High burst strength wetlaid nonwoven filtration media and method of production thereof

Abstract

Fibrous filter media and methods of making the same are provided. According to preferred embodiments, the filter media comprises a wet-laid, hot zone calendered nonwoven fibrous web comprising synthetic staple fibers, and from about 20 wt% to about 80 wt% of sheath-core bicomponent staple fibers dispersed throughout the fibrous web, based on the total weight of the fibrous web. The fibrous web exhibits a dry and wet burst strength greater than 10 bar, preferably greater than about 12 bar, for example greater than about 15 bar.

Description

[0001] This application is a divisional application of the invention patent application filed on April 16, 2019, with application number 201980026073.9 and entitled "High burst strength wet-laid nonwoven filter media and its production method". Technical Field

[0002] The embodiments disclosed herein generally relate to nonwoven filter media. In a preferred form, the nonwoven filter media comprises a low-density fibrous web (e.g., less than about 0.45 g / cm³). 3 It exhibits high dry and wet burst strength (e.g., greater than about 10 bar) and a relatively small (e.g., less than about 40 μm and, in some embodiments, less than about 25 μm) average flow orifice size, making it particularly suitable as a filter medium for gases and liquids. Background Technology

[0003] Spunbond nonwovens are now widely used in air filtration, such as dust collector filters, gas turbine inlet filters, powder coating filters, and sandblasting filters, as well as in liquid filtration, such as pool and hot spring filters, wastewater filters, and coolant filters, because these applications require high dry and wet burst strengths greater than 10 bar. This high burst strength requirement can be met by using spunbond nonwovens as the filter medium, but is generally not met by other types of filter media, such as nonwoven media formed by wet-laid cellulose fibers and melt-blown media.

[0004] However, spunbond media cannot meet current requirements for high filtration efficiency and long service life. In this respect, spunbond media has inherent limitations in filtration efficiency because its fiber diameter is relatively coarse, ranging from 15 to 18 μm, thus preventing conventional spunbond media from overcoming the efficiency standard of Class M filters according to EN779:2012.

[0005] Furthermore, conventional spunbond media exhibits lower dust retention capacity due to point bonding within the fibrous web. Typically, spunbond media for applications requiring high dry and wet burst strength are treated with hot point-calendering to ensure inter-fiber bonding within the web. This point bonding (i.e., since the spunbond media is entirely composed of thermoplastic fibers molten under point-calendering conditions) results in approximately 20% of the entire spunbond filter media area being essentially “dead space.” Consequently, conventional spunbond media suffers from lower dust retention capacity compared to other types of filter media.

[0006] To overcome the low efficiency of conventional spunbond media, other technologies (such as nanofiber coating or ePTFE membrane lamination) can be added to the spunbond media. However, these additional processing requirements inevitably increase the cost of the filter media and / or result in a very short filter lifespan.

[0007] Wet-laid nonwoven filter media typically offer higher filtration efficiency and dust retention capacity than typical spunbond media. Because wet-laid nonwoven media can be formed from a wide range of possible fiber diameters via the wet-laid process, fibers with significantly finer diameters compared to those used in conventional spunbond media can be employed, such as 0.8 denier fibers (approximately 9 μm in diameter), 0.3 denier fibers (approximately 5.5 μm in diameter), and 0.06 dtex fibers (approximately 2.6 μm in diameter). However, typical wet-laid nonwoven filter media are known to be unsuitable for filtration applications requiring high dry and wet burst strengths because conventional wet-laid filter media have dry and wet burst strengths of less than 10 bar, even if the wet-laid filter media can be saturated with binder resins and / or supplied with binder fibers.

[0008] Therefore, there is a strong desire to provide fibrous wet-laid filter media with high dry and wet burst strength (i.e., greater than 10 bar), so that they can be used in applications traditionally served by spunbond media. The aim is to meet such a need as addressed by the embodiments disclosed herein. Summary of the Invention

[0009] The filter media according to the embodiments disclosed herein comprises area-calendered, wet-laid nonwoven fibrous webs with high dry and wet burst strengths greater than 10 bar, typically greater than 12 bar, for example greater than about 15 bar. The calendered, wet-laid nonwoven fibrous webs will also exhibit high filtration efficiency and dust retention capabilities, which are unattainable with conventional spunbond filter media.

[0010] The embodiments disclosed herein are achieved by providing a wet-laid nonwoven fibrous web comprising, by weight of approximately 20 to approximately 80% symmetrical sheath-coretype staple fibers, with the remainder being other synthetic staple fibers, wherein the nonwoven web undergoes hot zone calendering bonding. The presence of more than 20% by weight of sheath-coretype staple fibers allows for zone bonding, resulting in significantly less filtration “dead space,” compared to the spot calendering bonding typically used for spunbond media. The higher proportion of sheath-coretype staple fibers and the uniform dispersion of such fibers throughout the nonwoven wet-laid mat allow the filtration media of the disclosed embodiments to achieve at least comparable and generally better dry and wet burst strengths compared to spunbond media composed of continuous filaments, even though the fibrous web of the present invention contains a large number of relatively short-cut (e.g., 1–24 mm) staple fibers without continuous filaments.

[0011] The present invention includes, for example, the following embodiments:

[0012] 1. A fibrous filter medium comprising a wet-laid, hot-zone-calendered nonwoven fibrous web, said fibrous web comprising:

[0013] Synthetic short fibers; and

[0014] Based on the total weight of the fibrous web, approximately 20% to approximately 80% by weight of core-sheath bicomponent short fibers are dispersed throughout the fibrous web, wherein...

[0015] The fibrous web exhibits a dry burst strength greater than 10 bar.

[0016] 2. The fibrous filter medium according to embodiment 1, wherein the dry burst strength of the fibrous web is greater than about 12 bar, preferably greater than about 15 bar.

[0017] 3. The fibrous filter medium according to embodiment 1 or 2, wherein the wet burst strength of the fibrous web is greater than about 10 bar, preferably greater than about 12 bar, and more preferably greater than about 15 bar.

[0018] 4. The fibrous filter medium according to any one of the foregoing embodiments, wherein the density of the fibrous web is less than about 0.45 g / cm³. 3 For example, less than approximately 0.40 g / cm³ 3 .

