JP7611786B2 - Nonwoven fabric manufacturing method - Google Patents

Description

The present invention relates to a method for producing nonwoven fabric.

Nonwoven fabrics are used as sheet materials that make up absorbent articles such as disposable diapers.

Patent Document 1 discloses a method for producing a nonwoven fabric in which a fiber assembly containing thermally adhesive fibers is heat-treated with hot air at a temperature equal to or higher than the melting point of the low-melting component at a wind speed of 0.2 to 5 m/sec and a heating time of 0.1 to 300 seconds, and then immediately thereafter cooled with low-temperature gas at a temperature of -30 to 45°C without wind pressure at a wind speed of 0.1 to 1 m/sec and a cooling time of 0.1 second or more.

The applicant has proposed a method of blowing hot air onto a nonwoven fabric on a conveyor belt or a rotating drum as a bulk restoration method for restoring bulk to a sheet of nonwoven fabric or the like (see Patent Document 2).

The applicant also proposed a three-dimensional sheet in which a first fiber layer and a second fiber layer made of nonwoven fabric are laminated, the first fiber and the second fiber contained in the first fiber layer contain a high melting point component and a low melting point component, respectively, and the diameter ratio of the high melting point component and the low melting point component is different (see Patent Document 3).

Japanese Patent Application Publication No. 6-158499 JP 2004-137655 A JP 2017-24411 A

The use of fibers with small fiber diameters in nonwoven fabrics is effective in improving texture and smoothness to the touch. However, when nonwoven fabrics containing such small diameter fibers are manufactured by the air-through method, the fibers have low bending rigidity, so the fiber web is easily crushed by the blowing of hot air, and the texture of the resulting nonwoven fabric is likely to deteriorate. Furthermore, reducing the speed of the hot air makes it difficult for the fibers to fuse together, and the fibers that make up the resulting nonwoven fabric are likely to fluff. The technologies described in Patent Documents 1 to 3 do not consider how to improve both of these points.

Therefore, the present invention relates to a method for producing a nonwoven fabric that has a good texture and little fiber fuzz.

The present invention relates to a method for producing a nonwoven fabric.
The above-mentioned production method preferably includes a step of blowing hot air onto a fiber web containing heat-fusible core-sheath composite fibers by an air-through method.
The fiber web preferably contains the core-sheath composite fiber having a fineness of 0.5 dtex or more and 1.8 dtex or less.
The fiber web preferably contains the core-sheath composite fiber having a core content of 10% by mass or more and 45% by mass or less and a sheath content of 55% by mass or more and 90% by mass or less.
The fiber web preferably contains 50% by mass or more of the core-sheath composite fiber.
It is preferable that the speed of the hot air is 0.3 m/sec or more and 0.6 m/sec or less.

The present invention makes it possible to produce nonwoven fabrics with good texture and little fiber fuzz.

FIG. 1 is a cross-sectional view that illustrates an embodiment of a production apparatus used in the production method of the present invention. FIG. 2 is a perspective view that illustrates an embodiment of a production apparatus used in the production method of the present invention.

The method for producing a nonwoven fabric of the present invention will be described based on a preferred embodiment. This method uses a fiber web containing heat-fusible fibers having a predetermined fineness as a raw material, and includes a step of blowing hot air onto the fiber web using an air-through method. This step is a step of turning the fiber web into a nonwoven fabric by fusing the intersections between the constituent fibers of the fiber web. In other words, the nonwoven fabric obtained by this method is an air-through nonwoven fabric. Details of the heat-fusible fibers contained in the fiber web will be described later.

The raw fiber web is typically obtained by forming the opened raw fiber into a web using a carding machine, and the constituent fibers are not fused together. The fiber web may be used as a single layer, or may be used in a multi-layer structure with multiple sheets stacked together. In this manufacturing method, there is essentially no change in the fiber composition, layer structure, and basis weight of the fiber web due to the blowing of hot air, so the fiber web and the resulting nonwoven fabric have substantially the same fiber composition, layer structure, and basis weight.

