A pleated filter assembly including a spunbond prefilter

Abstract

A pleated multilayer air filter assembly includes a primary filter layer and a prefilter layer bonded to and co-pleated with each other. The primary filter layer comprises meltblown electret fibers. The prefilter layer comprises meltspun spunbond electret fibers having a radially outer surface comprising polymethylpentene. A ratio of an effective fiber diameter of the meltspun fibers of the primary filter layer to an effective fiber diameter of the meltblown fibers of the primary filter layer is at least 1.5.

Description

Background Technology

[0001] Spunbond fiber webs have been used in a variety of applications, including backings for diapers and / or personal care products, carpet backings, geotextiles, and more. Summary of the Invention

[0002] This document discloses a pleated multilayer air filter assembly comprising a main filter layer and a pre-filter layer bonded and co-pleated together with each other. The main filter layer comprises meltblown electret fibers. The pre-filter layer comprises melt-spun bonded electret fibers having a radially outer surface comprising polymethylpentene. The ratio of the effective fiber diameter of the meltblown fibers in the main filter layer to the effective fiber diameter of the meltblown fibers in the main filter layer is at least 1.5. Attached Figure Description

[0003] Figure 1 This is a side sectional view of an exemplary pleated multilayer air filter assembly.

[0004] Figure 2 yes Figure 1 An enlarged side sectional view of a portion of a multi-layer air filter assembly, showing the individual layers of the multi-layer air filter assembly.

[0005] Figure 3 This is a side perspective sectional view of a portion of an exemplary sheath-core fiber that can be used in a pre-filter of a pleated multilayer air filter assembly.

[0006] Figure 4 The filtering performance data for the various implementation schemes discussed in this paper are shown.

[0007] All illustrations and figures in this document are not drawn to scale and have been selected for the purpose of illustrating different embodiments of the invention.

[0008] Glossary and Definitions

[0009] The term "spunbond" refers to a nonwoven web comprising a set of melt-spun fibers that are collected as a fiber web and subjected to one or more bonding operations (e.g., self-bonding) to hold the fibers together.

[0010] The term “melt spinning” refers to fibers formed by: extruding molten filaments from a set of orifices and passing the molten filaments through an air space (which may contain a flowing airflow) to cool the filaments, and then passing the filaments through attenuation (i.e., stretching) units to stretch the filaments.

[0011] The term "meltblown" refers to fibers formed by extruding molten filaments from a set of orifices into a converging high-speed airflow introduced through air vents located near the extrusion orifices. Those skilled in the art will recognize that meltblown is different from melt-spun fibers, and will further recognize that melt-spun fibers exhibit different properties than meltblown fibers, and are therefore distinguishable from meltblown fibers.

[0012] The term "self-bonding" refers to the melt bonding of fibers at elevated temperatures (e.g., through the use of an oven or a stream of hot air) without applying solid contact pressure to the web. Such bonding can be achieved by directing heated air onto / through the web.

[0013] The “effective fiber diameter” of the fiber web is a parameter obtained by measuring the pressure drop versus flow velocity relationship as described later in this document, which provides an estimate of the fiber diameter of the web.

[0014] The term "electret" fiber refers to a fiber containing at least a quasi-permanent charge with a long lifetime, as described in detail later in this article.

[0015] As used herein, the term "polymethylpentene" refers to a monomer unit comprising at least 90% by weight of 4-methyl-1-pentene (i.e., 4-methylpent-1,2-diyl) units.

[0016]

[0017] Polymers (homogeneous polymers and copolymers).

[0018] Polymethylpentene (referred to as “PMP” for convenience in this document) can be purchased, for example, under the trade name TPX from Mitsui Chemicals. Detailed Implementation

[0019] This document discloses a pleated multi-layer air filter assembly 1. The multi-layer assembly 1 includes a main filter layer 100 and a pre-filter layer 10 located upstream of the main filter layer 100 (the upstream and downstream sides of the assembly 1 are...). Figure 1 (U and D are used to represent the airflow, and the arrows indicate the general direction of airflow through the air filter assembly). Layers 100 and 10 are... Figure 2 The enlarged view shows this in more detail. The pre-filter layer 10 contains charged (electret) meltblown fibers 11, as discussed in detail later herein. The main filter layer 100 contains charged (electret) meltblown fibers 111, as discussed in detail later herein.

[0020] Component 1 and its layers 10 and 100 are pleated. (Reference) Figure 1The side view discusses the details of the fold geometry, where the folded component is viewed along the fold direction. In this configuration, the fold height (fold amplitude) is the distance from a fold apex 2 to the nearest neighboring fold trough 3 along a direction perpendicular to the overall principal plane of component 1. Figure 1 P in h By definition, the pleat height will be at least 2 mm. In various embodiments, the pleat height may be at least 4 mm, 6 mm, 8 mm, 10 mm, 20 mm, 30 mm, or 40 mm. In other embodiments, the pleat height may be at most 45 mm, 35 mm, 25 mm, 15 mm, 12 mm, 9 mm, or 7 mm.

[0021] Fold spacing ( Figure 1 P in s The fold spacing is the distance between the nearest adjacent same-side fold tips 2 (or the nearest adjacent same-side fold valleys 3) along the direction in the main plane of component 1. By definition, the fold spacing will be at least 2.0 mm. In various embodiments, the fold spacing may be up to 50 mm, 45 mm, 35 mm, 25 mm, 15 mm, 12 mm, 9 mm, 7 mm, or 5 mm. In other embodiments, the fold spacing may be at least 4 mm, 6 mm, 8 mm, 10 mm, 20 mm, 30 mm, or 40 mm.

[0022] Layers 10 and 100 are co-pleated, meaning that when pleating is performed, these layers are already in a state where they are bonded together (and thus include multi-layer components). Therefore, layer 10 will exhibit pleating parameters very similar to those of layer 100 (e.g., P...). h and P s ).

[0023] Component 1 can exhibit any suitable thickness (e.g., a combined thickness of layers 10 and 100). In various embodiments, component 1 can exhibit a thickness ranging from 0.5 mm to 5.0 mm. This thickness is a local thickness of the fiber layers (not to be confused with the pleat height of a pleated web), as described by... Figure 1 The thickness is indicated by the letter "t". In various embodiments, the thickness may be at least 0.7 mm, 1.0 mm, 1.5 mm, or 2.0 mm. In other embodiments, the thickness may be at most 4.0 mm, 3.0 mm, or 2.5 mm.

[0024] As described above, the air filter assembly 1 includes a main filter layer 100 and a pre-filter layer 10. The filter assembly 1 is configured such that the air to be filtered passes through the pre-filter layer 10 before entering the main filter layer 100. Also as described, the main filter layer 100 includes charged meltblown fibers (i.e., electret fibers) 111; the pre-filter layer 10 includes charged meltblown fibers (i.e., electret fibers) 111.

[0025] The fibers 11 of the pre-filter layer 10 will exhibit an average larger diameter than the fibers 111 of the main filter layer 110. In some embodiments, this difference can be characterized by the effective fiber diameter (EFD) of the fibers in each layer. In various embodiments, the ratio of the EFD of the melt-spun fibers of the main filter layer to the EFD of the meltblown fibers of the main filter layer can be at least 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, or 6.0. In other embodiments, such a ratio can be up to 20 or 10.

