Nonwoven fabric for filtration

Abstract

The application relates to a non-woven fabric for filtration, and relates to the technical field of non-woven fabrics.The non-woven fabric is a multi-layer structure and comprises a dry-process framework, an ultrafiltration membrane and a reverse osmosis treatment membrane arranged in sequence; wherein the dry-process framework is prepared by using the following raw materials in the following proportions by weight through a dry-process technology: polyester fiber 20-30 parts, polyester fiber 25-35 parts, flame-retardant fiber 3-5 parts, glass fiber 2-4 parts, reinforcing agent 10-15 parts, melt-blown fiber 8-16 parts and polytetrafluoroethylene film 6-14 parts.The dry-process framework is prepared by heating and melting the fiber cloth and then cooling, so that the compactness of the dry-process framework is enhanced, and the stiffness and strength of the dry-process framework are improved.The reverse osmosis treatment membrane, the ultrafiltration membrane and the dry-process framework are used in combination, so that the strength of the non-woven fabric is further enhanced.The step of impregnation treatment is omitted, so that the pungent smell is avoided, the prepared non-woven fabric is free of glue and formaldehyde, is more environmentally friendly, has higher production efficiency and stronger applicability.

Description

Technical Field

[0001] This application relates to the field of nonwoven fabric technology, and in particular to a nonwoven fabric for filtration. Background Technology

[0002] Non-woven fabric, also known as nonwoven cloth, needle-punched cotton, needle-punched nonwoven fabric, etc., is made from polyester fiber (PET) and manufactured through a needle-punching process, allowing for different thicknesses, textures, and hardnesses. Types of non-woven fabrics include spunlace non-woven fabric, thermally bonded non-woven fabric, spunbond non-woven fabric, and needle-punched non-woven fabric, with different types used for filtering different substances. Non-woven fabrics are characterized by moisture resistance, breathability, flexibility, lightness, flame retardancy, non-toxicity, odorlessness, low price, and recyclability. They can be used in various industries, such as sound insulation, heat insulation, heating elements, masks, clothing, medical applications, and filling materials.

[0003] Nonwoven fabrics, lacking warp and weft threads, are very convenient to cut and sew, and are lightweight and easy to shape, making them popular among craft enthusiasts. They are fabrics formed without spinning or weaving; instead, short textile fibers or filaments are oriented or randomly arranged to form a web structure, which is then reinforced using mechanical, thermal, or chemical methods. Unlike traditional textiles where individual yarns are interwoven or braided, the fibers are directly bonded together physically, resulting in the absence of individual threads, similar to the fusible interfacing in clothing. Nonwoven fabrics break through traditional textile principles and offer advantages such as shorter processing times, faster production speeds, higher output, lower costs, wider applications, and more diverse raw material sources.

[0004] Compared to woven fabrics, nonwoven fabrics have lower strength and durability. In the manufacturing process of nonwoven fabrics, impregnation is used to enhance their strength and stiffness. However, impregnation produces a pungent odor, is relatively complicated, and has low production efficiency. Summary of the Invention

[0005] This application provides a nonwoven fabric for filtration, which is manufactured using a dry-laid skeleton, an ultrafiltration membrane, and a reverse osmosis membrane. This allows the nonwoven fabric to achieve ideal stiffness and strength without the need for glue, formaldehyde, or chemical impregnation. It simplifies the production process, avoids pungent odors, accelerates production efficiency, and improves the applicability of the nonwoven fabric.

[0006] The technical solution adopted in this application is as follows:

[0007] A nonwoven fabric for filtration, the nonwoven fabric having a multi-layer structure, comprising a dry-laid skeleton, an ultrafiltration membrane, and a reverse osmosis treatment membrane arranged sequentially;

[0008] The dry skeleton is prepared by using the following raw materials in parts by weight through a dry process: 20-30 parts polyester fiber, 25-35 parts polyester fiber, 3-5 parts flame retardant fiber, 2-4 parts glass fiber, 10-15 parts reinforcing agent, 8-16 parts meltblown fabric, and 6-14 parts polytetrafluoroethylene film.

