High burst strength wet-laid nonwoven filtration media and method for producing same

Abstract

To provide a fibrous wet type filtration medium having high dry and wet bursting strength.SOLUTION: A filtration medium contains 20 wt.% to 80 wt.% of a core-sheath two-component staple fiber dispersed in a fiber web based on the total weight of a synthetic staple fiber and a fiber web, wherein the fiber web has a density of less than 0.45 g / cm3 and exhibits dry bursting strength of more than 10 bar, the synthetic staple fiber contains a mixture of at least two different kinds of synthetic fibers, and the synthetic staple fiber contains a first kind of a synthetic fiber having an average diameter of 2.5 μm to 10 μm, and a second kind of a synthetic fiber having an average diameter of 10 μm to 20 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Embodiments disclosed herein generally relate to nonwoven filtration media. In a preferred form, the nonwoven filtration media comprises a low density fibrous web (e.g., about 0.45 g / cm) that exhibits high dry and wet burst strength (e.g., greater than about 10 bar) and a relatively small mean flow pore size (e.g., less than about 40 μm, and in some embodiments, less than about 25 μm). 3 less than 100%), which are particularly suitable for use as filtration media for gases and liquids. [Background technology]

[0002] Spunbond nonwoven fabrics are currently widely used for air filtration, such as dust collector filters, gas turbine inlet air filters, powder paint filters, and jet filters, and liquid filtration, such as pool and spa filters, drain filters, and refrigerant filters, because such applications require high dry and wet burst strengths of greater than 10 bar. Such high burst strength requirements can be met by using spunbond nonwoven fabrics as filtration media, but typically cannot be met by other types of filtration media, such as media formed from cellulosic fiber wet-laid nonwoven media and meltblown media.

[0003] However, spunbond media cannot meet current demands for high filtration efficiency and long lifespan. In this regard, spunbond media have inherent limitations in filtration efficiency due to the relatively large fiber diameters in the range of 15-18 μm, which prevents conventional spunbond media from exceeding the efficiency standard of M-class filters according to the EN779:2012 standard.

[0004] In addition, conventional spunbond media have low dust holding capacity due to point bonds in the fibrous web. Typically, spunbond media for high dry and wet burst strength applications are processed by hot point calendering to ensure inter-fiber bonding within the web. Due to such point bonding (i.e., because the spunbond media contains thermoplastic fibers throughout that melt under point calendering conditions), approximately 20% of the total area of ​​the spunbond filtration media is essentially "dead space" due to fiber-to-fiber point bonds. As a result, conventional spunbond media have a lower dust holding capacity compared to other types of filtration media.

[0005] To overcome the low efficiency of traditional spunbond media, other technologies such as nanofiber coating or lamination with ePTFE membranes can be added to the spunbond media, however, these additional processing requirements inevitably increase the cost of the filtration material and / or result in a very short filter lifespan.

[0006] Wet-laid nonwoven filtration materials typically have higher filtration efficiency and dust retention capacity than typical spunbond media. Wet-laid nonwoven media can be formed by a wet process from a wide variety of possible fiber diameters, and therefore may employ fibers with diameters substantially smaller than those forming conventional spunbond media, such as 0.8 denier fibers (having a diameter of about 9 μm), 0.3 denier fibers (having a diameter of about 5.5 μm), and 0.06 dtex fibers (having a diameter of about 2.6 μm). However, typical wet-laid nonwoven filtration materials are not known to be usable for filtration applications requiring high dry and wet burst strengths, because the dry and wet burst strengths of conventional wet-laid filtration materials are less than 10 bar, even if the wet-laid filtration materials can contain binder resins and / or binder fibers. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, it would be highly desirable to provide a fibrous wet filtration media that possesses high dry and wet burst strengths (i.e., greater than 10 bar) and can be used in applications traditionally met by spunbond media. It is to this need that the embodiments disclosed herein are directed. [Means for solving the problem]

[0008] Filtration media according to embodiments disclosed herein include area-calendered wet-laid nonwoven fibrous webs that possess high dry and wet burst strengths of 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 holding capacity that cannot be achieved by conventional spunbond filtration media.

[0009] The embodiments disclosed herein are embodied by providing a wet-laid nonwoven fibrous web containing about 20 to about 80 weight percent, based on the total weight of the fibrous web, of symmetric sheath-core type bicomponent staple fibers, with the remainder being other synthetic staple fibers, and subjecting the nonwoven web to high-temperature zone calender bonding. The presence of greater than 20 weight percent sheath-core bicomponent fibers allows for zone bonding, resulting in substantially less filtration "dead space" than the point calender bonding typically used in spunbond media. Although the fibrous web of the present invention contains a high proportion of relatively short, chopped (e.g., 1 to 24 mm) staple fibers that lack continuous filaments, the high proportion of sheath-core bicomponent fibers and the uniform distribution of such fibers throughout the nonwoven wet-laid mat allow the filtration media of the embodiments disclosed herein to achieve dry and wet burst strengths at least comparable to, and typically better than, spunbond media composed of continuous filaments.

[0010] These and other attributes of various embodiments according to the present invention will be better understood with reference to the following detailed description.

[0011] Reference is made to the accompanying drawings, in which: [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows a scanning electron microscope (SEM) image of a cross section of a conventional wet-laid fibrous web according to Example 1 below, taken through the thickness of the medium.

[0013] [Figure 2] Figure 1 shows an SEM image of a cross section of a fibrous web, shown below as Example 2, taken through the thickness of such a media according to embodiments disclosed herein, showing that the media contains thermally bonded binder fibers throughout the depth of the media, which is believed to contribute to the high dry and wet burst strengths that the media exhibits.

[0014] [Figure 3] FIG. 1 shows an SEM image of a cross section of the comparative spunbond medium of Comparative Example 1 below, taken through its thickness.