The air-through method is a method of blowing hot air such as heated air so that at least a part of the hot air penetrates the thickness direction of the fiber web. Typically, as in the manufacturing apparatus 1 shown in FIG. 1, the fiber web 10 to be blown with hot air A is placed on a porous member 20 such as a net or a plate with many holes. In this state, the fiber web 10 is introduced into a hot air oven (not shown) and hot air is blown from the hot air blowing surface S side to thermally fuse the intersections between the fibers. The hot air blowing surface S includes the upper surface of the fiber web 10 and the surface of the porous member 20 on which the fiber web 10 is arranged. At least a part of the hot air blown on the upper surface of the fiber web 10 penetrates the fiber web 10 and the porous member 20 in the thickness direction Z and flows to the non-blowing surface T side, which is the surface opposite to the hot air blowing surface S. When the hot air is blown onto the fiber web 10, the fiber web 10 is preferably transported together with the porous member 20 in a direction intersecting the direction of blowing the hot air (preferably, a direction perpendicular to the direction of blowing the hot air). In the following description, the transport direction of the fiber web 10 is also referred to as the transport direction MD, and the direction perpendicular to the transport direction within the plane of the fiber web 10 is also referred to as the width direction CD.

From the viewpoint of preventing non-uniformity in the blowing of hot air while making the fiber web 10 less likely to be crushed in the thickness direction Z by external forces, and efficiently obtaining a high-quality nonwoven fabric with good flexibility and texture, it is preferable in this manufacturing method to suck in a part of the hot air A blown onto the fiber web 10 on the side of the blowing surface S of the fiber web 10 of the hot air A, and circulate it along the surface of the fiber web 10 on the blowing surface S side or along its surface direction, so that the entire amount of the blown hot air A does not penetrate the web thickness direction Z of the fiber web 10. Also, from the viewpoint of maintaining the temperature inside the hot air oven and productivity-wise controlling the flow rate and circulation of the hot air, it is more preferable to circulate the hot air sucked on the blowing surface S side along the surface direction of the non-blowing surface T side of the porous member 20, as described later. This reduces the generation of external forces that press the fiber web 10 in the thickness direction Z, which occurs when hot air is blown onto the fiber web, and allows a nonwoven fabric with sufficient flexibility to be obtained, even when small fineness fibers are used. In addition, a sufficient amount of heat can be secured to achieve nonwoven fabric formation, allowing the fibers to be appropriately fused together, resulting in a nonwoven fabric with reduced fluffing of the component fibers and sufficient strength. As a result, a high-quality nonwoven fabric can be obtained.

As an embodiment for sucking in a portion of the hot air A on the blowing surface S side, for example, as shown in Figs. 1 and 2, it is preferable to perform the process of blowing hot air onto the fiber web 10 by providing a suction device 30 that sucks in a portion of the hot air A. The suction device 30 is provided on at least one end side of the fiber web 10 in the width direction CD. From the viewpoint of uniformity of the hot air flow, it is preferably provided on both ends of the fiber web 10 in the width direction CD. The suction device 30 is provided alone or in multiple units in the hot air oven, and preferably multiple units are provided along the conveying direction MD. The suction device 30 is connected to an external power source (not shown).

From the viewpoint of reducing manufacturing costs by reducing equipment costs, it is preferable to use at least one of a suction fan and a blower as the suction device 30. These suction devices 30 are preferably configured so that the sucked hot air flows from the hot air blowing surface S side to the non-blowing surface T side through the suction device 30.

