Double-sided heterogenous non-woven fabric and preparation method thereof

Abstract

The invention discloses a double-sided heterogenous non-woven fabric and a preparation method thereof, the double-sided heterogenous non-woven fabric is prepared by a wet papermaking technology, and the double-sided heterogenous non-woven fabric is sequentially provided with a hydrophobic layer, a transition layer and a hydrophilic layer; the hydrophobic layer is composed of hydrophobic fibers; the hydrophilic layer is composed of hydrophilic fibers; the transition layer is an area formed by mixing hydrophobic fibers and hydrophilic fibers, the content of the hydrophobic fibers in the transition layer is gradually reduced from the side close to the hydrophobic layer to the side close to the hydrophilic layer, and the content of the hydrophilic fibers is gradually increased from the side close to the hydrophobic layer to the side close to the hydrophilic layer; in the hydrophilic fiber and the hydrophobic fiber, the density of one fiber is higher than that of water, and the density of the other fiber is lower than that of water; the hydrophilicity is derived from modification of the fiber body instead of a surface coating, the hydrophobic layer, the transition layer and the hydrophilic layer are integrally formed, no hot melt adhesive or chemical adhesive bonding interface exists, and the interlayer stripping layering risk and the influence of chemical reagents are avoided.

Description

Technical Field

[0001] This invention relates to the field of nonwoven materials technology, and in particular to a double-sided anisotropic nonwoven fabric and its preparation method. Background Technology

[0002] Nonwoven fabrics, also known as non-woven cloth, are composed of oriented or randomly arranged fibers and are widely used in many fields such as medical and health care, filtration materials, and packaging materials. However, existing nonwoven fabrics usually only possess a single hydrophobic or hydrophilic property, which is insufficient to meet the actual needs of some applications with special requirements for material surface properties. For example, in the medical and health care field, if nonwoven fabrics with only hydrophobic properties are used as wound dressings, they cannot effectively absorb wound exudate, easily causing wound infection; if nonwoven fabrics with only hydrophilic properties are used, it is difficult to prevent the invasion of external bacteria, liquids, etc.

[0003] In recent years, with the rapid development of fields such as medical and health care, environmental filtration, and smart textiles, double-sided asymmetrical nonwoven fabrics with both hydrophilic and hydrophobic properties have attracted much attention due to their unique unidirectional moisture-wicking properties, stain resistance, and multifunctional integration. Double-sided asymmetrical nonwoven fabrics are asymmetric nonwoven fabrics with one side being hydrophilic and the other hydrophobic. They typically achieve rapid liquid absorption by introducing hydrophilic groups or coatings on one side, while maintaining hydrophobicity on the other side to prevent backflow. This type of nonwoven fabric can be widely used in hygiene products, medical protective equipment, automotive interiors, and building waterproofing, improving product performance through directional flow guidance and anti-backflow functions, thus showing broad application prospects in hygiene products (such as diapers and sanitary napkins), medical protective equipment, and agricultural coverings.

[0004] In existing technologies, methods for achieving double-sided anisotropic nonwoven fabrics mainly fall into two categories. The first category is surface modification technology, which functionalizes the finished nonwoven fabric by coating one side with a hydrophilic or hydrophobic agent. However, this method suffers from problems such as easy coating peeling and poor durability. The second category is composite lamination technology, which first prepares a hydrophilic nonwoven layer and a hydrophobic nonwoven layer using dry or wet methods, and then laminates them using methods such as hot melting or adhesive bonding. However, this method requires multiple processing steps, leading to increased material thickness, decreased air permeability, and easy failure of the interlayer bonding interface due to aging. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a double-sided nonwoven fabric and its preparation method, which can avoid the risk of interlayer peeling and delamination, and the preparation method is simple.

[0006] To address the aforementioned technical problems, this invention provides a double-sided anisotropic nonwoven fabric, comprising a hydrophobic layer, a transition layer, and a hydrophilic layer sequentially arranged; the hydrophobic layer is composed of hydrophobic fibers; the hydrophilic layer is composed of hydrophilic fibers; the transition layer is a region formed by a mixture of hydrophobic and hydrophilic fibers, wherein the content of hydrophobic fibers in the transition layer gradually decreases from the side closer to the hydrophobic layer to the side closer to the hydrophilic layer, and the content of hydrophilic fibers gradually increases from the side closer to the hydrophobic layer to the side closer to the hydrophilic layer; among the hydrophilic and hydrophobic fibers, one fiber has a density higher than the density of water, and the other fiber has a density lower than the density of water; and the hydrophobic layer, the transition layer, and the hydrophilic layer are integrally formed.

[0007] In one feasible implementation, the density of the hydrophilic fiber is greater than that of water, and the density of the hydrophobic fiber is lower than that of water; the hydrophilic fiber includes a first host fiber and a first bonding fiber that have undergone hydrophilic modification, and the hydrophobic fiber includes a second host fiber and a second bonding fiber that are hydrophobic; in the double-sided nonwoven fabric, the mass proportion of the first host fiber is 10%~50%, the mass proportion of the first bonding fiber is 10%~40%, the mass proportion of the second host fiber is 10%~50%, and the mass proportion of the second bonding fiber is 10%~40%; the basis weight of the double-sided nonwoven fabric is 50 g / m2.