[0015] [Figure 4] FIG. 1 shows an SEM image of a cross section of the comparative spunbond medium of Comparative Example 2 below, taken through its thickness.

[0016] [Figure 5] 1 is a graph comparing the pore size ranges of a standard wetted media of Example 1 and a media of the present invention of Example 2 below.

[0017] [Figure 6] 1 is a graph comparing the pore size ranges of the inventive media of Example 2 below with typical spunbond media of Comparative Examples 1 and 2 below.

[0018] [Figure 7] FIG. 2 shows an SEM image of the surface of the media of the present invention in Example 2 below.

[0019] [Figure 8]FIG. 2 shows an SEM image of the surface of a typical spunbond medium of Comparative Example 1 below. [Figure 9] FIG. 1 shows an SEM image of the surface of a typical spunbond medium of Comparative Example 2 below.

[0020] [Figure 10] FIG. 1 is a schematic diagram of a calendaring process employed in embodiments of the invention disclosed herein.

[0021] [Figure 11] 1 is a graph of select pressure drop curves for media according to Example 2 below. [Figure 12] 1 is a graph of the selective pressure drop curve for media according to Comparative Example 1 below. [Figure 13] 1 is a graph of the selective pressure drop curve for media according to Comparative Example 2 below. DETAILED DESCRIPTION OF THE INVENTION

[0022] definition As used in this specification and the appended claims, the following terms are intended to have the following definitions.

[0023] A "fiber" is a fibrous or filamentary structure having a high aspect ratio (ratio of length to diameter).

[0024] "Filament" refers to a fiber of extreme or indefinite length.

[0025] By "staple fiber" is meant fiber that naturally possesses consistent, relatively short segments of consistent or discrete length, or that has been cut or further processed in this manner.

[0026] "Fibrous" means a material that is composed predominantly of fibers and / or staple fibers.

[0027] The terms "nonwoven," "web," or "mat" refer to a collection of fibers and / or staple fibers in many fibers that are randomly intermeshed, entangled, and / or bonded to one another to form self-supporting structural elements.

[0028] 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 siliceous (glass) materials. Such fibers may be produced by conventional filament production techniques such as melt spinning, solution spinning, and solvent spinning.

[0029] "Cellulosic fibers" are fibers composed of or derived from cellulose.

[0030] The term "thermoplastic" refers to a polymeric material that becomes flexible or moldable above a certain temperature and then returns to a solid state upon cooling.

[0031] The calendered nonwoven wetlaid media of the embodiments disclosed herein may be in the form of 100% synthetic staple fibers, e.g., a fibrous media comprised entirely of synthetic polymeric fibers, optionally containing other synthetic staple fibers (e.g., glass or other inorganic fibers). Thus, in a preferred form, the nonwoven media of the embodiments disclosed herein will be substantially (if not completely) free of cellulose or other natural staple fibers. In an especially preferred form, the calendered media of the embodiments disclosed herein will comprise a wetlaid nonwoven web comprised of 20-80% bicomponent staple fibers, with the remainder being synthetic staple fibers, preferably synthetic polymeric staple fibers.

[0032] A. Bicomponent Staple Fiber Nonwoven fibrous webs according to embodiments disclosed herein comprise synthetic bicomponent staple fibers. As is known per se, bicomponent staple fibers may be formed by extruding multiple polymer sources from separate extruders and spinning them together to form a single fiber. While typically two separate polymers are extruded, bicomponent fibers may also include the extrusion of the same polymeric material from separate extruders, with the polymeric material from each extruder having somewhat different properties (e.g., melting point). The extruded polymers are substantially always disposed in distinctly located zones across the cross-section of the bicomponent fiber and extend substantially continuously along the length of the bicomponent fiber. The bicomponent fiber configuration employed in the practice of embodiments disclosed herein is preferably a substantially symmetric sheath-core bicomponent fiber, whereby the polymeric sheath completely surrounds and envelops the polymeric core at a sheath-to-core area ratio of between about 25 / 75 and about 75 / 25, typically between about 50 / 50 and about 70 / 30.

[0033] Preferably, the bicomponent staple fiber is a polyethylene terephthalate (PET) staple fiber having a low-melting PET sheath surrounding a high-melting 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 about 190°C, more preferably between about 150°C and about 180°C, e.g., about 165°C (±3°C), and a PET core having a melting point at least about 50°C, typically at least about 75°C, e.g., about 100°C (±5°C), higher than that of the PET sheath. Thus, the PET core of the bicomponent staple fiber may have a melting point between about 220°C and about 280°C, typically between about 250°C and about 270°C, e.g., about 260°C (±5°C). One preferred bicomponent staple fiber employed in the practice of the embodiments disclosed herein 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 comprise other thermoplastic polymeric materials, including polyalkylenes (e.g., polyethylene, polypropylene, etc.) and polyamides (nylons, e.g., nylon-6, nylon 6,6, nylon-6,12, etc.).

[0034] The bicomponent staple fibers will be present in the filtration medium in an amount of from 20% to about 80% by weight, such as from about 25% to about 60% by weight, or even from about 30% to about 50% by weight (±0.5%), based on the total weight of fibers in the fibrous web.

[0035] B. Synthetic staple fibers The nonwoven fibrous webs of the embodiments described herein will also comprise synthetic fibers, including between about 20% and about 80% by weight, e.g., between about 40% and about 75% by weight, of thermoplastic staple fibers, based on the total weight of the fibrous web. Preferably, the thermoplastic staple fibers will have an average diameter of less than about 20 μm, e.g., between about 2.5 μm and about 15 μm, and a length of between about 1 mm and about 24 mm, e.g., between about 3 mm and about 12 mm.

