Nonwoven fabric and manufacturing method thereof

Abstract

To provide a nonwoven fabric excellent in dimension stability under high temperature environment.SOLUTION: A nonwoven fabric contains thermoplastic resin including syndiotactic polystyrene. Degree of crystallization of the syndiotactic polystyrene is 40% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to nonwoven fabrics and methods for making same. [Background technology]

[0002] Compared to glass cloth, nonwoven fabrics are superior in flexibility, uniformity, density, etc., because the fibers that make up the nonwoven fabric can be thinned. For this reason, nonwoven fabrics have a wide range of uses, including filters such as liquid filters and air filters, sanitary materials, medical materials, agricultural covering materials, civil engineering materials, building materials, oil adsorbents, automotive materials, separators, clothing, and packaging materials (see, for example, Patent Document 1). In particular, nonwoven fabrics have the advantage that they are less likely to be damaged by calendering or bending processes than glass cloths, and are therefore more suitable for processing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-24061 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional nonwoven fabrics lack heat resistance and have room for improvement. In particular, heat shrinkage occurs when heated, and dimensional stability cannot be ensured when the nonwoven fabric is used in a high-temperature environment. The present disclosure has been made in view of the above-described conventional circumstances, and aims to provide a nonwoven fabric having excellent dimensional stability in a high-temperature environment and a method for producing the same. [Means for solving the problem]

[0005] Specific means for achieving the above object are as follows. <1> Contains a thermoplastic resin including syndiotactic polystyrene, The nonwoven fabric, wherein the crystallinity of the syndiotactic polystyrene is 40% or more. <2> The average fiber diameter is 10 μm or less <1> The nonwoven fabric according to claim 1. <3> The proportion of the syndiotactic polystyrene in the thermoplastic resin is 50% by mass or more. <1> or <2> The nonwoven fabric according to claim 1. <4> Melting a thermoplastic resin comprising syndiotactic polystyrene; a step of discharging the molten thermoplastic resin together with heated gas from a spinneret having a plurality of holes, and stretching the thermoplastic resin with the heated gas to form a fibrous resin; collecting the fibrous resin to obtain a web; and heating the web in a fixed state to suppress deformation of the web in its surface direction due to heating. <5> The heating is carried out at 130°C to 240°C. <4> A method for producing the nonwoven fabric described in <6> The heating is carried out for 1 minute to 240 minutes. <4> or <5> A method for producing the nonwoven fabric described in <7> The melt flow rate of the thermoplastic resin at 300°C under a load of 1.2 kg is 5 g / 10 min to 10,000 g / 10 min. <4> ~ <6> 1. A method for producing the nonwoven fabric according to any one of claims 1 to 9. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a nonwoven fabric having excellent dimensional stability in a high-temperature environment and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0007] The present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0008] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable. In the present disclosure, the direction in which the fibers flow in a nonwoven fabric is referred to as the MD direction, and the direction perpendicular to the direction in which the fibers flow is referred to as the CD direction.

[0009] <Nonwoven fabric> The nonwoven fabric of the present disclosure contains a thermoplastic resin including syndiotactic polystyrene (hereinafter sometimes referred to as SPS), and the crystallinity of the SPS is set to 40% or more. As a result of extensive research, the present inventors have found that a nonwoven fabric with excellent dimensional stability in high-temperature environments can be realized by adjusting the crystallinity of the SPS contained in the thermoplastic resin to 40% or more, and have completed the invention described in the present disclosure. The nonwoven fabric of the present disclosure will be described in detail below.

[0010] (thermoplastic resin) The nonwoven fabric of the present disclosure contains a thermoplastic resin including SPS. SPS is a polystyrene polymer that primarily has a syndiotactic structure, which means that the stereochemical structure is a syndiotactic structure, i.e., a stereostructure in which phenyl groups, which are side chains, are alternately positioned in opposite directions relative to the main chain formed by carbon-carbon bonds. The tacticity of SPS is demonstrated by the use of nuclear magnetic resonance (NMR) spectroscopy with carbon isotopes ( 13 The tacticity of the syndiotactic structure can be expressed by the proportion of consecutive structural units present, for example, dyads when there are two, triads when there are three, and pentads when there are five. Typically, the racemic dyad is preferably a polystyrene polymer having a syndiotacticity of 75% or more, more preferably 85% or more, and the racemic pentad is preferably a polystyrene polymer having a syndiotacticity of 30% or more, more preferably 50% or more.

