WO2018152683A1

WO2018152683A1 - Layered filter assembly for enclosure protection

Info

Publication number: WO2018152683A1
Application number: PCT/CN2017/074345
Authority: WO
Inventors: Rajan Gidumal; Jiangwen YIN; Xiao Xi Liu; Hong NING; Pan WANG
Original assignee: W. L. Gore & Associates, Inc.; W. L. Gore & Associates Technologies (Shenzhen) Co, Ltd.
Priority date: 2017-02-22
Filing date: 2017-02-22
Publication date: 2018-08-30
Also published as: CN108770347B; CN108770347A

Abstract

A layered filter assembly can include a filtration layer and one or more porous support layers adjacent to the filter layer. The filter layer can be formed of polyester with non-uniform fiber sizes ranging from 0.1 micron to 10 micron.

Description

LAYERED FILTER ASSEMBLY FOR ENCLOSURE PROTECTION

TECHNICAL FIELD

The present disclosure relates generally to filter assemblies for capturing particulate and/or vapor contaminants, and methods for mitigating contamination of an electronic device enclosure.

BACKGROUND

Filter technology is utilized in many applications and environments, for protecting sensitive components of electronic devices (e.g. hard disk drives (HDD’s) ) from particulate and/or vapor contamination within electronic device enclosures.

Many enclosures that contain sensitive equipment must maintain very clean environments in order for the equipment to operate properly. Examples include enclosures for the following: optical surfaces or electronic components that are sensitive to particulates and gaseous contaminants which can interfere with mechanical, optical, or electrical operation； data recording devices, such as computer hard disk drives that are sensitive to particles, organic vapors, and corrosive vapors； processing and storage of thin films and semiconductor wafers； and electronic controls such as those used in automobiles and industrial applications that can be sensitive to particulates, moisture buildup and corrosion as well as contamination from fluids and vapors. Contamination in such enclosures originates from both inside and outside the enclosures. For example, HDD’s may be damaged as a result from external contaminants entering and/or recirculating within the enclosure for the HDD. The contaminants may also include particulates and vapors generated from inside the HDD enclosure.

Known filters are disclosed in, for example, U.S. Patent No. 7,306,659, (the ‘659 patent) which is hereby incorporated by reference for all purposes. The ‘659 patent discloses a device for filtering contaminants, such as particulates and vapor phase contaminants, from a confined environment such as electronic or optical devices susceptible to contamination (e.g. computer disk drives) by improving performance and possibly incorporating multiple filtration functions into a unitary filter. The filter includes flow layers which improve filter performance. Filtration functions include a passive adsorbent assembly and can include a combination of inlet, breather filter, and adsorbent filter. Moreover, recirculation filter, diffusion tube and outside mount functions can be added to the filter depending on desired functionality within the enclosure.

Typical adsorbent and recirculating filters require large volumes to be effective. However, space saving assemblies have been described in some of the following references. U.S. Patent No. 6,266,208 describes a unitary filter incorporating a recirculation filter, breather filter, and adsorbent filter. U.S. Patent No. 6,238,467 describes a rigid assembly filter incorporating a breather filter, adsorbent filter, and recirculation filter. U.S. Patent No. 6,296,691 describes a molded filter incorporating a breather filter and recirculation filter. U.S. Patent No. 6,395,073 describes incorporating a recirculation filter and a breather filter with an optional adsorbent filter into a low profile adhesive construction.

Traditional designs make use of a polypropylene electret felt as at least one of the filtration materials in recirculation filters for disk drives. However, polypropylene fiber from electret felt has been found to create a risk of damage to the head disk interface (HDI) , resulting in degradation of HDD reliability. Further, as disk drives decrease in size, solutions are sought which take up even less volume. Accordingly, there is a need for non-polypropylene filter technology for protecting sensitive components of electronic devices that can operate with a low profile in small enclosures without sacrificing airflow or adsorption performance.

BRIEF SUMMARY

According to one embodiment of the present disclosure there is provided a layered filter assembly comprising a filtration layer and one or more porous support layers adjacent to the filter layer. The porous support layers can be positioned along one side, or along both sides, of the filter layer； and can be configured to provide support for the filter layer without significantly adding to the air resistance of the layered filter assembly. In some embodiments, the porous support layers contact the filtration layer without any intervening layers. The assembly can have a filtration efficiency of 65％or greater, and a thickness on the order of 100 to 250 μm.

According to another embodiment there is provided a layered filter assembly comprising a filtration layer, one or more porous support layers, an adsorbent layer and a media layer, where the adsorbent layer is positioned between the filtration layer and the media layer. The one or more porous support layers are positioned adjacent to and exterior to the filtration layer and/or the media layer.

