Regenerated cellulose fibers, methods for producing the same, and fiber structures containing the same

Abstract

The present invention pertains to a recycled cellulose fiber that includes recycled natural cellulose microparticles, the median diameter of the recycled natural cellulose microparticles being 0.5-10 µm, inclusive. The recycled cellulose fiber including the recycled natural cellulose microparticles can be produced, for example, by extruding in a spinning bath, using a nozzle, a spinning solution obtained by adding an aqueous dispersion of the recycled natural cellulose microparticles having a median diameter of 0.5-10 µm, inclusive, to a spinning raw solution including cellulose, spinning and coagulating the solution, and generating the fiber. It is thereby possible to conserve resources and provide a recycled cellulose fiber including recycled natural cellulose that has good spinning properties, a method for manufacturing same, and a fiber structure including said fiber.

Description

[Technical Field]

[0001] This invention relates to regenerated cellulose fibers containing recycled natural cellulose microparticles, a method for producing the same, and a fibrous structure containing the same. [Background technology]

[0002] Cellulosic fibers are gentle on human skin and environmentally friendly, and are therefore used in a variety of applications such as clothing, building materials, and furniture. Cellulosic fibers include natural cellulose and regenerated cellulose fibers, and regenerated cellulose fibers using regenerated cellulose are known to be manufactured by various methods such as the viscose method, the copper ammonia method, and the solvent spinning method. Recently, there has been a trend to incorporate natural cellulose fibers into regenerated cellulose fibers. For example, Patent Document 1 proposes incorporating non-regenerated woody natural cellulose into fibrous filaments with a diameter of 20 to 400 μm, made from an aqueous suspension containing water and cellulose fibers. On the other hand, cotton fibers are being separated and reused from clothing and other items made with blended yarns containing cotton fibers. For example, Patent Document 2 describes using clothing made with blended yarns containing used cotton and polyester fibers, and using an organic acid-catalyzed hydrothermal reaction to decompose the cotton fibers, separate the cotton fibers from the polyester fibers, and recover the cotton fiber fragments. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2020-502390 [Patent Document 2] International Publication No. 2019 / 047174 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, when attempting to incorporate recycled natural cellulose into regenerated cellulose fibers, there was a problem with poor spinnability.

[0005] The present invention provides a regenerated cellulose fiber containing recycled natural cellulose that can conserve resources and has good spinnability, a method for producing the same, and a fiber structure containing the same. [Means for solving the problem]

[0006] The present invention relates to regenerated cellulose fibers comprising recycled natural cellulose fine particles, wherein the recycled natural cellulose fine particles have a median diameter of 0.5 μm or more and 10 μm or less.

[0007] The present invention also relates to a method for producing regenerated cellulose fibers containing recycled natural cellulose fine particles, comprising the steps of: adding an aqueous dispersion of recycled natural cellulose fine particles having a median diameter of 0.5 μm or more and 10 μm or less to a spinning stock containing cellulose and mixing it; and extruding the obtained spinning stock into a spinning bath from a nozzle and spinning it, and then coagulating and regenerating the fibers.

[0008] The present invention also relates to a fibrous structure containing the aforementioned regenerated cellulose fibers. [Effects of the Invention]

[0009] According to the present invention, by providing regenerated cellulose fibers containing recycled natural cellulose and fibrous structures containing the same, it is possible to reduce the waste of natural cellulose such as cotton fibers, thereby reducing the environmental burden caused by waste and conserving resources. Furthermore, the manufacturing method of the present invention makes it possible to obtain regenerated cellulose fibers that have good spinnability and contain recycled natural cellulose. [Brief explanation of the drawing]

[0010] [Figure 1]Figure 1 is an optical microscope image of the side surface of the rayon fiber obtained in Example 2. [Figure 2] Figure 2 is a scanning electron microscope image of the fiber cross-section of the rayon fiber obtained in Example 8. [Figure 3] Figure 3 is a scanning electron microscope image of the fiber cross-section of the rayon fiber obtained in Comparative Example 1. [Figure 4] Figure 4 shows the IR spectra obtained by microscopic infrared spectroscopy analysis of recycled natural cellulose powder (Reference Example 1), rayon fibers obtained in Example 2, and rayon fibers obtained in Comparative Example 1. [Figure 5] Figure 5 is a graph showing the results of the light shielding performance. [Figure 6] Figure 6 is a graph showing the results of the pH buffering. [Modes for carrying out the invention]

[0011] The inventors of this invention diligently studied how to incorporate recycled natural cellulose into regenerated cellulose fibers in order to conserve resources. As a result, they found that by using recycled natural cellulose as fine particles of a predetermined particle size, it is possible to incorporate recycled natural cellulose into regenerated cellulose fibers with good handling and spinnability. According to this invention, by incorporating recycled natural cellulose into regenerated cellulose fibers, it is possible to reduce the waste of natural cellulose such as cotton fibers, and the recycled natural cellulose can impart functionality to the regenerated cellulose fibers, for example, by improving the dyeability to direct dyes.

[0012] The regenerated cellulose fibers include recycled natural cellulose fine particles with a median diameter (50% particle diameter, also referred to as d50) of 0.5 μm or more and 10 μm or less. When the median diameter is 10 μm or less, the spinnability and productivity of the fibers are good. When the median diameter is 0.5 μm or more, the productivity and handling of the fine particles are good. From the viewpoint of practical productivity, the recycled natural cellulose fine particles preferably have a median diameter of 0.6 μm or more and 6 μm or less, and more preferably 0.7 μm or more and 5 μm or less.

