Nonwoven fabrics and their uses

Abstract

The present invention provides a nonwoven fabric that is biodegradable and has a good pleat retaining property, and an application thereof. The present invention relates to a nonwoven fabric comprising at least one fiber layer (I) which contains a polylactic acid polymer and which has an average fiber diameter of 10-30 μm, wherein in polarized Raman spectroscopy of the fiber layer (I), the value I / / / I⊥, which is the ratio of the peak intensity I / / at 872 cm-1 of a Raman spectrum measured with polarized light parallel to a fiber axis, to the peak intensity I at 872 cm-1 of a Raman spectrum measured with polarized light perpendicular to the fiber axis, is not more than 1.80. The present invention also relates to a filter material comprising the nonwoven fabric, and a filter for foods, an air filter, and a mask which each comprise the filter material.

Description

[Technical Field]

[0001] This invention relates to nonwoven fabrics and their applications. [Background technology]

[0002] Traditionally, nonwoven fabrics have been used as filter materials in products such as food filters, air filters, and masks. However, the resins that make up these nonwoven fabrics are generally non-biodegradable resins such as polyethylene, polypropylene, polyester, and polyamide, and there is a problem that they have a significant environmental impact when disposed of through incineration or other methods.

[0003] To address these problems, for example, Patent Document 1 below proposes a coffee extraction sheet material made of a melt-blown nonwoven fabric made of a biodegradable thermoplastic polymer, in which the air permeability and water absorption rate are controlled by the average fiber diameter. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-336570 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the coffee extraction sheet material described in Patent Document 1 is made of melt-blown nonwoven fabric and therefore does not have sufficient pleat retention.

[0006] In view of the prior art described above, the problem that the present invention aims to solve is to provide a nonwoven fabric that is biodegradable and has good pleat retention properties, as well as applications therefor. [Means for solving the problem]

[0007] As a result of intensive studies and repeated experiments to solve the above problems, the inventors have found that a non-woven fabric containing at least one fiber layer (I) made of a polylactic acid (hereinafter also referred to as PLA) polymer having an average fiber diameter of 10 μm or more and 30 μm or less, and in the fiber layer (I), by polarized Raman spectroscopy, the Raman spectrum measured with polarized light perpendicular to the fiber axis at 872 cm -1 The ratio value I / / / I⊥ of the peak intensity I / / of the Raman spectrum measured with polarized light parallel to the fiber axis to the peak intensity I⊥ at 872 cm -1 of the Raman spectrum measured with polarized light perpendicular to the fiber axis is 1.80 or less, unexpectedly found that the non-woven fabric can solve the above problems, and thus completed the present invention.

[0008] That is, the present invention is as follows. [1] A non-woven fabric containing at least one fiber layer (I) made of a polylactic acid polymer having an average fiber diameter of 10 μm or more and 30 μm or less, and in the fiber layer (I), by polarized Raman spectroscopy, the Raman spectrum measured with polarized light perpendicular to the fiber axis at 872 cm -1 The ratio value I / / / I⊥ of the peak intensity I / / of the Raman spectrum measured with polarized light parallel to the fiber axis to the peak intensity I⊥ at 872 cm -1 of the Raman spectrum measured with polarized light perpendicular to the fiber axis is 1.80 or less. [2] The non-woven fabric according to [1], wherein I / / / I⊥ is 1.40 or less. [3] The non-woven fabric according to [1] or [2], wherein I / / / I⊥ is 1.08 or more. [4] The non-woven fabric according to any one of [1] to [3], wherein the crystallinity determined by differential scanning calorimetry of the fiber layer (I) is 20% or more. [5] The non-woven fabric according to any one of [1] to [4], wherein the basis weight of the non-woven fabric is 10 g / m 2 or more and 50 g / m 2 or less. [6] The non-woven fabric according to any one of [1] to [5], wherein the non-woven fabric is thermally pressed, and the pressing area ratio is 5% or more and 40% or less. The nonwoven fabric according to any one of [1] to [6] above, further comprising at least one fiber layer (II) having an average fiber diameter of 0.3 μm or more and 7.0 μm or less. [8] The air permeability of the nonwoven fabric is 400 cc / cm 2 / sec or less, the nonwoven fabric according to any one of [1] to [7] above. [9] A filter material comprising the nonwoven fabric according to any one of [1] to [8] above.

