JP3308171B2 - Non-woven - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-woven fabric having good texture, good productivity, and a concave material for a mechanical fastener, and more particularly, to a non-woven fabric for a deployable disposable diaper. The present invention relates to a nonwoven fabric useful as a landing tape for a fastening tape system using a mechanical fastener.

[0002]

2. Description of the Related Art In recent years,
Various absorbent articles such as disposable diapers having a mechanical fastener as a fastening tape have been proposed and used. The mechanical fastener is intended to releasably adhere by bringing a so-called convex member and a concave material into contact with each other.
Normally, as shown in FIG. 6, a concave material sheet in which a laminate of a fiber knitted material 101 and a film sheet 102 is partially bonded to form a loop 103 for hooking the engaging portion 10 of the convex member is used. Have been. However, since such a sheet for a concave portion is a knitted material, it has a problem in that it has poor texture and shape retention, and is likely to cause neck-in in a processing step. Further, Japanese Patent Application Laid-Open No. 7-313213 proposes using a sheet using a needle punch for a concave material, but has a problem that the sheet is inferior in productivity and more expensive. .

[0003] In order to solve the above-mentioned problems, it has been proposed to use a nonwoven fabric having a good texture as the concave material. However, in the conventional nonwoven fabric, as shown in FIG. May be disengaged due to the force applied by the engaging portion 10 and may not exhibit a sufficient peeling strength as a concave member. And there is a problem that reuse becomes difficult. It has also been proposed to increase the fiber density to increase the peeling strength. In this case, however, as shown in FIG. There has been a problem that it is difficult to be caught and, as a result, the peeling strength decreases.

Further, Japanese Unexamined Patent Publication No. 6-507799 proposes a sheet for a concave material of a mechanical fastener using a nonwoven fabric, and a nonwoven fabric is also used in Japanese Unexamined Patent Publication No. 6-507800. A sheet for a concave material of a mechanical fastener has been proposed. However, these proposed concave member sheets are partially adhered to the backing material and are weak in strength, and have a problem of fluffing when the convex member is peeled off, and also maintain a bulk in which the convex member enters. It was also difficult to do.

Accordingly, an object of the present invention is to provide a good texture,
The productivity is good, the peel strength is excellent when the convex member of the mechanical fastener is adhered, and the fluff is small even when the convex member is peeled off after bonding, and the convex member is adhered again. It is an object of the present invention to provide a nonwoven fabric for a concave material of a mechanical fastener.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have used a heat-fusible conjugate fiber having a core / sheath structure composed of a specific core component and a sheath component. It has been found that a nonwoven fabric comprising the above can achieve the above object.

The present invention has been made based on the above findings, and has a core / sheath structure having a core / sheath structure in which the core component and the sheath component are the same kind of resin component and the sheath component has a lower melting point. Consisting of constituent fibers including conjugate fibers, the heat-fusible conjugate fibers ,
Its fused point strength is at least in and its content is constituent fibers in more than 50 wt% of 3 gf, there is provided a nonwoven fabric which is a recess member of a mechanical fastener.

Further, the present invention provides the above nonwoven fabric, wherein the heat-fusible conjugate fibers are fused at intersections between the heat-fusible conjugate fibers .

[0009] Further, the present invention provides the above nonwoven fabric, which is obtained by heat-treating a web comprising the above constituent fibers,
An object of the present invention is to provide the above nonwoven fabric, wherein the area shrinkage of the web by the heat treatment is less than 10% .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the nonwoven fabric of the present invention will be described in more detail. The nonwoven fabric of the present invention is characterized by comprising a constituent fiber containing a specific heat-fusible conjugate fiber at a specific content.

The specific heat-fusible conjugate fiber used in the present invention has a core / sheath structure in which the core component and the sheath component are the same type of resin component and the sheath component has a lower melting point. It is a fusible conjugate fiber. Here, the above-mentioned “same type of resin component” means that the sheath component and the core component are similar in the structure of the resin component constituting each (the main structures are the same),
It means that it has good compatibility. As the combination of the core component and the sheath component, specifically, polypropylene (PP) is used as the core component, and the low melting point P is used as the sheath component.
Combination using P, polyethylene terephthalate (PET) as core component, low melting point PE as sheath component
Examples include, but are not limited to, combinations using T, and the interface strength between the core component and the sheath component ≧ the fusion point strength> 3.
Combinations der between the core component and the sheath component which satisfies gf
Just do it .