[0013] The presence of recycled natural cellulose microparticles in regenerated cellulose fibers can be confirmed by observing the fibers with a microscope or scanning electron microscope, as well as by performing micro-infrared spectroscopy on the fibers. Specifically, the presence or absence of microparticles can be confirmed by observing the side and cross-section of the fibers with a microscope. The presence or absence of microparticles can be confirmed by observing the cross-section of the fibers with a scanning electron microscope, based on the roughness of the cross-section. Furthermore, the presence or absence of peaks originating from cellulose type I (natural cellulose) can be confirmed by performing micro-infrared spectroscopy on the fibers. For example, in the IR spectrum obtained by micro-infrared spectroscopy, at wavenumber 3320 cm⁻¹... -1 ~3370cm -1 If there is a shoulder-shaped peak in the range, it means that it contains natural cellulose.

[0014] In the present invention, the median diameter (volume cumulative average particle diameter d50) of the recycled natural cellulose microparticles can be measured by a laser diffraction / scattering particle size distribution measurement method. In the present invention, as will be described later, by spinning a spinning solution obtained by adding an aqueous dispersion of recycled natural cellulose microparticles to a spinning dope containing cellulose, the recycled natural cellulose microparticles are included in the regenerated cellulose fiber. Therefore, the recycled natural cellulose microparticles exist in the regenerated cellulose in a state where they are dispersed in the spinning solution or in a state close thereto. That is, the particle diameter of the recycled natural cellulose microparticles as a raw material and the particle diameter of the recycled natural cellulose microparticles in the regenerated cellulose fiber are substantially the same. The particle diameter of the recycled natural cellulose microparticles in the regenerated cellulose fiber of the present invention can be confirmed, for example, by performing a side observation using transmitted light with a microscope or by performing a cross-sectional observation with a scanning electron microscope.

[0015] The recycled natural cellulose microparticles may be derived from recycled natural cellulose. The recycled natural cellulose microparticles are not particularly limited, but from the viewpoints of resource conservation and environmental friendliness, recycled natural cellulose microparticles obtained by pulverizing or refining recycled natural cellulose powder obtained by subjecting used products or wastes such as clothing containing natural cellulose fibers such as cotton fibers to hydrothermal treatment in the presence of an organic acid are preferred. In the present specification, the recycled natural cellulose powder means those having a median diameter exceeding 10 μm.

[0016] Examples of the used products or wastes such as clothing containing natural cellulose fibers such as cotton fibers include woven or knitted fabrics using used cotton fibers and polyester fiber blended yarns (hereinafter, also referred to as used cotton / polyester woven or knitted fabrics).

[0017] The method for obtaining recycled natural cellulose powder by hydrothermally treating used clothing and other waste products containing natural cellulose fibers such as cotton fibers in the presence of an organic acid is not particularly limited, but examples include obtaining cotton fiber fragments by a hydrothermal reaction catalyzed by an organic acid, as described in International Publication No. 2019 / 047174. Recycled natural cellulose powder can be obtained, for example, as follows.

[0018] First, used cotton / polyester woven fabric is finely shredded and dispersed in an aqueous solution containing organic acids.

[0019] The organic acid can be a naturally derived, biodegradable organic acid. Such organic acids are preferable because they do not decompose during the process of separating and recycling cotton and polyester fibers from used cotton / polyester woven fabrics, and therefore do not cause secondary pollution to the environment. Examples of organic acids include methanesulfonic acid, oxalic acid, tartaric acid, citric acid, malic acid, formic acid, and acetic acid, with methanesulfonic acid, oxalic acid, or citric acid being preferred.

[0020] The aqueous solution containing the organic acid is an aqueous solution obtained by mixing the organic acid with water, and the content of the organic acid as a catalyst is preferably 0.1 to 30% by mass, and more preferably 0.5 to 10% by mass. A higher content of organic acid can accelerate the decomposition reaction and shorten the required reaction time, and furthermore, it can easily decompose thick fabrics and fabrics with tightly bonded fibers.

[0021] A solid-liquid mixture is obtained by fragmenting the used cotton / polyester woven fabric and dispersing it in an aqueous solution of an organic acid catalyst. The solid-liquid ratio (mass ratio) of the solid-liquid mixture is preferably 1:30 to 200, more preferably 1:50 to 150. Within this range, the hydrothermal reaction tends to be relatively fast.

[0022] Next, the solid-liquid mixture may be placed in a sealed high-pressure reactor and heated to 110-180°C at a rate of 4-6°C / min while stirring, and maintained for 0.5-3 hours to decompose the cotton fibers in the used cotton / polyester woven fabric. In this case, the pressure difference between the inside and outside of the high-pressure reactor may be set to 0.10-1 MPa.

[0023] Under the subcritical hydrothermal conditions described above, cotton fibers undergo a decomposition reaction, while polyester remains unaffected. The decomposed cotton fibers are detached from the woven fabric in the form of small flakes, separating them from the polyester fibers. By increasing the temperature or extending the reaction time, even smaller cotton fiber flakes can be obtained.

[0024] Next, the polyester fibers and cotton fibers are recovered separately by filtration. Specifically, the mixture is filtered through a screen (for example, a 20-mesh screen), and the filtrate is washed to obtain a polyester fiber aggregate. Then, the filtrate (the remaining mixture after filtration) is vacuum filtered through a filtration membrane such as a PTFE (polytetrafluoroethylene) membrane, and the filtrate is washed to obtain cotton fiber fragments.

[0025] Afterward, if necessary, the polyester fiber aggregate and cotton fiber fragments may be dried in a blast oven or similar device until they reach a certain mass.

[0026] The cotton fiber fragments (recycled natural cellulose powder) obtained in this manner preferably have a low degree of polymerization, exhibiting a relative viscosity (JIS P 8101:1994) of 1.0 to 2.0. Because the recycled natural cellulose powder with the aforementioned low degree of polymerization has a large amount of amorphous regions of cellulose, it tends to have high grinding efficiency, such as wet grinding, and the functionality of regenerated cellulose fibers containing fine particles obtained by grinding or micronizing the powder tends to improve.

