Filtration media particularly useful for filtering fluids associated with wire electrical discharge machining (WEDM) processes

Abstract

To provide a binder resin-free fibrous filtration media that can be employed to filter a wire electron discharge machining (WEDM) process fluid having a burst strength in a range between about 3 bar and about 6 bar.SOLUTION: A fibrous filtration media for filtering process fluids associated with electron discharge machining (EDM) contains a hot zone calendered wet-laid nonwoven fibrous web, wherein the hot zone calendered wet-laid nonwoven fibrous web contains 20 wt.% to 80 wt.% of bicomponent staple fibers based on the total weight of the fibrous web and 10 wt.% to 50 wt.% of fibrillated lyocell staple fibers based on the total weight of fibers in the medium, the fibrous web has a mean flow pore size of 20 μm or less, the fibrous web exhibits a wet burst strength of 3 bar to 6 bar, and the media contains 0 to 3 wt.% of a binder resin based on the total weight of the fibrous web.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001]

[0002] Embodiments disclosed herein generally relate to fibrous filtration mats or webs for filtering process fluids. In particular, embodiments disclosed herein relate to a fibrous filtration medium comprising a fibrous web comprising sheath-core type bicomponent fibers and fibrillated binder fibers (e.g., fibrillated lyocell microfibers), wherein the fibrous web has a wet burst strength of 3 bar or greater. The fibrous filtration medium disclosed herein is particularly useful for filtering process fluids (e.g., water) associated with wire electrical discharge machining (WEDM) processes. [Background technology]

[0002] Electrical discharge machining (EDM) is a controlled process used to shape electrically conductive materials, typically hard metals, by using electrical discharges. EDM is used to create fittings, molds, dies, production parts, and other prototypes that can be used in the aerospace, automotive, and electronics industries, among others. EDM is typically used for complex shapes or small workpieces that cannot be made with conventional cutting tools. Material is removed from the workpiece by a series of repeated electrical current discharges between two electrodes separated by a dielectric fluid. An electric spark is used as the cutting tool to cut (erode) the workpiece, producing a finished part with the desired shape. There are three different types of industrial EDM machines: die sinker EDM, wire cut EDM (WEDM), and small hole EDM. Die sinker EDM consists of an electrode and a workpiece immersed in an insulating fluid, such as oil or other dielectric fluid. Wire cut EDM (WEDM) is primarily used when low residual stresses are required because it does not use large cutting forces to remove material. WEDM typically uses deionized water as the dielectric fluid. Small hole EDM is used for very specialized applications that require creating a hole in metal.

[0003] The cutting process used in WEDM machines erodes material from the workpiece and wire electrode, which results in small particulate debris in the dielectric fluid (deionized water). Filtration systems are used to remove solid contaminants from the deionized water before it is recirculated back into the spark gap, the space between the electrode wire and the workpiece. Effective filtration is essential to maintain cutting speeds, prevent machine wear, and ensure dimensional accuracy of the final product.

[0004] Filter media for WEDM need to be limited to a high wet burst strength between 3 and 6 bar. WEDM filter media are displaced when wetted when the differential pressure (DP) exceeds 2.5 bar, typically 3 bar. Therefore, the filter media must have a minimum burst strength of 3 bar. As a safety requirement for WEDM machines, the filter media should burst once the differential pressure exceeds 6 bar. Therefore, the maximum burst strength of the filter media should be limited to 6 bar.

[0005] Typically, to meet the minimum burst strength requirement of 3 bar, most electrical discharge machined (EDM) filter media are saturated with phenolic or acrylic resins. For example, U.S. Pat. No. 8,662,316 discloses a wet-formed EDM filter media made of glass and cellulose pulp, to which a synthetic resin binder is applied in an amount of 5 to 20% by weight to increase the burst strength of the media. Japanese Patent Publication No. 2002085918 discloses a similar media made of glass fiber and cellulose pulp saturated with up to 20% by weight of binder resin. Chinese Patent Application No. 102444054 describes a wet-formed media made from a combination of glass, polyester, and wood pulp, saturated with phenolic resin. U.S. Pat. No. 5,288,402 discloses a two-layer media using an acrylic resin, in which both layers are saturated with acrylic. Korean Patent No. 10-0946979 discloses a two-layer laminated medium in which a polymer meltblown layer is adhered to a spunbond nonwoven fabric by using a hot melt binder resin. JP 2003038918 A describes a two-layer liquid filtration medium in which a resin binder is applied to one of the layers. (Each of the above-cited patent publications is expressly incorporated herein by reference.) Summary of the Invention [Problem to be solved by the invention]

[0006] However, the binder resins used in conventional EDM filter media tend to penetrate the pores of the media, reducing the surface area for particle capture and resulting in shorter filter life. Additionally, resin-saturated filter media contain ionic materials, which can be released as dissolved contaminants in deionized water. The release of many ionic materials shortens the lifespan of ion-exchange resins in EDM systems and limits the conductivity of deionized water. Because ionic materials increase the conductivity of deionized water, this can lead to discharge interference and inaccurate machining.