[0019] 5. The fibrous filter medium according to any one of the foregoing embodiments, wherein the minimum pore size of the fibrous web is 25 μm or less, preferably 22 μm or less.

[0020] 6. The fibrous filter medium according to any one of the foregoing embodiments, wherein the average flow pore size of the fibrous web is 40 μm or less, preferably 35 μm or less, more preferably 30 μm or less.

[0021] 7. The fibrous filter medium according to any one of the foregoing embodiments, wherein the maximum pore size of the fibrous web is 50 μm or less, typically 45 μm or less, for example 40 μm or less.

[0022] 8. The fibrous filter medium according to any one of the foregoing embodiments, wherein the pore size of the fibrous web is in the range of 25 μm or less, typically 22 μm or less.

[0023] 9. The fibrous filter medium according to any one of the foregoing embodiments, wherein the filter medium can be classified as an F7 filter medium according to the EN779:2012 standard.

[0024] 10. The fibrous filter medium according to any one of the foregoing embodiments, comprising less than 10% by weight of glass fiber based on the total weight of the fibrous web.

[0025] 11. The fibrous filter medium according to embodiment 10, wherein the glass fiber is glass microfiber.

[0026] 12. The fibrous filter medium according to any one of the foregoing embodiments, wherein the synthetic fibers comprise a mixture of at least two different types of synthetic fibers.

[0027] 13. The fibrous filter medium according to embodiment 12, wherein the synthetic fibers comprise a first type of synthetic fibers with an average diameter between about 2.5 μm and about 10 μm and a second type of synthetic fibers with an average diameter between about 10 μm and about 20 μm.

[0028] 14. The fibrous filter medium according to embodiment 13, wherein the average length of the first type of synthetic fibers is between about 1 mm and about 6 mm, and the average length of the second type of synthetic fibers is between about 5 mm and about 24 mm.

[0029] 15. The fibrous filter medium according to any one of the foregoing embodiments, wherein, based on the total weight of the fibrous web, the synthetic short fibers comprise between about 5% to about 30% by weight, typically between 10% to about 20% by weight, of regenerated cellulose fibers.

[0030] 16. The fibrous filter medium according to embodiment 15, wherein the regenerated cellulose fiber includes lyocell fiber.

[0031] 17. The fibrous filter medium according to any one of the foregoing embodiments, wherein the filter medium further comprises at least one additive selected from wet strength additives, optical brighteners, fiber retainers, colorants, fuel-water separation aids, and flame retardants or fire retardants.

[0032] 18. The fibrous filter media according to embodiment 17, wherein, based on the total weight of the fibrous web, the at least one additive comprises about 40 to about 80% by weight of flame-retardant fiber.

[0033] 19. The fibrous filter media according to any one of the foregoing embodiments, wherein the synthetic short fibers are in the form of polymers selected from: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof.

[0034] 20. The fibrous filter medium according to any one of the foregoing embodiments, wherein the sheath and core of the bicomponent short fibers are formed of polyethylene terephthalate (PET), wherein the melting temperature of the PET forming the sheath is lower than the melting temperature of the PET forming the core.

[0035] 21. A method for manufacturing fibrous webs, comprising:

[0036] (a) A fibrous web formed by wet-laid fabrication from an aqueous fibrous slurry, said aqueous fibrous slurry comprising synthetic short fibers and a core-sheath bicomponent short fiber comprising about 20% to about 80% by weight based on the total weight of the fibrous web; and

[0037] (b) The wet-laid fibrous web from step (a) is subjected to hot zone calendering to melt the skin of the bicomponent short fibers, thereby bonding the synthetic short fibers together and obtaining a fibrous web with a dry breaking strength greater than 10 bar.

[0038] 22. The method according to embodiment 21, wherein step (b) is carried out under calendering pressure conditions between about 1 kN / m and about 150 kN / m and calendering temperature conditions between about 110°C and about 250°C, wherein the calendering line speed is between about 1 m / min and about 50 m / min.

[0039] These and other properties of the various embodiments of the invention will be better understood by referring to the following detailed description. Attached Figure Description

[0040] Please refer to the attached diagram, in which:

[0041] Figure 1The images are scanning electron microscope (SEM) images of a cross section taken along the thickness of such a medium from a conventional wet-laid fibrous web according to Example 1 as described below.

[0042] Figure 2 The image is an SEM image of a cross section taken along the thickness of a medium of a fibrous web according to an embodiment disclosed herein and described below as Example 2, showing that the medium contains thermally bonded adhesive fibers throughout its depth, which is believed to contribute to the resulting high dry and wet breaking strength.

[0043] Figure 3 The following is an SEM image of a cross-section along the thickness of the comparative spunbond medium of Comparative Example 1.

[0044] Figure 4 The following is an SEM image of a cross-section along the thickness of the comparative spunbond medium of Comparative Example 2;

[0045] Figure 5 This is a graphical comparison of the pore size range of the standard wet-laid medium of Example 1 and the medium of the present invention in Example 2 as described below;

[0046] Figure 6 This is a graphical comparison of the pore size range of the medium of the present invention in Example 2 as described below with that of typical spunbond media in Comparative Examples 1 and 2 as described below;

[0047] Figure 7 Here is a SEM image of the surface of the medium of the present invention as described in Example 2 below;

[0048] Figure 8 and 9 These are SEM images of the surface of typical spunbond media in Comparative Examples 1 and 2 as described below;

[0049] Figure 10 This is a schematic diagram of the calendering method used in the embodiments of the invention disclosed herein; and

[0050] Figure 11-13 It is a graph of the selected pressure drop curves of the medium according to the following Example 2, Comparative Example 1 and Comparative Example 2.

[0051] definition

[0052] As used herein and in the appended claims, the following terms are intended to have the following definitions.

[0053] "Fiber" is a fibrous or filamentous structure (body) with a high length-to-diameter ratio.

[0054] "Filament" refers to fibers that are extremely long or indefinite in length.

[0055] "Short fiber" refers to fibers that naturally have or have been cut or further processed into defined, relatively short segments of a defined or individual length.

[0056] "Fibrous" refers to materials that are mainly composed of fibers and / or short fibers.