[0027] The recycled natural cellulose powder, including the cotton fiber fragments mentioned above, typically has a median diameter of approximately 22 μm or more. Recycled natural cellulose fine particles can be obtained by grinding the recycled natural cellulose powder so that the median diameter is between 0.5 μm and 10 μm. The grinding method is not particularly limited, and any known grinding method can be used as appropriate. It may be wet grinding or dry grinding. Wet grinding and dry grinding may also be used in combination. Due to the simplicity of the manufacturing process when preparing the spinning solution, wet grinding, or a combination of dry and wet grinding, is preferred.

[0028] The equipment used in the dry grinding method is not particularly limited, but examples include cutting mills, impact mills, airflow mills, and media mills. These may be used individually or in combination of two or more types, and furthermore, several stages of processing may be performed with the same type of equipment. Examples of media mills include vibrating ball mills. The equipment used in the wet grinding method includes mascolloiders, high-pressure homogenizers, and media mills. Examples of media mills include bead mill grinders.

[0029] In the case of wet grinding, although not particularly limited, for example, a horizontal wet grinder such as a bead mill can be used, and recycled natural cellulose powder having a median diameter of 10 μm or more can be added to water at a concentration of 1% by mass or more and 10% by mass or less. Grinding can then be performed under conditions of a dispersion supply flow rate of 5 L / hour or more and 50 L / hour or less, a disk peripheral speed of 8 m / sec or more and 14 m / sec or less, and 5 to 10 passes or less. As beads, zirconia beads, glass beads, alumina beads, zircon beads, steel beads, etc. with a particle size of 0.03 mm or more and 2 mm or less can be used.

[0030] Alternatively, recycled natural cellulose powder having a median diameter exceeding 10 μm may be added to water and then finely ground using a pulverizing disperser so that the median diameter is between 0.5 μm and 10 μm. As a pulverizing disperser, a powerful device with beating capabilities such as a homomixer at high speed rotation, an ultra-high pressure homogenizer, an ultrasonic dispersion machine, a beater, a disc refiner, a conical refiner, a double-disc refiner, or a grinder may be used. The resulting dispersion containing recycled natural cellulose fine particles may be mixed and dispersed using a screw mixer, paddle mixer, disper mixer, turbine mixer, disper, propeller mixer, kneader, blender, homogenizer, ultrasonic homogenizer, colloid mill, pebble mill, etc., to adjust the concentration, etc.

[0031] The regenerated cellulose fibers are not particularly limited, but from the viewpoint of recyclability and practicality, they preferably contain 0.5 parts by mass to 50 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of regenerated cellulose, more preferably 1.0 part by mass to 40 parts by mass, and even more preferably 1.5 parts by mass to 30 parts by mass.

[0032] The regenerated cellulose fibers are not particularly limited, but for example, for practical use, it is preferable that the standard strength (dry strength) measured in accordance with JIS L 1015:2010 is 1.0 cN / dtex or higher, and more preferably 1.1 cN / dtex or higher. Furthermore, it is preferable that the wet strength (wet strength) measured in accordance with JIS L 1015:2010 is 0.5 cN / dtex or higher, and more preferably 0.6 cN / dtex or higher.

[0033] The regenerated cellulose fibers are not particularly limited, but for example, for practical use, it is preferable that the standard elongation (dry elongation) measured in accordance with JIS L 1015:2010 is 11% or more, and more preferably 12-24%. Furthermore, it is preferable that the wet elongation (wet elongation) measured in accordance with JIS L 1015:2010 is 14% or more, and more preferably 15-27%.

[0034] The regenerated cellulose fibers are not particularly limited, but from the viewpoint of good spinnability such as stretching and easy regeneration during spinning bath, the single fiber fineness may be 60 dtex or less. From the viewpoint of suitable use as a textile fiber, it may be 0.3 dtex or more and 4.5 dtex or less, 0.5 dtex or more and 3.3 dtex or less, or 0.8 dtex or more and 2.5 dtex or less.

[0035] The regenerated cellulose fibers are not particularly limited, and their fiber length can be appropriately set depending on the intended use of the textile product. For example, when used in clothing, the fiber length may be between 30 mm and 130 mm.

[0036] The regenerated cellulose fibers tend to have a high dyeing rate for direct dyes and excellent exhaustability, such as dyeability. The dyeing rate can be used not only as an indicator of dyeability, showing the proportion of dyeing to the fibers using direct dyes, but also as an indicator of exhaustability in exhaust processing, where fibers or fiber structures are treated in a processing bath in which functional agents are dissolved or dispersed to diffuse and / or adsorb into the interior of the fibers. The dyeing rate of the regenerated cellulose fibers is preferably 60% or more, and more preferably 65% ​​or more. If the dyeing rate is less than 60%, sufficient exhaustability (dyeability) cannot be exhibited. There is no particular upper limit to the dyeing rate, but for example, when considering dyeability, it is preferably 90% or less. If the dyeing rate exceeds 90% in terms of dyeability, uneven coloring may occur when a fiber structure mixed with the regenerated cellulose fibers and other fibers is dyed with direct dyes.

[0037] The regenerated cellulose fibers may contain functional agents as needed. Functional agents may include organic and / or inorganic substances having one or more functions such as moisture absorption and release, pH buffering (pH control), deodorization, antibacterial, antiviral, anti-allergen, antifungal, anti-mite, anti-insect, anti-mosquito, photothermal conversion, temperature control, cooling sensation, heat storage, ultraviolet shielding (UV cut), heat ray shielding, ion exchange, and metal adsorption.

[0038] The functional agent can be added in an amount that does not impair the performance of the regenerated cellulose fibers containing recycled natural cellulose fine particles. Preferably, the functional agent is present in an amount of 0.05 parts by mass or more and 40 parts by mass or less per 100 parts by mass of regenerated cellulose, more preferably 0.1 parts by mass or more and 20 parts by mass or less, and even more preferably 0.2 parts by mass or more and 10 parts by mass or less.