In one embodiment of the manufacturing apparatus 1 shown in FIG. 2, in addition to the suction device 30, a first flow path 31 provided above the suction device 30 and a second flow path 32 provided below the suction device 30 are further provided. The first flow path 31, the suction device 30, and the second flow path 32 are each connected, and the sucked hot air is configured to flow through the first flow path 31, the suction device 30, and the second flow path 32 in that order. By further providing these flow paths 31 and 32, the hot air can be blown uniformly over the entire surface direction of the fiber web 10, while increasing the suction efficiency of the blown hot air A toward the side of the web, making it difficult for the fiber web 10 to be crushed in the thickness direction Z, so that a nonwoven fabric with good texture and little fiber fluff can be obtained with high productivity in a single process.

The first flow path 31 shown in FIG. 2 is located on the hot air blowing surface S side and is provided with a first opening 36 that opens inward in the width direction CD. The first opening 36 has a rectangular cross-sectional shape when viewed in a cross-sectional view along the opening surface. The first opening 36 is arranged so that the longitudinal direction of the cross-sectional shape coincides with the conveying direction MD. From the viewpoint of hot air suction efficiency, it is preferable that the first opening 36 has a portion in which the cross-sectional area decreases stepwise or continuously from the opening end toward the suction device 30 side when viewed in a cross-sectional view along the opening surface. This allows the suction force generated by the suction device 30 to be exerted on the hot air blowing surface S side, specifically, on the outside of the width direction CD side of the fiber web 10 on the blowing surface S side, so that a part of the hot air passes along the surface of the blowing surface S side of the fiber web 10 or along the surface direction of the same, and the nonwoven fabric can be efficiently formed even if the entire amount of hot air does not penetrate the thickness direction Z of the fiber web 10. As a result, the resulting nonwoven fabric is prevented from being excessively compacted, and the texture of the nonwoven fabric is improved. In addition, the fibers constituting the fiber web 10 are reliably fused to each other, so the resulting nonwoven fabric is less likely to become fuzzed.

The second flow path 32 shown in FIG. 2 is provided with a second opening 37 located on the non-blowing surface T side and opening inward in the width direction CD. The second opening 37 has a rectangular cross-sectional shape like the first opening 36, and is arranged so that the longitudinal direction of the shape coincides with the conveying direction MD. When viewed in cross section along the opening surface, the second opening 37 preferably has a portion in which the cross-sectional area decreases stepwise or continuously from the opening end toward the suction device 30 side. This allows the sucked hot air and the hot air that has penetrated the thickness direction Z of the fiber web 10 to merge on the non-blowing surface T side, making it easy to efficiently resupply and circulate these hot air in the hot air oven, thereby enabling efficient use of energy and reducing manufacturing costs. In addition, the sucked hot air can be passed along the non-blowing surface T side surface of the porous member 20 or along the surface direction thereof, so that a sufficient amount of heat can be secured to achieve nonwoven fabric formation.

When a portion of the blown hot air is sucked in, the hot air blown onto the fiber web is sucked in so that the ratio of the wind speed of the hot air passing through the fiber web to the wind speed of the blown hot air is preferably 30% or more, more preferably 35% or more, even more preferably 40% or more, and preferably 70% or less, more preferably 60% or less, even more preferably 50% or less.
By setting the wind speed within this range, a sufficient amount of heat can be secured to achieve nonwoven fabric formation, and the fibers can be appropriately fused to each other to obtain a nonwoven fabric with sufficient strength and reduced fluffing of the constituent fibers. In addition, even when constituent fibers with low rigidity such as small fineness are used, it is possible to reduce crushing of the fiber web caused by blowing hot air and obtain a nonwoven fabric with high flexibility. This is particularly advantageous when a fiber web containing core-sheath composite fibers satisfying the fineness described below is used as a raw material.

The speed of the blown hot air can be appropriately set depending on the constituent components of the fibers, but from the viewpoint of obtaining a high-quality nonwoven fabric while reducing production costs, it is 0.30 m/s or more, preferably 0.35 m/s or more, more preferably 0.40 m/s or more, and even more preferably 0.43 m/s or more. The speed of the blown hot air is 0.60 m/s or less, preferably 0.55 m/s or less, more preferably 0.50 m/s or less, and even more preferably 0.48 m/s or less. The speed of the blown hot air is based on the position on the blowing surface of the fiber web.
The hot air speed is based on the assumption that the hot air is not sucked in and all of the blown hot air passes through the thickness direction of the fiber web. However, even if part of the hot air is sucked in using the above-mentioned suction device 30, for example, the effects of the present invention can be fully achieved as long as the blown air speed is within the above-mentioned range.

