US20150211157A1

US20150211157A1 - Nonwoven cloth

Info

Publication number: US20150211157A1
Application number: US14/430,531
Authority: US
Inventors: Jun Okuda; Satoshi Mitsuno
Original assignee: Unicharm Corp
Current assignee: Unicharm Corp
Priority date: 2012-09-28
Filing date: 2013-09-20
Publication date: 2015-07-30
Also published as: AU2013321216A1; AU2013321216B2; CN103710883B; JP5840100B2; WO2014050762A1; EP2902537A4; KR20150060607A; CN203700710U; EP2902537A1; EP2902537B1; KR102117135B1; CN103710883A; JP2014070317A

Abstract

A nonwoven cloth provided with both improved softness and adequate thickness and specific volume having thermally fused composite fibers that are mutually intersecting and overlapping, and a constricted thermally adhesive section in which the thermally fused composite fibers are thermally fused in the intersection region. The constricted thermally adhesive section has a recessed surface facing a center line extending in a direction overlapping with the thermally fused composite fibers across the center of the intersection region. The distance between the thermally fused composite fibers is larger than the sum of the radii of the thermally fused composite fibers, the thickness under a load of 3.0 gf/cm²is 0.5-3.0 mm, and the specific volume is 6-300 cm³/g.

Description

TECHNICAL FIELD

The present invention relates to a nonwoven fabric.

BACKGROUND ART

A nonwoven fabric used as a component member, such as a top sheet, etc., of an absorbent article such as disposal diaper, sanitary napkin, etc., is usually formed into a strip form, is stored in the form of a wound roll, and is unwound from the roll for use.
If a nonwoven fabric is wound up in the form of a roll, the nonwoven fabric is compressed in the thickness direction and the bulkiness (thickness) of the nonwoven fabric is reduced, and the reduction in the bulkiness of the nonwoven fabric may result in the decrease in the liquid absorption rate and the decrease in flexibility of the nonwoven fabric.
As a method for restoring the bulkiness of a nonwoven fabric having a reduced bulkiness, a method in which hot air is applied to the nonwoven fabric by an air-through method to restore the bulkiness of the nonwoven fabric has been known (Patent Literature 1). In this method, hot air is applied to the nonwoven fabric in the thickness direction thereof (perpendicular to the nonwoven fabric).
In addition, as a method for producing a nonwoven fabric, a method for forming a nonwoven fabric from an aggregate of fibers by applying a water vapor stream to the aggregate of fibers (Patent Literature 2). In this method, a water vapor stream is applied to an aggregate of fibers in the thickness direction thereof (perpendicular to the fiber aggregate), and thereby the fibers are separated and a bridging structure (FIG. 4 of Patent Literature 2) is formed between the fibers. The bridging structure formed between the fibers improves the flexibility of a nonwoven fabric.

CITATIONS LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No. 2004-137655

Patent Literature 2: Japanese Unexamined Patent Publication No. 2009-177364

SUMMARY OF INVENTION

Problems to be Solved by the Invention

However, it is difficult to produce a nonwoven fabric having improved flexibility as well as sufficient thickness and specific volume by the methods of Patent Literatures 1 and 2, since pressure is applied to a nonwoven fabric or an aggregate of fibers in the thickness direction thereof (i.e., the opposite direction to the thickness increasing direction) by hot air or a water vapor stream.
Therefore, an object of the present invention is to provide a nonwoven fabric having an improved flexibility as well as sufficient thickness and specific volume.

Means for Solving the Problems

To overcome the above problems, the present invention is to provide a nonwoven fabric comprising heat-fusible conjugate fibers intersecting and overlapping with each other and heat-fused constriction parts at the intersection regions of the heat-fusible conjugate fibers, wherein when a virtual line extending in the overlapping direction of the heat-fusible conjugate fibers through the center of an intersection region is defined as a center line, the heat-fused constriction parts have a surface which is recessed toward the center line, wherein the distance between the heat-fusible conjugate fibers that are heat-fused through a heat-fused constriction part is larger than the total of the fiber radius of each heat-fusible conjugate fiber, and wherein the nonwoven fabric has a thickness of 0.5 to 3.0 mm under a load of 3.0 gf/cm², and a specific volume of 6 to 300 cm³/g.
In a preferred embodiment (Embodiment 1) of the nonwoven fabric of the present invention, the nonwoven fabric has a plurality of heat-fused parts at the intersection regions of the heat-fusible conjugate fibers intersecting and overlapping with each other, and wherein the proportion of the number of the heat-fused constriction parts to the total number of the heat-fused parts included in a predetermined region of the nonwoven fabric is 1/10 to 9/10.
In a preferred embodiment (Embodiment 2) of the nonwoven fabric of the present invention, the heat-fusible conjugate fibers have a fiber diameter of 10 to 30 μm. Embodiment 2 may be combined with Embodiment 1.
In a preferred embodiment (Embodiment 3) of the nonwoven fabric of the present invention, wherein the heat-fusible conjugate fibers comprise a first component and a second component having a melting point lower than that of the first component, wherein the weight ratio of the second component to the first component (the second component/the first component) is 4/6 to 8/2. Embodiment 3 may be combined with Embodiment 1 and/or Embodiment 2.
In a preferred embodiment (Embodiment 4) of the nonwoven fabric of the present invention, the nonwoven fabric is obtained by a bulkiness restoration treatment of a nonwoven fabric before bulkiness restoration, comprising heat-fused, heat-fusible conjugate fibers, wherein the bulkiness restoration treatment comprises a step of providing a heating chamber having an inlet and an outlet, and a step of, while conveying the nonwoven fabric before bulkiness restoration so as to enter into the heating chamber through the inlet, to proceed through the heating chamber, and then to exit from the heating chamber through the outlet, feeding a heated fluid at a velocity higher than the conveyance velocity of the nonwoven fabric before bulkiness restoration so as to enter into the heating chamber through one of the inlet and outlet, to proceed through the heating chamber while contacting the nonwoven fabric, and then to exit from the heating chamber through the other of the inlet and outlet. Embodiment 4 may be combined with one or two or more of Embodiments 1 to 3.
In a preferred embodiment (Embodiment 5) of the nonwoven fabric of Embodiment 4, the nonwoven fabric before bulkiness restoration is an air-through nonwoven fabric obtained by an air-through treatment of a web comprising heat-fusible conjugate fibers to heat-fuse the heat-fusible conjugate fibers.
In a preferred embodiment (Embodiment 6) of the nonwoven fabric of Embodiment 4 or 5, the heated fluid enters into the heating chamber through the inlet and exits from the heating chamber through the outlet. Embodiment 6 may be combined with Embodiment 4 and/or Embodiment 5.
In a preferred embodiment (Embodiment 7) of the nonwoven fabric according to any one of Embodiments 4 to 6, the nonwoven fabric before bulkiness restoration is conveyed through the heating chamber without being supported. Embodiment 7 may be combined with one or two or more of Embodiments 4 to 6.
In a preferred embodiment (Embodiment 8) of the nonwoven fabric according to any one of Embodiments 4 to 7, the heating chamber is defined by two walls that extend from the inlet to the outlet and are separated from each other, and the nonwoven fabric before bulkiness restoration is conveyed within the heating chamber so that both surfaces of the nonwoven fabric before bulkiness restoration respectively continue to face the walls. Embodiment 8 may be combined with one or two or more of Embodiments 4 to 7.

Advantageous Effects of Invention

A nonwoven fabric having an improved flexibility as well as sufficient thickness and specific volume is provided by the preset invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1( a) is a plan view of heat-fusible conjugate fibers intersecting and overlapping with each other, in which one of the fibers is located upside and the other fiber is located downside, when viewed in plan view, and FIG. 1( b) is a cross-sectional view along line I-I in FIG. 1( a).

FIG. 2( a) is a plan view of heat-fusible conjugate fibers intersecting and overlapping with each other, in which one of the fibers is located upside and the other fiber is located downside, and FIG. 2( b) is a cross-sectional view along line II-II in FIG. 2( a).

FIG. 3 is an overall view of the bulkiness restoration system according to one embodiment.

FIG. 4 is an enlarged cross-sectional view of the heating chamber.

FIG. 5 is a view of an end face of the heating chamber.

FIG. 6 is a view showing another embodiment of the bulkiness restoration system.

FIG. 7 is a view showing still another embodiment of the bulkiness restoration system.

FIG. 8 is an overall view of the bulkiness restoration system of a comparative example.

FIGS. 9( a) to (c) are electron microscope photographs of a nonwoven fabric before bulkiness restoration (before conveyance to the bulkiness restoration system).

FIGS. 10( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Example 1.

FIGS. 11( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Example 2.

FIGS. 12( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Comparative Example 1.

FIGS. 13( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Comparative Example 2.

FIGS. 14( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Comparative Example 3.