[0007] It would therefore be highly desirable to provide a binder-free fibrous filtration medium that can be satisfactorily employed to filter WEDM process fluids having burst strengths in the range of between about 3 bar and about 6 bar, and it is to this end that the embodiments disclosed herein are directed. [Means for solving the problem]

[0008] Embodiments disclosed herein relate to a fibrous filtration medium particularly useful for filtering WEDM process fluids. A preferred form of the fibrous filtration medium is usefully employed for filtering process fluids associated with electrical discharge machining (EDM), particularly wire electrical discharge machining (WEDM), and comprises a fibrous web comprising about 20% to about 80% by weight of bicomponent binder fibers, preferably sheath-core bicomponent fibers serving as the binder fibers, and between about 10% to about 50% by weight of fibrillated lyocell staple fibers, e.g., lyocell microfibers, based on the total weight of the fibrous web.

[0009] The fibrillated lyocell microfibers employed in the embodiments disclosed herein are sufficiently fibrillated to exhibit a Canadian Standard Freeness (CSF) of about 100 mL or less. Preferably, the fibrillated lyocell fibers contain less than 10% by weight of lyocell fibers longer than 1.0 mm. The fibrous webs of the embodiments disclosed herein can be produced using a standard wet-laid process, followed by subjecting the wet-laid media to a high-temperature calendering treatment to substantially (preferably completely) melt the low-melting polymer sheath component of the bicomponent fibers, thereby bonding the remaining core of the bicomponent fibers to the other fibers of the media.

[0010] Combining bicomponent binder fibers with fibrillated lyocell staple fibers, such as lyocell microfibers, in specific ratios described below results in fibrous webs with high wet burst strengths of 3 bar or greater, without necessarily adding additional binder resin to the media. The bicomponent binder fibers impart very high burst strength to the media without compromising the porosity of the media, because the fiber cores retain their shape in the media, even after high-temperature calendering. Interestingly, when homogeneously mixed and dispersed throughout the media, fibrillated lyocell microfibers also function as binder fibers due to the mechanical interlocking of lyocell fibrils with other fibrils and / or other fibrous components of the media (as seen in SEM images of the media of the present invention). This mechanical interlocking between adjacent fibers allows them to find each other, contributing to higher wet burst strengths in the absence of additional binder resin. Lyocell is a hydrophilic material and can retain good wet strength (e.g., lyocell media retains 70-90% of its dry burst strength in wet conditions, compared to cellulosic media that only retain 10-20% of their dry burst strength in wet conditions). As such, these properties of the fibrous filtration media according to embodiments disclosed herein are desirable for water treatment filters, particularly for EDM. [Effects of the Invention]

[0011] Fiber webs according to embodiments disclosed herein exhibit a greater number of pores, smaller pore sizes, and higher void ratios than those of the prior art. Accordingly, fiber webs according to embodiments disclosed herein advantageously possess high particle filtration efficiencies of over 95% for 5 μm particles and a longer service life compared to conventional EDM filter media. Fiber webs according to embodiments disclosed herein also exhibit very low ionic release and can therefore be used to fabricate filters for treating chemically sensitive liquids.

[0012] These and other attributes of various embodiments according to the present invention will be better understood with reference to the following detailed description. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 shows a scanning electron microscope (SEM) image of a binder-free fibrous filtration medium according to an embodiment described in Example 1 below.

[0014] [Figure 2] FIG. 2 shows an SEM image of a comparative fibrous media containing a binder resin according to Comparative Example 1 below. DETAILED DESCRIPTION OF THE INVENTION

[0015] definition As used in this specification and the appended claims, the following terms are intended to have the following definitions.

[0016] A "fiber" is a fibrous or filamentary structure having a high aspect ratio (ratio of length to diameter).

[0017] By "staple fiber" is meant fiber having a fixed or discrete length, naturally possessing fixed, relatively short segments, or being cut or further processed in this manner.

[0018] "Fibrous" means a material that is composed predominantly of fibers and / or staple fibers.

[0019] The terms "nonwoven" or "web" refer to a collection of fibers and / or staple fibers in a web or mat that are randomly intermeshed, entangled, and / or bonded to one another to form self-supporting structural elements.

[0020] 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.

[0021] "Cellulosic fibers" are fibers composed of or derived from cellulose.

[0022] "Freeness" is a measure, in mL, of the rate at which a dilute suspension of staple fibers (i.e., 3 g of staple fibers in 1 L of water) can be drained, as described in Technical Association of Pulp and Paper Industry (TAPPI) Canadian standard method T 227 om-94 (1994), the entire contents of which are expressly incorporated herein by reference (commonly referred to herein as "Canadian Standard Freeness" or "CSF").

[0023] "Fibrils" are very small, minute, irregular thread-like elements associated with staple fibers.