[10] A food filter comprising the filter material according to [9] above.

[11] An air filter comprising the filter material according to [9] above.

[12] A mask comprising the filter material according to [9] above. [Effect of the Invention]

[0009] The nonwoven fabric according to the present invention has biodegradability and good pleat retention. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, embodiments of the present invention will be described in detail. The nonwoven fabric of the present embodiment is a nonwoven fabric comprising at least one fiber layer (I) containing a polylactic acid-based polymer having an average fiber diameter of 10 μm or more and 30 μm or less. In the fiber layer (I), by polarized Raman spectroscopy, the 872 cm of the Raman spectrum measured with polarized light perpendicular to the fiber axis -1 The ratio value I / / / I⊥ of the peak intensity I / / at 872 cm of the Raman spectrum measured with polarized light parallel to the fiber axis to the peak intensity I⊥ at 872 cm is 1.80 or less. -1 is characterized by being 1.80 or less.

[0011] The fiber layer (I) may be composed of either short fibers or long fibers, but long fibers are preferred from the viewpoint of strength. In the case of long fibers, it is preferably manufactured by a known spunbond method, and it is preferable to uniformly disperse the yarn by frictional charging or corona charging during spinning.

[0012] The fiber layer (I) contains a polylactic acid polymer. The content of the polylactic acid polymer in the fiber layer (I) is preferably 70 to 100% by mass, when the total amount of resin is 100% by mass.

[0013] Examples of polylactic acid polymers include polymers of D-lactic acid, polymers of L-lactic acid, copolymers of D-lactic acid and L-lactic acid, copolymers of D-lactic acid and hydroxycarboxylic acid, copolymers of L-lactic acid and hydroxycarboxylic acid, copolymers of D-lactic acid, L-lactic acid, and hydroxycarboxylic acid, and blends of two or more of these polymers. The ratio of the D-isomer in the total mass of the polylactic acid polymer can be set within a range that does not impede spinnability and nonwoven fabric properties, but is preferably 0 to 15% by mass, more preferably 0.1 to 10% by mass, and even more preferably 0.1 to 6% by mass. When the D-isomer ratio is 0 to 15% by mass, spinnability is good, a stable nonwoven fabric can be obtained, and the melting point, crystallinity, etc. are within an appropriate range, making it easy to obtain a nonwoven fabric with sufficient strength and excellent pleat retention.

[0014] The melt flow rate (MFR) of the polylactic acid polymer is preferably 20 to 120 g / 10 min, and more preferably 30 to 70 g / 10 min. If the MFR is 20 g / 10 min or higher, the melt viscosity is appropriate, and fiber thinning occurs easily during the spinning process, resulting in good spinability. On the other hand, if the MFR is 120 g / 10 min or lower, the melt viscosity is appropriate, so single filament breakage occurs less frequently during the spinning process, resulting in good spinability.

[0015] The fiber layer (I) may contain a thermoplastic resin as a secondary component in addition to the polylactic acid polymer. The content of the thermoplastic resin as a secondary component is preferably more than 0% by mass and 30% by mass or less, more preferably 0.5 to 30% by mass, even more preferably 3 to 27% by mass, and most preferably 5 to 25% by mass, when the total amount of resin is 100% by mass. If the content of the thermoplastic resin as a secondary component is 0.5% by mass or more, the crystallization start temperature of the fiber layer (I) can be lowered, and crystallization can be promoted at a lower temperature. Therefore, when heat sealing is performed in the manufacture of nonwoven fabrics, fluffing is less likely to occur, and for example, when used as a beverage filter, fiber shedding can be suppressed during beverage extraction. On the other hand, if the amount added is 30% by mass or less, crystallization is not suppressed and crystallization proceeds sufficiently, making it easier to obtain sufficient strength and dimensional stability as a nonwoven fabric. The thermoplastic resin as a secondary component is preferably biodegradable.