[0036] Synthetic staple fibers employed in the practice of the embodiments disclosed herein can be virtually any staple fiber formed from a thermoplastic polymer material. Thus, exemplary thermoplastic staple fibers include polyesters (e.g., polyalkylene terephthalates such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.), polyalkylenes (e.g., polyethylene, polypropylene, etc.), polyacrylonitrile (PAN), and polyamides (nylons, e.g., nylon-6, nylon 6,6, nylon-6,12, etc.). PET fibers are preferred because they exhibit good chemical and heat resistance, making them suitable for filtration end-use applications.

[0037] In certain preferred embodiments, the nonwoven fibrous web will comprise a mixture of synthetic fibers of different sizes. In this regard, the medium may comprise between about 20% and about 80% by weight, based on the total weight of the fibrous web, of at least one type of synthetic polymeric fiber having an average diameter between about 2.5 μm and about 10 μm, and between about 30% and about 60% by weight, based on the total weight of the fibrous web, of a second type of synthetic polymeric fiber having an average diameter between about 10 μm and about 20 μm. The first type of synthetic fiber may have an average length between about 1 mm and about 6 mm, while the second type of synthetic fiber may have an average length between about 5 mm and about 24 mm.

[0038] The synthetic staple fibers employed in the wetlaid fibrous media may also comprise between about 5% and about 30% by weight, typically between 10% and about 20% by weight, of regenerated cellulose fibers, preferably lyocell staple fibers, based on the total weight of the fibrous web. The lyocell staple fibers may have an average diameter of about 25 μm or less, typically 15 μm or less, for example, between about 10 μm and about 15 μm. The average length of lyocell staple 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. A preferred lyocell fiber is commercially available from Engineered Fibers Technology, LLC of Shelton, CT, under the trade name TENCEL® lyocell fiber, and has a staple length of about 1.7 denier and about 4 mm.

[0039] Glass microfibers may also optionally be present in a sufficient amount to improve the efficiency of the fibrous media as a filter, blended with the aforementioned other synthetic fibers. Typically, glass microfibers, if present, will be employed in an amount of 0 to 20 weight percent, typically less than about 10 weight percent, based on the total weight of the fibrous web. Glass microfibers having average fiber diameters between about 0.2 μm and about 5 μm, typically between about 0.5 μm and about 2.5 μm ± about 0.1 μm, may be employed. Preferred glass microfibers for the fibrous media of the embodiments described herein are commercially available from Lauscha Fiber International of Summerville, SC, as C04 glass fiber (0.5 μm average fiber diameter), C06 glass fiber (0.65 μm average fiber diameter), and C26 glass fiber (2.6 μm average fiber diameter).

[0040] C. Optional Ingredients Additives conventionally employed in wet filtration media, such as wet strength additives, optical brighteners, fiber retention agents, colorants, separation aids (e.g., silicone additives and related catalysts), fire retardants or flame retardants (e.g., in particulate or fibrous form), and the like, may also be present in the fibrous web. If present, these additives may be included in an amount of 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. When flame-retardant fibers are incorporated into the fibrous web, the flame-retardant fibers may be used in an amount of from about 40% to about 80% by weight, based on the total weight of the fibrous web.

[0041] D. Method of Preparation The nonwoven fibrous webs described herein can be produced by any conventional "wet" papermaking technique. Thus, for example, a predetermined amount of synthetic fibers, sheath-core bicomponent staple fibers (along with any optional ingredients such as glass fibers, basic thermoplastic fibers, and / or additives), and water can be placed in a pulper or beater. The fibers are mixed and uniformly dispersed in water by the pulper or beater to form a slurry batch. Several mechanical operations can also be performed on the fibers to affect physical parameters such as permeability, surface properties, and fiber structure. The slurry batch can then be transferred to a mixing chest, where additional water is added to uniformly blend the fibers. The blended slurry can then be transferred to a machine chest, where one or more slurry batches can be combined and transferred from the batch to a continuous process. To ensure uniform fiber distribution, the consistency of the slurry is set and maintained by agitation. In this regard, the slurry can optionally be passed through a refiner to adjust the physical parameters.

[0042] The slurry is then transferred to a moving wire screen, where the water is removed by gravity and suction. As the water is removed, the fibers are formed into a nonwoven fibrous web or sheet with characteristics determined by several 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 modify surface characteristics. The wet fibrous web then travels through a drying section containing heated rollers (or "cans," in technical terms), where most of the remaining entrained water is removed. A binder resin may then be applied to the dried fibrous web by any conventional means, such as dipping, spray coating, roller (gravure) application, etc. Heat may then be applied to dry the web.

[0043] The nonwoven fibrous web may then be wound onto rolls for further processing into a finished sheet, or may be sent directly to a calendering section containing at least one pair, preferably a series of two pairs of opposing calendering rolls as shown in FIG. 10. The calendering rolls operate to pressurize (consolidate) the mass of nonwoven wet-laid fibers in a sheet to form the nonwoven fibrous web of the filtration media disclosed herein. In a preferred embodiment, the calendering rolls operate to pressurize 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 melt the sheath of the bicomponent staple fiber component and form bonds with the other synthetic fiber components in the nonwoven web. The line speed of the calender can be selected between about 1 m / min and about 50 m / min. Such calender line speeds and high temperatures / pressures described herein result in hot-zone calendering of the fibrous web.

[0044] The calendering rolls do not point bond the nonwoven fibrous web. Instead, they apply substantially uniform pressure and temperature across the entire surface area of ​​the web in the manner described above to uniformly calender (i.e., area calender) the web. Such high temperature area calendering melts substantially (if not entirely) the low melting point sheath polymer of the bicomponent staple fibers in the nonwoven web, thereby bonding the remaining thermoplastic core components of the bicomponent staple fibers to each other and to other synthetic staple fibers in the web.