[0008] In one feasible implementation, the first host fiber is selected from at least one of copolyester fiber and polyester fiber, wherein the copolyester fiber has a melting point of 100℃~180℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³; the polyester fiber has a melting point of 260±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³; the first bonding... The fiber is selected from at least one of polyethylene / polyester bicomponent fiber and copolyester / polyester bicomponent fiber, wherein the polyethylene / polyester bicomponent fiber has a melting point of 135±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.16±0.1g / cm³; the copolyester / polyester bicomponent fiber has a melting point of 130±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³.

[0009] In one feasible implementation, the second main fiber is a polypropylene fiber with a melting point of 160℃~170℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 0.90±0.1g / cm3; the second bonding fiber is a polyethylene / polypropylene bicomponent fiber with a melting point of 135±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 0.92±0.1g / cm3.

[0010] Accordingly, this application also provides a method for preparing a double-sided anisotropic nonwoven fabric, the method comprising the following steps: To obtain hydrophilic fibers and hydrophobic fibers; The hydrophilic fiber, the hydrophobic fiber, and the additives are mixed with water in a first preset ratio to form a slurry. After waiting for a first preset time, the fibers in the slurry naturally separate into layers. The slurry is then dehydrated, shaped, dried, and hot-pressed to obtain the double-sided nonwoven fabric. In the hydrophilic fiber and the hydrophobic fiber, one fiber has a density higher than that of water, and the other fiber has a density lower than that of water.

[0011] In one feasible implementation, the step of obtaining hydrophilic fibers includes a hydrophilic modification treatment, which involves the following operations: The first main fiber and the first bonding fiber are immersed in a hydrophilic modification solution containing polyvinyl alcohol and a crosslinking agent. After a first preset time, they are taken out, excess hydrophilic modification solution is removed from the surface, and then they are dried in an oven to obtain the hydrophilic fiber.

[0012] In one feasible implementation, the mass concentration of polyvinyl alcohol in the hydrophilic modified solution is 0.5%~10%, and the molecular weight of the polyvinyl alcohol is 100±10kDa; The mass concentration of the crosslinking agent in the hydrophilic modification solution is 0.5%~5%, and the crosslinking agent is glutaraldehyde.

[0013] In one feasible implementation, the step of obtaining the hydrophilic layer fiber further includes: pre-wetting and alkali treatment of the first host fiber and the first adhesive fiber before performing the hydrophilic modification operation; In one feasible implementation, the pre-wetting operation includes: wetting the first host fiber and the first bonding fiber with ethanol, then removing them and washing them with water to remove the ethanol; In one feasible implementation, the alkali treatment operation includes: immersing the first main fiber and the first adhesive fiber, which have undergone pre-wetting, in a sodium hydroxide solution at a first preset temperature for a first preset time, then removing them and washing them with water until neutral, wherein the mass concentration of sodium hydroxide in the sodium hydroxide solution is 1% to 10%.

[0014] In one feasible implementation, the additives include dispersants, penetrants, and defoamers; In one feasible implementation, the dispersant has a mass concentration of 0.5% to 5% of the total dry weight of the fibers, the penetrant has a mass concentration of 1% to 20% of the total dry weight of the fibers, and the defoamer has a mass concentration of 0.1% to 3% of the total dry weight of the fibers. In one feasible implementation, the dispersant is selected from at least one of polyacrylamide, polyethylene oxide, and sodium carboxymethyl cellulose; In one feasible implementation, the penetrant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and fatty alcohol polyoxyethylene ether; In one feasible implementation, the defoamer is selected from at least one of silicone defoamers and polyether-modified silicone defoamers.

[0015] In one feasible implementation, the dewatering and molding process includes the following steps: after the fibers in the slurry naturally separate into layers, vacuum dewatering is performed to form a wet fiber web; In one feasible implementation, the drying and hot-pressing process includes the following steps: the wet fiber web is first dried in a dryer, then hot-pressed using a roller press, followed by rapid cooling. The surface temperature of the dryer is 100-120°C, and the drying time is 1-10 minutes. The roller press is configured with a soft top and a hard bottom, and hot-pressing is performed 1-3 times. The surface temperature of the hard roller is 120-150°C, and the inter-roller linear pressure is 50 kg / cm.

[0016] Implementing this invention has the following beneficial effects: The double-sided anisotropic nonwoven fabric provided in this application, through a special structure of a hydrophobic layer, a transition layer, and a hydrophilic layer, exhibits good hydrophobicity on one side and good hydrophilicity on the other, meeting the specific surface performance requirements of materials in different application scenarios. By controlling the density of one of the hydrophilic and hydrophobic fibers to be higher than that of water and the other fiber to be lower than that of water, conditions are provided for subsequent nonwoven fabric preparation through natural fiber delamination, simplifying the manufacturing process. This structural design achieves a gradual transition from hydrophobic to hydrophilic, avoiding the obvious interface and delamination risks present in traditional laminated structures, and improving the overall structural stability and functionality. Utilizing density differences to achieve natural fiber delamination simplifies the manufacturing process. The hydrophobic layer, transition layer, and hydrophilic layer are integrally formed, solving the delamination problem of traditional composite nonwoven fabrics. Furthermore, the double-sided nonwoven fabric provided in this application modifies the fiber body, with hydrophilic groups tightly bonded to the fiber molecular chains. It naturally separates into layers through density differences, and the fibers are bonded together by hydrogen bonds, mechanical entanglement, and fiber fusion. There is no interface of hot melt adhesive or chemical adhesive, avoiding the risk of interlayer delamination and improving durability and service life. The hydrophilicity of the double-sided nonwoven fabric provided in this application comes from the modification of the fiber body rather than the surface coating, and its wash resistance and friction performance are significantly better than those of traditional coating processes. Attached Figure Description

[0017] Figure 1 This is a schematic cross-sectional view of a double-sided anisotropic nonwoven fabric shown in some embodiments of this application; Figure 2 This is a process flow diagram of the preparation method of double-sided anisotropic nonwoven fabric shown in some embodiments of this application; Figure 3 This is a diagram showing the water contact angles of the hydrophobic and hydrophilic surfaces of the double-sided anisotropic nonwoven fabric prepared in Example 1 of this application before and after immersion in hot water at 60°C.

