Polyester fiber and nonwoven fabric formed therefrom

Abstract

The purpose of the present invention is to provide, inter alia, a polyester fiber that exhibits an excellent white opacity without the use of titanium oxide.　A polyester fiber according to the present invention is a polyester fiber composed of a polyester-based resin and is characterized by: containing more than 1.0 mass% and not more than 30.0 mass% calcium carbonate in 100 mass% for the polyester fiber; exhibiting a crystal melting maximum peak temperature for the calcium carbonate-containing polyester-based resin, as measured by differential scanning calorimetry, of less than 255°C; and having an L value, indicating the hue of the fiber, of at least 91 and a b value of not more than 5.0.

Description

Polyester fibers and nonwoven fabrics formed therefrom

[0001] The present invention relates to a polyester fiber and a nonwoven fabric formed therefrom that maintain nonwoven fabric processability and are excellent in safety, hiding power, and sustainability, and that can be used in applications such as sanitary materials such as wet wipes and mask components, medical sanitary materials, daily living materials, general medical materials, clothing materials, bedding materials, filter materials, nursing care products, and pet products.

[0002] Some nonwoven fabrics used in hygiene products such as wet wipes and mask components are obtained by hydroentangling raw cotton made from polyester resin using the spunlace method, and are required to have a white color that gives an impression of cleanliness.

[0003] Titanium oxide is commonly incorporated into resins to improve the white color of the fibers that make up nonwoven fabrics. However, titanium oxide will be classified as carcinogenic in Category 2 (inhalation) under the European CLP Regulation in October 2021, raising safety concerns, such as the requirement for specific warning and labeling on products containing more than 1% titanium oxide by mass.

[0004] Titanium dioxide has a high refractive index and is highly stable, making it widely used as a white pigment added to resins, accounting for 70% of the white pigments currently in use. Other white pigments include zinc oxide, but they are less safe and stable than titanium dioxide, making them difficult to replace in hygiene and other applications. Furthermore, titanium dioxide is an underground resource (mineral resource), and is less sustainable than biological resources, which are environmentally friendly materials.

[0005] On the other hand, there have been many reported examples of incorporating inorganic particles other than titanium oxide and zinc oxide or talc into resins to improve the transparency and softness of fibers and nonwoven fabrics. However, because the refractive index of inorganic particles and talc is low and close to that of polyester resins, it has been thought that simply incorporating them into resins would not be able to produce a white color equivalent to that of titanium oxide.

[0006] For example, in Patent Document 1, calcium carbonate is used to impart soft feel and high rigidity to nonwoven fabric, but the color of the fiber is not considered.

[0007] Patent Document 2 describes that calcium carbonate is used to improve mechanical hardness and thermal conductivity, and to provide a multifilament fiber with increased opacity, but does not consider the color of the fiber.

[0008] In Patent Document 3, inorganic particles are added to improve the anti-transparency (concealment) properties of a two-component core-sheath composite fiber, with the amount of inorganic particles added to the core being 0.10 to 10 mass % and the amount of inorganic particles added to the sheath being 0.050 to 1.0 mass %, and the functionality is achieved by including inorganic particles in both the core and the sheath, with titanium oxide being the main inorganic particles. One of the examples describes an example in which calcium carbonate is used in the core and aluminum oxide in the sheath, but no study is made on improving the anti-transparency properties or hue by using calcium carbonate alone.

[0009] In Patent Document 4, recycled PET is used for the core of a recycled polyester sheath-core composite fiber, and 3 mass% or more of titanium oxide is added to improve the hue (L value, b value), but no other inorganic particles or talc are investigated. As shown in Patent Documents 3 and 4, titanium oxide is not suitable for use in plastic volume reduction, where the amount of resin is reduced by adding it at a high concentration.