According to further embodiments there is provided an article for filtering an enclosure is provided that includes a housing for retaining an electronic device, a layered assembly arranged inside the housing, and a filtration layer comprising a polyester layer. The layered assembly includes a filtration layer and one or more porous support layers adjacent to the filtration layer.

In each of these embodiments, the filter layer can be formed of nonwoven polyester with non-uniform fiber sizes ranging from 0.1 micron to 10 micron. According to one embodiment, the filter layer can be meltblown polyester that is substantially free of polypropylene. For purposes of this disclosure, substantially free means that the component is present in limited quantities of less than 0.1 wt. ％, and includes being completely free of the component.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood in view of the appended non-limiting figures.

FIG. 1 is a side cross-sectional view of an embodiment of a layered filter assembly.

FIG. 2 is a side cross-sectional view of a second embodiment of a layered filter assembly.

FIG. 3 is a side cross-sectional view of a third embodiment of a layered filter assembly.

FIG. 4 is a scanning electron micrograph (SEM) image showing a filtration material having substantially uniform fibers.

FIG. 5 is an SEM image showing a filtration material having non-uniform fiber size, according to embodiments described herein.

FIG. 6 is a side cross-sectional view of an electronic device assembly showing a layered filter assembly as per FIGS. 1-3 installed therein, according to embodiments described herein.

FIG. 7 is a side cross-sectional view of a filtration efficiency test assembly and system.

FIG. 8 is a chart illustrating filtration efficiency of various test samples.

DETAILED DESCRIPTION

Various embodiments described herein provide a layered filter assembly comprising a filtration layer and one or more porous support layers arranged adjacent to the filtration layer. In one embodiment the filtration layer includes polyester comprising fibers with a non-uniform fiber size ranging from 0.1 μm to 10 μm. In one embodiment the filtration layer may also be substantially free of polypropylene. The layered filter assemblies are suitable for use in, e.g., electronic device enclosures. The layered filter assemblies can be used to filter air therein without occupying too much space, without significantly impeding airflow, without shedding fibers into the enclosure, and without the drawbacks associated with conventional (e.g. polypropylene) filtration layers.

Further embodiments include an adsorbent layer and media layer, wherein the adsorbent layer is arranged between the filtration layer and the media layer. In one embodiment, the media layer is a non-polypropylene layer with greater air permeability than the filtration layer. The media layer may be a nonwoven polyester thermoplastic such as polyethylene terephthalate. In some other embodiments, the media layer may be polyethylene, a polyvinyl alcohol, a mixture of the above, or similar materials. The adsorbent layer may be positioned between the filtration layer and media layer, and the porous support layers arranged adjacent to the opposite surface of the filtration and media layers. The adsorbent layer can include any suitable adsorbent material, such as but not limited to, activated carbon or a porous substrate containing activated carbon. In some embodiments, the adsorbent layer may comprise ePTFE and an adsorbent material. Other suitable adsorbent materials can include, but are not limited to: sodium carbonate, calcium carbonate, calcium sulfate, potassium carbonate, any suitable mixture of the above, or a suspension of any suitable combination of the above in a substrate. In alternative embodiments, the media layer can have similar characteristics to the filtration layer, such that the adsorbent layer is positioned essentially between two layers with similar characteristics.

The disclosure may be better understood with reference to the Figures, in which like parts have like numbering.

Conventional filter assemblies, including filter assemblies for use in recirculation filters or the like, are traditionally made using filter media composed of polypropylene fiber that are electrostatically charged by a carding process. The resulting material, which is a polypropylene electret felt, is able to mechanically trap contaminants and also exert an electrostatic force on particles to increase the clean-up ability of the filter media. However, polypropylene fibers exhibit several downsides. For example, polypropylene fiber released from electret felt can threaten sensitive electronics, e.g. to the head disk interface (HDI) of a hard disc drive (HDD) , resulting in degradation of HDD reliability. In this regard, the demand for polypropylene free filter with adequate particle clean up performance is increasing. FIG. 4 is a scanning electron micrograph (SEM) image showing a filtration material 400 having substantially uniform fibers 402 in a conventional polypropylene electret felt material.

For purposes of comparison, FIG. 5 is an SEM image showing a polyester filtration material 500 having non-uniform fiber size, in accordance with some embodiments of the present disclosure.