[0026] While the effective fiber diameter can be a convenient way to characterize the average fiber size of the corresponding layer in many cases, in some embodiments, the fiber size can be characterized by the actual fiber diameter (AFD) of each layer. Methods for measuring the AFD of fiber layers can be found, for example, in U.S. Patent 8,162,153. In various embodiments, the ratio of the AFD of the melt-spun fibers of the main filter layer to the AFD of the meltblown fibers of the main filter layer can be at least 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, or 6.0. In other embodiments, such a ratio can be up to 20 or 10. Those skilled in the art will recognize that for a fiber web, EFD and AFD will generally be proportional in a relatively good manner; therefore, in some cases, the value of EFD can be used to infer a general range of AFD values, and vice versa (AFD and EFD and their relationship are discussed in detail in the aforementioned U.S. Patent '153').

[0027] In some embodiments, the meltblown fibers 111 of the main filter layer 100 may exhibit an EFD and / or AFD of 10 micrometers or smaller (such fibers are generally referred to as microfibers). In some embodiments, the meltblown fibers 111 of the pre-filter layer 10 may exhibit an EFD and / or AFD greater than 10, 15, 20, 25, or 30 micrometers. Those skilled in the art will understand that “microfibers” (especially charged microfibers) are generally more effective at filtering fine particles (e.g., particles smaller than 2.5, 2.0, or 1.0 micrometers) from the air compared to larger fibers (even if the larger fibers are also charged).

[0028] The pre-filter layer 10 comprises charged melt-spun fibers 11 as described above. At least some of these fibers will include a radially outer surface of polymethylpentene (PMP) (e.g., Figure 3 Surface 21). In various embodiments, at least 80%, 90%, 95%, 98%, or substantially 100% (number average) of these fibers will comprise a polymethylpentene outer surface. In some embodiments, such fibers may be polymethylpentene fibers (i.e., they may be made of polymethylpentene over their entire radial thickness).

[0029] In other embodiments, such fiber 11 may be a core-sheath fiber, comprising a polymethylpentene sheath 20 surrounding a core 30 of some other polymer (e.g., polypropylene). As will be known to those skilled in the art and as... Figure 3 As indicated by the general designation, the core-sheath fiber comprises a core portion 30 (first component) extending the long axis length of the fiber. The core portion 30 is circumferentially surrounded by a sheath portion 20 (second component) also extending the long axis length of the fiber. The inner surface 22 of the sheath 20 faces the outer surface 32 of the core 30 and is bonded to the outer surface of the core. Typically, except in cases where statistical fluctuations in actual production processes may cause occasional exposed areas of the surface 32, no portion of the outer surface 32 of the core 30 is exposed. That is, for the vast majority of fibers 11, the radially outer surface 21 of the sheath 20 will provide the outer surface of the fiber 11.

[0030] By definition, the bicomponent sheath-core fiber 11 disclosed herein will exhibit a sheath-core ratio of 5:95 to 85:15. This ratio is a volume ratio that can be obtained, for example, by microscopy of the fiber in a cross-sectional view (e.g., a sheath-core ratio of 40:60 means that the volume ratio of the sheath material to the core material is 40:60). If desired, any such volume ratio can be converted to a mass ratio by direct calculation using the densities of the respective sheath and core materials; if the densities of the sheath and core materials are different, the mass ratio may differ slightly from the volume ratio. (For example, based on the density of the materials, the volume sheath-core ratio of polymethylpentene sheath and polypropylene core is expected to be 20:80, corresponding to a mass sheath-core ratio of approximately 18:82.) In various embodiments, the bicomponent sheath-core fiber may exhibit a sheath-core volume ratio of at least 10:90, 15:85, 20:80, or 25:75. In another embodiment, the bicomponent sheath-core fiber may exhibit a sheath-core volume ratio of up to 60:40, 40:60, or 30:70 (note that the term "bicomponent" is used for convenience and indicates at least two components; it includes, for example, three or more components). The polymethylpentene sheath 20 of fiber 11 may have any suitable thickness.

[0031] In various embodiments, the average radial thickness of the sheath of fiber 11 can be from 1 micrometer to 8 micrometers, for example, from 1 micrometer to 5 micrometers or from 1 micrometer to 3 micrometers. Those skilled in the art will understand that, given that polymethylpentene is generally more expensive than polymers such as polypropylene, the use of sheath-core fibers offers a cost advantage (in other words, the sheath-core method minimizes the total amount of polymethylpentene). Furthermore, the use of sheath-core fibers allows for the use of core materials that are significantly stiffer than polymethylpentene (e.g., polypropylene); such an arrangement allows the pre-filter to make multilayer components easier to pleat and easier to maintain a pleated configuration compared to, for example, components in which the pre-filter fiber is polymethylpentene fiber. Other advantages not anticipated by those skilled in the art will be discussed later.

[0032] Whether used as polymethylpentene fibers or as a polymethylpentene sheath surrounding a core of some other material, any suitable polymethylpentene can be used in pre-filter fibers. Those skilled in the art will recognize that polymethylpentene is typically provided as a copolymer containing suitable amounts of other monomer units (e.g., to improve the processability or other properties of the resulting material) along with the polymethylpentene monomer unit. Therefore, the term "polymethylpentene" as used herein allows for the presence of a variety of other monomer units, such as alkylene units (e.g., ethylene, propyleneene, butylene, pentylene, hexylene, isooctylene), for example, in amounts of up to, for example, 2 wt%, 4 wt%, 6 wt%, 8 wt%, or 10 wt%. Any such polymethylpentene is a thermoplastic organic polymer material that can be obtained in many grades suitable for extrusion (including co-extrusion), for example, in melt-spun form. In many embodiments, it is advantageous to use pure polymethylpentene as the sheath or fiber to obtain the benefit of exposing as much polymethylpentene as possible to the radially outward surface of the pre-filter fiber, as described later herein. However, in some embodiments, polymethylpentene can be blended, for example, with a suitable extrudable thermoplastic organic polymer material. Such an arrangement is permitted as long as an effective amount of polymethylpentene is present. In various embodiments, in any such blend, polymethylpentene will account for at least 50%, 60%, 70%, 80%, 90%, 95%, or 98% by weight of the polymethylpentene skin (or polymethylpentene fiber).

[0033] The pre-filter layer 10 may have any geometric, physical, and / or mechanical properties commensurate with its function as a pre-filter as described herein. The pre-filter layer 10 will have appropriate porosity, which can be characterized by compaction. "Compaction" refers to a dimensionless ratio (recorded as a percentage) representing the proportion of the total volume of the fiber web occupied by solid (e.g., polymer fibers) material. Loft is 100% minus compaction and represents the proportion of the total volume of the fiber web not occupied by solid material. Methods for measuring such parameters are given in the embodiments. As disclosed herein, the pre-filter layer 10 may exhibit a compaction of 4.0% to 20.0% (i.e., a loft of 96.0% to 80%). In various embodiments, the pre-filter as disclosed herein will exhibit a compaction of at least 5.0%, 6.0%, 7.0%, 8.0%, or 9.0%. In other embodiments, the pre-filters disclosed herein will exhibit a density of up to 17.0%, 15.0%, 13.0%, 12.0%, 11.0%, or 10.0%.