[0039] For example, if the functional agent is to improve pH buffering (pH control), it is preferable that the functional agent be a compound containing a carboxyl group. Examples of compounds containing a carboxyl group include polyacrylic acid, acrylic acid copolymers, maleic acid copolymers, and their ester compounds.

[0040] The amount of the compound containing the carboxyl group added is preferably 1 part by mass or more and 30 parts by mass or less per 100 parts by mass of regenerated cellulose. More preferably, it is 2 parts by mass or more and 20 parts by mass or less. If the amount of the compound containing the carboxyl group added is less than 1 part by mass, there is no significant difference from ordinary rayon, and if it exceeds 30 parts by mass, the fiber strength tends to decrease, making it difficult to obtain fine fibers.

[0041] From the viewpoint of having excellent pH buffering capacity (pH controllability), regenerated cellulose fibers containing a functional agent that improves pH buffering capacity preferably have pH buffering capacity in the range of pH 3 to 10, and more preferably have pH buffering capacity in the range of pH 4 to 9.

[0042] In the aforementioned regenerated cellulose fibers, when a compound containing carboxyl groups is added as a functional agent, the total amount of carboxyl groups is 0.30 to 1.63 mmol / g, preferably 0.36 to 1.14 mmol / g. If the total amount of carboxyl groups is less than 0.30 mmol / g, the function of the compound containing carboxyl groups cannot be fully exhibited, and if it exceeds 1.63 mmol / g, the fibers tend to become alkaline, and yellowing of the cellulose is likely to occur during processing such as heating.

[0043] In this invention, the regenerated cellulose fiber containing recycled natural cellulose microparticles surprisingly exhibits light-shielding properties, particularly good ultraviolet and visible light shielding. Although the reason is unclear, it is thought that the presence of cellulose microparticles with different crystalline structures within the fiber causes light to scatter, resulting in light-shielding properties.

[0044] Light shielding properties can be further improved by adding functional agents. When adding a light shielding agent as a functional agent, it is preferable to use ceramic as the light shielding agent. The average particle size of the ceramic is preferably 0.01 to 5.0 μm. More preferably, the average particle size is 0.1 to 1.0 μm. The average particle size can be measured using laser diffraction / scattering particle size distribution measurement.

[0045] Examples of the aforementioned ceramics include titanium dioxide, silicon dioxide, and zinc dioxide. Among these, titanium dioxide is particularly preferred.

[0046] The amount of ceramic added is preferably 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of regenerated cellulose. More preferably, it is 1.5 parts by mass or more and 10 parts by mass or less. If the amount of ceramic added is less than 0.5 parts by mass, the ultraviolet shielding ability decreases significantly, and even if it exceeds 10 parts by mass, the performance does not increase.

[0047] The light shielding properties of the regenerated cellulose fibers are expressed as the average light transmittance, and the water-entangled nonwoven fabric (basis weight 50g / m²) is made of 100% by mass of regenerated cellulose fibers. 2 It is preferable that the average ultraviolet transmittance is 25% or less and / or the average visible light transmittance is 30% or less when the fiber is set to 25% or less. More preferably, the average ultraviolet transmittance is 22% or less and / or the average visible light transmittance is 25% or less. In particular, it is preferable that the average UVB transmittance is 20% or less and / or the average UVC transmittance is 22% or less in the ultraviolet region. More preferably, the average UVB transmittance is 18% or less and / or the average UVC transmittance is 20% or less. Ultraviolet light (ultraviolet region) refers to wavelengths from 250 to 380 nm, within the ultraviolet region, UVC is wavelengths from 250 nm to 280 nm, UVB is wavelengths from 280 nm to 315 nm, and visible light (visible region) refers to wavelengths from 380 to 780 nm. Ultraviolet transmittance and visible light transmittance are indicators of the light-shielding ability of a fiber. The lower the transmittance, the higher the light-shielding ability.

[0048] In the aforementioned regenerated cellulose fibers, if a light-shielding agent is further added as a functional agent, a water-entangled nonwoven fabric (basis weight 50 g / m²) made of 100% by mass of regenerated cellulose fibers is obtained. 2 Preferably, the average ultraviolet transmittance is 15% or less and / or the average visible light transmittance is 20% or less when the light is set to 15% or less. More preferably, the average ultraviolet transmittance is 10% or less and / or the average visible light transmittance is 18% or less. Particularly in the ultraviolet region, it is preferable that the average UVB transmittance is 10% or less and / or the average UVC transmittance is 12% or less. More preferably, the average UVB transmittance is 8% or less and / or the average UVC transmittance is 10% or less.

[0049] In one or more embodiments of the present invention, regenerated cellulose fibers containing recycled natural cellulose fine particles can be produced by adding an aqueous dispersion of recycled natural cellulose fine particles having a median diameter of 0.5 μm to 10 μm to a spinning stock containing cellulose, mixing the resulting spinning solution, extruding it through a nozzle into a spinning bath, spinning it, and then coagulating and regenerating it. Furthermore, if necessary, an aqueous solution and an aqueous dispersion of a functional agent can be added to the cellulose-containing spinning stock along with the aqueous dispersion of recycled natural cellulose fine particles.

[0050] From the viewpoint of recyclability and practicality, it is preferable to add an aqueous dispersion of recycled natural cellulose fine particles to a spinning stock containing cellulose in such a manner that the amount of recycled natural cellulose fine particles is 0.5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of cellulose in the spinning stock, more preferably 1 part by mass or more and 40 parts by mass or less, and even more preferably 1.5 parts by mass or more and 30 parts by mass or less.

