Nonwoven fabric and method for manufacturing same

Abstract

The present invention provides a nonwoven fabric having both flexibility and processing stability, and a method for manufacturing the same.　This nonwoven fabric includes thermally adhesive composite fibers having intersections thermally bonded. The nonwoven fabric has a specific volume of 100 cm3 / g or more, and the strength at 5% elongation with respect to the flow direction per unit basis weight is 40 mN / 5 cm or more.

Description

Nonwoven fabric and its manufacturing method

[0001] The present invention relates to a nonwoven fabric having excellent flexibility and processing stability, and a method for producing the same.

[0002] Bulkiness and flexibility have traditionally been required for nonwoven fabrics used in absorbent articles such as diapers and napkins, masks, filters, civil engineering materials, agricultural materials, heat insulating materials, clothing materials, bedding materials, nursing care products, etc. Known methods for achieving bulkiness and flexibility in nonwoven fabrics include a method using three-dimensionally crimped fibers (Patent Document 1) and a method for imparting a textured shape to a nonwoven fabric (Patent Document 2), but these methods do not necessarily provide satisfactory bulkiness and flexibility.

[0003] In light of this situation, the present applicant previously proposed that a bulky, flexible, and relatively high-strength nonwoven fabric can be obtained by thermally bonding the intersections of thermally bondable conjugate fibers under no pressure using superheated steam (Patent Document 3). However, the nonwoven fabric obtained in this manner can be significantly deformed by tension and other factors that occur during processing into textile products, and there is room for improvement in processing stability.

[0004] JP 2008-274473 A JP 2015-110846 A International Publication No. 2022 / 202142

[0005] 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 having both flexibility and processing stability, and a method for producing the same.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that by heat-treating a web containing a mixture of thermally adhesive conjugate fibers and heat-shrinkable fibers under specific conditions, a nonwoven fabric having a specific specific volume and strength at 5% elongation in the machine direction can be obtained, and that the nonwoven fabric thus obtained has both flexibility and processing stability, which led to the completion of the present invention.

[0007] That is, the present invention has the following configuration: [1] A nonwoven fabric containing thermally adhesive conjugate fibers whose intersections are thermally bonded, wherein the specific volume of the nonwoven fabric is 100 cm ３ / g or more, and a strength per unit area weight at 5% elongation in the machine direction of 40 mN / 5cm or more. [2] The nonwoven fabric according to [1], wherein the ratio of the strength at 5% elongation in the machine direction to the strength at 5% elongation in the direction perpendicular to the machine direction is 3.5 or more. [3] The nonwoven fabric according to [1] or [2], wherein the fiber density ratio between high-density regions and low-density regions in the nonwoven fabric is 1.4 or less. [4] A method for producing a nonwoven fabric, comprising the steps of: forming a web containing a mixture of thermally adhesive conjugate fibers and heat-shrinkable fibers; and heat-treating the web with a heating medium that satisfies the following (1) and (2): (1) A temperature higher than the heat shrinkage temperature of the heat-shrinkable fiber, higher than the melting point of the low-melting component of the thermal adhesive conjugate fiber, and lower than the high-melting component of the thermal adhesive conjugate fiber. (2) A wind speed of 0.5 m / s or less. [5] The method for producing a nonwoven fabric according to [4], wherein the weight ratio of the thermal adhesive conjugate fiber to the heat-shrinkable fiber is 99:1 to 85:15. [6] The nonwoven fabric according to [4] or [5], wherein the heating medium in the heat treatment step is superheated steam. [7] The method for producing a nonwoven fabric according to any one of [4] to [6], wherein the high-melting component of the thermal adhesive conjugate fiber is a polyester-based resin, the low-melting component is a polyolefin-based resin, and the resin constituting the heat-shrinkable fiber is a polyolefin-based resin with a melting point lower than that of the polyester-based resin. [8] An article using the nonwoven fabric according to claim 1.

[0008] According to the present invention, it is possible to provide a nonwoven fabric having both flexibility and processing stability, and a method for producing the same.

