Heat-fusible composite fiber and nonwoven fabric using same

Abstract

The present invention provides: a heat-fusible composite fiber allowing for a reduction in the consumption of fossil resources and enabling the production of a bulky nonwoven fabric that is resistant to shrinkage during processing; and a nonwoven fabric using the same.　The heat-fusible composite fiber is formed from a polylactic acid resin as a core component and a polyethylene resin as a sheath component, wherein the biomass-derived carbon content of the sheath component is 40% or more, and the fiber length heat shrinkage when applying a heat treatment at 130°C for 30 min is 1% or less.

Description

Heat-fusible composite fibers and nonwoven fabrics using the same

[0001] This invention relates to a heat-fusible composite fiber containing biomass-derived components and a nonwoven fabric obtained using the same.

[0002] Conventionally, heat-fusible composite fibers, which can be formed by heat fusion using the thermal energy of hot air or heated rolls, are widely used in sanitary materials such as diapers, napkins, and pads, as well as in household goods and industrial materials such as filters, because it is easy to obtain nonwoven fabrics with excellent bulkiness and flexibility.

[0003] Polyolefins, which have excellent mechanical strength, chemical stability, and low cost, are used as raw materials for such heat-fusible composite fibers. However, in recent years, with the growing demand for the creation of a circular economy, there is a desire to move away from fossil resources in the materials field, just as there is for energy, and the use of biomass-derived materials is attracting attention.

[0004] Biomass is an organic compound produced through photosynthesis from carbon dioxide and water (see, for example, Patent Documents 1 and 2). By utilizing such biomass-derived materials as starting materials, the amount of fossil resources used can be reduced. Alternatively, if biomass-derived materials such as polylactic acid are used as raw materials, even if they are incinerated after use and decomposed into carbon dioxide and water, these amounts will be equal to the amount of carbon dioxide and water before they were absorbed by plants through photosynthesis, making it possible to achieve carbon neutrality.

[0005] For example, Patent Document 3 presents a composite fiber using polyolefin and polylactic acid derived from biomass.

[0006] On the other hand, the method described in Patent Document 3 has the problem that when processed into a nonwoven fabric, dimensional deformation and a decrease in bulk occur due to fiber shrinkage, making it unsuitable for sanitary materials that require good flexibility and texture. Therefore, there is a need for composite fibers that use biomass raw materials without compromising physical properties.

[0007] Japanese Patent Publication No. 2017-214662, Japanese Patent Publication No. 2009-091694, Japanese Patent Publication No. 2010-065342

[0008] This invention was made against the backdrop of the above-mentioned prior art, and its purpose is to provide a heat-fusible composite fiber that can reduce the consumption of fossil resources and produce a bulky nonwoven fabric that does not shrink easily during processing, and a nonwoven fabric using the same.

[0009] The inventors of this invention conducted extensive research to solve the above problems. As a result, they discovered that a fiber having the following structure can solve the aforementioned problems, and thus completed the present invention.

[0010] In other words, the present invention has the following configuration: [1] A heat-fusible composite fiber comprising a core component of polylactic acid resin and a sheath component of polyethylene resin, wherein the biomass-derived carbon content of the sheath component is 40% or more, and the heat shrinkage rate of the fiber length calculated by the following measurement method is 1% or less. Heat shrinkage rate of fiber length (%) = {(10 (mm) - h1 (mm)) / 10 (mm)} × 100 h1 is the length after 50 fibers with a chuck distance of 10 mm are heated to 130°C at a heating rate of 5°C / min under a constant load of 0.02 mN / dtex, held for 30 minutes, and allowed to cool to 30°C. [2] The heat-fusible composite fiber according to [1], wherein the fiber length of the heat-fusible composite fiber is 5 to 150 mm. [3] The heat-fusible composite fiber according to [1] or [2], wherein the fineness of the heat-fusible composite fiber is 1.0 to 8.0 dtex. [4] The heat-fusible composite fiber according to any one of [1] to [3], wherein the heat shrinkage rate of the web formed by the carding method, calculated by the following measurement method, is 7% or less. Heat shrinkage rate of the web = {(25 (cm) - h2 (cm)) / 25 (cm)} × 100 (%) h2 is 25 cm long x 25 cm wide with a basis weight of 200 g / m ２ The web is the shorter of the lengthwise or widthwise after heat treatment at 145°C for 5 minutes. [5] A nonwoven fabric containing heat-fusible composite fibers as described in any of [1] to [4]. [6] The specific volume of the nonwoven fabric is 45 cm³. ３ [5] Nonwoven fabric having a tensile strength of 1.0 N / {50 mm·(g / m) or more. [7] The tensile strength per basis weight of the nonwoven fabric in the direction of machine passage is 1.0 N / {50 mm·(g / m ２ )} or the nonwoven fabric described in [5] or [6].