[0045] The resulting nonwoven fibrous web may be employed in the form of a filtration medium as is, or may be stacked with additional fibrous media, such as a preformed fibrous layer or a web formed from multiple layers in a wet-laid process. When multiple fibrous web layers provide the filtration medium, the hot zone calendered fibrous web layer of the embodiments disclosed herein is preferably positioned to be the outermost layer of the filtration medium. For example, the fibrous web may be formed in a thickness of, for example, about 1 to about 50 g / m. 2 or a multi-layer (e.g., two or three fibrous web layers) filtration medium is provided, wherein one of such multiple layers may be a hot field calendered fibrous web layer according to embodiments disclosed herein.

[0046] E. Media characteristics The resulting hot zone calendered fibrous web will exhibit high dry and wet burst strengths of greater than 10 bar, typically greater than 12 bar, for example greater than 15 bar. These high dry and wet burst strengths can be achieved by the hot zone calendering described herein, which melts the sheath of the bicomponent staple fibers across the web and bonds the remaining core components of the bicomponent staple fibers and synthetic staple fibers to one another throughout the fibrous web.

[0047] The density of the fibrous web is typically about 0.45 g / cm 3 less than, for example, about 0.40 g / cm 3It would be less than that.

[0048] The pore size range of the fibrous web is typically 25 μm or less, more typically 22 μm or less, and usually 20 μm or less, with the minimum pore size also typically being 25 μm or less, or more typically 22 μm or less. The mean flow pore size is 40 μm or less, typically 35 μm or less, for example 30 μm or less, and the maximum pore size may be 50 μm or less, typically 45 μm or less, for example 40 μm or less.

[0049] The filtration medium may be classified as an F7 filtration material according to the EN779:2012 standard, i.e., a filtration medium having an average filtration efficiency of 60-80% and a minimum filtration efficiency of at least 35% for 0.4 μm particles.

[0050] The present invention is further illustrated by the following non-limiting examples thereof. [Example]

[0051] 1. Test Method The following test methods were employed to obtain the data reported in the table below.

[0052] Pore ​​size: Pore size (μm) was determined according to American Society of Testing and Materials (ASTM) Standard 316-03 (2011) (fully incorporated herein by reference). The minimum, maximum, and average flow pore size and pore count of the media examples below were measured using a Porometer 3G manufactured by Quantachrome Instruments (1900 Corporate Drive, Boynton Beach, FL 33426 USA). The reported pore size and pore count data are the average of two samples tested on each side of the media (i.e., the wire side and the felt side for wet media).

[0053] Pore ​​size and pore count data are measured using a technique known as capillary flow porometry. First, the sample is wetted with a wetting fluid so that all of the sample's pores are filled. A non-reactive gas at increasing pressure is applied to one side of the wet sample, driving the liquid out of the pores. For the wet sample, the gas pressure and gas flow rate downstream of the sample are measured and plotted. After the sample dries, the test is repeated, and a curve of gas flow versus applied pressure is plotted for the dry sample. Using such capillary porometry techniques, the "maximum pore size," "minimum pore size," and "mean flow pore size" can be determined.

[0054] Maximum Pore Size: Using the capillary flow porometry techniques described herein above, the gas pressure at which air flow through the medium is first detected (i.e., the pressure at which air bubbles first begin to flow) is used to calculate the maximum pore size.

[0055] The minimum pore size is determined from the pressure at which the wet flow curve converges with the dry curve using the capillary flow porometry technique described herein above.

[0056] The mean flow pore size is the pore diameter at which the flow through a wet medium is 50% of the flow through a dry medium at the same pressure drop using the capillary flow porometry techniques described herein above.

[0057] The pore size range is defined as the difference between the maximum pore size and the minimum pore size (ie, pore size range = maximum pore size - minimum pore size).

[0058] Caliper: The caliper (thickness) of the media 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," which is incorporated herein by reference in its entirety.

[0059] Air Permeability: The air permeability of the media was measured according to ASTM Standard D737: Standard Test Method for Air Permeability of Textile Fabrics (herein incorporated by reference in its entirety) at a water pressure differential of 125 Pa. Air flow through the media is reported in cubic feet per minute per square foot of sample (cfm / sf or cfm).

[0060] Bursting Strength: The pressure required to break a media sample, either dry ("dry bursting strength") or wet ("wet bursting strength"), was measured according to ISO Standard 2758 (2014), "Paper - Determination of bursting strength," which is incorporated herein by reference in its entirety. Results are reported in kilogram force per square meter at media break and then converted to units of bar.

[0061] Void Ratio: The void ratio was determined by the following procedure. A 40 mm x 40 mm dry specimen of the medium having an initial weight (w1) was placed in a beaker with 200 cc of n-butyl alcohol, then placed in a desiccator and evacuated until no visible bubbles were observed emanating from the specimen. The specimen was removed from the n-butyl alcohol in the beaker and weighed immediately upon removal to obtain the initial weight (w2), and reweighed 30 seconds after removal to obtain the final wet weight (w3). The void ratio (%) was then calculated by the following formula: Void Ratio (%) = (w3 - w1) / (w3 - w2) x 100.

[0062] Air Filter Classification: Air filtration performance was determined in accordance with test standard EN779:2012, "Particulate air filters for general ventilation," which is incorporated herein by reference in its entirety. According to this standard, air filtration media performance is graded into nine classes of filters in three groups: coarse filters (G1-G4), medium filters (M5-M6), and fine filters (F7-F9). The grades for M and F class filters are based on the average efficiency for 0.4 μm particles (i.e., the fraction by number of 0.4 μm particles retained on the filter). F class filters must also meet an additional minimum efficiency criterion, where the minimum efficiency is the lowest of the following three values: initial efficiency, post-de-ionization efficiency, or efficiency over the entire loading sequence of the test.

[0063] Air Filtration Performance: Air filtration performance was determined according to International Organization for Standardization (ISO) 16890, "Air filters for general ventilation," which is incorporated herein by reference in its entirety.