[0009] The nonwoven fabric of the present invention contains thermally bonded composite fibers and heat-shrinkable fibers whose intersections are thermally bonded, and has a specific volume of 100 cm ３ / g or more, and the strength at 5% elongation in the machine direction per unit area weight (hereinafter, "strength at 5% elongation in the machine direction" may be referred to as "5% MD strength." In this application, "machine direction" means the machine direction (MD) of the fibers) is 40 mN / 5 cm or more. ３Furthermore, by making the 5% MD strength per unit area weight 40 mN / 5 cm or more, deformation of the nonwoven fabric due to tension or the like can be suppressed, and satisfactory processing stability can be obtained.

[0010] (Thermal adhesive conjugate fiber) The thermal adhesive conjugate fiber used in the present invention is not particularly limited as long as it can be melted by heat to form adhesive points, and its conjugate form can be exemplified by concentric sheath-core conjugate fiber, eccentric sheath-core conjugate fiber, or side-by-side conjugate fiber. In addition, the cross-sectional shape of the conjugate fiber is not particularly limited, and any of round shapes such as circle or ellipse, angular shapes such as triangle or square, irregular shapes such as star or octave, segmented shapes, and hollow shapes can be used.

[0011] The resin constituting the thermally bondable composite fiber is not particularly limited, and examples thereof include polyolefin resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), crystalline polypropylene (PP), or a copolymer of propylene and an α-olefin (excluding propylene) (Co-PP) having propylene as the main component; polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), copolymerized polyethylene terephthalate (Co-PET), polylactic acid (PLA), polyglycolic acid (PGA), or polybutylene succinate (PBS); polyvinyl alcohol resins, polyvinyl acetate resins, acrylic resins, polystyrene resins, polyurethane resins, polyamide resins, and fluorine-based resins. Among these, polyolefin resins and polyester resins are preferably used because of their excellent processability. The combination of resins constituting the thermally bondable conjugate fiber 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 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.

[0012] The volume ratio of the low-melting point component to the high-melting point component is not particularly limited, but a high ratio of the low-melting point component improves the strength of the bonded points between the thermal adhesive conjugate fibers, making it easier to improve the strength of the nonwoven fabric, while a high ratio of the high-melting point component improves the bulkiness and flexibility of the nonwoven fabric and makes it less susceptible to changes in thickness due to load. 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.

[0013] The resin constituting the thermally adhesive conjugate fiber 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.

[0014] The fineness of the thermal adhesive composite fiber is not particularly limited, and may be, for example, 0.5 to 100 dtex, and may be appropriately selected depending on the application and required properties.

[0015] The fiber length of the thermal adhesive conjugate fiber is not particularly limited, but in order to increase the entanglement of the fibers and improve the shape retention of the web and the strength of the nonwoven fabric, it is preferably 3 mm or more, more preferably 20 mm or more, and even more preferably 30 mm or more. Furthermore, in order to make it easier for the thermal adhesive conjugate fiber to orient in the thickness direction of the nonwoven fabric and improve bulkiness and flexibility, the fiber length is preferably 200 mm or less, more preferably 120 mm or less, and even more preferably 60 mm or less.

[0016] The crimp of the thermal adhesive conjugate fiber is not particularly limited, and crimp properties such as the number of crimps, crimp rate, residual crimp rate, and crimp modulus may be appropriately selected in consideration of the bulkiness, flexibility, mechanical properties, etc. of the nonwoven fabric. The shape of the crimp is also not particularly limited, and may be appropriately selected from zigzag mechanical crimps, spiral crimps, ohmic crimps, and the like.

[0017] (Nonwoven Fabric) The nonwoven fabric of the present invention contains the above-described thermally adhesive conjugate fibers, and the intersections of the thermally adhesive conjugate fibers are thermally bonded. By thermally bonding the intersections of the thermally adhesive conjugate fibers, the nonwoven fabric has excellent mechanical properties and little fluffing.

[0018] The specific volume of the nonwoven fabric in the present invention is 100 cm ３ / g or more. This improves the flexibility of the nonwoven fabric. From this viewpoint, the specific volume of the nonwoven fabric is 105 cm ３ / g or more, and ３ The upper limit of the specific volume is not particularly limited, but considering the balance with the specific volume per unit area, it is preferably 300 cm３ / g or less, and ３ / g or less, and more preferably 200 cm ３ The specific volume of the nonwoven fabric can be controlled by the weight ratio of the heat-adhesive conjugate fiber to the heat-shrinkable fiber in the web-forming step described below, or by the temperature, air velocity, treatment time, etc. of the heat medium in the heat treatment step.