MODE FOR CARRYING OUT THE INVENTION

The nonwoven fabric of the present invention will be described in detail below.
The nonwoven fabric of the present invention comprises heat-fusible conjugate fibers intersecting and overlapping with each other and heat-fused constriction parts at the intersection regions of the heat-fusible conjugate fibers.
The nonwoven fabric of the present invention has an improved flexibility, since the heat-fusible conjugate fibers are heat-fused through the heat-fused constriction parts. The flexibility of the nonwoven fabric can be evaluated on the basis of, for example, the compression properties of the nonwoven fabric. The compression properties of nonwoven fabrics include, for example, compression energy WC per 1 cm²of nonwoven fabric (N·m/m²) and compression resilience RC (%), measured in KES compression test. The WC value represents compression deformation properties, and the greater the WC value, the higher the compression deformation properties. In addition, the RC value represents compression recovery properties, and an RC value closer to 100% indicates higher compression recovery properties. In the KES compression test, for example, an automated compression tester KES-FB3 manufacture by Kato Tech Corp. can be used. The WC value is preferably 0.5 N·m/m²or more, and more preferably 1.0 N·m/m²or more. The RC value is preferably 30% or more, and more preferably 40% or more.
Although the nonwoven fabric of the present invention comprises many intersection regions of the heat-fusible conjugate fibers, the heat-fusible conjugate fibers are not needed to be heat-fused at all of the intersection regions, and the heat-fusible conjugate fibers may be heat-fused at some intersection regions.
In the nonwoven fabric of the present invention, the intersection regions of the feat-fusible conjugate fibers are regions where the heat-fusible conjugate fibers are intersecting and overlapping with each other, in which one of the fibers is located upside and the other fiber is located downside when viewed in plan view (see FIG. 1( a)), and are regions extending between the heat-fusible conjugate fibers in the overlapping direction (vertical direction) of the heat-fusible conjugate fibers in a cross sectional view (see FIG. 1( b)).
The nonwoven fabric of the present invention has a plurality of heat-fused parts at the intersection regions of the heat-fusible conjugate fibers intersecting and overlapping with each other. Although the heat-fused parts comprise a portion existing within an intersection region of the heat-fusible conjugate fibers, it is not necessary that the entire of the heat-fused part exists within the intersection region of the heat-fusible conjugate fibers, and the heat-fused parts may comprise a portion extending outside the intersection region of the heat-fusible conjugate fibers.
Some or all of the heat-fused parts included in the nonwoven fabric of the present invention are heat-fused constriction parts. The proportion of the number of the heat-fused constriction parts to the total number of the heat-fused parts included in a predetermined region of the nonwoven fabric is not particularly limited, but is preferably 1/10 to 9/10, and more preferably 2/8 to 8/10. The proportion of the number of the heat-fused constriction parts to the total number of the heat-fused parts can be determined by, for example, observing a nonwoven fabric with a microscope such as a scanning electron microscope and counting the number of the total number of the heat-fused parts and the heat-fused constriction parts within the visual field of the microscope. The magnification of the microscope at the time of observation is typically 100 to 500 times, and preferably 200 to 400 times.
When a virtual line extending in the overlapping direction of the heat-fusible conjugate fibers through the center of an intersection region of the heat-fusible conjugate fibers is defined as a center line, the heat-fused constriction parts have a surface which is recessed toward the center line.
An embodiment of the heat-fused constriction parts will be explained below with referring to heat-fusible conjugate fibers intersecting perpendicularly with each other as an example. For convenience of explanation, the intersection angle of the heat-fusible conjugate fibers is perpendicular, but the intersection angle of the heat-fusible fibers should not be limited to vertical.
FIG. 1( a) is a plan view of heat-fusible conjugate fibers F1, F2 intersecting and overlapping with each other, in which heat-fusible conjugate fiber F1 is located upside and heat-fusible conjugate fiber F2 is located downside. FIG. 1( b) is a cross sectional view along line I-I in FIG. 1( a). The direction of line I-I in FIG. 1( a) coincides with the direction of axis line L2 of heat-fusible conjugate fiber F2 in FIG. 1( a).
As shown in FIG. 1( a), heat-fusible conjugate fiber F1 extends along axis line L1, heat-fusible conjugate fiber F2 extends along axis line L2, and heat-fusible conjugate fibers F1, F2 intersect perpendicularly with each other.
In FIG. 1( a), although axis line L1 and axis line L2 are represented as straight lines, axis line L1 and axis line L2 should not be limited to straight lines and may be curved lines. When focused on a minute section where heat-fusible conjugate fibers F1, F2 intersect with each other, axis line L1 and axis line L2 can be approximated to substantially straight lines as shown in FIG. 1( a).
As shown in FIGS. 1( a) and (b), intersection region R1 of heat-fusible conjugate fibers F1, F2 is a region where heat-fusible conjugate fibers F1, F2 overlap with each other when viewed in plan view and which extends between heat-fusible conjugate fibers F1, F2 in overlapping direction Z1 (vertical direction) of heat-fusible conjugate fibers F1, F2 when viewed in cross sectional view.
As shown in FIG. 1( a), center P1 of intersection region R1 coincides with the intersection point of axis line L1 and axis line L2, when viewed in plan view.
As shown in FIG. 1( b), heat-fusible conjugate fibers F1, F2 are heat-fused with each other at heat-fused constriction part B1 in intersection region R1. In this embodiment, the entire of heat-fused constriction part B1 is formed inside intersection region R1, but may comprise a portion extending outside intersection region R1.
As shown in FIG. 1( b), when a virtual line extending in overlapping direction Z1 (vertical direction) of heat-fusible conjugate fibers F1, F2 through center P1 of intersection region R1 of heat-fusible conjugate fibers F1, F2 is defined as center line A1, heat-fused constriction part B1 has a surface which is recessed toward center line A1. Center line A1 coincides with the vertical line drawn from axis line L1 of heat-fusible conjugate fiber F1 to axis line L2 of heat-fusible conjugate fiber F2 in intersection region R1 of heat-fusible conjugate fibers F1, F2.
The outer peripheral surface of heat-fused constriction part B2 may be partly recessed toward center line A1, and almost entire of the outer peripheral surface is preferably recessed toward center line A1. The outer peripheral surface of heat-fused constriction part B1 may have a part where cracks have been generated.
In the nonwoven fabric of the present invention, the distance between the heat-fusible conjugate fibers that are heat-fused through a heat-fused constriction part is larger than the sum of the fiber radius of each heat-fusible conjugate fiber. The joining strength between the heat-fusible conjugate fibers through the heat-fused constriction part decreases with the increase in the distance between the heat-fusible conjugate fibers that are heat-fused through the heat-fused constriction part, and thereby the flexibility of the nonwoven fabric is improved. In addition, the thickness and specific volume (void volume) of the nonwoven fabric increase with the increase in the distance between the heat-fusible conjugate fibers that are heat-fused through the heat-fused constriction part. In the above embodiment, the distance (r3) between heat-fusible conjugate fibers F1, F2 that are heat-fused through heat-fused constriction part B1 is larger than the sum of the fiber radii (r1+r2) of heat-fusible conjugate fibers F1, F2, as shown in FIG. 1( b).
The heat-fused parts other than the heat-fused constriction parts included in the nonwoven fabric of the present invention include, for example, heat-fused bulge parts having a surface protruding toward the direction away from the center line, wherein a virtual line extending in the overlapping direction of the heat-fusible conjugate fibers F1, F2 through the center of an intersection region of the heat-fusible conjugate fibers is defined as the center line.
An embodiment of the heat-fused bulge parts will be explained below with referring to heat-fusible conjugate fibers intersecting perpendicularly with each other as an example. For convenience of explanation, the intersection angle of the heat-fusible conjugate fibers is perpendicular, but the intersection angle of the heat-fusible fibers should not be limited to vertical.
FIG. 2( a) is a plan view of heat-fusible conjugate fibers F3, F4 intersecting and overlapping with each other, in which heat-fusible conjugate fiber F3 is located upside and heat-fusible conjugate fiber F4 is located downside. FIG. 2( b) is a cross sectional view along line II-II in FIG. 2( a). The direction of line II-II in FIG. 2( a) coincides with the direction of axis line L4 of heat-fusible conjugate fiber F4 in FIG. 2( a).
As shown in FIG. 2( a), heat-fusible conjugate fiber F3 extends along axis line L3, heat-fusible conjugate fiber F4 extends along axis line L4, and heat-fusible conjugate fibers F3, F4 intersect perpendicularly with each other.
In FIG. 2( a), although axis line L3 and axis line L4 are represented as straight lines, axis line L3 and axis line L4 should not be limited to straight lines and may be curved lines. When focused on a minute section where heat-fusible conjugate fibers F3, F4 intersect with each other, axis line L3 and axis line L4 can be approximated to substantially straight lines as shown in FIG. 2( a).
As shown in FIGS. 2( a) and (b), intersection region R2 of heat-fusible conjugate fibers F3, F4 is a region where heat-fusible conjugate fibers F3, F4 overlap with each other when viewed in plan view and which extends between heat-fusible conjugate fibers F3, F4 in overlapping direction Z2 (vertical direction) of heat-fusible conjugate fibers F3, F4 when viewed in cross sectional view.
As shown in FIG. 2( a), center P2 of intersection region R2 coincides with the intersection point of axis line L3 and axis line L4, when viewed in plan view.
As shown in FIG. 2( b), heat-fusible conjugate fibers F3, F4 are heat-fused with each other at heat-fused bulge part B2 in intersection region R2. In this embodiment, heat-fused bulge part B2 comprises a portion existing inside intersection region R2 and a portion extending outside intersection region R2, but the entire of heat-fused bulge part B2 may exist inside intersection region R2.
As shown in FIG. 2( b), when a virtual line extending in overlapping direction Z2 (vertical direction) of heat-fusible conjugate fibers F3, F4 through center P2 of intersection region R2 of heat-fusible conjugate fibers F3, F4 is defined as center line A2, heat-fused bulge part B2 has a surface protruding toward the direction away from center line A2. Center line A2 coincides with the vertical line drawn from axis line L3 of heat-fusible conjugate fiber F3 to axis line L4 of heat-fusible conjugate fiber F4 in intersection region R2 of heat-fusible conjugate fibers F3, F4.
The outer peripheral surface of heat-fused bulge part B2 may partly protrude toward the direction away from center line A2, and almost entire of the outer peripheral surface is preferably protruding away from center line A2. The outer peripheral surface of heat-fused constriction part B2 may have a part where cracks have been generated.
As shown in FIG. 2( b), heat-fusible conjugate fibers F3, F4 are biting into each other, and accordingly distance (r3) between heat-fusible conjugate fibers F3, F4 is smaller than the sum of the fiber radii (r1+r2) of heat-fusible conjugate fibers F3, F4.
Thy nonwoven fabric of the present invention has a thickness (under a load of 3.0 gf/cm²) of 0.5 to 3.0 mm, and preferably 0.7 to 3.0 mm, and a specific volume of 6 to 300 cm³/g, and preferably 12 to 200 cm³/g. Accordingly, the nonwoven fabric of the present invention has sufficient thickness and specific volume. When the nonwoven fabric of the present is used as a top sheet of an absorbent article, the range less than the above lower limits of the thickness and specific volume may result in decrease in liquid permeability and thereby easily develop stickiness, whereas the range more than the above upper limits result in increase in the thickness of the entire absorbent article and thereby easily provides uncomfortable feeling during wearing of the absorbent article.