[0024] "Fibrillated" refers to staple fibers that inherently possess a large number of fibrils or that have been adapted to form a larger number of fibrils. The amount of fibrillation required to achieve a fibrillated fiber can be determined by the freeness of a dilute suspension of such fibers. Thus, by way of example, fibrillated lyocell microfibers used in the embodiments disclosed herein will be sufficiently fibrillated to exhibit a Canadian Standard Freeness (CSF) of about 100 mL or less, preferably about 90 mL or less, and typically between about 20 and about 80 mL. Advantageously, fibrillated lyocell staple fibers will exhibit a CSF of about 65 mL (±5 mL). Preferred lyocell staple fibers will contain less than 10% by weight, preferably less than 8% by weight, of lyocell staple fibers longer than 1.0 mm.

[0025] The term "thermoplastic" refers to a plastic that becomes flexible or moldable above a certain temperature and returns to a solid state upon cooling. Exemplary thermoplastic fibers suitable for this embodiment include polyesters (e.g., polyalkylene terephthalates such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT)), 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, properties important for use as an oil filter.

[0026] The term "siliceous" fibers refers primarily to "glass" fibers, such as glass microfibers. Such fibers are typically staple fibers and generally have an aspect ratio (ratio of length to diameter) of about 200 to about 1000 or more. Thus, preferred glass microfibers will have an average diameter of 0.1 μm to about 5 μm (typically about 0.4 μm to about 2.6 μm) and an average length of 20 μm to about 5 mm. Mixtures of glass microfibers of different diameters may also be employed, e.g., relatively long glass microfibers having an average diameter of about 2.5 μm ± 0.1 μm and relatively small glass microfibers having an average diameter of about 0.5 μm ± 0.1 μm.

[0027] The maximum pore size, minimum pore size, and mean flow pore size are measured using a technique known as capillary flow porometry. A sample of a nonwoven fibrous web is first wetted with a wetting fluid so that all pores in the sample are filled. A non-reactive gas at increasing pressure is applied to one side of the wet sample to drive the wetting fluid from the pores. The gas pressure and gas flow rate downstream of the wet sample are measured and plotted. After the sample dries, the test is repeated and a similar curve is plotted for the dry sample. The "maximum pore size" is calculated from the bubble point, i.e., the gas pressure at which air flow through the wet sample is first detected. The term "mean flow pore size" is calculated from the gas pressure at which the flow through the wet sample is 50% of the flow through the dry sample. The term "minimum pore size" is calculated from the pressure at which the wet flow curve converges with the dry flow curve. The term "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).

[0028] The fibrous filtration media of the embodiments disclosed herein will comprise a nonwoven fibrous web comprising a homogeneous wet blend of bicomponent staple binder fibers in an amount of about 20% to about 80% by weight and fibrillated lyocell fibers in an amount of about 10% to about 50% by weight, each based on the total weight of the fibrous web in the homogeneous wet blend. Certain preferred embodiments of the fibrous web will have a weight ratio of bicomponent staple fibers / fibrillated lyocell fibers in the range of between 0.5 and 3.

[0029] In certain embodiments, the fibrous web of the filtration medium will be essentially free of binder resin. By "essentially free," we mean that a small amount of binder resin, e.g., 0 to 3 weight percent based on the total weight of the fibrous web, may be present, but this does not affect the filtration properties of the medium. In particularly preferred embodiments, the filtration medium is completely free of binder resin, i.e., the medium contains no (0 weight percent) binder resin.

[0030] A. Bicomponent Staple Binder Fiber The fibrous web employed in the filtration media of the disclosed embodiments comprises synthetic bicomponent staple fibers that serve as binder fibers. Preferably, the bicomponent staple fibers are sheath-core 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, e.g., in a sheath-core configuration. While typically two separate polymers are extruded, bicomponent fibers may also involve the extrusion of the same polymer material from separate extruders, with the polymer material from each extruder having somewhat different properties (e.g., melting point). The extruded polymers are substantially always located 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 the embodiments disclosed herein is preferably a substantially symmetric sheath-core bicomponent fiber, whereby the polymeric sheath completely surrounds and encases the polymeric core in a sheath to core area ratio of between about 25 / 75 and about 75 / 25, typically between about 50 / 50 and about 70 / 30.

[0031] The bicomponent staple fibers are preferably bicomponent polyethylene terephthalate (PET) staple fibers, having a low melting point PET sheath surrounding a high melting point PET core. In a preferred form, the bicomponent PET staple fibers will comprise a PET sheath having a melting point between about 120°C and about 180°C, typically 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 the melting point 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).

[0032] The core portion of the bicomponent fiber can comprise a thermoplastic polymer material. Thus, exemplary core materials include polyalkylenes (e.g., polyethylene, polypropylene, etc.) and polyesters (e.g., polyalkylene terephthalates, such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT)). Meanwhile, the sheath portion of the bicomponent fiber can also comprise other thermoplastic polymer materials, such as polyalkylenes (e.g., polyethylene, polypropylene, etc.) and polyamides (nylons, e.g., nylon-6, nylon 6,6, nylon-6,12, etc.). One preferred bicomponent staple fiber employed in the practice of the embodiments disclosed herein is LMF50 bicomponent staple fiber, available from Huvis Corporation, having a denier of about 4 and a length of about 6 mm.