[0010] JP 2020-90771 A JP 2019-112759 A JP 2021-55231 A JP 2006-328600 A

[0011] In light of the above, in order to overcome the drawbacks of titanium oxide, a conventionally used white pigment, such as its safety and sustainability, and its use in reducing the volume of plastics due to its high concentration addition, it is desirable to provide a fiber that can contribute to reducing the environmental burden by adding other inorganic particles instead of titanium oxide, thereby reducing the amount of resin used without significantly affecting the quality of the fiber while maintaining post-processability into nonwoven fabrics, etc. Furthermore, it is also desirable to provide a safe and sustainable fiber by using inorganic substances that can be expected to utilize biological resources, which are environmentally friendly materials. An object of the present invention is to provide a polyester fiber that has excellent white hiding properties without using titanium oxide, and a nonwoven fabric formed therefrom. A preferred object of the present invention is to provide a polyester fiber that has excellent white hiding properties and good strength and elongation, and a nonwoven fabric formed therefrom.

[0012] The polyester fiber of the present invention, which has achieved the above-mentioned object, has the following gist: The polyester fiber of the present invention is a polyester fiber composed of a polyester resin, which contains more than 1.0 mass % and not more than 30.0 mass % of calcium carbonate relative to 100 mass % of the polyester fiber, and is characterized in that the calcium carbonate-containing polyester resin has a maximum crystalline melting peak temperature of less than 255°C as measured by a differential scanning calorimeter, and has an L value of 91 or more and a b value of 5.0 or less, which indicate the hue of the fiber.

[0013] It is also preferable that the calcium carbonate-containing polyester resin has a crystallization peak temperature of 190°C to 220°C as measured by a differential scanning calorimeter.

[0014] The polyester resin preferably contains polyethylene terephthalate.

[0015] The cross-sectional shape of the fiber may be solid or hollow. Preferably, the tensile strength of the fiber measured in accordance with JIS L1013 8.5.1 is 1.0 cN / dtex or more, and the elongation of the fiber measured in accordance with JIS L1013 8.5.1 is 10% or more.

[0016] The present invention also includes a nonwoven fabric formed from the polyester fibers.

[0017] According to the present invention, it is possible to provide a polyester fiber having excellent white hiding power and good strength and elongation, and a nonwoven fabric formed therefrom, without using titanium oxide. According to a preferred embodiment of the present invention, a polyester fiber having excellent white hiding power and good strength and elongation, and a nonwoven fabric formed therefrom are provided.

[0018] That is, the polyester fiber of the present invention can be used to produce nonwoven fabrics that are excellent in safety and environmental sustainability, while maintaining the same hue, hiding power, flexibility, bulkiness, and bulk recovery properties as conventional fibers to which a white pigment mainly composed of titanium oxide is added, and that also enable a reduction in the environmental load by reducing the volume of plastic.

[0019] Furthermore, titanium oxide has a high Mohs hardness and causes metal abrasion, so fibers containing titanium oxide on the fiber surface wear the metal rollers of the processing machine, particularly during processing to impart crimping, making sustained crimping difficult. In the present invention, by using calcium carbonate in polyester fibers, it is possible to reduce guide wear and traveler wear during stretching, which have traditionally been problems with fibers containing titanium oxide on the fiber surface. This makes it possible to obtain polyester fibers for nonwoven fabrics that have the same white color, hiding power, and softness as conventional fibers containing titanium oxide, while also having a smooth fiber surface.

[0020] FIG. 1 shows the results of differential scanning calorimetry of the calcium carbonate-containing polyester resin of the polyester fiber obtained in Comparative Example 1. FIG. 2 shows the results of differential scanning calorimetry of the calcium carbonate-containing polyester resin of the polyester fiber obtained in Example 1. FIG. 3 shows the results of differential scanning calorimetry of the calcium carbonate-containing polyester resin of the polyester fiber obtained in Example 2. FIG. 4(a) shows the orientation of polymer chains in an undrawn yarn. FIG. 4(b) shows the orientation of polymer chains after drawing an undrawn yarn of polymer chains that do not contain calcium carbonate. FIG. 4(c) shows the orientation of polymer chains after drawing an undrawn yarn of polymer chains that contain calcium carbonate.