[0011] The composite fibers of the present invention can reduce the consumption of fossil resources by using biomass-derived raw materials, and can also produce bulky nonwoven fabrics that are less prone to shrinkage during processing.

[0012] The heat-fusible composite fiber of the present invention is characterized in that the core component is made of polylactic acid resin and the sheath component is made of polyethylene resin, the biomass-derived carbon content of the sheath component is 40% or more, and the heat shrinkage rate of the fiber length when heat-treated at 130°C for 30 minutes is 1% or less.

[0013] First, let's discuss biomass-derived carbon. In this invention, biomass-derived carbon refers to carbon that was previously present in the atmosphere as carbon dioxide, which is incorporated into plants through carbon assimilation, and is present in polyolefins synthesized using this as a raw material. Carbon dioxide in the atmosphere contains １４ Because it contains a certain percentage of carbon (107 pMC (percent modern carbon)), it is useful for plants that take in carbon dioxide from the atmosphere to grow, such as corn. １４ It is also known that the C content is approximately 107 pMC. １４ Carbon dioxide (C) has a half-life of 5,370 years and returns to nitrogen atoms, and it takes 226,000 years for it to completely decay. Therefore, in fossil fuels such as coal, oil, and natural gas, which are thought to have been absorbed and fixed by plants and other organisms for more than 226,000 years, １４ It is known that it contains almost no carbon. Therefore, the total carbon atoms in the resin are １４ By measuring the proportion of C, the biomass-derived carbon content can be calculated. The method for calculating the biomass-derived carbon content in the resin in this invention will be described in detail in the examples below.

[0014] Examples of polylactic acid resins constituting the core component in the present invention include poly-D-lactic acid, poly-L-lactic acid, poly-DL-lactic acid which is a copolymer of poly-D-lactic acid and poly-L-lactic acid, a mixture of poly-D-lactic acid and poly-L-lactic acid (stereocomplex), a copolymer of poly-D-lactic acid and hydroxycarboxylic acid, a copolymer of poly-L-lactic acid and hydroxycarboxylic acid, a copolymer of poly-D-lactic acid or poly-L-lactic acid and aliphatic dicarboxylic acid and aliphatic diol, or a blend thereof.

[0015] Among these, it is preferable that the L / D or D / L ratio, which is the molar ratio of L-lactic acid to D-lactic acid when polymerizing lactide as a raw material, is 90 / 10 or higher, and more preferably 95 / 5 or higher. A higher L / D or D / L ratio results in better crystallinity, leading to an increased melting point and improved processability, hence the preference for 90 / 10, and more preferably 95 / 5 or higher.

[0016] The polylactic acid resin that constitutes the core component in this invention is generally made from biomass and can be said to be a material that contributes to the conservation of fossil resources.

[0017] The melt mass flow rate (hereinafter abbreviated as MFR) of the polylactic acid resin that can be suitably used is not particularly limited, but it is preferably 5 to 40 g / 10 min, and more preferably 10 to 20 g / 10 min, at a temperature of 190°C and a load of 21.18 N. An MFR of 5 to 40 g / 10 min or higher is preferred because it provides stable operability. Physical properties other than the above MFR, such as the Q value (weight-average molecular weight / number-average molecular weight), Rockwell hardness, and number of branched methyl chains, are not particularly limited as long as they satisfy the requirements of the present invention.

[0018] The polyethylene resin in the present invention is not particularly limited, and examples include high-density polyethylene, linear low-density polyethylene, low-density polyethylene, copolymers of ethylene and other components (e.g., α-olefins), or mixtures thereof. However, from the viewpoint of suppressing the phenomenon in which polyethylene resins exposed on the fiber surface fuse together without completely cooling and solidifying during spinning, it is preferable that the resin be composed solely of high-density polyethylene.

[0019] The sheath component is not particularly limited as long as it contains polyethylene resin, but preferably contains 80% by mass or more of polyethylene resin, and more preferably contains 90% by mass or more of polyethylene resin. Additives such as antioxidants, light stabilizers, ultraviolet absorbers, neutralizing agents, nucleating agents, epoxy stabilizers, lubricants, antibacterial agents, flame retardants, antistatic agents, pigments, or plasticizers may be added as appropriate and as needed, within the limits that do not hinder the effects of the present invention.