The above-mentioned "same kind of resin component" also includes a resin mixture (so-called blend). Therefore,
The core component may be PET and the sheath component may be a resin mixture mainly composed of PET, or the core component may be PP and the sheath component may be a resin mixture mainly composed of PP. The resin mixture mainly composed of PET used at this time includes P
A resin mixture obtained by blending 100 parts by weight of polyethylene (PE) with 100 parts by weight of ET or the like can be given. Further, as the resin mixture containing PP as a main component,
A resin mixture obtained by mixing 2 to 8 parts by weight of PE with 100 parts by weight of P is exemplified. The composition ratio (weight ratio) of the core component and the sheath component in the heat-fusible conjugate fiber.
Is generally preferably from 20 to 80:80 to 20, more preferably from 20 to 40:80 to 60.

The melting point of the sheath component is preferably 10 to 120 ° C. lower than the melting point of the core component. Specifically, the melting point of the core component is 125 to 260 ° C., and the melting point of the sheath component is , 90 to 150 ° C. As a specific example of the heat-fusible conjugate fiber, the core component has a melting point of 150 to 17.
0 ° C. polypropylene with a sheath component having a melting point of 130 to 1
PP / PP core / sheath fiber which is a low-melting polypropylene having a melting point of 50 ° C. (but lower than the melting point of the core component); a core component of polyethylene having a melting point of 120 to 140 ° C., and a sheath component of polyethylene having a melting point of 90 to 120 ° C. PE / PE core /
PET / PE in which the core component is polyethylene terephthalate having a melting point of 250 to 270 ° C. and the sheath component is low melting point polyethylene terephthalate having a melting point of 70 to 180 ° C.
T core / sheath fiber and the like.

As the low melting point polypropylene used as the sheath component in the PP / PP core-sheath fiber, a known low melting point polypropylene is used without any particular limitation.
In the PP / PP core-sheath fiber, the ratio of the sheath component to the core component is preferably 30 to 70 parts by weight for the sheath component and 70 to 30 parts by weight for the core component. In order to obtain strength, the above-mentioned sheath component is particularly preferably 40 to 60.
Parts by weight, and the core component is preferably 60 to 40 parts by weight. Such PP / PP core-sheath fibers include T
Commercially available products such as PC fiber (for example, trade name “TPC” manufactured by Chisso Corporation) and PR-P (for example, trade name “PR” manufactured by Ube Nitto Kasei Co., Ltd.) can also be used.

As the polyethylene used as the sheath component in the PE / PE core-sheath fiber, generally known polyethylene is used without any particular limitation. In the PE / PE core-sheath fiber, the ratio of the sheath component to the core component is preferably such that the sheath component is 30 to 70 parts by weight and the core component is 70 to 30 parts by weight. In order to obtain strength, it is particularly preferable that the sheath component is 40 to 60 parts by weight and the core component is 60 to 40 parts by weight.

The low-melting polyester used as a sheath component in the PET / PET core-sheath fiber includes:
Any low-melting polyester can be used without particular limitation. In the PET / PET core-sheath fiber, the ratio between the sheath component and the core component is such that the sheath component is 40 to 90%.
The core component is preferably 60 to 10 parts by weight, more preferably the sheath component is 50 to 90 parts by weight, and even more preferably the core component is 50 to 10 parts by weight. As a fiber having a core-sheath structure having such a low-melting polyester as a sheath component, ELK fiber (for example, trade name “EL
K "), TBF fiber (for example, trade name" TBF ") (all manufactured by Teijin Limited), and melty fiber (for example, trade name" Melty 4080 "manufactured by Unitika Ltd.) can be used.

The fineness of the heat-fusible conjugate fiber is 2
~ 12d (denier), preferably 4 ~ 10d
Is more preferable. Further, the length of the heat-fusible conjugate fiber is preferably 3 to 10 cm, and 4 to 8 c.
m is more preferable.