Referring to FIG. 1, there is shown a side cross-sectional view of an embodiment of a layered filter assembly 100. The layered filter assembly 100 includes a filtration layer 102 and two

porous support layers

104a, 104b positioned adjacent to the filtration layer and on either side of the filtration layer. The filtration layer 102 is a polyester layer having fibers with a non-uniform fiber size, in which fibers can range in size from 0.1 μm to 10 μm. It is understood that fiber size is determined by the cross-sectional diameter. A non-uniform fiber sizes means that the fibers in the polyester layer have different cross-sectional diameters that produces a distribution of fiber sizes. It should be understood that although the non-uniform fiber size may range from 0.1 μm to 10 μm, there may be some individual fibers that are smaller or larger. The distribution of the fiber sizes can vary, so that for example, in one embodiment a first portion of the fibers are in the range of 0.1 μm to 3.0 μm, and a second portion of the fibers are in the range of 3.0 μm to 10 μm. The first portion may be from 10％to 90％of the total fibers and the second portion may be from 90％to 10％of the total fibers. In one embodiment 85％of the fibers have a fiber size in the range from 0.1 μm to 3.0 μm, and 15％of the fibers have a fiber size in the range from 3.0 μm and 5.0 μm. In other embodiments, the fiber size can have a bimodal distribution, having a first average fiber size in the range of 0.1 to 3.0 μm, and a second average fiber size in the range of 3.0 to 5.0 μm. The first average fiber size range can include approximately 85 ％of the fibers, and the second average fiber size range can include approximately 15 ％of the fibers. In further embodiments, the fiber size distribution can be multimodal.

As described herein, the filtration layer 102 is a meltblown polyester polymer. In some embodiments, the filtration layer 102 is a meltblown polybutylene terephthalate. The filtration layer 102 can be substantially free of polypropylene. In some alternative embodiments, the filtration layer 102 may comprise an electrospun non-polypropylene polymer nonwoven, or a multicomponent spun non-polypropylene polymer nonwoven.

The suitable filtration layer has an adequate flow and resistance properties, while being thin and lightweight. According to some embodiments, the filtration layer 102 has a gas permeability of at least 15.24 cubic meters of air /min m² (m/min) , or 50 cubic feet air /min ft² (cfm /ft²) at 125 Pa. In some embodiments, the filtration layer 102 has a gas permeability in the range of 15.24 m/min to 30.5 m/min (i.e., 50 to 100 cfm /ft²) at 125 Pa. According to some exemplary embodiments, the filtration layer 102 can have an air resistance of less than 20 Pa. In addition, the filtration layer may be lightweight and is able to made thin for small enclosures. In one embodiment, the filtration layer 102 has a thickness 110 of less than 250 μm, e.g., less than 200 μm. In terms of range, a suitable filtration layer may have a thickness in the range of 100 μm to 250 μm. The filtration layer may have weight in the range of 15 g/m² to 50 g/m², e.g., from 22 g/m² to 40 g/m².

The filtration layer also has a sufficient collection efficiency over a wide range of particulate sizes, such as from 0.05 μm to 10 micrometers.

Two

porous support layers

104a, 104b are shown, but it will be understood that in some embodiments one of the two porous support layers may be omitted. The porous support layer or layers 104a, b preferably have a porosity that is significantly greater than that of the filtration layer 102, such that the porous support layer (s) do not significantly impair the gas permeability of or airflow through the filtration layer. The porous support layer (s) 104a, b can be constructed of any suitable support material, such as a woven scrim with a high gas permeability compared to that of the filtration layer 102. The porous support layer (s) 104a, b may be constructed of a non-polypropylene material, such as a polyester woven. In some alternative embodiments, the porous support layer (s) 104a, b may be constructed of, e.g. polyethylene, polyvinyl alcohol, a mixture of the above, or other similar material. Preferably, the porous support layer (s) have a gas permeability of at least 152 cubic meters air /m² (500 cfm /ft²) at 125 Pa. The porous support layers 104a, b can have thicknesses 112a, b, on the order of 100 to 400 μm.

The layered filter assembly 100 can be assembled, in some embodiments, by laying the porous support layers 104a, b across the filtration layer 102 so as to support the filtration layer and/or prevent release of fibers from the filtration layer. This means that the

distances

120, 122 between the filtration layer 102 and the porous support layers 104a, b can be very small, i.e. approximately zero microns. The filtration layer 102 and the porous support layers 104a, b may be joined at one or more sides or edges, e.g. by mechanical means (including clamps, potting, or any suitable mechanical fasteners) ； by joining or laminating along one or more sides or edges of an assembly, or by joining the layers by an adhesive. In some embodiments, the filtration layer 102 can include thermal melt adhesive layer (s) on one or more surfaces (not shown) capable of being adhered to one or more of the adjacent porous support layers 104a, b.

