Nonwoven fabric

Abstract

Provided is a nonwoven fabric that is bulky, has excellent flexibility, is smooth, and demonstrates an excellent bulk recovery rate. This nonwoven fabric has a first layer including thermally bonding composite fibers 1 in which at least some of intersections are thermally bonded, and a second layer including thermally bonding composite fibers 2 in which at least some of intersections are thermally bonded. The fiber diameter of the thermally bonding composite fibers 1 is 5-18 μm, the fiber diameter of the thermally bonding composite fibers 2 is 12-35 μm, the fiber diameter of the thermally bonding composite fibers 2 is larger than the fiber diameter of the thermally bonding composite fibers 1, and the specific volume of the first layer and the second layer is 150-400 cm3 / g.

Description

nonwoven fabric

[0001] The present invention relates to a nonwoven fabric that is bulky, has excellent softness, is smooth, and has an excellent bulk recovery rate.

[0002] Nonwoven fabrics used in applications that come into contact with human skin, such as hygiene products, are required to be more comfortable, specifically, to have excellent bulk and flexibility, and to have a smooth surface that does not feel rough when rubbed against the skin.

[0003] One of the most widely used nonwoven fabrics is a through-air nonwoven fabric. A through-air nonwoven fabric is obtained by heat-treating a web made of composite fibers composed of at least two types of thermoplastic resins with different melting points. Known methods for heat-treating a web include thermally bonding the composite fibers together using a heat treatment device (e.g., a hot air penetration type heat treatment device or a hot air blowing type heat treatment device) equipped with a transport support that supports and transports the web. However, because through-air nonwoven fabrics are produced by blowing hot air, the pressure from the hot air is applied to the web, which can cause problems such as loss of bulk and flexibility.

[0004] In view of these problems, the present applicant previously proposed that a bulky, flexible, and high-strength nonwoven fabric could be obtained by heat-fusing the intersections of thermally adhesive conjugate fibers under no pressure using superheated steam gas (Patent Document 1). However, because the nonwoven fabric obtained in this manner was very bulky, when the nonwoven fabric was made into a roll-shaped product, the bulk was sometimes crushed by the winding pressure.

[0005] International Publication No. 2022 / 202142

[0006] The present invention has been made against the background of the above-mentioned conventional technology, and an object of the present invention is to provide a nonwoven fabric that is bulky, has excellent softness, is smooth, and has an excellent bulk recovery rate.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that by forming a nonwoven fabric having a first layer and a second layer with specific fiber diameters and specific volumes, it is possible to obtain a nonwoven fabric that is bulky, has excellent flexibility, is smooth, and is resistant to loss of bulk due to winding pressure (has excellent bulk recovery rate), which has led to the completion of the present invention.

[0008] That is, the present invention has the following configuration: [1] A nonwoven fabric having a first layer containing thermally bonded conjugate fibers 1 at least some of whose intersections are thermally bonded, and a second layer containing thermally bonded conjugate fibers 2 at least some of whose intersections are thermally bonded, wherein the fiber diameter of the thermally bonded conjugate fibers 1 is 5 to 18 μm and the fiber diameter of the thermally bonded conjugate fibers 2 is 12 to 35 μm, the fiber diameter of the thermally bonded conjugate fibers 2 is larger than the fiber diameter of the thermally bonded conjugate fibers 1, and the specific volume of the first layer is 150 to 400 cm ３ / g, and the specific volume of the second layer is 150 to 400 cm ３ [2] The nonwoven fabric according to [1], wherein the first layer and the second layer are integrated by fusion bonding of the thermal adhesive conjugate fibers 1 and 2. [3] The fiber density of the first layer is 10 to 25 fibers / mm ２ and the fiber density of the second layer is 3 to 15 fibers / mm ２ [4] The nonwoven fabric according to any one of [1] to [3], wherein the fiber density ratio in the first layer is 1.4 or less and the fiber density ratio in the second layer is 1.4 or less. [5] The nonwoven fabric according to any one of [1] to [4], wherein the fiber diameter of the thermal adhesive conjugate fiber 2 is 1.1 to 2.5 times the fiber diameter of the thermal adhesive conjugate fiber 1.

[0009] According to the present invention, it is possible to provide a nonwoven fabric that is bulky, has excellent flexibility, is smooth, and has an excellent bulk recovery rate.

[0010] The nonwoven fabric of the present invention has a first layer containing thermally bonded conjugate fibers 1 at least some of whose intersections are thermally bonded, and a second layer containing thermally bonded conjugate fibers 2 at least some of whose intersections are thermally bonded, wherein the fiber diameter of the thermally bonded conjugate fibers 1 is 5 to 18 μm, the fiber diameter of the thermally bonded conjugate fibers 2 is 12 to 35 μm, the fiber diameter of the thermally bonded conjugate fibers 2 is larger than the fiber diameter of the thermally bonded conjugate fibers 1, and the specific volume of the first layer is 150 to 400 cm ３ / g, and the specific volume of the second layer is 150 to 400 cm ３ / g.

[0011] (Thermal adhesive conjugate fiber 1) The fiber diameter of the thermal adhesive conjugate fiber 1 used in the present invention is 5 to 18 μm. If the fiber diameter of the thermal adhesive conjugate fiber 1 is 5 μm or more, the fibers are less likely to be crushed by pressure and the bulk recovery rate of the nonwoven fabric can be increased, and if it is 18 μm or less, the roughness is reduced and the smoothness can be easily felt. From this viewpoint, it is preferably 6 to 16 μm, and more preferably 8 to 14 μm.

