-90977
Patent Document 2: International Publication WO 91/09581
Patent Document 3: Japanese Patent Laid Open JP-A-2003-103677
The present invention provides a stretchable absorbent core including a stretchable base sheet, and a plurality of separate and independent absorbers disposed at least on one side of the base sheet.
The present invention also provides a stretchable absorbent core in which the absorbers are fixed to the base sheet through respective fixing points in such a design that the shape of each of the absorbers is not deformed upon stretch of the base sheet, and stretchability is exhibited between the fixing points.
The present invention also provides an absorbent article including such a stretchable absorbent core.
a) and 3(b) are schematic diagrams showing stretch states of the stretchable absorbent core of
a) to 5(c) are process flow diagrams sequentially showing a process for producing the stretchable absorbent core of
a) is a schematic diagram showing a device for cutting the fibers constituting the fibrous sheet in the laminate, and
b) and 7(c) are schematic diagrams respectively showing different shapes of a first roll in the device shown in
a) and 8(b) are process flow diagrams sequentially showing a process for producing the stretchable absorbent core of
a) and 10(b) are vertical cross-sectional views respectively showing other embodiments of a stretchable absorbent core according to the present invention, each corresponding to
The present invention is described below according to preferred embodiments thereof with reference to the drawings.
The base sheet 20 is a sheet-like material that has stretch property in at least one direction within its plane. The base sheet 20 serves as a part for rendering the absorbent core 10 stretchable. The term “stretchable” refers to a property that allows an element to be extended and to be contracted by canceling the extended state. The direction in which the base sheet 20 extends and contracts within a plane depends, for example, on how the base sheet 20 is produced. Preferably, the base sheet 20 is stretchable in two directions—i.e., a certain direction within a plane and a direction orthogonal thereto—, and more preferably, stretchable in all directions within a plane.
The base sheet 20 may either be permeable to liquid, or impermeable or hardly permeable to liquid. The property of the base sheet 20 regarding liquid permeability can be selected as appropriate depending on the intended use of the stretchable absorbent core 10. The liquid permeability of the base sheet 20 is determined, for example, according to the type of constituent material used, whether a wettability improver is applied or not, and how the base sheet 20 is produced.
The base sheet 20 may be a single-layer sheet or a multi-layer laminate sheet in which a plurality of sheets are joined together.
The absorbers 30 disposed on one side of the base sheet 20 are parts capable of absorbing and retaining liquid. There is no particular limitation to the type of material constituting the absorbers 30, as long as they are capable of absorbing and retaining liquid. As shown, for example, in
When viewed from above, the absorber 30 has the shape of a circle or a rectangle whose corners are rounded and whose sides each take the form of a gentle curve slightly convex outward. The plan-view shape of the absorber 30, however, is not limited to the above. For example, the plan-view shape of the absorber 30 may be a square, a rectangle, or a rhombus. Further, two or more of these shapes may be used in combination.
The absorbers 30 are disposed on the base sheet 20 across the planar direction thereof according to a regular, scattered pattern. More specifically, the absorbers 30 are disposed so as to be lined up in a plurality of first rows 30A and a plurality of second rows 30B intersecting with the first rows 30A. The surface of the base sheet 20 is exposed between adjacent absorbers 30. Thus, spaces 40 are formed between adjacent absorbers 30, each space 40 including the exposed section of the base sheet 20. Where the stretchable absorbent core 10 of the present embodiment is used for example as an absorbent core of an absorbent article, the spaces 40 are designed to have a capacity, width, and/or height allowing permeation of liquid having passed through the topsheet as well as flow of liquid in the stretchable absorbent core 10.
The absorbers 30 are fixed to the base sheet 20 through respective fixing points 33 in such a design that the shape of each absorber 30 is not deformed upon stretch of the base sheet 20. For convenience' sake, the fixing points 33 are shown with bold lines in
In order to keep the stretchable absorbent core 10 from exhibiting stretchability at the fixing points 33, the stretchability of the base sheet 20 may be eliminated, for example, by forming the fixing points 33 through ultrasonic embossing. Forming the fixing points 33 with an adhesive such as a hot melt adhesive also allows the stretchability of the base sheet 20 to be eliminated.
