Solvent-free processes and resulting products

Abstract

The present invention relates to a method for producing an aqueous microfiber nonwoven fabric, and includes the following steps. 1) A fibrous material containing ultrafine fiber-generating fibers is impregnated with an aqueous dispersion containing polyurethane, an inorganic salt containing monovalent or divalent cations, and a crosslinking agent (first impregnation treatment). However, the polyurethane content is 15 to 40% by weight relative to the weight of the ultrafine fibers. 2) The polyurethane is fixed to the fiber material after the impregnation treatment (first solidification step). 3) The fibrous material is treated with an alkaline, acidic, or neutral aqueous solution to generate ultrafine fibers from the ultrafine fiber generating type fibers, thereby forming a microfiber material composed of ultrafine fibers. 4) The microfiber material is impregnated with an aqueous dispersion containing polyurethane, an inorganic salt containing monovalent or divalent cations, and a crosslinking agent; however, the polyurethane content is 15 to 40% by weight relative to the weight of the ultrafine fibers (second impregnation treatment). 5) The polyurethane is fixed to the fiber material after the impregnation treatment (second solidification step). However, the ratio of the polyurethane content from the second impregnation treatment to the polyurethane content from the first impregnation treatment is in the range of 100% to 250%, preferably in the range of 105% to 240%. The present invention also relates to a novel suede-like nonwoven fabric obtained by the solvent-free process of the present invention, which has excellent tactile properties, high elasticity, excellent resistance to yellowing, and high durability. This suede-like nonwoven fabric can be used in products for the fashion industry (e.g., clothing and accessories) and the automotive industry (e.g., car interior materials, especially seats, panels, and ceiling materials).

Description

[Technical Field]

[0001] This invention relates to a method for producing a suede-like synthetic microfiber nonwoven fabric that can be manufactured without using organic solvents. Furthermore, this invention relates to a nonwoven suede-like fabric obtained by the method of this invention, which has a pleasant feel (excellent texture), high elasticity, excellent resistance to yellowing, and high durability. This suede-like synthetic microfiber nonwoven fabric can be used in products for the fashion industry (clothing and accessories, etc.) and the automotive industry (especially for interior materials, such as seats, panels, and ceiling materials). Background of the Invention

[0002] There are already known prior art methods for manufacturing suede-like microfiber nonwoven fabrics using so-called "sea-island structure" fibers. This technology produces a binary fiber in which a component called an "island" is completely surrounded by a component called a "sea." This "sea" component is structured in such a way that it can be easily removed with a solvent. The "sea-island structure" fiber is obtained by supplying two types of polymer materials to a spinneret (for example, the methods described in U.S. Patents 3,692,423, 3,899,292, and 3,531,368). The fibers thus obtained are used to make felt using the needle-punching method or the high-pressure water jet method. The felt is then impregnated in aqueous solutions and organic solvents, and various processing steps are taken to fix the fibers and / or remove unwanted components. To produce a nonwoven fabric with a suede-like texture, the felt obtained by the needle-punching method or the high-pressure water jet method is first impregnated with an aqueous polyvinyl alcohol (PVA) solution. Next, the "sea" components are dissolved and removed with a solvent such as trichloroethylene (EP1323859). The resulting microfiber intermediate is then impregnated a second time with a polyurethane (PU) solution dissolved in an organic solvent (e.g., DMF). Finally, after one or more washing treatments, the PVA is removed, followed by cutting and subsequent finishing processes such as polishing and dyeing. The recovered PVA can be reused in the manufacturing process or sold for various uses. There are also solvent-free methods for manufacturing nonwoven fabrics, such as forming sea-island structured fibers and then impregnating the resulting felt with resins such as PVA or PU (EP1243691). Using water instead of conventional organic solvents (such as dimethylformamide (DMF) and trichloroethylene) offers significant advantages in terms of cost reduction, protection of worker health, and reduction of environmental impact. Nonwoven fabrics manufactured using solvent-free methods possess excellent resistance to yellowing, high durability, flexibility, elasticity, and high uniformity, while maintaining the same level of uniformity and resistance as those manufactured using solvent-based methods.

[0003] WO2019025964 discloses a method for producing a suede-like synthetic microfiber nonwoven fabric that can be manufactured without the use of organic solvents. The method includes the following steps: (a) producing a “sea-island structure” two-component fiber. Here, the sea component is a polymer soluble in hot water or an alkaline aqueous solution; (b) The two-component "sea island structure" fibers are punctured to produce felt; (c) The felt is heat-impregnated with an aqueous solution of polyvinyl alcohol (PVA) with a degree of saponification of 94% or higher. A water-soluble organic or inorganic salt may be added to this PVA aqueous solution as needed; (d) The PVA-impregnated felt obtained in step c) is immersed in a basic aqueous solution containing an alkali metal or alkaline earth metal hydroxide to remove the sea component and obtain a microfiber intermediate product; (e) The microfiber intermediate product obtained in step d) is washed with neutral water containing a water-soluble organic or inorganic salt, or with acidic water (however, if a water-soluble organic or inorganic salt has been added to the polyvinyl alcohol (PVA) aqueous solution used in step c), it is washed with neutral water); (f) The microfiber intermediate product obtained in step e) is cold-impregnated with a polyurethane (PU) solution dispersed in water containing a viscosity modifier and, if necessary, a water-soluble substance; (g) The PU dispersion is solidified and dried to fix the PU to the microfiber intermediate product. The fixing process can be carried out by solidification in high-temperature air, solidification in hot water, solidification in an electrolyte aqueous solution, solidification by high-frequency heating, solidification by microwave heating, solidification by ultrasound, solidification by IR (infrared) irradiation, or solidification by steam; h) remove the PVA added in step c), the salts optionally added in steps c) and / or e), and the additives added in step f); i) subject the obtained material to cutting, polishing on one or both sides, and dyeing.

[0004] The pure PVA, or PVA containing salts, used in step c) is characterized by significantly lower water solubility compared to the water solubility under the dissolution conditions of the "sea" component of the two-component fiber. The method of this invention uses highly saponified PVA. This highly saponified PVA is insoluble in an aqueous environment, and can therefore withstand the subsequent treatment to remove the sea component (step d) while maintaining its solubility in water in the final step (step h). In addition to using highly saponified PVA or adding salts, the solubility of PVA can also be achieved by high-temperature heat treatment (also called thermal polymerization) performed after the PVA impregnation treatment (step c) and drying treatment. In this way, the PVA is stably fixed to the felt, and the subsequent "sea" component removal process can be carried out without significant changes in the PVA content or distribution in the material.

[0005] However, all of the processes described above are energy-intensive, require many steps, and are therefore costly. Furthermore, they necessitate the use of auxiliary materials such as PVA, and additional steps and costs are incurred for recovery and / or disposal after removal. In addition, the heat treatment and crystallization processes consume large amounts of energy.

[0006] Several conventional methods using hot water solidification are known. Patent EP3112530 describes an invention for a method of producing a product with uniformity and feel equivalent to artificial leather obtained using an organic solvent-based polyurethane, which is environmentally sustainable and does not use solvents. The product described in EP3112530 uses a microfiber material made of ultrafine fibers and a polymer elastomer having hydrophilic groups as a binder. The manufacturing process consists of adding polyurethane, a polymer elastomer dispersed in water, a heat-sensitive solidifying agent, and a thickening agent to improve the viscosity of the composition to the microfiber material, and solidifying the polymer elastomer in hot water at 50°C to 100°C. However, a drawback of this method is the dispersion of polyurethane in the solidification tank, which easily clogs the pipes and requires frequent cleaning.

[0007] EP1353006 describes a method for manufacturing nonwoven fabrics, in which polyurethane (PU) is used in an aqueous solution or organic solvent instead of other auxiliary materials (in place of PVA in the first impregnation treatment) in both impregnation processes. According to this patent, polyurethane is fixed by saturated steam treatment and microwave / high-frequency drying, or treatment with an acidic or salt solution. Conventional air convection drying is not used because the aqueous polyurethane emulsion migrates to the outer edges of the nonwoven fabric, and the extremely slow processing speed prevents the fixed polyurethane from having sufficient porosity, thus negatively affecting the properties of the final product. The fixing techniques used in the method described in this document are generally costly in terms of energy consumption and capital investment. Furthermore, wet solidification treatment by contact with an acidic or salt solution requires additional equipment for wastewater pretreatment of the solidification water.

[0008] EP4079961 relates to a material manufacturing method that involves carrying out the following steps (1) to (3) in this order. (1) A felt made of ultrafine fiber-generating fibers is impregnated with an aqueous dispersion containing a hydrophilic elastomer precursor, an inorganic salt containing monovalent cations, and a crosslinking agent; next, the microfiber material impregnated with this aqueous dispersion is heat-dried at a temperature of 100°C to 180°C. The content of the inorganic salt containing monovalent cations in this aqueous dispersion is in the range of 10 to 100 parts by weight per 100 parts by weight of the elastomer precursor. (2) Ultrafine fiber generation process: A process of generating ultrafine fibers from ultrafine fiber generation type fibers and forming a microfiber material consisting of ultrafine fibers. (3) A step of impregnating a microfiber material consisting of ultrafine fibers with an aqueous dispersion containing an elastomer precursor having hydrophilic groups, an inorganic salt containing monovalent cations, and a crosslinking agent; thereafter, the microfiber material impregnated with the aqueous dispersion is heat-dried at a temperature of 100°C to 180°C. The content of the inorganic salt containing monovalent cations in this aqueous dispersion is in the range of 10 to 100 parts by weight per 100 parts by weight of the elastomer precursor.