The heat-fusible conjugate fiber has a fusion point strength of 3 gf or more, preferably 5 gf or more.
New The interface strength between the core component and the sheath component is preferably larger than the fusion point strength at the intersection of the heat-fusible conjugate fibers. When the fusion point strength is less than 3 gf, when the convex member of the mechanical fastener is peeled off from the nonwoven fabric of the present invention, breakage of the fusion point of each constituent fiber occurs, which causes fluffing, which is preferable. Absent. The above-mentioned fusion point strength is measured according to the following measuring method.

<Measurement Method of Fusing Point Strength> A pattern paper 41 having a square cut (a portion indicated by a dashed line 13 (a)) in the center as shown in FIG. The fibers 42, 42 ′ are placed so as to be orthogonal to each other and the intersection is located at the center of the above-mentioned square cut, and the fibers 42, 42 ′ are adhered to the pattern 41 with an adhesive.
Next, the pattern 4 to which the fibers 42 and 42 'are attached is attached.
1, hot air at a processing temperature of 143 ° C. and a wind speed of 2.3 m / sec.
At c, heat treatment is performed by spraying for 12 seconds. The heat-treated paper 41 to which the fibers are thermally bonded is cut along the dotted line shown in FIG. 1 (b), and the fibers 42 are cut as shown in FIG. 1 (c).
Square section 4 with the ends of 42 'glued to each other
3, 43 'are obtained. Next, each of the sections 43 and 43 'is pulled in the direction of the arrow shown in FIG. 1C at a speed of 50 mm / min, and the strength of the intersection is measured, and this is defined as the fusion point strength.

The specific content of the heat-fusible conjugate fiber is 50% by weight or more, preferably 70 to 100% by weight, based on the whole constituent fibers. If the content is less than 50 wt%, the strength of the fusion point between the constituent fibers is insufficient, and when the nonwoven fabric of the present invention is used as a concave material of a mechanical fastener, fluffing occurs. That is, all of the constituent fibers constituting the nonwoven fabric of the present invention may be constituted by the heat-fusible conjugate fibers, but the heat-fusible conjugate fibers may be contained in 50% by weight or more of the whole. For example, a fiber mixture obtained by mixing this with other fibers may be used. As the other fibers used at this time, ordinary polyester fiber, ordinary polypropylene fiber, ordinary rayon fiber, ordinary acrylic fiber, ordinary cotton fiber, ordinary nylon fiber,
Composite fiber of ordinary PP / PE (core / sheath) structure, ordinary P
Examples thereof include ET / PE (core / sheath) composite fibers and ordinary polyvinyl alcohol (PVA) fibers.

Next, the nonwoven fabric of the present invention comprising the above constituent fibers will be described. The nonwoven fabric of the present invention is a nonwoven fabric made of the above constituent fibers. In the nonwoven fabric, it is preferable that the heat-fusible conjugate fibers are fused at intersections between the heat-fusible conjugate fibers. Here, the phrase “fused at the intersection between the heat-fusible conjugate fibers” means that the fusion is performed only at the intersection and that the fusion is performed at all of the intersections. But not at least at the intersection (part of the intersection).

The nonwoven fabric of the present invention is obtained by heat-treating a web made of the above constituent fibers, and the area shrinkage of the web by the heat treatment is preferably less than 10% (0% is ideal). Yes, smaller is better). When the area shrinkage rate exceeds 10%, the fiber is set by shrinkage, and the nonwoven fabric is hardened. When the nonwoven fabric of the present invention is used as the concave material of the mechanical fastener, the space where the convex member enters cannot be maintained, In addition, the peeling force is undesirably small.

The area shrinkage can be adjusted as follows. That is, a method of lowering the draw ratio during fiber molding, a method of using a resin having a high rigidity as a resin component of a core component, a method of using a resin having a low melting point as a resin component of a sheath component, and a resin which is unlikely to cause distortion in molecules during heat treatment. Can be adjusted by performing a method of using as a resin component of constituent fibers. Further, it can also be adjusted by adjusting the conditions for processing the nonwoven fabric, such as setting the heat treatment temperature low and increasing the air volume.