The thickness and specific volume vary depending on the proportion of the heat-fused constriction part to the total number of the heat-fused parts, the form of the heat-fused constriction parts, the distance between the heat-fusible conjugate fibers that are heat-fused through a heat-fused constriction part, etc. The nonwoven fabric of the present invention can be produced by bulkiness restoration treatment of a nonwoven fabric before bulkiness restoration, comprising heat-fused, heat-fusible conjugate fibers, as described below, and the control of the conditions of bulkiness restoration treatment allows adjustment in the proportion of the heat-fused constriction part to the total number of the heat-fused parts, the form of the heat-fused constriction parts, the distance between the heat-fusible conjugate fibers that are heat-fused through a heat-fused constriction parts, etc., and therefore it is possible to adjust the thickness and specific volume of the nonwoven fabric to desired ranges. The thickness (mm) of the nonwoven fabric is measured with a thickness gauge (THICKNESS GAUGE UF-60 manufactured by Daiei Kagaku Seiki Manufacturing Co., Ltd.) while applying a load of 3.0 gf/cm²to the nonwoven fabric. Ten different points of the nonwoven fabric are measured for thickness in the same manner, and an average value of ten measurement values is determined as the thickness of the nonwoven fabric. The basis weight of the nonwoven fabric is measured in accordance with JIS L 1906 5.2. The density of the nonwoven fabric is calculated out on the basis of the following formula:
Density (g/cm³) of nonwoven fabric=basis weight (g/m²) of nonwoven fabric/thickness (mm) of nonwoven fabric×10⁻³,
and the specific volume of the nonwoven fabric is calculated out as an inverse of the density (g/m²) of the nonwoven fabric.
The basis weight of the nonwoven fabric of the present invention is not particularly limited, but is preferably 10 to 80 g/m², and more preferably 15 to 60 g/m².
The heat-fusible conjugate fibers included in the nonwoven fabric of the present invention are not particularly limited as long as they are capable of developing heat-fusible properties. The heat-fusible conjugate fibers include, for example, two-component composite fibers comprising a first component (hereinafter referred to as “high-melting point component”) and a second component (hereinafter referred as “low-melting point component”) having a melting point lower than that of the first component, wherein the second component exists on at least a part of the fiber surface continuously along the lengthwise direction. The component which develops heat-fusible properties is mainly the low-melting point component. The heat-fusible conjugate fibers may be composite fibers comprising three or more components having different melting points or softening points. The form of the heat-fusible conjugate fibers includes, for example, core-sheath type (concentric type, eccentric type, etc.), island-sea type, split-type, side-by-side type, etc., any type of conjugate fibers may be used. In the case of core-sheath type conjugate fibers, the sheath component and core component can be comprised of a low-melting point component and a high-melting point component, respectively. The heat-fusible conjugate fibers are preferably those having been subjected to a stretching treatment at the stage of raw material (prior to being used for the production of the nonwoven fabric).
The types of the high-melting point component and low-melting point component are not particularly limited as long as they have a fiber-forming ability. The high-melting point component and low-melting point component are generally synthetic resins. The high-melting point component includes, for example, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc., and the low-melting point component includes, for example, polyethylenes such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), etc., ethylene propylene copolymer, polystyrene, polypropylene (PP), copolymerized polyesters, etc. For example, in the case of core-sheath type conjugate fibers, the sheath component (low-melting point component) when the core component (high-melting point component) is PP, includes, for example, polyethylenes such as HDPE, LDPE, LLDPE, etc., ethylene propylene copolymer, polystyrene, etc., and the sheath component (low-melting point component) when the core component (high-melting point component) is PET, PBT, etc., includes, for example, PP, copolymerized polyesters, etc.
The heat-fusible composite fibers included in the nonwoven fabric of the present invention preferably contain a low-melting point component in an amount more than that of the high-melting point component, and the weight ratio of the low-melting point component to the high-melting point component (low-melting point component/high-melting point component) is preferably 4/6 to 8/2, and more preferably 5/5 to 7/3. This ensures heat-fusing by an air-through method, and thereby can effectively prevent the surfaces of the air-through nonwoven fabric after bulkiness restoration from fluffing. The weight ratio of the low-melting point component/high-melting point component can be calculated on the basis of the cross-sectional areas of the high-melting point component and low-melting point component determined by observing the cross section of the heat-fusible conjugate fibers as well as on the basis of the densities of the high-melting point component and low-melting point component.
The difference in melting point between the high-melting point component and low-melting point component is preferably 20° C., and more preferably 25° C. This feature results in the increase in difference in orientation, crystallinity, etc., of each component, and thereby improves the nonwoven fabric forming properties. The melting points can be measured as a melting peak temperature determined by thermal analysis on a finely cut fiber sample using a differential scanning calorimeter (for example, DSC 6200 manufactured by Seiko Instruments Inc.) at a heating rate of 10° C./min. If it is not possible to measure a melting point clearly, softening point may be used in place of melting point.
The fiber diameter of the heat-fusible conjugate fibers included in the nonwoven fabric of the present invention is not particularly limited, but is preferably 10 to 30 μm, and more preferably 15 to 25 μm, in view of decreasing the rough feeling of the surface. The fiber diameter of the heat-fusible conjugate fibers can be measured by, for example, observing the nonwoven fabric with a microscope such as a scanning electron microscope, etc.
The fineness of the heat-fusible conjugate fibers included in the nonwoven fabric is not particularly limited, but is preferably 1 to 6 dtex when the nonwoven fabric is used in the top sheet of an absorbent article. If the fineness is less than 1 dtex, the nonwoven fabric tends to reduce its air-permeability and liquid permeability due to the reduction in the thickness of the nonwoven fabric resulting from the decrease in the strength of the conjugate fibers, whereas, if the fineness is more than 6 dtex, the nonwoven fabric tends to reduce its touch feeling due to the increase in the strength of the conjugate fibers.
The amount of the heat-fusible conjugate fibers included in the nonwoven fabric of the present invention is preferably 20 to 100 wt %, and more preferably 30 to 100 wt %, on the basis of the total of the fibers that form the nonwoven fabric.
The nonwoven fabric of the present invention may comprises, in addition to the heat-fusible conjugate fibers, the other fibers (for example, monofilaments). The other fibers include, for example, natural fibers (wool, cotton, etc.), regenerated fibers (rayon, acetate, etc.), inorganic fibers (glass fibers, carbon fibers, etc.), synthetic fibers (polyethylene fibers, polypropylene fibers, polyester fibers, acryl fibers, etc.). Incorporation of the other fibers can imparts the nonwoven fabric with the functions of the other fibers (for example, in the case of cotton, moisture absorbing properties; and in the case of synthetic fibers, air-permeability, etc.). In addition, the nonwoven fabric of the present invention may be incorporated with hollow-type fibers; profiled fibers such as flat fibers, Y-shaped fibers, C-shaped fibers, etc.; latent crimping or actually crimped three-dimensionally crimp fibers; split fibers split by a physical load such as water stream, heat, embossing, etc.
When the nonwoven fabric of the present invention comprises fibers other than the heat-fusible conjugate fibers, the content of the fibers other than the heat-fusible conjugate fibers is preferably 80 wt % or less, and more preferably 70 wt % or less on the basis of the total of the fibers that form the nonwoven fabric.
The heat-fusible conjugate fibers included in the nonwoven fabric may be imparted with a three-dimensional crimped shape. The three-dimensional crimped shape includes, for example, a zigzag shape, and a Omega shape, a spiral shape, etc. The method for imparting a three-dimensional crimped shape includes, for example, mechanical crimping, shaping by heat shrinking, etc. Mechanical crimping can be controlled by the peripheral speed difference in line speed, heat, pressurization, etc., with respect to continuous linear fibers after spinning, and the greater the number of crimps per unit length of the crimped fibers, the greater the buckling strength of the fibers under external pressure. The number of crimps is typically 5 to 35 per inch, and preferably 15 to 30 per inch. Heat shrinking can provide a three-dimensional crimping by using the difference in heat shrinking resulting from the melting temperature difference.
When the nonwoven fabric comprises latent crimping fibers and/or actually crimped fibers, even if the fiber orientation primarily aligns to the planar direction, the fiber orientation partially aligns to the thickness direction. Accordingly, the buckling strength of the fibers in the thickness direction is improved, and thereby the nonwoven fabric is less likely to decrease the bulkiness thereof even if an external force is applied to the nonwoven fabric. In addition, when the heat-fusible conjugate fibers are imparted with a spiral shape, the nonwoven fabric readily restore the bulkiness when the external force to the nonwoven fabric is released. The latent crimping fibers and/or actually crimped fibers included in the nonwoven fabric of the present invention may be heat-fusible conjugate fibers having imparted with a three-dimensionally crimped shape or may be fibers other than heat-fusible conjugate fibers.
The nonwoven fabric of the present invention may be those subjected to a hydrophilizing treatment. Hydrophilized nonwoven fabrics can preferably be used as a liquid-permeable top sheet for absorbent articles, since when they contact hydrophilic excrement (such as urine, sweat, feces, etc.), they easily transmit the excrement within the absorbent article without leaving the excrement on the surface thereof. The hydrophilizing treatment includes, for example, a treatment with a hydrophilizing agent, kneading a hydrophilizing agent into the constituent fibers of the nonwoven fabric, coating a surfactant to the nonwoven fabric, etc.
The fibers which constitute the nonwoven fabric of the present invention may contain an inorganic filler such as titanium oxide, barium sulfate, calcium carbonate, etc., to increase whitening properties. In the case of core-sheath type fibers, the core component may contain an inorganic filler, or the sheath component may contain an inorganic filler.
The nonwoven fabric of the present invention may have a textured structure on a surface thereof. The presence or absence of the textured structure can be confirmed by, for example, in the cross-sectional shape in the direction (CD direction) perpendicular to the conveyance direction (MD direction). For example, the nonwoven fabric of the present invention may have a plurality of convex portions the interiors of which are comprised of heat-fusible conjugate fibers oriented relatively to the thickness direction of the nonwoven fabric and a plurality of concave portions comprised of heat-fusible conjugate fibers oriented in the planar direction of the nonwoven fabric. In the textured structure, the concave portions have a thickness smaller than that of the convex portions. When the surface of the nonwoven fabric is textured, the contact area with the skin can be decreased, and therefore such a nonwoven fabric is suitable as a top sheet for absorbent articles.
The nonwoven fabric of the present invention can be applied in various fields utilizing bulkiness, compression deformability, compression restorability, etc. The nonwoven fabric of the present invention can be suitably used as a top sheet, a second sheet (a sheet disposed between a top sheet and an absorbent body), a back sheet, and a leakage prevention sheet of absorbent articles in the field of disposal hygiene articles such as sanitary napkins, disposable diapers, etc. In addition, the nonwoven fabric of the present invention can be suitably used as a personal cleaning sheet, a skin care sheet, an article wiper, etc.