[0009] Currently, existing nonwoven fabric manufacturing processes employ wet processes. While nonwoven fabrics are more flexible than woven fabrics, their stiffness and strength are lower. Therefore, they require impregnation with adhesive to attach glue to the fiber fabric. The glue, after solidification, increases the stiffness and strength of the nonwoven fabric. However, this process produces a pungent odor and pollutes the environment. Furthermore, the impregnation process is cumbersome, requiring repeated impregnation to ensure uniform adhesion of the adhesive to the nonwoven fabric. This application employs a dry process to prepare a dry-laid framework, then combines a reverse osmosis membrane and an ultrafiltration membrane with the dry-laid framework to produce the nonwoven fabric. The combined use of the reverse osmosis membrane, ultrafiltration membrane, and dry-laid framework increases the density of the nonwoven fabric, reduces its flexibility, and improves its stiffness and hardness. This eliminates the impregnation step, simplifies the nonwoven fabric manufacturing process, accelerates production efficiency, and avoids the generation of a pungent odor. It enables the preparation of nonwoven fabrics with ideal stiffness and strength without glue or formaldehyde.

[0010] The reverse osmosis membrane has extremely small pores, enabling it to filter small molecules. The ultrafiltration membrane has larger pores than the reverse osmosis membrane, and the dry filter media has larger pores than the ultrafiltration membrane. By placing the reverse osmosis membrane as the top layer, the ultrafiltration membrane as the middle layer, and the dry filter media as the bottom layer, when filtering air or liquid, the molecules in the air or liquid pass through the dry filter media, ultrafiltration membrane, and reverse osmosis membrane in one pass. This results in three layers of filtration, with each layer filtering out progressively smaller particles, improving filtration efficiency and removing particles of different sizes from the filter media, further enhancing the filtration performance of the nonwoven fabric. This allows the nonwoven fabric to be used not only for filtering large molecules but also for filtering small molecules in air filter cartridges and liquid filter media, expanding its applicability.

[0011] Optionally, the dry process includes the following steps: opening the polyester fiber, the polyester fiber, the flame-retardant fiber, the glass fiber, the reinforcing agent, the meltblown fiber, and the polytetrafluoroethylene film to form layered fibers; and combing the layered fibers with an opening coefficient of 0.55-0.65.

[0012] The combed layered fibers are laid into a web to make fiber cloth;

[0013] The fiber cloth is heated and melted at 185℃-195℃ to form a dry skeleton.

[0014] First, the components are coarsely opened to facilitate the dispersion of fibers into a base layer, i.e., layered fibers. Meltblown fibers have a loose structure and strong resistance to wrinkles, enhancing the deformation resistance of the nonwoven fabric. The polytetrafluoroethylene (PTFE) film provides insulation and corrosion resistance, improving the corrosion resistance of the nonwoven fabric. Furthermore, the fibers themselves have a certain degree of crimp; by combing the layered fibers, a smaller opening coefficient is achieved, resulting in smoother combing of the coarsely opened layered fibers. An opening coefficient of 0.6 is preferred to ensure uniform fiber combing, facilitating the production of a uniformly textured fiber cloth and preventing knotting. The uniformly combed fibers are then processed into a fiber cloth using a web-laying process, resulting in more uniform melting during heating, which is beneficial for preparing a uniformly textured dry-laid skeleton.

[0015] The fiber has good heat resistance; when the temperature is set at 185℃-195℃, all components can melt, and after melting and cooling, a dry skeleton is formed. After melting, the gaps between the components decrease, resulting in a higher density of the dry skeleton, which is beneficial to improving the stiffness and strength of the dry skeleton itself.

[0016] The optimal temperature is 190℃, which ensures that all components melt to the same degree, avoiding uneven melting states and resulting in a more uniform dry-process skeleton.

[0017] Optionally, the flame-retardant fiber includes aramid fiber and / or polyimide fiber.

[0018] Preferably, the flame-retardant fiber is aramid fiber.

[0019] Optionally, the reinforcing agent includes polyethylene and / or acrylate.

[0020] Polyethylene and / or acrylate have stable chemical properties and high toughness. Adding them to the dry-process skeleton can enhance the toughness and strength of the skeleton, making it more rigid and stronger without impregnation.

[0021] Furthermore, polyethylene and / or acrylate have good low-temperature resistance. Their addition improves the low-temperature resistance of the dry skeleton, enabling the nonwoven fabric to be used in environments ranging from -70℃ to 90℃, further expanding the application range of nonwoven fabrics.

[0022] Optionally, the crimp rate of the layered fibers is 5-10%, the linear density of the layered fibers is 5-7 dtex, and the length is 30-35 mm.

[0023] The crimp rate affects the cohesion of layered fibers. An optimal crimp rate of 0.7% is considered optimal; a higher crimp rate leads to a larger coefficient of friction between fibers, which is detrimental to processing. A crimp rate of 0.7% is beneficial for fiber combing, reduces friction, and experiments have shown that the fiber cohesion effect is good, which is conducive to web formation into fiber cloth and increases the toughness of the fiber cloth.