[0021] [Polyester Fiber] The polyester fiber of the present invention is a polyester fiber composed of a polyester resin, characterized in that it contains more than 1.0 mass% and not more than 30.0 mass% of calcium carbonate relative to 100 mass% of the polyester fiber, and that the calcium carbonate-containing polyester resin has a maximum crystalline melting peak temperature of less than 255°C, as measured by a differential scanning calorimeter, and has an L value of 91 or more and a b value of 5.0 or less, which indicate the hue of the fiber. By stretching the calcium carbonate-containing polyester resin, the orientation of the polyester resin can be increased and the crystal size of the polyester resin can be increased, resulting in an increased whiteness (hiding ability) of the polyester fiber.

[0022] The polyester resin may be any resin that exhibits strength and low shrinkage, and examples thereof include polyethylene terephthalate (melting point 255°C), polybutylene terephthalate (melting point 230°C), polytrimethylene terephthalate (melting point 230°C), polyethylene naphthalate (melting point 265°C), polybutylene naphthalate (melting point 243°C), polyhydroxyalkanoate (melting point approximately 180°C), polyhydroxybutyric acid (melting point 175°C), and polylactic acid (melting point 170 to 175°C).

[0023] Among these, from the viewpoint of strength and low shrinkage, the polyester-based resin preferably contains a polyester-based resin having a melting point of 200 ° C or higher (preferably 210 ° C or higher, more preferably 220 ° C or higher and 280 ° C or lower), and more preferably contains polyethylene terephthalate (melting point 255 ° C), polybutylene terephthalate (melting point 230 ° C), polytrimethylene terephthalate (melting point 230 ° C), polyethylene naphthalate (melting point 265 ° C), polybutylene naphthalate (melting point 243 ° C), and even more preferably contains polyethylene terephthalate (melting point 255 ° C), polyethylene naphthalate (melting point 265 ° C), polybutylene naphthalate (melting point 243 ° C), and particularly preferably contains polyethylene terephthalate (melting point 255 ° C). The polyester-based resin may be one type or two or more types.

[0024] The polyester resin may have a predetermined intrinsic viscosity, and the intrinsic viscosity (IV) of the polyester resin is preferably 0.3 to 2.0 dl / g, more preferably 0.5 to 1.5 dl / g, and even more preferably 0.55 to 0.80 dl / g. The intrinsic viscosity (IV) of the polyester resin can be determined by pulverizing and drying a sample, dissolving it in a 6 / 4 (mass ratio) mixed solvent of phenol and 1,1,2,2-tetrachloroethane, centrifuging the solution to remove inorganic particles and the like, and then measuring the IV at a temperature of 30°C using an Ubbelohde viscometer.

[0025] The content of the polyester resin having a melting point of 200° C. or higher is preferably 80% by mass or higher, more preferably 90% by mass or higher, even more preferably 95% by mass or higher, still more preferably 97% by mass or higher, particularly preferably 99% by mass or higher, and most preferably 100% by mass, based on 100% by mass of the polyester resin. When the content of the polyester resin having a melting point of 200° C. or higher is within the above range, adding calcium carbonate and stretching the fiber promotes crystallization of the polyester resin, thereby increasing the whiteness of the fiber.

[0026] The content of the polyester resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, preferably less than 99% by mass, more preferably 98% by mass or less, even more preferably 97% by mass or less, and still more preferably 96% by mass or less, based on 100% by mass of the polyester fiber. If the content of the polyester resin is less than 70% by mass, the strength of the polyester fiber may decrease, and if the content of the polyester resin is 99% by mass or more, the crystallization of the polyester resin may not be promoted, and good whiteness may not be achieved.

[0027] The calcium carbonate contained in the polyester fiber may be ground calcium carbonate, light calcium carbonate, or a mixture thereof.