As described above, the stretchable absorbent core 10 of the present embodiment does not exhibit stretchability at the fixing points 33. In other words, only sections between the fixing points 33 exhibit stretchability in the stretchable absorbent core 10. That is, when the stretchable absorbent core 10 in its natural state (relaxed state) as shown in
Note that, although the fixing section 33 has a circular plan-view shape in
From the standpoint of achieving both stretchability and satisfactory absorbency of the stretchable absorbent core 10, it is preferable that the plan-view area of each absorber 30, in its natural state (relaxed state), is 10 to 900 mm2, and more preferably 50 to 450 mm2. Further, from the standpoint of improving the wearer's comfort of the absorbent article having the stretchable absorbent core 10 and the standpoint of reducing the rigidity of the stretchable absorbent core 10 to make the absorbent article having the stretchable absorbent core 10 adapt to the wearer's body, it is preferable that the thickness T (see
Further, from the standpoint of providing sufficient strength so that the absorber 30 does not fall off due to stretch of the base sheet 20, it is preferable that the area of each fixing point 33 for fixing the absorber 30 to the base sheet 20 is 1 to 100 mm2, and more preferably 5 to 50 mm2, provided that the area of the fixing point is smaller than that of the absorber 30 when viewed from above. Furthermore, from the standpoint of minimizing the area of the base sheet 20 in which stretchability is lost to minimize impairment of stretchability of the base sheet 20, it is preferable that the total sum of the area of the fixing points 33, as viewed from above, is 5% to 95%, and more preferably 20% to 70%, with respect to the area of the base sheet 20.
The distance D (see
The material constituting the absorber 30 is not particularly limited, and fibrous materials, porous elements, and combinations thereof may be used. Examples of fibrous materials that may be used include: natural fibers such as wood pulp, cotton, and hemp; single fibers made of synthetic resin including e.g. polyolefin-based resin such as polyethylene and polypropylene, polyester-based resin such as polyethylene terephthalate, and polyvinyl alcohol resin; conjugate fibers including two or more types of these resins; and semi-synthetic fibers such as acetate and rayon. In cases where a fiber made of synthetic resin is to be used, it may be a heat-shrinkable fiber that deforms by heat. For example, it is possible to employ a fiber whose fineness increases but whose fiber length decreases by heat, or a fiber whose fineness hardly changes by heat but whose apparent occupied length (the apparent length that the fiber occupies) decreases due to it deforming into a coil. Examples of porous elements that may be used include sponge, nonwoven fabrics, and an aggregate of high-absorbent polymer (i.e., an aggregate of high-absorbent polymer and fiber).
Preferable polymers for the high-absorbent polymer 32 contained in the absorber 30 include those that can absorb and retain body fluid of an amount five times or more of its own weight and that can gel. There is no particularly preferable shape therefor, and the polymer may be spherical, clump-like, botryoidal, powdered, or fibrous. Particulate polymers having a size of 1 to 1000 μm, and more preferably 10 to 500 μm, are preferred. Examples of such high-absorbent polymers may include starch, cross-linked carboxyl methyl cellulose, polymers or copolymers of acrylic acid or alkali metal salts thereof, polyacrylic acid or salts thereof, and graft polymers of polyacrylic acid salts. Preferable polyacrylic acid salts that can be used are sodium salts. It is also possible to preferably use copolymers in which a comonomer, such as maleic acid, itaconic acid, acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, 2-(meth)acryloyl ethane sulfonic acid, 2-hydroxyethyl (meth)acrylate, or styrene sulfonic acid, is copolymerized with acrylic acid within a range that does not deteriorate the performance of the high-absorbent polymer.
In the present invention, it is not essential for the absorber 30 to include the high-absorbent polymer 32. However, in cases where the absorber 30 includes the high-absorbent polymer 32, the ratio of the high-absorbent polymer 32 with respect to the weight of the absorber 30 is preferably 5% to 95% by weight. In cases where the stretchable absorbent core 10 is to be used as an absorbent core of a sanitary napkin or an article used for absorbing a small amount of excreted fluid such as light incontinence, the ratio of the high-absorbent polymer 32 with respect to the weight of the absorber 30 is preferably 10% to 30% by weight. In cases where the stretchable absorbent core 10 is to be used as an absorbent core of an article used for absorbing a large amount of excreted fluid, such as a disposable diaper, the ratio of the high-absorbent polymer 32 with respect to the weight of the absorber 30 is preferably 50% to 80% by weight.