[0011] The SPS is preferably at least one selected from polystyrene, poly(alkylstyrene), poly(halogenated styrene), poly(halogenated alkylstyrene), poly(alkoxystyrene), poly(vinyl benzoate ester), and hydrogenated polymers thereof, as well as mixtures of two or more selected from these, and copolymers containing these structural units as the main component.

[0012] Examples of poly(alkylstyrene) include poly(methylstyrene), poly(ethylstyrene), poly(isopropylstyrene), poly(t-butylstyrene), poly(phenylstyrene), poly(vinylnaphthalene), and poly(vinylstyrene). Examples of the poly(halogenated styrene) include poly(chlorostyrene), poly(bromostyrene), and poly(fluorostyrene). Examples of poly(halogenated alkylstyrene) include poly(chloromethylstyrene). Examples of poly(alkoxystyrene) include poly(methoxystyrene) and poly(ethoxystyrene).

[0013] Among these, preferred styrene polymers include polystyrene, poly(p-methylstyrene), poly(m-methylstyrene), poly(p-, t-butylstyrene), poly(p-chlorostyrene), poly(m-chlorostyrene), poly(p-fluorostyrene), hydrogenated polystyrene, and copolymers containing these structural units, with styrene homopolymers (polystyrene) being particularly preferred. The SPS may be used alone or in combination of two or more types.

[0014] The nonwoven fabric of the present disclosure may contain thermoplastic resins other than SPS. Other desirable thermoplastic resins include those with structural units compatible with SPS. Examples include polymers with styrene blocks, such as atactic polystyrene, isotactic polystyrene, styrene-butadiene block copolymer (SBR), hydrogenated styrene-butadiene block copolymer (SEB, SEBC), styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), styrene-isoprene block copolymer (SIR), hydrogenated styrene-isoprene block copolymer (SEP), and hydrogenated styrene-isoprene-styrene block copolymer (SEPS), as well as modified versions of these, polyphenylene ether and its modified versions, styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-styrene block copolymer (SIS), acrylonitrile-styrene (AS) resin, and acrylonitrile-butadiene-styrene (ABS) resin, as well as styrene-based polymers and styrene-based elastomers.

[0015] Further examples of thermoplastic resins include polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polycarbonate resin; polyphenylene sulfide resin (PPS); polyamide resins such as nylon 6, nylon 6,6, and nylon 4,6; thermoplastic polyimide; polyamideimide; polyether resins such as polyphenylene oxide, polysulfone, and polyethersulfone; acrylic resins such as polyacrylic acid, polyacrylic acid ester, and polymethyl methacrylate; polyolefin resins such as polyethylene, polypropylene, polybutene, poly4-methylpentene-1, ethylene-propylene copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, and ethylene-vinyl acetate copolymer; halogen-containing vinyl compound polymers such as polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride; polyoxymethylene; polyvinyl alcohol resin; polyacetal; amorphous polyarylate; and derivatives thereof. These other thermoplastic resins may be used alone or in combination of two or more. The thermoplastic resin used in the present disclosure may be a resin derived from biomass or a resin derived from fossil resources.

[0016] From the viewpoint of obtaining higher dimensional stability, the proportion of SPS in the thermoplastic resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass or less. The proportion of SPS in the thermoplastic resin is preferably 50% by mass to 100% by mass.

[0017] In the present disclosure, the crystallinity of SPS is set to 40% or more, and from the viewpoint of obtaining higher dimensional stability, it is preferably 50% or more, more preferably 55% or more, even more preferably 60% or more, and particularly preferably 65% ​​or more. The crystallinity of the SPS may be 100% or less in order to obtain higher dimensional stability. The crystallinity of the SPS is preferably 40% to 100%.