[0033] The bicomponent staple fibers may be present in the filtration medium in an amount of from 20% to about 80% by weight, such as between about 25% to about 35% by weight, or even about 30% by weight (±0.5% by weight), based on the total weight of the fibrous web.

[0034] B. Fibrillated Lyocell Fiber As briefly discussed above, fibrillated lyocell staple fibers will be employed in the fibrous web in an amount of about 10% to about 50% by weight, typically 12% to about 45% by weight, e.g., about 25% (±3%) by weight, based on the total weight of the fibrous web. The fibrillated lyocell fibers will be present in an amount sufficient to cause the fibrous web to have a weight ratio of bicomponent staple fiber weight / fibrillated lyocell fiber weight within the range of between 0.5 and 3.

[0035] The fibrillated lyocell staple fibers are most preferably nanofibers, i.e., staple fibers having an average diameter of about 1000 nanometers or less, or sometimes about 400 nanometers or less, for example, about 100 nanometers. Some particularly preferred embodiments will include fibrillated cellulose staple fibers of about 250 nanometers. The lyocell staple fibers employed in the embodiments disclosed herein will typically have a length greater than about 0.4 mm. Preferably, the lyocell staple fibers will contain less than 10%, for example, less than 8%, of lyocell fibers having a length of less than 1 mm.

[0036] Preferably, the lyocell staple fiber is highly fibrillated. Specifically, the lyocell staple fiber may be fibrillated to a degree that it possesses a Canadian Standard Freeness (CSF) of about 100 mL or less, preferably about 90 mL or less, for example, between about 20 mL and about 80 mL. Advantageously, the fibrillated lyocell staple fiber will exhibit a CSF of about 65 mL (±5 mL).

[0037] C. Optional Fiber Ingredients In addition to the bicomponent staple fibers and fibrillated lyocell staple fibers described above, the fibrous web and / or filtration medium may also include one or more other synthetic fibrous components. The additional fibrous components may be, for example, synthetic staple fibers formed from thermoplastic polymer materials. Thus, exemplary thermoplastic staple fibers that may be employed include polyesters (e.g., polyalkylene terephthalates such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT)), 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 end-use filtration applications.

[0038] Glass microfibers may also optionally be present in an amount sufficient to improve the efficiency of the fibrous media as a filter, for example, mixed with the other synthetic fibers described above. Typically, glass microfibers, when present, will be employed in an amount of up to about 40 weight percent, typically up to about 22 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. Suitable 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).

[0039] Other non-fibrillated cellulose staple fibers may optionally be blended into the fibrous component to impart additional stiffness to the filtration medium, and thus, according to some embodiments, loadings of non-fibrillated lyocell staple fibers from 0 up to about 40% by weight, e.g., 0% to about 30% by weight, or 0% to about 25% by weight, based on the total fiber weight of the medium, may be employed.

[0040] In certain preferred embodiments, the nonwoven fibrous web may comprise a mixture of synthetic fibers of different sizes. In this regard, the medium may comprise between about 0% and about 60% 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 0% 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 25 mm.

[0041] D. Optional Ingredients Additives conventionally employed in wet filtration media may also be employed in the filtration media and / or its fibrous web, such as, for example, 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), etc. If present, these additives may be included in an amount of from 0% to up to about 25% by weight, preferably up to about 20% by weight, e.g., from about 0.1% to about 20% by weight, based on the total weight of the fibrous web.

[0042] E. Method of Preparation The fibrous webs described herein can be produced by any conventional "wet" papermaking technique. Thus, for example, a predetermined amount of bicomponent staple fibers, fibrillated lyocell fibers, and optionally any other fibrous or non-fibrous components can be mixed with water and placed in a pulper or beater. The fibers and optional other components are mixed and uniformly dispersed in water by the pulper or beater to form a slurry batch. Some 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 and the fibers are uniformly blended. The blended slurry can then be transferred to a machine chest, where one or more slurry batches can be combined and transferred from a 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.

[0043] 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 in the wet mat are formed into a fibrous nonwoven web or sheet, with characteristics determined by several process variables, including, for example, slurry flow rate, machine speed, and drainage parameters. The formed sheet may optionally be compressed while still wet to densify the media 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.

[0044] The dried 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, and sometimes a series of two pairs, of opposing calender rolls. The calender rolls operate to pressurize (consolidate) the mass of nonwoven wet-laid fibers in the base sheet to form the fibrous web disclosed herein. In a preferred embodiment, the calender 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 fibrous web. The line speed of the calender can be selected from about 1 m / min to about 50 m / min. Such calender line speeds and high temperatures / pressures described herein result in hot-zone calendering of the fibrous web.

[0045] The calender 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. As a result, such high temperature area calendering melts a substantial portion (if not all) of 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 fibrous components in the web.

[0046] The resulting fibrous web may be employed 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 media, the hot zone calendered fibrous web layer of the embodiments disclosed herein is preferably positioned to be the outermost layer of the filtration media.

[0047] F. Media characteristics The resulting area calendered fibrous web will exhibit a wet burst strength of at least 3 bar to no more than about 6 bar.

[0048] The density of the fibrous web is typically about 0.15 g / cm 3 Over, for example, about 0.25 g / cm 3 It would be super.