[0009] In the method described in EP4079961, the melting conditions such as time, temperature, and alkali concentration are set very strictly in the process of producing ultrafine fibers (30 minutes, 95°C, 8 g / L); therefore, the energy consumption is very high, making it difficult to apply to industrial production. Furthermore, the total amount of elastomer resin relative to the ultrafine fibers is very small (less than half the amount contained in the material of the present invention); therefore, the appearance of the final material is closer to that of fabric than to nonwoven suede leather.

[0010] The object of the present invention is to provide a method for producing a solvent-free nonwoven microfiber suede-like fabric that has the same softness (feel), elasticity, resistance to yellowing, and abrasion resistance as suede-like microfiber nonwoven fabrics obtained by conventional solvent-based processes.

[0011] Compared to the conventional "non-solvent" processes described above, the method of the present invention achieves a significant reduction in energy consumption and equipment investment costs by using simpler and more compact equipment. [Overview of the Initiative]

[0012] The present invention relates to a method for producing a microfiber nonwoven fabric, and includes the following steps. 1) A fibrous material containing ultrafine fiber-generating fibers is impregnated with an aqueous dispersion containing polyurethane, an inorganic salt containing monovalent or divalent cations, and a crosslinking agent (first impregnation treatment); however, the polyurethane content is 15 to 40% by weight relative to the weight of the ultrafine fibers. 2) The polyurethane is fixed to the fiber material after the impregnation treatment (first solidification treatment). 3) The fibrous material is treated with an alkaline, acidic, or neutral aqueous solution to generate ultrafine fibers from the ultrafine fiber generating type fibers, thereby forming a microfiber material composed of ultrafine fibers. 4) The microfiber material is impregnated with an aqueous dispersion containing polyurethane, an inorganic salt containing monovalent or divalent cations, and a crosslinking agent; however, the polyurethane content is 15 to 40% by weight relative to the weight of the ultrafine fibers (second impregnation treatment). 5) The polyurethane is fixed to the fiber material after the impregnation treatment (second solidification treatment).

[0013] Preferably, the ratio of the polyurethane content obtained from the second impregnation treatment (step 4) to the polyurethane content obtained from the first impregnation treatment (step 1) is in the range of 100 to 250%, preferably in the range of 105 to 240%.

[0014] Preferably, the concentration of monovalent or divalent cations in the first and second impregnation treatments is in the range of 10 to 100% by weight relative to the weight of the polyurethane.

[0015] The present invention also relates to a suede-like microfiber nonwoven fabric obtained by the method of the present invention. This nonwoven fabric comprises the following components: (i) A microfiber material consisting of ultrafine fibers with an average diameter of 0.1 μm to 10.0 μm and polyurethane. (ii) In a cross section perpendicular to the thickness direction of the microfiber material, the area occupied by the polyurethane in contact with the cross section (however, the cross-sectional area is 50 μm²) 2 Multiple such independent regions exist in the cross-section, and the total area of ​​these independent regions ranges from 5.5% to 40.0% of the observation field of view. [Brief explanation of the drawing]

[0016] Other features and advantages of the present invention are described below and refer to the accompanying drawings. Figure 1 shows the structure of a microfiber non-woven fabric manufactured by a method based on the prior art. This method involves immersing in a polyurethane solution dissolved in a solvent and then performing a coagulation treatment to form a porous structure. This product is the current standard product in terms of appearance, touch, mechanical properties, wear resistance, etc.

[0017] Figure 2 shows the structure obtained by the conventionally used solvent-free method (a method combining an aqueous polyurethane composition with a wet coagulation method); this structure is different from the non-woven fabric obtained by the solvent-using method shown in Figure 1.

[0018] Figure 3 shows the structure of the microfiber non-woven fabric obtained by the method of the present invention. This structure is different from those of Figure 1 and Figure 2, and is obtained by combining an aqueous polyurethane composition with a hot air coagulation method and satisfying parameters such as the polyurethane content defined in the claims.

[0019] Figure 4 shows the area occupied by polyurethane in a cross-section perpendicular to the thickness direction of the microfiber material.

[0020] Figure 5 shows the results obtained in Examples 1 to 6 and Comparative Examples 7 to 13 according to the present invention. Detailed Description of the Invention

[0021] Prior to the impregnation treatment step 1), a) a spinning step of sea-island type bicomponent fibers, b) a manufacturing step of a fiber material using the bicomponent fibers, and c) a heat stabilization step of the fiber material using the bicomponent fibers are performed.

[0022] In procedure a), a two-component fiber is spun by combining two different polymer materials ("island" polymers that form microfibers and "sea" polymers that surround the microfibers). This two-component fiber is manufactured using a spinneret, resulting in a composite fiber in which one polymer (sea) is arranged around the microfibers of the other polymer (island). The fiber thus obtained is processed according to general post-processing methods in spinning technology. In particular, the two-component fiber before rolling is preferably 5 to 30 denier, more preferably 10 to 25 denier in thickness.

[0023] The components forming the "islands" are selected from the following polymers: polyethylene terephthalate (PET), copolymer polyesters containing terephthalic acid and isophthalic acid, and ethylene glycol, modified polyesters (such as polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT)), polyesters dyeable with cationic dyes, polyamides, polyethylene (PE), polypropylene and other polyolefins, polyhydroxyalkanoates (PHA), polyhydroxybutyric acid (PHB), polyethylene furanoates (PEF), and polylactic acid (PLA). These polymers are produced from renewable resource-derived raw materials (which completely or partially replace existing fossil resource-derived raw materials) or obtained by microbial conversion of renewable resource-derived raw materials.

[0024] Examples of polymers that can be manufactured from renewable resource-derived raw materials include PTT, PEF, PET, PLA, and PE. Examples of polymers obtained from microorganisms include PHA, PHB, and their copolymers. Polymers obtained through chemical or mechanical recycling are also considered. Chemically recycled polymers, obtained by decomposing other polymers or waste, purifying monomers, and then repolymerizing them, are preferred because their purity and performance are close to that of new raw materials. However, their production consumes a lot of energy and has a large environmental impact. On the other hand, mechanically recycled polymers have the advantage of a low environmental impact, but their mechanical performance may be inferior due to impurities remaining in the recycling process. PET, which can be obtained from both petroleum-based and renewable raw materials and is ultimately recoverable in (chemical and mechanical) recycling processes, is a particularly preferred material for obtaining final nonwoven fabrics with excellent light resistance and mechanical properties.

[0025] Examples of marine components include selections from the following polymer groups: polyvinyl alcohol (PVA), polystyrene (PS), polystyrene copolymers containing PVA (copolymer PVA-PS), polystyrene copolymers containing maleic anhydride or other organic monomers (copolymer PS), copolymer esters containing PVA (copolymer PVA-PES) or polyethylene glycol (copolymer PEG-PES), copolymer olefins such as polyethylene or polypropylene containing PVA (copolymer PVA-PE, copolymer PVA-PP, respectively), copolymer esters of a mixture of terephthalic acid, isophthalic acid, and 5-sulfoisophthalic acid, and copolymer esters containing both terephthalic acid and 5-sulfoisophthalic acid or their sodium salts (copolymer PES, abbreviated as TLAS), the latter of which is particularly preferred. Polymers recycled by chemical or mechanical means (that completely or partially replace existing fossil resource-derived raw materials) may also be considered. Polymers manufactured from raw materials combining fossil resources and renewable resources are also conceivable and can be made biodegradable to facilitate disposal after use (compostable polymers).

[0026] The ratio of island components to sea components in a two-component fiber should be such that both components can be spun quickly and efficiently using a spinneret. This ratio is preferably in the range of 20:80 to 90:10, and more preferably in the range of 50:50 to 90:10. If the ratio of island components to sea components is less than 50:50, the amount of sea component that needs to be removed increases, raising manufacturing costs and reducing the physical and mechanical properties of the fiber. Furthermore, the surface fiber density becomes low, resulting in poor appearance quality of the finished nonwoven fabric. On the other hand, if the ratio of island components to sea components exceeds 90:10, the island components become difficult to separate during spinning (making the production of two-component fibers difficult), and as a result, it becomes difficult to produce microfibers after removing the sea component.

[0027] Both the sea component and the island component can be mixed with the following components, respectively. Examples of island components include pigments, while sea components include incompatible polymer materials. Incompatible polymer materials (i.e., polymers that do not dissolve with the sea component, or only partially dissolve with it) form a non-uniform structure, and at the microscopic level, regions where only one polymer exists are dispersed within the matrix formed by the sea component. Generally, such structures are fragile, and using these polymers in the sea component makes the outer layer prone to damage during molding and felting processes. In particular, PVA added to copolymerized PES, and polyethylene glycol (PEG) added to PS and copolymerized PS are effective as incompatible polymer materials with the sea component.

[0028] Micro or nanoparticle-sized UV stabilizers and fillers can be added to the components of the island material; carbon black and carbon-based fillers are particularly preferred when manufacturing dark-colored, gray, or black nonwoven fabrics because they reduce the amount of dye used in the dyeing process. The UV stabilization properties of carbon-based fillers and the reduction in dye usage in the final dyeing process have the effect of suppressing fading due to UV irradiation. When the use of carbon black is not possible (for example, when manufacturing very light-colored or bright-colored nonwoven fabrics), the lightfastness of the dyed material can be improved by using UV stabilizers or lightfast pigments. However, dyes containing lightfast pigments or molecules tend to have a significant impact on the cost of the final product.