[0064] Pulse-jet cleanability: The cleanability of the cleanable filter media was determined according to ISO 11057:2011 "Air quality - Test method for filtration characterization of cleanable filter media," which is incorporated herein by reference in its entirety.

[0065] 2.Material The following materials were used:

[0066] LMF50: A 4 denier, 6 mm long (4De x 6mm) staple bicomponent low melt fiber commercially available from Huvis Corporation.

[0067] PET: polyethylene terephthalate fibers were used, including those commercially available from Toray Industries, Inc., with a 1.4 denier and a length of 12 mm (1.4 Denier x 12 mm), those commercially available from Huvis Corporation, with a 0.5 denier and a length of 5 mm (0.5 Denier x 5 mm), and those commercially available from Teijin Limited, with a 0.3 dtex and a length of 5 mm (0.3 Denier x 5 mm).

[0068] 3. Media examples The samples in Examples 1 and 2 below were produced by the wet process described above, with the sample in Example 2 being subjected to area calendering.

[0069] (Example 1) A base substrate was prepared by the method described above to form a 100% synthetic fiber wet-laid nonwoven medium containing 30 wt% LMF50 4De x 6mm bicomponent staple fiber and a blend of PET staple fibers consisting of 30 wt% PET 0.5De x 5mm staple fiber (Huvis), 20 wt% PET 1.4De x 12mm (Toray), and 20 wt% PET 0.3dt x 5mm (Teijin). The substrate had a weight of 210 g / m 2 It has a basis weight of 1.025 lbs, a 0.94mm flat sheet caliper, and 80 cfm air permeability.

[0070] (Example 2) The base substrate of Media Example 1 was calendered at a calendering nip pressure of 75 kN / m and a calendering temperature of 210°C to obtain a calendering strength of 210 g / m 2 A calendered wetlaid nonwoven medium was obtained having a basis weight of 1.00 lb, a flat sheet caliper of 0.60 mm, and an air permeability of 26 cfm.

[0071] (Comparative Example 1) (Kolon Finon L2270NW) The comparative media in Comparative Example 1 was a commercially available PET spunbond media produced by Kolon Industries (KOLON Tower, 11, Kolon-ro, Gwacheon-si, Gyeonggi-do, South Korea), which is conventionally used for APC (air pollution control) filtration media, and was 277 g / m 2 It has a basis weight of 1.00, a caliper of 0.61 mm, and a breathability of 25 cfm.

[0072] (Comparative Example 2) (Toray FSE21602A) The comparative media for Comparative Example 2 was another commercially available PET spunbond media produced by Toray Advanced Materials Korea Inc. (FKI Tower 35, 36 Fl., 24 Yeoui-daero, Yeongdeungpo-gu, Seoul, South Korea), which is conventionally used for APC (air pollution control) filtration media, and was 204 g / m 2 It has a basis weight of 1.025 lbs, a caliper of 0.48 mm, and a breathability of 28 cfm.

[0073] 4. Experimental Results 4.1 Experimental result 1 The above media examples were tested to determine pore size data (minimum, average flow, and maximum pore size) and to determine the number of pores. Additionally, each of the media examples was tested for dry and wet burst strength. The results are displayed in Table 1 below. [Table 1]

[0074] The above data show that the inventive media (Example 2) has much smaller maximum and mean flow pore sizes compared to the pore sizes of the standard wetlaid substrate (Example 1) and the comparative spunbond media examples. The inventive media (Example 2) also exhibited a greater number of pores per unit area than either the standard wetlaid sample or a typical spunbond media. The inventive media (Example 2) possesses an increased number of pores compared to the standard wetlaid substrate (Example 1), which is believed to be due to the compaction of multiple small areas near the media surface caused by the pressure of the hot calendering rolls. The inventive media (Example 2) also possesses a much greater number of pores compared to typical spunbond media (Comparative Examples 1 and 2), which is believed to be the result of area bonding achieved by the hot calendering of the former, instead of point bonding of the fibers in the latter. The inventive media (Example 2) also exhibits a greater void ratio than typical spunbond media (Comparative Examples 1 and 2), indicating that the inventive media is more porous.

[0075] Importantly, the inventive media (Example 2) exhibited a very tight, narrow pore size range compared to the other examples (see Figures 5 and 6). Pore size range is an important parameter because it indicates the variability in pore size within the media. A narrower pore size range represents a more uniform distribution of pores within the media, thereby increasing the filtration performance of the media. In addition, the calendered inventive media also possesses smaller pore sizes and a much lower web density than typical spunbond media. It is believed that the differences in the pore size range, packing (density), and pore structure of the media result in high filtration efficiency and dust holding capacity.

[0076] 4.2 Experimental result 2 Filtration performance test is carried out according to EN779:2012 test standard, Palas MFP 3000 produced by Palas GmbH (Greschbachstrasse 3 b 76229 Karlsruhe Germany).The media of the present invention and comparative example are tested according to the IPA static neutralization method in Annex A of test standard EN779:2012, without IPA static neutralization and with IPA static neutralization.Data is shown in Table 2 below. [Table 2]

[0077] The data in Table 2 above shows that the inventive media of Example 2 possesses much higher efficiency than the typical spunbond media of Comparative Examples 1 and 2. The efficiency of Example 2 is unaffected even after the media is discharged with IPA. This is a notable difference when compared to the spunbond media of Comparative Examples 1 and 2. The inventive media of Example 2 contained short, chopped synthetic fibers that were hydrophilic (due to the oil and surfactants used in the manufacturing process remaining on the surfaces of the fibers). However, the fibers in the spunbond media were not oiled and therefore possessed more positive charge than the inventive media of the embodiments disclosed herein, resulting in a much greater loss of efficiency after IPA discharge.