[0057] The terms “nonwoven fabric,” “web,” or “pad” refer to a collection of fibers and / or short fibers in a large number of such fibers that are randomly interlocked, entangled, and / or bonded together to form a self-supporting structural element.

[0058] The terms "synthetic fiber" and / or "man-made fiber" refer to fibers made from fiber-forming substances, including polymers synthesized from chemical compounds, modified or converted natural polymers, and silica (glass) materials. Such fibers can be produced using conventional melt spinning, solution spinning, solvent spinning, and similar filament production techniques.

[0059] Cellulose fibers are fibers composed of or derived from cellulose.

[0060] The term "thermoplastic material" refers to polymeric materials that become flexible or moldable above a certain temperature and then return to a solid state upon cooling. Detailed Implementation

[0061] The calendered nonwoven wet-laid medium of the embodiments disclosed herein can be in the form of 100% synthetic short fibers, for example, a fibrous medium composed entirely of synthetic polymer fibers, optionally containing other synthetic short fibers (e.g., glass or other inorganic fibers). Therefore, in a preferred form, the nonwoven medium of the embodiments disclosed herein will be substantially (if not entirely) free of cellulose or other natural short fibers. In a particularly preferred form, the calendered medium of the embodiments disclosed herein will comprise a wet-laid nonwoven web composed of 20-80% bicomponent short fibers, with the remainder being synthetic short fibers, preferably synthetic polymer short fibers.

[0062] A. Bicomponent short fibers

[0063] The nonwoven fibrous webs according to embodiments disclosed herein comprise synthetic bicomponent short fibers. As is known per se, bicomponent short fibers are formed by extruding polymer sources from separate extruders and spinning them together to form a single fiber. Typically, two separate polymers are extruded, but bicomponent fibers may comprise the same polymer material extruded from separate extruders, wherein the polymer materials in each extruder have slightly different properties (e.g., melting point). The extruded polymers are arranged in different regions of substantially constant position along the cross-section of the bicomponent fiber and extend substantially continuously along the length of the bicomponent fiber. The configuration of the bicomponent fibers used in practice with the embodiments disclosed herein is preferably a substantially symmetrical core-sheath bicomponent fiber, whereby the polymer sheath completely surrounds and encloses the polymer core with a sheath-to-core area ratio between about 25 / 75 and about 75 / 25, typically between about 50 / 50 and about 70 / 30.

[0064] The bicomponent staple fiber is preferably a bicomponent polyethylene terephthalate (PET) staple fiber having a lower melting point PET sheath surrounding a higher melting point PET core. In a preferred form, the bicomponent PET staple fiber will comprise: a PET sheath having a melting point between about 120°C and about 190°C, typically between about 140°C and 190°C, more preferably between 150°C and about 180°C, for example about 165°C (+ / -3°C); and a PET core having a melting point at least about 50°C higher than the melting point of the PET sheath, typically at least about 75°C, for example about 100°C (+ / -5°C). Thus, the melting point of the PET core of the bicomponent staple fiber can be between about 220°C and about 280°C, typically between about 250°C and about 270°C, for example about 260°C (+ / -5°C). In the practice of the embodiments disclosed herein, a preferred bicomponent staple fiber used is LMF50 bicomponent staple fiber, commercially available from Huvis Corporation, having a denier of about 4 and a length of about 6 mm. The sheath portion of the bicomponent fiber may also contain other thermoplastic polymer materials, including polyalkylene (e.g., polyethylene, polypropylene, etc.) and polyamides (nylon, e.g., nylon-6, nylon 6,6, nylon-6,12, etc.).

[0065] Based on the total weight of the fibers in the fibrous web, the bicomponent short fibers will be present in the filter media in an amount of 20% to about 80% by weight, for example, between about 25% to about 60% by weight, or even about 30% to 50% by weight (+ / - 0.5% by weight).

[0066] B. Synthetic short fibers

[0067] The nonwoven fibrous webs of the embodiments described herein will also comprise synthetic fibers, including short thermoplastic fibers of about 20% to about 80% by weight, for example, between about 40% to about 75% by weight, based on the total weight of the fibrous webs. Preferably, the average diameter of the short thermoplastic fibers will be less than about 20 μm, for example, between about 2.5 μm and about 15 μm, and the length will be between about 1 mm and about 24 mm, for example, between about 3 mm and about 12 mm.

[0068] The synthetic short fibers used in the practices of the embodiments disclosed herein can be virtually any short fiber formed from thermoplastic polymer materials. Thus, exemplary thermoplastic short fibers include: polyesters (e.g., polyalkylene terephthalates, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.), polyalkylene (e.g., polyethylene, polypropylene, etc.), polyacrylonitrile (PAN), and polyamides (e.g., nylon-6, nylon 6,6, nylon-6,12, etc.). Preferably, PET fibers exhibit good chemical and heat resistance suitable for filtration end-use applications.

[0069] In certain preferred forms, the nonwoven fibrous web will comprise a mixture of synthetic fibers of different sizes. In this regard, the medium may comprise a mixture of: at least one type of synthetic polymer fibers with an average diameter between about 2.5 μm and about 10 μm, comprising between about 20% and about 80% by weight of the total weight of the fibrous web; and a second type of synthetic polymer fibers with an average diameter between about 10 μm and about 20 μm, comprising between about 30% and about 60% by weight of the total weight of the fibrous web. The average length of the first type of synthetic fibers may be between about 1 mm and about 6 mm, while the average length of the second type of synthetic fibers may be between about 5 mm and about 24 mm.

[0070] Based on the total weight of the fibrous web, the synthetic short fibers used in the wet-laid fibrous medium may further include regenerated cellulose fibers, preferably lyocell short fibers, between about 5% to about 30% by weight, typically between 10% and about 20% by weight, from about 5% to about 30% by weight. The average diameter of the lyocell short fibers may be about 25 μm or less, typically 15 μm or less, for example, between about 10 μm and about 15 μm. The average length of the lyocell short fibers is typically between about 1 mm and about 8 mm, or between about 2 mm and about 6 mm, or between about 3 mm and about 4 mm. Preferred lyocell fibers are commercially available from Engineered Fibers Technology, LLC, Shelton, CT, under the trade name [trade name missing]. Lyocell fiber, which has a denier of about 1.7 and a short length of about 4 mm.