[0012] The fiber length of the thermal adhesive conjugate fiber 1 is not particularly limited, but is preferably 3 to 200 mm, more preferably 20 to 120 mm, and even more preferably 30 to 60 mm. If the fiber length is 3 mm or more, the fibers will be more entangled with each other, improving the shape retention of the web and the strength of the nonwoven fabric. If the fiber length is 200 mm or less, the fibers will be more likely to be oriented in the thickness direction of the nonwoven fabric, improving bulkiness and flexibility.

[0013] The thermally adhesive conjugate fiber 1 is not particularly limited as long as it can be melted by heat to form adhesive points, and examples thereof include concentric sheath-core conjugate fibers, eccentric sheath-core conjugate fibers, and side-by-side conjugate fibers. The cross-sectional shape of the conjugate fiber is not particularly limited, and any of round shapes such as circles and ellipses, angular shapes such as triangles and squares, irregular shapes such as stars and octave shapes, segmented shapes, and hollow shapes can be used.

[0014] The thermoplastic resin constituting the thermal adhesive conjugate fiber 1 is not particularly limited, and examples thereof include polyethylene-based resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE); polypropylene-based resins such as crystalline polypropylene (PP) and copolymers of propylene and α-olefins (excluding propylene) (Co-PP) containing propylene as the main component; polyester-based resins such as polyethylene terephthalate (PET), polybutylene terephthalate, copolymerized polyethylene terephthalate (Co-PET), polylactic acid, polyglycolic acid, and polybutylene succinate; polyvinyl alcohol-based resins, polyvinyl acetate-based resins, acrylic resins, polystyrene-based resins, polyurethane-based resins, polyamide-based resins, and fluorine-based resins. Among these, polyethylene-based resins, polypropylene-based resins, and polyester-based resins are preferably used because of their excellent processability. The combination of thermoplastic resins constituting the thermally bondable conjugate fiber 1 is not particularly limited, but from the viewpoint of widening the processing temperature range, the difference in melting point is preferably 10°C or more, more preferably 30°C or more, and even more preferably 50°C or more. Specific examples of combinations of high-melting point component / low-melting point component of thermoplastic resins include PP / HDPE, PP / LLDPE, PP / Co-PP, PET / HDPE, PET / LLDPE, PET / Co-PET, and PET / PP. From the viewpoints of texture, raw material costs, production stability, etc., the combination of PP / HDPE or PET / HDPE is preferred, and the combination of PET / HDPE is more preferred. Furthermore, from the viewpoint of thermal adhesion, the low-melting point component preferably occupies 50% or more, and more preferably 70% or more, of the surface of the thermally bondable conjugate fiber 1.

[0015] The volume ratio of the low-melting point component to the high-melting point component is not particularly limited, but a high proportion of the low-melting point component tends to improve the strength of the bonding points between the thermal adhesive conjugate fibers 1 or between the first layer and the second layer, resulting in a nonwoven fabric with high strength, while a high proportion of the high-melting point component tends to improve the bulk, flexibility, and bulk recovery rate of the nonwoven fabric. From this perspective, the volume ratio of the low-melting point component to the high-melting point component is preferably 20 / 80 to 80 / 20, and more preferably 30 / 70 to 70 / 30.

[0016] The thermoplastic resin constituting the thermal adhesive conjugate fiber 1 may contain additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizing agents, nucleating agents, epoxy stabilizers, lubricants, antibacterial agents, deodorizers, flame retardants, antistatic agents, pigments, or plasticizers, as needed, within the range that does not impair the effects of the present invention.

[0017] (First Layer) The fiber density of the first layer in the present invention is not particularly limited, but is preferably 10 to 25 fibers / mm ２ It is preferable that the number of wires is 12 to 22 wires / mm ２ More preferably, the number of fibers is 14 to 20 / mm ２ It is more preferable that the fiber density of the first layer is 10 fibers / mm ２ If the number of intersections between fibers is 25 / mm or more, the strength of the nonwoven fabric can be improved. ２ If the thickness is less than this, the number of intersections between the fibers decreases, and the bulkiness and flexibility of the nonwoven fabric can be improved.

[0018] The first layer in the present invention is not particularly limited, but preferably has a fiber density ratio of 1.4 or less. If the fiber density ratio in the first layer is 1.4 or less, even if thermal adhesive conjugate fibers 1 with a relatively small fiber warp are used, high fiber density areas in the first layer are unlikely to occur, and the flexibility of the nonwoven fabric is unlikely to be impaired. From this perspective, it is more preferably 1.3 or less, and even more preferably 1.2 or less. The lower limit of the fiber density ratio in the first layer is 1.0, and the closer to 1.0 the ratio is, the more uniform the fiber density becomes, i.e., the closer to the ideal state in the present invention.

[0019] Here, the fiber density ratio in this specification is expressed as the ratio of the fiber densities of the high-density portion and the low-density portion in each of the first and second layers. Furthermore, the "high-density portion" and the "low-density portion" refer to the portion with the higher fiber density when measuring the fiber density in the upper and lower portions obtained by dividing each layer into two equal halves in the thickness direction, and the "high-density portion" refers to the portion with the lower fiber density when measuring the fiber density in the upper and lower portions.