[0034] The term "basis weight" characterizes the weight (area density) of a fiber web per unit area and is reported as the weight of the fiber web in grams per square meter (g / m²). As disclosed herein, the pre-filter 10 may exhibit a basis weight ranging from 10 g / m² to 200 g / m². In various embodiments, the basis weight may be at least 20 g / m², 30 g / m², 40 g / m², 50 g / m², 60 g / m², 70 g / m², or 80 g / m². In other embodiments, the basis weight may be up to 160 g / m², 140 g / m², 130 g / m², 120 g / m², 110 g / m², 100 g / m², or 90 g / m².

[0035] In at least some embodiments, the component 1 as a whole and its respective fiber web layers 10 and 100 will be substantially non-fluorinated. The degree of fluorination of the material (e.g., the fiber) can be characterized by the percentage of fluorine atoms present on the surface of the material, as measured using an X-ray photoelectron spectroscopy (XPS) method as described in detail in U.S. Patent Application Publication 2011 / 0162653, the entire contents of which are incorporated herein by reference. "Substantially non-fluorinated" means that the average percentage of fluorine atoms present on the surface of fiber 11 and / or fiber 111 is less than 2.0. In other embodiments, the average percentage of fluorine atoms present on the surface of fiber 11 and / or fiber 111 will be less than 1.0, 0.5, 0.1, 0.05, or 0.01. The requirement that the fiber web layers be substantially non-fluorinated will exclude most webs that have been plasma-fluorinated to any significant degree, and will exclude most webs whose fibers contain non-trace amounts (e.g., greater than 0.1 wt%) of fluorinated melt additives.

[0036] In many implementations, non-fluorinated webs can be identified by their exhibited contact angle. The contact angle refers to the advancing contact angle using hexadecane as the standard wetting solution. Therefore, the contact angle is a geometric measurement that can be evaluated or estimated by any of several possible methods. For example, the contact angle of the fiber web can be obtained using the trapped bubble method described in application report AR251e entitled "Surface Energy of Textiles," purchased from KRUSS Ltd. (Of course, the contact angles of the fibers and the web can be estimated by contact measurements on a flat film of the same material.)

[0037] In many embodiments, the non-fluorinated pre-filter layer 10 (or the non-fluorinated main filter layer 100) will exhibit a contact angle of less than 40 degrees. Conversely, a mesh whose fibers have been, for example, plasma-fluorinated can exhibit a contact angle of 40 degrees or higher. It should be understood that the pre-filter layer disclosed herein can achieve its beneficial effects (as described below) without requiring the fibers of the pre-filter layer to exhibit the extremely high contact angles common in fluorinated meshes.

[0038] The fibers 11 of the pre-filter layer 10 (e.g., bicomponent sheath-core fibers) can be melt-spun using any suitable melt-spinning equipment, such as those described, for example, in U.S. Patents 8,240,484 and 8,506,669. Any such melt-spinning equipment and process will subject the fibers to an attenuation process (performed by an attenuator such as that described in U.S. Patent 6,607,624), which “stretches” the fibers to impart physical properties to the melt-spun fibers (as previously described herein, such properties allow melt-spun fibers to be distinguished from, for example, meltblown fibers that do not undergo this type of stretching). It is understood that melt-spun fiber webs have significant advantages over meltblown fiber webs. For example, melt-spun fibers are generally quite strong due to the stretching process, a property (e.g., along with the desired diameter of the melt-spun fibers) that makes fiber layers (or multilayer assemblies comprising such layers) very easy to pleat. Conversely, meltblown fibers are too weak for a standalone meltblown web to pleat.

[0039] After being collected as fiber blocks, melt-spun fibers 11 (e.g., sheath-core fibers) can be bonded together by any suitable bonding process to form a coherent web (this combination of melt spinning and bonding is the origin of the term "spunbond"; fibers are melt-spun and then bonded together). Thus, at least some fibers of the pre-filter layer 10 will bond to some other fibers of the pre-filter layer. In many convenient embodiments, this bonding of fibers 11 can take the form of self-bonding. As previously described, self-bonding is the melt bonding of fibers at elevated temperatures (e.g., by using an oven or a stream of air heated to a specific temperature) without applying solid contact pressure to the web. In the absence of compression / flattening areas due to solid contact pressure bonding (e.g., ultrasonic bonding or calendering), self-bonded fibers will be readily identified as fibers directly melt-bonded together (without, for example, latex or granular binders). Fibers 11 can be self-bonded using any suitable equipment, such as a controlled heating device of the general type described in U.S. Patent Application Publication 2008 / 0038976.

[0040] Other possible bonding methods that can be used (e.g., to enhance self-bonding, or instead of such bonding) include, for example, crosslapping, stitching, needle punching, hydroentangling, chemical bonding, and / or thermal bonding (it should be noted that any such method can be used to bond the multilayer component 1 as a whole or otherwise reinforce it, regardless of any method that may have been used to bond the pre-filter 10). It must be ensured that any such bonding does not unacceptably affect the filtration performance of the resulting multilayer air filter assembly (e.g., by introducing pinholes, etc.). In some embodiments, self-bonding will be the only type of bonding performed on the fibers 11 of the pre-filter layer 10, without using other types of bonding.

[0041] The fibers 11 of the pre-filter 10 (whether they are, for example, sheath-core fibers or PMP fibers) are charged, meaning that the fibers exhibit at least a quasi-permanent charge over a long lifespan. Such charged fibers are generally referred to herein as electret fibers. In some embodiments, some or all of such charge may reside at or near the radial outer surface of the fiber (e.g., surface 21) (however, as described below, this may not always be the case). Such fibers can be charged by any suitable charging method, such as water charging, corona charging, a combination of corona charging and water charging (in any order), etc. (most conveniently, after the fibers have been collected and formed into a coherent web).

[0042] More specifically, any charging method known in the art can be used. For example, charging can be performed in various ways, including triboelectric charging and corona discharge. In some embodiments, the fibers 11 of the pre-filter 10 can be charged alone by corona discharge, particularly DC corona discharge, without any additional charging method. Examples of potentially suitable corona discharge processes are described in U.S. Patent Re. No. 30,782 (van Turnhout), U.S. Patent Re. No. 31,285 (van Turnhout), U.S. Patent Re. No. 32,171 (van Turnhout), U.S. Patent 4,215,682 (Davis et al.), U.S. Patent 4,375,718 (Wadsworth et al.), U.S. Patent 5,401,446 (Wadsworth et al.), U.S. Patent 4,588,537 (Klaase et al.), U.S. Patent 4,592,815 (Nakao), U.S. Patent 6,365,088 (Knight et al.), British Patent 384,052 (Hansen), U.S. Patent 5,643,525 (McGinty et al.), and Japanese Patent 4,141,679B2 (Kawabe et al.). Other methods were discussed by M. Paajanen et al. in *Journal of Physics D: Applied Physics* (2001), vol.34, pp.2482-2488, and by G.M. Essler and J.E.West in *Journal of Electrostatics* (1975), vol.1, pp.111-123.