The nonwoven fabric of the present invention can be produced by bulkiness restoration treatment of the nonwoven fabric before bulkiness restoration, comprising heat-fused, heat-fusible conjugate fibers.
A preferred bulkiness restoration treatment comprises a step of providing a heating chamber having an inlet and an outlet, and a step of, while conveying the nonwoven fabric before bulkiness restoration so as to enter into the heating chamber through the inlet, to proceed through the heating chamber, and then to exit from the heating chamber through the outlet, feeding a heated fluid at a velocity higher than the conveyance velocity of the nonwoven fabric before bulkiness restoration so as to enter into the heating chamber through one of the inlet and outlet, to proceed through the heating chamber while contacting the nonwoven fabric, and then to exit from the heating chamber through the other of the inlet and outlet. Embodiment 4 may be combined with one or two or more of Embodiments 1 to 3.
The nonwoven fabric before bulkiness restoration is preferably an air-through nonwoven fabric obtained by air-through treatment of a web comprising heat-fusible conjugate fibers to heat-fuse the heat-fusible conjugate fibers. In the bulkiness restoration treatment, it is preferable that the heated fluid enters into the heating chamber through the inlet and exits from the heating chamber through the outlet, and that the nonwoven fabric before bulkiness restoration is conveyed through the heating chamber without being supported, that the heating chamber is defined by two walls that extend from the inlet to the outlet and are separated from each other, and the nonwoven fabric before bulkiness restoration is conveyed within the heating chamber so that both surfaces of the nonwoven fabric before bulkiness restoration respectively continue to face the walls.
An embodiment of the method for producing the nonwoven fabric of the present invention will be explained below, on the basis of the drawings.
This embodiment employs bulkiness restoration system 1 for restoring the bulkiness of nonwoven fabric F, as shown in FIG. 3.
Nonwoven fabric F is one comprising heat-fused, heat-fusible conjugate fibers. The nonwoven fabric includes, for example, an air-through nonwoven fabric, point-bond nonwoven fabric, spunbond nonwoven fabric, etc., and is preferably an air-through nonwoven fabric.
Air-through nonwoven fabrics are nonwoven fabrics obtained by passing hot air through a web comprising heat-fusible conjugate fibers to heat-fuse the intersections of the heat-fusible conjugate fibers. The web comprising heat-fusible conjugate fibers can be formed by a well-known web forming process using a carding machine, etc. The web forming process includes, for example, a process in which short fibers are conveyed by an air flow and are deposited on a net (air-laid method), etc. The web thus formed is a fiber aggregate before forming a nonwoven fabric and is not subjected to a treatment (for example, heat-fusing treatment in air-through method, calendering method, etc.) which will be applied to a nonwoven fabric production process, and therefore is in the form in which the fibers are extremely loosely entangled with each other. The air-through treatment for the web comprising heat-fusible conjugate fibers, can be carried out using, for example, a hot-air blowing apparatus. In an air-through treatment, a hot air heated to a predetermined temperature (for example, 120 to 160° C.) is blown to a web and is passed through the web, and thereby heat-fusing together the intersections of heat-fusible conjugate fibers in the web. The nonwoven fabric produced by such an air-through treatment includes, for example, nonwoven fabrics comprising mainly of core-sheath type conjugate fibers in which the sheath component is a high-density polyethylene and the core component is polyethylene terephthalate and having a fiber length of 20 to 100 mm, and preferably 35 to 65 mm, and a fineness of 1.1 to 8.8 dtex, and preferably 2.2 to 5.6 dtex.
Blowing hot air is an example of heat treatment for heat-fusing together the intersections of the heat-fusible conjugate fibers in a web. The heat treatment is not particularly limited as long as it can heat the heat-fusible conjugate fibers (low melting point component) to the melting point or more. The heat treatment can be carried out using hot air as well as a heat medium such as microwave, steam, infrared radiation, etc.
Nonwoven fabric F may have a texture on a surface thereof. The texture can be imparted to the surface of nonwoven fabric F by, for example, blowing hot air to the web, thereby allowing the formation of a plurality of convex portions the interiors of which are comprised of heat-fusible conjugate fibers oriented to the thickness direction of the nonwoven fabric and a plurality of concave portions comprised of heat-fusible conjugate fibers oriented in the planar direction of the nonwoven fabric.
As shown in FIG. 3, nonwoven fabric F is wound around roll R, resulting in decrease in bulkiness of nonwoven fabric F. Accordingly, to restore the bulkiness of nonwoven fabric F, bulkiness restoration system 1 is used.
Nonwoven fabric F comprises a plurality of heat-fused parts at the intersection regions of the heat-fusible conjugate fibers intersecting and overlapping with each other. The plurality of heat-fused parts included in nonwoven fabric F are mainly heat-fused bulge parts shown in FIG. 2. Then, some or all of the heat-fused bulge parts as shown in FIG. 2 change into heat-fused constriction parts as shown in FIG. 1 during the bulkiness restoration treatment with bulkiness restoration system 1. That is, during the bulkiness restoration treatment with bulkiness restoration system 1, the heat-fused bulge parts soften or melt, and the heat-fusible conjugate fibers heat-fused with each other via the heat-fused bulge parts are slightly spaced away from each other, and consequently the heat-fused bulge parts slightly extend and change into heat-fused constriction parts. Particularly, since, in the bulkiness restoration treatment with bulkiness restoration system 1, hot air flows in parallel to nonwoven fabric F before bulkiness restoration and the velocity of the hot air is higher than the velocity of the nonwoven fabric, a turbulent flow is generated within bulkiness restoration system 1, and thereby promoting heat transfer. In addition, since a force is not applied to the constituent fibers of nonwoven fabric F in the same direction but is applied to the constituent fibers along the flow of air, the heat-fused bulge parts slightly extend and change into heat-fused constriction parts.
The joining strength of the heat-fusible conjugate fibers by the heat-fused parts decreases due to the change in shape of the heat-fused parts from a bulge from to a constriction form. Due to the change in shape of the heat-fused parts from a bulge form to a constriction form, the degree of freedom of the fibers to compression deformation is increased, and thereby making it easier for the fibers to move. Accordingly, nonwoven fabric F subjected to the bulkiness restoration treatment has excellent compression deformation properties. In addition, since heat easily transfers to the heat-fusible conjugate fibers during bulkiness restoration treatment, the resins which constitute the heat-fusible conjugate fibers are oriented by the heat, and therefore have improved crystallinity. Therefore, in nonwoven fabric F subjected to the bulkiness restoration treatment, the initial strength of fibers is improved, and accordingly the fibers are less likely to deform by initial deformation, and thereby the shape retention properties are improved. Therefore, nonwoven fabric subjected to the bulkiness restoration treatment exhibits excellent compression restoration properties.
The basis weight of nonwoven fabric F is substantially constant before and after bulkiness restoration treatment. The basis weight to the nonwoven fabric is, for example, 10 to 80 g/m²(particularly 15 to 60 g/m²). The thickness of nonwoven fabric F is increased by the bulkiness restoration treatment. The thickness (under a load of 3.0 gf/cm²) of the nonwoven fabric F is increased, for example, from 0.2 to 0.6 mm (particularly 0.3 to 0.5 mm) (before bulkiness restoration treatment) to 0.5 to 3.0 mm (particularly 0.7 to 3.0 mm). The specific volume of nonwoven fabric F is increased by the bulkiness restoration treatment. The specific volume of nonwoven fabric F is increased, for example from 2.5 to 50 cm³/g (particularly 5 to 33 cm³/g) to 6 to 300 cm³/g (particularly 12 to 200 cm³/g).
As shown in FIG. 3, bulkiness restoration system 1 comprises conveyor 2 which conveys nonwoven fabric F in the form of a strip while unwinding it from a roll R. Conveyor 2 comprises two roller pairs 2 a, 2 b. Each roller pair 2 a, 2 b comprises a pair of rollers which rotate in opposite directions each other. When these rollers are rotated, nonwoven fabric F is conveyed. In this embodiment, nonwoven fabric F is conveyed in the machine direction MD which substantially coincides with the horizontal direction so that one surface and the other surface generally face upward and downward, respectively.
As shown in FIG. 3, bulkiness restoration system 1 further comprises heater 3 for heating nonwoven fabric F to be conveyed with a fluid. Heater 3 comprises fluid source 3 a, feed pipe 3 b which is connected to an outlet of fluid source 3 a, nozzle 3 c which is connected to an outlet of feed pipe 3 b, flowmeter 3 ba which is arranged in feed pipe 3 b, regulator 3 d which is arranged in feed pipe 3 b downstream of flowmeter 3 ba, electric heater 3 e which is arranged in feed pipe 3 b downstream of regulator 3 d, and housing 3 f. Nozzle 3 c has, for example, an elongated rectangular shaped outlet.
In this embodiment, the fluid is air, and fluid source 3 a is a compressor. When compressor 3 a is operated, air flows through feed pipe 3 b. Flowmeter 3 ba detects the flow rate of air which flows through feed pipe 3 b and outputs an air flow rate in the form of a quantity under standard condition (0° C., 1 atm). The air pressure in feed pipe 3 b is reduced by regulator 3 d from, for example, 0.6 MPaG to 3 MPaG to 0.01 MPaG. The air is then heated by electric heater 3 e. The heated air then flows out from nozzle 3 c. The flow rate of air flown out from the nozzle 3 c is, for example, 2380 L/min. (2.38 m³/min., standard condition). Air is heated by electric heater 3 e to, for example, 100 to 200° C. so that the temperature of the air flown out from nozzle 3 c is, for example, 70 to 160° C. The temperature of the air flown out from nozzle 3 c can be detected by a temperature sensor arranged in vicinity of the outlet of nozzle 3 c.
As shown in FIGS. 4 and 5, housing 3 f comprises upper wall 3 fu and bottom wall 3 fb which extend in the horizontal direction and apart from each other and a pair of side walls 3 fs and 3 fs arranged between upper wall 3 fu and bottom wall 3 fb. These upper wall 3 fu, bottom wall 3 fb, and side walls 3 fs and 3 fs define internal space 3 s having a cross-sectional rectangular shape. Internal space 3 s comprises a mutually facing pair of openings 3 si and 3 so.
Heating chamber 3 g having inlets 3 gi, 3 go is defined in internal space 3 s provided in the downstream side of the outlet of nozzle 3 c. In this embodiment, the outlet of nozzle 3 c is arranged at opening 3 si of internal space 3 s. Therefore, heating chamber 3 g coincides with internal space 3 s. In addition, inlet 3 gi of heating chamber 3 g coincides with opening 3 si of internal space 3 s, and outlet 3 go of heating chamber 3 g coincides with opening 3 so of internal space 3 s.
Nonwoven fabric F is conveyed by conveyor 2 so that it enters into heating chamber 3 g through inlet 3 gi, proceeds through heating chamber 3 g, and then exits from heating chamber 3 g through outlet 3 go. In this case, no roller or belt for conveying nonwoven fabric F is disposed within heating chamber 3 g. In other words, nonwoven fabric F is conveyed within heating chamber 3 g without being supported. Further, nonwoven fabric F is conveyed within heating chamber 3 g so that both surfaces Fs of nonwoven fabric F respectively continue to face upper wall 3 fu and bottom wall 3 fb that are the partition walls defining heating chamber 3 g.
On the other hand, the air flown out from nozzle 3 c enters into heating chamber 3 g through inlet 3 gi, proceeds through heating chamber 3 g while contacting nonwoven fabric F being conveyed, and then exits from heating chamber 3 g through outlet 3 go. In this case, air is fed so that the linear velocity of the air is higher than the conveyance velocity of nonwoven fabric F.
In this embodiment, upper wall 3 fu and bottom wall 3 fb are, for example, formed from stainless steel sheets having a thickness of 3 mm. Length L3 of housing 3 f or heating chamber 3 g in the machine direction MD is 1675 mm. Width W3 f of housing 3 f is 240 mm, and width W3 g of heating chamber 3 g is 200 mm. Height H3 f of housing 3 f is 11 mm, and height H3 g of heating chamber 3 g is 5 mm.