[0018] In the present disclosure, the crystallinity of SPS refers to a value determined by DSC (Differential Scanning Calorimetry) method. Even when SPS and other thermoplastic resins are used in combination as thermoplastic resins, the crystallinity of SPS and the crystallinity of the other thermoplastic resins can be determined for each thermoplastic resin by the DSC method.

[0019] From the viewpoint of productivity of the nonwoven fabric, the melt flow rate (MFR, 300°C, 1.2 kg load) of the thermoplastic resin is preferably 5 g / 10 min to 10,000 g / 10 min, more preferably 10 g / 10 min to 5,000 g / 10 min, and even more preferably 20 g / 10 min to 2,500 g / 10 min. When two or more thermoplastic resins are used in combination, the MFR (300°C, 1.2 kg load) of the thermoplastic resin refers to the MFR of the mixture of two or more thermoplastic resins.

[0020] The MFR is measured in accordance with ASTM D-1238 (Method B) under the following conditions: The measurement sample is pre-dried at 120°C for 6 hours before measurement. Test method: ASTM D1238 (Method B) ·Filling amount: 8.0g Test temperature: 300℃ Load capacity: 1.2kg Measurement is carried out three times under the above conditions, and the average value is calculated. As a measuring device, for example, a Melt Indexer F-F01 type (Toyo Seiki Seisakusho, Ltd.) can be used.

[0021] The melting point of the thermoplastic resin is preferably 200°C or higher from the viewpoint of suppressing voids, and more preferably 240°C or higher, even more preferably 260°C or higher, and particularly preferably 270°C or higher from the viewpoint of dimensional stability before and after curing of the prepreg and filling properties during prepreg production. The melting point of the thermoplastic resin may be 450°C or lower from the viewpoint of dimensional stability. The melting point of the thermoplastic resin is preferably 200°C to 450°C.

[0022] The thermoplastic resin may contain various known additives, such as antioxidants, heat stabilizers, weather stabilizers, antistatic agents, slip agents, antifogging agents, lubricants, dyes, pigments, natural oils, synthetic oils, waxes, fatty acid amides, etc., as needed, provided that the dimensional stability of the nonwoven fabric is not impaired. The content of these additives in the thermoplastic resin is preferably 0.1% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less.

[0023] (Nonwoven fabric form) The nonwoven fabric of the present disclosure may be composed of long fibers or short fibers, and from the viewpoint of productivity, it is preferable to be composed of long fibers. In this disclosure, "short fibers" refers to fibers with an average fiber length of 200 mm or less. "Long fibers" refers to fibers with an average fiber length of more than 200 mm.

[0024] In this disclosure, "nonwoven fabric" refers to a fiber assembly in which fibers are entangled and fused together to form a sheet. Specifically, when observed under an electron microscope (magnification: ×500), it is 2 If there are 50 or more fusion points between fibers within this range, it is called a "nonwoven fabric." On the other hand, if there are less than 50 fusion points between fibers, it is called a "cotton-like" fabric and is distinguished from a "nonwoven fabric."

[0025] (average fiber diameter) In consideration of applications, the nonwoven fabric of the present disclosure preferably has an average fiber diameter of 10 μm or less, more preferably 0.05 μm to 5 μm, and even more preferably 0.1 μm to 3 μm. The smaller the average fiber diameter, the thinner the filter can be and the more easily it can capture small particles. The method for setting the average fiber diameter of the nonwoven fabric within the above range is not particularly limited, and examples thereof include methods for controlling the spinning temperature, residence time, nozzle hole diameter, single-hole discharge rate (discharge rate per nozzle hole), heated air temperature, heated air flow rate, etc. during the production of the nonwoven fabric.

[0026] The average fiber diameter of the nonwoven fabric can be determined as follows. The surface of the nonwoven fabric to be measured is photographed at 1000x magnification using an electron microscope (model number: S-3500N, manufactured by Hitachi, Ltd.) From the photograph, 1000 fibers (n=1000) are randomly selected, the diameters (widths) of the selected fibers are measured, and the arithmetic mean value is calculated as the average fiber diameter (Da).

[0027] (Thickness) The thickness of the nonwoven fabric is preferably 0.5 mm or less, more preferably 0.005 mm to 0.5 mm, even more preferably 0.01 mm to 0.3 mm, and particularly preferably 0.02 mm to 0.2 mm. The smaller the thickness, the more small particles can be captured when made into a filter, and the thinner the filter can be.