The area shrinkage is measured as follows. [Measurement method of area shrinkage rate] A web having a basis weight of 30 g / m ² was prepared (45 cm long × 30 cm wide), and two points were marked at approximately the center of the web at intervals of 20 cm in the vertical and horizontal directions. 120 ° C
Is performed for 1 minute with hot air, and the distance between two marks in the vertical and horizontal directions after the heat treatment (distance between two points) is measured. Then, the obtained measured value is substituted into the following equation (Equation 1) to determine the area shrinkage.

[0025]

(Equation 1)

The tensile strength of the nonwoven fabric of the present invention is MD
1000g in the direction (machine flow direction during manufacture)
Weight / 50 mm or more, and preferably 200 g weight / 50 mm or more in the CD direction (direction perpendicular to the MD direction). Here, the above tensile strength is measured by the following measuring method. Tensile strength: As a measuring device, “Tensilon RTA-” manufactured by Orientec Co., Ltd.
100 ”and 200 × 5 nonwoven fabric as a sample
What was cut to 0 mm was prepared. Then, the sample was subjected to a chuck distance of 75 mm and a pulling speed of 300 m.
The sample was pulled under the condition of m / min, and the stress when the sample was broken was measured, and this was defined as the tensile strength. In addition, measurement is MD
The measurement was performed 10 times in both the direction and the CD direction, and the average value was used as the measured value.

The basis weight of the nonwoven fabric of the present invention is 20 to 50.
g / m ² , and the fiber density is from 0.01 to
It is preferably 0.05 g / cm ³ .

The nonwoven fabric of the present invention can be manufactured as follows. That is, the web can be easily obtained by preparing a web from the constituent fibers according to a conventional method and subjecting the obtained web to ordinary heat treatment.

The nonwoven fabric of the present invention can be used as a landing tape or a back sheet (when used as a back sheet) for a diaper using a convex member of a mechanical fastener as a fastening tape for a fastening tape system in a deployable disposable diaper. Is possible to omit the landing tape). The mechanical fastener convex member is a sheet or the like provided with a large number of convex engaging portions such as a key shape and a mushroom shape, and includes "magic tape" (registered trademark, manufactured by Kuraray Co., Ltd.), " Commercial products such as "Quicklon" (registered trademark, manufactured by YKK) and "Majicross" (registered trademark, manufactured by Kanebo Bell Touch) can be used without particular limitation. The concave member means a sheet or the like which can be engaged with the convex member.

[0030]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, each test in the following Examples was performed as follows, respectively.

(Tack Force) As shown in FIG. 2, the obtained nonwoven fabric 1 has a convex member 20 (30 × 30 mm) (see FIG. 3).
(“CS-200 900PPI” (trade name, manufactured by 3M)) is crimped, and the mount 22 on which the convex member 20 is provided is pulled at 300 mm / min in the vertical direction (arrow direction), and the convex member 20 is separated from the nonwoven fabric 1. Was determined as the tack force. Crimping is performed by placing the convex member 20 on the nonwoven fabric 1 and
The test was performed by applying a static load of 6.7 gf / cm ² for 10 seconds. As shown in FIG. 3, the convex member 20 is fixed on one surface of the mount 22 via a double-sided tape 23, and at a position facing the convex member 20 on the other surface of the mount 22. An acrylic plate 21 is fixed via a double-sided tape 23 to keep the peeling angle at 0 °. In addition, as shown in FIG.
It was used by being fixed thereon with a double-sided tape 2 interposed.

(Peeling Force) The nonwoven fabric 1 is cut into a size of 5 cm × 5 cm, and the nonwoven fabric 1 is placed on an outer nonwoven fabric (back sheet) of Merize pants (trade name, disposable diaper manufactured by Kao Corporation) using a double-sided tape. Pasted. Also, 3cm x 3
cm of a convex member, and the back side of the convex member is 3 cm × 3.
cm, and a base film having the same size as that of the convex member is pasted on the mount, and on one end side, a portion composed of only the mount is formed with a width of 10 mm. Sample 20 'was made. Next, as shown in FIG. 5, the convex member sample 20 'is
Is left on the non-woven fabric 1 except for 10 mm (a portion formed only by the mount), and the convex member sample 20 ′
The convex member sample 20 ′ was pressed against the nonwoven fabric 1 by reciprocating a 1 kg roller once. After that, with the one end 20a, the convex member sample 20 'is moved 30 degrees in the direction of the arrow (the same direction as the longitudinal direction of the convex member sample 20').
It was pulled at 0 mm / min, and the force required for the protruding member sample 20 ′ to be peeled from the nonwoven fabric 1 was measured. The same operation was repeated 10 times, and the average value was defined as the peeling force.
In addition, the data processing of the measurement data is performed by a peeling test mode data processing software [trade name “MP
-100P "(MS-DOS) Ver. 43.1], and the peeling force was evaluated based on the “5 point average load value”. The mount and the base film may be any as long as the convex member can be fixed.