[0020] In addition, the term "fiber density" as used herein refers to the number of fibers per unit area in the cross section of the nonwoven fabric, and is expressed in units of, for example, fibers / mm ２ The method for measuring the fiber density will be explained in detail in the Examples.

[0021] The basis weight of the first layer is not particularly limited, but is preferably 5 to 50 g / m ２ It is preferable that the density is 8 to 40 g / m ２ More preferably, it is 10 to 30 g / m ２ It is more preferable that the basis weight of the first layer is 5 g / m ２ If the density is 50 g / m or more, the roughness of the nonwoven fabric is small and it becomes easy to feel smooth. ２ If the thickness is below this, the thickness of the nonwoven fabric will not be too thick, and the drapeability will be easily maintained.

[0022] The thickness of the first layer is not particularly limited, but is preferably 0.5 to 20 mm, more preferably 1 to 10 mm, and even more preferably 2 to 5 mm. If the thickness of the first layer is 0.5 mm or more, a nonwoven fabric excellent in bulkiness and flexibility can be obtained, and if it is 20 mm or less, a nonwoven fabric excellent in drapeability can be obtained.

[0023] The specific volume of the first layer in the present invention is 150 to 400 cm ３ / g. The specific volume of the first layer is 150 cm ３ / g or more, a nonwoven fabric excellent in bulkiness and flexibility can be obtained, and ３ / g or less, the decrease in strength is suppressed, and a nonwoven fabric with excellent processability can be obtained. From this viewpoint, the specific volume of the first layer is 160 to 350 cm ３ / g, and 170 to 300 cm ３If the content is 1% by weight or more, an effect commensurate with the use can be obtained, and if the content is 30% by weight or less, a nonwoven fabric that is less likely to fluff can be obtained.

[0024] The first layer may contain fibers other than the thermally bondable conjugate fiber 1 described above, provided that the effects of the present invention are not impaired. Examples of fibers other than the thermally bondable conjugate fiber 1 include, but are not limited to, natural fibers (such as wood fibers), recycled fibers (such as rayon), semi-synthetic fibers (such as acetate), chemical fibers, and synthetic fibers (such as polyester fibers, acrylic fibers, nylon fibers, and vinyl chloride fibers) that do not have thermally bondable properties (hereinafter referred to as "non-thermally bondable fibers"), thermally bondable conjugate fibers with a fiber diameter of less than 5 μm, and thermally bondable conjugate fibers with a fiber diameter of more than 18 μm. When fibers other than the thermally bondable conjugate fiber 1 are contained, their proportion is not limited as long as the effects of the present invention are not impaired, and may be, for example, 1 to 30% by weight, and preferably 3 to 15% by weight.

[0025] In this specification, "non-thermobondable fiber" means a fiber that does not undergo thermal changes (such as melting or softening) that are involved in thermal bonding during the thermal bonding process carried out when producing a nonwoven fabric.

[0026] (Thermal adhesive conjugate fiber 2) The fiber diameter of the thermal adhesive conjugate fiber 2 used in the present invention is 12 to 35 μm. If the fiber diameter of the thermal adhesive conjugate fiber 2 is 12 μm or more, the cushioning properties and bulk recovery rate of the nonwoven fabric can be improved, and if it is 35 μm or less, the whiteness of the nonwoven fabric is improved, good hiding power can be obtained, and roughness and hardness can be reduced. From these viewpoints, the fiber diameter is preferably 14 to 30 μm, and more preferably 16 to 28 μm.

[0027] The effects of the present invention can be obtained if the fiber diameter of the thermal adhesive conjugate fiber 2 used in the present invention is larger than the fiber diameter of the above-mentioned thermal adhesive conjugate fiber 1. By making the fiber diameter preferably 1.1 to 2.5 times, more preferably 1.2 to 2.3 times, and even more preferably 1.3 to 2.2 times that of the thermal adhesive conjugate fiber 1, it becomes possible to obtain a nonwoven fabric with an excellent bulk recovery rate.

[0028] The fiber length, composite form, cross-sectional shape, thermoplastic resin, and combination of high-melting point component and low-melting point component of the thermal adhesive conjugate fiber 2 can be selected arbitrarily from the same configurations as those described for the thermal adhesive conjugate fiber 1.

[0029] (Second Layer) The fiber density of the second layer in the present invention is not particularly limited, but is preferably 3 to 15 fibers / mm ２ It is preferable that the number of wires is 4 to 14 wires / mm ２ More preferably, the number of fibers is 5 to 12 per mm. ２ It is more preferable that the fiber density of the second layer is 3 fibers / mm ２ If the number of intersections between fibers is 15 / mm or more, the strength of the nonwoven fabric can be improved. ２ If the thickness is less than this, the number of intersections between the fibers decreases, and the bulkiness and flexibility of the nonwoven fabric can be improved.

[0030] The second layer in the present invention is not particularly limited, but preferably has a fiber density ratio of 1.4 or less. If the fiber density ratio in the second layer is 1.4 or less, the roughness and hardness of the nonwoven fabric can be reduced even if thermal adhesive conjugate fibers 2 with a relatively large fiber warp are used. From this perspective, it is more preferably 1.3 or less, and even more preferably 1.2 or less. The lower limit of the fiber density ratio of the second layer is 1.0.