[0028] The thickness of the nonwoven fabric can be determined as follows. For 10 pieces of nonwoven fabric to be measured, the thickness is measured at five points, the center and four corners, and the average is calculated to determine the thickness of each nonwoven fabric. The average value of the thickness of the 10 pieces of nonwoven fabric is calculated and this is the thickness of the nonwoven fabric. The thickness is measured with a load of 7 gf / cm 2 Use a thickness gauge (measuring probe diameter 25mmφ).

[0029] (Metsuke) The basis weight of the nonwoven fabric is preferably set appropriately depending on the application, and is generally 500 g / m 2 It is preferable that: When using nonwoven fabric as a filter, the basis weight of the nonwoven fabric is 100 g / m 2 Preferably, it is 2 g / m or less. 2 ~90g / m 2 More preferably, it is 3 g / m 2 ~60g / m 2 It is more preferable that:

[0030] The basis weight of the nonwoven fabric can be determined as follows. Five test pieces of 100 mm (MD direction) x 100 mm (CD direction) are taken from the nonwoven fabric. The test pieces are taken from five locations in the CD direction. Next, the mass [g] of each test piece is measured using a top-pan electronic balance (manufactured by Kensei Kogyo Co., Ltd.) to determine the mass of each test piece. The average value is calculated from the masses obtained above, and the mass of 1 m 2 The mass per unit area is converted to g, and the basis weight of the nonwoven fabric is calculated as g / m 2 〕

[0031] There are no particular limitations on the method for adjusting the basis weight of the nonwoven fabric to fall within the above range, and examples thereof include a method of adjusting the speed of conveyance of the collecting belt during the production of the nonwoven fabric.

[0032] (breathability) The breathability of the nonwoven fabric is preferably adjusted depending on the application, such as a filter. 3 / cm 2 sec~200cm 3 / cm 2 sec is preferred, and 3 cm 3 / cm 2 sec~100cm 3 / cm 2 It is more preferable that the temperature is sec.

[0033] The air permeability of a nonwoven fabric can be determined as follows. A nonwoven fabric was prepared, and five 20cm x 20cm test pieces were taken from the nonwoven fabric in a temperature-controlled room at a temperature of 20±2°C and humidity of 65±2% as specified in JIS Z8703:1983 (standard conditions of the test location), in accordance with JIS L1096:2010 (8.26.1A method; Frazier type method). The amount of air passing through the test pieces (cm) was measured using a Frazier type tester. 3 / cm 2 ·sec) and calculate the average value.

[0034] (tensile strength) The tensile strength of the nonwoven fabric is preferably 5 N / 50 mm or more, more preferably 5 N / 50 mm to 200 N / 50 mm, and even more preferably 10 N / 50 mm to 100 N / 50 mm.

[0035] The tensile strength of the nonwoven fabric can be determined as follows. Five test pieces, each 50 mm wide (MD) x 200 mm long (CD), are taken from the nonwoven fabric to be measured, and measured using a tensile testing machine (e.g., Shimadzu Autograph AGS-J) with a chuck distance of 100 mm and a head speed of 100 mm / min. The average value is calculated to determine the tensile strength.

[0036] There are no particular limitations on the specific method for making the tensile strength of the nonwoven fabric fall within the above range, but an example of this is a method in which the position of the collection belt that collects the spinning material after spinning is brought closer to the nozzle.

[0037] (Applications of nonwoven fabric) The applications of the nonwoven fabric of the present disclosure are not particularly limited, and the fabric can be used for applications known for nonwoven fabrics. In particular, the nonwoven fabric of the present disclosure contains SPS, which provides excellent heat resistance and allows the average fiber diameter to be reduced, making it suitable for use as, for example, a filter, a sound absorbing material, a heat insulating material, or a sound insulating material. The filter can be suitably used in places where heat resistance is required, such as boiler and engine filters. As a sound absorbing material or heat insulating material, it can be installed in the space around the engine of a vehicle, or in places where heat resistance, flame retardancy, etc. are required.