[0020] In the present invention, the biomass-derived carbon content of the sheath component must be 40% or more, preferably 60% or more, more preferably 80% or more, and particularly preferably 100%. A biomass-derived carbon content of 40% or more in the sheath component is preferable because it is expected to reduce the consumption of fossil resources. Such a sheath component can be obtained by using a biomass-derived polyethylene resin, as described later, and adjusting it so that the biomass-derived carbon content of the sheath component is 40% or more. Specifically, a biomass-derived polyethylene resin may be used in which the polymerization ratio of biomass-derived ethylene and fossil resource-derived ethylene is adjusted, or the blend ratio of biomass-derived polyethylene resin and polyethylene resin consisting only of fossil resource-derived polyethylene resin may be adjusted.

[0021] In the present invention, the biomass-derived polyethylene resin refers to a polyethylene resin with a biomass-derived carbon content of 40% or more. To reduce the consumption of fossil resources, the biomass-derived carbon content is preferably 90% or more, and more preferably 94% or more. Such a biomass-derived polyethylene resin may be a polymer consisting only of biomass-derived monomers, or a polymer of biomass-derived monomers and fossil resource-derived monomers. Examples include a polymer of biomass-derived ethylene, a copolymer of biomass-derived ethylene and biomass-derived α-olefins (propylene, butylene, hexene, octene, etc.), a copolymer of biomass-derived ethylene and fossil resource-derived ethylene, a copolymer of biomass-derived ethylene and fossil resource-derived α-olefins, or a copolymer of biomass-derived α-olefins and fossil resource-derived ethylene. In particular, from the viewpoint of suppressing the adhesion of fibers during the molding of composite fibers, the biomass-derived polyethylene resin is preferably a polymer of biomass-derived ethylene or a polymer of biomass-derived ethylene and fossil resource-derived ethylene.

[0022] The biomass-derived polyethylene resin is not particularly limited, and any resin obtained by conventionally known methods may be used. For example, it can be produced by fermenting starch or sugar obtained from corn, sugarcane, or sweet potato with microorganisms to produce bioethanol, then dehydrating it to produce biomass-derived ethylene, and finally polymerizing it.

[0023] The polyethylene resin MFR that can be suitably used is not particularly limited, but it is preferably 10 to 40 g / 10 min, more preferably 16 to 20 g / 10 min, and even more preferably 17 to 19 g / 10 min at a temperature of 190°C and a load of 21.18 N. An MFR of 10 to 40 g / 10 min or more is preferable because it provides stable operability. Other physical properties besides the MFR, such as the Q value (weight-average molecular weight / number-average molecular weight), Rockwell hardness, and number of branched methyl chains, are not particularly limited as long as they satisfy the requirements of the present invention.

[0024] The biomass-derived carbon content of the heat-fusible composite fiber in the present invention is not particularly limited, but is preferably 50% or more, more preferably 60% or more, even more preferably 70%, and particularly preferably 90% or more. A biomass-derived carbon content of 50% or more in the composite fiber is preferable because it is expected to have the effect of reducing the consumption of fossil resources.

[0025] While there are no particular restrictions on the composition ratio when combining the core component and the sheath component, it is preferable that the core component / sheath component ratio be 20 / 80 to 80 / 20 (by weight), and more preferably 40 / 60 to 70 / 30 (by weight). This range of composition ratio is preferable because it tends to result in an excellent balance of strength, bulkiness, and processability of the nonwoven fabric.

[0026] The fineness of the heat-fusible composite fiber in the present invention is not particularly limited, but is preferably 1.0 to 8.0 dtex, more preferably 1.5 to 6.0 dtex, and even more preferably 2.0 to 4.4 dtex. A fineness of 1.0 dtex or higher is preferable because it makes it easier to obtain a nonwoven fabric with excellent bulkiness, and a fineness of 8.0 dtex or lower is preferable because it makes it easier to obtain a nonwoven fabric with excellent flexibility. By setting the fineness within this range, it is possible to achieve both bulkiness and flexibility.