From the standpoint of exhibiting stable absorbency even upon stretch of the base sheet 20, it is preferable that the amount of 0.9-percent-by-weight sodium chloride solution the stretchable absorbent core 10 can retain (i.e., the retention amount of the stretchable absorbent core 10) is equal to or above 0.1 g/g, and more preferably equal to or above 1 g/g, regardless of whether the absorbers 30 include the high-absorbent polymer or not. In order to achieve such a retention amount, it is advantageous to use, in combination, a highly-hydrophilic fiber having a strong capillary force (such as pulp or rayon), a synthetic fiber that does not sink down when wet (i.e., that is neither plasticized nor reduced in wet strength), and a high-absorbent polymer, as the material constituting the absorber 30.
The above-described retention amount is measured as follows. Measurement is carried out at 25±2° C. and at a relative humidity of 50% RH±5%. First, an evaluation sample is prepared by cutting out a stretchable absorbent core into a square 50 mm long and 50 mm wide, and the weight (M0) of the evaluation sample is measured. The evaluation sample is then placed in a 500 ml beaker containing 400 ml of a 0.9-percent-by-weight sodium chloride solution and immersed therein for one hour. After an hour, the evaluation sample is taken out from the beaker, and is placed on an acrylic plate inclined at 45 degrees and left thereon for ten minutes to drain. The weight (M1) after draining is then measured. The retention amount is calculated from the following equation, and an average value for n=5 (i.e., an average value for five evaluation samples) is considered as the retention amount of the stretchable absorbent core with respect to the sodium chloride solution.
Retention amount (g/g)=(M1−M0)/(M0)
Any kind of sheet having stretchability can be used, without particular limitation, as the base sheet 20 onto which the absorbers 30 are fixed. Examples of such sheets may include: nonwoven fabrics that include, as a constituent, fiber including elastic resin (i.e., elastic nonwoven fabrics); films including elastic resin (i.e., elastic films); and elastic porous elements made of elastic resin having a structure formed into a three-dimensional network by means of foaming etc. Any type of elastic nonwoven fabric, elastic film, or elastic porous element known in the present technical field can be used. It is preferable that the basis weight of the base sheet 20 is 5 to 50 g/m2, and more preferably 10 to 30 g/m2.
It is preferable that the degree of stretchability of the base sheet 20 is 60% or above, and more preferably 80% or above, in stretch ratio which is measured as follows, from the standpoint of providing particularly favorable adaptability to a wearer's body and conformability to a wearer's movement. The stretch ratio is measured as follows. Measurement is carried out using a tension/compression tester RTC-1210A (supplied by Orientec Co., Ltd.) in the “tension mode”. First, a measurement piece is sampled by cutting the base sheet 20 into a strip 25 mm wide and 150 mm long. The measurement piece is set between air chucks that are installed in the tension/compression tester at an initial sample length (chuck-to-chuck distance) of 100 mm, and the piece is extended by raising the chuck mounted to the load cell (rated output of 5 kg) of the tension/compression tester at a speed of 300 mm/min. When the measurement piece has been extended by a length 50% of the initial sample length, i.e., by 50 mm, the movement direction of the chuck is reversed, and the chuck is lowered at a speed of 300 mm/min and returned to the position of the initial sample length. During this operation, the relationship between the load detected by the load cell and the extension of the measurement piece is recorded in a chart, and the stretch ratio is obtained from the following equation (1) based on the chart.
Stretch ratio=Recovery extension/Maximum extension length (=50 mm) (1)
The “recovery extension” is defined as the distance the chuck has moved from the maximum extension length (=50 mm) at the time the load first becomes zero after starting to lower the chuck from the maximum extension length. Note that in cases where the measurement piece cannot extend up to the above-described size, measurement is carried out according to the following method.
Assuming that the length of the sheet in the chuck-to-chuck direction is L mm, the length of a section that is held is S mm, and the width of the sheet is C mm, a measurement piece is sampled by cutting the base sheet into a specimen (L+2S) mm long×C mm wide in such a manner that the length ratio L:C becomes 3:5.