[0071] Glass microfibers may also optionally be present in blends with other synthetic fibers as described above, in an amount sufficient to improve the efficiency of the fibrous media as a filter. Typically, glass microfibers (if present) will be used in an amount of 0-20% by weight, typically less than about 10% by weight, based on the total weight of the fibrous web. Glass microfibers with an average fiber diameter between about 0.2 μm and about 5 μm, typically between about 0.5 μm and about 2.5 μm ± about 0.1 μm, can be used. Preferred glass microfibers for the fibrous media used in the embodiments described herein can be C04 glass fiber (average fiber diameter of 0.5 μm), C06 glass fiber (average fiber diameter of 0.65 μm), and C26 glass fiber (average fiber diameter of 2.6 μm), commercially available from Lauscha Fiber International of Summerville, SC.

[0072] C. Optional components

[0073] The fibrous web may also contain additives commonly used in wet-laid filter media, such as wet strength additives, optical brighteners, fiber retainers, colorants, separation aids (e.g., silicone additives and associated catalysts), flame retardants, or fire retardants (e.g., in particulate or fibrous form). If present, these additives may be included in an amount up to about 30% by weight, preferably up to about 20% by weight, for example, between about 1% and about 20% by weight, based on the total weight of the fibrous web. If flame-retardant fibers are incorporated into the fibrous web, flame-retardant fibers may be used in amounts between about 40% and about 80% by weight, based on the total weight of the fibrous web.

[0074] D. Manufacturing method

[0075] The nonwoven fibrous webs described herein can be manufactured using any conventional wet-laid papermaking technique. Thus, for example, predetermined amounts of synthetic fibers and core-sheath bicomponent short fibers (along with any optional components, such as glass fibers, basic thermoplastic fibers, and / or additives) and water can be placed in a pulper or beater. The fibers are homogenously mixed and dispersed in water by the pulper or beater to form a pulp batch. Some mechanical processing can also be performed on the fibers to affect physical parameters, such as permeability, surface properties, and fiber structure. The pulp batch can then be transferred to a mixing tank, where additional water is added and the fibers are homogenized. The blended pulp can then be transferred to a machine tank, where one or more pulp batches can be combined, allowing a transition from a batch to a continuous process. The consistency of the pulp is determined and maintained by agitation to ensure uniform fiber dispersion. Optionally, the pulp can be passed through a refiner to adjust the physical parameters in this regard.

[0076] The slurry is then transferred to a moving wire mesh screen, where water is removed by gravity and suction. As water is removed, the fibers are formed into a nonwoven fibrous web or sheet with properties determined by a number of process variables, including, for example, slurry flow rate, machine speed, and drainage parameters. The formed web may optionally be compressed while still wet to compact the paper and / or alter its surface properties. The wet fibrous web is then moved through a drying section (or, in art terms, "cans") comprising heated rollers, where most of the remaining entrained water is removed. The dried fibrous web is then coated with an adhesive resin by any conventional method, such as impregnation, spraying, roller (gravure) application, etc. Heat may then be applied to dry the web.

[0077] The nonwoven fibrous web can then be wound onto rolls for further processing into finished paper sheets, or passed directly to a calendering section comprising at least one, preferably a series of, two pairs of opposing calendering rolls, such as... Figure 10 As shown. Calendering rolls are operated to press (consolidate) a mass of nonwoven wet-laid fibers in sheet form to form a nonwoven fibrous web as disclosed herein. In a preferred embodiment, the calendering rolls are operated to press the nonwoven fibrous web at a calendering pressure of about 1 kN / m to about 150 kN / m and a calendering temperature of 110°C to about 250°C, sufficient to allow the sheath of the bicomponent short fiber component to melt and bond with the other synthetic fiber components in the nonwoven web. The calendering machine line speed can be selected between about 1 m / min and about 50 m / min. The calendering machine line speed and increased temperature / pressure as described herein create hot-zone calendering of the fibrous web.

[0078] The calendering rolls do not point-bond the nonwoven fibrous web. Instead, the calendering rolls apply substantially uniform pressure and temperature over the entire surface area of ​​the web in the manner described above, thereby uniformly calendering the web (i.e., zone calendering). This hot zone calendering causes a considerable (if not all) partial melting of the lower-melting-point skin polymer of the bicomponent short fibers in the nonwoven web, thereby bonding the remaining thermoplastic core components of the bicomponent short fibers to each other and to the other synthetic short fibers in the web.

[0079] The resulting nonwoven fibrous web can be used as a filter medium, or it can be plied with other fibrous media (e.g., fibrous layers pre-formed during wet web forming or webs formed from multiple layers). When multiple fibrous web layers provide the filter medium, the hot-zone calendered fibrous web layers of the embodiments disclosed herein are preferably arranged as the outermost layer of the filter medium. For example, the fibrous web layers can be pressed to a basis weight of, for example, from about 1 to about 50 g / m². 2 The membrane is formed from expanded polytetrafluoroethylene (ePTFE), or a multilayer (e.g., two or three fibrous web layers) filter medium can be provided, wherein one of such multilayers is a fibrous web layer that is thermally calendered according to the embodiments disclosed herein.

[0080] E. Medium properties

[0081] The resulting hot-zone calendered fibrous web will exhibit high dry and wet breaking strengths of greater than 10 bar, typically greater than 12 bar, and for example greater than 15 bar. These high dry and wet breaking strengths can be achieved through hot-zone calendering as described herein, which melts the sheath of the bicomponent short fibers through the web, thereby causing the remaining core component of the bicomponent short fibers and the synthetic short fibers to bond together throughout the fibrous web.

[0082] The density of fibrous webs will typically be less than about 0.45 g / cm³. 3 For example, less than approximately 0.40 g / cm³ 3 .

[0083] The pore size range of the fibrous web will typically be 25 μm or smaller, more typically 22 μm or smaller, usually 20 μm or smaller, with the minimum pore size also typically 25 μm or smaller, or more typically 22 μm or smaller. The average flow pore size can be 40 μm or smaller, typically 35 μm or smaller, for example 30 μm or smaller, and the maximum pore size is 50 μm or smaller, typically 45 μm or smaller, for example 40 μm or smaller.