[0043] Another technique that can be used to charge the fibers 11 of the pre-filter layer 10 is water charging. Water charging of the fiber layer is performed by contacting the fibers with water in a manner sufficient to impart an electret charge to the fibers, followed by drying the fabric. An example of water charging involves impinging the fabric with a water jet or droplet at a pressure sufficient to provide an electret charge that enhances filtration, and then drying the fabric. The required pressure for optimal results varies depending on factors such as the type of atomizer used, the type of polymer forming the fabric, the type and concentration of additives added to the polymer, the thickness and density of the fabric, and whether pretreatment, such as corona surface treatment, is performed prior to water charging. Generally, water pressures in the range of about 10 psi to 500 psi (69 kPa to 3450 kPa) are suitable. A water jet or droplet can be provided by any suitable atomizing device. An example of a suitable atomizing device is a device for hydroentangled fibers. Examples of suitable water charging methods are described in U.S. Patent 5,496,507 (Angadjivand et al.). Other methods are described in U.S. Patents 6,824,718 (Eitzman et al.), 6,743,464 (Insley et al.), 6,454,986 (Eitzman et al.), 6,406,657 (Eitzman et al.), and 6,375,886 (Angadjivand et al.). Water charging of the grid can also be performed using the method disclosed in U.S. Patent 7,765,698 (Sebastian et al.).

[0044] In embodiments where at least some of the pre-filter fibers are sheath-core fibers, the core material can be selected to retain a significant amount of trapped electrostatic charge. Typically, such materials (e.g., thermoplastic organic polymer materials) have a charge greater than 10 at the intended use temperature. 14DC resistivity in ohms-cm. Polymers capable of trapping charge include polyolefins such as polypropylene and polyethylene (e.g., HDPE, LDPE, LLDPE, VLDPE; ULDPE, UHMW-PE grades); polyvinyl chloride; polystyrene; polycarbonate; polyesters, including polylactide; and perfluoropolymers and copolymers. Particularly useful materials include polypropylene. Examples of suitable thermoplastics include, for example, the following polypropylenes: ESCORENE PP 3746G, commercially available from ExxonMobil Corporation, Irving, Texas; TOTAL PP3960, TOTAL PP3860 and TOTAL PP3868, commercially available from Total Petrochemicals USA Inc., Houston, Texas; and METOCENE MF650W, commercially available from LyondellBasell Industries, Inc., Rotterdam, Netherlands.

[0045] The electret fiber 11 of the pre-filter layer 10 may contain one or more additives that enhance the fiber's ability to form a charge therein or on it, and its ability to retain such a charge over a long period of time (e.g., weeks, months, or years). These additives are referred to herein as charge-enhancing additives. Many charge-enhancing additives for preparing electret-containing fibers are known in the art. Exemplary charge-enhancing additives may include pigments, light stabilizers, primary and secondary antioxidants, metal passivators, hindered amines, hindered phenols, metal salts, triphosphites, phosphates, fluorinated compounds, and combinations thereof (in other words, materials with at least some other known functions, such as those used as antioxidants or light stabilizers, may also be used as charge-enhancing additives, as will be well understood by those skilled in the art).

[0046] Exemplary charge-enhancing additives include thermally stable organic triazine compounds or oligomers containing at least one nitrogen atom in addition to the nitrogen atom in the triazine ring, see, for example, U.S. Patents 6,268,495, 5,976,208, 5,968,635, 5,919,847 and 5,908,598, all granted to Rousseau et al. Another charge-enhancing additive known for enhancing electret formation and / or stabilization is “CHIMASSORB 944”: (poly[[6-(1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl][[(2,2,6,6-tetramethyl-4-piperidinyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidinyl)imino]]), available from BASF, Ludwigshafen, Germany. Charge-enhancing additives may be N-substituted amino aromatic compounds, specifically triamino-substituted compounds, such as 2,4,6-triphenylamino-p-(carbon-2'-ethylhexyl-1'-oxo)-1,3,5-triazine, available under the trade name UVINUL T-150 from BASF AG, Ludwigshafen, Germany. Another charge-enhancing additive is 2,4,6-tri-(octadecylamino)-triazine, also known as tristearate-based melamine (“TSM”). Further examples of charge-enhancing additives are provided in U.S. Patent Application Publications 2011 / 0162653 and 2011 / 0137082; and in U.S. Patents 8,613,795, 7,390,351, 5,057,710, 4,652,282, 4,789,504, and 8,790,449, all of which are incorporated herein by reference in their entirety.

[0047] In some embodiments, the electrostatic charge-enhancing additive is selected from: pigments, light stabilizers, primary and secondary antioxidants, metal passivators, hindered amines, hindered phenols, metal salts, triphosphites, phosphates, fluorinated compounds, and combinations thereof. In many convenient embodiments, any one or more of these charge-enhancing additives can be incorporated as melt additives into the thermoplastic material that will form fiber 11.

[0048] In cases where the fiber 11 of the pre-filter 10 is a sheath-core fiber, in some embodiments, one or more charge-enhancing additives may be included only in the core material. In other embodiments, one or more charge-enhancing additives may be included only in the sheath material. In other embodiments, one or more charge-enhancing additives may be included in both the core material and the sheath material.

[0049] Charge-enhancing additives can be used in any suitable amount. Typically, one or more charge-enhancing additives may be present in amounts of 0.1 wt% to 3 wt%, 0.1 wt% to 2 wt%, 0.2 wt% to 1.0 wt%, or 0.25 wt% to 0.5 wt%, depending on the weight of the material in which the additive is incorporated (e.g., fibrous material, core material, or sheath material).

[0050] As described above, in addition to the pre-filter layer 10, the multilayer assembly 1 also includes a main filter layer 100. The main filter layer 100 contains meltblown fibers 111, which, as previously described, are formed by extruding molten filaments from a set of orifices into a converging high-speed airflow introduced through air vents located near the extrusion orifices. Such meltblown fibers do not experience the attenuation / stretching type experienced by melt-spun fibers and are distinguishable from melt-spun fibers.

[0051] As described above, the fiber size (diameter) of the fibers 111 of the primary filter layer 100 will be smaller than the fiber size (diameter) of the fibers 11 of the pre-filter 10, regardless of their characteristics, such as effective fiber diameter and / or actual fiber diameter, as described above. The primary filter layer 100 can be characterized in a similar manner to the pre-filter layer 10 in terms of, for example, density, basis weight, etc. In various embodiments, the primary filter layer 100 may exhibit a density of, for example, 5.0%, 6.0%, 7.0%, or 8.0% to 12%, 11%, 10%, or 9.0%. In various embodiments, the primary filter layer 100 may exhibit a basis weight of, for example, 10 g / m², 20 g / m², or 30 g / m² to 80 g / m², 70 g / m², 60 g / m², or 50 g / m². In many embodiments, the fibers 111 of the layer 100 may be single-component fibers (rather than, for example, bicomponent fibers) made of any suitable thermoplastic organic polymer material that is readily melt-blown and charged. In many embodiments, polypropylene will be suitable; however, any other material may be used. Potentially suitable materials are disclosed, for example, in U.S. Provisional Patent Application 62 / 867941 and derived PCT Application PCT / IB2020 / 055548; and in U.S. Provisional Patent Application 62 / 867933 and derived PCT Application PCT / IB2020 / 055984, all of which are incorporated herein by reference in their entirety.