[0019] The 5% MD strength per unit basis weight of the nonwoven fabric of the present invention is 40 mN / 5cm or more. This suppresses deformation of the nonwoven fabric due to tension, etc., and achieves satisfactory processing stability. From this perspective, the 5% MD strength per unit basis weight is preferably 50 mN / 5cm or more, and more preferably 55 mN / 5cm or more. Furthermore, the upper limit of the strength at 5% elongation in the machine direction per unit basis weight of the nonwoven fabric is not particularly limited, but in consideration of the specific volume of the nonwoven fabric, it is preferably 300 mN / 5cm or less, more preferably 250 mN / 5cm or less, and even more preferably 200 mN / 5cm or less. The 5% MD strength per unit basis weight of the nonwoven fabric can be controlled by the weight ratio of the thermally adhesive conjugate fiber to the heat-shrinkable fiber in the web-forming step described below, the temperature of the heat medium in the heat treatment step, the wind speed, the treatment time, etc.

[0020] The ratio of the 5% MD strength of the nonwoven fabric of the present invention to the strength at 5% elongation in the direction perpendicular to the machine direction (hereinafter, "strength at 5% elongation in the direction perpendicular to the machine direction" may be referred to as "5% CD strength") is not particularly limited, but in order to improve the processing stability of the nonwoven fabric, it is preferably 3.5 or more, more preferably 4.0 or more, and even more preferably 4.5 or more. A larger ratio of the 5% MD strength to the 5% CD strength of the nonwoven fabric suggests that a larger proportion of the thermal adhesive conjugate fibers are oriented in the machine direction of the nonwoven fabric, and it is thought that deformation of the nonwoven fabric due to tension, etc. can be suppressed.

[0021] The maximum strength in the machine direction per unit basis weight of the nonwoven fabric (hereinafter, "maximum strength in the machine direction" may be referred to as "MD strength") is not particularly limited, but in order to make it less likely to cause fuzzing or breakage when force is applied during processing into textile products or during use, it is preferably 0.5 N / 5 cm or more, and more preferably 0.7 N / 5 cm or more.

[0022] The basis weight of the nonwoven fabric is not particularly limited, but is preferably 5 to 300 g / m ２ The thickness of the nonwoven fabric is not particularly limited, but may be 0.5 to 50 mm. The basis weight and thickness of the nonwoven fabric may be appropriately selected depending on the intended use.

[0023] The fiber density of the nonwoven fabric of the present invention is not particularly limited, but in order to increase the number of intersections between fibers and improve the strength of the nonwoven fabric, it is preferable to use a fiber density of 3 fibers / mm. ２ It is preferable that the number of fibers is 5 or more per mm. ２ More preferably, the number of fibers per mm is 8 or more. ２ In order to improve the flexibility of the nonwoven fabric, the fiber density is preferably 50 fibers / mm or more. ２ Preferably, the number of fibers is 40 or less per mm. ２ More preferably, it is 30 fibers / mm or less. ２ It is even more preferable that:

[0024] In order to obtain uniform properties in the thickness direction of the nonwoven fabric of the present invention, the fiber density ratio between the high-density region and the low-density region of the nonwoven fabric is preferably 1.4 or less, more preferably 1.3 or less, and even more preferably 1.2 or less. The lower limit of the fiber density ratio is 1.0, and the closer to 1.0 the ratio is, the more uniform the fiber density becomes. If the fiber density ratio is 1.4 or less, for example, when filtering a fluid in the thickness direction, the high-density region is less likely to clog the fluid.

[0025] 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 layer. Furthermore, the "high-density portion" and the "low-density portion" refer to the upper and lower portions of each layer divided into equal halves in the thickness direction, and the higher fiber density is referred to as the "high-density portion" and the lower fiber density is referred to as the "low-density portion" when the fiber densities are measured.

[0026] 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.

[0027] The compression work (WC) of the nonwoven fabric is not particularly limited, but is preferably 3.0 gf cm / cm ２ It is preferable that the viscosity is 4.0 gf cm / cm or more. ２ It is more preferable that the compression work load is equal to or greater than this. It is considered that a higher compression work load indicates a higher flexibility of the nonwoven fabric. The method for measuring the compression work load will be explained in detail in the Examples.