(Fuzziness) The fluffiness was evaluated on a five-point scale by visually observing the surface of the nonwoven fabric 1 after the measurement of the peeling force. 1st grade; no fuzziness 2nd grade; fuzzy small 3rd grade; fuzzy medium 4th grade; fuzzy large 5th grade;

[Example 1] A heat-fusible conjugate fiber 10 having low heat shrinkage and high fusion point strength using PP having a melting point of 162 ° C as a core component and PP having a melting point of 143 ° C as a sheath component.
A web is formed at 0 wt%, and the obtained web is
Heat treatment was performed with hot air at 46 ° C. for 30 seconds to obtain a nonwoven fabric of the present invention. In the heat-fusible conjugate fiber, the weight ratio between the core component and the sheath component was 60:40, the fineness was 4d, and the fiber length was 51 mm. The weight of the obtained nonwoven fabric was 40 g / m ² . With respect to the obtained nonwoven fabric, the area shrinkage and the fusion point strength were measured in accordance with the above-mentioned methods, and further, the tack force, the peeling force and the fluffing were evaluated. The results are shown in [Table 1].

[Example 2] 100% by weight of a heat-fusible conjugate fiber having low heat shrinkage and high fusion point strength, using PET having a melting point of 255 ° C as a core component and PET having a melting point of 137 ° C as a sheath component. A web was formed, and the obtained web was heat-treated with hot air at 146 ° C. for 30 seconds to obtain a nonwoven fabric of the present invention. In the heat-fusible conjugate fiber, the weight ratio between the core component and the sheath component was 30:70, and the fineness was 6d.
And the fiber length was 51 mm. The weight of the obtained nonwoven fabric was 43 g / m ² . About the obtained nonwoven fabric, the area shrinkage rate and the fusion point strength were measured in the same manner as in Example 1, and further, the tack force, the peeling force and the fluffing were evaluated. The results are shown in [Table 1].

[Comparative Example 1] A web was formed from 100% by weight of heat-fusible conjugate fibers using PP having a melting point of 163 ° C as a core component and PE having a melting point of 130 ° C as a sheath component. Was heat-treated with hot air at 140 ° C. for 30 seconds to obtain a nonwoven fabric. In the heat-fusible conjugate fiber, the weight ratio between the core component and the sheath component was 60:40, the fineness was 4d, and the fiber length was 51 mm. The weight of the obtained nonwoven fabric was 39 g / m ² .
About the obtained nonwoven fabric, the area shrinkage rate and the fusion point strength were measured in the same manner as in Example 1, and further, the tack force, the peeling force and the fluffing were evaluated. The results are shown in [Table 1].

[Comparative Example 2] 40% by weight of heat-fusible conjugate fiber using PP having a melting point of 160 ° C as a core component and PP having a melting point of 130 ° C as a sheath component, and P having a melting point of 250 ° C
A web was formed using 60 wt% of ET fiber, and the obtained web was heat-treated with hot air at 146 ° C. for 30 seconds to obtain a nonwoven fabric. In the heat-fusible conjugate fiber, the weight ratio between the core component and the sheath component is 60:40,
The fineness is 6d for PP / PP fiber and 6d for PET fiber.
d, and both fiber lengths were 51 mm. The basis weight of the obtained nonwoven fabric was 42 g / m ² . About the obtained nonwoven fabric, the area shrinkage rate and the fusion point strength were measured in the same manner as in Example 1, and further, the tack force, the peeling force and the fluffing were evaluated. The results are shown in [Table 1].