In this embodiment, upper wall 3 fu and bottom wall 3 fb extend in horizontal planes. Angle θ formed between the orientation line of nozzle 3 c and horizontal plane H (see FIG. 4) is preferably 0 to 30 degrees, more preferably 0 to 10 degrees, and most preferably 0 degree.
As shown in FIG. 3, bulkiness restoration system 1 further comprises cooler 4 for cooling nonwoven fabric F which is conveyed downstream from heater 3, with a fluid. Cooler 4 comprises fluid source 4 a, feed pipe 4 b connected to the outlet of fluid source 4 a, nozzle 4 c connected to the outlet of feed pipe 4 b, regulator 4 d and cooling device 4 e disposed in feed pipe 4 b, and housing 4 f.
In this embodiment, the fluid is air, and fluid source 4 a is a compressor. If compressor 4 a is operated, air flows through feed pipe 4 b. The air pressure inside feed pipe 4 b is reduced by regulator 4 d. The air is then cooled by cooling device 4 e. The cooled air then flows out from nozzle 4 c.
Similarly to housing 3 f of heater 3, housing 4 f of cooler 4 comprises an upper wall and a bottom wall which extend apart from each other and a pair of side walls and arranged between the upper wall and bottom wall, and these upper wall, bottom wall, and side walls define cooling chamber 4 g having a cross-sectional rectangular shape. Cooling chamber 4 g comprises inlet 4 gi and outlet 4 go mutually facing with each other.
Nonwoven fabric F is conveyed by conveyor 2 so that it enters into cooling chamber 4 g through inlet 4 gi, proceeds through cooling chamber 4 g, and then exits from cooling chamber 4 g through outlet 4 go. In this case, no roller or belt for conveying nonwoven fabric F is disposed within cooling chamber 4 g. In other words, nonwoven fabric F is conveyed within cooling chamber 4 g without being supported. Further, nonwoven fabric F is conveyed within cooling chamber 4 g so that both surfaces Fs of nonwoven fabric F respectively continue to face upper wall and bottom wall that are the partition walls defining cooling chamber 4 g.
In this embodiment, nozzle 4 c of cooler 4 is arranged at inlet 4 gi. Therefore, the air flown out from nozzle 4 c enters into cooling chamber 4 g through inlet 4 gi and proceeds through cooling chamber 4 g while contacting nonwoven fabric F being conveyed, and then exits from heating chamber 4 g through outlet 4 go. In this case, air is fed so that the linear velocity of the air is higher than the conveyance velocity of nonwoven fabric F.
Nonwoven fabric F unwound from roll R is conveyed so as to pass firstly through heating chamber 3 g of heater 3. Simultaneously, a heated air is fed from nozzle 3 c of heater 3 into heating chamber 3 g. Consequently, nonwoven fabric F is heated by contacting the heated air, and thereby the bulkiness of nonwoven fabric F is increased. That is, the bulkiness of nonwoven fabric F is restored.
In this case, air proceeds mainly along surfaces Fs of nonwoven fabric F. As a result, the restoration of bulkiness of the nonwoven fabric F is not disturbed by the flow of air. That is, the bulkiness of nonwoven fabric F is restored well.
Furthermore, in this embodiment, in heating chamber 3 g, the linear velocity of the air is higher than the conveyance velocity of nonwoven fabric F. As a result, turbulence is generated in the air flows adjacent to surfaces Fs of nonwoven fabric F. Therefore, various molecules contained in the air collide with surfaces Fs of nonwoven fabric F at random angles. Accordingly, the fibers of nonwoven fabric F are loosen, and thereby promoting the restoration of bulkiness. In addition, due to the turbulence in the air flows, nonwoven fabric F flaps within heating chamber 3 g. As a result, the heated air easily enters into the inside of nonwoven fabric F and nonwoven fabric F can be efficiently heated. Therefore, length L3 f of heating chamber 3 g or housing 3 f (FIG. 4) can be shortened.
Furthermore, housing 3 f does not require an equipment for feeding air or an equipment for sucking out air. Therefore, housing 3 f can be further reduced in size.
Furthermore, in heating chamber 3 g, nonwoven fabric F is conveyed without being supported by rollers, etc. As a result, the restoration of bulkiness of nonwoven fabric F is not disturbed by the rollers, etc.
Nonwoven fabric F conveyed out from heating chamber 3 g is then conveyed so as to pass through cooling chamber 4 g of cooler 4. Simultaneously, a cooled air is fed from nozzle 4 c of cooler 4 into cooling chamber 4 g. Consequently, nonwoven fabric F contacts the cooled air and is cooled.
In this case, air proceeds mainly along surfaces Fs of nonwoven fabric F. As a result, the decrease in bulkiness of nonwoven fabric F by the flow of air is prevented.
Further, the linear velocity of the air within cooling chamber 4 g is higher than the conveyance velocity of nonwoven fabric F. As a result, it is possible to cool the entire nonwoven fabric F located within cooling chamber 4 g. That is, nonwoven fabric F can be efficiently cooled. Therefore, cooling chamber 4 g and housing 4 f can be reduced in size.
Nonwoven fabric conveyed out from cooling chamber 4 g is then conveyed by conveyor 2 to, for example, a system for producing an absorbent product. In the system for producing an absorbent product, nonwoven fabric F is for example used as the top sheet of an absorbent product.
In this embodiment, since nonwoven fabric F comprises heat-fusible conjugate fibers, the temperature of the air flown out from nozzle 3 c of heater 3 is preferably equal to or more than the temperature which is lower than the melting point of the heat-fusible conjugate fibers (low-melting point component) by 50° C. and less than the melting point of the heat-fusible conjugate fibers. If the temperature of air is lower than the melting point minus 50° C., the bulkiness of the nonwoven fabric may not be restored sufficiently. If the temperature of air is equal to or more than the melting point, the fibers will melt.
In view of efficient heating of nonwoven fabric F, heating chamber 3 g is preferably small in cross-sectional area, that is, small in width W3 g and height H3 g. However, during conveyance, nonwoven fabric F meanders in the width direction and flaps in the thickness direction. Therefore, if width W3 g or height H3 g is excessively small, there is a possibility that nonwoven fabric F may collide with housing 3 f. In addition, if the cross-sectional area of heating chamber 3 g, i.e., the flow passage area for air, is excessively small, the pressure loss at heating chamber 3 g is larger. Considering these facts, width W3 g is preferably larger than the width of nonwoven fabric F by 5 to 40 mm, and is more preferably larger than the width of nonwoven fabric F by 10 to 20 mm. Further, height H3 g is preferably 2 to 10 mm, and more preferably 3 to 7 mm.
In the embodiments described above, nozzle 3 c of heater 3 was arranged at inlet 3 gi of heating chamber 3 g. In another embodiment, nozzle 3 c is arranged at outlet 3 go of heating chamber 3 g. In this case, air is fed so as to enter into heating chamber 3 g through outlet 3 go, to proceed through heating chamber 3 g while contacting nonwoven fabric F being conveyed, and then to exit from heating chamber 3 g through inlet 3 gi.
Accordingly, air is fed so as to enter into heating chamber 3 g through one of inlet 3 gi and outlet 3 go, to proceed through heating chamber 3 g while contacting nonwoven fabric F, and then to exit from heating chamber 3 g through the other of inlet 3 gi and outlet 3 go.
However, if nozzle 3 c is arranged at outlet 3 go, the machine direction MD of nonwoven fabric F and the air flow are in opposite directions from each other. Therefore, it is necessary to increase the force in the machine direction MD which acts on nonwoven fabric F for conveyance, that is, the tension. If the tension is increased, there is a possibility that the restoration of bulkiness of nonwoven fabric F may be prevented. A similar problem arises when nonwoven fabric F is allowed to meander in heating chamber 3 g in the machine direction MD and in the direction opposite to the machine direction MD alternately.
In contrast, in an embodiment shown in FIGS. 1 to 3, nozzle 3 c is arranged at inlet 3 gi, and nonwoven fabric F is conveyed through heating chamber 3 g so that the two surfaces Fs of nonwoven fabric F continue to face upper wall 3 fu and bottom wall 3 fb. Therefore, the machine direction MD of nonwoven fabric F and the air flow are in the same direction with each other within heating chamber 3 g. Therefore, the bulkiness restoration can be carried out while maintaining the tension applied to nonwoven fabric F for conveyance at a low level.
Further, in the embodiments described above, nozzle 3 c is arranged above nonwoven fabric F at inlet 3 gi. In another embodiment, nozzle 3 c is arranged below nonwoven fabric F. Furthermore, in another embodiment, nozzles 3 c are arranged both above and below nonwoven fabric F.
FIGS. 6(A) and 6(B) show another embodiment of nozzle 3 c. Referring to FIG. 6(A), nozzle 3 c comprises body 3 ca having, for example, a rectangular shape. Body 3 ca comprises internal space 3 cb, air inlet 3 cc and air outlet 3 cd which are communicated with internal space 3 cb, and air guide plate 3 ce which extends adjacent to air outlet 3 cd. Air inlet 3 cc is connected to feed pipe 3 b.
Nozzle 3 c is integrally fastened to housing 3 f. That is, as shown in FIG. 6(B), air guide plate 3 ce of nozzle 3 c is inserted into internal space 3 s through inlet 3 si of internal space 3 s of housing 3 f, and body 3 ca is fixed to upper wall 3 fu of housing 3 f. As a result, air passage 5 a is formed between air guide plate 3 ce and upper wall 3 fu, and nonwoven fabric passage 5 b is formed between air guide plate 3 ce and bottom wall 3 fb. In this case, for example, height H5 a of air passage 5 a and thickness t3 ce of air guide plate 3 ce are respectively 1 mm, and height H5 b of nonwoven fabric passage 5 b is 3 mm. The width of nozzle 3 c is substantially identical to the width of internal space 3 s.
Air passage 5 a is communicated with air outlet 3 cd of nozzle 3 c and is also communicated with internal space 3 s of housing 3 f. In this case, heating chamber 3 g is defined downstream of the outlet of air passage 5 a. Therefore, the heated air which is fed from feed pipe 3 b to body 3 ca flows through air outlet 3 cd into air passage 5 a, flows through air passage 5 a, and then flows through inlet 3 gi into heating chamber 3 g.
Nonwoven fabric passage 5 b is on the one hand communicated with the outside of housing 3 f, while on the other hand is communicated with heating chamber 3 g. Nonwoven fabric F enters into nonwoven fabric passage 5 b from outside of housing 3 f, proceeds through nonwoven fabric passage 5 b, and then enters into heating chamber 3 g through inlet 3 gi.
In this case, the flow passage area at outlet 3 go of heating chamber 3 g is larger than the flow passage area of nonwoven fabric passage 5 b, and accordingly the flow passage resistance at outlet 3 go is smaller than that of nonwoven fabric passage 5 b. Therefore, the air which flown into heating chamber 3 g through inlet 3 gi is prevented from flowing backward through nonwoven fabric passage 5 b, and thereby can flow steadily toward the outlet 3 go through heating chamber 3 g.
In the embodiment shown in FIG. 7, bottom wall 3 fb of housing 3 f is extended to below body 3 ca of nozzle 3 c, as compared with the embodiment which is shown in FIG. 6. As a result, nonwoven fabric passage 5 b is also extended to below body 3 ca of nozzle 3 c.
The arrangement of nozzle 4 c of cooler 4 is similar to the arrangement of nozzle 3 c of heater 3.
Furthermore, in the embodiments described above, cooler 4 is disposed downstream of heater 3. In another embodiment, cooler 4 is omitted. That is, nonwoven fabric F unloaded from heater 3 is conveyed to the production system without being cooled by cooler 4.
In still another embodiment, a heater for heating housing 3 f is disposed. The temperature of the inside surface of housing 3 f defining heating chamber 3 g is maintained by this heater at, for example, substantially the same temperature as the temperature of the air flown out from nozzle 3 c. In such an embodiment, restoration of bulkiness of the nonwoven fabric F can be promoted. A silicone rubber heater manufactured by Threehigh Co., Ltd., can be used as the heater for housing 3 f. In still another embodiment, a heater for heating nozzle 3 c is disposed.
In still another embodiment, a heat insulating material for covering housing 3 f is disposed. The temperature decrease inside housing 3 f or heating chamber 3 g is suppressed by the heat insulating material. In still another embodiment, a heat insulating material for covering nozzle 3 c is disposed.
Various embodiments described above may be combined with each other.