[0016] Examples of thermoplastic resins used as auxiliary components include aliphatic esters, aromatic esters, or homopolymers or copolymers of one or more monomers selected from the group consisting of (meth)acrylic acid monomers, olefins, caprolactone, hydroxyalkanoates, alkylene glycols, dibasic acids, and dialcohols. Furthermore, blends of multiple biodegradable individual polymers are also used. From the viewpoint of compatibility with the main component, the polylactic acid polymer, and spinnability, aliphatic esters and aromatic esters are preferred, and specifically, polybutylene succinate (hereinafter also referred to as PBS), polybutylene adipate terephthalate, and polybutylene succinate adipate are preferred.

[0017] The average fiber diameter of the fiber layer (I) is 10 μm or more from the viewpoint of spinning stability, preferably 12 μm or more, more preferably 13 μm or more, and from the viewpoint of strength and heat resistance, it is 30 μm or less, preferably 20 μm or less, and more preferably 18 μm or less. In this embodiment, the average fiber diameter of the fiber layer (I) is 10 μm or more and 30 μm, preferably 14 μm or more and 26 μm or less.

[0018] The shape of the cross-section of the fibers in the fiber layer (I) is not particularly limited, but from the viewpoint of strength, a round cross-section is preferred, and from the viewpoint of forming fine voids, irregularly shaped cross-section fibers such as flat fibers are preferred.

[0019] In the fiber layer (I), the Raman spectrum measured with polarization perpendicular to the fiber axis is obtained by polarized Raman spectroscopy at 872 cm⁻¹. -1 The 872 cm⁻¹ Raman spectrum measured with polarization parallel to the fiber axis for the peak intensity I⊥ at [location]. -1 The ratio value I / / / I⊥ of the peak intensity I / / is 1.80 or less, preferably 1.60 or less, and more preferably 1.40 or less. When I / / / I⊥ is 1.80 or less, excessive orientation is prevented, and the shape can be maintained after pleating, and when it is 1.40 or less, the cutability is further improved. From the viewpoint of pleat retention and cutability, a lower I / / / I⊥ is preferable, but for fibers containing polylactic acid polymers, it is generally 1.08 or higher. A detailed method for measuring I / / / I⊥ will be described later.

[0020] The methods for controlling the aforementioned I / / / I⊥ are not particularly limited, but when using a known spunbond method, they include the spinning speed of the yarn, spinning temperature, tensile force, draft ratio, intrinsic viscosity of the resin, thermocompression temperature, and heat retention length of the spun section.

[0021] In particular, the I / / / I⊥ can be easily controlled by adjusting the traction force. As a method for controlling the traction force, when using the known spunbond method, it is common to use a high-speed airflow traction device with an air jet, and the traction force can be adjusted by the amount of air introduced into the traction device. This traction force is measured by inserting two pieces of fishing line (0.235 mm in diameter) with the same length as the total length of the traction device (in this specification, Toray Industries' nylon fishing line "Ginrin (No. 2 / natural / 50m roll)") into the traction device, measuring the stress with a spring scale connected to the fishing line, and dividing by the length of the fishing line inserted to measure the traction force (mN / m). The traction force is preferably 40 to 90 mN / m, more preferably 40 to 80 mN / m, and most preferably 50 to 70 mN / m. By controlling the traction force within an appropriate range, yarn breakage during spinning can be sufficiently suppressed, and the I / / / I⊥ can be easily set within a desirable range.

[0022] In addition to the tensile force, another method that makes it easier to control the I / / / I⊥ is to adjust the heat retention length of the spinning section. The heat retention length of the spinning section is the length from directly below the spinneret to the cooling start point, and the heat retention length of the spinning section is preferably 100 mm or more, more preferably 120 to 250 mm. If the heat retention length of the spinning section is within the above range, yarn breakage during spinning can be sufficiently suppressed, and the I / / / I⊥ can be easily set within the preferred range.