[0018] The reference numerals in the figure: 10-Double-sided nonwoven fabric, 11-Hydrophobic layer, 12-Transition layer, 13-Hydrophilic layer. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Please refer to Figure 1 This application provides a double-sided anisotropic nonwoven fabric 10. The double-sided anisotropic nonwoven fabric 10 includes a hydrophobic layer 11, a transition layer 12, and a hydrophilic layer 13 sequentially disposed. The hydrophobic layer 11 is composed of hydrophobic fibers, and the hydrophilic layer 13 is composed of hydrophilic fibers. The transition layer 12 is a region formed by a mixture of hydrophobic and hydrophilic fibers. The content of hydrophobic fibers in the transition layer 12 gradually decreases from the side closer to the hydrophobic layer 11 to the side closer to the hydrophilic layer 13, while the content of hydrophilic fibers gradually increases from the side closer to the hydrophobic layer 11 to the side closer to the hydrophilic layer 13. The hydrophobic layer 11, the transition layer 12, and the hydrophilic layer 13 are integrally formed. Of the hydrophilic and hydrophobic fibers, one fiber has a density higher than the density of water, and the other fiber has a density lower than the density of water.

[0022] The double-sided anisotropic nonwoven fabric provided in this application, through a special structure of a hydrophobic layer, a transition layer, and a hydrophilic layer, exhibits good hydrophobicity on one side and good hydrophilicity on the other, meeting the specific surface performance requirements of materials in different application scenarios. Furthermore, by controlling the density of one of the hydrophilic and hydrophobic fibers to be higher than that of water and the other to be lower than that of water, conditions are provided for subsequent nonwoven fabric preparation through natural fiber delamination, simplifying the manufacturing process. This structural design achieves a gradual transition from hydrophobic to hydrophilic, avoiding the obvious interface and delamination risks present in traditional laminated structures, and improving the overall structural stability and functionality. Utilizing density differences to achieve natural fiber delamination simplifies the manufacturing process. The hydrophobic layer, transition layer, and hydrophilic layer are integrally formed, solving the delamination problem of traditional composite nonwoven fabrics. Furthermore, the double-sided nonwoven fabric provided in this application modifies the fiber body, with hydrophilic groups tightly bonded to the fiber molecular chains. It naturally separates into layers through density differences, and the fibers are bonded together by hydrogen bonds, mechanical entanglement, and fiber fusion. There is no hot melt adhesive or chemical bonding interface, avoiding the risk of interlayer peeling, improving durability and service life, and avoiding the influence of chemical reagents. The hydrophilicity of the double-sided nonwoven fabric provided in this application comes from the modification of the fiber body rather than the surface coating, and its wash resistance and friction performance are significantly better than traditional coating processes.

[0023] In one feasible implementation, the density of the hydrophilic fiber is greater than that of water, and the density of the hydrophobic fiber is less than that of water. This density difference allows for natural fiber stratification during wet molding, eliminating the need for complex separation equipment and processes, thus reducing production costs. Furthermore, the density difference between the hydrophilic and hydrophobic fibers is 0.4 g / cm³. 3 -0.5g / cm 3 Furthermore, since most chemical fibers are hydrophobic, hydrophobic fibers can be modified into hydrophilic fibers by hydrophilic modification. Hydrophilic modification can further increase the density of the fibers. The density of hydrophilic fibers is greater than that of hydrophobic fibers, which can facilitate further expansion of the density difference and facilitate natural sedimentation and separation.

[0024] In one feasible embodiment, the hydrophilic fiber comprises a first host fiber and a first bonding fiber that have undergone hydrophilic modification, and the hydrophobic fiber comprises a second host fiber and a second bonding fiber that are hydrophobic. The bonding fiber can improve the stability and reliability of the hydrophobic and hydrophilic layers, and also improve the stability and reliability of the transition and connection of the transition layer. Further, in the double-sided anisotropic nonwoven fabric, the mass proportion of the first host fiber is 10%~50%, and the mass proportion of the first bonding fiber is 10%~40%; the mass proportion of the second host fiber is 10%~50%, and the mass proportion of the second bonding fiber is 10%~40%. By clearly specifying the mass proportions of each host fiber and bonding fiber in the hydrophilic and hydrophobic fibers, as well as the basis weight of the nonwoven fabric, the performance and quality of the nonwoven fabric can be precisely controlled, ensuring product stability and consistency. By rationally proportioning the hydrophilic and hydrophobic components, a balance between the material's strength and function is ensured, and the optimized proportion of the bonding fiber balances interlayer bonding strength and breathability.

[0025] In one feasible implementation, the basis weight of the double-sided anisotropic nonwoven fabric is 25-75 g / m². 2 The basis weight (BG) of double-sided anisotropic nonwoven fabric refers to the weight of material per square meter. BG is a key indicator for measuring the thickness and physical properties of nonwoven fabric materials. During the manufacturing process, the BG can be set based on thickness and performance requirements to provide raw materials with a corresponding BG. Setting a BG range also helps control costs and meet lightweight requirements. However, double-sided anisotropic nonwoven fabrics prepared using existing processes are often limited by the technology, making it difficult to achieve such a BG. Furthermore, at similar BGs, the stability of the fusion or bonding between the hydrophobic and hydrophilic layers is difficult to match the stability and reliability of this application, posing a risk of interlayer delamination.