EXAMPLES

The present invention will now be explained in more detail on the basis of examples and comparative examples, and the present invention is not limited by the examples and comparative examples.
The measurement methods of the properties evaluated in examples and comparative examples are as follows.

[Basis Weight]

The basis weight was measured according to JIS L 1906, 5.2.

[Bulkiness]

The bulkiness was measured using a thickness gauge (THICKNESS GAUGE UF-60 manufactured by Daiei Kagaku Seiki Mfg. Co., Ltd.) while applying a load of 3.0 gf/cm²to a nonwoven fabric. Ten different points of the nonwoven fabric were measured for bulkiness (thickness), and an average value of the ten measurement values was determined as the bulkiness (thickness) of the nonwoven fabric.
[Compression Properties]
The compression properties were evaluated using an automated compression tester KES-FB3 manufactured by Kato Tech Corp.
The measurement conditions were as follows.

- SENS: 2
- Speed: 0.02 mm/sec.
- Stroke: 5 mm/10 V
- Compression area: 2 cm²
- Capture interval: 0.1 sec.
- Upper load limit: 50 g/cm²
- Repetition number: 1

The compression properties were evaluated based on the compressional energy per 1 cm²of nonwoven fabric, WC (N·m/m²), and the compressional resilience RC (%). Measurements were carried out total three times, and the average values of WC and RC are calculated. A higher WC value means that it is more easily to be compressed, and an RC value closer to 100% means higher recovery properties.
[Liquid Permeability]
The liquid permeability was evaluated using a LISTER strike-through tester manufactured by LENZING AG. The evaluation procedure is as follows.
(1) A sample cut out to a size of 100×100 mm is placed on 5 sheets of a filter paper (ADVANTEC FILTER PAPER GRADE 2) cut out to a size of 100×100 mm, and an electrical liquid permeation plate was placed thereon.
(2) The filter paper, sample and electrical liquid permeation plate were set on the strike-through tester.
(3) A 5 mL of physiological saline was poured into the body of the strike-through tester.
(4) The physiological saline (at room temperature) was allowed to drop from the body of the strike-through tester through an opening of the electrical liquid permeation plate.
(5) The electrification time of the electrical liquid permeation plate was recorded.
(6) The measurement was carried out three times, and an average value of the liquid permeation time is calculated out.
The liquid permeation time was 69.13 seconds when no sample was set, i.e., with only 5 sheets of the filter paper.