[0023] The degree of crystallinity of the fiber layer (I), as measured by differential scanning calorimeter, is preferably 20% or more, more preferably 25%, and even more preferably 30% or more. When the degree of crystallinity of the fiber layer (I) is 20% or more, sufficient strength and dimensional stability are obtained as a nonwoven fabric, and breakage during pleating can be prevented.

[0024] The nonwoven fabric of this embodiment may further include at least one fiber layer (II) with an average fiber diameter of 0.3 μm to 7 μm. The fiber layer (II) can be manufactured, for example, by a melt-blown method.

[0025] The average fiber diameter of the fiber layer (II) is 0.3 μm or more and 7 μm or less, preferably 0.4 μm or more and 5 μm or less, and more preferably 0.6 μm or more and 2 μm or less. If the fiber diameter is 0.3 μm or more, it can be spun under mild conditions, for example by the melt-blown method, and stable fibers can be obtained. On the other hand, if the average fiber diameter of the fiber layer (II) is 7 μm or less, the fiber layer (II) can penetrate into the gaps of the fiber layer (I) as fine fibers and fill these gaps, resulting in a dense structure, which improves the collection performance as a filter.

[0026] The material for the fiber layer (II) can be the same as the material that can be used for the fiber layer (I) described above.

[0027] Nonwoven fabrics can have a laminated structure consisting of one or more fiber layers (I) and one or more fiber layers (II). Examples of laminated structures include those with layer configurations such as I / II, I / II / I, I / II / II, I / II / II / I, I / II / I / II / I, I / II / I / I / II / I, etc.

[0028] The basis weight of the nonwoven fabric is 10 g / m². 2 More than 50g / m 2 The following is preferable, and more preferably, 12 g / m² 2 More than 47g / m 2 More preferably 15 g / m 2 More than 45g / m 2 The following applies: The basis weight of the nonwoven fabric is 10 g / m². 2 With these specifications, sufficient collection performance can be obtained as a filter, and the required strength during pleating can be easily achieved, resulting in excellent pleating processability. 50m 2 The following conditions prevent the structure from becoming excessively dense, thus avoiding high pressure loss. Furthermore, it facilitates the acquisition of flexibility, stretchability, and conformability in the nonwoven fabric, resulting in excellent pleating properties.

[0029] When heat bonding is performed in the manufacture of nonwoven fabrics, heat bonding can be performed between an embossing roll and a smooth roll (hereinafter also referred to as a flat roll), between two smooth rolls, or between hot flat plates. From the viewpoint of increasing strength, heat bonding between an embossing roll and a smooth roll is preferred.

[0030] When heat-sealing between an embossed roll and a smooth roll, it is preferable that the heat-sealing is performed such that the area ratio of the sealed area to the total surface area of ​​the nonwoven fabric (sealing area ratio) is 5% or more and 40% or less, and more preferably 7% or more and 35% or less. If the sealing area ratio is 5% or more, fluffing is reduced and dimensional stability can be achieved, and if it is 40% or less, the nonwoven fabric is less likely to become paper-like and mechanical properties such as elongation at break and tear strength are less likely to deteriorate. The heat-sealing temperature is preferably 30°C to 90°C lower than the melting point of the resin, which is mainly composed of polylactic acid polymer that makes up the fibers, and more preferably 40°C to 70°C lower. If the difference between the heat-sealing temperature and the melting point of the resin that makes up the fibers is within the above range, fluffing will be less likely to occur, fluffing due to pleating can be suppressed, and fiber shedding can be suppressed during beverage extraction.

[0031] The pressure used for heat sealing is preferably 10 N / mm to 100 N / mm, and more preferably 30 N / mm to 70 N / mm, from the viewpoint of mechanical strength, rigidity, and dimensional stability.

[0032] The shape of the heat-sealed area is not particularly limited, but examples include woven patterns, IL patterns (rectangular patterns), pinpoint patterns, diamond patterns, square patterns, tortoiseshell patterns, oval patterns, grid patterns, polka dot patterns, and circular patterns.

[0033] When heat-pressing between smooth rolls or between flat plates, the entire surface of the nonwoven fabric is heated. Therefore, it is preferable to perform heat-pressing at low pressure and low temperature to prevent the entire nonwoven fabric from becoming excessively crystallized and to avoid causing delamination.