[0051] The aqueous dispersion of recycled natural cellulose fine particles is not particularly limited, but may be used as is after wet grinding or micronizing the recycled natural cellulose powder described above in water, or it may be used after wet grinding or micronizing the recycled natural cellulose powder in water and diluting it to a predetermined concentration. From the viewpoint of being easily mixed with the spinning stock containing cellulose and easily kneaded into the regenerated cellulose fibers, the aqueous dispersion preferably contains 0.5% to 50% by mass of recycled natural cellulose fine particles, more preferably 1% to 40% by mass, and even more preferably 1.5% to 30% by mass.

[0052] The aqueous dispersion of recycled natural cellulose microparticles is not particularly limited, but may contain a dispersant to further improve the dispersibility of the recycled natural cellulose microparticles when mixed with a spinning solution containing cellulose. Examples of dispersants include anionic surfactants and nonionic surfactants.

[0053] The aforementioned regenerated cellulose fibers can be produced by known methods for producing regenerated cellulose fibers, except that an aqueous dispersion of recycled natural cellulose fine particles and, if necessary, an aqueous solution or aqueous dispersion of a functional agent are added to a spinning solution containing cellulose. As the spinning solution, a viscose solution containing cellulose (also called raw material viscose) can be used for viscose rayon fibers, a solution of cellulose dissolved in copper ammonium solution can be used for cupro, a solution of cellulose dissolved in a solvent can be used for lyocell, and acetylcellulose can be used for acetate.

[0054] When the regenerated cellulose fiber is rayon fiber, it can be manufactured by adding an aqueous dispersion of recycled natural cellulose microparticles and, if necessary, an aqueous solution or aqueous dispersion of a functional agent to a viscose stock solution, mixing the mixture, and then extruding the resulting spinning solution containing recycled natural cellulose microparticles through a nozzle into a spinning bath for spinning and coagulation regeneration.

[0055] As a viscose stock solution, it is preferable to use one that contains, for example, 7% to 10% by mass of cellulose, 5% to 8% by mass of sodium hydroxide, and 2% to 3.5% by mass of carbon disulfide.

[0056] As the (spinning) nozzle, for example, a nozzle with 1,000 to 20,000 holes can be used, and from the viewpoint of productivity and ease of obtaining uniform fibers, a nozzle with 3,000 to 12,000 holes is preferable. In addition, a normal circular nozzle with a diameter of 0.05 mm to 0.12 mm may be used, but a nozzle with an irregular cross-section may be used as needed.

[0057] As the spinning bath, it is preferable to use a Müller bath containing 95 g / L to 125 g / L of sulfuric acid and 10 g / L to 17 g / L of zinc sulfate. A more preferable sulfuric acid concentration is 100 g / L to 120 g / L. When the sulfuric acid concentration is 95 g / L or higher, productivity is good without slowing down regeneration, and when the sulfuric acid concentration is 125 g / L or lower, spinnability is good without speeding up regeneration. When the zinc sulfate concentration is 10 g / L or higher, regeneration on the surface of viscose is not accelerated. When the zinc sulfate concentration is 17 g / L or lower, viscose coagulation and regeneration can proceed at an appropriate rate.

[0058] The spinning speed is preferably in the range of 30 m / min to 80 m / min. Furthermore, the draw ratio is preferably between 39% and 55%. Here, the draw ratio indicates how much faster the sliver speed is after drawing, relative to the sliver speed before drawing (which is set to 100). Expressed as a ratio, this means the pre-draw ratio is 1, and the post-draw ratio is between 1.39 and 1.55.

[0059] The rayon fibers obtained as described above are cut to a predetermined length and subjected to a scouring process. The scouring process should be carried out in the usual manner, in the order of hot water treatment, hydrosulfurization treatment, bleaching, and acid washing. Afterwards, excess moisture is removed as needed by methods such as compression rollers or vacuum suction.

[0060] If pH buffering (pH controllability) is required, the rayon fiber yarn after the scouring process may be subjected to a pH adjustment treatment to adjust the pH of the fiber to between 3 and 10, if necessary.

[0061] In one or more embodiments of the present invention, the regenerated cellulose fibers can be used in fibrous structures such as tow, filament, spun yarn, padding, paper, nonwoven fabric, woven fabric, and knitted fabric. The fibrous structure may consist solely of the regenerated cellulose fibers containing the recycled natural cellulose fine particles, or it may be used in combination with other fibers. Other fibers include regenerated cellulose fibers other than those containing the recycled natural cellulose fine particles, natural fibers, synthetic fibers, etc. Examples of other regenerated cellulose fibers include rayon, cupro, solvent-spun cellulose, and polynosic. Examples of natural fibers include cotton fibers, hemp, wool, silk, and pulp. Examples of synthetic fibers include acrylic fibers, polyester fibers, polyamide fibers, polyolefin fibers, and polyurethane fibers. Synthetic fibers may be single fibers or composite fibers.

[0062] The aforementioned fiber structure is useful for clothing products such as underwear, undergarments, outerwear, scarves, stoles, hats, ear loops, and gloves; building materials such as wallpaper; furniture products such as carpets; and papermaking applications such as shoji paper. [Examples]