[0024] Optionally, the thickness of the dry process framework is 0.02-0.04 mm, the thickness of the ultrafiltration membrane is 0.01-0.015 mm, and the thickness of the reverse osmosis treatment membrane is 0.005-0.015 mm.

[0025] As the bottom layer of the nonwoven fabric, the dry-laid skeleton is preferably 0.03 mm thick. Too thin a skeleton will reduce strength, while too stiff a skeleton will prevent the nonwoven fabric from meeting flexibility requirements. The ultrafiltration membrane, as the intermediate layer, has the most suitable thickness. The reverse osmosis membrane has extremely small pores, and its thickness should not be too large, as this can easily lead to pore blockage. Therefore, the reverse osmosis membrane has the smallest thickness. After fabricating the three membranes into a nonwoven fabric, the thickness is between 0.25 mm and 0.7 mm, which is thinner than existing nonwoven fabrics. This allows for the production of ultra-thin nonwoven fabrics while maintaining improved stiffness and strength.

[0026] Optionally, activated carbon is also added to the dry process skeleton.

[0027] Adding activated carbon to the dry filtration frame enhances its adsorption capacity, enabling it to adsorb impurities from the air or water and improve its filtration performance. Furthermore, activated carbon's high hardness and strength provide better support for the fiber cloth within the dry filtration frame, increasing its rigidity and strength.

[0028] Optionally, after obtaining the fiber cloth, the dry process further includes sprinkling the activated carbon on the fiber cloth, laying the fiber cloth on the activated carbon, and hot pressing to obtain a multi-layer fiber material.

[0029] The multilayer fiber material is heated and melted to form a dry skeleton.

[0030] Placing activated carbon between two layers of fiber cloth helps to fix it in place and prevents it from piling up. By hot-pressing the multi-layered fiber material, the activated carbon is compressed into powder, allowing it to be evenly distributed between adjacent fiber cloths, which facilitates the addition of activated carbon. Activated carbon has strong adsorption properties and can adsorb harmful molecules in the air, making non-woven fabrics more suitable for air filtration. Activated carbon itself has high hardness; adding it can improve the overall strength of the fiber cloth, thereby strengthening the dry-lay skeleton.

[0031] Optionally, the hot pressing temperature is 200℃-240℃.

[0032] Activated carbon has strong heat resistance. Setting the hot-pressing temperature above 200℃ can change the brittleness of activated carbon. The brittleness of activated carbon increases after heating, making it easier to press into fine powder during hot pressing. Reducing the gap between the two layers of fiber cloth and tightly bonding the fiber cloth, activated carbon, and fiber cloth together helps to increase the density of the produced dry skeleton and enhance its stiffness and strength.

[0033] In summary, this application includes at least one of the following beneficial technical effects:

[0034] 1. This application employs a dry process to prepare the dry-laid skeleton. The fiber cloth is heated, melted, and then cooled to form the dry-laid skeleton, which enhances its density, stiffness, and strength. Furthermore, the use of a reverse osmosis membrane, an ultrafiltration membrane, and the dry-laid skeleton further strengthens the nonwoven fabric. The impregnation process is omitted, avoiding the generation of a pungent odor. The resulting nonwoven fabric is glue-free, formaldehyde-free, more environmentally friendly, has higher production efficiency, and wider applicability.

[0035] 2. Activated carbon is also added to the dry-laid skeleton of this application, so that the prepared nonwoven fabric has four-stage filtration capabilities, namely, reverse osmosis treatment membrane, ultrafiltration membrane, activated carbon and dry-laid skeleton, which improves the filtration performance of the nonwoven fabric and makes it more suitable for technical fields with high filtration requirements such as air filter cartridges. Detailed Implementation

[0036] The present application will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified in the following embodiments, the conditions are carried out according to conventional conditions or the conditions recommended by the manufacturer; unless otherwise specified, the raw materials used in the following embodiments can be obtained from commercially available sources.

[0037] Example

[0038] Example 1

[0039] Methods for preparing nonwoven fabrics include:

[0040] 1. Coarsely open 25 parts polyester fiber, 30 parts polyester fiber, 4 parts aramid fiber, 3 parts glass fiber, 12 parts polyethylene, 10 parts meltblown fiber and 10 parts polytetrafluoroethylene film to make layered fibers. The crimp rate of the layered fibers is 7%, the linear density is 6dtxe and the length is 32mm.