[0052] In some embodiments, other fibers (e.g., short fibers) may be mixed among the meltblown fibers of layer 100 in a general manner, for example, as described in U.S. Patent Application Publication 2011 / 0162653. In other embodiments, the meltblown fibers are the only fibers present in layer 100. In many embodiments, the main filter layer 100 may be substantially non-fluorinated in the manner previously described with respect to pre-filter layer 10. Similarly, in many embodiments, the main filter layer may exhibit a contact angle of, for example, less than 40 degrees, in the manner described above. The main filter layer 100 and its fibers 111 may be charged in a manner similar to that discussed with respect to pre-filter layer 10 (via any of the devices and methods described above). Similarly, the fibers 111 of layer 100 may contain one or more charge-enhancing additives, which may be any general type or specific composition disclosed above, for example.

[0053] The multilayer air filter assembly 1 disclosed herein can be prepared in any suitable manner. In some convenient embodiments, the pre-filter layer 10 can be prepared by melt-spun fibers 11, collecting the fibers (e.g., on a moving carrier), and then bonding (e.g., self-bonding) the fibers 11 to form a coherent web. In some embodiments, such a web can be stored (e.g., in rolls) for later deposition of the melt-blown main filter layer 100 thereon.

[0054] However, in some convenient embodiments, the formation of the meltblown main filter layer 100 on top of the pre-filter layer 10 can be performed continuously with the method for forming the pre-filter layer 10, without the layer 10 being stored, for example, in roll form. Such methods can rely on a production line having a meltblown unit connected in series with the meltblown unit. In some such production lines, an adhesive unit (e.g., a ventilated adhesive for self-adhesion) can be positioned between the meltblown and meltblown units to adhesive the meltblown fibers to form the pre-filter layer 10. The fibers 111 can then be meltblown onto the exposed main surface of the pre-filter layer 10, which thus acts as a receiving substrate on which the fibers 111 are deposited.

[0055] In some embodiments, fiber 111 may be sufficiently soft or sticky (and / or fiber 11 may become soft or sticky due to recent exposure to the self-bonding process) such that fiber 111 may be bonded to fiber 11 at least to some extent simply by contact between fiber 111 and fiber 11. However, in some embodiments, one or more auxiliary bonding processes may be performed to ensure that fiber 11 is sufficiently bonded to fiber 111 (i.e., to ensure that the main filter layer 100 is sufficiently bonded to the pre-filter layer 10). Any such auxiliary bonding process may take the form of, for example, self-bonding (e.g., by a ventilated adhesive), thermal calendering of layers (e.g., to facilitate the formation of a plurality of dot-like adhesive portions distributed over the entire length and width of the resulting multilayer assembly), etc. Thus, it can be understood that in some embodiments, the production line may have two separate adhesives, one for bonding melt-spun fibers together, and an auxiliary adhesive for ensuring that meltblown fibers are bonded to melt-spun fibers. Any such auxiliary bonding process that depends on any bonding method will be distinguished from a method in which a pre-existing main filter layer is laminated (e.g., adhesively laminated) to a pre-existing pre-filter layer.

[0056] The result of these processes will be a multilayer assembly. In some embodiments, individual layers 10 and 100, or their fibers, may be individually charged before forming the multilayer assembly. However, in some convenient embodiments, layers 10 and 100 may be simultaneously charged as a multilayer assembly using, for example, any of the aforementioned charging methods (this will be referred to as co-charging). In some embodiments, the multilayer assembly may be stored (e.g., in roll form) before being charged. However, in some embodiments, charging may be performed continuously with melt spinning, bonding, and / or meltblowing processes without the need to store the multilayer assembly before charging. Thus, for example, water charging units, corona charging units, or both may be continuously present in the fiber web production line (note that if both water charging and corona charging are performed, they may be performed in any desired order). Such an arrangement allows the fibers 11 of the pre-filter layer 10 and the fibers 111 of the main filter layer 100 to be charged in a single operation, without the need for separate charging operations on each individual layer.

[0057] The resulting charged multilayer components can then be pleated. In some embodiments, pleating can be performed continuously with the above operations. However, in some embodiments, the charged multilayer components can be stored (e.g., in rolls) and pleated at a later time. This can advantageously eliminate any need, for example, to match the speed at which the pleating unit processes the multilayer components with the speed of web production and / or the operation of the charging unit.

[0058] Pleating increases the surface area available for air filtration and thus improves the ability to remove particles from a flow of air without significantly increasing the pressure drop required to allow the air to pass through the fiber layer. In fact, it has been found that, for a given airflow, pleating generally results in a lower pressure drop compared to a flat mesh. The geometric pleating parameters (pleat height and pleat spacing) can be selected, for example, within the range disclosed earlier herein.

[0059] The resulting pleated, charged multilayer air filter assembly can then be stored or further processed (e.g., converted) into individual parts. In some embodiments, a peripheral support frame can be mounted on the peripheral edge of the individual parts to form a frame-type air filter. Any such air filter (whether framed or frameless) can be used in any situation where particles need to be filtered from flowing air (e.g., in indoor air purifiers, in forced air handling systems such as residential or commercial HVAC systems, etc.).

[0060] In some embodiments, the multi-layer air filter assembly 1 will consist only of a pre-filter layer 10 and a main air filter layer 100, wherein the main air filter layer is used for particulate filtration of the air and no other layers are present. In other embodiments, at least one additional layer may be present, such as an adsorbent layer containing adsorbent particles (e.g., activated carbon), which is configured to remove gases, vapors, odors, etc. In such embodiments, any such additional layer will be co-pleated with the pre-filter layer and the main filter layer.

[0061] In some embodiments, the pleated multilayer air filter assembly disclosed herein may be self-supporting. This means that when the pleated assembly (e.g., with a peripheral support frame) is placed in a conventional forced-air peripheral fixture (e.g., a HVAC system), it is able to withstand the forces generated when air impacts the upstream face of the pleated mesh, resulting in a pressure drop of at least 0.2 inches of water column when tested in the manner described in the embodiment portion of U.S. Patent 9,174,159. Being able to withstand such forces means that the pleats will not collapse, warp, deform, shift, break, etc., to the point that the performance of the air filter media becomes unsatisfactory. In some embodiments, the pleated air filter assembly may be non-self-supporting and / or may include one or more pleated stabilizing members, such as the common type of "bridging" filaments disclosed in U.S. Patent Application Publication 2019 / 0217239, which can help stabilize the pleated layers against the forces of moving air.