[0027] The tensile strength of the heat-fusible composite fiber is not particularly limited, but for composite fibers used in absorbent articles, for example, it is preferably 1.0 cN / dtex or higher, and more preferably 1.5 cN / dtex or higher. If the tensile strength of the composite fiber is 1.0 cN / dtex or higher, it is possible to obtain a nonwoven fabric with sufficient strength. Also, although not particularly limited, it is preferably 4.0 cN / dtex or lower. The elongation of the heat-fusible composite fiber is not particularly limited, but it is preferably 30 to 170%, and more preferably 50 to 150%. If the elongation of the heat-fusible composite fiber is 30% or higher, it is preferable because it can improve the flexibility and texture of the nonwoven fabric, and if it is 170% or lower, the rigidity of the heat-fusible composite fiber increases, and it is possible to improve the bulkiness of the nonwoven fabric.

[0028] Also, the crimp of the heat-sealable composite fiber is not particularly limited, and the presence or absence of crimp, the number of crimps, the crimp ratio, the residual crimp ratio, the crimp elastic modulus, etc. can be appropriately selected in consideration of the web formation method, the specifications of the web formation equipment, the productivity of the non-woven fabric, and the required physical properties. Also, the shape of the crimp is not particularly limited, and a zigzag mechanical crimp, a three-dimensional crimp such as a spiral shape or an ohm shape, etc. can be appropriately selected. Furthermore, the crimp may be apparent or latent in the heat-sealable composite fiber.

[0029] The fiber length of the heat-sealable composite fiber in the present invention is not particularly limited, but is preferably 5 to 150 mm, and more preferably 30 to 64 mm. Within such a range, it becomes easy to obtain a web excellent in fiber opening property and texture in the web formation step by the card method or the like, and a non-woven fabric having uniform physical properties can be obtained, which is preferable.

[0030] The heat shrinkage rate of the fiber length in the heat-sealable composite fiber of the present invention is 1% or less. By setting the heat shrinkage of the fiber length to 1% or less, it is possible to suppress the decrease in specific volume during heat treatment and the difficulty of shrinkage during non-woven fabric processing during the production of the non-woven fabric. From such a viewpoint, the heat shrinkage rate of the fiber length is preferably 0% or less, and more preferably -2% or less. Also, the lower limit value of the heat shrinkage rate of the fiber length is not particularly limited, but in order to obtain fibers with sufficient strength, it is preferably -10% or more, and more preferably -7% or more. The measurement method of the heat shrinkage rate of the fiber length will be described in detail in the examples.

[0031] The heat shrinkage rate of the web in the heat-sealable composite fiber of the present invention is not particularly limited, but in order to obtain a non-woven fabric excellent in bulkiness and difficulty of shrinkage during processing, it is preferably 7% or less, and more preferably 4% or less. Also, the lower limit value of the heat shrinkage rate of the web is not particularly limited, but in order to obtain a non-woven fabric that is difficult to be crushed in the thickness direction, it is preferably -2% or more. The measurement method of the heat shrinkage rate of the web will be described in detail in the examples.

[0032] The method for producing the heat-sealable composite fiber of the present invention is not particularly limited, and any known method for producing a heat-sealable composite fiber may be adopted. However, as a method for producing the heat-sealable composite fiber with high productivity and high yield, the method described below can be exemplified.

[0033] The polylactic acid resin serving as a raw material for the composite fiber of the present invention is arranged as a core component, and the polyethylene-based resin is arranged as a sheath component, and an unstretched fiber in which the core component and the sheath component are compositeized by melt spinning is obtained.

[0034] The temperature conditions during melt spinning are not particularly limited, but the spinning temperature is preferably 200 to 300°C, more preferably 220 to 280°C. If the spinning temperature is 200°C or higher, an unstretched fiber with fewer thread breakages during spinning and an elongation after spinning that is easy to retain can be obtained, and it is preferable because it is easy to make the fiber fineness finer. If it is 220°C or higher, these effects become more prominent, so it is preferable. On the other hand, in order to make the polylactic acid resin less likely to thermally decompose, 300°C or lower is preferable.

[0035] Also, the spinning speed is not particularly limited, but it is preferably 300 to 1500 m / min, more preferably 400 to 1000 m / min. If the spinning speed is 300 m / min or higher, it is preferable in that the single-hole discharge amount when obtaining an unstretched fiber with an arbitrary spinning fineness is increased, and satisfactory productivity can be obtained.