[0041] 2. Comb the layered fibers. The opening factor during combing is 0.6. Comb the fibers until they are uniform and flat.

[0042] 3. Lay the combed layered fibers into a web to make fiber cloth;

[0043] 4. Then, evenly sprinkle activated carbon on the upper surface of the fiber cloth, and then lay the same fiber cloth on the upper surface of the activated carbon. After hot pressing at 220℃, multi-layer fiber material is produced.

[0044] 5. The multi-layer fiber material was heated and melted at 190℃, and then cooled to room temperature to obtain a dry skeleton with a thickness of 0.03mm;

[0045] 6. Then, a 0.012 mm thick ultrafiltration membrane is hot-pressed onto the upper surface of the dry matrix, and a 0.01 mm thick reverse osmosis membrane is hot-pressed onto the surface of the ultrafiltration membrane. After cooling at room temperature, a nonwoven fabric is obtained.

[0046] Examples 2-4

[0047] The only difference between Examples 2-4 and Example 1 is the heating and melting temperature, which is shown in Table 1.

[0048] Table 1 Heating and melting temperature (°C)

[0049] Temperature (°C) Example 1 190℃ Example 2 185℃ Example 3 180℃ Example 4 200℃

[0050] The difference between Examples 5-7 and Example 1 lies in the different linear densities of the layered fibers, as shown in Table 2:

[0051] Table 2 Linear density of layered fibers

[0052] Linear density Example 1 6dtex Example 5 5dtex Example 6 4dtex Example 7 8dtex

[0053] Examples 8-9

[0054] The only difference between Examples 8-10 and Example 1 is the hot-pressing temperature, as shown in Table 3:

[0055] Table 3 Hot pressing temperature (°C)

[0056] Temperature (°C) Example 1 220℃ Example 8 200℃ Example 9 190℃ Example 10 250℃

[0057] Comparative Example

[0058] Comparative Example 1

[0059] The difference between Comparative Example 1 and Example 1 is that the nonwoven fabric was prepared by wet process without using ultrafiltration membrane or reverse osmosis membrane, and the prepared nonwoven fabric was impregnated with resin.

[0060] Comparative Example 2

[0061] The only difference between Comparative Example 2 and Comparative Example 1 is that Comparative Example 2 does not perform impregnation treatment on the prepared nonwoven fabric.

[0062] Comparative Example 3

[0063] The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses only a dry skeleton to make nonwoven fabric.

[0064] Comparative Example 4

[0065] The only difference between Comparative Example 4 and Example 1 is that no activated carbon was added to the nonwoven fabric prepared in Comparative Example 4.

[0066] Test methods and test data

[0067] The mechanical properties of the nonwoven fabrics prepared in Examples 1-11 and Comparative Examples 1-5 were tested according to GB / T2828.1-2012 standard, and the test data are shown in Table 4.

[0068] Table 4 Test Data Table

[0069]

[0070] By comparing Examples 1-2 and referring to Table 4, it can be concluded that in the existing technology, without impregnation treatment, the strength and other properties of the prepared nonwoven fabric are poor, and the extensibility is also poor, which cannot meet the application requirements. Therefore, in order to improve the various properties of nonwoven fabrics, the existing technology must adopt impregnation treatment to prepare nonwoven fabrics that meet the performance requirements.

[0071] Based on Example 1, Comparative Example 1, and Table 4, it can be concluded that the nonwoven fabric prepared in Comparative Example 1, due to its impregnation treatment, has poor air permeability and lower strength than the nonwoven fabric prepared in Example 1. Furthermore, the impregnation treatment not only produces a pungent odor but is also a cumbersome process with low production efficiency. In contrast, the nonwoven fabric produced in this application, using a dry-laid skeleton in conjunction with ultrafiltration and reverse osmosis membranes, exhibits better air permeability, superior performance, better stiffness and strength, and also possesses a certain degree of extensibility. Omitting the impregnation step effectively avoids the pungent odor, simplifies the production process, and improves productivity.

[0072] Examples 1-4 and Table 4 demonstrate that different melting temperatures have a significant impact on the properties of nonwoven fabrics. When the melting temperature is 185°C or lower, the properties of the prepared nonwoven fabric gradually decrease as the temperature decreases. Although the air permeability does not change significantly, the lower temperature results in an uneven texture in the melted nonwoven fabric, leading to varying air permeability in different areas. Therefore, a melting temperature of 190°C is preferred to melt all components to a uniform state, resulting in a more uniform texture and superior performance in the finished nonwoven fabric.