[0026] In one feasible embodiment, the first main fiber is selected from at least one of copolyester (COPET) fiber and polyester (PET) fiber. That is, the first main fiber can be copolyester fiber, polyester fiber, or a combination of both. Further, the copolyester fiber has a melting point of 100℃~180℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³. The polyester fiber has a melting point of 260±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³. Copolyester fiber and polyester fiber, as the first main fiber, possess good mechanical properties and chemical stability, ensuring the strength and durability of the nonwoven fabric. The modified copolyester fiber and polyester fiber exhibit stable hydrophilicity. These parameter settings allow the hydrophilic fiber to better exert its hydrophilic properties and, in conjunction with other fibers, ensure the comprehensive performance of the nonwoven fabric.

[0027] In one feasible embodiment, the first bonding fiber is selected from at least one of polyethylene (PE) / polyester (PET) bicomponent fiber and / or copolyester (COPET) / polyester (PET) bicomponent fiber, i.e., at least one of PE / PET bicomponent fiber and COPET / PET bicomponent fiber. That is, the first bonding fiber can be a combination of polyethylene / polyester bicomponent fiber, copolyester / polyester bicomponent fiber, or both. Further, the polyethylene / polyester bicomponent fiber has a melting point of 135±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.16±0.1g / cm³. The copolyester / polyester bicomponent fiber has a melting point of 130±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³. Polyethylene / polyester bicomponent fibers and copolyester / polyester bicomponent fibers are used as the first bonding fibers. The bonding fibers have a lower melting point than the main fibers, so they do not damage the main structure during hot pressing. Under suitable temperatures, they can achieve good bonding between fibers, improving the overall performance of the nonwoven fabric. Selecting bicomponent fibers with appropriate melting points as bonding fibers helps to form a strong three-dimensional network structure during hot pressing, enhancing the overall strength and durability of the material.

[0028] In one feasible embodiment, the second host fiber is polypropylene (PP) fiber. As the second host fiber, polypropylene fiber possesses excellent hydrophobicity and chemical stability, ensuring further improvement in the hydrophobic properties of the hydrophobic layer. The polypropylene (PP) fiber has a melting point of 160℃~170℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 0.90±0.1g / cm³. The low-density characteristics of polypropylene are suitable for layering processes.

[0029] In one feasible embodiment, the second bonding fiber is a polyethylene (PE) / polypropylene (PP) bicomponent fiber. The PE / PP bicomponent fiber, as the second bonding fiber, enables a strong bond between the hydrophobic fibers, enhancing the structural stability of the nonwoven fabric. Further, the PE / PP bicomponent fiber has a melting point of 135±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of approximately 0.92±0.1g / cm³. The low-density characteristics of polypropylene are suitable for layering processes, and the polyethylene component and polypropylene synergistically enhance the interlayer bonding force. The hydrophobic fiber, selected from polypropylene and its bicomponent fibers, not only possesses excellent hydrophobic properties but also facilitates bonding during hot pressing, improving the structural stability of the hydrophobic layer.

[0030] Furthermore, the selection of parameters such as density characteristics, melting point, linear density, and length of the aforementioned hydrophilic and hydrophobic fibers complement each other, which helps to improve the transition distribution of each component in the transition layer of the double-sided nonwoven fabric, forming a strong three-dimensional network structure and enhancing the overall strength and durability of the material.

[0031] Accordingly, this application also provides a method for preparing a double-sided anisotropic nonwoven fabric, used to prepare the aforementioned double-sided anisotropic nonwoven fabric. The preparation method includes the following steps S210 to S240: S210, obtaining hydrophilic fibers and obtaining hydrophobic fibers; In the hydrophilic fiber and the hydrophobic fiber, one fiber has a density higher than that of water, and the other fiber has a density lower than that of water.

[0032] In one feasible implementation, the step of obtaining hydrophilic fibers includes a hydrophilic modification treatment, wherein the hydrophilic modification treatment performs the following operations: The first main fiber and the first bonding fiber are immersed in a hydrophilic modification solution containing polyvinyl alcohol and a crosslinking agent. After a first preset time, they are removed, excess hydrophilic modification solution is removed from the surface, and then they are dried in an oven to obtain the hydrophilic fiber. Thus, immersing the first main fiber and the first bonding fiber in a hydrophilic modification solution containing polyvinyl alcohol and a crosslinking agent effectively improves the hydrophilic properties of the fiber. The action of polyvinyl alcohol and the crosslinking agent forms hydrophilic groups on the surface of the hydrophilic fiber, improving the fiber's adsorption and affinity for water, thereby ensuring good hydrophilic properties of the hydrophilic layer, and the modified layer is firm and not easily detached.