The layered filter assembly 100 is operable to filter a flow of air flowing therethrough by removing a substantial amount of entrained small particles. Exemplary embodiments of the layered filter assembly 100 were tested on a TSI-8130 Automated Filter Tester (TSI Inc. ) with 0.3 μm NaCL particles at a flow rate of 5.3 cm/s, as described in greater detail below with reference to Table 1. The exemplary embodiments of the layered filter assembly 100 achieved filtration efficiencies of at least 65 ％at a flow rate of 32 liters per minute (LPM) . According to one embodiment, the layered filter assembly 100 can also achieve filtration efficiencies of 80 ％or greater. The layered filter assembly 100 can have a total airflow resistance of less than 30 Pa, e.g. less than 20 Pa； or in the range from 10 Pa to 30 Pa, e.g. from 15 Pa to 20 Pa.

According to some embodiments, a layered filter assembly can further include one or more adhesive elements or layers positioned exterior to the one or more porous support layers 104a, b, e.g. for adhering to a housing or other device that receives the layered filter assembly. The layered filter assembly may also include a damping material for reducing vibration within the housing. Also, as described throughout this disclosure, the layered filter assembly can include additional layers, such as an adsorbent layer, media layer, and/or second filtration layer. Examples of layered filter assemblies having additional layers are described below with reference to FIG. 2 and FIG. 3.

FIG. 2 shows a side cross-sectional view of a second embodiment of a layered filter assembly 200. The second layered filter assembly 200 includes a filtration layer 202, as well as an adsorbent layer 206 and a media layer 208 positioned opposite the adsorbent layer from the filtration layer. The combination of the filtration layer 202, adsorbent layer 206, and media layer 208 can be bounded by adjacent

porous support layers

204a, 204b. In accordance with various embodiments, the filtration layer 202 and the porous support layers 204a, b can have structures and characteristics that are similar to the filtration layer 102 and porous support layers 104a, b described above with reference to FIG. 1.

The adsorbent layer 206 can include any suitable adsorbent porous support layer, such as but not limited to, activated carbon or a porous substrate containing activated carbon. For example, one suitable adsorbent porous support layer may include a plurality of activated carbon beads or grains disposed between two scrim. The adsorbent layer is preferably operable to adsorb vapor contamination from a flow of air flowing through the layered filter assembly 200 such as organic vapors.

The media layer 208, positioned adjacent to the adsorbent layer 206 and opposite the filtration layer 202, is operable to prevent dispersion of particulates from the adsorbent layer 206, but is generally more porous than the filtration layer 202, i.e. having a lower air resistance than the filtration layer. Air resistance of a media layer may less than the filtration layer, and may be less than 3 Pa. The media layer can have a thickness in the range of 0.5 to 1.3 mm, e.g., 1.0 to 1.3 mm. Suitable materials for the media layer can include, e.g., nonwovens and particularly nonwoven polyesters formed by a carding, spunbond, or meltblown process. In one embodiment, the media layer is polyester meltblown, such as a polyethylene terephthalate nonwoven.

In similar manner to the layered filter assembly 100 described above with reference to FIG. 1, the layers comprising the layered filter assembly 200 can be separated by

distances

220, 222, 224, 226. Some or all of the separation distances can be zero or approximately zero. For example, the layers may be assembled by mechanically fastening the layers into the layered filter assembly 200 at edges or at separated points along the filter assembly. In other embodiments, the layers may be bonded to one another at edges or at discrete points along the adjacent surfaces. In further embodiments, the layers may be bonded continuously along the adjacent surfaces to one another. In some embodiments, the filtration layer 202 and/or media layer 208 may include thermal melt adhesive layer (s) on one or more surfaces (not shown) capable of being adhered to one or more of the adjacent porous support layers 204a, b. Alternatively, or in combination, the filtration layer 202 and/or media layer 208 may be bonded to the adsorbent layer 206 by way of a melt adhesive layer or similar.

FIG. 3 is a side cross-sectional view of a third embodiment of a layered filter assembly 300. The third layered filter assembly 300 includes a first filtration layer 302a and a second filtration layer 302b which is positioned similar to the media layer 208 of the example assembly 200 shown in FIG. 2. The second filtration layer 302b may also be referred to as a media layer, and perform the same functions as the media layer 208 described above with reference to FIG. 2.

Also, in similar manner to the

layered filter assemblies

100 and 200 described above, the layers comprising the layered filter assembly 300 can be separated by

distances

320, 322, 324, 326. In some embodiments, the separation distances can be zero or approximately zero, and the layers may be attached together by one or more of the methods discussed above with reference to the

layered filter assemblies

100 and 200.