[0038] <Nonwoven fabric manufacturing method> The nonwoven fabric of the present disclosure may be produced by any method, including, for example, spunbonding, meltblown, flash spinning, wet spinning, carding, airlaid, electrospinning, and the like.

[0039] The nonwoven fabric is preferably a nonwoven fabric produced by the spunbond method (i.e., a spunbond nonwoven fabric) or a nonwoven fabric produced by the meltblown method (i.e., a meltblown nonwoven fabric). The spunbond method or the meltblown method makes it possible to easily produce a long-fiber nonwoven fabric with excellent productivity. In particular, from the viewpoint of further reducing the average fiber diameter, the nonwoven fabric is preferably a meltblown nonwoven fabric.

[0040] The method for improving the crystallinity of SPS contained in a nonwoven fabric is not particularly limited, and the crystallinity of SPS may be increased to 40% or more by heat-treating a nonwoven fabric obtained from a thermoplastic resin containing SPS. When heat-treating a nonwoven fabric, the nonwoven fabric may be heated while fixed to prevent shrinkage of the nonwoven fabric due to heating.

[0041] The method for producing a nonwoven fabric according to the present disclosure may include the steps of melting a thermoplastic resin containing syndiotactic polystyrene (hereinafter sometimes referred to as the melting step), discharging the molten thermoplastic resin together with heated gas from a spinneret having a plurality of holes and stretching the thermoplastic resin with the heated gas to form a fibrous resin (hereinafter sometimes referred to as the discharging step), collecting the fibrous resin to obtain a web (hereinafter sometimes referred to as the collecting step), and heating the web while the web is fixed in place to suppress changes in the shape of the web in the plane direction due to heating (hereinafter sometimes referred to as the heating step). According to the method for producing a nonwoven fabric of the present disclosure, the nonwoven fabric of the present disclosure can be produced efficiently. Each step constituting the method for producing the nonwoven fabric of the present disclosure will be described below.

[0042] (Melting process) In the melting step, the thermoplastic resin containing SPS is melted. The melting temperature is not particularly limited and is appropriately set in consideration of the melting point, softening point, etc. of the thermoplastic resin. The melting temperature may be, for example, 250°C to 400°C. The MFR (300°C, 1.2 kg load) of the thermoplastic resin used in the method for producing the nonwoven fabric of the present disclosure is the same as the range mentioned in the "Nonwoven Fabric" section.

[0043] The melting time in the melting step is not particularly limited and is set appropriately in consideration of the melting point, softening point, production scale, etc. of the thermoplastic resin. The melting time may be, for example, 5 to 30 minutes. The melting step may involve heating within the above temperature range only once, or may be repeated two or more times. When heating is repeated two or more times, the above time refers to the total time within the above temperature range.

[0044] In the melting step, from the viewpoint of suppressing unevenness in the kneading of the thermoplastic resin and kneading with precision, it is preferable to knead using two or more shafts. The shaft refers to a shaft used for kneading, and examples thereof include screws. The melting step may be carried out, for example, using a melt extruder equipped with two or more screws.

[0045] (Discharge process) In the extrusion process, a molten thermoplastic resin (hereinafter also referred to as "melt") is extruded together with heated gas from a spinneret having a plurality of holes, and the thermoplastic resin is stretched by the heated gas to form a fibrous resin. Specifically, the melt is pressured using an extruder and supplied to a spinneret having a nozzle formed therein, and the melt is ejected from the nozzle. The extruder is not particularly limited, and may be a single-screw extruder or a multi-screw extruder. The temperature of the melt during extrusion (extrusion temperature) is not particularly limited as long as it can maintain a molten state, and may be set, for example, within the same temperature range as the melting temperature. The extrusion temperature is preferably within -50°C to +50°C, more preferably within -20°C to +20°C, of ​​the melting temperature.