The above-mentioned wind speed is lower than the wind speed normally used in the air-through method. By blowing hot air at such a wind speed, even when fibers with a small fineness are used, the amount of heat required for nonwoven fabric formation can be uniformly imparted to the fiber web without impairing the bulk of the fiber web, thereby achieving nonwoven fabric formation, and a high-quality nonwoven fabric with good flexibility and texture can be obtained. This is particularly advantageous when using as a raw material a fiber web containing core-sheath composite fibers that meet the fineness described below.

From the viewpoint of obtaining a high-quality nonwoven fabric while reducing manufacturing costs, the wind speed of the hot air passing through the fiber web in the thickness direction is preferably 0.06 m/sec or more, more preferably 0.12 m/sec or more, even more preferably 0.20 m/sec or more, and preferably 0.49 m/sec or less, more preferably 0.40 m/sec or less, even more preferably 0.36 m/sec or less. The wind speed of the hot air passing through the web in the thickness direction is based on a position on the non-sprayed surface of the fiber web or in the vicinity thereof, and generally, if the wind speed directly below the conveyor belt in the manufacturing device is within the above-mentioned range, the effect of the present invention is sufficiently achieved.

The temperature of the hot air can be set appropriately depending on the components of the fiber. From the viewpoint of efficiently achieving nonwoven fabric formation while maintaining the shape of the fiber without excessively melting the components of the fiber, the temperature of the blown hot air is set to a temperature preferably 5°C or more higher than the minimum melting point (°C), more preferably 10°C or more higher than the melting point of the component with the lowest melting point (hereinafter also referred to as the minimum melting point). The temperature of the hot air is set to a temperature preferably 80°C or less lower than the maximum melting point (°C), more preferably 95°C or less lower than the melting point of the component with the highest melting point (hereinafter also referred to as the maximum melting point). If the components do not have a clear melting point, the softening point is used instead of the melting point.

For example, when a core-sheath composite fiber in which the constituent resin of the core is polyethylene terephthalate (melting point: approximately 250°C) and the constituent resin of the sheath is polyethylene (melting point: approximately 120°C) is used as the heat-fusible fiber, the minimum temperature is the melting point of polyethylene and the maximum temperature is the melting point of polyethylene terephthalate.
Therefore, from the viewpoint of obtaining a high-quality nonwoven fabric by achieving both efficient formation of a plurality of fusion points and maintenance of the fiber shape, when the above-mentioned core-sheath composite fiber is used, the temperature of the hot air blown can be preferably 125° C. or more, more preferably 130° C. or more, and preferably 170° C. or less, more preferably 155° C. or less.

The time for which hot air is blown onto the fiber web can be set appropriately depending on the fiber components and the speed of the hot air, but from the viewpoint of obtaining a high-quality nonwoven fabric while reducing production costs, the time is preferably 1 second or more, more preferably 3 seconds or more, and preferably 60 seconds or less, more preferably 30 seconds or less under the above-mentioned wind speed and temperature conditions. The blowing time can be adjusted appropriately, for example, by changing the conveying speed of the fiber web.

As described above, the fibers constituting the fiber web have thermal adhesive properties, and are preferably core-sheath composite fibers. Examples of fibers having thermal adhesive properties include fibers in which a thermoplastic resin is present on at least a portion of the fiber surface. Examples of the above-mentioned thermoplastic resin include at least one of polyolefins such as polyethylene and polypropylene (PP), polyesters such as polyethylene terephthalate (PET), and polyamides. Core-sheath composite fibers have a core and a sheath that covers the outer surface of the core, and the sheath forms the outer surface of the fiber, and are preferably composed of one or more of the above-mentioned thermoplastic resins.