[0031] The basis weight of the second layer is not particularly limited, but is preferably 5 to 50 g / m ２ It is preferable that the density is 8 to 40 g / m ２ More preferably, it is 10 to 30 g / m ２ It is more preferable that the basis weight of the second layer is 5 g / m ２ If the density is 40 g / m or more, the strength of the nonwoven fabric can be maintained and the bulk recovery rate can be improved. ２ If it is below this value, the nonwoven fabric will not be too hard and will have a good feel.

[0032] The thickness of the second layer is not particularly limited, but is preferably 0.5 to 20 mm, more preferably 1 to 10 mm, and even more preferably 2 to 5 mm. If the thickness of the second layer is 0.5 mm or more, a nonwoven fabric excellent in bulkiness and flexibility can be obtained, and if it is 20 mm or less, a nonwoven fabric excellent in drapeability can be obtained.

[0033] The specific volume of the second layer in the present invention is 150 to 400 cm ３ / g. The specific volume of the second layer is 150 cm ３ / g or more, a nonwoven fabric excellent in bulkiness and flexibility can be obtained, and ３ / g or less, the decrease in strength is suppressed, and a nonwoven fabric with excellent processability can be obtained. From this viewpoint, the specific volume of the second layer is 160 to 350 cm ３ / g, and 170 to 300 cm ３ It is more preferable that the SiO2 content is 1 / g.

[0034] The second layer may contain fibers other than the thermally bondable conjugate fibers 2 described above, provided that the effects of the present invention are not impaired. Examples of fibers other than the thermally bondable conjugate fibers 2 include, but are not limited to, non-thermally bondable fibers, thermally bondable conjugate fibers with a fiber diameter of less than 12 μm, and thermally bondable conjugate fibers with a fiber diameter of more than 35 μm. When fibers other than the thermally bondable conjugate fibers 2 are contained, the proportion thereof is not limited as long as it does not impair the effects of the present invention, and can be, for example, 1 to 30% by weight, and preferably 3 to 15% by weight. A proportion of 1% by weight or more provides an effect commensurate with the use, while a proportion of 30% by weight or less provides a nonwoven fabric that is less prone to pilling.

[0035] (Nonwoven Fabric) The nonwoven fabric of the present invention has the first and second layers described above, and by adopting such a configuration, a nonwoven fabric can be obtained that is bulky, has excellent flexibility, is smooth, and has an excellent bulk recovery rate. In particular, the improvement in bulk recovery rate is thought to be a novel effect achieved by combining specific layers, which cannot be expected from a single-layer nonwoven fabric consisting of only the first or second layer.

[0036] Although there are no particular limitations on the nonwoven fabric of the present invention, it is preferable that the first layer and the second layer are integrated by fusion, adhesive, entanglement, or the like. In particular, from the viewpoints of peel strength and skin irritation, it is preferable that the first layer and the second layer are integrated by fusion. When the first layer and the second layer are integrated by fusion, although there are no particular limitations on the method, it is preferable that they are integrated by fusion of the thermal adhesive conjugate fiber 1 and the thermal adhesive conjugate fiber 2. In particular, it is preferable that the low-melting point components of the thermal adhesive conjugate fiber 1 and the thermal adhesive conjugate fiber 2 are highly compatible resins, and that the layers are fused by melting at least one of the low-melting point components, more preferably both of them. Examples of highly compatible resin combinations include, but are not limited to, HDPE / HDPE, LDPE / LDPE, LLDPE / LLDPE, HDPE / LDPE, HDPE / LLDPE, LDPE / LLDPE, PP / PP, coPP / coPP, PP / coPP, PET / PET, coPET / coPET, and PET / coPET. From this viewpoint, HDPE / HDPE, LDPE / LDPE, LLDPE / LLDPE, HDPE / LDPE, HDPE / LLDPE, LDPE / LLDPE, PP / PP, coPP / coPP, and PP / coPP are preferred, and HDPE / HDPE, LDPE / LDPE, LLDPE / LLDPE, PP / PP, and coPP / coPP are more preferred.

[0037] The basis weight of the nonwoven fabric of the present invention is not particularly limited, but is preferably 10 to 100 g / m ２ It is preferable that the density is 16 to 80 g / m ２ More preferably, it is 20 to 60 g / m ２ It is more preferable that:

[0038] The basis weight ratio of the first layer to the second layer in the nonwoven fabric of the present invention is not particularly limited, but is preferably 20 / 80 to 80 / 20, more preferably 25 / 75 to 75 / 25, and even more preferably 30 / 70 to 70 / 30. Within the above ranges, a nonwoven fabric excellent in manufacturing stability and bulk recovery rate can be obtained.

[0039] The tensile strength per unit area weight of the nonwoven fabric is not particularly limited, but from the viewpoint of preventing fuzzing and preventing breakage and poor processability even when the basis weight is low, it is preferably 0.5 N / 50 mm or more, more preferably 0.7 N / 50 mm or more, and even more preferably 1.0 N / 50 mm or more. The upper limit of the tensile strength per unit area weight is not particularly limited, but in consideration of the balance with the specific volume of the nonwoven fabric, it is preferably 3.0 N / 50 mm or less, more preferably 2.5 N / 50 mm or less, and even more preferably 2.0 N / 50 mm or less.