[0034] Nonwoven fabrics can contain black pigments, flame retardants such as phosphorus-based agents, and water repellents, to the extent that they do not impair the desired effect. Furthermore, known post-processing treatments, such as the addition of deodorants and / or antibacterial agents, dyeing, water-repellent treatment, and water-permeable treatment, can also be applied.

[0035] Depending on the purpose, the nonwoven fabric may further contain one or more types of substances such as flame retardants, inorganic fillers, softeners, plasticizers, pigments, and antistatic agents.

[0036] The air permeability of nonwoven fabrics, as measured according to JIS L 1096, is 200 cc / cm³. 2 Preferably less than / sec, and more preferably 170cc / cm³ 2 / sec or less, more preferably 150cc / cm³ 2 It is less than / sec. The air permeability of the nonwoven fabric is 200cc / cm². 2 If the value is less than / sec, sufficient collection performance can be obtained when used as a filter material. [Examples]

[0037] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. In nonwoven fabric manufacturing, the flow direction (machine direction) is referred to as the MD direction, and the direction perpendicular to that direction, the width direction, is referred to as the CD direction. The physical properties in the following examples were obtained by measuring them using the methods described below. In principle, the physical properties in the following examples are measured using the methods described below; however, if there are circumstances that prevent measurement using these methods, they may be measured using a reasonable alternative method as appropriate.

[0038] (1) Basis weight (g / m 2 ) The weight was measured in accordance with JIS L 1913.

[0039] (2) Average fiber diameter (μm) Using a VHX-700F microscope manufactured by Keyence Corporation, 500x magnified images were taken, and the average value of 10 in-focus fibers in the observed field of view was used to determine the fiber ratio.

[0040] (3) Raman spectrum measured with polarization perpendicular to the fiber axis at 872 cm⁻¹ -1 The 872 cm⁻¹ Raman spectrum measured with polarization parallel to the fiber axis for the peak intensity (I⊥) at [location]. -1 The ratio of peak intensities (I / / ) in a given region (I / / / I⊥) Using the InViaReflex Raman spectrophotometer manufactured by Renishaw Corporation, the polarized Raman spectrum of any single fiber in the fiber layer (I) of the sample was measured with the sample positioned so that the plane of polarization of the excitation light was parallel to the fiber axis, and the value obtained was 872 cm⁻¹. -1 The peak intensity (I / / ) at was measured. Next, the sample was rotated 90°, and the polarization Raman spectrum was measured with the excitation light's polarization plane perpendicular to the fiber axis. The 872cm⁻¹ spectrum was then measured. -1 The peak intensity (I⊥) was measured. The ratio of (I / / ) to (I⊥), (I / / / I⊥), was calculated using the average value of 10 fibers. A larger value of (I / / / I⊥) indicates a higher orientation of the molecular chains relative to the fiber axis. The optical axis of the polarizer on the detection side of the polarized Raman spectrum was set parallel to the optical axis of the excitation light during the measurement. Furthermore, the measurement conditions using the Raman spectrophotometer are as follows: (Measurement conditions) Laser wavelength: 532nm Excitation light intensity at the measurement location: 5 mW Objective lens: 20x (NA 0.40) Diffraction grating: 1800 gr / mm Exposure time: 2 seconds Total number of times: 10

[0041] (4) Degree of crystallinity of the fiber layer (I) (%) Using a differential scanning calorimeter DSC6000 manufactured by PerkinElmer Corporation, 5 mg of nonwoven fabric sample was placed in an aluminum pan manufactured by PerkinElmer Corporation and heated from 30°C to the melting point of the fiber layer (I) + 50°C at a heating rate of 10°C / min. The exothermic peak heat quantity obtained from the differential curve of the resulting chart and the cold crystallization peak heat quantity were used in the following formula.

[0042]

number

[0043] Furthermore, in this embodiment, the following values ​​were used for the heat of fusion of the perfect crystal. Polylactic acid (PLA): 93.0 J / g Polyethylene terephthalate (PET): 126.4 J / g

[0044] (5) Air permeability Air permeability was measured in accordance with JIS L 1096 using a Textest FX3340 air permeability tester.