From the viewpoint of achieving both the formation of an appropriate number of fusion points between fibers and the expression of an appropriate stiffness of the fibers, thereby increasing the bulk of the obtained nonwoven fabric and improving its flexibility and texture, it is preferable to use a heat-fusible sheath-core composite fiber, and it is more preferable that the core-sheath composite fiber is composed of a core containing a thermoplastic resin and a sheath containing a thermoplastic resin having a melting point lower than that of the constituent resin of the core. Examples of such heat-fusible sheath-core composite fibers include those in which the constituent resin of the core is polyethylene terephthalate or polypropylene and the constituent resin of the sheath is polyethylene.
From the viewpoint of forming multiple fusion points between the fibers to easily achieve nonwoven fabric formation, increasing the rigidity of the fibers, preventing crushing of the fiber web in the thickness direction due to the blowing of hot air, and obtaining a nonwoven fabric with an even better texture, it is further preferred that the constituent resin of the core is polyethylene terephthalate and the constituent resin of the sheath is polyethylene.

The fineness of the heat-fusible core-sheath composite fiber is 0.5 dtex or more, preferably 0.7 dtex or more, and more preferably 0.9 dtex or more. The fineness of the heat-fusible core-sheath composite fiber is 1.8 dtex or less, preferably 1.6 dtex or less, and more preferably 1.4 dtex or less. By using fibers with such fineness, a nonwoven fabric with a good texture can be efficiently obtained.

The heat-fusible core-sheath composite fiber to be used has a core content of preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less.
The heat-fusible core-sheath composite fiber to be used has a sheath content of preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 65% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.
As described above, the core-sheath composite fiber used in the present production method preferably has a higher mass ratio of the sheath than that of the core. By using a core-sheath composite fiber in which the mass ratio of the sheath is higher than that of the core, the degree of melting of the sheath can be increased and the fusion area between the fibers can be increased, so that a nonwoven fabric with less fiber fluff while maintaining bulk can be easily obtained even when the hot air speed is reduced.

The proportion of heat-fusible core-sheath composite fibers constituting the fiber web is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass, in terms of the mass ratio of the total constituent fibers, i.e., the web is made up entirely of core-sheath composite fibers.

The fiber web may be composed of only the core-sheath composite fibers described above, or may further contain other fibers of different fiber types in addition to the core-sheath composite fibers. Examples of such other fibers include fibers that contain the thermoplastic resin described above and that are different from the core-sheath composite fibers in at least one of the constituent components, fineness, and physical structure. When other fibers are further contained, it is preferable that the fineness of the other fibers is in the same range as the fineness of the core-sheath composite fibers described above, in order to obtain a nonwoven fabric with a high texture. The content of other fibers in the fiber web is preferably 45% by mass or less, more preferably 30% by mass or less, and even more preferably 0% by mass, i.e., non-containing.

The fiber web may further contain other components that are generally used in the manufacture of nonwoven fabrics, such as pigments such as titanium oxide, additives such as antioxidants, and process agents such as oils required in the manufacture, as long as the effects of the present invention are achieved.

The nonwoven fabric obtained through the above steps may be used as is, or may be incorporated in a subsequent step as a component of a nonwoven fabric product such as an absorbent article, a sanitary product, or a heating device.
When a nonwoven fabric is used as a constituent material of a nonwoven fabric product, the nonwoven fabric produced by the above-mentioned method can be used as one of the constituent materials in any of the processes for producing the nonwoven fabric product, and the desired nonwoven fabric product can be produced by including one or more of the following processes: a process for cutting the nonwoven fabric, or a process for laminating or joining the nonwoven fabric with one or more other constituent materials that make up the nonwoven fabric product (e.g., an absorbent body, a sheet, an elastic member, etc.).