[0078] As the data in Table 2 show, the inventive media according to embodiments of the invention disclosed herein exhibit significantly better initial and discharge efficiencies for 0.4 μm particles, as well as better dust holding capacity, as well as better average efficiencies overall, compared to the conventional spunbond media of Comparative Examples 1 and 2. As such, the inventive media is rated as an F7 filtration material according to the EN779:2012 standard, while the conventional spunbond filtration media of Comparative Examples 1 and 2 can only achieve the lower ratings of M5 and M6, respectively.

[0079] 4.3 Experimental result 3 The inventive media of Example 2 and the comparative media of Comparative Examples 1 and 2 were also tested for pulse jet cleaning in accordance with the ISO 11057:2011 test standard using a FilTEq GmbH testing machine (Amthausstr. 14, D-76227 Karlsruhe, Germany). Each test consisted of four phases: Phase 1 (conditioning): 30 duty cycles with differential pressure controlled pulse jet cleaning and a cleaning set point of 1000 Pa Phase 2 (Aging): 10,000 pulse jet cleaning cycles with 5 second intervals Phase 3 (Stabilization): 10 duty cycles with differential pressure controlled pulse jet cleaning Phase 4 (measurement): 2-hour duty cycle with differential pressure controlled pulse jet cleaning

[0080] The pulse jet cleaning test data is displayed in Table 3 below. [Table 3] The data in Table 3 above show that the inventive media advantageously had cycle times approximately 2-5 times longer than the comparative spunbond media of Comparative Examples 1 and 2 at the 30th cycle. As can be seen from Figures 11-13, the inventive media of Example 2 also took longer to reach the target pressure drop, resulting in longer cycle times. After aging, the cycle times of the wet-calendered media continued to remain significantly longer (3-10 times longer) than the spunbond media. In addition, the wet-calendered inventive media of Example 2 also exhibited much less dust intrusion than the comparative media of Comparative Examples 1 and 2, both when measured at the 30th cycle and after aging. 4.4 Experimental Results - Fiber Webs Containing Flame-Retardant Fibers Disclosed below are embodiments made from flame retardant PET fibers without any additional chemical treatment.

[0081] A fibrous web was made using the same method as disclosed for Example 2 and contained 100% PET fibers, except that approximately 65% ​​by weight of the fibers were flame-retardant PET fibers commercially available from Toray Industries, Inc. The fibrous web contained 25% by weight of RM PET 4D x 6mm fibers (Huvis), 10% by weight of PET 0.3dt x 5mm fibers (Teijin), 45% by weight of FR PET 1.4D x 6mm fibers (Toray), and 20% by weight of FR PET 3D x 12mm fibers (Toray).

[0082] The resulting fibrous filtration media is F1 class flame retardant as tested by standard DIN 53 438. The physical properties are listed in Table 4 below. [Table 4] 4.5 Experimental Results - Multilayer Filtration Media In the following examples (Examples AD), the nonwoven fibrous web of the present invention was stacked with additional fibrous media to provide a multi-layer filtration media. Example A: Multilayer filtration media comprising a hot field calendered fibrous web laminated to an aluminized spunbond laminate. The resulting multilayer filtration media had a very low electrical resistance of less than 1000 ohms. Example B: A fibrous web was coated with PVDF nanofibers. Examples C and D: The fibrous web was laminated with expanded polytetrafluoroethylene (ePTFE). The resulting two-layer filter had high filtration efficiency and could be classified as E12 or H13 class filter media according to the EN 1822-1 test standard. The physical properties of Examples A-D are listed in Table 5. [Table 5] Embodiment Embodiments of the present invention include, among others: 1. Synthetic staple fibers; about 20% by weight to about 80% by weight, based on the total weight of the fibrous web, of sheath-core bicomponent staple fibers dispersed in the fibrous web; 1. A fibrous filtration medium comprising a hot zone calendered wetlaid nonwoven fibrous web, comprising: The above fibrous filtration media, wherein the fibrous web exhibits a dry burst strength of greater than 10 bar. 2. A fibrous filtration medium according to embodiment 1, wherein the fibrous web has a dry burst strength of greater than about 12 bar, preferably greater than about 15 bar. 3. A fibrous filtration medium according to embodiment 1, wherein the fibrous web has a wet burst strength of greater than about 10 bar, preferably greater than about 12 bar, more preferably greater than about 15 bar. 4. A fibrous filtration medium according to embodiment 1, wherein the fibrous web has a minimum pore size of 25 μm or less, preferably 22 μm or less. 5. A fibrous filtration medium according to embodiment 3, wherein the fibrous web has a mean flow pore size of 40 μm or less, preferably 35 μm or less, more preferably 30 μm or less. 6. A fibrous filtration medium according to embodiment 4, wherein the fibrous web has a maximum pore size of 50 μm or less, typically 45 μm or less, for example 40 μm or less. 7. A fibrous filtration medium according to embodiment 3, wherein the fibrous web has a pore size range of 25 μm or less, typically 22 μm or less. 8. The fibrous filtration medium of embodiment 1, wherein the filtration medium can be classified as an F7 filtration material according to the EN779:2012 standard. 9. The fibrous filtration medium of embodiment 1, comprising less than 10% by weight glass fibers, based on the total weight of the fibrous web. 10. The fibrous filtration medium of embodiment 8, wherein the glass fibers are glass microfibers. 11. The fibrous filtration media of embodiment 1, wherein the synthetic fibers comprise a mixture of at least two different types of synthetic fibers. 12. The fibrous filtration medium of embodiment 10, wherein the synthetic fibers comprise a first type of synthetic fibers having an average diameter between about 2.5 μm and about 10 μm and a second type of synthetic fibers having an average diameter between about 10 μm and about 20 μm. 13. The fibrous filtration medium of embodiment 11, wherein the first type of synthetic fibers have an average length between about 1 mm and about 6 mm, and the second type of synthetic fibers have an average length between about 5 mm and about 24 mm. 14. The fibrous filtration medium of embodiment 1, wherein the synthetic staple fibers comprise between about 5% and about 30% by weight, typically between 10% and about 20% by weight, of regenerated cellulose fibers, based on the total weight of the fibrous web. 15. The fibrous filtration medium of embodiment 13, wherein the regenerated cellulose fibers comprise lyocell fibers. 16. The fibrous filtration medium of embodiment 1, wherein the filtration medium further comprises at least one additive selected from the group consisting of wet strength additives, optical brighteners, fiber retention agents, colorants, fuel-water separation aids, and flame retardants or fire retardants. 17. The fibrous filtration medium of embodiment 15, wherein the at least one additive comprises flame-retardant fibers in an amount of about 40 to about 80 weight percent, based on the total weight of the fibrous web. 18. The fibrous filtration medium of embodiment 1, wherein the synthetic staple fibers are formed from a polymer selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof. 19. The fibrous filtration medium of embodiment 1, wherein the sheath and core of the bicomponent staple fiber are formed from polyethylene terephthalate (PET), and the PET forming the sheath has a melting temperature lower than the melting temperature of the PET forming the core. 20. (a) forming a wet-laid fibrous web from an aqueous fibrous slurry including synthetic staple fibers and about 20% to about 80% by weight of sheath-core bicomponent staple fibers, based on the total weight of the fibrous web; and (b) subjecting the wet-laid fibrous web from step (a) to hot zone calendering to fuse the sheaths of the bicomponent staple fibers together to achieve a fibrous web having a dry burst strength of greater than 10 bar. A method of making a fibrous web, comprising: 21. The method of embodiment 19, wherein step (b) is carried out under calendering pressure conditions of between about 1 kN / m and about 150 kN / m, and calendering temperature conditions of between about 110°C and about 250°C, with a calendering line speed of between about 1 m / min and about 50 m / min.