[0040] The specific volume of the nonwoven fabric is not particularly limited, but is preferably 150 cm ３ / g or more, and ３ / g or more, and 170 cm ３ / g or more. ３ If the specific volume is 1 / g or more, the bulkiness and flexibility of the nonwoven fabric are satisfactory. The upper limit of the specific volume is not particularly limited, but in consideration of the strength of the nonwoven fabric, it is preferably 400 cm ３ / g or less, and ３ / g or less, and more preferably 300 cm ３ It is more preferable that the SiO2 content is 1 / g or less.

[0041] The nonwoven fabric of the present invention may be laminated with a nonwoven fabric, film, or sheet other than the nonwoven fabric of the present invention, such as, but not limited to, a through-air nonwoven fabric, a spunbond nonwoven fabric, a meltblown nonwoven fabric, a spunlace nonwoven fabric, a needle-punched nonwoven fabric, a film, a mesh, or a net. By laminating, it is possible to control the permeability to soft stools and the liquid return resistance. The laminating method is not particularly limited, but examples thereof include a method of laminating with an adhesive such as a hot melt, and a method of laminating with thermal adhesion such as a through-air method or a hot embossing method.

[0042] The nonwoven fabric may be subjected to antistatic treatment, water-repellent treatment, hydrophilic treatment, antibacterial treatment, ultraviolet absorbing treatment, near-infrared absorbing treatment, electret treatment, or the like depending on the purpose, as long as the effects of the present invention are not impaired.

[0043] (Method for producing nonwoven fabric) The nonwoven fabric of the present invention is not particularly limited, but includes a step of forming web 1 containing thermally adhesive conjugate fibers 1 having a fiber diameter of 5 to 18 μm (hereinafter sometimes referred to as web formation step 1), a step of forming web 2 containing thermally adhesive conjugate fibers 2 having a fiber diameter of 12 to 35 μm (hereinafter sometimes referred to as web formation step 2), and a step of thermally bonding the intersections of thermally adhesive conjugate fibers 1 and 2 without pressure (hereinafter sometimes referred to as thermal bonding step). This method makes it possible to thermally bond the intersections of the fibers while maintaining the shape of the web, i.e., with little variation in density in the thickness direction, and to achieve a specific fiber density, and to obtain a nonwoven fabric that is bulky, highly flexible, smooth, and has an excellent bulk recovery rate.

[0044] The method for producing a nonwoven fabric from webs 1 and 2 is not particularly limited, and examples include a method in which webs 1 and 2 are superimposed and then subjected to a thermal bonding step to thermally bond the intersections of the thermally adhesive conjugate fibers 1 in web 1 and the intersections of the thermally adhesive conjugate fibers 2 in web 2, and to integrate the layers of webs 1 and 2, and a method in which webs 1 and 2 are separately thermally bonded at the intersections of the fibers, and the resulting layers are then superimposed and integrated into the first layer and the second layer by heat treatment, ultrasonic treatment, adhesive treatment, entanglement treatment, or the like. Among these, from the viewpoints of peel resistance, skin irritation, and simplified production, a method in which webs 1 and 2 are superimposed and then subjected to a thermal bonding step to thermally bond the intersections of the thermally adhesive conjugate fibers 1 in web 1 and the intersections of the thermally adhesive conjugate fibers 2 in web 2, and to integrate the layers of webs 1 and 2, is preferred.

[0045] Web 1 or 2 containing the thermally adhesive conjugate fiber is not particularly limited, and may be a long fiber web formed by a spunbonding method, a meltblown method, a tow-spreading method, or the like, or a short fiber web formed by a carding method, an airlaid method, a wet method, or the like using short fibers (staples or chopped fibers). From the viewpoint of improving bulkiness and flexibility, a short fiber web formed by a carding method or an airlaid method is preferred, and a short fiber web formed by a carding method is more preferred. In the present invention, the term "web" refers to a fiber assembly in which the fibers are somewhat entangled, and means a state in which the intersections of the conjugate fibers are not bonded.

[0046] Next, the intersections of the thermally bondable conjugate fibers in the obtained web 1 or 2 are thermally bonded without pressure. The heating medium in the thermal bonding step is not particularly limited, and examples thereof include hot air or superheated steam, but it is preferable to use superheated steam in terms of its resistance to pilling, excellent texture, and productivity of the nonwoven fabric. An example of the thermal bonding step is a method in which the web is introduced by a transport conveyor into a furnace filled with hot air or superheated steam, and a nonwoven fabric is continuously obtained.

[0047] The temperature of the heat medium is not particularly limited, but can be, for example, 0 to 30°C above the melting point or softening point of the low-melting point component constituting the composite fiber. The air speed at which the heat medium is blown is also not particularly limited, but is preferably less than 0.1 m / s to obtain a specific fiber density. The pressure at which the heat medium is blown is also not particularly limited, but is preferably less than 0.1 kPa to obtain a specific fiber density.

[0048] The nonwoven fabric of the present invention can be used for absorbent articles such as diapers, napkins, and incontinence pads; sanitary materials such as masks, gowns, surgical gowns, and bandages; interior materials such as wall sheets, shoji paper, and flooring; daily life materials such as cover cloths, cleaning wipers, and food waste covers; toiletry products such as disposable toilets and toilet covers; pet supplies such as pet sheets, pet diapers, and pet towels; industrial materials such as wiping materials, filters, cushioning materials, oil adsorbents, abrasives, and adsorbents for ink tanks; and textile products such as general medical materials, bedding, and nursing care products.