[0029] Before manufacturing the fibrous material according to process b), the two-component fibers are treated in a manner known in the prior art. Specifically, by adding lubricating oil during the rolling process, the axial orientation of the polymer chains is improved, thereby improving the physical and mechanical properties of the resulting fibers and reducing their thickness. This property is particularly important in the production of high-quality fibers.

[0030] The rolling ratio can generally be set in the range of 2 to 8, preferably in the range of 2.5 to 5, in which case the final fineness (denier) of the two-component fiber will be 2 to 8 denier (2.2 to 8.9 decitex), and the fineness of the island component will be 0.001 to 0.5 denier (0.01 to 0.56 decitex). The diameter of the microfiber after rolling is 0.1 to 10 microns. The rolled two-component fiber is processed into a curl shape using a dedicated device so that 4 to 15 curls are formed per centimeter. It is then cut to a length of 40 to 60 mm (preferably 45 to 55 mm). These steps facilitate the next fiber material manufacturing step (step b).

[0031] In a preferred embodiment of the present invention, the fineness (tex value) of the fibers before rolling is 5.5 to 19 denier, more preferably 7.0 to 15 denier. The rolling process is generally carried out at a magnification of 2 to 5 times, more preferably 2.1 to 4.5 times. After the rolling process, the fibers are cut to a predetermined length, producing short fibers with a length of 45 to 55 mm.

[0032] In the method of the present invention, the fibrous material in step b) is produced by puncturing the two-component sea-island fiber raw material obtained in step a). It is also possible to produce nonwoven fabric using the high-pressure water jet spunlace method.

[0033] In a particularly preferred embodiment, the fibrous material of step b) is obtained by cutting a two-component fiber made of PET and TLAS (which may contain a pigment in the island component and / or an inaffinity polymer in the sea component) into material about 51 mm in length, and then performing a pin-piercing process.

[0034] After step b), the resulting fibrous material is preferably 2-4 mm thick and has an apparent density of 0.1-0.5 g / cm³. 3 , more preferably 0.15~0.35 g / cm³ 3 These density and thickness values ​​are optimal in that they provide the final nonwoven product with excellent properties such as feel, softness, elasticity, appearance, and mechanical strength against processing conditions. The apparent density is 0.1 g / cm³. 3 If the value is less than 0.5 g / cm³, the appearance and mechanical properties of the final product will be inferior. 3 If it exceeds this value, the product will be heavy and hard.

[0035] Following the manufacturing process b) of the microfiber material, a heat stabilization treatment (process c) is performed. The purpose of this process is to stabilize the fiber material before the impregnation treatment (process 1), increase the fiber density, and improve the appearance of the final product.

[0036] The heat stabilization treatment of the nonwoven fabric in step c) can be carried out with hot water at 70°C to 95°C, preferably in the range of 80°C to 90°C.

[0037] The density of the nonwoven fabric, dimensionally stabilized by heat treatment (hot water treatment), is set to 0.25-0.50 g / cm³ to give the final product excellent softness. 3 , more preferably 0.30~0.45 g / cm³ 3 A thickness of 1.5 to 3.5 mm is preferable.

[0038] In a preferred embodiment aimed at cost reduction, the heat treatment of the fiber material (step c) and the first impregnation treatment (step 1) can be performed in a single step.

[0039] The first and second impregnation treatments (steps 1 and 4) using hydrophilic polyurethane (PU) can be carried out using a polyurethane emulsion / aqueous dispersion.

[0040] The polyurethane emulsion / aqueous dispersion used in these impregnation treatments may be the same or different in type, polyurethane content, and types of additives used in the first and second impregnation treatments.

[0041] In the first impregnation treatment, a polyurethane dispersion is used in which the polyurethane concentration is 5-20% (preferably 6-18%) by weight at room temperature. As a result, the polyurethane content of the ultrafine fibers after impregnation treatment becomes 15-40% (preferably 18-35%) by weight.

[0042] By controlling the amount of PU resin applied in the first impregnation step to within the specified range, the PU properly holds the fibers, and the dimensional stability of the fiber material is maintained even during the marine component removal step. If the PU resin content in the first impregnation step is less than 5%, the morphology of the fiber material will change significantly during the marine component removal step, which will likely reduce the surface quality and abrasion resistance of the final nonwoven fabric.

[0043] On the other hand, if the PU content exceeds 20% in the first impregnation treatment, the excess PU hinders the thorough removal of marine components. As a result, the surface of the final nonwoven fabric becomes uneven, and the softness of the product is compromised.

[0044] The polyurethane used in the first impregnation stage of the fiber material must withstand all manufacturing processes until the final dyed product is completed (dissolution conditions of marine components, resistance during the second impregnation stage, high-temperature acidic / alkaline treatments during the dyeing stage, etc.). Therefore, the polyurethane needs to undergo a solidification / fixing treatment. Furthermore, the fixed polyurethane is required to have excellent durability, such as resistance to hydrolysis and degradation by ultraviolet light. It is preferable to add inorganic salts to the polyurethane dispersion.

[0045] Examples of salts added to the polyurethane composition include monovalent or divalent inorganic cation salts (salts of alkali metals and alkaline earth metals). Both types of salts are effective in thermally destabilizing the polyurethane in the impregnation treatment steps 1) and 4). Monovalent cation salts such as sodium sulfate and sodium chloride are particularly preferred because their thermal destabilization mechanism facilitates the control of destabilization in the curing treatment steps 2) and 5).

[0046] When adding divalent cations such as magnesium sulfate or calcium chloride, even slight differences in the amount added can affect the stability of the aqueous dispersion, making it difficult to precisely control the gelation temperature. On the other hand, inorganic salts containing monovalent cations have a low ionic charge, so their impact on the stability of the aqueous dispersion is relatively small. Thus, by appropriately adjusting the amount of additive added, it becomes possible to precisely control the gelation temperature while ensuring the stability of the aqueous dispersion.

[0047] By using an inorganic salt containing monovalent cations, it becomes possible to impart heat-sensitive solidification properties to an aqueous dispersion, allowing for more precise control of the process. In this invention, "heat-sensitive solidification properties" refer to the property that when an aqueous dispersion is heated, its fluidity decreases and solidification occurs when it reaches a certain temperature (called the gelation temperature or "cloud point").

[0048] The salt concentration is in the range of 30-100%, preferably 40-80%, of the solid weight of the polyurethane. When the salt concentration exceeds 30%, the ions present in the aqueous dispersion act uniformly on the polyurethane particles, allowing the solidification reaction to be completed rapidly at a specific gelation temperature. As a result, the polyurethane solidifies while retaining a large amount of moisture in the fiber material, resulting in excellent flexibility and elasticity comparable to natural leather. On the other hand, when the salt concentration exceeds 100%, the adhesion to the fibers decreases, and the physical properties deteriorate significantly. Furthermore, the stability of the aqueous dispersion also worsens.

[0049] The preferred inorganic salt is sodium sulfate.

[0050] This dissolved electrolyte allows the polyurethane solidification reaction to proceed at low temperatures (below 70°C), resulting in significant energy savings.

[0051] The third step, which involves generating ultrafine fibers from ultrafine fiber generating fibers and forming a microfiber material consisting of these ultrafine fibers, is the step of removing marine components. For example, an aqueous solution of sodium hydroxide, an alkaline aqueous solution, an acidic aqueous solution, or hot water can be used. In the case of an aqueous solution of sodium hydroxide, the concentration is preferably 4-10% by weight, more preferably 5-8%.

[0052] Preferably, the processing temperature is set to a range of 50 to 75°C, more preferably 60 to 70°C, and the dissolution time for the marine components is 4 to 40 minutes. The dissolution conditions are optimized to minimize the degradation of the microfiber material by reducing the amount of polyurethane and island components dissolved as much as possible, while selectively dissolving only the marine components in the shortest possible time.

[0053] In one embodiment, when using a strongly acidic or strongly alkaline solution, washing with room temperature water at the end of step 3) can prevent the "island" component from partially dissolving.

[0054] The microfiber material from which marine components have been extracted undergoes a second impregnation treatment (step 4) at room temperature using an aqueous polyurethane dispersion with a concentration of 5-20% (preferably 7-20%). This results in polyurethane being present at a ratio of 15-40% (preferably 20-40%) relative to the weight of the microfiber material after impregnation. If the polyurethane concentration is less than 5%, the polyurethane cannot maintain a sufficient volume during the solidification process and will not be uniformly dispersed. On the other hand, if the polyurethane concentration exceeds 20%, the amount of polyurethane adhering to the fibers becomes excessive, resulting in a loss of softness in the product.

[0055] If the PU / PET blend ratio is less than 15%, the PU cannot adequately hold the fibers, resulting in an uneven distribution of PU, which leads to a poor appearance and reduced abrasion resistance of the product. On the other hand, if the PU / PET blend ratio exceeds 40%, the PU excessively covers the fibers, compromising the product's softness and reducing surface uniformity.