[0083] While the present invention has been described in terms of what are presently considered to be the most practicable and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. The content of the invention as claimed in the original patent application of this application is as follows: [Section 1] 1. A fibrous filtration medium comprising a hot zone calendered wetlaid nonwoven fibrous web, synthetic staple fibers; about 20% by weight to about 80% by weight, based on the total weight of the fibrous web, of sheath-core bicomponent staple fibers dispersed in the fibrous web; Including, The fibrous web exhibits a dry burst strength of greater than 10 bar. The fibrous filtration media described above. [Section 2] Item 1. The fibrous filtration medium of item 1, wherein the fibrous web has a dry burst strength of greater than about 12 bar, preferably greater than about 15 bar. [Section 3] 3. The fibrous filtration medium of claim 1 or 2, wherein the fibrous web has a wet burst strength of greater than about 10 bar, preferably greater than about 12 bar, and more preferably greater than about 15 bar. [Section 4] 4. The fibrous filtration medium of any one of paragraphs 1 to 3, wherein the fibrous web has a density of less than about 0.45 g / cm, for example less than about 0.40 g / cm. [Section 5] 5. The fibrous filtration medium of any one of paragraphs 1 to 4, wherein the fibrous web has a minimum pore size of 25 μm or less, preferably 22 μm or less. [Section 6] 6. The fibrous filtration medium of any one of paragraphs 1 to 5, wherein the fibrous web has a mean flow pore size of 40 μm or less, preferably 35 μm or less, and more preferably 30 μm or less. [Section 7] 7. The fibrous filtration medium of any one of paragraphs 1 to 6, wherein the fibrous web has a maximum pore size of 50 μm or less, typically 45 μm or less, for example 40 μm or less. [Section 8] 8. The fibrous filtration medium of any one of paragraphs 1 to 7, wherein the fibrous web has a pore size range of 25 μm or less, typically 22 μm or less. [Section 9] 9. The fibrous filtration medium of any one of paragraphs 1 to 8, wherein the filtration medium can be classified as an F7 filtration material according to the EN779:2012 standard. [Section 10] 10. The fibrous filtration medium of any one of paragraphs 1 to 9, comprising less than 10 wt. % glass fibers, based on the total weight of the fibrous web. [Section 11] Item 11. The fibrous filtration medium of item 10, wherein the glass fibers are glass microfibers. [Section 12] 12. The fibrous filtration media of any one of paragraphs 1 to 11, wherein the synthetic fibers comprise a mixture of at least two different types of synthetic fibers. [Section 13] Item 13. The fibrous filtration medium of item 12, wherein the synthetic fibers include a first type of synthetic fiber having an average diameter between about 2.5 μm and about 10 μm and a second type of synthetic fiber having an average diameter between about 10 μm and about 20 μm. [Section 14] Item 14. The fibrous filtration medium of item 13, wherein the first type of synthetic fibers have an average length between about 1 mm and about 6 mm, and the second type of synthetic fibers have an average length between about 5 mm and about 24 mm. [Section 15] Item 15. The fibrous filtration medium of any one of items 1 to 14, wherein the synthetic staple fibers comprise between about 5% and about 30% by weight, typically between 10% and about 20% by weight, of regenerated cellulose fibers, based on the total weight of the fibrous web. [Section 16] Item 16. The fibrous filtration medium of item 15, wherein the regenerated cellulose fibers comprise lyocell fibers. [Section 17] Item 17. The fibrous filtration medium of any one of items 1 to 16, wherein the filtration medium further comprises at least one additive selected from the group consisting of wet strength additives, optical brighteners, fiber retention agents, colorants, fuel-water separation aids, and flame retardants or fire retardants. [Section 18] Item 18. The fibrous filtration medium of item 17, wherein the at least one additive comprises flame-retardant fibers in an amount of about 40 to about 80 weight percent, based on the total weight of the fibrous web. [Section 19] 19. The fibrous filtration medium of any one of paragraphs 1 to 18, wherein the synthetic staple fibers are formed from a polymer selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof. [Section 20] 20. The fibrous filtration medium of any one of claims 1 to 19, wherein the sheath and core of the bicomponent staple fiber are formed from polyethylene terephthalate (PET), and the PET forming the sheath has a melting temperature lower than the melting temperature of the PET forming the core. [Section 21] 1. A method of making a fibrous web, comprising: (a) forming a wet-laid fibrous web from an aqueous fibrous slurry including synthetic staple fibers and about 20% to about 80% by weight of sheath-core bicomponent staple fibers, based on the total weight of the fibrous web; and (b) subjecting the wet-laid fibrous web from step (a) to hot zone calendering to melt the sheaths of the bicomponent staple fibers and bond the synthetic staple fibers to one another to achieve a fibrous web having a dry burst strength of greater than 10 bar. A method comprising: [Section 22] Item 22. The method according to item 21, wherein step (b) is carried out under a calendering pressure condition of about 1 kN / m to about 150 kN / m and a calendering temperature condition of about 110°C to about 250°C at a calendering line speed of about 1 m / min to about 50 m / min.