[0063] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0064] First, we will explain the measurement and evaluation methods. (1) Fiber fineness Measurements were taken in accordance with JIS L 1015:2010. (2) Strength and elongation The elongation under standard conditions and under wet conditions were measured in accordance with JIS L 1015:2010. (3) Micro-infrared spectroscopy Micro-infrared spectrophotometer was used to perform micro-infrared spectroscopy under the following measurement conditions. <Measurement conditions> Sample preparation: KBr method Measurement method Transmission measurement Total number of times: 20 Wavenumber range: 600-4000 cm -1 Wavenumber resolution 4cm -1 Data processing: No baseline correction / normalization. (4) Microscopic observation of fibers The side surface of the fiber was observed using an optical microscope (Nikon Instec, model number ECLIPSE LV100ND) at 320x magnification. The fiber cross-section was observed using a scanning electron microscope (Hitachi High-Tech Corporation, "SU3500"). (5) Particle size distribution The median diameter (volume-cumulative mean particle size d50) of recycled natural cellulose microparticles in an aqueous dispersion of recycled natural cellulose microparticles was measured using a laser diffraction / scattering particle size analyzer (Shimadzu Corporation, "SALD-7500"). (6) Dyeing rate A dyeing solution was prepared using a bath ratio of 1:100, with the direct dye Direct Sky Blue 6B at 0.2% by mass relative to the material to be dyed, and the auxiliary agent anhydrous sodium sulfate at 20% by mass relative to the material to be dyed. The dyeing rate was measured in accordance with JIS L 1015:2010. (7) Light shielding properties (average ultraviolet light transmittance and average visible light transmittance) Using a Shimadzu UV-3600 ultraviolet-visible-near-infrared spectrometer and a MPC-3100 multi-purpose large sample chamber, the transmittance of ultraviolet and visible light was measured. The transmittances of ultraviolet and visible light were averaged to obtain the average ultraviolet transmittance, average UVC transmittance, average UVB transmittance, and average visible light transmittance, respectively. The sample used was 100% by mass of rayon fiber (basis weight 50 g / m²). 2 A water-entangled nonwoven fabric was prepared and used. The wavelength range was 250-380 nm for ultraviolet light, with UVC wavelengths of 250-280 nm, UVB wavelengths of 280-315 nm, and visible light wavelengths of 380-780 nm. (8)pH buffering property Sample (100% by mass of rayon fiber (basis weight 50 g / m²)) 2A 1cm square of water-entangled nonwoven fabric was cut, and three pieces were stacked together. 0.1ml of pH standard solutions adjusted to pH 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11 were added dropwise to each piece, and the samples were immersed for 30-60 seconds. The pH of the samples immersed in the pH standard solutions was measured using a pH meter (HORIBA, "LAQUAtwinB-712"). Measurements were performed with n=4, and the values ​​were averaged. (9) Measurement of the total amount of carboxyl groups (1) 1.2 g of the sample (fiber) was immersed in 50 mL of 1 mol / L hydrochloric acid aqueous solution (pH 0.1), stirred, and left for 5 minutes. Then, it was stirred again to adjust the pH of the aqueous solution to 2.5. As a result, all carboxyl groups in the sample (fiber) exist in the H form. Next, the sample was washed with water and dried in a constant temperature forced-air dryer at 105°C for 2 hours until completely dry. Washing the sample with water removes all excess hydrochloric acid adhering to the fiber. (2) 100 mL of deionized water, 0.4 g of sodium chloride, and 20 mL of 0.1 mol / L sodium hydroxide solution were placed in a beaker. (3)1 g of the sample prepared in (1) was weighed precisely [W1(g)], cut into pieces small enough not to get tangled in the stirring bar, placed in the beaker prepared in (2), and stirred with a stirrer for 15 minutes. This converts all carboxyl groups in the sample (fiber) into salt forms. The stirred sample was filtered by suction. 60 mL of the filtrate was taken and titrated with 0.1 mol / L hydrochloric acid aqueous solution using phenolphthalein as an indicator, and the titration volume was set to X1(mL). (4) The total amount of carboxyl groups Y (mmol / g) was calculated based on the following formula. Thus, the amount of sodium hydroxide obtained by subtracting the amount of residual sodium hydroxide from the total amount of sodium hydroxide corresponds to the total amount of carboxyl groups in the sample (fiber). Total amount of carboxyl groups Y (mmol / g) = [[(0.1 × 20) - (0.1 × X 1)] × (120 / 60)] / W 1

[0065] (Example 1) [Preparation of recycled natural cellulose powder] A 15g white shirt with a polyester / cotton fiber mass ratio of 65 / 35 was finely cut, then placed in 1.8L of a 5% citric acid aqueous solution. While stirring, the mixture was heated in a high-pressure reactor at a rate of 5°C / min to 130°C, and maintained at that temperature for 1.5 hours to allow the decomposition reaction of the cotton fibers to occur. After the reaction was complete, the heater was switched off and the high-pressure reactor was cooled to room temperature before the contents were removed. The contents were screen filtered to separate the polyester fiber aggregate as the filtrate, and the remaining filtrate was vacuum filtered through a filter membrane to obtain cotton fiber fragments. The cotton fiber fragments were washed with deionized water and dried to obtain recycled natural cellulose powder. The relative viscosity (JIS P 8101:1994) of the obtained recycled natural cellulose powder was 1.4, confirming that it had a low degree of polymerization. [Preparation of an aqueous dispersion of recycled natural cellulose microparticles] The recycled natural cellulose powder obtained above was added to ion-exchanged water at a concentration of 10% by mass, and the recycled natural cellulose powder was pulverized using a horizontal wet pulverizer (manufactured by Shinmaru Enterprises Co., Ltd., model: Dynomill KDL-PILOT A). The pulverization conditions were: dispersion supply flow rate during pulverization: 25 L / hour, disc peripheral speed: 8 m / sec, bead material: zirconia beads with a particle size of 0.65 mm, and number of passes: 10. The resulting aqueous dispersion of pulverized recycled natural cellulose powder was diluted with ion-exchanged water to obtain an aqueous dispersion of recycled natural cellulose fine particles with a concentration of 4.2% by mass. [Preparation of spinning solution] An aqueous dispersion of recycled natural cellulose microparticles was added to the raw material viscose in an amount of 12 parts by mass per 100 parts by mass of cellulose, and the mixture was stirred and mixed using a mixer. The raw material viscose used contained 9.0% by mass of cellulose, 5.2% by mass of sodium hydroxide, and 3.2% by mass of carbon disulfide. [Spinning conditions] The obtained spinning solution was spun using a two-bath tension spinning method at a spinning speed of 50 m / min and a draw ratio of 43% to obtain fibers with a single fiber fineness of approximately 1.5 dtex. The composition of the first bath (spinning bath) was a Müller bath (50°C) containing 115 g / L sulfuric acid, 13 g / L zinc sulfate, and 350 g / L sodium sulfate. A nozzle with 10,692 holes with a pore diameter of 0.06 mm was used as the spinneret to discharge the spinning solution. No problems such as single fiber breakage occurred during spinning, and the spinnability of the spinning solution (mixed viscose) was good. [Scouring process] The viscose rayon yarn obtained in this way was cut to 38 mm and subjected to a scouring treatment. The scouring treatment involved hot water treatment followed by rinsing with water, then removing excess water with a compression roller, followed by treatment with a 0.8 mass% aqueous solution of sodium hydrosulfide at 55°C, followed by rinsing with water and removing moisture with a compression roller. Next, it was bleached with a 0.03 mass% aqueous solution of hypochlorous acid at room temperature (20°C ± 5°C), followed by rinsing with water and removing moisture with a compression roller. After that, it was treated with a 0.1 mass% aqueous solution of sulfuric acid at room temperature (20°C ± 5°C), followed by rinsing with water and removing excess water with a compression roller, then treated with a 1.0 mass% oil, and dried at 60°C for 7 hours to obtain rayon fibers.