Examples 1 to 2 and Comparative Examples 1 to 3

(1) Bulkiness Restoration Treatment

A nonwoven fabric in the form of roll was provided. This nonwoven fabric is an air-through nonwoven fabric having a texture on the air-through treated surface (the surface to which hot air has been applied). The properties of the nonwoven fabric are shown in Table 1. In Table 1, WF, tm, and t0 respectively represent the width of the nonwoven fabric, the thickness of the nonwoven fabric before it is wound around roll R, and the thickness before it is conveyed into the bulkiness restoration system. The thickness of the nonwoven fabric was measured using a thickness gauge FS-60 DS manufacture by Daiei Kagaku Seiki Manufacturing Co., Ltd. The surface area of the pressing plates was 20 cm²(circle), and the measurement load was 0.3 kPa (3 gf/cm²).

	TABLE 1

	Units

Web forming method	—	Card method
Fiber bonding method	—	Air through method (heat
		fusing)
Fiber structure	—	Core-sheath structure
Material of core	—	Polyethylene terephthalate
Material of sheath	—	Polyethylene
Multilayer structure	—	Double layer structure
of fiber

Top	Fiber length	mm	38
layer	Denier	dtex	1.3
	Basis weight	g/m²	7
Bottom	Fiber length	mm	45
layer	Denier	dtex	2.2
	Basis weight	g/m²	17

Total basis weight	g/m²	23.18
WF	m	0.16
Tm	mm	34

The bulkiness restoration system according to the embodiment shown in FIGS. 3 to 5 was used to carry out a bulkiness restoration treatment for the nonwoven fabric. Y747-304SS manufactured by Spraying Systems was used as nozzle 3 c. PFD-802-40 manufactured by CKD was used as flowmeter 3 ba. AR30-03 manufactured by SMC Corporation was used as regulator 3 d. Microcable Air Heater (Model Type: MCA-3P-5000, 200V, 5 kW) manufactured by Sakaguchi E. H. Voc Corporation was used as electric heater 3 e.
The treatment conditions in Examples 1 and 2 are shown in Table 2. In Table 2, THAi represents the temperature of the air at the inlet of the heating chamber, qHA represents the air flow (0° C.) discharged from the compressor, SHA (=W3 g·H3 g) represents the air flow passage area in the heating chamber, VHA (=qHA/SHA) represents the linear velocity of air in the heating chamber, VF represents the conveyance velocity of the nonwoven fabric, and τH (=L3 g/VF) represents the heating time of the nonwoven fabric, that is, the time during which the nonwoven fabric is retained in the heating chamber.

TABLE 2

Units	Example 1	Example 2

THAi	° C.	85	116
qHA	m³/min. (0° C.)	7.13	4.75
L3g	m	6.70	3.35
W3g	m	0.20	0.20
H3g	m	0.005	0.005
SHA	m²	0.001	0.001
VHA	m/min.	1783	2377
VF	m/min.	400	200
τH	sec.	1.005	1.005

Bulkiness Restoration Treatment in Comparative Examples 1 to 3

The same nonwoven fabric as that of Examples 1 and 2 was provided. The bulkiness restoration system shown in FIG. 8 was used to carry out a bulkiness restoration treatment for the nonwoven fabric. Referring to FIG. 8, the bulkiness restoration system for Comparative Examples 1 to 3 was comprised of air permeable belt 22 driven by a pair of rollers 21, 21, and the nonwoven fabric FF unwound from a roll was conveyed on belt 22 in the machine direction MD. The bulkiness restoration system was further comprised of hot air feeder 31 for feeding hot air, suction device 32 for sucking the air from hot air feeder 31, cold air feeder 41 for feeding a cold air, and suction device 42 for sucking the air from cold air feeder 41. Hot air feeder 31 was comprised of a fan. Hot air feeder 31 and suction device 32 were arranged facing with each other across space S3, and cold air feeder 41 and suction device 42 were arranged facing with each other across space S4. Belt 22 passed through these spaces S3 and S4, and therefore nonwoven fabric FF was conveyed through spaces S3 and S4. At the same time, hot air was fed from hot air feeder 31 perpendicular to a surface of the nonwoven fabric FF. The hot air passed through nonwoven fabric FF, and then was sucked by suction device 32. In the same manner, a cold air was fed from cold air feeder 41 perpendicular to a surface of nonwoven fabric FF. The cold air passed through nonwoven fabric FF, and then was sucked by suction device 42.
The treatment conditions in Comparative Examples 1 to 3 are shown in Table 3. In Table 3, THAi′ represents the temperature of the air flown out from hot air feeder 31, qHA′ represents the air flow (80° C.) discharged from hot air feeder 31, Ps′ represents the static pressure (80° C.) at hot air feeder 31, L3 g′ and W3 g′ represent the machine direction length and width of the parts where air flow is generated, in hot air feeder 31 and suction device 32, SHA′ (=L3 g′·W3 g′) represents the air flow passage area in space S3, VHA′ (=qHA′/SHA′) represents the linear velocity of air in space S3, SF′ (=L3 g′·WF) represents the surface area of the nonwoven fabric part located within space S3, that is, the nonwoven fabric part through which air passes, VF′ represents the conveyance velocity of the nonwoven fabric, and τH′ represents the heating time, that is, the time during which the nonwoven fabric is retained in space S3.

TABLE 3

	Comparative	Comparative	Comparative
Units	Example 1	Example 2	Example 3

THAi′	° C.	80	100	120
qHA′	m³/min.	20.4	20.4	20.4
L3g′	m	3.4	3.4	3.4
W3g′	m	0.2	0.2	0.2
SHA′	m²	0.68	0.68	0.68
VHA′	m/min.	30	30	30
SF′	m²	0.544	0.544	0.544
VF′	m/min.	40	40	40

(3) The Properties of Bulky Nonwoven Fabrics that have been Subjected to Bulkiness Restoration Treatment

The properties of the bulky nonwoven fabrics that have been subjected to the bulkiness restoration treatment under the conditions of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 4. T0 and Tm represent the thicknesses of a nonwoven fabric under a constant pressure (0.5 gf/cm²for T0, and 50 gf/cm²for Tm) during the compression test. The higher the T0 value, the better the fluffy feeling. In addition, the higher the Tm value, the better the thickness retention during compression. For example, when the nonwoven fabric is used as a top sheet of an absorbent article (for example, diaper), the nonwoven fabric is hard to crush even if a pressure (for example, a pressure generated when the wearer sit down, etc.) is applied to the absorbent article.

TABLE 4

Before
bulkiness
restoration
(before		Comparative
conveyance to	Examples	Examples

	system)	1	2	1	2	3

Basis weight	23.18	23.77	24.03	24.34	24.28	24.53
(g/m²)
Bulkiness	0.45	0.60	1.15	0.59	1.11	1.26
(mm)
Specific	19.41	25.24	47.86	24.23	45.72	52.18
volume
(cm³/g)
WC (N · m/m²)	0.37	0.69	1.56	0.65	1.41	1.77
RC (%)	60.49	62.28	55.00	59.41	52.33	48.16
T0 (mm)	0.61	0.89	1.57	0.85	1.38	1.57
Tm (mm)	0.18	0.19	0.37	0.18	0.27	0.38
Permeation	21.41	12.30	2.38	13.69	2.35	1.52
time (sec.)