[0036] The unstretched fiber obtained under the above conditions is subjected to a stretching treatment in a stretching step. The stretching temperature (the surface temperature of the hot roll) is not particularly limited, but it is preferably 10 to 60°C higher than the glass transition temperature of the polylactic acid resin constituting the core component and lower than the melting point of the polyethylene-based resin constituting the sheath component. More preferably, it is 20 to 50°C higher than the glass transition temperature of the polylactic acid resin and 5°C or lower than the melting point of the polyethylene-based resin.

[0037] The stretch ratio is not particularly limited, but is preferably 1.5 to 7 times, and more preferably 2 to 5 times. A stretch ratio of 1.5 to 7 times is preferable because it provides a good balance between the fineness of the heat-fusible composite fibers and rigidity, and makes it easier to obtain a nonwoven fabric with excellent bulkiness and flexibility. A stretch ratio of 2 to 5 times is more preferable because it suppresses shrinkage due to residual elongation and residual stress, making it easier to obtain a bulky nonwoven fabric.

[0038] Mechanical crimping may be applied to the drawn fibers obtained in the drawing process using a crimper or the like. The number of crimps applied in the crimping process is not particularly limited, but is preferably 10 to 25 crimps / 2.54 cm, and can be adjusted by appropriately changing, for example, the stuffing box pressure in a push-type crimper.

[0039] The stretched fibers obtained in the stretching process may be heat-treated. By heat-treating after stretching, residual stress on the polylactic acid resin, which is the core component of the heat-fusible composite fiber, can be relieved, and thermal shrinkage during nonwoven fabric processing can be suppressed. The heat treatment temperature is not particularly limited, but it is preferable to perform the treatment at a temperature of 30 to 70°C or higher, which is the glass transition temperature of the polylactic acid resin, and below the melting point of the polyethylene resin.

[0040] When a carding process is used to process the heat-fusible composite fibers of the present invention into a nonwoven fabric, it is necessary to cut the heat-fusible composite fibers to a desired length in order to pass them through the carding machine. The length to which the heat-fusible composite fibers are cut is preferably 5 to 150 mm, and more preferably 30 to 64 mm, from the viewpoint of fineness and passability through the carding machine.

[0041] Furthermore, the heat-fusible composite fibers of the present invention may have their surfaces treated with various fiber treatment agents, thereby imparting functions such as hydrophilicity, water repellency, antistatic properties, surface smoothness, and abrasion resistance. Examples of the fiber treatment agent application process include applying the fiber treatment agent with a kiss roll when the undrawn fibers are taken up, or applying it during and / or after drawing using methods such as the touch roll method, immersion method, or spray method.

[0042] Since the non-woven fabric of the present invention contains the above-described heat-fusible composite fibers, it suppresses the consumption of fossil resources and is excellent in bulkiness and difficult to shrink during non-woven fabric processing.

[0043] The biomass-derived carbon content rate of the non-woven fabric in the present invention is not particularly limited, but from the viewpoint of suppressing the consumption of fossil resources, it is preferably 50% or more, and more preferably 80% or more. In order to obtain such a non-woven fabric, only composite fibers having a biomass-derived carbon content rate of 50% or more may be used, or they may be mixed with other fibers so that the total biomass-derived carbon content rate is 50% or more. Examples of other fibers include natural fibers (such as wood fibers), regenerated fibers (such as rayon), semi-synthetic fibers (such as acetate), chemical fibers, synthetic fibers (such as polyester, acrylic, nylon, vinyl chloride), and the like. The mixing ratio of fibers other than such heat-fusible composite fibers is not limited as long as the effects of the present invention are not inhibited, but for example, it can be 1 to 50%.

[0044] The basis weight of the non-woven fabric is not particularly limited, but particularly when used as a non-woven fabric for sanitary materials, it is preferably 15 to 40 g / m ２ and more preferably 18 to 30 g / m ２ If the basis weight is 15 g / m ２ or more, it is preferable because it can maintain the texture and cushioning property and suppress liquid return. If it is 40 g / m ２ or less, it is preferable because it can maintain surface smoothness, air permeability, and liquid permeability.

[0045] The specific volume of the non-woven fabric in the present invention is not particularly limited, but particularly when used as a non-woven fabric for sanitary materials, it is preferably 45 to 100 cm ３ / g, and more preferably 60 to 80 cm ３ / g. The specific volume is a parameter used as an index of bulkiness, and the larger the specific volume, the more it can be evaluated that the non-woven fabric is bulky. If the specific volume is 45 cm ３ / g or more, a bulky height suitable for use as a sanitary material can be obtained, and if it is 100 cm ３A value of less than / g is preferable because it increases the strength of the nonwoven fabric, prevents it from becoming too thick, and results in excellent processability for use as a sanitary material.