[0045] (6) Biodegradable Nonwoven fabric samples were composted for up to 12 weeks using the ISO 16929 (JIS K 6952) pilot-scale aerobic disintegration measurement method. Finally, they were passed through a 2 mm mesh sieve, and evaluated according to the following criteria based on the ratio of the mass remaining after sieving to the mass before sieving. (Evaluation Criteria) ○: Less than 5% remaining in the sieve ×: More than 5% remaining in the sieve

[0046] (7) Pleat retention A rectangular nonwoven fabric sample, measuring over 75 mm in width (CD direction) and 75 mm in length (MD direction), was folded 180° 20 mm from one end in the MD direction. A 2 kg weight was placed on top of the folded line, completely covering it, and left undisturbed for 60 seconds. After removing the weight, the angle at which the nonwoven fabric sample unfolded was measured using a protractor after 30 seconds, and the pleat retention was evaluated according to the following evaluation criteria. (Evaluation Criteria) ◎: Opening and returning angle 80° or less ○: Opening and returning angle greater than 80° and less than or equal to 100° △: Opening and returning angle greater than 100° and less than or equal to 120° ×: Opening and returning angle exceeds 120°.

[0047] (8) Cutting properties A 100mm square nonwoven fabric sample was placed in the center of a Φ47mm circular punching blade and pressed using a flat plate press at room temperature. The cutability was evaluated according to the following criteria. (Evaluation Criteria) ○: The nonwoven fabric sample was cut according to the shape of the punching blade. ×: The nonwoven fabric sample was not cut according to the shape of the punching blade.

[0048] [Example 1] Polylactic acid (melting point 160°C, MFR value at 210°C 15g / 10min, D-isomer ratio 2.0%) resin is mixed with 10% by mass of polybutylene succinate (melting point 110°C), supplied to a known melt spinning apparatus and melted at 230°C. The mixture is then extruded from a spinneret having a circular cross-section spinning hole, and the yarn is cooled while being stretched using a high-speed airflow traction device with an air jet, maintaining a spinning section length of 130mm and a traction force of 60mN / m to form a spunbond web (basis weight 40.0g / m²). 2 Fibers with an average diameter of 17 μm were collected and formed on a net. The resulting web was heat-pressed using a woven pattern embossed roll and a flat roll with a pressure area ratio of 15%, with the surface temperature of the embossed roll at 130°C and the surface temperature of the flat roll at 130°C, and a calendering wire pressure of 30 N / mm, resulting in a basis weight of 40.0 g / m². 2 A nonwoven fabric was obtained. Its properties are shown in Table 1 below.

[0049] [Examples 2-8] A nonwoven fabric was obtained in the same manner as in Example 1, except that the tensile force was adjusted so that the average fiber diameter was the value shown in Table 1. Its properties are shown in Table 1 below.

[0050] [Examples 9-12] A nonwoven fabric was obtained in the same manner as in Example 1, except that the discharge rate and line speed were adjusted so that the basis weight was the value shown in Tables 1 and 2. Its characteristics are shown in Tables 1 and 2 below.

[0051] [Example 13] Weight: 11.7 g / m 2The web (based on a basis weight of 11.7 g / m²) was prepared in the same manner as in Example 1, except that the discharge rate and line speed were adjusted to achieve the same result. 2 On top of a fiber with an average fiber diameter of 17 μm, polylactic acid (melting point 160°C, MFR value at 210°C 80 g / 10 min, D-isomer ratio 1.4%) was melt-blown from a melt-blown nozzle at a spinning temperature of 230°C and heated air at 300°C for 1000 Nm 3 Direct ejection under the conditions of / hr, melt-blown web (basis weight 6.6g / m²) 2 A spunbond web with an average fiber diameter of 1.7 μm was formed. The distance from the melt-blown nozzle to the spunbond web was set to 110 mm, and the suction air velocity at the collection surface directly below the melt-blown nozzle was set to 7 m / sec. Furthermore, a polylactic acid spunbond web similar to the spunbond web was formed on the obtained melt-blown web. The resulting laminated web was then heat-pressed in the same manner as in Example 1, resulting in a total basis weight of 30.0 g / m². 2 A nonwoven fabric was obtained. Its properties are shown in Table 2 below.