[0056] To obtain a product with the same softness and appearance as conventional methods using organic solvents or one-step impregnation treatment with PU, it is necessary to adjust the ratio of the PU content in the second impregnation treatment (step 4) to the PU content in the first impregnation treatment (step 1) to 100-250% (preferably 120-240%). The PU used in the first impregnation treatment has no effect on abrasion resistance, but the PU used in the second impregnation treatment is not affected by the alkali treatment when removing marine components and directly bonds to the ultrafine fibers, thus greatly contributing to the abrasion resistance and texture of the product. If the polyurethane content in the second impregnation process is too low (less than 100% polyurethane), the adhesion between the polyurethane and the fibers will be weak, resulting in a product with reduced abrasion resistance and mechanical properties (the polyurethane applied in the first impregnation process is insufficient to hold all the fibers during the dissolution process); on the other hand, if the polyurethane content exceeds 250%, the strength of the material will decrease in the third process (removal of marine components), the nap will become shorter, the surface of the nonwoven fabric will become rough, and the product will have a different appearance from suede-like artificial leather. Furthermore, the surface texture of the material will also become hard and rough.

[0057] Furthermore, the distribution of polyurethane in the cross-section of the nonwoven fabric (along the thickness of the material) should be concentrated mainly in the center and not extend to the outer edges. To achieve this optimal polyurethane distribution, it is important to impregnate the polyurethane twice and maintain the appropriate mixing ratio of polyurethane to salt, as described above.

[0058] As is well known, polyurethane (PU) is a resin having a polymer chain consisting only of urethane bonds (-NH-(CO)-O-) or a mixture of urethane bonds and urea bonds (-NH-(CO)-NH-), and is synthesized by reacting a polyol or a polyol mixture with a diisocyanate. To uniformly disperse this resin in water, it is considered effective to add an ionomer (a molecule having an ionic group that bonds to isocyanate and polyol in the same way). In the present invention, polyurethane is preferably obtained by reacting a polyol with an average molecular weight of 500 to 5000 Da (preferably selected from polyethers, polyesters, polycarbonates, and polyether-polycarbonates) with an aliphatic or aromatic diisocyanate. It is also possible to use polyols obtained by fatty acid dimerization or olefin polymerization. By using these polyols, hydrophobic functional groups can be introduced into the molecular chains of polyurethane, improving resistance to hydrolysis and increasing the proportion of renewable resource-derived raw materials in the final product (simple olefins and ethers / esters are already known to be produced by fermentation processes followed by desaturation reactions). To improve mechanical properties and resistance to hydrolysis, it is also possible to synthesize hybrid polyurethanes by adding polydimethylsiloxane during the reaction. Furthermore, by adding small amounts of trifunctional monomers to the polyurethane chain body or aminosilane chain ends during the synthesis process, the hydrolysis resistance of the polymer after the crosslinking reaction can be improved.

[0059] The above raw materials can be obtained through manufacturing processes using first-generation renewable resources (such as food-derived raw materials), second-generation renewable resources (such as agricultural and industrial waste), or third-generation renewable resources (such as direct synthesis from CO2). In addition, some raw materials can be obtained through chemical recycling processes (such as hydrolysis, monomer purification, and resynthesis) or physicochemical recycling processes (such as separation of microfibers from polyurethane using solvents, or recovery of polyurethane components by selective hydrolysis of microfibers).

[0060] Impregnation treatment with PU resin can be carried out in the presence of additives such as surfactants, stabilizers, other alkali metal salts or alkaline earth metal salts, acid-generating agents that release protons upon heating (e.g., diethylene glycol acetate or diethylene glycol formate), water repellents, plasticizers, wetting agents, dispersants, silicone compounds, water-dispersible nanoparticles, nanofibers, and nanotubes. The amount of these additives added is 0-15%, more preferably 0-8%, relative to the PU resin. In addition, natural clays such as montmorillonite, synthetic clays such as laponite, or other silicates can be added to adjust the rheological properties and solidification properties of the composition.

[0061] After impregnation steps 1) and 4), the intermediate (fine) fibrous product is subjected to polyurethane (PU) fixing steps 2) and 5). This fixing can be carried out by methods such as air solidification, hot water solidification, solidification in an electrolyte aqueous solution, high-frequency solidification, microwave solidification, ultrasonic solidification, solidification by infrared irradiation, or steam solidification. Preferably, hot air solidification is used, and the polyurethane can be fixed by heat. Alternatively, solidification can also be carried out using an aqueous solution containing a salt (e.g., a salt of an alkali metal or alkaline earth metal) or an acid that destabilizes the dispersion (e.g., organic acids such as formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, maleic acid, fumaric acid, or inorganic acids such as hydrochloric acid, sulfuric acid, or phosphoric acid).

[0062] The hot air solidification method is particularly economical because it can be implemented using an air-circulating oven.

[0063] When using salt in a polyurethane dispersion, it is preferable to perform a washing step after the polyurethane solidification process to remove any excess salt. Washing with room temperature water is also possible.

[0064] The salt removed in the washing step of the intermediate can be recovered, purified, and reused in the production process, thereby reducing the environmental burden and realizing a sustainable production process (circular economy approach).

[0065] In the present invention, when a salt is added to the polyurethane solution, the fixing step 2) is performed by air solidification. This method minimizes thermal energy during drying while reducing the stability of the polyurethane. When a polyurethane emulsion containing salt is air solidified, the dissolved electrolyte allows the polyurethane to solidify at a low temperature (e.g., below 70°C), significantly reducing energy consumption. When polyurethane is hot-air solidified with added salt (preferably sodium sulfate), the polyurethane structure after solidification is unique and different from that of solvent solidification or water solidification. As a result, a flexible material with an appearance and feel similar to conventional artificial leather produced by solvent-based methods is obtained.

[0066] When hot air solidification is performed in fixing step 5), the material after the second impregnation treatment is brought into contact with air at a temperature of approximately 50°C to approximately 200°C (preferably approximately 50°C to 160°C); this allows for more effective control of polyurethane migration during heating. The heating time varies depending on the type of polyurethane used. When thermosetting polyurethane is used, the heating time of the intermediate product after impregnation treatment can be shortened, thus avoiding complete drying and reducing the energy consumption required for moisture evaporation. Preferably, the polyurethane is solidified on the microfiber intermediate product in an oven that is heated in the temperature range of 50°C to 160°C. This temperature gradient prevents the water from rapidly evaporating and the solid components of the dispersion from migrating to the surface before enough heat is supplied to decompose the surfactant stabilizing the polyurethane.

[0067] By using the hot air solidification method, products with excellent resistance and durability can be obtained. Polyurethane (PU) obtained by applying the hot air solidification method in the presence of salts (especially sodium sulfate) has a unique porous structure (see Figure 3), and due to the synergistic effect of this porous structure and excellent adhesion to fibers, the final product is very soft and has an appearance similar to materials obtained by conventional solvent-based processes, without compromising physical and mechanical properties.

[0068] When polyurethane is solidified in an aqueous solution containing an electrolyte (salts or acid), solidification can be performed at low temperatures (below 70°C), significantly reducing energy consumption. In this case, the impregnated intermediate product obtained after the second impregnation treatment is brought into contact with (preferably immersed in) water at approximately 20°C to 90°C (preferably 40°C to 80°C). This water contains a certain amount of polyurethane dispersion destabilizer (electrolyte), which can lower the solidification start temperature (gelation temperature or "cloud point") of the polyurethane. Examples of the dispersion destabilizer include halides and calcium and magnesium sulfates, with calcium chloride (CaCl2), magnesium chloride (MgCl2), and magnesium sulfate (MgSO4) being particularly preferred. In the case of steam solidification, the amount of dispersion destabilizer used is 0.01 to 8% (more preferably 1 to 6%) by weight, but when using hot water above 90°C, a salt concentration of about 20 to 30% relative to the weight of the polyurethane is required to prevent the polymer from dispersing in the water.

[0069] Hot water solidification is particularly suitable when it is desired to improve the softness of the final product compared to steam solidification. Another example of an stabilizing agent is an acid added to the solidification solution. The acid protonates the anionic groups present in the polyurethane chain (introduced during synthesis by adding the ionomer along with the polyol and isocyanate). Examples of such acids include organic acids such as formic acid, acetic acid, oxalic acid, maleic acid, and citric acid, or inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid. Comparing hot air solidification and water solidification, the former is more economical and simpler than the latter. In particular, by adding salt to the PU composition, the PU can be destabilized at a lower temperature.

[0070] To ensure the stability of the PU emulsion during the process, minimize the movement of polyurethane during the impregnation and solidification process, and / or reduce the loss of polyurethane in the solidification tank, it is also possible to add a thickening agent to the PU-containing composition to increase its viscosity. Preferably, this thickening agent is an affinity thickening agent, i.e., one that can bind to PU that has already formed a micelle structure in the aqueous dispersion, forming a more complex dispersion structure in which the micelles aggregate with each other. The mechanism of action of such affinity systems is well known to those skilled in the art.

[0071] Another example of a particularly effective thickener is polyacrylic acids. Polyacrylic acids not only increase the viscosity of a composition, but also alter the structure of the solidified polyurethane, creating a non-uniform and partially porous surface.

[0072] A mixture of two thickeners that act simultaneously on both the aqueous and polyurethane phases of the dispersion is also highly effective. In the hot air solidification method described in this invention, the stability of the composition can be ensured by mechanical stirring in the storage tank, thus eliminating the need for thickeners. This reduces manufacturing costs and results in a product with a softer feel. Generally, thickeners are known to increase the hardness of the product, and acrylic thickeners in particular increase the hardness of the added polyurethane.