[0066] (Example 2) Rayon fibers were obtained in the same manner as in Example 1, except that an aqueous dispersion of the pulverized recycled natural cellulose powder was diluted with deionized water to a concentration of 5.0% by mass of recycled natural cellulose fine particles, and the resulting aqueous dispersion of recycled natural cellulose fine particles with a concentration of 5.0% by mass was added to the raw material viscose in an amount of 20 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose.

[0067] (Example 3) The recycled natural cellulose powder obtained in the same manner as in Example 1 was added to ion-exchanged water at a concentration of 7% by mass, and the recycled natural cellulose powder was pulverized using a horizontal wet pulverizer (manufactured by Shinmaru Enterprises Co., Ltd., model: Dynomill KDL-PILOT A). The pulverization conditions were: dispersion supply flow rate during pulverization: 25 L / hour, disc peripheral speed: 14 m / sec, bead material: zirconia beads with a particle size of 0.65 mm, and number of passes: 5. After pulverization, the mixture was diluted with ion-exchanged water to obtain an aqueous dispersion of recycled natural cellulose fine particles with a concentration of 5.0% by mass. Rayon fibers were obtained in the same manner as in Example 1, except that the aqueous dispersion of recycled natural cellulose fine particles obtained above was added to the raw material viscose in an amount of 15 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose.

[0068] (Example 4) Rayon fibers were obtained in the same manner as in Example 3, except that an aqueous dispersion of recycled natural cellulose fine particles was added to the raw material viscose in an amount of 20 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose.

[0069] (Example 5) Rayon fibers were obtained in the same manner as in Example 3, except that an aqueous dispersion of recycled natural cellulose fine particles was added to the raw material viscose in an amount of 25 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose.

[0070] (Comparative Example 1) Rayon fibers were obtained in the same manner as in Example 1, except that the raw material viscose was spun directly.

[0071] (Comparative Example 2) In an attempt to produce rayon fibers in the same manner as in Example 1, except that the recycled natural cellulose powder obtained in the same manner as in Example 1 was added to ion-exchanged water at a concentration of 10% by mass and stirred and mixed in a mixer to obtain an aqueous dispersion of recycled natural cellulose powder, which was then added to the raw material viscose in an amount of 20 parts by mass of recycled natural cellulose powder per 100 parts by mass of cellulose, single filament breakage occurred shortly after spinning, making spinning impossible.

[0072] (Example 6) Rayon fibers were obtained in the same manner as in Example 3, except that an aqueous dispersion of recycled natural cellulose fine particles was added to the raw material viscose in an amount of 5 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose.

[0073] (Example 7) Rayon fibers were obtained in the same manner as in Example 3, except that an aqueous dispersion of recycled natural cellulose fine particles was added to the raw material viscose in an amount of 5 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose, an aqueous solution of acrylic acid-maleic acid copolymer salt (Aqualic TL400, manufactured by Nippon Shokubai Co., Ltd., an aqueous solution containing 40% by mass of sodium acrylic acid-maleic acid copolymer with a weight-average molecular weight of 50,000, viscosity: 1990 mPa·s, maleic acid content in sodium acrylic acid-maleic acid copolymer is 45% by mass) was added to the raw material viscose as a functional agent in an amount of 2.5 parts by mass of acrylic acid-maleic acid copolymer salt per 100 parts by mass of cellulose, and an aqueous dispersion of titanium dioxide with an average particle size of 0.309 μm dispersed in water (titanium dioxide concentration 15% by mass) was added to the raw material viscose in an amount of 1.8 parts by mass of titanium dioxide per 100 parts by mass of cellulose, mixed, and the resulting spinning solution was used.

[0074] (Example 8) Rayon fibers were obtained in the same manner as in Example 7, except that an aqueous dispersion of recycled natural cellulose fine particles was added to the raw material viscose in an amount of 10 parts by mass of recycled natural cellulose fine particles per 100 parts by mass of cellulose.

[0075] (Comparative Example 3) Rayon fibers were obtained in the same manner as in Comparative Example 1, except that an aqueous dispersion of titanium dioxide with an average particle size of 0.309 μm (titanium dioxide concentration 15% by mass), obtained by dispersing titanium dioxide in water, was added to the raw material viscose in a ratio of 1.8 parts by mass of titanium dioxide per 100 parts by mass of cellulose, mixed, and the resulting spinning solution was used to obtain a single fiber fineness of approximately 2.1 dtex.