[0033] In one feasible embodiment, the polyvinyl alcohol (PVA) in the hydrophilic modification solution has a mass concentration of 0.5% to 10%, and the molecular weight of the PVA is 100 ± 10 kDa. The crosslinking agent in the hydrophilic modification solution has a mass concentration of 0.5% to 5%, and the crosslinking agent is glutaraldehyde. Glutaraldehyde can enhance the adhesion of PVA; a reasonable concentration and molecular weight setting can ensure the optimization of the hydrophilic modification effect; a suitable concentration of PVA and crosslinking agent can form a uniform and firm hydrophilic layer on the fiber surface, ensuring hydrophilic properties without affecting the mechanical properties and other properties of the fiber. Furthermore, the crosslinking agent fixes PVA onto the polyester fiber, increasing the water resistance of PVA. The above drying process promotes the acetal reaction between GA and PVA, forming a three-dimensional crosslinked network. The oven temperature is 60 to 90°C, and the drying time is 1 to 30 minutes.

[0034] In one feasible embodiment, the step of obtaining hydrophilic fibers further includes: pre-wetting and alkali-treating the first host fiber and the first bonding fiber before performing the hydrophilic modification operation. Pre-wetting and alkali-treating the hydrophilic fibers before hydrophilic modification allows for sufficient wetting of the fibers, facilitating subsequent alkali treatment and hydrophilic modification, improving the permeability and binding force of the subsequent hydrophilic modification, thereby significantly improving hydrophilic properties. Furthermore, alkali treatment removes impurities and grease from the fiber surface, increases the surface roughness and the number of active groups, and enhances the binding force between the hydrophilic modification solution and the fiber, thereby further improving the hydrophilic properties of the hydrophilic fibers and ensuring that the hydrophilic layer can better absorb liquids.

[0035] Furthermore, the pre-wetting operation includes: wetting the first main fiber and the first bonding fiber with ethanol, then removing them and washing them with water to remove the ethanol.

[0036] Furthermore, the alkali treatment operation includes: immersing the first main fiber and the first adhesive fiber, after pre-wetting, in a sodium hydroxide solution at a first preset temperature for a first preset time, then removing them and washing them with water until neutral. The sodium hydroxide solution contains 1% to 10% sodium hydroxide by mass. This partially hydrolyzes the fiber surface to generate carboxylic acid groups, enhancing hydrophilicity; it also roughens the fiber surface, increasing the number of polyvinyl alcohol (PVA) anchoring points.

[0037] S220. The hydrophilic fiber, the hydrophobic fiber and the additive are mixed with water in a first preset ratio to form a slurry.

[0038] One method for preparing a slurry by mixing the ingredients evenly can be to place a certain proportion of hydrophilic fibers (including the first main fiber and the first bonding fiber), hydrophobic fibers (including the second main fiber and the second bonding fiber), water and additives in a mixer and stir until the fibers are completely dispersed.

[0039] Furthermore, the mass percentage of each fiber component in the slurry is as follows: the first main fiber accounts for 10%~50%, the first binder fiber accounts for 10%~40%, the second main fiber accounts for 10%~50%, and the second binder fiber accounts for 10%~40%. Furthermore, the slurry concentration is 0.3%. This proportion facilitates the dispersion and mixing of each component, and ensures uniformity during subsequent natural stratification.

[0040] In one feasible embodiment, the additives include dispersants, penetrants, and defoamers. Dispersants enable the hydrophilic and hydrophobic fibers to be uniformly dispersed in the sizing, preventing fiber agglomeration and ensuring the uniformity of properties across the nonwoven fabric. Penetrants reduce the surface tension of the fibers, promoting the absorption of water and other additives by the fibers and improving fiber treatment efficiency. Defoamers eliminate air bubbles in the sizing, preventing them from forming pores in the nonwoven fabric and affecting product quality. Appropriate additive types and concentrations can improve the stability of the preparation process and product quality. Adding appropriate amounts of additives can effectively improve the dispersion of fibers in water, prevent agglomeration, improve web uniformity, and enhance the quality of the finished product.

[0041] Furthermore, the dispersant has a mass concentration of 0.5% to 5% of the total dry weight of the fiber, the penetrant has a mass concentration of 1% to 20% of the total dry weight of the fiber, and the defoamer has a mass concentration of 0.1% to 3% of the total dry weight of the fiber.

[0042] Furthermore, the dispersant is selected from at least one of polyacrylamide, polyethylene oxide, and sodium carboxymethyl cellulose.

[0043] Furthermore, the penetrant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and fatty alcohol polyoxyethylene ether.

[0044] Furthermore, the defoamer is selected from at least one of silicone defoamers and polyether-modified silicone defoamers.

[0045] S230. Wait for the first preset time to allow the fibers in the slurry to naturally separate into layers.

[0046] Step S230 can be performed in a paper machine. Specifically, the pulp can be placed in the paper machine, diluted with water to 0.03%, and allowed to stand for 10-30 seconds to allow initial fiber separation before proceeding to subsequent steps. Optionally or preferably, the waiting time is 25-30 seconds; only separation is required, not complete separation.

[0047] S240. After dehydration, molding, drying and hot pressing, the double-sided nonwoven fabric is obtained.