[0052] [Examples 14, 15] A nonwoven fabric was obtained in the same manner as in Example 12, except that the tensile force was adjusted so that the average fiber diameter of each spunbond web was the value shown in Table 1. Its properties are shown in Table 2 below.

[0053] [Examples 16, 17] A nonwoven fabric was obtained in the same manner as in Example 12, except that the discharge rate and line speed were adjusted so that the basis weight of the spunbond web and the melt-blown web were the values ​​shown in Table 1. Its characteristics are shown in Table 2 below.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Comparative Example 1] Polylactic acid (melting point 160°C, MFR value at 210°C 15g / 10min, D-isomer ratio 2.0%) resin is mixed with 10% by mass of polybutylene succinate (melting point 110°C), supplied to a known melt spinning apparatus and melted at 230°C. The mixture is then extruded from a spinneret having a circular cross-section spinning hole, and the yarn is cooled while being stretched using a high-speed airflow traction device with an air jet, with a spinning section retention length of 80mm and a traction force of 75mN / m to form a spunbond web (S1) (basis weight 40.0g / m²). 2 Fibers with an average diameter of 12 μm were collected and formed on a net. The resulting web was heat-pressed using a woven pattern embossed roll and a flat roll with a heat-pressure area ratio of 15% during heat pressing. The surface temperature of the embossed roll was set to 130°C, and the surface temperature of the flat roll was also set to 130°C, and the calendering wire pressure was 30 N / mm, resulting in a basis weight of 40.0 g / m². 2 A nonwoven fabric was obtained. Its properties are shown in Table 3 below.

[0057] [Comparative Example 2] Polyethylene terephthalate (1% solution viscosity ηsp / c 0.77, melting point 263°C, using orthochlorophenol) resin is supplied to a known melt spinning apparatus and melted at 300°C. The melted resin is then extruded from a spinneret having a circular cross-section spinning hole, and the yarn is cooled while being stretched with a tensile force of 69 mN / m using a high-speed air jet traction device to form a spunbond web (basis weight 14.0 g / m²). 2 A web with an average fiber diameter of 14 μm was formed on a net. The resulting web was heat-pressed using a woven pattern embossed roll and a flat roll with a pressure area ratio of 15%, with the surface temperature of the embossed roll at 220°C and the surface temperature of the flat roll at 220°C, and a calendering wire pressure of 30 N / mm, resulting in a basis weight of 30.0 g / m². 2 A nonwoven fabric was obtained. Its properties are shown in Table 3 below.

[0058] [Comparative Example 3] Weight: 11.7 g / m 2 The spunbond web (basis weight 11.7 g / m²) was prepared in the same manner as in Comparative Example 2, except that the discharge rate and line speed were adjusted accordingly. 2On a fiber with an average fiber diameter of 14 μm, polyethylene terephthalate (also with a solution viscosity ηsp / c 0.50 and a melting point of 260°C) is melted from a melt-blown nozzle at a spinning temperature of 300°C and heated air at 320°C for a total length of 1000 Nm. 3 Direct ejection under the conditions of / hr, melt-blown web (basis weight 6.6g / m²) 2 A spunbond web with an average fiber diameter of 1.7 μm and a D-isomer ratio of 1.4% was formed. The distance from the melt-blown nozzle to the spunbond layer was set to 110 mm, and the suction air velocity at the collection surface directly below the melt-blown nozzle was set to 7 m / sec. Furthermore, a spunbond web of polyethylene terephthalate, similar to the spunbond web, was formed on the obtained melt-blown web. The resulting laminated web was heat-pressed in the same manner as in Comparative Example 5, resulting in a total basis weight of 30.0 g / m². 2 A nonwoven fabric was obtained. Its properties are shown in Table 3 below.