[0028] Heavy calcium carbonate may be obtained by crushing and classifying natural materials such as limestone, marble, calcite, and chalk, and is also called natural calcium carbonate. Light calcium carbonate may be obtained by precipitating crystals in a liquid through a chemical reaction (for example, by precipitating through the reaction of calcium hydroxide with carbon dioxide), and is also called synthetic calcium carbonate or precipitated calcium carbonate. Calcium carbonate may be surface-treated with a fatty acid, siloxane, resin, or the like. Examples of fatty acids include stearic acid, palmitic acid, myristic acid, and lauric acid, and may be used as a salt or ester of the fatty acid. Examples of resins include polyacrylate and polydiallyldimethylammonium chloride.

[0029] The calcium carbonate preferably has a predetermined average particle size d50 and top-cut particle size d90. The average particle size d50 means that 50% by mass of all particles have a particle size smaller than the indicated value, and the top-cut particle size d90 means that 90% by mass of all particles have a particle size smaller than the indicated value.

[0030] The average particle size d50 of calcium carbonate is preferably 0.02 to 3.0 μm, more preferably 0.35 to 1.75 μm, even more preferably 0.40 to 1.50 μm, and still more preferably 0.45 to 1.25 μm. The top cut particle size d90 of calcium carbonate is preferably 5.0 μm or less, more preferably 4.0 μm or less, even more preferably 3.0 μm or less, still more preferably 2.0 μm or less, and particularly preferably 1.0 μm or less, and is preferably 0.3 μm or more or 0.5 μm or more.

[0031] The calcium carbonate content is preferably more than 1.0% by mass and not more than 30.0% by mass, more preferably 2.0% by mass or more and not more than 25.0% by mass, even more preferably 3.0% by mass or more and not more than 20.0% by mass, and even more preferably 4.0% by mass or more and not more than 15.0% by mass, based on 100% by mass of polyester fiber. If the calcium carbonate content is 1.0% by mass or less, crystallization of the polyester resin may not be promoted, and the L value of the obtained fiber may be small. If the calcium carbonate content exceeds 30.0% by mass, the pressure rise rate of the filter used for spinning may increase, and fluffing and thread breakage may occur.

[0032] The fiber component may contain components other than the polyester resin and calcium carbonate as long as the effects of the present invention are achieved, and additives such as antioxidants, antistatic agents, antiblocking agents, pigments, heat stabilizers, ultraviolet absorbers, and lubricants may be added within limits that do not impair the effects of the present invention.

[0033] The content of the polyester resin and calcium carbonate contained in the polyester fiber is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, still more preferably 99% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the polyester fiber. It is preferable that the fiber component is substantially free of titanium oxide, and the content of titanium oxide is more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and still more preferably 0% by mass, based on 100% by mass of the fiber component.

[0034] The calcium carbonate-containing polyester resin may have a predetermined maximum crystalline melting peak temperature measured by a differential scanning calorimeter. The maximum crystalline melting peak temperature of the calcium carbonate-containing polyester resin is less than 255°C, preferably 243 to 254°C, more preferably 244 to 253°C, and even more preferably 245 to 252°C. A maximum crystalline melting peak temperature within the above range is observed when a component containing a polyester resin and calcium carbonate is stretched, and promotes crystallization of the polyester resin, thereby increasing the whiteness of the fiber. When unstretched, the maximum crystalline melting peak temperature of the core component containing a polyester resin and calcium carbonate is 255°C or higher, which does not promote crystallization of the polyester resin and prevents the whiteness of the fiber from being increased. Note that as the calcium carbonate content increases within the above range, the maximum crystalline melting peak temperature tends to increase within the above temperature range.