[0062] Advantages of the presence of a pre-filter

[0063] Those skilled in the art will understand that the pre-filters described herein can provide certain expected or predictable advantages. For example, a pre-filter comprising melt-spun fibers with a diameter larger than the meltblown fibers of the main filter layer will generally be very robust and rigid compared to the meltblown main filter layer, and will therefore make the resulting multilayer assembly more pleatable. However, the work of the present invention has revealed that using a pre-filter layer as disclosed herein (i.e., the fibers of the pre-filter layer comprising polymethylpentene and being charged) can provide other unexpected advantages.

[0064] Specifically, it has been found that the presence of a charged pre-filter containing polymethylpentene can reduce the sensitivity of the main filter layer to deactivation by contaminants. In other words, such a pre-filter can protect the charged main filter layer from damage by contaminants, thus preventing degradation of the main filter layer's filtration performance.

[0065] Such performance can be characterized by the media CCM test described in the embodiments herein. The media CCM test (as described in U.S. Provisional Patent Application 62 / 886129 and International (PCT) Publication WO2021 / / 028851 (Agent's File No. 82117WO003)) is based on the Chinese National Standard GB / T 18801-2015 and is used to test the performance of indoor air purifiers, but focuses on the performance of the air filter itself, rather than evaluating the combined effect of the air filter and the indoor air purifier using the air filter.

[0066] In media CCM testing, a sample of filter media (e.g., a multi-layer air filter assembly or a single layer that may be used in such an assembly) is exposed to an increasing amount of contaminants (cigarette smoke). The filtration performance of the filter media is monitored periodically as a function of this cumulative exposure to the contaminants. Filtration performance is measured according to the capture efficiency (the removal efficiency of particles for NaCl testing) as described in the US'129 provisional application. The test ends when the capture efficiency drops to half its initial value (i.e., the value before any exposure to the contaminants). Therefore, the media CCM value is a measure of the total amount of contaminants that the filter media must be exposed to for its particulate filtration performance to decrease by half. A higher media CCM value indicates that the filter media can withstand a higher level of contamination before its filtration performance significantly deteriorates.

[0067] The embodiments given later in this document illustrate the advantageous effects of the pre-filters disclosed herein. A reference embodiment is provided, which is a commercially available main filter layer in the form of a charged meltblown fiber web (capable of HEPA filtration) and exhibits a media CCM value of approximately 520 (reported in cigarette units per square meter of web area). Then, media CCM values ​​are presented for several pre-filters of the present invention (all such pre-filters are referred to as exemplary embodiments when tested individually); when tested in independent configurations, the pre-filters typically exhibit media CCM values ​​in the range of 40-70. Operating embodiments are then given, wherein each of the exemplary embodiment pre-filters is combined with the reference embodiment meltblown main layer to form a multilayer air filter assembly. Figure 4 As is clearly seen, the multi-layer air filtration assembly produced by enhancing the main filter layer with the pre-filter layer of the present invention exhibits a media CCM value that is significantly higher than the values ​​expected based on the individual media CCM values ​​of the pre-filter and main filter layers. For example, Figure 4 The pre-filter of the present invention (exemplary embodiment IE-3a) having a media CCM value of 55 can be combined with a main filter layer (reference embodiment RE) having a media CCM value of 520 to provide a multi-layer air filter assembly (operating embodiment WE-3a) exhibiting a media CCM value of 933.

[0068] These surprising results demonstrate that the pre-filter and main filter layer of the present invention work synergistically with the pre-filter to protect the main filter layer (from deactivation by contaminants) to a much greater extent than expected. Furthermore, these advantageous effects can be obtained without the use of relatively expensive methods involving, for example, fluorinated materials. It should also be noted that the advantageous effects of the pre-filter of the present invention used in combination with the main filter layer are not considered limited to, for example, the use of any particular charging method and / or any particular charge-enhancing additives in the pre-filter fibers (or in the fibers of the main filter layer).

[0069] The work of this invention reveals that the aforementioned unexpected effect requires the fibers of the pre-filter layer to be charged. While not wishing to be limited by theory or speculation, it appears that the presence of charge in the pre-filter fibers, and the surface energy of the polymethylpentene present on the surface of the pre-filter fibers, somehow serves to remove contaminants or eliminate their effects, preventing the contaminants from unduly affecting the main filter layer. Similarly, while not wishing to be limited by theory or speculation, it is assumed that at least some of these contaminants can take the form of droplets of oily liquid (e.g., aerosols) that can land on the surface of the fibers and wet the surface, enabling them to travel at least to some extent along the surface of the fibers. Such contaminants can contain, for example, charged and / or polar components, such that if the contaminant is sufficiently close to the electret charge of the fibers, the electret charge can be neutralized or otherwise deactivated.

[0070] Similarly, while not wishing to be limited by theory or speculation, polymethylpentene may provide a fairly oleophobic surface. Therefore, oily droplets can be attracted to the pre-filter fibers (by means of the electret charge present in or on the fibers) and thus can settle onto the fibers; however, such oily liquids have little tendency to move along the fibers, which would result in the charge on the pre-filter fibers being continuously encountered and neutralized (instead, the oily liquid can “bead” and remain in its initial position). Thus, a large amount of oily liquid can accumulate on the surface of the pre-filter fibers without deactivating the electret charge of the pre-filter fibers in a manner that prevents the pre-filter fibers from capturing additional amounts of oily liquid.

[0071] Regardless of the exact mechanism, the work of this invention indicates that charged pre-filter fibers comprising polymethylpentene have a high capacity to capture certain contaminants (e.g., oily liquids) while also having the capacity to hold large quantities of such contaminants. As discussed herein, this combination of properties is highly advantageous. It should be emphasized that such characteristics are not solely manifested in the media CCM value of the pre-filter (which is actually quite low); rather, these advantageous properties of the pre-filter are unexpectedly revealed only when such a pre-filter is combined with a main filter layer.

[0072] This invention provides additional insight into the protective role of filter fibers. As discussed in detail in the embodiments herein, working embodiment WE-2 includes charge-enhancing additives in both the core and sheath of the sheath-core fibers in the pre-filter layer. In contrast, working embodiments WE-1 and WE-3 contain charge-enhancing additives only in the core; such additives are absent in the sheath. Therefore, in working embodiments WE-1 and WE-3, it is anticipated that most of the electret charge will be "buried" in the core layer beneath the sheath (although the charging process is expected to result in some electret charge formation in the sheath, the charge is expected to be primarily associated with the charge-enhancing additives; that is, in the core).

[0073] right Figure 4 The examination revealed that working embodiments WE-1 (including samples WE-1a, WE-1b, and WE-1c) and WE-3 (including samples WE-3a and WE-3b) exhibited protective effects very similar to those exhibited by working embodiment WE-2. These results suggest that, in order for the pre-filter fibers to function as disclosed herein, the pre-filter fibers do not necessarily need to have a charge on or near the radially outer surface of the fiber. In other words, for the pre-filter fibers to function, the charge does not need to be “exposed” on the radially outward surface of the fiber. In fact, it may be advantageous for at least some of the electret charges in the pre-filter fibers to be “embedded” within the fiber, for example, making the electret charges less susceptible to contact with any oily-liquid contaminants, thereby being neutralized / deactivated by the oily liquid.