[0028] The width-cutting ratio of the nonwoven fabric is not particularly limited, but is preferably less than 5%, more preferably less than 3%. A smaller width-cutting ratio is considered to indicate that deformation of the nonwoven fabric due to tension, etc. during processing into a textile product can be suppressed and that processing stability is excellent. The method for measuring the width-cutting ratio will be described in detail in the Examples.

[0029] The nonwoven fabric of the present invention may contain fibers other than the above-described thermally adhesive conjugate fibers or heat-shrinkable fibers, as long as the effects of the present invention are not impaired. Examples of such fibers include, but are not limited to, natural fibers (such as wood fibers), regenerated fibers (such as rayon), and semi-synthetic fibers (such as acetate). When fibers other than thermally adhesive conjugate fibers or heat-shrinkable fibers are contained, the proportion of such fibers is not limited as long as the effects of the present invention are not impaired, but may be, for example, 1 to 30% by weight, and preferably 3 to 15% by weight.

[0030] The nonwoven fabric of the present invention may consist of one type of (single-layer) nonwoven fabric, or may consist of two or more types of (multi-layer) nonwoven fabrics differing in fineness, composition, density, etc. In the case of a multi-layer nonwoven fabric, for example, layers of different fineness may be laminated to produce a nonwoven fabric in which the size of the gaps formed between the fibers varies in the thickness direction of the nonwoven fabric, thereby controlling liquid permeability. The method for producing a multi-layer nonwoven fabric is not particularly limited, but an example is a method in which webs containing heat-bondable conjugate fibers and heat-shrinkable fibers differing in fineness, composition, density, etc. are overlapped and subjected to a heat bonding treatment.

[0031] Furthermore, 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 liquid permeability, liquid permeation rate, processability, etc. The method for laminating may be, but is not limited to, a method of laminating with an adhesive such as a hot melt, or a method of laminating with thermal adhesion such as a through-air method or a hot embossing method.

[0032] 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.

[0033] (Method for Producing Nonwoven Fabric) The method for producing a nonwoven fabric of the present invention includes a step of forming a web containing a mixture of thermally adhesive conjugate fibers and thermally shrinkable fibers (hereinafter sometimes referred to as the "web formation step"), and a step of heat-treating the web at an air speed of 0.5 m / s or less at a temperature higher than the heat shrinkage temperature of the heat-shrinkable fiber and the melting point of the low-melting-point component of the thermally adhesive conjugate fiber, but lower than the melting point of the high-melting-point component of the thermally adhesive conjugate fiber, thereby thermally bonding the intersections of the thermally adhesive conjugate fibers (hereinafter sometimes referred to as the "heat treatment step"). This production method can produce a nonwoven fabric that combines flexibility and processing stability. Without being bound by any particular theory, heat treatment at a temperature higher than the heat shrinkage temperature of the heat-shrinkable fiber and 0.5 m / s or less can orient the thermally adhesive conjugate fibers in the machine direction as the heat-shrinkable fiber shrinks, and can thermally bond the intersections of the thermally adhesive conjugate fibers while maintaining the bulk of the web. This is thought to result in a nonwoven fabric that has a specific specific volume and 5% MD strength, and that combines flexibility and processing stability.

[0034] (Web Forming Step) The method for forming a web containing a mixture of thermally adhesive conjugate fibers and heat-shrinkable fibers is not particularly limited, and may be a short fiber web forming method such as a carding method, air-laid method, or wet method using short fibers (staples or chopped) of the above-mentioned thermally adhesive conjugate fibers and heat-shrinkable fibers, or a long fiber web forming method such as a spunbonding method, meltblown method, or tow-spreading method, but from the viewpoint of making it easier to obtain the target specific volume, the carding method or air-laid method is preferred, and the 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 thermally adhesive conjugate fibers are not bonded.