Returning now to FIG. 5, exemplary large fibers 502 are shown with approximate diameters ranging from 3 μm to 5 μm in a nonwoven arrangement with small fibers 504 having approximate diameters ranging from 0.1 μm to 3 μm. In some embodiments, the filtration material 500 is meltblown polyester. Specific polyesters include, e.g., polybutylene terephthalate, but other polyester meltblown materials are within the scope of this disclosure. The distribution of fiber sizes in the meltblown polyester is varied. According to some embodiments, a suitable fiber size distribution includes a first range of fiber sizes between 0.1 μm and 3.0 μm comprising up to 85 ％of the fibers, and a second range of sizes between 3.0 μm and 5.0 μm comprising up to 15 ％of the fibers. Polyester meltblown materials such as the filtration material 500 described above can be formed by a one-step process in which high-velocity air blows a molten thermoplastic resin onto a conveyor. Suitable processes for producing polyester meltblown materials are discussed in, e.g., Dutton, K.C. (2008) . "Overview and analysis of the meltblown process and parameters" . Journal of Textile and Apparel, Technology and Management. 6； and in McCulloch, J. G. (1999) . "The history of the development of melt blowing technology" . International Nonwovens Journal. 8, which are hereby incorporated by reference.

The range of fiber sizes in the polyester filtration material 500 is operable to trap particles more effectively than a filtration material having a uniform fiber sizes, particularly for very small particles. However, based only on raw material properties of comparable filtration materials, this improvement of the polyester filtration material over the electret felt is unexpected. Sample raw material properties for the exemplary polypropylene 400 and polyester meltblown 500 filtration materials are shown below with reference to Table 1.

Table 1: Raw Material Properties of Electret Felt and Polyester Meltblown Filtration Materials

Table 1 shows materials properties for electret felt and polyester meltblown filtration materials described above, with the air resistance and efficiency metrics obtained on a TSI-8130 Automated Filter Tester (TSI Inc. ) with 0.3 μm NaCL particles at a flow rate of 5.3 cm/s. A polyethylene terephthalate media layer is also shown for comparison purposes, similar to the media layer 208 described above with reference to FIG. 2.

The polyester meltblown material has a thickness ranging from 102 –254 μm (about 4-10 mil) and a unit weight ranging from 22 –40 g/m² (Table 1) . The material is electrically charged to enhance particle capture capability. As a function of both electrical filtration and mechanical filtration, the filtration efficiency for meltblown is measured to be 80 –90％with 0.3 μm NaCL particles penetrating at a rate 5.3 cm/s. Meanwhile, the airflow resistance recorded in the same test is 14.7 to 19.6 Pa (about 1.5 -2.0 mm H₂O) . Compared with electret felt traditionally used in recirculation filters, the polyester meltblown material is 65％lighter and 85％thinner. Thus, overall thickness for a recirculation filter can be reduced by up to 50％and overall thickness of an adsorbent recirculation filter can be reduced by 30％. The meltblown materials have equal filtration efficiency but a much higher airflow resistance, e.g., 5 times larger than the airflow resistance of electret felt. Based solely on the raw materials properties, it would ordinarily be expected that the polyester meltblown material would have inferior filtration properties compared with the electret felt, particularly in recirculation filtering, due to its significantly reduced air permeability. However, as shown in the present disclosure, the polyester meltblown material having a non-uniform fiber size and being substantially free of polypropylene achieves equal or improved particle clean up performance. Without being bound by theory, the meltblown materials possess finer fiber sizes and broader fiber size distributions, which is more attractive to variety of particles sizes traveling at a variety of speeds.

FIG. 6 is a side cross-sectional view of an electronic device assembly 600 showing a layered filter assembly 608 as per FIGS. 1-3 installed therein, in accordance with embodiments. The specific device shown is a hard disk drive (HDD) employing the layered filter assembly 608 therein as a recirculation filter inside the electronic device housing 602. In operation, the internal components 604 of the electronic device assembly 600, which may include a head disk interface (HDI) , can generate particulates and/or vapors while inducing some amount of recirculation 610 within the interior 606 of the housing 602. The recirculation flow 610 passes through the layered filter assembly 608, where the particulates and/or vapor is captured.

Specific performance of layered filter assemblies can be achieved by simulating the end-use environment, e.g., by way of a continuous particle introduction test method.

TEST METHODS

FIG. 7 is a side cross-sectional view of a filtration test assembly and system 700, in accordance with embodiments. The test system 700 can be configured to obtain a particle clean-up performance (PCU) of example recirculation filters and/or vapor clean-up performance (VCU) .

The test system 700 includes a mass flow controller 702, a test apparatus 704 containing an electronic device enclosure 720, and an analyzer 706 which is under the control of a management component 708, such as a computer controller, which employs a processor 714 and nontransitory memory 716 storing instructions to control characteristics of the respective test. The test system 700 is operable to pass a test contaminant (e.g., particulates, vapor) through a valve 712 and into an injection port 724 of the enclosure 720, and to sample the air inside the enclosure periodically via a sample port 726.