[0035] The calcium carbonate-containing polyester resin may have a predetermined temperature-decreasing crystallization peak temperature measured by a differential scanning calorimeter, and the temperature-decreasing crystallization peak temperature of the calcium carbonate-containing polyester resin is, for example, 190° C. to 220° C., preferably 200° C. to 220° C., more preferably 202° C. to 218° C., even more preferably 204° C. to 216° C., and still more preferably 206° C. to 214° C. When the temperature-decreasing crystallization peak temperature of the calcium carbonate-containing polyester resin is within the above range, unoriented fine crystals are formed, which tends to promote crystallization of the polyester resin.

[0036] The single yarn fineness is preferably 0.1 to 8.0 dtex, more preferably 0.2 to 4.8 dtex, even more preferably 0.5 to 4.6 dtex, still more preferably 1.0 to 4.4 dtex, and particularly preferably 1.5 to 4.2 dtex. The single yarn fineness can be measured in accordance with JIS L-1095 9.4.1.

[0037] The cross-sectional shape of the fiber is preferably a solid cross-section or a hollow cross-section, and there may be two or more hollow cross-sections in the fiber.

[0038] The polyester fiber of the present invention is preferably a drawn polyester fiber. The polyester fiber contains calcium carbonate, and by drawing this polyester fiber, the L value can be made larger than the L value of the undrawn polyester fiber, to be 91 or more. Even if the undrawn polyester fiber contains calcium carbonate, the L value cannot be made 91 or more. (L value of drawn polyester fiber - L value of undrawn polyester fiber) is preferably more than 0, more preferably 1 or more and 10 or less, even more preferably 2 or more and 9 or less, still more preferably 3 or more and 8 or less, and particularly preferably 4 or more and 7 or less. The L value tends to increase as the draw ratio increases.

[0039] The polyester fiber of the present invention has a predetermined L value and b value as appropriate whiteness for appearance quality. That is, the L value indicating the hue of the fiber is 91 or more, and the b value is 5.0 or less. The L value is preferably 91.5 or more, more preferably 92 or more, even more preferably 92.5 or more, and still more preferably 93 or more, and preferably 99 or less or 98 or less. If the L value is less than 91, the fiber is not suitable for use as a nonwoven fabric for sanitary materials.

[0040] The b value is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, even more preferably 3.0 or less, particularly preferably 2.5 or less, and most preferably 2.0 or less. If the b value exceeds 5.0, the color tone will be yellowish and the nonwoven fabric will not be suitable for use as a sanitary material. The L value and b value can be measured using a color difference meter (for example, a spectrophotometer CM-3700d manufactured by MINOLTA).

[0041] The polyester fiber of the present invention may have a predetermined strength and elongation. The strength of the fiber, as a tensile strength measured in accordance with JIS L1013 8.5.1, is preferably 1 to 15 cN / dtex, more preferably 1.5 to 12 cN / dtex, even more preferably 2 to 10 cN / dtex, still more preferably 2.5 to 8 cN / dtex, and particularly preferably 3 to 8 cN / dtex.

[0042] The elongation of the fiber, as measured in accordance with JIS L1013 8.5.1, is preferably 10 to 200%, more preferably 15 to 190%, even more preferably 20 to 180%, still more preferably 25 to 170%, and particularly preferably 30 to 160%.

[0043] [Method for Preparing Polyester Fiber] The polyester fiber of the present invention preferably comprises at least a step of melt-spinning a polyester resin and calcium carbonate to prepare an undrawn yarn, and a step of drawing the undrawn yarn under heating conditions.

[0044] Calcium carbonate may be dispersed by adding and stirring a predetermined amount during or immediately after the polymerization of the resin, and then chipping the mixture while extruding it with an extruder, or by spinning the resin in a molten state. Examples of methods for uniformly dispersing calcium carbonate in a resin include a circulation dispersion method and a masterbatch method. The circulation dispersion method may be a method in which a predetermined amount of calcium carbonate is added immediately after the polymerization of the resin, and the resin melt is circulated to disperse the calcium carbonate. The masterbatch method may be a method in which a predetermined amount of calcium carbonate is previously wetted with water, a solvent, or the like, and mixed with a predetermined resin in a pressure kneader, and the calcium carbonate is dispersed while separating the water and solvent.