[0049] The pore size range of the fibrous web will be 20 μm or less, typically 15 μm or less, with a mean flow pore size of 20 μm or less, typically 15 μm or less, for example 14 μm or less, and a maximum pore size of 25 μm or less, typically 20 μm or less, for example 19 μm or less. [Example]

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

[0051] (i) 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 tested using a Porometer 3G manufactured by Quantachrome Instruments (1900 Corporate Drive, Boynton Beach, FL 33426 USA), and 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 calculated from the pressure at which the wet flow curve merges 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 bar.

[0061] Filtration Efficiency and Apparent Capacity: Filtration efficiency and apparent capacity are measured in accordance with International Organization for Standardization (ISO) standard ISO 19438 (2003), "Diesel fuel and petrol filters for internal combustion engines - Filtration efficiency using particle counting and contaminant retention capacity." Filter media samples are tested using ISO 12103-1 A3 medium test dust under the following test conditions: a face velocity of 0.344 cm / sec and a terminal pressure drop of 78.5 kPa.

[0062] 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.

[0063] (ii) Materials The following materials were used:

[0064] Bicomponent Staple Fiber: 4 denier, 6 mm long (4d x 6 mm) staple bicomponent low melt fiber (LMF) commercially available from Huvis Corporation.

[0065] Fibrillated Staple Fiber: Microfibrillated lyocell fibers were employed, having an average length (LWAFL) of 1.11 mm, an average fiber diameter of 20 μm, and an average fibril diameter of 150 nm, commercially available from Interlace Corporation under the trade name INTERLACE™.

[0066] Additional fibrous components: (1) 0.3 dtex x 5 mm polyethylene terephthalate (PET) staple fiber commercially available from Teijin Limited; (2) 0.06 dtex x 1.5 mm CYPREX™ 1001 PET microfiber commercially available from Eastman Chemical Company; (3) 1.7 dtex x 4 mm TENCEL™ non-fibrillated lyocell fiber commercially available from Lenzing Group; (4) 0.8 dtex x 5 mm PET staple fiber commercially available from Toray Industries, Inc.

[0067] (iii) Examples of media (Example 1) (Medium of the present invention) Single layer media was prepared having the fiber composition set forth in the table below. No wet end chemicals other than the fibers set forth in the table below were used. Additionally, the formed media was subjected to hot zone calendering in the absence of any additional binder resin. Fiber Ingredients in Example 1 [Table 1]

[0068] (Example 2) (Medium of the present invention) Two-ply media was prepared having the fiber composition set forth in the table below (weight percent is based on the total fiber weight in the media). No wet-end chemicals other than the fibers set forth in the table below were used. Additionally, the formed media was subjected to hot zone calendering in the absence of any additional binder resin. Fiber Ingredients of Example 2 Upper layer-25g / m 2 , 35.7% by weight of the total media basis weight [Table 2] Bottom layer-45g / m 2 , 64.3% by weight of the total media basis weight [Table 3]

[0069] (Comparative Example 1) A 100% cellulose-based single-ply media saturated with phenolic resin (19.5 wt. % resin based on total media weight) was produced by Ahlstrom-Munksjo of Korea using a Fourdrinier flat-wire paper machine. This Comparative Example 1 media is representative of known media products used in filtration of WEDM process fluids.

[0070] The physical properties of the inventive media according to Examples 1 and 2 and Comparative Example 1 are summarized in Table 1 below. [Table 4]

[0071] (iv) Experimental results The fibrous media of Examples 1 and 2 and Comparative Example 1 were subjected to burst strength and performance tests, and the results are summarized in the Experimental Results 1 and Experimental Results 2 tables below. [Table 5] [Table 6]

[0072] The above data shows that the media of Examples 1 and 2 of the present invention exhibit wet burst strengths of greater than 3 bar (but less than 6 bar) despite the absence of other wet end chemicals and binder resins in the media.

[0073] The media of Inventive Example 1 (see Figure 1) has a single layer and can therefore be compared to Comparative Example 1 (see Figure 2), which also has a single layer. The data shows that even though the media of Inventive Example 1 has a much lower basis weight and lower caliper than the media of Comparative Example 1, the media of the present invention exhibits much higher efficiency and longer life.