Examples of absorbent articles include, but are not limited to, disposable diapers, incontinence pads, sanitary napkins, panty liners, etc., and broadly include articles used to absorb liquids discharged from the human body.
Hygiene products include face masks and eye masks.
Examples of heating devices include disposable hand warmers and other devices that generate heat.

From the viewpoint of improving the texture of the nonwoven fabric, the thickness of the produced nonwoven fabric is preferably 1 mm or more, more preferably 2 mm or more, and preferably 6 mm or less, more preferably 5 mm or less. The thickness of the nonwoven fabric is measured using a laser displacement meter or the like under a load of 4.9 mN/ ^cm2 . The thickness of the nonwoven fabric can be appropriately adjusted, for example, by changing the hot air blowing conditions or the fiber fineness.

From the viewpoint of improving the texture of the nonwoven fabric, the produced nonwoven fabric has a basis weight of preferably 15 g/m ² or more, more preferably 17 g/m ² or more, and preferably 30 g/m ² or less, more preferably 27 g/m ² or less. The basis weight of the nonwoven fabric can be appropriately adjusted, for example, by changing the basis weight of the fiber web that is the raw material.

The present invention has been described above based on its preferred embodiment, but the present invention is not limited to the above embodiment and can be modified as appropriate. In addition, the above-mentioned configurations may be combined as appropriate.

The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. In the following table, columns marked with "-" indicate non-containance.

Example 1
As the raw fiber, a heat-fusible thermoplastic fiber consisting of a concentric core-sheath composite fiber (core/sheath mass ratio: 30% by mass/70% by mass) was used, in which the core resin was PET (melting point: 256°C) and the sheath resin was PE (melting point: 131°C). The minimum melting point of this raw fiber was 131°C. Using this raw fiber, a fiber web was produced in a conventional manner using a known carding machine so that the basis weight was 12.5 g/ ^m2 . A laminate (total basis weight: 25 g/ ^m2 ) was produced by stacking two sheets of the fiber web so that they were parallel to the machine direction (MD direction) during the production of this fiber web. This laminate was placed on a resin mesh belt and transported in the MD direction, and a process of blowing hot air by an air-through method was performed to produce the desired nonwoven fabric (basis weight: ²⁵ g/m2).

In this embodiment, a suction device and flow path having the configuration shown in FIG. 2 were provided, and a portion of the hot air was sucked in so that the ratio of the speed of the hot air penetrating the web thickness direction to the hot air blown was 50%. The conditions in the embodiment were as shown in Table 1 below. The hot air temperatures shown in Table 1 below were measured based on the central positions in both the MD and CD directions of the fiber web to be blown. The hot air speeds were measured in the web thickness direction on the blown surface side, with the position directly above the web as the reference, and on the non-blowed surface side, with the position directly below the mesh belt as the reference, with the hot air penetrating the web thickness direction.

Example 2
A nonwoven fabric (basis weight: 25 g/m ² ) was produced in the same manner as in Example 1, except that hot air was not suctioned.

Example 3
In addition to the heat-fusible thermoplastic fibers having a core-sheath structure (hereinafter also referred to as the first thermoplastic fibers) used in Example 1, a second heat-fusible thermoplastic fiber was further used as another fiber, which was a concentric core-sheath composite fiber (core/sheath mass ratio: 50% by mass/50% by mass) in which the resin of the core was PET and the resin of the sheath was PE.
A fiber web (basis weight: 12.5 g/ ^m2 ) was formed by blending 70% by mass of the first thermoplastic fiber and 30% by mass of the second thermoplastic fiber. Using this fiber web, a nonwoven fabric (basis weight: 25 g/ ^m2 ) was produced in the same manner as in Example 1. In this example, similar to Example 1, a suction device and a flow path having the configuration shown in Figure 2 were provided, and a part of the hot air was sucked in so that the ratio of the speed of the hot air penetrating the web in the thickness direction to the speed of the blown hot air was 50%.