[0084] The filter media can be classified as F7 filter media according to the EN779:2012 standard, which means that for 0.4μm particles, the average filtration efficiency of the filter media is 60-80% and the minimum filtration efficiency is at least 35%.

[0085] The present invention will be further illustrated by the following non-limiting embodiments.

[0086] Example

[0087] 1. Testing Method

[0088] The data reported in the table below were obtained using the following testing methods.

[0089] aperture Pore ​​size (μm) was determined according to ASTM Standard 316-03 (2011) (in its entirety by reference). The minimum, maximum, and average flow orifice size and orifice number for the following media examples were measured using a Porometer 3G manufactured by Quantachrome Instruments (1900 Corporate Drive Boynton Beach, FL 33426 USA). The reported orifice size and orifice number data are averages of two samples, one of which was tested on each side of the medium (i.e., the wire mesh side and the felt side in the case of wet-laid media).

[0090] Orifice size and pore number data are measured using a technique known as capillary flow porosimetry. First, the sample is wetted with a wetting fluid, filling all the pores. A non-reactive gas at increased pressure is applied to one side of the wet sample to displace the liquid from the pores. The gas pressure and flow rate downstream of the sample are measured and plotted against the wet sample. After the sample dries, the test is repeated to plot the gas flow rate against the applied pressure against the dry sample. Using this capillary porosimetry technique, the "maximum pore size," "minimum pore size," and "average flow pore size" can be determined.

[0091] Maximum aperture: The capillary flow pore measurement technique described above is used to first detect the gas pressure of the airflow through the medium (i.e., the pressure at which the bubbles first begin to flow) in order to calculate the maximum pore size.

[0092] Minimum aperture The capillary flow porosity measurement technique described above is used to determine the pressure when the wet velocity curve and the dry velocity curve are combined.

[0093] Average flow rate orifice diameterIt refers to the orifice diameter when the flow rate through the wet medium is 50% of the flow rate through the dry medium under the same pressure drop, using the capillary flow orifice measurement technique described above.

[0094] Aperture range Defined as the difference between the maximum aperture and the minimum aperture (i.e., aperture range = maximum aperture and minimum aperture).

[0095] Layer thickness (Caliper) The thickness of the medium was measured in accordance with the International Organization for Standardization (ISO) standard ISO 534 (2011), “Paper and board – Determination of thickness, density and specific volume” (incorporated in its entirety by reference).

[0096] air permeability The air permeability of the medium was measured under a water pressure differential of 125 Pa, according to ASTM standard D737: Standard Test Method for Air Permeability of Textile Fabrics (incorporated herein by reference in its entirety). The air flow rate through the medium was reported in cubic feet per minute per square foot sample (cfm / sf or cfm).

[0097] Tension strength According to ISO standard 2758 (2014), "Paper - Determination of bursting strength" (in whole or in part, by reference) measures the pressure required to cause a sample of a medium to burst when dry ("dry bursting strength") or wet ("wet bursting strength"). The results are reported in kilogram-forces per square meter at the point of bursting, and then converted to bars.

[0098] porosity The porosity was determined using the following procedure: A 40mm x 40mm dry test specimen of the medium with an initial weight (w1) was placed in a beaker containing 200cc of n-butanol. The specimen was then placed in a desiccator, which was evacuated until no bubbles were visually observed emanating from the test specimen. The test specimen was removed from the n-butanol in the beaker and weighed immediately after removal to obtain the initial weight (w2), and weighed again 30 seconds after removal to obtain the final wet weight (w3). The porosity (%) was then calculated using the following formula: Porosity (%) = (w3 - w1) / (w3 - w2) x 100.

[0099] Air filter classificationThe air filtration performance was determined according to the testing standard EN779:2012, "Particulate airfilters for general ventilation" (incorporated hereinforcingly by reference). According to this standard, the performance of air filter media is classified into three groups of nine filters: coarse filters: "G1-G4", medium filters: "M5-M6", and fine filters: "F7-F9". The classification of M and F class filters is based on the average efficiency for 0.4 μm particles (i.e., the fraction of 0.4 μm particles retained on the filter). F class filters also need to meet an additional minimum efficiency standard, which is the lowest of any one of the following three values: initial efficiency, discharge efficiency, or efficiency throughout the test loading process.

[0100] Air filtration performance The air filtration performance was measured according to the International Organization for Standardization (ISO) 16890, "Air filters for general ventilation" (which is incorporated herein by reference in its entirety).

[0101] Pulsejet cleaning properties The cleanability of the cleanable filter media was determined by ISO 11057:2011, "Air quality – Test method for filtration characterization of cleanable filter media" (incorporated in its entirety by reference).

[0102] 2. Materials

[0103] The following materials are used:

[0104] LMF50 Short bicomponent low-melting fiber with 4 denier and 6mm length (4De*6mm) is commercially available from Huvis Corporation.

[0105] PET The polyethylene terephthalate (PET) fibers used are available in 1.4 denier, 12mm long (1.4De*12mm), commercially available from Toray Industries; 0.5 denier, 5mm long (0.5De*5mm), commercially available from Huvis Corporation; and 0.3 dtex, 5mm long (0.3Dt*5mm), commercially available from Teijin Ltd.

[0106] 3. Medium Examples

[0107] The samples in Examples 1 and 2 below were prepared by the wet web forming method described above, wherein the sample in Example 2 has undergone zone calendering.

[0108] Example 1 The base substrate is prepared by the method described above to form a 100% synthetic fiber wet-laid nonwoven medium, comprising 30 wt% LMF50 4De*6mm bicomponent short fibers and a mixture of PET short fibers consisting of 30 wt% PET 0.5De*5mm (Huvis), 20 wt% PET 1.4De*12mm (Toray), and 20 wt% PET 0.3dt*5mm (Teijen). The basis weight of the substrate is 210 g / m². 2 The flat sheet thickness is 0.94 mm, and the air permeability is 80 cfm.

[0109] Example 2 The base material of Example 1 of the calendering medium was calendered at a calendering roll gap pressure of 75 kN / m and a calendering temperature of 210°C to obtain a calendered wet-laid nonwoven medium with a basis weight of 210 g / m. 2 The flat sheet has a thickness of 0.60 mm and an air permeability of 26 cfm.