PARTICLE CLEAN UP (PCU) TEST

The mass flow controller 702, under the control of the management component 708, can introduce a stream of particulate-laden air into the electronic device enclosure 720 through an injection port 714. The particulate-laden air will circulate throughout the enclosure 720 where it interacts with a layered filter assembly 722.

Air was sampled from the enclosure through a sample port 726 to get a concentration difference between unfiltered air particle content and filtered air particle content. The particles used were 0.1 um and 0.3 um polystyrene latex spheres (PSL) provided by Thermo Fischer Scientific Inc., which were suspended in water and then aerosolized using a 3076 Aerosol Generator from TSI Inc. The aerosol stream was then dried using a diffusion dryer and drawn into the enclosure 720 through the injection port 724 at a constant flow rate. The particle counter used for this test was a Laser Aerosol Spectrometer 3340 from TSI Inc. The result of the particle clean up test is recorded as T90, which is defined as the time needed to clean up 90％of the particles inside the drive. The second result, relative clean up ratio (RCUR) , is recorded as the recorded T90 with a filter over the recorded T90 without a filter. The smaller the T90 and the RCUR, the better the particle clean up performance. The PCU test results for electret felt (comparative) and polyester meltblown (inventive) samples for a recirculation filter (i.e., a recirculation filter without an adsorbent) similar to the recirculation filter shown in FIG. 1 are shown below in Table 2.

Table 2: PCU Test Results for a Recirculation Filter

As shown above in Table 2, the T90 and RCUR values for both the comparative, electret felt example and the inventive polyester meltblown example for a recirculation filter were comparable, indicating that the particle retentive properties of filter assemblies according to the embodiments described herein are similar to the particle retentive properties of the conventional electret felt filters. In fact, the polyester meltblown layered filtration assemblies slightly outperformed the conventional electret felt filters despite being significantly thinner, with T90 times on average 2-seconds faster than those of the conventional filter, and improvements in RCUR ratios of 6-7 ％.

Particle clean-up data was also obtained for an adsorbent recirculation filter constructed in similar manner to the adsorbent recirculation filter of FIG. 2, and using the same methods as discussed above. These PCU results are shown below in Table 3.

Table 3: PCU Test Results for an Adsorbent Recirculation Filter

As shown above in Table 3, the T90 data for the inventive meltblown example is found to be 13 seconds, while the T90 for a traditional electret felt is 10 -11 seconds. The RCUR data shows the difference between these two filters is less than 10％. Although judging from raw materials properties only, it might appear that meltblown materials would be inferior filtration materials compared with electret felt in recirculation filtering； these data show that the use of meltblown materials result in roughly equivalent particle clean up performance.

VAPOR CLEAN UP (VCU) TEST

Organic vapor breakthrough time can be measured by passing a flow of air containing a predetermined concentration of a volatile organic standard through an adsorbent breather assembly. The concentration of the volatile organic standard can be measured in the airflow exiting the adsorbent breather assembly. A common volatile organic standard used for such tests is trimethylpentane (TMP) . Although test results herein are disclosed in terms of TMP breakthrough, breakthrough times will tend to be comparable for similar organic vapors.

In a VCU test, a mass flow controller 702, under the control of the management component 708, can alternatively introduce a stream of vapor-containing air into the electronic device enclosure 720 through an injection port 714. The vapor-containing air will circulate throughout the enclosure 720 where it interacts with a layered filter assembly 722 containing an adsorbent layer, similar to the

layered filter assemblies

200, 300 shown in FIGS. 2 and 3.

In each VCU test, the tested layered filter assembly was positioned in the same type of enclosure 720 used for PCU testing as described above. A flow of 30 cc /min of air with 120 ppm of trimethylpentane (TMP) was injected into the enclosure through an injection port 724 in the cover of the enclosure 720. Air samples were drawn from the drive through the sampling port 726. A Gas Chromatographic Monitor (Agilent Technologies Inc. Gas Chromatograph 7820A) together with a data acquisition system was linked with the sampling port 726 and used to obtain an outlet TMP concentration over time. The vapor clean up efficiency is determined as the TMP break through concentration at 3 hours, i.e. a proportion of the outlet TMP concentration over the inlet TMP concentration. The lower the break through concentration, the better the vapor clean up efficiency.

FIG. 8 is a chart illustrating the filtration efficiency of a comparative electret felt filter assembly (Comparative Example 804) and an inventive polyester meltblown layered filter assembly (Example 1, 802) . The chart shows that both example filter assemblies possess VCU efficiencies near 10 ％ (approaching 9.7 ％for the comparative example at 3 hours, approaching 11.7 ％for Example 1) . Thus, the VCU test illustrates that the layered filter assembly using the polyester meltblown filtration layer can achieve comparable VCU efficiencies to a conventional electret felt-based filtration assembly, despite being significantly thinner.