[0048] In one feasible embodiment, the dewatering and forming process includes the following steps: after the fibers in the pulp naturally separate into layers, vacuum dewatering is performed to form a wet fiber web. This step can be carried out using a paper machine. The drying process includes the following steps: the wet fiber web is first dried in a dryer, then hot-pressed using a roller press, followed by rapid cooling. The surface temperature of the dryer is 100~120℃, and the drying time is 1min~10min. This allows the surface layers of the first and second bonding fibers in the wet fiber web to melt, causing adhesion at the fiber intersections and initially establishing bonding strength. The roller press is soft on top and hard on the bottom, with 1~3 hot presses performed. The surface temperature of the hard roller is 120~150℃, and the inter-roller pressure is 50kg / cm². 2 After hot pressing, the nonwoven fabric is quenched to obtain the double-sided anisotropic nonwoven fabric. Vacuum dehydration forms a wet fiber web, effectively removing moisture from the slurry and allowing the fibers to initially take shape. Roller pressing and dryer drying further remove moisture and increase fiber density. Hot pressing with a roller press allows for better bonding between fibers, improving the strength and stability of the nonwoven fabric. Appropriate hot pressing temperature, pressure, and number of presses ensure optimal performance of the nonwoven fabric. The combination of vacuum dehydration and hot pressing fully shapes the fibers, enhancing structural stability and ensuring good fusion of the transition layers, thus improving overall mechanical properties. This one-step forming process allows the fibers of the resulting double-sided anisotropic nonwoven fabric to be bonded together through hydrogen bonds, mechanical entanglement, and fiber fusion, without the need for hot melt adhesives or chemical adhesives at the interface, avoiding the risk of interlayer delamination.

[0049] The method for preparing double-sided anisotropic nonwoven fabric provided in this application involves mixing hydrophilic fibers, hydrophobic fibers, and auxiliaries with water to form a slurry. The density difference between the hydrophilic and hydrophobic fibers allows for natural stratification. The fabric is then dehydrated, formed, dried, and washed to obtain the double-sided anisotropic nonwoven fabric. This preparation process is simple, convenient, and requires no complex equipment or processes, effectively reducing production costs and improving production efficiency. Furthermore, the natural stratification allows for precise control of the fiber composition and structure of each layer of the nonwoven fabric, ensuring product quality stability and consistency. This method achieves natural stratification based on fiber density differences, eliminating the need for complex lamination equipment, simplifying the process, reducing production costs, and enabling continuous production. Furthermore, the fiber body modification tightly binds the hydrophilic groups to the fiber molecular chains, naturally stratifying through density differences. The fibers are bonded together by hydrogen bonds, mechanical entanglement, and fiber fusion, eliminating the need for hot melt adhesives or chemical adhesives at the interface and avoiding the risk of interlayer delamination. The hydrophilicity of the nonwoven fabric originates from the fiber body modification rather than surface coating, resulting in significantly better wash resistance and friction performance than traditional coating processes. The process integration is high, with fiber body modification and physical density stratification significantly outperforming traditional surface modification and composite lamination technologies in terms of process simplification and cost control, making it suitable for large-scale needs in fields such as hygiene and medical care.

[0050] Referring to the above implementation details, in order to make the technical solution of this application more specific, clear, and easy to understand, examples of the technical solution of this application are given below. However, it should be noted that the content to be protected by this application is not limited to the following embodiments.

[0051] Example 1 The first main fiber is COPET fiber, with a melting point of 180℃, a linear density of 1.5 D, a length of 4 mm, and a density of approximately 1.38 g / cm³. The first bonding fiber is a PE / PET bicomponent fiber with a melting point of about 135°C, a linear density of 0.5D, a length of 3mm, and a density of about 1.16g / cm³. The second main fiber is PP fiber, with a melting point of 160℃, a linear density of 0.5D, a length of 6mm, and a density of approximately 0.90g / cm³. 3 ; The second bonding fiber is ES fiber, with a melting point of approximately 135°C, a linear density of 0.8D, a length of 5 mm, and a density of approximately 0.92 g / cm³. 3 .

[0052] The first main fiber and the first bonding fiber were wetted with ethanol, washed with water to remove the ethanol, and then soaked in a 5% NaOH solution at 60°C for 30 minutes. After washing with water until neutral, the pretreated fiber was obtained.

[0053] The pretreated fibers were immersed in 5% polyvinyl alcohol and 1% glutaraldehyde for 20 minutes, and the excess solution on the surface was drained. The fibers were then dried in an oven at 60°C for 20 minutes to obtain hydrophilic fibers.

[0054] The fibers, water, and additives were placed in a mixer and stirred until the fibers were completely dispersed. The percentages of each fiber in the total fiber composition were as follows: 30% for the first main fiber, 20% for the first bonding fiber, 25% for the second main fiber, and 25% for the second bonding fiber. The slurry concentration was 0.3%. The additives included 2% polyacrylamide as a dispersant; 10% sodium dodecylbenzenesulfonate as a penetrant; and 2% polyether-modified silicone defoamer as a defoamer. The percentages of each additive were based on the total dry weight of the fibers.

[0055] The above pulp was placed in a paper machine, diluted with water to a concentration of 0.03%, and stirred evenly. After 20 seconds to allow initial fiber stratification, it was vacuum dewatered and formed to obtain a wet fiber web. The wet fiber web was then pressed by idler rollers and dried in a dryer at a surface temperature of 120°C for 8 minutes. It was then hot-pressed three times using a roller press (soft top, hard bottom), with the hard roller surface temperature at 135°C and the inter-roll linear pressure at 50 kg / cm. After hot pressing, the nonwoven fabric was quenched to obtain the nonwoven base paper.

[0056] The basis weight of the obtained double-sided nonwoven fabric is 50 g / m². 2 .

[0057] Figure 3 This is a diagram showing the water contact angles of the hydrophobic and hydrophilic surfaces of the double-sided anisotropic nonwoven fabric prepared in Example 1 of this application before and after immersion in hot water at 60°C.

[0058] Example 2 This embodiment is basically the same as Example 1, except that: The first main fiber is PET fiber, which has a melting point of about 260°C, a linear density of 0.5D, a length of 6 mm, and a density of about 1.38 g / cm³.