[0074] The data also show that the media of Examples 1 and 2 of the present invention each had a greater apparent capacity per caliper than Comparative Example 1, i.e., 2.7 and 1.5 for Examples 1 and 2 versus 1.3 for Comparative Example 1. Embodiment Embodiments of the present invention include, among others: 1. about 20% by weight to about 80% by weight of bicomponent staple fibers, based on the total weight of the fibrous web; About 10% by weight to about 50% by weight of fibrillated lyocell staple fibers, based on the total weight of fibers in the medium. A fibrous filtration medium comprising a wet-laid nonwoven fibrous web comprising: The above fibrous filtration media, wherein the fibrous web exhibits a wet burst strength of 3 bar or greater. 1. The fibrous filtration medium of embodiment 1, wherein the fibrous web has a wet burst strength of from about 3 bar to about 6 bar. 2. The fibrous filtration medium of embodiment 1, wherein the fibrillated lyocell staple fibers have a Canadian Standard Freeness (CSF) of about 100 mL or less. 3. A fibrous filtration medium according to embodiment 3, wherein the fibrous web has a mean flow pore size of 20 μm or less, preferably 15 μm or less, for example about 10 μm (±2 μm). 4. A fibrous filtration medium according to embodiment 4, wherein the fibrous web has a maximum pore size of 25 μm or less, typically 20 μm or less, for example about 19 μm (±2 μm). 6. The fibrous filtration medium of embodiment 1, wherein the fibrous web comprises at least one other fibrous component comprising fibers selected from the group consisting of polyester (e.g., polyalkylene terephthalate, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT)), polyalkylene (e.g., polyethylene, polypropylene, etc.), polyacrylonitrile (PAN), polyamide (nylon, e.g., nylon-6, nylon 6,6, nylon-6,12, etc.), cellulosic materials, and glass. 7. The fibrous filtration media of embodiment 1, wherein the media is essentially free of binder resin. 8. The fibrous filtration medium of embodiment 1, further comprising a blend of synthetic staple fiber components comprising a first type of synthetic fibers having an average diameter between about 0% and about 60% by weight, based on the total weight of the fibrous web, and a second type of synthetic fibers having an average diameter between about 0% and about 60% by weight, based on the total weight of the fibrous web. 9. The fibrous filtration media of embodiment 8, 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 25 mm. 10. The fibrous filtration medium of embodiment 1, further comprising between about 0% and about 40% by weight, typically between 0% and about 30% by weight, of regenerated cellulose fibers, based on the total weight of the fibrous web. 11. The fibrous filtration medium of embodiment 10, wherein the regenerated cellulose fibers comprise non-fibrillated lyocell fibers. 12. 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. 13. The fibrous filtration medium of embodiment 1, wherein the fibrous web comprises bicomponent staple fibers and fibrillated lyocell fibers present in a weight ratio of bicomponent staple fibers to fibrillated lyocell fibers in the range of 0.5 to 3. 14. The fibrous filtration medium of embodiment 1, wherein the bicomponent staple fibers are sheath / core bicomponent staple fibers having a sheath comprising polyethylene terephthalate (PET) having a melting temperature between about 120°C and about 180°C. 15. The fibrous filtration medium of embodiment 14, wherein the bicomponent staple fiber core comprises PET having a melting temperature between about 220°C and about 280°C. 16. A wire electrical discharge machine (EDM) comprising a filter unit comprising the fibrous filtration media of embodiment 1. 17. (a) forming a wet-laid fibrous web from an aqueous fibrous slurry comprising about 20% to about 80% by weight, based on the total weight of the wet-laid fibrous web, of sheath-core bicomponent staple fibers and about 10% to about 50% by weight, based on the total weight of the wet-laid fibrous web, of fibrillated lyocell staple fibers; and (b) subjecting the wet-laid sheet from step (a) to high temperature calendering to melt the sheaths of the bicomponent staple fibers and bond the fibrillated lyocell staple fibers to one another to achieve a fibrous filtration medium having a wet burst strength of 3 bar or greater; A method of making a fibrous web, comprising: 18. The method of embodiment 17, wherein step (a) is carried out such that the bicomponent staple fibers and fibrillated lyocell fibers are present in a weight ratio of bicomponent staple fibers to fibrillated lyocell fibers in the range of 0.5 to 3. 19. The fibrous filtration medium of embodiment 1, wherein the bicomponent staple fibers are sheath / core bicomponent staple fibers having a sheath comprising polyethylene terephthalate (PET) having a melting temperature between about 120°C and about 180°C, and the fibrillated lyocell staple fibers have a Canadian Standard Freeness (CSF) of about 100 mL or less. 20. A method of filtering water during wire electrical discharge machining (WEDM), comprising passing water associated with a WEDM process through the fibrous filtration media of embodiment 1.