[0035] The heat-shrinkable fiber used in the present invention is not particularly limited as long as it heat-shrinks at a temperature lower than the melting point of the high-melting point component of the thermal adhesive conjugate fiber, and examples thereof include single-component fibers, conjugate fibers such as concentric sheath-core conjugate fibers, eccentric sheath-core conjugate fibers, and side-by-side conjugate fibers. The resin constituting such heat-shrinkable fibers 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, from the viewpoint of increasing the strength of the nonwoven fabric, it is preferable that the heat-shrinkable fiber contains the same kind of component as the low-melting-point component of the thermally adhesive conjugate fiber. Specifically, when the thermally adhesive conjugate fiber is a conjugate fiber composed of PP / HDPE, it is preferable to use a single-component fiber composed of LDPE, LLDPE, or HDPE as the heat-shrinkable fiber. Furthermore, when the thermally adhesive conjugate fiber is a conjugate fiber composed of PET / HDPE, it is preferable to use a single-component fiber composed of LDPE, LLDPE, or HDPE, or a conjugate fiber composed of PP / LDPE, PP / LLDPE, or PP / HDPE as the heat-shrinkable fiber.

[0036] The cross-sectional shape of the heat-shrinkable fiber, the combination of the low-melting point component and the high-melting point component, the additives, the fiber diameter, the fiber length, the crimp, and the like can be selected arbitrarily from the same configurations as those described for the thermally adhesive composite fiber.

[0037] The weight ratio of the heat-adhesive conjugate fiber to the heat-shrinkable fiber is not particularly limited, but is preferably 99:1 to 85:15 to facilitate the production of a nonwoven fabric that combines flexibility and processing stability. If the proportion of the heat-shrinkable fiber is 1% by weight or more, the orientation effect of the heat-adhesive conjugate fiber due to the shrinkage of the heat-shrinkable fiber is more likely to be achieved, thereby improving 5% MD strength and processing stability. Furthermore, if the proportion of the heat-shrinkable fiber is 15% by weight or less, it is believed that the nonwoven fabric can be stably produced without excessive heat shrinkage due to heat treatment, and that deterioration in specific volume and texture is less likely to occur. From this perspective, the weight ratio of the heat-adhesive conjugate fiber to the heat-shrinkable fiber is more preferably 98:2 to 88:12, and even more preferably 97:3 to 90:10. In the nonwoven fabric of the present invention, the heat-shrinkable fiber does not necessarily need to retain its fibrous shape; it may shrink and melt to form a mass or film.

[0038] (Heat Treatment Step) The obtained web is then heat-treated with a heat medium at a temperature higher than the heat shrinkage temperature of the heat-shrinkable fiber, higher than the melting point of the low-melting component of the heat-adhesive conjugate fiber, and lower than the melting point of the high-melting component of the heat-adhesive conjugate fiber, and at an air speed of 0.5 m / s or less. This allows the heat-adhesive conjugate fibers to be oriented in the flow direction of the nonwoven fabric as the heat-shrinkable fiber shrinks, while thermally bonding the intersections of the heat-adhesive conjugate fibers. The air speed of the heat medium is preferably 0.3 m / s or less, more preferably 0.1 m / s or less, and even more preferably less than 0.1 m / s, in order to improve the flexibility of the nonwoven fabric. The temperature of the heat transfer medium may be adjusted as appropriate so that the specific volume and 5% MD strength fall within specific ranges. Preferably, the temperature is at least 5°C higher than the heat shrinkage temperature of the heat-shrinkable fiber and at least 5°C lower than the melting point of the high-melting component of the heat-adhesive composite fiber, and more preferably, the temperature is at least 10°C higher than the heat shrinkage temperature of the heat-shrinkable fiber and at least 10°C lower than the melting point of the high-melting component of the heat-adhesive composite fiber.

[0039] Here, the heat shrinkage temperature of the heat shrinkable fiber in the present invention means the melting temperature of the component with the highest melting point when a single-component fiber, a concentric sheath-core composite fiber, or an eccentric sheath-core composite fiber is used as the heat shrinkable fiber.

[0040] The heat medium used in the heat treatment step of the present invention is not particularly limited, and examples include hot air or superheated steam. However, from the viewpoint of the mechanical properties and productivity of the nonwoven fabric, it is preferable to use superheated steam. Examples of the heat treatment step include a method in which the web is introduced into an oven filled with hot air or superheated steam using a conveyor or the like, or a method in which a heat medium such as hot air or superheated steam is blown onto the web to obtain a nonwoven fabric. Examples of the heat medium include a method in which the heat medium is blown onto at least one of the top and bottom surfaces of the web, or a method in which the web is introduced into a (non-weathered) oven filled with a heat medium. The above heat treatment may be carried out under atmospheric pressure, low pressure, or vacuum, but is preferably carried out under atmospheric pressure from the viewpoint of simplifying the equipment. Furthermore, the heat treatment step is preferably a method in which the web is introduced into an oven using a conveyor or the like to continuously obtain a nonwoven fabric.