[0073] Alternatively, by using additives that increase the viscosity of the dispersion medium (water), it is possible to make it more difficult for the polyurethane to move through the microfiber substrate during drying and solidification. This type of additive includes acrylic acid derivatives (e.g., polyacrylates and urethane / acrylic resins), synthetic polymers (e.g., PVA), and compounds derived from natural polymers (e.g., polysaccharides such as carboxymethylcellulose (CMC) and xanthan gum). Affinity thickeners and acrylic thickeners, used alone or in combination, are particularly preferred.

[0074] Furthermore, by using non-Newtonian fluid thickeners, it is possible to use aqueous polyurethane emulsions and dispersions at higher viscosities than usual (i.e., viscosities exceeding the specified upper limit). Such non-Newtonian fluid thickeners have the property of temporarily reducing the viscosity of polyurethane emulsions and aqueous dispersions during the impregnation process using rolling rollers. This phenomenon is caused by the strong shear stress exerted by the rolling rollers. After the impregnation process and shear stress are completed, the viscosity of the polyurethane emulsion or aqueous dispersion increases again, thus preventing the polyurethane from migrating to the surface.

[0075] To obtain the desired mechanical properties and solvent resistance, the impregnation in steps 1) and 4) is carried out in the presence of a crosslinking agent, which is activated in the drying step of the PU at a temperature range of approximately 60°C to 200°C (preferably approximately 70°C to 160°C). This crosslinking reaction generally takes less than 5 minutes in the above temperature range and is usually completed within 24 hours.

[0076] The crosslinking agent is preferably used in an amount of 1 to 10% by weight, more preferably 3 to 7% by weight, relative to the solid polyurethane content. Specifically, examples include melamine, aziridine, epoxides, zirconium compounds, carbodiimides, isocyanate derivatives, or blocked isocyanates or polyisocyanates having a particularly low deblocking temperature (the temperature at which particularly stable groups are released from the molecule and the isocyano groups are regenerated and react again with the polyurethane chain). Carbodiimides and blocked isocyanates are particularly preferred because the reaction is easy to control and the dispersion is highly stable. The crosslinking reaction can also be promoted or activated by ultraviolet light if the reaction is initiated by the absorption of ultraviolet light by the crosslinking agent or other additives. Furthermore, it is possible to promote curing to the inner layers far from the surface by rapidly preheating the polyurethane dispersion by irradiating it with an infrared lamp, high frequency, or microwave prior to the curing treatment. Among these pretreatment methods, the method using an infrared lamp is particularly excellent because infrared light evenly transfers heat from the surface to the entire polyurethane and allows control of component migration in the thickness direction. Methods involving direct microwave or high-frequency drying with an output of 5-20kW can also be considered.

[0077] Polyurethane can also be colored by adding micro- to nano-sized fillers such as carbon black, nanofibers, and nanotubes. This allows for coloring the final product while making the dyed polyurethane less noticeable.

[0078] The nonwoven fabric is then dried in a hot air dryer and proceeds to the next steps. These steps include bisection in the cross-sectional direction, suedeing, dyeing, and finishing. The conditions for each of these steps follow those of a typical nonwoven fabric manufacturing process.

[0079] According to the method of the present invention, a suede-like microfiber nonwoven fabric having the following components can be obtained. (i) Microfiber material containing ultrafine fibers and polyurethane, wherein the average diameter of each fiber is 0.1 μm to 10.0 μm, (ii) In a cross-section perpendicular to the thickness direction of the microfiber material, there are a plurality of regions occupied by polyurethane, each of these regions is in contact with the cross-section to be observed, and the cross-sectional area of each region is 50 μm 2 or more (independent regions), and the total area of these independent regions is in the range of 5.5% to 40.0% of the entire observation field of view.

[0080] The characteristic value described in item (ii) is calculated by cutting a cross-sectional sample perpendicular to the thickness direction of the non-woven fabric and observing the cross-section magnified 500 times with a scanning electron microscope (SEM). The obtained images (at least 5 pieces) are analyzed using image processing software, and the ratio of the non-porous polyurethane regions with an area of 50 μm 2 or more that are in contact with the cross-section is calculated. For the calculation of this parameter, only the polyurethane regions with an area of 50 μm 2 or more that are in contact with the cross-section are targeted. The polyurethane regions located lower than the cross-section are excluded from the calculation. In FIG. 4, the polyurethane regions in contact with the cross-section (that is, the regions to be calculated) are shown by solid black lines. Furthermore, the total ratio of the area of the polyurethane region to the field of view area (usually 4×1×10 4 μm 2 ) of each SEM image is calculated, and the average value of the 5 images is calculated.

[0081] By comparing FIG. 1 and FIG. 2 with FIG. 3 showing the product obtained by the method of the present invention, the structural differences between the products can be understood. FIG. 1 shows a product obtained by a method using a solvent. In this product, polyurethane (PU) has a porous structure that is not in close contact with the microfibers, so it becomes a soft and durable product (excellent physical and mechanical properties and wear resistance). On the other hand, FIG. 2 shows a product obtained by a coagulation method without using a solvent. In this product, PU does not have a porous structure and is very closely adhered to the microfibers, so it becomes a very hard product. FIG. 3 according to the present invention shows a PU structure with high roughness. As can be seen from the scanning electron micrograph, although the bonding with the microfibers is strong, a very soft product with excellent physical and mechanical properties and wear resistance can be obtained.

Examples

[0082] The present invention will be described in more detail by the following embodiments.

[0083] Other physical characteristics and performance parameters were measured using the following methods.

[0084] Diameter of ultrafine fibers: The ultrafine fibers in the material were observed at 1000x magnification using a scanning electron microscope (SEM, TESCAN VEGA3), and the average diameter of 20 randomly selected fibers within a 30 μm × 30 μm field of view was determined.

[0085] Softness of the material: The measurements were performed according to the EN ISO 17235 standard (a non-destructive method for measuring the flexibility of leather products, applicable to all non-hard leathers). The measurement involved using a piston to push the sample into a 20 mm diameter hole, measuring how far the sample sank into the hole. A larger measurement (amount of sank into the hole, mm) indicates greater material flexibility.

[0086] Method for measuring the gelation temperature of an aqueous dispersion: Place 20g of aqueous dispersion into a test tube with an inner diameter of 12mm, and insert the tip of a thermometer below the liquid surface. After sealing the test tube, immerse it in a 95°C hot water bath, ensuring that the liquid surface of the aqueous dispersion is below the liquid surface in the bath. While measuring the temperature rise inside the test tube with the thermometer, lift the test tube slightly as needed and shake it for less than 5 seconds at each test to check whether the surface of the aqueous dispersion is fluid. Determine the gelation temperature of the aqueous dispersion at the temperature at which the surface loses fluidity. Repeat this measurement three times for each type of aqueous dispersion and calculate the average value.

[0087] Appearance evaluation of materials: The surface appearance of the obtained materials was evaluated by quality inspectors based on the following criteria. The surface appearance was evaluated visually by placing the object horizontally on the inspection table and maintaining a 45-degree angle from the table surface and a distance of 50 cm from the inspector. An LED light was also installed 100 cm vertically from the top surface of the inspection table. A grade of 4 or 5 was considered acceptable. Grade 5: The fibers are evenly distributed, the pile is in good condition, and the appearance is excellent. Grade 4: An intermediate level between Grade 5 and Grade 3. Grade 3: The fiber distribution is not uniform, and some fibers are not sufficiently separated. There is some pile overall, but the appearance is fair. Grade 2: An intermediate level between Grade 3 and Grade 1. Grade 1: Low fiber content, very poor fiber distribution, and very inferior appearance.

[0088] Material wear evaluation For abrasion evaluation, a "Martindale Abrasion and Napping Tester (Model 406)" manufactured by James H. Heale was used. The company's "Abrasion Test Fabric SM25" was used as the standard fabric. The evaluation criteria were set on a 5-point scale (in 0.5 increments), and the results were evaluated in comparison to a standard image. If the appearance after the abrasion test showed no change from the pre-test condition, it was graded 5. If 30 or more napped areas with a diameter of 1 mm or more were present, it was graded 1. A standard image-based evaluation scale was used for the appearance evaluation after the Martindale test. The weight loss after the Martindale test was calculated using the following formula. Weight loss (mg) = Weight before abrasion test (mg) - Weight after abrasion test (mg).

[0089] Method for calculating the proportion of mass accounted for by non-porous polyurethane (P-parameter) Artificial leather samples were cut longitudinally or transversely, and the cross-sectional structure of the artificial leather was observed at 500x magnification using a scanning electron microscope (SEM, TESCAN VEGA3). Each image (5 images in total) was analyzed using image processing software (NIKON NIS ELEMENTS). This software analyzes the 50 μm layer in contact with the cross-section of the observed object.2 The proportion of the non-porous polyurethane portion can be calculated from all the polyurethane portions observed throughout the cross-section. Furthermore, this region is within the field of view (4 × 10) of each SEM image. 4 μm 2 The ratio of the area of ​​the cross-section of the nonwoven fabric to the total area was calculated, and finally the average value of the five images was taken. The back side of the cross-section (the part not in contact with the cross-section) was excluded from the calculation (see Figure 4). [Example 1]

[0090] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate (PET) as the island component, with a weight ratio of sea component to island component of 43:57, 16 islands per filament, and an average fiber diameter of 22 μm. The resulting composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The resulting nonwoven fabric was immersed in 80°C hot water for 3 minutes, and then dried at 100°C for 5 minutes.