[0059] The resulting double-sided nonwoven fabric has a basis weight of 50 g / m². 2 .

[0060] Example 3 This embodiment is basically the same as Example 1, except that: The mass percentage of each fiber in the slurry is as follows: the first main fiber is 10%, the first bonding fiber is 40%, the second main fiber is 10%, the second bonding fiber is 40%, and the slurry concentration is 0.3%. The resulting double-sided nonwoven fabric has a basis weight of 50 g / m². 2 .

[0061] Example 4 This embodiment is basically the same as Example 1, except that: The alkaline treatment was performed by immersing the patient in a 0.1% NaOH solution at 60°C for 30 minutes. The resulting double-sided nonwoven fabric has a basis weight of 50 g / m². 2 .

[0062] Example 5 This embodiment is basically the same as Example 1, except that: The additives include 2.5% polyethylene oxide as a dispersant; 10% sodium dodecyl sulfate as a penetrant; and 2% silicone defoamer as a defoaming agent.

[0063] The resulting double-sided nonwoven fabric has a basis weight of 50 g / m². 2 .

[0064] Example 6 This example is essentially the same as Example 1, except that in this example, the nonwoven fabric basis weight is 25 g / m². 2 .

[0065] Comparative Example 1 Wet papermaking was performed using unmodified polyester fibers, with other procedures the same as in Example 1. The resulting nonwoven fabric had a basis weight of 50 g / m². 2 .

[0066] Comparative Example 2 Surface modification for preparing heterogeneous nonwoven fabrics: First, a nonwoven fabric base paper was prepared using the method in Comparative Example 1. Then, the nonwoven fabric base paper was wetted with ethanol. Next, a 5% polyvinyl alcohol and 1% glutaraldehyde solution was coated on the polyester surface. Then, it was placed in an oven and dried at 60°C for 20 minutes. After drying, the surface-modified anisotropic nonwoven fabric was obtained.

[0067] The obtained nonwoven fabric has a basis weight of 50 g / m². 2 .

[0068] Comparative Example 3 Composite lamination preparation of nonwoven fabric with different shapes (wet hot pressing): Same as Example 1, except that the first main fiber and the first bonding fiber are prepared into wet hydrophilic layers, and the second main fiber is prepared into a wet hydrophobic layer. Then the two are laminated together and then hot-pressed together. The obtained nonwoven fabric has a basis weight of 50 g / m². 2 .

[0069] Performance testing 1. Water contact angle; measured according to GB / T 42694-2023; 2. Tensile strength; determined according to GB / T 12914-2018 method; 3. Air permeability: Tested according to GB / T 24218.15-2018; 4. Thickness: Measured according to GB / T 451.3-2002; 5. Aging test: The non-woven fabric was soaked in hot water at 60℃ for 7 days, and then the above indicators were tested.

[0070] The performance test results are shown in Tables 1 and 2: Table 1: Table 2: As shown in the table above, compared with the nonwoven fabric provided in the comparative example, the double-sided anisotropic nonwoven fabric provided in this application exhibits good performance in all aspects before the aging test, with a large difference in the water contact angle between the two sides, indicating good functionality. After the aging test, i.e., after 7 days in hot water at 60℃, the performance parameters of the double-sided anisotropic nonwoven fabric provided in this application show little change, indicating good stability. This demonstrates that the preparation method provided in this application improves the durability and service life of the double-sided anisotropic nonwoven fabric. Furthermore, the preparation method of the double-sided anisotropic nonwoven fabric provided in this application can produce double-sided anisotropic nonwoven fabrics with lower basis weight and thinner thickness.

[0071] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.

[0072] Furthermore, this specification uses specific terms to describe embodiments thereof. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Moreover, certain features, structures, or characteristics in one or more embodiments of this specification can be appropriately combined.

[0073] Furthermore, unless expressly stated in the claims, the order of processing elements and sequences, the use of numbers and letters, or other names described in this specification are not intended to limit the order of the processes and methods described herein. Although some inventive embodiments that are currently considered useful have been discussed by way of various examples in the foregoing disclosure, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments. Rather, the claims are intended to cover all modifications and equivalent combinations that conform to the substance and scope of the embodiments described herein.

[0074] Similarly, it should be noted that, in order to simplify the description disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments in this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.

[0075] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of range in some embodiments of this specification are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

[0076] For each patent, patent application, patent application publication, and other material such as articles, books, specifications, publications, and documents referenced in this specification, the entire contents of which are incorporated herein by reference. This excludes historical application documents that are inconsistent with or conflict with the content of this specification, as well as documents that limit the broadest scope of the claims in this specification (currently or subsequently appended to this specification). It should be noted that in the event of any inconsistency or conflict between the descriptions, definitions, and / or terminology used in the supplementary materials to this specification and the content of this specification, the descriptions, definitions, and / or terminology used in this specification shall prevail.

[0077] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be illustrative rather than limiting, and should be considered consistent with the teachings of this specification. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.

Claims

1. A double-sided anisotropic nonwoven fabric, characterized in that, The double-sided nonwoven fabric includes a hydrophobic layer, a transition layer and a hydrophilic layer arranged sequentially. The hydrophobic layer is composed of hydrophobic fibers; The hydrophilic layer is composed of hydrophilic fibers; The transition layer is a region formed by a mixture of hydrophobic and hydrophilic fibers. The content of hydrophobic fibers in the transition layer gradually decreases from the side closer to the hydrophobic layer to the side closer to the hydrophilic layer, while the content of hydrophilic fibers gradually increases from the side closer to the hydrophobic layer to the side closer to the hydrophilic layer. In the hydrophilic fiber and the hydrophobic fiber, one fiber has a density higher than that of water, and the other fiber has a density lower than that of water; Furthermore, the hydrophobic layer, transition layer, and hydrophilic layer are formed integrally.