The invention has now been described in detail for the purposes of clarity and understanding. However, those skilled in the art will appreciate that certain changes and modifications may be practiced within the scope of the appended claims.

In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present invention. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.

Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the present invention or claims.

Where a range of values is provided, it is understood that each intervening value, to the smallest fraction of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Any narrower range between any stated values or unstated intervening values in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of those smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the present invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a” , “an” , and “the” include plural references unless the context clearly dictates otherwise. Also, the words “comprise, ” “comprising, ” “contains, ” “containing, ” “include, ” “including, ” and “includes, ” when used in this specification and in the following claims, are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.

In the following, further examples are described to facilitate the understanding of the disclosure:

E1. A layered filter assembly, comprising a filtration layer comprising a polyester comprising fibers having a non-uniform fiber size ranging from 0.1 μm to 10 μm； and one or more porous support layers adjacent to the filtration layer.

E2. The layered filter assembly of any of the preceding examples, wherein the non-uniform fiber size ranges from 0.1 μm to 5 μm.

E3. The layered filter assembly of any of the preceding examples, wherein the one or more porous support layers comprises first and second porous support layers positioned adjacent to first and second sides of the filtration layer, respectively.

E4. The layered filter assembly of any of the preceding examples wherein the polyester is meltblown.

E5. The layered filter assembly of any of the preceding examples wherein the filtration layer is substantially free of polypropylene.

E6. The layered filter assembly of any of the preceding examples, wherein the one or more porous support layers are contacting the filtration layer without intervening layers.

E7. The layered filter assembly of any of the preceding examples wherein the assembly has a filtration efficiency of at least 65％according to TSI 8130 using 0.3 micron particles at a flow rate of 5.3 cm /s.

E8. The layered filter assembly of any of the preceding examples wherein the non-polypropylene meltblown polymer comprises fibers having two or more average fiber sizes within the range from 0.1 μm to 10 μm.

E9. The layered filter assembly of any of the preceding examples wherein the non-polypropylene meltblown polymer comprises fibers having two or more average fiber sizes including a first subset of fibers having average diameters of 0.1 μm to 3 μm and comprising at least 85 ％of the fibers.

E10. The layered filter assembly of any of the preceding examples, wherein the non-polypropylene meltblown polymer comprises a second subset of fibers having average diameters from 3 μm to 5 μm and comprising 15 ％of the fibers.

E11. The layered filter assembly of any of the preceding examples wherein the non-polypropylene meltblown polymer is a polybutylene terephthalate.

E12. The layered filter assembly of any of the preceding or subsequent examples wherein the one or more porous support layers have a gas permeability of at least 500 cfm /ft2 at 125 Pa.

E13. The layered filter assembly of any of the preceding or subsequent examples wherein the filtration layer has a gas permeability in the range of 50 to 100 cfm /ft2 at 125 Pa.

E14. The layered filter assembly of any of the preceding or subsequent examples, wherein the filtration layer and the one or more porous support layers are laid across one another without an adhesive.

E15. The layered filter assembly of any of the preceding or subsequent examples wherein the filtration layer and the one or more porous support layers are joined at an edge of the filtration layer.

E16. The layered filter assembly of any of the preceding or subsequent examples further comprising one or more thermal melt adhesive layers, wherein the one or more thermal melt adhesive layers join the filtration layer with the one or more porous support layers.

E17. The layered filter assembly of any of the preceding or subsequent examples wherein the one or more thermal melt adhesive layers are pre-laminated to the filtration layer.

E18. The layered filter assembly of any of the preceding or subsequent examples wherein the filtration layer and the one or more porous support layers are joined at an edge of the filtration layer by way of an ultrasonic weld.

E19. The layered filter assembly of any of the preceding or subsequent examples wherein the filtration layer has a thickness in the range of 100 microns to 250 microns.

E20. The layered filter assembly of any of the preceding or subsequent examples wherein the filtration layer has a unit weight in the range of 15 g/m2 to 50 g/m2.

E21. The layered filter assembly of any of the preceding or subsequent examples, wherein the filtration layer has a unit weight in the range of 22 g/m2 to 40 g/m2.

E22. The layered filter assembly of any of the preceding or subsequent examples wherein the assembly has an airflow resistance in the range of 10 Pa to 30 Pa.

E23. The layered filter assembly of any of the preceding or subsequent examples wherein the assembly has an airflow resistance in the range of 15 Pa to 20 Pa.