[0091] First impregnation treatment - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane, and diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. Laboratory measurements showed that the gelation temperature was 65°C.

[0092] The nonwoven fabric was immersed in an aqueous dispersion of polyurethane, sodium sulfate, and carbodiimide, and then fixed in a hot air dryer at 160°C for 20 minutes to obtain an impregnated fiber intermediate in which the polyurethane content corresponded to 18% of the fiber weight.

[0093] Removal of marine components: The impregnated fibrous intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fibers. Subsequently, it was washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated microfiber intermediate.

[0094] Second impregnation treatment: 32 parts by mass of sodium sulfate as a heat-sensitive coagulant and 7.5 parts by mass of a carbodiimide-based crosslinking agent were added to 100 parts by mass of polyether-based polyurethane, and the mixture was adjusted with water to achieve a solid content concentration of 11% by mass of the polyurethane component. According to laboratory measurements, the gelation temperature was 65°C.

[0095] The microfiber-like material obtained above was immersed in the aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes to obtain a nonwoven microfiber product. In this product, the polyurethane content derived from the second impregnation treatment was 25% of the fiber weight, and the total polyurethane content from the first and second impregnation treatments combined was 43% of the fiber weight.

[0096] Furthermore, the ratio of polyurethane content between the first and second impregnation treatments is 139%.

[0097] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper to achieve a final thickness of 0.75 mm.

[0098] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0099] The resulting stained material exhibited a softness of 3.3 mm, a surface appearance grade of 5, and a Martindale abrasion resistance grade of 4.5 at 60,000 cycles / 9 kPa. This material has potential applications in the fashion and accessories industry. To further improve the softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 3.8 mm. SEM measurements of the cross-section of the material after dyeing and softening treatment showed a P value of 15%. [Example 2]

[0100] Felt manufacturing method - A composite sea-island structure fiber was manufactured using TLAS as the sea component and polyethylene terephthalate as the island component (weight ratio of sea component to island component: 43:57, number of islands per fiber: 16, average fiber diameter: 22 μm). The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes, and then dried at 100°C for 5 minutes.

[0101] First impregnation treatment - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) as a heat-sensitive coagulation salt and 7.5 parts by mass of a carbodiimide-based crosslinking agent as a crosslinking agent were added to 100 parts by mass of polyether-based polyurethane. The mixture was then diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. Laboratory measurements showed that the gelation temperature was 65°C. After immersing the nonwoven fabric in the aqueous dispersion, it was fixed in a hot air dryer at 160°C for 20 minutes to obtain an impregnated fiber intermediate in which the polyurethane content was 15% by mass relative to the fiber weight.

[0102] Removal of marine components: The resulting impregnated microfiber intermediate was immersed in an 8% sodium hydroxide solution (by weight) at 63°C for 8 minutes to remove marine components from the fibers. Subsequently, the material was washed with water to remove any residue of the sodium hydroxide aqueous solution, and a partially impregnated, microfiber-like intermediate was obtained.

[0103] Second impregnation treatment - 32 parts by mass of sodium sulfate as a heat-sensitive coagulant and 7.5 parts by mass of a carbodiimide-based crosslinking agent were added to 100 parts by mass of polyether-based polyurethane, diluted with water, and adjusted so that the polyurethane component concentration upon drying was 15% by mass. According to laboratory measurements, the gelation temperature was 65°C.

[0104] The microfiber-like material obtained above was immersed in the aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes to produce a microfiber nonwoven fabric product. In this product, the polyurethane content attached by the second impregnation treatment was 35% of the fiber weight, and the total polyurethane content was 50% of the fiber weight.

[0105] The ratio of the amount of polyurethane resin impregnation from the first to the second impregnation treatment is 233%.

[0106] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper so that the final thickness was 0.75 mm.

[0107] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0108] The dyed material exhibited a softness of 3.2 mm, a surface appearance grade of 5, and abrasion resistance grade of 4.5 in the Martindale abrasion test at 60,000 cycles / 9 kPa.

[0109] This material has potential applications in the fashion and accessories industries.

[0110] To further improve softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 3.7 mm. Cross-sectional analysis by SEM revealed that the P value of the dyed material after softening treatment was 17%. [Example 3]

[0111] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component, with a weight ratio of sea component to island component of 43:57, 16 islands per filament, and an average fiber diameter of 22 μm. The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The resulting nonwoven fabric was immersed in 80°C hot water for 3 minutes, and then dried at 100°C for 5 minutes.

[0112] First impregnation treatment - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane. This mixture was diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. According to laboratory measurements, the gelation temperature was 64°C.

[0113] The partially impregnated nonwoven fabric was immersed in the aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes to obtain an impregnated fiber intermediate in which the polyurethane content was 18% by weight relative to the fiber weight.

[0114] Removal of marine components: The impregnated microfiber intermediates were immersed in an 8% sodium hydroxide aqueous solution (by weight) at 63°C for 8 minutes to remove marine components from the fibers. After washing the aforementioned material with water to remove any residue of the sodium hydroxide solution, a partially impregnated microfiber-like intermediate was obtained.

[0115] Second impregnation treatment: 32 parts by mass of sodium sulfate and 7.5 parts by mass of a carbodiimide-based crosslinking agent were added to 100 parts by mass of polyether-based polyurethane as a heat-sensitive coagulant, and diluted with water to adjust the polyurethane component concentration to 25% by mass upon drying. According to laboratory measurements, the gelation temperature was 64°C. The obtained microfiber-like material was immersed in an aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes to produce a microfiber nonwoven fabric product. In this product, the polyurethane content attached by the second impregnation treatment was 25% of the fiber weight, and the total polyurethane content was 43% of the fiber weight.

[0116] The ratio of the amount of polyurethane resin impregnation from the first to the second impregnation treatment was 139%.

[0117] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper so that the final thickness was 0.75 mm.

[0118] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then reduced and washed with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0119] The resulting stained material had a softness of 2.8 mm, a surface appearance grade of 4, and a Martindale abrasion resistance grade of 4.0 at 60,000 cycles / 9 kPa.

[0120] This material has potential applications in the fashion and accessories industries.

[0121] To further improve the softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 3.1 mm.

[0122] SEM cross-sectional observation of the material after staining and softening treatment showed a p-value of 6.5%. [Example 4]

[0123] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component (mass ratio of sea component: 43%, mass ratio of island component: 57%, number of islands: 16 / fiber, average fiber diameter: 22 μm). The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes to shrink it, and then dried at 100°C for 5 minutes.

[0124] First impregnation step - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane. The mixture was then diluted with water to adjust the solid content concentration of the polyurethane component to 11% by mass. According to laboratory measurements, the gelation temperature of this solution was 65°C. The nonwoven fabric obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded a polyurethane-impregnated fiber intermediate with a polyurethane content of 30% by mass relative to the fiber weight.

[0125] Removal of marine components - The obtained impregnated fibrous intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fibers.

[0126] Subsequently, the material was washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated microfiber-like intermediate.

[0127] Second impregnation treatment - 32 parts by mass of sodium sulfate and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane as a heat-sensitive coagulant, and diluted with water to adjust the solid content concentration of the polyurethane component to 11% by mass. According to laboratory measurements, the gelation temperature of this solution was 64°C.

[0128] The microfiber material obtained above was immersed in the aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This resulted in a microfiber nonwoven fabric product in which the polyurethane content derived from the second impregnation treatment was 20% by mass of the fiber weight, and the total polyurethane content was 50% by mass of the fiber weight.

[0129] The ratio of polyurethane content from the first and second impregnation treatments is 67%.

[0130] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper so that the final thickness was 0.75 mm.

[0131] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0132] The resulting dyed material had a softness of 2.8 mm, a surface appearance grade of 4, and a Martindale abrasion resistance test grade of 4.0 at 60,000 cycles / 9 kPa.

[0133] This material has potential applications in the fashion and accessories industries.

[0134] To further improve the softness, the dyed material was subjected to a mechanical softening treatment, resulting in a softness value of 3.1 mm.

[0135] SEM cross-sectional analysis of the material after dyeing and softening treatment showed a p-value of 15%. [Example 5]

[0136] Similar to Example 1, the desired fiber was obtained in a composite sea-island structure fiber with a sea component weight ratio of 30%, an island component weight ratio of 70%, 16 islands per filament, an average fiber diameter of 22 μm, using TLAS for the sea component and polyethylene terephthalate for the island component.

[0137] The resulting dyed fibers exhibited a softness of 3.4 mm, a surface texture grade of 5, and a Martindale abrasion resistance test grade of 4.5 (60,000 cycles / 9 kPa).

[0138] This material can be used in applications such as seat covers and ceiling materials in the automotive industry.

[0139] To improve the softness, the dyed material was subjected to a mechanical softening treatment, resulting in a softness value of 3.8 mm.

[0140] When the cross-section of the material after dyeing and softening treatment was measured using SEM, the p-value was 15%. [Example 6]

[0141] Similar to Example 2, the desired fiber was obtained in a composite sea-island structure fiber with a sea component weight ratio of 30%, an island component weight ratio of 70%, 16 islands per filament, an average fiber diameter of 22 μm, using TLAS as the sea component and polyethylene terephthalate as the island component.

[0142] After dyeing, this fiber exhibited a softness of 3.3 mm, a surface appearance grade of 5, and a Martindale abrasion resistance grade of 4.5 at 60,000 cycles / 9 kPa.