[0046] The tensile strength per basis weight of the nonwoven fabric in the machine passage direction in this invention is not particularly limited, but is 1.0 N / {50 mm·(g / m ２ Preferably, it is 1.2 N / {50 mm·(g / m ２ It is more preferable that the value be 1.6 N / {50 mm·(g / m ２ It is even more preferable that the tensile strength per basis weight be 1.0 N / {50 mm·(g / m)} or greater. ２ )} or higher is preferable because it results in excellent processability for sanitary materials.

[0047] The nonwoven fabric of the present invention may consist of one type (single layer) of nonwoven fabric, or it may be made by laminating two or more types of nonwoven fabrics that differ in the fineness, composition, or density of the heat-fusible composite fibers used. When two or more types of nonwoven fabrics are laminated, for example, by laminating nonwoven fabrics with different finenesses of heat-fusible composite fibers, the size of the gaps formed between the fibers changes in the thickness direction of the nonwoven fabric, thereby controlling the permeability, flow rate, and surface texture. Alternatively, for example, by laminating nonwoven fabrics with different compositions of heat-fusible composite fibers, the hydrophilicity and hydrophobicity of the nonwoven fabric change in the thickness direction, thereby controlling the permeability and flow rate.

[0048] Furthermore, the nonwoven fabric of the present invention is not particularly limited, but may be laminated and integrated with other nonwoven fabrics, films, or sheets such as through-air nonwoven fabrics, airlaid nonwoven fabrics, spunbond nonwoven fabrics, meltblown nonwoven fabrics, spunlace nonwoven fabrics, needle-punched nonwoven fabrics, films, meshes, or nets. By laminating and integrating, it is possible to control liquid permeability, liquid permeability, liquid return properties, etc. There are no particular limitations on the method of lamination and integration, but examples include lamination and integration using adhesives such as hot melt, and lamination and integration using thermal bonding such as through-air or thermal embossing.

[0049] The nonwoven fabric may be subjected to shaping, perforation, antistatic treatment, water-repellent treatment, hydrophilic treatment, antibacterial treatment, ultraviolet absorption treatment, near-infrared absorption treatment, or electret treatment, as appropriate, to the extent that it does not impair the effects of the present invention.

[0050] The method for manufacturing the nonwoven fabric is not particularly limited, but an example is a method in which a web containing the heat-fusible composite fibers described above is formed and integrated by heat or entanglement.

[0051] The method for forming the web is not particularly limited, and examples include the spunbond method, meltblown method, tow opening method, carding method, and airlaid method. However, from the viewpoint of imparting bulkiness and flexibility to the nonwoven fabric, the carding method or airlaid method is preferred, and the carding method is more preferred. In this invention, "web" refers to a fiber aggregate in which fibers are somewhat entangled, and the intersections of the heat-fusible composite fibers are not fused.

[0052] The method for integrating the web by heat or entanglement is not particularly limited, and examples include the through-air method, thermal calendering method, water flow entanglement method, or needle punching method. However, the through-air method is preferred from the viewpoint of imparting bulkiness and flexibility to the nonwoven fabric. As for the through-air method, known equipment and conditions may be applied, such as a method of heat-fusing heat-fusible composite fibers together using a heat treatment device equipped with a conveying support for supporting and transporting the web (for example, a hot air penetration type heat treatment machine, a hot air blowing type heat treatment machine).

[0053] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0054] The physical properties in this invention were evaluated by the following method. <Biomass-derived carbon content> The sample was analyzed using an accelerator mass spectrometer (AMS) (a combination of a tandem accelerator and a mass spectrometer) to determine the total carbon content and １４ The carbon content was measured. The total carbon and carbon content in the sample were measured. １４ Based on the C content, the biomass-derived carbon content of the sample was calculated using the following formula: Biomass-derived carbon content (%) = (Biomass-derived carbon in the sample ( １４C) Amount / Total amount of carbon in the sample) × 100

[0055] <MFR of Polylactic Acid Resin> MFR was measured in accordance with ISO 1133-A, under the conditions of a test temperature of 190°C and a load of 2.16 kg (21.18 N). <MFR of Polyethylene Resin> MFR was measured in accordance with JIS K 7210. The measurement was performed in accordance with condition D of Annex A Table 1 (test temperature 190°C, load 2.16 kg (21.18 N)).