E24. The layered filter assembly of any of the preceding or subsequent examples further comprisingan adsorbent layer； and a media layer, wherein: the adsorbent layer is positioned between the filtration layer and the media layer； and the one or more porous support layers adjacent to the filtration layer and the media layer on an opposite side of the adsorbent layer.

E25. The layered filter assembly of any of the preceding or subsequent examples, wherein the media layer is a non-polypropylene meltblown polymer.

E26. The layered filter assembly of any of the preceding or subsequent examples wherein the media layer is a polyethylene terephthalate nonwoven.

E27. The layered filter assembly of any of the preceding or subsequent examples wherein the media layer is a nonwoven polyester formed by one of a carding, spunbond, or meltblown process.

E28. The layered filter assembly of any of the preceding or subsequent examples wherein the media layer has a thickness in the range of 0.5 –1.3 mm.

E29. The layered filter assembly of any of the preceding or subsequent examples, wherein the media layer has a thickness in the range of 1.0 –1.3 mm.

E30. The layered filter assembly of any of the preceding or subsequent examples wherein the adsorbent layer comprises activated carbon.

E31. An article for filtering an enclosure, comprising a housing for retaining an electronic device； and a layered assembly arranged inside the housing, the layered assembly comprising: a filtration layer comprising a polyester layer comprising fibers having a non-uniform fiber size ranging from 0.1 μm to 10 μm； and one or more porous support layers adjacent to the filtration layer.

E32. The article for filtering an enclosure of any of the preceding or subsequent examples wherein the polyester layer is a polyester meltblown polymer.

E33. The article for filtering an enclosure of any of the preceding or subsequent examples, wherein the article further comprises an adsorbent layer and a media layer； the adsorbent layer is positioned between the filtration layer and the media layer； and the one or more porous support layers are adjacent to the media layer on an opposite side of the adsorbent layer.

E34. The article for filtering an enclosure of any of the preceding or subsequent examples wherein the media layer has a lower air resistance than the filtration layer.

E35. The article for filtering an enclosure of any of the preceding or subsequent examples wherein the media layer is a polyethylene terephthalate nonwoven.

E36. The article for filtering an enclosure of any of the preceding or subsequent examples wherein the media layer is polyester meltblown polymer having a non-uniform fiber size ranging from 0.1 μm to 10 μm.

E37. The article for filtering an enclosure of any of the preceding or subsequent examples, wherein the filtration layer is not an electret felt filter media.

Claims

A layered filter assembly, comprising:

a filtration layer comprising a polyester comprising fibers having a non-uniform fiber size ranging from 0.1 μm to 10 μm, preferably from 0.1 μm to 0.5 μm； and

one or more porous support layers adjacent to the filtration layer.
The assembly of claim 1, wherein the one or more porous support layers comprises first and second porous support layers positioned adjacent to first and second sides of the filtration layer, respectively.
The assembly of any of the preceding claims, wherein the polyester is a meltblown nonwoven.
The assembly of any of the preceding claims, wherein the filtration layer is substantially free of polypropylene.
The assembly of any of the preceding claims, wherein the one or more porous support layers are contacting the filtration layer without intervening layers.
The assembly of any of the preceding claims, wherein the non-polypropylene meltblown polymer comprises fibers having two or more average fiber sizes within the range from 0.1 μm to 10 μm.
The assembly of any of the preceding claims, wherein the non-polypropylene meltblown polymer comprises fibers having two or more average fiber sizes including a first subset of fibers having average diameters of about 0.1 μm to 3 μm and comprising at least 85 ％of the fibers.
The assembly of any of the preceding claims, wherein the filtration layer comprises polybutylene terephthalate.
The assembly of any of the preceding claims, wherein the filtration layer has a unit weight in the range of 15 g/m² to 50 g/m², preferably 22 g/m² to 40 g/m².
The assembly of any of the preceding claims, wherein the assembly has an airflow resistance in the range of 10 Pa to 30 Pa, preferably from 15 Pa to 20 Pa.
The assembly of any of the preceding claims, further comprising:

an adsorbent layer； and

a media layer, wherein:

the adsorbent layer is positioned between the filtration layer and the media layer； and

the one or more porous support layers adjacent to the filtration layer and the media layer on an opposite side of the adsorbent layer.
The assembly of claim 11, wherein the media layer is a non-polypropylene meltblown polymer.
The assembly of claims 11 or 12, wherein the media layer is a polyethylene terephthalate nonwoven.
The assembly of any of claims 11-13, wherein the adsorbent layer comprises activated carbon.
An article for filtering an enclosure, comprising:

a housing for retaining an electronic device； and the layered assembly of any of claims 1-14 arranged inside the housing.