[0143] This material can be applied to applications in the automotive industry, such as seat covers and ceiling materials.

[0144] To further improve softness, the dyed fibers were subjected to a mechanical softening treatment, resulting in a softness value of 3.7 mm.

[0145] SEM measurements of the cross-section of the material after staining and softening treatment showed a P-value of 17%. Comparative Example 7

[0146] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component (weight ratio of sea component to island component: 43:57, 16 islands / fiber, average fiber diameter: 22 μm). The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes, and then dried at 100°C for 5 minutes.

[0147] First impregnation step - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) as a heat-sensitive coagulant and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane. The mixture was then diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. Laboratory measurements showed that the gelation temperature was 63°C.

[0148] The nonwoven fabric was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded a polyurethane-impregnated fibrous intermediate with a polyurethane content of 10% by mass relative to the fiber weight.

[0149] Removal of marine components - The resulting impregnated fibrous intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fibers.

[0150] Subsequently, the material was washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated microfiber-like intermediate.

[0151] Second impregnation treatment - 32 parts by mass of sodium sulfate and 7.5 parts by mass of a carbodiimide-based crosslinking agent were added to 100 parts by mass of polyether-based polyurethane as a heat-sensitive coagulant, and diluted with water to adjust the solid content concentration of the polyurethane component to 30% by mass. According to laboratory measurements, the gelation temperature was 63°C. The microfiber-like material obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This resulted in a microfiber nonwoven fabric product in which the polyurethane content derived from the second impregnation treatment was 45% by mass of the fiber weight, and the total polyurethane content was 55% by mass of the fiber weight.

[0152] The ratio of the amount of polyurethane resin impregnation from the first to the second impregnation treatment is 450%.

[0153] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, the surface was finished, and a suede-like texture was given using sandpaper so that the final thickness was 0.75 mm.

[0154] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then reduced and washed with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0155] The resulting dyed material exhibited a softness of 2.0 mm, a surface appearance grade of 2.5, and a Martindale abrasion resistance test grade of 3.0 (60,000 cycles / 9 kPa).

[0156] This material has potential applications in the fashion and accessories industries.

[0157] To further improve softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 2.2 mm. Cross-sectional observation of the material after dyeing and softening treatment using SEM yielded a P value of 1.5%. Comparative Example 8

[0158] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component (mass ratio of sea component: 43%, mass ratio of island component: 57%, number of islands: 16 / fiber, average fiber diameter: 22 μm). The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes to shrink it, and then dried at 100°C for 5 minutes.

[0159] First impregnation step - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane. The mixture was then diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. According to laboratory measurements, the gelation temperature of this solution was 65°C.

[0160] The microfiber nonwoven fabric was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded a polyurethane-impregnated microfiber intermediate with a polyurethane content of 20% by mass relative to the fiber weight.

[0161] Removal of marine components - The resulting impregnated fibrous intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fibers.

[0162] The material was then washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated microfiber intermediate.

[0163] Second impregnation treatment - 32 parts by mass of sodium sulfate and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane as a heat-sensitive coagulant, and diluted with water to adjust the polyurethane component content to 33% by mass upon drying. According to laboratory measurements, the gelation temperature was 65°C.

[0164] The microfiber-like material obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This resulted in a microfiber nonwoven fabric product in which the polyurethane content derived from the second impregnation treatment was 45% by mass of the fiber weight, and the total polyurethane content was 65% by mass of the fiber weight.

[0165] The ratio of the first to second impregnation treatments in terms of polyurethane impregnation amount is 225%.

[0166] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper so that the final thickness was 0.75 mm.

[0167] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0168] The dyed material had a softness of 1.8 mm, a surface appearance grade of 2, and a Martindale abrasion resistance test grade of 3.0 at 60,000 cycles / 9 kPa.

[0169] This material has potential applications in the fashion and accessories industries.

[0170] To further improve softness, the dyed material was subjected to a mechanical softening treatment, resulting in a softness value of 2.0 mm. Cross-sectional analysis by SEM revealed that the P value of the dyed material after the softening treatment was 3.3%. Comparative Example 9

[0171] Felt Production - A composite sea-island structure fiber was prepared using TLAS as the sea component and polyethylene terephthalate as the island component, with a weight ratio of 43% for the sea component, 57% for the island component, 16 islands per fiber, and an average fiber diameter of 22 μm. The prepared composite sea-island structure fibers were cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinning. The resulting nonwoven fabric was immersed in 80°C hot water for 3 minutes to shrink it, and then dried at 100°C for 5 minutes.

[0172] First impregnation step - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane. The mixture was then diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. Laboratory measurements showed that the gelation temperature was 64°C.

[0173] The nonwoven fabric obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded a polyurethane-impregnated fiber intermediate with a polyurethane content of 10% by mass relative to the fiber weight.

[0174] Removal of marine components - The obtained impregnated fibrous intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fibers. Subsequently, the material was washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated microfiber-like intermediate.

[0175] Second impregnation treatment - 32 parts by mass of sodium sulfate as a heat-sensitive coagulant and 7.5 parts by mass of a carbodiimide-based crosslinking agent were added to 100 parts by mass of polyether-based polyurethane, and diluted with water to adjust the solid content concentration of the polyurethane component to 25% by mass. According to laboratory measurements, the gelation temperature was 65°C. The microfiber material obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This resulted in a microfiber nonwoven fabric product in which the polyurethane content derived from the second impregnation treatment was 30% by mass of the fiber weight, and the total polyurethane content was 40% by mass of the fiber weight.

[0176] The ratio of the first to second impregnation treatments in terms of polyurethane resin impregnation amount is 300%.

[0177] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, the surface was finished, and a suede-like texture was given using sandpaper so that the final thickness was 0.75 mm.

[0178] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0179] The resulting dyed material had a softness of 2.3 mm, a surface appearance grade of 2, and a Martindale abrasion resistance test grade of 3.5 at 60,000 cycles / 9 kPa.

[0180] This material has potential applications in the fashion and accessories industries.

[0181] To further improve softness, the dyed material was subjected to a mechanical softening treatment, resulting in a softness value of 2.6 mm. Cross-sectional analysis by SEM revealed that the P value of the dyed material after the softening treatment was 2.9%. Comparative Example 10

[0182] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component, with a weight ratio of sea component to island component of 43:57, 16 islands per filament, and an average fiber diameter of 22 μm. The resulting composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinning. The resulting nonwoven fabric was immersed in 80°C hot water for 3 minutes, and then dried at 100°C for 5 minutes.

[0183] First impregnation treatment - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane, and diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. Laboratory measurements showed that the gelation temperature was 65°C. The partially impregnated nonwoven fabric was immersed in the aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded an impregnated fiber intermediate with a polyurethane content of 10% by mass relative to the fiber weight.

[0184] Removal of marine components - The resulting impregnated fibrous intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fibers. Subsequently, the material was washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated, microfiber-like intermediate.

[0185] Second impregnation treatment - 32 parts by mass of sodium sulfate and 7.5 parts by mass of a carbodiimide-based crosslinking agent were added to 100 parts by mass of polyether-based polyurethane as a heat-sensitive coagulant, and diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. According to laboratory measurements, the gelation temperature was 64°C. The microfiber-like material obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This resulted in a microfiber nonwoven fabric product in which the polyurethane content derived from the second impregnation treatment was 10% by mass of the fiber weight, and the total polyurethane content was 20% by mass of the fiber weight.

[0186] The ratio of polyurethane resin content from the first and second impregnation treatments is 100%.

[0187] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, the surface was finished, and a suede-like texture was given using sandpaper so that the final thickness was 0.75 mm.

[0188] The resulting suede-like nonwoven fabric was dyed with disperse dyes at a temperature of 120°C using a jet dyeing machine, and then reduced and washed with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0189] The resulting dyed material had a softness of 2.3 mm, a surface appearance grade of 3, and a Martindale abrasion endurance test grade of 3.5 at 60,000 cycles / 9 kPa.

[0190] This material has potential applications in the fashion and accessories industries.

[0191] To further improve softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 2.5 mm. Cross-sectional analysis of the dyed and softened material by SEM revealed a P-value of 3.5%. Comparative Example 11

[0192] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component, with a weight ratio of 43% sea component, 57% island component, 16 islands per fiber, and an average fiber diameter of 22 μm. The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinching. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes to shrink it, and then dried at 100°C for 5 minutes.

[0193] First impregnation treatment - 100 parts by mass of polyether-based polyurethane was mixed with 7.5 parts by mass of a carbodiimide-based crosslinking agent, diluted with water, and adjusted so that the polyurethane component content upon drying was 15% by mass. According to laboratory measurements, the gelation temperature of this mixture was 65°C. The partially impregnated nonwoven fabric was immersed in the aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded an impregnated fiber intermediate containing 30% by mass of polyurethane relative to the fiber weight.

[0194] Removal of marine components - The obtained impregnated fiber intermediate was immersed in an 8% sodium hydroxide aqueous solution at 63°C for 8 minutes to remove marine components from the fiber. Subsequently, the material was washed with water to remove any residue of the sodium hydroxide solution, yielding a partially impregnated, microfiber-like intermediate.

[0195] Second impregnation treatment - 7.5 parts by mass of a carbodiimide crosslinking agent was added to 100 parts by mass of polyether-based polyurethane, and diluted with water to adjust the solid content concentration of the polyurethane component to 15% by mass. According to laboratory measurements, the gelation temperature was 65°C.