[0056] <Fineness of undrawn fibers, fineness of heat-fusible composite fibers, tensile strength, and elongation> Measured in accordance with JIS-L-1015.

[0057] <Thermal Shrinkage Rate of Fiber Length of Heat-Fusible Composite Fibers> Using a thermomechanical analyzer (manufactured by Rigaku Corporation, product name TMA-8310), 50 fibers arranged in parallel were mounted with a chuck distance of 10 mm, and under a constant load of 0.02 mN / dtex, the temperature was raised to 130°C at a heating rate of 5°C / min, held for 30 minutes, and then allowed to cool to 30°C. The thermal shrinkage rate of the fiber length was calculated from the length h1 after cooling using the following formula: Thermal shrinkage rate of fiber length (%) = {(10 (mm) - h1 (mm)) / 10 (mm)} × 100

[0058] <Balance of Nonwoven Fabric> Six pieces of 50 mm x 150 mm nonwoven fabric were cut out, the weight of each was measured, converted to a unit area, and the average of the obtained values ​​was defined as the basis weight of the nonwoven fabric.

[0059] <Specific Volume of Nonwoven Fabric> Using a laser thickness gauge (manufactured by KEYENCE Co., Ltd., product name IL-S065) with a 35 mm diameter pressure bar (load), the specific volume was determined to be 3.5 gf / cm². ２ A pressure of (0.34 kPa) was applied, and the thickness was measured. The specific volume was calculated from the measured thickness using the following formula: Specific volume (cm³) ３ (g / m) = Thickness (mm) ÷ Basis Weight (g / m) ２ ) × 1000

[0060] <Tensile Strength per Basis Weight of Nonwoven Fabric in the Machine Passing Direction> A sample measuring 50 mm x 150 mm, cut into a long length in the machine passing direction, was pulled using an Autograph (manufactured by Shimadzu Corporation, product name AGX-J) at a chuck distance of 100 mm and a tensile speed of 100 mm / min. The maximum strength at which it broke was defined as the tensile strength of the nonwoven fabric. From the obtained tensile strength, the tensile strength per basis weight was calculated using the following formula: Tensile strength per basis weight (N / {50 mm·(g / m)}) ２ )}) = Tensile strength (N / 50mm) ÷ Basis weight (g / m) ２ )

[0061] <Thermal shrinkage rate of the web> Approximately 50g of sample fiber was carded into a web using a 500mm sample roller card tester (manufactured by Yamato Kiko Co., Ltd.) with a cylinder peripheral speed of 432 m / min and a duffel peripheral speed of 7.2 m / min (peripheral speed ratio 60:1), and then wound onto a drum at a peripheral speed of 7.5 m / min to obtain a basis weight of 200 g / m². ２ A web was prepared. This web was cut to 25 x 25 cm and heat-treated at 145°C for 5 minutes using a commercially available hot air circulating dryer. After the heat-treated web was allowed to cool, the shorter of either the length or width was measured at three points, and the average value h² (cm) was calculated. The shrinkage rate was then calculated using the following formula: Heat shrinkage rate of web (%) = {(25 (cm) - h² (cm)) / 25 (cm)} × 100

[0062] The resins used in the examples and comparative examples are as follows: <Resin 1> Polylactic acid (abbreviated as PLA) with a biomass-derived carbon content of 100%, MFR (190°C, load 21.18N) of 10 g / 10 min, and a melting point of 175°C. <Resin 2> High-density polyethylene (abbreviated as bioPE) derived from biomass with a biomass-derived carbon content of 94%, MFR (190°C, load 21.18N) of 18 g / 10 min, and a melting point of 128°C. <Resin 3> High-density polyethylene (abbreviated as fossil PE) derived from fossil resources with a biomass-derived carbon content of 0%, MFR (190°C, load 21.18N) of 16 g / 10 min, and a melting point of 130°C.