Comparative Example 1
A nonwoven fabric (basis weight: 25 g/m2) was produced in the same manner as in Example 1, except that heat-fusible thermoplastic fibers consisting of concentric core-sheath composite fibers (core/sheath mass ratio: 50% by mass/50% by ^mass ) with a core resin of PET and a sheath resin of PE were used instead of the raw fiber in Example 1. In this comparative example, as in Example 1, a suction device and flow path having the configuration shown in Figure 2 were provided, and a portion of the hot air was sucked in so that the ratio of the speed of the hot air penetrating in the thickness direction of the web to the speed of the blown hot air was 50%.

Comparative Example 2
A nonwoven fabric (basis weight: 25 g/m ² ) was produced in the same manner as in Comparative Example 1, except that hot air was not suctioned.

Comparative Example 3
A nonwoven fabric (basis weight: 25 g/m2) was produced in the same manner as in Example 3, except that the ^ratio of fibers contained in the fiber web was adjusted to a blend of 30 mass% of the first thermoplastic fibers and 70 mass% of the second thermoplastic fibers among the production conditions of Example 3. In this comparative example, as in Example 3, a suction device and a flow path having the configuration shown in Figure 2 were provided, and a part of the hot air was sucked in so that the ratio of the wind speed of the hot air penetrating the web in the thickness direction to the blown hot air was 50%.

[Evaluation of Texture]
The nonwoven fabric obtained by the methods of the Examples and Comparative Examples was evaluated by moving the palm of the hand along the MD direction on the surface. The texture was evaluated by three expert panelists, and the texture of the outer layer of Merries Pants Big Size (Kao Corporation, manufactured in 2019, sold in Japan) was given a score of 1, and the evaluation was performed according to the following criteria. The arithmetic average of the panelists' scores was rounded to the nearest integer digit to calculate a value. The higher this value, the better the texture of the nonwoven fabric. The results are shown in Table 1 below.

<Evaluation criteria for texture>
5 points: Feeling much better than the evaluation standard product.
4 points: Feeling better than the evaluation standard product.
3 points: Feeling better than the evaluation standard product.
2 points: Feeling slightly better than the evaluation standard product.
Score 1: The texture is equivalent to that of the evaluation standard product, and there is no particular problem with the texture.

[Evaluation of fiber fluff]
The nonwoven fabrics obtained by the methods of the Examples and Comparative Examples were evaluated for the degree of fiber fluffing by the following method.
First, a disk (diameter 70 mm, 350 g) was attached to the tester with its center shifted 20 mm from the rotation axis. The surface of this disk was covered with urethane foam (urethane foam manufactured by Inoatec Co., Ltd., product name: Malt Filter MF-30 type, thickness 5 mm, surface friction coefficient 0.508).
Next, the nonwoven fabric to be measured is fixed on the table of the tester, the disk is placed on the nonwoven fabric, and the disk is rotated with the main surface of the disk in contact with the surface T of the nonwoven fabric that is not blown with hot air. At this time, the load applied to the nonwoven fabric is only the weight of the disk. This rotation is performed for 10 cycles, with one cycle being three clockwise and two counterclockwise. The rotation time is 3 seconds per rotation.

The surface of the nonwoven fabric at the position where the disk had been in contact was visually observed, and the air-through nonwoven fabric used on the skin-facing side of Merries Pants Big Size (Kao Corporation, manufactured in 2019, sold in Japan) was peeled off as the evaluation standard product, and the fuzzing of the surface side (skin-facing side) treated with the above method was scored as 5 points and evaluated according to the following criteria. A higher score indicates less fiber fuzzing, less quality deterioration over long periods of use, and a nonwoven fabric that can maintain a high texture. The results are shown in Table 1 below.

<Evaluation criteria for fiber fluff>
5 points: Equivalent to the evaluation standard product, with very little fiber fuzz.
4 points: Somewhat inferior to the evaluation standard product, but with little fiber fuzz.
3 points: Inferior to the evaluation standard product, but the amount of pilling is not problematic.
2 points: Clearly inferior to the evaluation standard product, with a lot of fiber fluff.
1 point: Significantly inferior to the evaluation standard product, with a great deal of fiber fluff.