[0059] [Comparative Example 4] A spinning solution was prepared consisting of 11 parts by mass of polylactic acid (6060D) manufactured by NatureWorks, 44.5 parts by mass of dimethylformamide, and 44.5 parts by mass of dichloromethane. Next, the spinning solution was supplied at a rate of 2.0 mL / hr to a nozzle with an inner diameter of 0.22 mm using a syringe pump, and a voltage of 32.5 kV was applied to the nozzle to electrospin ultrafine fibers made of polylactic acid. (Balance weight 0.9 g / m²) 2 (Average fiber diameter 0.3 μm) The distance between the nozzle and the grounded collector was set to 22.5 cm. By changing the feed rate of the polyethylene terephthalate nonwoven fabric placed between the nozzle and the collector, nonwoven fabrics with different basis weights of the ultrafine fiber structure made of polylactic acid were obtained. Their characteristics are shown in Table 3 below. Note that in Table 3, since the nonwoven fabric of Comparative Example 4 does not have a fiber layer corresponding to fiber layer (I), the crystallinity measurement shown is that of the fiber layer corresponding to fiber layer (II).

[0060] [Comparative Example 5] Using a polylactic acid resin with an MFR (230°C, 2160g load) of 190g / 10min and a D-isomer content of 23.9%, under conditions of 280°C and a single-hole discharge rate of 0.4g / min·hole, an average fiber diameter of 8.2μm and 50g / m² was obtained. 2A melt-blown web was formed from polylactic acid ultrafine fibers having a basis weight, and a melt-blown nonwoven fabric was produced by partially heat-fusing the constituent fibers of the web in a heat embossing process. The pressure area at this time was 15%. The properties of this nonwoven fabric are shown in Table 3. Note that in Table 3, since the nonwoven fabric of Comparative Example 5 does not have a fiber layer corresponding to fiber layer (I), the degree of crystallinity shown is the measured value of the fiber layer corresponding to fiber layer (II).

[0061] [Comparative Example 6] A nonwoven fabric was obtained in the same manner as in Comparative Example 5, except that the discharge rate and line speed were adjusted so that the average fiber diameter and basis weight were the values ​​shown in Table 2. Its characteristics are shown in Table 3. Note that in Table 3, since the nonwoven fabric of Comparative Example 5 does not have a fiber layer corresponding to fiber layer (I), the degree of crystallinity shown is the measured value of the fiber layer corresponding to fiber layer (II).

[0062] [Table 3] [Industrial applicability]

[0063] The nonwoven fabric according to the present invention has excellent pleating properties, maintains the shape of the pleats applied, and can provide a filter material with high collection efficiency and low pressure loss. Furthermore, since it is composed of biodegradable resin, it biodegrades in the natural environment after use, resulting in a low environmental impact. More specifically, the nonwoven fabric according to the present invention is suitably usable for food filters, including tea filters and coffee filters, air filters for air conditioners and automobiles, and masks.

Claims

1. A filter material comprising a nonwoven fabric containing at least one fiber layer (I) containing a polylactic acid polymer with an average fiber diameter of 10 μm or more and 30 μm or less, wherein the Raman spectrum measured by polarized Raman spectroscopy with polarization perpendicular to the fiber axis is 872 cm⁻¹ －１ The 872 cm⁻¹ of the Raman spectrum measured with polarization parallel to the fiber axis for the peak intensity I⊥ at [location]. －１ The ratio of peak intensities I / / in the nonwoven fabric is 1.08 or more and 1.40 or less, the degree of crystallinity determined by differential scanning calorimetry of the fiber layer (I) is 20% or more and 34% or less, and the basis weight of the nonwoven fabric is 10 g / m². ２ 50g / m or more ２ The following are pleated filter materials.

2. The filter material according to claim 1, wherein the nonwoven fabric further comprises at least one fiber layer (II) containing a polylactic acid polymer with an average fiber diameter of 0.3 μm or more and 7.0 μm or less, and has an I / II / I laminated structure.

3. A food filter comprising the filter material described in claim 1 or 2.

4. An air filter comprising the filter material described in claim 1 or 2.

5. A mask comprising the filter material according to claim 1 or 2.

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