The specimen is set to the tension/compression tester at a chuck-to-chuck distance of L, and the chuck is raised at a speed of 100×(L/30) mm/min until the measurement piece is extended by a length 50% of the initial sample length. The movement direction of the chuck is then reversed, and the chuck is lowered at a speed of 100×(L/30) mm/min and returned to the position of the initial sample length. Calculation is made according to the following equation (2):
Stretch ratio=Recovery extension/Maximum extension length (=L/2 mm) (2)
Now, a preferable process for producing the stretchable absorbent core 10 of the present embodiment is described with reference to
After the fibrous sheet 300 is placed on one side of the base sheet 20, the sheets are partially joined together to form a plurality of fixing points 33 as shown in
Then, high-absorbent polymer is sprinkled onto the fibrous sheet 300 as necessary (not shown). Thereafter, the fibers constituting the fibrous sheet 300 are cut between adjacent fixing sections 33, as shown in
In order to cut the fibers constituting the fibrous sheet 300 of the laminate 310, it is possible, for example, to use a cutting device 400 including a first roll 401 and a second roll 402 as shown in
After cutting the fibers constituting the fibrous sheet 300, heat is applied to the laminate 310 to cause the heat-shrinkable fiber contained in the fibrous sheet 300 to shrink. The temperature of the applied heat is set equal to or above the shrink-start temperature of the heat-shrinkable fiber and below the melt temperature. Through heat shrinking, the fibers constituting the fibrous sheet 300 gather toward each fixing point 33 as well as rise up in the thickness direction as shown in
Then, as shown in
By blowing air as shown in
Note that the operation shown in
The following describes another way of producing the stretchable absorbent core 10. First, a multitude of cut sections consisting of through holes or incisions are formed in advance in the fibrous sheet 300 before being joined to the base sheet 20. Note that the cut sections are formed to have such a size and/or shape and/or arrangement pattern that allows the fibrous sheet 300 to maintain its form as a sheet and that allows the fibrous sheet 300 to separate into a multitude of cut pieces at the cut sections when the fibrous sheet 300 is extended. Then, the fibrous sheet 300 and the base sheet 20 are joined together. Following this, the base sheet 20 is extended, which in turn causes the fibrous sheet 300 to separate into a multitude of cut pieces that are fixed to the base sheet 20 respectively at the positions of the fixing points 33. This state corresponds to the state shown in
The stretchable absorbent core 10 obtained in this way is preferably used as a constituent core of various absorbent articles such as sanitary napkins and disposable diapers. A typical absorbent article has a topsheet, a backsheet, and a liquid-retainable absorbent core disposed between the two sheets. A pair of three-dimensional guards may be disposed on the right and left sides on the topsheet. In an absorbent article having such a structure, the stretchable absorbent core 10 is used as the liquid-retainable absorbent core disposed between the topsheet and the backsheet or as the three-dimensional guard.
There is no particular limitation to the material constituting the topsheet 101 and the backsheet 102. However, taking account of the fact that the absorbent core 10 is stretchable, it is preferable that the topsheet 101 and the backsheet 102 also are stretchable or deformable. In this way, the absorbent article 100 as a whole will exhibit stretchability. As a stretchable topsheet 101, it is possible to use, for example, a nonwoven fabric that includes, as its constituent, fibers including elastic resin, or a perforated film including elastic resin. As a deformable topsheet 101, it is possible to use, for example, a projecting-and-depressed sheet having a wavy cross section, a nonwoven fabric made by needle-punching and having a multitude of holes, or a pleated nonwoven fabric. Such nonwoven fabrics and films are permeable to liquid. As a stretchable backsheet 102, it is possible to use a film including elastic resin, the film being impermeable or hardly permeable to liquid. The film may be moisture permeable.
In the absorbent article 100 shown in
Aside from the absorbent article 100 shown in
Next, other embodiments of the present invention are described with reference to
In a stretchable absorbent core 10 according to the embodiment shown in
In a stretchable absorbent core 10 according to the embodiment shown in
In the present invention, it is also possible to use an intermediate product in the process of producing the stretchable absorbent core 10 shown in FIG. 1—i.e., the intermediate product in the state shown in
Although the present invention has been described according to preferred embodiments thereof, the invention is not to be limited to those embodiments. For example, instead of disposing the stretchable absorbent core 10 alone between the topsheet 101 and the backsheet 102 as in the foregoing embodiment, it is possible to also dispose a fiber stack made of pulp, or a fiber stack made of pulp and high-absorbent polymer, beneath the stretchable absorbent core 10.
The stretchable absorbent core of the present invention is superior in adaptability to a wearer's body and conformability to a wearer's movement, and a reduction in absorbency due to stretch is less likely to occur.
Number | Date | Country | Kind |
---|---|---|---|
2007-316239 | Dec 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2008/071319 | 11/25/2008 | WO | 00 | 8/6/2010 |