[0074] Therefore, in some specific embodiments, the charge-enhancing additive may be present in the core of the sheath-core fiber 11 of the pre-filter 10. In some such embodiments, the charge-enhancing additive may not be present in the sheath of such fibers.

[0075] Another parameter commonly used to characterize the performance of filter media is the so-called quality factor (QF). The quality factor is a measure of overall filtration performance, taking into account both the achieved particle removal and the pressure drop (and thus energy) required to pass air through the filter to achieve particle removal. Methods for measuring the quality factor (using NaCl or DOP test particles) are described, for example, in U.S. Patent 7,691,168, which is incorporated herein by reference in its entirety. When tested individually as illustrative embodiments (using NaCl test particles), the various pre-filters disclosed in the embodiments herein exhibit quality factors in the range of approximately 0.5 to 0.8 (QF is in units of the reciprocal of the pressure drop, i.e., 1 / mm H2O). When tested individually, the meltblown primary filter layer of the reference embodiment exhibits a quality factor of approximately 0.63. The multilayer assembly of the working embodiments, obtained by combining a pre-filter layer with a primary filter layer, exhibits a quality factor in the range of approximately 0.6 to 0.7.

[0076] Therefore, it is clear that the advantages in contaminant resistance when using the pre-filter disclosed herein are not offset by any decrease in filtration performance in terms of quality factor. On the contrary, the quality factor of the multi-layer air filter assembly in the working embodiment is perfectly acceptable. However, it is clear that when these items are evaluated according to quality factor (since the reference, exemplary, and working embodiments all exhibit quality factors within a similar range), no advantage has been demonstrated from the presence of the pre-filter layer upstream of the main filter layer. Rather, only the work of the present invention (where the behavior of the filter layer is evaluated in the presence of specific contaminants, such as in media CCM testing) reveals unexpected, previously unrecognized advantages of the method disclosed herein.

[0077] Example

[0078] Test methods

[0079] Density, bulk, basis weight, effective fiber diameter, and actual fiber diameter can be obtained using the process presented in U.S. Patent 8,162,153, the entire contents of which are incorporated herein by reference. Quality factors can be obtained using the method described in U.S. Patent 7,691,168, the entire contents of which are incorporated herein by reference.

[0080] Medium CCM

[0081] Media CCM testing was conducted to assess the impact of a representative pollutant (cigarette smoke) on particulate filtration performance. The media CCM test used methods similar to those in the Chinese National Standard GB / T 18801-2015 (which tests the cumulative clean mass (CCM) performance of air purifiers in which air filters are installed), but was configured to evaluate the performance of the air filter alone, rather than the combined effect of the air filter and the air purifier in which the air filter is installed.

[0082] In media CCM experiments, 5.25-inch (13.3 cm) diameter filter media spheres (e.g., by die-cutting) are prepared and placed in a holder that exposes 4.5-inch (11.4 cm) diameter media spheres. The holder is placed in a test chamber such that the test chamber is divided into two parts, with the filter media sample being the only internal path between them.

[0083] A sample, in the form of a cigarette or a portion thereof (with the filter removed), is burned within a portion of the test chamber. During this process, a fan operates, drawing air from one portion of the test chamber and directing it through an external duct leading to another portion of the test chamber. The fan thus continuously recirculates the air, drawing the smoky air through the filter media sample. The fan continues to run until smoke appears (visually observable) to indicate complete removal from the chamber. The test is then continued with a new cigarette sample, and the process is repeated until the test is complete.

[0084] The ability of the filter media to capture particles (including initial values, prior to exposure to cigarette smoke) was monitored at various stages of the cigarette smoke loading process by testing the capture efficiency of the filter media (i.e., 100 minus the percentage of penetration, recorded as a percentage). The capture efficiency was tested using a TSI 8130 automated filter tester with 85 liters / minute of NaCl aerosol (face velocity of 14 cm / s).

[0085] A second-order polynomial regression equation was applied to the cigarette quantity and capture efficiency data to determine the point at which the capture efficiency had decreased to 50% of its initial value, consistent with the general method of the GB / T standard. The output of this test is called the Media CCM test and is normalized to the filter media area. In other words, the test results are presented based on the total number of cigarettes required to halve the capture efficiency (per square meter of filter media area).

[0086] Media CCM testing can be performed using standard reference cigarettes available from the University of Kentucky under the brand name University of Kentucky, Tobacco-Health Research, Research Cigarettes Type 1R4F or Type 1R6F, or commercially available CAMEL cigarettes from RJ Reynolds Tobacco Company. Related work has shown that all of these cigarettes provide comparable results.

[0087] The media CCM test (along with other tests such as capture efficiency, penetration percentage, quality factor and density) is discussed in detail in U.S. Provisional Patent Application 62 / 886,129 and International Publication (PCT) WO2021 / 028851 (Attorney’s File No. 82117WO003), both of which are incorporated herein by reference in their entirety.

[0088] Reference Implementation Examples

[0089] The reference example (RE) fiber air filter is a general type of air filter product available from 3M Company, St. Paul, MN, under the trade names FILTRETE TRUE HEPA ROOM AIRPURIFER FILTER FAPF-F2-H and FAPF-A2-4. This mesh is a meltblown polypropylene electret mesh whose fibers contain one or more charging additives. The mesh exhibits an effective fiber diameter of approximately 4.9 microns, a basis weight of approximately 42 g / m², and a density of approximately 8.1%.

[0090] Exemplary Examples

[0091] An exemplary embodiment (IE) of preparing a pre-filter using melt-spun yarn of a general type disclosed in U.S. Patent 8,506,669, differs in that the melt-spun yarn is fed by an extrusion apparatus that supplies two separate molten plastic materials to a melt-spinning die comprising concentric holes configured to produce bicomponent fibers in a sheath-core orientation. All fibers are sheath-core fibers with a core-sheath ratio of approximately 80:20, wherein the core is polypropylene (Total 3860 from Total Petrochemicals) and the sheath is polymethylpentene (TPX Grade DX820 from Mitsui Chemicals). These are nominal mass ratios (as determined by the metering pump used to feed the corresponding molten materials into the extruder), which can be readily converted into the volume ratio of the resulting bicomponent fibers. The fibers are extruded, stretched, and collected, and then self-bonded using a hot-air bonding unit (supplying air at a temperature in the range of approximately 230°C) of the general type described in U.S. Patent Application Publication 2008 / 0038976.

[0092] For the materials of exemplary embodiments IE-1 and IE-3, a charge-reinforcing melt additive is included in the polypropylene (about 0.1 wt%) of the core to form the sheath-core fiber, while no charge-reinforcing additive is included in the polymethylpentene of the sheath to form the sheath-core fiber. For exemplary embodiment IE-2, the same charge-reinforcing additive present in the core of exemplary embodiments IE-1 and IE-3 is present in the core (at the same level of about 0.1 wt%). The fiber of exemplary embodiment IE-2 also includes a charge-reinforcing additive (about 1 wt%) in the polymethylpentene sheath.