[0045] <Melt Spinning Step> The calcium carbonate-containing polyester resin is preferably melted and extruded from a spinneret via a spin pack. The extrusion is performed through a spinneret having preferably 10 to 1,000 holes, more preferably 50 to 800 holes, even more preferably 100 to 600 holes, and even more preferably 200 to 400 holes, at a spinning temperature 10 to 30°C higher than the melting point of the polyester resin. Air at preferably 10 to 25°C is then applied to the spun yarn at a flow rate of preferably 50 to 100 m / min to cool it, a spinning oil may be applied, and the undrawn yarn may be collected in a container (e.g., a can) preferably at a take-up speed of 1,000 to 1,500 m / min.

[0046] <Drawing Step> The obtained undrawn yarn is preferably drawn using a liquid phase or a gas phase at 60°C to 130°C, at a draw ratio of preferably 1.5 to 6.0. Drawing may be in one stage or two or more stages. In the case of two-stage drawing, the first stage drawing is preferably carried out at a temperature of 60 to 90°C (preferably 60 to 80°C) and a draw ratio of 2.0 to 4.0 (preferably 3.6 or less, more preferably 3.2 or less). The second stage drawing is preferably carried out at a temperature of 90 to 130°C (preferably 100 to 120°C) and a draw ratio of 0.8 to 1.2 (preferably 0.9 to 1.1).

[0047] The method for producing a polyester fiber of the present invention may include a crimping step, a post-heat treatment step, and a cutting step in addition to the above steps. The crimping step may involve crimping using a crimper such as a stuffer box crimper. The post-heat treatment step may involve treating the obtained fiber at a temperature of 90 to 140°C (preferably 100 to 130°C) without applying tension to the fiber.

[0048] When polyester fibers are cut into short fibers, the average length of the short fibers is preferably 30 to 80 mm, more preferably 31 to 70 mm, and even more preferably 32 to 60 mm.

[0049] The polyester fiber may be surface-treated with an oil agent that exhibits hydrophilicity or water repellency, and may be treated with an oil agent in any step after cutting, drying, or the like.

[0050] By adding calcium carbonate to a resin and then performing drawing and crystallization treatments, the crystalline structure of the drawn yarn can be controlled to obtain a polyester fiber that combines whiteness (white color, opacity, and anti-transparency) with the mechanical properties required for raw cotton for nonwoven fabrics. The mechanism by which whiteness is improved in the present invention is shown in Figures 4(a) to 4(c). Figure 4(a) shows the orientation of polymer chains in an undrawn yarn. Figure 4(b) shows the orientation of polymer chains after drawing an undrawn yarn containing polymer chains that do not contain calcium carbonate. Figure 4(c) shows the orientation of polymer chains after drawing an undrawn yarn containing polymer chains that contain calcium carbonate. As shown in Figure 4(a), the polymer chains contained in the undrawn resin are randomly oriented. As shown in Figure 4(b), in the absence of inorganic particles such as calcium carbonate, unoriented crystals (e.g., spherulites) grow during the process of neck deformation of the undrawn yarn upon drawing, and act as a factor that inhibits the orientation of the polymer chains contained in the resin. In contrast, as shown in Figure 4(c), the addition of inorganic particles such as calcium carbonate acts as a nucleating agent for polyester resins (e.g., PET resins), reducing the size of unoriented crystals formed in the system (the nucleating agent effect promotes crystallization of unoriented, small crystals). This allows for the application of linear, uniform stress to the undrawn yarn compared to systems without calcium carbonate, promoting oriented crystallization and resulting in drawn yarns with crystal sizes that diffuse visible light (larger crystal sizes result in higher visible light diffusion and higher whiteness). The phenomenon of calcium carbonate acting as a nucleating agent for polyester resins (e.g., PET resins) can be inferred from the temperature-reducing crystallization peak temperature in differential scanning calorimetry (DSC) (Figures 2 and 3). As the calcium carbonate concentration increases, the temperature-reducing crystallization peak temperature increases, suggesting that the nucleating agent effect promotes the formation of unoriented, small crystals.