Claims

1. A fibrous filtration medium comprising a wet-laid nonwoven fibrous web, Contains synthetic staple fibers, the synthetic staple fibers comprise from 20% to 80% by weight, based on the total weight of the fibrous web, of sheath-core bicomponent staple fibers dispersed in the fibrous web; The fiber web has a density of 0.45 g / cm ３ and has a density of less than 10 bar and a dry burst strength of more than 10 bar; the synthetic staple fibers further comprise a mixture of at least two different types of synthetic fibers, the synthetic staple fibers comprising a first type of synthetic fiber having an average diameter between 2.5 μm and 10 μm and a second type of synthetic fiber having an average diameter between 10 μm and 20 μm, the synthetic staple fibers being in the form of a polymer selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof; The fibrous filtration media described above.

2. 10. The fibrous filtration medium of claim 1, wherein the fibrous web has a dry burst strength of greater than 12 bar.

3. 3. The fibrous filtration medium of claim 1 or 2, wherein the fibrous web has a wet burst strength of greater than 10 bar.

4. The fiber web has a density of 0.40 g / cm ３ 4. The fibrous filtration medium of claim 1 having a density of less than 1000 .mu.m.

5. 5. The fibrous filtration medium of any one of claims 1 to 4, wherein the fibrous web has a mean flow pore size of 40 μm or less.

6. 6. The fibrous filtration medium of any one of claims 1 to 5, wherein the fibrous web has a maximum pore size of 50 μm or less.

7. 7. The fibrous filtration medium of any one of claims 1 to 6, wherein the fibrous web has a pore size range of 25 μm or less.

8. 8. The fibrous filtration medium of claim 1, wherein the filtration medium can be classified as an F7 filtration material according to the EN779:2012 standard.

9. 9. The fibrous filtration medium of any one of claims 1 to 8, comprising less than 10% by weight of glass fibers, based on the total weight of the fibrous web.

10. 10. The fibrous filtration media of claim 9, wherein the glass fibers are glass microfibers.

11. 11. The fibrous filtration media of claim 10, wherein the first type of synthetic fibers have an average length between 1 mm and 6 mm, and the second type of synthetic fibers have an average length between 5 mm and 24 mm.

12. 12. The fibrous filtration medium of any one of claims 1 to 11, wherein the synthetic staple fibers comprise between 5% and 30% by weight of regenerated cellulose fibers, based on the total weight of the fibrous web.

13. 13. The fibrous filtration medium of claim 12, wherein the regenerated cellulose fibers comprise lyocell fibers.

14. 14. The fibrous filtration medium of any one of claims 1 to 13, wherein the filtration medium further comprises at least one additive selected from the group consisting of wet strength additives, optical brighteners, fiber retention agents, colorants, fuel-water separation aids, and flame retardants or fire retardants.

15. 15. The fibrous filtration medium of claim 14, wherein the at least one additive comprises flame retardant fibers in an amount of 40 to 80 weight percent, based on the total weight of the fibrous web.

16. 16. The fibrous filtration medium of any one of claims 1 to 15, wherein the sheath and core of the bicomponent staple fibers are formed from polyethylene terephthalate (PET), the PET forming the sheath having a melting temperature lower than the melting temperature of the PET forming the core.

17. 1. A method of making a fibrous web, the method comprising: (a) forming a wet-laid fibrous web from an aqueous fibrous slurry comprising synthetic staple fibers, the synthetic staple fibers comprising 20% ​​to 80% by weight of sheath-core bicomponent staple fibers, based on the total weight of the fibrous web; and (b) subjecting the wet-laid fibrous web from step (a) to hot zone calendering at calendering temperature conditions of 110°C to 250°C to melt the sheath of the bicomponent staple fibers and bond the synthetic staple fibers to each other to form a web of 0.45 g / cm ３ and achieving a fibrous web having a density of less than 1000 kJ / cm and a dry burst strength of more than 10 bar. Including, 10. The method of claim 1, wherein the synthetic staple fibers further comprise a mixture of at least two different types of synthetic fibers, the synthetic staple fibers comprising a first type of synthetic fiber having an average diameter between 2.5 μm and 10 μm and a second type of synthetic fiber having an average diameter between 10 μm and 20 μm, the synthetic staple fibers being in the form of a polymer selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene (PE), polypropylene (PP), nylon-6, nylon 6,6, nylon-6,12, and combinations thereof.

18. 18. The method of claim 17, wherein step (b) is carried out under a calendering pressure condition of 1 kN / m to 150 kN / m with a calendering line speed of 1 m / min to 50 m / min.

19. 17. Use of the fibrous filtration medium of any one of claims 1 to 16 as a filtration medium for gases and liquids where high dry and wet burst strength is required.

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