[0196] The microfiber material obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This resulted in a microfiber nonwoven fabric product in which the polyurethane content derived from the second impregnation treatment was 20% by mass of the fiber weight, and the total polyurethane content was 50% by mass of the fiber weight.

[0197] The ratio of polyurethane content from the first and second impregnation treatments is 67%.

[0198] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper so that the final thickness was 0.75 mm.

[0199] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0200] The resulting dyed material had a softness of 1.8 mm, a surface appearance grade of 3, and a Martindale abrasion endurance test grade of 3.5 at 60,000 cycles / 9 kPa.

[0201] This material has potential applications in the fashion and accessories industries. To further improve the softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 2.0 mm.

[0202] SEM cross-sectional observation of the material after staining and softening treatment showed a P value of 0.5%. Comparative Example 12

[0203] Felt Production - A composite sea-island structure fiber was produced using TLAS as the sea component and polyethylene terephthalate as the island component (mass ratio of sea component: 43%, mass ratio of island component: 57%, number of islands: 16 / fiber, average fiber diameter: 22 μm). The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and then formed into a nonwoven fabric by pinning. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes, and then dried at 100°C for 5 minutes.

[0204] Impregnation Treatment - 45 parts by mass of sodium sulfate (indicated as "Na2SO4" in Table 1 of Figure 5) and 7.5 parts by mass of a carbodiimide crosslinking agent were added to 100 parts by mass of polyether polyurethane, and diluted with water to adjust the solid content concentration of the polyurethane component to 8% by mass. According to laboratory measurements, the gelation temperature was 64°C.

[0205] The nonwoven fabric obtained above was immersed in this aqueous dispersion and then fixed in a hot air dryer at 160°C for 20 minutes. This yielded a polyurethane-impregnated fiber intermediate with a polyurethane content of 25% by mass relative to the fiber weight.

[0206] Removal of marine components - The obtained impregnated fiber intermediate was immersed in an 8% sodium hydroxide aqueous solution (by weight) at 63°C for 8 minutes to remove marine components from the fiber. Afterward, the product was washed with water to remove any residue of the sodium hydroxide solution, and a microfiber nonwoven fabric product was obtained.

[0207] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, its surface was finished, and a suede-like texture was given to it using sandpaper to achieve a final thickness of 0.74 mm. This suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then subjected to a reducing wash treatment with sodium hydrosulfite in an alkaline solution at 80°C. This completely removed any dyes that were not firmly bound to the fibers.

[0208] The resulting dyed material had a softness of 2.8 mm, a surface appearance grade of 3, and a Martindale abrasion endurance test grade of 2.0 at 60,000 cycles / 9 kPa.

[0209] This material has potential applications in the fashion and accessories industries.

[0210] To further improve softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 3.4 mm. Cross-sectional analysis of the dyed and softened material by SEM showed a p-value of 2%. Comparative Example 13

[0211] Felt manufacturing method - A composite sea-island structure fiber was manufactured using TLAS as the sea component and polyethylene terephthalate as the island component (mass ratio of sea component: 43%, mass ratio of island component: 57%, number of islands: 16 / fiber, average fiber diameter: 22 μm). The obtained composite sea-island structure fiber was cut to a length of 51 mm, passed through a carding machine and a cross wrapper to form a fiber mat, and formed into a nonwoven fabric by pinching. The obtained nonwoven fabric was immersed in 80°C hot water for 3 minutes to shrink it, and then dried at 100°C for 5 minutes.

[0212] Impregnation Treatment - 100 parts by mass of polyether polyurethane was mixed with 7.5 parts by mass of a carbodiimide crosslinking agent, and diluted with water to adjust the solid content concentration of the polyurethane component to 11% by mass. According to laboratory measurements, the gelation temperature was 65°C. The impregnated nonwoven fabric was immersed in this solution and then fixed in a hot air dryer at 160°C for 20 minutes to obtain an impregnated nonwoven fabric intermediate containing 35% by mass of polyurethane relative to the fiber weight.

[0213] Removal of marine components - The obtained impregnated fiber intermediates were immersed in an 8% by weight sodium hydroxide solution at 63°C for 8 minutes to remove marine components from the fibers. The product was washed with water to remove any residue of the sodium hydroxide solution, and a microfiber nonwoven fabric was obtained.

[0214] The resulting microfiber nonwoven fabric was cut in half perpendicular to its thickness, the surface was finished, and a suede-like texture was given using sandpaper so that the final thickness was 0.74 mm.

[0215] The resulting suede-like nonwoven fabric was dyed with disperse dyes using a jet dyeing machine at a temperature of 120°C, and then reduced and washed with sodium hydrosulfite in an alkaline solution at 80°C to completely remove any dyes that were not bound to the fibers.

[0216] The resulting dyed material had a softness of 2.6 mm, a surface appearance grade of 4, and a Martindale abrasion resistance test grade of 2.0 at 60,000 cycles / 9 kPa.

[0217] This material has potential applications in the fashion and accessories industries.

[0218] To further improve softness, the dyed material was subjected to mechanical softening treatment, resulting in a softness value of 3.2 mm. Cross-sectional analysis by SEM after dyeing and softening treatment showed a p-value of 4.2%.

[0219] Figure 5 is a table summarizing the obtained results. Excellent results and processing conditions that influenced those results are shown in bold.

Claims

1. 1. A method for manufacturing microfiber nonwoven fabric, comprising the following steps: 1) A fibrous material containing ultrafine fiber-generating fibers is impregnated with an aqueous dispersion containing polyurethane, an inorganic salt containing monovalent or divalent cations, and a crosslinking agent (first impregnation treatment). However, the polyurethane content is 15 to 40% by weight relative to the weight of the ultrafine fibers. 2) The polyurethane is fixed to the fiber material after the impregnation treatment (first solidification treatment). 3) The fibrous material is treated with an alkaline, acidic, or neutral aqueous solution to generate ultrafine fibers from the ultrafine fiber generating type fibers, thereby forming a microfiber material composed of ultrafine fibers. 4) The microfiber material is impregnated with an aqueous dispersion containing polyurethane, an inorganic salt containing monovalent or divalent cations, and a crosslinking agent; however, the polyurethane content is 15 to 40% by weight relative to the weight of the ultrafine fibers (second impregnation treatment). 5) The polyurethane is fixed to the fiber material after the impregnation treatment (second solidification treatment). However, the ratio of the polyurethane content from the second impregnation treatment to the polyurethane content from the first impregnation treatment is in the range of 100% to 250%, preferably in the range of 105% to 240%.

2. A method for manufacturing according to claim 1, wherein the concentration of monovalent or divalent cations in the first and second impregnation treatments is in the range of 10 to 100% by weight relative to the weight of polyurethane.

3. A manufacturing method according to claim 1 or 2, wherein, prior to the impregnation treatment step 1), a) a spinning step of sea-island type two-component fibers, b) a step of manufacturing a fiber material from the two-component fibers, and c) a step of thermal stabilization of the fiber material are carried out.

4. A manufacturing method according to any one of claims 1 to 3, wherein the polyurethane dispersion used in the first impregnation treatment contains polyurethane at a concentration of 5 to 20% (preferably 6 to 18%) by weight at room temperature, and by impregnation treatment using the dispersion, polyurethane is contained in a proportion of 15 to 40% (preferably 18 to 35%) by weight relative to the weight of the ultrafine fibers after impregnation.

5. A method for producing an inorganic salt containing a monovalent cation, according to any one of claims 1 to 4, wherein the inorganic salt is selected from sodium sulfate or sodium chloride.

6. A method for manufacturing according to any one of claims 1 to 5, wherein the salt concentration is in the range of 30 to 100%, preferably 40 to 80%, of the solid content weight of the polyurethane.

7. A manufacturing method according to any one of claims 1 to 6, wherein the removal of marine components in step 3) is performed by removal with an aqueous alkaline solution, preferably an aqueous sodium hydroxide solution, an aqueous acid solution, or hot water.

8. A manufacturing method according to any one of claims 1 to 7, wherein an aqueous polyurethane dispersion having a concentration of 5 to 20% (preferably 7 to 20%) at room temperature is used in a second impregnation treatment, so that polyurethane accounts for 15 to 40% (preferably 20 to 40%) of the weight of the ultrafine fibers after the impregnation treatment.

9. A manufacturing method according to any one of claims 1 to 8, wherein the fixing treatment in steps 2) and 5) is carried out by air solidification, hot water solidification, solidification in an aqueous electrolyte solution, high-frequency solidification, microwave solidification, ultrasonic solidification, solidification by infrared irradiation, or vapor solidification, preferably using hot air solidification.

10. A method for producing a product according to any one of claims 1 to 9, wherein the crosslinking agent is selected from melamine, aziridine, epoxide, zirconium compound, carbodiimide, isocyanate or polyisocyanate having a low deprotection temperature.

11. It is a suede-like microfiber nonwoven fabric, A microfiber material consisting of ultrafine fibers with an average diameter of 0.1 μm to 10.0 μm and polyurethane, wherein the cross section perpendicular to the thickness direction of the microfiber material has a region occupied by the polyurethane in contact with the cross section (however, the cross-sectional area is 50 μm). 2 A suede-like microfiber nonwoven fabric having a component in which multiple independent regions (as described above) exist in the cross-section, and the total area of ​​these independent regions is in the range of 5.5% to 40.0% of the entire cross-section in the observation field of view.

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