[0041] The treatment time of the heat treatment step is not particularly limited, but is preferably 60 seconds or less, and more preferably 30 seconds or less. If the treatment time is 60 seconds or less, it is possible to produce a nonwoven fabric with satisfactory productivity.

[0042] The nonwoven fabric of the present invention can be used in a wide variety of 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; 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.

[0043] 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.

[0044] <Fineness of Thermally Adhesive Conjugate Fiber> The fineness of the thermally adhesive conjugate fiber was measured in accordance with JIS L 1015.

[0045] <Fiber Density of Nonwoven Fabric> (1) Method of Preparing Observation Samples A nonwoven fabric cut into a size of 1 cm (machine direction of the nonwoven fabric) x 3 cm (direction perpendicular to the machine direction; CD) was impregnated with a photocurable resin (UV-LED Resin Hoshi no Shizuku [Soft] manufactured by PADICO Corporation (Hoshi no Shizuku is a registered trademark)) 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 fiber layer 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, the fiber layer was divided in half in the thickness direction, and the upper and lower portions were selected (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 fiber layer, the portion with a higher fiber density was designated as a high-density portion, and the portion with a lower fiber density was designated as a low-density portion. From the fiber densities of each portion obtained, the fiber density of the fiber layer was calculated by the following formula. The fiber density of each portion was calculated as the average value of measurements taken at two locations. Fiber density (threads / mm ２ ) = (fiber density of high density part (fibers / mm ２ ) + fiber density of low density area (fibers / mm ２ ))÷2

[0046] <Fiber density ratio> From the fiber density in each region obtained by the above method, the fiber density ratio was calculated by the following formula: Fiber density ratio = fiber density of high-density region (fibers / mm ２ ) ÷ fiber density of low density area (fibers / mm ２ )

[0047] <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 calculated as the average value of two measurements.

[0048] <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 when a pressure of 68.6 Pa was applied for 5 seconds was taken as the thickness of the nonwoven fabric. The thickness was measured at 5 locations and the average value was taken as the thickness.

[0049] <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

[0050] <MD strength and 5% MD strength per unit basis weight> A sample cut to a size of 50 mm in the CD direction x 150 mm in the MD direction was pulled using an autograph (AGX-J, manufactured by Shimadzu Corporation) at a chuck distance of 100 mm and a pulling speed of 100 mm / min. The maximum strength when pulled was defined as the MD strength (N / 5cm) of the nonwoven fabric, and the strength at 5% elongation was defined as the 5% MD strength (N / 5cm). The MD strength and 5% MD strength were taken as the average values ​​of three measurements. Next, the maximum MD strength and 5% MD strength per unit basis weight were calculated using the following formula: MD strength per unit basis weight (N / 5cm) = MD strength (N / 5cm) ÷ basis weight (g / m ２ ) 5% MD strength per unit basis weight (mN / 5cm) = 5% MD strength (N / 5cm) ÷ basis weight (g / m ２ ) x 1000

[0051] <CD Strength and 5% CD Strength per Unit Basis Weight> A sample measuring 50 mm in the MD direction and 150 mm in the CD direction was cut out and pulled using an Autograph (AGX-J (Autograph is a registered trademark) manufactured by Shimadzu Corporation) at a chuck distance of 100 mm and a pulling speed of 100 mm / min. The maximum strength when pulled was defined as the CD strength (N / 5 cm) of the nonwoven fabric, and the strength at 5% elongation was defined as the 5% CD strength (N / 5 cm). The CD strength and 5% CD strength were taken as the average values ​​of three measurements. Next, the maximum CD strength and 5% CD strength per unit basis weight were calculated using the following formula: CD strength per unit basis weight (N / 5 cm) = CD strength (N / 5 cm) ÷ basis weight (g / m ２ ) 5% CD strength per unit basis weight (mN / 50 mm) = 5% CD strength (N / 5 cm) ÷ basis weight (g / m ２ ) x 1000

[0052] <Ratio of 5% MD strength to 5% CD strength> The ratio of 5% MD strength to 5% CD strength was calculated from the 5% MD strength and 5% CD strength obtained by the above measurement method using the following formula: Ratio of 5% MD strength to 5% CD strength = 5% MD strength (N / 5 cm) ÷ 5% CD strength (N / 5 cm)