(4) Electron Microscope Observation on Heat-Fused Parts

The heat-fused parts of the heat-fusible conjugate fibers in the nonwoven fabrics before bulkiness restoration (before conveyance to the bulkiness restoration system) and in the bulky nonwoven fabrics obtained by bulkiness restoration treatment under the conditions of Examples 1 and 2 and Comparative Examples 1 to 3 were observed by Real Surface View Microscope VE-7800 manufactured by KEYENCE Corporation. At this time, the accelerating voltage was set to 2 kv, the magnification was set to 30 to 1500 times, and the stage height was set to 10 mm. Each bulky nonwoven fabric was cut out into a predetermined size with a sharp razor, and was fixed to an observation stage with a double-sided tape.
First, the textured surface of each nonwoven fabric was observed under a magnification of 300 times, about 5 heat-fused parts could be observed for the nonwoven fabric before bulkiness restoration, and about 10 heat-fused parts could be observed for the bulky nonwoven fabrics after bulkiness restoration treatment, and therefore each heat-fused part was magnified by 1500 times to observe the form of the heat-fused parts.
The electron microscope photographs of the heat-fused parts under a magnification of 1500 times are shown in FIGS. 9 to 14.
FIGS. 9( a) to (c) are electron microscope photographs of a nonwoven fabric before bulkiness restoration (before conveyance to the bulkiness restoration system), FIGS. 10( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Example 1, FIGS. 11( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Example 2, FIGS. 12( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Comparative Example 1, FIGS. 13( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Comparative Example 2, and FIGS. 14( a) to (c) are electron microscope photographs of a nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Comparative Example 13.
As shown in FIG. 9, in the nonwoven fabric before bulkiness restoration, heat-fusible conjugate fibers are biting into each other at the heat-fused parts, and the distance between the heat-fusible conjugate fibers F3 is smaller than the sum of the fiber radii of each heat-fusible conjugate fiber. A sample for observing a cross-section cut to a direction (CD direction) perpendicular to the conveyance direction (MD direction) during the manufacture of a nonwoven fabric was prepared, and was observed for the heat-fused parts in the vicinity of the texture surface, the middle part of the texture surface and a flat surface, and in the vicinity of a flat surface to find out that heat-fusible conjugate fibers are biting into each other at almost every parts.
As shown in FIGS. 12 to 14, in the nonwoven fabrics that have been subjected to the bulkiness restoration treatment under the conditions of Comparative Examples 1 to 3, the heat-fusible conjugate fibers are biting into each other as in the nonwoven fabric before bulkiness restoration. In addition, a tendency of increasing in the surface area of the heat-fused parts in the surface direction of the heat-fusible conjugate fibers was observed with the increase in temperature of the hot air (80° C. in Comparative Example 1, 100° C. in Comparative Example 2, and 120° C. in Comparative Example 3).
As shown in FIGS. 10 and 11, heat-fused bulge parts as shown in FIG. 1 were observed in the nonwoven fabrics that have been subjected to bulkiness restoration treatment under the conditions of Examples 1 and 2. The heat-fusible conjugate fibers are slightly spaced away from each other at the heat-fused bulge parts, and the distance between the heat-fusible conjugate fibers is larger than the sum of the fiber radii of each heat-fusible conjugate fiber. In addition, a part where cracks have been generated was observed. Moreover, the constriction of the heat-fused parts became remarkable with the increase in temperature during the bulkiness restoration treatment.
It is considered that the difference in for of heat-fused parts as shown in FIGS. 9 to 14 is due to the presence or absence of the bulkiness restoration treatment and the type of the bulkiness restoration treatment.
That is, in the air-through method used in Comparative Examples 1 to 3, heat is less likely to be transferred to the movable conveyor on which a nonwoven fabric before bulkiness restoration is disposed, the hot air is required to have a high temperature to achieve a sufficient bulkiness restoration. In addition, although the velocity of the hot air may be relatively low, when hot air passes through the conveyor surface on which the nonwoven fabric is disposed, a force which compresses the nonwoven fabric before bulkiness restoration is applied in the direction perpendicular to the conveyor surface. Therefore, in Comparative Examples 1 to 3, it is considered that the surfaces of the heat-fusible conjugate fibers easily melt by a high-temperature hot air, and the molten, heat-fusible conjugate fibers are compressed with each other by the action of the high-temperature hot air, and thereby the heat-fusible conjugate fibers are biting with each other.
In contrast, in Examples 1 and 2, hot air flows in parallel to the nonwoven fabric before bulkiness restoration, and the velocity of the hot air is higher than the velocity of the nonwoven fabric, and therefore a turbulent flow is generated within the bulkiness restoration system, thereby promoting heat transfer. In addition, since a force is not applied to the constituent fibers of nonwoven fabric F in the same direction but is applied to the constituent fibers along the flow of air, the heat-fused bulge parts slightly extend and change into heat-fused constriction parts.

(5) Observation

As shown in Table 4, the bulky nonwoven fabrics obtained by the bulkiness restoration treatment under the conditions of Examples 1 and 2 have a basis weight which is substantially the same as that of the nonwoven fabric before bulkiness restoration, but have a bulkiness, a specific volume, a WC value and a RC value larger than those of the nonwoven fabric before bulkiness restoration. At the same basis weight, the greater the bulkiness, the higher the void volume (specific volume), and the higher the WC value, the greater the compression deformation properties, and an RC value closer to 100% indicates higher compression recovery properties. Therefore, the bulky nonwoven fabrics obtained by bulkiness restoration treatment under the conditions of Examples 1 and 2 have a high void volume (specific volume) and have excellent compression deformation properties and compression recovery properties, as compared with the nonwoven fabric before bulkiness restoration.
In addition, the bulky nonwoven fabrics obtained by the bulkiness restoration treatment under the conditions of Examples 1 and 2 have a basis weight which is substantially the same as that of the nonwoven fabrics obtained under the conditions of Comparative Examples 1 to 3, but have a bulkiness, a specific volume, a WC value and a RC value that are similar to or greater than those of the nonwoven fabrics obtained under the conditions of Comparative Examples 1 to 3. In particular, comparing Example 1 and Comparative Example 1 in which the hot air temperature is similar to each other (85° C. for Example 1, and 80° C. for Comparative Example 1), Example 1 exhibited a WC value representing compression deformation properties and a RC value representing compression recovery properties higher than those of Comparative Example 1. In the nonwoven fabric subjected to bulkiness restoration treatment under conditions of Example 1, heat-fused bulge parts were changed into heat-fused constriction parts, and the joining strength between heat-fusible conjugate fibers through a heat-fused part has been decreased due to the change in shape of the heat-fused parts from a bulge from to a constriction form.
Therefore, it is considered that the nonwoven fabric subjected to the bulkiness restoration under the conditions of Example 1 has a degree of freedom to compression deformation higher than that of the nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Comparative example 1, and thereby making it easier for the fibers to move. Accordingly, it is considered that nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Example 1 has a WC value representing compression deformation properties higher than that of the nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Comparative Example 1.
In addition, it is considered that, in the nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Example 1, heat easily transfers to the heat-fusible conjugate fibers during bulkiness restoration treatment, and therefore the resins which constitute the heat-fusible conjugate fibers are oriented by the heat, and thereby the crystallinity is improved. Therefore, it is considered that, in the nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Example 1, the initial strength of fibers is improved, and accordingly the fibers are less likely to deform by initial deformation, and thereby the shape retention properties are improved, as compared to Comparative Example 1. Therefore, it is considered that the nonwoven fabric subjected to the bulkiness restoration treatment under the conditions of Example 1 has a RC value representing compression restoration properties higher than that of the nonwoven fabric subjected to bulkiness restoration treatment under the conditions of Comparative Example 1.

EXPLANATION OF SYMBOLS

F1 to F4 Heat-fusible conjugate fibers
R1, R2 Intersection regions of heat-fusible conjugate fibers
B1 Heat-fused constriction part
B2 Heat-fused bulge part
P1, P2 Center of the intersection region of heat-fused conjugate fibers
Z1, Z2 Overlapping direction of heat-fusible conjugate fibers
A1, A2 Center line (a virtual line extending in overlapping direction of the heat-fusible conjugate fibers through the center of intersection region of the heat-fusible conjugate fibers)
r1, r2 Fiber radii of heat-fusible conjugate fibers
r3 Distance between heat-fusible conjugate fibers

Claims

1. A nonwoven fabric comprising heat-fusible conjugate fibers intersecting and overlapping with each other and heat-fused constriction parts at the intersection regions of the heat-fusible conjugate fibers,

wherein when a virtual line extending in the overlapping direction of the heat-fusible conjugate fibers through the center of an intersection region is defined as a center line, the heat-fused constriction parts have a surface which is recessed toward the center line,

wherein the distance between the heat-fusible conjugate fibers that are heat-fused through a heat-fused constriction part is larger than the sum of the fiber radius of each heat-fusible conjugate fiber,

wherein the nonwoven fabric has a thickness of 0.5 to 3.0 mm under a load of 3.0 gf/cm²and a specific volume of 6 to 300 cm³/g.

2. The nonwoven fabric according to claim 1, wherein the nonwoven fabric has a plurality of heat-fused parts at the intersection regions of the heat-fusible conjugate fibers intersecting and overlapping with each other, and

wherein the proportion of the number of the heat-fused constriction parts to the total number of the heat-fused parts included in a predetermined region of the nonwoven fabric is 1/10 to 9/10.

3. The nonwoven fabric according to claim 1, wherein the heat-fusible conjugate fibers have a fiber diameter of 10 to 30 μm.

4. The nonwoven fabric according to claim 1, wherein the heat-fusible conjugate fibers comprise a first component and a second component having a melting point lower than that of the first component, and wherein the weight ratio of the second component to the first component is 4/6 to 8/2.

5. The nonwoven fabric according to claim 1, wherein the nonwoven fabric is obtained by a bulkiness restoration treatment of a nonwoven fabric before bulkiness restoration, comprising heat-fused, heat-fusible conjugate fibers, wherein the bulkiness restoration treatment comprises:

a step of providing a heating chamber having an inlet and an outlet, and

a step of, while conveying the nonwoven fabric before bulkiness restoration so as to enter into the heating chamber through the inlet, to proceed through the heating chamber, and then to exit from the heating chamber through the outlet, feeding a heated fluid at a velocity higher than the conveyance velocity of the nonwoven fabric before bulkiness restoration so as to enter into the heating chamber through one of the inlet and outlet, to proceed through the heating chamber while contacting the nonwoven fabric, and then to exit from the heating chamber through the other of the inlet and outlet.

6. The nonwoven fabric according to claim 5, wherein the nonwoven fabric before bulkiness restoration is an air-through nonwoven fabric obtained by air-through treatment of a web comprising heat-fusible conjugate fibers to heat-fuse the heat-fusible conjugate fibers.

7. The nonwoven fabric according to claim 5, wherein the heated fluid enters into the heating chamber through the inlet and exits from the heating chamber through the outlet.

8. The nonwoven fabric according to claim 5, wherein the nonwoven fabric before bulkiness restoration is conveyed through the heating chamber without being supported.

9. The nonwoven fabric according to claim 5, wherein the heating chamber is defined by two walls that extend from the inlet to the outlet and are separated from each other, and wherein the nonwoven fabric before bulkiness restoration is conveyed within the heating chamber so that both surfaces of the nonwoven fabric before bulkiness restoration respectively continue to face the walls.