[0046] The nozzle hole diameter is preferably 0.06 mm to 0.50 mm, and more preferably 0.10 mm to 0.40 mm. The discharge rate per hole in the nozzle (single hole discharge rate) is preferably 5 mg / min to 150 mg / min, more preferably 7 mg / min to 100 mg / min, and even more preferably 10 mg / min to 70 mg / min. The temperature of the heated gas is preferably 250°C to 420°C, and more preferably 290°C to 410°C. The flow rate of the heating gas is 250 Nm 3 / hr / m~750Nm 3 / hr / m, preferably 630Nm 3 / hr / m~740Nm 3 / hr / m is more preferable. By setting the nozzle hole diameter, discharge rate, and temperature and flow rate of the heated gas within these ranges, the average fiber diameter of the obtained nonwoven fabric can be made small, and the generation of resin particles tends to be reduced.

[0047] (Collection process) In the collecting step, the fibrous resin is collected to obtain a web. The web is collected on a collecting belt. In the spunbonding method, the fibrous resin is cooled and collected, whereas in the meltblown method, the fibrous resin is collected without being cooled, and therefore the fibers tend to fuse together on the collector. Therefore, the closer the distance between the spinneret and the collecting belt, the more the fibers are collected on the collecting belt in a fused state, forming a nonwoven fabric. On the other hand, the farther the distance between the spinneret and the collecting belt, the more the temperature of the fibrous resin drops before it is collected on the collecting belt, and therefore the more likely the fibers are to become flocculent without fusing together.

[0048] From the viewpoint of obtaining a nonwoven fabric, the distance between the spinneret and the collecting belt is preferably 120 mm or less, more preferably 10 mm to 110 mm, and even more preferably 30 mm to 80 mm.

[0049] The collecting step may be carried out while sucking air from the back side of the collecting belt. Suction of air from the back side tends to prevent the fibers from scattering.

[0050] In the collection step, a collection material may be placed on the collection belt. The collection material can be wound up together with the nonwoven fabric. Examples of the collection material include nonwoven fabrics other than the nonwoven fabric of the present disclosure. The use of the collection material tends to make winding easier. The collection material preferably has a basis weight that does not hinder air suction.

[0051] (Heating process) In the heating step, the web is heated. In order to suppress deformation of the web in the plane direction due to heating, the heating step is performed while the web is fixed. By heating the web, the crystallinity of the thermoplastic resin is set to 40% or more. The change in shape of the web in the plane direction may be caused by shrinkage of the web due to heating. The heating conditions for the web are not particularly limited, and are appropriately set in consideration of the type of thermoplastic resin, the degree of crystallinity required for the thermoplastic resin, the melting point, and the like. The heating step is preferably carried out at a temperature of 130°C to 240°C, more preferably 135°C to 230°C, and even more preferably 140°C to 210°C. The heating in the heating step is preferably carried out for 1 minute to 240 minutes, more preferably 3 minutes to 180 minutes, and even more preferably 5 minutes to 120 minutes. The method for cooling the heated web is not particularly limited. The heated web may be cooled naturally, or the cooling rate may be adjusted by applying cold air to the web.

[0052] Examples of methods for fixing the web include a method in which the longitudinal and lateral sides of the web cut into sheets are fixed with a large number of pins, a method in which the web is wound into a roll, etc. By winding the web into a roll, shrinkage of the web does not occur even when heated.

[0053] (Other processes) The method for producing a nonwoven fabric according to the present disclosure may include other steps in addition to the steps described above. Other steps include a step of preparing a thermoplastic resin containing SPS (hereinafter sometimes referred to as a preparation step), a step of subjecting the nonwoven fabric that has been subjected to a heating step to secondary processing, etc. The nonwoven fabric may be subjected to secondary processing before the heating step. Examples of secondary processing include entanglement, pressing, gear processing, printing, coating, laminating, shaping, hydrophilic processing, water-repellent processing, and pressing.

[0054] In the preparation step, the thermoplastic resin containing SPS may be heated to thermally decompose a portion of the thermoplastic resin, thereby adjusting the MFR of the thermoplastic resin. Methods for thermally decomposing a thermoplastic resin include, for example, heating with an extruder, adding a decomposition accelerator (degrading agent) to the thermoplastic resin, and the like.

[0055] Examples of the entanglement treatment include heat embossing, ultrasonic fusion, water jet treatment, hot air through treatment, and needle punch treatment.