[0053] <Compression Work and Flexibility per Unit Basis Weight> Using a handy compressor (KES-G5, manufactured by Kato Tech Co., Ltd.), the compression work (WC) 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 (gf cm / cm) was calculated by numerical processing based on the following formula (1): ２ The compression work was calculated as the average value of 10 measurements. ｍ is 50 gf / cm ２ Thickness under load (4.9 kPa), T ０ is 0.5 gf / cm ２ (49.0 Pa) indicates the thickness when loaded. Next, the compression work load per unit basis weight was calculated using the following formula: Compression work load per unit basis weight (gf cm / cm ２ ) = compression work (gf cm / cm ２ ) ÷ basis weight (g / m ２ The greater the compression work load per unit basis weight, the more flexible the fabric is. In the present invention, the flexibility was evaluated according to the following criteria: Compression work load per unit basis weight (gf·cm / cm ２ ) is 0.16 or more...◎ Compression work per unit weight (gf cm / cm ２ ) is 0.12 or more and less than 0.16... 〇 Compression work per unit basis weight (gf cm / cm ２ ) is less than 0.12... ×

[0054] <Width-cut ratio> A sample cut to a size of 50 mm in the CD direction and 150 mm in the MD direction was pulled using an Autograph (manufactured by Shimadzu Corporation, AGX-J (Autograph is a registered trademark)) at a chuck distance of 100 mm and a pulling speed of 10 mm / min, with a tensile load per unit basis weight of 0.06 N (for example, when the basis weight of the nonwoven fabric is 25 g / m ２ In the case of １ The width (mm) was measured, and the width reduction rate was calculated using the following formula: Width reduction rate (%) = (1 - L １ (mm) ÷ 50 (mm) × 100 The smaller the width insertion amount, the more excellent the processing stability is, and in the present invention, the processing stability was evaluated according to the following criteria: Width insertion rate (%) is less than 3%: ◎ Width insertion rate (%) is 3% or more but less than 5%: ○ Width insertion rate (%) is 5% or more: ×

[0055] [Example 1] A thermally adhesive composite fiber 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 ３A concentric sheath-core composite fiber (fineness 1.7 dtex, fiber length 45 mm) was prepared, in which a polypropylene core (melt flow rate (230°C, load 21.18 N): 16 g / 10 min, melting point 130°C) was used as the core and a high-density polyethylene (density: 0.956 g / cm) core was used as the sheath. ３ A concentric sheath-core type thermal adhesive composite fiber (fineness 1.1 dtex, fiber length 38 mm) was prepared, which had a volume ratio of 50 / 50 and a melt flow rate (190°C, load 21.18 N): 16 g / 10 min, melting point 130°C). The thermal shrinkage temperature of this heat-shrinkable fiber was 165°C. The thermal adhesive composite fiber and the heat-shrinkable fiber were mixed in a weight ratio of 97:3, and a web was produced by carding. The resulting web was then introduced into an oven filled with superheated steam at 180°C for 10 seconds to obtain a nonwoven fabric. The wind speed of the superheated steam was 0.1 m / s or less.

[0056] [Examples 2 to 4, Comparative Example 1] Nonwoven fabrics were obtained in the same manner as in Example 2, except that the weight ratio of the thermal adhesive conjugate fiber to the heat-shrinkable fiber was changed to 95:5 (Example 2), 93:7 (Example 3), 90:10 (Example 4), and 100:0 (Comparative Example 1).

[0057] Comparative Example 2 An attempt was made to produce a nonwoven fabric in the same manner as in Example 2, except that the weight ratio of the thermal adhesive conjugate fiber to the heat-shrinkable fiber was changed to 80:20. However, a nonwoven fabric in good condition could not be obtained, possibly because the heat shrinkage was too large.

[0058] Comparative Example 3, Example 5 Nonwoven fabrics were obtained in the same manner as in Example 2, except that the temperature of the superheated steam was changed to 160° C. (Comparative Example 3) and 200° C. (Example 5).

[0059] Comparative Example 4 A 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.