[Comparative Example 3] A web was formed by using 100 wt% of heat-fusible conjugate fibers using PET having a melting point of 250 ° C as a core component and PE having a melting point of 130 ° C as a sheath component. Was heat-treated with hot air at 146 ° C. for 30 seconds to obtain a nonwoven fabric. In the heat-fusible conjugate fiber, the weight ratio between the core component and the sheath component was 60:40, the fineness was 4d, and the fiber length was 51 mm. The weight of the obtained nonwoven fabric was 43 g / m ² .
About the obtained nonwoven fabric, the area shrinkage rate and the fusion point strength were measured in the same manner as in Example 1, and further, the tack force, the peeling force and the fluffing were evaluated. The results are shown in [Table 1].

[0039]

[Table 1]

As is clear from the results shown in Table 1,
While the nonwoven fabric of the present invention is excellent in tack force, peeling force, and even fluffing, the nonwoven fabric of Comparative Example 1 has a small interface strength between the core component and the sheath component, and has a large peeling force, but has a large fluffing force. There are many. In the nonwoven fabric of Comparative Example 2,
The peeling force is not so high, and further, there is much fuzz. Further, the nonwoven fabric of Comparative Example 3 has a low fusion point strength and a large peeling force, but also has a lot of fluff.

[0041]

The nonwoven fabric of the present invention has a good texture, good productivity, excellent peeling strength when a convex member of a mechanical fastener is bonded, and is peeled after bonding the convex member. The concave material of the mechanical fastener has a small amount of fuzz even when it is used, and the convex member can be adhered again.
And as being useful. The reason why the nonwoven fabric of the present invention exhibits the above-mentioned effects is not clear, but the heat-fusible composite fiber whose core / sheath component is not a component of the same series [for example, polypropylene (PP) / polyethylene (PE), polyethylene] Terephthalate (PET) / Polyethylene (PE)]
In the case of, since the force required for peeling the core / sheath interface (core / sheath peeling force) is smaller than the fusion point strength, peeling of the core / sheath occurs at the time of peeling from the convex member, and as a result, after peeling The fluff of the nonwoven fabric becomes larger, and the peeling force decreases when the peeling is repeated. On the other hand, when the core component and the sheath component are components of the same series, peeling of the core / sheath is unlikely to occur (core / sheath peeling force is large), and the peeling force at the time of peeling from the convex member is lower than the fusion point strength. Dependent. Therefore, if a composite fiber having the same series component as the core / sheath component is used and the fusion point strength is increased, a nonwoven fabric having a small fluff, a large peeling force, and a large peeling force even after repeated peeling is obtained. It is thought that it is possible to obtain.

[Brief description of the drawings]

1 (a) to 1 (c) are schematic diagrams each showing a method for measuring a fusion point strength.

FIG. 2 is a schematic diagram showing a method of measuring a tack force.

FIG. 3 is a schematic view showing a method of attaching a convex member of a mechanical fastener when measuring a tack force.

FIG. 4 is a schematic diagram showing a method of attaching a nonwoven fabric when measuring tack force.

FIG. 5 is a schematic view showing a method for measuring a peeling force.

FIG. 6 is a partially enlarged view of a conventional concave member sheet.

FIG. 7 is a partially enlarged view showing a conventional nonwoven fabric.

FIG. 8 is a partially enlarged view showing a conventional nonwoven fabric.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-258951 (JP, A) JP-A-7-160269 (JP, A) JP-A-7-3534 (JP, A) JP-A-2- 41156 (JP, A) JP-A-2-191735 (JP, A) JP-A-6-33359 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D04H 1/00-18 / 00 A44B 13/00-18/00

Claims (3)

(57) [Claims] 1. A heat-fusible composite fiber having a core / sheath structure, wherein the core component and the sheath component are the same kind of resin component and the sheath component has a lower melting point. Nonwoven fabric characterized in that the adhesive composite fiber has a fusion point strength of 3 gf or more and a content of 50 wt% or more of constituent fibers and is used as a concave material of a mechanical fastener. 2. The nonwoven fabric according to claim 1, wherein the heat-fusible conjugate fibers are fused at intersections between the heat-fusible conjugate fibers. Wherein said nonwoven fabric is one obtained by heat-treating the web consisting of the constituent fibers, to claim 1 or 2 areal shrinkage of the web due to the heat treatment is equal to or less than 10% The described nonwoven fabric.