[0110] Comparative Example 1 (Kolon Finon L2270NW) The comparative medium in Comparative Example 1 was a commercially available PET spunbond medium, which is commonly used in APC (Air Pollution Control) filter media manufactured by Kolon Industries (KOLON Tower, 11, Kolon-ro, Gwacheon-si, Gyeonggi-do, South Korea), with a basis weight of 277 g / m³. 2 The layer thickness is 0.61 mm, and the air permeability is 25 cfm.

[0111] Comparative Example 2 (Toray FSE21602A) The comparative medium in Comparative Example 2 is another commercially available PET spunbond medium, which is conventionally used in APC (Air Pollution Control) filter media manufactured by Toray Advanced Materials Korea Inc. (FKI Tower 35, 36Fl., 24Yeoui-daero, Yeongdeungpo-gu, Seoul, South Korea), with a basis weight of 204 g / m³. 2 The layer thickness is 0.48 mm, and the air permeability is 28 cfm.

[0112] 4. Experimental Results

[0113] 4.1 Experimental Results 1

[0114] The media embodiments described above were tested to determine pore size data (minimum, average flow rate, and maximum pore size) and the number of pores. Additionally, the dry and wet burst strength of each media embodiment was tested. The data are shown in Table 1 below.

[0115] Table 1

[0116] Table 1: Physical properties of the medium of the present invention and comparative embodiments

[0117]

[0118] The data above show that, compared to the standard wet-laid substrate (Example 1) and the comparative spunbond media examples, the medium of the present invention (Example 2) has a much smaller maximum and average flow pore size. The medium of the present invention (Example 2) also exhibits a higher number of pores per unit area than the standard wet-laid sample or typical spunbond media. Compared to the standard wet-laid substrate (Example 1), the medium of the present invention (Example 2) has an increased number of pores, believed to be due to consolidation in several sub-regions near the medium surface caused by the pressing of the hot calendering rollers. Compared to typical spunbond media (Comparative Examples 1 and 2), the medium of the present invention (Example 2) also has a much larger number of pores, believed to be a result of regional bonding achieved by the latter's hot calendering rather than point bonding of fibers in the former. The medium of the present invention (Example 2) also exhibits a greater porosity, indicating that the medium of the present invention has more pores than typical spunbond media (Comparative Examples 1 and 2).

[0119] Significantly, compared to other embodiments, the medium of the present invention (Example 2) exhibits a very tight, narrow pore size range (see [reference]). Figure 5 and 6 The pore size range is an important parameter because it indicates the variation in pore size within the medium. A narrower pore size range indicates a more uniform pore distribution within the medium, thereby improving the filtration performance. Furthermore, compared to typical spunbond media, the calendered media of this invention also have smaller pore sizes and much lower web density. It is believed that the differences in pore size range, packing (density), and pore structure of the media result in higher filtration efficiency and dust retention capacity.

[0120] 4.2 Experimental Results 2

[0121] Filtration performance tests were conducted according to EN779:2012 testing standard using a Palas MFP 3000 manufactured by Greschbachstraße 3 b 76229 Karlsruhe, Germany. The media of the present invention and comparative examples were tested with and without IPA discharge, based on the IPA discharge method in Annex A of the testing standard EN779:2012. Data are provided in Table 2 below.

[0122] Table 2: Air filtration performance of the medium of the present invention and comparative embodiments

[0123]

[0124] The data in Table 2 above show that the dielectric of the present invention in Example 2 has higher efficiency than the typical spunbond dielectrics of Comparative Examples 1 and 2. The efficiency of Example 2 is unaffected after the dielectric is discharged with an IPA. This is significantly different when compared to the spunbond dielectrics of Comparative Examples 1 and 2. The dielectric of the present invention in Example 2 comprises hydrophilic chopped synthetic fibers (due to oil and surfactant residues on the fiber surface from the manufacturing process). However, the fibers in spunbond dielectrics are not oiled, and therefore exhibit higher electrostatic charge and a greater efficiency drop after IPA discharge compared to the dielectrics of the present invention in the embodiments disclosed herein.

[0125] As shown in Table 2, compared with the conventional spunbond media of Comparative Examples 1 and 2, the media of the present invention according to the embodiments disclosed herein exhibits not only significantly better initial and discharge efficiency for 0.4 μm particles, but also better overall average efficiency and better dust retention capacity. Therefore, according to EN779:2012, the media of the present invention is classified as an F7 filter media, while the conventional spunbond filter media of Comparative Examples 1 and 2 can only achieve lower M5 and M6 grades, respectively.

[0126] 4.3 Experimental Results 3

[0127] The pulse jet cleaning of the media of the present invention in Example 2 and the comparative media of Comparative Examples 1 and 2 were also tested according to ISO 11057:2011 testing standards using a FilTEq GmbH tester (Amthausstr. 14, D-76227 Karlsruhe, Germany). Each test included the following four stages:

[0128] Phase 1 (Conditioning): 30 loading cycles, using differential pressure controlled pulse jet cleaning with a cleaning setpoint of 1000 Pa.

[0129] Phase 2 (Aging): 10,000 pulse jet cleaning cycles, each with a 5-second interval.

[0130] Phase 3 (Stabilization): 10 loading cycles, using differential pressure controlled pulse jet cleaning.

[0131] Phase 4 (Measurement): 2-hour loading cycle, using differential pressure controlled pulse jet cleaning.

[0132] The data from the pulse jet cleaning test are shown in Table 3 below.

[0133] Table 3: Pulse jet cleaning performance of the medium of the present invention (Example 2) and the media of comparative Examples 1 and 2.

[0134]

[0135] The data in Table 3 above show that, compared with the comparative spunbond media of Comparative Examples 1 and 2, the media of the present invention advantageously has a cycle time that is about 2-5 times longer at the 30th cycle. Figure 11-13 As can be seen, the medium of the present invention in Example 2 takes a longer time to reach the target pressure drop, resulting in a longer cycle time. After aging, the cycle time of the wet-laid calendered medium continues to be significantly longer than that of the spunbond medium (3-10 times longer). In addition, the wet-laid calendered medium of the present invention in Example 2 also exhibits a much lower dust permeability than the comparative examples of Comparative Examples 1 and 2 when measured at the 30th cycle and after aging.