[0060] Examples 6 and 7 Nonwoven fabrics were obtained in the same manner as in Example 2, except that the fineness of the heat-shrinkable fiber was changed to 2.2 dtex (Example 6) and 3.3 dtex (Example 7).

[0061] 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 was changed to 3.3 dtex and the volume ratio of the core component to the sheath component was changed to 60 / 40.

[0062] Example 9 A nonwoven fabric was obtained in the same manner as in Example 2, except that the fineness of the thermal adhesive conjugate fiber was changed to 4.4 dtex.

[0063] The physical properties of the nonwoven fabrics obtained in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1, and the physical properties of the nonwoven fabrics obtained in Examples 5 to 9 and Comparative Example 4 are shown in Table 2.

[0064]

[0065]

[0066] In comparison with Examples 1 to 4 and Comparative Example 1, the nonwoven fabric of Comparative Example 1, which was composed solely of thermally bondable composite fibers, had a high specific volume and excellent flexibility, but had a low 5% MD strength per basis weight and poor processing stability. In contrast, the nonwoven fabrics of Examples 1 to 4, which contained heat-shrinkable fibers and were heat-treated at a temperature higher than the heat shrinkage temperature of the heat-shrinkable fibers and the melting point of the low-melting-point component of the thermally bondable composite fibers but lower than the melting point of the high-melting-point component of the thermally bondable composite fibers, and at an air speed of 0.5 m / s or less, had a high specific volume and excellent flexibility, as well as a high 5% MD strength and excellent processing stability. Similar trends were observed in the nonwoven fabrics of Examples 6 to 9, which were obtained by varying the fineness of the thermally bondable composite fibers and heat-shrinkable fibers. On the other hand, the nonwoven fabric of Comparative Example 3, which was heat-treated at a temperature lower than the heat shrinkage temperature of the heat-shrinkable fibers, had a high specific volume and excellent flexibility, but had a low 5% MD strength per basis weight and poor processing stability. This is thought to be because the heat treatment temperature was low, which resulted in insufficient shrinkage of the heat-shrinkable fibers and prevented the orientation of the thermal adhesive composite fibers in the flow direction of the nonwoven fabric. Furthermore, the nonwoven fabric of Comparative Example 4, which was heat-treated under conditions where the air speed of the heat medium exceeded 0.5 m / s, had a high 5% MD strength per unit area weight and excellent processing stability, but had a low specific volume and poor flexibility.

[0067] The nonwoven fabric of the present invention has both flexibility and processing stability, and therefore can be used in a variety of 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; 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; general medical materials, bedding, and nursing care products.

Claims

1. A nonwoven fabric containing thermally bondable composite fibers whose intersections are thermally bonded, and the specific volume of the nonwoven fabric is 100 cm ３ / g or more, and the strength at 5% elongation in the machine direction per unit basis weight is 40 mN / 5 cm or more.

2. The nonwoven fabric according to claim 1, wherein the ratio of the strength at 5% elongation in the machine direction to the strength at 5% elongation in the direction perpendicular to the machine direction is 3.5 or more.

3. The nonwoven fabric according to [1] or claim 2, wherein the fiber density ratio between the high density area and the low density area in the nonwoven fabric is 1.4 or less.

4. A method for producing a nonwoven fabric, comprising the steps of forming a web containing a mixture of heat-adhesive composite fibers and heat-shrinkable fibers, and heat-treating the web with a heat medium that satisfies the following conditions (1) and (2): (1) a temperature higher than the heat-shrinkage temperature of the heat-shrinkable fibers, a temperature higher than the melting point of the low-melting component of the heat-adhesive composite fibers, and a temperature lower than the high-melting component of the heat-adhesive composite fibers; and (2) a wind speed of 0.5 m / s or less.

5. The method for producing a nonwoven fabric according to claim 4, wherein the weight ratio of the thermal adhesive composite fiber to the heat shrinkable fiber is 99:1 to 85:

15.

6. The nonwoven fabric according to claim 4 or 5, wherein the heat medium used in the heat treatment step is superheated steam.

7. A method for producing a nonwoven fabric according to claim 4 or 5, wherein the high melting point component of the thermally adhesive composite fiber is a polyester resin, the low melting point component is a polyolefin resin, and the resin constituting the heat-shrinkable fiber is a polyolefin resin having a melting point lower than that of the polyester resin.

8. An article using the nonwoven fabric according to claim 1.

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