[0056] From the viewpoint of maintaining a better balance between rigidity and breathability, the entanglement treatment preferably includes a heat embossing treatment. When the nonwoven fabric of the present disclosure is thermally bonded by thermal embossing, the embossed area ratio (thermocompression bonded portion) is preferably in the range of 5% to 30%, more preferably in the range of 5% to 20%. Examples of the imprint shape include circle, ellipse, oval, square, diamond, rectangle, rectangle, quilt, lattice, tortoiseshell, and continuous shapes based on these shapes.

[0057] From the viewpoint of controlling the thickness, rigidity, density, breathability, etc. of the nonwoven fabric of the present disclosure, the secondary processing preferably includes a pressing process. The pressing means for pressing the nonwoven fabric in the pressing process is not particularly limited, but may be, for example, a pressing means that applies pressure in the thickness direction of the nonwoven fabric (in the case of a nonwoven fabric laminate, the lamination direction of the laminate). Examples of pressing processes include a method in which two or more layers of nonwoven fabric (more preferably melt-blown nonwoven fabric) stacked in a sheet form are press-molded; and roll molding in which the nonwoven fabric is pressed with a roll; and among these, roll molding is preferably included. [Example]

[0058] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present disclosure.

[0059] -Preparing the materials- The following materials were used as SPS: The MFR of SPS was measured by the method described above. SPS: Syndiotactic polystyrene (Idemitsu Kosan Co., Ltd., MFR at 300°C and a load of 1.2 kg is 67.5 g / 10 min)

[0060] [Example 1] SPS was melted at 320°C, the spinneret temperature was 320°C, the nozzle hole diameter was 0.12 mm, the single-hole discharge rate was 14 mg / min, and the heating gas flow rate was 690 Nm 3 The melt-blown nonwoven fabric was obtained by extruding the SPS fiber from the spinneret under the following conditions: a flow rate of 1000 rpm, a heating gas temperature of 320°C, a distance between the spinneret and the collection belt of 60 mm, and an extrusion temperature of 320°C. The fibrous SPS was collected on the collection belt. The resulting meltblown nonwoven fabric was then cut to A4 size, and the nonwoven fabric was then placed on an A4 size metal plate, and the four corners of the nonwoven fabric were fixed with clips. The nonwoven fabric was placed in a fixed state in a thermostatic oven set at 140°C and subjected to heat treatment for 5 minutes. In this way, nonwoven fabric 1 of Example 1 was obtained.

[0061] (evaluation) The nonwoven fabric and thermoplastic resin were evaluated as follows. The evaluation results are shown in Table 1. -Crystallization- The crystallinity of the SPS contained in the nonwoven fabric 1 (thermoplastic resin) was determined as follows. 10 mg of nonwoven fabric 1 was accurately weighed and heated from 40°C to 300°C at a heating rate of 20°C / min using a differential scanning calorimeter (DSC-1 manufactured by PerkinElmer). The crystallinity of the SPS was determined based on the obtained DSC curve. -Melting point- For SPS, the temperature was increased at a rate of 20°C / min using the differential scanning calorimeter (DSC). The melting endothermic curve was measured, and the temperature at which the endothermic reaction peaked was determined as the melting point of the resin. -Average fiber diameter- The average fiber diameter of nonwoven fabric 1 was determined by taking a photograph of the surface of nonwoven fabric 1 at 1000x magnification using an electron microscope (model number: S-3500N, manufactured by Hitachi, Ltd.), randomly selecting 1000 fibers (n=1000) from the photograph, measuring the diameter (width) of the selected fibers, and calculating the arithmetic mean value as the average fiber diameter (Da). -Metsuke- Five test pieces measuring 100 mm (MD) x 100 mm (CD) were taken from the nonwoven fabric 1. The test pieces were taken from five locations in the CD direction. Next, the mass [g] of each test piece was measured using a top-pan electronic balance (manufactured by Kensei Kogyo Co., Ltd.) to determine the mass of each test piece. The average value was calculated from the masses obtained above, and the mass of 1 m 2 The weight per unit of nonwoven fabric is calculated as the mass [g] per unit [g / m 2 〕 -Thickness- Five test pieces measuring 100 mm (MD) x 100 mm (CD) were taken from nonwoven fabric 1. The test pieces were taken from five locations across the CD. Next, the thickness of each of the five test pieces was measured at five locations, the center and four corners, and these were averaged to determine the thickness of each nonwoven fabric. The average value of the thicknesses of the five nonwoven fabrics was calculated, and this was designated as the thickness of nonwoven fabric 1. The thickness was measured using a load of 7 gf / cm 2 A thickness gauge (measuring probe diameter 25 mmφ) was used.