[0136] 4.4 Experimental Results: Fibrous Webs Containing Flame-Retardant Fibers

[0137] The following discloses an embodiment made of flame-retardant PET fiber, which requires no additional chemical treatment.

[0138] The fibrous web was manufactured using the same method disclosed in Example 2 and comprised 100% PET fiber, of which approximately 65% ​​by weight was flame-retardant PET fiber commercially available from Toray Industries. The fibrous web comprised 25% by weight RM PET 4D*6mm fiber (Huvis), 10% by weight PET 0.3dt*5mm fiber (Teijin), 45% by weight FRPET 1.4D*6mm fiber (Toray), and 20% by weight FR PET 3D*12mm fiber (Toray).

[0139] The resulting fibrous filter media is an F1 class flame retardant, which passed the test of DIN 53 438 standard. The physical properties are shown in Table 4 below.

[0140] Table 4. Physical properties of the media of the present invention containing flame-retardant fibers

[0141]

[0142] 4.5 Experimental Results Multilayer Filter Media

[0143] In the following embodiments (Examples A to D), the nonwoven fibrous web of the present invention is combined with other fibrous media to provide a multilayer filter media.

[0144] Example A: A multilayer filter medium in which a fibrous web calendered in a hot zone is laminated onto a thin aluminized spunbond layer. The resulting multilayer filter medium has a very low electrical resistance, below 1000 ohms.

[0145] Example B: PVDF nanofiber coating on fibrous webs.

[0146] Examples C and D: Lamination of fibrous webs with expanded polytetrafluoroethylene (ePTFE). According to the EN 1822-1 test standard, the resulting two-layer filter has high filtration efficiency and can be classified as E12 or H13 class filter media.

[0147] The physical properties of Examples A through D are shown in Table 5.

[0148] Table 5. Examples of fibrous filter media formed from multiple fibrous web layers

[0149]

[0150] Implementation Plan

[0151] The embodiments of the present invention include the following:

[0152] 1. A fibrous filter medium comprising a wet-laid, hot-zone-calendered nonwoven fibrous web, said fibrous web comprising:

[0153] Synthetic short fibers; and

[0154] Based on the total weight of the fibrous web, approximately 20% to approximately 80% by weight of core-sheath bicomponent short fibers are dispersed throughout the fibrous web, wherein...

[0155] The fibrous web exhibits a dry burst strength greater than 10 bar.

[0156] 2. The fibrous filter medium according to embodiment 1, wherein the dry burst strength of the fibrous web is greater than about 12 bar, preferably greater than about 15 bar.

[0157] 3. The fibrous filter medium according to embodiment 1, wherein the wet burst strength of the fibrous web is greater than about 10 bar, preferably greater than about 12 bar, and more preferably greater than about 15 bar.

[0158] 4. The fibrous filter medium according to embodiment 1, wherein the minimum pore size of the fibrous web is 25 μm or less, preferably 22 μm or less.

[0159] 5. The fibrous filter medium according to embodiment 3, wherein the average flow pore size of the fibrous web is 40 μm or less, preferably 35 μm or less, more preferably 30 μm or less.

[0160] 6. The fibrous filter medium according to embodiment 4, wherein the maximum pore size of the fibrous web is 50 μm or less, typically 45 μm or less, for example 40 μm or less.

[0161] 7. The fibrous filter medium according to embodiment 3, wherein the pore size of the fibrous web is 25 μm or less, typically 22 μm or less.

[0162] 8. The fibrous filter medium according to embodiment 1, wherein the filter medium can be classified as an F7 filter medium according to the EN779:2012 standard.

[0163] 9. The fibrous filter medium according to embodiment 1, comprising less than 10% by weight of glass fiber based on the total weight of the fibrous web.

[0164] 10. The fibrous filter medium according to embodiment 8, wherein the glass fiber is glass microfiber.

[0165] 11. The fibrous filter medium according to embodiment 1, wherein the synthetic fibers comprise a mixture of at least two different types of synthetic fibers.

[0166] 12. The fibrous filter medium according to embodiment 10, wherein the synthetic fibers comprise a first type of synthetic fibers with an average diameter between about 2.5 μm and about 10 μm and a second type of synthetic fibers with an average diameter between about 10 μm and about 20 μm.

[0167] 13. The fibrous filter medium according to embodiment 11, wherein the average length of the first type of synthetic fibers is between about 1 mm and about 6 mm, and the average length of the second type of synthetic fibers is between about 5 mm and about 24 mm.

[0168] 14. The fibrous filter medium according to embodiment 1, wherein, based on the total weight of the fibrous web, the synthetic short fibers comprise between about 5% to about 30% by weight, typically between 10% to about 20% by weight, of regenerated cellulose fibers.

[0169] 15. The fibrous filter medium according to embodiment 13, wherein the regenerated cellulose fiber includes lyocell fiber.

[0170] 16. The fibrous filter medium according to embodiment 1, wherein the filter medium further comprises at least one additive selected from wet strength additives, optical brighteners, fiber retainers, colorants, fuel-water separation aids, and flame retardants or fire retardants.

[0171] 17. The fibrous filter media according to embodiment 15, wherein, based on the total weight of the fibrous web, the at least one additive comprises about 40 to about 80% by weight of flame-retardant fiber.

[0172] 18. The fibrous filter media according to embodiment 1, wherein the synthetic short fibers are in the form of polymers selected from: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof.

[0173] 19. The fibrous filter medium according to embodiment 1, wherein the sheath and core of the bicomponent short fibers are formed of polyethylene terephthalate (PET), wherein the melting temperature of the PET forming the sheath is lower than the melting temperature of the PET forming the core.

[0174] 20. A method for manufacturing fibrous webs, comprising:

[0175] (a) A fibrous web formed by wet-laid fabrication from an aqueous fibrous slurry, said aqueous fibrous slurry comprising synthetic short fibers and a core-sheath bicomponent short fiber comprising about 20% to about 80% by weight based on the total weight of the fibrous web; and

[0176] (b) The wet-laid fibrous web from step (a) is subjected to hot zone calendering to melt the skin of the bicomponent short fibers, thereby bonding the synthetic short fibers together and obtaining a fibrous web with a dry breaking strength greater than 10 bar.