[0093] The IE-1 mesh exhibits an effective fiber diameter of approximately 22 micrometers, a basis weight of approximately 102 g / m², and a density of approximately 12%. The IE-2 mesh exhibits an effective fiber diameter of approximately 27 micrometers, a basis weight of approximately 76 g / m², and a density of approximately 10%. The IE-3 mesh exhibits an effective fiber diameter of approximately 27 micrometers, a basis weight of approximately 80 g / m², and a density of approximately 10%.

[0094] These networks are charged according to various general methods. Exemplary embodiments IE-1a, IE-1b, IE-2, and IE-3a are corona-charged (wherein IE-1a and IE-2 use a slightly modified corona-charging method compared to IE-1b and IE-3a). Embodiments IE-1c and IE-3b are charged using a combination of corona-charging (using the method of embodiments IE-1b and IE-3a) and water charging (where water charging is performed first).

[0095] Working Example

[0096] Various working embodiment (WE) samples are produced by combining one of the pre-filter layers of the exemplary embodiments listed above with a layer of the main filter layer of the reference embodiment. For these pilot-scale studies, the layers are not bonded together; instead, for each media CCM experiment, the exemplary embodiment pre-filter layer and the reference embodiment main filter layer are held together securely in the holder of the media CCM test apparatus. However, as previously mentioned, in actual large-scale production, it may be advantageous to bond such layers together in series. Similarly, in these pilot-scale studies, the pre-filter and main filter layers are charged separately, while in large-scale production, it may be advantageous to charge the final multilayer assembly.

[0097] CCM characterization of media

[0098] Various working embodiments were characterized in media CCM testing (each combination of a sample corresponding to one of the pre-filter layers of the exemplary embodiments listed above and a sample of the main filter layer of the reference embodiment). Figure 4 The results of this test are shown, along with the results of the reference embodiment (RE) network and the exemplary embodiment (IE) network when tested separately. Figure 4As shown, and as previously described, the Reference Embodiment (RE) network exhibits a media CCM value of approximately 520. The Exemplary Embodiment (IE) network exhibits a media CCM value in the range of 40-70. The Working Embodiment (WE) multilayer assembly exhibits a media CCM value in a general range of approximately 750 to approximately 950 (ranging from a low value of 759 in Working Embodiment WE-3b to a high value of 933 in Working Embodiment WE-3a). These values ​​are surprisingly high and cannot be predicted from the media CCM values ​​of the Reference Embodiment and the Exemplary Embodiment.

[0099] other

[0100] The foregoing embodiments and discussion are enhanced by reference to U.S. Provisional Patent Application 62 / 867941 and resulting PCT Publication WO2020 / 261034; and U.S. Provisional Patent Application 62 / 867933 and resulting PCT Publication WO2020 / 261150 (which are incorporated herein by reference in their entirety). These documents provide embodiments illustrating, for example, the use of various charging additives, further details of charging methods, etc., which further illustrate the principles demonstrated in the foregoing embodiments.

[0101] The above embodiments are provided merely for a clear understanding of the invention and should not be construed as unnecessary limitations. The tests and test results described in the embodiments are intended to be illustrative rather than predictive, and variations in the testing process may yield different results. All quantitative values ​​in the embodiments should be understood as approximations based on generally known tolerances involved in the processes used.

[0102] It will be apparent to those skilled in the art that the specific exemplary elements, structures, features, details, configurations, etc., disclosed herein are subject to modification and / or combination in many embodiments. The inventors intend that all such variations and combinations are within the scope of the conceived invention, and not merely those representative designs chosen for illustrative purposes. In the event of any conflict or contradiction between the disclosures in this written specification and any documents incorporated herein by reference, the disclosures in this written specification shall prevail.

Claims

1. A pleated multilayer air filter assembly, the pleated multilayer air filter assembly comprising a main filter layer and a pre-filter layer bonded together and co-pleated with each other, The main filter layer comprises meltblown electret fibers. The pre-filter layer comprises melt-spun bonded electret fibers having a radially outer surface comprising polymethylpentene. and The effective fiber diameter of the melt-spun electret fiber in the pre-filter layer is at least 20 micrometers, the effective fiber diameter of the meltblown electret fiber in the main filter layer is at most 10 micrometers, and the ratio of the effective fiber diameter of the melt-spun electret fiber in the pre-filter layer to the effective fiber diameter of the meltblown electret fiber in the main filter layer is in the range of 2.0 to 20. At least 95% of the melt-spun electret fibers in the pre-filter layer are bicomponent sheath-core fibers, which have a polymethylpentene sheath and a core of a thermoplastic organic polymer material that is not polymethylpentene. and, The bicomponent sheath-core fibers exhibit a sheath-core volume ratio of 5:95 to 85:

15.

2. The pleated multilayer air filter assembly according to claim 1, wherein the melt-spun electret fiber of the pre-filter layer is a self-bonding fiber.

3. The pleated multilayer air filter assembly according to claim 1, wherein the pleated multilayer air filter assembly exhibits a pleat spacing of 3 mm to 50 mm, a pleat height of 5 mm to 50 mm, a density of 4% to 20%, a basis weight of 20 g / m² to 200 g / m², and a thickness of 0.5 mm to 5.0 mm.

4. The pleated multilayer air filter assembly according to claim 1, wherein at least 95% of the melt-spun spun electret fibers of the pre-filter layer are polymethylpentene fibers.

5. The pleated multilayer air filter assembly according to claim 1, wherein the bicomponent sheath-core fiber has a polypropylene core.

6. The pleated multilayer air filter assembly of claim 1, wherein at least one of the sheath and the core comprises a charge-enhancing additive.

7. The pleated multilayer air filter assembly according to claim 6, wherein the charge-enhancing additive is selected from: pigments, light stabilizers, primary and secondary antioxidants, metal passivators, hindered amines, hindered phenols, metal salts, triphosphites, phosphates, fluorinated compounds, and combinations thereof.

8. The pleated multilayer air filter assembly of claim 1, wherein the core comprises a charge-enhancing additive.

9. The pleated multilayer air filter assembly of claim 1, wherein the skin does not contain charge-enhancing additives.

10. The pleated multilayer air filter assembly of claim 1, wherein the pleated multilayer air filter assembly exhibits a media CCM value greater than 700.

11. The pleated multilayer air filter assembly of claim 1, wherein the pleated multilayer air filter assembly does not include any air filter layers other than the main filter layer and the pre-filter layer.

12. The pleated multilayer air filter assembly according to claim 1, wherein the pleated multilayer air filter assembly further comprises an adsorbent-containing layer that is co-pleated with the main filter layer and the pre-filter layer.

13. The pleated multilayer air filter assembly of claim 1, wherein the upstream surface of the pre-filter layer exhibits a contact angle of less than 40 degrees.

14. The pleated multilayer air filter assembly of claim 1, wherein both the main filter layer and the pre-filter layer are at least fluorine-free.

15. The pleated multilayer air filter assembly according to claim 1, wherein the pleated multilayer air filter assembly is a frame-type air filter assembly including a peripheral support frame.

16. An indoor air purifier, the indoor air purifier comprising the pleated multilayer air filter assembly according to claim 1.

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