[0049] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The measurement methods or definitions of the physical properties shown in the examples are as follows. All of the following physical property measurements were carried out after the nonwoven fabric was heat-treated in an oven at 110°C for 5 minutes to reset the stress of the nonwoven fabric.

[0050] <Fiber diameter of thermal adhesive composite fibers 1 and 2> Images of the first layer and the second layer were taken at a magnification of 100 to 200 times using a scanning electron microscope (SU-8000, manufactured by Hitachi High-Technologies Corporation). The fiber diameters of thermal adhesive composite fibers 1 and 2 were measured using image analysis software (ImageJ). The fiber diameter was taken as the average value when 50 fibers were measured.

[0051] <Fiber diameter ratio between thermal adhesive composite fiber 1 and thermal adhesive composite fiber 2> From the fiber diameters of the thermal adhesive composite fibers 1 and 2 obtained above, the fiber diameter ratio was calculated according to the following formula: Fiber diameter ratio (times) = fiber diameter of thermal adhesive composite fiber 2 ÷ fiber diameter of thermal adhesive composite fiber 1

[0052] <Fiber Density of First and Second Layers> (1) Method of Preparing Observation Samples A nonwoven fabric cut to a size of 1 cm (machine direction of the nonwoven fabric; MD) x 3 cm (cross direction of the nonwoven fabric; CD) was impregnated with a photocurable resin (UV-LED Resin Hoshi no Shizuku [Soft], manufactured by PADICO Corporation) and cured by UV irradiation. Next, using a microtome (Leica, RM2265), the cured sample was cut to a thickness of 10 μm in the machine direction, yielding an observation sample measuring 10 μm (machine direction) x 3 cm (CD) x thickness (thickness direction). (2) Measurement of Fiber Density A sample for observation placed on a glass slide was placed between two polarizing plates arranged in a crossed Nicol position, and an image of the microtome-cut surface of the sample for observation (3 cm (CD) × thickness (thickness direction)) was taken at 30x magnification using a microscope (KEYENCE Corporation, VHX-6000). The number of fibers in the first and second layers was measured using image analysis software (ImageJ) and divided by the area to calculate the number of fibers. Specifically, the image was converted to 16 bits using ImageJ, and then binarized to distinguish between fibers and non-fibers. Next, in the first and second layers, a range was selected between the upper and lower portions divided equally in the thickness direction (5 mm (CD) × half the thickness of the first and second layers (thickness direction)), and the number of fibers in the selected portion was measured using the "Analyze Particle" function of ImageJ. The number of fibers obtained was divided by the area of ​​the selected site to determine the number of fibers (fibers / mm ２ ) was calculated. Here, in the upper and lower portions of the first layer, the portion with a higher fiber density was designated as the high-density portion of the first layer, and the portion with a lower fiber density was designated as the low-density portion of the first layer. In the upper and lower portions of the second layer, the portion with a higher fiber density was designated as the high-density portion of the second layer, and the portion with a lower fiber density was designated as the low-density portion of the second layer. From the fiber densities of each obtained portion, the fiber densities of the first and second layers were calculated by the following formula. The fiber density of each portion was calculated as the average value when measured at two locations. Fiber density of the first layer (threads / mm ２ ) = (fiber density of high density portion of first layer (counts / mm ２ ) + fiber density of the low density portion of the first layer (counts / mm ２ )) ÷ 2 Fiber density of the second layer (threads / mm２ ) = (fiber density of high density portion of second layer (counts / mm ２ ) + fiber density of the low density portion of the second layer (counts / mm ２ ))÷2

[0053] <Fiber density ratio in the first layer and the second layer> From the fiber densities in each region obtained by the above method, the fiber density ratio in the first layer and the second layer was calculated by the following formula: Fiber density ratio in the first layer = Fiber density (strands / mm ２ ) ÷ fiber density of the low-density portion of the first layer (fibers / mm ２ ) Fiber density ratio in the second layer = fiber density (threads / mm ２ ) ÷ fiber density of the low-density portion of the second layer (fibers / mm ２ )

[0054] <Basis Weight> The weight of a nonwoven fabric cut into a 150 mm x 150 mm piece was measured, and the value converted to a unit area was used as the basis weight (g / m ２ The basis weight was measured by averaging two measurements. The basis weights of the first and second layers were measured after the obtained nonwoven fabric was peeled off into the first and second layers (using a solvent or the like, if necessary).

[0055] <Thickness> 0.7 gf / cm was measured using a laser thickness meter (IL-S065, manufactured by KEYENCE Corporation). ２ The thickness (mm) of the nonwoven fabric was measured when a pressure of 68.6 Pa (68.6 Pa) was applied for 5 seconds. The thickness was measured at five locations and averaged. The basis weights of the first and second layers were measured after the obtained nonwoven fabric was peeled off into the first and second layers (using a solvent, if necessary).

[0056] <Specific volume> The basis weight (g / m ２ The specific volume of the nonwoven fabric was calculated from the diameter (cm) and thickness (mm) using the following formula. The larger the specific volume, the higher the bulkiness. ３ / g) = Thickness (mm) ÷ Basis weight (g / m ２ ) x 1000

[0057] <Tensile strength> A sample measuring 50 mm in the CD direction and 150 mm in the MD direction was cut out and pulled using an autograph (AGX-J, manufactured by Shimadzu Corporation) at a chuck distance of 100 mm and a pulling rate of 100 mm / min. The maximum stress when this was measured was taken as the tensile strength (N / 50 mm) of the nonwoven fabric. The tensile strength was measured three times and the average value was used.