[Evaluation of fusion points]
The nonwoven fabrics obtained by the methods of the Examples and Comparative Examples were evaluated for the number of fusion points of the fibers by the following method.
A 10 mm x 30 mm area is cut out from the nonwoven fabric to be measured using a sharp razor, and this is used as the measurement sample. If a sample of this size cannot be taken out, a sample as large as possible is cut out. Three measurement samples are prepared. The surface of the measurement sample on the side T on which the hot air is not blown is photographed at a magnification of 200 times using a scanning electron microscope (SEM, JCM-6000 product name, manufactured by JEOL Ltd.) to photograph an area of 500 μm x 400 μm (observation area). In this SEM photographing, the focus is on the fiber located at the top of the photographed surface of the measurement sample. Five different positions are photographed for each measurement sample, and a total of 15 SEM images are obtained for the three measurement samples.
Next, in each SEM image, fibers that are in focus are selected, and the number of heat fusion points where these fibers are heat fused to each other is counted. "In-focus fibers" are fibers whose outlines are not blurred in the observation area. The total number of heat fusion points measured for each SEM image is then regarded as the number of heat fusion points on the surface T of the nonwoven fabric that is not blown with hot air.
The fusion points were defined as the intersections of the fibers where the boundaries of the fibers were unclear. The measurement results for the surface T side not subjected to hot air blowing are shown in Table 1 below.

<Evaluation of fusion points>
The number of fusion points is 60 or more and 120 or less: The fusion points are appropriately formed, and the texture is excellent.
The number of fusion points is 121 or more: Many fusion points are formed, the nonwoven fabric is hard, and the feel is poor.
The number of fusion points is 59 or less: The number of fusion points is small, and the strength of the nonwoven fabric is low.

As shown in Table 1, the Examples using sheath-core composite fibers having a predetermined fineness and core/sheath mass ratio are able to obtain high-quality nonwoven fabrics that have both good texture and less fiber fuzz, as compared with the Comparative Examples. Of these, Examples 1 and 3, which were carried out by sucking in a portion of the blown hot air, are able to obtain nonwoven fabrics of even higher quality that have both good texture and less fiber fuzz at a high level, and it can also be seen that the effect of Example 1, in which only the sheath-core composite fiber having a predetermined fineness and core/sheath mass ratio was used, is more pronounced.

Claims (6)

The method includes a step of blowing hot air onto a fiber web containing heat-fusible core-sheath composite fibers by an air-through method,
The fiber web contains 50% by mass or more of the core-sheath composite fiber having a fineness of 0.5 dtex or more and 1.8 dtex or less, a core content of 10% by mass or more and 45% by mass or less, and a sheath content of 55% by mass or more and 90% by mass or less,
The method for producing a nonwoven fabric, wherein the hot air has a wind speed of 0.3 m/sec or more and 0.6 m/sec or less. The core and the sheath in the core-sheath composite fiber contain a thermoplastic resin,
The thermoplastic resin constituting the core is polyethylene terephthalate,
The method according to claim 1 , wherein the thermoplastic resin constituting the sheath is polyethylene. The manufacturing method according to claim 1 or 2, in which a portion of the hot air blown onto the fiber web is sucked onto the side of the fiber web onto which the hot air is blown, so that the entire amount of the hot air does not penetrate the fiber web in the thickness direction. The manufacturing method according to claim 3, wherein the process is performed while sucking in the hot air blown onto the fiber web so that the ratio of the speed of the hot air that penetrates the fiber web in the thickness direction to the speed of the hot air blown onto the fiber web is 30% or more and 70% or less. The manufacturing method according to claim 3 or 4, in which the process is carried out by providing a hot air suction device. The method according to claim 5 , wherein the suction device is a fan or a blower.

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