[0076] The side and cross-sections of the rayon fibers of the examples and comparative examples were observed as described above, and the results are shown in Table 1 and Figures 1-3 below. Micro-infrared spectroscopy analysis was also performed on the rayon fibers of the examples and comparative examples as described above, and the results are shown in Tables 1-2 and Figure 4 below. Furthermore, the elongation strength, dyeing rate, light shielding properties, and pH buffering properties of the rayon fibers of the examples and comparative examples were measured as described above, and the results are shown in Tables 1-2 and Figures 5-6 below. In addition, the d50 of the recycled natural cellulose fine particles in the aqueous dispersion of recycled natural cellulose fine particles used in the examples was measured as described above, and the results are shown in Tables 1-2 below. In Comparative Example 2, the d50 of the recycled natural cellulose powder in the aqueous dispersion of recycled natural cellulose powder was also measured using the particle size distribution described above. In Tables 1-2 below, "amount added" is the amount of recycled natural cellulose fine particles or functional agent added per 100 parts by mass of cellulose in the viscose raw material.

[0077] [Table 1]

[0078] [Table 2]

[0079] Figure 1 is an optical microscope image (320x magnification) of the side surface of the rayon fiber obtained in Example 2. From Figure 1, it can be confirmed that fine particles are present inside the fiber. Figure 2 is a scanning electron micrograph (2000x magnification) of the cross-section of the rayon fiber obtained in Example 8. From Figure 2, it can be confirmed that fine particles are present inside the fiber. Figure 3 is a scanning electron micrograph (2000x magnification) of the cross-section of the rayon fiber in Comparative Example 1. From Figure 3, it can be confirmed that no fine particles are present inside the fiber.

[0080] Figure 4 is an IR spectrum showing the microscopic infrared spectroscopic analysis results of the recycled natural cellulose powder (Reference Example 1), the rayon fiber obtained in Example 2, and the rayon fiber obtained in Comparative Example 1. As can be seen from Figure 4, the rayon fiber of Example 2, like the natural cellulose powder of Reference Example 1, has a shoulder-type peak derived from cellulose I in the range of wave numbers 3320 cm -1 ~3370 cm -1 and it was confirmed that it contains recycled natural cellulose fine particles.

[0081] Although not shown in the figure, as shown in Tables 1 and 2, the rayon fibers of the examples contained recycled natural cellulose fine particles. Also, the rayon fibers containing recycled natural cellulose fine particles of Examples 1 to 5 had a higher dyeing rate for direct dyes than the regular rayon fiber of Comparative Example 1. <00003​​​​​As can be seen from Figure 6, the nonwoven fabric using rayon fibers containing a pH buffer in addition to the recycled natural cellulose microparticles of Example 7 exhibited high pH buffering capacity in the pH range of 3 to 10. [Industrial applicability]

[0083] The regenerated cellulose fibers of the present invention can be used, for example, in fibrous structures such as tow, filament, spun yarn, padding, paper, nonwoven fabric, and woven / knitted fabrics. Furthermore, fibrous structures using the regenerated cellulose fibers of the present invention are useful for clothing products such as underwear, undergarments, outerwear, scarves, stoles, hats, ear loops, and gloves; building materials such as wallpaper; furniture products such as carpets; and papermaking applications such as shoji paper.

Claims

1. Contains recycled natural cellulose microparticles, The aforementioned recycled natural cellulose microparticles are derived from recycled cotton fibers. The recycled natural cellulose fine particles are characterized by having a median diameter of 0.5 μm or more and 10 μm or less.

2. A product comprising recycled natural cellulose fine particles (excluding tea grain powder), The recycled natural cellulose fine particles are characterized by having a median diameter of 0.5 μm or more and 10 μm or less.

3. The recycled natural cellulose fine particles have a relative viscosity of 1.0 to 2.0 as measured by JIS P 8101 1994, as described in Claim 1 or 2.

4. The regenerated cellulose fiber according to any one of claims 1 to 3, comprising 0.5 parts by mass or more and 50 parts by mass or less of the recycled natural cellulose fine particles per 100 parts by mass of regenerated cellulose.

5. The regenerated cellulose fiber according to any one of claims 1 to 4, wherein the regenerated cellulose fiber has a single fiber fineness of 0.3 dtex or more and 4.5 dtex or less.

6. The regenerated cellulose fiber according to any one of claims 1 to 5, further comprising a functional agent.

7. A method for producing regenerated cellulose fibers containing recycled natural cellulose fine particles, A process of adding and mixing an aqueous dispersion of recycled natural cellulose fine particles with a median diameter of 0.5 μm or more and 10 μm or less to a spinning stock containing cellulose, and The process includes the step of extruding the obtained spinning solution from a nozzle into a spinning bath, spinning it, and then coagulating and regenerating it. A method for producing regenerated cellulose fibers, wherein the recycled natural cellulose microparticles are derived from recycled cotton fibers.

8. A further step of obtaining recycled natural cellulose powder by hydrothermally treating used products and / or waste containing cotton fibers in the presence of an organic acid, A method for producing regenerated cellulose fibers according to claim 7, comprising the step of crushing or micronizing the recycled natural cellulose powder to obtain recycled natural cellulose fine particles.

9. A method for producing regenerated cellulose fibers according to claim 7 or 8, wherein the aqueous dispersion is added to the spinning stock containing cellulose in such a manner that the recycled natural cellulose fine particles are in an amount of 0.5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of cellulose in the spinning stock.

10. The method for producing regenerated cellulose fibers according to any one of claims 7 to 9, wherein the aqueous dispersion contains 1% by mass or more and 10% by mass or less of recycled natural cellulose fine particles.

11. A fibrous structure comprising regenerated cellulose fibers according to any one of claims 1 to 6.

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