[0058] <Compression Work (WC)> Using a handy compressor (KES-G5, manufactured by Kato Tech Co., Ltd.), the compression work was measured as follows. First, a nonwoven fabric was placed on a sample stage, and a sample with an area of ​​2 cm ２ The pressure probe was applied from above the sample at a SENS (sensitivity): 2, a speed: 0.1 mm / sec, and a stress of 50 gf / cm ２ (4.9 kPa), and a stress curve Pa versus distance was obtained. From the obtained Pa, the compression work was calculated by numerical processing based on the following formula (1). The compression work was taken as the average value of 10 measurements. In the following formula, T ｍ is 50 gf / cm ２ Thickness under load (4.9 kPa), T ０ is 0.5 gf / cm ２ The greater the compression work, the more flexible the material is. In the present invention, the thickness is 3 gf cm / cm ２ This is considered to be excellent flexibility.

[0059] <Mean deviation of friction coefficient (MMD)> The mean deviation of friction coefficient was measured using a surface tester (KES-FB4, manufactured by Kato Tech Co., Ltd.) as follows. The first layer was used as the measurement surface, and a pressure of 10 gf / cm was applied using a contact. ２ The average deviation of the friction coefficient was measured by moving the contactor in the MD direction with a load of 0.98 kPa (0.98 kPa) applied, with SENS (sensitivity): High and a contactor speed: 1.0 mm / sec. The average deviation of the friction coefficient was taken as the average value of 10 measurements. The smaller the average deviation of the friction coefficient, the smoother the sample. In the present invention, a value of 0.007 or less was determined to be excellent in smoothness.

[0060] <Bulk Recovery Rate> Using a vacuum storage food sealer (VPF-385T, manufactured by Iris Ohyama Co., Ltd.), two pieces of nonwoven fabric cut into 10 cm squares were placed in a dedicated airtight bag, vacuum sealed, and stored at room temperature for 24 hours. The thickness 5 minutes after opening the airtight bag was measured using the method described above in <Thickness> measurement, and this was taken as the thickness after opening (mm). The bulk recovery rate was calculated from the thickness before sealing and the thickness after opening using the following formula. In the present invention, a bulk recovery rate of 40% or more was considered to be excellent in bulk recovery. Bulk recovery rate (%) = thickness after opening (mm) ÷ thickness before sealing (mm) × 100

[0061] [Example 1] A thermally adhesive composite fiber 1 was prepared by using a polyethylene terephthalate core (intrinsic viscosity (measured using an equal weight mixed solvent of phenol and tetrachloroethane at a concentration of 0.5 g / 100 ml and a temperature of 20°C): 0.65 dl / g, melting point 250°C) and a high density polyethylene sheath (density: 0.956 g / cm ３ A concentric sheath-core type composite fiber having a fineness of 1.3 dtex and a fiber length of 45 mm was prepared, in which the composite fibers had a melt flow rate (190°C, load 21.18N): 16 g / 10 min, a melting point of 130°C) and a volume ratio of 50 / 50. The composite fibers were then fabricated into a web 1 (basis weight: 12 g / m) consisting of the thermal adhesive composite fiber 1 by a carding method. ２ As the thermal adhesive conjugate fiber 2, a concentric sheath-core type conjugate fiber having a fineness of 4.4 dtex and a fiber length of 51 mm was prepared, in which the core was made of the same polyethylene terephthalate as in the thermal adhesive conjugate fiber 1 and the sheath was made of the same high-density polyethylene as in the thermal adhesive conjugate fiber 1 at a volume ratio of 50 / 50. Web 2 (basis weight: 12 g / m) made of the thermal adhesive conjugate fiber 2 was then fabricated by a carding method. ２ A multilayer web, in which Web 2 was superimposed on Web 1, was introduced into a furnace filled with superheated steam at 180°C for 10 seconds to obtain a nonwoven fabric. The wind speed of the superheated steam was less than 0.1 m / sec.

[0062] Example 2 A nonwoven fabric was obtained in the same manner as in Example 1, except that the fineness of the thermal adhesive conjugate fiber 1 was changed to 1.7 dtex.

[0063] Example 3 A nonwoven fabric was obtained in the same manner as in Example 1, except that the fineness of the thermal adhesive conjugate fiber 1 was changed to 2.2 dtex and the fiber length to 51 mm.

[0064] Example 4 A nonwoven fabric was obtained in the same manner as in Example 1, except that the fineness of the thermal adhesive conjugate fiber 1 was changed to 0.9 dtex.

[0065] Example 5 A nonwoven fabric was obtained in the same manner as in Example 2, except that the fineness of the thermal adhesive conjugate fiber 2 was changed to 2.2 dtex.

[0066] Example 6 A nonwoven fabric was obtained in the same manner as in Example 2, except that the volume ratio of the core component to the sheath component of the thermal adhesive conjugate fiber 2 was changed to 60 / 40 and the fineness was changed to 3.3 dtex.

[0067] Example 7 A nonwoven fabric was obtained in the same manner as in Example 2, except that the fineness of the thermal adhesive conjugate fiber 2 was changed to 5.6 dtex.

[0068] Example 8 A nonwoven fabric was obtained in the same manner as in Example 2, except that the fineness of the thermal adhesive conjugate fiber 2 was changed to 9.0 dtex.