[0063] [Example 1, Comparative Examples 1-3] Heat-fusible composite fibers and nonwoven fabrics of the examples and comparative examples were manufactured according to the conditions shown in Table 1. (Manufacturing of heat-fusible composite fibers)

[0064] Using the resins shown in Table 1, spun fibers were obtained at a spinning temperature of 240°C with the core / sheath ratio (by weight) shown in Table 1 to obtain undrawn fibers with a concentric sheath-core structure. The obtained undrawn fibers were then drawn using a drawing machine under the conditions shown in Table 1. Subsequently, the fibers were crimped to a crimp count of 8 to 25 crimps / 2.54 cm, heat-treated for 5 minutes at the heat treatment temperature shown in Table 1, and cut to a fiber length of 51 mm to obtain heat-fusible composite fibers. (Nonwoven fabric processing)

[0065] The obtained heat-fusible composite fibers were passed through a roller carding machine to collect a web, and a 100 cm x 30 cm section was cut from the web. This section was then heat-treated using a hot air circulation type heat treatment machine at a processing temperature of 130°C to heat-fuse the sheath components and obtain a nonwoven fabric.

[0066] Table 1 summarizes the manufacturing conditions and physical property evaluation results for each example and comparative example.

[0067]

[0068] Table 1 shows that in Comparative Example 1, the biomass-derived carbon content of the sheath component was 100%, and the thermal shrinkage rate of the fiber length was 1.0% or more, resulting in a low specific volume and a high thermal shrinkage rate of the web when made into a nonwoven fabric. On the other hand, in Examples 1 to 4, despite the biomass-derived carbon content of the sheath component being 45% or more, the fibers were less susceptible to thermal shrinkage, resulting in a high specific volume and a low thermal shrinkage rate when made into a nonwoven fabric. Furthermore, although Comparative Example 2, which used fossil PE, had a high specific volume, the biomass-derived carbon content in the composite fiber was low at 50%, and the consumption of fossil resources could not be reduced. In Examples 1 to 4, despite the biomass-derived carbon content of 70% or more in the composite fiber, fibers and nonwoven fabrics that can be used for various textile products were obtained.

[0069] The heat-fusible composite fibers and nonwoven fabrics of the present invention use polylactic acid resin as the core component and biomass-derived polyethylene resin as the sheath component, and by appropriately controlling the processing conditions to suppress the shrinkage rate of the fibers, it is possible to provide bulky nonwoven fabrics that do not shrink easily during processing while reducing the consumption of fossil resources. Therefore, they can be used in a variety of textile products such as sanitary materials such as diapers, napkins, or incontinence pads; medical materials such as masks, gowns, or surgical gowns; interior materials such as wall sheets, shoji paper, or flooring materials; lifestyle-related materials such as cover cloths, cleaning wipers, or garbage covers; toiletry products such as disposable toilets or toilet covers; pet supplies such as pet sheets, pet diapers, or pet towels; industrial materials such as wiping materials, filters, cushioning materials, oil absorbents, or ink tank absorbents; covering materials, humping materials, bedding materials, and nursing care products.

Claims

1. A heat-fusible composite fiber having a core component made of polylactic acid resin and a sheath component made of polyethylene resin, wherein the biomass-derived carbon content of the sheath component is 40% or more, and the heat shrinkage rate of the fiber length calculated by the following measurement method is 1% or less. Heat shrinkage rate of fiber length (%) = {(10 (mm) - h1 (mm)) / 10 (mm)} × 100 h1 is the length after 50 fibers with a chuck distance of 10 mm are heated to 130°C at a heating rate of 5°C / min under a constant load of 0.02 mN / dtex, held for 30 minutes, and allowed to cool to 30°C.

2. The heat-fusible composite fiber according to claim 1, wherein the fiber length of the heat-fusible composite fiber is 5 to 150 mm.

3. The heat-fusible composite fiber according to claim 1 or 2, wherein the fineness of the heat-fusible composite fiber is 1.0 to 8.0 dtex.

4. The heat-fusible composite fiber according to claim 1 or 2, wherein the heat shrinkage rate of the web formed by the carding method, calculated by the following measurement method, is 7% or less. Heat shrinkage rate of the web = {(25 (cm) - h2 (cm)) / 25 (cm)} × 100 (%) h2 is 25 cm long x 25 cm wide with a basis weight of 200 g / m ２ This is the shorter of the two lengths, either lengthwise or widthwise, after heat treatment of the web at 145°C for 5 minutes.

5. A nonwoven fabric containing heat-fusible composite fibers as described in claim 1 or 2.

6. The specific volume of the nonwoven fabric is 45 cm³. ３ The nonwoven fabric according to claim 5, wherein the weight is 1 / g or more.

7. The tensile strength per basis weight of the nonwoven fabric in the direction of machine passage is 1.0 N / {50 mm·(g / m)}. ２ The nonwoven fabric according to claim 5, wherein the above conditions are met.

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