[0075] 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 intended to be 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 for filtering process fluids associated with electrical discharge machining (EDM), particularly wire electrical discharge machining (WEDM), comprising a wet-laid nonwoven fibrous web, the wet-laid nonwoven fibrous web comprising: about 20% to about 80% by weight of bicomponent staple fibers, based on the total weight of the fibrous web; and about 10% by weight to about 50% by weight of fibrillated lyocell staple fibers, based on the total weight of fibers in the medium; The fibrous web exhibits a wet burst strength of 3 bar or more. The fibrous filtration media described above. [Section 2] Item 1. The fibrous filtration medium of item 1, wherein the fibrous web has a wet burst strength of about 3 bar to about 6 bar. [Section 3] Item 3. The fibrous filtration medium of item 1 or 2, wherein the fibrillated lyocell staple fibers have a Canadian Standard Freeness (CSF) of about 100 mL or less. [Section 4] 4. The fibrous filtration medium of any one of paragraphs 1 to 3, wherein the fibrous web has a mean flow pore size of 20 μm or less, preferably 15 μm or less, for example about 10 μm (±2 μm). [Section 5] 5. The fibrous filtration medium of any one of paragraphs 1 to 4, wherein the fibrous web has a maximum pore size of 25 μm or less, typically 20 μm or less, for example about 19 μm (±2 μm). [Section 6] Item 6. The fibrous filtration medium according to any one of items 1 to 5, wherein the fibrous web comprises at least one other fibrous component comprising a fiber selected from the group consisting of polyester (e.g., polyalkylene terephthalate such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT)), polyalkylene (e.g., polyethylene, polypropylene, etc.), polyacrylonitrile (PAN), polyamide (nylon, e.g., nylon-6, nylon 6,6, nylon-6,12, etc.), cellulosic material, and glass. [Section 7] 7. The fibrous filtration media of any one of paragraphs 1 to 6, wherein the media is essentially free of binder resin. [Section 8] Item 8. The fibrous filtration medium of any one of items 1 to 7, further comprising a blend of synthetic staple fiber components comprising about 0% to about 60% by weight of a first type of synthetic fiber having an average diameter based on the total weight of the fibrous web, and about 0% to about 60% by weight of a second type of synthetic fiber having an average diameter based on the total weight of the fibrous web. [Section 9] Item 9. The fibrous filtration medium of item 8, 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 25 mm. [Section 10] Item 10. The fibrous filtration medium according to any one of items 1 to 9, further comprising about 0% to about 40% by weight, typically 0% to about 30% by weight, of regenerated cellulose fibers, based on the total weight of the fibrous web. [Section 11] Item 11. The fibrous filtration medium of item 10, wherein the regenerated cellulose fibers comprise non-fibrillated lyocell fibers. [Section 12] Item 12. The fibrous filtration medium of any one of items 1 to 11, 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 13] Item 13. The fibrous filtration medium of any one of items 1 to 12, wherein the fibrous web comprises bicomponent staple fibers and fibrillated lyocell fibers present in a weight ratio of bicomponent staple fibers to fibrillated lyocell fibers in the range of 0.5 to 3. [Section 14] Item 14. The fibrous filtration medium of any one of items 1 to 13, wherein the bicomponent staple fibers are sheath / core bicomponent staple fibers having a sheath comprising polyethylene terephthalate (PET) having a melting temperature of between about 120°C and about 180°C. [Section 15] Item 15. The fibrous filtration media of item 14, wherein the bicomponent staple fiber core comprises PET having a melting temperature of between about 220°C and about 280°C. [Section 16] Item 16. A wire electrical discharge machine (EDM) comprising a filter unit comprising the fibrous filtration medium of any one of items 1 to 15. [Section 17] 1. A method of making a fibrous web, comprising: (a) forming a wet-laid fibrous web from an aqueous fibrous slurry comprising about 20% to about 80% by weight, based on the total weight of the wet-laid fibrous web, of sheath-core bicomponent staple fibers and about 10% to about 50% by weight, based on the total weight of the wet-laid fibrous web, of fibrillated lyocell staple fibers; (b) subjecting the wet-laid sheet from step (a) to high temperature calendering to melt the sheaths of the bicomponent staple fibers and bond the fibrillated lyocell staple fibers to one another to achieve a fibrous filtration medium having a wet burst strength of 3 bar or greater. A method comprising: [Section 18] Item 18. The method of item 17, wherein step (a) is carried out such that the bicomponent staple fibers and fibrillated lyocell fibers are present in a weight ratio of bicomponent staple fibers to fibrillated lyocell fibers in the range of 0.5 to 3. [Section 19] Item 1. The fibrous filtration medium of item 1, wherein the bicomponent staple fibers are sheath / core bicomponent staple fibers having a sheath comprising polyethylene terephthalate (PET) having a melting temperature of about 120°C to about 180°C, and the fibrillated lyocell staple fibers have a Canadian Standard Freeness (CSF) of about 100 mL or less. [Section 20] 16. A method for filtering water during wire electrical discharge machining (WEDM), comprising passing water associated with a WEDM process through the fibrous filtration media of any one of paragraphs 1 to 15. [Section 21] 16. Use of the fibrous filtration media of any one of paragraphs 1 to 15 in filtering process fluids associated with wire electrical discharge machining (WEDM).

Claims

1. 1. A fibrous filtration medium for filtering process fluids associated with electrical discharge machining (EDM), comprising a hot field calendered wet-laid nonwoven fibrous web, comprising: The fibrous web is 20% to 80% by weight of sheath-core bicomponent staple fibers, based on the total weight of the fibrous web; 10% to 50% by weight of fibrillated lyocell staple fibers, based on the total weight of fibers in the medium; the fibrous web has a mean flow pore size of 20 μm or less; the fibrous web exhibits a wet burst strength of 3 bar to 6 bar; the medium comprises 0 to 3 weight percent of a binder resin (and not said sheath-core bicomponent staple fibers), based on the total weight of the fibrous web; The fibrous filtration media described above.

2. 10. The fibrous filtration medium of claim 1, wherein the fibrillated lyocell staple fibers have a Canadian Standard Freeness (CSF) of 100 mL or less.