[0069] [Example 9] The basis weight of the web 1 is 8 g / m ２ , the basis weight of the web 2 is 16 g / m ２ A nonwoven fabric was obtained in the same manner as in Example 2, except that:

[0070] [Example 10] The basis weight of the web 1 is 16 g / m ２ , the basis weight of the web 2 is 8 g / m ２ A nonwoven fabric was obtained in the same manner as in Example 2, except that:

[0071] Example 11 A nonwoven fabric obtained in the same manner as in Example 2 was further treated for 10 seconds with hot air at 130°C and a circulating air speed of 1.0 m / sec in a hot air circulation dryer to obtain a nonwoven fabric.

[0072] Example 12 A nonwoven fabric was obtained in the same manner as in Example 2, except that Web 1 was superimposed on Web 2.

[0073] Comparative Example 1 A nonwoven fabric was obtained in the same manner as in Example 1, except that the volume ratio of the core component to the sheath component of the thermal adhesive conjugate fiber 1 was changed to 60 / 40, the fineness to 3.3 dtex, and the fiber length to 51 mm.

[0074] Comparative Example 2 A multilayer web obtained in the same manner as in Example 2 was treated for 10 seconds with hot air at 130° C. and a circulating air speed of 1.0 m / sec in a hot air circulation dryer to obtain a nonwoven fabric.

[0075] [Comparative Example 3] Web 1 (basis weight: 24 g / m) obtained in the same manner as in Example 2 ２ The resulting mixture was introduced into a furnace filled with superheated steam at 180°C for 10 seconds to obtain a single-layer nonwoven fabric consisting of only the first layer. The wind speed of the superheated steam was less than 0.1 m / s.

[0076] [Comparative Example 4] Web 2 (basis weight: 24 g / m) obtained in the same manner as in Example 1 ２ The resulting nonwoven fabric was introduced into a furnace filled with superheated steam at 180°C for 10 seconds to obtain a single-layer nonwoven fabric consisting of only the second layer. The wind speed of the superheated steam was less than 0.1 m / s.

[0077] The physical properties of the nonwoven fabrics obtained in Examples 1 to 8 are shown in Table 1, and the physical properties of the nonwoven fabrics obtained in Examples 9 to 12 and Comparative Examples 1 to 4 are shown in Table 2.

[0078]

[0079]

[0080] As can be seen from Tables 1 and 2, the nonwoven fabrics of Examples 1 to 12, which satisfied the constituent requirements of the present invention, were bulky, had excellent softness, were smooth, and had an excellent bulk recovery rate. On the other hand, Comparative Example 1, in which the fiber diameter of the thermal adhesive composite fiber in the first layer was large, had satisfactory bulk, softness, and bulk recovery rate, but felt rough (not smooth). Comparative Example 2, in which the specific volumes of the first and second layers were small, had satisfactory smoothness and bulk recovery rate, but was low in bulk and poor in softness. Comparative Example 3, which was composed only of the first layer, had satisfactory bulk, softness, and smoothness, but a low bulk recovery rate. Comparative Example 4, which was composed only of the second layer, had satisfactory bulk and softness, but felt rough and had a low bulk recovery rate.

[0081] The nonwoven fabric of the present invention is bulky, has excellent flexibility, is smooth, and has an excellent bulk recovery rate, and therefore can be used in a variety of textile products, including absorbent articles such as diapers, napkins, and incontinence pads; sanitary materials such as masks, gowns, surgical gowns, and bandages; interior materials such as wall sheets, shoji paper, and flooring; household materials such as cover cloths, cleaning wipers, and food waste covers; toiletry products such as disposable toilets and toilet covers; pet supplies such as pet sheets, pet diapers, and pet towels; industrial materials such as wiping materials, filters, cushioning materials, oil adsorbents, abrasives, and adsorbents for ink tanks; and general medical materials, bedding, and nursing care products.

Claims

1. A nonwoven fabric having a first layer including thermally adhesive composite fibers 1, at least some of the intersections of which are thermally bonded, and a second layer including thermally adhesive composite fibers 2, at least some of which are thermally bonded, wherein the fiber diameter of the thermally adhesive composite fibers 1 is 5-18 μm and the fiber diameter of the thermally adhesive composite fibers 2 is 12-35 μm, the fiber diameter of the thermally adhesive composite fibers 2 is larger than the fiber diameter of the thermally adhesive composite fibers 1, and the specific volume of the first layer is 150-400 cm ３ / g, and the specific volume of the second layer is 150 to 400 cm ３ / g of nonwoven fabric.

2. The nonwoven fabric according to claim 1, wherein the first layer and the second layer are integrated together by fusion of the thermally adhesive composite fiber 1 and the thermally adhesive composite fiber 2.

3. The fiber density of the first layer is 10 to 25 threads / mm ２ and the fiber density of the second layer is 3 to 15 fibers / mm ２ The nonwoven fabric according to claim 1 or 2, 4. The nonwoven fabric according to claim 1 or 2, wherein the fiber density ratio in the first layer is 1.4 or less, and the fiber density ratio in the second layer is 1.4 or less.

5. The nonwoven fabric according to claim 1 or 2, wherein the fiber diameter of said thermally adhesive composite fiber 2 is 1.1 to 2.5 times the fiber diameter of said thermally adhesive composite fiber 1.

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