[0177] 21. The method according to embodiment 19, wherein step (b) is carried out under calendering pressure conditions between about 1 kN / m and about 150 kN / m and calendering temperature conditions between about 110°C and about 250°C, wherein the calendering line speed is between about 1 m / min and about 50 m / min.

[0178] **********************

[0179] Although the invention has been described in conjunction with embodiments currently considered to be the most practical and preferred, it should be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within its spirit and scope.

Claims

1. A fibrous filter medium comprising a wet-laid, hot-zone-calendered nonwoven fibrous web, said fibrous web comprising: Synthetic short fibers; and Based on the total weight of the fibrous web, 20% to 80% by weight of core-sheath bicomponent short fibers are dispersed throughout the fibrous web, wherein... The density of the fibrous web is less than 0.45 g / cm³. 3 It exhibits a dry fracture strength greater than 10 bar.

2. The fibrous filter medium according to claim 1, wherein the dry burst strength of the fibrous web is greater than 12 bar.

3. The fibrous filter medium according to claim 1, wherein the dry burst strength of the fibrous web is greater than 15 bar.

4. The fibrous filter medium according to any one of claims 1 to 3, wherein the wet burst strength of the fibrous web is greater than 10 bar.

5. The fibrous filter medium according to any one of claims 1 to 3, wherein the wet burst strength of the fibrous web is greater than 12 bar.

6. The fibrous filter medium according to any one of claims 1 to 3, wherein the wet burst strength of the fibrous web is greater than 15 bar.

7. The fibrous filter medium according to any one of claims 1 to 3, wherein the density of the fibrous web is less than 0.40 g / cm³. 3 .

8. The fibrous filter medium according to any one of claims 1 to 3, wherein the average flow pore size of the fibrous web is less than or equal to 40 μm.

9. The fibrous filter medium according to any one of claims 1 to 3, wherein the average flow pore size of the fibrous web is less than or equal to 35 μm.

10. The fibrous filter medium according to any one of claims 1 to 3, wherein the average flow pore size of the fibrous web is less than or equal to 30 μm.

11. The fibrous filter medium according to any one of claims 1 to 3, wherein the maximum pore size of the fibrous web is less than or equal to 50 μm.

12. The fibrous filter medium according to any one of claims 1 to 3, wherein the maximum pore size of the fibrous web is less than or equal to 45 μm.

13. The fibrous filter medium according to any one of claims 1 to 3, wherein the maximum pore size of the fibrous web is less than or equal to 40 μm.

14. The fibrous filter medium according to any one of claims 1 to 3, wherein the pore size of the fibrous web is less than or equal to 25 μm.

15. The fibrous filter medium according to any one of claims 1 to 3, wherein the pore size of the fibrous web is less than or equal to 22 μm.

16. The fibrous filter medium according to any one of claims 1 to 3, wherein the filter medium can be classified as an F7 filter medium according to the EN779:2012 standard.

17. The fibrous filter media according to any one of claims 1 to 3, comprising less than 10% by weight of glass fiber based on the total weight of the fibrous web.

18. The fibrous filter medium according to claim 17, wherein the glass fiber is glass microfiber.

19. The fibrous filter medium according to any one of claims 1 to 3, wherein the synthetic fiber comprises a mixture of at least two different types of synthetic fibers.

20. The fibrous filter medium of claim 19, wherein the synthetic fibers comprise synthetic fibers of a first type with an average diameter between 2.5 μm and 10 μm and synthetic fibers of a second type with an average diameter between 10 μm and 20 μm.

21. The fibrous filter medium according to claim 20, wherein the average length of the first type of synthetic fiber is between 1 mm and 6 mm, and the average length of the second type of synthetic fiber is between 5 mm and 24 mm.

22. The fibrous filter medium according to any one of claims 1 to 3, wherein, Based on the total weight of the fibrous web, synthetic short fibers comprise between 5% and 30% by weight of regenerated cellulose fibers.

23. The fibrous filter medium according to any one of claims 1 to 3, wherein, Based on the total weight of the fibrous web, synthetic short fibers comprise between 10% and 20% by weight of regenerated cellulose fibers.

24. The fibrous filter medium according to claim 22, wherein the regenerated cellulose fiber comprises lyocell fiber.

25. The fibrous filter medium according to any one of claims 1 to 3, wherein the filter medium further comprises at least one additive selected from wet strength additives, optical brighteners, fiber retainers, colorants, fuel-water separation aids, and flame retardants or fire retardants.

26. The fibrous filter medium according to claim 25, wherein, Based on the total weight of the fibrous web, the at least one additive contains 40 to 80% by weight of flame-retardant fiber.

27. The fibrous filter media according to any one of claims 1 to 3, wherein the synthetic short fibers are in the form of polymers selected from: polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof.

28. The fibrous filter medium according to any one of claims 1 to 3, wherein the sheath and core of the bicomponent short fibers are formed of polyethylene terephthalate (PET), wherein the melting temperature of the PET forming the sheath is lower than the melting temperature of the PET forming the core.

29. A method for manufacturing fibrous webs, comprising: (a) A fibrous web formed by wet-laid process from an aqueous fibrous slurry, the aqueous fibrous slurry comprising synthetic short fibers and 20% to 80% by weight of core-sheath bicomponent short fibers based on the total weight of the fibrous web; and (b) The wet-laid fibrous web from step (a) is subjected to hot zone calendering to melt the skin of the bicomponent short fibers, thereby bonding the synthetic short fibers together and obtaining a density of less than 0.45 g / cm³. 3 , and fiber web with a dry breaking strength greater than 10 bar.

30. The method of claim 29, wherein step (b) is carried out under calendering pressure conditions between 1 kN / m and 150 kN / m and calendering temperature conditions between 110°C and 250°C, wherein the calendering line speed is between 1 m / min and 50 m / min.

31. Use of the fibrous filter media according to any one of claims 1 to 28, as a filter media for gases and liquids requiring high dry and wet burst strength.

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