[0062] -Dimensional stability- Five test pieces of 100 mm (MD) x 100 mm (CD) were taken from the nonwoven fabric 1. The test pieces were taken at five locations across the CD. The obtained test piece was placed in a thermostatic oven set at 150°C, 190°C or 260°C and subjected to heat treatment for 2 minutes. The lengths of each test piece in the MD and CD directions after heat treatment were measured. The shrinkage ratio was calculated by calculating the ratio of the measured lengths in the MD and CD directions to the lengths of each test piece before heat treatment. The shrinkage ratio was used as the dimensional stability at each heating temperature. -Tensile strength- The tensile strength was measured for Nonwoven Fabric 1. Five test pieces, each 50 mm wide (MD) x 200 mm long (CD), were taken from Nonwoven Fabric 1 and measured using a tensile tester with a chuck distance of 100 mm and a head speed of 100 mm / min. The average value was calculated to determine the tensile strength in the CD direction. The tensile strength was evaluated according to the following criteria. A:25N / 50mm or more B: 20N / 50mm or more, less than 25N / 50mm C: Less than 20N / 50mm -Solvent resistance- Test pieces were prepared in the same manner as described in the tensile strength section, and each test piece was immersed in toluene at 25°C for 5 minutes. After immersion, the tensile strength of the test piece was measured. Based on the tensile strength value after immersion in toluene, the solvent resistance was evaluated according to the following criteria. A:25N / 50mm or more B: 20N / 50mm or more, less than 25N / 50mm C: Less than 20N / 50mm

[0063] [Example 2] Nonwoven fabric 2 of Example 2 was obtained in the same manner as in Example 1, except that the heat treatment time was changed from 5 minutes to 3 minutes. Nonwoven fabric 2 was evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

[0064] [Example 3] Nonwoven fabric 3 of Example 3 was obtained in the same manner as in Example 1, except that the heat treatment time was changed from 5 minutes to 1 minute. Nonwoven fabric 3 was evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

[0065] [Comparative Example 1] Comparative nonwoven fabric 1 of Comparative Example 3 was obtained in the same manner as in Example 1, except that the heat treatment time was changed from 5 minutes to 0 minute. Comparative nonwoven fabric 1 was evaluated in the same manner as in Example 1. The obtained results are shown in Table 1.

[0066] [Table 1]

[0067] The evaluation results shown in Table 1 show that the nonwoven fabrics of Examples 1-3, in which the crystallinity of SPS was 40% or more, were superior in dimensional stability in a high-temperature environment to the nonwoven fabric of Comparative Example 1.

Claims

1. Contains a thermoplastic resin including syndiotactic polystyrene, The crystallinity of the syndiotactic polystyrene is 40% or more.

2. 2. The nonwoven fabric according to claim 1, wherein the average fiber diameter is 10 μm or less.

3. 2. The nonwoven fabric according to claim 1, wherein the syndiotactic polystyrene accounts for 50% by mass or more of the thermoplastic resin.

4. Melting a thermoplastic resin including syndiotactic polystyrene; A step of discharging the molten thermoplastic resin together with a heated gas from a spinneret having a plurality of holes and stretching the thermoplastic resin by the heated gas to form a fibrous resin; collecting the fibrous resin to obtain a web; and heating the web in a fixed state to suppress deformation of the web in a planar direction due to heating.

5. The method for producing a nonwoven fabric according to claim 4, wherein the heating is carried out at 130°C to 240°C.

6. The method for producing a nonwoven fabric according to claim 4, wherein the heating is carried out for 1 minute to 240 minutes.

7. The method for producing a nonwoven fabric according to claim 4, wherein the thermoplastic resin has a melt flow rate of 5 g / 10 min to 10,000 g / 10 min at 300° C. under a load of 1.2 kg.

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