[0051] The phenomenon in which the crystal size of drawn yarns increases depending on the drawing and crystallization conditions in systems containing calcium carbonate can be inferred from the results of differential scanning calorimetry (DSC). In the DSC curve (FIG. 1) of Comparative Example 1, which was not drawn after adding calcium carbonate, the PET-derived crystalline melting curve appears as a single broad absorption curve with a peak near 255°C. This is a crystalline melting curve derived from unoriented crystals (spherulites) that are not accompanied by orientation of the polymer chains contained in the resin. In contrast, the DSC curve (FIG. 2) of Example 1 shows an absorption curve with a maximum peak temperature near 250°C. This is a crystalline melting curve that arises due to drawing and is derived from crystals accompanied by orientation of the polymer chains contained in the resin. As the draw ratio is increased to near the break region, the broad absorption curve with a peak near 255°C attenuates, and the peak near 255°C is no longer observed (only an absorption curve with a maximum peak temperature near 250°C remains). The drawn yarn in this state has excellent whiteness, but is not suitable for nonwoven fabric applications because its elongation is significantly reduced. Therefore, in order to obtain a drawn yarn that has both excellent whiteness and mechanical properties, it is important that the maximum peak temperature of crystalline melting of the drawn yarn is measured at a temperature lower than 255°C.

[0052] Increasing the draw ratio of the calcium carbonate-containing polyester resin can promote the formation of oriented crystals and improve whiteness. In the DSC curve of Example 1 (Figure 2), the maximum peak temperature of oriented crystals (crystals with high visible light diffusivity) is measured at 250°C, whereas in Example 2 (Figure 3), which contains a higher calcium carbonate concentration, the maximum peak temperature of oriented crystals is measured at 251-252°C. The shift of the crystal melting peak to the higher temperature side suggests that the crystal size of oriented crystals increases as the draw ratio increases.

[0053] The polyester fibers of the present invention may be long fibers (filaments), short fibers (staple), or a combination thereof.

[0054] The present invention encompasses nonwoven fabrics formed from polyester fibers. The nonwoven fabric is preferably formed by conventionally known fleece formation and fleece bonding methods. Fleece formation can be achieved by dry laying, wet laying, spunbonding, melt flow bonding, etc., while fleece bonding can be achieved by thermal bonding, chemical bonding, needle punching, spunlace, stitch bonding, steam jet bonding, etc. Methods for fleece formation and fleece bonding can be selected from the above depending on the desired nonwoven fabric. However, from the viewpoints of hygiene and aesthetics, the spunlace method, which does not use a binder such as an adhesive, is preferred.

[0055] This application claims the benefit of priority based on Japanese Patent Application No. 2023-170385, filed on September 29, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-170385, filed on September 29, 2023, are incorporated herein by reference.

[0056] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the invention with appropriate modifications within the scope of the above and below-described aims, and all such modifications are included within the technical scope of the present invention. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass." The sample size is based on the size described below, but when the sample was insufficient, measurements were carried out using the largest possible sample size.

[0057] (1) Materials Polyethylene terephthalate (PET) with an intrinsic viscosity (IV) of 0.63 dL / g was used as the polyester component. KRS1 manufactured by Maruo Calcium Co., Ltd. was used as the calcium carbonate.

[0058] (2) Color Tone Measurement The L value and b value were measured using a MINOLTA CM-3700d color difference meter with settings that excluded reflected light. The L value and b value in the present invention were measured using samples in which the obtained fibers were wound on a black backing and visually confirmed that the color of the backing did not show through. The L value is an index of the whiteness of the color, and the b value is an index of the yellowness of the color. If the L value is less than 85 or the b value exceeds 5.0, when used as a nonwoven fabric, the appearance of the color tone will be poor and the quality will be poor, with insufficient hiding power. Although anti-see-through properties can be obtained even with an L value of 90 or less, an L value of 91 or more is desirable for nonwoven fabrics used as sanitary materials.