2. The double-sided anisotropic nonwoven fabric according to claim 1, characterized in that, The density of the hydrophilic fiber is greater than that of water, and the density of the hydrophobic fiber is less than that of water. The hydrophilic fiber comprises a first host fiber and a first bonding fiber that have undergone hydrophilic modification; the hydrophobic fiber comprises a second host fiber and a second bonding fiber that are hydrophobic. In the double-sided nonwoven fabric, the mass proportion of the first host fiber is 10%~50%, the mass proportion of the first bonding fiber is 10%~40%, the mass proportion of the second host fiber is 10%~50%, and the mass proportion of the second bonding fiber is 10%~40%. The basis weight of the double-sided nonwoven fabric is 25~75 g / m². 2 .

3. The double-sided anisotropic nonwoven fabric according to claim 2, characterized in that, The first main fiber is selected from at least one of copolyester fibers and polyester fibers, wherein, The copolyester fiber has a melting point of 100℃~180℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³; the polyester fiber has a melting point of 260±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³. The first bonding fiber is selected from at least one of polyethylene / polyester bicomponent fiber and copolyester / polyester bicomponent fiber, wherein, The polyethylene / polyester bicomponent fiber has a melting point of 135±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.16±0.1g / cm³; the copolyester / polyester bicomponent fiber has a melting point of 130±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 1.38±0.1g / cm³.

4. The double-sided anisotropic nonwoven fabric according to claim 2, characterized in that, The second main fiber is polypropylene fiber, which has a melting point of 160℃~170℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 0.90±0.1g / cm³. 3 ; The second bonding fiber is a polyethylene / polypropylene bicomponent fiber, wherein the polyethylene / polypropylene bicomponent fiber has a melting point of 135±5℃, a linear density of 0.5D~3D, a length of 3mm~6mm, and a density of 0.92±0.1g / cm³. 3 .

5. A method for preparing a double-sided anisotropic nonwoven fabric, used to prepare the double-sided anisotropic nonwoven fabric as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: To obtain hydrophilic fibers and hydrophobic fibers; The hydrophilic fiber, the hydrophobic fiber, and the additives are mixed with water in a first preset ratio to form a slurry. After waiting for a first preset time, the fibers in the slurry naturally separate into layers. The slurry is then dehydrated, shaped, dried, and hot-pressed to obtain the double-sided nonwoven fabric. In the hydrophilic fiber and the hydrophobic fiber, one fiber has a density higher than that of water, and the other fiber has a density lower than that of water.

6. The preparation method according to claim 5, characterized in that, The step of obtaining hydrophilic fibers includes a hydrophilic modification treatment, which includes the following operations: The first main fiber and the first bonding fiber are immersed in a hydrophilic modification solution containing polyvinyl alcohol and a crosslinking agent. After a first preset time, they are taken out, excess hydrophilic modification solution is removed from the surface, and then they are dried in an oven to obtain the hydrophilic fiber.

7. The preparation method according to claim 6, characterized in that, The mass concentration of polyvinyl alcohol in the hydrophilic modified solution is 0.5%~10%, and the molecular weight of the polyvinyl alcohol is 100±10kDa; The mass concentration of the crosslinking agent in the hydrophilic modification solution is 0.5%~5%, and the crosslinking agent is glutaraldehyde.

8. The preparation method according to claim 5, characterized in that, The step of obtaining the hydrophilic layer fiber further includes: pre-wetting and alkali treatment of the first main fiber and the first adhesive fiber before performing the hydrophilic modification operation; The pre-wetting operation includes: wetting the first main fiber and the first bonding fiber with ethanol, then taking them out and washing them with water to remove the ethanol; The alkaline treatment operation includes: immersing the first main fiber and the first adhesive fiber, which have undergone pre-wetting, in a sodium hydroxide solution at a first preset temperature for a first preset time, then removing them and washing them with water until neutral. The sodium hydroxide solution contains 1% to 10% sodium hydroxide by mass.

9. The preparation method according to claim 5, characterized in that, The additives include dispersants, penetrants, and defoamers; The dispersant has a mass concentration of 0.5% to 5% of the total dry weight of the fibers, the penetrant has a mass concentration of 1% to 20% of the total dry weight of the fibers, and the defoamer has a mass concentration of 0.1% to 3% of the total dry weight of the fibers. The dispersant is selected from at least one of polyacrylamide, polyethylene oxide, and sodium carboxymethyl cellulose. The penetrant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and fatty alcohol polyoxyethylene ether; The defoamer is selected from at least one of silicone defoamers and polyether-modified silicone defoamers.

10. The preparation method according to claim 5, characterized in that, The dehydration and molding process includes the following steps: after the fibers in the slurry naturally separate into layers, vacuum dehydration is performed to form a wet fiber web; The drying and hot-pressing process includes the following steps: the wet fiber web is first dried in a dryer, then hot-pressed in a roller press, and then rapidly cooled after hot pressing; wherein, the surface temperature of the dryer is 100~120℃, the drying time is 1min~10min; the roller press is soft on top and hard on the bottom, hot pressing is performed 1~3 times, the surface temperature of the hard roller is 120~150℃, and the inter-roller linear pressure is 50kg / cm.

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