3. 3. The fibrous filtration medium of claim 1 or 2, wherein the fibrous web has a mean flow pore size of 15 microns or less.

4. 4. The fibrous filtration medium of any one of claims 1 to 3, wherein the fibrous web has a maximum pore size of 25 μm or less.

5. 5. The fibrous filtration medium of any one of claims 1 to 4, wherein the fibrous web comprises at least one other fibrous component comprising fibers selected from the group consisting of polyester, polyalkylene, polyacrylonitrile (PAN), polyamide, cellulosic material, and glass.

6. 6. The fibrous filtration medium of any one of claims 1 to 5, further comprising a blend of synthetic staple fiber components comprising: between 0% and 60% by weight, based on the total weight of the fibrous web, of a first type of synthetic fiber having an average diameter between 2.5 μm and 10 μm; and between 0% and 60% by weight, based on the total weight of the fibrous web, of a second type of synthetic fiber having an average diameter between 10 μm and 20 μm.

7. 7. The fibrous filtration media of claim 6, 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 25 mm.

8. The fibrous filtration medium of any one of claims 1 to 7, further comprising between 0% and 40% by weight of regenerated cellulose fibers, based on the total weight of the fibrous web.

9. 9. The fibrous filtration medium of claim 8, wherein the regenerated cellulose fibers comprise non-fibrillated lyocell fibers.

10. 10. The fibrous filtration medium of any one of claims 1 to 9, 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.

11. 11. The fibrous filtration medium of any one of claims 1 to 10, wherein the fibrous web comprises sheath-core bicomponent staple fibers and fibrillated lyocell fibers in a weight ratio of sheath-core bicomponent staple fibers to fibrillated lyocell fibers in the range of 0.5 to 3.

12. A fibrous filtration medium described in any one of claims 1 to 11, wherein the core-sheath bicomponent staple fiber is a core-sheath bicomponent staple fiber having a sheath comprising polyethylene terephthalate (PET) having a melting temperature between 120°C and 180°C.

13. The fibrous filtration medium of claim 12, wherein the core of the sheath-core bicomponent staple fiber comprises polyethylene terephthalate (PET) having a melting temperature between 220°C and 280°C.

14. 14. The fibrous filtration medium of any one of claims 1 to 13, wherein the electrical discharge machining (EDM) is selected from wire electrical discharge machining (WEDM).

15. 15. The fibrous filtration medium of any one of claims 1 to 14, wherein the fibrous web has a maximum pore size of 20 μm or less.

16. 16. The fibrous filtration medium of any one of claims 5 to 15, wherein the polyester is selected from polyalkylene terephthalates.

17. 17. The fibrous filtration medium of any one of claims 5 to 16, wherein the polyalkylene terephthalate is selected from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

18. 18. The fibrous filtration medium of any one of claims 5 to 17, wherein the polyalkylene is selected from polyethylene and polypropylene.

19. 19. The fibrous filtration medium of any one of claims 5 to 18, wherein the polyamide is selected from nylon, nylon-6, nylon 6,6, and nylon-6,12.

20. The fibrous filtration medium of any one of claims 1 to 7, further comprising between 0% and 30% by weight of regenerated cellulose fibers, based on the total weight of the fibrous web.

21. A fibrous filtration medium as described in claim 1, wherein the core-sheath bicomponent staple fibers are core-sheath bicomponent staple fibers having a sheath comprising polyethylene terephthalate (PET) having a melting temperature between 120°C and 180°C, and the fibrillated lyocell staple fibers have a Canadian Standard Freeness (CSF) of 100 mL or less.

22. 22. A wire electrical discharge machine (EDM) comprising a filter unit comprising the fibrous filtration media of any one of claims 1 to 21.

23. 1. A method of making a fibrous web, comprising: (a) forming a wet-laid fibrous web from an aqueous fibrous slurry comprising 20% ​​to 80% by weight of sheath-core bicomponent staple fibers, based on the total weight of the wet-laid fibrous web, and 10% to 50% by weight of fibrillated lyocell staple fibers, based on the total weight of the wet-laid fibrous web; (b) subjecting the wet-laid sheet from step (a) to high temperature calendering to melt the sheaths of the sheath-core bicomponent staple fibers and bond the fibrillated lyocell staple fibers to one another to achieve a fibrous filtration medium having a wet burst strength of 3 bar to 6 bar and a mean flow pore size of 20 μm or less, the medium comprising 0 to 3 wt. % of binder resin (and not the sheath-core bicomponent staple fibers), based on the total weight of the fibrous web; A method comprising:

24. The method of claim 23, wherein step (a) is carried out so that the sheath-core bicomponent staple fibers and fibrillated lyocell fibers are present in a weight ratio of sheath-core bicomponent staple fibers to fibrillated lyocell fibers in the range of 0.5 to 3.

25. 22. A method of filtering water during wire electrical discharge machining (WEDM), comprising passing water associated with a WEDM process through the fibrous filtration media of any one of claims 1 to 21.

26. 22. Use of the fibrous filtration media of any one of claims 1 to 21 in the filtration of process fluids associated with wire electrical discharge machining (WEDM).

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