[0059] (3) Differential Scanning Calorimetry Measurement The crystal melting peak temperature was measured at a heating rate of 10°C / min using a differential scanning calorimeter manufactured by TA Instruments. The temperature at the extreme value of the measured melting absorption curve was defined as the crystal melting maximum peak temperature. The cooling crystallization peak temperature was measured at a cooling rate of 10°C / min.

[0060] (4) Fineness, Single Yarn Fineness Measured by the method described in JIS L-1095 9.4.1. The single yarn fineness was calculated by dividing the fineness by the number of filaments.

[0061] (5) Maximum stress (also simply referred to as strength) and maximum elongation (also simply referred to as elongation) were measured in accordance with JIS L1013 8.5.1. The stress at the maximum load was defined as the maximum stress, and the elongation at the maximum load was defined as the maximum elongation.

[0062] [Example 1] Polyethylene terephthalate (PET) as a polyester-based resin was dried by a conventional method, and then the calcium carbonate content was adjusted to 5.0% by mass together with the PET and fed to a fiber spinning machine. The mixture was melt-extruded at 285°C using an extruder attached to the spinning machine, and spun using a spinneret with multiple holes. The spun yarn was cooled by airflow, oiled using an oiling guide, and bundled using a bundle guide. It was then pulled by a roller at a spinning speed of 1240 m / min and wound on a winder. The resulting fiber (unstretched yarn) had a single yarn fineness of 5.0 dtex. It was then stretched in a stretching apparatus at a speed of 40 m / min at a stretching temperature of 70°C to a ratio of 2.9, followed by a stretching ratio of 0.95 at a stretching temperature of 110°C and heat-set at 120°C. Through these spinning and drawing steps, polyester fibers having a single fiber fineness of 1.8 dtex were obtained.

[0063] [Example 2] The same procedure as in Example 1 was carried out, except that an undrawn yarn was obtained by the method of Example 1 and then the single yarn fineness was adjusted to 1.5 dtex by the draw ratio.

[0064] Comparative Example 1 The same procedure as in Example 1 was carried out except that the stretching and heat treatment were not carried out.

[0065]

[0066] The polyester fiber of the present invention can be suitably used for applications such as sanitary materials such as wet wipes and mask components, medical sanitary materials, daily living materials, general medical materials, clothing materials, bedding materials, filter materials, nursing care products, and pet products.

Claims

1. A polyester fiber composed of a polyester resin, containing more than 1.0% by mass and not more than 30.0% by mass of calcium carbonate in 100% by mass of polyester fiber, the polyester fiber having a maximum crystal melting peak temperature of less than 255°C as measured by a differential scanning calorimeter, and an L value indicating the hue of the fiber of 91 or more and a b value of 5.0 or less.

2. The polyester fiber according to claim 1, wherein said polyester fiber is a stretched polyester fiber.

3. The polyester fiber according to claim 1 or 2, wherein the calcium carbonate-containing polyester resin has a crystallization peak temperature during cooling of 190°C to 220°C as measured by a differential scanning calorimeter.

4. The polyester fiber according to claim 1 or 2, wherein the polyester resin comprises polyethylene terephthalate.

5. The polyester fiber according to claim 1 or 2, wherein the cross-sectional shape of the fiber is a solid cross section or a hollow cross section.

6. The polyester fiber according to claim 1 or 2, wherein the tensile strength of the fiber measured in accordance with JIS L1013 8.5.1 is 1.0 cN / dtex or more.

7. The polyester fiber according to claim 1 or 2, which has a fiber elongation of 10% or more as measured in accordance with JIS L1013 8.5.

1.

8. A nonwoven fabric formed from the polyester fiber according to claim 1 or 2.

Images