[0073] By implementing Examples 1 and 5-7 and referring to Table 1, it can be concluded that the linear density of the fiber determines its fineness; the higher the linear density, the coarser the fiber. When the linear density is less than 6 dtex, although the air permeability is good, the excessively fine fiber density will reduce the stiffness and strength of the nonwoven fabric. When the linear density is greater than 6 dtex, the fiber is too coarse, resulting in poor air permeability, excessive stiffness and strength, and generally poor extensibility, which will reduce the applicability of the nonwoven fabric. Therefore, the preferred fiber linear density is 6 dtex, which provides moderate strength and stiffness, good extensibility, and facilitates the application of nonwoven fabrics in multiple fields.

[0074] Based on Examples 1, 8-10, and Table 4, it can be concluded that activated carbon has high hardness and high temperature resistance. When the hot-pressing temperature is below 220℃, the hardness of the activated carbon decreases from the inside out. The outer layer is easier to crush into powder, while the inner layer is not easily crushed, resulting in uneven distribution of activated carbon on the fiber cloth and loose adhesion between adjacent fiber cloths, reducing the density of the nonwoven fabric. When the temperature is above 220℃, the activated carbon undergoes brittle deformation. After hot pressing, the activated carbon is crushed into dust, reducing its support and thus decreasing the hardness and strength of the nonwoven fabric. Therefore, the preferred hot-pressing temperature is 220℃. At this temperature, the activated carbon retains a certain particle size, which can support the fiber cloth and increase the stiffness and strength of the nonwoven fabric. Furthermore, it allows adjacent fiber cloths to adhere tightly, reducing the gaps between the layers of the nonwoven fabric and improving its density.

[0075] By referring to Examples 1, Comparative Examples 1 and 3, and Table 4, it was found that when using only a dry-laid skeleton to prepare the nonwoven fabric, its air permeability was better, although the performance of each property was slightly reduced compared to Examples 1 and Comparative Examples 1. Therefore, this application combines reverse osmosis membranes and ultrafiltration membranes with a dry-laid skeleton to prepare nonwoven fabrics with superior performance.

[0076] Based on Example 1, Comparative Example 4, and Table 4, it can be concluded that adding activated carbon slightly improves the hardness and strength of nonwoven fabrics, and the activated carbon provides internal support to the nonwoven fabric. Activated carbon also enhances the filtration performance of nonwoven fabrics, enabling them to adsorb impurities from air or liquids, thus facilitating their better application in fields such as air filtration.

[0077] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A nonwoven fabric for filtration, characterized in that: The nonwoven fabric has a multi-layer structure, including a dry skeleton, an ultrafiltration membrane, and a reverse osmosis treatment membrane arranged in sequence. The dry skeleton is prepared by using the following raw materials in parts by weight through a dry process: 20-30 parts polyester fiber, 25-35 parts polyester fiber, 3-5 parts flame retardant fiber, 2-4 parts glass fiber, 10-15 parts reinforcing agent, 8-16 parts meltblown fiber, and 6-14 parts polytetrafluoroethylene film. The dry process also includes the addition of activated carbon, and the process steps include: The polyester fiber, the polyester fiber, the flame retardant fiber, the glass fiber, the reinforcing agent, the meltblown fiber, and the polytetrafluoroethylene film are opened to form layered fibers; The layered fibers are combed, and the opening factor is 0.55-0.65; The combed layered fibers are laid into a web to make fiber cloth; Activated carbon is sprinkled on the fiber cloth, and the fiber cloth is laid on the activated carbon and hot-pressed to obtain a multi-layer fiber material; wherein the hot-pressing temperature is 200℃-240℃. The multilayer fiber material is heated and melted at 185℃-195℃ to produce a dry skeleton containing activated carbon interlayers.

2. The nonwoven fabric according to claim 1, characterized in that: The crimp rate of the layered fibers is 5-10%, the linear density of the layered fibers is 5-7 dtex, and the length is 30-35 mm.

3. The nonwoven fabric according to claim 1, characterized in that: The thickness of the dry process substrate is 0.02-0.04 mm, the thickness of the ultrafiltration membrane is 0.01-0.015 mm, and the thickness of the reverse osmosis membrane is 0.005-0.015 mm.

4. The nonwoven fabric according to claim 1, characterized in that: The flame-retardant fibers include aramid fibers and / or polyimide fibers.

5. The nonwoven fabric according to claim 1, characterized in that: The reinforcing agent includes polyethylene and / or acrylate.

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